Oestrogen and progestins differently prevent glutamate toxicity in cortical neurons depending on prior hormonal exposure via the induction of neural nitric oxide synthase

Brain-derived neuerotrophic factor and related mechanisms that mediate and influence progesterone-induced neuroprotection

Historically, progesterone has been studied significantly within the context of reproductive biology. However, there is now an abundance of evidence for its role in regions of the central nervous system (CNS) associated with such non-reproductive functions that include cognition and affect. Here, we describe mechanisms of progesterone action that support its brain-protective effects, and focus particularly on the role of neurotrophins (such as brain-derived neurotrophic factor, BDNF), the receptors that are critical for their regulation, and the role of certain microRNA in influencing the brain-protective effects of progesterone. In addition, we describe evidence to support the particular importance of glia in mediating the neuroprotective effects of progesterone. Through this review of these mechanisms and our own prior published work, we offer insight into why the effects of a progestin on brain protection may be dependent on the type of progestin (e.g., progesterone versus the synthetic, medroxyprogesterone acetate) used, and age, and as such, we offer insight into the future clinical implication of progesterone treatment for such disorders that include Alzheimer's disease, stroke, and traumatic brain injury.

Nitric oxide regulates the firing rate of neuronal subtypes in the guinea pig ventral cochlear nucleus

The gaseous free radical, nitric oxide (NO) acts as a ubiquitous neuromodulator, contributing to synaptic plasticity in a complex way that can involve either long term potentiation or depression. It is produced by neuronal nitric oxide synthase (nNOS) which is presynaptically expressed and also located postsynaptically in the membrane and cytoplasm of a subpopulation of each major neuronal type in the ventral cochlear nucleus (VCN). We have used iontophoresis in vivo to study the effect of the NOS inhibitor L-NAME (L-NG-Nitroarginine methyl ester) and the NO donors SIN-1 (3-Morpholinosydnonimine hydrochloride) and SNOG (S-Nitrosoglutathione) on VCN units under urethane anaesthesia. Collectively, both donors produced increases and decreases in driven and spontaneous firing rates of some neurones. Inhibition of endogenous NO production with L-NAME evoked a consistent increase in driven firing rates in 18% of units without much effect on spontaneous rate. This reduction of gain produced by endogenous NO was mirrored when studying the effect of L-NAME on NMDA(N-Methyl-D-aspartic acid)-evoked excitation, with 30% of units showing enhanced NMDA-evoked excitation during L-NAME application (reduced NO levels). Approximately 25% of neurones contain nNOS and the NO produced can modulate the firing rate of the main principal cells: medium stellates (choppers), large stellates (onset responses) and bushy cells (primary-like responses). The main endogenous role of NO seems to be to partly suppress driven firing rates associated with NMDA channel activity but there is scope for it to increase neural gain if there were a pathological increase in its production following hearing loss.

Amperometric Microsensors Monitoring Glutamate-Evoked In Situ Responses of Nitric Oxide and Carbon Monoxide from Live Human Neuroblastoma Cells

In the brain, nitric oxide (NO) and carbon monoxide (CO) are important signaling gases which have multifaceted roles, such as neurotransmitters, neuromodulators, and vasodilators. Even though it is difficult to measure NO and CO in a living system due to their high diffusibility and extremely low release levels, electrochemical sensors are promising tools to measure in vivo and in vitro NO and CO gases. In this paper, using amperometric dual and septuple NO/CO microsensors, real-time NO and CO changes evoked by glutamate were monitored simultaneously for human neuroblastoma (SH-SY5Y) cells. In cultures, the cells were differentiated and matured into functional neurons by retinoic acid and brain-derived neurotrophic factor. When glutamate was administrated to the cells, both NO and CO increases and subsequent decreases returning to the basal levels were observed with a dual NO/CO microsensor. In order to facilitate sensor’s measurement, a flower-type septuple NO/CO microsensor was newly developed and confirmed in terms of the sensitivity and selectivity. The septuple microsensor was employed for the measurements of NO and CO changes as a function of distances from the position of glutamate injection. Our sensor measurements revealed that only functionally differentiated cells responded to glutamate and released NO and CO.

Brain diffusion changes in Eisenmenger syndrome

OBJECTIVE

This preliminary study aimed to evaluate whether there are changes in the apparent diffusion coefficient (ADC) values of the brain in patients presenting with Eisenmenger syndrome (ES).

METHODS

This cross-sectional study included 10 consecutively recruited patients with ES and 10 healthy control subjects. In the patients and controls, eight distinct neuroanatomical locations were selected for analysis. Quantitative measurements of ADC values of the frontal white matter (FWM), occipital white matter, lentiform nucleus (LN), thalamus, frontal cortex, anterior and posterior limbs of the internal capsule and caudate nucleus were measured. Statistical analysis was performed using SPSS^® (IBM Corp., New York, NY; formerly SPSS Inc., Chicago, IL) for Windows v. 20. Data were presented as mean ± standard deviation values. The Kruskal-Wallis test was used to assess differences in the ADC values of each brain location between the ES group and the control group. Statistical significance was accepted at the level of p < 0.05.

RESULTS

The ADC values of the FWM and LN were significantly higher in the ES group than that in the control group. The mean ADC levels of other brain regions were not significantly different between the groups.

CONCLUSION

Chronic hypoxia in patients with ES may lead to diffusion changes in the brain tissue. There is a need for further studies to assess the clinical significance of cerebral ADC values in patients with ES. Advances in knowledge: The ratio of extracellular volume to intracellular volume in the FWM and LN can be considered to be increased in patients with ES.

Use of estetrol with other steroids for attenuation of neonatal hypoxic-ischemic brain injury: to combine or not to combine?

Estetrol (E4), estradiol (E2) and progesterone (P4) have important antioxidative and neuroprotective effects in neuronal system. We aimed to study the consequence of combined steroid therapy in neonatal hypoxic-ischemic encephalopathy (HIE). In vitro the effect of E4 combined with other steroids on oxidative stress and the cell viability in primary hippocampal cultures was evaluated by lactate dehydrogenase and cell survival assays. In vivo neuroprotective and therapeutic efficacy of E4 combined with other steroids was studied in HIE model of immature rats. The rat pups rectal temperature, body and brain weights were evaluated.The hippocampus and the cortex were investigated by histo/immunohistochemistry: intact cell number counting, expressions of markers for early gray matter lose, neuro- and angiogenesis were studied. Glial fibrillary acidic protein was evaluated by ELISA in blood samples. In vitro E4 and combinations of high doses of E4 with P4 and/or E2 significantly diminished the LDH activity and upregulated the cell survival.In vivopretreatment or treatment by different combinations of E4 with other steroids had unalike effects on body and brain weight, neuro- and angiogenesis, and GFAP expression in blood. The combined use of E4 with other steroids has no benefit over the single use of E4.

Estrogens and progestins: molecular effects on brain cells

Sex steroids are known to regulate brain function and their role is so important that several diseases are strictly correlated with the onset of menopause when estrogen-progesterone deficiency makes neural cells much more vulnerable to toxic stimuli. Although in the past years several scientists have focused their studies on in vitro and in vivo effects of sex steroids on the brain, we are still far from complete knowledge. Indeed, contrasting results from large clinical trials have made the entire issue much more complicated. Currently we know that protective effects exerted by sex steroids depend on several factors among which the dose, the health of the cells and the type of molecule being used. In this review, we present an overview of the direct and indirect effects of estrogen and progesterone on the brain with specific focus on the molecular mechanisms by which these molecules act on neural cells.

Actions and interactions of estradiol and glucocorticoids in cognition and the brain: Implications for aging women

Menopause involves dramatic declines in estradiol production and levels. Importantly, estradiol and the class of stress hormones known as glucocorticoids exert countervailing effects throughout the body, with estradiol exerting positive effects on the brain and cognition, glucocorticoids exerting negative effects on the brain and cognition, and estradiol able to mitigate negative effects of glucocorticoids. Although the effects of these hormones in isolation have been extensively studied, the effects of estradiol on the stress response and the neuroprotection offered against glucocorticoid exposure in humans are less well known. Here we review evidence suggesting that estradiol-related protection against glucocorticoids mitigates stress-induced interference with cognitive processes. Animal and human research indicates that estradiol-related mitigation of glucocorticoid damage and interference is one benefit of estradiol supplementation during peri-menopause or soon after menopause. The evidence for estradiol-related protection against glucocorticoids suggests that maintaining estradiol levels in post-menopausal women could protect them from stress-induced declines in neural and cognitive integrity.

Differential effects of synthetic progestagens on neuron survival and estrogen neuroprotection in cultured neurons

Progesterone and other progestagens are used in combination with estrogens for clinical purposes, including contraception and postmenopausal hormone therapy. Progesterone and estrogens have interactive effects in brain, however interactions between synthetic progestagens and 17β-estradiol (E2) in neurons are not well understood. In this study, we investigated the effects of seven clinically relevant progestagens on estrogen receptor (ER) mRNA expression, E2-induced neuroprotection, and E2-induced BDNF mRNA expression. We found that medroxyprogesterone acetate decreased both ERα and ERβ expression and blocked E2-mediated neuroprotection and BDNF expression. Conversely, levonorgestrel and nesterone increased ERα and or ERβ expression, were neuroprotective, and failed to attenuate E2-mediated increases in neuron survival and BDNF expression. Other progestagens tested, including norethindrone, norethindrone acetate, norethynodrel, and norgestimate, had variable effects on the measured endpoints. Our results demonstrate a range of qualitatively different actions of progestagens in cultured neurons, suggesting significant variability in the neural effects of clinically utilized progestagens.

17β-estradiol delays 6-OHDA-induced apoptosis by acting on Nur77 translocation from the nucleus to the cytoplasm

Nuclear receptors (Nurs) represent a large family of gene expression regulating proteins. Gathering evidence indicates an important role for Nurs as transcription factors in dopamine neurotransmission. Nur77, a member of the Nur superfamily, plays a role in mediating the effects of antiparkinsonian and neuroleptic drugs. Besides, Nur77 survival and apoptotic roles depend largely on its subcellular localization. Estrogens are known for their neuroprotective properties, as demonstrated in animal and clinical studies. However, their action on Nur77 translocation pertaining to neuroprotection has not been investigated yet. The aim of our study was to perform a kinetic study on the effect of neurotoxic 6-hydroxydopamine (6-OHDA) and 17β-estradiol (E2) on the subcellular localization of Nur77 with reference to the modulation of apoptosis in PC12 cells. Our results demonstrate that E2 administration alone does not affect Nur77 cytoplasmic/nuclear ratio, mRNA levels, or apoptosis in PC12 cells. The neurotoxin 6-OHDA significantly enhances cytoplasmic localization of Nur77 after merely 3 h, while precipitating apoptosis. 6-OHDA also increases Nur77 transcription, which could partly explain the rise in cytoplasmic localization of the protein. Finally, treatment with both E2 and 6-OHDA delays Nur77 accumulation in the cytoplasm and delays cell death for a few hours in our cellular paradigm. Pre-treatment with E2 does not alter the increase in levels of Nur77 mRNA produced by 6-OHDA, suggesting that a raise in nuclear translocation is likely responsible for the stabilization of the cytoplasmic/nuclear ratio until 6 h. These results suggest an intriguing cooperation between E2 and Nur77 toward cellular fate guidance.

Brain diffusion changes in obstructive sleep apnoea syndrome

BACKGROUND

Obstructive sleep apnoea syndrome (OSAS) is a disorder characterized by repeated apnoeic episodes during sleep. Neurocognitive changes secondary to OSAS are likely to occur due to hypoxia in certain brain locations. Advances in magnetic resonance imaging technology, such as diffusion-weighted imaging (DWI), enable non-invasive and accurate identification of OSAS-induced changes.

OBJECTIVE

We aimed to use DWI to investigate changes in the brain secondary to hypoxia in OSAS.

METHODS

Eighty-eight patients underwent polysomnography and were classified as non-OSAS, mild-moderate OSAS and severe OSAS sufferers. DWI was used to evaluate 14 areas of the brain, and apparent diffusion coefficients (ADCs) were calculated. We investigated whether there were differences in the ADC values in specific areas of the brain between the non-OSAS and OSAS patients.

RESULTS

We measured the ADC values of the 68 newly diagnosed OSAS patients (21 mild, 15 moderate and 32 severe) and of 20 healthy controls. There were significant increases in the ADC values in the hippocampus, amygdala and putamen in OSAS patients. Compared to the non-OSAS subjects, the ADC values of the putamen in severe OSAS patients, those of the hippocampus in moderate or severe OSAS patients and those of the amygdala in moderate OSAS patients were significantly increased. A negative correlation between the lowest oxygen saturation during sleep and the ADC values of the hippocampus and amygdala was found.

CONCLUSIONS

Increased ADC levels in the hippocampus, amygdala and putamen in OSAS patients indicate hypoxia and likely cause vasogenic oedema in specific regions of the brain.

Effects of progesterone and medroxyprogesterone on actin remodeling and neuronal spine formation

Sex steroids are important regulators of neuronal cell morphology, and this is critical for gender differences in brain function and dysfunction. Neuronal morphology is controlled by multiprotein complexes including moesin (a member of the ezrin/radixin/moesin family), focal adhesion kinase (FAK), or the Wiskott-Aldrich syndrome protein-family verprolin homologous (WAVE1) protein, controlling dynamic remodeling of the cytoskeleton and cell membrane. We investigated the actions of natural progesterone (P) and of the synthetic progestin medroxyprogesterone acetate (MPA) on actin remodeling, focal adhesion complex formation, and actin branching in rat cortical neurons. Treatment with P and, to a lesser extent, MPA, increases the number and density of dendritic spines. P increases the phosphorylation of moesin, FAK, and WAVE1, and their redistribution toward cell membrane sites where spines are formed. Signaling to moesin is achieved by PR via a Gα/Gβ-dependent signaling to the small GTPase Ras homolog gene family, member A and its related kinase, Rho-associated kinase-2. In parallel, WAVE1 recruitment is triggered by a Gαi/Gβ-dependent signaling of PR to c-Src, FAK, and Rac1 GTPase. Rac1 recruits cyclin-dependent kinase-5, which phosphorylates WAVE1. Silencing of moesin, FAK, or WAVE1 abrogates the increase in dendritic spines induced by progesterone. In all applications, MPA is found to act similar to P, albeit with a lower efficacy. In conclusion, our findings indicate that the control of actin polymerization and branching and focal adhesion complex formation via moesin, FAK, and WAVE1 is a key function of progesterone receptor in neurons, which may be relevant for the regulation of dendritic spine turnover and neuronal plasticity.

Progesterone and neuroprotection

Numerous studies aimed at identifying the role of estrogen on the brain have used the ovariectomized rodent as the experimental model. And while estrogen intervention in these animals has, at least partially, restored cholinergic, neurotrophin and cognitive deficits seen in the ovariectomized animal, it is worth considering that the removal of the ovaries results in the loss of not only circulating estrogen but of circulating progesterone as well. As such, the various deficits associated with ovariectomy may be attributed to the loss of progesterone as well. Similarly, one must also consider the fact that the human menopause results in the precipitous decline of not just circulating estrogens, but in circulating progesterone as well and as such, the increased risk for diseases such as Alzheimer's disease during the postmenopausal period could also be contributed by this loss of progesterone. In fact, progesterone has been shown to exert neuroprotective effects, both in cell models, animal models and in humans. Here, we review the evidence that supports the neuroprotective effects of progesterone and discuss the various mechanisms that are thought to mediate these protective effects. We also discuss the receptor pharmacology of progesterone's neuroprotective effects and present a conceptual model of progesterone action that supports the complementary effects of membrane-associated and classical intracellular progesterone receptors. In addition, we discuss fundamental differences in the neurobiology of progesterone and the clinically used, synthetic progestin, medroxyprogesterone acetate that may offer an explanation for the negative findings of the combined estrogen/progestin arm of the Women's Health Initiative-Memory Study (WHIMS) and suggest that the type of progestin used may dictate the outcome of either pre-clinical or clinical studies that addresses brain function.

Progesterone, brain-derived neurotrophic factor and neuroprotection

While the effects of progesterone in the CNS, like those of estrogen, have generally been considered within the context of reproductive function, growing evidence supports its importance in regulating non-reproductive functions including cognition and affect. In addition, progesterone has well-described protective effects against numerous insults in a variety of cell models, animal models and in humans. While ongoing research in several laboratories continues to shed light on the mechanism(s) by which progesterone and its related progestins exert their effects in the CNS, our understanding is still incomplete. Among the key mediators of progesterone's beneficial effects is the family of growth factors called neurotrophins. Here, we review the mechanisms by which progesterone regulates one important member of the neurotrophin family, brain-derived neurotrophic factor (BDNF), and provides support for its pivotal role in the protective program elicited by progesterone in the brain.

Progesterone inhibition of neuronal calcium signaling underlies aspects of progesterone-mediated neuroprotection

Progesterone is being utilized as a therapeutic means to ameliorate neuron loss and cognitive dysfunction following traumatic brain injury. Although there have been numerous attempts to determine the means by which progesterone exerts neuroprotective effects, studies describing the underlying molecular mechanisms are lacking. What has become clear, however, is the notion that progesterone can thwart several physiological processes that are detrimental to neuron function and survival, including inflammation, edema, demyelination and excitotoxicity. One clue regarding the means by which progesterone has restorative value comes from the notion that these aforementioned biological processes all share the common theme of eliciting pronounced increases in intracellular calcium. Thus, we propose the hypothesis that progesterone regulation of calcium signaling underlies its ability to mitigate these cellular insults, ultimately leading to neuroprotection. Further, we describe recent findings that indicate neuroprotection is achieved via progesterone block of voltage-gated calcium channels, although additional outcomes may arise from blockade of various other ion channels and neurotransmitter receptors. This article is part of a Special Issue entitled 'Neurosteroids'.

Sex steroids and their receptors: molecular actions on brain cells

Sex steroids exert actions of paramount importance on brain cells. They contribute to shape the central nervous system during embryo development. They modulate the formation and the turnover of the interconnections between neurons. They control the function of glial cells. And they do it through a signaling machinery that is apparently simple, but that hides a level of complexity that has been unveiled only in part. Different receptor isoforms, different interactions between receptors and co-regulators, chains of events originating at the cell membrane and leading to effects in the nucleus (or the other way around) all interact to determine selective modulations of brain cells. All these actions end up in phenomenal effects on brain function that change through adolescence, pregnancy, adulthood, up to menopause and ageing. Many of these actions are relevant for degenerative processes and research may offer soon new strategies to counteract these diseases.

Actin cytoskeleton remodelling by sex steroids in neurones

Cell morphology and its interaction with the extracellular environment are integrated processes involving a number of intracellular controllers orchestrating cytoskeletal proteins and their interaction with the cell membrane and anchorage proteins. Sex steroids are effective regulators of cell morphology and tissue organisation, and recent evidence indicates that this is obtained through the regulation of the actin cytoskeleton. Intriguingly, many of these regulatory actions related to cell morphology are achieved through the rapid, nonclassical signalling of sex steroid receptors to kinase cascades, independently from nuclear alteration of gene expression or protein synthesis. The identification of the mechanistic basis for these rapid actions on cell cytoskeleton has special relevance for the characterisation of the effects of sex steroids under physiological conditions, such as for the development of neurone/neurone interconnections and dendritic spine density. This is considered to be critical for gender-specific differences in brain function and dysfunction. Recent advancements in the characterisation of the molecular basis of the extranuclear signalling of sex steroids help to clarify the role of oestrogen and progesterone in the brain, and may turn out to be of relevance for clinical purposes. This review highlights the regulatory effects of oestrogens and progesterone on actin cytoskeleton and neurone morphology, as well as recent progresses in the characterisation of these mechanisms, providing insights and working hypotheses on possible clinical applications for the modulation of these pathways in the central nervous system.

Introduction to the interaction between gonadal steroids and the central nervous system

The sex steroids are frequently referred to as the gonadal steroids and are erroneously assumed to be exclusively linked to the ovaries in women or the testes in men and the functions of the reproductive tract. This chapter will provide an overview of some of the extragonadal effects of these hormones, focusing on the central nervous system, and the mechanisms of hormone action. Hormone synthesis and metabolism within the CNS will be discussed with particular focus on the role of aromatase. Sex steroids exert many of their effects via intracellular receptors and these genomic responses tend to be slow in onset, however, some responses to steroids occur more quickly and are mediated via membrane receptors and involve interactions with many different transduction pathways to produce a diverse array of responses. These complexities do pose challenges but also offer opportunity for novel approaches for therapeutic exploitation as the pharmacological tools with which to modulate systems become increasingly available.

Nitric oxidergic cells related to ejaculation in gerbil forebrain contain androgen receptor and respond to testosterone

Two clusters of forebrain neurons-one in the posterodorsal preoptic nucleus (PdPN) and one in the lateral part of the posterodorsal medial amygdala (MeApd)-are activated at ejaculation in male rats and gerbils as seen with Fos immunocytochemistry. To understand the functions of these cells and how they respond synchronously, it may be useful to identify their neurotransmitters. Nitric oxide (NO) was of interest because its levels in the preoptic area affect ejaculation, and it could synchronize clustered neurons through paracrine/volume transmission. Thus, we determined whether the ejaculation-related cells produce NO by assessing Fos co-localization with NO synthase (NOS) in recently mated male gerbils. We also studied NOS-Fos co-localization in the medial part of the medial preoptic nucleus (MPNm), where half of the neurons that express Fos after mating reflect ejaculation. We also quantified NOS co-localization with androgen receptor (AR) and NOS sensitivity to androgens at these sites. Without quantification, we extended these analyses throughout the hypothalamus and amygdala. Many mating-activated PdPN, lateral MeApd, and MPNm cells contained NOS (32-54%), and many NOS neurons at these sites expressed Fos (34-51%) or AR (25-69%). PdPN and MPNm NOS cells were sensitive to testosterone but not its androgenic metabolite dihydrotestosterone. The overall distribution of NOS and NOS-AR cells was similar to that in rats. These data suggest that NO may help to synchronize the activation of PdPN and lateral MeApd neurons at ejaculation and that NOS in PdPN and MPNm cells is regulated by testosterone acting via estradiol or without undergoing metabolism.

Progestogen effects at vascular level: the endothelial cells

Progesterone and progestogens are active molecules on the cardiovascular system. However, their action is not as well-characterized as the effects of estrogens. Data of the last clinical trials suggest the possibility of harmful cardiovascular effects of progestogens, and the debate on the role of progesterone and progestins on the vascular wall is open. From an experimental point of view, each progestogen presents typical effects on the cardiovascular system and their administration results in diverse modifications of the effects of estrogens, sometimes acting synergically, others being neutral or antagonizing effects of estrogens. In this paper, we review the most important data from in vivo and in vitro studies which have been published on the effects of progesterone and progestogens on vascular cells. Endothelium is a target tissue for sex steroids and progesterone is able to regulate endothelial cell function and morphology. Even if the perfect molecule does not exist, the understanding of the molecular basis of each progestogen in vascular tissue is therefore of paramount importance for the most appropriate use with an optimal cardiovascular profile.

Extra-nuclear signaling of ERalpha to the actin cytoskeleton in the central nervous system

Cell morphology is controlled by a complex and redundant array of intracellular signaling pathways devoted to the regulation of the actin cytoskeleton and of its relationship with the cell membrane and the extracellular matrix. Sex steroids are effective regulators of cell morphology and tissue organization, and recent evidence indicates that this is obtained through the regulation of the cytoskeleton. Intriguingly, many of these regulatory actions related to cell morphology are achieved through rapid, non-classical signaling of sex steroid receptors to kinase cascades, independently from nuclear alteration of gene expression or protein synthesis. The identification of the mechanistic basis for these rapid actions on cell cytoskeleton has special relevance for the characterization of the effects of sex steroids in physiological conditions, such as their role in the control of brain cell remodeling. Brain cell morphology is controlled by estrogens that regulate the development of neuron/neuron interconnections and dendritic spine density. This is thought to be critical for gender-specific differences in brain function and dysfunction. The recent advancements in the characterization of the molecular basis of the extra-nuclear signaling of estrogen helps to understand the role of estrogen in the brain, and may in the future turn out to be of relevance for clinical purposes. This review highlights the regulatory effects on the cytoskeleton and cell morphology of estrogens as well as the recent advances in the characterization of these mechanisms, providing insights and working hypotheses on possible clinical applications for the modulation of these pathways in the central nervous system.

Rapid signaling of estrogen to WAVE1 and moesin controls neuronal spine formation via the actin cytoskeleton

Estrogens are important regulators of neuronal cell morphology, and this is thought to be critical for gender-specific differences in brain function and dysfunction. Dendritic spine formation is dependent on actin remodeling by the WASP-family verprolin homologous (WAVE1) protein, which controls actin polymerization through the actin-related protein (Arp)-2/3 complex. Emerging evidence indicates that estrogens are effective regulators of the actin cytoskeleton in various cell types via rapid, extranuclear signaling mechanisms. We here show that 17beta-estradiol (E2) administration to rat cortical neurons leads to phosphorylation of WAVE1 on the serine residues 310, 397, and 441 and to WAVE1 redistribution toward the cell membrane at sites of dendritic spine formation. WAVE1 phosphorylation is found to be triggered by a Galpha(i)/Gbeta protein-dependent, rapid extranuclear signaling of estrogen receptor alpha to c-Src and to the small GTPase Rac1. Rac1 recruits the cyclin-dependent kinase (Cdk5) that directly phosphorylates WAVE1 on the three serine residues. After WAVE1 phosphorylation by E2, the Arp-2/3 complex concentrates at sites of spine formation, where it triggers the local reorganization of actin fibers. In parallel, E2 recruits a Galpha(13)-dependent pathway to RhoA and ROCK-2, leading to activation of actin remodeling via the actin-binding protein, moesin. Silencing of WAVE1 or of moesin abrogates the increase in dendritic spines induced by E2 in cortical neurons. In conclusion, our findings indicate that the control of actin polymerization and branching via moesin or WAVE1 is a key function of estrogen receptor alpha in neurons, which may be particularly relevant for the regulation of dendritic spines.