Hippocampus: a target for estrogen action in mammalian brain

Effects of long-term testosterone administration on cognition in older men with low or low-to-normal testosterone concentrations: a prespecified secondary analysis of data from the randomised, double-blind, placebo-controlled TEAAM trial

BACKGROUND

The effects of testosterone on cognitive function in older men are incompletely understood. We aimed to establish the effects of long-term testosterone administration on multiple domains of cognitive function in older men with low or low-to-normal testosterone concentrations.

METHODS

We did the randomised, double-blind, placebo-controlled, parallel-group TEAAM trial at three medical centres in Boston, Phoenix, and Los Angeles, USA. Men aged 60 years and older with low or low-to-normal testosterone concentrations (3·47-13·9 nmol/L, or free testosterone <173 pmol/L) were randomly assigned (1:1), via computer-generated randomisation, to receive either 7·5 g of 1% testosterone gel or placebo gel daily for 3 years. Randomisation was stratified by age (60-75 years vs >75 years) and study site. The testosterone dose was adjusted to achieve concentrations of 17·3-31·2 nmol/L. Participants and all study personnel were masked to treatment allocation. Multiple domains of cognitive function were assessed as prespecified secondary outcomes by use of standardised tests at baseline and months 6, 18, and 36. We did analyses by intention to treat (in men who had baseline assessments of cognitive function) and per protocol (restricted to participants who completed the study drug and had both baseline and 36 month assessments of cognitive function). The TEAAM trial is registered with ClinicalTrials.gov, number NCT00287586.

FINDINGS

Between Sept 1, 2004, and Feb 12, 2009, we randomly assigned 308 participants to receive either testosterone (n=156) or placebo (n=152). 280 men had baseline cognitive assessments (n=140 per group). Mean follow-up time was 29·0 months (SD 11·5) in the testosterone group and 31·1 months (9·5) in the placebo group. The last participant completed the study on May 11, 2012. In the testosterone group, mean concentrations of serum total testosterone increased from 10·6 nmol/L (SD 2·2) to 19·7 nmol/L (9·2) and free testosterone concentrations increased from 222 pmol/L (62) to 364 pmol/L (222). In the placebo group, mean concentrations of serum total testosterone were 10·7 nmol/L (SD 2·3) at baseline and 11·1 nmol/L (3·2) post-intervention and free testosterone concentrations were 210 pmol/L (61) and 172 pmol/L (49), respectively. We recorded no between-group differences in changes in visuospatial ability (mean difference: Complex Figure Test -0·51, 95% CI -2·0 to 1·0), phonemic or category verbal fluency (phonemic fluency test 0·90, -1·3 to 3·1; categorical fluency test 1·1, -0·3 to 2·6), verbal memory (paragraph recall test 0·29, -1·2 to 1·8), manual dexterity (Grooved Pegboard Test 4·2, -1·3 to 9·7), and attention or executive function (Stroop Interference Test -2·6, -7·4 to 2·3) after adjustment for age, education, and baseline cognitive function. In both the intention-to-treat and per-protocol (n=86 per group) populations, changes in cognitive function scores were not related significantly to changes in total or free testosterone, or oestradiol concentrations.

INTERPRETATION

Testosterone administration for 36 months in older men with low or low-to-normal testosterone concentrations did not improve cognitive function. Future long-term trials are needed to investigate the efficacy of testosterone replacement in patients with impaired cognition, such as people with Alzheimer's disease.

FUNDING

AbbVie Pharmaceuticals, Aurora Foundation, Boston Claude D Pepper Older Americans Independence Center, and Boston University's Clinical and Translational Science Institute.

Sex hormones and adult hippocampal neurogenesis: Regulation, implications, and potential mechanisms

Neurogenesis within the adult hippocampus is modulated by endogenous and exogenous factors. Here, we review the role of sex hormones in the regulation of adult hippocampal neurogenesis in males and females. The review is framed around the potential functional implications of sex hormone regulation of adult hippocampal neurogenesis, with a focus on cognitive function and mood regulation, which may be related to sex differences in incidence and severity of dementia and depression. We present findings from preclinical studies of endogenous fluctuations in sex hormones relating to reproductive function and ageing, and from studies of exogenous hormone manipulations. In addition, we discuss the modulating roles of sex, age, and reproductive history on the relationship between sex hormones and neurogenesis. Because sex hormones have diverse targets in the central nervous system, we overview potential mechanisms through which sex hormones may influence hippocampal neurogenesis. Lastly, we advocate for a more systematic consideration of sex and sex hormones in studying the functional implications of adult hippocampal neurogenesis.

Contribution of estrogen receptor subtypes, ERα, ERβ, and GPER1 in rapid estradiol-mediated enhancement of hippocampal synaptic transmission in mice

Estradiol rapidly modulates hippocampal synaptic plasticity and synaptic transmission; however, the contribution of the various estrogen receptors to rapid changes in synaptic function is unclear. This study examined the effect of estrogen receptor selective agonists on hippocampal synaptic transmission in slices obtained from 3-5-month-old wild type (WT), estrogen receptor alpha (ERαKO), and beta (ERβKO) knockout female ovariectomized mice. Hippocampal slices were prepared 10-16 days following ovariectomy and extracellular excitatory postsynaptic field potentials were recorded from CA3-CA1 synaptic contacts before and following application of 17β-estradiol-3-benzoate (EB, 100 pM), the G-protein estrogen receptor 1 (GPER1) agonist G1 (100 nM), the ERα selective agonist propyl pyrazole triol (PPT, 100 nM), or the ERβ selective agonist diarylpropionitrile (DPN, 1 µM). Across all groups, EB and G1 increased the synaptic response to a similar extent. Furthermore, prior G1 application occluded the EB-mediated enhancement of the synaptic response and the GPER1 antagonist, G15 (100 nM), inhibited the enhancement of the synaptic response induced by EB application. We confirmed that the ERα and ERβ selective agonists (PPT and DPN) had effects on synaptic responses specific to animals that expressed the relevant receptor; however, PPT and DPN produced only a small increase in synaptic transmission relative to EB or the GPER1 agonist. We demonstrate that the increase in synaptic transmission is blocked by inhibition of extracellular signal-regulated kinase (ERK) activity. Furthermore, EB was able to increase ERK activity regardless of genotype. These results suggest that ERK activation and enhancement of synaptic transmission by EB involves multiple estrogen receptor subtypes.

Epigenetic regulation of estrogen-dependent memory

Hippocampal memory formation is highly regulated by post-translational histone modifications and DNA methylation. Accordingly, these epigenetic processes play a major role in the effects of modulatory factors, such as sex steroid hormones, on hippocampal memory. Our laboratory recently demonstrated that the ability of the potent estrogen 17β-estradiol (E2) to enhance hippocampal-dependent novel object recognition memory in ovariectomized female mice requires ERK-dependent histone H3 acetylation and DNA methylation in the dorsal hippocampus. Although these data provide valuable insight into the chromatin modifications that mediate the memory-enhancing effects of E2, epigenetic regulation of gene expression is enormously complex. Therefore, more research is needed to fully understand how E2 and other hormones employ epigenetic alterations to shape behavior. This review discusses the epigenetic alterations shown thus far to regulate hippocampal memory, briefly reviews the effects of E2 on hippocampal function, and describes in detail our work on epigenetic regulation of estrogenic memory enhancement.

Rapid effects of oestrogen on synaptic plasticity: interactions with actin and its signalling proteins

Oestrogen rapidly enhances fast excitatory postsynaptic potentials, facilitates long-term potentiation (LTP) and increases spine numbers. Each effect likely contributes to the influence of the steroid on cognition and memory. In the present review, we first describe a model for the substrates of LTP that includes an outline of the synaptic events occurring during induction, expression and consolidation. Briefly, critical signalling pathways involving the small GTPases RhoA and Rac/Cdc42 are activated by theta burst-induced calcium influx and initiate actin filament assembly via phosphorylation (inactivation) of cofilin. Reorganisation of the actin cytoskeleton changes spine and synapse morphology, resulting in increased concentrations of AMPA receptors at stimulated contacts. We then use the synaptic model to develop a specific hypothesis about how oestrogen affects both baseline transmission and plasticity. Brief infusions of 17β-oestradiol (E2 ) reversibly stimulate the RhoA, cofilin phosphorylation and actin polymerisation cascade of the LTP machinery; blocking this eliminates the effects of the steroid on transmission. We accordingly propose that E2 induces a weak form of LTP and thereby increases synaptic responses, a hypothesis that also accounts for how it markedly enhances theta burst induced potentiation. Although the effects of E2 on the cytoskeleton could be a result of the direct activation of small GTPases by oestrogen receptors on the synaptic membrane, the hormone also activates tropomyosin-related kinase B receptors for brain-derived neurotrophic factor, a neurotrophin that engages the RhoA-cofilin sequence and promotes LTP. The latter observations raise the possibility that E2 produces its effects on synaptic physiology via transactivation of neighbouring receptors that have prominent roles in the management of spine actin, synaptic physiology and plasticity.

Estrogens and memory in physiological and neuropathological conditions

Ovarian hormones can influence brain regions crucial to higher cognitive functions, such as learning and memory, acting at structural, cellular and functional levels, and modulating neurotransmitter systems. Among the main effects of estrogens, the protective role that they may play against the deterioration of cognitive functions occurring with normal aging is of essential importance. In fact, during the last century, there has been a 30 years increase in female life expectancy, from 50 to 83 years; however, the mean age of spontaneous menopause remains stable, 50-51 years, with variability related to race and ethnicity. Therefore, women are now spending a greater fraction of their lives in a hypoestrogenic state. Although many cognitive functions seem to be unaffected by normal aging, age-related impairments are particularly evident in tasks involving working memory (WM), whose deficits are a recognized feature of Alzheimer's disease (AD). Many studies conducted over the past two decades showed that the female gonadal hormone estradiol can influence performance of learning and memory tasks, both in animal and humans. There is a great deal of evidence, mostly from animal models, that estrogens can facilitate or enhance performance on WM tasks; therefore, it is very important to clarify their role on this type of memory. To this aim, in this review we briefly describe the most relevant neurobiological bases of estrogens, that can explain their effects on cognitive functioning, and then we summarize the results of works conducted in our laboratory, both on animals and humans, utilizing the menstrual/estrous cycle as a useful noninvasive model. Finally, we review the possible role of estrogens in neuropathological conditions, such as AD and schizophrenia.

Gender differences and the role of estrogen in cognitive enhancements with nicotine in rats

Research has reported that nicotine can increase accuracy, response times and rates of learning with evidence of different effects on males and females. The goal of our research was to study further sex differences by examining the role played by estrogen in the effects of nicotine on learning and memory in female rats. In experiment 1, 48 male and female rats were administered 0.3 mg or 0.7 mg/kg bwt of nicotine (nic) or vehicle only (veh) and tested in a visual spatial orientation (VSO) paradigm designed to maximize the benefits of nicotine on spatial working memory. Females exposed to 0.3 mg nic performed superior to all other groups of both genders. In experiment 2, ovariectomized females (N=40) were exposed to 30 microg estradiol/kg bwt (E2), 3 mg nicotine/kg bwt, a combination of both E2 and nic, or veh, and tested as in experiment 1. The rankings of scores in the VSO task by group were E2+nic>nic alone>E2 alone>veh. The E2+nic combination group also demonstrated the highest rate of acquisition. Collectively, the findings suggest that estrogen can synergize the ability of chronic nicotine to enhance acetylcholine-hippocampal interactions underlying performance in the VSO paradigm.

Acute effects of estrogen on neuronal physiology

It has been known for more than 30 years that estrogen can alter the intrinsic and synaptic physiology of neurons within minutes. The physiological significance of these acute effects has been unclear, however, because some effects require higher concentrations of estrogen than are detected in plasma, and because estrogen secreted by the ovary rises and falls over a time course of days, not minutes. These concerns may be answered by new research demonstrating that estrogen is produced at high levels within the brain itself, and that production of estrogen in the brain may be regulated by neuronal activity. Additionally, recent studies indicate that classical estrogen receptor proteins are found not only in the nucleus where they regulate gene expression but also at extranuclear sites, including at synapses. These findings, together with evidence for new types of extranuclear estrogen receptors, suggest that estrogen might act directly at synapses to activate second messenger signaling, thereby rapidly altering neuronal excitability, synaptic transmission, and/or synaptic plasticity.

Ultrastructural localization of estrogen receptor beta immunoreactivity in the rat hippocampal formation

Several lines of evidence indicate that estrogen affects hippocampal synaptic plasticity through rapid nongenomic mechanisms, possibly by binding to plasma membrane estrogen receptors (ERs). We have previously shown that ERalpha immunoreactivity (ir) is in select interneuron nuclei and in several extranuclear locations, including dendritic spines and axon terminals, within the rat hippocampal formation (Milner et al., [2001] J Comp Neurol 429:355). The present study sought to determine the cellular and subcellular locations of ERbeta-ir. Coronal hippocampal sections from diestrus rats were immunolabeled with antibodies to ERbeta and examined by light and electron microscopy. By light microscopy, ERbeta-ir was primarily in the perikarya and proximal dendrites of pyramidal and granule cells. ERbeta-ir was also in a few nonprincipal cells and scattered nuclei in the ventral subiculum and CA3 region. Ultrastructural analysis revealed ERbeta-ir at several extranuclear sites in all hippocampal subregions. ERbeta-ir was affiliated with cytoplasmic organelles, especially endomembranes and mitochondria, and with plasma membranes primarily of principal cell perikarya and proximal dendrites. ERbeta-ir was in dendritic spines, many arising from pyramidal and granule cell dendrites. In both dendritic shafts and spines, ERbeta-ir was near the perisynaptic zone adjacent to synapses formed by unlabeled terminals. ERbeta-ir was in preterminal axons and axon terminals, associated with clusters of small, synaptic vesicles. ERbeta-labeled terminals formed both asymmetric and symmetric synapses with dendrites. ERbeta-ir also was detected in glial profiles. The cellular and subcellular localization of ERbeta-ir was generally similar to that of ERalpha, except that ERbeta was more extensively found at extranuclear sites. These results suggest that ERbeta may serve primarily as a nongenomic transducer of estrogen actions in the hippocampal formation.

Abilities in tactile discrimination of textures in adult rats exposed to enriched or impoverished environments

In previous studies, we have shown that housing in enriched environment for about 3 months after weaning improved the topographic organization and decreased the size of the receptive fields (RFs) located on the glabrous skin surfaces in the forepaw maps of the primary somatosensory cortex (SI) in rats [Exp. Brain Res. 121 (1998) 191]. In contrast, housing in impoverished environment induced a degradation of the SI forepaw representation, characterized by topographic disruptions, a reduction of the cutaneous forepaw area and an enlargement of the glabrous RFs [Exp. Brain Res. 129 (1999) 518]. Based on these two studies, we postulated that these representational alterations could underlie changes in haptic perception. Therefore, the present study was aimed at determining the influence of housing conditions on the rat's abilities in tactile texture discrimination. After a 2-month exposure to enriched or impoverished environments, rats were trained to perform a discrimination task during locomotion on floorboards of different roughness. At the end of every daily behavioral session, rats were replaced in their respective housing environment. Rats had to discriminate homogeneous (low roughness) from heterogeneous floorboards (combination of two different roughness levels). To determine the maximum performance in texture discrimination, the roughness contrast of the heterogeneous texture was gradually reduced, so that homogeneous and heterogeneous floorboards became harder to differentiate. We found that the enriched rats learned the first steps of the behavioral task faster than the impoverished rats, whereas both groups exhibited similar performances in texture discrimination. An individual "predilection" for either homogeneous or heterogeneous floorboards, presumably reflecting a behavioral strategy, seemed to account for the absence of differences in haptic discrimination between groups. The sensory experience depending on the rewarded texture discrimination task seems to have a greater influence on individual texture discrimination abilities than the sensorimotor experience related to housing conditions.

Estrogens in the Nervous System: Mechanisms and Nonreproductive Functions

The past decade has witnessed a growing interest in estrogens and their activity in the central nervous system, which was originally believed to be restricted to the control of reproduction. It is now well accepted that estrogens modulate the activity of all types of neural cells through a multiplicity of mechanisms. Estrogens, by binding to two cognate receptors ERalpha and ERbeta, may interact with selected promoters to initiate the synthesis of target proteins. Alternatively, the hormone receptor complex may interfere with intracellular signaling at both cytoplasmic and nuclear levels. The generation of cellular and animal models, combined with clinical and epidemiological studies, has allowed us to appreciate the neurotrophic and neuroprotective effects of estrogens. These findings are of major interest because estradiol might become an important therapeutic agent to maintain neural functions during aging and in selected neural diseases.

Proteomic dissection of dome formation in a mammary cell line: role of tropomyosin-5b and maspin

In this work we extended the study of genes controlling the formation of specific differentiation structures called "domes" formed by the rat mammary adenocarcinoma cell line LA7 under the influence of DMSO. We have reported previously that an interferon-inducible gene, rat-8, and the beta-subunit of the epithelial sodium channel (ENaC) play a fundamental role in this process. Now, we used a proteomic approach to identify proteins differentially expressed either in DMSO-induced LA7 or in 106A10 cells. Two differentially expressed proteins were investigated. The first, tropomyosin-5b, strongly expressed in DMSO-induced LA7 cells, is needed for dome formation because its synthesis inhibition by the antisense RNA technology abolished domes. The second protein, maspin, strongly expressed in the uninduced 106A10 cell line, inhibits dome formation because 106A10 cells, transfected with rat8 cDNA (the function of which is required for the organization of these structures), acquired the ability to develop domes when cultured in presence of an antimaspin antibody. Dome formation in these cultures are accompanied by ENaC beta-subunit expression in the absence of DMSO. Therefore, dome formation requires the expression of tropomyosin-5b, in addition to the ENaC beta-subunit and the rat8 proteins, and is under the negative control of maspin.

Oestrogen prevention of neural cell death correlates with decreased expression of mRNA for the pro-apoptotic protein nip-2

We have recently identified nip-2 as a gene target for 17beta-oestradiol activity in the neuroblastoma SK-ER3 cells expressing the oestrogen receptor (ER) alpha. Here we show 17beta-oestradiol treatment of neuroblastoma and rat embryo neurones in culture blocks the increase in nip-2 mRNA induced by apoptotic stimuli and prevents cell death as indicated by cell counting, 3,(4,5-dimethylthiazol-2-yl)2,5-diphenil-tetrazoliumbromi de and DNA fragmentation assays. Neither of these effects are observed in the presence of the specific ER antagonist ICI 182,780, and are absent in neuroblastoma cells not expressing ER. We propose that nip-2 plays a relevant role in neural cell apoptosis and that a decrease in its expression is instrumental for the oestrogen anti-apoptotic effect described here. The experimental evidence presented supports the recent hypothesis of a protective role of oestrogens in neurodegenerative diseases such as Alzheimer's disease and highlights the importance of the development of new ER ligands for the prevention of neural cell damage.

Upregulation of estrogen receptors in the forebrain of aromatase knockout (ArKO) mice

Estrogens have numerous reproductive and nonreproductive functions in brain. The actions of estrogens are mediated by estrogen receptors (ERs), and estrogens are believed to down-regulate their own receptors in many tissues. Assuming this to be true, if estrogens are removed there should be an upregulation of ERs. We have developed a mouse model in which estrogen synthesis is completely eliminated by homologous recombination to delete the gene encoding aromatase cytochrome P450 (P450(arom)). The P450(arom) enzyme catalyzes the synthesis of estrogens from androgens in the brain. The localization and density of ERs was studied in the brains of aromatase knockout (ArKO) and wild type male mice by using immunohistochemistry with a peptide antibody to ERalpha (ER-21) and computer imaging. In the wild-type animals a high density of ERalpha was found in a small number of hypothalamic cells; in the medial preoptic area, periventricular, arcuate, and ventromedial nuclei. A low and medium density of ERalpha was observed in cells of the lateral preoptic area, supraoptic, bed nucleus of the stria terminalis, and in central, medial and anterior cortical amygdaloid nuclei. The number of cells containing ERalpha-immunoreactivity was significantly increased (244%) in the medial preoptic area of the ArKO mice. In neither wild type nor ArKO animals was immunoreactivity observed in the cerebral cortex or striatum. There was intense ER-immunostaining in the nucleus of neurons in both wild type and ArKO mice. These data indicate that in the absence of estrogens there is as much as a 2-fold increase in the number of cells with ERalpha-immunoreactivity in certain hypothalamic and limbic regions. Thus, estrogens can down-regulate ERalpha in brain.

Transcription map of Xq27: candidates for several X-linked diseases

Human Xq27 contains candidate regions for several disorders, yet is predicted to be a gene-poor cytogenetic band. We have developed a transcription map for the entire cytogenetic band to facilitate the identification of the relatively small number of expected candidate genes. Two approaches were taken to identify genes: (1) a group of 64 unique STSs that were generated during the physical mapping of the region were used in RT-PCR with RNA from human adult and fetal brain and (2) ESTs that have been broadly mapped to this region of the chromosome were finely mapped using a high-resolution yeast artificial chromosome contig. This combined approach identified four distinct regions of transcriptional activity within the Xq27 band. Among them is a region at the centromeric boundary that contains candidate regions for several rare developmental disorders (X-linked recessive hypoparathyroidism, thoracoabdominal syndrome, albinism-deafness syndrome, and Borjeson-Forssman-Lehman syndrome). Two transcriptionally active regions were identified in the center of Xq27 and include candidate regions for X-linked mental retardation syndrome 6, X-linked progressive cone dystrophy, X-linked retinitis pigmentosa 24, and a prostate cancer susceptibility locus. The fourth region of transcriptional activity encompasses the FMR1 (FRAXA) and FMR2 (FRAXE) genes. The analysis thus suggests clustered transcription in Xq27 and provides candidates for several heritable disorders for which the causative genes have not yet been found.

Estrogen modulates neuronal Bcl-xL expression and beta-amyloid-induced apoptosis: relevance to Alzheimer's disease

Recent findings indicate that estrogen is neuroprotective, a cellular effect that may contribute to its clinical benefits in delaying the development of Alzheimer's disease. In this report, we identify a novel neuronal action of estrogen that may contribute to its neuroprotective mechanism(s). Specifically, we report that estrogen significantly increases the expression of the antiapoptotic protein Bcl-xL in cultured hippocampal neurons. This effect presumably reflects classic estrogen transcriptional regulation, as we identified a putative estrogen response element in the bcl-x gene. Estrogen-induced enhancement of Bcl-xL is associated with a reduction in measures of beta-amyloid-induced apoptosis, including inhibition of both caspase-mediated proteolysis and neurotoxicity. A similar relationship between estrogen, Bcl-xL expression, and resistance to degeneration was also observed in human hippocampus. We report neuronal colocalization of estrogen receptor and Bcl-xL immunoreactivities that is most prominent in hippocampal subfield CA3, a region that shows relatively little immunoreactivity to paired helical filament-1, a marker of Alzheimer's disease neurodegeneration. These data suggest a novel mechanism of estrogen neuroprotection that may be relevant to estrogen's suggested ability to modulate neuronal viability across the life span, from neural sexual differentiation and development through age-related neurodegenerative conditions.

Mapping of the MYCL2 processed gene to Xq22-23 and identification of an additional L MYC-related sequence in Xq27.2

We report here the identification of a human genomic sequence from the q27.2 region of the X chromosome which shows a high homology to the L-MYC proto-oncogene. This sequence is not the MYCL2 homology, previously mapped to the long arm of the X chromosome at q22-qter by Morton et al., as we located the MYCL2-processed gene in Xq22-23, using a panel containing a combination of hybrid DNA carrying different portions of the human X chromosome. Based on computer analysis, the MYC-like sequence (MYCL3) is 98.2% identical to a portion of exon 3 of the MYCL1 gene and maps to the Xq27.2 region, between the DXS312 and DXS292 loci.

Effects of ovarian hormones and environment on radial maze and water maze performance of female rats

The effects of gonadal hormones and environment on performance in an eight-arm radial maze and in the Morris water maze were determined in female rats. Long-Evans female rats were ovariectomized or sham ovariectomized at 35 days of age, and housed in complex environments or in isolation for the duration of the study. One month following surgeries, spatial working memory performance in the radial maze was assessed. Exposure to complex environmental conditions independently enhanced performance, as indicated by increased arm choice accuracy during 20 days of maze training. Additionally, gonadally intact females significantly outperformed ovariectomized females before cyclicity was disrupted by food deprivation. Following radial maze training, spatial reference memory performance was assessed in the same females utilizing the Morris water maze. Gonadally intact females housed in isolation performed significantly more poorly during 16 days of place training trials and displayed significantly shorter times in the platform quadrants and fewer target crossings during probe trials than gonadally intact and ovariectomized females housed in complex environments and ovariectomized rats housed in isolation. Consequently, acquisition and retention of the water maze was impaired by the presence of ovaries, and this impairment was counteracted by exposure to complex environments. Performance did not differ between groups on cued trials, indicating that sensorimotor and motivational functions did not differ between groups. Results of these experiments indicate that endogenous gonadal hormones can differentially affect performance on tasks of spatial working and spatial reference memory, and that environmental conditions can interact with gonadal hormones to affect behavior.

Posttraining estrogen and memory modulation

The present paper provides a review of recent research carried out in this laboratory investigating the effects of posttraining peripheral and intrahippocampal injection of estradiol on memory in rats, and estradiol-acetylcholine interactions in memory modulation. Ovariectomized rats received an eight-trial training session in a hippocampal-dependent hidden platform water maze task. Immediately following training, rats received a posttraining peripheral or intrahippocampal injection of estradiol-cyclodextrin complex or vehicle. Twenty-four hours later rats were returned to the maze for a retention test session, and latency to escape was used as a measure of memory for the previous day's training. Peripheral posttraining injection of estradiol enhances memory relative to vehicle-treated rats. Injections of estradiol given 2 h posttraining has no effect on retention, indicating a time-dependent effect of estradiol on memory storage processes. A time-dependent memory enhancing effect of posttraining intrahippocampal injections of estradiol has also been observed in both male and ovariectomized female rats. The memory enhancing effect of peripheral posttraining injection of estradiol in ovariectomized rats is blocked by a subeffective dose of the acetylcholine muscarinic receptor antagonist scopolamine, suggesting that estradiol interacts with cholinergic systems in memory modulation. Concurrent peripheral posttraining injection of a subeffective dose of estradiol and a subeffective dose of the cholinergic agonist oxotremorine produces a synergistic memory enhancing effect. The findings suggest that: (1) estradiol selectively influences memory storage independent of an effect on nonmnemonic processes, (2) the hippocampus is a potential neuroanatomical site of action mediating estrogenic effects on memory, and (3) estradiol interacts with cholinergic systems in memory modulation.

Divergent pathways regulate ligand-independent activation of ER alpha in SK-N-BE neuroblastoma and COS-1 renal carcinoma cells

The alpha-estrogen receptor (ER alpha) transcriptional activity can be regulated either by binding to the cognate ligand or by intracellular signaling pathways responsive to a variety of factors acting through cell membrane receptors. Studies carried out in HeLa and COS-1 cells demonstrated that the cross-coupling between estrogen and growth factor receptors is mediated by p21ras and requires phosphorylation of a specific serine residue (Ser 118 in the human ER alpha and Ser 122 in mouse ER alpha) located in the ER alpha N-terminal activation function 1 (AF-1). Likewise, in the SK-N-BE neuroblastoma cell line p21ras is involved in the cross-coupling between insulin and ER alpha receptors. However, in this cell line Ser 122 is not necessary for insulin-dependent activation of unliganded ER alpha. In addition, after insulin activation, the electrophoretic mobility associated to serine hyperphosphorylation of ER alpha in SK-N-BE and in COS-1 cells is different. Our study rules out the possibility of tyrosine phosphorylation in unliganded ER alpha activation by means of transactivation studies of ER alpha tyrosine mutants and analysis of Tyr phosphorylation immunoreactivity. The two cofactors for steroid receptors RIP 140 and SRC-1 do not seem to be specifically involved in the insulin-induced ER alpha transactivation. The present study demonstrates the possibility of an alternative, cell-specific pathway of cross-coupling between intracellular and membrane receptors, which might be of importance for the understanding of the physiological significance of this mode of activation in the nervous system.

The rat gene homologous to the human gene 9-27 is involved in the development of the mammary gland

We have developed a model system for studying differentiation in the mammary gland, by using two clonal cultures deriving from a rat breast adenocarcinoma. They differ in the ability to form domes, structures the significance of which is unknown. By using the subtractive cDNA library approach, we isolated a cDNA that is highly expressed in the dome-forming cells, and identical to the rat8 gene and highly homologous to the human 9-27 gene. Antisense treatment of the dome-forming cells specifically and reproducibly abolishes dome formation, while forced expression of the gene in non-dome-forming cells causes morphological changes suggestive of "flat" domes. In situ hybridization on rat tissues shows that the gene is expressed in epithelia, especially in those forming tubular structures, suggesting a relatedness between these structures and domes. Cytokeratin 8 and E cadherin are strongly expressed in the domes but not outside them, suggesting that the rat8 gene triggers the cells to express molecules that tighten the lateral connections between the cells; the process is likely to parallel that occurring during the differentiation of the mammary gland.

Seizure occurrence during ovulatory and anovulatory cycles in patients with temporal lobe epilepsy: a prospective study

We investigated the influence of ovulatory and anovulatory menstrual cycles on seizure occurrence in female patients with complex partial seizures. We prospectively documented seizures in relation to menstrual cycles (defined by measurement of basal body temperature and progesterone serum concentrations) in 39 female patients. One hundred and thirty-two cycles of 35 patients entered final analysis. Only eight patients had anovulatory cycles, in 18 patients all cycles were ovulatory. In the remaining nine patients anovulatory as well as ovulatory cycles were documented. In ovulatory cycles the mean frequency of seizures during the days of menstruation was significantly higher as compared to the periovulatory or the luteal phase of the cycles. During anovulatory cycles seizure frequency was significantly lower during menstruation than in the remaining days of the cycles. Since progesterone is known to exhibit anticonvulsant effects, seizure occurrence during menstruation seems to be related to ovulatory cycles, possibly due to the premenstrual decrease of progesterone. Therapeutic recommendations for the treatment of seizures related to the menstrual cycle (catamenial seizures) include the administration of hormones, as progesterone (recommended especially for women with catamenial epilepsy who have a documented inadequate luteal phase) or the suppression of the menstrual hormonal cycle by synthetic gonadotropin releasing hormone analogs.

Postnatal development and sex difference in neurons containing estrogen receptor-alpha immunoreactivity in the preoptic brain, the diencephalon, and the amygdala in the rat

Estrogen has been considered as a key substance that induces sexual differentiation of the brain during fetal and neonatal life in the rat. Thus, to define the brain regions involved in the brain sexual differentiation, we examined the regions where the estrogen receptor (ER) is located in the developing rat brain. We examined immunohistochemical distribution of the cells containing estrogen receptor-alpha (ER-alpha) in the preoptic region, the diencephalon, and the amygdala in male and female rats on postnatal days 1-35 (PD1-PD35). The antibody used recognizes ER-alpha equally well for both occupied and unoccupied forms. ER-alpha immunostaining was restricted to the cell nuclei of specific cell groups. In PD1 rats, ER-alpha-immunoreactive (ER-IR) signals were detected in the lateral septum, the organum vasculosum lamina terminalis, the medial preoptic nucleus (MPN), the median preoptic nucleus, the bed nucleus of the stria terminalis, the hypothalamic periventricular nucleus, the lateral habenula, the posterodorsal part of the medial amygdala nucleus, the posterior part of the cortical amygdala nucleus, the hypothalamic ventromedial nucleus (VMH), the hypothalamic arcuate nucleus, and the posterior hypothalamic periventricular nucleus. The distribution pattern of ER-IR cells in the newborn rat was much the same as that in the adult in the preoptic-hypothalamic and amygdala regions. Moreover, the signals in the MPN and the VMH were stronger in the female than in the male, perhaps reflecting the ability ofestrogen generated by aromatization of testosterone in the male to down-regulate the ER signal. Thus, the brain regions showing sex differences may be sites of sexual differentiation of the brain by aromatizable androgen during the neonatal period.

Distribution and hormone regulation of estrogen receptor immunoreactive cells in the hippocampus of male and female rats

Estrogen regulates the synaptic plasticity and physiology of the hippocampus as well as learning behaviors that are mediated by the hippocampus. The density of dendritic spines and synapses, the number of N-methyl-D-aspartate (NMDA) binding sites, the levels of NMDA receptor subunit NR1 protein, muscimol binding to the gamma-amino butyric acid (GABA)A receptor, and levels of glutamic acid decarboxylase message in the CA1 region of the hippocampus are altered with estrogen treatment. In addition, some of these parameters exhibit sex differences in their response to estrogen treatment. To establish that estrogen can have a direct effect on the hippocampus and to determine whether or not sex differences in estrogen responsiveness are due to sex differences in estrogen receptor (ER) levels, we used immunocytochemistry with the AS409 antibody to map the location of ER-immunoreactive (ER-ir) cells in the hippocampus of male and female rats. We found that (1) the ERs appear to be in interneurons rather than pyramidal or granule cell neurons, (2) ER-ir cells are located in greatest concentration in the hilus of the dentate gyrus and the stratum radiatum of the CA1 region, (3) the density of ER-ir cells exhibits a rostral to caudal gradient in the hilus and the CA1 regions, (4) there are no sex differences in either the number or immunostaining intensity of ER-ir cells in the hippocampus, (5) the ER levels are down-regulated by estrogen in both male and female rats, and (6) the mean intensity of staining for the ER-ir cells in the hippocampus is about 25% of that in the ER-ir cells of the hypothalamus. From this, we can conclude that estrogen can have a direct effect on hippocampal neurons and that any sex differences in estrogen responsiveness is due to something other than sex differences in ER levels or function in the hippocampus.

Estrogen enhances performance of female rats during acquisition of a radial arm maze

Estrogen can influence the expression of behaviors not associated directly with reproduction, including learning and memory. However, the effects of estrogen on learning and memory in mammals are complex, dependent on a variety of factors. The radial arm maze is a traditional experimental task that takes advantage of the natural foraging strategy of rats and provides an appropriate measure for studying the effects of estrogen on working memory in this species. In the experiments reported here, ovariectomized rats were implanted subcutaneously with 5-mm Silastic capsules containing 25% estradiol diluted with cholesterol. Control females received 5-mm Silastic capsules containing 100% cholesterol. Results of three separate experiments demonstrated that estradiol administered by Silastic implants for 30 days prior to eight-arm radial maze training, during the 24 days of maze training, or both significantly improved working memory performance compared to females treated with cholesterol alone, as indicated by improved arm choice accuracy over trials. The positive effect of estradiol exposure prior to training suggests that estrogen may induce neuronal changes that persist beyond the period of exposure with functional consequences for behavior.

Identification of estrogen-responsive genes in neuroblastoma SK-ER3 cells

To evaluate the role of estrogen receptor in the differentiation of cells of neural origin, we developed a molecular approach aimed at the identification of estrogen target genes by mRNA differential display PCR (ddPCR) in human neuroblastoma SK-ER3 cells. More than 3000 RNAs were examined, a few of which displayed a differential regulation pattern in response to 17beta-estradiol (E2). Sequence analysis of three differentially amplified ddPCR products showed homology with the growth-associated nuclear protein prothymosin-alpha (PTMA), the Bcl2-interacting protein Nip2, and one mRNA previously described by others in fetal human brain. Two ddPCR products, referred to as P4 and P10, corresponded to new DNA sequences. Northern analysis confirmed that estrogen treatment of SK-ER3 cells resulted in the upregulation and downregulation of expression of these messages. In particular, PTMA was found to accumulate at both 1 and 17 hr after E2 treatment, whereas P10 product accumulated only at 1 hr. Conversely, P4, Nip2, and the fetal brain-related mRNAs were significantly decreased by the treatment. Further time course analysis of PTMA and Nip2 mRNAs levels indicated that the hormone exerted a marked biphasic regulatory effect on expression of both messages during the course of cell differentiation. In the present study we report for the first time the identification of a panel of estrogen target genes in neural cells that provide new insights in the molecular mechanism of action of E2 in cells of neural origin.

Exogenous estrogen acts differently on production of estrogen receptor in the preoptic area and the mediobasal hypothalamic nuclei in the newborn rat

Expression of the estrogen receptor (ER) in the preoptic area (POA) and the mediobasal hypothalamus (MBH) in newborn female rats was studied by immunohistochemistry (IHC) and in situ hybridization histochemistry (ISHH). The number of ER immunoreactive (ER-IR) cells decreased and expression of ER mRNA was suppressed in the arcuate (ARH) and the ventromedial (VMH) hypothalamic nuclei by daily injections of estradiol benzoate (EB) for ten consecutive days. In contrast, in the POA, expression of ER mRNA was not suppressed by EB treatment, while the ER immunoreactivity and the number of ER-IR cells was decreased by EB treatment. Results of quantification of ER mRNA by reverse transcription-polymerase chain reaction correlated well with results from ISHH: that is, ER mRNA expression decreased in the MBH but not in the POA. Thus, estrogen affects ER gene expression differently in these two brain regions.

In vitro models for the effects of sex hormones on neurons

The results of these two in vitro models share some striking similarities. In both, estrogen was able to induce or promote the formation of either dendrites themselves in hippocampal neurons or dendritic specializations in PC12 neurites, and these specializations were then able to induce interneural interactions. In both models, androgen was able to promote the development of axons that branched frequently, while not directly fostering interneuronal contact. These findings recapitulate in part some of the effects of estrogen and androgen on neurons in vivo and suggest the inherent ability of cells of neural crest origin to respond to these hormones with specific neural morphogenetic programs designed to alter interneuronal communication. In these ways, it seems likely that both sex hormones are acting as neural growth factors in cells that express the appropriate receptor, leading to stereotyped changes in neural growth and pattern formation. Through the examination of such subcellular mechanisms, we hope to further understand the effects of sex hormones on brain development and the ontogeny of behavioral, cognitive, and reproductive differences between the sexes.

Expression and regulation of aromatase and 17 beta-hydroxysteroid dehydrogenase type 4 in human THP 1 leukemia cells

Estradiol is active in proliferation and differentiation of sex-related tissues like ovary and breast. Glandular steroid metabolism was for a long time believed to dominate the estrogenic milieu around any cell of the organism. Recent reports verified the expression of estrogen receptors in "non-target" tissues as well as the extraglandular expression of steroid metabolizing enzymes. Extraglandular steroid metabolism proved to be important in the brain, skin and in stromal cells of hormone responsive tumors. Aromatase converts testosterone into estradiol and androstenedione into estrone, thereby activating estrogen precursors. The group of 17 beta-hydroxysteroid dehydrogenases catalyzes the oxidation and/or reduction of the forementioned compounds, e.g. estradiol/estrone, thereby either activating or inactivating estradiol. Aromatase is expressed and regulated in the human THP 1 myeloid leukemia cell line after vitamin D/GMCSF-propagated differentiation. Aromatase expression is stimulated by dexamethasone, phorbolesters and granulocyte/macrophage stimulating factor (GMCSF). Exons I.2 and I.4 are expressed in PMA-stimulated cells only, exon I.3 in both PMA- and dexamethasone-stimulated cells. Vitamin D-differentiated THP 1 cells produce a net excess of estradiol in culture supernatants, if testosterone is given as aromatase substrate. In contrast, the 17 beta-hydroxysteroid dehydrogenase type 4 (17 beta-HSD 4) is abundantly expressed in unstimulated THP 1 cells and is further stimulated by glucocorticoids (2-fold). The expression is unchanged after vitamin D/GMCSF-propagated differentiation. 17 beta-HSD 4 expression is not altered by phorbolester treatment in undifferentiated cells but is abolished after vitamin D-propagated differentiation along with downregulation of beta-actin. Protein kinase C activation therefore appears to dissociate the expression of aromatase and 17 beta-HSD 4 in this differentiation stage along the monocyte/phagocyte pathway of THP 1 myeloid cells. The expression of steroid metabolizing enzymes in myeloid cells is able to create a microenvironment which is uncoupled from dominating systemic estrogens. These findings may be relevant in the autocrine, paracrine or iuxtacrine cellular crosstalk of myeloid cells in their respective states of terminal differentiation, e.g. in bone metabolism and inflammation.

Estradiol abolishes autologous down regulation of glucocorticoid receptors in brain

We have previously reported that estrogen treatment of steroid-free, ovariectomized-adrenalectomized (OVX-ADX) rats, increased binding to glucocorticoid type II receptors (GR) in some brain regions. The present report studied the effects of estradiol in OVX-ADX rats receiving chronic corticosterone (CORT) treatment. Using binding assays, GR was reduced by CORT replacement in cytosol of hippocampus and septum, but not in whole hypothalamus. GR were recovered after 4 days of estradiol therapy. Using Mab7, a monoclonal antibody against the activated nuclear form of GR, we observed that estrogen treatment increased immunoreactivity measured by computerized densitometry in areas targeted by glucocorticoids. Significantly higher staining for GR developed in CA1 and CA2 hippocampal subfields, paraventricular nucleus of the hypothalamus and lateral ventral septal nuclei of estradiol-receiving, CORT-treated OVX-ADX rats. The amplification of the glucocorticoid biological signal by female sex hormones, may thus affect several neuroendocrine parameters and the outcome of stress-related diseases.

Estrogenic control of monoamine oxidase A activity in human neuroblastoma cells expressing physiological concentrations of estrogen receptor

Several lines of evidence support the hypothesis of a role played by estrogens in the manifestation of affective disorders in women. The analysis of the mechanism of action of a number of antidepressant drugs clearly demonstrated the involvement of the catecholaminergic system in the etiology of these complex behavioral pathologies. The present in vitro study was therefore undertaken to investigate the presence of a functional link between estrogen and catecholamine metabolism in cells of neural origin. The model system utilized was a human neuroblastoma cell line which was obtained by stable transfection of the estrogen receptor cDNA (SK-ER3). The present study shows that in SK-ER3 activation of the estrogen receptor correlates with a marked decrease in monoamine oxidase A activity. This effect is observed following treatment with a physiological concentration of 17 beta-estradiol and can be blocked by the specific antagonist of the steroid receptor, ICI 182,780. Dibutyryl cyclic AMP acting, like estrogens, on the state of differentiation of SK-ER3 cells did not affect monoamine oxidase A activity. The present study provides strong evidence of a strict relationship between estrogen receptor and monoamine oxidase A activity in human cells of neural origin, thus favoring the hypothesis of an antidepressive effect of estrogens exerted via inhibition of the monoamine oxidative pathway.

Estrogen receptor mRNA alterations in the developing rat hippocampus

We previously reported transiently elevated ER protein levels in the postnatal rat hippocampus suggesting that this brain region may be sensitive to estrogenic trophic and organizational influences during a 'critical period' of sexual differentiation. In order to examine whether alterations in ER gene expression underlie the ontogenetic pattern of the hippocampal ER, we examined ER mRNA levels over the early postnatal period and in adult rats. This was accomplished by both a highly quantitative RNase protection assay and in situ hybridization histochemistry. Hippocampal ER mRNA levels increased significantly (P < 0.005) between birth and postnatal day (PDN) 4 when peak concentrations were found and then declined by PND-10. Adult male hippocampal ER mRNA values were similar to those found in newborn and PND-10 animals but were significantly less (P < 0.05) than those observed on PND-4. Results from the in situ hybridization experiments correlated well with those from the RNase protection analysis. High levels of ER mRNA were present in the CA3 pyramidal layer with somewhat lower labeling intensities present in CA1 and the dentate gyrus of the PND-4 animal. In contrast, adult male animals demonstrated little hybridization throughout the hippocampus. Thus, the temporal pattern in ER mRNA levels in the hippocampus found in the present study correlates well with our previous developmental profile of the ER protein. These findings suggest that the ontogeny of ER in the hippocampus is regulated by alterations in ER gene expression in specific neuronal populations.

Expression and regulation of aromatase cytochrome P450 in THP 1 human myeloid leukaemia cells

Aromatase cytochrome P450 mRNA and activity was strongly expressed in THP 1 myeloid leukaemia cells after treatment with phorbol-myristate-acetate (PMA) and dexamethasone, low level expression was caused by calcitriol. mRNA species of 4.0, 3.0, 2.4 and 1.1 kb size were differentially stimulated. After calcitriol-mediated differentiation (72 h, measured by CD 14 expression) mRNA expression was further enhanced by PMA (45-fold), dexamethasone (15-fold), oestradiol (3.7-fold), testosterone (2.5-fold) and androstenedione (3.5-fold). Forskolin, cAMP and follicle stimulating hormone had no stimulatory effect. Oestradiol formation from testosterone (oestradiol radioimmunoassay in culture supernatants) increased to > 2000 pg/ml/10(6) cells/24 h after PMA-stimulation, mirrored mRNA expression and was suppressed below 10% of original values in the presence of 4-OH-androstenedione. Exons I.2 and I.4 were expressed in PMA-stimulated cells only, exon I.3 in both PMA- and dexamethasone-stimulated cells. A new splicing variant was expressed after calcitriol-stimulation, which did not hybridize to an exon II-derived oligonucleotide but to an exon III-derived one. Local aromatisation of androgens into oestradiol may be important in the concerted crosstalk of cells of the monocyte/macrophage lineage with their respective tissues in inflammation and bone metabolism.

Systemic and cerebral kinetics of 16 alpha [18F]fluoro-17 beta-estradiol: a ligand for the in vivo assessment of estrogen receptor binding parameters

Estrogen receptors are expressed in several brain areas of various animal species, and steroid hormones exert physiologic and biochemical effects on the central nervous system. The aim of the present study was to evaluate in female adult rats, the suitability of 16 alpha [18F]fluoro-17 beta-estradiol ([18F]FES), a selective estrogen receptor ligand, for the in vivo assessment of brain estrogen receptors. This was considered to be a preliminary step in evaluating the potential usefulness of [18F]FES for studies of cerebral estrogen receptors with positron emission tomography (PET) in nonhuman primates and human subjects. We evaluated (a) the time course of the metabolic degradation of [18F]FES in blood; (b) the time course of distribution of the tracer in discrete cerebral areas; (c) the inhibitory effect of increasing doses of cold estradiol on cerebral [18F]FES uptake; and (d) the possibility of in vivo quantification of estrogen receptor binding parameters using both equilibrium and dynamic kinetic analyses. We quantified [18F]FES binding to estrogen receptors using both equilibrium and dynamic kinetic analyses. The results of this study indicate that [18F]FES is a suitable tracer for the measurement of estrogen receptors in the pituitary and hypothalamus, using either the equilibrium or the kinetic analysis. However, [18F]FES is inadequate for the in vivo investigation of estrogen binding sites in brain areas with low receptor density, such as the hippocampus.

Transient expression of estrogen receptor-immunoreactivity (ER-IR) in the layer V of the developing rat cerebral cortex

Occurrence of estrogen receptor-immunoreactivity (ER-IR) in the cerebral cortex was examined in neonatal and adult rats. In newborn rats of postnatal day 1 (= day of birth) and postnatal day 5 (PD1 and PD5, respectively), ER-IR was not evident in the neocortex. On postnatal days 7, 10 and 13 (PD7, PD10 and PD13 respectively), a group of cells with distinct ER-IR appeared in the layer V of the auditory cortex. At the PD10, weak but specific ER-IR were also appeared in the somatosensory and the visual cortices. Among these areas, the ER-IR positive neurons occurred most frequently in the auditory cortex at PD10 rats. By examination of adjacent sections, one stained with Cresyl violet and the another stained with acethylcholinesterase (AChE) histochemistry, it was revealed that the region with ER-IR at PD7 to PD13 was limited to layer V of the neocortex. These signals, however, disappeared at PD15. In layer II of the neocortex, on the other hand, weak ER-IR signals were detected throughout the area sporadically at PD21 and in adults. The ER-IR detected transiently in the auditory cortex by the antiserum might contribute to maturation and establishment of the neurons of the rat auditory circuit.

Steroid hormone influences on spatial memory

Our studies have shown that both stress-induced, enhanced secretion of corticosterone and adrenalectomy-induced, reduced secretion of corticosterone are associated with impaired spatial memory performance. On the other hand, estradiol administration is associated with enhancements in spatial memory performance. Although these changes in performance are small, they are consistent with structural changes induced by these hormones (or their lack) on specific cells within the hippocampus which form the tri-synaptic loop (a summary of the behavioral and morphological effects is shown in Figs. 1 and 2). Thus, these results suggest that the morphological changes induced by the hormones have an impact on hippocampal function. Important goals of future studies are to seek ways to maximize gonadal hormone-dependent enhancements in memory function and to minimize adrenal steroid-dependent impairments in memory function as well as to understand the mechanisms behind these behavioral and morphological changes.

Estrogen receptor found in the facial nucleus of the newborn rat is suppressed by exogenous estrogen: immuno- and in situ hybridization histochemical studies

Expression of the messenger RNA coding estrogen receptor (ER-mRNA) was detected in the ventromedial subnucleus of the facial nucleus of the newborn rat by in situ hybridization histochemistry (ISHH). The hybridization signal in this subnucleus increased from 1 to 6 days of age, then decreased at 11 days. By immunohistochemistry (IHC) using an antiserum which detects estrogen receptor (ER) specifically, immunopositive signals were also detected in the same subnucleus of the adjacent sections. On the other hand, neither of these signals were encountered in the same subnucleus of the adult rat. Thus, the present result extend our previous work (Yokosuka and Hayashi, 1992) showing that the expression of the ER in the facial nucleus is transient. A sex difference in the expression of ER molecules was not apparent by ISHH and IHC. Moreover, daily injections of estradiol from the day of birth suppressed the expression of ER in the subnucleus at 6 and 11 days of age. Thus, as has been detected in the mediobasal hypothalamus, ER-mRNA was revealed to be down-regulated by estrogen.

Acute effects of 17 beta-estradiol on brain excitability studied in vitro and in vivo

The acute effects of 17 beta-estradiol on brain excitability were studied in vitro and in vivo utilizing rat hippocampal slices and a cat cerveau isolé preparation. The hippocampal slices were perfused with 17 beta-estradiol (10(-7)-10(-10) M) for 30 min. No effects were observed on synaptic activation and inhibition and on the response to iontophoretically applied GABA in intact and ovariectomized female rats (n = 43). In males (n = 32), however, a small (12%) but significant increase in population spike amplitude was observed after 30 min exposure to 10(-9) M 17 beta-estradiol. Higher and lower concentrations were ineffective. In vivo, no acute effects of 17 beta-estradiol on focal epileptic seizure thresholds, evoked potentials, or augmenting response were observed in the visual cortex of non-estrous female cats (n = 11; median dose 1 micrograms/kg, range 0.5 microgram/kg-10 mg/kg).

Long-term in vivo desipramine or estrogen treatment fails to affect serotonin-induced outward current in hippocampal pyramidal cells of the rat

The effect of castration combined with either long-term treatment with the tricyclic antidepressant drug desipramine or the sex steroid 17 beta-estradiol on serotonin responses in area CA1 of the hippocampus of male and female rats was examined. Using single-electrode current and voltage-clamp techniques serotonin-induced hyperpolarizations and outward currents were recorded from hippocampal pyramidal cells. Neither in male nor in female castrated rats treatment effects were observed on the magnitude of the 5-hydroxytryptamine 1A mediated outward currents (0.26 nA) and membrane hyperpolarizations (11 mV) induced by superfusion of serotonin (15 microM), or on the effect of serotonin on the afterhyperpolarization and extracellularly recorded population spike. In voltage-clamp experiments using microelectrodes filled with potassium-chloride, but not with potassium-acetate, the sole observable effect was that the membrane resistance drop due to application of serotonin was significantly larger in the ovariectomized group (31% approximately 19 M omega) as compared to the ovariectomized/estrogen supplemented group (23% approximately 15 M omega). Spiperone (3 microM) completely antagonized the serotonin-induced outward currents and input resistance changes under all treatments. Apart from these changes the majority of passive and active membrane properties of cells from ovariectomized animals were not affected by chronic desipramine or steroid treatment. Neither did castration alone, nor in combination with long-term 17 beta-estradiol treatment, affect CA1 pyramidal cell membrane properties of male rats. Since we attained physiological levels of 17 beta-estradiol in the blood plasma (30-50 pg/ml) using subcutaneous silastic implants containing a mixture of cholesterol/estrogen, we conclude that both long-term estrogen and long-term desipramine treatment do not affect serotonergic neurotransmission in CA1 of the rat hippocampus.

Estrogen regulation of dopamine release in the nucleus accumbens: genomic- and nongenomic-mediated effects

The ability of estrogen to modulate mesolimbic dopamine (DA) was examined using in vivo voltammetry. Estrogen priming (5 micrograms, 48 h) of ovariectomized (ovx) female rats resulted in a slight decrease in K(+)-stimulated DA release measured in the nucleus accumbens: this decrease was accompanied by a significant increase in both DA reuptake and DA clearance times. Following estrogen priming nomifensine, a potent inhibitor of the DA uptake carrier, was still able to potentiate K(+)-stimulated DA release and alter the time course of DA availability, but the response was attenuated compared with ovx controls. Direct infusion of 17 beta-estradiol hemisuccinate (17 beta-E, 20-50 pg) into the nucleus accumbens resulted in a biphasic potentiation of K(+)-stimulated release. An initial increase in release was observed 2 min after 17 beta-E infusion; this increase, although reduced by 15 min, was still significantly higher than control values. A subsequent potentiation was observed 60 min after the initial 17 beta-E infusion; this response remained for at least an additional 60 min. Nomifensine did not significantly alter K(+)-stimulated DA release following 17 beta-E infusion, but was still able to potentiate the total time DA was available extracellularly. These data suggest that the mesolimbic A10 DA neurons that terminate in the nucleus accumbens can be modulated in vivo by estrogen and that this modulation may be mediated by both genomic (long term) and nongenomic (short term) mechanisms.

Theoretical considerations for the application of competitive polymerase chain reaction to the quantitation of a low abundance mRNA: estrogen receptor

The necessary theoretical considerations for the development of a correct quantitative analysis of a low abundance messenger RNA (mRNA), estrogen receptor mRNA, by competitive polymerase chain reaction (PCR) are presented together with a series of experimental data. When compared to other methodologies currently utilized for RNA quantitation, this PCR application proved to be a very reliable, rapid and sensitive method. Furthermore, the PCR-based quantitative method described is of particular interest since it does not require the use of radiolabeled compounds.

Estrogen Induction of Cytochrome c Oxidase Subunit III in Rat Hippocampus

Differential screening of a cDNA library prepared from mRNA of the hippocampus of estrogen-stimulated ovariectomized female rats led to the identification of a single estrogen-induced clone. Analysis of the sequence identified this cDNA as the gene coding for subunit III of the enzyme cytochrome c oxidase. Cytochrome c oxidase subunit III mRNA levels significantly increased as early as 3 h following the administration of a single dose of hormone. This effect was visible in the hippocampus and in the hypothalamus, but not in the other brain areas examined. Because subunit III of the cytochrome c oxidase is of mitochondrial origin, the mechanism involved in the estrogenic effect is still unknown. The observation that the activity of cytochrome c oxidase can also be induced by estrogens in the hippocampus indicates that this induction may be secondary to the increased expression of the other subunits of cytochrome c oxidase or to the general increase of neuronal activity.

A rapid method for the quantitation of estrogen receptors in small amounts of tissue

A rapid and highly reproducible protocol which permits the detection of quantities of estrogen receptor as low as 5 fmol/mg protein is described. The separation of free and receptor-bound hormone is achieved by specific immunoprecipitation of the hormone-receptor complex. This procedure can be performed without perturbing the equilibrium of the binding reaction.

Steroid hormones as mediators of neural plasticity

Steroid and thyroid hormone receptors are expressed in the developing brain and persist throughout adult life. They mediate a variety of effects on the brain, ranging from developmental effects of thyroid hormone and the process of sexual differentiation to the cyclic changes during reproductive cycles in adult female animals. This review summarizes data from the author's laboratory on three topics: (1) actions of extradiol and progesterone on the ventromedial nucleus of the hypothalamus in adult female and male rats, showing both the cyclicity and the consequences of brain sexual differentiation; (2) actions of estradiol on the cholinergic neurons of the basal forebrain of the female and male rat, reflecting the plasticity of the adult cholinergic system as well as sex differences which are developmentally programmed; and (3) diverse actions of estrogens, thyroid hormone and glucocorticoids on the morphology of hippocampal neurons. The review concludes by discussing the interactions between "organizational" (i.e. developmental) effects and the "activational" effects of steroids on the mature nervous system in relation to the environmental control of brain gene expression.

Electrophysiological evidence for a rapid membrane action of the gonadal steroid, 17 beta-estradiol, on CA1 pyramidal neurons of the rat hippocampus

The rapid electrophysiological effects of 17 beta-estradiol on CA1 pyramidal neurons (n = 86) were investigated utilizing intracellular recording from the rat hippocampal slice preparation. Bath application of 17 beta-estradiol, but not 17 alpha-estradiol, caused a reversible depolarization and increased input resistance with a latency of less than 1 min in 19.8% of CA1 neurons tested. There was no significant difference in the percentage of estradiol-responsive cells between male and female rats. Estradiol-responsive cells were identified from prepubertal female rats, as well as females in all stages of the estrous cycle. 17 beta-estradiol had no effect on the slow afterhyperpolarization or accommodative properties of CA1 neurons. In 2 out of 4 cells tested, the specific antiestrogen, tamoxifen, blocked the excitatory response to 17 beta-estradiol.

Estrogens up-regulate type I and type II glucocorticoid receptors in brain regions from ovariectomized rats

The effects of 1-4 days of estradiol (E2) treatment on type I and type II glucocorticoid receptors (GCR) were determined in cytosolic fractions from brain regions of ovariectomized rats. Four days after E2 administration, type I GCR increased in septum, amygdala, hypothalamus and hippocampus, but decreased in the anterior pituitary. Type II GCR increased in septum and hypothalamus only. For both receptor types, changes occurred earlier in septum (1 day) than in the other regions. The E2 increment was due to an increase in Bmax, without changes in Kd. The up-regulation of type II GCR by E2 was also confirmed immunocytochemically in four nuclei of the septal area. In a parallel study, E2 receptors were determined in nuclear and cytosol fractions from the same regions analyzed for GCR. In rats receiving E2, estrogen receptors decreased in cytosol and increased in nuclei from septum, amygdala, hypothalamus and anterior pituitary, but did not change in hippocampus. The results suggest that GCR in certain neuroendocrine regions are regulated by E2, without taking into account whether the areas involved contain high (anterior pituitary), moderate (septum, hypothalamus, amygdala) or low (hippocampus) levels of E2 receptors. Our model may shed light on sex differences in GCR and on E2 regulation of glucocorticoid action in brain and the pituitary.

Transient elevation of estrogen receptors in the neonatal rat hippocampus

The presence of sex differences in hippocampal morphology and function suggests that this brain region may be sensitive to the organizational actions of gonadal steroids. We therefore examined the postnatal development of estrogen receptor (ER) in the rat hippocampal formation. ER was measured by the in vitro binding of [3H]estradiol to a cytosolic preparation. Radioinert R2858 (moxestrol) was used to determine nonspecific binding. Hippocampal ER concentrations increased from birth through postnatal day (PND) 4 when levels peaked (10.05 +/- 1.2 fmol/mg protein); these were maintained through PND-7 (9.45 +/- 1.4) and declined thereafter to low levels characteristic of the adult (2.05 +/- 0.35). This ontogenic profile is similar to that found in several neocortical regions, as well as in the cingulate cortex, but is distinct from that observed in the hypothalamus, where ER levels remain high in the adult. Saturation analysis of PND-7 hippocampal cytosols demonstrated a single, high affinity binding site (Kd: 5.51 +/- 1.7 X 10(-10) M). [3H]Estradiol binding was specific in that it was displaced by radioinert R2858, diethylstilbestrol (DES), and 17 beta-estradiol but not by nonestrogenic steroids. Significantly greater ER levels were found in hippocampal nuclear extracts from DES-treated PND-7 animals compared to controls (9.74 +/- 2.27 vs. 0.49 +/- 0.24 fmol/mg DNA, P less than 0.01). The presence of functional ER was also shown by the ability of receptors to be retained on DNA cellulose. DNA cellulose column chromatography elution profiles for PND-7 hippocampal and medial basal hypothalamic (MBH) cytosols following incubation with [3H]estradiol were similar. The presence of elevated hippocampal ER levels during the perinatal critical period and evidence of functional transformation to the DNA binding state following DES treatment in vivo or estrogen incubation in vitro suggests that the hippocampus is a potential substrate for estrogen-mediated organizational events.