Internal anal sphincter response after electrical stimulation of the rectal myenteric nerve plexus in the rabbit

The internal anal sphincter response to electrical stimulation of the rectal mucosa was studied in six rabbits. The anal canal was dissected free and then opened with an anterior, longitudinal incision to yield a flat sphincter preparation. After the external sphincter had been paralysed, isometric recordings of internal sphincter activity were performed. Electrical stimulation applied to the rectal mucosa elicited sphincter relaxations in all rabbits. Division of the gut beneath the point of stimulation blocked the response, as did local submucous anaesthesia. The results show (1) that electrical stimulation of the rectum can elicit internal sphincter relaxation, and (2) that the response is mediated via the myenteric and submucosal nerve plexuses.