GAD-65 and GAD-67, glutamate decarboxylases, function to catalyze the production of GABA (g-aminobutyric acid). In the central nervous system GABA functions as the main inhibitory transmitter by increasing a Cl-conductance that inhibits neuronal firing. GABA has been shown to activate both ionotropic (GABAA) and metabotropic (GABAB) receptors as well as a third class of receptors called GABAC. Both GABAA and GABAC are ligand-gated ion channels, however, they are structurally and functionally distinct. Members of the GABAA receptor family include GABAA R alpha 1-6, GABAA R beta 1-3, GABAA R(C)1-3, GABAA R?, GABAA R gamma, GABAA R delta 1 and GABAA R delta 2. The GABAB family is composed of GABAB R1 alpha and GABAB R1 beta. GABA transporters have also been identified and include GABA T-1, GABA T-2 and GABA T-3 (also designated GAT-1, -2 and -3). The GABA transporters function to terminate GABA action.