γ-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 GABA
A. and GABA
A receptors. The GABA
A 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 GABA
A receptor subunits. Therefore, it is suggested that multiple GABA
A receptors generate various functions in the brain. In contrast, the GABA
B receptor exhibits various metabotropic actions for the inhibitory neurotransmission, since it is coupled with GTP-binding proteins. The GABA
B receptor of approximately 80kDa protein in its molecular weight was purified from the bovine cerebral cortex and the presence of another molecular species of the GABA
B 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 GABA ergic neurons in the brain.
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