Chapter 13

Question 1

List the three main types of ionotropic glutamate receptor:

Answer 1

AMPA
kainate
NMDA

Question 2

What effect does magnesium have on NMDA receptor?

Answer 2

Magnesium is a voltage and use-dependent blocker of the NMDA receptor associated ion channel.

Question 3

What does the NMDAR conducts?

Answer 3

It conducts Na+, Ca2+, K+ but it is blocked by Mg2+

Question 4

What effect do phencyclidine and ketamine have on NMDAR?

Answer 4

They both act as blockers of the NMDAR ion channel.

Question 5

What happens at +20mV to the action of Mg2+ on NMDAR?

Answer 5

At +20mV the net flow of current is outward mainly carried by K+ ions leaving the cell, under these conditions Mg2+ does not enter or block the channel as it normally does at -60mV.

Question 6

What does the activation of NMDA requires?

Answer 6

The binding of glutamate and the binding of the co-agonist glycine (or D-serine)

Question 7

Where are the glutamate and the glycine binding sites located on the NMDAR?

Answer 7

Glutamate binding is located on the GluN2 subunit. The glycine co-agonist binds to the GluN1 subunit.

Question 8

List the characteristics of NMDA receptor:

Answer 8

Conducts Ca2+ and it is blocked by Mg2+
Glycine or D-serine as a co agonist
Blocked by APV (competitive receptor agonist) and by the channel blockers MK801, ketamine and PCP.
Implicated in LTP and consequently cognition
Implicated in neurodegeneration that occurs after brain ischaemia “stroke”.

Question 9

What is Excitatory Post Synaptic Current:

Answer 9

Under whole-cell voltage clamp conditions ​ the response generated in the post-synaptic neuron​ by neurally-evoked glutamate activating synaptically-located ​ionotropic (cation-conducting) glutamate receptors.​

Question 10

Describe the synergistic interplay of synaptic AMPA receptors and NMDA receptors at an excitatory synapse (STEP 1):

Answer 10

Neurally released glutamate activates synaptic AMPA receptors, but although glutamate also binds to NMDA receptors the associated ion channel does not initially conduct due to ion channel blockade by Mg2+.

Question 11

Describe the synergistic interplay of synaptic AMPA receptors and NMDA receptors at an excitatory synapse (STEP 2):

Answer 11

The Na influx caused by activation of AMPA receptors causes a depolarisation of the spine. The depolarisation causes Mg2+ unblocking of the NMDA receptor and consequently the appearence of a slow synaptic depolarisation.

Question 12

What is the role of high frequencies synaptic activity in excitatory synapse with both AMPA and NMDA?

Answer 12

High frequencies of presynaptic activity will favour NMDA receptor activation.

Question 13

What is the molecular structure of both NMDA and AMPA receptors?

Answer 13

They are both tetramers.

Question 14

What do AMPA receptors mediate?

Answer 14

They mediate fast synaptic transmission in the CNS and are composed of GluA1-4 subunits.

Question 15

Define the structure of the majority of AMPAs (with and example):

Answer 15

The majority of AMPARs are heteromers containing the GluA1 subunits. For example in the forebrain, including hippocampus and cerebral cortex GluA2/GluA1.

Question 16

Describe the importance of the GluA2 subunits in AMPARs:

Answer 16

The GluA2 subunit is critical in determining receptor function, including Ca2+ permeability, single channel conductance, block by endogenous polyamines.

Question 17

What is the result of genetic manipulation of GluA2?

Answer 17

It causes profound changes to AMPA receptors properties.

Question 18

What are the postranscription modification that produced GluA2?

Answer 18

The majority of GluA2 subunits are RNA edited resulting in the mature protein containing an arginine (R) residue in the re-entrant M2 loop compared to the genomically encoded glutamine (Q)

Question 19

Describe the functional differences betwen GluA607Q and GluA607R:

Answer 19

The GluA607Q IS Ca2+ permeable and blocked by internal polyamines whereas GluA2607R is Ca2+ impermeable, is insensitive to internal polyamines and has a reduced single channel conductance.

Question 20

Describe AMPAR sensitization:

Answer 20

AMPA receptor desensitization is reduced by AMPA-kines such as cyclothiazide. Such drugs are attracting interest as they appear to enhance cognition.

Question 21

What does the M2 Q/R site regulates?

Answer 21

The M2 Q/R site regulates Ca2+ permeability.

Question 22

Desrcribe the effect and action of spermine as an AMPAR ion channel antagonist:

Answer 22

It blocks the outward current carried by cations, it blocks all AMPAR channles including Glua2(Q) but has no effect on edited GluA(R).

Question 23

What effect does repetitive stimulation have on spermine blocking action?

Answer 23

The blockage by spermine is relieved upon repetitive activation, therefore, at higher frequencies of nerve stimulation the postsynaptic response may increase (a form of synaptic plasticity).

Question 24

What are the four components of an ionotropic glutamate receptor subunit?

Answer 24

ATD: Amino terminal domain
CTD: Carboxy terminal domain
M1-4: Transmembrane domain
S1-2: Ligand binding domain

Question 25

Describe S1-2 domain peculiarity:

Answer 25

S1 and S2 domains show sequence homology to bacterial amino acid binding proteins.

Question 26

What is the function performed by the two bacterial amino acid binding proteins homologous to S1 and S2?

Answer 26

They bind amino acid between 2 lobes of a clam shell that are in dynamic equilibrium between open and closed states (ligand binding stabilises the closed states)

Question 27

What happen if you swap S1 and S2 domains between GluA3 (AMPAR) and Glu6 (kainate R)?

Answer 27

The swapping causes appropriate changes to the agonist pharmacology.

Question 28

What conformational change does binding of ligand trigger in S1S2 domain?

Answer 28

Formation of H bonds and 20° rotation.

Question 29

Describe the structure of NMDA receptors:

Answer 29

Most NMDARs are composed of GluN1+GluN2 subunits. The NMDAR subunits have a similar topology to the AMPA and kainate subunits.

Question 30

What do NR1 and GluN2 subunits bind?

Answer 30

NR1 subunit binds glycine and the GluN2 subunit binds glutamate.

Question 31

What do NMDARs have at the equivalent of the AMPAR Q/R site?

Answer 31

NMADRs have an asparagine residue (N)- site of Mg2+ block.

Question 32

List the 8 steps that lead to neuronal cell death and that link NMDARs to brain ischemia:

Answer 32

1) Depletion of glucose, glycogen, creatine phosphate
2) Failure of Na+/K+ ATPase and other ion pumps
3) Membrane potential rundown
4) Action potential firing
5) Glutamate release
6) AMPA and NMDAR activation lead to excessive influx of Ca2+
7) Activation of proteases, lipases, caspases etc.
8) Neuronal cell death

Question 33

What is a potential treatment for ischemia-induced neuronal cell death?

Answer 33

Potential treatment with agonist (use)-dependant channel blockers such as PCP, ketamine, MK801.

Question 34

What is the probel with monoaminergic antidepressants?

Answer 34

Patients require several weeks to months for symptonm remission. Some patients may be resistant to drugs.

Question 35

Describe the advantage and disadvantages of using ketamine as an antidepressant:

Answer 35

(R, S)- Ketamine exerts a rapid and sustained antidepressant effects after a single dose in patients.
It has serious side effects and abuse liability.

Question 36

How does (R, S)-Ketamine works?

Answer 36

It is a potent NMDAR ion channel blocker, a metabolite of ketamine (2R, 6R-HNK) increases frequency and amplitude of AMPAR-mediated mEPSCs recorded from hippocampal neurons.

Question 37

Describe the function of 2R, 6R-HNK:

Answer 37

It enhances the amplitude and frequency of AMPAR-mediated mEPCS, whereas ketamine is inert. 2R, 6R-HNK has no effect on NMDAR-mediated response, whereas ketamine block NMDAR channel.

Question 38

What is long term potentiation:

Answer 38

An electrophysiological correlate of learning and memory that involves the activity-dependent changes in synaptic excitatory transmission mediate by glutamate receptors.

Question 39

Describe what physiological changes are associated with long term potentiation:

Answer 39

Changes in AMPA receptor expression and trafficking at excitatory synapses.

Question 40

Describe the physiological process that might be involved in long term potentiation:

Answer 40

1) Glutamate release activates NMDA and this cause a Ca2+ influx
2) INDUCTION: AMPA (GluA1) receptors (already synthesized) are up-regulated and incorporated into excitatory synapses.
3) STABILIZATION: Ca2+ permeation via GluA1 homomers lead to replacement of GluA1 receptors with heteromeric GluA1/GluA2 receptors.

Question 41

Describe the induction phase in LTP mechanism:

Answer 41

AMPA (GluA1) receptors (already synthesized) are up-regulated and incorporated into excitatory synapses.

Question 42

Describe the stabilization phase in LTP mechanism:

Answer 42

Ca2+ permeation via GluA1 homomers lead to replacement of GluA1 receptors with heteromeric GluA1/GluA2 receptors.

Question 43

What is the link between LTP and AMPA?

Answer 43

LTP may involve movement of AMPARs from an extrasynaptic location to a synaptic location.

Question 44

Describe Huntington’s Disease:

Answer 44

Is an incurable neurodegenerative disease characterised by motor dysfunction, however cognitive deficits often precede the appearence of motor problems. It is caused b CAG repeats in the huntingtin gen leading to a polyQ huntingtin protein.

Question 45

What does the AMPAkine CX929 does?

Answer 45

It is an AMPAkine that improves the LTP and cognition in a HD mouse model (CAG140).