Regulation of Estrogen Receptor and Progesterone Receptor Messenger Ribonucleic Acid by Estrogen in the Brain of the Whiptail Lizard (Cnemidophorus uniparens)

Abstract

Receptive behavior in females vertebrates is controlled by hormones, principally estrogen, secreted by the ovary. Estrogen influences behavior by interacting with a specific estrogen binding protein, or receptor, located in target cells in certain hypothalamic nuclei. To better understand the molecular mechanisms involved in the control of receptive behavior in whiptail lizards, we investigated the effects of exogenous estrogen on the regulation of estrogen receptor and progesterone receptor expression in several regions of the brains of Cnemidophorus uniparens. First we determined a dosage of 17 beta-estradiol 3-benzoate (0.5 micrograms) which reliably induced receptive behavior in ovariectomized C. uniparens. Then using in situ hybridization, we examined the effects of that dosage on the expression of estrogen receptor and progesterone receptor mRNA in the brain 24 h after injection. Estrogen treatment resulted in a significant up-regulation of estrogen receptor mRNA expression in the ventromedial nucleus of the hypothalamus and torus semicircularis, down-regulation of estrogen receptor mRNA expression in the lateral septum, and no change in the periventricular nuclei of the hypothalamus, the periventricular nucleus of the preoptic area, and the dorsal hypothalamus. The same dosage resulted in increased progesterone receptor mRNA expression in the ventromedial nucleus of the hypothalamus and the periventricular nucleus of the preoptic area; no significant changes in progesterone receptor mRNA expression were observed in the periventricular nuclei of the hypothalamus or the torus semicircularis, although the differences in progesterone receptor expression in the torus semicircularis approached statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex Differences in Estrogen and Progesterone Receptor Messenger Ribonucleic Acid Regulation in the Brain of Little Striped Whiptail Lizards

“…Male C. inornatus did respond to EB treat ment with a decrease in ER-mRNA levels in the lateral septum and a trend towards a similar decrease in the peri ventricular preoptic area. Moreover, the pattern of change in ER-mRNA with treatment (significant treatment ef fect) in the lateral septum is similar between male and female C. inornatus, and supports a previous finding of lower ER-mRNA abundance in the lateral septum of C. uniparens with this EB administration protocol [20], The possibility that male C. inornatus possess ER-mRNA but not ER protein in the nuclei examined also appears unlikely based on ER-like immunoreactivity demon strated in these nuclei in male C. inornatus with a mam malian ER antibody [Gahr and Crews, unpubl. data].…”

“…Both the parthenogen C. unipa rens and female C. inornatus exhibit more ER-mRNA and PR-mRNA in the VMH and a stimulation of recep tive behavior in response to a 0.5-pg EB injection [20], Because these effects of EB were replicated for female C. inornatus here, the finding of a lack of such effects in male C. inornatus is strengthened. It might be argued that although this EB dose and administration protocol are effective both behaviorally and in increasing ER-and PRmRNAs in female C. inornatus, male C. inornatus are not physiologically responsive to it for some reason.…”

“…The protocols and validation of the in situ hybridization, autora diography, and grain quantification procedures used in this study have been described [1,20]. Figure 1 illustrates the LYCUERlb and LYCUPR3a clones used to generate riboprobes and their structures relative to human receptor structures.…”

“…commun.] on a Macintosh Ilci computer equipped with an image-capture system exactly as previously described [20], Control slides hybridized to sense strand control probes exhibited uniform background densities of silver grains and no specific labeling of cells. Sample sizes differ for different nuclei because sections were some times lost in cryosectioning.…”

“…Addition ally, variations in the abundance of ER-and PR-mRNA in discrete limbic nuclei have been compared between female C. inornatus and C. uniparens both over the course of the ovarian cycle and in response to exogenous estradiol benzoate [20,21], As in rats, the expression of estrogen-induced PR-mRNA is strongly correlated to the expression of female-typical receptive behavior in both C. inornatus and C. uniparens [22], This study compares the relative expression of ER-and PR-mRNAs between female and male C. inornatus in two conditions: gonadectomized and following injection of a dosage of estradiol benzoate which effectively induces receptive behavior in females. We do not attempt a gener al characterization of sex differences in the control of ste roid receptor mRNAs in Cnemidophorus here.…”