BMS11004 - WEEK 3 THURSDAY

Question 1

how can we determine if an NT is present

Answer 1

immunostaining

Question 2

how can experimentally determine if molecules are NT

Answer 2

1. presence
2. do cells express enzymes synthesising it or transporter proteins storing it
3. is it released
4. does it affect postsynaptic cell
5. can we block NT

Question 3

how can we test if cell express enzyme to synthesis or transporter proteins to store NTs

Answer 3

immunostaining
in-situ hybridisation to detect if RNA is expressing in cells

Question 4

how can we test if NT has been released

Answer 4

collect fluid around neurons after stimulating them and then carry out chemical analysis

Question 5

how can we test if NT is present and affects postsynaptic cell

Answer 5

test if molecule mimics effect of stimulating presynaptic cell

Question 6

how can we block NT to test if molecules are NT

Answer 6

apply drugs, delete genes encoding enzymes/transporters/receptors. if you can block neurotransmission, NT present

Question 7

give 2 broad categories of NT

Answer 7

small molecules (amino acids and amines)
large molecules (peptides)

Question 8

what are amino acids and amine NTs

Answer 8

small molecules stored in synaptic vesicles, binding to ligand-gated ion channels, or G-protein coupled receptors

Question 9

what are peptides

Answer 9

chains of aa made in RER and processed through protein secretion pathway, stored in secretory granules, and only bind to G-protein coupled receptors

Question 10

what do peptide-releasing neurons also release when releasing peptides

Answer 10

co-transmitters

Question 11

name 2 type of NT receptor

Answer 11

ligand-gated ion channels (ionotropic receptor, directly depolarise/hyperpolarise postsynaptic cell
G-protein coupled receptor (metabotropic receptor, indirectly initiates more complex effects)

Question 12

give structure of G-protein coupled receptor

Answer 12

single polypeptides with 7 membrane-spanning alpha helix
2 extracellular loop to form transmiter binding site (variations determine what NT, agonist, antagonist can bind)
2 intracellular loops to bind/activate G-proteins

Question 13

give examples for G-protein coupled receptors

Answer 13

GABA, glutamate, Ach, serotonin, dopamine, noreinephrine, opioids, cannabinoid, ATP, adenosine

Question 14

give an example for G-protein

Answer 14

GTP

Question 15

explain G-protein subunit cycle

Answer 15

each G-protein has 3 subunit (a, b, y)
1. resting state = GCP molecule bound to Ga
2. if GDP-bound G-protein bump into specific receptors, if receptor has transmitter bound, G-protein release GDP, exchanged for GTP in cytosol
3. activated GTP-bound G-protein split into Ga+GTP and Gby complex
4. Ga is enzyme and break down GTP into GDP so eventually terminate own activity
5. Ga and Gb join, allow cycle to begin again

Question 16

define convergence

Answer 16

multiple NT acting on multiple receptors, which can then sum-up and act on one effector system

Question 17

define divergence

Answer 17

single NT acting on multiple receptors, each receptor activate different effector system
allows one single molecule to have diverse effects on/in cells

Question 18

explain prevalence of glutamate

Answer 18

CNS most common excitatory NT
aa, so is found in all neuron (cannot use enzymes that make glutamate as marker for gluatminergic neuron, as all neurons contain it)

Question 19

what are the 3 ionotropic glutamate receptor subtypes (based on drugs acting as selective agonist)

Answer 19

AMPAreceptors, kinase, NMDA
action terminated by selective uptake into presynaptic terminal, glia

Question 20

name structure of ionotropic and metabotropic glutamate receptor and mechanisms of working

Answer 20

ionotropic glutamate receptor = 4 subunits forming gated-ion channel eg: AMPAR, NMDAR. mechasism- open ion channel
metabotropic glutamate receptor = G-protein coupled receptor eg: mGluR1, mGluR2. mechanism- activate g-protein and trigger downstream signal casc.

Question 21

what type of transmission do AMPA (ionotropic, glutamate) receptors mediate

Answer 21

fast excitatory transmission

Question 22

how does AMPA receptors (ionotropic glutamate) work

Answer 22

when glutamate bind opens AMPA receptors (permeable for Na, K)
both Na in and K out, depolarising cell and causing EPSP

Question 23

how do NMDA receptors (ionotropic glutamate) work

Answer 23

coexisting with AMPA receptors
at rest = Mg2+ blocking pore so nothing etner
1. when depolarised lessens electrical force so Mg2+ leave
2. NMDA receptor also permeable to Ca so allow in, downstream signalling

Question 24

what makes GABA

Answer 24

synthesised from GAD enzyme

Question 25

how does GABA work as NT

Answer 25

usually inhibitory NT, however depend on exact circumstances (membrane potential, current actual potentials of chloride in/out of cell)
opens channel and cause hyperpolarisation

Question 26

why is having right amount of inhibition via GABA important

Answer 26

too much= coma as silences all neurons in brain
too little= seizures, as not enough inhibition to dampen down brain activity so uncontrolled excitation

Question 27

what other chemicals can bind to GABA receptors

Answer 27

but has no effect without GABA binding
ethanol - alcoholics brain adapts and reduce GABA receptor. cold turkey causes seizures as lacking enough GABA for inhibitions
benzodiazapine
barbituates (sedative)- overdose stop breathing
neurosteroid (metabolise steroid hormone)

Question 28

how can GABA act through metabotropic receptors

Answer 28

mGluRs, GABAb receptors are examples of GPCRs
can:
1. open K+ channels
2. close Ca2+ channels
3. trigger other second messengers like cAMP
4. often presynaptic or autoinhibitory

Question 29

what is glycine

Answer 29

regular amino acid NT, inhibitory through binding to glycine gated Cl- channels but also can bind to NMDA receptor

Question 30

explain dendritic integration

Answer 30

each EPSP not enough to trigger AP so need several EPSPS to depolarise cells to threshold

Question 31

what molecule is glutamate and glycine synthesised from

Answer 31

glucose

Question 32

what are GABA synthesised from

Answer 32

not an aa
synthesis in large quantities by neurons using it as NT
glutamate precursor, and GAD enzyme

Question 33

where can you find glutamate, glycine and GABA

Answer 33

glutamate and glycine made from aa so in all body cells
GABA only present in neurons that make it

Question 34

if AMPA receptors are permeable to both Na+ and K+, why does activating them cause depolarisation

Answer 34

more Na+ enters cell due to electric pull which makes membrane less negative, and so results in depolarisation

Question 35

what would happen if GABA opens GABAa receptor and membrane potential is below Cl Nernst potential

Answer 35

net inflow of Cl- ions