Neurochemical and molecular pharmacological aspects of the GABAB receptor

Metabotropic gamma -aminobutyric acid (GABA)(B) receptors are known to modulate the synaptic release of various neurotransmitters in the nervous system. Activation of GABA(B) receptor induces the inhibition of adenylyl cyclase activity, while it does not stimulate the formation of inositol phosphates. Activation of a potassium conductance and suppression of a calcium conductance are also recognized, similarly to some of G protein-coupled receptors. Recent molecular cloning has revealed that GABA(B) receptor possesses a large extracellular domain including the binding site for GABA and seven transmembrane domains. Their molecular structures in the brain are unique and interesting because of heterodimerization consisting of two distinct genes: GABABR1 and GABABR2. Such assembled receptors can be classified as a novel type of the metabotropic receptor superfamily.