Recent Advances in Studies of GABA Receptors : Neurochemical Aspects

gamma-Aminobutyric acid (GABA) has been established as a major inhibitory neurotransmitter in the brain. The GABA-induced inhibitory transmission is mediated by two distinct types of GABA receptors which are termed as GABAA and GABAA receptors. The GABAA receptor forms a Cl- channel that consists of several subunits. The recent development of molecular cloning clarified the presence of multiple and heterogeneous molecules in the GABAA receptor subunits. Therefore, it is suggested that multiple GABAB receptors generate various functions in the brain. In contrast, the GABAB receptor exhibits various metabotropic actions for the inhibitory neurotransmission, since it is coupled with GTP-binding proteins. The GABAB receptor of approximately 80 kDa protein in its molecular weight was purified from the bovine cerebral cortex and the presence of another molecular species of the GABAB receptor was also suspected. These results indicate that studies on the molecular diversity of the GABA receptors is important for elucidating the functional roles of GABAergic neurons in the brain.