Differential distribution of chicken-I and chicken-II GnRH in the turtle brain.

Chicken-I and chicken-II gonadotropin-releasing hormone (cI-GnRH and cII-GnRH) were shown to be differentially distributed in the brain of a turtle, Trachemys scripta, by HPLC and specific radioimmunoassays. The cI-GnRH was most concentrated in the median eminence (ME), while cII-GnRH was most concentrated in the caudal brain regions, especially medulla and cerebellum. The ratio of cI- to cII-GnRH in the ME of adults was 8:1. Age- and sex-related differences in GnRH concentrations were observed exclusively in the ME: adult females had significantly higher cI-GnRH than younger females and adult males; adult females also had significantly higher cII-GnRH than hatching females. Their differential distribution and sex- and age-related differences suggest that the two peptides may have distinct physiological roles; cI-GnRH is likely the form responsible for stimulating gonadotropin release.