Synaptic Transmission Flashcards
What’s the differnece b/w the type of GABAa + GABAb r? (4)
GABA A =
ionotropic (ligand gated)
GABA B =
metabotropic
(GPCR)
What does the hippocampus have, in terms of GABA neuron density? (2)
Lots of different GABAergic cell types
loads of interneurons in hippo - each are distinct in morphology + pharm
How do we characterise these GABAergic cells? (2)
via their embryonic origin
Diversity and different embryonic developmental
sources
What is feed-forward inhibition? (2)
usually:
1) 2 excitatory cells (eg CA1 + CA3 - connected)
2) AP flows through 1st cell’s axon - exciting next cell through the synapse
in feed-forward:
1) 1st excitatory cell will not target another excitatory cell but instead an inhibitory interneuron
2) 2nd cell is inhibited
What is feed-back (recurrent) inhibition? (2)
so instead of the 2nd cell targeting another/different cell - it feeds back into the original circuit
= switches off the cell
Describe inhibition of inhibition (3)
1)1st AP from excitatory cell targets 1st inhibitory cell/interneuron
2)1st in turn = inhibits 2nd interneuron
3)2nd interneuron cannot act on the excitatory cell ==> inhibition of inhibition
Why do you need inhibition? (1)
To avoid hyperexcitability –> seizures
What is PTZ ands why is it used? (2)
Gaba antagonist = induces seizures
- helps to model hyperexcitability
How can you model hyperexcitability in zebrafish? (3)
put PTZ drug into bath solution => osmosis => see excitatory response in fish via calcium imaging (fluorescence)
GABA chemical structure (1)
C4H6NH2OH
GABAergic synapses do not usually occur on…(1)
dendritic spines
what is GABA made from? (1)
from glutamate - using glutamate decarboxylase (GAD)
How is GABA made + synaptic transmission? - steps (8)
1) TCA cycle
2) Glutamate production
3) Glut –> GABA (GAD)
4) GABA packaged + moves to edge of TM in V’s (VGAT)
5) GABA V’s fuse + release
6) (GABA + GABAAr) or (GABA + GABABr)
7) GAT transports GABA back into synapse - glial or astrocytes
8) TCA cycle
GABAA structure (5)
-pentamer
-2x A1
- 2x B2
-1x gamma2 (or delta)
- most common combination: a1,b2,g2
-binding site b/w a + b subnits
Describe GABAA’s MOA binding to GABA (3)
1) GABA binds to r at a + b binding site
2) opens cl- channels in pore (main inhib molecule)
3) drive of cl- (prevents AP generation)
Why is cl- inhibitory? (3)
look at the equilibrium potential - ECl
see that it is v negative (just shy of EK)
ECl is much more depolarised in juvenile neurons
Different subunits have different localisations - so? (2)
essential for drug targeting
eg alpha6 only found in cerebellum
What is the plus side and what is the minus side in the TM domain? (2)
+ = TM2 and TM3
- = TM2 and TM1
GABAA Agonists + binding site (4)
GABA
Muscimol
Gaboxadol
BS: between alpha + beta subunits
GABAA Antagonists+ binding site (4)
Bicuculline
GABAzine
Picrotoxin
BS: between alpha + gamma subunits
GABAA modulators + binding site(5)
Benzodiazepines (BZD)
Barbiturates
Neurosteroids
Anaesthetics
Alcohol
BS: differing
Why would you use positive allosteric modulators for GABAA? (4)
common for drug target
but if you use antagonise gaba = seizures
so want to bind elsewhere - not where primary ligand binds also
= modulators
BZD - SSRI’s
Why would you use antagonists for GABAA? (3)
for inhibition of GABAergic circuit studies/experiments
= blocks components
but not for recreational use = seizures
So what is GABAC
then? (4)
GABAC r’s were identified as ligand-gated ion channels (like GABAA) but =
- insensitive to the classical GABAA antagonist bicuculline -
- 500x less sensitive
to the potent competitive GABAA antagonist GABAzine
-high-level structural similarity of GABAC to GABAA = now classified as a subgroup of GABAA
Simple GABAA receptor-mediated synaptic transmission is often seen via… (2)
patch clamp tests by measuring the chnages in voltage/membrane potential.
IPSP- completely blocked by bicuculline, GABAzine, Picrotoxin
- enhanced by Benzodiazepines, barbiturates and neurosteriods
Explain how + why sometimes IPSPs are longer and biphasic (3)
pattern:
1) stimulus
2) fast + short depolarisation (GABAA)
3) slow + longer hyperpolarisaton (GABAB)
How was GABAB r identified? (6)
1) found that it was:
- activated by GABA
- not blocked by GABAA receptor antagonists
- activated by a selective agonist
2) Use of Baclofen:
1) hyperpolarizes postsynaptic cells by increasing K+ conductance (this is why it makes an IPSP)
2) reduces neurotransmitter release from presynaptic terminals (by inhibiting voltage gated Ca2+ channels)
3) Reduces production of cAMP by adenylate cyclase
How is GABAB created? (3 + 2)
1) GABA binds GABAB
-R1
2)G-proteins interacts with GABAB
-R2
3)2 N-terminal splice variants of GABAB
-R1
Knocking gene out for either receptor
kills all GABAB
type responses
= made from 2 interacting proteins (gene products) both w/
classic GPCR (7TM) structure
GABAB agonists (3)
GABA
Baclofen
SKF 97541
GABAB antagonists (3)
Saclofen
CGP-55845
SCH 50911
GABAB modulators (3)
rac BHFF
GS 39783
CLH304a
How is the classical biphasic IPSP produced? (1)
Synchronous release of GABA results in the
simultaneous activation of both GABAA and GABAB
receptors
GABAB receptors are negatively coupled to adenylyl cyclase. So, explain the Activation of Gi/o coupled receptors (3)
1) Inhibits cAMP production
2) Activates GIRK K+ channels (IPSP)
3) Inhibits voltage-sensitive Ca2+ channels
What’s the difference in the role of GABAB r pre + postsynaptically? (2)
pre: regulate release of neurotransmitters to modulate VGCC opening
post: inhibit AP’s by activating K+ channels = hyperpolarising cell
field ESPS of pre-syn GABAB (4)
1) stimulate Dentate gyrus - by adding agonist (eg baclofen)
2) electrode in CA3 (to target basket cells)
3) recording response in CA1
= Presynaptic GABAB
receptors depress glutamate release in hippocampus
How does GABAB
receptor-mediated short-term plasticity? (3)
Short-term plasticity of GABAergic synaptic inputs to CA1 pyramidal cells:
If two identical presynaptic stimuli are given in rapid
succession (30-1000 ms), the second IPSP is smaller (reduces amplitude)
– driven by pre-synaptic GABAB r
= known as GABAB autoreceptor-mediated suppression of
inhibition
GABAB autoreceptor-mediated suppression of
inhibition explained (3)
- activation of presynaptic GABAB r’s negatively coupled to VGCC
= restricts Ca2+ entry to presynaptic cell
= Therefore conditioned (2nd) stimuli results in reduced Ca2+ dependent exocytosis: less GABA released
What are monoamines + give examples? (2)
A compound having a single amine group in its molecule, especially one which is a neurotransmitter
eg serotonin or adrenaline
What are the 3 main ascending pathways of the Raphe nucleus + what do they innervate? (3)
1) dorsal: NAcc + Chordate Putamen + Globulus Putamen
2) Medial: Substantia nigra + caudate putamen
3) ventral: multiple frontal pathways eg PFC , olfactory bulb, hippo, hypo
Biosynthesis of 5-HT - steps (3)
1) Tryptophan
—- Tryptophan hydroxylase (TPH)—–
2) 5-hydroxytrytophan
— L-aromatic acid decarboxylase—
3) Serotonin
What is the rate limiting step in 5-HT synthesis? (1)
—- Tryptophan hydroxylase (TPH)—–
What is 5-HT excreted as and how? (1 + 3)
5-HIAA excreted through
urine
via further biosynthesis:
1) serotonin
—–MAO——
2) xyz
—–Aldehyde dehydrogenase—-
3) 5-HIAA
Where is 5-HT found? (2)
10% CNS
90% in gut: GI tract, ECs, Neurons
5-HTr info (3)
- 7 r subtypes (5-HT1 - 7)
- 6 are GCPR
- 5-HT3 = ligand gated ion channel (Na+, K+)
5-HTr subtype signalling: (4)
5-HT1: Gi/Go (red. cAMP)
5-HT2: Gq/G11 (inc. IP3, Ca2+)
5-HT3: ligand gated ion channel
5-HT4-7: Gs (inc. cAMP)
Describe synaptic transmission of 5-HT (7)
1) tryptophan
2) 5-hydroxytrophan
3)5-HT
4) VMAT helps package into v’s + move to M + fuse
5) releases in cleft
6) SERT reuptake
7) (MAO) –> 5-hydroxyindole
Serotonin selective re-uptake inhibitors
(SSRIs) use + eg’s (1 + 6)
- Blocks Serotonin transporter (SERT) = increase monoamine neurotransmitters in the synaptic cleft (esp serotonin)
- Major depressive disorder
- Generalised anxiety disorder
- OCD
- PTSD
- Social anxiety disorder
- Bulimia nervosa
Citalopram (1)
Escitalopram (1-3)
Fluoxetine (1,6)
Fluvoxamine (1)
Paroxetine (1,3-5)
Sertraline (1,6)
side effects of SSRI’s (4)
- nausea
- vomiting
- constipation/diarrhoea
-Insomnia
5-HT1A r info (5)
- Inhibitory pre-synaptic receptors
- Auto-receptor that decreases 5-HT release
- This eventually decreases w/ chronic SSRI treatment
- Desensitisation = inc. 5-HT release
- Therapeutic threshold reached
5-HT1A r locations (5)
- Brain stem (raphe nuclei)
- Hippocampus
- Hypothalamus
- Amygdala
- Entorhinal cortex
How do we evaluate depressive-like behaviour
in pre-clinical drug studies? (animals) (3)
- Historically most studies
have used rats
-Wistar
-Sprague Dawley
-Long-Evans - Mice
Some have used:
* Rhesus monkeys
* Squirrel monkeys
Forced Swim Tests
(not recommended) (6)
- Rats – placed in a container with water
- Try to swim and climb to safety
- Until – immobility i.e. a state of despair
- More time in immobility = more depressive-like
Anti-depressants reduce immobility time (i.e. prolonged escape response
Latency: Time to first period of immobility: therefore anti-depressant increase latency
Sucrose preference test (recommended)
(3)
- Animals have access to water and water + sucrose
- Reduced preference for sucrose = depressive-like behaviour
- Depressive-like behaviours induced i.e. by
- chronic stress
-Restraint stress
-Early life stress
-Intruder stress - Anti-depressives increase sucrose preference relative to depressive animals but not in healthy animals (i.e. doesn’t induce a ”sweet tooth” per se.
Progressive Ratio Test (4)
-Rats/mice trained to press a lever for a reward
-However, to receive the reward, they have to work progressively harder
i.e. 1, 2, 4, 8 etc Until breakpoint — Where reward isn’t worth the effort
- Increased breakpoint (N) = more motivated
-Decreased breakpoint = less motivated
Progressive ratio explained (diff types tested) (3)
- 5-HT2C receptor inverse agonist
- Mice trained to press levers for evaporated milk
- Treated with or without 5-HT2C modulator SB242084
Progressive ratio q’s (4)
- Potential confounders?
- Increased general locomotor activity?
- Hungrier?
- How would you assess/control for this?
New method of SSRI functioning hypothesis (4)
- SSRI’s take weeks/months to work despite being absorbed and taking affect immediately
- suggests that there may be more at play that thought
- they’re GPCR’s = complex signalling cascades are at play - affecting: metabolism, neuron expression etc.
- includes processes like neurogenesis = increasing neurons
- also a theory of the increase of cell connectivity = effective
Neurogenesis def (1)
proliferation of new cells in the mature adult brain
