Glutamatergic Signalling

Question 1

How can glutamate donate protons ?

Answer 1

From both carboxyl groups

Question 2

What effect does glutamate have?

Answer 2

Excitatory

Question 3

What are some non-neuronal roles of glutamatergic signalling?

Answer 3

bone, testis, pancreas, hormonal system and gut

Question 4

What is EAAT?

Answer 4

Transporter for recycling glutamate through glial cells

Question 5

Where are EAAT1-5 located?

Answer 5

o EAAT1 and 2 – astrocytes and microglia
o EAAT3 – cerebral neurons
o EAAT4 – cerebellar neurons
o EAAT5 retinal

Question 6

Describe the synthesis and recycling of glutamate

Answer 6

• Takes place in CNS as glutamate cant cross the BBB
• Derived from glutamine
• Normally made in astrocytes
• Recycled back to glial cells to turn back into glutamine before being synthesised back to glutamate in a cycle

Question 7

Which ion does ionotropic signalling of glutamate allow influx of?

Answer 7

Ca2+

Question 8

What are the receptor agonists for glutamate receptors?

Answer 8

NMDA – requires glycine as a co-agonist, calcium flux related to synaptic plasticity important in learning and memory
o AMPA - plasticity and synaptic transmission, particularly LTP
o Kainate – both pre-synaptic and post synaptic, synaptic plasticity
o Non-selective cation channels: Na+ and K+

Question 9

Describe the action of metabotropic glu receptors

Answer 9

• Glu binds to receptor
• Causes conformational change
• Causes alteration to post synaptic molecules – 2nd messengers cause change in metabolism within cell
• Can cause apoptosis, movement of Ca2+ molecules, gene transcription

Question 10

How can you distinguish between different ionotropic glu receptors?

Answer 10

agonist dependency

Question 11

What occurs on the post- synaptic membrane?

Answer 11

receptor clustering

Question 12

What types of proteins are involved in formation of the postsynaptic scaffold?

Answer 12

membrane bound
cytoskeletal
scaffolding
modulatory

Question 13

What is glutamate homeostasis regulataed by? What is the IC level of glu compared to EC?

Answer 13

• IC level is 1m times that of EC level

* Regulated by sodium dependent glutamate transporters mainly on the astrocytes

Question 14

What are some of the mechanisms for calcium regulation?

Answer 14

o	Ca2+ ATPase – efflux 
o	Na/Ca2+ exchanger – efflux 
o	Ca2+ sequestration by ER 
o	Ca2+ sequestration by mitochondria 
o	IC Ca2+ buffering by Ca2+ binding proteins

Question 15

What are the concs of IC and EC Ca2+?

Answer 15

• IC Ca2+ is 100nM (if you include bound cytosolic its 1mM)

* EC Ca2+ is 1uM

Question 16

What is glutamate excitotoxicity implicated in?

Answer 16

• Implicated in ischaemia, trauma, hypoglycaemia, hypoxia, seizures, AD, PD, Huntington’s and ALS

Question 17

What can GluR overactivation lead to?

Answer 17

Ca2+ overload 
Cell death via: 
o	Membrane breakdown
o	Cyctoskeletal alterations
o	NO-derived free radicals – leads to peroxynitrite generation which damages cells

Question 18

What are they two hypotheses for the relationship between Ca2+ influx and neurotoxicity? What is evidence?

Answer 18

• Debates whether linear relationship between Ca2+ influx and neurotoxicity (Ca2+ load hypothesis) or distinct Ca2+ signalling pathways are related to influx and therefore neurotoxicity (source specific hypothesis)
o Evidence for SSH – distinct influx pathways determine vulnerability

Question 19

What is the structure of AMPA receptors ?

Answer 19

• Consist of 4 potential subunits in a heterotetrameric structure

Question 20

What is the basis of excitotoxicity in Parkinson’s?

Answer 20

• Normally balance between striatal activatation through NMDA receptors and inhibition through D2 receptors
• Depletion of dopamine results in glutamatergic overactivity and change in NMDDA subunits (NR1, NR2B decrease and NR2A unchanged)
• There PD is a secondary glutamate overactivity syndrome

Question 21

What is the treatment for glutamate overactivation in Parkinsons in animal models?

Answer 21

o Many non-selective NMDA antagonists tried in animals
o Show reduction in Parkinsonian findings
o Not well tolerated in primates due to hallucinations and sedation

Question 22

How is glutamate excitotoxicity thought to be involved in AD?

Answer 22

• Glutamate may be a major executor of neuronal damage in AD
• Amyloid beta and tau are related to glutamate
• Activation of NMDA receptors enhances production of these factors

Question 23

What treatment mechanisms are involved in the treatment for AD glutamate excitotoxicity?

Answer 23

• Treatment:
o NMDA antagonist, memantine, has been approved for AD treatment
o An uncompetitive antagonist with improved voltage dependent kinetics and affinity, leads to functional improvement in AD and well tolerated

Question 24

Is there evidence for glu excitotoxicity in Huntington’s?

Answer 24

• Indirect evidence
• Injections of kainite into rat striatum killed striatal neurons, required glutamatergic afferents
• Agonist for NMDA receptors can reproduce some HD behavioural features in rats