Gamma-aminobutyric acid neurons (GABA)
GABA is synthesized by transforming glutamate into GABA via the glutamic acid decarboxylase enzyme. It is then stored in the axon for release. There are 2 different GABA receptors (A and B). The more common GABA-A is a ligand-gated chloride channel and the GABA-B is a G-protein linked receptor. These receptors can be further subtyped, but the functionality of the different subtypes has yet to be made clear.
GABA produces its inhibitory response when it binds to the GABA-A receptor, causing a influx of chloride ion and decreasing the membrane potential further away from threshold (see graph). Several CNS-active drugs bind to this receptor and enhance GABA's binding effects.
The GABA-B receptor effects are much weaker than that of GABA-A.
There are relatively few GABA producing neurons, thus their influence is limited.
Extra info: GABA is released from a variety of neurons and as such has a wide distribution.
GABA-A and -B receptors can be found in the membranes of serotonin, norepinephrine and dopamine neurons.
Extra info: Not only is GABA released from a variety of neurons, but it can effect many different kinds.
GABA-B receptors increase the influx of calcium ions into the cell.
Extra info: The GABA-A receptor controls the influx of CHLORIDE into the cell.