The distribution and ontogeny of gastrin/CCK-, somatostatin- and neurotensin-immunoreactive cells in the gastrointestinal tract of the chicken.

The distribution and time of appearance of cells with gastrin/CCK-, neurotensin- and somatostatin-like immunoreactivity were studied in samples from eight regions of the gastrointestinal tract of chick embryos from 11 days of incubation to hatching. No immunoreactive cells were found in any region at 11 days of incubation. Somatostatin- and neurotensin-immunoreactive cells appeared for the first time in the proventriculus, pyloric region and duodenum at 12 days of incubation with cells immunoreactive for neurotensin occurring in the rectum at the same stage. Gastrin/CCK-immunoreactive cells were detected in the small intestine first at 14 days and in the pyloric region two days later. Cells immunoreactive for somatostatin and neurotensin appeared in the upper and lower ileum at 14 days of incubation for the first time; neurotensin-immunoreactive cells, present in the caecum at 14 and 16 days, were rare. Cells of all three types were plentiful in the pyloric region by 17 1/2 days of incubation. No immunoreactive cells were detected in the gizzard at any stage studied. Endocrine cells were present in the relatively undifferentiated surface epithelium which occurs throughout the gastrointestinal tract of chick embryos at 12 days of incubation. Thereafter cells of all three types were detected in the glandular epithelium at or very soon after morphogenesis and differentiation of the latter had occurred.