WEEK 9 - glutamate receptor types and molecular basis and LTM

Question 1

what are the main excitatory neurotransmitters

Answer 1

Glu and Ach

Question 2

Neurotransmitter receptors

Answer 2

binds two different types of receptor
- ionictropic
- metabotropic

binding of NT causes binding of receptor to G-proteins which regulate Adenyl-cyclase producing cAMP and PLC up-regulating Ca2+ levels

Question 3

structure of ionotropic neurotransmitter receptors

Answer 3

Common to all:
- Channels
- Channels made of several subunits (usually each encoded by different genes, meaning different complexities, also different structure dependent on location in neuron)

neurotransmitter receptor channel made up of multiple subunits

• binding of distinct neurotransmitter types
• are all channels

Question 4

Glu receptors: the ionotropic Glu receptor (AMPAR)

Answer 4

4 membrane-associated segments but 1 does not have traverse membrane
2 extracellular domains associate to form binding site for neurotransmitter

conserved residues:
- Q (Gln): Ca2+ permeability of non-NMDA receptor
- In NMDAR this is Asn, which interacts with Mg2+
- D (Asp) also forms part of cation binding site

Question 5

Glu receptors:
the NMDAR receptor, coincident detector

Answer 5

Ca2+ channel blocked by Mg2+ at rest

concerted Glu binding and depolarisation are required to release Mg2+, unblock the channel and allow Ca2+ entry

Glu binding and depolarisation at the same time
- Neuron has to receive two events / high frequency
Releases magnesium

conincident detector:
essential for LTP

Question 6

The Glu NMDAR: coincident detector and long term potentiation
resting potental

Answer 6

at resting potential magnesium ions block channel

Question 7

The Glu NMDAR: coincident detector and long term potentiation
activation

Answer 7

activation of NMDAR requires both Glu and depolarisation

activation of NMDAR results in long-term potentiation of synaptic function

Question 8

The Glu NMDAR: coincident detector and long term potentiation
glutamate and depolarisation

Answer 8

depolarisation liberates Mg2+ allowing Na+, Ca2+ to enter

calcium ions flowing through the NMDAR induce up-regulation of AMPAR increasing neuronal excitability

sustained depolarisation (LTP)

long-lasting changes in post synaptic neurons (new synapses)

Question 9

Glu receptors: metabotropic mGluR glutamate receptors

Answer 9

metabotropic receptors are G-protein coupled receptors

excitatory:
mGluR1, 5 bing Gq to activate PLCbeta, resulting in DAG to activate PKC and IP3 causing the release of Ca2+ from ER

Inhibitory:
mGluR2, 3 bind Gi/o to open K+ channels, reduce overall probability of opening Ca2+ channels and inhibit Adenyl Cyclase (AC)

Question 10

the molecular basis of LTM

Answer 10

ionotropic and G-protein coupled receptors

Question 11

the molecular basis of LTM: ionotropic and G-protein coupled receptors

Answer 11

the cAMP pathway and the Ca2+ pathway are the 2 pathways that work to activate CREB

activation of CREB (transcription factor) results in gene expression and protein synthesis

ends in the formation of new synapses
–> basis of LTM

Question 12

metabotropic receptors: interconversion of G-protein subunits into active and inactive states

Answer 12

G-GDP (in inactive state)

two mechanisms
1. displacement of GDP with GTP
—> Gbetagamma
—> activates effectors

2. self-inactivation by GTPase activity
   —>Galpha-GTP
   —> activates effectors

Question 13

metabotropic receptors are G-protein coupled receptors:
Amplification and timing by G proteins

Answer 13

OFF state –phosphatase activity–> time-limited ON state

GTPase activity of G protein is a (internal) timer and amplifier

binding of neurotransmitters activates timing mechanism by displacement of GDP by GTP

Question 14

metabotropic receptors produce cAMP as

Answer 14

a second messenger

Question 15

metabotropic receptors produce cAMP as a second messenger

Answer 15

cAMP activates Protein Kinase A (PKA)

PKA phosphorylates multiple targets, including Ca2+ channels

phosphorylation of Ca2+ channels increases their open probability

leads to changes in membrane conductance

Question 16

metabotropic receptors activate the PLC pathway

Answer 16

increasing Ca2+ levels

DAG activates, which phosphorylates substrates

IP3 opens a Ca2+ channel in ER releasing Ca2+ from intracellular stores, increasing cytosolic

Ca2+ activates CaMKII which phosphorylates substrates

Question 17

pre synaptic metabotropic receptors modulate..

Answer 17

neurotransmitter release

Question 18

presynaptic metabotropic receptors modulate neurotransmitter release
facilitation

Answer 18

serotonin receptor

reduced open probability of K+ channels increases excitability

Question 19

presynaptic metabotropic receptors modulate neurotransmitter release
Inhibition

Answer 19

GABA receptor

reduced open probability of Ca2+ channels and increased opening of K+ and Cl- channels reduces excitability

Question 20

molecular basis of memory

Answer 20

cAMP and Ca2+ pathways and activation of CREB

activation of metabotropic receptors activates AC producing cAMP which activates PKA

an increase in Ca2+ levels via activity, NMDAR and PLC activates CaMKII which phosphorylates AMPAR

PKA and CaMKII also phosphorylate CREB which activates gene expression causing long-lasting changes of synapses

Question 21

protein kinases in learning and memory

Answer 21

PKA, PKG, CaMKII and PKC

Question 22

protein kinases in learning and memory:
catalytic domains are normally maintained inactive by…

Answer 22

an autoinhibitory domain

Question 23

molecular basis of memory:
protein kinases in learning and memory:
regulatory domains are..

Answer 23

binding sites for second messengers

cAMP, cGMP, Ca2+, calmodulin, DAG etc

Question 24

molecular basis of memory:
the adenyl-cyclase and cAMP pathways
activation of…

Answer 24

PKA by cyclic AMP

auto-inhibitory segment prevents binding of substrates to binding site

binding of cAMP reduces affinity for regulatory subunit for catalytic subunit
liberates catalytic subunit as an active subunit

At high levels of cAMP regulatory subunit degraded
PKA can have longer lasting and wider effect on target

Question 25

molecular basis of memory:
long term stimulation converts PKA into a…

Answer 25

constitutively active form

in high cAMP regulatory subunits are degraded

dissociation is reversible if cAMP levels are low

with long term stimulation PKA is consitiutively active

Question 26

molecular basis of memory:
PKA
structure

Answer 26

regulatory subunit (when inactive) attached to the catalytic subunit

Question 27

molecular basis of memory:
calcium and the activation of CaMKII dependent on…

Answer 27

neuronal stimulation

auto-phosphorylation upon Ca2+ binding when neighbouring subunits are bound to calmodulin

at high frequency there is no time for dissociation, increasing the probability of phosphorylation

pCaMKII is consitutively active

Question 28

molecular basis of memory:
cross talk between kinases and phosphatases modulates the response

Answer 28

DOPAMINE RECEPTOR
activates cAMPP and PKA activating DARP-32 resulting in inhibition of protein phosphatase 1 (PP1) and phosphorylation of substartes

this is counteracted by CALCINERUIN
Activation of NMDAR and rise in Ca2+ activate calcineurin which de-inhibits PP1 dephosphorylating substrates

In reality much more dynamic in neuron
Dynamics between phosphorylation and dephosphorylation
- Contrasting mechaninsms

Question 29

molecular basis of memory:
what is required for LTM

Answer 29

postsynaptic depolarization can induce new gene expression

long term memory requires protein synthesis

this results in formation of new synapses and circuit remodelling

Question 30

what is the essential mechanism of learning and memory

Answer 30

that Ca2+ pathway

the cAMP pathway

together activate CREB