Innervation and regulation of the pancreas by neurons in the gut

Experiments were done in order to test the hypothesis that enteric neurons project to the pancreas and can modify pancreatic endocrine and exocrine activity. Injections of the retrograde tracer Fluoro-Gold (FG) into the rat pancreas labeled neurons in the myenteric plexus of the antrum of the stomach and in the first 6 cm of the duodenum. A subset of myenteric neurons were found in both the antrum and duodenum that were doubly labeled by retrograde transport of FG and anti-serotonin (5-HT) sera; therefore, some of the enteric neurons that innervate the pancreas are serotonergic. Within the pancreas, 5-HT-immunoreactivity was not found in any neuronal cell bodies; however, 5-HT-immunoreactive axons were observed. Varicose 5-HT-immunoreactive terminal axons were most commonly found in pancreatic ganglia. Anterograde tracers were microinjected into individual myenteric ganglia in order to determine the pancreatic targets of the enteric innervation. Following the microinjection of the B subunit of cholera toxin (B-CT) or 1,1", dioctadecyl-3,3,3',3'-tetramethylcarbocyanine (Dil) into myenteric ganglia in the duodenum, labeled fibers were found in the pancreatic parenchyma. B-CT-immunoreactive terminals were most commonly observed in pancreatic ganglia, suggesting that pancreatic ganglia are the major targets in the pancreas of the enteric innervation. Experiments were also performed physiologically to determine whether enteric stimuli can influence pancreatic exocrine or endocrine activity via a neural pathway. For this purpose enteric neurons were stimulated in vitro by luminal application of veratridine (Ver), and the metabolic activity of neurons, islet, and acinar cells was determined in attached segments of pancreas by measuring their cytochrome oxidase (CO) activity.(ABSTRACT TRUNCATED AT 250 WORDS)