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.