Cell type-specificity of nonclassical estrogen signaling in the developing midbrain

Non-genomic Effect of Estradiol on the Neurovascular Unit and Possible Involvement in the Cerebral Vascular Accident

Cerebrovascular diseases, such as ischemic cerebral vascular accident (CVA), are responsible for causing high rates of morbidity, mortality, and disability in the population. The neurovascular unit (NVU) during and after ischemic CVA plays crucial roles in cell regulation and preservation, the immune and inflammatory response, and cell and/or tissue survival and repair. Cellular responses to 17β-estradiol (E2) can be triggered by two mechanisms: one called classical or genomic, which is due to the activation of the "classical" nuclear estrogen receptors α (ERα) and β (ERβ), and the non-genomic or rapid mechanism, which is due to the activation of the G protein-coupled estrogen receptor 1 (GPER) that is located in the plasma membrane and some in intracellular membranes, such as in the Golgi apparatus and endoplasmic reticulum. Nuclear receptors can regulate gene expression and cellular functions. On the contrary, activating the GPER by E2 and/or its G-1 agonist triggers several rapid cell signaling pathways. Therefore, E2 or its G-1 agonist, by mediating GPER activation and/or expression, can influence several NVU cell types. Most studies argue that the activation of the GPER may be used as a potential therapeutic target in various pathologies, such as CVA. Thus, with this review, we aimed to summarize the existing literature on the role of GPER mediated by E2 and/or its agonist G-1 in the physiology and pathophysiology of NVU.

Dose Optimization of Anxiolytic Compounds Group in Valeriana jatamansi Jones and Mechanism Exploration by Integrating Network Pharmacology and Metabolomics Analysis

Anxiety disorder impacts the quality of life of the patients. The 95% ethanol extract of rhizomes and roots of Valeriana jatamansi Jones (Zhi zhu xiang, ZZX) has previously been shown to be effective for the treatment of anxiety disorder. In this study, the dose ratio of each component of the anxiolytic compounds group (ACG) in a 95% ethanol extract of ZZX was optimized by a uniform design experiment and mathematical modeling. The anxiolytic effect of ACG was verified by behavioral experiments and biochemical index measurement. Network pharmacology was used to determine potential action targets, as well as predict biological processes and signaling pathways, which were then verified by molecular docking analysis. Metabolomics was then used to screen and analyze metabolites in the rat hippocampus before and after the administration of ZZX-ACG. Finally, the results of metabolomics and network pharmacology were integrated to clarify the anti-anxiety mechanism of the ACG. The optimal dose ratio of ACG in 95% ethanol extract of ZZX was obtained, and our results suggest that ACG may regulate ALB, AKT1, PTGS2, CYP3A4, ESR1, CASP3, CYP2B6, EGFR, SRC, MMP9, IGF1, and MAPK8, as well as the prolactin signaling pathway, estrogen signaling pathway, and arachidonic acid metabolism pathway, thus affecting the brain neurotransmitters and HPA axis hormone levels to play an anxiolytic role, directly or indirectly.

Emergence of sex differences in the development of substance use and abuse during adolescence

Substance use and abuse begin during adolescence. Male and female adolescent humans initiate use at comparable rates, but males increase use faster. In adulthood, more men than women use and abuse addictive drugs. However, some women progress more rapidly from initiation of use to entry into treatment. In animal models, adolescent males and females consume addictive drugs similarly. However, reproductively mature females acquire self-administration faster, and in some models, escalate use more. Sex/gender differences exist in neurobiologic factors mediating both reinforcement (dopamine, opioids) and aversiveness (CRF, dynorphin), as well as intrinsic factors (personality, psychiatric co-morbidities) and extrinsic factors (history of abuse, environment especially peers and family) which influence the progression from initial use to abuse. Many of these important differences emerge during adolescence, and are moderated by sexual differentiation of the brain. Estradiol effects which enhance both dopaminergic and CRF-mediated processes contribute to the female vulnerability to substance use and abuse. Testosterone enhances impulsivity and sensation seeking in both males and females. Several protective factors in females also influence initiation and progression of substance use including hormonal changes of pregnancy as well as greater capacity for self-regulation and lower peak levels of impulsivity/sensation seeking. Same sex peers represent a risk factor more for males than females during adolescence, while romantic partners increase risk for women during this developmental epoch. In summary, biologic factors, psychiatric co-morbidities as well as personality and environment present sex/gender-specific risks as adolescents begin to initiate substance use.

Developmental effects of perinatal exposure to PBDE and PCB on gene expression in sexually dimorphic rat brain regions and female sexual behavior

The developing nervous system is a potential target of environmental contaminants such as polybrominated diphenylethers (PBDE), which accumulate in the biosphere. We compared effects of 2,2',4,4',5-pentabromo-BDE (PBDE99), a PBDE congener present in environmental samples, and PCB on brain development. Time-pregnant rats were subcutaneously injected with PBDE99 (1 or 10mg/kg), the PCB mixture Aroclor 1254 (10mg/kg), or vehicle from gestational day 10-18. mRNA levels of genes involved in central control of reproductive functions and sexual behavior were analyzed by real time RT PCR in two sexually dimorphic brain regions, medial preoptic area (MPO) and ventromedial hypothalamus (VMH) of adult offspring of both sexes. Exposure to PBDE99 or the PCB mixture during pre- and postnatal development affected mRNA expression levels in a treatment-, region- and sex-specific manner, and changed the sensitivity of target genes to estradiol. The sex difference in progesterone receptor mRNA levels of VMH normally seen in untreated controls was abolished by both, PBDE99 and PCB. Estrous cycles were significantly affected, and preliminary experiments suggest an impairment of female sexual behavior. Our data indicate that developmental exposure to PBDE99 at doses below signs of general toxicity affects the regulation of estrogen target genes in rat brain. Since PBDE99 was detected in blood and adipose tissue of adult offspring, these effects may result from interactions with developmental processes, with adult functions, or a combination of both.

Involvement of estrogen receptors in the resveratrol-mediated increase in dopamine transporter in human dopaminergic neurons and in striatum of female mice

Treatment with resveratrol (RSV) has been shown to protect vulnerable neurons after various brain injuries and in neurodegenerative diseases. The mechanisms for the effects of RSV in brain are not fully understood, but RSV may affect the expression of various gene products. RSV is structurally related to the synthetic estrogen, diethylstilbestrol so the effects of RSV may be gender-specific. Here we studied the role of RSV in the regulation of dopamine transporter (DAT) in the striatum using male and female mice. The basic levels of DAT in the striatum showed no sex difference, but the levels increased significantly by RSV (20 mg/kg i.p.) in female but not in male mice. Pretreatment of mice with the selective estrogen receptor (ER), ERα- and ERβ antagonist ICI 182,780, led to a complete block of RSV effect on DAT protein levels, suggesting that ERs are involved in the up-regulation of DAT by RSV. Similar data was also obtained in culture using human MESC2.10 and mouse SN4741 dopaminergic cells after treatment with RSV. Data further showed that RSV specifically induced gene transcription of DAT in the dopaminergic cells. These results show that estrogen receptors are involved in the up-regulation of DAT by RSV in the dopaminergic neurons, demonstrating a sex-dependent effect of RSV in the brain that may be of clinical importance. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

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

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

Oestrogen influences on mitochondrial gene expression and respiratory chain activity in cortical and mesencephalic astrocytes

The regulation of mitochondrial energy metabolism plays an essential role in the central nervous system (CNS). Abnormalities of the mitochondrial respiratory chain often accompany neurodegenerative diseases. This makes mitochondria a perfect target for strategies of cellular protection against toxic compounds and pathological conditions. Steroid hormones, such as oestrogen, are well-known to fulfil a protective role in the brain during ischaemic and degenerative processes. Because astrocytes function as the major energy supplier in the CNS, we have analysed oestrogen effects on the mitochondrial respiratory chain of this cell type. In our studies, we applied semi- and quantitative polymerase chain reaction analysis of gene expression and polarographic measurements of the respiratory chain activity of mitochondria. We observed that structural and functional properties were regulated dependent on the oestrogen exposure time and the brain region, but independent of the nuclear oestrogen receptors. We could demonstrate that long-term oestrogen exposure increases the subunit gene expression of respiratory chain complexes and the mitochondrial DNA content, thereby indicating an up-regulation of the amount of mitochondria per cell together with an increase of mitochondrial energy production. This could represent an important indirect mechanism by which long-term oestrogen exposure protects neurones from cell death under neurotoxic conditions. On the other hand, we observed short-term effects of oestrogen on the activity of mitochondrial, proton-pumping respiratory chain complexes. In astrocytes from the cortex, respiratory chain activity was decreased, whereas it was increased in astrocytes from the mesencephalon. An increased production of reactive oxygen species would be the consequence of an increased respiratory chain activity in mesencephalic astrocytes. This could explain the different efficiencies of oestrogen-mediated short-term protection in distinct brain regions, but also indicates the limitations for a therapeutic short-term application of oestrogen.

PI3 kinase/Akt activation mediates estrogen and IGF-1 nigral DA neuronal neuroprotection against a unilateral rat model of Parkinson's disease

Recently, using the medial forebrain bundle (MFB) 6-hydroxydopmaine (6-OHDA) lesion rat model of Parkinson's disease (PD), we have demonstrated that blockade of central IGF-1 receptors (IGF-1R) attenuated estrogen neuroprotection of substantia nigra pars compacta (SNpc) DA neurons, but exacerbated 6-OHDA lesions in IGF-1 only treated rats (Quesada and Micevych [2004]: J Neurosci Res 75:107-116). This suggested that the IGF-1 system is a central mechanism through which estrogen acts to protect the nigrostriatal DA system. Moreover, these results also suggest that IGF-1R-induced intracellular signaling pathways are involved in the estrogen mechanism that promotes neuronal survival. In vitro, two convergent intracellular signaling pathways used by estrogen and IGF-1, the mitogen-activated protein kinase (MAPK/ERK), and phosphatidyl-inositol-3-kinase/Akt (PI3K/Akt), have been demonstrated to be neuroprotective. Continuous central infusions of MAPK/ERK and PI3K/Akt inhibitors were used to test the hypothesis that one or both of these signal transduction pathways mediates estrogen and/or IGF-1 neuroprotection of SNpc DA neurons after a unilateral administration of 6-OHDA into the MFB of rats. Motor behavior tests and tyrosine hydroxylase immunoreactivity revealed that the inhibitor of the PI3K/Akt pathway (LY294002) blocked the survival effects of both estrogen and IGF-1, while an inhibitor of the MAPK/ERK signaling (PD98059) was ineffective. Western blot analyses showed that estrogen and IGF-1 treatments increased PI3K/Akt activation in the SN; however, MAPK/ERK activation was decreased in the SN. Indeed, continuous infusions of inhibitors blocked phosphorylation of PI3K/Akt and MAPK/ERK. These findings indicate that estrogen and IGF-1-mediated SNpc DA neuronal protection is dependent on PI3K/Akt signaling, but not on the MAPK/ERK pathway.

Neuroactive properties of reproductive steroids

Migraine is 3 times more common in postpubertal women than in men. Migraine is frequently exacerbated perimenstrually and commonly occurs exclusively at that time. It is often benefited by pregnancy and menopause. Estrogen withdrawal has been implicated as a mechanism for triggering migraines. The mechanism, however, is not well understood. Reproductive steroids have neuroactive properties that can modulate neuronal morphology and physiology. Increasing evidence suggests that circulating reproductive steroid levels regulate the balance of neuroexcitatory and neuroinhibitory activities in some brain regions by influencing synaptic plasticity. Estrogen has neuroexcitatory, whereas progesterone has neuroinhibitory, effects in most preclinical and clinical models. Several neurotransmitter systems that are implicated in migraine vary with reproductive steroid levels during the reproductive cycle. Estrogen stabilization may provide effective treatment in susceptible women, especially for catamenially exacerbated migraine.

Rapid signaling mechanisms of estrogens in the developing cerebellum

The steroid hormone 17beta-estradiol regulates the normal function and development of the mammalian nervous system. Many of estradiol's effects are mediated via the nuclear hormone estrogen receptors ERalpha and ERbeta. In addition to regulating estrogen-responsive gene expression, estradiol also acts in an immediate and cell-specific fashion to regulate various intracellular signal transduction pathways. The goal of this review is to develop a contextual framework to understand the generalized function of estrogen during development of brain regions not known to be sexually specialized. However, it is first important to build this framework on the more well-developed foundation of estrogen's gonad-driven sex-specific actions. As a result, a discussion of known and proposed mechanisms of estrogen actions in reproductive and other tissues will be presented. Building upon this information, a review of our research group's recent in vitro and in vivo studies that have focused on elucidating the mechanisms of estrogen actions in neurons of the non-sexually specialized cerebellum will be presented. While the full spectrum of estrogen action during normal cerebellar development remains unresolved, results of recent studies have revealed a pathologic role for estrogen and estrogen receptors in medulloblastoma, common pediatric brain tumors that arise from cerebellar granule cell-like precursors. The potential use of anti-estrogen signaling agents as adjuvant therapy for medulloblastoma is proposed based on those finding.

Sex differences in the chloride cotransporters, NKCC1 and KCC2, in the developing hypothalamus

In immature neurones, high basal [Cl(-)](i) results in membrane depolarisation following GABA(A) receptor activation, which is critical for various developmental processes including steroid-mediated sexual differentiation of the hypothalamus. Previously, we demonstrated that oestradiol enhances GABA-mediated Ca(2+) influx in neonate hypothalamus and that Ca(2+) induced activation of the transcription factor, cyclicAMP response element binding protein (CREB), was higher in male (high oestradiol) relative to female neonate hypothalamus. Based on these results, we hypothesised that expression of developmentally regulated chloride cotransporters may be sexually dimorphic. Here, we investigate the expression of the chloride cotransporters, NKCC1 (Na-K-2Cl(-)) and KCC2 (K-Cl(-)) in neonate mediobasal hypothalamus of male and female rats. The NKCC1 transporter moves Cl(-) into cells and helps maintain depolarising GABA action while the KCC2 transporter has the opposite effect by moving Cl(-) out of cells. NKCC1 mRNA levels were higher in males than females on the day of birth (postnatal day 0; PND 0) and total NKCC1 protein levels were significantly higher in males than females on embryonic day (ED) 20 and PND0. Levels of activated phosphorylated NKCC1 (pNKCC1) were not sexually dimorphic. Females were treated with a masculinising dose of oestradiol benzoate (EB; 100 microg; EB-females) on PND0. Total NKCC1 protein levels in tissue processed on PND1 and PND2 were similar in EB-females and oil-treated PND0 males and females. However, pNKCC1 protein levels measured on PND2 (but not PND1) were significantly higher in EB-treated females relative to oil-treated males and females. By contrast, KCC2 mRNA levels were significantly lower in males relative to females on PND0. KCC2 protein was not detectable on ED20 or PND0 but was significantly lower in males relative to females on PND5. These results suggest a complex relationship between KCC2 and NKCC1 mRNA and protein in developing brain that is not easily linked to regulation by oestradiol.

beta-Estradiol induces synaptogenesis in the hippocampus by enhancing brain-derived neurotrophic factor release from dentate gyrus granule cells

We investigated the effect of beta-estradiol (E2) on synaptogenesis in the hippocampus using organotypic hippocampal slice cultures and subregional hippocampal neuron cultures. E2 increased the expression of PSD95, a postsynaptic marker, specifically in stratum lucidum of Cornu Ammonis 3 (CA3SL) in cultured hippocampal slices. E2 also increased the spine density at the proximal site of CA3 apical dendrites in CA3SL and PSD95 was clustered on these spine heads. The effects of E2 on the expression of PSD95 and the spine density disappeared when the dentate gyrus (DG) had been excised at 1 day in vitro (DIV). FM1-43 analysis of subregional hippocampal neuron cultures which were comprised of Ammon's horn neurons, DG neurons, or a mixture of these neurons, revealed that E2 increased the number of presynaptic sites in the cultures that contained DG neurons. K252a, a potent inhibitor of the high affinity receptor of brain-derived neurotrophic factor (BDNF), and function-blocking antibody to BDNF (BDNFAB) completely inhibited the effects of E2 in hippocampal slice cultures and subregional neuron cultures, whereas ICI182,780 (ICI), a strong antagonist of nuclear estrogen receptors (nERs), did not. Expression of BDNF in DG neurons was markedly higher than that in Ammon's horn neurons and E2 did not affect these expression levels. E2 significantly increased the BDNF release from DG neurons. KT5720, a specific inhibitor of 3'-5'-cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA), and Rp-adenosine 3', 5'-cyclic monophosphorothioate triethylammonium salt (Rp-cAMP), a non-hydrolyzable diastereoisomer and a potent inhibitor of PKA, completely suppressed the E2-induced increase in BDNF release, whereas ICI and U0126, a potent inhibitor of MAP kinase kinase (MEK), did not. These results suggest that E2 induces synaptogenesis between mossy fibers and CA3 neurons by enhancing BDNF release from DG granule cells in a nER-independent and PKA-dependent manner.

Estradiol-induced conditioned place preference may require actions at estrogen receptors in the nucleus accumbens

Intrinsic rewarding effects of estradiol (E(2)) may underlie some of the sex differences that emerge postpuberty for the prevalence of drug use and behavioral responses to drugs, but the effects and mechanisms of E(2) for reward have not been well characterized. Conditioned place preference (CPP), as measured by the time spent on the nonpreferred/drug-associated side of the chamber, was utilized as a functional assay to investigate the effects and mechanisms of E(2) in the nucleus accumbens for reward. To determine whether intracellular estrogen receptors (ERs) are important for E(2)-induced CPP, rats were administered E(2) (10 microg; subcutaneously (s.c.)), which produced CPP in each experiment, and/or ER blockers, such as tamoxifen (Experiment 1), ICI 182,780 (Experiment 2), or antisense oligonucleotides targeted to ERs (Experiment 3). Experiment 1: E(2) significantly increased the time spent on the originally nonpreferred side of the chamber. Coadministration of tamoxifen (10 mg/kg; s.c.) attenuated effects of E(2) to produce a CPP, but tamoxifen alone, increased time spent on the nonpreferred side. Experiment 2: coadministration of ICI 182,780 (10 microg/microl) to the nucleus accumbens attenuated effects of E(2) to enhance CPP and did not produce a CPP when administered alone. Experiment 3: coadministration of s.c. E(2) with ER antisense oligonucleotides to the nucleus accumbens significantly decreased time spent on the nonpreferred side and expression of ERs in the nucleus accumbens compared to scrambled antisense oligonucleotides or saline vehicle administration. Thus, E(2)'s rewarding effects may involve actions at ERs in the nucleus accumbens.

Neuroprotection by estrogen against MPP+-induced dopamine neuron death is mediated by ERalpha in primary cultures of mouse mesencephalon

Estrogen involvement in neuroprotection is now widely accepted, although the specific molecular and cellular mechanisms of estrogen action in neuroprotection remain unclear. This study examines estrogenic effects in a mixed population of cells in attempts to identify the contributing cells that result in estrogen-mediated neuroprotection. Utilizing primary mesencephalic neurons, we found expression of both estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta) with a predominance of ERalpha on both dopamine neurons and astrocytes. We also found that 17beta-estradiol protects dopamine neurons from injury induced by the complex I inhibitor, 1-methyl-4-phenyl pyridinium (MPP(+)) in a time- and ER-dependent manner. At least 4 h of estrogen pre-treatment was required to elicit protection, an effect that was blocked by the ER antagonist, ICI 182,780. Moreover, ERalpha mediated the protection afforded by estrogen since only the ERalpha agonist, HPTE, but not the ERbeta agonist, DPN, protected against dopamine cell loss. Since glial cells were shown to express significant levels of ERalpha, we investigated a possible indirect mechanism of estrogen-mediated neuroprotection through glial cell interaction. Removal of glial cells from the cultures by application of the mitotic inhibitor, 5-fluoro-2'-deoxyuridine, significantly reduced the neuroprotective effects of estrogen. These data indicate that neuroprotection provided by estrogen against MPP(+) toxicity is mediated by ERalpha and involves an interplay among at least two cell types.

Sexual Differentiation of the Vocal Control System of Birds

Birds evolved neural circuits of various complexities in relation to their capacity to produce learned or unlearned vocalizations. These vocalizations, in particular those that function in the realm of reproduction, are frequently sexually dimorphic, both in vocal learners (songbirds, parrots, some hummingbirds) and vocal nonlearners (all other birds). In many cases, the development and/or the adult differentiation of vocalizations of sociosexual function is sensitive to sex hormones, androgens and estrogens. The underlying mechanisms have been studied in detail in songbirds, a bird group that comprises about half of all bird species. Next to unlearned calls, songbirds produce learned songs that require forebrain vocal control areas that express receptors for androgens and estrogens. These forebrain vocal areas are sexually dimorphic in many species, but a clear relation between the degree of "brain sex" and sex differences in vocal pattern is lacking, except that a minimum number of vocal neurons is necessary to sing learned songs. Genetic brain-intrinsic mechanisms are likely to determine the neuron pools that develop into forebrain song control areas. Subsequently, gonadal steroid hormones, androgens and estrogens, modulate the fate of these neurons and thus the functionality of the vocal control systems. Further action of gonadal hormones, and may be other factors signaling the sociosexual and physical environment, affect the phenotype of vocal control areas in adulthood. Despite the clear evidence of hormone dependency of both adult vocalizations and phenotypes of vocal neuron pools, their causal relation is little understood.

The neurology of menopause

BACKGROUND

Menopause is a normal milestone experienced annually by 2 million American women each year, and many women are concerned about the relation between menopause and health. Associated hormonal changes have the potential to influence neurologic disease, as do hormonal therapies prescribed for menopausal symptoms or other conditions. The objective of this article is to increase neurologists' awareness of the relation between menopause and neurologic illness.

REVIEW SUMMARY

This was a focused review of 4 common neurologic disorders potentially influenced by menopause or by estrogen-containing hormone therapy: stroke, epilepsy, Parkinson disease, and Alzheimer disease. Hormonal effects are germane to each illness, although clinical implications are clearer for stroke and Alzheimer disease than for epilepsy and Parkinson disease. For women with epilepsy, few clinical data directly address the role of menopause or estrogen-containing hormone therapy on seizure frequency. Relevant clinical research findings on Parkinson disease are inconsistent and provide an inadequate basis for practice guidelines. There is clinical trial evidence that hormone therapy does not reduce stroke incidence and may increase risk of ischemic stroke; hormone therapy cannot be recommended for stroke prevention. The natural menopausal transition is not characterized by objective memory loss. There is clinical trial evidence that hormone therapy should not be used for the postmenopausal woman age 65 years or older for the preservation of cognitive skills, prevention of dementia, or treatment of dementia due to Alzheimer disease. Long-term cognitive consequences of short-term hormone therapy used by younger women for menopausal symptoms remains an important area of uncertainty.

CONCLUSIONS

Increased awareness of hormonal influences on neurologic illness is important for the practicing neurologist.

A review and update of mechanisms of estrogen in the hippocampus and amygdala for anxiety and depression behavior

Estrogen (E2) has many effects in the central nervous system, including effects on anxiety and depression behavior. This review will address effects of E2 on behaviors related to anxiety and depression in women and animal models and include recent findings from our laboratory related to this topic. E2's antianxiety and antidepressant-like effects may depend upon many factors, including the regimen of E2 utilized and interactions with the hypothalamic-pituitary-adrenal axis. Brain targets for E2's effects on anxiety and depression include the hippocampus and amygdala. Administration of E2, compared to vehicle, subcutaneously or to the hippocampus or amygdala of ovariectomized rats decreases anxiety and depressive behavior. Intracellular estrogen receptors (ERs) may be important for E2's anxiolytic and antidepressant-like effects. Administration of an ER antagonist to the hippocampus, but not amygdala, increases anxiety and depression behavior of naturally receptive female rats. Studies utilizing ER knockout mice or selective ER modulators suggest that ER-mediated effects of E2 on anxiety and depressive behavior may require ERbeta. In addition, the behavioral effects of E2 may involve membrane actions and/or changes in cell cycle processes involved in energy expenditure. Elucidating the mechanisms by which E2 affects anxiety and depression is important in order to enhance its therapeutic potential. It is particularly important to investigate the putative receptor mechanisms and brain targets for E2 to determine whether mood-enhancing effects of E2 can occur without deleterious proliferative effects in reproductive tissues.

Sex- and cell-type-specific patterns of GABAAreceptor and estradiol-mediated signaling in the immature rat substantia nigra

The substantia nigra pars reticulata (SNR) is involved in movement and seizure control. In male but not female postnatal day 15 (PN15) rats, GABAA receptor agonists depolarize the SNR neurons and increase the expression of the calcium-regulated gene KCC2 (potassium/chloride cotransporter). Moreover, in PN15 rat SNR, 7beta-estradiol down-regulates KCC2 expression only in the presence of depolarizing GABAA receptor responses. The hypothesis tested here was that GABAA receptors and estradiol also regulate the expression of the phosphorylated form of the transcription factor cAMP responsive element binding protein (phosphoCREB), in PN15 rat SNR and substantia nigra pars compacta (SNC). Rats were injected with muscimol or 17beta-estradiol or their vehicles, and killed 1 h later. Sections were stained with an antibody specific for phosphoCREB alone or counterstained with either tyrosine hydroxylase (TH)- or parvalbumin (PRV)-specific antibodies. Muscimol increased phosphoCREB-ir in male but not in female SN neurons. Using gramicidin perforated patch clamp of PN14-15 SNC neuron, it was shown that muscimol bath application depolarized male SNC neurons but did not significantly alter membrane potential in females. In males, 17beta-estradiol decreased phosphoCREB expression in all studied cell types. In females, 17beta-estradiol did not influence phosphoCREB expression in PRV-ir SNR cells, but increased it in the dopaminergic SN neurons. These data suggest that GABAA receptor activation and estradiol promote the sexual differentiation of the SN in a cell-type-specific manner, by influencing calcium-regulated gene transcription, and therefore promoting the acquisition of sex-specific roles of the SN in movement and seizure control.

Rapid neural Fos responses to oestradiol in oestrogen receptor alphabeta double knockout mice

The standard mode of action for oestradiol is via activation of nuclear oestrogen receptors (ERs), which initiate DNA transcription leading to protein formation. In the present study, we examined the rapid and potentially ER-independent action of oestradiol using Fos as a marker of neural activity. We assessed Fos immunoreactivity (ir) in brains of mice with functional versus nonfunctional ERs. Fos-ir was compared in brains of control mice that did and did not receive oestradiol treatment prior to sacrifice, and cell numbers in the preoptic area (POA), ventromedial nucleus of the hypothalamus (VMH), area 2 of cingulate cortex (CG2), granular layer of accessory olfactory bulb (Gr-AOB), olivary pretectal nucleus (OPT) and pyramidal layer of field CA3 of hippocampus (Py-CA3) were increased 90 min after oestradiol treatment. By contrast, in brains of double oestrogen receptor alphabeta knockout (ERalphabetaKO) female mice, no change in Fos-ir was noted after oestradiol treatment in the POA, VMH, Gr-AOB or Py-CA3, suggesting that these responses to oestradiol depend on ERalpha and/or ERbeta. However, Fos-ir was induced by oestradiol in the OPT and CG2 in ERalphabetaKO mice. These regions do not contain ERalpha-ir in control brains. In ERalphabetaKO brains as well, ERalpha-ir was absent, suggesting that the mutant ERalpha (E1) present in ERalphaKO brain is also absent in these regions. We speculate that oestradiol has rapid effects in the OPT and CG2 via a novel mechanism that does not require either classic oestrogen receptor.

Ovarian Hormones and Migraine Headache: Understanding Mechanisms and Pathogenesis-Part I

Ovarian hormones have a significant effect on the central nervous system of female migraineurs. Reproductive milestones such as menarche, pregnancy, and menopause are associated with changes in the clinical course of migraine headache. Migraine attacks are commonly triggered during declines in serum estrogen levels that occur before and during the time of menstruation. Therefore, substantial clinical evidence suggests that changes in ovarian hormones affect migraine headache. This represents the first of two manuscripts defining the role of ovarian hormones in the pathogenesis of migraine headache. The purpose of the first article will be to review the molecular and neurophysiologic effects of estrogen and progesterone on neurotransmitter systems and pain processing networks relevant to migraine headache. The second manuscript will focus on the clinical studies detailing the influence of estrogen and progesterone on migraine headache.

Calcium-mediated aponecrosis plays a central role in the pathogenesis of estrogenic chemical-induced neurotoxicity

Estrogen is traditionally associated with females but is also present in males, and influences aspects of brain chemistry and brain morphology in males, females and also during prenatal development. Humans as well as animals are additionally exposed to environmental products that mimic estrogen activity, also known as endocrine disrupters (EDCs). This hypothesis article investigates the role of estrogen (and also EDCs) in the brain and how it influences the Ca2+ pathway. Ca2+ and its movement in and out of the cell is an extremely important ion controlling normal cell physiology. Any dysfunction in the movement from outside to inside the cell or between organelles may have fundamentally negative effects and the disturbance may even lead to apoptosis and/or necrosis. Therefore we consider whether estrogen and EDCs may alter the Ca2+ physiology and whether these changes may be one of the main causes of interference in physiology that is seen when humans and animals are exposed to EDCs. We come to the conclusion that on a molecular level Ca2+ and Ca2+ fluxes ([Ca2+]i, endocrine disrupting chemicals, redox modulation, mitochondria and cytochrome c followed by apoptosis, necrosis or most likely aponecrosis may contribute to chemical-mediated developmental toxicity. Similarly, we hypothesize that calcium-mediated aponecrosis do not only play a central role in the pathophysiology of estrogenic chemical-induced neurotoxicity, but can contribute to chemical-mediated developmental toxicity in general, thereby affecting almost all cells and organs of the living organism.

Estrogen stimulates release of secreted amyloid precursor protein from primary rat cortical neurons via protein kinase C pathway

AIM

To investigate the mechanism of the action of estrogen, which stimulates the release of secreted amyloid precursor protein alpha (sAPP(alpha)) and decreases the generation of amyloid-beta protein (A(beta)), a dominant component in senile plaques in the brains of Alzheimer's disease patients.

METHODS

Experiments were carried out in primary rat cortical neurons, and Western blot was used to detect sAPP(alpha) in a culture medium and the total amount of cellular amyloid precursor protein (APP) in neurons.

RESULTS

17beta-Estradiol (but not 17alpha-estradiol) and beta-estradiol 6-(O-carboxymethyl) oxime: BSA increased the secretion of sAPP(alpha) and this effect was blocked by protein kinase C (PKC) inhibitor calphostin C, but not by the classical estrogen receptor antagonist ICI 182,780. Meanwhile, 17beta-estradiol did not alter the synthesis of cellular APP.

CONCLUSION

The effect of 17beta-estradiol on sAPP(alpha) secretion is likely mediated through the membrane binding sites, and needs molecular configuration specificity of the ligand. Furthermore, the action of the PKC-dependent pathway might be involved in estrogen-induced sAPP(alpha) secretion.

Estradiol and raloxifene protect cultured SN4741 neurons against oxidative stress

A large body of research has documented neuroprotective effects of estrogen against oxidative stress. Some neurodegenerative diseases such as Parkinson's disease, in which oxidative stress has been implicated as a contributing factor, affect more males than females, suggesting a possible protective effect of estrogen. We used the clonal substantia nigra cell line SN4741 to compare the neuroprotective properties of estrogen and raloxifene against oxidative stress, and to determine whether raloxifene acted as an estrogen agonist or antagonist in this system. We pretreated SN4741 cultures with alpha-estradiol, beta-estradiol, and raloxifene, and exposed them to hydrogen peroxide. Low nanomolar levels of raloxifene, beta-estradiol, and alpha-estradiol all significantly reduced cell death caused by oxidative stress. The estrogen receptor (ER) antagonist ICI 182,780 failed to reverse the neuroprotection by beta-estradiol, suggesting that the effect is not mediated by a classical ER. Western blotting using an antibody to the C-terminus region of ER-alpha revealed two bands, one at approximately 67 kDa (corresponding to ER-alpha) and a more prominent band at approximately 55-56 kDa. These results suggest that, in this cell line, both raloxifene and estrogen may be acting via a non-classical estrogen receptor.

Plasma membrane oestrogen receptor mediates neuroprotection against beta-amyloid toxicity through activation of Raf-1/MEK/ERK cascade in septal-derived cholinergic SN56 cells

Rapid oestrogen neuroprotection against beta-amyloid peptide (Abeta)-induced toxicity, a main feature of Alzheimer's disease, may be partially initiated at the plasma membrane. However, the mechanism by which this oestrogen effect occurs is unknown. In a septal murine cell line (SN56), we observed that short exposures to either 17beta-oestradiol (E2) or membrane impermeant E2 bound to horseradish peroxidase (E-HRP) induced a biphasic stimulation of extracellular-signal regulated protein kinase (ERK1/2) phosphorylation, with peak inductions detected around 4-8 min in the early phase and a second maximum around 8 h after treatment. ERK1/2 phosphorylation was abolished by ERK1/2 kinase (MEK) inhibitors PD98059 and U0126. Interestingly, PD98059 was also shown to block rapid E2-related prevention of death in cells exposed to Abeta fragment 1-40 (Abeta1-40) for 24 h. In contrast, no neuroprotective effects were obtained when MEK inhibitor was used to selectively abolish the late phosphorylation phase. Furthermore, both ERK1/2 activation and E2-associated protection were blocked by an inhibitor of Raf-1 kinase. Raf-1 may be involved in these effects because oestrogen caused the rapid serine 338 (Ser338) phosphorylation of this protein. In addition, the oestrogen receptor (ER) antagonist ICI 182,780 was also observed to block ERK1/2 phosphorylation. We propose a novel mechanism in SN56 cells by which rapid effects of oestrogen leading to neuroprotection are signalled through Raf-1/MEK/ERK1/2 pathway, possibly by activation of a membrane-related ER.

Spatial, temporal, and cellular distribution of the activated extracellular signal regulated kinases 1 and 2 in the developing and mature rat cerebellum

The extracellular signal regulated kinases 1 and 2 (ERK1/2) are important members of an intracellular signaling cascade that is involved in many aspects of the cellular physiology and development of neurons and glia. ERK1/2 are expressed in many brain regions including the cerebellum; however, their role during cerebellar development is poorly understood. Immunohistochemical approaches using phosphorylation-state specific antiserum that recognizes only the activated-ERK1/2 (pERK) were used to characterize the spatial and temporal patterns of activated-ERK in the developing and adult rat cerebellum. The distribution and cell type-specificity of pERK-immunoreactivity (IR) followed an age-related pattern, with the density of pERK-IR Purkinje cells decreasing between P6 and P15 and increasing at later times. Immunopositive granule cell neurons increased from P6 to P12, became decreased during much of late postnatal cerebellar development, and absent in adults. Co-localization of pERK with glial fibrillary acidic protein or the neuronal marker beta-tubulin revealed that activated ERK is present in maturing Purkinje and granule cells, and the soma of Bergmann glia on P4, P10 and P15; pERK was detected in astrocytes on P10 and P15. Associated with weaning, there was a general increase in activated-ERK in all cell types on P22. In adults, pERK-IR was confined to the Purkinje cell layer and scattered cells in the corpus medullare. In summary, a high degree of developmental plasticity was observed in the spatiotemporal distribution of cerebellar pERK-IR suggesting that the ERK-pathway plays a dynamic role in regulating neuronal and glial migration, proliferation and differentiation in the developing cerebellum. In the mature cerebellum, ERK signaling may also mediate postsynaptic information processing.

Local synthesis and dual actions of progesterone in the nervous system: neuroprotection and myelination

Progesterone (PROG) is synthesized in the brain, spinal cord and peripheral nerves. Its direct precursor pregnenolone is either derived from the circulation or from local de novo synthesis as cytochrome P450scc, which converts cholesterol to pregnenolone, is expressed in the nervous system. Pregnenolone is converted to PROG by 3beta-hydroxysteroid dehydrogenase (3beta-HSD). In situ hybridization studies have shown that this enzyme is expressed throughout the rat brain, spinal cord and dorsal root ganglia (DRG) mainly by neurons. Macroglial cells, including astrocytes, oligodendroglial cells and Schwann cells, also have the capacity to synthesize PROG, but expression and activity of 3beta-HSD in these cells are regulated by cellular interactions. Thus, Schwann cells convert pregnenolone to PROG in response to a neuronal signal. There is now strong evidence that P450scc and 3beta-HSD are expressed in the human nervous system, where PROG synthesis also takes place. Although there are only a few studies addressing the biological significance of PROG synthesis in the brain, the autocrine/paracrine actions of locally synthesized PROG are likely to play an important role in the viability of neurons and in the formation of myelin sheaths. The neuroprotective effects of PROG have recently been documented in a murine model of spinal cord motoneuron degeneration, the Wobbler mouse. The treatment of symptomatic Wobbler mice with PROG for 15 days attenuated the neuropathological changes in spinal motoneurons and had beneficial effects on muscle strength and the survival rate of the animals. PROG may exert its neuroprotective effects by regulating expression of specific genes in neurons and glial cells, which may become hormone-sensitive after injury. The promyelinating effects of PROG were first documented in the mouse sciatic nerve and in co-cultures of sensory neurons and Schwann cells. PROG also promotes myelination in the brain, as shown in vitro in explant cultures of cerebellar slices and in vivo in the cerebellar peduncle of aged rats after toxin-induced demyelination. Local synthesis of PROG in the brain and the neuroprotective and promyelinating effects of this neurosteroid offer interesting therapeutic possibilities for the prevention and treatment of neurodegenerative diseases, for accelerating regenerative processes and for preserving cognitive functions during aging.

Hormone-Dependent Neural Plasticity in the Juvenile and Adult Song System: What Makes a Successful Male?

The sexual quality of adult song is the result of genetic and epigenetic mechanisms shaping the neural song system throughout life. Genetic brain-intrinsic mechanisms determine the neuron pools that develop into forebrain song control areas independent of gonadal steroid hormones, androgens and estrogens. One fate of these neurons is the potential to express sex steroid receptors, such as androgen and estrogen receptors. Genetic brain-intrinsic mechanisms, too, determine the activity of hypothalamic-pituitary-gonad (HPG) axis, i.e., the working range and responsiveness of HPG axis to produce gonadal hormones. The epigenetic action of gonadal steroid hormones (androgens and estrogens) on determined vocal neurons is required to maintain and increase the pool of determined vocal neurons and to complete the connections of the vocal system, i.e., to make it function motorically. The subsequent influence of environmental information, including both external (socio-sexual and physical) and internal (body physiology) signals, specify the further neural phenotype of vocal areas either through acting on the HPG axis and differential release of gonadal hormones or through non-gonadal hormone systems, both of which have target neurons in the functional vocal system. Despite the clear evidence of hormone dependency of the development of both the adult song phenotype and song system phenotype, their causal relation is complex.

17beta-estradiol protects oligodendrocytes from cytotoxicity induced cell death

During pregnancy, changes in circulating levels of hormones, including estrogens, correlates with a significant decrease in the relapse incidence in women with Multiple Sclerosis (MS). In the present study, we demonstrate that both primary and cell line cultures of rat oligodendrocytes express the estrogen receptor (ER)-alpha and ERbeta estrogen receptors in the cytosol and nucleus, and that nuclear compartmentalization becomes more pronounced as the cells mature. Moreover, 17beta-estradiol significantly decreases the cytotoxic effects of the peroxynitrite generator 3-(4-morpholinyl)-sydnonimine (SIN-1) in both immature and mature oligodendrocytes in a dose dependent manner. This protective mechanism requires pretreatment with 17beta-estradiol and is blocked by ICI 182,780, a selective ERalpha/ERbeta antagonist. These results strongly suggest that 17beta-estradiol protects oligodendrocytes against SIN-1 mediated cytotoxicity through the activation of the estrogen receptors and provides new insights into the roles of the estrogen signaling pathways in myelin forming cells that are lost in demyelinating disorders.

Role of sex hormones in the sexually dimorphic expression of KCC2 in rat substantia nigra

KCC2 is a neuronal-specific potassium chloride cotransporter. The level of KCC2 expression is a factor determining whether GABA(A) receptor agonists depolarize or hyperpolarize neurons. Substantia nigra reticulata (SNR) neurons of male postnatal day 15 (PN15) rats have low KCC2 mRNA expression and respond to GABA(A) receptor activation with depolarization and activation of calcium-regulated gene expression. Female PN15 SNR neurons have high KCC2 mRNA expression and GABA(A) receptor agonists cannot activate calcium-dependent signaling processes. We investigate whether sex hormones regulate KCC2 mRNA expression in PN15 rat SNR. Using in situ hybridization, we studied the effects of acute (4 h) or prolonged (52 h) subcutaneous (s.c.) administration of testosterone (100 microg), dihydrotestosterone (180 microg) or 17beta-estradiol benzoate (5 microg) on KCC2 mRNA expression in male and female PN15 rat SNR. Different doses of estradiol (1 and 10 microg s.c., 4 h) were also acutely administered in female PN15 rats. Controls received oil injections. Separate groups of PN15 male rats were pretreated with antagonists of L-type voltage-sensitive calcium channels (L-VSCCs) [nifedipine, 100 mg/kg s.c.] or GABA(A) receptors [bicuculline, 2 mg/kg intraperitoneally (i.p.)] or their vehicles, 30 min before estradiol (5 microg s.c., 4 h). Testosterone and dihydrotestosterone upregulated KCC2 mRNA in both sexes. Estradiol downregulated KCC2 mRNA in males but not in females. Both acute and prolonged hormonal administration had similar effects. In male PN15 SNR, nifedipine and bicuculline decreased KCC2 mRNA acutely and prevented further downregulation of KCC2 mRNA by estradiol. Estradiol therefore downregulates KCC2 mRNA in male PN15 SNR, by interacting with the GABA(A) receptor and L-VSCC signaling pathway.

Regulation of Gene Expression in the Developing Midbrain by Estrogen: Implication of Classical and Nonclassical Steroid Signaling

Estrogen plays an important role during midbrain development. This is indicated by the presence of nuclear estrogen receptors and the transient expression of the estrogen-forming enzyme aromatase. A number of recent studies have shown that estrogen promotes the differentiation and survival, as well as physiological performance, of midbrain dopaminergic cells. In addition, we have reported that both ways of cellular estrogen signaling (classical and nonclassical) as well as interactions with nonneuronal target cells are involved in the transmission of intra- and intercellular estrogen effects in this brain region. This study provides additional evidence that (i) estrogen is capable of regulating gene expression in cultured embryonic neurons and astrocytes differently and (ii) both signaling mechanisms, i.e., classically through nuclear receptors and nonclassically through the stimulation of membrane-estrogen receptors, which are coupled to distinct intracellular signal transduction cascades, contribute diversely to gene regulation. These data reveal a high degree of complexity of estrogen action at the genomic level in the developing brain. Further studies are warranted to unravel the exact contribution of the differently regulated genes for developmental estrogen action.

Pharmacogenomics of multigenic diseases: sex-specific differences in disease and treatment outcome

Numerous genetic variations have been shown to affect disease susceptibility and drug response. Pharmacogenomics aims at improving therapy on the basis of genetic information for each individual patient. Furthermore, sex chromosomes broadly determine biological differences between males and females. Consequently, substantial sex differences exist in phenotypic manifestation of disease and treatment response. This review discusses the role of sex in coronary artery disease, schizophrenia, and depression--complex multigenic disorders with considerable sex differences in frequency and presentation. Moreover, genetic factors underlying disease and drug response appear to differ between male and female patients. This appears to result at least in part from different physiological effects exerted by sex hormones such that polymorphisms in susceptibility genes may have physiological relevance only in males or females. However, few examples have been discovered to play a role in complex multigenic diseases, and the mechanistic basis of genetic variants as sex-dependent susceptibility factors has yet to be explored. Therefore, pharmacogenomic studies must consider sex differences in an effort to optimize individual drug therapy.

β-estradiol influences differentiation of hippocampal neurons in vitro through an estrogen receptor-mediated process

We utilized morphometric analysis of 3 day cultures of hippocampal neurons to determine the effects of both estradiol and the synthetic estrogen receptor modulator raloxifene on several parameters of neuronal growth and differentiation. These measurements included survival, neurite production, dendrite number, and axon and dendrite length and branching. 17 beta-Estradiol (10 nM) selectively stimulated dendrite branching; this effect was neither mimicked by alpha-estradiol, nor blocked by the estrogen receptor antagonist ICI 182780. The selective estrogen receptor modulator raloxifene (100 nM) neither mimicked nor reversed the effects of estradiol on dendritic branching. Western immunoblotting for the alpha and beta subtypes of estrogen receptor revealed the presence of alpha, but not beta, estrogen receptors in our hippocampal cultures. There is growing recognition of the effects of 17 beta-estradiol on neuronal development and physiology, with implications for brain sexual dimorphism, plasticity, cognition, and the maintenance of cognitive function during aging. The role of estradiol in hippocampal neuronal differentiation and function has particular implications for learning and memory. These data support the hypothesis that 17 beta-estradiol is acting via alpha estrogen receptors in influencing hippocampal development in vitro. Raloxifene, prescribed to combat osteoporosis in post-menopausal women, is a selective estrogen receptor modulator with tissue-specific agonist/antagonist properties. Because raloxifene had no effect on dendritic branching, we hypothesize that it does not interact with the alpha estrogen receptor in this experimental paradigm.

Membrane receptors for oestrogen in the brain

Oestrogen is important for the development of neuroendocrine centres and other neural networks including limbic and motor systems. Later in adulthood, oestrogen regulates the functional performance of different neural systems and is presumably implicated in the modulation of cognitive efficiency. Although still a matter of controversial discussion, clinical and experimental studies point at a potential neuroprotective role of oestrogen. Concerning the concept of cellular oestrogen action, it is undisputed that it comprises the binding and activation of nuclear receptors. The last decades have, however, immensely broadened the spectrum of steroid signalling within a cell. Novel steroid-activated intracellular signalling mechanisms were described which are usually termed 'non-classical' or 'non-genomic'. The brain appears to be a rich source of this new mode of oestrogen action. Studies from the past years have pinpointed non-classical oestrogen effects in many CNS regions. All available data support the view that non-classical oestrogen action requires interactions with putative membrane binding sites/receptors. In this article, we aim at compiling the most recent findings on the nature and identity of membrane oestrogen receptors with respect to the brain. We also attempt to turn readers attention to the coupling of these 'novel' receptors to distinct intracellular signalling pathways.

Estrogens inhibit l-glutamate uptake activity of astrocytes via membrane estrogen receptor alpha

We investigated the effects of estrogen-related compounds including xenoestrogens [17beta-estradiol (E2), 17alpha-ethynylestradiol (EE), diethylstilbestrol (DES), p-nonylphenol (PNP), bisphenol A (BPA) and 17alpha-estradiol (17alpha)] on l-glu uptake by cultured astrocytes via glutamate-aspartate transporter (GLAST). After 24 h treatment, E2 inhibited the l-glu uptake at 1 micro m and higher concentrations. EE and DES also inhibited the l-glu uptake at 1 nm and higher concentrations. The other four compounds had no effect. The effects of E2, EE and DES were completely blocked by 10 nm of ICI182 780 (ICI). beta-Estradiol 17-hemisuccinate : bovine serum albumin (E2-BSA), a membrane-impermeable conjugate of E2, also elicited the inhibition of l-glu uptake at 1 nm and higher concentrations, and the effect was blocked by ICI. 16alpha-Iodo-17beta-estradiol (16alphaIE2), an estrogen receptor alpha (ERalpha) selective ligand, revealed an inhibitory effect at 10 nm, while genistein, an ERbeta selective ligand, failed to reveal such an effect at this concentration. Western blot analysis showed that the predominant ER of cultured astrocytes was ERalpha. The colocalization of ERalpha with GLAST on plasma membranes was immunohistochemically detected in these cells. From these results, we concluded that estrogens down-regulate l-glu uptake activity of astrocytes via membrane ERalpha.

Cellular strategies of estrogen-mediated neuroprotection during brain development

The role of estrogen during brain development is well documented. Estrogen influences cell survival and differentiation and also controls the formation and maintenance of neural networks. Knowledge of trophic estrogen action in the central nervous system (CNS) was the basis for the establishment of research programs directed toward a potential function of estrogen as a neuroprotective factor in the adult brain. Considerable evidence has accumulated over the years supporting this hypothesis. Experimental and epidemiologic studies as well as clinical trials have demonstrated that estrogen is beneficial for the course of neurodegenerative disorders such as Parkinson and Alzheimer diseases but may also protect neurons from postischemic neuronal degeneration. In this article, we aim to unravel potential physiologic responses and cell survival strategies that allow a more detailed understanding of estrogen-mediated neuroprotection in the brain. In particular, we focus on the participation of estrogen in the regulation of apoptotic processes. Furthermore, we present data on reciprocal estrogen-growth factor interactions. Both of these mechanisms were found to operate during brain development and to conciliate estrogen effects on neurons. This makes them likely candidates for taking part in conveying estrogen-dependent neuroprotection in the adult CNS.

Estrogen regulates tyrosine hydroxylase expression in the neonate mouse midbrain

Estrogen plays an important role during differentiation of midbrain dopaminergic neurons. This is indicated by the presence of estrogen receptors and the transient expression of the estrogen-forming enzyme aromatase within the dopaminergic cell groups. We have previously shown that estrogen regulates the plasticity of dopamine cells through the stimulation of neurite growth/arborization. In this study, we have analyzed the capability of estrogen to influence the activity of developing mouse dopamine neurons. The expression of tyrosine hydroxylase (TH) was assessed by competitive RT-PCR and Western blotting. The developmental expression of TH in the ventral midbrain was studied from embryonic day 15 until postnatal day 15 and revealed highest TH levels early postnatally. This profile coincides with the transient aromatase expression in this brain area. Using cultured midbrain cells, we found that estrogen increased TH mRNA/protein levels. The application of the estrogen receptor antagonist ICI 182,780 resulted in a complete inhibition of estrogen effects. To verify these data in vivo, fetuses were exposed in utero from E15 until birth to the aromatase inhibitor CGS 16949A or to CGS supplemented with estrogen. CGS caused a robust reduction in TH mRNA/protein levels in the midbrain, which could be restored by estrogen substitution. Taken together, our data strongly suggest that estrogen controls dopamine synthesis in the developing nigrostriatal dopaminergic system and support the concept that estrogen is implicated in the regulation of ontogenetic steps but also in the function of midbrain dopamine neurons.