GAD-65 and GAD-67, glutamate decarboxylases, function to catalyze the production of GABA (gamma-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 Rα1-6, GABAA R β1-3, GABAA Rγ1-3, GABAA Rδ, GABAA Rε, GABAA Rρ1 and GABAA Rρ2. The GABAB family is composed of GABAB R1α and GABAB R1β. 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.