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

Pathological and immunohistochemical investigations were carried out on the medium intestine of uninfected and parasitized brown trout, Salmo trutta Linnaeus, 1758, from the Ceresone Channel in North Italy. Eighty-six specimens of brown trout were sampled with electrofishing, and 32 (37.2%) were infected with Cyathocephalus truncatus Pallas, 1781 (Cestoda). The intensity of infection ranged from 1 to 82 parasites per host and the most infected segments were the anterior (near the pyloric caeca region) and the central part of the brown trout medium intestine. Immunohistochemical tests were applied on sections of intestinal tissue of healthy and infected fish, and the presence of substance P (SP), calcitonin gene related peptide (CGRP), met-enkephalin, vasoactive intestinal peptide (VIP), neuropeptide Y (NPY) and serotonin (5-HT) was documented. Endocrine epithelial cells of the tunica mucosa were positive to SP-, CGRP-, met-enkephalin-, and NPY-like peptides and 5-HT antisera; moreover, a higher number of these cells was recorded in the intestine of infected trout in comparison to uninfected fish. In addition, in parasitized S. trutta, SP-like and 5-HT immunoreactivities were found in likely immuno-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 antisera. These data provide evidence for the role of the neuroendocrine system of S. trutta in the modulation of inflammatory responses to C. truncatus. Results are discussed with respect to a peptidergic involvement and host immune response to an intestinal tapeworm.