GABA and Diamine Oxidase Activity in the Gastrointestinal Mucosa: Possible Links

Gamma-aminobutyric acid (GABA) has a transmitter function in the mammalian enteric nervous system. The intestine contains endogenous GABA [1, 24, 32] and its synthesizing and degrading enzymes, i.e., glutamic acid decarboxylase (GAD, EC 4.1.1.15) [24, 32] and GABA-transaminase (GABA-T, EC 2.6.1.19) [32], respectively. Endogenous and labeled GABA may be released from the intestine by electrical transmural Stimulation [44] or by the application of substance P [43]. Finally, the presence of GABAergic neurons in the intestine has been demonstrated by immunohistochemical methods [3, 10, 23]. GABA may act on both inhibitory and excitatory neurons of the enteric plexus [26] and these effects appear to be mediated by both subtypes of GABA receptors, i.e., GABAA and GABAB [25].