Which of the following is the major inhibitory neurotransmitter in the brain?
GABA
GABA (gamma aimno butyric acid) is the major inhibitory neurotransmitter of the brain.
GABA binds to transmembrane receptors which triggers the opening of ion channels causing hyperpolarisation of the neuron (by letting chloride ions in or potassium ions out). This hyperpolarisation means that the neurone is less likely to depolarise (hence inhibitory effect).
There are two types of GABA receptor:
- GABA-A - ligand-gated ion channel complex
- GABA-B - metabotropic receptors, which are G protein-coupled receptors that open or close ion channels via intermediaries (G proteins)
It is synthesized in the brain. It is synthesized from glutamate. In general, it does not cross the bloodbrain barrier.
It is degraded by GABA transaminase (valproate is a GABA-transaminase inhibitor).
| GABA type | Receptor type | Agonists | Antagonists |
|---|---|---|---|
| GABA-A | ionotropic | ethanol benzodiazepines z-drugs barbiturates | flumazanil |
| GABA-B | metabotropic | baclofen GHB |
