A study of the origin of the electric activity of the rectum: is it neurogenic or myogenic?

The rectum possesses electric activity, the origin of which is yet undetermined. The current study investigates the possible source of these waves. Three electrodes were sutured serially to the serosal surface of the rectum in 10 dogs. The rectal pressure was measured by a perfused catheter. Simultaneous recordings of the electric activity and rectal pressure were done before and after bilateral pelvic ganglionectomy and rectal myotomy. Regular slow waves or pacesetter potentials (PPs) followed by inconsistent action potentials (APs) were recorded. They exhibited the same frequency, amplitude and velocity from three electrodes in the individual animal. APs were associated with minor rectal pressure rise. After pelvic ganglionectomy, PPs and APs were recorded but with irregular frequency, amplitude and conduction, a picture of 'rectoarrhythmia'. The rectoarrhythmic waves were registered proximally but not distally to the myotomy. In conclusion, the rectal electric waves persist after bilateral pelvic ganglionectomy but exhibit a 'rectoarrhythmic' pattern. This is suggested to indicate that the waves are not initiated by, but may be under the control of, the extrarectal autonomic innervation. A 'pacemaker' is postulated to exist at the rectosigmoid junction triggering impulses that spread in the rectal wall along the muscle bundles or the myenteric nerve plexus.