Estrogens are reported to have both anxiogenic and anxiolytic properties. This dichotomous neurobiological response to estrogens may be mediated by the existence of two distinct estrogen receptor (ER) systems, ERalpha and ERbeta. In brain, ERalpha plays a critical role in regulating reproductive neuroendocrine function, whereas ERbeta may be more important in regulating nonreproductive functions. To determine whether estrogen's anxiolytic actions could be mediated by ERbeta, we examined anxiety-related behaviors after treatment with ER subtype-selective agonists. Ovariectomized female rats, divided into four treatment groups, were injected with the selective ERbeta agonist diarylpropionitrile (DPN), the ERalpha-selective agonist propyl-pyrazole-triol (PPT), 17beta-estradiol, or vehicle daily for 4d. After injections, behavior was monitored in the elevated plus maze or open field. Rats treated with DPN showed significantly decreased anxiety-related behaviors in both behavioral paradigms. In the elevated plus maze, DPN significantly increased the number of open arm entries and time spent on the open arms of the maze. Furthermore, DPN significantly reduced, whereas PPT increased, anxiogenic behaviors such as the number of fecal boli and time spent grooming. In the open field, DPN-treated females made more rears, interacted more with a novel object, and spent more time in the middle of the open field than did control or PPT-treated rats. To confirm that DPN's anxiolytic actions are ER mediated, the nonselective ER antagonist tamoxifen was administered alone or in combination with DPN. Tamoxifen blocked the previously identified anxiolytic actions of DPN. Taken together, these findings suggest that the anxiolytic properties of estrogens are ERbeta mediated.

Humans have acquired an ability to exclusively synthesize S-equol from the precursor soy isoflavone daidzein, and it is significant that, unlike R-equol, this enantiomer has a relatively high affinity for estrogen receptor beta.

Estrogen receptor ␤ (ER␤) and androgen receptor (AR) are found in high levels within populations of neurons in the hypothalamus. To determine whether AR or ER␤ plays a role in regulating hypothalamo-pituitary-adrenal (HPA) axis function by direct action on these neurons, we examined the effects of central implants of 17␤-estradiol (E2), 5␣-dihydrotestosterone (DHT), the DHT metabolite 5␣-androstan-3␤,17␤-diol (3␤-diol), and several ER subtype-selective agonists on the corticosterone and adrenocorticotropin (ACTH) response to immobilization stress. In addition, activation of neurons in the paraventricular nucleus (PVN) was monitored by examining c-fos mRNA expression. Pellets containing these compounds were stereotaxically implanted near the PVN of gonadectomized male rats. Seven days later, animals were killed directly from their home cage (nonstressed) or were restrained for 30 min (stressed) before they were killed. Compared with controls, E2 and the ER␣-selective agonists moxestrol and propyl-pyrazole-triol significantly increased the stress induced release of corticosterone and ACTH. In contrast, central administration of DHT, 3␤-diol, and the ER␤-selective compound diarylpropionitrile significantly decreased the corticosterone and ACTH response to immobilization. Cotreatment with the ER antagonist tamoxifen completely blocked the effects of 3␤-diol and partially blocked the effect of DHT, whereas the AR antagonist flutamide had no effect. Moreover, DHT, 3␤-diol, and diarylpropionitrile treatment significantly decreased restraint-induced c-fos mRNA expression in the PVN. Together, these studies indicate that the inhibitory effects of DHT on HPA axis activity may be in part mediated via its conversion to 3␤-diol and subsequent binding to ER␤.

Equol (7-hydroxy-3[4'hydroxyphenyl]-chroman) is the major metabolite of the phytoestrogen daidzein, one of the main isoflavones found abundantly in soybeans and soy foods. Equol may be an important biologically active molecule based on recent studies demonstrating that equol can modulate reproductive function. In this study, we examined the effects of equol on prostate growth and LH secretion and determined some of the mechanisms by which it might act. Administration of equol to intact male rats for 4-7 days reduced ventral prostate and epididymal weight and increased circulating LH levels. Using binding assays, we determined that equol specifically binds 5alpha-dihydrotestosterone (DHT), but not testosterone, dehydroepiandrosterone, or estrogen with high affinity. Equol does not bind the prostatic androgen receptor, and has a modest affinity for recombinant estrogen receptor (ER) beta, and no affinity for ERalpha. In castrated male rats treated with DHT, concomitant treatment with equol blocked DHT's trophic effects on the ventral prostate gland growth and inhibitory feedback effects on plasma LH levels without changes in circulating DHT. Therefore, equol can bind circulating DHT and sequester it from the androgen receptor, thus altering growth and physiological hormone responses that are regulated by androgens. These data suggest a novel model to explain equol's biological properties. The significance of equol's ability to specifically bind and sequester DHT from the androgen receptor have important ramifications in health and disease and may indicate a broad and important usage for equol in the treatment of androgen-mediated pathologies.

The complexity of gonadal steroid hormone actions is reflected in their broad and diverse effects on a host of integrated systems including reproductive physiology, sexual behavior, stress responses, immune function, cognition, and neural protection. Understanding the specific contributions of androgens and estrogens in neurons that mediate these important biological processes is central to the study of neuroendocrinology. Of particular interest in recent years has been the biological role of androgen metabolites. The goal of this review is to highlight recent data delineating the specific brain targets for the dihydrotestosterone metabolite, 5α-androstane, 3β, 17β-diol (3β-Diol). Studies using both in vitro and in vivo approaches provide compelling evidence that 3β-Diol is an important modulator of the stress response mediated by the hypothalmo-pituitary-adrenal axis. Further, the actions of 3β-Diol are mediated by estrogen receptors, and not androgen receptors, often through a canonical estrogen response element in the promoter of a given target gene. These novel findings compel us to re-evaluate the interpretation of past studies and the design of future experiments aimed at elucidating the specific effects of androgen receptor signaling pathways.

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The hormonal response to stress is enhanced by oestrogen but inhibited by androgens. To determine underlying changes in activity of neuropeptide neurones in the paraventricular nucleus of the hypothalamus (PVN), we examined the effect of oestrogen and androgen treatment on restraint-induced c-fos mRNA, corticotropin-releasing hormone (CRH) heteronuclear RNA, and arginine vasopressin hnRNA expression in the PVN. Male rats were gonadectomized and injected with oestradiol benzoate (EB) or dihydrotestosterone propionate (DHTP; s.c., daily for 4 days). Rats were stressed by restraint for 10 min or 30 min before killing. Other rats were stressed for 30 min and then returned to their home cage for 20 min before killing. Corticosterone and adrenocorticotropic hormone responses to restraint stress were signi®cantly greater in EB-treated rats and lower in DHTP-treated rats at the 30-min timepoint compared to controls. c-fos mRNA increases following stress were augmented by EB but inhibited by DHTP. CRH hnRNA expression increased signi®cantly in the PVN in response to restraint stress, and this increase was augmented by EB treatment, but decreased by DHTP treatment. Vasopressin hnRNA expression was also increased in response to stress, and this increase was attenuated by DHTP. These ®ndings indicate that gonadal hormones in¯uence the reactivity of the hypothalamic-pituitary adrenal axis to stress.Stressful events, either actual or perceived, activate neurones within the paraventricular nucleus (PVN) of the hypothalamus, resulting in the enhanced synthesis and secretion of hypothalamic neuropeptides (1±3). The major secretogogues regulating the hypothalamic-pituitary adrenal axis (HPA axis) are corticotopin-releasing hormone (CRH) and arginine vasopressin. These neuropeptides can subsequently act alone or in concert to stimulate the synthesis and release of adrenocorticotropic hormone (ACTH) from anterior pituitary corticotrophs. ACTH drives adrenal cortical hormone secretion. HPA axis activity is subsequently terminated by negative feedback in which the major inhibitory tone comes from circulating corticosterone.There exists a sex difference in HPA function due at least in part to circulating sex steroid hormones (1±3). When stressed, females display a more robust HPA response than males (1±5). It appears that, in males, androgens act to inhibit (3±5) whereas, in females, oestrogens function to enhance (1±3) the activity of the HPA axis. This is in contrast to behavioural responses to stress where oestrogen appears to reduce fear related behaviour, but androgens enhance their appearance (2).Endocrine manipulation studies in females show that ovariectomy can reduce the stress-induced secretion of ACTH and corticosterone. This can be reversed via oestrogen administration (1±3). However, the precise mechanisms by which oestrogen enhances levels of ACTH and corticosterone are not completely understood. Some evidence indicates that oestrogen directly in¯uences cellular activity and gene expression within neurosecretory neurones ...

5α-Androstane-3β, 17β-diol (3βAdiol) is a metabolite of the potent androgen, 5α-dihydrotestosterone. Recent studies showed that 3βAdiol binds to estrogen receptor (ER)-β and regulates growth of the prostate gland through an estrogen, and not androgen, receptor-mediated pathway. These data raise the possibility that 3βAdiol could regulate important physiological processes in other tissues that produce 3βAdiol, such as the brain. Although it is widely accepted that the brain is a target for 5α-dihydrotestosterone action, there is no evidence that 3βAdiol has a direct action in neurons. To explore the molecular mechanisms by which 3βAdiol might act to modulate gene transcription in neuronal cells, we examined whether 3βAdiol activates ER-mediated promoter activity and whether ER transactivation is facilitated by a classical estrogen response element (ERE) or an AP-1 complex. The HT-22 neuronal cell line was cotransfected with an expression vector containing ERα, ER-β1, or the ERβ splice variant, ER-β2 and one of two luciferase-reporter constructs containing either a consensus ERE or an AP-1 enhancer site. Cells were treated with 100 nm 17β-estradiol, 100 nm 3βAdiol, or vehicle for 15 h. We show that 3βAdiol activated ER-β1-induced transcription mediated by an ERE equivalent to that of 17β-estradiol. By contrast, 3βAdiol had no effect on ERα- or ER-β2-mediated promoter activity. Moreover, ER-β1 stimulated transcription mediated by an ERE and inhibited transcription by an AP-1 site in the absence of ligand binding. These data provide evidence for activation of ER signaling pathways by an androgen metabolite in neuronal cells.