GABA Overview

Question 1

Who first discovered GABA?

Answer 1

Roberts and Frankel in 1950

Question 2

How was GABA discovered?

Answer 2

Paper chromatography of brain extracts

Question 3

Florey 1953

Answer 3

Showed that brain extracts have inhibitory action on crayfish stretch receptor organ

Question 4

Kuffler 1958

Answer 4

Applied GABA mimicked inhibitory action on crayfish stretch receptor organ

Question 5

Roberts: 1950s and 60s

Answer 5

Elucidated GABA metabolism through radioactive precursors

Question 6

Obata 1967

Answer 6

Iontophoretic gather application mimics inhibitory action of Purkinje cells and released into ventricles on Purkinje stimulation

Question 7

GABA levels in the brain

Answer 7

2500 nmol/gram

Question 8

Is there more inhibition or excitation in the brain?

Answer 8

Inhibition

Question 9

How is GABA distributed?

Answer 9

Throughout the brain (30% of all nerve endings) inhibitory interneurons everywhere long axon tracts: cortex-substantia nigra; cerebellar Purkinje cells (and many others)

Question 10

How was the distribution of GABA determined?

Answer 10

Distribution of GABA receptors (Promoter:fusion/mRNA/Protein) Distribution of metabolising enzymes (GAD, GABA-T) Distribution of GABA and/or vesicular GABA transporter Uptake of 3H GABA Electrophysiology (gold standard)

Question 11

Recurrent inhibition

Answer 11

Draw diagram

Question 12

Afferent inhibition

Answer 12

Draw diagram

Question 13

The GABA shunt

Answer 13

Question 14

GABA transaminase (GABA-T)

Answer 14

Catalyses the conversion of Alpha-ketoglutarate to glutamate

Question 15

Glutamic acid decarboxylase (GAD)

Answer 15

Catalyses the conversion of glutamate to GABA

Question 16

Vesicular transport of GABA

Answer 16

VGAT

Question 17

Reuptake

Answer 17

2Na+/1Cl- per GABA 4 Distinct Genes:GAT-1,2,3 & BGT-3 ( GABA/betaine transporter) Nerve Terminals and Glial membranes

Question 18

Which of the GABA transporters have established blockers?

Answer 18

GAT etc… (VGAT doesn’t)

Question 19

Coupling of synthesis and transport

Answer 19

Draw diagram

Question 20

What is GABA synthesis coupled to?

Answer 20

GABA synthesis is functionally coupled to vesicular transport into synaptic vesicles

Question 21

How many variants of GAD are there in humans?

Answer 21

There are two variants: 65 and 67

Question 22

Why is GABA synthesized by SV-associated GAD is preferentially transported into the SV by vesicular GABA transporters (VGATs)?

Answer 22

VGAT forms a protein complex with GAD on the SV

Question 23

Succinic semialdehyde dehydrogenase deficiency

Answer 23

First documented inborn error of GABA metabolism symptoms include mental retardation, ataxia, motor deficiencies

Question 24

Disorders related to aberrant GABA transmission

Answer 24

Epilepsy, Huntington’s disease, Parkinson’s disease, tardive dyskinesia, alcoholism, sleep disorders

Question 25

Physiology of GABAergic transmission

Answer 25

Draw diagram

Question 26

When is GABA transmission excitatory?

Answer 26

In invertebrates and developing neurons

Question 27

GABAergic transmission in. embryonic neurons

Answer 27

Draw diagram

Question 28

GABAergic transmission in some adult neurons

Answer 28

Draw a diagram

Question 29

GABA receptors

Answer 29

Historically there were three classes but now there are technically two, as C is now a subtype of A

Question 30

GABAA, and GABAC

Answer 30

Classic Ligand-gated ion channels analogous to nicotinic receptor - postsynaptic

Question 31

GABAB

Answer 31

7TM G-Coupled receptors – presynaptic (coupled to K+ channels)

Question 32

Identification of the GABA receptors

Answer 32

Hans Mohler – 1980’s Photolabelling Eric Barnard & Anne Stephenson – 1980’s Purified and reconstituted protein Eric Barnard’s & Peter Seeburg’s groups – 1986-7 Sequenced via cDNA based on peptides

Question 33

GABAA receptors

Answer 33

19 different subunits α1-6, β1-4, γ1-3,δ,ε,θ 8 families alternative splicing exists most common form: α12,β22,γ21

Question 34

Mechanism of activation

Answer 34

Two agonist molecules needed to open channel Agonist binding is very rapid, low affinity (Kd 100 µmol) rapid confirmation change opens channel (milliseconds) Desensitisation involves transition to high affinity state (Kd > 1 µmol)

Question 35

Which proteins are GABAA receptors usually clustered with?

Answer 35

GABARAP Neuroligin-2 Gephyrin Collybistin

Question 36

How does clustering affect GABAA receptor kinetics?

Answer 36

Clustering decreases affinity and decreases the rate of desensitisation Clusters have properties consistent with those of native synaptic transmission

Question 37

Extrasynaptic GABAA receptors

Answer 37

Lower EC50 thus more sensitive

Usually delta or alpha 5

Question 38

Tonic inhibition in clustered and diffuse GABAA receptors

Answer 38

Draw diagrams IPSP in clustered but not diffuse