GABA receptor function in the parasympathetic ganglia

The criteria required to establish gamma-aminobutyric acid (GABA) as a neurotransmitter have been fulfilled in the enteric nervous system of the mammalian intestine. In the intestine, GABA-A receptors are located on somato-dendritic regions of the postganglionic cholinergic neurons and mediate the release of acetylcholine (ACh). GABA-B receptors are located on nerve terminals of the cholinergic neurons and mediate inhibition of nerve-stimulated release of ACh. In the urinary bladder, GABA is possibly a noncholinergic, nonadrenergic inhibitory neurotransmitter. Both GABA-A and GABA-B receptors seem to be present in the parasympathetic ganglia and mediate inhibition of ACh release from the cholinergic neurons. Thus, the functional property of GABA-A receptor is different between the intestine and urinary bladder. GABA-A receptors are also located on the GABAergic nerve terminals as an autoreceptor, and mediate inhibition of GABA release both in the intestine and urinary bladder.