Ontogeny of galanin-immunoreactive elements in the intrinsic nervous system of the chicken gut

Galanin is a brain-gut peptide that is present in the central and periphera l nervous systems. In the gut, it is contained exclusively in intrinsic and extrinsic nerve supplies, and it is involved overall in the regulation of gut motility. To obtain information about the ontogeny of galanin, we under took an immunohistochemical study of chicken embryos. The time of first appearance and the distribution patterns of galanin were investigated with fluorescence and streptavidin-biotin-peroxidase (ABC) imm unohistochemical protocols by using a galanin polyclonal antiserum. The var ious regions of the gut and the pancreas were obtained from chicken embryos aged from 3 days of incubation to hatching. All specimens were fixed in bu ffered picric acid-paraformaldehyde, frozen, and cut with a cryostat. Galanin-immunoreactive neuroblasts were first detected at 4 days in the mes enchyme of the proventriculus/gizzard primordium and within the Remak gangl ion. They then extended cranially and caudally, reaching all of the other g ut regions at 6.5 days. Galanin-immunoreactive nerve elements mainly occupi ed the sites of myenteric and submucous plexuses. From day 15, galanin-immu noreactive nerve fibers tended to invade the circular muscular layer and pa rt of the lamina propria of the mucosa. In the pancreas, weak galanin-immun oreactive nerve elements were detected at 5.5 days. They tended to be distr ibuted among the glandular lobules according to the organ differentiation. The widespread distribution during the earlier embryonic stages represents evidence indicating that the neuropeptide galanin may have a role as a diff erentiating or growth factor. From late embryonic life, its predominant pre sence in sympathetic nerves and in muscular layers fits with the functions demonstrated previously in adults of other vertebrates for galanin as a mod ulator of intestinal motility. Anat Rec 254:28-38, 1999. (C) 1999 Wiley-Lis s, Inc.