GABA

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Gamma-aminobutyric acid (GABA) is the major inhibitory mediator in the brain, where it is the transmitter at 20% of CNS synapses.

Contents

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.

Receptors

Three types have been described:

  1. GABA A receptor (most common)
  2. GABA B receptor
  3. GABA C receptor

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.


Action

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.

Agonists

Include:

  • Benzodiazepines
  • Anticonvulsants
  • Sedatives
  • Barbiturates
  • Alcohol
  • The steroid hormones progesterone and deoxycorticosterone

References

Ganong WF. Review of medical physiology. 22nd ed. New York: Lange Medical Books/McGraw-Hill; 2005.

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