ABSTRACT
The present study revealed that in Biomphalaria alexandrina, the coordinated responses to Schistosoma mansoni infection are modulated by receptor-mediated opioid signals. The comprehensive tests in susceptible and resistant snails demonstrated the presence of endogenous opioids in the snail hemolymph [in particular, Leu- enkephalin-like material]. The in vitro treatment of snail hemocytes with synthetic Leu-enkephalin analogue [DADLE] resulted in the modulation of cellular adherence and phagocytic activity. The addition of naloxone, either alone or in combination with DADLE, generally reduced the hemocyte activity indicating opioid-receptor- mediated mechanism. The presence of DADLE or naloxone modulated the level of IL-2-, TNF-gamma- and FNF-alpha-like molecules in S. Mansoni resistant and susceptible snails. Specifically, DADLE and DADLE in combination with naloxone, generally, were found to be capable of modulating the resistant snail hemocytes at concentrations of 10-6 and 10-8 M. Similar actions after incubation with the same concentrations were not detected in the susceptible snails