IMMUNOREACTIVE ENDOCRINE-CELLS AND NERVE ELEMENTS IN THE GUT OF THE ITALIAN CAVE SALAMANDER

The presence and distribution of eleven different types of immunoreact ive endocrine cells and nine types of immunoreactive nerve elements we re immunohistochemically identified in the gut and pancreas of the ita lian cave salamander, Hydromantes ambrosii. The majority of gastrointe stinal endocrine cells were of open-type, often presenting basal cytop lasmic processes. Gastrin- and substance P-immunoreactive cells in the fundus and bombesin-immunoreactive cells in the intestinal portion we re instead of closed type. Immunoreactive nerve fibres were particular ly numerous in the muscular layers and blood vessel wall; bombesin- an d substance P-immunoreactive nerve fibres were also abundant beneath g astro-intestinal epithelium. Besides substance P-, caerulein- and chol ecystokinin-immunoreactive nerve fibres, all the other immunopositive nerve fibres seemed to be of intrinsic types. By the use of four diffe rent gastrin/cholecystokinin antisera three variously distributed subp opulations of endocrine cells and nerve elements were detected. Most o f the pancreatic endocrine cells were organised in chord-like islets, polarized in the direction of blood vessels. A sparse network of bombe sin-immunoreactive fibres was also found in the pancreas. The distribu tion of bombesin- and of the gastrin/cholecystokinin-immunoreactive ma terial in the stomach and the presence of closed type endocrine cells indicate a more evoluted organization of the gastroenteropancreatic ne uroendocrine system thus confirming the position of Hydromantes ambros ii among the higher urodeles.