In the central nervous system (CNS), γ-aminobutyric acid (GABA) is the maininhibitory neurotransmitter that functions to regulate neuronal firing. GABAexerts its effects through two different kinds of receptors: ionotropic receptors(GABAA R and GABAC R), which produce fast inhibitory signals, and metabotropicreceptors (GABAB R), which produce slow inhibitory signals. TheGABAB R receptor is a heterodimer that consists of two multi-pass membraneproteins, designated GABAB R1 and GABAB R2, both of which belong to theG protein-coupled receptor family and are highly expressed in brain tissue.Together, GABAB R1 and GABAB R2 play a crucial role in the fine-tuning ofinhibitory synaptic transmissions and are implicated in slow wave sleep,muscle relaxation, hippocampal long-term potentiation and antinociceptionevents. Both GABAB R1 and GABAB R2 are regulated by G proteins that havea variety of functions, including activation of potassium channels, inhibitionof adenylyl cyclase (A cyclase) activity and modulation of inositol phospholipidhydrolysis.
