Changes in estrogen receptor-alpha mRNA in the mouse cortex during development

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.

Epigenetic programming for obesity and noncommunicable disease: From womb to tomb

Several epidemiological, clinical and experimental studies in recent decades have shown the relationship between exposure to stressors during development and health outcomes later in life. The characterization of these susceptible phases, such as preconception, gestation, lactation and adolescence, and the understanding of factors that influence the risk of an adult individual for developing obesity, metabolic and cardiovascular diseases, is the focus of the DOHaD (Developmental Origins of Health and Disease) research line. In this sense, advancements in molecular biology techniques have contributed significantly to the understanding of the mechanisms underlying the observed phenotypes, their morphological and physiological alterations, having as a main driving factor the epigenetic modifications and their consequent modulation of gene expression. The present narrative review aimed to characterize the different susceptible phases of development and associated epigenetic modifications, and their implication in the development of non-communicable diseases. Additionally, we provide useful insights into interventions during development to counteract or prevent long-term programming for disease susceptibility.

DNA methylation and demethylation shape sexual differentiation of neurochemical phenotype

Some of the best-studied neural sex differences depend on differential cell death in males and females, but other sex differences persist even if cell death is prevented. These include sex differences in neurochemical phenotype (i.e., stable patterns of gene expression). Work in our laboratory over the last several years has tested the hypothesis that sex differences in DNA methylation early in life underlie sexual differentiation of neuronal phenotype. We have shown that 1) expression of enzymes that place or remove DNA methylation marks is greatest during the first week of life in the mouse brain and overlaps with the perinatal critical period of sexual differentiation; 2) a transient inhibition of DNA methylation during neonatal life abolishes several sex differences in cell phenotype in the mouse hypothalamus; 3) both DNA methylation and de-methylation contribute to the development of neural sex differences; and 4) the effects of DNA methylation and de-methylation are brain region- and cell type-specific.

Postnatal Expression Patterns of Estrogen Receptor Subtypes and Choline Acetyltransferase in Different Regions of the Papez Circuit

The Papez circuit is crucial for several brain functions, including long-term memory and emotion. Estradiol modulates cognitive functions based on the expression pattern of its receptor subtypes including estrogen receptor (ER) α, β, and G protein-coupled receptor 30 (GPR30). Similarly, the activity in the cholinergic system correlates with several brain functions, such as learning and memory. In this study, we used immunofluorescence to examine the expression patterns of ERβ and Western blotting to analyze GPR30 and choline acetyltransferase (ChAT) expression, in different regions of the Papez circuit, including the prefrontal cortex, hippocampus, hypothalamus, anterior nucleus of the thalamus, and cingulum in female rats at postnatal days (PND) 1, 10, and 56. Our main finding was that the highest expression of ERβ and GPR30 was noted in each brain area of the Papez circuit in the PND1 rats, whereas the expression of ChAT was the highest in PND10 rats. These results provide vital information on the postnatal expression patterns of ER subtypes and ChAT in different regions of the Papez circuit.

Emerging Genetic and Epigenetic Mechanisms Underlying Pubertal Maturation in Adolescence

The adolescent transition begins with the onset of puberty which, upstream in the brain, is initiated by the gonadotropin-releasing hormone (GnRH) pulse generator that activates the release of peripheral sex hormones. Substantial research in human and animal models has revealed a myriad of cellular networks and heritable genes that control the GnRH pulse generator allowing the individual to begin the process of reproductive competence and sexual maturation. Here, we review the latest knowledge in neuroendocrine pubertal research with emphasis on genetic and epigenetic mechanisms underlying the pubertal transition.

Sex differences in neural mechanisms mediating reward and addiction

There is increasing evidence in humans and laboratory animals for biologically based sex differences in every phase of drug addiction: acute reinforcing effects, transition from occasional to compulsive use, withdrawal-associated negative affective states, craving, and relapse. There is also evidence that many qualitative aspects of the addiction phases do not differ significantly between males and females, but one sex may be more likely to exhibit a trait than the other, resulting in population differences. The conceptual framework of this review is to focus on hormonal, chromosomal, and epigenetic organizational and contingent, sex-dependent mechanisms of four neural systems that are known-primarily in males-to be key players in addiction: dopamine, mu-opioid receptors (MOR), kappa opioid receptors (KOR), and brain-derived neurotrophic factor (BDNF). We highlight data demonstrating sex differences in development, expression, and function of these neural systems as they relate-directly or indirectly-to processes of reward and addictive behavior, with a focus on psychostimulants and opioids. We identify gaps in knowledge about how these neural systems interact with sex to influence addictive behavior, emphasizing throughout that the impact of sex can be highly nuanced and male/female data should be reported regardless of the outcome.

Neuronal Dnmt1 Deficiency Attenuates Diet-Induced Obesity in Mice

Aberrant neuronal DNA methylation patterns have been implicated in the promotion of obesity development; however, the role of neuronal DNA methyltransferases (Dnmts), enzymes that catalyze DNA methylation, in energy balance remains poorly understood. We investigated whether neuronal Dnmt1 regulates normal energy homeostasis and obesity development using a neuronal Dnmt1 knockout (ND1KO) mouse model, Dnmt1fl/fl Synapsin1Cre, which specifically deletes Dnmt1 in neurons. Neuronal Dnmt1 deficiency reduced adiposity in chow-fed mice and attenuated obesity in high-fat diet (HFD)-fed male mice. ND1KO male mice had reduced food intake and increased energy expenditure with the HFD. Furthermore, these mice had improved insulin sensitivity, as measured using an insulin tolerance test. The HFD-fed ND1KO mice had smaller fat pads and upregulation of thermogenic genes in brown adipose tissue. These data suggest that neuronal Dnmt1 plays an important role in regulating energy homeostasis. Notably, ND1KO male mice had elevated estrogen receptor-α (ERα) gene expression in the medial hypothalamus, which previously has been shown to control body weight. Immunohistochemistry experiments revealed that ERα protein expression was upregulated specifically in the dorsomedial region of the ventromedial hypothalamus, a region that might mediate the central effect of leptin. We conclude that neuronal Dnmt1 regulates energy homeostasis through pathways controlling food intake and energy expenditure. In addition, ERα expression in the dorsomedial region of the ventromedial hypothalamus might mediate these effects.

Generation and characterization of an estrogen receptor alpha-iCre knock-in mouse

Two estrogen receptors, ESR1 and ESR2, are responsible for the classical actions of estrogens in mammalian species. They display different spatiotemporal expression patterns and nonoverlapping functions in various tissues and physiological conditions. In this study, a novel knock-in mouse line that expresses codon-improved Cre recombinase (iCre) under regulation of the natural Esr1 promoter (Esr1-iCre) was developed. Functional characterization of iCre expression by crossing them with reporter lines (ROSA26-lacZ or Ai9-RFP) showed that iCre is faithfully expressed in Esr1-lineage cells. This novel transgenic mouse line will be a useful animal model for lineage-tracing Esr1-expressing cells, selective gene ablation in the Esr1-lineage cells and for generating global Esr1 knockout mice.

Does puberty mark a transition in sensitive periods for plasticity in the associative neocortex?

Postnatal brain development is studded with sensitive periods during which experience dependent plasticity is enhanced. This enables rapid learning from environmental inputs and reorganization of cortical circuits that matches behavior with environmental contingencies. Significant headway has been achieved in characterizing and understanding sensitive period biology in primary sensory cortices, but relatively little is known about sensitive period biology in associative neocortex. One possible mediator is the onset of puberty, which marks the transition to adolescence, when animals shift their behavior toward gaining independence and exploring their social world. Puberty onset correlates with reduced behavioral plasticity in some domains and enhanced plasticity in others, and therefore may drive the transition from juvenile to adolescent brain function. Pubertal onset is also occurring earlier in developed nations, particularly in unserved populations, and earlier puberty is associated with vulnerability for substance use, depression and anxiety. In the present article we review the evidence that supports a causal role for puberty in developmental changes in the function and neurobiology of the associative neocortex. We also propose a model for how pubertal hormones may regulate sensitive period plasticity in associative neocortex. We conclude that the evidence suggests puberty onset may play a causal role in some aspects of associative neocortical development, but that further research that manipulates puberty and measures gonadal hormones is required. We argue that further work of this kind is urgently needed to determine how earlier puberty may negatively impact human health and learning potential. This article is part of a Special Issue entitled SI: Adolescent plasticity.

Epigenetic impacts of endocrine disruptors in the brain

The acquisition of reproductive competence is organized and activated by steroid hormones acting upon the hypothalamus during critical windows of development. This review describes the potential role of epigenetic processes, particularly DNA methylation, in the regulation of sexual differentiation of the hypothalamus by hormones. We examine disruption of these processes by endocrine-disrupting chemicals (EDCs) in an age-, sex-, and region-specific manner, focusing on how perinatal EDCs act through epigenetic mechanisms to reprogram DNA methylation and sex steroid hormone receptor expression throughout life. These receptors are necessary for brain sexual differentiation and their altered expression may underlie disrupted reproductive physiology and behavior. Finally, we review the literature on histone modifications and non-coding RNA involvement in brain sexual differentiation and their perturbation by EDCs. By putting these data into a sex and developmental context we conclude that perinatal EDC exposure alters the developmental trajectory of reproductive neuroendocrine systems in a sex-specific manner.

Influence of sex steroid hormones on the adolescent brain and behavior: An update

This review explains the main effects exerted by sex steroids and other hormones on the adolescent brain. During the transition from puberty to adolescence, these hormones participate in the organizational phenomena that structurally shape some brain circuits. In adulthood, this will propitiate some specific behavior as responses to the hormones now activating those neural circuits. Adolescence is, then, a critical "organizational window" for the brain to develop adequately, since steroid hormones perform important functions at this stage. For this reason, the adolescent years are very important for future behaviors in human beings. Changes that occur or fail to occur during adolescence will determine behaviors for the rest of one's lifetime. Consequently, understanding the link between adolescent behavior and brain development as influenced by sex steroids and other hormones and compounds is very important in order to interpret various psycho-affective pathologies. Lay Summary : The effect of steroid hormones on the development of the adolescent brain, and therefore, on adolescent behavior, is noticeable. This review presents their main activational and organizational effects. During the transition from puberty to adolescence, organizational phenomena triggered by steroids structurally affect the remodeling of brain circuits. Later in adulthood, these changes will be reflected in behavioral responses to such hormones. Adolescence can then be seen as a fundamental "organizational window" during which sex steroids and other hormones and compounds play relevant roles. The understanding of the relationship between adolescent behavior and the way hormones influence brain development help understand some psychological disorders.

Neonatal hyperoxia induces alterations in neurotrophin gene expression

Each year in the United States, nearly 500,000 infants a year are born prematurely. Babies born before 35 weeks gestation are often placed on ventilators and/or given supplemental oxygen. This increase in oxygen, while critical for survival, can cause long-term damage to lungs, retinas and brains. In particular, hyperoxia causes apoptosis in neurons and alters glial activity. Brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) are members of the neurotrophin family of proteins that function to promote the growth, differentiation and development of the nervous system. We hypothesized that hyperoxia can alter the regulation of these genes and by doing so adversely affect the development of the brain. We predicted that mice exposed to hyperoxic conditions would have differences in BDNF and GDNF mRNA expression and relative level of methylated promoter regions coinciding with differences in the relative levels of DNMT1 and DNMT3a mRNA expression. To test this hypothesis, newborn C57Bl/6 mice and their littermates were placed in hyperoxic or normoxic conditions from postnatal day 7 to 12. There were significant decreases in BDNF mRNA expression in the prefrontal cortex following hyperoxia, but a significant increase in the isocortex. GDNF mRNA expression was significantly increased in both the isocortex and prefrontal cortex following hyperoxia. DNMT1 mRNA expression was significantly decreased in the isocortex but significantly increased in the prefrontal following hyperoxia. Together these data suggest that short-term exposure to hyperoxic conditions can affect the regulation and expression of BDNF and GDNF potentially leading to alterations in neural development.

Expression of estrogen receptor α in the mouse cerebral cortex

Although estrogen receptor alpha (ERα) and 17β-estradiol play critical roles in protecting the cerebral cortex from ischemia-induced damage, there has been some controversy about the expression of ERα in this region of the brain. We have examined ERα mRNA and protein levels in the cerebral cortices of female mice at postnatal days 5 and 17 and at 4, 13, and 18 months of age. We found that although ERα transcript levels declined from postnatal day 5 through 18 months of age, ERα protein levels remained stable. Importantly, expression of the E2-regulated progesterone receptor gene was sustained in younger and in older females suggesting that age-related changes in estrogen responsiveness in the cerebral cortex are not due to the absence of ERα protein.

Sex differences in spatiotemporal expression of AR, ERα, and ERβ mRNA in the perinatal mouse brain

It has been shown that every masculinized function might be organized by a particular contribution of androgens vs. estrogens in a critical time window. Here, we aimed to investigate the sex differences in brain testosterone levels and in the spatiotemporal dynamics of steroid receptor mRNA expression in perinatal mice, by using enzyme immunoassay and real-time PCR, respectively. We found that testosterone levels in the forebrain transiently increased around birth in male mice. During the perinatal period, levels of androgen receptor mRNA in the hypothalamus (hypo) and prefrontal cortex (PFC) were higher in male mice than in female mice. Estrogen receptor α (ERα) mRNA levels in the hypo and hippocampus were higher in male mice than in female mice before birth. In contrast, ERβ mRNA expression in the PFC was higher in female mice immediately after birth. These spatiotemporal sex differences in steroid receptor expression might contribute to organizing sex differences of not only reproductive function, but also anxiety, stress responses, and cognition in mice.

Estrogen receptor β expression in the mouse forebrain: age and sex differences

Estrogen receptors regulate multiple brain functions, including stress, sexual, and memory-associated behaviors as well as controlling neuroendocrine and autonomic function. During development, estrogen signaling is involved in programming adult sex differences in physiology and behavior. Expression of estrogen receptor α changes across development in a region-specific fashion. By contrast, estrogen receptor β (ERβ) is expressed in many brain regions, yet few studies have explored sex and developmental differences in its expression, largely because of the absence of selective reagents for anatomical localization of the protein. This study utilized bacterial artificial chromosome transgenic mice expressing ERβ identified by enhanced green fluorescent protein (EGFP) to compare expression levels and distribution of ERβ in the male and female mouse forebrain on the day of birth (P0), on postnatal day 4 (P4), and on P21. By using qualitative analysis, we mapped the distribution of ERβ-EGFP and found developmental alterations in ERβ expression within the cortex, hippocampus, and hypothalamic regions including the arcuate, ventromedial, and paraventricular nuclei. We also report a sex difference in ERβ in the bed nucleus of the stria terminalis, with males showing greater expression at P4 and P21. Another sex difference was found in the anteroventral periventricular nucleus of P21, but not P0 or P4, mice, in which ERβ-EGFP-immunoreactive cells were densely clustered near the third ventricle in females but not males. These developmental changes and sex differences in ERβ indicate a mechanism through which estrogens might differentially affect brain functions or program adult physiology at select times during development.

Neonatal overexpression of estrogen receptor-α alters midbrain dopamine neuron development and reverses the effects of low maternal care in female offspring

Maternal behavior is dependent on estrogen receptor-alpha (ERα; Esr1) and oxytocin receptor (OTR) signaling in the medial preoptic area (MPOA) of the hypothalamus, as well as dopamine signaling from the ventral tegmental area (VTA) to forebrain regions. Previous studies in rats indicate that low levels of maternal care, particularly licking/grooming (LG), lead to reduced levels of MPOA ERα and VTA dopamine neurons in female offspring and predict lower levels of postpartum maternal behavior by these offspring. The aim of this study was to determine the functional impact on maternal behavior of neonatal manipulation of ERα in females that had experienced low versus high levels of postnatal maternal LG. Adenovirus expressing ESR1 was targeted to the MPOA in female pups from low and high LG litters on postnatal day 2-3. Overexpression of ESR1 in low LG offspring elevated the level of ERα-immunoreactive cells in the MPOA and of tyrosine hydroxylase cells in the VTA to that observed in high LG females. Amongst juvenile female low LG offspring, ESR1 overexpression also decreased the latency to engage in maternal behavior toward donor pups. These results show that virally mediated expression of ESR1 in the neonatal rat hypothalamus results in lasting changes in ESR1 expression through the juvenile period, and can "rescue" hormone receptor levels and behavior of offspring reared by low LG dams, potentially mediated by downstream alterations within reward circuitry. Thus, the transmission of maternal behavior from one generation to the next can be augmented by neonatal ERα in the MPOA.

Epigenetic mechanisms in pubertal brain maturation

Puberty is a critical period of development during which the reemergence of gonadotropin-releasing hormone secretion from the hypothalamus triggers a cascade of hormone-dependent processes. Maturation of specific brain regions including the prefrontal cortex occurs during this window, but the complex mechanisms underlying these dynamic changes are not well understood. Particularly, the potential involvement of epigenetics in this programming has been under-examined. The epigenome is known to guide earlier stages of development, and it is similarly poised to regulate vital pubertal-driven brain maturation. Further, as epigenetic machinery is highly environmentally responsive, its involvement may also lend this period of growth to greater vulnerability to external insults, resulting in reprogramming and increased disease risk. Importantly, neuropsychiatric diseases commonly present in individuals during or immediately following puberty, and environmental perturbations including stress may precipitate disease onset by disrupting the normal trajectory of pubertal brain development via epigenetic mechanisms. In this review, we discuss epigenetic processes involved in pubertal brain maturation, the potential points of derailment, and the importance of future studies for understanding this dynamic developmental window and gaining a better understanding of neuropsychiatric disease risk.

The effects of different doses of estradiol (E2) on cerebral ischemia in an in vitro model of oxygen and glucose deprivation and reperfusion and in a rat model of middle carotid artery occlusion

BACKGROUND

Because neuroprotective effects of estrogen remain controversial, we aimed to investigate the effect of different doses of estradiol (E2) on cerebral ischemia using both in vivo and in vitro experiments.

RESULTS

PC12 cells were cultured at physiological (10 nM and 20 nM) or pharmacological (10 μM and 20 μM) dosages of E2 for 24 hours (h). The results of 5-bromodeoxyuridine (Brdu) incorporation and flow cytometric analysis showed that physiological doses of E2 enhanced cell proliferation and pharmacological doses of E2 inhibited cell proliferation. After the cells were exposed to oxygen and glucose deprivation (OGD) for 4 h and reperfusion for 20 h, the results of 3-(4, 5-dimethylthiazol-2-yl) 2, 5-diphenyl tetrazolium bromide (MTT) assay, lactate dehydrogenase (LDH) release assay, flow cytometric analysis and Western blot analysis showed that physiological doses of E2 enhanced cell viability, reduced cell apoptosis and decreased the expression of pro-apoptotic protein caspase-3. In contrast, pharmacological doses of E2 decreased cell viability and induced cell apoptosis. In vivo, adult ovariectomized (OVX) female rats received continuous subcutaneous injection of different doses of E2 for 4 weeks. Transient cerebral ischemia was induced for 2 h using the middle cerebral artery occlusion (MCAO) technique, followed by 22 h of reperfusion. The results of Garcia test, 2, 3, 5-triphenyltetrazolium chloride (TTC) staining showed that 6 μg/kg and 20 μg/kg E2 replacement induced an increase in neurological deficit scores, a decrease in the infarct volume and a reduction in the expression of caspase-3 when compared to animals in the OVX group without E2 treatment. However, 50 μg/kg E2 replacement treatment decreased neurological deficit scores, increased the infarct volume and the expression of caspase-3 when compared to animals in the control group and 6 up/kg or 20 μg/kg E2 replacement group.

CONCLUSION

We conclude that physiological levels of E2 exhibit neuroprotective effects on cerebral ischemia; whereas, pharmacological or supraphysiological doses of E2 have damaging effects on neurons after cerebral ischemia.

A place for ultrastructural analysis of platelets in cerebral ischemic research

It is well known that estrogen is neuroprotective through various mechanisms which suggest that sex hormone levels, thrombotic mechanisms, and inflammatory processes are strongly interconnected in predicting the outcome and consequences of cerebral ischemia. Because platelet ultrastructure is altered in conditions like thrombosis and associated with stroke, the question arises whether ultrastructural analyses of platelet morphology may provide further insight into the role of estrogen during ischemic insult. In the current study, a hyperglycemic modification to the two-vessel occlusion model for inducing experimental cerebral ischemia was employed, in order to correlate neural tissue integrity levels between three experimental groups to corresponding platelet ultrastructure so as to determine whether there is an association between cerebral ischemia and the presence of inflammatory or necrotic platelet ultrastructure. It is apparent in the results that under the influence of estrogen in cyclic or intact females, there is lesser neural tissue damage as well as a reduced degree of inflammation evident in platelet activation morphology when compared to males and acyclic or ovariectomized females. It is unmistakable that neural injury is closely shadowed, if not preceded, by inflammatory changes in the coagulation system, particularly manifested in platelet ultrastructure. It is therefore suggested that platelets may indeed be used successfully to follow the progression of events of cerebral ischemia and possibly assist in the assessment of treatment strategies and their effects on hemostasis.

Visualisation and characterisation of oestrogen receptor α-positive neurons expressing green fluorescent protein under the control of the oestrogen receptor α promoter

Oestrogen receptor (ER)α plays important roles in the development and function of various neuronal systems through activation by its ligands, oestrogens. To visualise ERα-positive neurons, we generated transgenic (tg) mice expressing green fluorescent protein (GFP) under the control of the ERα promoter. In three independent tg lines, GFP-positive neurons were observed in areas previously reported to express ERα mRNA, including the lateral septum, bed nucleus of the stria terminalis, medial preoptic nucleus (MPO), hypothalamus, and amygdala. In these areas, GFP signals mostly overlapped with ERα immunoreactivity. GFP fluorescence was seen in neurites and cell bodies of neurons. In addition, the network and detailed structure of neurites were visible in dissociated and slice cultures of hypothalamic neurons. We examined the effect of oestrogen deprivation by ovariectomy on the structure of the GFP-positive neurons. The area of ERα-positive cell bodies in the bed nucleus of the stria terminalis and MPO was measured by capturing the GFP signal and was found to be significantly smaller in ovariectomy mice than in control mice. When neurons in the MPO were infected with an adeno-associated virus that expressed small hairpin RNA targeting the ERα gene, an apparent induction of GFP was observed in this area, suggesting a negative feedback mechanism in which ERα controls expression of the ERα gene itself. Thus, the ERα promoter-GFP tg mice will be useful to analyse the development and plastic changes of the structure of ERα-expressing neurons and oestrogen and its receptor-mediated neuronal responses.

Stroke: understanding the differences between males and females

Stroke is a significant cause of death and long-term disability in the USA. The incidence, mortality, and outcomes of stroke are significantly different between men and women. As with many diseases that affect men and women differently, an understanding on the reasons underlying those differences is critical to effective diagnosis and treatment. This review will examine the sex differences in stroke in both humans and animal models of stroke and review what is known about potential mechanisms underlying these differences. It is clear that there is a complex interaction between hormonal, genetic, and unknown factors at play in generating the sex differences in stroke.

Developmental regulation of neuronal genes by DNA methylation: environmental influences

Steroid hormones have wide-ranging organizational, activational and protective actions in the brain. In particular, the organizational effects of early exposure to 17β-estradiol (E2) and glucocorticoids are essential for long-lasting behavioral and cognitive functions. Both steroid hormones mediate many of their actions through intracellular receptors that act as transcription factors. In the rodent cerebral cortex, estrogen receptor mRNA and protein expression are high early in postnatal life and declines dramatically as the animal approaches puberty. An understanding of the molecular mechanisms driving this developmental regulation of gene expression is critical for understanding the complex events that determine lasting brain physiology and prime the plasticity of neurons. Gene expression can be suppressed by the epigenetic modification of the promoter regions by DNA methylation that results in gene silencing. Indeed, the decrease in ERα mRNA expression in the cortex during development is accompanied by an increase in promoter methylation. Numerous environmental stimuli can alter the DNA methylation that occurs for ERα, glucocorticoid receptors, as well as many other critical genes involved in neuronal development. For example, maternal behavior toward pups can alter epigenetic regulation of ERα mRNA expression. Additionally perinatal stress and exposure to environmental estrogens can also have lasting effects on gene expression by modifying DNA methylation of these important genes. Taken together, there appears to be a critical window during development where, outside factors that alter epigenetic programming can have lasting effects on neuronal gene expression.

Sexually dimorphic expression of receptor-alpha in the cerebral cortex of neonatal Caiman latirostris (Crocodylia: Alligatoridae)

In mammals, estrogens have been described as endocrine and paracrine modulators of neuronal differentiation and synapse formation. However, the functional role of circulating estrogens and the distribution of estrogen receptors (ERs) in the cerebral cortex of reptiles have not been clearly established. Caiman latirostris (C. latirostris) is a South American species that presents temperature-dependent sex determination (TSD). By using immunohistochemistry, we have studied the distribution of ERα in the cerebral cortex of neonatal caimans. We studied brain samples from ten-day-old TSD-females and TSD-males and from female caimans that were administered estradiol during embryonic development (hormone-dependent sex determination, HSD-females). ERα was detected in the medial (MC), dorsal (DC) and lateral (LC) cortices. ERα expression in the MC showed sex-associated differences, being significantly greater in TSD-females compared to TSD-males. Interestingly, the highest ERα expression in the MC was exhibited by HSD-females. In addition, the circulating levels of estradiol were significantly higher in females (both TSD and HSD) than in TSD-males. Double immunostaining showed that ERα is expressed by neural precursor cells (as detected by ERα/doublecortin or ERα/glial fibrillary acidic protein) and mature neurons (ERα/neuron-specific nuclear protein). Our results demonstrate that the expression of ERα in the neonatal caiman cortex is sexually dimorphic and is present in the early stages of neuronal differentiation.

Hormonal programming across the lifespan

Hormones influence countless biological processes across an animal's lifespan. Many hormone-mediated events occur within developmental sensitive periods, during which hormones have the potential to cause permanent tissue-specific alterations in anatomy and physiology. There are numerous selective critical periods in development with different targets being affected during different periods. This review outlines the proceedings of the Hormonal Programming in Development session at the US-South American Workshop in Neuroendocrinology in August 2011. Here we discuss how gonadal steroid hormones impact various biological processes within the brain and gonads during early development and describe the changes that take place in the aging female ovary. At the cellular level, hormonal targets in the brain include neurons, glia, or vasculature. On a genomic/epigenomic level, transcription factor signaling and epigenetic changes alter the expression of critical hormone receptor genes across development and following ischemic brain insult. In addition, organizational hormone exposure alters epigenetic processes in specific brain nuclei and may be an important mediator of sexual differentiation of the neonatal brain. Brain targets of hormonal programming, such as the paraventricular nucleus of the hypothalamus, may be critical in influencing the development of peripheral targets, such as the ovary. Exposure to excess hormones can cause abnormalities in the ovary during development leading to polycystic ovarian syndrome (PCOS). Exposure to excess androgens during fetal development also has a profound effect on the development of the male reproductive system. In addition, increased activity of the sympathetic nerve and stress during early life have been linked to PCOS symptomology in adulthood. Finally, we describe how age-related decreases in fertility are linked to high levels of nerve growth factor (NGF), which enhances sympathetic nerve activity and alters ovarian function.

Regulation of estrogen receptor alpha gene expression in the mouse prefrontal cortex during early postnatal development

Estrogens have many functions in the developing rodent brain, and most of these depend on the presence of estrogen receptors. Understanding how expression of these receptors are regulated is crucial for understanding the roles of estradiol in the male and female brain during development In rodents, the prefrontal cortex (PFC) has been shown to be involved in working memory, attention, and behavioral inhibition. Many studies have demonstrated an effect of estradiol on sex difference in these functions attributed to differences in the PFC. We have previously demonstrated that estrogen receptor alpha (ERα) expression decreases in the isocortex across early postnatal development. This decrease corresponds with an increase in methylation of many sites along the ERα promoter. Here we have examined both ERα and ERβ mRNA expression in the PFC to determine if methylation also plays a role in this important brain region. We investigated expression of alternate promoters for ERα and methylation of CpG sites along two of these promoters. We found that the pattern of ERα mRNA expression in PFC was similar to the pattern of ERα expression in the isocortex and that there were no sex differences in the level of expression across development. We did, however, find subtle differences in promoter expression and methylation that may indicate a sex-specific difference in PFC during development resulting in a difference in adult response.

Cell Models for the Study of Sex Steroid Hormone Neurobiology

To date many aspects of neurons and glia biology remain elusive, due in part to the cellular and molecular complexity of the brain. In recent decades, cell models from different brain areas have been established and proven invaluable toward understanding this complexity. In the field of steroid hormone neurobiology, an important question is: what is the profile of steroid hormone receptor expression in these specific cell lines? Currently, a clear summary of such receptor profiling is lacking. For this reason, we summarized in this review the expression of estrogen, progesterone, and androgen receptors in several widely used cell lines (glial and neuronal) derived from the forebrain and midbrain, based on our own data and that from the literature. Such information will aid in the selection of specific cell lines used to test hypotheses related to the biology of estrogens, progestins, and/or androgens.

Expression of Estrogen Receptor α and β in Rat Astrocytes in Primary Culture: Effects of Hypoxia and Glucose Deprivation

Estrogen replacement therapy could play a role in the reduction of injury associated with cerebral ischemia in vivo, which could be, at least partially, a consequence of estrogen influence of glutamate buffering by astrocytes during hypoxia/ischemia. Estrogen exerts biological effects through interaction with its two receptors: estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ), which are both expressed in astrocytes. This study explored effects of hypoxia and glucose deprivation (HGD), alone or followed by 1 h recovery, on ERα and ERβ expression in primary rat astrocyte cultures following 1 h exposure to: a) 5 % CO2 in air (control group-CG); b) 2 % O2/5 % CO2 in N2 with glucose deprivation (HGD group-HGDG); or c) the HGDG protocol followed by 1 h CG protocol (recovery group-RG). ERα mRNA expression decreased in HGDG. At the protein level, full-length ERα (67 kDa) and three ERα-immunoreactive protein bands (63, 60 and 52 kDa) were detected. A significant decrease in the 52 kDa band was seen in HGDG, while a significant decrease in expression of the full length ERα was seen in the RG. ERβ mRNA and protein expression (a 54 kDa single band) did not change. The observed decrease in ERα protein may limit estrogen-mediated signalling in astrocytes during hypoxia and recovery.

Sexual dimorphism in ischemic stroke: lessons from the laboratory

Ischemic stroke is emerging as a major health problem for elderly women. Women have lower stroke incidence than men until an advanced age, when the epidemiology of ischemic stroke shifts and incidence rises dramatically in women. Experimental models of rodent stroke have replicated this clinical epidemiology, with exacerbated injury in older compared with young female rodents. Many of the detrimental effects of aging on ischemic stroke outcome in females can be replicated by ovariectomy, suggesting that hormones such as estrogen play a neuroprotective role. However, emerging data suggest that the molecular mechanisms leading to ischemic cell death differ in the two sexes, and these effects may be independent of circulating hormone levels. This article highlights recent clinical and experimental literature on sex differences in stroke outcomes and mechanisms.

Expression and localization of aromatase P450AROM, estrogen receptor-α, and estrogen receptor-β in the developing fetal bovine frontal cortex

The enzyme aromatase (P450(AROM)) converts testosterone (T) into 17-β estradiol (E(2)) and is crucial for the control of development of the central nervous system during ontogenesis. The effects of E(2) in various brain areas are mediated by the estrogen receptor alpha (ER-α) and the estrogen receptor beta (ER-β). During fetal development, steroids are responsible for the sexual differentiation of the hypothalamus. Estrogens are also able to exert effects in other brain areas of the fetus including the frontal cortex, where they act through estrogen receptors (ERs) modulating cognitive function and affective behaviors. In this study we have determined the expression profiles of P450(AROM) and ERs in the fetal bovine frontal cortex by quantitative Real-Time PCR (qRT-PCR) throughout the prenatal development. The data show that the patterns of expression of both ERs are strongly correlated during pregnancy and increase in the last stage of gestation. On the contrary, the expression of P450(AROM) has no correlation with ERs expression and is not developmentally regulated. Moreover, we performed immunochemical studies showing that fetal neurons express P450(AROM) and the ERs. P450(AROM) is localized in the cytoplasm and only seldom present in the fine extensions of the cells; ER-α is detected predominantly in the soma whereas ER-β is only present in the nucleus of a few cells. This study provides new data on the development of the frontal cortex in a long gestation mammal with a large convoluted brain.

Epigenetic underpinnings of developmental sex differences in the brain

Sexual differentiation of the brain is a crucial developmental process that enables the lifelong expression of sexually dimorphic behaviors, including those necessary for successful reproduction. During a perinatal sensitive period, gonadal hormones defeminize and masculinize the male brain, and a lack of gonadal steroids allows for feminization in the female. This hormonally-induced differentiation permanently alters neural structures, creating highly dimorphic brain regions; however, the mechanism by which hormones exert their long-lasting effects are still largely unknown. Epigenetic processes such as DNA methylation and histone modifications serve as an interface for environmental stimuli to exert control over the genome. These modifications have the capacity to activate or repress gene expression, thereby shaping the developmental outcomes of cells, circuits, and structures in the brain. Sex differences in methylation, methyl-binding proteins, and chromatin modifications indicate that epigenetic mechanism may be important for sexual differentiation of the brain. The data outlined in this review provide evidence that gonadal hormones in the neonatal brain influence epigenetic processes such as DNA methylation and histone acetylation, but also emphasize the primitive status of our current understanding of epigenetics and sexual differentiation and the brain.

Estrogen receptor-alpha gene expression in the cortex: sex differences during development and in adulthood

17β-estradiol is a hormone with far-reaching organizational, activational and protective actions in both male and female brains. The organizational effects of early estrogen exposure are essential for long-lasting behavioral and cognitive functions. Estradiol mediates many of its effects through the intracellular receptors, estrogen receptor-alpha (ERα) and estrogen receptor-beta (ERβ). In the rodent cerebral cortex, estrogen receptor expression is high early in postnatal life and declines dramatically as the animal approaches puberty. This decline is accompanied by decreased expression of ERα mRNA. This change in expression is the same in both males and females in the developing isocortex and hippocampus. An understanding of the molecular mechanisms involved in the regulation of estrogen receptor alpha (ERα) gene expression is critical for understanding the developmental, as well as changes in postpubertal expression of the estrogen receptor. One mechanism of suppressing gene expression is by the epigenetic modification of the promoter regions by DNA methylation that results in gene silencing. The decrease in ERα mRNA expression during development is accompanied by an increase in promoter methylation. Another example of regulation of ERα gene expression in the adult cortex is the changes that occur following neuronal injury. Many animal studies have demonstrated that the endogenous estrogen, 17β-estradiol, is neuroprotective. Specifically, low levels of estradiol protect the cortex from neuronal death following middle cerebral artery occlusion (MCAO). In females, this protection is mediated through an ERα-dependent mechanism. ERα expression is rapidly increased following MCAO in females, but not in males. This increase is accompanied by a decrease in methylation of the promoter suggesting a return to the developmental program of gene expression within neurons. Taken together, during development and in adulthood, regulation of ERα gene expression in the cortex can occur by DNA methylation and in a sex-dependent fashion in the adult brain.

A developmental sex difference in hippocampal neurogenesis is mediated by endogenous oestradiol

Background

Oestradiol is a steroid hormone that exerts extensive influence on brain development and is a powerful modulator of hippocampal structure and function. The hippocampus is a critical brain region regulating complex cognitive and emotional responses and is implicated in the aetiology of several mental health disorders, many of which exhibit some degree of sex difference. Many sex differences in the adult rat brain are determined by oestradiol action during a sensitive period of development. We had previously reported a sex difference in rates of cell genesis in the developing hippocampus of the laboratory rat. Males generate more new cells on average than females. The current study explored the effects of both exogenous and endogenous oestradiol on this sex difference.

Methods

New born male and female rat pups were injected with the mitotic marker 5-bromo-2-deoxyuridine (BrdU) and oestradiol or agents that antagonize oestradiol action. The effects on cell number, proliferation, differentiation and survival were assessed at several time points. Significant differences between groups were determined by two- or thee-Way ANOVA.

Results

Newborn males had higher rates of cell proliferation than females. Oestradiol treatment increased cell proliferation in neonatal females, but not males, and in the CA1 region many of these cells differentiated into neurons. The increased rate of proliferation induced by neonatal oestradiol persisted until at least 3 weeks of age, suggesting an organizational effect. Administering the aromatase inhibitor, formestane, or the oestrogen receptor antagonist, tamoxifen, significantly decreased the number of new cells in males but not females.

Conclusion

Endogenous oestradiol increased the rate of cell proliferation observed in newborn males compared to females. This sex difference in neonatal neurogenesis may have implications for adult differences in learning strategy, stress responsivity or vulnerability to damage or disease.

Epigenetic regulation of estrogen receptor alpha gene expression in the mouse cortex during early postnatal development

Estrogens play a critical role in brain development by acting on areas that express estrogen receptors. In the rodent cortex, estrogen receptor alpha (ER alpha) mRNA expression is high early in postnatal development but declines starting at postnatal day (PND) 10 and is virtually absent in the adult cortex. The mechanisms controlling this regulation are largely unknown. Methylation is important for gene silencing during development in many tissues, including the brain. In the present study, we examined the methylation status of ER alpha 5' untranslated exons during early postnatal development in male and female mice using methylation-specific PCR and pyrosequencing. Several regions of ER alpha promoter displayed a significant increase in methylation at PND 18 and 25 compared with PND 4. DNA methyltransferases (DNMT) are important for the initiation and maintenance of methylation. Real-time PCR showed that DNMT3A, the de novo DNMT peaked at PND 10 and was decreased by PND 25. DNMT1, which is important for maintenance of methylation, increased across development and stayed high in adult cortex. The methyl-CpG-binding protein 2 (MeCP2) is also important for stabilization of methylation. A chromatin immunoprecipitation assay showed a correlation between association of MeCP2 with ER alpha promoter and the increase in methylation and decrease in ER alpha expression after PND 10. In mice containing a mutant MeCP2 protein, ER alpha mRNA expression and promoter methylation patterns across development were different compared with wild-type mice. These data suggest that methylation of ER alpha promoters regulates ER alpha mRNA expression in the cortex during postnatal development in a MeCP2-dependent fashion.

Estradiol: a hormone with diverse and contradictory neuroprotective actions

The concept that estrogens exert important neuroprotective actions has gained considerable attention during the past decade. Numerous studies have provided a deep understanding of the seemingly contradictory actions of estrogens. We realize more than ever that the effects of estrogens (with and without simultaneous or sequential progestins) are diverse and sometimes opposite, depending on the use of different estrogenic and progestinic compounds, on different delivery routes, on different concentrations, on treatment sequence, and on the age and health status of the women who receive hormone therapy. During the past few years, we have gained an increasing appreciation of the impact of estrogens on the immune system and on inflammation. In addition, we have learned that estrogens cannot only protect against cell death, but can also stimulate the birth of new neurons. Here we posit the concept that estrogen's modulation of the immune status may be the basic mechanism that underlies its ability to protect against neurodegeneration and its powerful neuroregenerative actions. We hope that this update will encourage even richer dialogues between basic and clinical scientists to ensure that future clinical studies fully consider the information that can be derived from basic science studies. Only then will we have a better understanding of the impact of hormones on the menopausal and postmenopausal period in a woman's life.

The epigenetics of sex differences in the brain

Epigenetic changes in the nervous system are emerging as a critical component of enduring effects induced by early life experience, hormonal exposure, trauma and injury, or learning and memory. Sex differences in the brain are largely determined by steroid hormone exposure during a perinatal sensitive period that alters subsequent hormonal and nonhormonal responses throughout the lifespan. Steroid receptors are members of a nuclear receptor transcription factor superfamily and recruit multiple proteins that possess enzymatic activity relevant to epigenetic changes such as acetylation and methylation. Thus steroid hormones are uniquely poised to exert epigenetic effects on the developing nervous system to dictate adult sex differences in brain and behavior. Sex differences in the methylation pattern in the promoter of estrogen and progesterone receptor genes are evident in newborns and persist in adults but with a different pattern. Changes in response to injury and in methyl-binding proteins and steroid receptor coregulatory proteins are also reported. Many steroid-induced epigenetic changes are opportunistic and restricted to a single lifespan, but new evidence suggests endocrine-disrupting compounds can exert multigenerational effects. Similarly, maternal diet also induces transgenerational effects, but the impact is sex specific. The study of epigenetics of sex differences is in its earliest stages, with needed advances in understanding of the hormonal regulation of enzymes controlling acetylation and methylation, coregulatory proteins, transient versus stable DNA methylation patterns, and sex differences across the epigenome to fully understand sex differences in brain and behavior.

Neuroprotective effects of estrogens following ischemic stroke

Our laboratory has investigated whether and how 17beta-estradiol (E(2)) protects the brain against neurodegeneration associated with cerebrovascular stroke. We have discovered that low, physiological concentrations of E(2), which are strikingly similar to low-basal circulating levels found in cycling mice, dramatically protect the brain against stroke injury, and consequently revealed multiple signaling pathways and key genes that mediate protective action of E(2). Here we will review the discoveries comprising our current understanding of neuroprotective actions of estrogens against ischemic stroke. These findings may carry far reaching implications for improving the quality of life in aging populations.

Functional interaction of DYX1C1 with estrogen receptors suggests involvement of hormonal pathways in dyslexia

Dyslexia, or specific reading disability, is the unexpected failure in learning to read and write when intelligence and senses are normal. One of the susceptibility genes, DYX1C1, has been implicated in neuronal migration, but little is known about its interactions and functions. As DYX1C1 was suggested to interact with the U-box protein CHIP (carboxy terminus of Hsc70-interacting protein), which also participates in the degradation of estrogen receptors alpha (ERalpha) and beta (ERbeta), we hypothesized that the effects of DYX1C1 might be at least in part mediated through the regulation of ERs. ERs have shown to be important in brain development and cognitive functions. Indeed, we show that DYX1C1 interacts with both ERs in the presence of 17beta-estradiol, as determined by co-localization, co-immunoprecipitation and proximity ligation assays. Protein levels of endogenous ERalpha or exogenous ERbeta were reduced upon over-expression of DYX1C1, resulting in decreased transcriptional responses to 17beta-estradiol. Furthermore, we detected in vivo complexes of DYX1C1 with ERalpha or ERbeta at endogenous levels along neurites of primary rat hippocampal neurons. Taken together, our data suggest that DYX1C1 is involved in the regulation of ERalpha and ERbeta, and may thus affect the brain development and regulate cognitive functions. These findings provide novel insights into the function of DYX1C1 and link neuronal migration and developmental dyslexia to the estrogen-signaling effects in the brain.

Regulation of oestrogen receptor gene expression: new insights and novel mechanisms

17Beta-oestradiol is a pleiotropic hormone with organisational, activational and protective actions in both male and female mammals. It is responsible for numerous aspects of brain development, including sexual differentiation of the brain. The organisational effects of early oestrogen exposure are essential for long-lasting cognitive and behavioural functions. Oestradiol mediates its effects through several intracellular or membrane-associated receptor proteins. In the rodent cerebral cortex, oestrogen receptor (ER) expression, as demonstrated by hormone binding studies, is high early in postnatal life and declines precipitously as the animal approaches puberty. This decline is caused by a decreased expression of ERalpha mRNA. An understanding of the mechanisms involved in the regulation of ERalpha gene expression is critical for understanding the developmental as well as postpubertal expression of the ER. Despite recent data indicating the current hormone replacement therapies can be detrimental in older women, numerous animal studies have shown that the endogenous oestrogen, 17beta-oestradiol, is neuroprotective. Specifically, low levels of oestradiol protect the cortex from cell death caused by middle cerebral artery occlusion (MCAO). The attenuation of cell death by oestradiol in this model is mediated through an ERalpha-dependent mechanism. To this end, ERalpha expression is rapidly increased after MCAO, suggesting a return to the developmental programme of gene expression within neurones. One mechanism of suppressing gene expression is by the epigenetic modification of the promoter regions, which results in gene silencing. Of the epigenetic modifications utilised by cells, DNA methylation has been intensively studied as a mechanism by which genes are both permanently and reversibly silenced. Little is known about the mechanisms of ER gene regulation in the brain; however, in breast cancer cells, both ERalpha and ERbeta are down-regulated by promoter methylation, and subsequent binding of the methyl-CpG-binding protein, MeCP2. Data from our laboratory demonstrate that the promoters of the ERalpha gene are also methylated during development and after neuronal injury, suggesting a role of DNA methylation in regulating ER expression in the brain.

Oestrogen receptor alpha localisation in the prefrontal cortex of three mammalian species

Oestrogen modulates cognitive function and affective behaviours subserved by the prefrontal cortex (PFC). Identifying and localising oestrogen receptor (ER)alpha, in human PFC will contribute to our understanding of the molecular mechanism of oestrogen action in this region. Inferences about the site of action of oestrogen in human brain are derived largely from studies performed in nonhuman mammalian species; however, the congruence of findings across species has not been demonstrated. Furthermore, the laminar, cellular, and subcellular localisation of ERalpha in the cortex is debated. Therefore, we compared the distribution of ERalpha in human dorsolateral prefrontal cortex (DLPFC) with that of monkey DLPFC and rat medial PFC. Immunohistochemistry performed on frontal cortex from the three species demonstrated ERalpha positive cells throughout all layers of the PFC, in pyramidal and nonpyramidal neurones, with both nuclear and cytoplasmic immunoreactivity. Western blot analyses and preabsorption studies confirmed that the antibody used recognised ERalpha and not ERbeta. A strong ERalpha immunoreactive band corresponding to the full-length ERalpha protein (65-67 kDa) in the frontal cortex of all three species matched the size of the predominant immunoreactive band detected in breast cancer cell lines known to express ERalpha. Additionally, other ERalpha immunoreactive proteins of varying molecular weight in breast cancer cells, rat ovary and mammalian brain were detected, suggesting that ERalpha may exist in more than one form in the mammalian frontal cortex. The present study provides evidence that ERalpha protein exists in neurones in mammalian PFC and that ERalpha is anatomically well-positioned to directly mediate oestrogen action in these neurones.

Dynamic regulation of estrogen receptor-alpha gene expression in the brain: a role for promoter methylation?

Estrogen has long been known to play an important role in coordinating the neuroendocrine events that control sexual development, sexual behavior and reproduction. Estrogen actions in other, non-reproductive areas of the brain have also been described. It is now known that estrogen can also influence learning, memory, and emotion and has neurotrophic and neuroprotective properties. The actions of estrogen are largely mediated through at least two intracellular estrogen receptors. Both estrogen receptor-alpha and estrogen receptor-beta are expressed in a wide variety of brain regions. Estrogen receptor-alpha (ERalpha), however, undergoes developmental and brain region-specific changes in expression. The precise molecular mechanisms that regulate its expression at the level of gene transcription are not well understood. Adding to the complexity of its regulation, the estrogen receptor gene contains multiple promoters that drive its expression. In the cortex in particular, the ERalpha mRNA expression is dynamically regulated during postnatal development and again following neuronal injury. Epigenetic modification of chromatin is increasingly being understood as a mechanism of neuronal gene regulation. This review examines the potential regulation of the ERalpha gene by such epigenetic mechanisms.

Epigenetic regulation of the estrogen receptor alpha promoter in the cerebral cortex following ischemia in male and female rats

Permanent middle cerebral artery occlusion (MCAO) causes neuronal cell death in the striatum and cortex. In rodents, estradiol treatment protects the cortex from cell death in an estrogen receptor alpha (ERalpha) dependent manner. ERalpha is only transiently expressed in the cortex during neonatal development and is very low in uninjured adult cortex. Following MCAO, ERalpha mRNA expression is upregulated in the cortex of female rats, but the mechanism of this increase is still unknown. It is also unknown whether a similar increase in ERalpha expression in seen in males. In the following studies, male and vehicle or estradiol-treated ovariectomized (OVX) female rats underwent MCAO to investigate the regulation of ERalpha expression after ischemia. Twenty-four hours after surgery, mRNA or genomic DNA was collected from 1 mm micropunches taken from 300 mum brain sections for quantitative reverse transcription-polymerase chain reaction (RT-PCR) or methylation-specific (MSP) PCR, respectively. Additionally, adjacent 20 mum sections were processed for ERalpha immunohistochemistry. In OVX females, ERalpha mRNA and protein were increased in the ischemic cortex, but unchanged in males. We hypothesized that this increase in ERalpha in females is due to a reversal of gene silencing by DNA methylation. Using MSP targeting of CpG islands within the 5' untranslated region (UTR) of the rat ERalpha gene, we found that ischemia decreased methylation in the ischemic cortex of both groups of females, but there was no change in methylation in males. Using chromatin immunoprecipitation, we found that MeCP2 associates with ERalpha 5'UTR corresponding with the methylation status of the promoter. These data are the first to demonstrate a difference in the regulation of ERalpha expression in response to MCAO between males and females and that methylation of the ERalpha gene corresponds with mRNA levels in the brain.