Dual intrinsic and extrinsic origins of CGRP- and NPY-immunoreactive nerves of rat gut and pancreas

The origins of nerves containing calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), and substance P were investigated in the rat stomach, pancreas, and colon, using immunocytochemistry combined with retrograde tracing and surgical and chemical denervation procedures. Compared with nerves containing vasoactive intestinal polypeptide (VIP) and galanin, which have primarily local origins in mammalian gut, CGRP-, NPY-, and substance P-immunoreactive nerves revealed dual extrinsic and intrinsic origins. Immunocytochemistry combined with retrograde tracing showed that the extrinsic CGRP- and substance P-immunoreactive nerves in the stomach and pancreas originate from bilateral dorsal root ganglia mainly at levels T8-T11, while those of the colon are derived from bilateral ganglia at S1 and, to a lesser extent, L1 and L6. Chemical denervations showed that neurons in these ganglia form a sensory input to the gut, and that those containing CGRP form the largest proportion. The results of combined retrograde tracing and immunocytochemistry indicated that extrinsic NPY-immunoreactive nerves originate from postganglionic sympathetic neurons lying in the coeliac and inferior mesenteric ganglia. These nerves were located mainly around blood vessels in gut and pancreas, showed sensitivity to 6-hydroxydopamine, and thus are likely to be noradrenergic. The present study provides a detailed mapping of the origins of some of the major peptide-containing nerves of the rat gastroenteropancreatic tract, thus providing further information on the anatomy of the enteric innervation.