BACKGROUND: This study investigated the existence of direct neural connections 
between the duodenum and the biliary tract in the Australian possum.
METHODS: Retrogradely transported neuronal dyes, Fast Blue and Dil, were 
injected into the wall of the gallbladder and the sphincter of Oddi. The 
duodenum, biliary tract, and sympathetic and sensory ganglia were examined for 
the presence of labeled cell bodies.
RESULTS: Two to 3 weeks after gallbladder injection, labeled nerve cell bodies 
were found in the myenteric plexus of the proximal duodenum but were rare in the 
duodenum distal to the sphincter of Oddi. No neurons were found in the submucous 
plexus. Labeled nerve cells were also found in the sphincter of Oddi. After 
injection of the sphincter, labeled neurons were in both the submucous and 
myenteric plexuses of the duodenum, on either side. Approximately one third of 
labeled myenteric neurons were immunoreactive for enkephalin. Labeled cell 
bodies were also in the coeliaco-mesenteric, nodose, and dorsal root ganglia 
after both gallbladder and sphincter injection. After a myotomy on the proximal 
duodenum, no neurons were labeled on the pyloric side of the lesion by 
subsequent sphincter injection of dye.
CONCLUSIONS: Direct neural pathways connect the duodenum with the gallbladder 
and the sphincter of Oddi, and the sphincter with the gallbladder; this implies 
that enteric nerve circuits participate in coordinating duodenal and biliary 
functions.