Co-localization of Trk neurotrophin receptors and regulatory peptides in the endocrine cells of the teleostean stomach

Recently it has been observed that a subpopulation of gut endocrine cells i n vertebrates express Trk-like proteins, suggesting that neurotrophins coul d regulate the synthesis and storage of amines and peptides of these cells. Nevertheless, the peptides and amines present in the endocrine cells that express Trks have not been characterized. In this study we used immunohisto chemistry to investigate the occurrence of Trk-like proteins (TrkA-like, Tr kB-like and TrkC-like) and the possible co-localization of these with pepti des and/or biogenic amines in the endocrine cells of the stomach of three t eleost (bass, gilt-head and scorpionfish). No TrkA-like immunoreactivity (I R) was detected in the stomach of these species, whereas TrkB-like IR and T rkC-like IR were observed in numerous cells of the gastric epithelium. TrkB -like immunoreactive cells were present in all three species examined, and were particularly abundant in the blind sac. Conversely, TrkC-like immunore active cells were found only in the bass stomach, apparently co-localized w ith TrkB-like IR. TrkB-like IR was found co-localized with somatostatin IR in scorpionfish, and with somatostatin and CGRP IR in gilt-head and bass. G astric endocrine cells expressing 5-HT, glucagon, insulin, met-, leu-enkeph alin, substance P, PYY, VIP, CCK, NPY, bombesin and motilin were unreactive for Trk-like proteins. The present results provide direct evidence fbr the occurrence of Trk-like neurotrophin receptor proteins in a subpopulation o f the teleostean gastric endocrine cells and suggest that neurotrophins cou ld regulate, as in neurons, the expression of some neuropeptides such as so matostatin and CGRP. Anat Rec 256:219-226, 1999. (C) 1999 Wiley-Liss, Inc.