Two molecular forms of gonadotropin-releasing hormone from the brain of the frog, Rana ridibunda: Purification, characterization, and distribution

The molecular forms of GnRH in amphibia have not been characterized structurally. An antiserum to mammalian GnRH that shows appreciable cross-reactivity with chicken GnRH-I ([Gln⁸]GnRH), chicken GnRH-II ([His⁵,Trp⁷,Tyr⁸]GnRH), and salmon GnRH ([Trp⁷, Leu⁸]GnRH) was used in a RIA to detect GnRH-related peptides in an extract of the brain of the European green frog, Rana ridibunda. Two peptides were purified to apparent homogeneity, and determination of their primary structures showed that they are identical to mammalian GnRH and chicken GnRH-II. Salmon GnRH and lamprey GnRH-I ([Tyr³,Leu⁵,Glu⁶,Trp⁷,Lys ⁸]GnRH) were not identified in this species of frog. Immunocytochemical analysis using specific antisera has identified regions of the frog diencephalon and telencephalon in which chicken GnRH-II and mammalian GnRH are localized to different populations of neurons. This differential distribution suggests distinct physiological roles for the two forms of GnRH in amphibia.