CEREBRAL GABA(A) AND GABA(B) RECEPTORS

gamma-Aminobutyric acid (GABA) is widely known as one of the major inhibitory neurotransmitters in the mammalian central nervous system (CNS).(1) In general, it has been considered that neuronal activity in the brain is inhibited by the activation of GABAergic neurons. This inhibitory action of GABA is mediated by GABA receptors, which are divided into two types-GABA(A) and GABA(B).(2) It was initially thought that GABA(A) receptor, a bicuculline-sensitive type, forms the GABA-gated Cl- channel, and that the activation of GABA(A) receptor induces the fast inhibitory postsynaptic potential (IPSP). Subsequently, the presence of CABA(B) receptor, which is insensitive to bicuculline and sensitive to baclofen, was revealed, and it was found that this receptor is one of the metabotropic types that couple with GTP-binding protein. The activation of the GABA(B) receptor is known to induce slow IPSP. Therefore, it is suggested that both GABA(A) and GABA(B) receptors have inhibitory roles in the CNS, although these actions are mediated by different molecular mechanisms. In this paper, current concepts on GABA(A) and GABA(B) receptors in the mammalian CNS are described, with special reference to their pharmacological, neurochemical, and molecular biological characteristics.