EFFECT OF LONG-TERM CASTRATION AND LONG-TERM ANDROGEN TREATMENT ON SEXUALLY DIMORPHIC ESTROGEN-INDUCIBLE PROGESTERONE-RECEPTOR MESSENGER-RNA LEVELS IN THE VENTROMEDIAL HYPOTHALAMUS OF WHIPTAIL LIZARDS

In whiptail lizards, as in laboratory rodents, females will respond to exogenous estrogen by increasing progesterone receptor (PR) or PR mRN A in the ventromedial hypothalamus (VMH) while males show an attenuate d response to the same treatment. In rodents, neonatal hormone manipul ations affect the adult expression of this trait; however, few investi gators have examined the effects of hormone treatment in adulthood. Th erefore the current study was carried out to determine whether observe d sex differences in the estrogen response in adulthood may be modifie d by steroid hormone manipulation. We castrated male whiptail lizards for 1 week (short term) or 6 weeks (long term). We also gonadectomized female whiptails and implanted them with either a Silastic capsule co ntaining testosterone or an empty capsule. At the end of that time all implants were removed and the animals were injected with either estra diol benzoate (EB) or steroid suspension vehicle and their brains were assayed for PR mRNA expression using in situ hybridization. The resul ts demonstrate that in male whiptail lizards, long-term castration inc reases sensitivity to estradiol as measured by induction of PR mRNA in the VMH; EB-injected long-term castrated males were not different fro m EB-injected females. However, longterm androgenization did not atten uate the estrogen response in females. This suggests that attenuation of the estrogen response in males requires activation by testicular se cretions, but that females cannot be made to show a male phenotype via testosterone administration. (C) 1998 Academic Press.