Immunoreactive endocrine cells and nerve elements in the gut of the Italian cave salamander

The presence and distribution of eleven different types of immunoreactive endocrine cells and nine types of immunoreactive nerve elements were immunohistochemically identified in the gut and pancreas of the italian cave salamander, Hydromantes ambrosii. The majority of gastrointestinal endocrine cells were of open-type, often presenting basal cytoplasmic processes. Gastrin- and substance P-immunoreactive cells in the fundus and bombesin-immunoreactive cells in the intestinal portion were instead of closed type. Immunoreactive nerve fibres were particularly numerous in the muscular layers and blood vessel wall; bombesin- and substance P-immunoreactive nerve fibres were also abundant beneath gastro-intestinal epithelium. Besides substance P-, caerulein- and cholecystokinin-immunoreactive nerve fibres, all the other immunopositive nerve fibres seemed to be of intrinsic types. By the use of four different gastrin/cholecystokinin antisera three variously distributed subpopulations of endocrine cells and nerve elements were detected. Most of the pancreatic endocrine cells were organised in chord-like islets, polarized in the direction of blood vessels. A sparse network of bombesin-immunoreactive fibres was also found in the pancreas. The distribution of bombesin- and of the gastrin/cholecystokinin-immunoreactive material in the stomach and the presence of closed type endocrine cells indicate a more evoluted organization of the gastroenteropancreatic neuroendocrine system thus confirming the position of Hydromantes ambrosii among the higher urodeles.