Androgenic regulation of steroid hormone receptor mRNAs in the brain of whiptail lizards

Sex and species differences in androgenic regulation of steroid hormone rec eptor mRNAs were examined in the diencephalon of two species of whiptail li zards: Cnemidophorus inornatus is a sexual species and the direct evolution ary ancestor to Cnemidophorus uniparens, an all-female parthenogenetic spec ies. Lizards were gonadectomized and treated with different doses of either aromatizable testosterone or nonaromatizable dihydrotestosterone. The rela tive abundances of androgen-, oestrogen-, and progesterone-receptor mRNAs w ere compared in various nuclei following in situ hybridization with homolog ous riboprobes. A diversity of patterns in androgenic regulation was observ ed, with effects differing according to brain region, the steroid-receptor mRNA being considered and, in some cases, between androgens. In the ancestr al sexual species, intact males had lower androgen-receptor mRNA abundances than castrated, blank-implanted males in the medial preoptic area. Testost erone significantly decreased androgen-receptor mRNA abundance in the media l preoptic area of castrated males. Males had higher androgen-receptor mRNA levels in the preoptic area than females generally and neither the sexual or parthenogenetic females showed a decrease in androgen-receptor mRNA with androgen treatment. Both testosterone and dihydrotestosterone increased oe strogen-receptor mRNA abundance in the ventromedial hypothalamus of C. inor natus, but no sex differences in this effect were observed. Gonadectomy dec reased, whereas androgen treatment increased, progesterone-receptor mRNA ab undance in the ventromedial hypothalamus. There was a sex difference in thi s response to androgen in the sexual species, with males having greater amo unts than females in this brain area. The parthenogenetic species exhibited a similar pattern to females of the sexual species, but the levels were hi gher overall, possibly because Cnemidophorus uniparens is triploid. The per iventricular preoptic area showed a different pattern, with testosterone tr eatment increasing progesterone-receptor mRNA abundance in both sexes of th e sexual species and in the parthenogenetic species, while dihydrotestoster one did not. The diversity of patterns in androgen effects indicates that g onadal sex, aromatization of androgen, and perhaps gene dosage all influenc e the expression of steroid-receptor mRNAs in the lizard brain.