Presence of VIP immunoreactivity in the digestive tract of Stenophis citrinus Domergue, 1994 (Reptilia, Colubridae, Boiginae) from western Madagascar.

The recently resurrected genus Stenophis includes all the Malagasy species of Colubridae Boiginae which were formerly ascribed to the genus Lycodryas. Stenophis citrinus, described by Domergue in 1995, is an arboreal snake known from a few regions of western Madagascar - Beroboka (TT), Kirindy, Ankarafantsika, Antsingy - which is very poorly known, except for external morphological features related with taxonomic research. In the framework of a scientific cooperation between the University of Antananarivo and the Aquarium of Genoa (Acquario di Genova), six specimens belonging to this taxon were collected in the Antsingy forest and transferred alive to Genoa Aquarium. Gastrointestinal functions and cell proliferation and differentiation in the digestive tract of vertebrates are controlled by a large number of regulatory peptides. No information are present till now about the histology of the gastrointestinal tract of S. citrinus and the presence and localization of the regulatory peptides. Aim of this study was to investigate the presence of vasoactive intestinal polypeptide (VIP) immunoreactivity in the intestinal wall of S. citrinus. For the histological and immunohistochemical studies, the gastrointestinal tract of one specimen was fixed in Bouin’s fluid, embedded in paraffin and sectioned at 4m thickness. The histomorphology of the intestinal wall was studied with haematoxilin-eosin staining and PAS-Alcian blue reaction. VIP immunoreactivity was detected by the indirect immunofluorescence (IF) and immunoperoxidase (IP) methods (1:200, CRB, UK). VIP-immunoreactive fibres were localized in the submucosa and in muscolar layers. In the latter, the localization of nerve IR fibres was in the myentheric plexus surrounding non IR nervous cells bodies. In the circular muscolar layer, VIP-IR fibres ran within and in parallel with the muscolar fibres. No VIP-IR cells were detected among the intestinal epithelial cells.