Development and Differentiation of Gonadotropin-Releasing Hormone Neuronal Systems in Pejerrey, Odontesthes bonariensis. Its Relations with Thermolabile Sex Determination.

STROBL-MAZZULLA, P.H.; SOMOZA, G.M.; MIRANDA, L.A.

Villa Carlos Paz, Argentina.

Congreso; XXXVII Annual Meeting of the Argentine Society of Biochemistry and Molecular Biology Research; 2001

The ontogeny of the olfactory, preoptic and midbrain gonadotropin-releasing hormone (GnRH) neuronal systems was analyzed by immunocytochemistry in pejerrey and its possible relationship with thermolabile sex determination (TSD) suggested. In this species, the proportion of females changes gradually from 100% at 15-19C to 0% at 29C being the critical time of TSD 1-5 weeks according to temperature. Larvae were obtained by artificial insemination using gametes from captive-reared broodstock and kept, immediately after hatching at 17, 24 and 29C for 11 weeks. The results showed the ontogenetic appearance of the three GnRH systems in the brain of larvae kept at different temperatures. The olfactory GnRH neuronal system was observed since hatching. The midbrain system was revealed since day 3 after hatching (DAH) at all temperatures. Meanwhile the appearance of preoptic system varied with rearing (between 21-24 DAH at 17C; 3-21 DAH at 24C and 3-7 at 29C) coincident with the pituitary innervations by the brain. The fact that the differentiation of the preoptic GnRH systems and the innervations of the pituitary appeared just before the development of gonadotrophs and gonadal differentiation at all temperatures regimens, lead us to hypothesize that the brain-pituitary axis is related with TSD in O. bonariensis.