Early expression of pituitary adenylate cyclase-activating polypeptide andactivation of its receptor in chick neuroblasts

To investigate the involvement of pituitary adenylate cyclase-activating po lypeptide (PACAP) and GH-releasing factor (GRF) during early chick brain de velopment, we established neuroblast-enriched primary cell cultures derived from embryonic day 3.5 chick brain. We measured increases in cAMP generate d by several species-specific forms of the peptides. Dose-dependent increas es up to 5-fold of control values were measured in response to physiologica l concentrations of human/salmon, chicken, and tunicate PACAP27. Responses to PACAP38 were more variable, ranging from 5-fold for human PACAP38 to 4-f old for chicken PACAP38, to no significant response for salmon PACAP38, com pared with control values. The responses to PACAP38 may reflect a greater d ifference in peptide structure compared with PACAP27 among species. Increas es in cAMP generated by human, chicken, and salmon/carp GRF were not statis tically significant, whereas increases in response to lower-range doses of tunicate GRF27-like peptide were significant, but small. We also used immun ocytochemistry and Western blot to show synthesis of the PACAP38 peptide. R T-PCR was used to demonstrate that messenger RNAs for PACAP and GRF and a P ACAP-specific receptor were present in the cells. This is a first report su ggesting an autocrine/ paracrine system for PACAP in early chick brain deve lopment, based on the presence of the ligand, messages for the ligand and r eceptor, and activation of the receptor in neuroblast-enriched cultures.