The GABA [[receptor]]s are a class of receptors that respond to the [[neurotransmitter]] gamma-aminobutyric acid ([[GABA]]), the chief inhibitory compound in the mature vertebrate central nervous system. There are two classes of GABA receptors: GABAA and GABAB. GABAA receptors are ligand-gated ion channels (also known as ionotropic receptors); whereas GABAB receptors are G protein-coupled receptors, also called metabotropic receptors.