Three serial neurones in the innervation of the colon by the sacral parasympathetic nerve of the dog.

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Abstract
Electrophysiological and histological techniques were used to study the nature of the innervation of the colon by the sacral parasympathetic nerve of the dog. Many cells which incorporate horseradish peroxidase (HRP) were observed in ganglia of the pelvic plexus, but not in the sacral cord, after HRP was injected into the wall of the distal colon. Stimulation of the pelvic ganglia by an application of dimethylphenylpiperazinium contracted the distal colon. The contraction was reduced by nicotine applied to the colon. Compound action potentials in responses of rectal strands of the pelvic nerve to stimulation of the sacral ventral roots decreased or disappeared after hexamethonium bromide (C6) was applied to the pelvic plexus. Conduction velocities of the potentials showed that most of the preganglionic fibers were B fibers, and nearly all the post-ganglionic fibers were C fibers. Many C fibers were observed by EM in the rectal strands after degeneration of the pelvic and hypogastric nerves. Stimulation of such rectal strands caused a contraction of the colon, which diminished after C6 was applied to the distal colon. Apparently, the sacral parasympathetic nerve innervating the colon comprises 3 serial neurons located in the sacral spinal cord, the pelvic plexus and the myenteric plexus.