RESPONSE OF DIENCEPHALON BUT NOT THE GONAD TO FEMALE-PROMOTING TEMPERATURE WITH ELEVATED ESTRADIOL LEVELS IN THE SEA-TURTLE LEPIDOCHELYS OLIVACEA

Although temperature sex determination is well known in several reptil e species, the physiological mechanism underlying this process remains to be elucidated. In the current work, we analyzed the levels of test osterone (T) and estradiol (E2) in the gonads; two brain regions-telen cephalon (Te) and diencephalon/mesencephalon (Di)-and the serum of dev eloping embryos of the olive ridley Lepidochelys olivacea incubated at male-or female-promoting temperatures. (C)onversion of pregnenolone ( P5) to T and T to E2 were studied in the gonads and brain. The analyse s were performed during three periods: the thermosensitive period (TSP ), histologically undifferentiated gonads (UDG), and differentiated go nads (DG). In the gonads, serum, and brain, T concentrations were high er at the female-promoting temperature during the three periods, where as in the gonads and serum, E2 levels were similar at the female and m ale-promoting temperature. In Di, the concentration of E2 was signific antly higher at the female-promoting temperature. Biotransformation of P5 to T in gonadal tissues were slightly higher at the female-promoti ng temperature in TSP and increased during UDC; and DG. Conversion of T to E2, however, was similar at the two temperatures during the three periods. In the brain, the Di showed a higher efficiency for transfor ming T to E2 at the female-promoting temperature. Our present results do not allow us to decide whether the diencephalon is the cause or the effect, but they conclusively demonstrate that, in L. olivacea, this region of the brain senses temperature during sex determination. (C) 1 998 Wiley-Liss, Inc.