Propagation of electrical spiking activity along the small intestine: intrinsic versus extrinsic neural influences.

Abstract

The electrical activity of the small intestine of the conscious dog, recorded by chronically implanted electrodes, was related to the transit time estimated by phenol red infusion and its propagation observed after a single or double transection and following either isolation or removal of a 50-cm jejunal loop. In the fasted dog, the activity was characterized by the propagation of myoelectric complexes at a velocity of 4 cm/min during which the mean transit time averaged 13 min/m. About 2/3 of these complexes were seen to pass beyond a single section and anastomosis of the jejunum with a delay of 15 min. This number was reduced to 1/3 and the delay doubled when a 2nd section was performed 50 cm distally. In dogs with an isolated jejunal loop, most of the myo-electric complexes passed from the proximal intestine to the loop and then to the intestine beyond the site of anastomosis within 37 min. Some complexes passed directly through the anastomosis within 30-32 min, affecting or not the loop. Others started on the loop and/or on the intestine beyond the anastomosis. The total number of complexes recorded on the distal jejunum was greater than on the duodenum, an effect which disappeared after removal of the isolated loop. The propagation of the complexes occurred at a lower velocity after denervation of a jejunal segment in situ but was arrested in the case of an isolated-denervated jejunal loop. Continuity of structures in the bowel is essential for the propagation of a myo-electric complex which is stopped and replaced by another complex at the level of an anastomosis, the number of complexes reorganized beyond an anastomosis and their velocity of propagation depending upon both intrinsic and extrinsic neural influences.