Estrogen receptor beta (ERbeta) mRNA and protein in serotonin neurons of macaques

Effect of ovarian hormones on genes promoting dendritic spines in laser-captured serotonin neurons from macaques

Dendritic spines are the elementary structural units of neuronal plasticity and the cascades that promote dendritic spine remodeling center on Rho GTPases and downstream effectors of actin dynamics. In a model of hormone replacement therapy, we sought the effect of estradiol (E) and progesterone (P) on gene expression in these cascades in laser-captured serotonin neurons from rhesus macaques with complementary DNA array analysis. Ovariectomized rhesus macaques were treated with either placebo, E or E+P through Silastic implant for 1 month before euthanasia. The midbrain was obtained, sectioned and immunostained for tryptophan hydroxylase (TPH). TPH-positive neurons were laser captured using an Arcturus Laser Dissection Microscope (PixCell II). RNA from laser-captured serotonin neurons (n=2 animals/treatment) was hybridized to Rhesus Affymetrix GeneChips. With E±P treatment, there was a significant change in 744 probe sets (analysis of variance, P<0.05), but 10,493 probe sets exhibited a twofold or greater change. Pivotal changes in pathways leading to dendritic spine proliferation and transformation included twofold or greater increases in expression of the Rho GTPases called CDC42, Rac1 and RhoA. In addition, twofold or greater increases occurred in downstream effectors of actin dynamics, including p21-activated kinase (PAK1), Rho-associated coiled-coil-containing protein kinase (ROCK), PIP5K, IRSp53, Wiskott-Aldrich syndrome protein (WASP), WASP family Verprolin-homologous protein (WAVE), MLC, cofilin, gelsolin, profilin and three subunits of actin-related protein (ARP2/3). Finally, twofold or greater decreases occurred in CRIPAK, LIMK2 and myosin light chain kinase (MLCK). The regulation of RhoA, Rac1, CDC42, ROCK, PIP5k, IRSp53, WASP, WAVE, LIMK2, CRIPAK1, MLCK, ARP2/3 subunit 3, gelsolin, profilin and cofilin was confirmed with nested quantitative reverse transcriptase-PCR on laser-captured RNA (n=3 animals/treatment). The data indicate that ovarian steroids target gene expression of the Rho GTPases and pivotal downstream proteins, that in turn would promote dendritic spine proliferation and stabilization on serotonin neurons of the dorsal raphe nucleus.

Ovarian steroid regulation of the midbrain corticotropin releasing factor and urocortin systems in macaques

A significant number of postmenopausal women report increased anxiety and vulnerability to stress, which has been linked to decreased secretion of ovarian steroids. Communication between the serotonin system and the corticotropin releasing factor (CRF) system determines stress sensitivity or resilience. This study examines the effects of the ovarian steroids, estradiol (E) and progesterone (P) on the CRF system components that impact serotonin neurons in the midbrain of nonhuman primates. Ovariectomized rhesus macaques were treated with placebo, E alone for 1 month, or E supplemented with P for the last 2 weeks. Quantitative (q)RT-PCR and immunocytochemistry were employed. E±P treatment decreased CRF-R1 and increased CRF-R2 gene expression in hemi-midbrain blocks and in laser captured serotonin neurons. Also in hemi-midbrains, E treatment increased urocortin 1 (UCN1) and CRFBP gene expression, but supplemental P treatment reversed these effects. E±P decreased CRF fiber density in the dorsal, interfascicular and median raphe nuclei and decreased CRF-R1 immunostaining in the dorsal raphe. E increased CRF-R2 immunostaining in the dorsal and median raphe. E±P increased UCN1 immunostaining in the cell bodies and increased UCN1 fiber density in the caudal linear nucleus. Estrogen receptor beta (ERβ), but not ERα was detected in the nucleus of UCN1-positive neurons. While the mechanism of ovarian hormone regulation of the midbrain CRF system requires further investigation, these studies clearly demonstrate another pathway by which ovarian hormones may have positive effects on anxiety and mood regulation.

ERbeta: recent understanding of estrogen signaling

The discovery of a second estrogen receptor, ERbeta, and the finding that 5alpha-androstane-3beta,17beta-diol (3betaAdiol) strongly binds to ERbeta, have opened up a new aspect of estrogen signaling. Some of the major shifts in our understanding come from finding ERbeta in tissues which do not express ERalpha but are estrogen-responsive; these were called sites of 'indirect estrogen action'. Two key sites that fall into this category are the brain and the prostate. Studies of ERbeta in the past 10 years have led us to hypothesize that estrogen signaling depends on the balance between ERalpha and ERbeta, and that inadequate predominance of one or the other isoform could lead to disease.

Ovarian steroids decrease DNA fragmentation in the serotonin neurons of non-injured rhesus macaques

We previously found that ovarian steroids promote neuroprotection in serotonin neurons by decreasing the expression of pro-apoptotic genes and proteins in the dorsal raphe nucleus of rhesus macaques, even in the absence of overt injury. In this study, we questioned whether these actions would lead to a reduction in DNA fragmentation in serotonin neurons. Ovariectomized (OVX) rhesus monkeys were implanted with silastic capsules that were empty (placebo) or containing estradiol (E), progesterone (P) or estradiol and progesterone (E+P) for 1 month. In all animals, eight levels of the dorsal raphe nucleus in a rostral-to-caudal direction were immunostained using the terminal deoxynucleotidyl transferase nick end labeling (TUNEL) method. Two staining patterns were observed, which are referred to as type I, with complete dark staining of the nucleus, and type II, with peripheral staining in the perinuclear area. A montage of the dorsal raphe was created at each level with a Marianas Stereology Microscope and Slidebook 4.2, and the TUNEL-positive cells were counted. In direct comparison with OVX animals, P treatment and E+P treatment significantly reduced the total number of TUNEL-positive cells (Mann-Whitney test, both treatments P=0.04) and E+P treatment reduced the number of TUNEL-positive cells per mm(3) (Mann-Whitney test, P=0.04). Double immunocytochemistry for TUNEL and tryptophan hydroxylase (TPH) indicated that DNA fragmentation was prominent in serotonin neurons. These data suggest that in the absence of ovarian steroids, a cascade of gene and protein expression leads to an increase in DNA fragmentation in serotonin neurons. Conversely, ovarian steroids have a neuroprotective role in the non-injured brain and prevent DNA fragmentation and cell death in serotonin neurons of nonhuman primates.

Oestrogen receptor beta is involved in the actions of oestrogens in the brain for affective behaviour, but not trophic effects in peripheral tissues

The steroid, 17beta-oestradiol (E(2)) has pervasive psychological and physical effects throughout the lifespan. The question arises as to whether there are divergent oestrogen receptor (ER)-mediated mechanisms for these effects in the central nervous system (CNS) and periphery. This review focuses on results of studies using a whole animal model (i.e. female rats and mice) to investigate the relative effects and mechanisms of oestrogens in the CNS and the periphery. By using this approach, it has been possible to differentiate the enhancing effects of E(2) on behavioural processes mediated by the hippocampus, such as affective behaviour, and the trophic effects that increase tumourigenesis and uterine growth. Studies using pharmacological manipulations and knockout mice suggest that a likely mechanism underlying the beneficial effects of E(2) for hippocampal function (but not proliferative effects in the body) involves actions at ERbeta, changes in cell cycle/division (e.g. cyclin D1) and/or histone modifications. Thus, it may be possible to differentiate the beneficial effects of oestrogens through ERbeta, particularly in the CNS, from the negative proliferative effects on peripheral, E(2)-sensitive tissues.

Effects of phytoestrogen genistein on genioglossus function and oestrogen receptors expression in ovariectomized rats

OBJECTIVE

This study was designed to investigate the effects of genistein on genioglossal muscle function and the expression of oestrogen receptors (ERs) in the ovariectomized rats.

DESIGN

Fifty female Sprague-Dawley rats were randomly divided into 5 groups: the control group (SHAM), the ovariectomized group (OVX), the ovariectomized rats receiving low genistein dosage (OVX+L), the moderate genistein dosage group (OVX+M) and the high genistein dosage group (OVX+H). Oestradiol level was detected by radioimmunity. The isometric twitch tension (P(t)) and tetanic tension (P(0)) of the GG muscle were measured in response to electrical field stimulation. The expression of ERs on the mRNA and protein levels was measured by real-time PCR and western blot respectively.

RESULTS

Ovariectomy decreased muscle fatigue resistance and the expression of different ERs significantly. Genistein treatment resulted in a dose-dependent protective effect on muscle fatigability and a parallel dose-responsive increase in the expression of oestrogen receptors mRNA and protein levels in genioglossus, with larger effects on oestrogen receptor beta vs. alpha. In contrast to the improvements in fatigability, there was no treatment effect on isometric twitch or tetanic tensions.

CONCLUSION

The results indicated that genistein increased muscle fatigue resistance in addition to effects on receptors, and the up-regulation of receptors expression may be a possible mechanism by which genistein improved fatigue.

Protective actions of ovarian hormones in the serotonin system of macaques

The serotonin neurons of the dorsal and medial raphe nuclei project to all areas of the forebrain and play a key role in mood disorders. Hence, any loss or degeneration of serotonin neurons could have profound ramifications. In a monkey model of surgical menopause with hormone replacement and no neural injury, E and P decreased gene expression in the dorsal raphe nucleus of c-jun n-terminal kinase (JNK1) and kynurenine mono-oxygenase (KMO) that promote cell death. In concert, E and P increased gene expression of superoxide dismutase (SOD1), VEGF, and caspase inhibitory proteins that promote cellular resilience in the dorsal raphe nucleus. Subsequently, we showed that ovarian steroids inhibit pivotal genes in the caspase-dependent and caspase-independent pathways in laser-captured serotonin neurons including apoptosis activating factor (Apaf1), apoptosis-inducing factor (AIF) and second mitochondria-derived activator of caspases (Smac/Diablo). SOD1 was also increased specifically in laser-captured serotonin neurons. Examination of protein expression in the dorsal raphe block revealed that JNK1, phosphoJNK1, AIF and the translocation of AIF from the mitochondria to the nucleus decreased with hormone therapy, whereas pivotal execution proteins in the caspase pathway were unchanged. In addition, cyclins A, B, D1 and E were inhibited, which would prevent re-entry into the cell cycle and catastrophic death. These data indicated that in the absence of gross injury to the midbrain, ovarian steroids inhibit the caspase-independent pathway and cell cycle initiation in serotonin neurons. To determine if these molecular actions prevented cellular vulnerability or death, we examined DNA fragmentation in the dorsal raphe nucleus with the TUNEL assay (terminal deoxynucleotidyl transferase nick end labeling). Ovarian steroids significantly decreased the number of TUNEL-positive cells in the dorsal raphe. Moreover, TUNEL staining prominently colocalized with TPH immunostaining, a marker for serotonin neurons. In summary, ovarian steroids increase the cellular resilience of serotonin neurons and may prevent serotonin neuron death in women facing decades of life after menopause. The survival of serotonin neurons would support cognition and mental health.

Estrogen receptor beta regulates the expression of tryptophan-hydroxylase 2 mRNA within serotonergic neurons of the rat dorsal raphe nuclei

Dysfunctions of the brain 5-HT system are often associated with affective disorders, such as depression. The raphe nuclei target the limbic system and most forebrain areas and constitute the main source of 5-HT in the brain. All 5-HT neurons express tryptophan hydroxylase-2 (TPH2), the brain specific, rate-limiting enzyme for 5-HT synthesis. Estrogen receptor (ER) beta agonists have been shown to attenuate anxiety- and despair-like behaviors in rodent models. Therefore, we tested the hypothesis that ER beta may contribute to the regulation of gene expression in 5-HT neurons of the dorsal raphe nuclei (DRN) by examining the effects of systemic and local application of the selective ER beta agonist diarylpropionitrile (DPN) on tph2 mRNA expression. Ovariectomized (OVX) female rats were injected s.c. with DPN or vehicle once daily for 8 days. In situ hybridization revealed that systemic DPN-treatment elevated basal tph2 mRNA expression in the caudal and mid-dorsal DRN. Behavioral testing of all animals in the open field (OF) and on the elevated plus maze (EPM) on days 6 and 7 of treatment confirmed the anxiolytic nature of ER beta activation. Another cohort of female OVX rats was stereotaxically implanted bilaterally with hormone-containing wax pellets flanking the DRN. Pellets contained 17-beta-estradiol (E), DPN, or no hormone. Both DPN and E significantly enhanced tph2 mRNA expression in the mid-dorsal DRN. DPN also increased tph2 mRNA in the caudal DRN. DPN- and E-treated rats displayed a more active stress-coping behavior in the forced-swim test (FST). No behavioral differences were found in the OF or on the EPM. These data indicate that ER beta acts at the level of the rat DRN to modulate tph2 mRNA expression and thereby influence 5-HT synthesis in DRN subregions. Our results also suggest that local activation of ER beta neurons in the DRN may be sufficient to decrease despair-like behavior, but not anxiolytic behaviors.

Serotonergic projections from the caudal raphe nuclei to the hypoglossal nucleus in male and female rats

The respiratory control system is sexually dimorphic. In many brain regions, including respiratory motor nuclei, serotonin (5HT) levels are higher in females than in males. We hypothesized that there could be sex differences in 5HT input to the hypoglossal nucleus, a region of the brainstem involved in upper airway control. Adult Fischer 344 rats were anesthetized and a retrograde transsynaptic neuroanatomical tracer, Bartha pseudorabies virus (PRV), was injected into the tongue. Sections through the medulla were reacted immunocytochemically for the presence of (i) PRV, (ii) tryptophan hydroxylase (TPH; marker of 5HT neurons), (iii) PRV combined with TPH, and (iv) 5HT. Sex hormone levels were measured in female rats and correlated with TPH immunoreactivity, as hypoglossal 5HT levels vary with the estrous cycle. The number of PRV neurons was comparable in male and female rats. The number and distribution of TPH immunoreactive neurons in the caudal raphe nuclei were similar in male and female rats. The subset of 5HT neurons that innervate hypoglossal motoneurons was also similar in male and female rats. With the exception of the ventrolateral region of the hypoglossal nucleus, 5HT immunoreactivity was similar in male and female rats. These data suggest that sex differences in 5HT modulation of hypoglossal motoneurons in male and female rats are not the result of sex differences in TPH or 5HT, but may result from differences in neurotransmitter release and reuptake, location of 5HT synaptic terminals on hypoglossal motoneurons, pre- and postsynaptic 5HT receptor expression, or the distribution of sex hormone receptors on hypoglossal or caudal raphe neurons.

Estrogen receptor-alpha immunoreactive neurons in the brainstem and spinal cord of the female rhesus monkey: species-specific characteristics

The distribution pattern of estrogen receptors in the rodent CNS has been reported extensively, but mapping of estrogen receptors in primates is incomplete. In this study we describe the distribution of estrogen receptor alpha immunoreactive (ER-alpha IR) neurons in the brainstem and spinal cord of the rhesus monkey. In the midbrain, ER-alpha IR neurons were located in the periaqueductal gray, especially the caudal ventrolateral part, the adjacent tegmentum, peripeduncular nucleus, and pretectal nucleus. A few ER-alpha IR neurons were found in the lateral parabrachial nucleus, lateral pontine tegmentum, and pontine gray medial to the locus coeruleus. At caudal medullary levels, ER-alpha IR neurons were present in the commissural nucleus of the solitary complex and the caudal spinal trigeminal nucleus. The remaining regions of the brainstem were devoid of ER-alpha IR neurons. Spinal ER-alpha IR neurons were found in laminae I-V, and area X, and were most numerous in lower lumbar and sacral segments. The lateral collateral pathway and dorsal commissural nuclei of the sacral cord and the thoracic intermediolateral cell column also contained ER-alpha IR neurons. Estrogen treatment did not result in any differences in the distribution pattern of ER-alpha IR neurons. The results indicate that ER-alpha IR neurons in the primate brainstem and spinal cord are concentrated mainly in regions involved in sensory and autonomic processing. Compared with rodent species, the regional distribution of ER-alpha IR neurons is less widespread, and ER-alpha IR neurons in regions such as the spinal dorsal horn and caudal spinal trigeminal nucleus appear to be less abundant. These distinctions suggest a modest role of ER-alpha in estrogen-mediated actions on primate brainstem and spinal systems. These differences may contribute to variations in behavioral effects of estrogen between primate and rodent species.

Regulation of pseudosexual behavior in the parthenogenetic whiptail lizard, Cnemidophorus uniparens

Neuroendocrine mechanisms underlying complementary behaviors like male-typical mounting and female-typical receptivity are most often studied independently in males and females, respectively. Cnemidophorus uniparens is a unisexual lizard species consisting only of females that alternately express male- and female-like pseudosexual behavior across the ovarian cycle. Intact, postovulatory (PostOv), and ovariectomized (OVX), androgen-implanted animals [OVX plus testosterone (T)] exhibit male-like mounting, but not receptivity, whereas intact, preovulatory (PreOv), and OVX lizards injected with estradiol [OVX plus estrogen (E)] express receptivity, but not mounting. We tested whether the serotonergic system in the preoptic area (POA) and ventromedial nucleus of the hypothalamus (VMN) gates the reciprocal inhibition characterizing this alternating expression of mounting and receptivity. Serotonergic signaling at the POA appears to be key to gating male-like behavior. Postovulatory and OVX plus T animals have lower intracellular serotonin (5-HT) levels, and greater abundance of inhibitory 5-HT1A receptor mRNA in the POA compared with both PreOv and OVX plus E lizards. Moreover, injecting 5-HT into the POA of OVX plus T animals suppresses mounting, whereas injection into VMN of OVX plus E lizards suppresses receptivity. Although 5-HT levels in the VMN do not differ across the ovarian cycle or between hormonally manipulated animals, PreOv and OVX plus E lizards have a lower abundance of 5-HT2A mRNA in the VMN. Stimulating 5-HT1A receptors using systemic drug administration inhibits mounting, whereas activating 5-HT2A receptors facilitates receptivity. This study illuminates how male- and female-typical sexual behaviors share common neural circuits, and that 5-HT regulates these naturally complementary, and mutually exclusive, behaviors.

Differential effects of ovarian steroids and raloxifene on serotonin 1A and 2C receptor protein expression in macaques

To further understand the role of ovarian hormones in the function of the serotonin neural system, we investigated the effects of estradiol (E), progesterone (P), and raloxifene on 5HT 1A and 2C receptor protein expression in the dorsal raphe region using Western blot analysis. Adult rhesus macaques (Macaca mulatta) were ovariectomized (Ovx) and implanted with Silastic capsules containing E or P. In the first paradigm, animals that had been Ovx for 6-16 months were treated for 1 month with E (El) or E + P (EP1) and compared to animals that were untreated and Ovx for 5 months (n = 4 per group). In the second paradigm, comparisons were made between animals that were Ovx and untreated for 5 months, or Ovx and immediately implanted with Silastic capsules containing E or E + P for 5 months (E5, EP5), or administered raloxifene in the diet for 5 months (Ral5) (n = 4 per group). The dorsal raphe region was harvested, homogenized and a crude membrane fraction was obtained for examination of receptor proteins. In the first paradigm, 5HT1A receptor protein expression was significantly lower in E1 and EPI treatment groups compared to the Ovx-control group (ANOVA P = 0.01; posthoc P < 0.03), but 5HT2C receptor expression was unaffected by 1 month of E or EP treatment. In the second paradigm, there was no difference in 5HT1A receptor expression between the Ovx-control group and the E5 group, but 5HT1A receptor expression was significantly suppressed in the EP5 group (ANOVA P = 0.04; posthoc P < 0.05). In addition, 5HT2C expression increased in the E5 treatment group relative to the Ovx-control group. Addition of P to the E5 regimen prevented the E5-induced increase in 5HT2C receptor expression and significantly reduced 5HT2C receptor expression to a level below that observed in the Ovx-control group (ANOVA P = 0.001; posthoc P < 0.05). Thus, 5HT1A receptor may lose sensitivity to the suppressive effect of E after 5 months, whereas the 5HT2C receptor increases. However, addition of P in the EP5 regimen maintains the regulatory effects observed with 1 month of treatment. 5HT1A receptor protein levels were higher with raloxifene treatment than in Ovx-control animals (P < 0.01), suggesting that raloxifene may antagonize residual E in Ovx animals.

Ovarian steroid treatment decreases corticotropin-releasing hormone (CRH) mRNA and protein in the hypothalamic paraventricular nucleus of ovariectomized monkeys

Corticotropin-releasing hormone (CRH) gene and protein expression were examined in the paraventricular nucleus (PVN) of ovariectomized female macaques treated with placebo or hormone therapy (HT) consisting of either estrogen (E) for 28 days, or progesterone (P) for the last 14 of 28 days, or E for 28 days supplemented with P for the last 14 of 28 days using Silastic capsules implanted s.c. in the periscapular region (n=4/group). Perfusion fixed sections (25 microm) at five levels of the PVN (rostral to caudal at 250 microm intervals) were immunostained (ICC) with an antibody to human CRH or processed in an in situ hybridization (ISH) assay with a monkey specific CRH riboprobe. The immunostained CRH-positive area was quantified with a Marianas Stereology Workstation and Slidebook 4.2. There was a significant decrease in the immunological CRH signal with E, P, and E+P treatment as measured by total or average pixels and microns (analysis of variance (ANOVA), p<0.002; Student-Newman-Keul's post hoc test versus placebo control group, p<0.05). There was also a decrease in the number of detectable CRH neurons (ANOVA, p<0.03) with HT. The sections processed for ISH were exposed to autoradiographic films. The CRH mRNA signal was analyzed with NIH Image. The average optical density and positive pixel area of the CRH mRNA signal was significantly suppressed by ovarian HT (ANOVA p<0.002; Student-Newman-Keul's post hoc test versus placebo control group, p<0.05). In summary, 1 month of stable treatment with a moderate dose of E, P or E+P significantly reduced CRH mRNA and protein in the PVN of ovariectomized monkeys. These results suggest that this hormone treatment regimen may increase stress resilience in surgically menopausal primates.

Effect of ovarian hormones on survival genes in laser captured serotonin neurons from macaques

We sought the effect of estradiol (E) and progesterone (P) on survival gene expression in laser captured serotonin neurons and in the dorsal raphe region of monkeys with cDNA array analysis. Spayed rhesus macaques were treated with either placebo, E or E + P via Silastic implant for 1 month prior to killing. First, RNA from a small block of midbrain containing the dorsal raphe was hybridized to Rhesus Gene Chips (n = 3/treatment). There was a significant change in 854 probe sets with E +/- P treatment (anova, p < 0.05); however, only 151 probes sets exhibited a twofold or greater change. Twenty-five genes related to cell survival changed significantly. The expression of vascular endothelial growth factor, superoxide dismutase (SOD1), and the caspase inhibitor, BIRC4, was confirmed with quantitative RT-PCR. Then, RNA from laser captured serotonin neurons (n = 2/treatment) was hybridized to Rhesus Gene Chips. There was a significant change in 744 probe sets, but 10 493 probe sets exhibited a twofold or greater change. Pivotal changes in apoptosis and cell cycle pathways included twofold or greater increases in SOD1, IkappaBalpha, Fas apoptotic inhibitory molecule, fibroblast growth factor-receptor 2 (FGFR2), neurotrophic tyrosine kinase receptor 2 (NTRK2), phosphoinositide-3-kinase (p85 subunit), cyclic AMP dependent protein kinase (PKA) (catalytic subunit), calpain 2, and ataxia telangectasia mutated (ATM). Twofold or greater decreases occurred in TNF receptor interacting serine-threonine kinase 1 (RIP1), BH3 interacting domain death agonist (BID), apoptotic peptidase activating factor 1 (Apaf1), caspase recruitment domain 8 (CARD8), apoptosis inducing factor (AIF), Diablo and Cyclins A, B, D, and E. The regulation of SOD1, calpain 2, Diablo, and Cyclin D was confirmed with quantitative RT-PCR (n = 3/treatment). The data indicate that ovarian steroids target the cytokine-signaling pathway, caspase-dependent and -independent pathways and cell cycle proteins to promote serotonin neuron survival.

The ratio of estrogen receptor alpha to estrogen receptor beta in adipose tissue is associated with leptin production and obesity

The loss of estrogen associated with menopause is suspected to play an important regulatory role in changes of fat metabolism and obesity. To evaluate the relationship between obesity and the ratio of estrogen receptor subtypes (ERalpha/ERbeta) in adipose tissues in pre- and postmenopausal women, we measured the anthropometric indices of 31 premenopausal women and 12 postmenopausal women. Serum samples, subcutaneous and omental adipose tissues were also obtained from study participants. Serum leptin, adiponectin, IL-6, and TNF-alpha levels were measured using ELISA methods. Real-time RT-PCR analysis was performed to detect and to compare mRNA levels of leptin and estrogen receptor subtypes (ERalpha and ERbeta) from adipose tissues. The ratio of abdominal subcutaneous to omental adipose tissue for the ER subtypes (Sc-Om ratio of the ER subtypes), i.e., subcutaneous ERalpha/ERbeta over omental ERalpha/ERbeta, showed significant correlations with anthropometric indices including BMI (r=0.801, p<0.05) and waist circumference (r=0.696, p<0.05) in both pre- and postmenopausal women. The Sc-Om ratio of the ER subtypes also had a significant correlation with the serum leptin level (r=0.735, p<0.05) as well as the mRNA level of leptin in omental adipose tissue (r=0.753, p<0.05). However, there were no significant differences between the pre- and postmenopausal groups with regard to the expressed level of ER subtypes. In conclusion, our study results showed that the ratio of ERalpha to ERbeta in adipose tissue was associated with obesity as well as the serum level and production of leptin in omental adipose tissue.

The serotonin transporter gene: polymorphism and haplotype analysis in Russian suicide attempters

The focus on gender-specific genes associated with female suicide is justified by the possible dimorphic nature of the serotonergic system and by the greater number of suicide attempts in females. We performed analysis of the promoter (5-HTTLPR) and intron 2 (STin2 VNTR) polymorphisms and haplotypes of the serotonin transporter gene in Russian suicide attempters, separately in men and women. Our findings indicate the contribution of the SLC6A4 gene to susceptibility for suicidal behavior in women, but not in men. The L/L genotype (p = 0.013, OR = 2.09) and L10 haplotype (p = 0.04, OR = 1.77) were associated with suicide in Russian women only. Further investigations of this gene in different phenotypic groups are necessary.

Detection and localization of an estrogen receptor beta splice variant protein (ERβ2) in the adult female rat forebrain and midbrain regions

Estrogens regulate neural processes such as neuronal development, reproductive behavior, and hormone secretion, and signal through estrogen receptor (ER) alpha and ERbeta (here called ERbeta1). Recent studies have found variations in ERalpha and ERbeta1 mRNA splicing in rodents and humans. Functional reporter gene assays suggest that these splicing variations alter ER-mediated transcriptional regulation. Estrogen receptor beta 2 (ERbeta2), an ERbeta1 splice variant containing an 18 amino acid (AA) insert in the ligand binding domain, binds estradiol with approximately 10-fold lower affinity than ERbeta1, suggesting that it may serve as a low-affinity ER. Moreover, ERbeta2 reportedly acts in a dominant-negative fashion when heterodimerized with ERbeta1 or ERalpha. To explore the function of ERbeta2 in brain, an antiserum (TwobetaER.1) targeting the 18 AA insert was developed and characterized. Western blot analysis and transient expression of ERbeta2 in cell lines demonstrated that TwobetaER.1 recognizes ERbeta2. In the adult female rat brain, ERbeta2 immunoreactivity is localized in the cell nucleus and is expressed with a distribution similar to that of ERbeta1 mRNA. ERbeta2 immunoreactive cell numbers were high in, for example, piriform cortex, paraventricular nucleus, supraoptic nucleus, arcuate nucleus, and hippocampal CA regions, whereas it was low in the dentate gyrus. Moreover, ERbeta2 is coexpressed in gonadotropin-releasing hormone and oxytocin neurons. These studies demonstrate ERbeta splice variant proteins in brain and support the hypothesis that ER signaling diversity depends not only on ligand or coregulatory proteins, but also on regional and phenotypic selectivity of ER splice variant proteins.

Structure-function relationship of estrogen receptor alpha and beta: impact on human health

17Beta-estradiol (E2) controls many aspects of human physiology, including development, reproduction and homeostasis, through regulation of the transcriptional activity of its cognate receptors (ERs). The crystal structures of ERs with agonists and antagonists and the use of transgenic animals have revealed much about how hormone binding influences ER conformation(s) and how this conformation(s), in turn, influences the interaction of ERs with co-activators or co-repressors and hence determines ER binding to DNA and cellular outcomes. This information has helped to shed light on the connection between E2 and the development or progression of numerous diseases. Current therapeutic strategy in the treatment of E2-related pathologies relies on the modulation of ER trancriptional activity by anti-estrogens; however, data accumulated during the last five years reveal that ER activities are not only restricted to the nucleus. ERs are very mobile proteins continuously shuttling between protein targets located within various cellular compartments (e.g., membrane, nucleus). This allows E2 to generate different and synergic signal transduction pathways (i.e., non-genomic and genomic) which provide plasticity for cell response to E2. Understanding the structural basis and the molecular mechanisms by which ER transduce E2 signals in target cells will allow to create new pharmacologic therapies aimed at the treatment of a variety of human diseases affecting the cardiovascular system, the reproductive system, the skeletal system, the nervous system, the mammary gland, and many others.

Estradiol increases alpha7 nicotinic receptor in serotonergic dorsal raphe and noradrenergic locus coeruleus neurons of macaques

Acetylcholine, acting on presynaptic nicotinic receptors (nAChRs), modulates the release of neurotransmitters in the brain. The rat dorsal raphe nucleus (DR) and the locus coeruleus (LC) receive cholinergic input and express the alpha7nAChR. In previous reports, we demonstrated that estradiol (E) administration stimulates DR serotonergic and LC noradrenergic function in the macaque. In addition, it has been reported that E induces the expression of the alpha7nAChR in rats. We questioned whether E increased the expression of the alpha7nAChR in the macaque DR and LC. We utilized double immunostaining to study the effect of a simulated preovulatory surge of E on the expression of the alpha7nAChR in the DR and the LC and to determine whether alpha7nAChR colocalizes with serotonin and tyrosine hydroxylase (TH) in macaques. There was no difference in the number of alpha7nAChR-positive neurons between ovariectomized (OVX) controls and OVX animals treated with a silastic capsule containing E (Ecap). However, supplemental infusion of E for 5-30 hours to Ecap animals (Ecap + inf) significantly increased the number of alpha7nAChR-positive neurons in DR and LC. In addition, supplemental E infusion significantly increased the number of neurons in which alpha7nAChR colocalized with serotonin and TH. These results constitute an important antecedent for study of the effects of nicotine and ovarian steroid hormones in the physiological functions regulated by the DR and the LC in women.

Estrogen receptor-β gene disruption potentiates estrogen-inducible aggression but not sexual behaviour in male mice

Aggressive behaviour of gonadally intact male mice is increased by estrogen receptor (ER)-beta gene disruption, whereas sexual behaviour remains unchanged. The elevated aggression levels following ER-beta gene disruption is pronounced during repeated aggression tests in young animals and the first aggression test in adults. In the present study, the roles of ER-beta activation in the regulation of aggressive and sexual behaviour were investigated in gonadectomized ER-beta knockout (betaERKO) and wild-type (WT) male mice treated with various doses of estrogen. Overall, estradiol benzoate (EB) treatment induced higher levels of aggression in betaERKO mice than in WT mice. In WT mice, the levels of aggression induced by EB were highest in the lowest-dose (2.5 microg/day) group and gradually decreased in higher-dosage groups. On the other hand, equally high levels of aggressive behaviour were induced by all three doses of EB in betaERKO mice. A marked genotype difference in dose responses is inferred, such that the ER-alpha-mediated facilitatory action of estrogen is more pronounced at lower and physiological doses and the ER-beta-mediated inhibitory action is only unveiled at higher doses of estrogen. In contrast to aggression, the levels of sexual behaviour induced by EB were not different between betaERKO and WT at either dose of EB (2.5 and 12.5 microg/day) examined. These findings support the notion that ER-beta activation may exert an attenuating action on male aggression induced by estrogen through ER-alpha-mediated brain mechanisms, whereas its effect on male sexual behaviour is relatively small.

Anxiolytic property of estrogen related to the changes of the monoamine levels in various brain regions of ovariectomized rats

Anxiety is a symptom reflecting the dysregulation of monoaminergic neurotransmitters which may be modulated by estrogen. In our current study, we investigated the effects of chronic estrogen administration (10 microg/kg, s.c. for 4 weeks) on anxiety-like behavior using the elevated plus-maze with the corresponding changes of monoamines in the brain regions contributing to anxiety. The behavioral test revealed that estrogen-treated rats (Ovx+E(2)) spent more time in the open arm of the maze as well as a higher time/entry ratio in open arms than ovariectomized (Ovx) rats, indicating an anxiolytic property of estrogen. The increase in open arm time corresponded to an increase in uterine weight, indicated a correlation between the function of estrogen and its anxiolytic effect. Measurements of brain monoamines following estrogen treatment revealed decreases in norepinephrine, dopamine and serotonin in all of the brain regions studied, which also lead to an increase in turnover rates. The concentrations of norepinephrine in caudate putamen, of dopamine in nucleus accumbens, of serotonin in frontal cortex, hippocampus, caudate putamen, nucleus accumbens, and substantia nigra and of the serotonin metabolite, the 5-hydroxyindolacetic acid in substantia nigra of Ovx+E(2) rats were significantly lower than those of Ovx rats. Interestingly, the uterine weight was negatively correlated with the changes of dopamine and serotonin (with the exception of the hippocampus), suggesting a regulatory role of estrogen on these systems. From these data, we concluded that, in fact, there is a relationship between estrogen and monoamines (i.e. serotonin, dopamine) in modulating the anxiety-like behaviors in female rats.

Nuclear factor kappa B in the dorsal raphe of macaques: an anatomical link for steroids, cytokines and serotonin

OBJECTIVE

Nuclear factor kappa B (NFkappaB) is a transcription factor that activates gene expression in response to proinflammatory cytokines, and elevated cytokines are associated with depression, which has a serotonergic component. We questioned (1) whether serotonin neurons contain NFkappaB, (2) whether NFkappaB detection with immunocytochemistry is changed in the dorsal raphe nucleus (DRN) by ovarian hormone treatment and (3) whether ovarian hormones regulate midbrain NFkappaB gene or protein expression.

METHODS

Monkeys were spayed and treated with placebo, estrogen (E), progesterone (P) or E+P for 1 month (n = 4 animals/treatment group), and the midbrain was harvested for immunocytochemistry and stereology. An antibody that detects nuclear location-specific (NLS)-NFkappaB p65 was applied, and the numbers of NLS-NFkappaB-immunopositive cells were counted in 9 sections of the DRN. Additional monkeys were used for Western blot analysis and quantitative reverse transcription-polymerase chain reaction (RT-PCR) for NFkappaB p65.

RESULTS

In placebo-treated macaques, neurons were double-immunostained for serotonin and nuclear NFkappaB p65 throughout the DRN. The mean total number of NFkappaB-positive cells equalled 2178 (and standard error of the mean [SEM] 129) in the placebo group, 1631 (SEM 221) in the E-treated group, 2314 (SEM 186) in the P-treated group and 1162 (SEM 100) in the E+P-treated group (analysis of variance p = 0.003). The E-treated and E+P-treated groups had a significantly lower density of cells stained positive for NFkappaB than the placebo or P-treated groups (post hoc). Unmasking of NLS-NFkappaB immunostaining in the DRN revealed dense immunostaining in the cytoplasm of large dorsal raphe neurons. There was no difference between treatment groups in the amount of NFkappaB p65 detected by Western blot or in the relative expression of NFkappaB p65 mRNA with quantitative RT-PCR.

CONCLUSIONS

These observations are consistent with the notion that gene and protein expression of NFkappaB are constitutive but that ovarian hormones can decrease the nuclear location of NFkappaB in dorsal raphe neurons and, thereby, decrease the ability of NFkappaB to drive gene expression in response to cytokines.

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.

Gender difference in association between polymorphism of serotonin transporter gene regulatory region and anxiety

OBJECTIVE

The objective of this study was to verify the hypothesis that variation of the serotonin transporter gene promoter region (5-HTTLPR) is associated with sensitivity to stress.

METHODS

Genotyping of 5-HTTLPR and evaluation of emotional states were performed on 194 participants. Participants' emotional states were evaluated using the Perceived-Stress Scale (PSS), the State-Trait Anxiety Inventory (STAI), and the Self-rating Depression Scale (SDS).

RESULTS

There was significant GenderxGenotype interaction in STAI (state, P<.05; trait, P<.05). Females with the l/s genotype showed higher anxiety than those with the s/s genotype in both state and trait anxiety. Oppositely, males with the s/s genotype showed higher anxiety than those with the l/s genotype.

CONCLUSION

On all emotional scales, females with the l/s genotype showed high scores, contrary to males with the same genotype. Therefore, our results suggest that 5-HTTLPR l allele may be one pathway that activates negative emotion in females but acts contrary in males.

Neuroactive steroid effects on cognitive functions with a focus on the serotonin and GABA systems

This article will review neuroactive steroid effects on serotonin and GABA systems, along with the subsequent effects on cognitive functions. Neurosteroids (such as estrogen, progesterone, and allopregnanolone) are synthesized in the central and peripheral nervous system, in addition to other tissues. They are involved in the regulation of mood and memory, in premenstrual syndrome, and mood changes related to hormone replacement therapy, as well as postnatal and major depression, anxiety disorders, and Alzheimer's disease. Estrogen and progesterone have their respective hormone receptors, whereas allopregnanolone acts via the GABA(A) receptor. The action of estrogen and progesterone can be direct genomic, indirect genomic, or non-genomic, also influencing several neurotransmitter systems, such as the serotonin and GABA systems. Estrogen alone, or in combination with antidepressant drugs affecting the serotonin system, has been related to improved mood and well being. In contrast, progesterone can have negative effects on mood and memory. Estrogen alone, or in combination with progesterone, affects the brain serotonin system differently in different parts of the brain, which can at least partly explain the opposite effects on mood of those hormones. Many of the progesterone effects in the brain are mediated by its metabolite allopregnanolone. Allopregnanolone, by changing GABA(A) receptor expression or sensitivity, is involved in premenstrual mood changes; and it also induces cognitive deficits, such as spatial-learning impairment. We have shown that the 3beta-hydroxypregnane steroid UC1011 can inhibit allopregnanolone-induced learning impairment and chloride uptake potentiation in vitro and in vivo. It would be important to find a substance that antagonizes allopregnanolone-induced adverse effects.

Effect of estrogen-serotonin interactions on mood and cognition

Both the neurotransmitter serotonin and the ovarian steroid estrogen have been implicated in the modulation of mood and cognition. Although significant functional interactions between estrogen and serotonin are acknowledged, the nature of their relationship has not been fully elucidated. Research using ovariectomized animals has identified estrogen-induced changes in serotonin transmission, binding, and metabolism in brain regions implicated in the regulation of affect and cognition. Studies in humans, particularly of menopausal women undergoing estrogen treatment, have provided some support for these findings and identified instances in which change in mood or cognition is accompanied by alterations in serotonin function and hormonal status. However, it is apparent that further research is required to understand the neural processes involved in the interplay between estrogen and serotonin. By reviewing animal and human data regarding estrogen and serotonin's effects on mood and cognition, the authors aim to better define their relationship and highlight areas for further research.

ERbeta protein expression in female cynomolgus monkey and CF-1 mouse brain: Western analysis

In humans and rodents, multiple ERbeta variants with sizes ranging from 477-549 amino acids (aa) have been described. The identification of these variants in target tissues has important implications for estrogen signaling and cellular responsiveness. Western blot analysis using two anti-ERbeta antibodies specific for mammalian ERbeta sequences (PA1-310B and PA1-311) was employed to examine ERbeta protein expression in neural tissues from ovariectomized (OVX) cynomolgus macaques and CF-1 mice as well as to assess potential regulatory effects of acute and extended estradiol (E(2)) treatment. In hypothalamic extracts from both species, a single ERbeta immunoreactive (ERbeta-ir) band was detected at approximately 54 kDa, corresponding to the expected molecular weight for ERbeta477 and/or 485. In cynomolgus females, oral E(2) administration for 16 weeks had no apparent effect on hypothalamic ERbeta protein expression. In mouse, a single injection of E(2) did not change hypothalamic ERbeta protein levels 1.5, 4, 8, 16, or 24 h after injection. Extending the hormonal treatment to 4 or 21 days in OVX female mice also had no effect on the level of hypothalamic ERbeta protein. Additional regional analyses in female mouse brain with PA1-310B antibody showed that a second, 59 kDa ERbeta-ir band was present in cortex, striatum, hippocampus, and amygdala that could represent one or both of the larger ERbeta variants (530 and 549aa). The expression level of the second ERbeta isoform exhibited regional variation, with the strongest immunoreactivity detected in cortex and amygdala. Elucidating the functions of these ERbeta isoforms in the CNS will facilitate our understanding of the tissue- and promoter-specific actions of estrogen.

Cyclic estradiol replacement attenuates stress-induced c-Fos expression in the PVN of ovariectomized rats

Estradiol modulates stress reactions in female rats. Several studies showed anxiolytic effects of estradiol in behavioral tests, but the underlying mechanisms are still unclear. The aim of the current study was to explore how estradiol-treated rats respond to acute and chronic stress compared to ovariectomized rats. Ovariectomized rats received vehicle or 17beta-estradiol injections (10 microg/250 g) once every 4 days, which induced alternating high and low plasma 17beta-estradiol levels. Stress was presented by daily exposure to an adverse environment in which the animals received five footshocks for either 3 or 22 days. Under control conditions no differences were observed, but as soon as stress was applied, reactions of ovariectomized and estradiol-treated rats diverged. Both acute and chronic stress increased the c-Fos protein expression in the paraventricular nucleus (PVN) of the hypothalamus. Cyclic estradiol treatment reduced this stress-induced activation of the PVN, an effect that seems to be dependent on the plasma estradiol levels. No differences in stress-induced corticosterone responses were revealed between the treatment groups. An increase in the number of ERbeta-expressing cells in the PVN of ovariectomized and estradiol-treated rats during chronic stress implied increased ERbeta-mediated mechanisms during these conditions. The dampening effect of estradiol on the excessive stress-induced activity in the PVN may be beneficial for the animal in its response to chronic recurrent stress by reducing the output of the PVN.

Estrogen receptor-alpha and -beta immunoreactive neurons in the brainstem and spinal cord of male and female mice: relationships to monoaminergic, cholinergic, and spinal projection systems

For many populations of estrogen-sensitive neurons it remains unknown how they are associated with central nervous system circuitries that mediate estrogen-induced modulation of behavioral components. With the use of double-labeling immunohistochemistry and tracing techniques, the relationships of estrogen receptor (ER)-alpha- and ER-beta-immunoreactive (IR) neurons in the mouse brainstem and spinal cord to monoaminergic, cholinergic, and spinal projection systems are explored. Similar distributions of ER-IR neurons were present in females and males, with differences in labeling intensity of ER-alpha immunoreactivity among males and estrogen-, and oil-treated females. Barrington's nucleus, the ventrolateral medulla, and the nucleus of the solitary tract contained spinal-projecting ER-alpha-IR neurons, whereas ER-alpha-IR neurons in the periaqueductal gray, parabrachial nucleus, and catecholaminergic A1 cell group received spinal input. Numerous tyrosine hydroxylase (TH)-IR ER-alpha-IR neurons were present in the ventral periaqueductal gray, nucleus of the solitary tract, A1 cell group, and lumbosacral cord. The dorsal raphe nucleus contained ER-alpha-IR and ER-beta-IR neurons that colocalized with serotonin (5HT), and the reticulotegmental nucleus contained 5HT-IR ER-alpha-IR neurons. Fibers IR for vesicular acetylcholine transporter (VAChT), TH, and 5HT were located among ER-alpha-IR neurons in the dorsal horn and spinal autonomic regions. Robust staining for TH and VAChT, but not 5HT, was present among ER-alpha-IR neurons in the lumbosacral lateral collateral pathway. Possible modulatory actions of estrogen on each of these ER-IR populations are discussed in the context of their specific function, including micturition, sexual behavior, ejaculation, cardiovascular and respiratory control, tactile and nociceptive sensory processing, anti-nociception, endocrine regulation, and feeding.

A second tryptophan hydroxylase isoform, TPH-2 mRNA, is increased by ovarian steroids in the raphe region of macaques

Recently, a second gene that codes for the rate-limiting enzyme in serotonin synthesis was found in brain, named tryptophan hydroxylase-2 (TPH-2). We sequenced overlapping segments (251 and 510 bp) of 5' monkey TPH-2 and questioned whether TPH-2 is regulated by estrogen (E) and progesterone (P) in serotonin neurons of macaques. Monkey TPH-2 was 97% homologous to human TPH-2 and 65% homologous to monkey TPH-1 in the coding region. Spayed monkeys were administered placebo, E-only, P-only, or E + P for 1 month via Silastic implants (n = 4/treatment) and the midbrain was utilized for TPH-2 in situ hybridization (ISH). Additional monkeys (n = 3/treatment) were used to determine the relative abundance of TPH-2 mRNA with quantitative (q) RT-PCR. In the ISH assay, all of the hormone treatments caused a significant and similar increase in TPH-2 mRNA optical density (fourfold; P < 0.004) and positive pixel area (twofold; P < 0.002) over spayed controls. Treatment with E or E + P for 1 month increased the relative abundance of TPH-2 mRNA over spayed controls in the qRT-PCR assay (ANOVA P < 0.05 and P < 0.007, respectively). In conclusion, ovarian steroids stimulate TPH-2 mRNA expression, which could in turn cause an increase in serotonin synthesis. This would impact many of the neural functions that are governed by serotonin.

Estrogen receptor beta in health and disease

Estrogens, acting through its two receptors, ESR1 (hereafter designated ER alpha) and ESR2 (hereafter designated ER beta), have diverse physiological effects in the reproductive system, bone, cardiovascular system, hematopoiesis, and central and peripheral nervous systems. Mice with inactivated ER alpha, ER beta, or both show a number of interesting phenotypes, including incompletely differentiated epithelium in tissues under steroidal control (prostate, ovary, mammary, and salivary glands) and defective ovulation reminiscent of polycystic ovarian syndrome in humans (in ER beta-/- mice), and obesity, insulin resistance, and complete infertility (both in male and female ER alpha-/- mice). Estrogen agonists and antagonists are frequently prescribed drugs with indications that include postmenopausal syndrome (agonists) and breast cancer (antagonists). Because the two estrogen receptors (ERs) have different physiological functions and have ligand binding pockets that differ enough to be selective in their ligand binding, opportunities now exist for development of novel ER subtype-specific selective-ER modulators.

Preliminary array analysis reveals novel genes regulated by ovarian steroids in the monkey raphe region

We hypothesize that ovarian hormones may improve serotonin neuron survival. We sought the effect of estradiol (E) and progesterone (P) on novel gene expression in the macaque dorsal raphe region with Affymetrix array analysis. Nine spayed rhesus macaques were treated with either placebo, E or E+P via Silastic implant for 1 month prior to euthanasia (n=3 per treatment). RNA was extracted from a small block of midbrain containing the dorsal raphe and examined on an Agilent Bioanalyzer. The RNA from each monkey was labeled and hybridized to an Affymetrix HG_U95AV Human GeneChip Array. After filtering and sorting, 25 named genes remained that were regulated by E, and 24 named genes remained that were regulated by supplemental P. These genes further sorted into functional categories that would promote neuronal plasticity, transmitter synthesis, and trafficking, as well as reduce apoptosis. The relative abundance of four pivotal genes was examined in all nine animals with quantitative RT-PCR and normalized by glyceraldehyde 3-phosphate dehydrogenase (GAPDH). E+/-P caused a significant threefold reduction in JNK-1 (a pro-apoptosis gene, p<0.007); and a significant sixfold decrease in kynurenine mono-oxygenase (produces neurotoxic quinolones, p<0.05). GABA-A receptor (alpha3 subunit; benzodiazepine site) and E2F1 (interferes with cytokine signaling) were unaffected by E, but increased sevenfold (p<0.02) and fourfold (p<0.009), respectively, upon treatment with P. In summary, subsets of genes related to tissue remodeling or apoptosis were up- or down-regulated by E and P in a tissue block containing the dorsal raphe. These changes could promote cellular resilience in the region where serotonin neurons originate.

Reflections on the discovery and significance of estrogen receptor beta

We have known for many years that estrogen is more than the female hormone. It is essential in the male gonads, and in both sexes, estrogen has functions in the skeleton and central nervous system, on behavior, and in the cardiovascular and immune systems. An important aspect of the discovery of estrogen receptor (ER) beta is that the diverse functions of estrogen can now be divided into those mediated by ERalpha and those mediated by ERbeta. Pharmacological exploitation of this division of the labors of estrogen is facilitated by the ligand-binding specificity and selective tissue distribution of the two ERs. Because the ligand binding domains of ERalpha and ERbeta are significantly different from each other, selective ligands can be (and have been) developed to target the estrogenic pathway that is malfunctioning, without interfering with the other estrogen-regulated pathways. Because of the absence of ERbeta from the adult pituitary and endometrium, ERbeta agonists can be used to target ERbeta with no risk of adverse effects from chemical castration and uterine cancer. Some of the diseases in which there is hope that ERbeta agonists will be of benefit are prostate cancer, autoimmune diseases, colon cancer, malignancies of the immune system, and neurodegeneration.

Estrogen receptor-beta regulates tryptophan hydroxylase-1 expression in the murine midbrain raphe

BACKGROUND

Distinct expression patterns of estrogen receptor (ER)-alpha and ER-beta are displayed in the murine central nervous system. ER-beta is the predominant form of the receptor expressed in the murine midbrain dorsal raphe nucleus (DRN). Tryptophan hydroxylase (TPH) is abundantly expressed in the serotonergic neurons of the DRN and is regulated by estrogen in both the monkey and the guinea pig.

METHODS

In this study we used immunocytochemistry to show that ER-beta and TPH are colocalized in the serotonergic cells of the murine DRN. We utilized the ER-alpha and ER-beta gene deletion mouse models and in situ hybridization to demonstrate that ER-beta is responsible for regulating TPH1 mRNA expression.

RESULTS

Estrogen increased TPH1 mRNA expression in the DRN of wild type and ER-alpha knockout mice (alpha-ERKO) but not ER-beta knockouts (beta-ERKO).

CONCLUSIONS

These data indicate that ER-beta is responsible for mediating estrogen regulated TPH1 expression in the murine DRN.

Differential distribution of estrogen receptor (ER)-α and ER-β in the midbrain raphe nuclei and periaqueductal gray in male mouse: Predominant role of ER-β in midbrain serotonergic systems

We examined the distribution of estrogen receptor (ER)-alpha and ER-beta immunoreactive (ir) cells in the dorsal (DRN) and median/paramedian (MPRN) raphe nuclei in male mice. ER-alpha ir neurons were scattered across the three subdivisions (ventral, dorsal, and lateral) of the DRN and the MPRN. Robust ER-beta ir cells were observed throughout the raphe nuclei, and were particularly abundant in the ventral and dorsal subdivisions of the DRN. Using dual-label immunocytochemistry for ER-alpha or ER-beta with tryptophan hydroxylase (TPH), the rate-limiting enzyme for 5-hydroxytryptamine (5-HT) synthesis, over 90% of ER-beta ir cells exhibited TPH-ir in all DRN subdivisions, whereas only 23% of ER-alpha ir cells contained TPH. Comparisons of ER-alpha knockout (alphaERKO) as well as ER-beta knockout (betaERKO) mice with their respective wild-type (WT) littermates revealed that gene disruption of either ER-alpha or ER-beta did not affect the other ER subtype expression in the raphe nuclei. In situ hybridization histochemistry revealed that there was a small but statistically significant decrease in TPH mRNA expression in the ventral DRN subdivision in betaERKO mice compared with betaWT mice, whereas TPH mRNA levels were not affected in alphaERKO mice. These findings support a hypothesis that ER-beta activation may contribute to the estrogenic regulation of neuroendocrine and behavioral functions, in part, by acting directly on 5-HT neurons in the raphe nuclei in male mice.

Effects of ovarian steroids and raloxifene on proteins that synthesize, transport, and degrade serotonin in the raphe region of macaques

In the monkey dorsal raphe, we reported that 1-month (mo) of estrogen replacement, with or without progesterone supplementation for 14 days, significantly increased tryptophan hydroxylase-1 (TPH-1) mRNA; decreased serotonin reuptake transporter (SERT) mRNA and decreased monoamine oxidase (MAO)-A mRNA, but had no effect on MAO-B mRNA. Here, we questioned what effect would 1 or 5 mo of ovarian hormones or the selective estrogen receptor modulator (SERM), raloxifene, have on TPH protein and phosphorylation, and on protein expression of SERT, MAO-A or MAO-B? Raloxifene antagonizes estrogen in breast or uterus, but estrogen-like activities in the brain have been reported. Cytoplasmic and membrane extracts of the dorsal raphe region were processed for Western blotting. TPH, phosphoserine, SERT, MAO-A, and MAO-B were detected with specific antibodies. The optical densities of the signals were measured with NIH image and analyzed by ANOVA. Both 1 and 5 mo of estrogen, with or without progesterone, and 5 mo of raloxifene significantly increased TPH protein. Administration for 5 mo of estrogen plus progesterone and raloxifene also increased TPH phosphorylation. Estrogen, with or without progesterone, for 1 mo had no effect on SERT protein. However, 5 mo of estrogen and 5 mo of raloxifene increased SERT protein. Estrogen alone or combined with progesterone for 1 mo caused a significant reduction in MAO-A. Yet, after 5 mo of the same treatments, MAO-A was not different from spayed controls. Estrogen alone had no effect on MAO-B. However, the addition of progesterone significantly increased MAO-B. Raloxifene for 5 mo had no effect on MAO-A or MAO-B. Thus, to various extents, estrogen, progesterone, and raloxifene may increase serotonin production and transport. The expression of the degradative enzymes suggests a complex combination of gene transcription, post-transcriptional processing, and substrate feedback mechanisms.

Serotonin neurons derived from rhesus monkey embryonic stem cells: similarities to CNS serotonin neurons

We sought an in vitro primate model for serotonin neurons. Rhesus monkey embryonic stem (ES) cell colonies were isolated and differentiated into embryoid bodies (EBs), then transferred to serum-free medium with 1% insulin-transferrin-selenium for 7 days to induce neural precursor cell (NPC) formation. NPCs were cultured in medium with 1% N-2 neural supplement and human fibroblast growth factor 2 (FGF2, 10 ng/ml) for 7 days to stimulate cell proliferation. Lastly, NPCs were dispersed into single cells and cultured without FGF2 for another 7 days to obtain terminal differentiation. Terminal cells were characterized for neuronal and serotonergic markers. Over 95% of the NPCs were immunopositive for nestin and Musashi1. Terminally differentiated cells appeared in both small and large morphologies. Most (>95%) of the mature cells (both small and large) were immunopositive for neuron-specific nuclear protein (NeuN), synaptophysin, microtubule-associated protein (MAP2C), Tau-1, neurofilament 160 (NF-160), beta-tubulin (TujIII), tryptophan hydroxylase (TPH), serotonin, the serotonin reuptake transporter (SERT), estrogen receptor-beta (ERbeta), and progestin receptor (PR), but not estrogen receptor-alpha (ERalpha). Less than 2-3% of cells were positive for tyrosine hydroxylase (TH). Reverse transcriptase polymerase chain reaction (RT-PCR) detected mRNA transcripts for TPH-1, TPH-2, SERT, 5-HT1A-autoreceptor, ERbeta, and PR in the differentiated population. A low level of expression of ERalpha mRNA was also detected. Quantitative RT-PCR indicated that the relative abundance of TPH-2 mRNA was greater than TPH-1 mRNA. Serotonin as measured by ELISA increased 3-fold in the mature stage compared to the selection and expansion stages. In summary, a remarkably high percentage of cells derived from monkey ES cells exhibited neuronal plus serotonergic markers as well as nuclear steroid receptors similar to primate CNS serotonin neurons, suggesting that these cells may serve as a useful primate model for serotonergic neurons.

Cognition, mood disorders, and sex hormones

Macaques (Macaca spp.) are useful models to evaluate effects of ovarian sex steroids and selective estrogen receptor modulators (SERMs) on mood and cognitive function due to similarities to women in their reproductive and central nervous systems. The results of nonhuman primate studies support the hypothesis that estrogen mediates specific aspects of attention and memory, yet much work is needed to understand which cognitive processes are affected, whether natural versus surgical menopause effects are different, and the interaction of age and ovarian senescence on cognitive function. This knowledge is necessary to determine whether to support the cognitive function of women in the menopausal phase of life and, if so, to determine efficacious therapeutic interventions. Mood disorders are prevalent in women and are associated with reproductive function in women and macaques. Exogenous steroid therapies, including oral contraceptives and postmenopausal hormone replacement therapies, have behavioral effects in women and appear to affect the behavior and underlying neural substrates of monkeys. Additional research is necessary to confirm and extend these observations. Ovarian steroids have multiple effects on serotonin synthesis, reuptake, and degradation, on neural activity that drives serotonin release, and on receptor activation in primates. This system modulates cognitive function and mood and is the target of a broad class of antidepressant therapies. Understanding the effects of ovarian steroids on the neural serotonergic system is necessary to understand depression in women. These studies are best carried out in primate models, which are more similar to humans in neural serotonergic function than other animal models.

Expression of estrogen receptors (alpha, beta) and androgen receptor in serotonin neurons of the rat and mouse dorsal raphe nuclei; sex and species differences

Sex steroids have been inferred to be involved in the regulation of affective status at least partly through the serotonergic (5-HT) system, particularly in the dorsal raphe nucleus (DRN), which innervates enormous projections to the cerebral cortex and limbic system. In the present study, the expression of estrogen receptors-alpha and -beta (ERalpha, ERbeta), androgen receptor (AR) and 5-HT was examined immunohistochemically in the rat and mouse DRN in both sexes. The results showed that large numbers of ERalpha- and/or ERbeta-immunoreactive (ERalpha-I, ERbeta-I) cells were found in the DRN of both male and female mice, whereas only small numbers of ERalpha-I cells and no ERbeta-I cells were seen in the rat DRN of each sex. With respect to AR-immunoreactive (AR-I) cells, moderate numbers of such cells were present only in male rats and mice, and no or very few could be observed in female ones. The ERalpha-I, ERbeta-I, and AR-I cells were mainly distributed in the rostral DRN. In double-immunostaining, many 5-HT-I neurons were found to show ERalpha and/or ERbeta expression specifically in the rostral DRN (particularly dorsal, ventral and interfascicular parts) of mice of both sexes, but not in that of rats. In contrast, only a few 5-HT neurons were observed to show AR expression in the DRN of both rodents. The current results strongly suggest that sex steroids can modulate the affective regulation of the serotonergic system through ERalpha and/or ERbeta in 5-HT neurons of the mouse rostral DRN (but not so much through AR), and that such effects might be different depending on the sex and species, as shown by the prominent sex differences in AR expression and prominent species differences in ERalpha and ERbeta expression.

Distribution of estrogen receptor alpha and beta in the mouse central nervous system: in vivo autoradiographic and immunocytochemical analyses

Although the distribution of estrogen receptor beta (ERbeta) immunoreactivity in the rat central nervous has been reported, no such data are available in the mouse. The present study used in vivo autoradiography utilizing a (125)I-estrogen that has equal binding affinity for both receptors as well as immunohistochemistry for ERbeta and ERalpha, to investigate and compare the distribution of the two ERs in the mouse CNS. The use specific antisera against ERalpha and ERbeta allowed us to evaluate the contribution of these receptors to the binding detected with autoradiography. In addition, data were collected in ovariectomized wildtype and ERalpha KO (knockout) mice to examine developmental regulation of ERbeta expression by ERalpha. These studies revealed that in the mouse CNS, combining immunoreactivity for ERalpha with that for ERbeta accounted for all regions where binding was seen using autoradiography. Therefore, these data strongly suggest that the major contributors of estrogen binding in the mouse CNS are ERalpha and ERbeta. Together, these data provide an anatomical foundation for future studies and advance our understanding of estrogen action in the CNS. Moreover, since the immunocytochemical images were similar in wildtype and ERalpha KO mice, these studies suggest that the lack of ERalpha does not influence the expression of ERbeta in the central nervous system.

Increased aggressive behavior and decreased affiliative behavior in adult male monkeys after long-term consumption of diets rich in soy protein and isoflavones

Estrogen produced by aromatization of gonadal androgen has an important facilitative role in male-typical aggressive behavior that is mediated through its interaction with estrogen receptors (ER) in the brain. Isoflavones found in soybeans and soy-based dietary supplements bind ER and have dose- and tissue-dependent effects on estrogen-mediated responses. Yet, effects of isoflavone-rich diets on social and aggressive behavior have not been studied. We studied the effects of long-term (15 months) consumption of diets rich in soy isoflavones on spontaneous social behavior among adult male cynomolgus macaques (Macaca fascicularis) (n = 44) living in nine stable social groups. There were three experimental conditions which differed only by the source of dietary protein: casein and lactalbumin (no isoflavones), soy protein isolate containing 0.94 mg isoflavones/g protein, and soy protein isolate containing 1.88 mg isoflavones/g protein. In the monkeys fed the higher amount of isoflavones, frequencies of intense aggressive (67% higher) and submissive (203% higher) behavior were elevated relative to monkeys fed the control diet (P's < 0.05). In addition, the proportion of time spent by these monkeys in physical contact with other monkeys was reduced by 68%, time spent in proximity to other monkeys was reduced 50%, and time spent alone was increased 30% (P's < 0.02). There were no effects of treatment on serum testosterone or estradiol concentrations or the response of plasma testosterone to exogenous gonadotropin-releasing hormone (GnRH). The results indicate that long-term consumption of a diet rich in soy isoflavones can have marked influences on patterns of aggressive and social behavior.

Comparative distribution of estrogen receptor α and β immunoreactivities in the forebrain and the midbrain of the female guinea pig

Estrogen plays an important role in regulating gonadotropin secretion and reproductive behavior. The estrogen receptor alpha (ERalpha) was believed to be the only receptor which mediated the actions of the hormone until the identification of a novel ER called ERbeta. In the present study, the map of ERalpha immunoreactive (IR) neurons was compared with the distribution pattern of ERbeta-IR neurons in the forebrain and midbrain of ovariectomized guinea pigs using immunocytochemistry. The immunoreactivities appeared to be mainly nuclear in their subcellular distribution. Both ERalpha- and ERbeta-like immunoreactivities were highly expressed in the bed nucleus of the stria terminalis and the ventrolateral hypothalamic nucleus but were found to be differentially expressed in discrete subregions of the amygdaloid complex. A large number of intensely labeled ERalpha cells were observed throughout the rostrocaudal extent of the preoptic region, whereas only a few ERbeta-IR neurons were found in the periventricular preoptic nucleus bordering the third ventricle or scattered in the medial preoptic area. In contrast, only ERalpha-immunoreactivity was seen in the septum, and in the magnocellular supraoptic, paraventricular, arcuate, and premammillary nuclei. In the midbrain, neurons containing ERalpha were observed throughout the rostrocaudal extent of the gray matter, whereas ERbeta was only detected within the dorsal raphe nucleus. These observations provide evidence of a distinct neuroanatomical pattern for the two subtypes of the ER which may have different roles in regulating behavior and the neuroendocrine mechanisms of reproduction. Species similarities and differences in the distributions of ERalpha and ERbeta immunoreactivities are discussed.

Estrogen reduces serotonin-1A receptor-mediated oxytocin release and Galpha(i/o/z) proteins in the hypothalamus of ovariectomized rats

The present study examined the effect of estradiol on hypothalamic serotonin-1A (5-HT(1A)) receptor signaling in female rats. We first examined the time-course effects of a single injection of the 5-HT(1A) receptor agonist (+/-)8-OH-DPAT (5, 15 or 30 min prior to decapitation), and dose response of (+)8-OH-DPAT (50, 100, 200 or 500 microg/kg, s.c.) on plasma hormones in ovariectomized rats that received a daily injection of beta-estradiol 3-benzoate (10 microg/day, s.c.) or vehicle (sesame oil) for 2 days. In vehicle- and estrogen-treated rats, the peak response of hormones occurred at 15 min after injection and the time-course of oxytocin and adrenocorticotropic hormone (ACTH) responses to an injection of 8-OH-DPAT were comparable. However, only the oxytocin response was reduced by estrogen treatment. A second experiment compared the ACTH and oxytocin responses with doses of 50 or 200 microg/kg, s.c. of (+)8-OH-DPAT vs. (+/-)8-OH-DPAT in ovariectomized rats that were treated with oil or beta-estradiol 3-benzoate (10 microg/day, s.c.) for 2 days. (+)8-OH-DPAT and (+/-)8-OH-DPAT produced a similar magnitude of increase in plasma levels of ACTH and oxytocin. Treatment with beta-estradiol 3-benzoate produced a significant and comparable reduction in the oxytocin response to the highest dose (200 microg/kg, s.c.) of both (+)8-OH-DPAT and (+/-)8-OH-DPAT but did not alter the ACTH response to either (+)8-OH-DPAT or (+/-)8-OH-DPAT. In the dose-response experiment, a dose of 50 microg/kg of (+)8-OH-DPAT produced a maximal increase in plasma levels of ACTH, while the maximal oxytocin response was achieved with a dose of 200 microg/kg, s.c. Treatment with beta-estradiol 3-benzoate reduced the maximal oxytocin response to (+)8-OH-DPAT (by 29%) but did not alter the ACTH response to any doses of (+)8-OH-DPAT. To examine potential mechanisms mediating the effects of estrogen on 5-HT(1A) receptor signaling, we measured the levels of Galpha(i), Galpha(o) and Galpha(z) proteins, which couple 5-HT(1A) receptors to their effector enzymes, in two subregions of the hypothalamus. The levels of Galpha(z) protein were reduced in the mediobasal hypothalamus (containing the ventromedial and arcuate nuclei), which mainly expresses estrogen receptor-alpha, but not in the paraventricular hypothalamus, which mainly expresses estrogen receptor-beta. Estradiol reduced the levels of Galpha(i2) and Galpha(i3 )proteins in both hypothalamic regions but did not affect Galpha(i1) levels in either area. Combined, the data suggest that racemic and stereoselective 8-OH-DPAT have similar neuroendocrine effects and that both estrogen receptor-alpha and estrogen receptor-beta mediate the reduction in levels of Galpha(i2,3) proteins.

Characterization of reproductive steroid receptors and response to estrogen in a rat serotonergic cell line

Study of the cellular and molecular consequences of steroid hormone action in the serotonin neural system will provide new avenues for pharmacotherapeutic intervention in mental illness related to reproductive function. However, it is difficult to probe intracellular mechanisms with whole animal models. We sought the steroid receptor compliment and estrogen response of two rat serotonin cell lines in order to determine if they could be of future assistance in this matter. Immunohistochemistry with a panel of antibodies, RT-PCR and a serotonin ELISA were utilized to characterize the RN46A-V1 cells (herein called RN46A), and the subclone RN46A-B14 (herein called B14) that is stably transfected with brain derived neurotrophic factor (BDNF). RN46A and B14 cells express estrogen receptor beta (ERbeta), androgen receptors (AR) and nuclear factor kappa B (NFkappaB) but not estrogen receptor alpha (ERalpha) or progestin receptors (PR). RT-PCR confirmed the presence of ERbeta and the absence of ERalpha and PR in both cell lines. B14 cells contain more immunodetectable BDNF and serotonin than the RN46A parent line. In addition, immunofluorescence for the serotonin reuptake transporter (SERT) was observed in the cell body region of undifferentiated B14 cells. After differentiation at a nonpermissive temperature, SERT immunostaining was observed in both the cell body region and along the extent of the axons. Serotonin content as determined by ELISA was higher in B14 than RN46A cells. Estrogen (0.1 and 1.0 nM) stimulated serotonin in the B14 cells in serum free medium. In summary, the RN46A cells and the B14 subclone contain the same compliment of nuclear steroid receptors as rat raphe serotonin neurons and thus may provide a convenient in vitro model for study of intracellular mechanisms of action of steroid hormones in the context of a serotonin neuron.

Soy and social stress affect serotonin neurotransmission in primates

Stress and sex steroidal milieu can each influence mood in women. The purpose of this study was to compare the effect of long-term conjugated equine estrogen (CEE), soy phytoestrogen (SPE), and social subordination stress on dorsal raphe serotonin neurotransmission of ovariectomized cynomolgus monkeys. Tryptophan hydroxylase (TPH) and serotonin reuptake transporter (SERT) protein content were determined, and the in vitro degradation of macaque SERT protein was examined in the presence and absence of protease inhibitors, serotonin (5-HT), and citalopram. Like CEE, SPE increased TPH protein levels. Social subordinates had markedly lower TPH protein levels than dominants regardless of hormone replacement. Therefore, these two variables had independent and additive effects. CEE and SPE increased SERT, and social status had no effect. Thus, the hormone-induced increase in SERT was accompanied by increased 5-HT synthesis and neuronal firing, which appears biologically reasonable as 5-HT prevented SERT degradation in vitro.

Estrogen receptor beta. Potential functional significance of a variety of mRNA isoforms

Recent cloning of estrogen receptor beta (ERbeta) was followed by the discovery of a variety of its isoforms. This review describes the complexity of ERbeta mRNAs in various species for which most data have been gathered so far. The most surprising finding is the great variation in isoform structure among various mammalian species. This may reflect either the fact that only a very limited number of isoforms have been described so far or between-species specificity, especially as common elements in closely related species could still be noted. Isoform variations, as detected mainly at the mRNA sequence level, should result in profound functional differences at the level of proteins as already shown in selected cases. Thus, it is proposed that the diversity of ERbeta isoforms implies a functional role of this phenomenon in cellular physiology and pathology of estrogen response.

Estrogen actions in the brain

Understanding of the mechanisms of estrogen action in the brain has always been poor. Neurons in several brain regions do not harbor estrogen receptor alpha (ERalpha) and yet are estrogen responsive. It was formerly thought that these responses represented indirect actions of estrogen. It is now evident that these neurons express ERbeta and that estrogen receptors have diverse actions in the central nervous system. By clear delineation of the cellular expression and function of the two estrogen receptors, it is likely that, in the future, selective ERalpha and ERbeta ligands will be developed and used for treatment of depression and behavioral disorders and may be useful in preventing degenerative diseases, such as Alzheimer's and Parkinson's disease.