AN IMMUNOHISTOCHEMICAL ANALYSIS OF THE ONTOGENY, DISTRIBUTION AND COEXISTENCE OF 12 REGULATORY PEPTIDES AND SEROTONIN IN ENDOCRINE-CELLS AND NERVE-FIBERS OF THE DIGESTIVE-TRACT OF THE TURBOT, SCOPHTHALMUS-MAXIMUS (TELEOSTEI)

The ontogeny of endocrine cells and nerve fibers containing immunoreac tivities for 12 regulatory peptides and serotonin was studied in the d igestive tract of a flatfish, the turbot (Scophthalmus maximus), using antisera specific for mammalian and teleostean hormones. Transient in sulin-immunoreactive (-IR) endocrine cells were detected from day 5 to day 10 in stomach and intestine I. Somatostatin (SOM)-IR cells appear ed at day 8 in the stomach anlage and intestine I. In contrast to the islet cells, they reacted with antisera against mammalian (m) SOM-14 a nd salmon (s) SOM-25. Infrequent nerve fibers reacting only with anti- mSOM-14 appeared around day 24. Thus, different forms of SOM seem to b e present in the gastro-entero-pancreatic system and the enteric nervo us system. Neuropeptide Y (NPY)-, salmon pancreatic polypeptide (sPP)- and mPP-immunoreactivities coexisted throughout development. In enter o-endocrine cells, NPY/PP-immunoreactivity was first observed at day 8 and around day 24 in enteric nerve fibers. Glucagon (GLUC)-IR entero- endocrine cells appeared at day 5. No coexistence of NPY/PP- and GLUC- immunoreactivities was observed. The first insulin-like growth factor I(IGF-I)-IR cells were identified around day 8. They seemed to contain none of the other peptides. Their number and distribution exhibited g reat interindividual differences. Vasoactive intestinal polypeptide (V IP)-IR entero-endocrine cells appeared as late as around day 24. The f irst VIP-IR nerve fibers, however, were identified at day 5. Infrequen t neurotensin (NT)-IR cells appeared along the intestine around day 10 and NT-IR nerve fibers at day 17. The first serotonin (SER)-IR cells were observed in the stomach anlage around day 10 and SER-IR nerve fib ers at day 15 throughout the gastro-intestinal tract. Gastrin (GAS)/ch olecystokinin (CCK)-IR cells appeared around day 11 in stomach and int estine I. The first substance P (SP)-IR enteric nerve fibers were dete cted around day 8 and SP-IR endocrine cells at day 11. Pancreastatin ( PST)-IR cells were identified in the stomach anlage and intestine I ar ound day 8 and contained NT-, GAS/CCK- and SER-immunoreactivities in c oexistence. Thus, several developmental phases can be distinguished: ( 1) at the onset of exogenous feeding only transient INS-IR cells and V IP-IR nerve fibers are present; (2) a differentiated entero-endocrine system establishes during the early phase of exogenous feeding; (3) be fore the final differentiation of stomach and gut GAS/CCK-IR cells app ear; (4) after metamorphosis most of the different types of regulatory peptide-containing nerve fibers develop, probably setting up the fine regulation of gastro-intestinal blood flow and motility.