LOCALIZATION OF NEUROKININ-3 (NK3) RECEPTOR IMMUNOREACTIVITY IN THE RAT GASTROINTESTINAL-TRACT

The localisation of the neurokinin 3 receptor (NK3r) in the rat gastro intestinal tract has been studied by using a polyclonal antiserum agai nst the C-terminal portion (amino acids 388-452) of the rat NK3r. In t he oesophagus, immunoreactivity for the NK3r was found on smooth muscl e cells of the muscularis mucosae. NK3r immunoreactivity was not prese nt on muscle cells of other regions. Nerve cell bodies immunoreactive for NK3r were seen in the myenteric and submucous plexuses of the smal l and large intestine, but not in the stomach or oesophagus. Immunorea ctivity was largely confined to nerve cell surfaces. The reaction prod uct was on the cell soma and initial parts of axons. Reactivity was no t seen on nerve terminals. Immunoreactive nerve cells had Dogiel Type II morphology. Patterns of co-localisation of NK3r and immunoreactivit y for other markers were examined in the ileum, to provide a basis fro m which to deduce the functional identity of NK3r-immunoreactive nerve cells. Most of the NK3r-immunoreactive nerve cells were also immunore active for the calcium-binding proteins, calretinin and calbindin, and all were immunoreactive for the NK1 receptor (NK1r). Nerve cells that were immunoreactive for nitric oxide synthase were not immunoreactive for either NK3r or NK1r. The projections of the calbindin and calreti nin neurons were determined by nerve lesion studies. Their morphology, projections to the mucosa and other ganglia and immunoreactivity for the calcium-binding proteins suggest that the NK3r-immunoreactive neur ons are intrinsic sensory neurons.