Somatostatin immunopositive neurons in the small intestine of the bullfrog (Rana catesbeiana).

Somatostatin immunopositive neurons in the small intestine of the bullfrog (Rana catesbeiana) were studied using immunohistochemistry and surgical denervation of the mesenteric nerve. Immunopositive nerve elements were distributed throughout the small intestine, including nerve fibers in the myenteric plexus, circular muscle layer, submucosal layer, and mucosa. Somatostatin immunopositive nerve cell bodies occurred in the myenteric plexus but not in the submucosal layer. These cell bodies were surrounded by immunopositive nerve fibers forming basket-like terminals, and thus some of these cells may be interneurons. After denervation of the mesenteric nerve, adrenaline immunopositive nerve fibers disappeared almost completely from the small intestine, but no changes occurred in the distribution of somatostatin immunopositive neurons. Neurons in the coeliac ganglion projecting into the small intestine were adrenaline immunopositive but somatostatin immunonegative. The results indicate that somatostatin immunopositive neurons in the small intestine of the bullfrog are primarily intrinsic in origin.