Somatostatin immunoreactive nerve elements in the rat small intestine: light and electron microscopic studies.

Somatostatin-containing nerve elements were identified by light and electron microscopic immunocytochemistry in the rat small intestine. Labelled nerve cell bodies were found in the submucous plexus. In the myenteric plexus and the mucosa, numerous somatostatin positive fibers were found. Labelled fibers were observed in the vicinity of blood vessels, close to the smooth muscle cell membrane and to the lamina basalis of epithelial cells. In both plexuses, there were many synapses between the labelled and unlabelled nerve elements. After transection of the nn. mesenteric some of the degenerated nerve fibers originating outside the wall of the small intestine contained also somatostatin immunoreactivity. These observations suggest that somatostatin nerves not only influence the blood flow, but participate in regulation of smooth muscle activity and, by the aid of their interneuronal synapses they have a regulatory or transmitter effect on the other intrinsic nerve elements.