Gamma-aminobutyric acid (GABA) is the major inhibitory mediator in the brain, where it is the transmitter at 20% of CNS synapses.
Synthesis and Metabolism
GABA is formed by the decarboxylation of glutamate, which is catalyzed by glutamic acid decarboxylase (GAD) which can be found in the nerve endings. A vesicular GABA transporter (VGAT) transports GABA into secretory vesicles
GABA is metabolized primarily by transamination to succinic semialdehyde (by GABA transaminase) and then to succinate in the citric acid cycle. There is also active reuptake of GABA via the GABA transporter.
Three types have been described:
GABAA and GABAB receptors are widespread in the CNS, while GABAC receptors are primarily found in the retina.
GABAA and GABAC receptors are ionotropic, while GABAB is metabotropic.
GABA mediates the inhibitory actions of local interneurons in the brain, including inhibition within the cerebral cortex and between the caudate nucleus and the substantia nigra
May also mediate presynaptic inhibition within the spinal cord.
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Ganong WF. Review of medical physiology. 22nd ed. New York: Lange Medical Books/McGraw-Hill; 2005.