Androgenic Regulation of Steroid Hormone Receptor mRNAs in the Brain of Whiptail Lizards

Abstract

Sex and species differences in androgenic regulation of steroid hormone receptor mRNAs were examined in the diencephalon of two species of whiptail lizards: Cnemidophorus inornatus is a sexual species and the direct evolutionary ancestor to Cnemidophorus uniparens, an all-female parthenogenetic species. Lizards were gonadectomized and treated with different doses of either aromatizable testosterone or nonaromatizable dihydrotestosterone. The relative abundances of androgen-, oestrogen-, and progesterone-receptor mRNAs were compared in various nuclei following in situ hybridization with homologous riboprobes. A diversity of patterns in androgenic regulation was observed, with effects differing according to brain region, the steroid-receptor mRNA being considered and, in some cases, between androgens. In the ancestral sexual species, intact males had lower androgen-receptor mRNA abundances than castrated, blank-implanted males in the medial preoptic area. Testosterone significantly decreased androgen-receptor mRNA abundance in the medial 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 oestrogen-receptor mRNA abundance in the ventromedial hypothalamus of C. inornatus, but no sex differences in this effect were observed. Gonadectomy decreased, whereas androgen treatment increased, progesterone-receptor mRNA abundance in the ventromedial hypothalamus. There was a sex difference in this response to androgen in the sexual species, with males having greater amounts than females in this brain area. The parthenogenetic species exhibited a similar pattern to females of the sexual species, but the levels were higher overall, possibly because Cnemidophorus uniparens is triploid. The periventricular preoptic area showed a different pattern, with testosterone treatment increasing progesterone-receptor mRNA abundance in both sexes of the sexual species and in the parthenogenetic species, while dihydrotestosterone did not. The diversity of patterns in androgen effects indicates that gonadal sex, aromatization of androgen, and perhaps gene dosage all influence the expression of steroid-receptor mRNAs in the lizard brain.

Sex and species differences in plasma testosterone and in counts of androgen receptor-positive cells in key brain regions of Sceloporus lizard species that differ in aggression

“…Our work is consistent with other studies of reptiles finding androgen receptor labeling or AR mRNA expression in the POA and the VMH [12, 23, 44, 52, 55, 64]. In vertebrates the VMH is often implicated in mediating female-typical behaviors.…”

“…If activational effects of testosterone (TESTO) contribute to sex and/or species differences in aggression, differences in plasma TESTO levels should correlate with differences in aggression. Similarly, differences in sensitivity to steroid hormones can correlate with status, sex, or species differences in behavior [6, 7, 19, 33], including in reptiles [23]. Thus, if sensitivity differences contribute to differences in aggression seen among these Sceloporus lizards, then differences in density of brain androgen receptors should correlate with differences in aggression.…”

Relationships among Sex, Season and Testosterone in the Expression of Androgen Receptor mRNA and Protein in the Green Anole Forebrain

“…We detected the main effects of sex in the AMY, with females having a greater number and density of cells expressing AR mRNA than males; this pattern mirrors previous sex differences of AR in the anole brain [Rosen et al, 2002]. In other reptilian and mammalian species, the sex difference is often in the opposite direction, with males having more AR mRNA and/or protein in the POA and hypothalamic areas [Lu et al, 1998;Wood and Newman, 1999;Fernandez-Guasti et al, 2000;Godwin et al, 2000;Moga et al, 2000]. Although AR transcripts can be either up-or downregulated in response to androgen administration across vertebrate species [Krongrad et al, 1991;Gonzalez-Cadavid et al, 1993;Drengler et al, 1996;Godwin et al, 2000], increased AR in female anoles is not likely due to circulating androgens.…”

“…In other reptilian and mammalian species, the sex difference is often in the opposite direction, with males having more AR mRNA and/or protein in the POA and hypothalamic areas [Lu et al, 1998;Wood and Newman, 1999;Fernandez-Guasti et al, 2000;Godwin et al, 2000;Moga et al, 2000]. Although AR transcripts can be either up-or downregulated in response to androgen administration across vertebrate species [Krongrad et al, 1991;Gonzalez-Cadavid et al, 1993;Drengler et al, 1996;Godwin et al, 2000], increased AR in female anoles is not likely due to circulating androgens. Gonadally intact female anoles have only a fraction of the circulating T levels of males, regardless of the season [Lovern et al, 2001], and the sex difference was not present in the intact animals in this study.…”

Molecular characterization and brain distribution of the progesterone receptor in whiptail lizards

“…In whiptails, expression of PR is regulated by estrogens [20], progestins [21], and androgens [19] in both the ancestral and descendant species. In mammals, the regulation of PR by estrogens is well established [46,51,55].…”