Distribution and origin of calcitonin gene-related peptide in the rat stomach and duodenum: an immunocytochemical analysis.

We studied the three-dimensional distribution of structures with calcitonin gene-related peptide-like immunoreactivity (CGRPI) in the rat stomach and duodenum, including the origins of these structures, using indirect immunofluorescence in both muscle strips and frozen sections. There was a very dense meshwork of CGRPI fibers in the circular and longitudinal muscle layers, and also in the myenteric and submucous plexuses of the stomach and duodenum. No CGRPI neurons were seen in the stomach, even in rats treated with colchicine; in the duodenum, there was a group of CGRPI cells in the myenteric and submucous ganglia. No regional differences were seen in the stomach and duodenum. We found by experimental manipulations that CGRPI fibers in the stomach were exclusively extrinsic in origin; some of such fibers in the duodenum were intrinsic in origin, though most were supplied by CGRPI cells outside the duodenum.