LOCALIZATION OF REGULATORY PEPTIDES IN THE GASTROINTESTINAL-TRACT OF THE STRIPED DOLPHIN, STENELLA-COERULEOALBA (MAMMALIA, CETACEA) - AN IMMUNOHISTOCHEMICAL STUDY

Samples of oesophagus, first, second and third stomach, duodenal ampul la, proximal intestine and distal intestine including rectum were obta ined from striped dolphins (Stenella coeruleoalba) stranded along Ital ian coasts, fixed in formalin and used for immunohistochemistry. The p ossible presence of neuropeptides and the biogenic amine serotonin was investigated by a labelled streptavidin-biotin method. Neuropeptide Y (NPY)-, substance P-, calcitonin gene-related peptide (CGRP)-, metenk ephalin-, gastrin releasing peptide (GRP)/ bombesin-, and somatostatin -like immunoreactivities were present in the submucosal as well as the myenteric plexuses, even with differences of distribution in the vari ous organs. Vasoactive intestinal poly-peptide (VIP)-like immunoreacti vity was detected in the submucosal plexus, whereas beta-endorphin- an d leu-enkephalin-like immunoreactivities were shown in the myenteric p lexus only. NPY-, substance P-, CGRP-and VIP-like-immunoreactivities w ere also observed in perivascular nerve fibres. In addition, VIP-, GRP - and somatostatinlike immunoreactivities were detected in myelinated nervous bundles. These were localized in the submucosal and muscular l ayers all along the gastrointestinal tract, and possibly sustain an ex ceptionally rapid response of the target structures. It is noteworthy that peptidergic axons in the wall of the gut of the majority of mamma ls are unmyelinated. A somatostatin-like peptide was identified in epi thelial cells only in the second stomach, whereas in terrestrial mamma ls this endocrine cell type occurs widely. Immunoreactivity to seroton in was never detected, and this is a further difference in comparison with the majority of other mammals.