Multiple ERbeta antisera label in ERbeta knockout and null mouse tissues

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's sex-specific effects on ischemic cell death and estrogen receptor mRNA expression in rat cortical organotypic explants

Estrogens, such as the biologically active 17-β estradiol (E2), regulate not only reproductive behaviors in adults, but also influence neurodevelopment and neuroprotection in both females and males. E2, contingent upon the timing and concentration of the therapy, is neuroprotective in female and male rodent models of stroke. In Vivo studies suggest that E2 may partially mediate this neuroprotection, particularly in the cortex, via ERα. In Vitro studies, utilizing a chemically induced ischemic injury in cortical explants from both sexes, suggest that ERα or ERβ signaling is needed to mediate the E2 protection. Since we know that the timing and concentration of E2 therapy may be sex-specific, we examined if E2 (1 nM) mediates neuroprotection when female and male cortical explants are separately isolated from postnatal day (PND) 3-4 rat. Changes in basal levels ERα, ERβ, and AR mRNA expression are compared across early post-natal development in the intact cortex and the corresponding days in vitro (DIV) for cortical explants. Following ischemic injury at 7 DIV, cell death and ERα, ERβ and AR mRNA expression was compared in female and male cortical explants. We provide evidence that E2-mediated protection is maintained in isolated cortical explants from females, but not male rats. In female cortical explants, the E2-mediated protection at 24 h occurs secondarily to a blunted transient increase in ERα mRNA at 12 h. These results suggest that cortical E2-mediated protection is influenced by sex and supports data to differentially treat females and males following ischemic injury.

Steroid hormone-mediated regulation of sexual and aggressive behaviour by non-genomic signalling

Sex and aggression are well studied examples of social behaviours that are common to most animals and are mediated by an evolutionary conserved group of interconnected nuclei in the brain called the social behaviour network. Though glucocorticoids and in particular estrogen regulate these social behaviours, their effects in the brain are generally thought to be mediated by genomic signalling, a slow transcriptional regulation mediated by nuclear hormone receptors. In the last decade or so, there has been renewed interest in understanding the physiological significance of rapid, non-genomic signalling mediated by steroids. Though the identity of the membrane hormone receptors that mediate this signalling is not clearly understood and appears to be different in different cell types, such signalling contributes to physiologically relevant behaviours such as sex and aggression. In this short review, we summarise the evidence for this phenomenon in the rodent, by focusing on estrogen and to some extent, glucocorticoid signalling. The use of these signals, in relation to genomic signalling is manifold and ranges from potentiation of transcription to the possible transduction of environmental signals.

Neurosteroids and the mesocorticolimbic system

The mesocorticolimbic system coordinates executive functions, such as working memory and behavioral flexibility. This circuit includes dopaminergic projections from the ventral tegmental area to the nucleus accumbens and medial prefrontal cortex. In this review, we summarize evidence that cells in multiple nodes of the mesocorticolimbic system produce neurosteroids (steroids synthesized in the nervous system) and express steroid receptors. Here, we focus on neuroandrogens (androgens synthesized in the nervous system), neuroestrogens (estrogens synthesized in the nervous system), and androgen and estrogen receptors. We also summarize how (neuro)androgens and (neuro)estrogens affect dopamine signaling in the mesocorticolimbic system and regulate executive functions. Taken together, the data suggest that steroids produced in the gonads and locally in the brain modulate higher-order cognition and executive functions.

Localisation of oestrogen receptors in stem cells and in stem cell-derived neurons of the mouse

Oestrogen receptors (ER) transduce the effects of the endogenous ligand, 17β-estradiol in cells to regulate a number of important processes such as reproduction, neuroprotection, learning and memory and anxiety. The ERα or ERβ are classical intracellular nuclear hormone receptors while some of their variants or novel proteins such as the G-protein coupled receptor (GPCR), GPER1/GPR30 are reported to localise in intracellular as well as plasma membrane locations. Although the brain is an important target for oestrogen with oestrogen receptors expressed differentially in various nuclei, subcellular organisation and crosstalk between these receptors is under-explored. Using an adapted protocol that is rapid, we first generated neurons from mouse embryonic stem cells. Our immunocytochemistry approach shows that the full length ERα (ERα-66) and for the first time, that an ERα variant, ERα-36, as well as GPER1 is present in embryonic stem cells. In addition, these receptors typically decrease their nuclear localisation as neuronal maturation proceeds. Finally, although these ERs are present in many subcellular compartments such as the nucleus and plasma membrane, we show that they are specifically not colocalised with each other, suggesting that they initiate distinct signalling pathways.

Optimized Mouse-on-mouse Immunohistochemical Detection of Mouse ESR2 Proteins with PPZ0506 Monoclonal Antibody

Despite the physiological significance of ESR2, a lack of well-validated detection systems for ESR2 proteins has hindered progress in ESR2 research. Thus, recent identification of a specific anti-human ESR2 monoclonal antibody (PPZ0506) and its specific cross-reactivity against mouse and rat ESR2 proteins heightened momenta toward development of appropriate immunohistochemical detection systems for rodent ESR2 proteins. Building upon our previous optimization of ESR2 immunohistochemical detection in rats using PPZ0506, in this study, we further aimed to optimize mouse-on-mouse immunohistochemical detection using PPZ0506. Our assessment of several staining conditions using paraffin-embedded ovary sections revealed that intense heat-induced antigen retrieval, appropriate blocking, and appropriate antibody dilutions were necessary for optimization of mouse-on-mouse immunohistochemistry. Subsequently, we applied the optimized immunostaining method to determine expression profiles of mouse ESR2 proteins in peripheral tissues and brain subregions. Our analyses revealed more localized distribution of mouse ESR2 proteins than previously assumed. Moreover, comparison of these results with those obtained in humans and rats using PPZ0506 revealed interspecies differences in ESR2 expression. We expect that our optimized methodology for immunohistochemical staining of mouse ESR2 proteins will help researchers to solve multiple lines of controversial evidence concerning ESR2 expression.

Immunoblot Detection of the Phosphorylation of the Estrogen Receptor α as an Outcome of GPR30 /GPER1 Activation

Phosphorylation of the serine residues in estrogen receptor (ER) α is important in transcriptional activation. Hence, methods to detect such posttranslational modification events are valuable. We describe, in detail, the analysis of the phosphorylated ERα by electrophoretic separation of proteins and subsequent immunoblotting techniques. In particular, phosphorylation of the ERα is one possible outcome of activation of the putative membrane estrogen receptor (mER), GPR30 or GPER1. Hence, phosphorylation represents a crosstalk event between GPR30 and ERα and may be important in estrogen-regulated physiology.

Tamoxifen offers long-term neuroprotection after hippocampal silent infarct in male rats

Silent infarcts (SI) are a cerebral small vessel disease characterized by small subcortical infarcts. These occur in the absence of typical ischemia symptoms but are linked to cognitive decline and dementia. While there are no approved treatments for SI, recent results from our laboratory suggest that tamoxifen, a selective estrogen receptor modulator, is a viable candidate. In the present study, we induced SI in the dorsal hippocampal CA1 region of rats and assessed the effects of systemic administration of tamoxifen (5 mg/kg, twice) 21 days after injury on cognitive and pathophysiological measures, including cell loss, apoptosis, gliosis and estrogen receptors (ERs). We found that tamoxifen protected against the SI-induced cognitive dysfunction on the hippocampal-dependent, place recognition task, cell and ER loss, and increased apoptosis and gliosis in the CA1. Exploratory data analyses using a scatterplot matrix and principal component analysis indicated that SI-tamoxifen rats were indistinguishable from sham controls while they differed from SI rats, who were characterized by enhanced cell loss, apoptosis and gliosis, lower ERs, and recognition memory deficit. Supervised machine learning using support vector machine (SVM) determined predictors of progression from the early ischemic state to the dementia-like state. It showed that caspase-3 and ERα in the CA1 and exploration proportion were reliable and accurate predictors of this progression. Importantly, tamoxifen ameliorated SI-induced effects on all three of these variables, providing further evidence for its viability as a candidate treatment for SI and prevention of associated dementia.

Impact of pubertal onset on region-specific Esr2 expression

In female rats, pubertal onset is associated with maturation of the medial prefrontal cortex (mPFC) and mPFC-mediated behaviours. These behavioural and anatomical changes are likely a result of the effects of oestrogens at the nuclear oestrogen receptor (ER)β, which is expressed at higher levels than the ERα isoform in the adult mPFC. Researchers have previously quantified ERβ protein and Esr2 RNA in rodents during early postnatal development and adulthood, although an adolescent-specific trajectory of this receptor in the mPFC has not been documented. Given that Esr2 expression can fluctuate in the presence or absence of oestrogens, puberty and the subsequent rise in gonadal hormones could influence levels of ERβ in the adolescent brain. To further explore this, we used RNAscope® technology to quantify the amount of Esr2 mRNA in pre-pubertal adolescent, recently post-pubertal adolescent and adult female rats. We show that Esr2 expression decreases significantly in the mPFC, striatum and motor cortex between pre-pubertal adolescence and adulthood. In the mPFC, this decrease occurs rapidly at pubertal onset, with no significant decrease in Esr2 levels between the recently post-pubertal and adult cohort. By contrast, the striatum and motor cortex had no significant differences in the amount of Esr2 mRNA between pre- and post-pubertal females. Insofar as the amount of Esr2 expression is proportional to functional ERβ, these results suggest ERβ decreases in a region-specific pattern in response to pubertal onset and highlight a role for this receptor in the maturational events that occur in the female rat mPFC at puberty.

BRCA1 Antibodies Matter

Breast cancer susceptibility gene 1 (BRCA1) encodes a tumor suppressor that is frequently mutated in familial breast and ovarian cancer patients. BRCA1 functions in multiple important cellular processes including DNA damage repair, cell cycle checkpoint activation, protein ubiquitination, chromatin remodeling, transcriptional regulation, as well as R-loop formation and apoptosis. A large number of BRCA1 antibodies have been generated and become commercially available over the past three decades, however, many commercial antibodies are poorly characterized and, when widely used, led to unreliable data. In search of reliable and specific BRCA1 antibodies (Abs), particularly antibodies recognizing mouse BRCA1, we performed a rigorous validation of a number of commercially available anti-BRCA1 antibodies, using proper controls in a panel of validation applications, including Western blot (WB), immunoprecipitation (IP), immunoprecipitation-mass spectrometry (IP-MS), chromatin immunoprecipitation (ChIP) and immunofluorescence (IF). Furthermore, we assessed the specificity of these antibodies to detect mouse BRCA1 protein through the use of testis tissue and mouse embryonic fibroblasts (MEFs) from Brca1^+/+ and Brca1^Δ11/Δ11 mice. We find that Ab1, D-9, 07-434 (for recognizing human BRCA1) and 287.17, 440621, BR-64 (for recognizing mouse BRCA1) are specific with high quality performance in the indicated assays. We share these results here with the goal of helping the community combat the common challenges associated with anti-BRCA1 antibody specificity and reproducibility and, hopefully, better understanding BRCA1 functions at cellular and tissue levels.

Perinatal activation of ER and ER but not GPER-1 masculinizes female rat caudate-putamen medium spiny neuron electrophysiological properties

Exposure to steroid sex hormones such as 17β-estradiol (estradiol) during early life potentially permanently masculinize neuron electrophysiological phenotype. In rodents, one crucial component of this developmental process occurs in males, with estradiol aromatized in the brain from testes-sourced testosterone. However, it is unknown whether most neuron electrophysiological phenotypes are altered by this early masculinization process, including medium spiny neurons (MSNs) of the rat caudate-putamen. MSNs are the predominant and primary output neurons of the caudate-putamen and exhibit increased intrinsic excitability in females compared to males. Here, we hypothesize that since perinatal estradiol exposure occurs in males, then a comparable exposure in females to estradiol or its receptor agonists would be sufficient to induce masculinization. To test this hypothesis, we injected perinatal female rats with estradiol or its receptor agonists and then later assessed MSN electrophysiology. Female and male rats on postnatal day 0 and 1 were systemically injected with either vehicle, estradiol, the estrogen receptor (ER)α agonist PPT, the ERβ agonist DPN, or the G-protein-coupled receptor 1 (GPER-1) agonist G1. On postnatal days 19 ± 2, MSN electrophysiological properties were assessed using whole cell patch clamp recordings. Estradiol exposure abolished increased intrinsic excitability in female compared to male MSNs. Exposure to either an ERα or ERβ agonist masculinized female MSN evoked action potential firing rate properties, whereas exposure to an ERβ agonist masculinized female MSN inward rectification properties. Exposure to ER agonists minimally impacted male MSN electrophysiological properties. These findings indicate that perinatal estradiol exposure masculinizes MSN electrophysiological phenotype via activation of ERα and ERβ.NEW & NOTEWORTHY This study is the first to demonstrate that estradiol and estrogen receptor α and β stimulation during early development sexually differentiates the electrophysiological properties of caudate-putamen medium spiny neurons, the primary output neuron of the striatal regions. Overall, this evidence provides new insight into the neuroendocrine mechanism by which caudate-putamen neuron electrophysiology is sexually differentiated and demonstrates the powerful action of early hormone exposure upon individual neuron electrophysiology.

Optimization of immunohistochemical detection of rat ESR2 proteins with well-validated monoclonal antibody PPZ0506

Although there are few well-validated antibodies against ESR2 proteins, a recent validation assessment identified a specific monoclonal antibody against human ESR2 proteins (PPZ0506). Furthermore, our previous study confirmed its cross-reactivity and specificity against rodent ESR2 proteins, enabling the determination of true ESR2 distribution profiles in rodents. Therefore, we aimed to determine optimal conditions for ESR2 detection by PPZ0506 immunostaining and analyze ESR2 distribution in rats. We evaluated several staining conditions using paraffin-embedded and frozen ovary sections. Immunohistochemical staining with PPZ0506 antibody required strong antigen retrieval and appropriate antibody dilution. Subsequent immunohistochemical analysis in multiple tissues under optimized conditions revealed that rat ESR2 proteins are expressed in a more localized manner than previously assumed. Our results suggest that previous immunohistochemical studies using inadequately validated antibodies against ESR2 proteins overestimated their distribution profiles. We expect that optimized immunohistochemical detection with PPZ0506 antibody can help researchers solve several conflicting problems in ESR2 research.

Estrogen receptor alpha, G-protein coupled estrogen receptor 1, and aromatase: Developmental, sex, and region-specific differences across the rat caudate-putamen, nucleus accumbens core and shell

Sex steroid hormones such as 17β-estradiol (estradiol) regulate neuronal function by binding to estrogen receptors (ERs), including ERα and GPER1, and through differential production via the enzyme aromatase. ERs and aromatase are expressed across the nervous system, including in the striatal brain regions. These regions, comprising the nucleus accumbens core, shell, and caudate-putamen, are instrumental for a wide-range of functions and disorders that show sex differences in phenotype and/or incidence. Sex-specific estrogen action is an integral component for generating these sex differences. A distinctive feature of the striatal regions is that in adulthood neurons exclusively express membrane but not nuclear ERs. This long-standing finding dominates models of estrogen action in striatal regions. However, the developmental etiology of ER and aromatase cellular expression in female and male striatum is unknown. This omission in knowledge is important to address, as developmental stage influences cellular estrogenic mechanisms. Thus, ERα, GPER1, and aromatase cellular immunoreactivity was assessed in perinatal, prepubertal, and adult female and male rats. We tested the hypothesis that ERα, GPER1, and aromatase exhibits sex, region, and age-specific differences, including nuclear expression. ERα exhibits nuclear expression in all three striatal regions before adulthood and disappears in a region- and sex-specific time-course. Cellular GPER1 expression decreases during development in a region- but not sex-specific time-course, resulting in extranuclear expression by adulthood. Somatic aromatase expression presents at prepuberty and increases by adulthood in a region- but not sex-specific time-course. These data indicate that developmental period exerts critical sex-specific influences on striatal cellular estrogenic mechanisms.

Estrogen Receptor α Regulates Ethanol Excitation of Ventral Tegmental Area Neurons and Binge Drinking in Female Mice

Elevations in estrogen (17β-estradiol, E2) are associated with increased alcohol drinking by women and experimentally in rodents. E2 alters the activity of the dopamine system, including the VTA and its projection targets, which plays an important role in binge drinking. A previous study demonstrated that, during high E2 states, VTA neurons in female mice are more sensitive to ethanol excitation. However, the mechanisms responsible for the ability of E2 to enhance ethanol sensitivity of VTA neurons have not been investigated. In this study, we used selective agonists and antagonists to examine the role of ER subtypes (ERα and ERβ) in regulating the ethanol sensitivity of VTA neurons in female mice and found that ERα promotes the enhanced ethanol response of VTA neurons. We also demonstrated that enhancement of ethanol excitation requires the activity of the metabotropic glutamate receptor, mGluR1, which is known to couple with ERα at the plasma membrane. To investigate the behavioral relevance of these findings, we administered lentivirus-expressing short hairpin RNAs targeting either ERα or ERβ into the VTA and found that knockdown of each receptor in the VTA reduced binge-like ethanol drinking in female, but not male, mice. Reducing ERα in the VTA had a more dramatic effect on binge-like drinking than reducing ERβ, consistent with the ability of ERα to alter ethanol sensitivity of VTA neurons. These results provide important insight into sex-specific mechanisms that drive excessive alcohol drinking.SIGNIFICANCE STATEMENT Estrogen has potent effects on the dopamine system and increases the vulnerability of females to develop addiction to substances, such as alcohol. We investigated the mechanisms by which estrogen increases the response of neurons in the VTA to ethanol. We found that activation of the ERα increased the ethanol-induced excitation of VTA neurons. 17β-Estradiol-mediated enhancement of ethanol-induced excitation required the metabotropic glutamate receptor mGluR1. We also demonstrated that ERs in the VTA regulate binge-like alcohol drinking by female, but not male, mice. The influence of ERs on binge drinking in female mice suggests that treatments for alcohol use disorder in women may need to account for this sex difference.

Detection and Characterization of Estrogen Receptor Beta Expression in the Brain with Newly Developed Transgenic Mice

Two types of nuclear estrogen receptors, ERα and ERβ, have been shown to be differentially involved in the regulation of various types of behaviors. Due to a lack of tools for identifying ERβ expression, detailed anatomical distribution and neurochemical characteristics of ERβ expressing cells and cellular co-expression with ERα remain unclear. We have generated transgenic mice ERβ-RFP^tg, in which RFP was inserted downstream of ERβ BAC promotor. We verified RFP signals as ERβ by confirming: (1) high ERβ mRNA levels in RFP-expressing cells collected by fluorescence-activated cell sorting; and (2) co-localization of ERβ mRNA and RFP proteins in the paraventricular nucleus (PVN). Strong ERβ-RFP signals were found in the PVN, medial preoptic area (MPOA), bed nucleus of the stria terminalis, medial amygdala (MeA), and dorsal raphe nucleus (DRN). In the MPOA and MeA, three types of cell populations were identified; those expressing both ERα and ERβ, and those expressing exclusively either ERα or ERβ. The majority of PVN and DRN cells expressed only ERβ-RFP. Further, ERβ-RFP positive cells co-expressed oxytocin in the PVN, and tryptophan hydroxylase 2 and progesterone receptors in the DRN. In the MeA, some ERβ-RFP positive cells co-expressed oxytocin receptors. These findings collectively suggest that ERβ-RFP^tg mice can be a powerful tool for future studies on ERβ function in the estrogenic regulation of social behaviors.

Neurochemical Characterization of Neurons Expressing Estrogen Receptor β in the Hypothalamic Nuclei of Rats Using in Situ Hybridization and Immunofluorescence

Estrogens play an essential role in multiple physiological functions in the brain, including reproductive neuroendocrine, learning and memory, and anxiety-related behaviors. To determine these estrogen functions, many studies have tried to characterize neurons expressing estrogen receptors known as ERα and ERβ. However, the characteristics of ERβ-expressing neurons in the rat brain still remain poorly understood compared to that of ERα-expressing neurons. The main aim of this study is to determine the neurochemical characteristics of ERβ-expressing neurons in the rat hypothalamus using RNAscope in situ hybridization (ISH) combined with immunofluorescence. Strong Esr2 signals were observed especially in the anteroventral periventricular nucleus (AVPV), bed nucleus of stria terminalis, hypothalamic paraventricular nucleus (PVN), supraoptic nucleus, and medial amygdala, as previously reported. RNAscope ISH with immunofluorescence revealed that more than half of kisspeptin neurons in female AVPV expressed Esr2, whereas few kisspeptin neurons were found to co-express Esr2 in the arcuate nucleus. In the PVN, we observed a high ratio of Esr2 co-expression in arginine-vasopressin neurons and a low ratio in oxytocin and corticotropin-releasing factor neurons. The detailed neurochemical characteristics of ERβ-expressing neurons identified in the current study can be very essential to understand the estrogen signaling via ERβ.

Applicability of Anti-Human Estrogen Receptor β Antibody PPZ0506 for the Immunodetection of Rodent Estrogen Receptor β Proteins

Several lines of controversial evidence concerning estrogen receptor β (ERβ) remain to be solved because of the unavailability of specific antibodies against ERβ. The recent validation analysis identified a monoclonal antibody (PPZ0506) with sufficient specificity against human ERβ. However, the specificity and cross-reactivity of PPZ0506 antibody against ERβ proteins from laboratory animals have not been confirmed. In the present study, we aimed to validate the applicability of PPZ0506 to rodent studies. The antibody exhibited specific cross-reactivity against mouse and rat ERβ proteins in immunoblot and immunocytochemical experiments using transfected cells. In immunohistochemistry for rat tissue sections, PPZ0506 showed immunoreactive signals in the ovary, prostate, and brain. These immunohistochemical profiles of rat ERβ proteins in rat tissues accord well with its mRNA expression patterns. Although the antibody was reported to show the moderate signals in human testis, no immunoreactive signals were observed in rat testis. Subsequent RT-PCR analysis revealed that this species difference in ERβ expression resulted from different expression profiles related to the alternative promoter usage between humans and rats. In conclusion, we confirmed applicability of PPZ0506 for rodent ERβ studies, and our results provide a fundamental basis for further examination of ERβ functions.

Pituitary estrogen receptor alpha is involved in luteinizing hormone pulsatility at mid-gestation in the South American plains vizcacha, Lagostomus maximus (Rodentia, Caviomorpha)

The South American plains vizcacha, Lagostomus maximus, is a caviomorph rodent native from Argentina, Bolivia and Paraguay. It shows peculiar reproductive features like pre-ovulatory follicle recruitment during pregnancy with an ovulatory process at around mid-gestation. We have described the activation of the hypothalamic - pituitary - ovarian (HPO) axis during pregnancy. A progressive decrease of progesterone (P4) at mid-pregnancy elicits the delivery of gonadotropin-releasing hormone (GnRH) with the consequent secretion of follicle stimulating hormone (FSH) and estradiol (E₂) followed by luteinizing hormone (LH) release resulting in follicular luteinization and the P4 concentration recover. Pituitary gland is the central regulator of the HPO axis being E₂ a key hormone involved in the regulation of its activity. In this work we analyzed the action of E₂ on the pituitary response to the GnRH wave as well as its involvement on LH secretion at mid-gestation in L. maximus. The expression of GnRHR at the pituitary pars distalis showed a significant decrease at mid-pregnancy compared to early- and term-gestating females. ERα showed a significant increment from mid-gestation whereas ERβ did not show variations throughout pregnancy; whereas the LH expression in the pituitary pars distalis showed a significant increase at mid-gestation, concordantly with serum LH, which was followed by a decrease at term-gestation with similar values than at early-pregnancy. The number of cells with co-localization of ERα and GnRHR showed a decline at mid-pregnancy related to early- and term-gestation, whereas the cells with co-localization of ERα and LH increased at mid- and term-pregnancy. On the other hand, ex vivo measuring of LH pulsatility showed a significant increment in the total mass of LH delivered at mid-pregnancy followed by a decrease at term-gestation. The stimulation of ERα with the PPT specific agonist induced a significant increment in the total mass of LH released, whereas no changes were determined when ERβ was stimulated with its specific agonist MPP. These results suggest that LH pulsatility rise at mid-pregnancy would be enabled by the increase of E₂ acting through ERα.

Estrus-Cycle Regulation of Cortical Inhibition

Female mammals experience cyclical changes in sexual receptivity known as the estrus cycle. Little is known about how estrus affects the cortex, although alterations in sensation, cognition and the cyclical occurrence of epilepsy suggest brain-wide processing changes. We performed in vivo juxtacellular and whole-cell recordings in somatosensory cortex of female rats and found that the estrus cycle potently altered cortical inhibition. Fast-spiking interneurons were strongly activated with social facial touch and varied their ongoing activity with the estrus cycle and estradiol in ovariectomized females, while regular-spiking excitatory neurons did not change. In situ hybridization for estrogen receptor β (Esr2) showed co-localization with parvalbumin-positive (PV⁺) interneurons in deep cortical layers, mirroring the laminar distribution of our physiological findings. The fraction of neurons positive for estrogen receptor β (Esr2) and PV co-localization (Esr2⁺PV⁺) in cortical layer V was increased in proestrus. In vivo and in vitro experiments confirmed that estrogen acts locally to increase fast-spiking interneuron excitability through an estrogen-receptor-β-dependent mechanism.

Estrogenic regulation of social behavior and sexually dimorphic brain formation

It has long been known that the estrogen, 17β-estradiol (17β-E), plays a central role for female reproductive physiology and behavior. Numerous studies have established the neurochemical and molecular basis of estrogenic induction of female sexual behavior, i.e., lordosis, in animal models. In addition, 17β-E also regulates male-type sexual and aggressive behavior. In males, testosterone secreted from the testes is irreversibly aromatized to 17β-E in the brain. We discuss the contribution of two nuclear receptor isoforms, estrogen receptor (ER)α and ERβ to the estrogenic regulation of sexually dimorphic brain formation and sex-typical expression of these social behaviors. Furthermore, 17β-E is a key player for social behaviors such as social investigation, preference, recognition and memory as well as anxiety-related behaviors in social contexts. Recent studies also demonstrated that not only nuclear receptor-mediated genomic signaling but also membrane receptor-mediated non-genomic actions of 17β-E may underlie the regulation of these behaviors. Finally, we will discuss how rapidly developing research tools and ideas allow us to investigate estrogenic action by emphasizing behavioral neural networks.

Estrogen receptor beta modulates permeability transition in brain mitochondria

Recent evidence highlights a role for sex and hormonal status in regulating cellular responses to ischemic brain injury and neurodegeneration. A key pathological event in ischemic brain injury is the opening of a mitochondrial permeability transition pore (MPT) induced by excitotoxic calcium levels, which can trigger irreversible damage to mitochondria accompanied by the release of pro-apoptotic factors. However, sex differences in brain MPT modulation have not yet been explored. Here, we show that mitochondria isolated from female mouse forebrain have a lower calcium threshold for MPT than male mitochondria, and that this sex difference depends on the MPT regulator cyclophilin D (CypD). We also demonstrate that an estrogen receptor beta (ERβ) antagonist inhibits MPT and knockout of ERβ decreases the sensitivity of mitochondria to the CypD inhibitor, cyclosporine A. These results suggest a functional relationship between ERβ and CypD in modulating brain MPT. Moreover, co-immunoprecipitation studies identify several ERβ binding partners in mitochondria. Among these, we investigate the mitochondrial ATPase as a putative site of MPT regulation by ERβ. We find that previously described interaction between the oligomycin sensitivity-conferring subunit of ATPase (OSCP) and CypD is decreased by ERβ knockout, suggesting that ERβ modulates MPT by regulating CypD interaction with OSCP. Functionally, in primary neurons and hippocampal slice cultures, modulation of ERβ has protective effects against glutamate toxicity and oxygen glucose deprivation, respectively. Taken together, these results reveal a novel pathway of brain MPT regulation by ERβ that could contribute to sex differences in ischemic brain injury and neurodegeneration.

The effects of chronic stress on the human brain: From neurotoxicity, to vulnerability, to opportunity

For the last five decades, science has managed to delineate the mechanisms by which stress hormones can impact on the human brain. Receptors for glucocorticoids are found in the hippocampus, amygdala and frontal cortex, three brain regions involved in memory processing and emotional regulation. Studies have shown that chronic exposure to stress is associated with reduced volume of the hippocampus and that chronic stress can modulate volumes of both the amygdala and frontal cortex, suggesting neurotoxic effects of stress hormones on the brain. Yet, other studies report that exposure to early adversity and/or familial/social stressors can increase vulnerability to stress in adulthood. Models have been recently developed to describe the roles that neurotoxic and vulnerability effects can have on the developing brain. These models suggest that developing early stress interventions could potentially counteract the effects of chronic stress on the brain and results going along with this hypothesis are summarized.

Kisspeptin system in ovariectomized mice: Estradiol and progesterone regulation

The kisspeptin system is clustered in two main groups of cell bodies (the periventricular region, RP3V and the arcuate nucleus, ARC) that send fibers mainly to the GnRH neurons and in a few other locations, including the paraventricular nucleus, PVN. In physiological conditions, gonadal hormones modulate the kisspeptin system with expression changes according to different phases of the estrous cycle: the highest being in estrus phase in RP3V and PVN (positive feedback), and in ARC during the diestrus phase (negative feedback). In this work we wanted to study these hormonal fluctuations during the estrous cycle, investigating the role played by progesterone (P) or estradiol (E₂), alone or together, on the kisspeptin system. Gonadectomized CD1 female mice were treated with P, E₂ or both (E₂ + P), following a timing of administration that emulates the different phases of estrous cycle, for two cycles of 4 days. As expected, the two cell groups were differentially affected by E₂; the RP3V group was positively influenced by E₂ (alone or with the P), whereas in the ARC the administration of E₂ did not affect the system. However P (alone) induced a rise in the kisspeptin immunoreactivity. All the treatments significantly affected the kisspeptin innervation of the PVN, with regional differences, suggesting that these fibers arrive from both RP3V and ARC nuclei.

GPER1/GPR30 in the brain: Crosstalk with classical estrogen receptors and implications for behavior

The GPER1/GPR30 is a membrane estrogen receptor (mER) that binds 17β-estradiol (17β-E) with high affinity and is thought to play a role in cancer progression and cardiovascular health. Though widespread in the central nervous system, less is known about this receptor's function in the brain. GPER1 has been shown to activate kinase cascades and calcium flux within cells rapidly, thus fitting in with the idea of being a mER that mediates non-genomic signaling by estrogens. Signaling from GPER1 has been shown to improve spatial memory, possibly via release of neurotransmitters and generation of new spines on neurons in the hippocampus. In addition, GPER1 activation contributes to behaviors that denote anxiety and to social behaviors such as social memory and lordosis behavior in mice. In the male hippocampus, GPER1 activation has also been shown to phosphorylate the classical intracellular estrogen receptor (ER)α, suggesting that crosstalk with ERα is important in the display of these behaviors, many of which are absent in ERα-null mice. In this review, we present a number of categories of such crosstalk, using examples from literature. The function of GPER1 as an ERα collaborator or as a mER in different tissues is relevant to understanding both normal physiology and abnormal pathology, mediated by estrogen signaling.

Estrogen Receptor β in the Nucleus Accumbens Regulates the Rewarding Properties of Cocaine in Female Mice

BACKGROUND

Females are more vulnerable to developing cocaine addiction compared with males, a phenomenon that may be regulated by the steroid hormone 17β-estradiol. 17β-Estradiol enhances cocaine reward as measured by the conditioned place preference test. It is currently not known which estrogen receptor is involved or the neuroanatomical locations in which estrogen receptors act to enhance cocaine responses. The purpose of this study was to determine if the estrogen receptors ERα and ERβ regulate cocaine conditioned place preference in mice and whether they act in the nucleus accumbens, a brain region critically involved in the development of cocaine abuse.

METHODS

Ovariectomized mice were treated with 17β-estradiol or agonists selective for ERα or ERβ and tested for cocaine conditioned place preference and for c-fos expression in the nucleus accumbens. Female mice with intact ovaries were also tested for cocaine conditioned place preference after RNA interference-mediated knockdown of ERα or ERβ in the nucleus accumbens.

RESULTS

We found that mice treated with 17β-estradiol or an ERβ agonist exhibited increased cocaine conditioned place preference, while knockdown of ERβ, but not ERα, in the nucleus accumbens of females with intact ovaries abrogated cocaine conditioned place preference. Acute treatment with 17β-estradiol or an ERβ agonist induced expression of the immediate-early gene c-fos in the nucleus accumbens, whereas the ERα agonist did not.

CONCLUSIONS

These data indicate that ERβ in the nucleus accumbens regulates the development of cocaine conditioned place preference in female mice. 17β-Estradiol may activate neurons in the nucleus accumbens via ERβ. We speculate that this might increase the saliency of cocaine cues that predict drug reward.

Distribution and chemical composition of estrogen receptor β neurons in the paraventricular nucleus of the female and male mouse hypothalamus

Activation of estrogen receptor beta (ERβ)-expressing neurons regulates the mammalian stress response via the hypothalamic-pituitary-adrenal (HPA) axis. These neurons densely populate the paraventricular nucleus of the hypothalamus (PVN). Recent research has revealed striking differences between rat and mouse PVN cytochemistry, but careful exploration of PVN ERβ neurons in mice has been hindered by a lack of specific ERβ antisera. Therefore, we used male and female transgenic mice expressing EGFP under the control of the mouse ERβ promoter (ERβ-EGFP) to examine the chemical architecture of PVN ERβ cells. Using immunohistochemistry, we found that 90% of ERβ-immunoreactivity (-ir) colocalized with EGFP. Cellular colocalization of EGFP with neuropeptides, transcription modulators, and neuronal tracers was examined throughout the PVN. ERβ-EGFP cells expressed oxytocin more abundantly in the rostral (71 ± 3%) than caudal (33 ± 8%) PVN. Arginine vasopressin colocalized with EGFP more often in females (18 ± 3%) than males (4 ± 1%). Moreover, estrogen receptor α-ir colocalized with ERβ-EGFP at low levels (15 ± 3%). Using a corticotropin releasing hormone-cre driver X tdTomato reporter mouse, we found a moderate colocalization with ERβ-ir (48 ± 16%) in the middle PVN. Peripheral injection of fluorogold revealed that the rostral PVN ERβ-EGFP cells are neuroendocrine neurons whereas non-neuroendocrine (presumably pre-autonomic) ERβ-EGFP neurons predominated in the posterior PVN. These data demonstrate chemoarchitectural differences in ERβ neurons of the mouse PVN that are different from that previously described for the rat, thus, elucidating potential neuronal pathways involved in the regulation of the HPA axis in mice.

Regulation of aromatase expression in the anterior amygdala of the developing mouse brain depends on ERβ and sex chromosome complement

During development sex differences in aromatase expression in limbic regions of mouse brain depend on sex chromosome factors. Genes on the sex chromosomes may affect the hormonal regulation of aromatase expression and this study was undertaken to explore that possibility. Male E15 anterior amygdala neuronal cultures expressed higher levels of aromatase (mRNA and protein) than female cultures. Furthermore, treatment with oestradiol (E2) or dihydrotestosterone (DHT) increased Cyp19a1 expression and aromatase protein levels only in female neuronal cultures. The effect of E2 on aromatase expression was not imitated by oestrogen receptor (ER) α agonist PPT or the GPER agonist G1, but it was fully reproduced by DPN, a specific ligand of ERβ. By contrast, the effect of DHT on aromatase expression was not blocked by the anti-androgen flutamide, but completely abrogated by the ERβ antagonist PHTPP. Experiments using the four core genotype model showed a sex chromosome effect in ERβ expression (XY > XX) and regulation by E2 or DHT (only XX respond) in amygdala neurons. In conclusion, sex chromosome complement governs the hormonal regulation of aromatase expression through activation of ERβ in developing mouse brain.

Insufficient antibody validation challenges oestrogen receptor beta research

The discovery of oestrogen receptor β (ERβ/ESR2) was a landmark discovery. Its reported expression and homology with breast cancer pharmacological target ERα (ESR1) raised hopes for improved endocrine therapies. After 20 years of intense research, this has not materialized. We here perform a rigorous validation of 13 anti-ERβ antibodies, using well-characterized controls and a panel of validation methods. We conclude that only one antibody, the rarely used monoclonal PPZ0506, specifically targets ERβ in immunohistochemistry. Applying this antibody for protein expression profiling in 44 normal and 21 malignant human tissues, we detect ERβ protein in testis, ovary, lymphoid cells, granulosa cell tumours, and a subset of malignant melanoma and thyroid cancers. We do not find evidence of expression in normal or cancerous human breast. This expression pattern aligns well with RNA-seq data, but contradicts a multitude of studies. Our study highlights how inadequately validated antibodies can lead an exciting field astray.

A large body of work into the role of oestrogen receptor b (ERb) in breast cancer is contradictory, hindering future progress. Here the authors conduct extensive validation of anti-ERb antibodies , and show that normal and cancerous breast tissue do not express ERb, consistent with RNA-seq data.

Exposure to extrinsic stressors, social defeat or bisphenol A, eliminates sex differences in DNA methyltransferase expression in the amygdala

Chemical and psychological stressors can exert long lasting changes in brain function and behaviour. Changes in DNA methylation have been shown to be an important mechanism mediating long lasting changes in neural function and behaviour, especially for anxiety-like or stress responses. In the present study, we examined the effects of either a social or chemical stressor on DNA methyltransferase (DNMT) gene expression in the amygdala, an important brain region modulating stress responses and anxiety. In adult California mice (Peromyscus californicus) that were naïve to social defeat, females had higher levels of Dnmt1 expression in punch samples of the central amygdala (CeA) than males. In addition, mice that underwent social defeat stress showed reduced Dnmt1 and Dnmt3a expression in the CeA of females but not males. A second study using more anatomically specific punch samples replicated these effects for Dnmt1. Perinatal exposure (spanning from periconception through lactation) to bisphenol A or ethinyl oestradiol (oestrogens in birth control pills) also abolished sex differences in Dnmt1 expression in the CeA but not the basolateral amygdala. These findings identify a robust sex difference in Dnmt1 expression in the CeA that is sensitive to both psychological and chemical stressors. Future studies should aim to examine the impact of psychological and chemical stressors on DNA methylation in the CeA and also investigate whether Dnmt1 may have an underappreciated role in plasticity in behaviour.

Of Oestrogens and Sperm: A Review of the Roles of Oestrogens and Oestrogen Receptors in Male Reproduction

The crucial role that oestrogens play in male reproduction has been generally accepted; however, the exact mechanism of their action is not entirely clear and there is still much more to be clarified. The oestrogen response is mediated through oestrogen receptors, as well as classical oestrogen receptors’ variants, and their specific co-expression plays a critical role. The importance of oestrogen signalling in male fertility is indicated by the adverse effects of selected oestrogen-like compounds, and their interaction with oestrogen receptors was proven to cause pathologies. The aims of this review are to summarise the current knowledge on oestrogen signalling during spermatogenesis and sperm maturation and discuss the available information on oestrogen receptors and their splice variants. An overview is given of species-specific differences including in humans, along with a detailed summary of the methodology outcome, including all the genetically manipulated models available to date. This review provides coherent information on the recently discovered mechanisms of oestrogens’ and oestrogen receptors’ effects and action in both testicular somatic and germ cells, as well as in mature sperm, available for mammals, including humans.

Integrative medicine: Breaking down silos of knowledge and practice an epigenetic approach

The future of medicine is discussed in the context of epigenetic influences during the entire life course and the lived experiences of each person, avoiding as much as possible the "medicalization" of the individual and taking a more humanistic view. The reciprocal communication between brain and body via the neuroendocrine, autonomic, metabolic and immune systems and the plasticity of brain architecture provide the basis for devising better "top down" interventions that engage the whole person in working towards his or her welfare. The life course perspective emphasizes the importance of intervening early in life to prevent adverse early life experiences, including the effects of poverty, that can have lifelong consequences, referred to as "biological embedding". In the spirit of integrative, humanistic medicine, treatments that "open windows of plasticity" allow targeted behavioral interventions to redirect brain and body functions and behavior in healthier directions. Policies of government and the private sector, particularly at the local, community level, can create a supporting environment for such interventions. See "Common Ground for Health: Personalized, Precision and Social Medicine McEwen & Getz - https://www.youtube.com/watch?v=IRy_uUWyrEw.

Redistribution of NMDA Receptors in Estrogen-Receptor-β-Containing Paraventricular Hypothalamic Neurons following Slow-Pressor Angiotensin II Hypertension in Female Mice with Accelerated Ovarian Failure

Hypertension in male and aging female rodents is associated with glutamate-dependent plasticity in the hypothalamus, but existing models have failed to capture distinct transitional menopausal phases that could have a significant impact on the synaptic plasticity and emergent hypertension. In rodents, accelerated ovarian failure (AOF) induced by systemic injection of 4-vinylcyclohexane diepoxide mimics the estrogen fluctuations seen in human menopause including the perimenopause transition (peri-AOF) and postmenopause (post-AOF). Thus, we used the mouse AOF model to determine the impact of slow-pressor angiotensin II (AngII) administration on blood pressure and on the subcellular distribution of obligatory N-methyl-D-aspartate (NMDA) receptor GluN1 subunits in the paraventricular hypothalamic nucleus (PVN), a key estrogen-responsive cardiovascular regulatory area. Estrogen-sensitive neuronal profiles were identified in mice expressing enhanced green fluorescent protein under the promoter for estrogen receptor (ER) β, a major ER in the PVN. Slow-pressor AngII increased arterial blood pressure in mice at peri- and post-AOF time points. In control oil-injected (nonhypertensive) mice, AngII decreased the total number of GluN1 in ERβ-containing PVN dendrites. In contrast, AngII resulted in a reapportionment of GluN1 from the cytoplasm to the plasma membrane of ERβ-containing PVN dendrites in peri-AOF mice. Moreover, in post-AOF mice, AngII increased total GluN1, dendritic size and radical production in ERβ-containing neurons. These results indicate that unique patterns of hypothalamic glutamate receptor plasticity and dendritic structure accompany the elevated blood pressure in peri- and post-AOF time points. Our findings suggest the possibility that distinct neurobiological processes are associated with the increased blood pressure during perimenopausal and postmenopausal periods.

Strategies for immunohistochemical protein localization using antibodies: What did we learn from neurotransmitter transporters in glial cells and neurons

Immunocytochemistry and Western blotting are still major methods for protein localization, but they rely on the specificity of the antibodies. Validation of antibody specificity remains challenging mostly because ideal negative controls are often unavailable. Further, immunochemical labeling patterns are also influenced by a number of other factors such as postmortem changes, fixation procedures and blocking agents as well as the general assay conditions (e.g., buffers, temperature, etc.). Western blotting similarly depends on tissue collection and sample preparation as well as the electrophoretic separation, transfer to blotting membranes and the immunochemical probing of immobilized molecules. Publication of inaccurate information on protein distribution has downstream consequences for other researchers because the interpretation of physiological and pharmacological observations depends on information on where ion channels, receptors, enzymes or transporters are located. Despite numerous reports, some of which are strongly worded, erroneous localization data are being published. Here we describe the extent of the problem and illustrate the nature of the pitfalls with examples from studies of neurotransmitter transporters. We explain the importance of supplementing immunochemical observations with other measurements (e.g., mRNA levels and distribution, protein activity, mass spectrometry, electrophysiological recordings, etc.) and why quantitative considerations are integral parts of the quality control. Further, we propose a practical strategy for researchers who plan to embark on a localization study. We also share our thoughts about guidelines for quality control. GLIA 2016;64:2045-2064.

Development and Characterization of Novel Rat Anti-mERβ Sera

Estrogens regulate normal sexual and reproductive development in females. Their actions are mediated mainly by estrogen receptor (ER)α and ERβ. Understanding the function of ERs necessitates knowing their cellular location and protein partners, which, in turn, requires reliable and specific antibodies. Several antibodies are available for ERα; however, discrepancies in immunoreactivity have been reported for ERβ. Here, we have developed antisera for mouse ERβ (mERβ) using a specific C-terminal 18-amino acid peptide conjugated to mariculture keyhole limpet hemocyanin. Sprague Dawley rats were immunized, and the resulting antisera were characterized by Western blot analysis of nuclear extracts from tissues of wild-type (WT) mice, and mice genetically modified to lack either ERα (CERαKO) or ERβ (CERβKO). An approximately 56-kDa protein was detected in the hypothalamus, uterus, ovary, mammary gland, testes, and epididymis of WT mice, consistent with the predicted molecular size of ERβ. In addition, the same protein band was identified in in vitro synthesized mERβ protein and in the mammary glands of CERαKO mice. The approximately 56-kDa protein was not observed in in vitro synthesized mERα protein or in any tissue examined in the CERβKO mice. Immunohistochemistry using the antisera revealed ERβ staining in the granulosa cells of WT ovaries and in the mediobasal hypothalamus, paraventricular nucleus, and cerebral cortex in the WT adult mouse brain. These data suggest that the novel rat anti-mERβ sera are specific to ERβ to allow investigators to explore to cellular and physiological role of ERβ in the brain and other mouse tissues.

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 Prepubertal or Adult Site-Specific Knockdown of Estrogen Receptor β in the Medial Preoptic Area and Medial Amygdala on Social Behaviors in Male Mice

Testosterone, after being converted to estradiol in the brain, acts on estrogen receptors (ERα and ERβ) and controls the expression of male-type social behavior. Previous studies in male mice have revealed that ERα expressed in the medial preoptic area (MPOA) and medial amygdala (MeA) are differently involved in the regulation of sexual and aggressive behaviors by testosterone action at the time of testing in adult and/or on brain masculinization process during pubertal period. However, a role played by ERβ in these brain regions still remains unclear. Here we examined the effects of site-specific knockdown of ERβ (βERKD) in the MPOA and MeA on male social behaviors with the use of adeno-associated viral mediated RNA interference methods in ICR/Jcl mice. Prepubertal βERKD in the MPOA revealed that continuous suppression of ERβ gene expression throughout the pubertal period and adulthood decreased aggressive but not sexual behavior tested as adults. Because βERKD in the MPOA only in adulthood did not affect either sexual or aggressive behaviors, it was concluded that pubertal ERβ in the MPOA might have an essential role for the full expression of aggressive behavior in adulthood. On the other hand, although neither prepubertal nor adult βERKD in the MeA had any effects on sexual and aggressive behavior, βERKD in adulthood disrupted sexual preference of receptive females over nonreceptive females. Collectively, these results suggest that ERβ in the MPOA and MeA are involved in the regulation of male sexual and aggressive behavior in a manner substantially different from that of ERα.

17β-Estradiol upregulates ecto-5'-nucleotidase (CD73) in hippocampal synaptosomes of female rats through action mediated by estrogen receptor-α and -β

17β-Estradiol (E2) crucially affects several processes in the hippocampus of both sexes. E2 acts upon estradiol receptors ERα and ERβ, influencing target gene expression and/or modulates intracellular signaling cascades. Another potent modulator of hippocampal function is nucleoside adenosine, the final product of ectonucleotidase cascade, enzymes which hydrolyze extracellular ATP to adenosine. The last and rate-limiting step of the hydrolysis is catalyzed by membrane-bound ecto-5'-nucleotidase (eN). Previous findings obtained on adenosine metabolism in brain suggest that eN may be modulated by ovarian steroids. Therefore, the present study reports that the activity and protein abundance of membrane-bound eN fluctuates across the estrus cycle in the hippocampal synaptosomes of female rats. Further, we analyzed the role of E2 and its intracellular receptors on the expression of eN in ovariectomized females. We found that E2 upregulated eN activity and protein abundance in the hippocampal synaptosomes. Application of nonspecific ER antagonist, ICI 182,780 and selective ERα and ERβ agonists, PPT and DPN, respectively, demonstrated the involvement of both receptor subtypes in observed actions. Selective ERα receptor agonist, PPT, induced upregulation of both the protein level and activity of eN, while application of selective ERβ receptor agonist, DPN, increased only the activity of eN. In both cases, E2 entered into the intracellular compartment and activated ER(s), which was demonstrated by membrane impermeable E2-BSA conjugate. Together these results imply that E2-induced effects on connectivity and functional properties of the hippocampal synapses may be in part mediated through observed effect on eN.

In pursuit of resilience: stress, epigenetics, and brain plasticity

The brain is the central organ for adaptation to experiences, including stressors, which are capable of changing brain architecture as well as altering systemic function through neuroendocrine, autonomic, immune, and metabolic systems. Because the brain is the master regulator of these systems, as well as of behavior, alterations in brain function by chronic stress can have direct and indirect effects on cumulative allostatic overload, which refers to the cost of adaptation. There is much new knowledge on the neural control of systemic physiology and the feedback actions of physiologic mediators on brain regions regulating higher cognitive function, emotional regulation, and self-regulation. The healthy brain has a considerable capacity for resilience, based upon its ability to respond to interventions designed to open "windows of plasticity" and redirect its function toward better health. As a result, plasticity-facilitating treatments should be given within the framework of a positive behavioral intervention; negative experiences during this window may even make matters worse. Indeed, there are no magic bullets and drugs cannot substitute for targeted interventions that help an individual become resilient, of which mindfulness-based stress reduction and meditation are emerging as useful tools.

Detection of the Phosphorylation of the Estrogen Receptor α as an Outcome of GPR30 Activation

Phosphorylation of the serine residues in estrogen receptor (ER) α is important in transcriptional activation. Hence, methods to detect such posttranslational modification events are valuable. We describe, in detail, the analysis of the phosphorylated ERα by electrophoretic separation of proteins and subsequent immuno-blotting techniques. In particular, phosphorylation of the ERα is one possible outcome of activation of the putative membrane estrogen receptor (mER), GPR30. Hence, phosphorylation represents a cross talk event between GPR30 and ERα and may be important in estrogen-regulated physiology.

Delayed pubertal onset and prepubertal Kiss1 expression in female mice lacking central oestrogen receptor beta

Ovarian oestradiol is essential for pubertal maturation and adult physiology of the female reproductive axis. It acts at central and peripheral sites through two main oestrogen receptors (ER) α and β. Here we investigate the role of ERβ on central effects of oestradiol, by generating a mouse line specifically lacking the ERβ gene in neuronal and glial cells. Central ERβ deletion delays the age at vaginal opening and first oestrous and reduces uterine weight without affecting body growth. Analysis of factors necessary for pubertal progression shows reduced levels of Kiss1 transcripts at postnatal (P) day 25 in the preoptic area, but not in the mediobasal hypothalamus (MBH) of mutant females. In agreement with these data, the number of kisspeptin-immunoreactive neurons was decreased by 57-72% in the three subdivisions of the rostral periventricular area of the third ventricle (RP3V), whereas the density of kisspeptin-immunoreactive fibres was unchanged in the arcuate nucleus of mutant mice. These alterations do not involve changes in ERα mRNAs in the preoptic area and protein levels in the RP3V. The number and distribution of GnRH-immunoreactive cells were unaffected, but gonadotropin-releasing hormone (GnRH) transcript levels were higher in the P25 preoptic area of mutants. At adulthood, mutant females have normal oestrous cyclicity, kisspeptin system and exhibit unaltered sexual behaviour. They display, however, reduced ovary weight and increased anxiety-related behaviour during the follicular phase. This argues for the specific involvement of central ERβ in the regulation of pubertal onset in female reproduction, possibly through prepubertal induction of kisspeptin expression in the RP3V.

Rapid modulation of synaptogenesis and spinogenesis by 17β-estradiol in primary cortical neurons

In the mammalian forebrain, the majority of excitatory synapses occur on dendritic spines. Changes in the number of these structures is important for brain development, plasticity and the refinement of neuronal circuits. The formation of excitatory synapses involves the coordinated formation of dendritic spines and targeting of multi-protein complexes to nascent connections. Recent studies have demonstrated that the estrogen 17β-estradiol (E2) can rapidly increase the number of dendritic spines, an effect consistent with the ability of E2 to rapidly influence cognitive function. However, the molecular composition of E2-induced spines and whether these protrusions form synaptic connections has not been fully elucidated. Moreover, which estrogen receptor(s) (ER) mediate these spine-morphogenic responses are not clear. Here, we report that acute E2 treatment results in the recruitment of postsynaptic density protein 95 (PSD-95) to novel dendritic spines. In addition neuroligin 1 (Nlg-1) and the NMDA receptor subunit GluN1 are recruited to nascent synapses in cortical neurons. The presence of these synaptic proteins at nascent synapses suggests that the machinery to allow pre- and post-synapses to form connections are present in E2-induced spines. We further demonstrate that E2 treatment results in the rapid and transient activation of extracellular signal-regulated kinase 1/2 (ERK1/2), Akt and the mammalian target of rapamycin (mTOR) signaling pathways. However, only ERK1/2 and Akt are required for E2-mediated spinogenesis. Using synthetic receptor modulators, we further demonstrate that activation of the estrogen receptor beta (ERβ) but not alpha (ERα) mimics rapid E2-induced spinogenesis and synaptogenesis. Taken together these findings suggest that in primary cortical neurons, E2 signaling via ERβ, but not through ERα, is capable of remodeling neuronal circuits by increasing the number of excitatory synapses.

Estrogen directly and specifically downregulates NaPi-IIa through the activation of both estrogen receptor isoforms (ERα and ERβ) in rat kidney proximal tubule

We have previously demonstrated that estrogen (E2) downregulates phosphate transporter NaPi-IIa and causes phosphaturia and hypophosphatemia in ovariectomized rats. In the present study, we examined whether E2 directly targets NaPi-IIa in the proximal tubule (PT) and studied the respective roles of estrogen receptor isoforms (ERα and ERβ) in the downregulation of NaPi-IIa using both in vivo and an in vitro expression systems. We found that estrogen specifically downregulates NaPi-IIa but not NaPi-IIc or Pit2 in the kidney cortex. Proximal tubules incubated in a "shake" suspension with E2 for 24 h exhibited a dose-dependent decrease in NaPi-IIa protein abundance. Results from OVX rats treated with specific agonists for either ERα [4,4',4″;-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol, PPT] or ERβ [4,4',4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol, DPN] or both (PPT + DPN), indicated that only the latter caused a sharp downregulation of NaPi-IIa, along with significant phosphaturia and hypophosphatemia. Lastly, heterologous expression studies demonstrated that estrogen downregulated NaPi-IIa only in U20S cells expressing both ERα and ERβ, but not in cells expressing either receptor alone. In conclusion, these studies demonstrate that rat PT cells express both ERα and ERβ and that E2 induces phosphaturia by directly and specifically targeting NaPi-IIa in the PT cells. This effect is mediated via a mechanism involving coactivation of both ERα and ERβ, which likely form a functional heterodimer complex in the rat kidney proximal tubule.

Membrane-initiated non-genomic signaling by estrogens in the hypothalamus: cross-talk with glucocorticoids with implications for behavior

The estrogen receptor and glucocorticoid receptor are members of the nuclear receptor superfamily that can signal using both non-genomic and genomic transcriptional modes. Though genomic modes of signaling have been well characterized and several behaviors attributed to this signaling mechanism, the physiological significance of non-genomic modes of signaling has not been well understood. This has partly been due to the controversy regarding the identity of the membrane ER (mER) or membrane GR (mGR) that may mediate rapid, non-genomic signaling and the downstream signaling cascades that may result as a consequence of steroid ligands binding the mER or the mGR. Both estrogens and glucocorticoids exert a number of actions on the hypothalamus, including feedback. This review focuses on the various candidates for the mER or mGR in the hypothalamus and the contribution of non-genomic signaling to classical hypothalamically driven behaviors and changes in neuronal morphology. It also attempts to categorize some of the possible functions of non-genomic signaling at both the cellular level and at the organismal level that are relevant for behavior, including some behaviors that are regulated by both estrogens and glucocorticoids in a potentially synergistic manner. Lastly, it attempts to show that steroid signaling via non-genomic modes may provide the organism with rapid behavioral responses to stimuli.

Recognizing Resilience: Learning from the Effects of Stress on the Brain

As the central organ of stress and adaptation to stressors, the brain plays a pivotal role in behavioral and physiological responses that may lead to successful adaptation or to pathophysiology and mental and physical disease. In this context, resilience can be defined as "achieving a positive outcome in the face of adversity". Underlying this deceptively simple statement are several questions; first, to what extent is this ability limited to those environments that have shaped the individual or can it be more flexible; second, when in the life course does the brain develop capacity for flexibility for adapting positively to new challenges; and third, can such flexibility be instated in individuals where early life experiences have limited that capacity? Brain architecture continues to show plasticity throughout adult life and studies of gene expression and epigenetic regulation reveal a dynamic and ever-changing brain. The goal is to recognize those biological changes that underlie flexible adaptability, and to recognize gene pathways, epigenetic factors and structural changes that indicate lack of resilience leading to negative outcomes, particularly when the individual is challenged by new circumstances. Early life experiences determine individual differences in such capabilities via epigenetic pathways and laying down of brain architecture that determine the later capacity for flexible adaptation or the lack thereof. Reactivation of such plasticity in individuals lacking such resilience is a new challenge for research and practical application. Finally, sex differences in the plasticity of the brain are often overlooked and must be more fully investigated.

Energy status determines hindbrain signal transduction pathway transcriptional reactivity to AMPK in the estradiol-treated ovariectomized female rat

Dorsal vagal complex (DVC) AMPK regulation of food intake in the estradiol-treated ovariectomized (OVX) female rat is energy state-dependent. Here, RT-PCR array technology was used to identify estradiol-sensitive AMPK-regulated DVC signal transduction pathways that exhibit differential reactivity to sensor activation during energy balance versus imbalance. The AMP mimetic AICAR correspondingly reduced or stimulated cDVC phosphoAMPK (pAMPK) and estrogen receptor-beta (ERβ) proteins in full-fed (F) versus 12-h food-deprived (D) estradiol-treated ovariectomized (OVX) rats, but elevated ER-alpha (ERα) in F only. Estradiol suppressed DVC ERβ protein and hypoxia, NFκB, STAT3, STAT6, and Hedgehog signaling pathway marker genes against oil-implanted OVX controls. F+(A)ICAR and D+(S)aline groups each exhibited further inhibition of NFκB, STAT3, and Hedgehog pathway genes, and diminished PPAR, Notch, and STAT5 transcripts versus F+S. Conversely, genes in these six pathways were up-regulated by AICAR treatment of D. Results show that in this animal model, acute AMP augmentation or feeding cessation each inhibit both pAMPK and ERβ expression, but in combination increase these protein profiles. pAMPK protein and DVC TNF (NFκB), SOCS3 (JAK/STAT), WNT6 (Hedgehog), and FABP1 (PPAR) mRNAs were down- or upregulated in parallel by AICAR in F versus D states, respectively. Further research is needed to determine the impact of ERβ on opposing directionality of these responses, and to characterize the role of the aforementioned signaling pathways in hyperphagic responses in the female to AICAR-induced DVC AMPK activation during acute interruption of feeding.

17α-estradiol is generated locally in the male rat brain and can regulate GAD65 expression and anxiety

Increasing evidence suggests that 17β-estradiol, a sex hormone, is synthesized by neurons. In addition, 17α-estradiol, the stereoisomer of 17β-estradiol, is reported to be the dominant form in the male mouse brain. However, probably because the method to detect these isomers requires unusual and precise experimental design, the presence of this endogenous 17α-estradiol has not been reported subsequently and the actual role is therefore not well elucidated. We first quantified the estradiol level in hippocampal extracts using gas chromatography/mass spectrometry. As a result, 17α-estradiol was found in all of the male rats tested, while that of 17β-estradiol was detected only in a certain subset. The estrogen-biosynthesis inhibitor letrozole decreased the expression of the major presynaptic GABA synthesizing enzyme GAD65 in cultured neurons and the effect was abrogated by exogenously supplied 17α-estradiol. Next, injection of the inhibitor into the brain reduced the 17α-estradiol level, indicating its biogenesis in the brain. Under the same conditions, immuno-staining of GAD65 was also decreased. Furthermore, the inhibitor treatment increased anxiety index of rats in the open field and this was ameliorated by the addition of 17α-estradiol. We showed that 17α-estradiol was generated in the brain and acted as a regulator of inhibitory neurotransmission as well as behavior. These results may have implications for a variety of diseases, such as the menopausal depression and Alzheimer's disease that have been reported to be related to estrogen levels.