Light and electron microscopy of neuropeptide Y-containing nerves in human liver, gallbladder, and pancreas.

Neuropeptide Y-containing nerve fibers were identified by light and electron microscopic immunocytochemistry in the human liver, gallbladder, and pancreas. In the liver, neuropeptide Y-containing nerve fibers were distributed richly in Glisson's sheath and were prominent around the walls of the interlobular vein, interlobular hepatic artery, and hepatic bile duct. The fibers also formed a dense network surrounding the hepatocytes. The nerve terminals were found close to the endothelial cells of blood vessels, as well as being distributed in Disse's space, where they appeared to terminate. Occasionally these terminals contacted directly the membrane of a hepatocyte. In the gallbladder, neuropeptide Y fibers were found in each layer, with an especially dense network in the lamina propria. The fibers also ran close to the epithelium and parallel to the muscle bundles. Blood vessels throughout the gallbladder were well supplied with such nerve fibers. In the pancreas, neuropeptide Y fibers were found mainly near blood vessels and partly in gaps between exocrine glands, seeming to terminate on certain endocrine cells. Nerve terminals were located in the vascular walls and adjacent to the surface of exocrine acinar cells. These studies provide a basis for correlating the neuropeptide Y distribution with pharmacological and physiological studies in humans.