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

Sex steroid hormone synthesis, metabolism, and the effects on the mammalian olfactory system

Sex steroid hormones influence olfactory-mediated social behaviors, and it is generally hypothesized that these effects result from circulating hormones and/or neurosteroids synthesized in the brain. However, it is unclear whether sex steroid hormones are synthesized in the olfactory epithelium or the olfactory bulb, and if they can modulate the activity of the olfactory sensory neurons. Here, we review important discoveries related to the metabolism of sex steroids in the mouse olfactory epithelium and olfactory bulb, along with potential areas of future research. We summarize current knowledge regarding the expression, neuroanatomical distribution, and biological activity of the steroidogenic enzymes, sex steroid receptors, and proteins that are important to the metabolism of these hormones and reflect on their potential to influence early olfactory processing. We also review evidence related to the effects of sex steroid hormones on the development and activity of olfactory sensory neurons. By better understanding how these hormones are metabolized and how they act both at the periphery and olfactory bulb level, we can better appreciate the complexity of the olfactory system and discover potential similarities and differences in early olfactory processing between sexes.

Estrogen receptor alpha, G-protein coupled estrogen receptor 1, and aromatase: Developmental, sex, and region-specific differences across the rat caudate-putamen, nucleus accumbens core and shell

Sex steroid hormones such as 17β-estradiol (estradiol) regulate neuronal function by binding to estrogen receptors (ERs), including ERα and GPER1, and through differential production via the enzyme aromatase. ERs and aromatase are expressed across the nervous system, including in the striatal brain regions. These regions, comprising the nucleus accumbens core, shell, and caudate-putamen, are instrumental for a wide-range of functions and disorders that show sex differences in phenotype and/or incidence. Sex-specific estrogen action is an integral component for generating these sex differences. A distinctive feature of the striatal regions is that in adulthood neurons exclusively express membrane but not nuclear ERs. This long-standing finding dominates models of estrogen action in striatal regions. However, the developmental etiology of ER and aromatase cellular expression in female and male striatum is unknown. This omission in knowledge is important to address, as developmental stage influences cellular estrogenic mechanisms. Thus, ERα, GPER1, and aromatase cellular immunoreactivity was assessed in perinatal, prepubertal, and adult female and male rats. We tested the hypothesis that ERα, GPER1, and aromatase exhibits sex, region, and age-specific differences, including nuclear expression. ERα exhibits nuclear expression in all three striatal regions before adulthood and disappears in a region- and sex-specific time-course. Cellular GPER1 expression decreases during development in a region- but not sex-specific time-course, resulting in extranuclear expression by adulthood. Somatic aromatase expression presents at prepuberty and increases by adulthood in a region- but not sex-specific time-course. These data indicate that developmental period exerts critical sex-specific influences on striatal cellular estrogenic mechanisms.

Ameliorative effect of vitamin B12 on seminiferous epithelium of cimetidine-treated rats: a histopathological, immunohistochemical and ultrastructural study

Cimetidine is an H2 receptor antagonist that has an antiandrogenic effect. It intervenes with the conversion of testosterone into estrogen in the Sertoli cells with accompanying testicular structural changes. In the present study, the microscopic and the ultrastructural changes induced by cimetidine and the effect of vitamin B12 as a protective agent on rat testes were studied. Immunoexpression of estrogen receptor β (ERβ) in testes was evaluated. Twenty-four adult male rats were divided into four groups: control, cimetidine-treated, vitamin B12 treated, and combined cimetidine and vitamin B12 treated. The experimental rats were administered with cimetidine and/or vitamin B12 for 52 days. Group II rats showed marked atrophy of the seminiferous tubules with a significant increase in tubular diameter and decrease in the tubular luminal and epithelial areas. Ultrastructure of this group showed irregular Sertoli cells with basal cytoplasmic vacuolation and significantly thickened basement membrane. ERβ immunoexpression was similar to controls. Group III rats showed near normal seminiferous tubular structures with minimal cellular alterations and the immunoreactivity of the testicular sections was very close to normal. However, group IV rats showed markedly immunopositive detached cells, spermatids, and primary spermatocytes. Cimetidine interferes with the control of spermatogenesis as evidenced by microscopic and ultrastructural studies and affection of ERβ receptors and vitamin B12 has a protective action against this harmful effect.

Impact of aromatase absence on murine intraocular pressure and retinal ganglion cells

We hypothesize that aromatase, an enzyme that regulates estrogen production, plays a significant role in the control of intraocular pressure (IOP) and retinal ganglion cells (RGCs). To begin to test our hypothesis, we examined the impact of aromatase absence, which completely eliminates estrogen synthesis, in male and female mice. Studies were performed with adult, age-matched wild type (WT) and aromatase knockout (ArKO) mice. IOP was measured in a masked fashion in both eyes of conscious mice at 12 and 24 weeks of age. Retinas were obtained and processed for RGC counting with a confocal microscope. IOP levels in both 12- and 24-week old female ArKO mice were significantly higher than those of age- and sex-matched WT controls. The mean increase in IOP was 7.9% in the 12-week-, and 19.7% in the 24-week-old mice, respectively. These changes were accompanied by significant 9% and 7% decreases in RGC numbers in the ArKO female mice, relative to controls, at 12- and 24-weeks, respectively. In contrast, aromatase deficiency did not lead to an increased IOP in male mice. There was a significant reduction in RGC counts in the 12-, but not 24-, week-old male ArKO mice, as compared to their age- and sex-matched WT controls. Overall, our findings show that aromatase inhibition in females is associated with elevated IOP and reduced RGC counts.

Oestradiol Exposure Early in Life Programs Daily and Circadian Activity Rhythms in Adult Mice

Hormone signalling during critical periods organises the adult circadian timekeeping system by altering adult hormone sensitivity and shaping fundamental properties of circadian rhythmicity. However, the timing of when developmental oestrogens modify the timekeeping system is poorly understood. To test the hypothesis that alterations in postnatal oestrogenic signalling organise adult daily activity rhythms, we utilised aromatase knockout mice (ArKO), which lack the enzyme required for oestradiol synthesis. ArKO and wild-type (WT) males and females were administered either oestradiol (E) or oil (OIL) daily for the first 5 postnatal days (p1-5E and p1-5OIL , respectively) because this time encompasses the emergence of clock gene rhythmicity and light responsiveness in the suprachiasmatic nucleus, a bilateral hypothalamic structure regarded as the 'master oscillator'. After sexual maturation, gonadectomy and exogenous oestradiol supplementation, locomotor parameters were assessed. We determined that altered oestrogenic signalling in early life exerts organisational control over the expression of daily and circadian activity rhythms in adult mice. Specifically, p1-5E reduced total wheel running activity in male and female ArKO and female WT mice but had no effect on WT male activity levels. In females, wheel running was consolidated by p1-5E to the early versus late evening, a phenomenon characteristic of male mice. The time of peak activity was advanced by p1-5E in WT and ArKO females but not males. P1-5E shortened the length of the active phase (alpha) in WT males but had no effect on ArKO males or females of either genotypes. Finally, p1-5E altered the magnitude of photic-induced shifts, suggesting that developmental oestrogenic signalling impacts adult circadian functions. In the present study, we further define both a critical period of development of the adult timekeeping system and the role that oestrogenic signalling plays in the expression of daily and circadian activity rhythms throughout life.

Hypothalamic expression of oestrogen receptor α and androgen receptor is sex-, age- and region-dependent in mice

Sex steroid hormones act on developing neural circuits regulating the hypothalamic-pituitary-gonadal axis and are involved in hormone-sensitive behaviours. These hormones act mainly via nuclear receptors, such as oestrogen receptor (ER)-α and androgen receptor (AR). By using immunohistochemistry, we analysed the expression level of ERα and AR throughout perinatal life [at embryonic (E) day 19 and postnatal (P) days 5, 15 and 25] and in adulthood in several hypothalamic nuclei controlling reproduction in both wild-type and aromatase knockout (ArKO) (i.e. which cannot convert testosterone into oestradiol) mice to determine whether there are sex differences in hypothalamic ERα and AR expression and, if so, whether these are established by the action of oestradiol. As early as E19, ERα immunoreactivity (-IR) was observed at same expression levels in both sexes in the anteroventral periventricular nucleus (AVPv), the medial preoptic area (MPOA), the bed nucleus of the stria terminalis (BnST), the ventrolateral part of the ventromedial hypothalamic nucleus and the arcuate nucleus (ARC). Sex differences (female > male) in ERα-IR were observed not only during the prepubertal period in the BnST (P5 to P25) and the MPOA (P15), but also in adulthood in these two brain regions. Sex differences in AR-IR (male > female) were observed at P5 in the AVPv and ARC, and at P25 in the MPOA and ARC, as well as in adulthood in all hypothalamic regions analysed. In adulthood, gonadectomy and hormonal treatment (oestradiol or dihydrotestosterone) also strongly modulated ERα-IR and AR, respectively. Taken together, sex differences in ERα-IR and AR-IR were observed in all hypothalamic regions analysed, although they most likely do not reflect the action of oestradiol because ArKO mice of both sexes showed expression levels very similar to wild-type mice throughout perinatal development.

Characterization of aromatase expression in the adult male and female mouse brain. I. Coexistence with oestrogen receptors α and β, and androgen receptors

Aromatase catalyses the last step of oestrogen synthesis. There is growing evidence that local oestrogens influence many brain regions to modulate brain development and behaviour. We examined, by immunohistochemistry, the expression of aromatase in the adult male and female mouse brain, using mice in which enhanced green fluorescent protein (EGFP) is transcribed following the physiological activation of the Cyp19A1 gene. EGFP-immunoreactive processes were distributed in many brain regions, including the bed nucleus of the stria terminalis, olfactory tubercle, medial amygdaloid nucleus and medial preoptic area, with the densest distributions of EGFP-positive cell bodies in the bed nucleus and medial amygdala. Differences between male and female mice were apparent, with the density of EGFP-positive cell bodies and fibres being lower in some brain regions of female mice, including the bed nucleus and medial amygdala. EGFP-positive cell bodies in the bed nucleus, lateral septum, medial amygdala and hypothalamus co-expressed oestrogen receptor (ER) α and β, or the androgen receptor (AR), although single-labelled EGFP-positive cells were also identified. Additionally, single-labelled ERα-, ERβ- or AR-positive cell bodies often appeared to be surrounded by EGFP-immunoreactive nerve fibres/terminals. The widespread distribution of EGFP-positive cell bodies and fibres suggests that aromatase signalling is common in the mouse brain, and that locally synthesised brain oestrogens could mediate biological effects by activating pre- and post-synaptic oestrogen α and β receptors, and androgen receptors. The higher number of EGFP-positive cells in male mice may indicate that the autocrine and paracrine effects of oestrogens are more prominent in males than females.

Differential control of sex differences in estrogen receptor α in the bed nucleus of the stria terminalis and anteroventral periventricular nucleus

The principal nucleus of the bed nucleus of the stria terminalis (BNSTp) and anteroventral periventricular nucleus of the hypothalamus (AVPV) are sexually dimorphic, hormone-sensitive forebrain regions. Here we report a profound sex difference in estrogen receptor-α (ERα) immunoreactivity (IR) in the BNSTp, with robust ERα IR in females and the near absence of labeling in males. This sex difference is due to the suppression of ERα IR by testicular hormones in adulthood: it was not present at birth and was not altered by neonatal treatment of females with estradiol; gonadectomy of adult males increased ERα IR to that of females, whereas gonadectomy of adult females had no effect. Treating gonadally intact males with an aromatase inhibitor partially feminized ERα IR in the BNSTp, suggesting that testicular suppression required aromatization. By contrast, in AVPV we found a modest sex difference in ERα IR that was relatively insensitive to steroid manipulations in adulthood. ERα IR in AVPV was, however, masculinized in females treated with estradiol at birth, suggesting that the sex difference is due to organizational effects of estrogens. The difference in ERα IR in the BNSTp of males and females appears to be at least in part due to greater expression of mRNA of the ERα gene (Esr1) in females. The sex difference in message is smaller than the difference in immunoreactivity, however, suggesting that posttranscriptional mechanisms also contribute to the pronounced suppression of ERα IR and presumably to functions mediated by ERα in the male BNSTp.

Influence of aromatase absence on the gene expression and histology of the mouse meibomian gland

PURPOSE

We hypothesize that aromatase, an enzyme that controls estrogen biosynthesis, plays a major role in the sex-related differences of the meibomian gland. To begin to test this hypothesis, we examined the influence of aromatase absence, which completely eliminates estrogen production, on glandular gene expression and histology in male and female mice.

METHODS

Meibomian glands were obtained from adult, age-matched wild-type (WT) and aromatase knockout (ArKO) mice. Tissues were processed for histology or the isolation of total RNA, which was analyzed for differentially expressed mRNAs by using microarrays.

RESULTS

Our results show that aromatase significantly influences the expression of more than a thousand genes in the meibomian gland. The nature of this effect is primarily sex-dependent. In addition, the influence of aromatase on sex-related differences in gene expression is predominantly genotype-specific. However, many of the sex-related variations in biological process, molecular function, and cellular component ontologies, as well as in KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways, are remarkably similar between WT and ArKO mice. The loss of aromatase activity has no obvious effect on the histology of meibomian glands in male or female mice.

CONCLUSIONS

Our findings demonstrate that aromatase has a significant impact on gene expression in the meibomian gland. The nature of this influence is sex-dependent and genotype-specific; however, many of the sex-related variations in gene ontologies and KEGG pathways are similar between WT and ArKO mice. Consequently, it appears that aromatase, and by extension estrogen, do not play a major role in the sex-related differences of the mouse meibomian gland.

Epigenetic setting for long-term expression of estrogen receptor α and androgen receptor in cells

Epigenetic regulation of the nuclear estrogen and androgen receptors, ER and AR, constitutes the molecular basis for the long-lasting effects of sex steroids on gene expression in cells. The effects prevail at hundreds of gene loci in the proximity of estrogen- and androgen-responsive elements and many more such loci through intra- and even inter-chromosomal level regulation. Such a memory system should be active in a flexible manner during the early development of vertebrates, and later replaced to establish more stable marks on genomic DNA. In mammals, DNA methylation is utilized as a very stable mark for silencing of the ERα and AR isoform expression during cancer cell and normal brain development. The factors affecting the DNA methylation of the ERα and AR genes in cells include estrogen and androgen. Since testosterone induces brain masculinization through its aromatization to estradiol in a narrow time window of the perinatal stage in rodents, the autoregulation of estrogen receptors, especially the predominant form of ERα, at the level of DNA methylation to set up the "cell memory" affecting the sexually differentiated status of brain function has been attracting increasing attention. The alternative usage of the androgen-AR system for brain masculinization and estrogenic regulation of AR expression in some species imply that the DNA methylation pattern of the AR gene can be established by closely related but different systems for sex steroid-induced phenomena, including brain masculinization.

Behavioral analysis of genetically modified mice indicates essential roles of neurosteroidal estrogen

Aromatase in the mouse brain is expressed only in the nerve cells of specific brain regions with a transient peak during the neonatal period when sexual behaviors become organized. The aromatase-knockout (ArKO) mouse, generated to shed light on the physiological functions of estrogen in the brain, exhibited various abnormal behaviors, concomitant with undetectable estrogen and increased androgen in the blood. To further elucidate the effects of neurosteroidal estrogens on behavioral phenotypes, we first prepared an brain-specific aromatase transgenic (bsArTG) mouse by introduction of a human aromatase transgene controlled under a -6.5 kb upstream region of the brain-specific promoter of the mouse aromatase gene into fertilized mouse eggs, because the -6.5 kb promoter region was previously shown to contain the minimal essential element responsible for brain-specific spatiotemporal expression. Then, an ArKO mouse expressing the human aromatase only in the brain was generated by crossing the bsArTG mouse with the ArKO mouse. The resulting mice (ArKO/bsArTG mice) nearly recovered from abnormal sexual, aggressive, and locomotive (exploratory) behaviors, in spite of having almost the same serum levels of estrogen and androgen as the adult ArKO mouse. These results suggest that estrogens locally synthesized in the specific neurons of the perinatal mouse brain directly act on the neurons and play crucial roles in the organization of neuronal networks participating in the control of sexual, aggressive, and locomotive (exploratory) behaviors.

Perinatal exposure to bisphenol-A changes N-methyl-D-aspartate receptor expression in the hippocampus of male rat offspring

Bisphenol-A (BPA) is one of the most common environmental endocrine disrupters with mixed estrogen agonist/antagonist properties. The toxicity of BPA has been extensively evaluated in a variety of tests in rodents, including developmental and reproductive toxicity, and carcinogenicity. The objective of the present study is to evaluate whether or not perinatal maternal exposure to BPA at 0.05, 0.5, 5, 50, and 200 mg/kg/d affects N-methyl-D-aspartate (NMDA) receptor (NMDAR) subunits NR1, NR2A, 2B, estrogen receptor beta (ERbeta), and aromatase cytochrome P450 (P450arom) protein expressions of hippocampus in male rat offspring during postnatal development. Western-blotting analyses showed that perinatal exposure to BPA significantly affected the expression of NMDAR subunits. At the lower doses of 0.05 to 50 mg/kg/d, BPA concentration dependently inhibited the expression of NMDAR subunits. However, at the higher dose (200 mg/kg/d), the effects of BPA on these subunits were different, with a stronger inhibition of NR1 expression and a slighter inhibition of NR2A, 2B expression when compared with those at the lower dosage of BPA. In addition, perinatal exposure to BPA inhibited the expression of ERbeta protein, but increased P450arom protein expression in a concentration-dependent manner, especially during the early postnatal period (the first 1-3 postnatal weeks). No significant influence of BPA on P450arom was observed at postnatal week 8. These data suggest that environmental BPA exposure may affect the development of the brain, enhancing the local biosynthesis of estrogen in the brain, inhibiting ERbeta and NMDAR expressions.

Enhanced ERbeta immunoexpression and apoptosis in the germ cells of cimetidine-treated rats

BACKGROUND

Cimetidine, refereed as antiandrogenic drug, causes hormonal changes in male patients such as increased testosterone and FSH levels. In the rat testis, structural alterations in the seminiferous tubules have been related to germ cell loss and Sertoli cell death by apoptosis. Regarding the important role of Sertoli cells in the conversion of testosterone into estrogen, via aromatase, the immunoexpression of estrogen receptors-beta (ERbeta) was evaluated in the germ cells of untreated and treated rats with cimetidine. A relationship between ERbeta immunoreactivity and apoptosis was also investigated in the germ cells of damaged tubules.

METHODS

Immunohistochemistry for detection of ERbeta and TUNEL method were performed in testicular sections of adult male rats treated with 50 mg/Kg of cimetidine (CmG) or saline solution (CG) for 52 days.

RESULTS

In CG, a cytoplasmic immunoexpression for ERbeta was observed in spermatogonia, primary spermatocytes and spermatids. An evident ERbeta immunoreactivity was always observed in the flagellum and residual bodies of late spermatids. In CmG, the cytoplasm or cytoplasm and nuclei of germ cells of the damaged tubules by cimetidine showed enhanced ERbeta immunostaining. TUNEL-labeling was usually observed in the same germ cell types exhibiting enhanced ERbeta immunoreactivity.

CONCLUSION

The presence of ERbeta immunolabeling in the flagellum and residual bodies of spermatids reinforces the role of estrogen in spermiogenesis. The overexpression of ERbeta in the germ cells of CmG could be related to a possible interference of cimetidine on tubular androgenization and/or on the intratubular aromatase due to Sertoli cell damage. The parallelism between ERbeta overexpression and apoptosis indicates a participation of ERbeta on germ cell death.

Effects of organisational oestradiol on adult immunoreactive oestrogen receptors (alpha and beta) in the male mouse brain

Steroid hormones act on developing neural circuits that regulate the hypothalamic-pituitary-gonadal axis and are involved in hormone-sensitive behaviours. To test the hypothesis that developmental exposure to oestradiol (E(2)) organises the quantity of adult oestrogen receptors (ERalpha and ERbeta), we used male mice with a targeted mutation of the aromatase enzyme gene (ArKO) and their wild-type (WT) littermates. These mice are unable to aromatise testosterone to E(2), but still express both ERalpha and beta. To evaluate adult responsiveness to E(2), gonadectomised males were implanted with Silastic capsules containing E(2), or an empty implant, 5 days prior to sacrifice. Immunoreactivity for ERalpha and ERbeta was quantified in the caudal ventromedial nucleus (VMN) and the medial preoptic area (POA). Regardless of genotype, adult treatment with E(2) reduced ERalpha-immunoreactive (ir) and ERbeta-ir cell numbers in the POA, as well as ERbeta-ir, but not ERalpha-ir, cell numbers in the VMN. Genotype, and thus endogenous exposure to E(2), produced opposite effects on ER expression in the two brain areas. In the VMN, ArKO males had more ERalpha-ir and ERbeta-ir cells than did WT males. In the POA, ArKO males had fewer ERalpha-ir and ERbeta-ir cells than did WT males. Thus, numbers of immunoreactive neurones containing both ERs in the adult ArKO male were enhanced in the POA, but decreased in the VMN, and most likely these patterns were established during the developmental critical period. Furthermore, although both ERalpha and beta-ir cell numbers are altered by the disruption of the aromatase gene, ERbeta is altered in a more robust and region-specific manner.

Sexual behavior activity tracks rapid changes in brain estrogen concentrations

Estrogens are classically viewed as hormones that bind to intracellular receptors, which then act as transcription factors to modulate gene expression; however, they also affect many aspects of neuronal functioning by rapid nongenomic actions. Brain estrogen production can be regulated within minutes by changes in aromatase (estrogen synthase) activity as a result of calcium-dependent phosphorylations of the enzyme. To determine the effects of rapid changes in estrogen availability on male copulatory behavior, we mimicked in male mice the rapid upregulation and downregulation of brain estrogen concentration that should occur after inactivation or activation of aromatase activity. A single injection of different aromatase inhibitors [Vorozole, 1,4,6-androstatrien-3,17-dione (ATD), or its metabolite 17-OH-ATD (1,4,6-androstatrien-17beta-ol-3-one)] almost completely suppressed male sexual behavior (mounts and intromissions) expressed 10-20 min later by C57BL/6J mice but did not affect behavior in aromatase knock-out (ArKO) mice, activated by daily injections of estradiol benzoate, thereby confirming the specificity of the behavioral inhibition observed in wild-type mice. The rapid ATD-induced inhibition was reversed by the simultaneous injection of a large dose of estradiol. A single injection of estradiol to ArKO mice also activated male sexual behavior within 15 min. Thus, rapid increases or decreases in brain estrogen concentrations are followed within minutes by corresponding changes in male sexual behavior. Sexual behavior can thus be used to monitor changes in local estrogen concentrations and analyze the mechanisms mediating the rapid decline in estrogen signaling that takes place after inhibition of estrogen synthesis.

Comparison of urinary odor-induced glomerular activation in the main olfactory bulb of aromatase knock-out and wild type female mice

Previously [D.W. Wesson, M. Keller, Q. Douhard, M.J. Baum, J. Bakker, Enhanced urinary odor discrimination in female aromatase knockout mice, Horm. Behav. 49 (2006) 580-586] female aromatase knock out mice successfully learned to discriminate in a food-motivated go/no-go task between urinary volatiles from ovariectomized female mice treated with estradiol as opposed to estradiol plus progesterone whereas wild type females failed to learn this odor discrimination. We asked whether this behavioral difference is reflected in the ability of these two types of urinary volatiles to differentially stimulate Fos expression in juxtaglomerular cells (an index of glomerular activation) of the main olfactory bulb (MOB) in wild type versus ArKO female mice. Statistically significant differences in the profiles of MOB glomerular activation were seen in ovariectomized, estrogen-treated ArKO as well as WT female subjects following exposure to urinary volatiles from ovariectomized females given estradiol alone as opposed to estradiol plus progesterone. Therefore, previously observed differences between females of the two genotypes in their behavioral responses to these odors must reflect differential processing in more central segments of the olfactory pathway instead of in the MOB.

Antiepileptic Drugs Affect Neuronal Androgen Signaling via a Cytochrome P450-Dependent Pathway

Recent data imply an important role for brain cytochrome P450 (P450) in endocrine signaling. In epileptic patients, treatment with P450 inducers led to reproductive disorders; in mouse hippocampus, phenytoin treatment caused concomitant up-regulation of CYP3A11 and androgen receptor (AR). In the present study, we established specific in vitro models to examine whether CYP3A isoforms cause enhanced AR expression and activation. Murine Hepa1c1c7 cells and neuronal-type rat PC-12 cells were used to investigate P450 regulation and its effects on AR after phenytoin and phenobarbital administration. In both cell lines, treatment with antiepileptic drugs (AEDs) led to concomitant up-regulation of CYP3A (CYP3A11 in Hepa1c1c7 and CYP3A2 in PC-12) and AR mRNA and protein. Inhibition of CYP3A expression and activity by the CYP3A inhibitor ketoconazole or by CYP3A11-specific short interfering RNA molecules reduced AR expression to basal levels. The initial up-regulation of AR signal transduction, measured by an androgen-responsive element chloramphenicol-acetyltransferase reporter gene assay, was completely reversed after specific inhibition of CYP3A11. Withdrawal of the CYP3A11 substrate testosterone prevented AR activation, whereas AR mRNA expression remained up-regulated. In addition, recombinant CYP3A11 was expressed heterologously in PC-12 cells, thereby eliminating any direct drug influence on the AR. Again, the initial up-regulation of AR mRNA and activity was reduced to basal levels after silencing of CYP3A11. In conclusion, we show here that CYP3A2 and CYP3A11 are crucial mediators of AR expression and signaling after AED application. These findings point to an important and novel function of P450 in regulation of steroid hormones and their receptors in endocrine tissues such as liver and brain.

Estradiol stimulates progenitor cell division in the ventricular and subventricular zones of the embryonic neocortex

Two distinct populations of cerebral cortical progenitor cells that generate neurons during embryogenesis have been identified: radial glial cells and intermediate progenitor cells. Despite advances in our understanding of progenitor cell populations, we know relatively little about factors that regulate their proliferative behaviour. 17-beta-Estradiol (E2) is present in the adult and developing mammalian brain, and plays an important role in central nervous system processes such as neuronal differentiation, survival and plasticity. E2 also stimulates neurogenesis in the adult dentate gyrus. We examined the role of E2 during embryonic cortical neurogenesis through immunohistochemistry, in situ hybridization, functional enzyme assay, organotypic culture and in utero administration of estradiol-blocking agents in mice. We show that aromatase, the E2 synthesizing enzyme, is present in the embryonic neocortex, that estrogen receptor-alpha is present in progenitor cells during cortical neurogenesis, that in vitro E2 administration rapidly promotes proliferation, and that in utero blockade of estrogen receptors decreases proliferation of embryonic cortical progenitor cells. Furthermore, the E2 inhibitor alpha-fetoprotein is expressed at high levels by radial glial cells but at lower levels by intermediate progenitor cells, suggesting that E2 differentially influences the proliferation of these cortical progenitor cell types. These findings demonstrate a new functional role for E2 as a proliferative agent during critical stages of cerebral cortex development.

Ultrastructure and Estrogen Regulation of the Lymphatic Stomata of Ovarian Bursa in Mice

The ovarian bursa is a key player in maintaining adaptive ovarian microenvironment for ovulation. The lymphatic stomata are believed to be a major contributor to execute the function of the ovarian bursa, whereas little is known about their ultrastructure and regulation. Here, we examined the ultrastructure of lymphatic stomata in mouse ovarian bursa by scanning electron microscopy and transmission electron microscopy and investigated its regulation by estrogen. We found that the mesothelium on the visceral layer of mouse ovarian bursa was composed of the cuboidal and flattened cells. The lymphatic stomata with round and oval shapes were mainly among the cuboidal cells. The particles, cells, and fluid passed through the stomata and entered into the lymphatic drainage unit composed of connective tissue and lymphatic endothelial cells beneath the stomata. We also used trypan blue as a tracer and found that the absorption of trypan blue through the lymphatic stomata was increased by estrogen that enlarged the average opening area of lymphatic stomata. Furthermore, we detected that there existed estrogen receptors in the nuclei of the mesothelial cells on the visceral ovarian bursa by using immunoelectron microscopy. Taken together, these data suggest that both the absorption and opening area of the lymphatic stomata in mouse ovarian bursa may be influenced by estrogen.

Enhanced urinary odor discrimination in female aromatase knockout (ArKO) mice

We asked whether odor discrimination abilities are sexually dimorphic in mice and, if so, whether the perinatal actions of estradiol contribute to these sex differences. The ability to discriminate different types of urinary odors was compared in male and female wild-type (WT) subjects and in mice with a homozygous-null mutation of the estrogen synthetic enzyme, aromatase (aromatase knockout; ArKO). Olfactory discrimination was assessed in WT and ArKO male and female mice after they were gonadectomized in adulthood and subsequently treated with estradiol benzoate. A liquid olfactometer was used to assess food-motivated olfactory discrimination capacity. All animals eventually learned to distinguish between urinary odors collected from gonadally intact males and estrous females; however, WT males as well as ArKO mice of both sexes learned this discrimination significantly more rapidly than WT females. Similar group differences were obtained when mice discriminated between urinary odors collected from gonadally intact vs. castrated males or between two non-social odorants, amyl and butyl acetate. When subjects had to discriminate volatile urinary odors from ovariectomized female mice treated with estradiol sequenced with progesterone versus estradiol alone, ArKO females quickly acquired the task whereas WT males and females as well as ArKO males failed to do so. These results demonstrated a strong sex dimorphism in olfactory discrimination ability, with WT males performing better than females. Furthermore, female ArKO mice showed an enhanced ability to discriminate very similar urinary odorants, perhaps due to an increased sensitivity of the main olfactory nervous system to adult estradiol treatment as a result of perinatal estrogen deprivation.

Diminished aromatase immunoreactivity in the hypothalamus, but not in the basal forebrain nuclei in Alzheimer's disease

In previous studies we have shown in Alzheimer's disease (AD) an enhanced nuclear estrogen receptor (ER) alpha expression in the cholinergic basal forebrain nuclei, i.e. the vertical limb of the diagonal band of Broca (VDB) and the nucleus basalis of Meynert (NBM), and in a number of hypothalamic nuclei, i.e. the supraoptic nucleus (SON), the infundibular nucleus (INF), the medial mamillary nucleus (MMN). We aimed at determining whether the increase in nuclear ERalpha seen in AD patients was related to a rise in local production of estrogens by aromatase (P-450arom), which is a key enzyme that catalyzes the biosynthesis of estrogens from precursor aromatizable androgens. We confirmed for the first time the presence of aromatase mRNA in neurons and glial cells in the human NBM and the tuberomamillary nucleus by RT-QPCR using laser microdissection. Enhanced aromatase immunoreactivity (ir) was indeed observed in the NBM in AD. However, in contrast a decreased aromatase-ir was found in the SON, INF and MMN of AD patients. In addition, P-450arom-ir was clearly diminished in ependymal and choroid plexus cells in AD. While an increase in aromatase-ir was found in the NBM and SON during normal aging, a decrease in staining was observed in the MMN. No sex differences in young control, elderly control or AD patients were present in any of the nuclei studied. In conclusion, brain P-450arom-ir and the relationship of its regulation with plasma sex steroid levels, estrogen and androgen receptors in the human hypothalamus and basal forebrain are region-specific.

Characterization of a cetacean aromatase (CYP19) and the phylogeny and functional conservation of vertebrate aromatase

Aromatase (cytochrome P450 19, CYP19, P450arom) is the enzyme responsible for the production of estrogens, hormones critical for development and reproduction. Aromatase was sequenced from a white-sided dolphin (Lagenorhynchus acutus) ovary, transiently transfected into HEK 293 cells, and the expressed protein was characterized for aromatase activity in the presence of androstenedione and testosterone and after exposure to the aromatase inhibitor letrazole. The Kms for androstenedione and testosterone were 63.5 and 75 nM, respectively, values that are very similar to those reported for other mammalian aromatases. A Bayesian phylogenetic analysis of the vertebrate aromatases was performed on the amino acid sequences of aromatases from fish, amphibians, reptiles, birds, and mammals. Based on known species phylogeny, the cetacean aromatase showed an expected grouping with artiodactyls (cow, sheep, and goat). An analysis of functional divergence showed strong conservation of aromatase across the entire protein, which indicates that the observed sequence divergence is functionally neutral.

Estrogen synthesis in the central nucleus of the amygdala following middle cerebral artery occlusion: Role in modulating neurotransmission

Stroke-induced lesions of the insular cortex in the brain have been linked to autonomic dysfunction (sympathoexcitation) leading to arrhythmogenesis and sudden cardiac death. In experimental models, systemic estrogen administration in male rats has been shown to reduce stroke-induced cell death in the insular cortex as well as prevent sympathoexcitation. The central nucleus of the amygdala has been postulated to mediate sympathoexcitatory output from the insular cortex. We therefore set out to determine if endogenous estrogen levels within the central nucleus of the amygdala are altered following stroke and if microinjection of estrogen into the central nucleus of the amygdala modulates autonomic tone. Plasma estrogen concentrations were not altered by middle cerebral artery occlusion (22.86+/-0.14 pg/ml vs. 21.24+/-0.33 pg/ml; P>0.05). In contrast, estrogen concentrations in the central nucleus of the amygdala increased significantly following middle cerebral artery occlusion (from 20.83+/-0.54 pg/ml to 76.67+/-1.59 pg/ml; P<0.05). Local infusion of an aromatase inhibitor, letrozole, into the central nucleus of the amygdala at the time of middle cerebral artery occlusion prevented the increase in estrogen concentration suggesting that this increase was dependent on aromatization from testosterone. Furthermore, bilateral microinjection of estrogen (0.5 microM in 200 nl) directly into the central nucleus of the amygdala significantly decreased arterial pressure and sympathetic tone and increased baroreflex sensitivity, and these effects were enhanced following co-injection with either an N-methyl-D-aspartate or non-N-methyl-D-aspartate receptor antagonist. Taken together, the results suggest that middle cerebral artery occlusion resulted in synthesis of estrogen within the central nucleus of the amygdala and that this enhanced estrogen level may act to attenuate overstimulation of central nucleus of the amygdala neurons to prevent middle cerebral artery occlusion-induced autonomic dysfunction.

Differential hormonal regulation of estrogen receptors ERalpha and ERbeta and androgen receptor expression in rat efferent ductules

Estrogen receptors, in addition to the androgen receptor (AR), are expressed at high levels in efferent ductules of the male reproductive tract and it is now well recognized that estrogen receptor (ER) alpha is required for the maintenance of normal structure and function of the ductules. However, little is known regarding the hormonal regulation of the receptors themselves in the male. In the present study, efferent ductule ligation and castration, followed by replacement with testosterone, dihydro-testosterone (DHT) or estradiol was used to investigate the relative importance of circulating and luminal sources of steroid for the modulation of ERalpha, ERbeta and AR in rat efferent ductules. Uni- or bilateral castration and ligation did not affect the expression of ERalpha and ERbeta, but bilateral castration caused down-regulation of AR. Replacement with DHT and testosterone alone or in combination with estradiol caused the recovery of AR expression to control levels. A slight recovery of AR was also observed after estrogen replacement. ERalpha expression was decreased to nearly undetectable levels after estrogen replacement. On the other hand, ERbeta did not show evident effects following any of the treatments, suggesting a constitutive expression of this receptor. This differential modulation of the steroid hormone receptors highlights the importance of maintaining a physiological androgen-estrogen balance to regulate the structure and function of efferent ductules in the male.

4-Hydroxytamoxifen attenuates methamphetamine-induced nigrostriatal dopaminergic toxicity in intact and gonadetomized mice

The present study was undertaken to assess the ability of 4-hydroxytamoxifen (4-OHT) to alter methamphetamine-induced nigrostriatal dopaminergic toxicity. Three daily doses of 4-OHT (6 micro g/day) effectively attenuated methamphetamine-induced nigrostriatal dopamine depletions in both sexes of intact and gonadectomized C57BL/6 J mice. 4-OHT alone did not alter the dopamine content levels in the striatum. Both male and female mice exhibited similar Cu, Zn-superoxide dismutase protein levels in the striata whether after gonadectomy or 4-OHT treatment. Furthermore, basal body temperature and methamphetamine-induced hyperthermia were not affected by 4-OHT treatment in either sex of mice. Using a lucigenen-derived chemiluminescence assay, we found that 4-OHT by itself can serve as a potent superoxide anion radical scavenger in vitro. The protective effects of 4-OHT against methamphetamine-induced nigrostriatal dopamine depletion can be, in part, due to its antioxidative characteristics. The free radical-scavenging ability of 4-OHT calls for further investigations for its uses in clinical practice.

Immunolocalization of estrogen receptor beta in the hypothalamic paraventricular nucleus of female mice during pregnancy, lactation and postnatal development

Previous studies have shown that estrogen receptor beta (ERbeta) is the predominant estrogen receptor in the hypothalamic paraventricular nucleus (PVN) of mouse, mediating estrogen regulation of the neuroendocrine activities of the PVN, but the exact roles that ERbeta plays in the PVN remain unclear. In this study, we used immunocytochemistry to investigate the expression of ERbeta in the maternal PVN of mice during pregnancy (pregnant days 8, 10, 12, 15 and 18), lactation (postpartum days 1, 4 and 8) as well as in the PVN of the females from postnatal days 1, 3, 5, 7, 9, 15, 30 and 70. We found out that ERbeta was predominantly localized in the magnocellular divisions of PVN. In the pregnant female brain, generally, the ERbeta was lower than that of the postnatal development, the lowest level was found at gestational days 10-12; then from gestational day 18 to postpartum day 1, it increased to higher levels, followed by a decrease from postpartum day 4. During the postnatal development, the highest level of ERbeta was found at early postnatal days (before postnatal day 15), thereafter, it decreased to a lower level. The above results indicate that circulating sex steroids may differentially regulate the expression of ERbeta in the PVN of mice. It also suggests that this receptor may play important roles in the regulation of parturition and in the development, food intake and body weight increases of the newborns by acting on the neuropeptides, which were also detected in the PVN.

Aromatase cytochrome P450 and extragonadal estrogen play a role in ischemic neuroprotection

Female animals are protected from many forms of neurological injury and degeneration relative to their male counterparts, in part attributable to their native estrogens. We hypothesized that estradiol aromatized from precursor androgens via the cytochrome P450 aromatase contributes to ischemic neuroprotection in the female. Female homozygous aromatase knock-out (ArKO) mice and randomly cycling, wild-type (WT) female littermates were treated with reversible middle cerebral artery occlusion (90 min; 22 hr reperfusion). Total and regional ischemic damage was greater in female ArKOs (total, 33.5 +/- 4.8%; cortical, 47.4 +/- 5.7%; striatal, 44.8 +/- 7.8%) compared with WT (total, 14.2 +/- 5%; cortical, 14.2 +/- 4.5%; striatal, 17.5 +/- 8%). Baseline blood pressure and intra-ischemic cortical perfusion were comparable in knock-outs and WT, suggesting that vascular factors do not explain ArKO ischemic sensitivity. Injury was smaller in ovariectomized WT than in ArKO, emphasizing that extragonadal local estradiol plays a critical role in females. Similar increases in cortical and striatal damage were observed in female WT mice chronically treated with the aromatase inhibitor fadrozole compared with vehicle-treated control mice. Restoration of plasma 17beta-estradiol to physiological levels completely reversed the ArKO female's susceptibility to injury. These findings indicate that the biosynthetic enzyme P450 aromatase is key to endogenous neuroprotection in females and suggest that enhancing local, nongonadal estrogen formation could have therapeutic implications is ischemic neuropathology.

The menopausal mouse: a new neural paradigm of a distressing human condition

Progressive and long-term sex hormone imbalance in the FSH-R haploinsufficient menopausal mouse leads to degenerative changes in the CNS associated with increased anxiety. The brain region most affected by aging in these mice is the hippocampus. Choline acetyltransferase (ChAT) enzymatic activity and synapsin immunoreactivity are reduced at 20 months of age. Neurons in the dentate gyrus show signs of progressive degenerative changes, hypertrophy and glyosis, and subsequent cell shrinkage and death. These results suggest that the menopausal mouse mimics degenerative changes in the hippocampus of hormonally imbalanced aging humans. We propose using this animal model to test the effectiveness of potential therapeutics in paradigms of accelerated aging.

Regulation of the membrane estrogen receptor-alpha: role of cell density, serum, cell passage number, and estradiol

We used modified immunocytochemical conditions to quantify a membrane form of estrogen receptor-alpha (mERalpha) in a rat pituitary tumor cell line, GH3/B6/F10. We studied the regulation of mERalpha vs. levels of intracellular ERalpha (iERalpha) using our 96-well plate immunoassay. The anti-ERalpha antibody C542 was used to label the ERalpha (via conjugated alkaline phosphatase) in fixed permeabilized (for iERalpha) vs. nonpermeabilized cells (for mERalpha). Expression of mERalpha was highest at low cell densities (<1000 cells/well) and decreased significantly at densities where cellular processes touched, whereas the more abundant iERalpha increased with increasing cell density over the same range. Serum starvation for 48 h caused increases in mERalpha, whereas iERalpha levels showed no significant changes. A large decline in mERalpha and iERalpha levels with cell passage number was observed. Minutes after nM 17beta-estradiol (E2) treatment, a portion of the cells rounded up and detached from the culture plate, whereas nM cholesterol had no such effect. Although E2 treatment did not change mERalpha levels, the antigen was reorganized from a fine particulate to aggregation into asymmetric large granules of staining. That common culturing conditions favor down-regulation of mERalpha may explain the relatively few reports of this protein in other experimental systems.

Aromatase inhibition for ovarian stimulation: future avenues for infertility management

Ovarian stimulation is applied during infertility management either alone or in conjunction with intrauterine insemination and assisted reproductive technologies. At the present time, the two main medications used for ovarian stimulation include an oral antiestrogen, clomiphene citrate, and injectable gonadotropins. In spite of the high ovulation rate with the use of clomiphene citrate, the pregnancy rate is much lower. In clomiphene citrate failures, gonadotropin injections have generally been used as the next treatment option. Treatment with gonadotropins is difficult to control and characteristically associated with increased risk of severe ovarian hyperstimulation syndrome and high multiple pregnancies. Therefore, an effective oral treatment that could be used without risk of hyperstimulation and with minimal monitoring is the preferred therapy. We hypothesize that aromatase inhibitors can be administered early in the follicular phase to induce ovulation by releasing the hypothalamus or pituitary from estrogen negative feedback. Based on this hypothesis, we have reported the success of aromatase inhibitors in induction and augmentation of ovulation in addition to improving ovarian response to gonadotropin stimulation. Moreover, there are other potential applications for aromatase inhibitors in infertility management, including improving implantation in assisted reproduction and in-vitro maturation.

Are estrogens of import to primate/human ovarian folliculogenesis?

The notion that estrogens play a meaningful role in ovarian folliculogenesis stems from a large body of in vitro and in vivo experiments carried out in certain rodent models, (e.g., rats) wherein the stimulatory role of estrogen on granulosa cell growth and differentiation is undisputed. However, evidence derived from these polyovulatory species may not be readily generalizable to the monoovulatory subhuman primates, let alone the human. Only recently, significant observations on the ovarian role(s) of estrogen have been reported for the primate/human. It is thus the objective of this communication to review the evidence for and against a role for estrogens in primate/human ovarian follicular development with an emphasis toward the application of the concepts so developed to contemporary reproductive physiology and to the practice of reproductive medicine. The role(s) of estrogens will be examined not only by analyzing the physiological evidence to the effect that these hormones control ovarian function and follicular growth, but also by summarizing the molecular evidence for the existence and distribution of the cognate receptors.

Histochemistry and cytochemistry of nuclear receptors

Receptors of steroid hormones, thyroid hormones and several kinds of vitamins have been shown to act as nuclear transcription factors and to form a nuclear receptor (NR) family. Histochemical techniques including autoradiography using radio-labeled ligands, immunohistochemistry and in situ hybridization histochemistry, have displayed that target cells of these receptors are distributed not only in the classical target organs but also widely in a variety of tissues; these techniques can demonstrate the presence of receptor proteins and mRNAs, even though they are expressed in a small cell population of tissues. On the other hand, many studies have been performed to demonstrate the interaction between NRs and nuclear and cytoplasmic proteins, and to clarify the mechanism of transcriptional regulation through NRs in artificial conditions which are created in gene transfer experiments or under cell-free conditions. Some data coincide with those obtained from histochemical techniques, however, some histochemical data do not support the results of studies in vitro. This review focuses on the following topics: histochemical methodologies to detect NRs, the distribution and function of NRs in the tissues, the intracellular and intranuclear localization of NRs, roles of gonadal steroid receptors and their ligands on developing tissues including cell communications such as mesenchymal-stromal interaction, and the interaction between other cellular components and NRs. In addition, the agreement and disagreement between the results of histochemical studies and those from the experiments in the model systems or in vitro are discussed.