The appearance and development of somatostatin-like immunoreactivity (SLI) in the peripheral nervous system of quail embryos were studied using radioimmunoanalysis and immunocytochemistry. In vivo, no SLI is observed in neural crest cells before or during migration. SLI appears between days 3 and 4 of incubation in sympathetic ganglia, immediately following ganglion formation, and between days 4 and 5 of incubation in the adrenal gland, soon after the adrenal gland primordium first appears. The development of SLI in the adrenal gland differs from that in the sympathetic ganglia. While in the former the amount of SLI and the number of SLI-containing cells increase as the embryo ages, in the sympathetic ganglia the amount of SLI and the percentage of SLI-containing cells decrease. When migrating neural crest cells are obtained from the sclerotomal part of 3-day embryos and grown in culture, they first display SLI after 48 hr, and the amount of SLI increases thereafter. When the sympathoadrenal precursors are removed at 4 days of incubation and grown in vitro, SLI appears after 24 hr in culture and increases during the next few days. Our results demonstrate that SLI is present very early in the quail embryo and that its appearance parallels the differentiation of neural crest cells into autonomic sympathetic ganglionic cells. We also show that the differentiation of neural crest into SLI-containing cells can be reproduced in culture, thus permitting the study of peptide production and expression in vitro.
The development of substance P (SP) and VIP containing structures of the quail and chick guts was studied by immunocytochemistry. The appearance of VIP and substance P nerves follows a rostrocaudal pattern from day 9 in the quail and day 10 in the chick embryo. Immunoreactive fibres are first visible in the oesophagus and at 12 days they extend over the whole length of the intestine. VIP and substance P ganglionic cells are first localized in the foregut (day 9 for VIP containing neurons and day 13 for SP ones) and observed in the mid- and hind-gut just before hatching. Transplantation on the chorioallantoic membrane (CAM) of fragments of various parts of the digestive tract were carried out to see whether in such circumstances the pattern of VIP and SP containing nerves was comparable to normal. The explants contained numerous SP and VIP immunofluorescent nerve fibres. In addition, cell bodies with VIP and SP immunoreactivity appeared brightly fluorescent in the enteric ganglia of the graft showing that these peptidergic nerve cells belong to the intrinsic innervation of the gut.
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