Projections to the alimentary canal from the dopaminergic neurons in the dorsal motor nucleus of the vagus of the rat

The motility of the alimentary canal is regulated not only by neurons that contain acetylcholine or adrenaline, but also by nonadrenergic noncholinergic neurons. There are many neurons containing dopamine in the dorsal motor nucleus of the vagus (DMV). We examined the projections of these dopaminergic neurons to the alimentary canal with double-labeling immunohistochemistry for tyrosine hydroxylase (TH) and the retrograde tracer cholera toxin subunit b following its injection into the subdiaphragmatic esophagus, the cardia, the pylorus, the duodenum, the jejunum, and the ascending colon. Almost all double-labeled neurons were found in the half of the DMV caudal to the area postrema. In the caudal half of the DMV, about 58% of the TH-immunoreactive neurons projected to the cardia, about 36% projected to the pylorus, and about 28% projected to the subdiaphragmatic esophagus. Only a few TH-immunoreactive neurons projected to the duodenum, the jejunum, or the ascending colon. As a whole, less than 10% of the neurons in the DMV that projected to the alimentary canal showed TH-like immunoreactivity. These results suggest that some of the dopaminergic neurons in the DMV might regulate the activities of the stomach and the subdiaphragmatic esophagus.