Influence of vagus nerves on electrical activity of opossum small intestine

Experiments were performed in anesthetized opossums to study the nature of vagal control on the small bowel. Electrical activity was recorded in the duodenum, jejunum, and ileum with silver chloride electrodes. Slow waves and spike potentials were observed at all three sites. There was a decreasing frequency gradient of slow waves and the incidence of slow waves with spikes in the aboral direction. Vagotomy had no effect on the electrical activity. Vagal stimulation at threshold stimuli inhibited spike potentials in all three segments of small intestine, but slow waves were not affected. Vagal stimulation after sectioning of the gut proximal to the electrodes converted the response from inhibition to excitation. These studies suggest that a) vagus carries both excitatory and inhibitory influences to the small bowel; b) inhibitory influences are dominant in the intact opossum small intestine; and c) the nature of the response obtained with vagal stimulation may be explained on the basis of the paths taken by inhibitory and excitatory fibers.