IMMUNOREACTIVE MAMMALIAN AND CHICKEN-II GNRHS IN RANA-ESCULENTA BRAINDURING DEVELOPMENT

Two forms of gonadotropin-releasing hormone (mammalian, mGnRH and chic ken-II, cGnRH-II) were measured by radioimmunoassay in the nasal area (containing peripheral terminal nerve), brain and pituitary of Rana es culenta during larval development, metamorphosis, and until prior to b ecoming reproductively active. Small amounts of both forms of GnRH wer e first detected in the brain extract of early tadpoles (stage 26-27, when hindlimbs begin to develop). Later, there was a gradual, but cons tant, stage-dependent increase in the brain content of GnRHs, with the most remarkable increase recorded at postclimax and in young frogs. I n tadpoles, postclimax froglets, and young frogs, the brain concentrat ion of mGnRH was higher than that of cGnRH-II, with a ratio of approxi mately 2:1 in favor of mGnRH. In juveniles, however, the brain extract contained more cGnRH-II than mGnRH. No GnRH immunoreactivity was dete cted in the nasal area until stage 31. In successive stages of develop ment, however, only mGnRH was present in the nasal area, and this conf irmed our previous immunohistochemical analysis which showed that the peripheral terminal nerve contains only mGnRH-immunoreactive neurons a nd fibers. Although both GnRH forms were detected in the anterior (tel encephalon, diencephalon) and posterior (mesencephalon, rhombencephalo n) brain halves from juveniles, mGnRH content predominated in the ante rior half, whereas in the posterior half cGnRH-II was present in great er amounts. Pituitaries from male and female postclimax froglets and y oung frogs contained both forms of GnRH in a ratio of approximately 10 :1 in favor of mGnRH. This finding may shed light on the question of w hich GnRH(s) regulate gonadotropin release from the pituitary. The dev elopmental changes in GnRH-immunoreactive content of the brain and pit uitary have been discussed in the light of functional maturation of th e brain-pituitary-gonad axis.