Antisense oligodeoxynucleotides for estrogen receptor-beta and alpha attenuate estradiol's modulation of affective and sexual behavior, respectively

Antidepressant- and Anxiolytic-like Effects of Pomegranate: Is It Acting by Common or Well-Known Mechanisms of Action?

The pharmacological effects of pomegranates have been described considering metabolic aspects such as hypoglycemic and hypolipidemic activities. The pomegranate extract has activity on the central nervous system (CNS) as a natural antidepressant and anxiolytic. The chemical composition of pomegranates is complex since the bioactive compounds are multiple secondary metabolites that have been identified in the extracts derived from the peel, seed, flowers, leaves, or in their combination; so, it has not been easy to identify an individual compound as responsible for its observed pharmacological properties. From this point of view, the present review analyzes the effects of crude extracts or fractions of pomegranates and their possible mechanisms of action concerning antidepressant- and anxiolytic-like effects in animal models. Serotonin receptors, estrogen receptors, the peroxisome proliferator-activated receptor gamma (PPARγ), or monoamine oxidase enzymes, as well as potent antioxidant and neuroplasticity properties, have been described as possible mediators involved in the antidepressant- and anxiolytic-like behaviors after pomegranate treatment. The pharmacological effects observed on the CNS in experimental models associated with a specific stress level suggest that pomegranates could simultaneously modulate the stress response by activating several targets. For the present review, scientific evidence was gathered to integrate it and suggest a possible pathway for mediators to be involved in the mechanisms of action of the pomegranate's antidepressant- and anxiolytic-like effects. Furthermore, the potential benefits are discussed on comorbid conditions with anxiety and depression, such as perimenopause transition and pain.

Reproductive function and behaviors: an update on the role of neural estrogen receptors alpha and beta

Infertility is becoming a major public health problem, with increasing frequency due to medical, environmental and societal causes. The increasingly late age of childbearing, growing exposure to endocrine disruptors and other reprotoxic products, and increasing number of medical reproductive dysfunctions (endometriosis, polycystic ovary syndrome, etc.) are among the most common causes. Fertility relies on fine-tuned control of both neuroendocrine function and reproductive behaviors, those are critically regulated by sex steroid hormones. Testosterone and estradiol exert organizational and activational effects throughout life to establish and activate the neural circuits underlying reproductive function. This regulation is mediated through estrogen receptors (ERs) and androgen receptor (AR). Estradiol acts mainly via nuclear estrogen receptors ERα and ERβ. The aim of this review is to summarize the genetic studies that have been undertaken to comprehend the specific contribution of ERα and ERβ in the neural circuits underlying the regulation of the hypothalamic-pituitary-gonadal axis and the expression of reproductive behaviors, including sexual and parental behavior. Particular emphasis will be placed on the neural role of these receptors and the underlying sex differences.

Estrogen Receptor α Agonist is Beneficial for Young Female Rats Against Chronic Unpredicted Mild Stress-Induced Depressive Behavior and Cognitive Deficits

BACKGROUND

Women are reported more likely to develop depression and dementia. However, the involved mechanism is poorly understood.

OBJECTIVE

Here, we clarified the role of estrogen receptor α (ERα) in depression and cognitive deficit in young female rats.

METHODS

After being exposed to 7-weeks' chronic unpredicted mild stress (CUMS), the depression resilient rats (Res rats) and depressed rats (Dep rats) were selected according to their records in sucrose preference test, forced swimming test, and open field test. Their cognition abilities were tested by Morris water maze. Proteomic assay, immunoprecipitation, western blotting, immunohistochemical, and Nissl staining were also used to understand the involved mechanism.

RESULTS

Compared with control rats and Res rats, Dep rats showed cognitive deficits and hippocampal impairments revealed by proteomic data, neuron losses, increased cleaved caspase-3, β-catenin phosphorylation, and glycogen synthase kinase3β (GSK3β) activation. As ERα, but not ERβ, was found declined in hippocampi of Dep rats, 4,4k,4a-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol (PPT, an ERα agonist, 1 mg/kg/day), was used to treat Dep rats (Dep + PPT). Twenty days later, the depressive behaviors, cognition deficits, and hippocampal neuron loss were rescued in Dep + PPT rats. Furthermore, Res and Dep + PPT rats had higher levels of β-catenin combined with ERα and lower levels of β-catenin combined with GSK3β than Dep rats in hippocampi.

CONCLUSION

These results demonstrated hippocampal ERα is an important pro-resilient factor in CUMS-induced depressive behaviors and cognitive deficits. It was also given that the neuroprotection afforded by hippocampal ERα/Wnt interactions have significant implications for cognition and emotion in young females.

Pro-social and anxiolytic-like behavior following a single 24-h exposure to 17β-estradiol in adult male zebrafish

Estradiol (17β-estradiol, E₂) is a crucial estrogen hormone that regulates sexual, cognitive, social and affective behaviors in various species. However, complex central nervous system (CNS) effects of E₂, including its activity in males, remain poorly understood. The zebrafish (Danio rerio) is rapidly becoming a powerful novel model system in translational neuroscience research. Here, we evaluate the effects of a single 24-h exposure to 20 μg/L of E₂ on behavioral and endocrine (cortisol) responses in adult male zebrafish. Overall, E₂ exerted pro-social effect in the social preference test, reduced whole-body cortisol levels, elevated exploration in the novel tank test and increased the shoal size in the shoaling test, indicative of an anxiolytic-like profile of this hormone in male zebrafish. Supporting mounting human and rodent evidence on the role of E₂ in behavioral regulation, the observed pro-social and anxiolytic-like effects of E₂ in male zebrafish reinforce the use of this aquatic organism in studying steroid-mediated CNS mechanisms of complex affective and social behaviors.

Behavioral responses to emotional challenges in female rats living in a seminatural environment: The role of estrogen receptors

Estrogen receptors (ERs) are involved in sexual as well as non-sexual behaviors. In the present study we assessed the effects of stimuli inducing positive or negative affect on sociosexual, exploratory and fear-related behaviors of female rats housed in groups (4 females, 3 males) in a seminatural environment. Ovariectomized females were treated with oil, 17β‑estradiol benzoate (EB, 18 μg/kg), the ERα agonist propylpyrazoletriol (PPT), or the ERβ agonist diarylpropionitrile (DPN) (both 2 × 10 mg/rat). On the test day, the females were exposed to a sequence of events consisting of lavender odor, Mozart's Sonata for Two Pianos K448, chocolate pellets, white noise and fox odor (2,3,5‑Trimethyl‑3‑thiazoline, TMT). All these events are known to induce positive or negative affect. Behavior was carefully observed from the video record. White noise suppressed sexual behaviors and reduced the time spent in the open area of the environment. TMT had no consistent effect whereas exposure to music caused avoidance of the open area. Exposure to chocolate increased exploratory and social behavior. Lavender odor enhanced exploratory behavior. PPT and EB stimulated sexual behaviors, whereas DPN was ineffective. Co-occurrence analyses of the sequence of behavioral patterns revealed that PPT and EB consistently belonged to clusters different from oil and DPN, whereas DPN was separate from oil only under fear-inducing experimental conditions. These data, from a procedure with external validity, confirm that the ERα is crucial for sexual behaviors, that these behaviors are reduced under stressful conditions, and that the ERβ may have some role in fear-related behaviors.

Epigenetic regulation of motivated behaviors by histone deacetylase inhibitors

Growing evidence has begun to elucidate the contribution of epigenetic mechanisms in the modulation and maintenance of gene expression and behavior. Histone acetylation is one such epigenetic mechanism, which has been shown to profoundly alter gene expression and behaviors. In this review, we begin with an overview of the major epigenetic mechanisms including histones acetylation. We next focus on recent evidence about the influence of environmental stimuli on various motivated behaviors through histone acetylation and highlight how histone deacetylase inhibitors can correct some of the pathologies linked to motivated behaviors including substance abuse, feeding and social attachments. Particularly, we emphasize that the effects of histone deacetylase inhibitors on motivated behaviors are time and context-dependent.

Winning agonistic encounters increases testosterone and androgen receptor expression in Syrian hamsters

Winning aggressive disputes is one of several experiences that can alter responses to future stressful events. We have previously tested dominant and subordinate male Syrian hamsters in a conditioned defeat model and found that dominant individuals show less change in behavior following social defeat stress compared to subordinates and controls, indicating a reduced conditioned defeat response. Resistance to the effects of social defeat in dominants is experience-dependent and requires the maintenance of dominance relationships for 14days. For this study we investigated whether winning aggressive interactions increases plasma testosterone and whether repeatedly winning increases androgen receptor expression. First, male hamsters were paired in daily 10-min aggressive encounters and blood samples were collected immediately before and 15min and 30min after the formation of dominance relationships. Dominants showed an increase in plasma testosterone at 15min post-interaction compared to their pre-interaction baseline, whereas subordinates and controls showed no change in plasma testosterone. Secondly, we investigated whether 14days of dominant social status increased androgen or estrogen alpha-receptor immunoreactivity in brain regions that regulate the conditioned defeat response. Dominants showed more androgen, but not estrogen alpha, receptor immuno-positive cells in the dorsal medial amygdala (dMeA) and ventral lateral septum (vLS) compared to subordinates and controls. Finally, we showed that one day of dominant social status was insufficient to increase androgen receptor immunoreactivity compared to subordinates. These results suggest that elevated testosterone signaling at androgen receptors in the dMeA and vLS might contribute to the reduced conditioned defeat response exhibited by dominant hamsters.

Estrogen receptor α and β are involved in the activation of lordosis behavior in estradiol-primed rats

The present study was designed to assess the participation of estrogen receptors alpha (ERα) and beta (ERβ) in the short-term facilitation of lordosis behavior in ovariectomized (ovx), estradiol (E₂) primed rats. In experiment 1, dose response curves for PPT and DPN (ERα and ERβ agonists, respectively) facilitation of lordosis behavior (lordosis quotient and lordosis score) were established by infusing these agonists into the right lateral ventricle (icv) in female rats injected 40h previously with 5μg of E₂ benzoate. PPT doses of 0.08 and 0.4ng produced high lordosis quotients starting at 30min and continuing at 120 and 240min post-injection. DPN induced high levels of lordosis behavior at all times tested. However, the intensity of lordosis induced by both agonists was weak. In experiment 2, we tested the involvement of each ER in facilitation of lordosis by icv infusion of MPP (ERα-selective antagonist) or PHTPP (ERβ-selective antagonist) prior to infusion of 2ng of free E₂. Icv infusion of either MPP or PHTPP 30min before free E2 significantly depressed E₂ facilitation of lordosis. The results suggest that both forms of ER are involved in the short-latency facilitation of lordosis behavior in E₂-primed rats.

Improvement of neurological disorders in postmenopausal model rats by administration of royal jelly

OBJECTIVE

Royal jelly (RJ) from honeybees (Apis mellifera) has estrogenic activity. Estrogen deficiency after menopause leads to a high risk of memory impairment and depression as well as metabolic syndrome and osteoporosis. We here investigated the effect of RJ on memory impairment and depression-like behaviors in ovariectomized (OVX) rats.

METHODS

OVX rats were administered with RJ for 82 days. Hippocampus-dependent spatial memory and depression-like behaviors were assessed by the Morris water maze test and the forced swimming test, respectively. The weights of body, brain and uterus and the contents of protein and myelin galactolipids including galactosylceramide and sulfatide were measured.

RESULTS

Memory impairment and depression-like behaviors in OVX rats were recovered to the levels of sham-operated rats by RJ administration. Increased body weight and decreased uterine weight in OVX rats were recovered to the levels of sham-operated rats by 17β-estradiol (E2) administration but not by RJ administration. In contrast, brain weight was slightly increased by RJ administration but not by E2 administration. The contents of protein and myelin galactolipids were higher in the brains of RJ-administered OVX rats than in the brains of E2-administered OVX rats.

CONCLUSION

The results suggest that RJ has a beneficial effect on neurological symptoms of a menopausal disorder.

Revisiting the neural role of estrogen receptor beta in male sexual behavior by conditional mutagenesis

Estradiol derived from neural aromatization of gonadal testosterone plays a key role in the perinatal organization of the neural circuitry underlying male sexual behavior. The aim of this study was to investigate the contribution of neural estrogen receptor (ER) β in estradiol-induced effects without interfering with its peripheral functions. For this purpose, male mice lacking ERβ in the nervous system were generated. Analyses of males in two consecutive tests with a time interval of two weeks showed an effect of experience, but not of genotype, on the latencies to the first mount, intromission, pelvic thrusting and ejaculation. Similarly, there was an effect of experience, but not of genotype, on the number of thrusts and mating length. Neural ERβ deletion had no effect on the ability of males to adopt a lordosis posture in response to male mounts, after castration and priming with estradiol and progesterone. Indeed, only low percentages of both genotypes exhibited a low lordosis quotient. It also did not affect their olfactory preference. Quantification of tyrosine hydroxylase- and kisspeptin-immunoreactive neurons in the preoptic area showed unaffected sexual dimorphism of both populations in mutants. By contrast, the number of androgen receptor- and ERα-immunoreactive cells was significantly increased in the bed nucleus of stria terminalis of mutant males. These data show that neural ERβ does not play a crucial role in the organization and activation of the neural circuitry underlying male sexual behavior. These discrepancies with the phenotype of global ERβ knockout models are discussed.

Effects of Long-Term Treatment with Estradiol and Estrogen Receptor Subtype Agonists on Serotonergic Function in Ovariectomized Rats

Acute estradiol treatment was reported to slow the clearance of serotonin via activation of estrogen receptors (ER)β and/or GPR30 and to block the ability of a selective serotonin reuptake inhibitor (SSRI) to slow serotonin clearance via activation of ERα. In this study, the behavioral consequences of longer-term treatments with estradiol or ER subtype-selective agonists and/or an SSRI were examined in the forced swim test (FST). Ovariectomized rats were administered the following for 2 weeks: estradiol, ERβ agonist (diarylpropionitrile, DPN), GPR30 agonist (G1), ERα agonist (PPT), and/or the SSRI sertraline. Similar to sertraline, longer-term treatment with estradiol, DPN or G1 induced an antidepressant-like effect. By contrast, PPT did not, even though it blocked the antidepressant-like effect of sertraline. Uterus weights, used as a peripheral measure of estrogenic activity, were increased by estradiol and PPT but not DPN or G1 treatment. A second part of this study investigated, using Western blot analyses in homogenates from hippocampus, whether these behavioral effects are accompanied by changes in the activation of specific signaling pathways and/or TrkB. Estradiol and G1 increased phosphorylation of Akt, ERK and TrkB. These effects were similar to those obtained after treatment with sertraline. Treatment with DPN increased phosphorylation of ERK and TrkB, but it did not alter that of Akt. Treatment with PPT increased phosphorylation of Akt and ERK without altering that of TrkB. In conclusion, activation of at least TrkB and possibly ERK may be involved in the antidepressant-like effect of estradiol, ERβ and GPR30 agonists whereas Akt activation may not be necessary.

Endogenous nociceptin system involvement in stress responses and anxiety behavior

The mechanisms underpinning stress-related behavior and dysfunctional events leading to the expression of neuropsychiatric disorders remain incompletely understood. Novel candidates involved in the neuromodulation of stress, mediated both peripherally and centrally, provide opportunities for improved understanding of the neurobiological basis of stress disorders and may represent targets for novel therapeutic development. This chapter provides an overview of the mechanisms by which the opioid-related peptide, nociceptin, regulates the neuroendocrine stress response and stress-related behavior. In our research, we have employed nociceptin receptor antagonists to investigate endogenous nociceptin function in tonic control over stress-induced activity of the hypothalamo-pituitary-adrenal axis. Nociceptin demonstrates a wide range of functions, including modulation of psychological and inflammatory stress responses, modulation of neurotransmitter release, immune homeostasis, in addition to anxiety and cognitive behaviors. Greater appreciation of the complexity of limbic-hypothalamic neuronal networks, together with attention toward gender differences and the roles of steroid hormones, provides an opportunity for deeper understanding of the importance of the nociceptin system in the context of the neurobiology of stress and behavior.

Periodic Estrogen Receptor-Beta Activation: A Novel Approach to Prevent Ischemic Brain Damage

In women, the risk for cerebral ischemia climbs rapidly after menopause. At menopause, production of ovarian hormones; i.e., progesterone and estrogen, slowly diminishes. Estrogen has been suggested to confer natural protection to premenopausal women from ischemic stroke and some of its debilitating consequences. This notion is also strongly supported by laboratory studies showing that a continuous chronic 17β-estradiol (E2; a potent estrogen) regimen protects brain from ischemic injury. However, concerns regarding the safety of the continuous intake of E2 were raised by the failed translation to the clinic. Recent studies demonstrated that repetitive periodic E2 pretreatments, in contrast to continuous E2 treatment, provided neuroprotection against cerebral ischemia in ovariectomized rats. Periodic E2 pretreatment protects hippocampal neurons through activation of estrogen receptor subtype beta (ER-β). Apart from neuroprotection, periodic activation of ER-β in ovariectomized rats significantly improves hippocampus-dependent learning and memory. Difficulties in learning and memory loss are the major consequence of ischemic brain damage. Periodic ER-β agonist pretreatment may provide pharmacological access to a protective state against ischemic stroke and its debilitating consequences. The use of ER-β-selective agonists constitutes a safer target for future research than ER-α agonist or E2, inasmuch as it lacks the ability to stimulate the proliferation of breast or endometrial tissue. In this review, we highlight ER-β signaling as a guide for future translational research to reduce cognitive decline and cerebral ischemia incidents/impact in post-menopausal women, while avoiding the side effects produced by chronic E2 treatment.

Activation of the GPR30 receptor promotes lordosis in female mice

BACKGROUND/AIMS

Estrogens are important effectors of reproduction and are critical for upregulating female reproductive behavior or lordosis in females. In addition to the importance of transcriptional regulation of genes by 17β-estradiol-bound estrogen receptors (ER), extranuclear signal transduction cascades such as protein kinase A (PKA) are also important in regulating female sexual receptivity. GPR30 (G-protein coupled receptor 30), also known as GPER1, a putative membrane ER (mER), is a G protein-coupled receptor that binds 17β-estradiol with an affinity that is similar to that possessed by the classical nuclear ER and activates both PKA and extracellular-regulated kinase signaling pathways. The high expression of GPR30 in the ventromedial hypothalamus, a region important for lordosis behavior as well as kinase cascades activated by this receptor, led us to hypothesize that GPR30 may regulate lordosis behavior in female rodents.

METHOD

In this study, we investigated the ability of G-1, a selective agonist of GPR30, to regulate lordosis in the female mouse by administering this agent prior to progesterone in an estradiol-progesterone priming paradigm prior to testing with stud males.

RESULTS

As expected, 17β-estradiol benzoate (EB), but not sesame oil, increased lordosis behavior in female mice. G-1 also increased lordosis behavior in female mice and decreased the number of rejective responses towards male mice, similar to the effect of EB. The selective GPR30 antagonist G-15 blocked these effects.

CONCLUSION

This study demonstrates that activation of the mER GPR30 stimulates social behavior in a rodent model in a manner similar to EB.

Oral contraceptives and nicotine synergistically exacerbate cerebral ischemic injury in the female brain

Oral contraceptives (OC) and smoking-derived nicotine (N) are known to synergistically increase the risk and severity of cerebral ischemia in women. Although it has been known for some time that long-term use of OC and nicotine will have an increased risk of peripheral thrombus formation, little is known about how the combination of OC and nicotine increases severity of brain ischemia. Recent laboratory studies simulating the conditions of nicotine exposure produced by cigarette smoking and OC regimen of women in female rats confirms that the severity of ischemic hippocampal damage is far greater in female rats simultaneously exposed to OC than to nicotine alone. These studies also demonstrated that the concurrent exposure of OC and nicotine reduces endogenous 17β-estradiol levels and inhibits estrogen signaling in the brain of female rats. The endogenous 17β-estradiol plays a key role in cerebrovascular protection in women during their pre-menopausal life and loss of circulating estrogen at reproductive senescence increases both the incidence and severity of cerebrovascular diseases. Therefore, OC and nicotine induced severe post-ischemic damage might be a consequence of lack of estrogen signaling in the brain. In the present review we highlight possible mechanisms by which OC and nicotine inhibits estrogen signaling that could be responsible for severe ischemic damage in females.

Dissociating behavioral, autonomic, and neuroendocrine effects of androgen steroids in animal models

Developments in behavioral assessment, autonomic and/or baseline reactivity, psychopharmacology, and genetics, have contributed significantly to the assessment of performance-enhancing drugs in animal models. Particular classes of steroid hormones: androgenic steroids are of interest. Anecdotally, the performance enhancing effects of androgens are attributed to anabolic events. However, there is a discrepancy between anecdotal evidence and investigative data. While some androgen steroids may promote muscle growth (myogenesis), effects of androgens on performance enhancement are not always seen. Indeed, some effects of androgens on performance may be attributable to their psychological and cardiovascular effects. As such, we consider androgen effects in terms of their behavioral, autonomic, and neuroendocrine components. Techniques are discussed in this chapter, some of which are well established, while others have been more recently developed to study androgen action. Androgens may be considered for their positive impact, negative consequence, or psychotropic properties. Thus, this review aims to elucidate some of the effects and/or mechanisms of androgens on behavioral, autonomic, and/or neuroendocrine assessment that may underlie their controversial performance enhancing effects.

Sexual responses of the male rat medial preoptic area and medial amygdala to estrogen I: site specific suppression of estrogen receptor alpha

Male rat copulation is mediated by estrogen-sensitive neurons in the medial preoptic area (MPO) and medial amygdala (MEA); however, the mechanisms through which estradiol (E(2)) acts are not fully understood. We hypothesized that E(2) acts through estrogen receptor α (ERα) in the MPO and MEA to promote male mating behavior. Antisense oligodeoxynucleotides (AS-ODN) complementary to ERα mRNA were bilaterally infused via minipumps into either brain area to block the synthesis of ERα, which we predicted would reduce mating. Western blot analysis and immunocytochemistry revealed a knockdown of ERα expression in each brain region; however, compared to saline controls, males receiving AS-ODN to the MPO showed significant reductions in all components of mating, whereas males receiving AS-ODN to the MEA continued to mate normally. These results suggest that E(2) acts differently in these brain regions to promote the expression of male rat sexual behavior and that ERα in the MPO, but not in the MEA, promotes mating.

The anxiolytic effect of testosterone in the rat is mediated via the androgen receptor

Endogenous and exogenous testosterone affects several behavioural traits as shown in human and animal studies. The effects of testosterone can be mediated via androgen or oestrogen receptors, but also via rapid non-genomic effects. The aim of this study was to evaluate whether a single testosterone injection has effects, mediated via the androgen receptor, on anxiety in intact male rats. We hypothesised that administration of testosterone will have an anxiolytic effect, mediated by the androgen receptor. Intact adult male Wistar rats were divided into groups: control, flutamide, testosterone and testosterone with flutamide. Testosterone and flutamide (as an androgen receptor blocker) were applied once, intramuscularly, at a dose of 5mg/kg. Twenty four hours later, rats underwent the following behavioural tests to analyse anxiety: open field test, elevated plus maze and light-dark box. Testosterone was measured in plasma to confirm elevated levels in groups that received testosterone. The levels of testosterone were 2.5-3 fold higher amongst rats administered with testosterone compared to controls. Flutamide did not affect plasma testosterone concentrations. Testosterone administration had no effect on anxiety in the open field and elevated plus maze. In the light-dark transition task, testosterone increased the time spent in the light part of the maze by 80%, an effect which was blocked by flutamide, and which was in support of our hypothesis. Flutamide-treated rats spent more time in the central square of the open field. Using the light-dark box we have shown that a single injection of testosterone decreases anxiety in adult male rats. This effect of increased testosterone was mediated via the androgen receptor as flutamide blocked the anxiolytic effect of exogenous testosterone. Treatment with flutamide blocked the effects of endogenous testosterone and had anxiolytic effects in the open field, suggesting a non-linear relationship between genomic effects of T and anxiety.

Comparison of the effects of estradiol and progesterone on serotonergic function

BACKGROUND

Ovarian hormones may contribute to the vulnerability to depression, as well as to the response to antidepressants (ADs). Previously, we reported that acute systemic treatment with estradiol or progesterone blocked the ability of the selective serotonin reuptake inhibitor, fluvoxamine, to inhibit serotonin transporter function in ovariectomized rats. In this study, behavioral consequences, as well as receptor mechanisms underlying these hormonal effects, were investigated.

METHODS

Using the forced swimming test, the acute effect of estradiol and/or progesterone on fluvoxamine's AD-like effects was investigated. Using in vivo chronoamperometry, the effect of local application of estradiol or progesterone into the hippocampus of ovariectomized rats on serotonin (5-HT) clearance, as well as on the ability of fluvoxamine to slow 5-HT clearance, were investigated.

RESULTS

The decreased immobility and increased swimming caused by fluvoxamine in the forced swimming test was blocked in rats treated with estradiol and/or progesterone. Local application of estradiol, but not progesterone, slowed 5-HT clearance and both hormones blocked the ability of fluvoxamine to slow 5-HT clearance. Use of hormone receptor agonists and antagonists, revealed that the effects of estradiol are mediated by activation of membrane, as well as nuclear estrogen receptors (ER). The AD-like effect of estradiol involved ER beta and G-protein coupled receptor 30, whereas its blockade of fluvoxamine's effects was ER alpha-mediated. The effects of progesterone occurred solely by activation of intracellular progesterone receptors.

CONCLUSIONS

Targeting of ER beta or G-protein coupled receptor 30 might reveal a strategy to permit beneficial effects of estrogen without its deleterious effect on selective serotonin reuptake inhibitor efficacy.

Maternal programming of reproductive function and behavior in the female rat

Parental investment can be used as a forecast for the environmental conditions in which offspring will develop to adulthood. In the rat, maternal behavior is transmitted to the next generation through epigenetic modifications such as methylation and histone acetylation, resulting in variations in estrogen receptor alpha expression. Natural variations in maternal care also influence the sexual strategy adult females will adopt later in life. Lower levels of maternal care are associated with early onset of puberty as well as increased motivation to mate and greater receptivity toward males during mating. Lower levels of maternal care are also correlated with greater activity of the hypothalamus-pituitary-gonadal axis, responsible for the expression of these behaviors. Contrary to the transition of maternal care, sexual behavior cannot simply be explained by maternal attention, since adoption studies changed the sexual phenotypes of offspring born to low caring mothers but not those from high caring dams. Indeed, mothers showing higher levels of licking/grooming have embryos that are exposed to high testosterone levels during development, and adoption studies suggest that this androgen exposure may protect their offspring from lower levels of maternal care. We propose that in the rat, maternal care and the in utero environment interact to influence the reproductive strategy female offspring display in adulthood and that this favors the species by allowing it to thrive under different environmental conditions.

Antidepressive and anxiolytic activity of selective estrogen receptor modulators in ovariectomized mice submitted to chronic unpredictable stress

Estradiol has antidepressive and anxiolytic actions. However, its therapeutic use is limited by its peripheral effects. Selective estrogen receptor modulators may represent an alternative to estradiol for the treatment of depressive symptoms. Here we report that tamoxifen and raloxifene decrease immobility time in the forced swim test and increases the time spent in open arms in the elevated plus maze in ovariectomized mice submitted to chronic unpredictable stress.

Long-term ovariectomy modulates the antidepressant-like action of estrogens, but not of antidepressants

Controversial results related to effectiveness of estrogen replacement therapy (ERT) to alleviate depression are frequently reported. The discrepancies could be related to (a) time when ERT is initiated after the beginning of menopause and/or (b) type of estrogen used. Furthermore, estrogens modulate the antidepressant effect of different compounds; therefore, the effectiveness of antidepressant drugs could also depend on the menopausal status. The aim of the present study was to analyze whether the time after estrogen decline can influence antidepressant-like effects of two estrogens and/or two antidepressants. Thus, the antidepressant-like actions of 17β-estradiol (E(2)), 17α-ethynyl-estradiol (EE(2)), fluoxetine (FLX) and desipramine (DMI) were studied at different periods (1, 3 and 12 weeks) after ovariectomy (OVX), using the forced swimming test (FST). Results showed that OVX increased depressive-like behavior only 1 week after OVX. The antidepressant-like actions of E(2), but not those of EE(2), were cancelled 12 weeks after OVX. Conversely, antidepressant-like actions of FLX and DMI were observed at 1, 3 and 12 weeks after OVX. In conclusion, while the antidepressant-like effects of estrogens depended on the time at which treatment is initiated after OVX as well as on the estrogenic compound used, antidepressant-like effects of FLX and DMI were not blocked by OVX.

Acquisition of sexual receptivity: roles of chromatin acetylation, estrogen receptor-alpha, and ovarian hormones

Sexually naïve, hormone-primed, C57BL/6J female mice are not receptive to mating attempts by conspecific males. Repeated experience with sexually active males and concurrent treatment with estradiol and progesterone gradually increases female receptivity over the course of five trials to maximal levels. Ovarian hormones activate their cognate nuclear steroid receptors estrogen receptor-α and progesterone receptor to induce female sexual receptivity. Nuclear receptors recruit coactivators of transcription that include histone acetyltransferases to hormone responsive genes. In this set of studies, we found that the histone deacetylase inhibitor sodium butyrate enhances the experiential acquisition of receptivity. Evidence is provided that the actions of sodium butyrate on receptivity require activated estrogen receptor-α and progesterone.

Antidepressant effects of estrogens: a basic approximation

The use of estrogenic compounds as antidepressants or as coadjuvants to facilitate the effect of antidepressants has reported controversial results, suggesting that many factors could influence their actions. This review analyzes, from a basic research perspective, the possible factors that may underlie the antidepressant action of estrogens alone or in combination. The possible mechanisms of action of estrogens alone and in combination with the selective serotonin reuptake inhibitor, fluoxetine, the selective noradrenaline reuptake inhibitor, desipramine, and the mixed serotonin/noradrenaline reuptake inhibitor, venlafaxine are reviewed, focusing on monoaminergic systems and estrogen receptors as main targets. The antidepressant effect of estrogens depends on the type of estrogen, treatment duration, doses, sex, time after ovariectomy, and age. Estrogens potentiate the antidepressant-like action of fluoxetine, venlafaxine, and desipramine and drastically shorten their latency of action. The antidepressant-like effect of estrogens alone or in combination with antidepressants seems to be mediated by monoaminergic and classic estrogen receptors, as WAY100635, an antagonist to the serotonin 1A receptor, idaxozan, an antagonist to alpha2 adrenergic receptors, and RU 58668, an estrogen receptor antagonist, blocked their antidepressant-like effect. In conclusion, estrogens produce antidepressant-like actions by themselves and importantly facilitate the action of clinically used antidepressants.

ERbeta: recent understanding of estrogen signaling

The discovery of a second estrogen receptor, ERbeta, and the finding that 5alpha-androstane-3beta,17beta-diol (3betaAdiol) strongly binds to ERbeta, have opened up a new aspect of estrogen signaling. Some of the major shifts in our understanding come from finding ERbeta in tissues which do not express ERalpha but are estrogen-responsive; these were called sites of 'indirect estrogen action'. Two key sites that fall into this category are the brain and the prostate. Studies of ERbeta in the past 10 years have led us to hypothesize that estrogen signaling depends on the balance between ERalpha and ERbeta, and that inadequate predominance of one or the other isoform could lead to disease.

The role of the estrogen receptor alpha in the medial amygdala and ventromedial nucleus of the hypothalamus in social recognition, anxiety and aggression

Social recognition manifests itself in decreased investigation of a previously encountered individual. Estrogen receptor alpha (ERalpha) knock out mice show deficient social recognition and anxiety. These data show that the ERalpha is involved in these effects, but they do not say anything about the brain sites important for these effects. In this study, an shRNA encoded within an AAV viral vector directed against the ERalpha receptor gene (or containing luciferase control), was injected bilaterally into the posterodorsal amygdala (MePDA) or the ventromedial nucleus of the hypothalamus (VMN) of female rats. An 81% reduction of ERalpha expression in the MePDA eliminated social recognition. Moreover, this diminution of ERalpha in the MePDA reduced anxiety in the light/dark choice test. In contrast, social recognition was unaffected after ERalpha knockdown in the VMN while aggressiveness against the juvenile was enhanced. In conclusion, social recognition and anxiety in female rats are modulated by the ERalpha in the amygdala. Moreover, aggression against juveniles but not against adults could, at least partly, depend on the ERalpha in the VMN.

Oestrogen receptor beta is involved in the actions of oestrogens in the brain for affective behaviour, but not trophic effects in peripheral tissues

The steroid, 17beta-oestradiol (E(2)) has pervasive psychological and physical effects throughout the lifespan. The question arises as to whether there are divergent oestrogen receptor (ER)-mediated mechanisms for these effects in the central nervous system (CNS) and periphery. This review focuses on results of studies using a whole animal model (i.e. female rats and mice) to investigate the relative effects and mechanisms of oestrogens in the CNS and the periphery. By using this approach, it has been possible to differentiate the enhancing effects of E(2) on behavioural processes mediated by the hippocampus, such as affective behaviour, and the trophic effects that increase tumourigenesis and uterine growth. Studies using pharmacological manipulations and knockout mice suggest that a likely mechanism underlying the beneficial effects of E(2) for hippocampal function (but not proliferative effects in the body) involves actions at ERbeta, changes in cell cycle/division (e.g. cyclin D1) and/or histone modifications. Thus, it may be possible to differentiate the beneficial effects of oestrogens through ERbeta, particularly in the CNS, from the negative proliferative effects on peripheral, E(2)-sensitive tissues.

Estrogen attenuates ischemic oxidative damage via an estrogen receptor alpha-mediated inhibition of NADPH oxidase activation

The goal of this study was to elucidate the mechanisms of 17beta-estradiol (E(2)) antioxidant and neuroprotective actions in stroke. The results reveal a novel extranuclear receptor-mediated antioxidant mechanism for E(2) during stroke, as well as a hypersensitivity of the CA3/CA4 region to ischemic injury after prolonged hypoestrogenicity. E(2) neuroprotection was shown to involve a profound attenuation of NADPH oxidase activation and superoxide production in hippocampal CA1 pyramidal neurons after stroke, an effect mediated by extranuclear estrogen receptor alpha (ERalpha)-mediated nongenomic signaling, involving Akt activation and subsequent phosphorylation/inactivation of Rac1, a factor critical for activation of NOX2 NADPH oxidase. Intriguingly, E(2) nongenomic signaling, antioxidant action, and neuroprotection in the CA1 region were lost after long-term E(2) deprivation, and this loss was tissue specific because the uterus remained responsive to E(2). Correspondingly, a remarkable loss of ERalpha, but not ERbeta, was observed in the CA1 after long-term E(2) deprivation, with no change observed in the uterus. As a whole, the study reveals a novel, membrane-mediated antioxidant mechanism in neurons by E(2) provides support and mechanistic insights for a "critical period" of E(2) replacement in the hippocampus and demonstrates a heretofore unknown hypersensitivity of the CA3/CA4 to ischemic injury after prolonged hypoestrogenicity.

Tamoxifen produces conditioned taste avoidance in male rats: an analysis of microstructural licking patterns and taste reactivity

Estrogen receptor activation has been shown to reduce body weight and produce a conditioned reduction in food intake in male rats that is putatively mediated by estradiol's suggested aversive effects. Evidence has shown that the selective estrogen receptor modulator tamoxifen used in the prevention and treatment of breast cancer may also produce changes in food intake and body weight, which are known to impact cancer development and survival. The purpose of the present study was to examine whether tamoxifen produces a conditioned reduction in intake similar to estradiol by producing a conditioned aversion. A one bottle lickometer test was used to examine conditioned changes in sucrose drinking, while the taste reactivity test was used to measure rejection reactions, which serve to index aversion in rats. A backward conditioning procedure that consisted of 3 conditioning days and one vehicle test day was used to examine conditioned changes in 0.3 M sucrose intake and taste reactivity. Our results show that tamoxifen produced a conditioned reduction in sucrose drinking in a one bottle fluid intake test that was similar to the effects produced by estradiol (positive control); however, no active rejection reactions were produced by either tamoxifen (1 and 10 mg/kg) or estradiol. The present results suggest that tamoxifen, at the doses used in the present study, acts as an estrogen receptor agonist to regulate food intake and that the conditioned reduction in intake produced by tamoxifen and estradiol reflects conditioned taste avoidance rather than conditioned taste aversion.

Effects of two estradiol regimens on anxiety and depressive behaviors and trophic effects in peripheral tissues in a rodent model

BACKGROUND

With aging and menopause, which are associated with decreases in ovarian steroids such as 17beta-estradiol (E(2)), women might experience negative psychological symptoms, including anxiety and depression. Some women use E(2)-based therapies to alleviate these symptoms, but E(2) has been associated with trophic effects that might increase vulnerability to some steroid-sensitive cancers, such as breast cancer, in both premenopausal and postmenopausal women.

OBJECTIVE

This study investigated the relationships between the possible beneficial effects of E(2) on anxiety and depressive behaviors concurrent with trophic effects using an animal model of E(2) decline and replacement.

METHODS

Dose-dependent effects of E(2) on affective, sexual, and motor behavior of young adult rats were studied. Ovariectomized (OVX) rats were administered the chemical carcinogen 7,12-dimethylbenz(a) anthracene (DMBA) 1.25 mg or inactive vehicle (vegetable oil; control) by gavage. E(2) (0.03 or 0.09 mg/kg) or vehicle was administered subcutaneously 44 to 48 hours before assessments of anxiety (light-dark transition), depression (forced swim test), sexual (lordosis), and motor (activity monitor) behaviors. Fourteen weeks after carcinogen exposure, E(2) concentrations in plasma and brain regions (cortex, hippocampus, and hypothalamus) were determined. Incidences and numbers of tumors and uterine weight were analyzed.

RESULTS

Administration of E(2) (0.09 mg/kg) was associated with significant increases in antianxiety-like behavior in the light-dark transition task, antidepressant-like behavior in the forced swim test, and physiologic circulating and central E(2) concentrations compared with E(2) (0.03 mg/kg) and vehicle. Compared with vehicle, E(2) (0.9 > 0.3 mg/kg) was associated with significant increases in lordosis and uterine weight. Administration of DMBA was associated with significant increases in the incidences and numbers of tumors; this effect was augmented by E(2)administration.

CONCLUSIONS

Based on the findings in this rat model, the hypothesis that E(2) may be effective in reducing anxiety and depressive behaviors and enhance sexual behavior in OVX rats, concurrent with trophic effects in the periphery, was supported. Moderate physiologic levels of E(2) might have beneficial effects on affective and sexual behaviors in female rodents, but regimens including E(2) might increase tumorigenic capacity.

Adult female wildtype, but not oestrogen receptor beta knockout, mice have decreased depression-like behaviour during pro-oestrus and following administration of oestradiol or diarylpropionitrile

Studies in people and animal models suggest that depression is influenced by natural fluctuations in the levels of 17beta-oestradiol (E(2)), as well as administration of E(2)-based therapies, such as selective oestrogen receptor modulators (SERMs). Elucidating the effects and mechanisms of E(2) is important to improve future E(2)-based therapeutics. An important question is whether effects of E(2) or SERMs for mood regulation act at the alpha or beta isoform of the oestrogen receptor (ER) because some of the unwanted trophic effects of E(2)-based therapies may involve actions at ERalpha, rather than ERbeta. In the present study, whether there are sex differences in depression-like behaviour of adult mice (experiment 1), and the effects of natural fluctuations in E(2) (experiment 2), or administration of E(2) or a SERM that has higher affinity for ERbeta than for ERalpha (diarylpropionitrile; DPN) to ovariectomised (experiment 3) wildtype and ERbeta knockout (betaERKO) mice were investigated. Results of this study supported our hypotheses that: there would be sex differences favouring males for depression-like behaviour and endogenous increases in, or exogenous administration of, E(2) or administration of an ERbeta SERM would decrease depression-like behaviour in wildtype, but not betaERKO, mice. In experiment 1, adult male mice spent less time immobile in the forced swim test (i.e., showed less depression-like behaviour) compared with female mice. In experiment 2, pro-oestrous (higher circulating E(2) levels), compared with dioestrous (lower circulating E(2) levels), mice had reduced immobility in the forced swim test; this effect was not observed in betaERKO mice. In experiment 3, administration of E(2) or DPN to ovariectomised wildtype, but not betaERKO, mice decreased immobility compared with vehicle administration, these data suggest that ERbeta may be required for some of the anti-depressant-like effects of E(2).

The phytoestrogen ferutinin improves sexual behavior in ovariectomized rats

The present study was designed to examine the effect of ferutinin chronic administration on sexual behavior of ovariectomized non-estrogen-primed rats. Starting from 3 weeks after ovariectomy, female rats were orally treated with ferutinin at the doses of 0.2 and 0.5 mg/kg, daily for 4 weeks. Ferutinin's effect was compared with that of estradiol benzoate, subcutaneously injected at the dose of 1.5 microg/rat twice a week. Animals were tested for sexual motivation, receptivity and proceptivity after 1, 2 and 3 weeks of treatment and for paced mating behavior after 4 weeks of treatment. Before each experimental test, they received progesterone injection (500 microg/rat). Both dosages of ferutinin significantly increased the receptive behavior in a time-dependent manner, as well as estradiol benzoate did. Also proceptive behaviors increased in ferutinin-treated animals in comparison with control ones. During the partner preference test ferutinin was able to induce a significant preference for a sexually active male over a sexually receptive female. Moreover, ferutinin restored a normal paced mating behavior, which had been suppressed by ovariectomy. These results show that ferutinin exerts an estrogenic activity in ovariectomized non-estrogen-primed female rats.

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.

Depression-like behavior of aged male and female mice is ameliorated with administration of testosterone or its metabolites

There may be a role of age-related decline in androgen production and/or its metabolism for late-onset depression disorders of men and women. Thus, the anti-depressant-like effects of testosterone (T) and its metabolites are of interest. Given that these androgens have disparate mechanisms of action, it is important to begin to characterize and compare their effects in an aged animal model. We hypothesized that there would be sex differences in depression behavior of aged mice and that androgens would reduce depression-like behaviors in the forced swim test. To investigate this, male and female mice (approximately 24 months old) were subcutaneously administered T, or one of its 5alpha-reduced metabolites (dihydrotesterone-DHT, 5alpha-androstane,17beta-diol-3alpha-diol), or aromatized metabolite (estradiol--E(2)), or oil vehicle. Mice were administered androgens (1 mg/kg) 1 h before being tested in the forced swim test, an animal model of depression. We found that males spent more time immobile, and less time swimming, than females. Administration of T, DHT, or 3alpha-diol similarly reduced time spent immobile, and increased time spent struggling, of male and female mice. E(2), compared to vehicle administration, decreased time spent immobile of males and females, but increased time spent swimming of females and time spent struggling of male mice. Together, these data suggest that T and its 5alpha-reduced and aromatized metabolites have anti-depressant-like effects in aged male and female mice.

Estradiol or diarylpropionitrile decrease anxiety-like behavior of wildtype, but not estrogen receptor beta knockout, mice

Clinical and basic studies demonstrate that estrogen (E-sub-2)-based therapies influence anxiety and mood, but the receptor targets (e.g., a or ss isoform of the estrogen receptor, ER) for these effects requires further investigation. To address the specificity of E2's anxiolytic-like effects through ERss, anxiety, motor, and nociceptive behavior of ovariectomized, wildtype (WT), and ERss knockout (ssERKO) mice was examined. Mice were administered oil vehicle or ER agonists, 17ss-E2 (E2; 0.1 mg/kg; similar affinity for ERa and ERss), and a selective ER modulator, diarylpropionitrile (DPN; 0.1 mg/kg; greater affinity for ERss than ERa). Performance of mice in anxiety (open field, elevated plus maze, elevated zero maze, social interaction), motor activity (activity monitor) and nociception (tailflick, pawlick) measures was compared. Results supported our hypothesis that ERss is important in modulation of anxiety-like behavior by E2 in some tasks. Administration of E2 or DPN to WT, but not ssERKO, mice increased open field central entries, plus maze open arm time, zero maze open quadrant time, and social interaction. This pattern was neither seen in motor activity nor pain threshold measures. Thus, actions of ERss may be important for modulating anxiety-like behavior of mice.

The phytoestrogen ferutinin affects female sexual behavior modulating ERalpha expression in the hypothalamus

This study was designed to assess the effect of the phytoestrogenic compound ferutinin, chronically administered in ovariectomized progesterone primed rats, alone or in combination with estradiol benzoate. After 2, 3 and 4 weeks of treatments, female rats were tested for receptive (lordosis) and proceptive behaviors (hops, darts and ear wigglings). Ferutinin given alone markedly increased the intensity of the lordotic response in ovariectomized rats but failed to significantly affect proceptivity. On the other hand estradiol benzoate significantly increased both receptive and proceptive behaviors. When administered in combination with estradiol, ferutinin reduced the increase in receptivity and proceptivity due to estrogen effects, acting as an antiestrogen. At the end of the behavioral experiments, animals were sacrificed and Western blot analysis of estrogen receptor alpha (ERalpha) levels was performed in the dissected hypothalami. Ferutinin increased ERalpha expression when administered alone, as estradiol did, but decreased the response to estradiol when administered in combination. These results suggest that ferutinin displays estrogenic or antiestrogenic activity through ERalpha in the hypothalamus, depending on the absence or the presence of estrogen priming.

Transgenerational epigenetic programming of the brain transcriptome and anxiety behavior

Embryonic exposure to the endocrine disruptor vinclozolin during gonadal sex determination promotes an epigenetic reprogramming of the male germ-line that is associated with transgenerational adult onset disease states. Further analysis of this transgenerational phenotype on the brain demonstrated reproducible changes in the brain transcriptome three generations (F3) removed from the exposure. The transgenerational alterations in the male and female brain transcriptomes were distinct. In the males, the expression of 92 genes in the hippocampus and 276 genes in the amygdala were transgenerationally altered. In the females, the expression of 1,301 genes in the hippocampus and 172 genes in the amygdala were transgenerationally altered. Analysis of specific gene sets demonstrated that several brain signaling pathways were influenced including those involved in axon guidance and long-term potentiation. An investigation of behavior demonstrated that the vinclozolin F3 generation males had a decrease in anxiety-like behavior, while the females had an increase in anxiety-like behavior. These observations demonstrate that an embryonic exposure to an environmental compound appears to promote a reprogramming of brain development that correlates with transgenerational sex-specific alterations in the brain transcriptomes and behavior. Observations are discussed in regards to environmental and transgenerational influences on the etiology of brain disease.

Rapid and estrogen receptor beta mediated actions in the hippocampus mediate some functional effects of estrogen

The steroid hormone, estradiol (E(2)), has numerous targets in the central nervous system, including the hippocampus, which plays a key role in cognition and affective behavior. This review focuses on our evidence from studies in rodents that E(2) has diverse mechanisms in the hippocampus for its functional effects. E(2) has rapid, membrane-mediated effects in the hippocampus to enhance cognitive performance. Administration of E(2) to the hippocampus of rats for 10 min following training enhances performance in a hippocampus-mediated task. Increased cell firing in the hippocampus occurs within this short-time frame. Furthermore, administration of free E(2) or an E(2) conjugate, E(2):bovine serum albumin (BSA), to the hippocampus produces similar performance-enhancing effects in this task, suggesting that E(2) has membrane actions in the hippocampus for these effects. Further evidence that E(2) has rapid, membrane-mediated effects is that co-administration of E(2) and inhibitors of mitogen-activated protein kinase (MAPK), rather than intracellular E(2) receptors (ERs) or protein synthesis, attenuate the enhancing effects of E(2) in this task. Despite these data that demonstrate E(2) can have rapid and/or membrane-mediated effects in the hippocampus, there is clear evidence to suggest that intracellular ERs, particularly the beta (rather than alpha) isoform of ERs, may be important targets for E(2)'s functional effects for hippocampal processes. Administration of ligands that are specific for ERbeta, but not ERalpha, have enhancing effects on hippocampal processes similar to that of E(2) (which has similar affinity for ERalpha and ERbeta). These effects are attenuated when ERbeta expression is knocked down in transgenic models or with central administration of antisense oligonucleotides. Thus, there may be a convergence of E(2)'s actions through rapid, membrane-mediated effects and intracellular ERs in the hippocampus for these functional effects.

Proestrous compared to diestrous wildtype, but not estrogen receptor beta knockout, mice have better performance in the spontaneous alternation and object recognition tasks and reduced anxiety-like behavior in the elevated plus and mirror maze

17beta-Estradiol (E(2)) may influence cognitive and/or affective behavior in part via the beta isoform of the estrogen receptor (ERbeta). Endocrine status and behavior in cognitive (object recognition, T-maze), anxiety (open field, elevated plus maze, mirror maze, emergence), and motor/coordination (rotarod, activity chamber) tasks of proestrous and diestrous wildtype (WT) and ERbeta knockout (betaERKO) mice was examined. Proestrous (WT or betaERKO), versus diestrous, mice had higher E(2) and progestin levels in plasma, hippocampus, and cortex. The only effect of genotype on hormone levels was for corticosterone, such that betaERKO mice had higher concentrations of corticosterone than did WT mice. Proestrous WT, but not betaERKO, mice had improved performance in the object recognition (greater percentage of time with novel object) and T-maze tasks (greater percentage of spontaneous alternations) and less anxiety-like behavior in the plus maze (increased duration on open arms) and mirror chamber task (increased duration in mirror) than did diestrous mice. This pattern was not seen in the rotarod, open field, or activity monitor, suggesting effects may be specific to affective and cognitive behavior, rather than motor behavior/coordination. Thus, enhanced performance in cognitive tasks and anti-anxiety-like behavior of proestrous mice may require actions of ERbeta in the hippocampus and/or cortex.