Coexistence of peptide immunoreactivity in sensory neurons of the cat

The coexistence of the neuropeptides substance P, cholecystokinin, somatostatin and vasoactive intestinal polypeptide in cat sensory neurons has been examined using peroxidase-anti-peroxidase immunocytochemistry. Attempts were also made to locate cells containing bombesin, neurotensin, [Met]enkephalin and [Leu]enkephalin but no immunoreactivity was found when antisera to these peptides was used. Cells in the dorsal root ganglia were studied by cutting 5 microns serial wax sections or 15 microns cryostat sections. Coexistence was established by applying the antiserum to each peptide to serially adjacent 5 microns sections and establishing the presence of peptide-like immunoreactivity in each of 4 different sections through a single cell. Results showed that the distribution and combinations of coexistence of these neuropeptides in the cat is extremely complex; three and sometimes all four antisera showing immunoreactivity with a single cell. About 21% of all ganglion cells contained some immunoreactivity but there were certainly some small cells which did not contain any immunoreactivity. The coexistence of these peptides differed markedly from that previously reported in the rat suggesting that interspecific differences in the neuropeptide content of cells might be much greater than they are for classical neurotransmitters. The results are discussed in relation to the possible role of neuropeptides and the regulation of their production by sensory neurons.