Brain content of cGnRH I and II during embryonic development in chickens

We used specific radioimmunoassays to measure chicken gonadotropin-releasing hormones I and II (cGnRH I and II) in extracts of chicken brain as a first step in determining whether these peptides may function identically during embryonic development in birds. In three experiments chicken embryo brains were removed at various times between Day 6 of incubation and hatching. In Experiment 3, the sex of embryos was identified by means of polymerase chain reaction amplification of a W chromosome-specific DNA sequence. Brain concentrations of cGnRH I increased sharply from Day 6 of incubation to Day 8, then decreased until Day 10 to Day 12, followed by an increase beginning on approximately Day 17 and continuing until hatch. In contrast, cGnRH II concentration remained low until about Day 14 of incubation, then increased progressively until, at hatch, brain content of cGnRH II was approximately 9 to 11 times that of cGnRH I. The difference in development pattern and total content of these peptides supports the view that any physiologic function they may have might be differentiated as early as Day 7 of incubation.