Neurotrophin-3 and neurotrophin receptor immunoreactivity in peptidergic enteric neurons

In the rat small intestine, neurotrophin-3 immunoreactivity was identified in ganglion cells and in processes mostly innervating the mucosa and occasionally the muscle layer and vasculature. The vast majority of neurotrophin-3 immunoreactive neurons contained vasoactive intestinal polypeptide (VIP), but not substance P or related tachykinin (SP/TK). Neurotrophin receptors visualized by pan-trk immunoreactivity were found in numerous ganglion cells of both plexuses and in nerve processes in the intestinal wall. Pan-trk submucosal neurons contained VIP (36%) or SP/TK-IR (47%). Pan-trk myenteric neurons contained VIP-IR (57%) or SP/TK (27%). Our data suggest that neurotrophin-3 and neurotrophin receptors may be involved in the maintenance of enteric neuronal circuits, transmission and phenotypic expression.