Immunohistochemical and pathological studies were carried out on the digestive tract of parasitized and uninfected specimens of Salmo trutta (L.). A total of 124 brown trout were collected on several occasions from 3 tributaries of the Brenta River, northern Italy. Twenty-eight individuals of S. trutta (22.6%) were parasitized with Pomphorhynchus laevis (Müller, 1776). The occurrence of P. laevis in the trout gut significantly increased the number of endocrine cells immunoreactive to calcitonin gene-related peptide (CGRP), β-endorphin, met-enkephalin, neuropeptide Y (NPY) and Substance P (SP) antisera. Moreover, bombesin-, cholecistokinin-8-(CCK-8), leu-enkephalin-and serotonin-(5-HT)-like immunoreactive cells were less numerous in the intestine of the parasitized brown trout. A strong positive immunoreactivity was observed in nerve fibres and neurones of the myenteric plexus of the parasitized fish; the antisera involved in this positive reactivity were bombesin, metenkephalin, SP and vasoactive intestinal peptide (VIP). More neurones immunoreactive to anti-CGRP and anti-5-HT sera were noted in the myenteric plexus and in the inner layer of the tunica muscularis of the infected fish. Most of the above-mentioned neuromodulators are known to control gut motility, digestive/absorptive processes, as well as the immune response. The changes induced by parasites in the neuroendocrine system of the brown trout are discussed.
KEY WORDS: Acanthocephalan infection · Immunohistochemical · Neuromodulators · Digestive tract · Salmo trutta
Resale or republication not permitted without written consent of the publisherDis Aquat Org 51: [27][28][29][30][31][32][33][34][35] 2002 Pomphorhynchus laevis is a common parasite of several species of freshwater fishes (Bykhovskaya-Pavlovskaya 1964); indeed, in the study area, among the acanthocephalan parasites of Salmo trutta, P. laevis was the most frequent (Dezfuli et al. 2001). Histopathological effects of this worm on fishes, such as Leuciscus cephalus were reported by Mehlhorn et al. (1988) and Dezfuli (1991).Host structural modifications due to enteric helminths are the counterpart of biochemical and physiological changes (Castro 1992, Fairweather 1997. In mammals, the nervous, endocrine, and immune systems cooperate to elicit host responses to the intestinal parasites (Fairweather 1997), and many peptides and amines are involved in the communication among cells of these systems (Blalock 1989, O'Dorisio & Panerai 1990. With reference to mammals, the topic that enteric helminths can affect the distribution of neuromodulators of the host gut and induce host responses has drawn the attention of a number of workers in the recent past (McKay et al. 1991, Varilek et al. 1991, Foster & Lee 1996, Fairweather 1997. However, to date, there have been only very limited observations on the occurrence and distribution of neuromodulators in the intestine of infected fishes (Maule et al. 1989, Dezfuli et al. 2000. Recently, with immunohistochemical methods, the presence and freque...