Immunohistochemical detection of neuromodulators in the intestine of Salmotrutta L. naturally infected with Cyathocephalus truncatus Pallas (Cestoda)

Pathological and immunohistochemical investigations were carried out on the middle intestine of uninfected and parasitized brown trout, Salmo trutta L ., from the Ceresone Channel in North Italy. Eighty-six brown trout were sa mpled by electrofishing, and 32 (37.2%) were infected with Cyathocephalus t runcatus Pallas, 1781 (Cestoda). The intensity of infection ranged from 1 t o 82 parasites per host and the most infected segments were the anterior (n ear the pyloric caeca region) and the central part of the middle intestine. Immunohistochemical tests were applied on sections of intestinal tissue of healthy and infected fish, and the presence of substance P (SP), calcitoni n gene related peptide (CGRP), met-enkephalin, vasoactive intestinal peptid e (VIP), neuropeptide Y (NPY) and serotonin (5-HT) was documented. Endocrin e epithelial cells of the tunica mucosa were positive to SP-, CGRP-, met-en kephalin-, and NPY-like peptides and 5-HT antisera; moreover, a higher numb er of these cells were recorded in the intestine of infected trout in compa rison to uninfected fish. In addition, in parasitized S. trutta, SP-like an d 5-HT immunoreactivities were found in likely immune-related cells of the tunica propria-submucosa. Nerve cell bodies and terminals in the myenteric plexus were immunoreactive to almost all the tested peptides and 5-HT antis era. These data provide evidence for the role of the neuroendocrine system of S. trutta in the modulation of inflammatory responses to C. truncatus. R esults are discussed with respect to a peptidergic involvement and host imm une response to an intestinal tapeworm.