The gastro-enteric-pancreatic neuroendocrine system in two reptilian species: Chalcides chalcides and Zoonosaurus madascariensis (Sauridae).

The presence, localization and distribution of some regulatory peptides and serotonin were investigated by single and double immunohistochemical methods in the digestive system of two reptiles, Chalcides chalcides and Zonosaurus madascariensis. Both immunoreactive (IR) cells and nerve elements were demonstrated, showing different distributions according to the antisera tested. Similar results were observed in the two saurian species. Chromogranin-SPI-, serotonin-, somatostatin14-, pancreatic polypeptide (PP)-, and gastrin-IR cells were present along the gut epithelium. Cholecystokinin (CCK)-, and insulin-IR cells seemed to be more concentrated in the intestinal portion, while very few glucagon containing cells were observed. Bombesin-IR cells were found in the stomach and they constituted the only endocrine cells of the closed type in the gut. Vasoactive intestinal polypeptide (VIP)-, insulin-, and bombesin-IR nerve terminals were also seen. In the pancreatic duodenal portion of Z madascariensis, the insulin-, glucagon-, PP-, and somatostatin 14-IR cells were present as single elements or grouped in endocrine islets showing a typical topographical distribution. By double immunohistochemical techniques, chromogranin-SPI was found co-localized with the serotonin- and somatostatin-immunoreactivity, but CCK-IR cells were always negative to chromogranin-SP1 antiserum. The present work demonstrates that the chromogranin antiserum is not useful for identifying all the gut endocrine cell types; furthermore, the presence of insulin-immunoreactivity in the endocrine cells is confirmed, and, for the first time, insulin-immunoreactivity is shown in reptilian gut nerve fibres.