Peripheral Neural Transmission

Question 1

What receptors does NA bind to

Answer 1

Binds to α&raquo_space;> β

But still activates β eg in SNS to heart

Question 2

How are small molecule NTs acquired?

Answer 2

synthesised locally within presynaptic terminals

Question 3

Where are the enzymes needed to locally synthesise neurotransmitters produced?

Answer 3

in the soma and then transported to the nerve terminus by slow axonal transport

Question 4

Where do the precursor molecules for synthesising new small molecule NTs come from

Answer 4

may pre-exist within the nerve terminal but more commonly they are brought inside by some transporters found in the plasma membrane of the nerve terminus.

Question 5

True or false:

small molecule NTs can be synthesised inside the vesicles

Answer 5

True
For some small-molecule neurotransmitters, the final steps of synthesis occur inside the vesicles where the necessary enzymes are presen

Question 6

Where are neuropeptides usually synthesised

What happens next

Answer 6

in the soma where they are packaged into vesicles where further processing takes place

peptide filled vesicles are transported along the axon to the nerve terminal via fast axonal transport

Question 7

What do fast and slow axonal transport in nerves transport?

Answer 7

fast: peptide filled vesicles (neuropeptides)
slow: small molecule neurotransmitters

Question 8

True or false

all neurotransmitters are loaded into vesicles soon after synthesis

Answer 8

False
Gaseous transmitters eg NO are not

all others are

Question 9

Briefly describe the membrane and the interior of the vesicles for NT transport

Answer 9

phospholipid bilayer

aqueous interior

Question 10

What is the size of vesicles of small molecule transmitters

Answer 10

40-60nm

Question 11

Describe the appearance of small molecule NT vesicles

Hence what are they known as

Answer 11

appear clear in EM

small, clear core vesicles

Question 12

What is another name for small, clear core vesicles

Why?

Answer 12

synaptic vesicles

they are more abundant and cluster at the active zone

Question 13

Where are neuropeptides loaded into vesicles

What size are these vesicles

Answer 13

in the soma

90-250nm in diameter

Question 14

What are neuropeptide vesicles known as?

why

Answer 14

large dense core vesicles

they appear electron dense in EM

Question 15

How are neuropeptide vesicles different to those of small molecule transmitters

Answer 15

neuropeptide - larger,
more e- dense
do not cluster at the active zone

small molecule:
small, clear-core vesicles,
gather at the active zone

Question 16

How are vesicles released (as discovered by Katz)

Answer 16

in a quantal manner where 1 quantum is the content of a single vesicle (as we saw in HOM last year)

Question 17

Which ion channels in the presynaptic nerve terminal open in response to depolarisation ?

What types of channel specifically?

Answer 17

voltage gated Ca2+ channels

Cav2 series: mainly P/Q and N type

Question 18

How long does it take for Ca to trigger exocytosis

Answer 18

required conc of Ca is very quickly reached

Question 19

Why is the required conc of Ca for exocytosis very quickly reached in the presynaptic terminal

Answer 19

Cavs are clustered around the active zone and some vesicles are already docked to release sites so release of contents can be v rapid

Question 20

What is the releasable pool?

Answer 20

the presynaptic vesicles that are already docked to release sites in the terminal

Question 21

How much of the total amount of vesicles is represented by the releasable pool

Answer 21

Only a v small amount

Their numbers can be enhanced on demand when vesicles from the reserve pool join them

Question 22

What cell structure is the reserve pool associated with

Answer 22

cytoskeleton

Question 23

What are the 6 steps of vesicle release and recycle

Answer 23

1) Transmitter loading
2) mobilisation of vesicles toward active zone
3) Docking
4) Priming
5) Exocytosis
6) recycling of vesicles

Question 24

Describe the transmitter loading stage of the presynaptic vesicle life cycle

What precedes and follows it

Answer 24

NT imported using ATP
Proton pump acidifies interior to create an electrochemical gradient across vesicle membrane
Gradient provides energy for NT uptake by specialized transporters

Preceded by recycling of vesicle
Followed by mobilisation of vesicles

Question 25

What protein family is important for mobilization of vesicles towards the active zone

What modification is important in this process

Answer 25

synapsins

phosphorylation

Question 26

Describe vesicle mobilisation toward the active zone in presynaptic terminals

Answer 26

non phosphorylated synapsins reversibly bind to vesicles and actin to cross link them to each other, keeping the vesicles tethered to the reserve pool

Ca2+ increase (following depolarisation) activates CaMKII, which phosphorylates synapsins, allowing dissociation from vesicles.

The vesicles are now free to move

Question 27

What is CaMKII

Answer 27

Ca2+ /calmodulin dependant protein kinase (type II)

Question 28

Describe the docking stage of the presynaptic vesicle life cycle

What step precedes and follows it

Answer 28

At the active zone vesicles dock to nerve membrane via SNARE proteins

preceded by vesicle mobilization
followed by vesicle priming

Question 29

What occurs at the priming stage of the vesicle cycle

Answer 29

Docked vesicles undergo ATP dependent prefusion that primes them for Ca induced release

Question 30

Which type of protein is vvv important in vesicle priming

Are these the only proteins involved

Answer 30

SNARE

no - many others involved

Question 31

What is the main purpose of priming vesicles

Answer 31

to organize SNAREs into correct conformation for membrane fusion

Question 32

Describe the exocytosis step of vesicle release

What follows and precedes it?

Answer 32

Ca2+ (sensed by synaptotagmins) triggers complete fusion of vesicle with membrane in a rapid reaction

Question 33

Which protein sense Ca2+ to initiate vesicle-membrane fusion

Answer 33

synaptotagmin

Question 34

What are the 3 different routes that can be taken for vesicle recycling after release of the contents

Answer 34

reversible fusion pore
endocytosis
bulk retrieval pathway

Question 35

Describe the reversible fusion pore route of vesicle recycling

Answer 35

vesicle does not completely fuse with nerve membrane - contents are released via a fusion pore instead

Vesicle is retrieved by closing the pore

Spent vesicles can either stay fused to membrane (kiss and stay) or relocate to reserve pool ( kiss and run)

Question 36

How quickly can reversible fusion pore occur

Answer 36

vvv quickly

in tens to hundreds of milliseconds

Question 37

What does ‘kiss and stay’ and ‘kiss and run’ refer to

Answer 37

reversible fusion pore

stay: spent vesicle remains fused to nerve membrane
run: spent vesicle relocates to reserve pool of vesicles

Question 38

Describe the endocytosis pathway for vesicle return

What happens after the vesicle is recycled

Answer 38

vesicle coated in clathrin
the coat is later shed and the vesicle returned to interior of synaptic nerve terminal

empty vesicles either refill immediately with NT or pass through endosomal sorting

Question 39

Describe the bulk retrieval pathway for vesicle return

Answer 39

excess membrane re-enters the terminal by budding from uncoated pits - not very common .

Question 40

Why do many congenital myasthenic syndromes arise

Answer 40

defects in ACh release due to inadequate number of synaptic vesicles available for release.

Question 41

What happens in familial infantile myasthenia

Answer 41

synaptic vesicles are much smaller

NOT a shortage of vesicles

Question 42

What happens in Lambert Eaton myasthenic syndrome (LEMS)

What other disease can this syndrome be a complication of

Answer 42

ACh release is reduced due to autoimmune destruction of neuronal Cav channels in active zone

cancer

Question 43

Why is vesicle- membrane fusion difficult

Answer 43

Because a membrane bilayer is a stable structure, fusion of the synaptic vesicle and plasma membrane must overcome a large unfavourable activation energy

Question 44

What does SNARE stand for

Answer 44

soluble N-ethylmaleimide-sensitive factor attachment receptors

Question 45

How conserved are SNARE proteins

Answer 45

SNAREs are universally involved in membrane fusion, from yeast to humans

Question 46

How are SNAREs categorised

Answer 46

v- SNARE (v for vesicle)

t-SNARE - (t for target membrane)

Question 47

What part of the SNARE protein is highly conserved

Answer 47

cytosolic domain:

the SNARE motif, that is 60-70 residues long and form coiled-coil alpha-helical structures

Question 48

What SNAREs does each synaptic vesicle have

Answer 48

a single type of v-SNARE:

synaptobrevin (AKA VAMP)

Question 49

What is another name for synaptobrevin

Answer 49

vesicle associated membrane protein or VAMP

Question 50

What SNARE proteins are present in the target membrane of the presynaptic active zone

Answer 50

2 types:
syntaxin
SNAP25

Question 51

What happens to the SNARE proteins during exocytosis

Answer 51

form a trans-SNARE complex

Question 52

What does the trans-SNARE complex consist of

Answer 52

4 alpha helices - one each from synaptobrevin and syntaxin and two from SNAP-25

Other proteins involved are:
Munc 13, Munc 18, complexins, Rab3A

Question 53

What must happen to the trans-SNARE complex after fusion

Answer 53

dissemble via the action of NSF and SNAP (an adaptor protein)

Question 54

What proteins mediate dissembly of the SNARE complex

What is the action

Answer 54

cytoplasmic ATPase called NSF (N-ethylmaleimide-sensitive fusion protein) binds to SNARE complexes via an adaptor protein called SNAP

NSF and SNAP use the energy of ATP hydrolysis to dissociate SNARE complexes, thereby regenerating free SNAREs.

Question 55

What ion is involved in vesicle fusion?

What does this mean?

Answer 55

Ca2+

process should implicate a Ca2+ sensor - a role fulfilled by synaptotagmins

Question 56

How are synaptotagmins associated to the vesicle

Give another fact about their structure

Answer 56

anchored to synaptic vesicles via their N termini while their C-termini contain two C2 domains - C2A and C2B, that bind Ca2+.

Question 57

What do the C2 and 3 domains of synaptotagmins do respectively

Answer 57

C2: when Ca2+ is bound, C2 binds sytaxin and SNAP 25, and also binds to membranes containing acidic phospholipids

Question 58

Describe the Ca2+ binding of the C2 domain of synaptotagmins

Answer 58

low binding affinity so large [Ca2+] required for activation

Question 59

How do nerves ensure C2 domains of synaptotagmins get enough Ca2+

Answer 59

by co-localisation of synaptotagmin with Cav channels that cluster the active zone

Question 60

Where do Ca2+ rich microdomains develop in the presynaptic terminal

Answer 60

in the vicinity of Cav pores due to the poor diffusibility of Ca2+

Question 61

Why is the high [Ca2+] near Cav channels important

Answer 61

high local [Ca2+] can then be sensed by the synaptotagmins present in close proximity with these channels

Question 62

Name 2 toxins that target SNARE proteins

How they both work very generally

Answer 62

botulinum toxins (BoTx)

Tetanus (TeNT)

Both selectively cleave SNARES

Question 63

What are the 2 types of target proteins on the postsynaptic membrane for released transmitters

Answer 63

ionotropic (ligand gated ion channels) receptors

metabotropic receptors (GPCRs)

Question 64

How do most small molecule NTs interact with postsynaptic receptors

Answer 64

bind to their cognate LGICs to mediate a fast post-synaptic response which could be the generation of either excitatory or inhibitory post-synaptic currents

or could bind to GPCR for a slower response (catecholamines and neuropeptides also do this second one)

Question 65

Which postsynaptic receptor family is important in synaptic plasticity

Answer 65

GPCR - modulate strength of synaptic transmission by altering function/availability of LGICs in the postjunctional membrane

Question 66

Can neurotransmitters change K+ position

Answer 66

binding to post synaptic GPCRs can open K+ channels leading to K efflux and reduced excitability of post synaptic membrane

Question 67

True or false
Very little neurotransmitter is released upon stimulation

What does this mean for removal

Answer 67

False
Neurotransmitters are released typically in large amounts and timely removal of transmitters from the synaptic cleft is critical to synaptic transmission

Question 68

How can NT be removed from the synaptic cleft

Answer 68

reuptake (either into presynaptic terminal or into surrounding, non neuronal cells eg glia)
Destruction of neurotransmitter (eg proteolysis of neuropeptides)

Question 69

How is ACh removed from the synaptic cleft

Answer 69

hydrolyzed by AChE

Question 70

Which are removed more quickly from the synaptic cleft:

neuropeptides or small molecule transmitters

Answer 70

small molecule transmitters are removed faster than neuropeptides

Question 71

What is homotypic interaction at synapses

What is this also called

Answer 71

When released transmitters modulate further release of their own from the same nerve terminals

Homotropic interaction

Question 72

What is heterotropic interaction at synapses

AKA?

Answer 72

when released neurotransmitters modulate release of other transmitters from different nerve terminals through activating cognate receptors (GPCRs) in the presynaptic terminal membrane

AKA heterotypic interaction

Question 73

What receptors regulate homotropic and heterotropic interactions?

Answer 73

GPCRs called presynaptic autoreceptors (if homotropic interaction)
or

presynaptic heteroreceptors (if bind NTs from other synapses)

Question 74

What are presynaptic hetero/autoreceptors usually coupled to

Answer 74

inhibitory G proteins (Gi or Go) leading to reduced [cAMP]] and enhanced K+ efflux - ultimately reduces NT release

Question 75

Give an example of one of the few cases where released NT acting on a presynaptic GPCR leads to enhanced NT released

Answer 75

motor neurons connecting the skeletal muscle fibre

Question 76

Is it only neurotransmitters that can act on presynaptic GPCRs?

Answer 76

No
sometimes, chemicals that are not canonical transmitters (e.g. prostaglandins, endocannabinoids, NO etc.) and produced by the post synaptic neurons/ effector tissues, can also modify neurotransmission through this pre-synaptic routes.

Question 77

Give 3 chemicals that are not canonical transmitters but can modify NT release via presynaptic GPCRs

Answer 77

prostaglandins,
endocannabinoids,
NO

Question 78

Other than action on presynaptic GPCRs what can affect release of NT

Answer 78

anything that interferes with the generation of Ca2+ signals in the presynaptic terminal
eg by inhibiting Cav channels or by chelating Ca2+

Question 79

Give 2 agents which inhibit Cav channels in the presynaptic terminal

Answer 79

verapamil

aminoglycoside antibiotics

Question 80

Which drugs chelate Ca2+ in the presynaptic terminal

Answer 80

tetracyclines

Question 81

Where are LDCVs located in the presynaptic terminal

Answer 81

away from the active zone

Question 82

What does exocytosis of synaptic/ clear core vesicles result from

What can trigger this

Answer 82

transient but large and local increases in intracellular Ca2+

a single depolarising event is enough to provide such Ca2+ signals.

Question 83

What do LDCVs require to by exocytosed? (compared to clear core vesicles)

How is this requirement often met

Answer 83

smaller but sustained rise in global Ca2+ concentration

by a rapid train of action potentials (= repetitive firing of the nerve).

Question 84

Why are the different requirements for exocytosis of LDCVs and clear core vesicles useful

Answer 84

specific patterns of electrical activity in a neuron may lead to the preferential release of a neuropeptide or a small-molecule NT

Question 85

What are the 3 main broad sites of pharmacological intervention at the synapse

Answer 85

presynaptic nerve terminal,

sypatic/ junctional cleft

the post-synaptic/post-junctional target membrane

Question 86

What are the 2 ways a pharmacological agent can modulate peripheral neurotransmission

Answer 86

direct (binds to postsynaptic target as an agonist, antagonist or pore blocker)

indirect (reduces/ enhances amount of NT released)

Question 87

What was the first neurotransmitter to be discovered

Answer 87

ACh (1914)

Question 88

Where is ACh found in the peripheral nervous system (5)

Answer 88

• motor nerves that innervate the skeletal (voluntary) muscles
• all autonomic pre-ganglionic nerves
• nerves terminating at the adrenal medulla
• postganglionic parasympathetic nerves at neuro-effector junctions
• postganglionic sympathetic nerves innervating the sweat glands

Question 89

The availability of what chemical is vital for ACh synthesis?

How do we acquire it?

Answer 89

choline

primarily from diet as there is little de novo synthesis in neurons
can be recycled after ACh breakdown

Question 90

What is ACh hydrolysed to

Answer 90

acetate and choline

Question 91

What happens to the products of AChE

Answer 91

much of the choline is taken up by ChT1 for ACh synthesis

Question 92

What is usually the rate limiting step in ACh synthesis

Answer 92

reuptake and availability of choline

Question 93

What mediates choline reuptake into the presynaptic terminal

Answer 93

ChT1

Question 94

Describe ChT1

What is it a family of

what can it transport

what inhibits it?

Answer 94

high affinity choline transporter
a member of the solute carrier family of proteins

transports Na+ and can be inhibited by hemicholinium

Question 95

Is hemicholinium used clinically?

Answer 95

no

Question 96

How is ACh formed from choline

Answer 96

Within the cytoplasm of the pre-synaptic nerves, choline is acetylated to form ACh by choline acetyltransferase (ChAT or CAT)

Question 97

Where does the acetyl group for choline in ACh synthesis come from

Answer 97

acetyl CoA from the Mt

Question 98

What is Triethylcholine

Answer 98

competes with choline as a substrate for CAT and is converted to acetyltriethylcholine which is in turn released instead of ACh

Question 99

What does the release of acetyltriethylcholine mean

Answer 99

it is far less potent than ACh so acts as a false transmitter

Question 100

How is ACh stored in the presynaptic terminal

Answer 100

in cholinergic vesicles

Question 101

How does ACh enter the vesicles in the presynaptic terminal

Answer 101

by vesicular ACh transporters (VAChTs)

Question 102

How do VAChTs work

Answer 102

high H+ gradient to allow exchange of H+ for ACh

Question 103

What provides the H+ gradient across the ACh vesicle wall

Answer 103

V- type ATPase

Question 104

What kind of vesicle is ACh stored in

Answer 104

clear core generally

contain ATP also at a ratio of 10:1

Question 105

Do cholinergic presynaptic vesicles ever have dense core vesicles?

Answer 105

yes - some have vesicles containing VIP

Question 106

Why do cholinergic vesicles sometimes contain ATP and VIP

Answer 106

ATP and VIP function as co transmitters at some synapses

Question 107

What drug targets ACh storage

Answer 107

vesamicol

an experimental compound, is a non-competitive and reversible blocker of VAChT.

Question 108

What is vesamicol

Answer 108

an experimental compound, is a non-competitive and reversible blocker of VAChT.

Question 109

Which pharmacological agents target ACh release?

Answer 109

Botulinum (BoTXs/BoTNs)
β bungarotoxin (β-BuTx)
α- latrotoxin (α-LTX)
Tetanus neurotoxin (TeNT)

Question 110

What produces botulinum

Answer 110

Clostridium botulinum
a Gram-positive bacterium responsible for botulism that may happen through food poisoning, colonisation of the gut in an infant or via exposed wounds

Question 111

What do botulinum toxins target

Answer 111

cholinergic peripheral synapses (NMJ)

Question 112

Describe the action of BoTX (think about their structure)

Answer 112

heavy chains bind to some gangliosides specific to the target nerves which allow them to be endocytosed specifically into these nerves.

C termini are proteases that are selective for SNARE

Question 113

What are symptoms of botulism (2)

Answer 113

skeletal muscle weakness (which may lead to respiratory paralysis)

autonomic signs that would be associated with loss of cholinergic activity (e.g. constipation, blurred vision, dry mouth, difficulty in swallowing, urinary retention etc.).

Question 114

Where is β - BuTx found

Answer 114

Venom of branded kraits

Question 115

What is the action of β BuTx

Answer 115

Causes irreversible damage to pre-synaptic terminals which then lose synaptic vesicles

ACh release block is probs via its phospholipase A2 action - degrades phospholipids in active zone

Question 116

Does β BuTx attack all nerves

Why

Answer 116

Only cholinergic motor nerves

May stem from its interaction with the substrate phospholipids that are unique to these nerves

Question 117

How does β BuTx kill you

Answer 117

Respiratory failure

Question 118

Where is α latrotoxin found

Answer 118

Black widow spider venom

Question 119

How does α LTX cause paralysis

Answer 119

Causing a massive release and subsequent depletion of the ACh at the NMJ

ACh release in absence of depolarisation/ Ca entry

Question 120

How do we think α LTX works

Answer 120

As a tetramer, It can form a calcium permeable ion channel

Question 121

What produces TeNT

How does it enter the nervous system

Answer 121

Clostridium tetani (another Gram-positive bacterium)

enters the nervous system at the NMJs

Question 122

How can TeNT enter the nervous system via the NMJ

Answer 122

the C-terminal heavy chain of TeNT binds to some gangliosides that are enriched on the peripheral terminals of motor neurons and this binding enables endocytosis.

Question 123

What happens once TeNT enters through the NMJ

Answer 123

trapped in endosomes, TeNT progresses towards soma via retrograde axonal transport and is then discharged into the intersynaptic space within the spinal cord

Question 124

What happens after TeNT is released into the inter synaptic space in the spinal cord

Answer 124

binds to presynaptic membrane of inhibitory interneurons to be endocytosed into the synaptic vesicles of these neurons

Question 125

What happenns to TeNT after it is endocytosed into the synaptic vesicles of presynaptic inhibitory neurons of the spinal cord

Answer 125

acidic nature of vesicles causes insertion of N terminal light chain into cytoplasm and cleaves synaptobrevin

Question 126

What is the result of TeNT’s N terminal cleaving synaptobrevin on the synaptic vesicles in the inhibitory presynaptic neurons in the spinal cord

Answer 126

the inhibitory interneurons are unable to release glycine, causing disinhibition of the motor neuron which then results in violent (tetanic) contractions of skeletal muscle.

Question 127

True or false

ACh is a physiological inhibitor of itself

Answer 127

true
At postganglionic parasympathetic nerve endings, inhibitory muscarinic M2 receptors participate in auto inhibition of ACh release;

other mediators, such as noradrenaline (NA), also inhibit the release of ACh.

Question 128

How does ACh modulate its own release at NMJ

What is the purpose

Answer 128

pre-synaptic nicotinic receptors (nAChRs) facilitate ACh release

allows synapse to function reliable during prolonged high frequency activity

Question 129

What are cholinoceptors

Answer 129

cholinergic receptors that ACh binds to after its release

Question 130

Where are cholinoceptors found and how can they be classified

Answer 130

post synaptic membrane

muscarinic and nicotinic

Question 131

How can you experimentally determine a nicotinic and muscarinic AChR

Answer 131

on the basis of their different affinities for agents that mimic the action of ACh (cholinomimetic agents)

Question 132

What are nAChRs

Answer 132

LGIC belonging to the ‘Cys Loop’ family

Question 133

Where are nAChRs found

Answer 133

at the NMJs, autonomic ganglia, adrenal medulla, the CNS and some other non-neuronal (notably various immune and epithelial) cells

Question 134

Describe the structure of a functional nAChR

Answer 134

a pentamer consisting of α,β, γ, δ and ε subunits with at least 2α subunits present. Each subunit consists of four transmembrane (M1-M4) helices and the M2 helix from all five subunits together form the pore. ACh binds to the interface between the α and neighbouring δ or γ subunits and minimally 2 molecules of ACh are required for the activation of the channel leading to the opening its pore.

Question 135

What are most isoforms of the nAChR permeable to

Is this always the case?

Answer 135

Na and K

No- one of the CNS isoforms namely the (α7)5 channel, is highly Ca2+ permeable.

Question 136

What does activation of nAChRs cause

Answer 136

depolarisation and therefore an EPP (muscle) or EPSP (peripheral ganglia)

Question 137

What happens if an EPp is strong enough

Answer 137

An action potential is generated

Question 138

True or false

nAChRs can be desensitised

Answer 138

True

Usually by prolonged or much stronger agonist stimulation

Question 139

How can nicotinic AChRs be divided based on location

Answer 139

Nm (muscle) and Nn (neuronal)

Question 140

What is the major isoform of the Nn nAChR

Where is it found

Answer 140

(α3)2(β2)3

Autonomic ganglia

Question 141

What is the major variant of Nm nAChR?

Where is this found

Answer 141

(α1)2(β2)δε

Adult skeletal muscle membrane

Question 142

What are the predominant Nm isoforms of the nAChR in the CNS

Answer 142

(α4)2(β2)3

(α7)5

Question 143

True or false

All nAChRs are metabotropic

Answer 143

False

All mAChRs are metabotropic (GPCRs)

Question 144

Why are they called muscarinic AChRs?

Answer 144

in addition to binding ACh, also recognize muscarine, an alkaloid that is present in certain poisonous mushrooms.

Question 145

How do AChRs respond to nicotine?

Answer 145

nAChR: affinity
mAChR: low affinity

Question 146

What do mAChRs mediate

Answer 146

postganglionic transmission in the peripheral nervous system, being present on the membranes of effector tissues including heart, tissue-specific smooth muscles (lung, some blood vessels, bladder, gut etc.) and glands (salivary, lacrimal etc). They also occur in the CNS

Question 147

Where is the M2 mAChR found

What is its action here

Answer 147

pre-synaptically on the endings of noradrenergic nerves and cholinergic nerves

its activation causes a decrease in transmitter release

Question 148

How many subtypes of mAChRs are there

Which are the most important in the periphery

Answer 148

5: M1-5

M1, 2, 3

Question 149

Are M1, 2, 3 mAChRs found in autonomic ganglia

Answer 149

. Some of these isoforms may be present in autonomic ganglia but they are mostly present in the effector tissue membrane and they mediate the signalling leading to the biological functions of cholinergic stimulation.

Question 150

Is AChE usually floating about?

Answer 150

no it is tethered to the post synaptic membrane

a soluble AChE is found in the cytoplasm of the presynaptic neuron (obvs doesnt affect life span of released ACh)

Question 151

What does neurotransmission in autonomic ganglia involve

Answer 151

release of ACh by pre-ganglionic fibres and the rapid depolarization of post-ganglionic nerve membranes via the activation of neuronal nAChRs (Nn).

Question 152

How is the structure of cholinergic autonomic ganglia different to the NMJ

Answer 152

Unlike the NMJs, ganglia do not have discrete end plates with focal localization of receptors; rather, the dendrites and nerve cell bodies contain the receptors

Question 153

Which Nn is insensitive to alpha bungarotoxin

What can inhibit these

Answer 153

(α3)2(β2)3

trimetaphan (a competitive antagonists) and hexamethonium

Question 154

What are the 4 different changes in membrane potential of postganglionic nerves from cholinergic stimulation

Answer 154

• an initial EPSP (via Nn receptors) that may result in an action potential
• an IPSP mediated by muscarinic M2 receptors
  (Gi/o-coupled)
• a secondary slow EPSP mediated by muscarinic M1 receptors (Gq/11-coupled)
• a late, slow EPSP mediated by various neuropeptides

Question 155

What is the issue with agents acting at the autonomic ganglia

Answer 155

lack of selectivity between sympathetic and parasympathetic ganglia and few can also have effects on the CNS. Their peripheral action is largely governed by the extent of the sympathetic and parasympathetic control of the tone of the effector systems.

Question 156

What are the 2 categories in which ganglionic stimulants can be grouped

Answer 156

Nn agonists

mAChR agonists

Question 157

Name a member of the Nn receptor group of ganglionic stimulants

Answer 157

nicotine

Question 158

What is nicotine

Answer 158

a tertiary amine found in tobacco leaves

Question 159

What does nicotine do at low and high concentrations

Answer 159

stimulates Nn channels whilst at higher doses, it desensitizes the channel (typical of for LGICs)

Question 160

Name some products that use nicotine as an aid for smoking cessation

Answer 160

gums, lozenge, e-cigarettes (‘vapes’) and transdermal patches as part of the nicotine replacement therapy (NRT)

Question 161

What is varenicline used for

Answer 161

used as a smoking cessation ‘aid’ along with counselling and behavioural therapy to help people stop smoking

Question 162

What drug is used to aid smoking cessation in conjunction with therapy

Describe its action

Answer 162

varenicline

high affinity partial agonist for the α4β2 receptors (mainly implicated in nicotine addiction) and also a full agonist on α7 receptors

both are in the CNS

Question 163

What receptor is mainly implicated in nicotine addiction

Answer 163

α4β2 Nn receptor

Question 164

Name 2 ganglionic stimulants that act as Nn agonists

Are these drugs

Answer 164

tetramethylammonium (TMA)

dimethylphenylpiperazinium (DMPP)

not drugs but useful for experiments

Question 165

What are mAChR agonists blocked by

Answer 165

atropine

Question 166

What do mAChR agonists mimic

Answer 166

the slow EPSP

Question 167

How does nicotine act as an Nn receptor blocking agent

Answer 167

initially stimulates the ganglia by an ACh-like action and then blocks them by causing a persistent depolarization

Question 168

Do all ganglionic blocking agents act in the same way as nicotine

Answer 168

no other ones
impair transmission either by competing with ACh for binding at ganglionic Nn receptors (e.g. trimethaphan) sites or by blocking the channel pores (hexamethonium).

equivalent to non depolarising blockers at NMJ

Question 169

What does trimethaphan do

Answer 169

competes with ACh binding at ganglionic Nn receptors

Question 170

Which drug blocks channel pores at ganglionic cholinergic synapses

What is important to remember when prescribing this drug

Answer 170

hexamethonium

Blockade of ganglionic Nn channels by hexamethonium manifests use dependence.

Question 171

What were the earliest antihypertensive agents

Are they still used?

Answer 171

ganglionic blocking agents

no - clinically obsolete by now due to numerous side effects, largely coming from their inability to discriminate between sympathetic and parasympathetic ganglia.

Question 172

How many nerves innervate one muscle fibre

Answer 172

only one nerve fibre supplies each muscle fibre - the end plate

Question 173

What happens at the NMJ structurally

Answer 173

the pre-synaptic axon terminal boutons synapse with the muscle fibre membrane (sarcolemma) that is deeply-infolded as ‘junctional folds’

Question 174

Where are Nm nAChRs present in the sarcolemma

What else is near them

Answer 174

on the crest of the junctional folds

volatage gated Na channels are deep in the folds and in the non junctional part of the sarcolemma

Question 175

What happens when ACh binds to Nm receptors

Answer 175

the nAChRs open to allow Na influx and K efflux

generates the EPP and if threshold for Nav channels is reached an AP is elicited

Question 176

Nm channels are equally permeable to Na and K - does this mean equal amounts of Na enter and K leave?

Answer 176

No
the prevailing electrochemical gradients for Na+ is much greater than that of K+, so more Na+ enters than K+ leaves the cytoplasm

Question 177

How is ACh removed from the NMJ

Answer 177

hydrolysed by AChE present in the basal lamina within the junctional cleft.

Question 178

where is ACh found in the NMJ

Answer 178

in the basal lamina within the junctional cleft.

Question 179

hat do directly acting agents modulating NMJ transmission act on?

Answer 179

directly on the Nm receptors on the sarcolemma

Question 180

How do the subunits of the Nm receptor at the NMJ vary between the adult and foetus

Answer 180

The adult Nm is represented by (α1)2β1δε

the foetal form has gamma in place of the ε subunit

Question 181

What is the adult Nm receptor irreversibly antagonized by

Answer 181

α-bungarotoxin

Question 182

What is the main clinical use of neuromuscular blocking agents

Answer 182

as an adjuvant in surgical anaesthesia to obtain relaxation of skeletal muscles.

Question 183

How do muscle relaxants improve the safety of anaesthesia ?

Answer 183

less anaesthetic is required, minimizing respiratory and cardiovascular depression and allowing rapid post-anaesthetic recovery

Question 184

What is used in conjuction with GA during laryngoscopy, bronchoscopy, and esophagoscopy

Why do we not have to worry about these drugs having a wide spread effect

Answer 184

Short-acting drugs are used to facilitate endotracheal intubation

charged so don’t cross BBB and action remains peripheral

Question 185

What are the 2 types of NMJ blockers

Answer 185

Depolarising and • non-depolarizing neuromuscular blocking agents

Question 186

How do depolarising NMJ blockers work

Answer 186

Nm agonists so open Nm channels but are not readily hydrolysed by AChE

depolarisation last longer leading to some fasciculations,
followed by blocking of neuromuscular transmission and flaccid paralysis (called phase I block).

The depolarisation from the Nm channels leaves Nav channels in a inactivated state

with increasing [depolarising blocker] over time the block converts from phase 1 to phase II (membrane gradually repolarizes but now the Nm channels become desensitized)

Question 187

How can a depolarising blockade be potentiated

Answer 187

Anti-AChE agents

Question 188

Name depolarising NMJ blocker

Answer 188

Suxamethonium (succinylcholine)

Question 189

Why is succinylcholine considered unique

Answer 189

Suxamethonium (succinylcholine) represents the only depolarizing blocking agent being used in the clinics at present.

Question 190

What is phase I and II of the depolarising block at the NMJ

Answer 190

Phase I: extended depolarisation leads to fasciculations before flaccid paralysis because the open Nm receptors maintain the depolarized state of the sarcolemma and thus leaving all the Nav channels in inactivated state

Phase II: agent increases and membrane gradually repolarizes but now the Nm channels become desensitized.

Question 191

When is succinylcholine used despite its side effects

Answer 191

still in conditions where fast onset and brief duration of action are required, e.g. with tracheal intubation

Question 192

Why does succinyl-Ch have a v brief duration of action

Answer 192

due to its rapid hydrolysis in the plasma by butyrylcholinesterase (BuChE, also known as pseudocholinesterase).

Question 193

Where is BuChE synthesised

What does this mean when administering NMJ blockers?

Answer 193

liver

patients with liver disease or genetic deficiency of this enzyme therefore run the risk of prolonged action of suxamethonium (which is hydrolysed by BuChE)

Question 194

Whyy must you check a patient doesnt have electrolyte imbalance before administering succinyl-Ch

Answer 194

suxamethonium is a depolarising NMJ blocker and causes

K+ loss from the muscles into blood, which may lead to hyperkalemia and can be life-threatening for patients with electrolyte imbalance

Question 195

What are non depolarising NMJ blockers essentially

Answer 195

competitive antagonists of Nm channels

Question 196

true or false

non-depolarising NMJ blockers lead to flaccid paralysis

Answer 196

true
they prevent depolarization of the sarcolemma and inhibit muscular contraction, leading to a flaccid paralysis

fasciculations are not seen with these

Question 197

How can the competitive action of non depolarising NMJ blockers be overcome

Why is this useful clinically?

Answer 197

by administration of anti-cholinesterases (e.g. neostigmine), which increase the [ACh] in the NMJ.

gives anaesthesiologists an option to shorten the duration of the neuromuscular blockade.

Question 198

What was the first known non depolarising block

Answer 198

curare - a cocktail of natural alkaloids used as arrow poison by South American Indians to paralyze prey

Question 199

What is the major constituent of curare

Is it used clinically?

Answer 199

d-tubocurarine

no due to poor selectivity between the ganglionic and NMJ-specific nAChRs

Question 200

What are synthetic non-depolarising blocking drugsdivided into

Answer 200

the aminosteroid group (the ones with uronium suffix) such as pancuronium, rocuronium etc.
and
the benzylisoquinolinium group (the ones with the urium suffix) such as atracurium

Question 201

Describe the aminosteriod group of drugs

Give 2 examples

Answer 201

synthetic NMNJ non-depolarising blocking drugs

Ends in uronium

pancuronium, rocuronium

Question 202

Describe the benzylisoquinolinium group of drugs

eg?

Answer 202

synthetic non-depolarising blocking drugs

(the ones with the urium suffix) such as atracurium, mivacurium

Question 203

How does the onset of rocuronium compare to succinyl choline

Answer 203

succinyl Ch has a faster onset

non-depolarising neuromuscular blocking drugs have a slower onset of action than suxamethonium

Question 204

How can non-depolarising neuromuscular blocking drugs be divided based on action?

Answer 204

by their duration of action as short-acting (15–30 minutes), intermediate-acting (30–40 minutes), and long-acting (60–120 minutes), although duration of action is dose-dependent

Question 205

Which kinds of non-depolarising neuromuscular blocking drug is used more commonly in practice

Answer 205

Drugs with a shorter or intermediate duration of action, such as atracurium and rocuronium, are more widely used than those with a longer duration of action, such as pancuronium

Question 206

Name 2 non depolarising NMJ drugs which have an intermediate duration of action

Which has a longer duration

Answer 206

atracurium and rocuronium

pancuronium

Question 207

What is common about NMJ non depolarising blocker structure

Answer 207

quaternary ammonium (=charged) compounds therefore poorly absorbed (cannot be given orally) and rapidly excreted.

For the same reason, they do not cross the placenta (which allows them to be safe in obstetric anaesthesia) as well as the blood-brain barrier.

Question 208

What do anesthetists use to monitor postoperative recovery of neuromuscular transmission?

Answer 208

tetanic fade

Question 209

What is tetanic fade

Answer 209

non-depolarising blocking agents also block facilitatory pre-synaptic autoreceptors and thus inhibit the release of ACh during repetitive stimulation of the motor nerve

Question 210

What are some of the clinical responses to NMJ blocking agents caused by

Answer 210

release of histamine

Question 211

Name 4 NMJ blocking agents that cause histamine release

Answer 211

Suxamethonium, mivacurium,
atracurium

to a lesser extent than d-tubocurarine unless administered rapidly

Question 212

Which NMJ blockers are less likely to cause histamine release

Answer 212

amino steroids such as pancuronium and rocuronium

Question 213

Why is histamine released by muscle relaxants?

Answer 213

Histamine release typically is a direct action of the muscle relaxant on the mast cell rather than an outcome of individual’s allergic hypersensitivity

Question 214

How does alpha- bungarotoxin work

What is it often used in

Answer 214

irreversibly binds to the ACh binding site on the adult Nm receptors at the NMJ and thus block the transmission.

a- BuTx, specially its various antibody/fluorophore conjugates are widely used in biochemical and structural studies of Nm receptors and NMJs.

Question 215

How are distinct bungarotoxins different

Answer 215

α-Bungarotoxin inhibits the binding of acetylcholine (ACh) to nicotinic acetylcholine receptors; β- and γ-bungarotoxins act presynaptically causing excessive acetylcholine release and subsequent depletion

Question 216

How is BoTX used clinically

Answer 216

BoTX-A
injected locally for cosmetics

can treat certain ophthalmic conditions associated with spasms of eye muscles (e.g., blepharospasm).

Question 217

how do anti-AChEs at on NMJ transmission

Answer 217

act indirectly by prolonging the life time of release ACh within the junctional cleft.

Question 218

Why must patients with myasthenia gravis be careful with certain antibiotics

Answer 218

members of the aminoglycoside antibiotics (e.g. streptomycin, neomycin etc.), in large doses inhibit Cav channels and thus can produce neuromuscular blockade, especially in patients with myasthenia gravis

Question 219

Which antibiotics can block Cav channels at the NMJ

Give 2 examples

Answer 219

aminoglycoside antibiotics

e.g. streptomycin, neomycin

Question 220

What is the effect of aminoglycoside antibiotics on patients treated with a NMJ blocker

What other drug class has a similar effect

Answer 220

in normal or low doses can unpredictably prolong muscle paralysis

tetracyclines

Question 221

Where are mAChRs primarily found

What is a key exception

Answer 221

present in autonomic ganglia and vascular endothelial cells

also on autonomic effector cells innervated by post-ganglionic parasympathetic nerves

exception: postganglionic sympathetic nerves to sweat glands are cholinergic and the released ACh acts via mAChRs present in the gland

Question 222

What is unusual about mAChRs being in vascular endothelial cells

Answer 222

they receive little or no cholinergic innervations

Question 223

In the majority of cases how many types of mAChR are present in the effector tissue

Answer 223

at least two muscarinic receptor subtypes (typically M3 and M1/M2)

Question 224

What is the ‘neural’ subtype of mAChR

Answer 224

M1

Question 225

Where are M1 mAChRs mainly found

Answer 225

on CNS, autonomic ganglia and on gastric parietal cells

Question 226

How to remember what the different classes of mAChR are coupled to

Answer 226

all odd ones (M1, 3, 5); coupled to Gq/11

Question 227

what does agonist binding to mAChR M1 lead to

What other mAChR types would behave in the same way

Answer 227

activation of PLCβ -> hydrolyses PIP2 to IP3 and DAG
IP3 mediates intracellular Ca2+ release
DAG activates PKC

M3 and M5

Question 228

Why can IP3 readily diffuse through the cytosol

What do the characteristics of DAG mean for it respectively

Answer 228

it is polar and activates the ER membrane-bound IP3 receptors which then mediate intracellular Ca2+ release

DAG being lipophilic, stays in the membrane and activates PKC

Question 229

Does DAG only activate PKC ?

Answer 229

No
also activates several members of the TRP family of ion channels which are mainly involved in sensory perception and several of them are also Ca2+ permeable, mediating Ca2+ influx.

Question 230

What else (other than PLC) mediates [DAG]

Answer 230

DAG lipase to produce arachidonic acid (AA).

Question 231

What is the importance of the production of AA from the action of DAG lipase on DAG

Answer 231

may trigger a distinct Ca2+ influx pathway in some cells

most importantly, it is the precursor of biologically active lipid-derived molecules eg prostaglandins and leukotrienes .

Question 232

What do M1 receptors in neurons inhibit

How does it do this (2)

What is the purpose?

Answer 232

K+ conductance (the m channel)

through the depletion of the PIP2 in the postganglionic nerve membrane. In certain case, the Ca2+ signals via calmodulin (CaM) and PKC, also contributes to the process

brings about a late depolarisation in the autonomic ganglion which occurs many seconds after the initial, fast EPSP induced by Nn receptors

Question 233

What are M channels that conduct K+ known to be composed of

Answer 233

subunits of the Kv7/ KCNQ channel family.

Question 234

Describe the M2 mAChR receptor

What are they coupled to

What does this mean they activate

Answer 234

cardiac subtype

Gi/o proteins

the inhibition of adenylyl cyclase (AC) which results in decreased cAMP production and thus decreased activation of protein kinase A (PKA)

Question 235

What does M2 activation ultimately lead to

Answer 235

in decreased phosphorylation of a number of proteins that notably include the voltage-gated Ca2+ channels (CaVs), reducing probability of opening and Ca2+ influx

This decreases NT release from neurons

Question 236

What is the predominant mAChR subtype in the heart

How are they distributed

Answer 236

M2

largely confined to the SAN and AVN to some extent in the atria but much less in the ventricles.

Question 237

What does stimulation of the M2 receptors in the heart result in

Answer 237

negative chronotropic effect

Question 238

How does activation of M2 channels in the heart

Answer 238

reduced Ca2+ current via the L and T-type Cavs due to reduced PKA-mediated phosphorylation of these channels

βγ opens g protein coupled inwardly rectifying K+ channels in the nodal pacemaker cells. This causes hyperpolarisation by K+ efflux

threshold for opening of the HCN channels which mediate the slowly-depolarizing inward Na+ current (the If current), is shifted towards a more negative value.

Reduces atrial contractility via triggering I(K-ACh)

Question 239

What are the inwardly rectifying K+

Answer 239

GIRK1

Kir3.1

Question 240

What is the K+ efflux current following M2 stimulations in the heart called

Answer 240

I (K-ACh)

Question 241

What causes the threshold opening of the HCN channels which mediate the slowly-depolarizing inward Na+ current (the If current), to shift towards a more negative value.

Answer 241

reduced [cAMP]

Question 242

What can the M3 mAChR subtype be classed as

Answer 242

glandular subtype

Question 243

What are M3 receptors coupled to

What is usually the result of stimulation of these mAChRs

Answer 243

Gq and G11

stimulation of glandular secretions, e.g. saliva, sweat etc

Question 244

What doe activation of M3 receptors in smooth muscle lead to

Answer 244

contraction because of the increase in cytosolic free [Ca2+]i

Question 245

What causes [Ca2+]i to increase when M2 mAChRs are activated in smooth muscle

Why is the effect different in vascular smooth muscle

Answer 245

IP3 invoked Ca2+ release from ER

increased endothelial [Ca2+]i binds to CaM
Ca2+-CaM then activates eNOS to produce NO leading to smooth muscle relaxation

Question 246

What are the following:
CaM
eNOS
EDRF

Answer 246

CaM = calmodulin
eNOS: endothelial nitric oxide synthase
EDRF: ‘endothelium-derived relaxation factor’ ie NO

Question 247

What is the effect of CaM-Ca2+ activating eNOS in smooth muscle

Answer 247

NO activates soluble guanylyl cyclase, produces cGMP and ultimately relaxes the vascular smooth muscle

Question 248

How can pharmacological agents modulate muscarinic cholinergic synapses (2)

Answer 248

the activity of mAChRs by physically binding to these receptors (directly-acting agents)
- the amount/life-time of ACh released from the post-gangilonic nerve terminal (indirectly-acting agents)

Question 249

What happens to vascular smooth muscle if you rub away the endothelium and add ACh

Answer 249

no relaxation until the ACh is washed away

Question 250

Which mAChR is mainly present in the eye and which parts of the eye

Answer 250

mainly M3 - constrictor pupillae; ciliary muscles; lacrimal glands

Question 251

What does stimulation of M3 receptors in the constrictor pupillae lead to

Answer 251

contraction
shortens pupil diameter (miosis)
lowers intraocular pressure

Question 252

What does stimulation of M3 receptors in the ciliary muscles lead to

Answer 252

contraction to reduce focal length of lenses, allowing accommodation

Question 253

What does stimulation of M3 receptors in the lacrimal glands lead to

Answer 253

increased secretion

Question 254

What is the distribution of mAChR in the detrusor muscle and mucosa/submucosa of the bladder

Answer 254

detrusor: M2=80%
M3=20%
(some beta 3 ARs present too)

mucosa and submucosa: M2 and M3

Question 255

What is the PNS supply to the bladder

Answer 255

via pelvic nerve

Question 256

What is the distribution of mAChRs throughout the lungs

Answer 256

pre-junctional terminal: M2 to reduce ACh release

postganglionic cell body: M1

airway smooth muscle cells: M2 and 3 for bronchoconstriction

at submucosal glands: M1, M3, to increase mucus secretion

Question 257

How does the Vagus affect the lungs

Answer 257

tonically fires to
contract (mainly via M3-
PLC(beta)-IP3 mediated) airway
smooth muscle during
normal breathing - vagal tone

Question 258

What effect does the vagus nerve have on the lungs when irritants are present

Who is this dangerous for

Answer 258

irritants stimulate sensory vagal afferents, activating a reflex PNS activity via the vagal efferents causing bronchospasm

it is major
bronchoconstricting factor for COPD patients

Question 259

True or false:

It’s relatively easy to develop directly acting mAChR ligands that are subtype selective

Answer 259

False
No it is very challenging

the classical (orthosteric) binding site (= where ACh binds to) is highly conserved across mAChR subtypes

Question 260

What have we used to discover that the ACH binding site is conserved across mAChRs

Answer 260

Analysis of amino acid sequence and recent X-ray crystallographic studies

Question 261

What have we used to overcome the problems of the conserved binding site of mAChRs

Answer 261

these receptors possess distinct allosteric sites located often within the extracellular loops or the outer segments of different transmembrane (TM) helices.

Because these regions show a considerable degree of sequence variation across M1–M5 receptors, considerable progress has been made in developing subtype specific allosteric modulators.

Question 262

How do allosteric modulators affect mAChRs

Answer 262

by altering the affinity or efficacy of orthosteric muscarinic ligands.

Question 263

What are PAMs in relation to mAChRs

What is another related drug type

Answer 263

Positive allosteric modulators (PAMs)

enhance orthosteric activity,

negative allosteric modulators (NAMs) inhibit it

Question 264

allosteric modulators have lead to development of new therapeutic agents with increased efficacy and reduced side effects. Name 2 diseases where this research is focussed

Answer 264

several severe disorders of the CNS, including Alzheimer disease and schizophrenia.

Question 265

Other than allosteric modulators, what is another potential strategy for mAChR subtype selectivity

Answer 265

development of hybrid, bitopic ligands that interact with both the orthosteric binding cavity and an allosteric site

Question 266

Why are hybrids that bind to both the orthosteric and allosteric sites of mAChRS being developed?

Answer 266

By targeting orthosteric and allosteric sites simultaneously, bitopic ligands can potentially achieve both high affinity and receptor subtype selectivity.

Question 267

How can directly-acting parasympathomimetic or cholinomimetic agents (muscarinic agonists) be classified?

Answer 267

1) choline esters

2) naturally occurring cholinomimetic alkaloids

Question 268

Name some choline esters

Answer 268

include ACh and synthetic esters of choline, such as carbachol (carbamylcholine) and bethanechol

Question 269

Name 2 synthetic choline esters

Answer 269

carbachol (carbamylcholine) and bethanechol

Question 270

name a cholinomimetic alkaloid

Answer 270

pilocarpine

Question 271

True or false

. All of the direct-acting cholinergic drugs have a longer duration of action than ACh.

Answer 271

True

All of the direct-acting cholinergic drugs have a longer duration of action than ACh.

Question 272

What is Bethanechol

What does it activate and where does it not have action?

Answer 272

chemically a hybrid of methacholine and carbachol

non-selectively activates mAChRs
lacks nicotinic action

Question 273

What is the effect of bethanechol on the bladder

Answer 273

stimulates the detrusor muscle of the bladder (via M3 receptor), whereas the trigone and sphincter muscles are relaxed

ie produces urination

Question 274

What is bethanechol licensed for

Is it very common?

Answer 274

for acute postoperative, postpartum and neurogenic urinary retention

its use has largely been superseded by catheterisation

Question 275

What is pilocarpine used for

Answer 275

to treat glaucoma

Question 276

What is the drug of choice for emergency lowering of intraocular pressure for glaucoma patients?

How is it administered?

Answer 276

pilocarpine

by instillation as eye drops and it is readily absorbed across the conjunctival membrane

Question 277

How is pilocarpine absorbed

Answer 277

administered by instillation as eye drops and it is readily absorbed across the conjunctival membrane

Question 278

What is the action of pilocarpine once it has been absorbed across the conjunctiva

Answer 278

contracts the ciliary muscle to produce traction on the trabecular meshwork around the Schlemm canal, causing an immediate drop in intraocular pressure as a result of the increased drainage of aqueous humour

Question 279

How quickly does pilocarpine act

How long does it last

Is it repeatable?

Answer 279

action occurs within a few minutes

lasts 4 to 8 hours

can be repeated.

Question 280

Why may patients who have taken pilocarpine struggle to focus their eyesight?

Answer 280

pilocarpine causes miosis, which is experienced as a spasm of accommodation and vision is fixed at a random distance

Question 281

What is the effect of atropine on the eye

Answer 281

opposes the effects of pilocarpine as atropine is a muscarinic blocker

Question 282

Name 2 diseases where pilocarpine is used to increase secretion

Answer 282

xerostomia

Sjögren’s syndrome

Question 283

What is Sjögren’s syndrome

Answer 283

syndrome which is an autoimmune disease of glands that secrete fluid

Question 284

What is xerostomia

Answer 284

chronic dry mouth problem, most common complications associated with radiotherapy of head and neck cancer)

Question 285

How do pharmacological antagonists of mAChRs work

Answer 285

directly acting anti-cholinergic or cholinolytic agents

Question 286

What site do competitive inhibitors of mAChRs block

Where are these receptors found?

Answer 286

the othosteric site

on effector cells at parasympathetic neuroeffector junctions in the peripheral ganglia (as well as the CNS).

Question 287

True or false

mAChR competitive inhibitors can block SNS transmission

Answer 287

True - mostly acts on PNS but can act on cholinergic junctions eg sweat and salivary glands

Question 288

Do mAChR competitive inhibitors affect AChRs

What does this mean

Answer 288

no

little or no action at NMJs or autonomic ganglia.

Question 289

Describe the chemical structure of anti-muscarinic agents

Answer 289

contain an ester and basic groups like that of ACh but bulky aromatic group replacing the acetyl moiety

Question 290

What kind of drug is scopolamine

Name another of this type

Answer 290

a naturally occurring alkaloid mAChR inhibitor

atropine (you need to know this one)

Question 291

WHat are the 3 different types of anti-muscarinic agent

Name one of each

Answer 291

naturally occurring alkaloid (atropine)

natural alkaloid semisynthetic derivative (ipratropium)

synthetic agents (solifenacin)

Question 292

Name 2 semi synthetic anti muscarinic agents

Answer 292

homatropine,
methscopolamine,
ipratropium

Question 293

Name 5 synthetic muscarinic agents

Answer 293

tropicamide, 
cyclopentolate, 
pirenzepine, 
darifenacin, 
solifenacin

Question 294

Give example of some relatively selective mAChR blockers (4)

What are most mAChR antagonists?

Answer 294

pirenzepine = M1
MT7= M1
darifenacin and solifenacin =M3

most are non selective

Question 295

What is MT7

Answer 295

A toxin in the venom of the African green mamba that selectively targets M1.

Question 296

What are mAChR blockers used for clinically

Answer 296

to inhibit effects of parasympathetic activity in the respiratory tract, eye, urinary tract, GI tract and heart

Question 297

Which muscarinic blockers are used on the eye clinically

Answer 297

topically for mydriasis and cycloplegia in ophthalmic examinations

Question 298

Would you want to use atropine for an ophthalmic examination?

Answer 298

Short-acting, relatively weak mydriatics, such as tropicamide (action lasts for 4–6 hours) and cyclopentolate (action up to 24 hours), are typically preferred over atropine (action may last up to 7 days).

Question 299

What drugs would you use to make funduscopy easier (2)

What effects do they cause that make this beneficial

Answer 299

tropicamide
cyclopentolate

mydriasis
cycloplegia

Question 300

What is used as the standard treatment of poisoning

Answer 300

atropine in large doses by irreversible, long lasting inhibition of AChE

Question 301

What is the main effect of antimuscarinic agents on the heart

Answer 301

main effect is on rate - dominant effect= tachycardia

clinical doses may lead to transient bradycardia

Question 302

How does the effect of atropine on the heart change as its dose changes

Answer 302

Larger doses of atropine cause progressive tachycardia by blocking M2 receptors on the SA nodal pacemaker cells, thereby antagonizing parasympathetic (vagal) tone to the heart

Question 303

in which type of patient is the effect of atropine more profound

Answer 303

healthy young adults, in whom the vagal tone is considerable

Question 304

What is atropine useful for clinically

Answer 304

to manage bradycardia associated with the excessive use of the ‘beta blockers’ and acute myocardial infarctions.

Question 305

Which mAChR is involved in bronchoconstriction

What happens if these receptors are activated on lung epithelia

Answer 305

M3 on airway smooth muscle

mucous secretion

Question 306

Describe a ‘vagally-mediated reflex bronchospasm’

Answer 306

lung M3 mAChR activation happens normally as a ‘vagal tone’ but many irritants (dust, allergens, histamine, some gases etc.) via local sensory nerves can make it more prominent in the form of a ‘vagally-mediated reflex bronchospas

Question 307

What is the relevance of vagal tone in COPD

Is this the same in asthma

Answer 307

it is the major reversible brochoconstrictive component

no

Question 308

What does M3 blockade in bronchial smooth muscle result in?

How does the effect of these blockers differ from a normal patient to a COPD patient

Answer 308

bronchorelaxation/ bronchodilation due to decreased muscle tone

minimal effect in normal airways but significant in COPD

Question 309

What are the 2 categories of mAChR blockers used in COPD

Give an example of each

Answer 309

LAMA (long acting muscarinic antagonist) - tiotropium

SAMA (short acting muscarinic antagonist) - ipratropium

Question 310

Name 2 LAMA drugs

Answer 310

tiotropium and glycopyrronium

Question 311

True or false

All drugs in both SAMA and LAMA categories have higher selectivity for one type of mAChR

Answer 311

True
Higher selectivity for M3 than M2

LAMA also dissociate much faster from M2 than 3

Question 312

Where does the longevity of LAMA action come from

Answer 312

their slow dissociation from M3 receptors

Question 313

What kind of anti muscarinic agent can be used if asthma is not being adequately controlled by beta-AR stimulants

Answer 313

LAMA as additional bronchodilators

Question 314

What do you use to treat urinary incontinence

Give 2 examples

How does this work

Answer 314

M3 selective antagonists

eg solifenacin and darifenacin

selective inhibition of M3 receptors that mediate contraction of bladder’s detrusor muscle

Question 315

Which anti-muscarinic drug can be used to reduce excessive salivation

Which feature allows this

Answer 315

glycopyrronium

cannot cross BBB

Question 316

Why might someone have the symptom of excessive drooling

Answer 316

drug induced or associated with heavy-metal poisoning and Parkinson’s disease

Question 317

What are the 2 types of cholinesterase

Describe the specificity of each

Answer 317

BuChE (AKA pseudocholinesterase)
AChE

AChE = only ACh
BuChE= much broader

Question 318

Name 2 drugs that BuChE can break down

Answer 318

procaine (a local anaesthetic)

suxamethonium (depolarising NMJ blocker)

Question 319

Where is BuChE made

Where can it be found in the body (4)

Answer 319

liver

mostly blood
traces in: skin, gut, and brain

Question 320

Where is AChE found (2) and what form does it take in these locations

Answer 320

both in the presynaptic nerve ending (as a soluble form in the cytoplasm) and in the synaptic cleft (as tethered to the postsynaptic neuronal membrane/junctional fold).

Question 321

What is the presynaptic purpose of AChE (2)

Answer 321

guards against the accumulation of cytoplasmic ACh outside storage vesicles

termination of ACh action

Question 322

How is AChE attached to the post synaptic terminal

Answer 322

3 tetramers of AChE are attached by disulphide bonds to a long collagenous tail which tethers the enzyme to the postsynaptic/post-junctional target membrane.

Question 323

Where in the synpase is the AChE primarily responsible for ending ACh action ?

Answer 323

membrane-bound oligomeric form of AChE

Question 324

What is the turnover of AChE

Answer 324

> 10,000 mol per active site per second

Question 325

What kind of enzyme are the cholinesterases?

Answer 325

serine hydrolases

Question 326

What part of the Ser group in Ser hydrolases performs the nucleophilic attack

What is the purpose of this attack

Answer 326

hydroxyl (-OH) group

An intermediary adduct with the substrate is formed, which then undergoes hydrolysis

Question 327

What is the 3D structure of AChE

Where is the catalytic site? Give measurements and a specific name

Answer 327

hourglass

at the base of a deep (~about 20Å from the surface) and narrow (~ 5Å wide) tunnel named the aromatic gorge.

Question 328

What is the peripheral anionic site?

What is the purpose of this?

Answer 328

the entrance too the aromatic gorge of AChE

recognition of ACh

Question 329

What is one of the key interaction s of the peripheral anionic site

Answer 329

a weak cation-pi interaction between the heteroaromatic ring of a particular tryptophan residue (W279 for mammalian AChE) and the charged quaternary nitrogen of ACh

Question 330

What happens after the peripheral anionic site recognizes ACh

Answer 330

transferred down the aromatic gorge to the active site

Question 331

How is the ACh helped down the aromatic gorge after being recognised by the peripheral anionic site?

Answer 331

14 conserved aromatic residues line the gorge and help in pushing the ACh downwards towards the catalytic centre through cation-pi interactions with ACh. An electrostatic gradient running down the gorge also favours such movement of ACh.

Question 332

What happens to ACh when it reaches the end of the aromatic gorge

Answer 332

to the ‘catalytic anionic site’ (CAS) which helps in properly positioning ACh against the catalytic triad consisting of specific glutamate, histidine and serine

Question 333

Describe the tetrahedral intermediate formed by nucleophilic attack of Ser on ACh in AChE (a Ser hydrolyase)

Answer 333

has a charged oxygen

intermediate is stabilised by backbone amide groups (oxyanion hole)

from this the ACh bond is broke, releasing choline, and leaving acetyl-serine behind

Question 334

After choline has been released from AChE, an acetyl serine is left. What happens next

Answer 334

The serine¬-acetate bond is then spontaneously hydrolysed by water to release acetate and regenerate the enzyme

Question 335

How fast is the action of AChE

Answer 335

one of the fastest known : >10^4 molecules of ACh are hydrolyzed per second by a single AChE molecule, requiring only about 100microsec.

Question 336

What are anticholinesterases also referred to as

Answer 336

as indirectly acting cholinergic/cholinomimetic agents because they generally do not activate receptors directly

Question 337

Why are anti-AChE agents often used as toxins

Give a famous example of how they were used recently

Answer 337

cholinergic synapses are widely distributed throughout the body

deployment of nerve gas (novichok) in an attempt to assassinate victims in Salisbury in 2018

Question 338

What is a necessary feature of an anti-AChE agent used to treat Alzheimer’s

Give 2 examples

Answer 338

can cross BBB

rivastigmine
donepizil

Question 339

How can you categorise anti-AChE agents by:

a) mechanism of inhibition
b) duration of action

Give examples

Answer 339

a) • Reversible: a) non-covalent (edrophonium) b) covalent inhibitors (physostigmine, neostigmine etc)
• Irreversible - organophosphates such as dyflos, parathion, ecothiophate

b) • Short acting (edrophonium)
• Intermediate acting (the ‘stigmines’)
• Long acting (the organophosphates

Question 340

What is edrophonium

Answer 340

Non-covalent, reversible, short acting anticholinesterase

Question 341

Describe the structure of edrophonium

Where can it act

Answer 341

a quaternary ammonium compound

restricted to the periphery

Question 342

Name a non-covalent, reversible, short acting anticholinesterases and describe how it interacts with AChE

Answer 342

edrophonium

interacts only to the catalytic anionic site (CAS) of the enzyme, primarily through a cation- π interaction between its quaternary nitrogen and the aromatic (indole) ring of a tryptophan (W84) residue of AChE

the reversible nature of this interaction explains the short duration of edrophonium action

Question 343

What is the duration of edrophonium action

Answer 343

2-10 min

Question 344

What is edrophonium used for

…

Answer 344

the tensilon test -
in order to diagnose myasthenia gravis

HOWEVER:
Edrophonium is discontinued in the UK as its use as a diagnostic tool in myasthenia gravis has been largely superseded by antibody testing and the use of electrical conduction studies.

Question 345

What does a positive result in the tensilon test look like?

Mention drug used and illness diagnosed

Answer 345

A myasthenia positive individual characteristically feels temporary improvement in the facial weakness and ptosis within 5-10min of edrophonium injection

Question 346

Describe Covalent, reversible, medium acting anti-cholinesterases as a group

Give 4 examples

Answer 346

esters of carbamic acid (instead of acetic acid as with ACh) and have the suffix ‘stigmine’ and include physostigmine, neostigmine, pyridostigmine and rivastigmine.

All except rivastigmine are charged and therefore act only peripherally.

Question 347

How does neostigmine interact with AChE?

What kind of drug is this

Answer 347

With their basic group, they interact with the anionic site of AChE and transfer carbamyl group to the hydroxy group of Ser 203. Carbamylated AChE is more stable than acetylated AChE and takes minutes to hydrolyze. Hence these are medium acting agents.

Covalent, reversible, medium acting anti-cholinesterases

Question 348

How and when is neostigmine administered

Answer 348

intravenously to reverse neuromuscular blockade after surgery and orally to treat myasthenia gravis

Question 349

How is pyridostigmine administered

When

Why this drug

Answer 349

orally

myasthenia gravis

longer action than neostigmine

Question 350

How is ACh relevant to Alzheimer’s

Answer 350

there is significant loss of cholinergic neurons in the basal forebrain and the resultant reduced cholinergic neurotransmission is considered to underlie, at least in part, the dementia, intellectual deterioration, and personality changes associated with AD.

Question 351

Describe irreversible, long acting anti-cholinesterases as a chemical group

Answer 351

organophosphorous compounds containing a pentavalent phosphorous atom connected to three oxygen atoms (sometimes two oxygen and one sulfur atoms) along with a labile group, such as fluoride (dyflos or DFP) or an organic group (ecothiophate, parathion)

Question 352

How do irreversible, long acting anti-AChE work

Answer 352

labile group released and Ser’s -OH phosphorylated

this is v stable and lasts hundreds of hours

Question 353

How is the AChE-organophosphate complex following administration of irreversible long acting anti-AChE drugs

Answer 353

subject to a process known as ‘aging’, in which oxygen–phosphorus bonds within the inhibitor undergo spontaneous rearrangement in favour of stronger bonding between the enzyme and the inhibitor. Once aging occurs, the duration of AChE inhibition is increased even further.

Thus, organophosphate inhibition is essentially irreversible, and the body must synthesize new AChE proteins to restore AChE activity.

Question 354

How are irreversible, long acting anti-AChE used clinically

Use specific examples

What other uses do they have

Answer 354

limited clinical uses

Ecothiophate- used locally in glaucoma

insecticides
chemical warfare nerve gases eg sarin and novichok

Question 355

Name 4 nerve gases

What kind of drug is this

Answer 355

sarin, tabun, soman, and novichok

irreversible, long-lasting anti-AChE

Question 356

What does acute poisoning by irreversible anti-AChEs result in

When does it become fatal

Answer 356

excessive salivation, severe bradycardia, hypotension and difficulty in breathing

when combined with a depolarising neuromuscular block and central effects

Question 357

How do you treat anti-AChE poisoning

Answer 357

large doses of atropine as it can reach brain and periphery

Question 358

What is the effect of atropine of peripheral NMJ compromise

what other drug is used in a compromised NMJ

Answer 358

no effect

pralidoxime (2-PAM, a AChE reactivator) must be used instead

Question 359

What is 2-PAM used for

How does it work

Answer 359

to reactivate AChE

cationic group of pralidoxime interacts with the anionic site of AChE, which brings the oxime group into close proximity with the phosphorylated serine. The oxime group is a very strong nucleophile and lures the phosphate group away from the Ser hydroxyl of the enzyme

Question 360

How is the AChE reactivation by 2-PAM limited

Give the chemistry behind this

Answer 360

effectiveness is limited to within a few hours of exposure

phosphorylated AChE undergoes ageing, rendering phosphorylated groups no longer susceptible to nucleophilic attack

Question 361

Name 3 catecholamines

Why are they known as catecholamines#?

Answer 361

noradrenaline
adrenaline
dopamine

they possess a catechol and amine connected by a 2 carbon linkage

Question 362

How is the 2 carbon linkage in dopamine different to the other catecholamines

Answer 362

NA, Adr, and ISO all have an alcoholic -OH on the beta C (the C closest to the catechol)

DA does not

Question 363

What is a catechol

What is an amine group

Answer 363

catechol: aromatic ring with two proximal hydroxyl groups
amine: -NHR, where R = H or alkyl group

Question 364

What is the difference between noradrenaline and Adr

Answer 364

NA is effectively Adr lacking the methyl on the amine

Question 365

What is the main NT in the SNS

Answer 365

NA

Question 366

What is the precursor of NA?

Where does this precursor have important action

Answer 366

dopamine

mainly in the CNS and dopaminergic nerves

Question 367

How does Adr mainly act

Where is it made

Answer 367

as a hormone

adrenal glands

Question 368

True or false

NA is effectively the N-methylated version of Adr

Answer 368

False

Adr is effectively N-methylated NA

Question 369

How could you convert NA to Adr

Where does this take place

Answer 369

methylation

place in the chromaffin cells of adrenal medulla in presence of the enzyme PNMT (phenylethanolamine N-methyltransferase

Question 370

How much of the catecholamines in the adrenal medulla are Adr

Answer 370

80%=Adr

20%= NA

Question 371

What is ISO

Answer 371

isoprenaline
a synthetic (= N-isopropyl) derivative of NA, often used experimentally.

Question 372

How does ISO differ from NA

Answer 372

amine group on NA is just -NH2

ISO: -NH-CH-(CH3)2

Question 373

What is the starting material for biosynthesis of catecholamines? (Give the specific type)

How is this taken to to form catecholamines?

Answer 373

L-tyrosine

present in bodily fluid and taken up from the circulation by catecholaminergic nerves and converted into DOPA (dihydroxyphenylalanine) by tyrosine hydroxylase (TOH)

Question 374

What is the rate limiting step in catecholamine biosynthesis

Answer 374

conversion of L-tyrosine to DOPA by tyrosine hydroxylase (TOH)

Question 375

Where is TOH found

Answer 375

ONLY in catecholaminergic nerves

Question 376

Give each step of Adr synthesis with the enzyme for each equation (5)

Answer 376

1. L-tyrosine
   enzyme: TOH
2. DOPA
   Enzyme: DOPA decarboxylase
3. Dopamine
   enzyme: Dopamine beta-hydroxylase
4. NA
   enzyme: PNMT

5.Adr

Question 377

what is DOPA decarboxylase also known as?

Why?

Answer 377

L-aromatic acid decarboxylase

it’s relatively non-selective and catalyzes decarboxylation of other L-aromatic acids such as L-histidine or L-tryptophan to produce histamine and serotonin (5-HT), respectively

Question 378

What is the effect of L-aromatic acid decarboxylase on the following:

a) L-histidine
b) L- tryptophan

Answer 378

converts them to

a) histamine
b) 5-HT

Question 379

What happens to dopamine after it is formed (not conversion to NA)

What drives this process

Answer 379

stored into vesicles via the vesicular monoamine transporter (VMAT)

transvesicular H+ gradient

Question 380

What happens to dopamine inside the vesicles

Answer 380

hydroxylated at its β-carbon to form NA and this is catalyzed by dopamine β-hydroxylase (DBH).

Question 381

Where can DBH be found

How do you stop DB being released with NA when NA vesicles fuse with presynaptic membrane

Answer 381

exclusively within noradrenergic nerves

you don’t - small amounts of DBH are co-released with NA

Question 382

What happens to released DBH

What can we use this as an indicator for

Answer 382

not rapidly degraded or susceptible to any uptake mechanism, so its concentration in plasma and body fluids can be used as an index of overall sympathetic nerve activity.

Question 383

Where is PNMT mainly expressed in the adrenal medulla

Answer 383

in the adrenaline-releasing (A) cells that are distinct from the smaller proportion of noradrenaline-releasing (N) cells

Question 384

What controls PNMT expression

Answer 384

glucocorticoids eg cortisol from adrenal cortex

Question 385

How does cortisol affect catecholamine production (2)

Answer 385

Reduction in cortisol levels causes a decrease in production of PNMT and, hence, in the Adr:NA ratio.

also increases activity of dopamine β-hydroxylase (DBH).

Question 386

Which pharmalogical agent is used experimentally to block NA production

Answer 386

α-Methyltyrosine -

a competitive inhibitor of TOH

Question 387

What is the importance of blocking TOH as a way of reducing amount of NT produced?

Answer 387

it is the rate limiting step using α-Methyltyrosine is the only effective way to reduce amount of catecholamine produced

Question 388

Give an example of the clinical use of α-Methyltyrosine

Answer 388

in the past was used pre-op before treatment for pheochromocytoma (adrenal gland tumour, increasing Adr and NA secretion)

Question 389

What is the most effective way to increase production of catecholamines pharmacologically

Answer 389

bypass the step catalysed by TOH through using substrate for one of the later enzymes

Question 390

What happen in Parkinson’s disease

Answer 390

dopaminergic neurons in the substantia nigra pars compacta (SNc) are selectively degenerated

Question 391

Why can we not just use exogenous DA to replace that which is lost by destruction of dopaminergic neurons in Parkinson’s?

What is used instead?

Answer 391

DA does not cross the BBB

L-DOPA, DA’s natural precursor, can cross
Therefore L-DOPA is used to boost DA synthesis in the Parkinsonian brain

Question 392

What accounts for the unwanted peripheral effects of L DOPA therapy

Answer 392

A substantial fraction of the administered L-DOPA undergoes decarboxylation in the periphery by peripheral decarboxylase to produce DA and NA

Question 393

How to overcome the peripheral side effects of L-DOPA therapy

Answer 393

use in combination with carbidopa

carbidopa cannot cross the BBB but can inhibit peripheral decarboxylases

this ensures L-DOPA conversion to DA only occurs in CNS

Question 394

Which drug is used to inhibit DBH

How is it used clinically

Answer 394

Disulfiram

as an adjunct in the treatment of alcohol dependence

Question 395

How does disulfiram work

What is the basis of its action in dealing with alcoholism?

Answer 395

act by chelating the Cu2+ ion which is an essential co-factor of DBH or it may attack the sulphur-handling system for the methyl donor, S-adenosyl methionine

inhibition of aldehyde dehydrogenase

Question 396

How selective are the enzymes in the biosynthesis of catecholamine biosynthesis

What does this mean

Answer 396

TOH- selective
DDC and DBH - non selective

can result in the production and storage of a variety of other amines in the synaptic vesicle

Question 397

What happens when α-Methyldopa is taken into noradrenergic nerve terminals

Answer 397

converted successively into α-methyldopamine (α-methyl DA), and α-methylnoradrenaline (α-methyl NA)

Question 398

What happens to α-methyl NA in nerve terminals

Answer 398

stored within synaptic vesicles and released with NA as a false transmitter

Question 399

Describe the action of α-methyl NA compared to NA

Answer 399

functional but less active than NA at alpha 1 ARs and more selective towards alpha 2

Question 400

Name 2 drugs that target alpha 2 more selectively than NA does normally

What do they both result in? How?

Answer 400

clonidine
α-methyl NA

decrease BP
inhibition of NA release (via presynaptic alpha2 AR stimulation) and central action

Question 401

What kind of vesicle is NA usually stored in

What is often stored with it

Answer 401

clear core

ATP

Question 402

what transports NA and DA into vesicles

What family is it part of

What does it use to power the active transport?

Answer 402

VMAT2 (vesicular monoamine transporter)

SLC protein family

trans-vesicular H+ gradient

Question 403

How many H+ are transported per amine by the VMAT2

Answer 403

2H+ extruded per amine imported into the vesicle

Question 404

How is the H+ gradient in catecholamine vesicles set up

Answer 404

up by an ATP-dependent proton pump (a v-ATPase).

Question 405

What is VMAT1 also known as

Where is it found

Answer 405

chromaffin granule amine transporter

in non-neural tissues including the chromaffin cells of the adrenal medulla and few other cells of the GI tract.

Question 406

What is reserpine

What does it do

Answer 406

– a naturally occurring alkaloid (not used clinically),

binds to the amine site of the VMAT2 with high affinity and irreversibly blocks the uptake of monoamines (DA, NA and 5-HT) into vesicles

Question 407

What does reserpine’s action eventually lead to

Why does this happen

Answer 407

long lasting depletion of stored NA (and 5-HT in the CNS)

vesicles do allow leakage of the stored catecholamines into the cytoplasm where it is metabolised

Question 408

What was reserpine used for originally

Why was it discontinued?

Answer 408

as an anti-hypertensive

lead to profound psychological depression (due to decreased central 5-HT)

Question 409

Have any VMAT2 inhibitors been approved by the FDA

What are they approved for

Answer 409

a few - namely tetrabenazine and valbenazine

to manage abnormal involuntary movements associated with Huntington’s disease, tardive dyskinesia etc

Question 410

What do the 2 VMAT2 inhibitors have in common

Answer 410

both pro-drugs

upon in vivo metabolism, produce the active metabolite alpha-dihydrotetrabenazine (DTBZ)

Question 411

How does DTBZ differ from reserpine, meaning it is safer

Which monoamine is most affected

Answer 411

DTBZ REVERSIBLY inhibits VMAT2 unlike reserpine

DA

Question 412

How can you alter release of catecholamines

Answer 412

1) direct blockade of catecholaminergic neurons
2) triggering release in absence of any depolarisation (indirectly-acting and mixed-acting sympathomimetic drugs)
3) through stimulating pre-synaptic receptors.
4) alter storage

Question 413

Give an agent that directly blocks adrenergic neurons by acting on vesicles in the presynaptic terminal

Answer 413

Guanethidine

Question 414

How does guanethidine enter noradrenergic neurons

Answer 414

accumulates selectively into noradrenergic nerves by Uptake 1/NET

Question 415

Is guanethidine selective?

Answer 415

yes - complex, selective action on noradrenergic nerves - not fully understood

Question 416

How does guanethidine action vary based on dosage

Answer 416

At low doses, guanethidine blocks impulse conduction in these nerves, like the local anesthetics. It also accumulates into the synaptic vesicles via VMAT2, causing gradual, long-lasting depletion of NA (like reserpine).

At a very high dose, it irreversibly damages the nerve, effectively serving as a neurotoxin selective to noradrenergic neurons

Question 417

What happens to guanethidine at low doses

Answer 417

guanethidine blocks impulse conduction in these nerves, like the local anesthetics. It also accumulates into the synaptic vesicles via VMAT2, causing gradual, long-lasting depletion of NA (like reserpine).

Question 418

What happens to guanethidine at very high doses

Answer 418

irreversibly damages the nerve, effectively serving as a neurotoxin selective to noradrenergic neurons

Question 419

What was guanethidine used treat

Answer 419

uncontrolled hypertension

no longer recommended in the UK

Question 420

What is tyramine (2)

Answer 420

an indirectly acting sympathomimetic

a dietary amine

Question 421

Name an Indirectly acting sympathomimetic (NOT tyramine)

How does it act generally

Answer 421

dexamphetamine

capable of releasing stored transmitter from noradrenergic nerve endings by a Ca2+-independent process.

Question 422

Are tyramine and dexamphetamine AR agonists ?

Answer 422

NO - they are substrates for monoamide transporters

Question 423

How are tyramine and dexamphetamine taken up into nerves

What happens to them inside the nerve

How is this helpful?

Answer 423

are avidly taken up into noradrenergic nerve endings by Uptake1/NET

loaded into vesicles by VMAT2, displacing NA

NA is instead expelled into synaptic cleft by reverse NET action

Question 424

When can a tyramine rich diet become a serious problem

Answer 424

Tyramine-riched food intake in presence of MAO inhibition can lead to severe hypertensive crisis

Question 425

What kind of drugs are MDMA and ecstasy

Answer 425

Indirectly acting sympathomimetics

they are CNS stimulants, often abused for recreational purposes

Question 426

Name a mixed acting sympathomimetic amine

How do they work generally

Answer 426

ephedrine

indirectly release NE like tyramine and dexamphetamine but they also can directly activate adrenoreceptors (ARs)

Question 427

How is ephedrine used usually

Answer 427

as a nasal decongestant as it results in NA-mediated vasoconstriction in some blood vessels to the nose

Question 428

What does ephedrine act on

Answer 428

some direct action on bronchial β2-ARs and thus can help in relaxing the airways.

Also used to treat urinary incontinence in female dogs after the surgical removal of their reproductive organs.

Question 429

What effect do tyramine, ephedrine, amphetamine, and related drugs cause?

How does this differ from reserpine action

Answer 429

a relatively rapid and brief liberation of the transmitter, producing a sympathomimetic effect indirectly

reserpine, by irreversibly blocking the loading of monoamines into synaptic vesicles, produces a slow, prolonged depletion of NA (and other monoamines) from the presynaptic nerves.

Question 430

Through which presynaptic receptor is NA release most prominently regulated

Answer 430

α2-adrenoceptors (coupled to Gi/o) which, when stimulated, decrease the amount of NA released

Question 431

Is it only presynaptic α2-adrenoceptors that modulate NA release

Answer 431

no

there can be pre-synaptically located β2-ARs (coupled to Gs) which upon stimulation, enhance NA release

Question 432

How does cAMP affect NA release

Answer 432

increased cAMP production increases Ca2+ channel activating phosphorylation by PKA - more NA released

Question 433

Other than decreasing AC activity via the Gi/o, how does activating presynaptic alpha2-ARs on noradrenergic nerves decrease NA release

Answer 433

beta-gamma subunit, also results in the opening of K+ channels (GIRK)s which causes hyperpolarisation of the nerve terminal membrane and reduces its excitability

Question 434

Are the presynaptic the predominant α2-ARs and the occasional β2-ARs autoreceptors?

Answer 434

yes usually as released NA interacts with them

However, In some cases, there can be pre-synaptic heteroreceptors (e.g. muscarinic M2 receptors and δ-opioid receptors) which upon activation by cognate agonists, decrease NA release.

Question 435

How are catecholamines inactivated?

What are the 2 processes involved?

Which process is more important pharmacologically

Answer 435

removal from cleft

one into the presynaptic neuron (Uptake 1) and the other into postjunctional effector cells (Uptake 2).

Uptake 1: inhibiting this process enhances and prolongs the actions of released NA whereas inhibiting Uptake 2 does not affect the response.

Question 436

Describe Uptake 1 in noradrenergic synpases

Answer 436

This is a high affinity, low capacity system mediated by a transporter called NET (norepinephrine transport protein).

Question 437

What is NET

Answer 437

a member of the solute carrier (SLC) family of transporters. It is Na+-dependent, and blocked by many drugs including cocaine

Question 438

What kind of drugs block NET

Answer 438

cocaine

tricyclic antidepressants eg imipramine

Question 439

Name a tricyclic antidepresant

Answer 439

imipramine

Question 440

How much of the NA released from SNS neurons is recaptured by NET

Answer 440

> 75%

Question 441

VMAT2 has a much higher affinity for NA than does MAO. What does this mean for NA storage

Answer 441

most of the recaptured NE is resequestered into storage vesicles.

Question 442

What is in charge of transmission from noradrenergic neurons in the periphery

Answer 442

Uptake 1

Question 443

What is 6-OHDA

Answer 443

6-Hydroxydopamine (AKA oxidopamine)

a synthetic neurotoxic organic compound that is experimentally used (injected into brain areas) to selectivity destroy dopaminergic (and noradrenergic) neurons in the brain.

Question 444

How do you induce Parkinson’s disease in animals

Answer 444

inject oxidopamine which induces nigrostriatal damage

Question 445

How selective is 6-OHDA

Where does this come from

Answer 445

selective for catecholaminergic

its selective uptake into these neurons via NET

Question 446

What happens to oxidopamine once it has been taken up into the noradrenergic neuron via NET

Answer 446

it is readily oxidized into reactive metabolites including 6-OHDA quinone and hydrogen peroxide that damage to the neurones

Question 447

Describe Uptake 2 at noradrenergic synapses

Answer 447

lower affinity, higher capacity system of uptake of NA that hasnt been collected by Uptake 1

Question 448

What transporter mediates Uptake 2

Answer 448

ENT: extraneuronal amine transporter

Question 449

What transporter family does ENT belong to

Answer 449

to a largely and widely distributed family of Organic Cation Transporters (OCTs).

Question 450

Which of Uptake 1 and 2 is Na+ dependent

What does this mean

Answer 450

Uptake 1

ENT in Uptake 2 is not Na+ dependent (unlike NET)

they have different pharmacological profiles

Question 451

What inhibits ENT

Answer 451

the irreversible α-AR blocking agent - phenoxybenzamine (which will also block NET at much higher concentrations).

normetanephrine, a metabolite of NA, corticosteroids (such as corticosterone and hydrocortisone)

Question 452

Name a irreversible α-AR blocking agent of ENT

What is its effect on NET

Answer 452

phenoxybenzamine

will also block NET at much higher concentrations

Question 453

Where does most metabolism of catecholamines take place?

Why?

Answer 453

in the same cells where the amines are synthesized and stored

There is ongoing passive leakage of catecholamines from vesicular storage granules of sympathetic neurons and adrenal medullary chromaffin cells

Question 454

What happens to most of the catecholamines that leak into the neuron cytoplasm?

What happens to the rest

Answer 454

VMAT2 effectively sequesters 90% of the amines leaking back into storage vesicles

10% escapes sequestration and is metabolized.

Question 455

Which 2 enzymes are responsible for catecholamine metabolism

Answer 455

monoamine oxidase (MAO) and catechol O-methyltransferase (COMT)

Question 456

How should MAO and COMT work in theory vs practice

Answer 456

Although these enzymes in principle can act on the catecholamines in any order and the final metabolites should be the same but, in practice, two different metabolites (VMA and MOPEG) are found in the urine

VMA= from periphery
MOPEG= from CNS

Question 457

What do the following stand for:
VMA
COPEG

Answer 457

vanillylmandelic acid

3-methoxy-4-hydroxyphenylethyleneglycol

Question 458

How does MAO work

Answer 458

removes the amine group from the catecholamines and converts them into corresponding aldehydes, which, in the periphery, are rapidly metabolised into the corresponding carboxylic acids.

Question 459

Where does MAO action occur

Answer 459

in the outer membrane of mitochondria and it is abundant in noradrenergic nerve terminals but is also present in liver, intestinal epithelium and other tissue

Question 460

What is the main role of MAO in

a) nerve terminals
b) liver

Answer 460

a) degrade NA and DA leaking from vesicles

b) inactivates circulating monoamines such as tyramine

Question 461

What are the 2 isoforms of MAO

How do they differ

Answer 461

MAO-A and -B

MAO-A degrades 5-HT, NA and DA, while MAO-B degrades DA more rapidly than the other monoamines.

Question 462

How does pharmacological treatment aimed at MAO differ between isoforms

Answer 462

Non-selective or selective MAO-A inhibitors are used in depression and anxiety disorders whilst selective MAO-B inhibitors is used in the treatment of Parkinson’s disease.

Question 463

Why might there be an increase in blood pressure if you are eating lots of cheese and wine while on MAO inhibitors

What is this known as

Answer 463

Cheese and red wine contain tyramine, which is usually metabolised by MAO in liver/gut before reaching circulation

a large amount of tyramine-rich food is ingested, then significantly higher amount of tyramine reaches the blood and then can trigger release of NA. The latter can be sufficient to cause widespread vasoconstriction and a fatal hypertension

The cheese effect

Question 464

What other foods can the ‘cheese effect’ result from

Answer 464

tyramine rich foods: red wines, pickled herring, yeast extracts, soya beans

Question 465

Where is COMT found

Answer 465

in cytosol, primarily liver and chromaffin cells (adrenal medulla)

ABSENT FROM NORADRENERGIC NERVE CELLS

Question 466

is COMT free in the cytosol of chromaffin cells

Answer 466

no - it is membrane
bound.
This is also true of COMT in the liver cells

Question 467

what does COMT do chemically ?

Answer 467

methylates one of the aromatic hydroxyls (at position 3 of the aromatic ring) in the catecholamines (or their deaminated metabolites produced by MAO).

Question 468

What is the main end product of catecholamine metabolism by MAO then COMT

How is it excreted

How is this fact used clinically

Answer 468

VMA

via urine

in phaeochromocytoma VMA excretion is markedly increased

Question 469

What is used as an inhibitor of COMT

What is this used for

Answer 469

Entacapone

used in Parkinson’s disease in combination with L-DOPA and Carbidopa

Question 470

Why is entacapone used with L-DOPA to treat Parkinson’s disease

Answer 470

. It reduces metabolism of L-DOPA in the periphery so that more L-DOPA could reach the CNS where it is needed to produce DA for the Parkinson’s patient and less side effects occur from activation of dopamine receptors present in various peripheral tissues.

Question 471

How does ISO affect the different ARs differently?

Answer 471

it barely activates α adrenoceptor subtypes but it possesses significantly higher potency at β adrenoceptor subtypes compared to Adr and NA.

Question 472

Give 9 major effects of stimulation of α1-ARs

Answer 472

• Dilatation of pupils (mydriasis)
• Constriction of blood vessels supplied to vicera, brain and skin
• Salivary secretion
• Decreased gastrointestinal motility and tone (due to relaxation of smooth muscles)
• Localized (e.g. in palms of hands) secretion of sweat
• Piloerection (goose bumps)
• Contraction of trigone and sphincter muscles of urinary bladder
• Ejaculation of sperms
• Increased glycogenolysis and gluconeogenesis

Question 473

Give 4 effects of α2 AR stimulation

Answer 473

• Inhibition of neurotransmitter release (mentioned earlier)
• Platelet aggregation
• vasoconstriction
• Inhibition of insulin release from pancreatic beta cell

Question 474

Give 2 results of β1 AR stimulation

Answer 474

• Increased force of myocardial contraction

* Increased heart rate

Question 475

Give 4 results of β2 AR stimulation

Answer 475

• Relaxation of tracheal and bronchial smooth muscle
• Relaxation of smooth muscle of blood vessels supplied to heart and skeletal muscle
• Relaxation of uterine smooth muscle (for non-pregnants)
• Hepatic glycogenolysis

Question 476

Give 2 actions of β3 AR stimulation

Answer 476

• lipolysis
• thermogenesis

This is the least studied thus far

Question 477

What are the key effects of NA

Via which receptor?

Answer 477

Through α1 AR stimulation, Increases TPR due to vasoconstriction in most vascular beds (including kidney)

Both diastolic and systolic pressures increase enough to trigger reflex bradycardia which decreases pulse rate

Question 478

Which receptors does adrenaline activate and what is this attributed to

Answer 478

α and β -ARs

The present of a missile group at the amino N atom

Question 479

What are the 7 broad types of reaction caused by catecholamines or sympathomimetics

Answer 479

1. A peripheral excitatory (= contractile) action on certain types of smooth muscle, such as those in blood vessels supplying skin, kidney, and mucous membranes; and on gland cells, such as those in salivary and sweat glands.
2. A peripheral inhibitory (= relaxing) action on certain other types of smooth muscle, such as those in the wall of the gut, in the bronchial tree, and in blood vessels supplying skeletal muscle (we need to breathe more, our leg muscles need to have more blood supply to have energy for ‘fight or flight’).
3. A cardiac excitatory action that increases heart rate and force of contraction. (remember what happens if we are exposed to stress/danger or we simply do some exercise)
4. Metabolic actions that include enhanced glycogen breakdown in liver and muscle and liberation of free fatty acids from adipose tissue (remember the benefits of exercise which corresponds to increased sympathetic activity, we also need more energy for ‘fight or flight’).
5. Endocrine actions, such as modulation (increasing or decreasing) of the secretion of insulin, renin, and pituitary hormones.
6. Actions in the central nervous system (CNS), such as respiratory stimulation, an increase in wakefulness and psychomotor activity, and a reduction in appetite.
7. Prejunctional actions that either inhibit or facilitate the release of neurotransmitters, the inhibitory action being physiologically more important

Question 480

How does NA predominantly act (ie which receptors)

Why is this

Answer 480

NA predominantly acts via apha-ARs

and this is attributed to the presence of a methyl (-CH3) group at the amino N atom.

Question 481

What is the effect of Adr when it activates β1-ARs

Answer 481

Positive inotropic and chronotropic affects (thus increase pulse rate)

Question 482

What is the effect of Adr stimulating β2 ARs

Answer 482

Compensates for constriction of arterioles in skin, mucus membranes, and viscera by Faisel dilation of skeletal muscle vascular bed which also reduces TPR

Question 483

What are the α1 mediated effects of Adr

Answer 483

Construction of arterioles in the skin, mucus membranes, and viscera

Question 484

What is the net effect of adrenaline stimulating ARs

Answer 484

Increase in systolic pressure coupled with a slight decrease in diastolic pressure

Question 485

True or false

Isoprenaline only manifests α1 AR mediated effects

Answer 485

False
Only manifests β-AR effects

This selectivity towards β adrenoreceptors stems from
A bulkier substituent (isopropyl) at the amino N atom

Question 486

What are the effects of isoprenaline? Describe the effects through the receptors which are stimulated

What is the net effect

Answer 486

β1 AR: Intense stimulation of the heart, increasing rate, contractility, and cardiac output

β2: Delete arterioles of the skeletal muscle, resulting in marked decrease in TPR

Because of its cardiac stimulatory action, may increase systolic pressure slightly, but this is outweighed by reduction in TPR with a net reduction in mean arterial and diastolic blood pressures

Question 487

What are adrenoceptor agonists also known ask

Answer 487

Directly acting sympathomimetic agents

Question 488

What do non-selective AR agonists act on

Answer 488

Both α and β ARs

Question 489

Give a non-selective adrenoreceptor agonist

When is this used

Answer 489

Adrenaline

Acute cardiac failure, acute severe asthma or anaphylactic shock. In all these cases it can be life-saving
Carried in an Epipen

Adr is also used by anaesthetists

Question 490

What is status astmaticus

Answer 490

Acute severe asthma

Question 491

How is adrenaline given in cases of anaphylactic shock

What does the Adr do (2)

Answer 491

Intramuscularly,

To counteract the systematic vasodilation and reduction in test you perfusion that is largely caused by massive histamine release

Also acts on bronchial smooth-muscle to relieve bronchospasm

Question 492

How do you anaesthetists use adrenaline

Answer 492

Local anaesthetic preparations often contain low concentrations of adrenaline which greatly increases the duration of local anaesthesia by producing vasoconstriction at the sight of injection

Allows local anaesthetic to persist at the injection site before being absorbed into systemic circulation

Keeping anaesthesia local avoids systemic effects

Question 493

What do selective α-AR agonists do

Answer 493

Selective for α ARs over β

But poorly discriminate between α-ARs

Question 494

Name a selective α AR agonist

How is it administered

What is it used for

Answer 494

Xylometazoline

Topically

To relieve nasal congestion

Question 495

How does xylometazoline relieve nasal congestion

Answer 495

Causes vasodilation in nasal mucosa – dilated blood vessels in nasal mucosa is an underlying feature of stuffy nose

Question 496

Name a selective α1 agonist

What is it used for (3)

Answer 496

Phenylephrine (oxymetazoline is also one)

To treat nasal congestion, to produce mydriasis, and treat acute hypotension (eg in septic shock)

Question 497

Name 2 α2 selective AR agonists

What are they used for

Answer 497

Clonidine and α-methylNA (from α-methyldopa)

Anti-hypertensives

Question 498

How do clonidine and α-methylNA reduce BP

Answer 498

Partly by inhibiting NA release from peripheral nerve endings

Also on CNS neurons that reduces SNS discharge to periphery

Question 499

What receptor, other than α2-AR, does clonidine bind to

What is the consequence

Answer 499

I1 receptors

Unknown

Question 500

What is an example of an α2-AR agonist used in veterinary medicine

How is it used

Answer 500

Xylazine

As a sedative with analgesic and muscle relaxant properties

Question 501

What is a non selective β AR agonist

What is it used for

What was the issue

What has replaced it

Answer 501

ISO

In asthma to relax bronchi through actions on β2- adrenoreceptors but

But increased heart rate from β1- AR stimulation was a major problem

β2-AR selective agonists

Question 502

Name a β1 AR selective agonist

What is it used for

What is the issue

Answer 502

Dobutamine

In cases of cardiogenic shock to increase cardiac output

All β1-AR agonists can cause cardiac arrhythmias

Question 503

Name 2 short acting β2 AR selective agonists (SABA)

What are they used for

Answer 503

Salbutamol (need to know)
Terbutaline

Mainly for bronchodilator effects in asthma

Question 504

What is salbutamol

How is taken usually

How long does it take for maximum effect

How long does it last

What else can it be used for

Answer 504

The blue puff asthma inhaler

Inhaled as needed

Within 30 mins

3-5 hours

Prophylactically against allergen and exercise induced bronchospasm

Question 505

Name 2 long acting β2 agonists
Which do you NEED to know

How long counts as long lasting

How are they used

Answer 505

Salmeterol (need to know)
Formoterol

8-12 hours

Used prophylactically in chronic asthma

Question 506

What is clenbuterol

Answer 506

A horse LABA

Question 507

What kind of drug that acts on ARs is used to treat COPD

Eg

Answer 507

LABAs

Especially very long lasting ones like indacaterol

Question 508

What is mirabegron

Answer 508

A β3- AR agonist that relaxes detrusor smooth muscle to increase bladder capacity

Question 509

Who would take mirabegron

Answer 509

Patients with an overactive bladder

Question 510

Give 2 other names for AR antagonists

How are they classified

Answer 510

Adrenergic blockers or sympatholytics

Based on relative affinity to α or β ARs in the SNS

Question 511

Name 2 α-AR antagonists that do not discriminate between α subtype (which do you need to know✅)

What did they treat but are now obsolete for? Why!

Answer 511

Phentolamine
Phenoxybenzamine ✅

Anti hypertensives (largely replaced by α1 antagonists) - as they may reduce blood pressure so much that it triggers reflex tachycardia

Question 512

What does phentoxybenzamine do chemically

What is its specific clinical use therefore

Answer 512

Covalently binds to alpha-AR, causing long lasting inhibition

Preparing patients with phaeochromocytoma for surgery since surgical manipulation tends to cause massive catecholamine release

Question 513

What is prazosin

What does it do

So what is it used for

Answer 513

Selective and competitive α1-AR antagonist

decreases TPR and BP by relaxing arterial and venous smooth muscle

as an anti-hypertensive without causing the same degree of reflex tachycardia observed with the non-selective α-AR antagonists

Question 514

What are the negative side effects of α1-AR antagonists

Give an explanation

Answer 514

postural hypotension and incontinence, the latter occurring because α1-ARs mediate contraction of the smooth muscle of the bladder, which is now inhibited

Question 515

Name 2 α1-AR antagonists (need to know both)

Answer 515

prazosin

tamsulosin

Question 516

How are α1-AR antagonists used to treat some prostate pathologies

Answer 516

cause relaxation of the prostate capsule and inhibit prostate hypertrophy, which has lead to the development of drugs like tamsulosin. These are selective α1A-AR antagonists that allow better bladder emptying and thus reducing urinary retention associated with benign prostatic hypertrophy

Question 517

What is tamsulosin

Answer 517

a selective α1A-AR antagonists

Question 518

What is the benefit of selective α1A-AR antagonists

Answer 518

Since α1B-ARs largely mediate vasoconstriction, these α1A-AR antagonists produce much less postural hypotension which is a common problem with non-selective and α1-selective AR antagonists.

Question 519

What is Yohimbine

What is it useful for

Answer 519

a naturally occurring alkaloid, is a selective α2-AR selective antagonist

no clinical use for the humans (but is in animals), being only a useful experimental tool to determine α-AR subtype response in a given tissue

Question 520

Name a a naturally occurring alkaloid, is a selective α2-AR selective antagonist

Answer 520

yohimbine

Question 521

True or false

All of the clinically available β-blockers are competitive antagonists for the beta-AR

Answer 521

true

Question 522

What do cardioselective beta blockers primarily block

Answer 522

β1 -ARs.

Question 523

What is the clinical use of β2 -AR blockers

Answer 523

there arent any

Question 524

Do beta blockers cause postural hypotension?

What does this mean?

Answer 524

no
because the α ARs remain unaffected.

Therefore, normal sympathetic control of the vasculature is maintained

Question 525

What do all beta blockers result in

What is the effect on blood pressure

Answer 525

negative inotropic and chronotropic effects (block β1-ARs)

decrease blood pressure in hypertensive patients, but have no effect in normotensive individuals

Question 526

What contributes to the antihypertensive effects of beta blockers

Answer 526

decreases in peripheral vascular resistance and cardiac output both contribute to the antihypertensive effect of these drugs observed in patients with high blood pressure.

Question 527

Name 7 general conditions that beta blockers can be used in

Answer 527

primarily indicated in hypertension and angina but can be useful in cardiac arrhythmias, myocardial infarction, heart failure, hyperthyroidism, and glaucoma

Question 528

How to recognise a beta blocker name

exceptions?

Answer 528

ends in -olol

except for labetalol and carvedilol

Question 529

What is the prototypical β blocker

Describe its selectivity

What is the effect

Answer 529

Propranolol

Non selective among β ARs.

Reduces hypertension

Question 530

What are the mechanisms of propanolol that decrease hypertension (4)

Answer 530

Decreased cardiac output

Inhibition of renin release

Decrease TPR with long-term use

Decrease SNS outflow from CNS

Question 531

What do the undesirable side-effects of propanolol and other non-selective β- blockers stem from

Give examples

Answer 531

Blockade of β2

β2 blockade in COPD and asthma patients can exacerbate their condition and lead to a serious crisis

β2 blockage also causes loss of vasodilation to cutaneous blood vessels leading to coldness in extremities

Question 532

What are 2nd generation β blockers

Eg? (You need to know this drug)

Answer 532

β1 selective antagonists
AKA cardioselective β blockers

Atenolol

Question 533

What is the benefit of 3rd generation β blockers

Eg

Answer 533

Polypharmacological benefits

Nebivolol - selectively blocks β1 But also offers additional benefit as vasodilator and cardioprotective agent

Question 534

How is Nebivolol cardioprotective

Answer 534

Through promoting NO release from endothelium and in myocardium

Question 535

What is carvedilol

Answer 535

A mixed α1/β-AR antagonist with anti-oxidant and anti - inflammatory properties

Question 536

What are NANC transmitters

Eg

Answer 536

Non-adrenergic, non-cholinergic transmitters

Eg purines: ATP+ derivatives
Neuropeptides
Volatile substances: NO

Question 537

What are small molecule NANC NTs stored in

What about neuropeptides

Answer 537

Clear core vesicles

LDCVs

Question 538

Where are neuropeptides synthesised and stored

Answer 538

Synthesised, processed and packaged into large dense core vesicles in the cell body and then move down along the axon towards the nerve terminal via axonal transport

Question 539

How does storage of ATP in adrenergic nerves compare to cholinergic nerves

Release?

Answer 539

ATP and ACh coexist in cholinergic vesicles whilst ATP, NPY, and catecholamines are found within storage granules in adrenergic nerves and the adrenal medulla

similarly, ATP is released along with NTs

Question 540

Which 2 peptides are mostly implicated in ANS transmission?

Name 9 other notable neuropeptides or groups of peptides

What do all these work on

Answer 540

Vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY)

the enkephalins, 
substance P and other tachykinins, 
somatostatin, 
gonadotropin-releasing hormone (GnRH), 
cholecystokinin (CCK), 
calcitonin gene–related peptide (CGRP), 
galanin 
chromogranins

their cognate GPCR

Question 541

How are NANC transmitters often released in the periphery

eg?

Answer 541

concurrently with the classical neurotransmitters as the nerves are depolarised

eg: ATP is released with ACh and NA in the urinary bladder and vas deferens, respectively.

Question 542

what is suramin

Answer 542

ATP antagonist (blocks P2X and some P2Y subtypes)

Question 543

If you have a typical biphasic or twin-peaked contractions of the guinea pig vas deferens measured in response to electrical stimulation of sympathetic nerves innervating the tissue, how will the peaks be affected by suramin and prazosin

Answer 543

suramin: ATP antagonist
prazosin: α1-adrenoceptor antagonist

suramin alone abolishes early peak
prazosin alone abolishes late peak
response is completely eliminated with both S+P

Question 544

How do neurons that release many NTs, do so?

How do they interact with the postsynaptic membrane

Answer 544

Many other neurons contain and release more than one transmitter, sometimes from the same vesicles and sometimes from different ones

each NT has its own receptor

Question 545

Which NTs are commonly released alongside NA in the SNS

Answer 545

ATP and NPY

Question 546

What does co-transmission allow

Elaborate

Answer 546

greater complexity of signalling

NT time course may vary
Often NTs are released independently of each other

Question 547

What does the different time course of NTs in co-transmission allow

Answer 547

allow different types of responses to be elicited in the postsynaptic cell. Transmitters with a prolonged action, because of slow removal from the synaptic cleft, can also act on more than one target group of cells

Question 548

Give example of NTs being released independently of each other from same presynaptic neuron

Answer 548

e.g. higher concentrations of Ca2+ are required to elicit release of peptide transmitters (discussed early in this handout), so they are preferentially released at high rates of neural stimulation (i.e depolarisation).

Question 549

What does a substance have to meet to be considered a neurotransmitter

Answer 549

Dale’s criteria

Question 550

How is the action of ATP and its derivatives mediated

Answer 550

through purinergic receptors or purinoceptors:
Adenosine receptors
Ionotropic P2X receptors
Metabotropic P2Y receptors

Question 551

What are the 3 types of purinergic receptors?

Elaborate briefly on each

Answer 551

a) Adenosine receptors – A1, A2A, A2B and A3 (all are GPCRs)
b) Ionotropic P2X1-7 receptors – all are homo/heterotrimeric ATP-gated cation channels
c) Metabotropic P2Y1,2,4,6,11-14 receptors – all are GPCRs whilst few still remain as ‘orphan’ i.e. the natural agonists are yet to be known.

Question 552

What is an orphan receptor

Answer 552

one where the natural agonists are yet to be known

Question 553

How is ATP stored in nerve terminals (2) and how may it be released (3)

Answer 553

may be present in the cytosol or stored into vesicles by the vesicular nucleotide transporter (VNUT)

can be released by exocytosis in Ca2+-dependent way or through large membrane channels called the pannexins or via the nucleotide transporters (NtT).

Question 554

How does ATP enter vesicles

Answer 554

VNUT: vesicular nucleotide transporter

Question 555

When may cytoplasmic ATP cause neurotoxicity

Answer 555

released from dying or necrotic cells including degenerating neurons and excessive release in this way could lead to further cellular damage/neurotoxicity

Question 556

What happens when ATP is released into the extracellular space

Answer 556

broken down into ADP, AMP and adenosine by action of ecto-nucleotidases

Question 557

How is ATP converted to ADP etc in the extracellular space

What does this lead to

Answer 557

by action of ecto-nucleotidases

termination of transmission at the P2X and P2Y receptors

Question 558

Conversion of ATP to its derivatives by ecto-nucleotidases ceases transmission at P2Y and P2X receptors. Does this mean transmission at the synapse has ceased

Answer 558

no adenosine can still act ?

• maybe ask Ritter about this not sure

Question 559

Where is adenosine present

Answer 559

in the cytosol of all cells and is taken up and released via a specific membrane-bound nucleoside transporter(s) (NsT).

Question 560

How is adenosine taken up and released from cells

Answer 560

via a specific membrane-bound nucleoside transporter(s) (NsT).

Question 561

How can you get inosine?

Answer 561

hydrolyze adenosine by adenosine deaminase

Question 562

What are P2X receptors

Answer 562

non- selective cation channels (i.e. equally permeable to Na+ and K+ and with significant Ca2+ permeability.

Question 563

What is the permeability of P2X channels

Answer 563

equally permeable to Na+ and K+ and with significant Ca2+ permeability.

Question 564

when do P2X channels open

Answer 564

open within milliseconds of the binding of extracellular ATP

Question 565

How many P2X receptor isoforms are there in mammals

Answer 565

7

assemble as homo or heterotrimers to form a functional channel

Question 566

Where are P2X receptors found

Answer 566

have a widespread tissue distribution, being expressed on both central and peripheral neurons, where they are involved in synaptic and/or neuromuscular transmission.

Question 567

What are the dominant P2X receptor types in neurons

Answer 567

2, 4, 6

Question 568

What is the dominant P2X subtypes in smooth muscle

Answer 568

P2X1

Question 569

What is the importance of P2X receptors in pathology

Answer 569

Changes in the expression of P2X receptors have been characterized in many pathological conditions of the cardiovascular, gastrointestinal, respiratory, and urinogenital systems and in the brain and special senses

Question 570

In the vas deferens and blood vessels, which NT produces the fast and slow response from SNS innervation

Answer 570

ATP produces fast responses mediated by P2X1 receptors, followed by a slower component mediated by G protein-coupled alpha-ARs.

Question 571

Give an experiment demonstrating the importance of P2X receptors

Answer 571

Male mice lacking the P2X1 receptor gene have a drastically reduced fertility because of much reduced sperm count in the ejaculate

Question 572

What receptor could be targeted for a male contraceptive

Answer 572

P2X1

Question 573

How is adenosine an atypical NT

Answer 573

• it is neither stored in vesicles nor released by a Ca2+-dependent process

Question 574

Where is adenosine found

Answer 574

found in the cytosol as well as in the extracellular fluid throughout the body, including the central and peripheral nervous system`

Question 575

How is adenosine produced extracellularly

How is it then taken up

Answer 575

adenosine is produced following ectonucleotidase-catalyzed hydrolysis of ATP and then taken up by cells through a nucleoside transporter (NsT).

Question 576

What does dipyridamole do

Answer 576

blocks NsT to increase [adenosine]e

Question 577

What is methotrexate

What does it do and what is the mechanism

Answer 577

an anticancer and immunosuppressant drug, also appears to increase the extracellular concentration of adenosine, through mechanism(s) not very clear to date

Question 578

What does adenosine boosting do

Answer 578

believed to contribute to its immunosuppressive action significantly.

Question 579

What kind of range are [adenosine]i and e kept within

Answer 579

submicromolar

Question 580

What are the 2 ways adenosine can be metabolised

Answer 580

to inosine (by adenosine deaminase) or to adenine nucleotides (by adenosine kinase)

Question 581

Why can [adenosine]e increase under stressful conditions

Answer 581

large amount of ATP can be released from the injured cells (e.g. endothelial cells, neutrophils, cardiomyocytes, smooth muscle cells, glial cells etc.) via large pore-containing channels such as pannexins or connexins (or directly after necrotic cell death) and subsequently dephosphorylated to adenosine by ecto-nucleotidases

intracellular production may also increase

Question 582

What is a autacoid

Answer 582

locally acting hormone

Question 583

How are all biological actions of adenosine mediated

Answer 583

through adenosine receptors

through the activation (A2A and A2B) or inhibition (A1 and A3) of adenylyl cyclase and thus cAMP signalling

Question 584

Which adenosine receptors are activatory and which are inhibitory

Do they have any other effects (3)

Answer 584

A2a and A2b activated AC and increase [cAMP]
A1 and A3 inhibit AC

Some, if not all, of these receptors have also been reported to activate phospholipase C (and thereby trigger intracellular Ca2+ release) and mitogen-activated protein kinase (MAPK).
Also modulate Cav and K+ channel function

Question 585

How do adenosine receptors affect ion channels at the PM

Answer 585

modulate function of voltage-gated Ca2+ channels (via influencing their level of phosphorylation) and K+ channels (via βγ subunit and/or altering phosphorylation states).

Question 586

What is the effect of adenosine on the heart

What the receptor mediating

Answer 586

negative inotropic and chronotropic effects (A1 receptor)

Question 587

How can the effects of adenosine on the heart be used therapeutically

How is it administered

Is it safe? why?

Answer 587

to terminate supraventricular tachycardia

an intravenous bolus injection

due to its short duration of action (destroyed/taken up in seconds of intravenous administration) it is considered safer than other alternative drugs

Question 588

What is the effect of adenosine on smooth muscle?

Which receptors mediate this effect and what are they coupled to

Answer 588

relaxation

A2A and A2B receptors that are Gs coupled

Question 589

What is the effect to adenosine pre-synaptically

Via which receptor?

Answer 589

exerts pre-synaptic inhibitory effects on the release of excitatory transmitters in the CNS and periphery

presynaptic A1

Question 590

How does caffeine work

Answer 590

blocks inhibitory action of adenosine on presynaptic A1 receptors

Question 591

Name a methylxanthine agent

What kind of drug is it

Answer 591

caffeine

competitive antagonist of A1 receptors.

Question 592

Name an adenosine derivative drug

What kind of drug is it

what effect is it used for

Answer 592

Regadenoson (Trade names: Lexiscan or Rapiscan)

selective A2A adenosine receptor agonist

coronary vasodilatory activity

Question 593

What has the FDA approved regadenoson for?

Answer 593

for diagnostic purpose only in a type of heart scan called ‘radionuclide myocardial perfusion imaging’

Question 594

What diagnostic procedure can regadenoson be used for?

What does this procedure assess?

Why is regadenoson useful?

Answer 594

‘radionuclide myocardial perfusion imaging’

to see the blood flow in the heart muscle

it acts as a stress agent that has a similar effecton the heart as exercise

Question 595

How big is the neuropeptide family

Answer 595

> 100 members

Question 596

How big are neuropeptides

Answer 596

3-36 amino acids

Question 597

Where are neuropeptides made

Answer 597

soma

Question 598

How are neuropeptides made

Answer 598

synthesis is a multistep process that takes places in the soma and begins with the transcription of the gene that encodes one or more prepropeptides in the nucleus, splicing of the resulting primary RNA transcript to produce a mRNA

Prepropeptide mRNA is exported to cytoplasm for translation, which makes the prepropeptide. This can become several different neuropeptides

Question 599

Name a prepropeptide

Answer 599

pre-POMC

Question 600

What do prepropeptides contain characteristically

Answer 600

contain an N-terminal signal sequence (or “pre” sequence) that directs the newly synthesized protein into the lumen of the rough ER and thus into the proper, regulated secretory pathway

Question 601

What does remval of the pre sequence from a prepropeptide result in

What happens to it

Answer 601

in a propeptide (e.g. POMC)

released from the ribosome after translation is complete, transferred to the Golgi complex, and subsequently packaged within large dense core vesicles (LDCVs)

Question 602

What happens to the propeptide within the golgi and LDCVs

Answer 602

undergoes additional posttranslational processing, which involves additional cleavages and covalent modifications.

Question 603

What is the main neuropeptide at cholinergic synapses

Answer 603

VIP

Question 604

Why do neuropeptides produce a longer response

What terminates their action

Answer 604

because they are not rapidly removed from the ECF

response is terminated either by diffusion or by extracellular peptidases

Question 605

What receptors do neuropeptides activate

how can they thus be described

Answer 605

GPCRs

neuromodulators (more appropriate than neurotransmitter)

Question 606

What do neuropeptides account for in autonomic ganglia

be specific

Answer 606

released neuropeptides (for e.g. GnRH) account for the late slow EPSP.

Question 607

True or false
Receptors for neuropeptides bind their ligands with greater affinities than do the receptors for small-molecule transmitters

Answer 607

true
. This high affinity implies that neuropeptides can act at low concentrations, which is what would be expected if they often diffuse for great distances.

Question 608

What is needed to make NO normally

How does this differ in pathology

Answer 608

nitric oxide synthase (NOS) which converts L-arginine to NO and L-citrulline

cells eg vascular smooth muscle can generate NO independent of Ca2+ after stress

Question 609

What are the different isotypes of NOS

Answer 609

nNOS (NOS I)
iNOS (NOSII)
eNOS (NOS III)

Question 610

Where is nNOS expressed

Answer 610

neuronal NOS (nNOS, or NOS I) expressed in the CNS and NANC nerves

Question 611

Where is NOS II expressed

Answer 611

inducible NOS (iNOS, or NOS II) is usually absent but its expression is induced in macrophages and other cells by bacterial lipopolysaccharide and/or inflammatory cytokines, notably interferon-γ.

Question 612

Which cells produce iNOS when induced to do so

Answer 612

fibroblasts, vascular smooth muscle cells, endothelial cells, Kupffer cells, neutrophils

Question 613

Which inflammatory cytokine induces iNOS expression in some cells

Answer 613

interferon-γ.

Question 614

Where is eNOS expressed

Answer 614

expressed in platelets as well as endothelial cells

Question 615

Where does NO go after produced

Answer 615

diffuses all directions - across the presynaptic membrane and the membranes of non-neuronal cells producing it.

Question 616

What does NO activate

Answer 616

sGC (soluble guanylyl cyclase)

Question 617

How does NO activate sGC chemical

Answer 617

through interacting with the haem moiety of the enzyme

Question 618

What does the cGMP produced by NO action do

Answer 618

can act directly on effector proteins eg ion channels but more commonly through the activation of (PKG). PKG phosphorylates various proteins and leads to relaxation of smooth muscle, particularly in the blood vessels and this accounts for the term endothelium-derived relaxation factor (EDRF) that is used to denote NO

Question 619

what are nitrergic nerves

Answer 619

NO releasing

Question 620

Where are innervations with nitrergic (i.e. NO releasing) postganglionic nerves present

Answer 620

in several peripheral tissues that notably include upper airways, gastrointestinal tract (the enteric neurons) and male sexual organs

Question 621

What kind of NOS do enteric nitrergic neurons express

What role does the released NO play in the GI tract (6)

Answer 621

nNOS

NO regulates the muscle tone of the sphincter in the lower esophagus, pylorus, sphincter of Oddi, and anus.

regulates the accommodation reflex of the fundus and the peristaltic reflex of the intestine

Question 622

What is reduced nNOS associated with in the GI tract

eg

Answer 622

GI tract motility disorders

nNOS-/- mice had ~50% loss of inhibitory NANC transmission in small intestine and showed distended stomach and pyloric hypertrophy

Question 623

How is nNOS expression associated with diabetes (use a mouse experiment)

Answer 623

Diabetic mice often show delayed gastric emptying that has been attributed to negligible expression of nNOS protein and thus inadequacy in NO-mediated NANC transmission.

Insulin promotes nNOS protein expression and thereby restored NANC-mediated pyloric relaxation

Question 624

How is insulin associated with nNOS

Answer 624

promotes nNOS protein expression

Question 625

What happens to nitrergic neurons in achalasia

Answer 625

, there is selective loss of the nitrergic neurons supplied to oesophageal sphincter muscles, which incapacitates oesophagus to move food along.

Question 626

What is the blood pressure like in mice who lack the gene coding NOS III?

Why?

Answer 626

they are hypertensive

The L-arginine/NO pathway is tonically active in resistance vessels, reducing peripheral vascular resistance and hence systemic blood pressure

Question 627

How is Nebivolol associated with NO

Answer 627

the selective 1-AR blocker Nebivolol (more correctly speaking, its metabolite) also triggers NO production

Question 628

What class of drug use NO to vasodilate

Answer 628

nitrovasodilators

donate NO to relax blood vessels