The presence, distribution and development of vasoactive intestinal polypeptide (VIP)-like immunoreactivity in the gastro-entero-pancreatic system of a cartilaginous fish Scyliorhinus stellaris (L.) was investigated by immunohistochemical methods utilizing mammalian VIP antisera. In the gut VIP-like immunoreactivity was observed in both nerves and endocrine cells. Endocrine cells with VIP-like material were only detected in the intestinal epithelium while nerve fibres containing VIP-like material were noted along the whole gastro-entero-pancreatic system, being more numerous in the pyloric sphincter and in the intestinal portion. Immunoreactive nerve cell bodies were encountered in the stomach and intestinal portions localized in the submucosa and in the myenteric plexus. Intestinal immunoreactive endocrine cells were already present in the first developmental stage considered (embryos aged 4 months). They grow in number and before birth reach a frequency higher than in adults. Nerves and cell bodies showing VIP-like immunoreactivity, appear later, before birth, as a few elements in the smooth muscular layer, but only after birth their distribution and frequency are similar to those found in adults. The faint immunofluorescence shown by the immunoreactive endocrine cells and their developmental pattern, which is always different from that observed in nervous elements, suggest the presence of at least two VIP-like substances in the gastro-entero-pancreatic system of S. stellaris.
A number of regulatory peptides and serotonin were studied by immunocytochemistry with respect to their appearance and distribution in the developing gastrointestinal tract of the selachian Scyliorhinus stellaris. In the earliest stage studied (fourth month developmental stage) glucagon-, somatostatin-, serotonin-, vasoactive intestinal peptide (VIP)-, cholecystokinin (CCK)-, and gastrin-immunoreactive cells were detected in the already differentiated intestinal epithelium, whereas only glucagon-, somatostatin-, and serotonin-immunoreactive cells were seen in the not yet differentiated stomach epithelium. Glucagon-immunoreactive cells were present in the gastric portion only; in the pyloric portion, they appeared in the next stage, together with CCK-, peptide histidine isoleucine (PHI)-, and bombesin-immunoreactive cells, and disappeared before birth. PHI-immunoreactive cells were restricted to the pyloric portion, whereas VIP-and gastrin-immunoreactive cells were detected in the spiral gut only. At the beginning, immunoreactive cells were few, but they grew in number until birth, when some of them presented a more elevated frequency than that seen in adults. Immunoreactive endocrine cells were of open type and showed a distribution similar to that seen in adults. PHI-immunoreactive nerve fibers appeared early, first in the lamina propria, then in the muscular layer; the opposite was seen for VIPimmunoreactive fibers that were shown successively, first in the muscular layer, then in the lamina propria. Intestinal bombesin and P-endorphin were shown after birth only. The early appearance of the peptides tested is consistent with the hypothesis that they play a role on cell growth and differentiation.
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