The neurotransmitter gamma-aminobutyric acid (GABA) mediates an inhibitory signal upon binding to two ligand-gated channels, GABA-A and GABA-C receptors, and a G-protein linked receptor, GABA-B. The GABA-B receptor is a heterodimeric complex composed of two 7-transmembrane GPCRs termed GABA-B R1 and GABA-B R2. GABA-B receptors have been implicated in the GABA-induced modulation of sympathetic and catecholaminergic pathways in the central nervous system.