The distribution and chemical coding of neurons supplying the sphincter of Oddi in mammals

The major duodenal papilla (papilla of Vater) is an important structure associated with the biliary tract and, in some species, the pancreas. It usually represents a slight elevation on the intestinal mucosa where the dilated junction (ampulla of Vater) of the commmon bile duct and pancreatic duct enters the duodenum. The ampulla is surrounded by a specifically arranged muscle structure called the sphincter of Oddi (SO) which controls the flow of bile and pancreatic fluid. The function of the sphincter is regulated by a complex system that involves many hormonal and neural factors. The literature in the field contains detailed data on the morphology of the SO in a number of mammalian species. However, the comprehensive information about the anatomy and neurochemistry of the innervation of this structure is very limited. The present review article summarizes the current knowledge on the innervation of the SO in mammals. Special emphasis has been put on the localization and chemical coding of neurons contributing to this nerve supply.