Enteric gamma-aminobutyric acid-containing neurons and the relevance to motility of the cat colon.

gamma-Aminobutyric acid (GABA)-containing neurons were identified and the functional relevance in the motility of the colon was studied. Autoradiography of the cat colon treated with [3H]GABA demonstrated scattered neurons in the myenteric plexus selectively labeled with [3H]GABA. Electrical transmural stimulation of the isolated cat colon led to an increase in the Ca2+-dependent, tetrodotoxin-sensitive release of endogenous GABA. gamma-Aminobutyric acid increased the amplitude of rhythmic contractions of the circular muscle of the colon and also the release of acetylcholine, which was Ca2+-dependent and tetrodotoxin-sensitive. Scopolamine inhibited the GABA-evoked rhythmic contractions, without effect on the evoked release of acetylcholine. Bicuculline and furosemide reduced the amplitude of spontaneous rhythmic contractions and the tone, which was reversed by GABA. These results suggest that GABA-containing neurons are involved in the control of motility of the cat colon, due to the stimulation of cholinergic neurons.