Co-localization of TRPV1-expressing nerve fibers with calcitonin-gene-related peptide and substance P in fundus of rat stomach.

The localization of vanilloid receptor TRPV1 was studied in rat gastric fundus by an immunohistochemical technique. Numerous TRPV1-immunoreactive nerve fibers were found around arterioles in the submucosal layer. A large number of the nerve fibers were also seen in the smooth muscle layer and in the myenteric nerve plexus, but the cell bodies could not be found. TRPV1 nerve fibers within the circular muscle layers were running parallel to the muscle fibers. Virtually all TRPV1 axons were immunoreactive for calcitonin-gene-related peptide (CGRP), with particularly extensive double labeling seen in axons of the submucosa around blood vessels. TRPV1 nerve fibers containing substance P were found running in longitudinal muscle and circular muscle. The TRPV1 axons seem to be predominantly extrinsic and contain CGRP and substance P in gastric fundus. TRPV1 neurons are thought to be sensory afferent neurons that operate to maintain gastric motility and blood flow.