DIFFERENTIAL DISTRIBUTION AND RESPONSE TO EXPERIMENTAL SEXUAL-MATURATION OF 2 FORMS OF BRAIN GONADOTROPIN-RELEASING-HORMONE (GNRH) IN THE EUROPEAN EEL, ANGUILLA-ANGUILLA

Using specific radioimmunoassays for the two GnRH molecular forms pres ent in the European eel, Anguilla anguilla, (mGnRH and cGnRH II), we c ompared their distributions in the pituitary and different parts of th e brain of female silver eels, as well as the modifications of their l evels in experimentally matured female eels (treated with carp pituita ry extract). In control eels, mGnRH levels were higher than cGnRH II l evels in the pituitary, olfactory lobes and telencephalon, di- and mes encephalon, while the opposite was found in the posterior part of the brain (met- and myelencephalon). Experimental sexual maturation of the gonads significantly increased mGnRH levels in the pituitary and ante rior parts of the brain; such a positive effect was not observed on th e low cGnRH II levels, which were, in contrast, reduced. These data in dicate that the positive feedback of gonadal hormones on GnRH, that we previously demonstrated, would specifically affect the mGnRH form. Th e differential distribution and control of mGnRH and cGnRH II suggest that these two forms have different physiological roles in the eel. Th e large increase in mGnRH during sexual maturation suggests the prime implication of this form in the neuroendocrine control of reproduction .