Role for the membrane estrogen receptor alpha in the sexual differentiation of the brain

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.

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.

Role of membrane estrogen receptor alpha (ERα) in the rapid regulation of male sexual behavior

The activation of male sexual behavior depends on brain estrogen synthesis. Estrogens act through nuclear and membrane receptors producing effects within hours/days or seconds/minutes, respectively. In mice, estrogen receptor alpha (ERα) is the main estrogen receptor (ER) controlling the activation of male sexual behavior. Although neuroestrogens rapidly modulate mouse sexual behavior, it is not known whether these effects involve membrane ERα (mERα). This study combines two complementary approaches to address this question. C451A-ERα mice carry an ERα that cannot signal at the membrane, while estetrol (E4) is a natural estrogen acting as an agonist on nuclear ERα but as an antagonist on membrane ERα. In wild-type males, E4 decreased the number of mounts and intromissions after 10 min. In C451A-ERα males, E4 also altered sexual performance but after 30 min. E4 did not affect time spent near the female in both wild-type and C451A-ERα mice. However, regardless of genotype, the aromatase inhibitor 1,4,6-Androstatriene-3,17-dione (ATD) decreased both sexual performance and the time spent near the female after 10 and 30 min, confirming the key role of aromatization in the rapid control of sexual behavior and motivation. In conclusion, the shift in timing at which the effect of E4 is observed in mice lacking mERα suggests a role for mERα in the regulation of rapid effects of neuroestrogens on sexual performance, thus providing the first demonstration that E4 acts as an antagonist of a mER in the brain. The persisting effect of ATD on behavior in C451A-ERα mice also suggests the implication of another ER.

Emerging Evidence on Membrane Estrogen Receptors as Novel Therapeutic Targets for Central Nervous System Pathologies

Nuclear- and membrane-initiated estrogen signaling cooperate to orchestrate the pleiotropic effects of estrogens. Classical estrogen receptors (ERs) act transcriptionally and govern the vast majority of hormonal effects, whereas membrane ERs (mERs) enable acute modulation of estrogenic signaling and have recently been shown to exert strong neuroprotective capacity without the negative side effects associated with nuclear ER activity. In recent years, GPER1 was the most extensively characterized mER. Despite triggering neuroprotective effects, cognitive improvements, and vascular protective effects and maintaining metabolic homeostasis, GPER1 has become the subject of controversy, particularly due to its participation in tumorigenesis. This is why interest has recently turned toward non-GPER-dependent mERs, namely, mERα and mERβ. According to available data, non-GPER-dependent mERs elicit protective effects against brain damage, synaptic plasticity impairment, memory and cognitive dysfunctions, metabolic imbalance, and vascular insufficiency. We postulate that these properties are emerging platforms for designing new therapeutics that may be used in the treatment of stroke and neurodegenerative diseases. Since mERs have the ability to interfere with noncoding RNAs and to regulate the translational status of brain tissue by affecting histones, non-GPER-dependent mERs appear to be attractive targets for modern pharmacotherapy for nervous system diseases.

Role of estrogen receptors in thyroid toxicity induced by mono (2-ethylhexyl) phthalate via endoplasmic reticulum stress: An in vitro mechanistic investigation

Mono(2-ethylhexyl) phthalate (MEHP) can influence the expression of estrogen receptors (ERs) and induce thyroid injury. The expression of ERs can be related to thyroid disease and abnormal expression of ERs has been associated with activation of endoplasmic reticulum stress. This study aimed to clarify the role of ERs in MEHP-induced thyroid damage via endoplasmic reticulum stress. We exposed Nthy-ori 3-1 cells to different doses of MEHP. We found that after the exposure, the cell viability and the expression levels of thyroid hormone metabolism-related proteins decreased, while the apoptosis level and the expression levels of ERs (ERα and GPR30) increased. Three endoplasmic reticulum stress-related signaling pathways were activated by MEHP. After ERα and GPR30 were knocked down, these three pathways were inhibited and the thyroid toxicity was alleviated. Taken together, our results indicate that MEHP can induce thyroid toxicity by upregulating the expression of ERs, further activating endoplasmic reticulum stress.

Membrane-Initiated Estrogen, Androgen, and Progesterone Receptor Signaling in Health and Disease

Rapid effects of steroid hormones were discovered in the early 1950s, but the subject was dominated in the 1970s by discoveries of estradiol and progesterone stimulating protein synthesis. This led to the paradigm that steroid hormones regulate growth, differentiation, and metabolism via binding a receptor in the nucleus. It took 30 years to appreciate not only that some cellular functions arise solely from membrane-localized steroid receptor (SR) actions, but that rapid sex steroid signaling from membrane-localized SRs is a prerequisite for the phosphorylation, nuclear import, and potentiation of the transcriptional activity of nuclear SR counterparts. Here, we provide a review and update on the current state of knowledge of membrane-initiated estrogen (ER), androgen (AR) and progesterone (PR) receptor signaling, the mechanisms of membrane-associated SR potentiation of their nuclear SR homologues, and the importance of this membrane-nuclear SR collaboration in physiology and disease. We also highlight potential clinical implications of pathway-selective modulation of membrane-associated SR.

Estrogen Receptor α Inactivation in 2 Sisters: Different Phenotypic Severities for the Same Pathogenic Variant

CONTEXT

Estrogens play an essential role in reproduction. Their action is mediated by nuclear α and β receptors (ER) and by membrane receptors. Only 3 females and 2 males, from 3 families, with a loss of ERα function have been reported to date.

OBJECTIVE

We describe here a new family, in which 2 sisters display endocrine and ovarian defects of different severities despite carrying the same homozygous rare variant of ESR1.

METHODS

A 36-year-old woman from a consanguineous Jordanian family presented with primary amenorrhea and no breast development, with high plasma levels of 17β-estradiol (E2), follicle-stimulating hormone and luteinizing hormone, and enlarged multifollicular ovaries, strongly suggesting estrogen resistance. Her 18-year-old sister did not enter puberty and had moderately high levels of E2, high plasma gonadotropin levels, and normal ovaries.

RESULTS

Genetic analysis identified a homozygous variant of ESR1 leading to the replacement of a highly conserved glutamic acid with a valine (ERα-E385V). The transient expression of ERα-E385V in HEK293A and MDA-MB231 cells revealed highly impaired ERE-dependent transcriptional activation by E2. The analysis of the KISS1 promoter activity revealed that the E385V substitution induced a ligand independent activation of ERα. Immunofluorescence analysis showed that less ERα-E385V than ERα-WT was translocated into the nucleus in the presence of E2.

CONCLUSION

These 2 new cases are remarkable given the difference in the severity of their ovarian and hormonal phenotypes. This phenotypic discrepancy may be due to a mechanism partially compensating for the ERα loss of function.

Effects of early life adversity on male reproductive behavior and the medial preoptic area transcriptome

Early life adversity can alter reproductive development in humans, changing the timing of pubertal onset and sexual activity. One common form of early adversity is limited access to resources. This adversity can be modeled in rats using the limited bedding/nesting model (LBN), in which dams and pups are placed in a low resource environment from pups' postnatal days 2-9. Our laboratory previously found that adult male rats raised in LBN conditions have elevated levels of plasma estradiol compared to control males. In females, LBN had no effect on plasma hormone levels, pubertal timing, or estrous cycle duration. Estradiol mediates male reproductive behaviors. Thus, here we compared reproductive behaviors in adult males exposed to LBN vs. control housing. LBN males acquired the suite of reproductive behaviors (mounts, intromissions, and ejaculations) more quickly than their control counterparts over 3 weeks of testing. However, there was no effect of LBN in males on puberty onset or masculinization of certain brain regions, suggesting LBN effects on estradiol and reproductive behaviors manifest after puberty. In male and female rats, we next used RNA sequencing to characterize LBN-induced transcriptional changes in the medial preoptic area (mPOA), which underlies male reproductive behaviors. LBN produced sex-specific alterations in gene expression, with many transcripts showing changes in opposite directions. Numerous transcripts altered by LBN in males are regulated by estradiol, linking hormonal changes to molecular changes in the mPOA. Pathway analysis revealed that LBN induced changes in neurosignaling and immune signaling in males and females, respectively. Collectively, these studies reveal novel neurobiological mechanisms by which early life adversity can alter reproductive strategies.

Deletion of neural estrogen receptor alpha induces sex differential effects on reproductive behavior in mice

Estrogen receptor (ER) α is involved in several estrogen-modulated neural and peripheral functions. To determine its role in the expression of female and male reproductive behavior, a mouse line lacking the ERα in the nervous system was generated. Mutant females did not exhibit sexual behavior despite normal olfactory preference, and had a reduced number of progesterone receptor-immunoreactive neurons in the ventromedial hypothalamus. Mutant males displayed a moderately impaired sexual behavior and unaffected fertility, despite evidences of altered organization of sexually dimorphic populations in the preoptic area. In comparison, males deleted for both neural ERα and androgen receptor (AR) displayed greater sexual deficiencies. Thus, these data highlight a predominant role for neural ERα in females and a complementary role with the AR in males in the regulation of sexual behavior, and provide a solid background for future analyses of neuronal versus glial implication of these signaling pathways in both sexes.

Neural deletion of the estrogen receptor, ERα, inhibits sexual behavior in female mice, but only has moderately effect in male mice. These results contrast with previous studies using global ERα knockouts, which found that ERα is mandatory for reproductive behavior in both sexes.

Segregation of nuclear and membrane-initiated actions of estrogen receptor using genetically modified animals and pharmacological tools

Estrogen receptor alpha (ERα) and beta (ERβ) are members of the nuclear receptor superfamily, playing widespread functions in reproductive and non-reproductive tissues. Beside the canonical function of ERs as nuclear receptors, in this review, we summarize our current understanding of extra-nuclear, membrane-initiated functions of ERs with a specific focus on ERα. Over the last decade, in vivo evidence has accumulated to demonstrate the physiological relevance of this ERα membrane-initiated-signaling from mouse models to selective pharmacological tools. Finally, we discuss the perspectives and future challenges opened by the integration of extra-nuclear ERα signaling in physiology and pathology of estrogens.

Hypothalamic Estrogen Signaling and Adipose Tissue Metabolism in Energy Homeostasis

Obesity has become a global epidemic, and it is a major risk factor for other metabolic disorders such as type 2 diabetes and cardiometabolic disease. Accumulating evidence indicates that there is sex-specific metabolic protection and disease susceptibility. For instance, in both clinical and experimental studies, males are more likely to develop obesity, insulin resistance, and diabetes. In line with this, males tend to have more visceral white adipose tissue (WAT) and less brown adipose tissue (BAT) thermogenic activity, both leading to an increased incidence of metabolic disorders. This female-specific fat distribution is partially mediated by sex hormone estrogens. Specifically, hypothalamic estrogen signaling plays a vital role in regulating WAT distribution, WAT beiging, and BAT thermogenesis. These regulatory effects on adipose tissue metabolism are primarily mediated by the activation of estrogen receptor alpha (ERα) in neurons, which interacts with hormones and adipokines such as leptin, ghrelin, and insulin. This review discusses the contribution of adipose tissue dysfunction to obesity and the role of hypothalamic estrogen signaling in preventing metabolic diseases with a particular focus on the VMH, the central regulator of energy expenditure and glucose homeostasis.

Membrane-initiated actions of sex steroids and reproductive behavior: A historical account

It was assumed for a long time that sex steroids are activating reproductive behaviors by the same mechanisms that produce their morphological and physiological effects in the periphery. However during the last few decades an increasing number of examples were identified where behavioral effects of steroids were just too fast to be mediated via changes in DNA transcription. This progressively forced behavioral neuroendocrinologists to recognize that part of the effects of steroids on behavior are mediated by membrane-initiated events. In this review we present a selection of these early data that changed the conceptual landscape and we provide a summary the different types of membrane-associated receptors (estrogens, androgens and progestagens receptors) that are playing the most important role in the control of reproductive behaviors. Then we finally describe in more detail three separate behavioral systems in which membrane-initiated events have clearly been established to contribute to behavior control.

Bisphenol A and Its Analogues Deteriorate the Hormones Physiological Function of the Male Reproductive System: A Mini-Review

BPA is identified as an endocrine-disrupting chemical that deteriorates the physiological function of the hormones of the male reproductive system. Bisphenol F (BPF), bisphenol S (BPS), and bisphenol AF (BPAF) are actively explored as substitutes for BPA and are known as BPA analogues in most manufacturing industries. These analogues may demonstrate the same adverse effects as BPA on the male reproductive system; however, toxicological data explaining the male reproductive hormones' physiological functions are still limited. Hence, this mini-review discusses the effects of BPA and its analogues on the physiological functions of hormones in the male reproductive system, focusing on the hypothalamus-pituitary-gonad (HPG) axis, steroidogenesis, and spermatogenesis outcomes. The BPA analogues mainly show a similar negative effect on the hormones' physiological functions, proven by alterations in the HPG axis and steroidogenesis via activation of the aromatase activity and reduction of spermatogenesis outcomes when compared to BPA in in vitro and in vivo studies. Human biomonitoring studies also provide significant adverse effects on the physiological functions of hormones in the male reproductive system. In conclusion, BPA and its analogues deteriorate the physiological functions of hormones in the male reproductive system as per in vitro, in vivo, and human biomonitoring studies.

Estrogens and the regulation of glucose metabolism

The main estrogens: estradiol, estrone, and their acyl-esters have been studied essentially related to their classical estrogenic and pharmacologic functions. However, their main effect in the body is probably the sustained control of core energy metabolism. Estrogen nuclear and membrane receptors show an extraordinary flexibility in the modulation of metabolic responses, and largely explain gender and age differences in energy metabolism: part of these mechanisms is already sufficiently known to justify both. With regard to energy, the estrogen molecular species act essentially through four key functions: (1) Facilitation of insulin secretion and control of glucose availability; (2) Modulation of energy partition, favoring the use of lipid as the main energy substrate when more available than carbohydrates; (3) Functional protection through antioxidant mechanisms; and (4) Central effects (largely through neural modulation) on whole body energy management. Analyzing the different actions of estrone, estradiol and their acyl esters, a tentative classification based on structure/effects has been postulated. Either separately or as a group, estrogens provide a comprehensive explanation that not all their quite diverse actions are related solely to specific molecules. As a group, they constitute a powerful synergic action complex. In consequence, estrogens may be considered wardens of energy homeostasis.

Estetrol and Mammary Gland: Friends or Foes?

Estrogens have pleiotropic effects on many reproductive and non-reproductive tissues and organs including the mammary gland, uterus, ovaries, vagina, and endothelium. Estrogen receptor α functions as the principal mediator of estrogenic action in most of these tissues. Estetrol (E4) is a native fetal estrogen with selective tissue actions that is currently approved for use as the estrogen component in a combined oral contraceptive and is being developed as a menopause hormone therapy (MHT, also known as hormone replacement therapy). However, exogenous hormonal treatments, in particular MHTs, have been shown to promote the growth of preexisting breast cancers and are associated with a variable risk of breast cancer depending on the treatment modality. Therefore, evaluating the safety of E4-based formulations on the breast forms a crucial part of the clinical development process. This review highlights preclinical and clinical studies that have assessed the effects of E4 and E4-progestogen combinations on the mammary gland and breast cancer, focusing in particular on the estrogenic and anti-estrogenic properties of E4. We discuss the potential advantages of E4 over current available estrogen-formulations as a contraceptive and for the treatment of symptoms due to menopause. We also consider the potential of E4 for the treatment of endocrine-resistant breast cancer.

The potential role of stress and sex steroids in heritable effects of sevoflurane

Most surgical procedures require general anesthesia, which is a reversible deep sedation state lacking all perception. The induction of this state is possible because of complex molecular and neuronal network actions of general anesthetics (GAs) and other pharmacological agents. Laboratory and clinical studies indicate that the effects of GAs may not be completely reversible upon anesthesia withdrawal. The long-term neurocognitive effects of GAs, especially when administered at the extremes of ages, are an increasingly recognized health concern and the subject of extensive laboratory and clinical research. Initial studies in rodents suggest that the adverse effects of GAs, whose actions involve enhancement of GABA type A receptor activity (GABAergic GAs), can also extend to future unexposed offspring. Importantly, experimental findings show that GABAergic GAs may induce heritable effects when administered from the early postnatal period to at least young adulthood, covering nearly all age groups that may have children after exposure to anesthesia. More studies are needed to understand when and how the clinical use of GAs in a large and growing population of patients can result in lower resilience to diseases in the even larger population of their unexposed offspring. This minireview is focused on the authors' published results and data in the literature supporting the notion that GABAergic GAs, in particular sevoflurane, may upregulate systemic levels of stress and sex steroids and alter expressions of genes that are essential for the functioning of these steroid systems. The authors hypothesize that stress and sex steroids are involved in the mediation of sex-specific heritable effects of sevoflurane.

Cellular and molecular features of EDC exposure: consequences for the GnRH network

The onset of puberty and the female ovulatory cycle are important developmental milestones of the reproductive system. These processes are controlled by a tightly organized network of neurotransmitters and neuropeptides, as well as genetic, epigenetic and hormonal factors, which ultimately drive the pulsatile secretion of gonadotropin-releasing hormone. They also strongly depend on organizational processes that take place during fetal and early postnatal life. Therefore, exposure to environmental pollutants such as endocrine-disrupting chemicals (EDCs) during critical periods of development can result in altered brain development, delayed or advanced puberty and long-term reproductive consequences, such as impaired fertility. The gonads and peripheral organs are targets of EDCs, and research from the past few years suggests that the organization of the neuroendocrine control of reproduction is also sensitive to environmental cues and disruption. Among other mechanisms, EDCs interfere with the action of steroidal and non-steroidal receptors, and alter enzymatic, metabolic and epigenetic pathways during development. In this Review, we discuss the cellular and molecular consequences of perinatal exposure (mostly in rodents) to representative EDCs with a focus on the neuroendocrine control of reproduction, pubertal timing and the female ovulatory cycle.

Key role of estrogen receptor β in the organization of brain and behavior of the Japanese quail

Estrogens play a key role in the sexual differentiation of the brain and behavior. While early estrogen actions exert masculinizing effects on the brain of male rodents, a diametrically opposite effect is observed in birds where estrogens demasculinize the brain of females. Yet, the two vertebrate classes express similar sex differences in the brain and behavior. Although ERα is thought to play a major role in these processes in rodents, the role of ERβ is still controversial. In birds, the identity of the estrogen receptor(s) underlying the demasculinization of the female brain remains unclear. The aim of the present study was thus to determine in Japanese quail the effects of specific agonists of ERα (propylpyrazole triol, PPT) and ERβ (diarylpropionitrile, DPN) administered at the beginning of the sensitive period (embryonic day 7, E7) on the sexual differentiation of male sexual behavior and on the density of vasotocin-immunoreactive (VT-ir) fibers, a known marker of the organizational action of estrogens on the quail brain. We demonstrate that estradiol benzoate and the ERβ agonist (DPN) demasculinize male sexual behavior and decrease the density of VT-ir fibers in the medial preoptic nucleus and the bed nucleus of the stria terminalis, while PPT has no effect on these measures. These results clearly indicate that ERβ, but not ERα, is involved in the estrogen-induced sexual differentiation of brain and sexual behavior in quail.

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.

17β-estradiol promotes acute refeeding in hungry mice via membrane-initiated ERα signaling

Objective

Estrogen protects animals from obesity through estrogen receptor α (ERα), partially by inhibiting overeating in animals fed ad libitum. However, the effects of estrogen on feeding behavior in hungry animals remain unclear. In this study, we examined the roles of 17β-estradiol (E2) and ERα in the regulation of feeding in hungry female animals and explored the underlying mechanisms.

Methods

Wild-type female mice with surgical depletion of endogenous estrogens were used to examine the effects of E2 supplementation on acute refeeding behavior after starvation. ERα-C451A mutant mice deficient in membrane-bound ERα activity and ERα-AF2⁰ mutant mice lacking ERα transcriptional activity were used to further examine mechanisms underlying acute feeding triggered by either fasting or central glucopenia (induced by intracerebroventricular injections of 2-deoxy-D-glucose). We also used electrophysiology to explore the impact of these ERα mutations on the neural activities of ERα neurons in the hypothalamus.

Results

In the wild-type female mice, ovariectomy reduced fasting-induced refeeding, which was restored by E2 supplementation. The ERα-C451A mutation, but not the ERα-AF2⁰ mutation, attenuated acute feeding induced by either fasting or central glucopenia. The ERα-C451A mutation consistently impaired the neural responses of hypothalamic ERα neurons to hypoglycemia.

Conclusion

In addition to previous evidence that estrogen reduces deviations in energy balance by inhibiting eating at a satiated state, our findings demonstrate the unexpected role of E2 that promotes eating in hungry mice, also contributing to the stability of energy homeostasis. This latter effect specifically requires membrane-bound ERα activity.

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Endogenous E2 is required to maintain acute refeeding in hungry female mice after starvation.

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Membrane-bound ERα activity in female mice is required for efficient refeeding after starvation.

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Membrane-bound ERα activity is required for hypothalamic ERα neurons to respond to hypoglycemia.

Sex matters in neuroscience and neuropsychopharmacology

Prevalence and symptoms of most psychiatric and neurological disorders differ in men and women and there is substantial evidence that their neurobiological basis and treatment also differ by sex. This special issue sought to bring together a series of empirical papers and targeted reviews to highlight the diverse impact of sex in neuroscience and neuropsychopharmacology. This special issue emphasizes the diverse impact of sex in neuroscience and neuropsychopharmacology, including 9 review papers and 17 research articles highlighting investigation in different species (zebrafish, mice, rats, and humans). Each contribution covers scientific topics that overlap with genetics, endocrinology, cognition, behavioral neuroscience, neurology, and pharmacology. Investigating the extent to which sex differences can impact the brain and behavior is key to moving forward in neuroscience research.

Does GPER1 Play a Role in Sexual Dimorphism?

Estrogens are critical in driving sex-typical social behaviours that are ethologically relevant in mammals. This is due to both production of local estrogens and signaling by these ligands, particularly in an interconnected set of nuclei called the social behavioural network (SBN). The SBN is a sexually dimorphic network studied predominantly in rodents that is thought to underlie the display of social behaviour in mammals. Signalling by the predominant endogenous estrogen, 17β-estradiol, can be either via the classical genomic or non-classical rapid pathway. In the classical genomic pathway, 17β-estradiol binds the intracellular estrogen receptors (ER) α and β which act as ligand-dependent transcription factors to regulate transcription. In the non-genomic pathway, 17β-estradiol binds a putative plasma membrane ER (mER) such as GPR30/GPER1 to rapidly signal via kinases or calcium flux. Though GPER1's role in sexual dimorphism has been explored to a greater extent in cardiovascular physiology, less is known about its role in the brain. In the last decade, activation of GPER1 has been shown to be important for lordosis and social cognition in females. In this review we will focus on several mechanisms that may contribute to sexually dimorphic behaviors including the colocalization of these estrogen receptors in the SBN, interplay between the signaling pathways activated by these different estrogen receptors, and the role of these receptors in development and the maintenance of the SBN, all of which remain underexplored.