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
Kl. Wennstrom et D. Crews, 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, Hormones and behavior (Print), 34(1), 1998, pp. 11-16
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.