The androgen 5alpha-dihydrotestosterone and its metabolite 5alpha-androstan-3beta, 17beta-diol inhibit the hypothalamo-pituitary-adrenal response to stress by acting through estrogen receptor beta-expressing neurons in the hypothalamus

Estrogen receptor beta regulates the expression of tryptophan-hydroxylase 2 mRNA within serotonergic neurons of the rat dorsal raphe nuclei

Dysfunctions of the brain 5-HT system are often associated with affective disorders, such as depression. The raphe nuclei target the limbic system and most forebrain areas and constitute the main source of 5-HT in the brain. All 5-HT neurons express tryptophan hydroxylase-2 (TPH2), the brain specific, rate-limiting enzyme for 5-HT synthesis. Estrogen receptor (ER) beta agonists have been shown to attenuate anxiety- and despair-like behaviors in rodent models. Therefore, we tested the hypothesis that ER beta may contribute to the regulation of gene expression in 5-HT neurons of the dorsal raphe nuclei (DRN) by examining the effects of systemic and local application of the selective ER beta agonist diarylpropionitrile (DPN) on tph2 mRNA expression. Ovariectomized (OVX) female rats were injected s.c. with DPN or vehicle once daily for 8 days. In situ hybridization revealed that systemic DPN-treatment elevated basal tph2 mRNA expression in the caudal and mid-dorsal DRN. Behavioral testing of all animals in the open field (OF) and on the elevated plus maze (EPM) on days 6 and 7 of treatment confirmed the anxiolytic nature of ER beta activation. Another cohort of female OVX rats was stereotaxically implanted bilaterally with hormone-containing wax pellets flanking the DRN. Pellets contained 17-beta-estradiol (E), DPN, or no hormone. Both DPN and E significantly enhanced tph2 mRNA expression in the mid-dorsal DRN. DPN also increased tph2 mRNA in the caudal DRN. DPN- and E-treated rats displayed a more active stress-coping behavior in the forced-swim test (FST). No behavioral differences were found in the OF or on the EPM. These data indicate that ER beta acts at the level of the rat DRN to modulate tph2 mRNA expression and thereby influence 5-HT synthesis in DRN subregions. Our results also suggest that local activation of ER beta neurons in the DRN may be sufficient to decrease despair-like behavior, but not anxiolytic behaviors.

Arginine vasopressin regulation in pre- and postpubertal male rats by the androgen metabolite 3beta-diol

Arginine vasopressin (AVP) is a nonapeptide expressed in several brain regions. In addition to its well-characterized role in osmoregulation, AVP regulates paternal behavior, aggression,circadian rhythms, and the stress response. In the bed nucleus of the stria terminalis (BST), AVP gene expression is tightly regulated by gonadal steroid hormones. However, the degree by which AVP is regulated by gonadal steroid hormones in the suprachiasmatic nucleus (SCN) and medial amygdala (MeA) is unclear. Previous studies have shown that AVP expression in the brain of gonadectomized rats is restored with testosterone, 17beta-estradiol, and 5alpha-dihydrotestosterone(DHT) replacement. In addition, we have demonstrated that 3beta-diol, a metabolite of DHT,increased AVP promoter activity in a neuronal cell line and that the effects of 3beta-diol on AVP promoter activity were mediated by estrogen receptor-beta. To test whether 3beta-diol has a physiological role in the regulation of central AVP expression in vivo, we gonadectomized pre- and postpubertal male rats and followed with once daily injections of estradiol benzoate (EB),DHT-propionate, 3beta-diol-dipropionate, or vehicle. The SCN, BST, and MeA were analyzed for AVP mRNA expression using in situ hybridization. In the BST, intact juveniles had significantly fewer AVP-expressing cells than adults. GDX abolished all AVP mRNA expression in the BST in both age groups, whereas treatment with EB restored >80% and DHTP <10% of the AVP expression. Interestingly, 3beta-diol-proprionate was more effective at inducing AVP expression in juveniles than in adults, suggesting that the regulation of AVP by 3beta-diol might be age dependent [corrected].

Genetic, epigenetic and environmental impact on sex differences in social behavior

The field of behavioral neuroendocrinology has generated thousands of studies that indicate differences in brain structure and reactivity to gonadal steroids that produce sex-specific patterns of social behavior. However, rapidly emerging evidence shows that genetic polymorphisms and resulting differences in the expression of neuroactive peptides and receptors as well as early-life experience and epigenetic changes are important modifiers of social behavior. Furthermore, due to its inherent complexity, the neurochemical mechanisms underlying sex differences in social behavior are usually studied in a tightly regulated laboratory setting rather than in complex environments. Importantly, specific hormones may elicit a range of different behaviors depending on the cues present in these environments. For example, individuals exposed to a psychosocial stressor may respond differently to the effects of a gonadal steroid than those not exposed to chronic stress. The objective of this review is not to re-examine the activational effects of hormones on sex differences in social behavior but rather to consider how genetic and environmental factors modify the effects of hormones on behavior. We will focus on estrogen and its receptors but consideration is also given to the role of androgens. Furthermore, we have limited our discussions to the importance of oxytocin and vasopressin as targets of gonadal steroids and how these effects are modified by genetic and experiential situations. Taken together, the data clearly underscore the need to expand research initiatives to consider gene-environment interactions for better understanding of the neurobiology of sex differences in social behavior.

Gonadal steroids maintain 24 h acetylcholine release in the hippocampus: organizational and activational effects in behaving rats

Extracellular acetylcholine (ACh) levels in the dorsal hippocampus increases during learning or exploration, exhibiting a sex-specific 24 h release profile. To examine the activational effect of gonadal steroid hormones on the sex-specific ACh levels and its correlation with spontaneous locomotor activity, we observed these parameters simultaneously for 24 h. Gonadectomy severely attenuated the ACh levels, whereas the testosterone replacement in gonadectomized males or 17beta-estradiol replacement in gonadectomized females successfully restored the levels. 17beta-Estradiol-priming in gonadectomized males could not restore the ACh levels, and testosterone replacement in gonadectomized females failed to raise ACh levels to those seen in testosterone-primed gonadectomized males, revealing a sex-specific activational effect. Spontaneous locomotor activity was not changed in males by gonadectomy or the replacement of gonadal steroids, but 17beta-estradiol enhanced the activity in gonadectomized females. Gonadectomy severely reduced the correlation between ACh release and activity levels, but the testosterone replacement in gonadectomized males or 17beta-estradiol replacement in gonadectomized females successfully restored it. To further analyze the sex-specific effect of gonadal steroids, we examined the organizational effect of gonadal steroids on the ACh release in female rats. Neonatal testosterone or 17beta-estradiol treatment not only increased the ACh levels but also altered them to resemble male-specific ACh release properties without affecting levels of spontaneous locomotor activity. We conclude that the activational effects of gonadal steroids maintaining the ACh levels and the high correlation with spontaneous locomotor activity are sex-specific, and that the organizational effects of gonadal steroids suggest estrogen receptor-mediated masculinization of the septo-hippocampal cholinergic system.

Estrogen receptor-beta agonist diarylpropionitrile: biological activities of R- and S-enantiomers on behavior and hormonal response to stress

Estrogens have been shown to have positive and negative effects on anxiety and depressive-like behaviors, perhaps explained by the existence of two distinct estrogen receptor (ER) systems, ERalpha and ERbeta. The ERbeta agonist, diarylpropionitrile (DPN) has been shown to have anxiolytic properties in rats. DPN exists as a racemic mixture of two enantiomers, R-DPN and S-DPN. In this study, we compared R-DPN and S-DPN for their in vitro binding affinity, ability to activate transcription in vitro at an estrogen response element, and in vivo endocrine and behavioral responses. In vitro binding studies using recombinant rat ERbeta revealed that S-DPN has a severalfold greater relative binding affinity for ERbeta than does R-DPN. Furthermore, cotransfection of N-38 immortalized hypothalamic cells with an estrogen response element-luc reporter and ERbeta revealed that S-DPN is a potent activator of transcription in vitro, whereas R-DPN is not. Subsequently, we examined anxiety-like behaviors using the open-field test and elevated plus maze or depressive-like behaviors, using the forced swim test. Ovariectomized young adult female Sprague Dawley rats treated with racemic DPN, S-DPN, and the ERbeta agonist, WAY-200070, showed significantly decreased anxiety-like behaviors in both the open-field and elevated plus maze and significantly less depressive-like behaviors in the forced swim test compared with vehicle-, R-DPN-, or propylpyrazoletriol (ERalpha agonist)-treated animals. In concordance with the relative binding affinity and transcriptional potency, these results demonstrate that the S-enantiomer is the biologically active form of DPN. These studies also indicate that estrogen's positive effects on mood, including its anxiolytic and antidepressive actions, are due to its actions at ERbeta.

Stressor controllability and Fos expression in stress regulatory regions in mice

Controllability is an important determinant of the effects of stress on behavior. We trained mice with escapable (ES) and inescapable (IS) shock and examined behavioral freezing and Fos expression in brain regions involved in stress to determine whether stressor controllability produced differential activation of these regions. Mice (C57BL/6J) were trained to escape footshock by moving to a safe chamber in a shuttlebox. This terminated shock for both ES mice (n=5) and yoked-control mice receiving IS (n=5). Handling control (HC) mice (n=5) experienced the shuttlebox, but never received footshock. Training took place on three days (20 trials per day, 0.2 mA, 5.0 s maximum duration, 1.0 min interstimulus interval). On day 3, the animals were killed 2 h after training and the brains were processed for Fos expression in the amygdala, hypothalamic paraventricular nucleus (PVN), laterodorsal tegmental nucleus, locus coeruleus and dorsal raphe nucleus. Fos expression after IS was greater than after ES and HC in all regions (p<.05). Fos expression after ES was greater than HC only in PVN (p<.05). Freezing in ES mice was equal to or greater than in IS mice whereas HC mice showed minimal freezing. Differential activation of brain regions implicated in stress may, in part, account for differences in behavior in the aftermath of uncontrollable and controllable stress.

Sex differences in psychopathology: of gonads, adrenals and mental illness

Stress-related disorders such as anxiety and depression are disproportionately prevalent in women. Women are more likely to experience depression and anxiety disorders during periods of marked hormonal fluctuations, suggesting that gonadal hormones are involved in stress pathology. Depression and anxiety are both associated with aberrant secretion of glucocorticoids, which also show marked fluctuations across the reproductive cycle and in response to gonadal steroids. Thus, interactions between gonadal and stress hormones may play a major role in predisposing females to stress-related disease. The purpose of this brief review is to highlight preclinical data regarding the role of estrogens in depression and anxiety-like behaviors. While it is evident the exogenous estrogens modulate affective behavior in rodents, there is some disagreement in the literature, perhaps related to experimental designs that vary with respect to administration parameters and stress. Beneficial effects of estrogens on mood are most likely due to estrogen receptor (ER)beta signaling. The antidepressant and anxiolytic effects of ERbeta are consistent with its role in attenuating glucocorticoid responses to stress, suggesting that estrogens, acting at ERbeta, may improve mood by suppressing glucocorticoid hyperactivity. However, additional studies demonstrate that ERbeta signaling in the hippocampus is sufficient to induce antidepressant and anxiolytic behaviors. Thus, ERbeta may improve mood via primary actions on hypothalamic (i.e., paraventricular nucleus) and/or extra-hypothalamic sites. Overall, the preclinical research suggests that selective ER modulators targeting ERbeta may be an attractive alternative or adjunct treatment to currently prescribed antidepressants or anxiolytics.

Activational and organisational effects of gonadal steroids on sex-specific acetylcholine release in the dorsal hippocampus

Acetylcholine (ACh) release in the dorsal hippocampus increases during stress, exploration or learning, exhibiting sex-specific 24-h release profile. We review the role of gonadal steroids on the ACh release in the dorsal hippocampus. In our studies, we found that male rats showed higher extracellular ACh levels than females, but gonadectomy decreased ACh levels in both sexes of rats and subsequently eliminated the sex difference. To examine the sex difference under comparable gonadal steroid levels, we implanted steroid capsules after gonadectomy. Oestradiol supplementation maintained circulating oestradiol to the levels in proestrous female rats, whereas testosterone capsules maintained circulating testosterone to the levels similar to intact male rats. Under comparable gonadal steroids levels, ACh levels were sex-specific. Testosterone replacement in orchidectomised rats clearly restored ACh levels, which were greater than ovariectomised testosterone-primed rats. Similarly, oestradiol replacement in ovariectomised rats successfully restored ACh levels, which were higher than orchidectomised oestradiol-primed rats. These results suggest sex-specific activational effects of gonadal steroids on ACh release. To further examine the organisational effect, female pups were neonatally treated with oil, testosterone, oestradiol, or dihydrotestosterone. These rats were bilaterally ovariectomised and a testosterone capsule was implanted at postnatal week 8. Neonatal treatment of either testosterone or oestradiol clearly increased ACh levels, whereas neonatal dihydrotestosterone treatment failed to change levels. These results suggest that: (i) gonadal steroids maintain the sex-specific ACh release in the dorsal hippocampus and (ii) neonatal activation of oestrogen receptors is sufficient to mediate masculinisation of the septo-hippocampal cholinergic system.

A role for the androgen metabolite, 5alpha-androstane-3beta,17beta-diol, in modulating oestrogen receptor beta-mediated regulation of hormonal stress reactivity

Activation of the hypothalamic-pituitary-adrenal (HPA) axis is a basic response of animals to environmental perturbations that threaten homeostasis. These responses are regulated by neurones in the paraventricular nucleus of the hypothalamus (PVN) that synthesise and secrete corticotrophin-releasing hormone (CRH). Other PVN neuropeptides, such as arginine vasopressin and oxytocin, can also modulate activity of CRH neurones in the PVN and enhance CRH secretagogue activity of the anterior pituitary gland. In rodents, sex differences in HPA reactivity are well established; females exhibit a more robust activation of the HPA axis after stress than do males. These sex differences primarily result from opposing actions of sex steroids, testosterone and oestrogen, on HPA function. Ostreogen enhances stress activated adrenocorticotrophic hormone (ACTH) and corticosterone (CORT) secretion, whereas testosterone decreases the gain of the HPA axis and inhibits ACTH and CORT responses to stress. Data show that androgens can act directly on PVN neurones in the male rat through a novel pathway involving oestrogen receptor (ER)beta, whereas oestrogen acts predominantly through ERalpha. Thus, we examined the hypothesis that, in males, testosterone suppresses HPA function via an androgen metabolite that binds ERbeta. Clues to the neurobiological mechanisms underlying such a novel action can be gleaned from studies showing extensive colocalisation of ERbeta in oxytocin-containing cells of the PVN. Hence, in this review, we address the possibility that testosterone inhibits HPA reactivity by metabolising to 5alpha-androstane-3beta,17beta-diol, a compound that binds ERbeta and regulates oxytocin containing neurones of the PVN. These findings suggest a re-evaluation of studies examining pathways for androgen receptor signalling.

Aromatase and 5alpha-reductase inhibition during an exogenous testosterone clamp unveils selective sex steroid modulation of somatostatin and growth hormone secretagogue actions in healthy older men

BACKGROUND

How endogenous testosterone (Te), 5alpha-dihydrotestosterone (DHT), and estradiol (E(2)) regulate pulsatile GH secretion is not understood.

HYPOTHESIS

Conversion of Te to androgenic (Te-->DHT) or estrogenic (Te-->E(2)) products directs GH secretion. SUBJECTS AND LOCATION: Healthy older men (N = 42, ages 50-79 yr) participated at an academic medical center.

METHODS

We inhibited 5alpha-reduction with dutasteride and aromatization with anastrozole during a pharmacological Te clamp and infused somatostatin (SS), GHRH, GH-releasing peptide-2 (GHRP-2), and L-arginine/GHRH/GHRP-2 (triple stimulus) to modulate GH secretion.

ENDPOINTS

Deconvolution-estimated basal and pulsatile GH secretion was assessed.

RESULTS

Administration of Te/placebo elevated Te by 2.8-fold, DHT by 2.6-fold, and E(2) concentrations by 1.9-fold above placebo/placebo. Te/dutasteride and Te/anastrozole reduced stimulated DHT and E(2) by 89 and 86%, respectively. Stepwise forward-selection regression analysis revealed that 1) Te positively determines mean (P = 0.017) and peak (P < 0.001) GH concentrations, basal GH secretion (P = 0.015), and pulsatile GH secretion stimulated by GHRP-2 (P < 0.001); 2) Te and E(2) jointly predict GH responses to the triple stimulus (positively for Te, P = 0.006, and negatively for E(2), P = 0.031); and 3) DHT correlates positively with pulsatile GH secretion during SS infusion (P = 0.011). These effects persisted when abdominal visceral fat was included in the regression.

CONCLUSION

The present outcomes suggest a tetrapartite model of GH regulation in men, in which systemic concentrations of Te, DHT, and E(2) along with abdominal visceral fat determine the selective actions of GH secretagogues and SS.

Differential sensitivity of the perioculomotor urocortin-containing neurons to ethanol, psychostimulants and stress in mice and rats

The perioculomotor urocortin-containing population of neurons (pIIIu: otherwise known as the non-preganglionic Edinger-Westphal nucleus) is sensitive to alcohol and is involved in the regulation of alcohol intake. A recent study indicated that this brain region is also sensitive to psychostimulants. Since pIIIu has been shown to respond to stress, we investigated how psychostimulant-induced pIIIu activation compares to stress- and ethanol-induced activation, and whether it is independent from a generalized stress response. Several experiments were performed to test how the pIIIu responds to psychostimulants by quantifying the number of Fos immunoreactive nuclei after acute i.p. injections of saline, 10-30 mg/kg cocaine, 5 mg/kg methamphetamine, 5 mg/kg amphetamine, 2.5 g/kg ethanol, 2 h of restraint stress, 10 min of swim stress, or six applications of mild foot shock in male C57BL/6 J mice. We also compared Fos immunoreactivity in pIIIu after acute (20 mg/kg cocaine) and repeated cocaine exposure (7 days of 20 mg/kg cocaine) injections in male C57BL/6 J mice in order to investigate the potential habituation of this response. Finally, we quantified the number of Fos immunoreactive nuclei in pIIIu after administration of saline, 2.5 g/kg ethanol, 20 mg/kg cocaine, or 2 h of restraint stress in male Sprague-Dawley rats. We found that exposure to psychostimulants and ethanol induced significantly higher Fos levels in pIIIu compared to stress in mice. Furthermore, repeated cocaine injections did not decrease Fos immunoreactivity as would be expected if this response were due to stress. In rats, exposure to ethanol, psychostimulant and restraint stress all induced pIIIu Fos immunoreactivity compared to saline-injected controls. In both mice and rats, ethanol- and cocaine-induced Fos immunoreactivity occurred exclusively in urocortin 1-positive, but not in tyrosine hydroxylase-positive, cells. These results provide evidence that the pIIIu Fos-response to psychostimulants is independent of a generalized stress in mice, but not rats. They additionally show that the pIIIu response to stress differs significantly between species.

Systemic administration of diarylpropionitrile (DPN) or phytoestrogens does not affect anxiety-related behaviors in gonadally intact male rats

The development of highly selective agonists for the two major subforms of the estrogen receptor (ERalpha and ERbeta) has produced new experimental methodologies for delineating the distinct functional role each plays in neurobehavioral biology. It has also been suggested that these compounds might have the potential to treat estrogen influenced behavioral disorders, such as anxiety and depression. Prior work has established that the ERbeta agonist, diarylpropionitrile (DPN) is anxiolytic in gonadectomized animals of both sexes, but whether or not this effect persists in gonadally intact individuals is unknown. Isoflavone phytoestrogens, also potent but less selective ERbeta agonists, have also been shown to influence anxiety in multiple species and are becoming more readily available to humans as health supplements. Here we determined the effects of 0.5, 1 or 2 mg/kg DPN, 1 mg/kg of the ERalpha agonist propyl-pyrazole-triol (PPT), 3 or 20 mg/kg of the isoflavone equol (EQ) and 3 or 20 mg/kg of the isoflavone polyphenol resveratrol (RES) on anxiety behavior in the gonadally intact male rat using the light/dark box and the elevated plus maze. We first determined that DPN can be successfully administered either orally or by subcutaneous injection, although plasma DPN levels are significantly lower if given orally. Once injected, plasma levels peak rapidly and then decline to baseline levels within 3 h of administration. For the behavioral studies, all compounds were injected and the animals were tested within 3 h of treatment. None of the compounds, at any of the doses, significantly altered anxiety-related behavior. Plasma testosterone levels were also not significantly altered suggesting that these compounds do not interfere with endogenous androgen levels. The results suggest that the efficacy of ERbeta agonists may depend on gonadal status. Therefore the therapeutic potential of ERbeta selective agonists to treat mood disorders may be limited.

Estrogen impairs glucocorticoid dependent negative feedback on the hypothalamic-pituitary-adrenal axis via estrogen receptor alpha within the hypothalamus

Numerous studies have established a link between individuals with affective disorders and a dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, most notably characterized by a reduced sensitivity to glucocorticoid negative (-) feedback. Furthermore there is a sex difference in the etiology of mood disorders with incidence in females being two to three times that of males, an association that may be a result of the influence of estradiol (E2) on HPA axis function. In these studies, we have examined the effect of E2 on glucocorticoid-mediated HPA axis (-) feedback during both the diurnal peak and the stress-induced rise in corticosterone (CORT). Young adult female Sprague-Dawley (SD) rats were ovariectomized (OVX) and 1 week later treated subcutaneous (s.c.) with oil or estradiol benzoate (EB) for 4 days. On the 4th day of treatment, animals were injected with a single dose of dexamethasone (DEX), or vehicle. EB treatment significantly increased the evening elevation in CORT and the stress-induced rise in CORT. In contrast, DEX treatment reduced the diurnal and stress induced rise in CORT and adrenocorticotropic hormone (ACTH), and this reduction was not apparent following co-treatment with EB. To determine a potential site of E2's action, female SD rats were OVX and 1 week later, wax pellets containing E2, the estrogen receptor beta (ERbeta) agonist diarylpropionitrile (DPN), or the estrogen receptor alpha (ERalpha) agonist propylpyrazoletriol (PPT), was implanted bilaterally and dorsal to the paraventricular nucleus of the hypothalamus (PVN). Seven days later, animals were injected s.c. with a single dose of DEX, or vehicle to test for glucocorticoid-dependent (-) feedback. Results show that E2 and PPT increased, while DPN decreased the diurnal peak and stress-induced CORT and ACTH levels as compared to controls. Furthermore, E2 and PPT impaired the ability of DEX to inhibit both the diurnal and the stress-induced rise in CORT and ACTH, whereas DPN had no effect. Neuronal activation was measured by c-fos mRNA expression within the PVN following restraint. E2 and PPT increased c-fos mRNA, and impaired the normal DEX suppression of neuronal activation in the PVN. Taken together, these data indicate that estradiol causes a dysregulation of HPA axis (-) feedback as evidenced by the inability of DEX to suppress diurnal and stress-induced CORT and ACTH secretion. Additionally, the ability of E2 to inhibit glucocorticoid (-) feedback occurs specifically via ERalpha acting at the level of the PVN.

Androgens with activity at estrogen receptor beta have anxiolytic and cognitive-enhancing effects in male rats and mice

Testosterone (T) and its metabolites may underlie some beneficial effects for anxiety and cognition, but the mechanisms for these effects are unclear. T is reduced to dihydrotestosterone (DHT), which can be converted to 5alpha-androstane,3alpha,17beta-diol (3alpha-diol) and/or 5alpha-androstane-3beta,17beta-diol (3beta-diol). Additionally, T can be converted to androstenedione, and then to androsterone. These metabolites bind with varying affinity to androgen receptors (ARs; T and DHT), estrogen receptors (ERbeta; 3alpha-diol, 3beta-diol), or GABA(A)/benzodiazepine receptors (GBRs; 3alpha-diol, androsterone). Three experiments were performed to investigate the hypothesis that reduced anxiety-like and enhanced cognitive performance may be due in part to actions of T metabolites at ERbeta. Experiment 1: Gonadectomized (GDX) wildtype and ERbeta knockout mice (betaERKO) were subcutaneously (SC) administered 3alpha-diol, 3beta-diol, androsterone, or oil vehicle at weekly intervals, and tested in anxiety tasks (open field, elevated plus maze, light-dark transition) or for cognitive performance in the object recognition task. Experiment 2: GDX rats were administered SC 3alpha-diol, 3beta-diol, androsterone, or oil vehicle, and tested in the same tasks. Experiment 3: GDX rats were androsterone- or vehicle-primed and administered an antagonist of ARs (flutamide), ERs (tamoxifen), or GBRs (flumazenil), or vehicle and then tested in the elevated plus maze. Both rats and wildtype mice, but not betaERKO mice, consistently had reduced anxiety and improved performance in the object recognition task. Androsterone was only effective at reducing anxiety-like behavior in the elevated plus maze and this effect was modestly reduced by flumazenil administration. Thus, actions at ERbeta may be required for T's anxiety-reducing and cognitive-enhancing effects.

Selective contributions of the medial preoptic nucleus to testosterone-dependant regulation of the paraventricular nucleus of the hypothalamus and the HPA axis

Previous data have consistently demonstrated an inhibitory effect of androgens on stress-induced hypothalamic-pituitary-adrenal (HPA) responses. Several brain regions may influence androgen-mediated inhibition of the HPA axis, including the medial preoptic area. To test the role of the medial preoptic nucleus (MPN) specifically, we examined in high- and low-testosterone-replaced gonadectomized rats bearing discrete bilateral lesions of the MPN basal and stress-induced indexes of HPA function, and the relative levels of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) mRNA in the amygdala. High testosterone replacement decreased plasma adrenocorticotropin hormone (ACTH) and paraventricular nucleus (PVN) Fos responses to restraint exposure in sham- but not in MPN-lesioned animals. AVP-, but not CRH-immunoreactivity staining in the external zone of the median eminence was increased by testosterone in sham animals, and MPN lesions blocked this increment in AVP. A similar interaction between MPN lesions and testosterone occurred on AVP mRNA levels in the medial nucleus of the amygdala. These findings support an involvement of MPN projections in mediating the AVP response to testosterone in both the medial parvocellular PVN and medial amygdala. We conclude that the MPN forms part of an integral circuit that mediates the central effects of gonadal status on neuroendocrine and central stress responses.

Membrane-initiated estrogen signaling in hypothalamic neurons

It is well known that many of the actions of 17beta-estradiol (E2) in the central nervous system are mediated via intracellular receptor/transcription factors that interact with steroid response elements on target genes. However, there is compelling evidence for membrane steroid receptors for estrogen in hypothalamic and other brain neurons. But it is not well understood how estrogen signals via membrane receptors, and how these signals impact not only membrane excitability but also gene transcription in neurons. Indeed, it has been known for sometime that E2 can rapidly alter neuronal activity within seconds, indicating that some cellular effects can occur via membrane delimited events. In addition, E2 can affect second messenger systems including calcium mobilization and a plethora of kinases to alter cell signaling. Therefore, this review will consider our current knowledge of rapid membrane-initiated and intracellular signaling by E2 in the hypothalamus, the nature of receptors involved and how they contribute to homeostatic functions.

Activation of ERbeta increases levels of phosphorylated nNOS and NO production through a Src/PI3K/Akt-dependent pathway in hypothalamic neurons

Estrogen plays a role in restoring homeostatic balance during the stress response by altering hypothalamic function and NO production in the brain. While we know that estrogen acts on the hypothalamus to stimulate the NO system through an ERbeta-dependent mechanism in neurons, the molecular mechanisms responsible for these effects are unknown. Because phosphorylation of nNOS at Ser(1412) increases nNOS activity which leads to increased NO production, we investigated the effects of ERbeta activation on nNOS phosphorylation at Ser(1412) and NO production in primary hypothalamic neurons. Using the selective ERbeta agonist, DPN (10nM), we show that activation of ERbeta rapidly increases phosphorylation levels of nNOS at Ser(1412) and NO production. We also show that the PI3K pathway, but not the MAPK pathway, mediates the increases in levels of Ser(1412) phosphorylation and NO production induced by ERbeta activation, as the selective PI3K inhibitor, LY294002 (10microM), blocked the effects of ERbeta activation. Finally, we demonstrate that Src kinase acts upstream of the PI3K/Akt pathway based on our finding that the selective Src inhibitor, PP2 (10microM), blocked the increases in nNOS phosphorylation levels, NO production, and PI3K/Akt activity induced by ERbeta activation. Together, our results show that Src kinase mediates ERbeta-induced increases in phosphorylation levels of nNOS at Ser(1412) and NO production by activating the PI3K/Akt pathway. These findings provide novel insight into the signaling mechanisms through which E2 stimulates the NO system in hypothalamic neurons.

Characterization of human DHRS4: an inducible short-chain dehydrogenase/reductase enzyme with 3beta-hydroxysteroid dehydrogenase activity

Human DHRS4 is a peroxisomal member of the short-chain dehydrogenase/reductase superfamily, but its enzymatic properties, except for displaying NADP(H)-dependent retinol dehydrogenase/reductase activity, are unknown. We show that the human enzyme, a tetramer composed of 27kDa subunits, is inactivated at low temperature without dissociation into subunits. The cold inactivation was prevented by a mutation of Thr177 with the corresponding residue, Asn, in cold-stable pig DHRS4, where this residue is hydrogen-bonded to Asn165 in a substrate-binding loop of other subunit. Human DHRS4 reduced various aromatic ketones and alpha-dicarbonyl compounds including cytotoxic 9,10-phenanthrenequinone. The overexpression of the peroxisomal enzyme in cultured cells did not increase the cytotoxicity of 9,10-phenanthrenequinone. While its activity towards all-trans-retinal was low, human DHRS4 efficiently reduced 3-keto-C(19)/C(21)-steroids into 3beta-hydroxysteroids. The stereospecific conversion to 3beta-hydroxysteroids was observed in endothelial cells transfected with vectors expressing the enzyme. The mRNA for the enzyme was ubiquitously expressed in human tissues and several cancer cells, and the enzyme in HepG2 cells was induced by peroxisome-proliferator-activated receptor alpha ligands. The results suggest a novel mechanism of cold inactivation and role of the inducible human DHRS4 in 3beta-hydroxysteroid synthesis and xenobiotic carbonyl metabolism.

Androgen cell signaling pathways involved in neuroprotective actions

As a normal consequence of aging in men, testosterone levels significantly decline in both serum and brain. Age-related testosterone depletion results in increased risk of dysfunction and disease in androgen-responsive tissues, including brain. Recent evidence indicates that one deleterious effect of age-related testosterone loss in men is increased risk for Alzheimer's disease (AD). We discuss recent findings from our laboratory and others that identify androgen actions implicated in protecting the brain against neurodegenerative diseases and begin to define androgen cell signaling pathways that underlie these protective effects. Specifically, we focus on the roles of androgens as (1) endogenous negative regulators of beta-amyloid accumulation, a key event in AD pathogenesis, and (2) neuroprotective factors that utilize rapid non-genomic signaling to inhibit neuronal apoptosis. Continued elucidation of cell signaling pathways that contribute to protective actions of androgens should facilitate the development of targeted therapeutic strategies to combat AD and other age-related neurodegenerative diseases.

An alternate pathway for androgen regulation of brain function: activation of estrogen receptor beta by the metabolite of dihydrotestosterone, 5alpha-androstane-3beta,17beta-diol

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, 5alpha-androstane, 3beta,17beta-diol (3beta-Diol). Studies using both in vitro and in vivo approaches provide compelling evidence that 3beta-Diol is an important modulator of the stress response mediated by the hypothalmo-pituitary-adrenal axis. Furthermore, the actions of 3beta-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.

Pituitary and/or peripheral estrogen-receptor alpha regulates follicle-stimulating hormone secretion, whereas central estrogenic pathways direct growth hormone and prolactin secretion in postmenopausal women

BACKGROUND

Estradiol (E(2)) stimulates GH and prolactin secretion and suppresses FSH secretion in postmenopausal women. Whether central nervous system (CNS) or pituitary mechanisms (or both) mediate such actions is not known.

OBJECTIVE

Our objective was to distinguish between hypothalamic and pituitary or peripheral (hepatic) actions of E2.

SETTING

This study was performed in an academic medical center.

DESIGN

This was a double-blind, prospectively randomized, placebo (Pl)-controlled study.

METHODS

The capability of a selective, noncompetitive, non-CNS permeant estrogen receptor (ER)-alpha antagonist, fulvestrant (FUL) to antagonize the effects of transdermal E2 and Pl on GH, prolactin, and FSH secretion was assessed in 43 women (ages 50-80 yr) in a four parallel-cohort study. Each woman received four secretagogue infusions to stimulate GH secretion. IGF-I and its binding proteins were measured secondarily.

RESULTS

Administration of Pl/E2 increased GH and prolactin concentrations by 100%, and suppressed FSH concentrations by more than 50% (each P<or=0.004 compared with Pl/Pl). Treatment with FUL/E2 compared with Pl/E2 partially relieved estrogen's inhibition of FSH secretion (P=0.041), without altering E2's stimulation of prolactin secretion. ANOVA further revealed that: 1) estrogen milieu (P=0.014) and secretagogue type (P<0.001) each determined GH concentrations; 2) FUL/Pl suppressed IGF-I concentrations (P<0.001); 3) FUL abrogated estrogen's elevation of IGF binding protein-1 concentrations (P<0.001); and 4) FUL did not oppose estrogen's suppression of IGF binding protein-3 concentrations (P<0.001).

SUMMARY AND CONCLUSIONS

Responses to a non-CNS permeant ERalpha antagonist indicate that E2 inhibits FSH secretion in part via pituitary/peripheral ERalpha, drives prolactin output via nonpituitary/nonperipheral-ERalpha effects, and directs GH secretion and IGF-I-binding proteins by complex mechanisms.

The role of androgen receptors in the masculinization of brain and behavior: what we've learned from the testicular feminization mutation

Many studies demonstrate that exposure to testicular steroids such as testosterone early in life masculinizes the developing brain, leading to permanent changes in behavior. Traditionally, masculinization of the rodent brain is believed to depend on estrogen receptors (ERs) and not androgen receptors (ARs). According to the aromatization hypothesis, circulating testosterone from the testes is converted locally in the brain by aromatase to estrogens, which then activate ERs to masculinize the brain. However, an emerging body of evidence indicates that the aromatization hypothesis cannot fully account for sex differences in brain morphology and behavior, and that androgens acting on ARs also play a role. The testicular feminization mutation (Tfm) in rodents, which produces a nonfunctional AR protein, provides an excellent model to probe the role of ARs in the development of brain and behavior. Tfm rodent models indicate that ARs are normally involved in the masculinization of many sexually dimorphic brain regions and a variety of behaviors, including sexual behaviors, stress response and cognitive processing. We review the role of ARs in the development of the brain and behavior, with an emphasis on what has been learned from Tfm rodents as well as from related mutations in humans causing complete androgen insensitivity.

Effects of perinatal oxycodone exposure on the response to CRH in late adolescent rats

We hypothesized that prenatal oxycodone exposure suppresses the Hypothalamic-Pituitary-Adrenal (HPA) response to stress in late adolescence. Dark Agouti rats were given either intravenous oxycodone or vehicle (controls, CON) daily from gestation day 8 until postnatal day (PD) 5. At PD 45, the male and female offspring received intravenously either ovine corticotropin releasing hormone (CRH) or saline. Plasma adrenocorticotropic hormone (ACTH) and corticosterone (CORT) levels were determined before, and 15, 30, and 60 min after injection. Prenatal oxycodone had no effect on baseline ACTH values; CRH elicited a greater ACTH response than saline. In males, prenatal oxycodone delayed and enhanced the peak ACTH response to CRH, but had no effect in females. The CORT response to CRH was not different between oxycodone and CON; however mean CORT levels in females were significantly higher than those in males at baseline and after stimulation. These results demonstrate that prenatal oxycodone increases pituitary response to CRH in late adolescent male rats, but not in females. The absence of an enhanced adrenal response in oxycodone-exposed males suggests either desensitization or maximal adrenal response to a high CRH dose. The mechanisms of postnatal sex-specific HPA dysregulation following prenatal oxycodone remain to be elucidated.

Estrogen receptors: their roles in regulation of vasopressin release for maintenance of fluid and electrolyte homeostasis

Long standing interest in the impact of gonadal steroid hormones on fluid and electrolyte balance has led to a body of literature filled with conflicting reports about gender differences, the effects of gonadectomy, hormone replacement, and reproductive cycles on plasma vasopressin (VP), VP secretion, and VP gene expression. This reflects the complexity of gonadal steroid hormone actions in the body resulting from multiple sites of action that impact fluid and electrolyte balance (e.g. VP target organs, afferent pathways regulating the VP neurons, and the VP secreting neurons themselves). It also reflects involvement of multiple types of estrogen receptors (ER) in these diverse sites including ERs that act as transcription factors regulating gene expression (i.e. the classic ERalpha as well as the more recently discovered ERbeta) and potentially G-protein coupled, membrane localized ERs that mediate rapid non-genomic actions of estrogen. Furthermore, altered expression of these receptors in physiologically diverse conditions of fluid and electrolyte balance contributes to the difficulty of using simplistic approaches such as gender comparisons, gonadectomy, and hormone replacement to assess the role of gonadal steroids in regulation of VP secretion for maintenance of fluid and electrolyte homeostasis. This review catalogs these inconsistencies and provides a frame work for understanding them by describing: (1) the effect of gonadal steroids on target organ responsiveness to VP; (2) the expression of multiple types of estrogen receptors in the VP neurons and in brain regions monitoring feedback signals from the periphery; and (3) the impact of dehydration and hyponatremia on expression of these receptors.

Neuroendocrine regulation of fluid and electrolyte balance by ovarian steroids: contributions from central oestrogen receptors

Like other hormonally mediated mechanisms, maintenance of body fluid osmolality requires integrated responses from multiple signals at various tissue locales, a large number of which are open to modulation by circulating endocrine factors including the ovarian steroid, oestrogens (E(2)). However, the precise mechanism and the site of action of E(2) in regulating fluid osmolality are not properly understood. More importantly, the biological significance of this action is not clear and the physiological circumstances in which this modulation is engaged remain incomplete. The demonstration of oestrogen receptors (ER) in neural tissues that bear no direct relation to reproduction led us to examine and characterise the expression of ER in brain nuclei that are critical for the maintenance of fluid osmolality. In the rat, ERbeta is prominently expressed in the vasopressin magnocellular neuroendocrine cells of the hypothalamus, whereas ERalpha is localised extensively in the sensory circumventricular organ neurones in the basal forebrain. These nuclei are the primary brain sites that are engaged in defense of fluid perturbation, thus providing a neuroendocrine basis for oestrogenic influence on body fluid regulation. Plasticity in receptor expression that accompanies fluid disturbances at these central loci suggests the functional importance of the receptors and implicates E(2) as one of the fluid regulating hormones in water homeostasis.

Androgen receptor expressing neurons that project to the paraventricular nucleus of the hypothalamus in the male rat

Androgen receptors are distributed throughout the central nervous system and are contained by a variety of nuclei that are known to project to or regulate the paraventricular nucleus (PVN) of the hypothalamus, the final common pathway by which the brain regulates the hypothalamic-pituitary-adrenal (HPA) response to homeostatic threat. Here we characterized androgen receptor staining within cells identified as projecting to the PVN in male rats bearing iontophoretic or crystalline injections of the retrograde tracer FluoroGold aimed at the caudal two-thirds of the nucleus, where corticotropin-releasing hormone-expressing neurons are amassed. Androgen receptor (AR) and FluoroGold (FG) double labeling was revealed throughout the limbic forebrain, including scattered numbers of cells within the anterior and posterior subdivisions of the bed nuclei of the stria terminalis; the medial zone of the hypothalamus, including large numbers of AR-FG-positive cells within the anteroventral periventricular and medial preoptic cell groups. Strong and consistent colabeling was also revealed throughout the hindbrain, predominantly within the periaqueductal gray and the lateral parabrachial nucleus, and within various medullary cell groups identified as catecholaminergic, predominantly C1 and A1 neurons of the ventral medulla. These connectional data predict that androgens can act on a large assortment of multimodal inputs to the PVN, including those involved with the processing of various types of sensory and limbic information, and provide an anatomical framework for understanding how gonadal status could contribute to individual differences in HPA function.

Sexual dimorphism in rats: effects of early maternal separation and variable chronic stress on pituitary‐adrenal axis and behavior

The pituitary-adrenal axis response is gender-dependent, showing lower activity in male rats. Furthermore, males showed low emotional behavior and females high emotionality when exposed to such chronic stress situations. The gender of an animal is a relevant factor in the development of responses to stress. The aim of the present study was to investigate the influence of early maternal separation on the pituitary-adrenal activity and emotional behavior of adult male and female rats subjected to chronic variable stress. Male and female Wistar rats were isolated 4.5 h daily, during the three first weeks of life. At 48 days of age, the rats were exposed to variable chronic stress (five different stressors during 24 days). Non-maternally separated and maternally separated males showed lower levels of ACTH compared to females (p<0.01). In male rats exposed to variable chronic stress, the maternally separated animals showed a diminution in the levels of ACTH and Corticosterone (p<0.05) compared to non-maternally separated rats. In the Open Field test, the maternally separated and non-maternally separated-stressed males showed lower emotional reactivity compared with female rats. This was indicated by increase in ambulation (p<0.05) and decrease in defecation (p<0.05). Male rats subjected to variable chronic stress presented low emotional behavior seen in their lower defecation (p<0.05). Stressed females displayed decreased ambulation (p<0.05) and increased defecation (p<0.05), showing high emotional reactivity after exposure to chronic stress. Maternally separated males showed higher emotionality after the exposure to chronic variable stress. This was indicated by decrease in ambulation (p<0.05), decrease in rearing (p<0.05) and increase in defecation (p<0.05). Thus, maternal separation and variable chronic stress caused long-term gender-dependent alterations in pituitary-adrenal activity and emotional behavior.

Androgen regulation of beta-amyloid protein and the risk of Alzheimer's disease

Advancing age is the most significant risk factor for the development of Alzheimer's disease (AD), however the age-related changes that underlie this effect remain unclear. In men, one normal consequence of aging is a robust decline in circulating and brain levels of the sex steroid hormone testosterone. Testosterone depletion leads to functional impairments and increased risk of disease in androgen-responsive tissues throughout the body, including brain. In this review we discuss the relationship between age-related testosterone depletion and the development of AD. Specifically, we focus on androgen regulation of beta-amyloid protein (Abeta), the accumulation of which is a key initiating factor in AD pathogenesis. Emerging data suggest that the regulatory actions of androgens on both Abeta and the development of AD support consideration of androgen therapy for the prevention and treatment of AD.

Estrogen receptor-beta mediates dihydrotestosterone-induced stimulation of the arginine vasopressin promoter in neuronal cells

Arginine vasopressin (AVP) is a neuropeptide involved in the regulation of fluid balance, stress, circadian rhythms, and social behaviors. In the brain, AVP is tightly regulated by gonadal steroid hormones in discrete regions with gonadectomy abolishing and testosterone replacement restoring normal AVP expression in adult males. Previous studies demonstrated that 17beta-estradiol, a primary metabolite of testosterone, is responsible for restoring most of the AVP expression in the brain after castration. However, 5alpha-dihydrotestosterone (DHT) has also been shown to play a role in the regulation of AVP expression, thus implicating the involvement of both androgen and estrogen receptors (ER). Furthermore, DHT, through its conversion to 5alpha-androstane-3beta,17beta-diol, has been shown to modulate estrogen response element-mediated promoter activity through an ER pathway. The present study addressed two central hypotheses: 1) that androgens directly modulate AVP promoter activity and 2) the effect is mediated by an estrogen or androgen receptor pathway. To that end, we overexpressed androgen receptor, ERbeta, and ERbeta splice variants in a neuronal cell line and measured AVP promoter activity using a firefly luciferase reporter assay. Our results demonstrate that DHT and its metabolite 5alpha-androstane-3beta,17beta-diol stimulate AVP promoter activity through ERbeta in a neuronal cell line.

Estrogen receptor beta in the brain: from form to function

Estrogens have numerous effects on the brain, both in adulthood and during development. These actions of estrogen are mediated by two distinct estrogen receptor (ER) systems, ER alpha (ERalpha) and ER beta (ERbeta). In brain, ERalpha plays a critical role in regulating reproductive neuroendocrine function and behavior, however, a definitive role for ERbeta in any neurobiological function has been slow in forthcoming. Clues to the function of ERbeta in the central nervous system can be gleaned from the neuroanatomical distribution of ERbeta and the phenotypes of neurons that express ERbeta. ERbeta immunoreactivity has been found in populations of GnRH, CRH, vasopressin, oxytocin and prolactin containing neurons in the hypothalamus. Utilizing subtype-selective estrogen receptor agonists can help determine the roles for ERbeta in non-reproductive behaviors in rat models. ERbeta-selective agonists exert potent anxiolytic activity when animals were tested in a number of behavioral paradigms. Consistent with this, ERbeta-selective agonists also inhibited the ACTH and corticosterone response to stress. In contrast, ERalpha selective agonists were found to be anxiogenic and correspondingly increased the hormonal stress response. Taken together, our studies implicate ERbeta as an important modulator of some non-reproductive neurobiological systems. The molecular and neuroanatomical targets of estrogen that are mediated by ERbeta remain to be determined. A number of splice variants of ERbeta mRNA have been reported in brain tissue. Imaging of eGFP labeled chimeric receptor proteins transfected into cell lines shows that ERbeta splice variation can alter trafficking patterns and function. The originally described ERbeta (herein termed ERbeta1) is characterized by possessing a high affinity for estradiol. Similar to ERalpha, it is localized in the nucleus and is trafficked to nuclear sites termed "hyperspeckles" following ligand binding. In contrast, ERbeta2 contains an 18 amino acid insert within the ligand-binding domain and as a result can be best described as a low affinity form of ERbeta. A delta3 (delta3) variant of ERbeta has a deletion of the 3rd exon (coding for the second half of the DNA-binding domain) and as a result does not bind an estrogen response element in DNA. delta3 variants are trafficked to a unique low abundance and larger nuclear site following ligand binding. A delta4 (delta4) variant lacks exon 4 and as a result is localized to the cytoplasm. The amount of individual splice variant mRNAs varies depending upon brain region. Examination of neuropeptide promoter regulation by ERbeta splice variants demonstrates that ERbeta functions as a constitutively active transcription factor. Moreover, it appears that splice variation of ERbeta alters its ability to regulate transcription in a promoter-dependent and ligand-dependent fashion.

In search of neuroprotective therapies based on the mechanisms of estrogens

Although estradiol is a neuroprotective factor, estrogen therapy in older women increases the risk of adverse cognitive outcomes and poses additional peripheral risks, requiring careful use of estrogenic compounds as treatments for neurodegenerative conditions or neural injury. Potential alternatives to estrogen therapy to promote neuroprotection might include treatment with molecules that are able to interact with estrogen receptors, with alternative mechanisms of action, or with molecules that induce local estradiol synthesis in the brain, or a combination of all. However, before considering the broad clinical applications, more basic research is required to clarify the mechanisms of action and potential risks of some of these estrogen-based treatments.

Differential vascular adaptive response to stress exposure in male and female rats: role of gonadal hormones and endothelial cells

Although there are reports concerning a vascular adaptive response to stress in males, this is not yet defined in females. The aim of this study was to delineate functional gender differences in the rat vascular adaptive response to stress and to determine the ability of sex hormones to modulate the stress-induced vascular adaptive response. Responses to noradrenaline were evaluated in aortas, with and without endothelium, from intact, gonadectomized and gonadectomized-hormone-replaced males and females submitted or not to stress (2-h immobilization). Reactivity of the aorta of stressed and non-stressed intact males and females (n = 6-14 per group) was also examined in the presence of L-NAME or indomethacin. Stress decreased and gonadectomy increased maximal responses to noradrenaline in aortas with intact endothelium from both genders. Stress also reduced noradrenaline potency in males. In females, but not males, stress decreased the gonadectomy-induced noradrenaline hyper-reactivity to near that of intact non-stressed rats. Hormone replacement restored the gonadectomy-induced impaired vascular adaptive response to stress. L-NAME, but not indomethacin, abolished the stress-induced decrease in aorta reactivity of males and females. None of the procedures altered reactivity of aortas denuded of endothelium.

CONCLUSION

Stress-induced vascular adaptive responses show gender differences. The magnitude of the adaptive response is dependent on testicular hormones and involves endothelial nitric oxide-system hyperactivity.

Androgen and estrogen receptor-beta distribution within spinal-projecting and neurosecretory neurons in the paraventricular nucleus of the male rat

Activation of the hypothalamic-pituitary-adrenal (HPA) axis is initiated by neurosecretory neurons residing within the medial parvicellular part of the hypothalamic paraventricular nucleus (PVN). Despite the potency by which sex steroids operate on HPA and medial parvocellular responses to stress, previous topographic and phenotypic studies suggest that gonadal steroid hormone receptors are scarcely, if at all, expressed by PVN neurons controlling anterior pituitary corticotropes. Guided by the pattern of retrograde accumulation of fluorogold, we used a direct connectional approach to define the distribution of androgen receptors (AR) and estrogen-beta receptors (ER-beta) within populations of neurosecretory vs. nonneurosecretory neurons in the PVN. Juxtaposition of AR-immunoreactivity (ir) and ER-beta mRNA to the pattern of intravenous fluorogold labeling showed these steroid hormone receptors to be concentrated within portions of the PVN devoid of neurosecretory neurons. Superimposing receptor profiles onto the pattern of spinal retrograde labeling confirmed a selective distribution of AR-ir within autonomic-related cells of the medial parvocellular division, including its dorsal, lateral, and ventral medial components. ER-beta mRNA expression was likewise concentrated within regions accumulating spinal tracer, highest within the ventral aspect of the PVN. These results indicate a direct influence of gonadal hormones on preautonomic effector neurons and remain in keeping with an indirect influence of androgens on adrenocorticotropin-regulating neurons in the PVN.

Effect of sex hormones on renal estrogen and angiotensin type 1 receptors in female and male rats

Although the mechanisms are not understood, evidence suggests that 17β-estradiol (E2) confers protection from cardiovascular and renal complications in many diseases. We have reported that E2 decreases angiotensin type 1 receptors (AT1Rs) in different tissues and hypothesize that E2 exerts tonic inhibition on AT1Rs, reducing effects of ANG II. This study determined the effects of E2 and dihydrotestosterone (DHT) on cortical estrogen receptors (ERs) and glomerular AT1R binding in rats. Animals underwent sham operation, ovariectomy (Ovx) or orchidectomy (Cas) and were treated (Ovx ± E2; Cas ± DHT) for 3 wk. Cortical ERα protein was 2.5 times greater, and ERβ was 80% less in females vs. males ( P < 0.01). Glomerular AT1R binding was lower in females than males [4,657 ± 838 vs. 7,457 ± 467 counts per minute (cpm), P < 0.01]. Ovx reduced ERα protein by 50%, whereas E2 increased ERα expression after Ovx. The decrease in cortical ERα in Ovx rats was associated with a significant increase in AT1R binding (6,908 ± 609 cpm), and E2 prevented this increase. There was no change in ERα or AT1R binding following Cas ± DHT (25 mg) treatment, although Cas did elevate cortical ERβ (P < 0.01). Interestingly, the high dose DHT (200 mg) elevated ERα 150% above intact levels and profoundly decreased AT1R binding (1,824 ± 705 cpm, P < 0.001 vs. intact male). This indicates that under normal conditions, glomerular AT1R binding is significantly greater in male than female animals, which may be important in development of cardiovascular and renal disease in males. Furthermore, E2 regulates ERα and is inversely associated with glomerular AT1R binding, supporting our hypothesis that E2 tonically suppresses AT1Rs and suggesting a potential mechanism for the protective effects of estrogen.

Androgens regulate the development of neuropathology in a triple transgenic mouse model of Alzheimer's disease

Normal age-related testosterone depletion in men is a recently identified risk factor for Alzheimer's disease (AD), but how androgen loss affects the development of AD is unclear. To investigate the relationship between androgen depletion and AD, we compared how androgen status affects the progression of neuropathology in the triple transgenic mouse model of AD (3xTg-AD). Adult male 3xTg-AD mice were sham gonadectomized (GDX) or GDX to deplete endogenous androgens and then exposed for 4 months to either the androgen dihydrotestosterone (DHT) or to placebo. In comparison to gonadally intact 3xTg-AD mice, GDX mice exhibited robust increases in the accumulation of beta-amyloid (Abeta), the protein implicated as the primary causal factor in AD pathogenesis, in both hippocampus and amygdala. In parallel to elevated levels of Abeta, GDX mice exhibited significantly impaired spontaneous alternation behavior, indicating deficits in hippocampal function. Importantly, DHT treatment of GDX 3xTg-AD mice attenuated both Abeta accumulation and behavioral deficits. These data demonstrate that androgen depletion accelerates the development of AD-like neuropathology, suggesting that a similar mechanism may underlie the increased risk for AD in men with low testosterone. In addition, our finding that DHT protects against acceleration of AD-like neuropathology predicts that androgen-based hormone therapy may be a useful strategy for the prevention and treatment of AD in aging men.

Ultrastructure and Estrogen Regulation of the Lymphatic Stomata of Ovarian Bursa in Mice

The ovarian bursa is a key player in maintaining adaptive ovarian microenvironment for ovulation. The lymphatic stomata are believed to be a major contributor to execute the function of the ovarian bursa, whereas little is known about their ultrastructure and regulation. Here, we examined the ultrastructure of lymphatic stomata in mouse ovarian bursa by scanning electron microscopy and transmission electron microscopy and investigated its regulation by estrogen. We found that the mesothelium on the visceral layer of mouse ovarian bursa was composed of the cuboidal and flattened cells. The lymphatic stomata with round and oval shapes were mainly among the cuboidal cells. The particles, cells, and fluid passed through the stomata and entered into the lymphatic drainage unit composed of connective tissue and lymphatic endothelial cells beneath the stomata. We also used trypan blue as a tracer and found that the absorption of trypan blue through the lymphatic stomata was increased by estrogen that enlarged the average opening area of lymphatic stomata. Furthermore, we detected that there existed estrogen receptors in the nuclei of the mesothelial cells on the visceral ovarian bursa by using immunoelectron microscopy. Taken together, these data suggest that both the absorption and opening area of the lymphatic stomata in mouse ovarian bursa may be influenced by estrogen.

Preclinical characterization of selective estrogen receptor beta agonists: new insights into their therapeutic potential

It has now been over 10 years since Jan-Ake Gustafsson revealed the existence of a second form of the estrogen receptor (ERbeta) at a 1996 Keystone Symposium. Since then, substantial success has been made in distinguishing its potential biological functions from the previously known form (now called ERalpha) and how it might be exploited as a drug target. Subtype selective agonists have been particularly useful in this regard and suggest that ERbeta agonists may be useful for a variety of clinical applications without triggering classic estrogenic side effects such as uterine stimulation. These applications include inflammatory bowel disease, rheumatoid arthritis, endometriosis, and sepsis. This manuscript will summarize illustrative data for three ERbeta selective agonists, ERB-041, WAY-202196, and WAY-200070.

Regulation of adenosine 5',monophosphate-activated protein kinase and lipogenesis by androgens contributes to visceral obesity in an estrogen-deficient state

Menopause is associated with an accumulation of visceral fat. An emerging concept suggests that relatively elevated levels of circulating androgens, compared with estrogens in postmenopausal women, underlie this shift in body fat distribution. In this study we administered dihydrotestosterone (DHT) to ovariectomized mice to examine the effect of relative androgen excess on adipose tissue distribution and function in estrogen-deficient mice. Compared with controls, DHT-treated mice exhibited increased body weight and visceral fat mass associated with triglyceride accumulation. Phosphorylation of AMP-activated protein kinase (AMPK) and acetyl CoA carboxylase was significantly decreased by DHT in visceral fat. In 3T3-L1 cells, DHT decreased phosphorylation of AMPK in a dose-dependent manner. In addition, DHT increased the expression of lipogenic genes (fatty acid synthase, sterol regulatory element binding protein-2, and lipoprotein lipase) in visceral fat. These data provide the first in vivo evidence that an increased androgen to estrogen ratio can promote visceral fat accumulation by inhibiting AMPK activation and stimulating lipogenesis.

Estrogen in the paraventricular nucleus attenuates L-glutamate-induced increases in mean arterial pressure through estrogen receptor beta and NO

Estrogen (E2) acts in the brain to decrease blood pressure (BP) responses to psychological stress. A likely site for the effects of E2 is the hypothalamic paraventricular nucleus (PVN), an important regulator of autonomic functions. We studied the effects of E2 in the PVN on BP and heart rate (HR) responses to l-glutamate injections into the PVN of male urethane-anesthetized rats. Microinjections of l-glutamate (50 nmol) into the PVN increased BP by 14+/-2.5 mm Hg and HR by 30+/-5.6 bpm. Microinjections of E2 (0.1, 1, and 10 pmol) into the PVN 30 minutes before l-glutamate dose-dependently attenuated the pressor response by 25%, 34%, and 59%, respectively, but did not affect HR. We determined that E2 receptor (ER) beta mediates the effect of E2, because activation of ERbeta with diarylpropionitrile (50 pmol) attenuated the response by 57%, whereas activation of ERalpha with propyl-pyrazole-triol (20 pmol) had no effect. Furthermore, inhibition of ERbeta with R,R-tetrahydrochrysene (50 pmol) blocked the effect of E2, but inhibition of ERalpha with methyl-piperidino-pyrazole (1 nmol) did not. Finally, we found that the effect of E2 is mediated by NO, because the NO synthase (NOS) inhibitor, N(G)-nitro-l-arginine methyl ester (2 nmol), the neuronal NOS inhibitor, 7-nitroindazole sodium salt (0.1 pmol), and the endothelial NOS inhibitor, N5-(1-iminoethyl)-l-ornithine (200 pmol) blocked the effect of E2. The effect was partially blocked with the gamma-aminobutyric acid(A) receptor inhibitor bicuculline. Our results demonstrate that E2 in the PVN attenuates the l-glutamate-induced pressor response and that this effect is mediated by ERbeta, NO produced by neuronal NO synthase and eNOS, and partly by gamma-aminobutyric acid.

Acute estradiol application increases inward and decreases outward whole-cell currents of neurons in rat hypothalamic ventromedial nucleus

Acute estradiol (E2) can potentiate the excitatory responses of hypothalamic ventromedial nucleus (VMN) neurons to neurotransmitters. To investigate the mechanism(s) underlying the potentiation, the whole-cell patch voltage clamp technique was used to study VMN neurons in hypothalamic slices prepared from female juvenile (3-5 weeks) rats. A voltage step and/or ramp was applied every 5 min to evoke whole-cell currents before, during and after a treatment with E2 (10 nM), corticosterone (10 nM) or vehicle for up to 20 min. Acute E2 increased inward currents in 38% of neurons tested. Their average peak inward current amplitudes started to increase within 5 min and reached the maximum of 163% of pretreatment level (Pre) at 20 min of treatment before recovering toward Pre. These increases are significantly greater than the Pre and corresponding vehicle controls and non-responsive neurons. Outward currents were decreased significantly by E2 in 27% of E2-treated cells, down to 60% of Pre levels. E2 also appeared to affect the kinetics of the inward and outward currents of estrogen-responsive neurons. Whenever observed, the effects of acute E2 were reversible after a 5- to 10-min washing. Probability analysis indicates that E2 affected the inward and the outward currents independently. The E2 effects are specific in that they were not produced by similar treatment with vehicle or corticosterone. Pharmacological characterizations using ion replacement and channel blockers showed that the inward currents were mediated practically all by Na(+) and the outward currents mainly by K(+). Thus, acute E2 can enhance inward Na(+) and attenuate outward K(+) currents. Since both effects will lead to an increase in neuronal excitability, they may explain our previous observation that E2 potentiates the excitation of VMN neurons.