The sphincter of Oddi is a small muscular cuff named after the 19th century Italian scientist, Ruggero Oddi, who first studied it. Located at the junction of the common bile duct and the intestine, it regulates the flow of bile from the gallbladder into the intestine. Although we know that the nervous system is involved, the exact mechanisms of its regulation are not entirely clear. As part of my doctoral dissertation research, completed in 1999 under Dr. Gary Mawe of the Department of Anatomy and Neurobiology at the University of Vermont College of Medicine, I examined the neural mechanisms by which the sphincter of Oddi is regulated. Working with guinea pigs, Dr. Mawe and I identified a neural connection linking a section of the small intestine called the duodenum with the sphincter of Oddi.
Neurons work by releasing chemicals called neurotransmitters from their nerve endings.
We expanded our studies of the neurons going to the sphincter of Oddi by determining what neurotransmitters they synthesize. The technique of immunohistochemistry examines the neurons based on their coding patterns for different chemicals. As a result, scientists can determine the function of a given population of neurons based on the presence or absence of particular chemicals within the cell. Using immunohistochemical technique, we were able to determine the types of duodenal neurons sending nerve fibers to the sphincter of Oddi. We determined that these neurons synthesize excitatory neurotransmitters, which cause the sphincter muscle to contract.