Location of bodies of peripheral (sympathetic) afferent neurons participating in peripheral reflexes of the small intestine

Abstract

Acute electrophysiological experiments on cats have shown that after preliminary decentralization of the solar plexus, accompanied by degeneration of spinal and vagal afferent and preganglionic efferent fibers in its postganglionic (mesenteric) nerves, only slow activity of the C-afferents is recorded in the peripheral segments of the mesenteric nerves instead of activity of the A-, B-, and C-fibers in the control (before degeneration). Activity of the C-afferents is intensified with the appearance of spontaneous contractions of the small intestine and also after gentle stretching of the corresponding segment of the intestine by inflation of a rubber balloon. After preliminary division of the mesenteric nerves, accompanied by degeneration of the postganglionic fibers in their peripheral segments, activity of C-afferents only also was observed, but it was much weaker than in the first series of experiments. After preliminary decentralization of the solar plexus and division of the mesenteric nerves application of a single electrical stimulus to the central part of one of the divided mesenteric nerves evokes a reflex electrical response in the other mesenteric nerves which disappears after treatment of the ganglia of the solar plexus with azamethonium bromide and also after electrical stimulation of the mesenteric nerves at 10–20 Hz. However, after decentralization only, this response was much weaker than after division of the mesenteric nerves. It is concluded that these peripheral responses of the intestinal nerves are due to excitation of two types of peripheral afferent neurons: the bodies of some lie in the small intestine and their long axons (C-afferents) run to the ganglia of the solar plexus; the bodies of the others lie in the ganglia of the solar plexus and their long axons (also C-afferents) run to the intestine, where they terminate in its receptors.