Amino Acid Transmitters

Question 1

list the main three amino acid transmitters and the CNS and state whether they are inhibitory or excitatory

Answer 1

1) glutamate - excitatory
2) GABA - inhibitory
3) glycine - inhibitory

Question 2

through which two types of receptors do glutamate and gaba regulate their effects

Answer 2

ion channels (ionotropic) and g protein coupled receptors (metabotropic)

Question 3

where is glutamate synthesised? what are the two mechanisms of synthesis

Answer 3

the brain

1) synthesised from glutamine (from astrocytes) to glutamate by glutaminase
2) glucose metabolism

Question 4

how is glutamate stored?

Answer 4

stored in synaptic vesicles.

H+ conc higher in vesicle than in cytoplasm. outflow of H+ allows transport of glutamate into vesicle

Question 5

what is the mechanism of synaptic release of glutamate

Answer 5

the same as for ACh

Question 6

how is glutamate mainly removed from the synaptic cleft

Answer 6

glutamate transporters on astrocytes.

1) co-transport of (2/3 Na)/H and glutamate
2) exchanging K+ for glutamate

Question 7

name 3 ionotropic glutamate receptors

Answer 7

NMDA, AMPA, Kainate

Question 8

how many polypeptide subunits make up one ionotropic glutamate receptor

Answer 8

4, they are clustered together to form a cylinder with a pore

Question 9

where is the binding site on the glutamate ionotropic receptors

Answer 9

outside, near the N terminus

Question 10

what ions are ampa receptors permeable to

Answer 10

Na and K

Question 11

what ions are NMDA receptors permeable to

Answer 11

Na, K and Ca

Question 12

what ions are kainate receptors permeable to

Answer 12

Na

Question 13

binding of glutamate to AMPA and NMDA receptors causes what type of post synaptic potential

Answer 13

Excitatory post synaptic potential (they depolarise the cell)

Question 14

which other amino acid needs to bind to NMDA receptors for them to function

Answer 14

glycine

Question 15

how many types of metabotropic glutamate receptors are there and how many groups are there

Answer 15

8, grouped in 3 groups

Question 16

where are metabotropic glutamate channels found on neurons

Answer 16

presynaptic and postsynaptic terminals

Question 17

what happens to a g protein once glutamate has bound a metabotropic receptor

Answer 17

gdp is exchanged for gtp on alpha unit.

alpha unit dissociates from beta/gamma heteromer

activates intracellular proteins

Question 18

what intracellular effects are observed when glutamate binds to type I metabotropic receptors

Answer 18

activated alpha subunit causes activation of phospholipase C, creates IP3/DAG

IP3 causes calcium release, DAG activates Protein Kinase C which phosphorylates other proteins

beta/gamma heteromer binds ion channels and modifies function

Question 19

what intracellular effects does the binding of glutamate on type II and type III mReceptors have

Answer 19

activates g protein G alpha(i) which inhibits production of cAMP

modifies ion channels

Question 20

what are the effects of glutamate binding on presynaptic metabotropic channels

Answer 20

causes beta/gamma heteromer to block voltage gated calcium channels - leads to less excitability

Question 21

what are the effects of glutamate binding on postsynaptic metabotropic receptors

Answer 21

usually opens K+ channels leading to hyperpolarisation and less excitability

Question 22

what is the precursor and enzyme needed for GABA synthesis

Answer 22

glutamate and glutamic acid decarboxylase

Question 23

GABA is broken down by what enzyme

Answer 23

GABA transaminase

Question 24

how is GABA packed into vesicles

Answer 24

H+ ions move out of the vesicle and simultaneously GABA moves in

Question 25

how is GABA removed from synaptic cleft

Answer 25

1) taken up into astrocytes through a co-transporter protein which brings Na and GABA into cell (degraded by GABA transaminase)
2) into postsynaptic neurons (degraded by GABA transaminase)
3) taken up into presynaptic neurons and recycled

Question 26

what kind of receptors does GABA act on

Answer 26

postsynpatic ionotropic

pre/postsynaptic metabotropic