GABA (gamma-aminobutyric acid) is the major inhibitory neurotransmitter in the central nervous system and plays a crucial role in the modulation of neuronal activity.nThe GABA transmitter interacts with three types of receptors: the ionotropic receptors, GABA (A) R and GABA (C) R, and the metabotropic GABA (B) receptor, [GABA (B) R].The latter belongs to the G-protein-coupled receptor (GPCR) superfamily and mediates slow synaptic inhibition in the brain and spinal cord.nThe functional GABA (B) receptor [GABA (B)R] is a heterodimer consisting of two subunits, the GABA (B) R1 and the GABA (B) R2. These subunits were demonstrated to have complementary roles essential for the functional receptor.nGABA (B) R2 has been shown to be essential for trafficking and for G-protein binding while the GABA (B) R1 subunit has been demonstrated to be important for agonist and antagonist binding. GABA (B) R2 is highly expressed in brain, especially in the cerebral cortex, thalamus, and hippocampus, spinal cord, and, to a lesser extent, in testis.