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 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.5,6 The GABA (B)R1 subunit was demonstrated to be important for agonist and antagonist binding, while GABA (B)R2 was shown to be essential for trafficking and for G-protein binding.nTo date, eight alternatively spliced isoforms of GABA (B) R1 have been proposed. These are named 1a-1h, of which 1a and 1b are the most prominent. Only 1a, 1b, and 1c appear to act as functional subunits.They are widespread, being expressed in testis, stomach, spinal cord, and brain. Isoform 1b is also expressed in kidney and liver.