Sex differences in estrogen and progesterone receptor messenger ribonucleic acid regulation in the brain of little striped whiptail lizards.

Sex differences in the regulation of steroid hormone receptors in brain areas controlling female- and male-typical sexual behavior may be important in determining sex differences in the display of these behaviors. This study examined sex differences in estrogenic effects on the relative abundance of messenger RNA for estrogen receptor (ER) and progesterone receptor (PR) in discrete brain areas of whiptail lizards, Cnemidophorus inornatus, by in situ hybridization with radiolabeled riboprobes. Gonadectomized females and males received an estradiol benzoate (EB) injection (0.5 microgram) which effectively induces receptive behavior in females; controls received vehicle alone. Sex and regional differences in estrogenic effects on ER- and PR-mRNA abundance were found. Females responded to EB treatment with increases in ER- and PR-mRNA relative abundance in the ventromedial nucleus of the hypothalamus (VMH). Males had similar relative mRNA abundances to females in gonadectomized controls, but did not exhibit increases with EB treatment. EB treatment increased ER-mRNA abundance in the dorsal hypothalamus of females, but not males. ER-mRNA decreases in the lateral septum and PR-mRNA increases in the posterior hypothalamus with hormone treatment were also found, but did not differ by sex. Neither sex nor treatment effects were definitively shown for ER- or PR-mRNA abundance in the anterior hypothalamus-preoptic area. The VMH controls female-typical receptive behavior in this species. Sex differences in the response to estrogen in this nucleus may therefore underlie sex differences in the display of receptive behavior.(ABSTRACT TRUNCATED AT 250 WORDS)