Neonatal imprinting and regulation of estrogen receptor alpha and beta mRNA expression by estrogen in the pituitary and hypothalamus of the male rat

Tamoxifen Treatment in the Neonatal Period Affects Glucose Homeostasis in Adult Mice in a Sex-Dependent Manner

Tamoxifen is a selective estrogen receptor modulator used to activate the CREERT2 recombinase, allowing tissue-specific and temporal control of the somatic mutagenesis to generate transgenic mice. Studies integrating development and metabolism require a genetic modification induced by a neonatal tamoxifen administration. Here, we investigate the effects of a neonatal tamoxifen administration on energy homeostasis in adult male and female C57BL/6J mice. C57BL/6J male and female mouse pups received a single injection of tamoxifen 1 day after birth (NTT) and were fed a high-fat/high-sucrose diet at 6 weeks of age. We measured weight, body composition, glucose and insulin tolerance, basal metabolism, and tibia length and weight in adult mice. The neonatal tamoxifen administration exerted long-term, sex-dependent effects on energy homeostasis. NTT female mice became overweight and developed impaired glucose control in comparison to vehicle-treated littermates. NTT females exhibited 60% increased fat mass, increased food intake, decreased physical activity and energy expenditure, impaired glucose and insulin tolerance, and fasting hyperglycemia and hyperinsulinemia. In contrast, NTT male mice exhibited a modest amelioration of glucose and insulin tolerance and long-term decreased lean mass linked to decreased bone weight. These results suggest that the neonatal tamoxifen administration exerted a marked and sex-dependent influence on adult energy homeostasis and bone weight and must therefore be used with caution for the development of transgenic mouse models regarding studies on energy homeostasis and bone biology.

Maternal Exposure to Dibutyl Phthalate (DBP) or Diethylstilbestrol (DES) Leads to Long-Term Changes in Hypothalamic Gene Expression and Sexual Behavior

Xenobiotic exposure during pregnancy and lactation has been linked to perinatal changes in male reproductive outcomes and other endocrine parameters. This pilot study wished to assess whether brief maternal exposure of rats to xenobiotics dibutyl phthalate (DBP) or diethylstilbestrol (DES) might also cause long-term changes in hypothalamic gene expression or in reproductive behavior of the resulting offspring. Time-mated female Sprague Dawley rats were given either DBP (500 mg/kg body weight, every second day from GD14.5 to PND6), DES (125 µg/kg body weight at GD14.5 and GD16.5 only), or vehicle (n = 8–12 per group) and mild endocrine disruption was confirmed by monitoring postnatal anogenital distance. Hypothalamic RNA from male and female offspring at PND10, PND24 and PND90 was analyzed by qRT-PCR for expression of aromatase, oxytocin, vasopressin, ER-alpha, ER-beta, kisspeptin, and GnRH genes. Reproductive behavior was monitored in male and female offspring from PND60 to PND90. Particularly, DES treatment led to significant changes in hypothalamic gene expression, which for the oxytocin gene was still evident at PND90, as well as in sexual behavior. In conclusion, maternal xenobiotic exposure may not only alter endocrine systems in offspring but, by impacting on brain development at a critical time, can have long-term effects on male or female sexual behavior.

Effects of diisopentyl phthalate exposure during gestation and lactation on hormone-dependent behaviours and hormone receptor expression in rats

Phthalates are found in different plastic materials, such as packaging, toys and medical devices. Some of these compounds are endocrine disruptors, comprising substances that are able to induce multiple hormonal disturbances and downstream developmental effects, including the disruption of androgen-dependent differentiation of the male reproductive tract and changes in pathways that regulate hormone-dependent behaviours. In a previous study, metabolites of diisopentyl phthalate (DiPeP), a potent anti-androgenic phthalate, were found in the urine of Brazilian pregnant women. Therefore, the present study aimed to evaluate the effects of DiPeP exposure during critical developmental periods on behaviours controlled by sex hormones in rats. Pregnant Wistar rats were treated with DiPeP (1, 10 or 100 mg kg day^-1 ) or canola oil by oral gavage between gestational day 10 and post-natal day (PND) 21. Male offspring were tested in a behavioural battery, including the elevated plus maze task, play behaviour, partner preference and sexual behaviour. After the behavioural tests, the hypothalamus and pituitary of these animals were removed on PND 60-65 and PND 145-160 to quantify gene expression for aromatase, androgen receptor (Ar) and oestrogen receptors α (Esr1) and β (Esr2). Male rats exposed to 1 and 10 mg kg day^-1 DiPeP displayed no preference for the female stimulus rat in the partner preference test and 1 mg kg day^-1 DiPeP rats also showed a significant increase in mount and penetration latencies when mated with receptive females. A decrease in pituitary Esr1 expression was observed in all DiPeP treated groups regardless of age. A reduction in hypothalamic Esr1 expression in rats exposed to 10 mg kg day^-1 DiPeP was also observed. No significant changes were found with respect to Ar, Esr2 and aromatase expression in the hypothalamus. These results suggest that DiPeP exposure during critical windows of development in rats may induce changes in behaviours related to mating and the sexual motivation of males.

17β-Estradiol augments antidepressant efficacy of escitalopram in ovariectomized rats: Neuroprotective and serotonin reuptake transporter modulatory effects

The prevalence or recurrence of depression is seriously increased in women during the transition to and after menopause. The chronic hypo-estrogenic state of menopause may reduce the response to antidepressants; however the influence of estrogen therapy on their efficacy is still controversial. This study aimed at investigating the effects of combining escitalopram with 17β-estradiol on depression and cognitive impairment induced by ovariectomy, an experimental model of human menopause. Young adult female Wistar rats were subjected to either sham operation or ovariectomy. Ovariectomized animals were treated chronically with escitalopram (10mg/kg/day, i.p) alone or with four doses of 17β-estradiol (40μg/kg, s.c) given prior to the behavioral tests. Co-administration of 17β-estradiol improved escitalopram-induced antidepressant effect in forced swimming test verified as more prominent decrease in the immobility time without opposing its memory enhancing effect in Morris water maze. 17β-estradiol augmented the modulatory effects of escitalopram on the hippocampal levels of brain-derived neurotrophic factor and serotonin reuptake transporter as well as tumor necrosis factor-alpha without altering its effects on the gene expressions of serotonin receptor 1A, estrogen receptors alpha and beta, or acetylcholinestearase content. This combined therapy afforded synergistic protective effects on the brain histopathological architecture, particularly, the hippocampus. The antidepressant effect of 17β-estradiol was abolished by pretreatment with estrogen receptor antagonist, tamoxifen (10mg/kg, p.o). In conclusion, 17β-estradiol-induced antidepressant effect was confined to intracellular estrogen receptors activation. Moreover, 17β-estradiol enhanced escitalopram's efficiency in ameliorating menopausal-like depression, via exerting synergistic neuroprotective and serotonin reuptake transporter modulatory effects, without impeding escitalopram-mediated cognitive improvement.

Dynamic postnatal developmental and sex-specific neuroendocrine effects of prenatal polychlorinated biphenyls in rats

Gestational exposures to estrogenic compounds, both endogenous hormones and exogenous endocrine-disrupting chemicals (EDCs), have long-term effects on reproductive physiology and behavior. We tested the hypothesis that prenatal treatment of rats with low doses of Aroclor 1221 (A1221), a weakly estrogenic polychlorinated biphenyl mix previously used in industry, or estradiol benzoate (EB), alters development of the hypothalamus in a sexually dimorphic manner and subsequently perturbs reproductive function. Pregnant Sprague-Dawley rats were injected on embryonic days 16 and 18 with vehicle (dimethylsulfoxide), A1221 (1 mg/kg), or EB (50 μg/kg). Developmental milestones were monitored, and on postnatal days 15, 30, 45, and 90, 1 male and 1 female per litter were euthanized. Because of their key roles in the mediation of steroid actions on reproductive function, the anteroventral periventricular nucleus (AVPV) and the arcuate nucleus (ARC) were punched for a low-density quantitative PCR array of 48 neuroendocrine genes and analysis of DNA methylation of a subset of genes. Gestational exposure to A1221 or EB delayed the timing of puberty in males and disrupted estrous cyclicity in females. In the AVPV, 28 genes were affected by treatment in a developmental stage-specific manner, mostly in females, which exhibited a masculinized expression profile. This included 2 clock genes, Per2 and Arntl, implicating circadian circuits as being vulnerable to endocrine disruption. DNA methylation analysis of 2 genes, Per2 and Ar, showed no effect of EDCs and suggested alternative mechanisms for the altered mRNA levels. In the ARC, 12 genes were affected by treatment, mostly in males, again with dynamic developmental changes. Bionetwork analysis of relationships among genes, hormones, and physiological markers showed sexually dimorphic effects of estrogenic EDC exposures, with the female AVPV and the male ARC being most vulnerable, and provided novel relationships among hypothalamic genes and postnatal reproductive maturation.

Hormonal imprinting in the central nervous system: causes and consequences

The notion of the perinatal „hormonal imprinting” has been published at first in 1980 and since that time it spred expansively. The imprintig develops at the first encounter between the developing receptor and the target hormone – possibly by the alteration of the methylation pattern of DNA – and it is transmitted to the progeny generations of the cell. This is needed for the complete development of the receptor’s binding capacity. However, molecules similar to the target hormone (hormone-analogues, drugs, chemicals, environmental pollutants) can also bind to the developing receptor, causing faulty imprinting with life-long consequences. This can promote pathological conditions. Later it was cleared that in other critical periods such as puberty, imprinting also can be provoked, even in any age in differentiating cells. The central nervous system (brain) also can be mistakenly imprinted, which durably influences the dopaminergic, serotonergic and noradrenergic system and this can be manifested – in animal experiments – in alterations of the sexual and social behavior. In our modern age the faulty hormonal imprintig is inavoidable because of the mass of medicaments, chemicals, the presence of hormone-like materials (e.g. soya phytosteroids) in the food, and environmental pollutants. The author especially emphasizes the danger of oxytocin, as a perinatal imprinter, as it is used very broadly and can basically influence the emotional and social spheres and the appearance of certain diseases such as auitism, schizophrenia and parkinsonism. The danger of perinatal imprinters is growing, considering their effects on the human evolution. Orv. Hetil., 2013, 154, 128–135.

Effects of the natural endocrine disruptor equol on the pituitary function in adult male rats

Equol (EQ), a potent biologically active metabolite of the soy isoflavone daidzein, interacts with estrogen receptors (ERs), however, as suggested recently, EQ may also exert anti-androgenic actions in androgen regulated tissues like prostate and seminal vesicles in adult male rats. However, data regarding a putative anti-androgenic activity of EQ on pituitary function in male individuals are still lacking. Therefore, we investigated the effects of EQ on androgen- and estrogen-regulated gene expressions in the pituitary and circulating luteinizing hormone (LH) and prolactin (PRL) levels in adult male rats. 3-Month-old male Sprague-Dawley rats (n=12 per group) were treated by gavage for 5 days with either EQ (100 and 250 mg/kg BW/day) or vehicle olive oil (1 ml/rat/day). As reference compound, the pure anti-androgenic drug flutamide (FLUT) was employed at a dose of 100 mg/kg BW/day. At day 5, animals were sacrificed. Levels of pituitary hormones and gene expression were measured by radioimmunoassays and quantitative TaqMan(®) real-time reverse transcription polymerase chain reaction, respectively. The present findings revealed that the pituitary mechanisms involved in the effects of EQ and FLUT were different due to the opposite changes in the mRNA expression levels of estrogen receptor subtype alpha (ERα)-, truncated estrogen receptor product-1 (TERP-1)- and -2 (TERP-2)-, gonadotropin releasing hormone receptor (GnRH receptor)-, beta-subunit of LH (LHβ)-, and gonadotropin alpha subunit (α-subunit) genes. EQ displayed typical ER-agonistic actions as shown by the significant increases in ERα-, TERP-1/-2 mRNA expressions and serum PRL levels along with the significant reduction in serum LH levels, whereas FLUT exerted opposite effects on gonadotropin secretion and expression. Taken together, our findings are the first in vivo data that upon sub-acute oral exposure of EQ show an estrogenic effect on reproductive endocrine activity of the pituitary in adult male rats. However, EQ did not exert anti-androgenic effects on male rat pituitary function as observed at the levels of mRNA expression of androgen- and estrogen-regulated genes and circulating pituitary hormones.

Retinoic acid stimulates 17beta-estradiol and testosterone synthesis in rat hippocampal slice cultures

The hippocampus is essentially involved in learning and memory processes. Its functions are affected by various neuromodulators, including 17beta-estradiol, testosterone, and retinoid. Brain-synthesized steroid hormones act as autocrine and paracrine modulators. The regulatory mechanism underlying brain steroidogenesis has not been fully elucidated. Synthesis of sex steroids in the gonads is stimulated by retinoic acids. Therefore, we examined the effects of retinoic acids on estradiol and testosterone biosynthesis in the rat hippocampus. We used cultured hippocampal slices from 10- to 12-d-old male rats to investigate de novo steroidogenesis. The infant rat hippocampus possesses mRNAs for steroidogenic enzymes and retinoid receptors. Slices were used after 24 h of preculture to obtain maximal steroidogenic activity because steroidogenesis in cultured slices decreases with time. The mRNA levels for P450(17alpha), P450 aromatase and estrogen receptor-beta in the slices were increased by treatment with 9-cis-retinoic acid but not by all-trans-isomer. The magnitude of stimulation and the shape of the dose-response curve for the mRNA level for P450(17alpha) were similar to those for cellular retinoid binding protein type 2, the transcription of which is activated by retinoid X receptor signaling. 9-cis-Retinoic acid also induced a 1.7-fold increase in the protein content of P450(17alpha) and a 2-fold increase in de novo synthesis of 17beta-estradiol and testosterone. These steroids may be synthesized from a steroid precursor(s), such as pregnenolone or other steroids, or from cholesterol, as so-called neurosteroids. The stimulation of estradiol and testosterone synthesis by 9-cis-retinoic acid might be caused by activation of P450(17alpha) transcription via retinoid X receptor signaling.

Developmental profiles of neuroendocrine gene expression in the preoptic area of male rats

Reproductive function is controlled by GnRH cells and their steroid-sensitive regulatory inputs. The proper maturation of this system is critical to sexual development and maintenance of adult function. However, the molecular mechanisms underlying these developmental changes, and the potential roles of gonadal hormones in sculpting these processes, have not been fully explored. We performed a developmental profile from postnatal day (P) 1 through P60 of a network of five genes in the preoptic area (POA) that are critical to reproduction in male Sprague Dawley rats. GnRH, estrogen receptors-alpha, and -beta, androgen receptor (AR), and progesterone receptor (PR) mRNAs in the POA were assayed, and serum hormones were measured, in developing male rats. We also used a Taqman low-density array to identify candidate genes that may be important in development. Of the five targeted genes, only AR and PR changed robustly (7- and 3- to 4-fold increases, respectively) during development. All of the gonadal serum hormones changed markedly and with very different patterns from their receptor mRNAs: testosterone decreased from P1 to P30 and then increased to P60; progesterone peaked on P30; and estradiol decreased from P1 to P30. Using the Taqman low-density array, we identified several genes that changed dramatically in the POA with development, particularly G protein-coupled receptor 30, IGF-I, vitamin D receptor, estrogen-related receptor-alpha, and thyroid receptor-alpha. Our data demonstrate developmental stage-specific changes in neuroendocrine genes, particularly AR and PR. Moreover, the relationships between hormones and their corresponding receptors undergo dynamic changes across development in male rats.

Persistent impairment of hypothalamic KiSS-1 system after exposures to estrogenic compounds at critical periods of brain sex differentiation

Attainment of reproductive capacity at puberty relies on a complex series of maturational events that include sexual differentiation of the brain; a hormonally driven phenomenon that takes place at early stages of development (critical period). Alterations of sex steroid milieu during such critical period disrupt pubertal maturation and gonadotropic function later in life, through mechanisms that remain partially unknown. Kisspeptins, products of the KiSS-1 gene acting via G protein-coupled receptor 54, have recently emerged as essential gatekeepers of puberty onset and reproductive function. By using rat models of neonatal administration of estrogenic compounds, we provide herein compelling evidence for the functional impairment of the hypothalamic KiSS-1 system at the time preceding puberty after early inappropriate exposures during brain sex differentiation. Neonatal injection of estradiol benzoate to male and female rats resulted in a dose-dependent decrease in hypothalamic KiSS-1 mRNA levels at the prepubertal stage, linked to lowering of serum LH concentrations. Yet, despite persistently decreased basal gonadotropin levels in estrogenized animals, intracerebral injection of kisspeptin evoked potent LH and FSH secretory responses, similar in magnitude to those of control animals. Estrogenized rats also showed defective levels of hypothalamic KiSS-1 mRNA and circulating gonadotropins in response to gonadectomy, whereas exogenous kisspeptin was capable to enhance further LH and FSH secretion in this model. Finally, protocols of neonatal exposure to high doses of an environmentally relevant estrogen, bisphenol-A, mimicked the effects of estradiol benzoate in terms of hypothalamic expression of KiSS-1 gene at the prepubertal period. Altogether, our data document the sensitivity of the hypothalamic KiSS-1 system to alterations in sex steroid milieu during critical periods of brain sex differentiation, and suggest that lowering of endogenous kisspeptin tone induced by early exposures to xeno-estrogens might be mechanistically relevant for disruption of gonadotropin secretion and puberty onset later in life.

Aromatase and 5alpha-reductase inhibition during an exogenous testosterone clamp unveils selective sex steroid modulation of somatostatin and growth hormone secretagogue actions in healthy older men

BACKGROUND

How endogenous testosterone (Te), 5alpha-dihydrotestosterone (DHT), and estradiol (E(2)) regulate pulsatile GH secretion is not understood.

HYPOTHESIS

Conversion of Te to androgenic (Te-->DHT) or estrogenic (Te-->E(2)) products directs GH secretion. SUBJECTS AND LOCATION: Healthy older men (N = 42, ages 50-79 yr) participated at an academic medical center.

METHODS

We inhibited 5alpha-reduction with dutasteride and aromatization with anastrozole during a pharmacological Te clamp and infused somatostatin (SS), GHRH, GH-releasing peptide-2 (GHRP-2), and L-arginine/GHRH/GHRP-2 (triple stimulus) to modulate GH secretion.

ENDPOINTS

Deconvolution-estimated basal and pulsatile GH secretion was assessed.

RESULTS

Administration of Te/placebo elevated Te by 2.8-fold, DHT by 2.6-fold, and E(2) concentrations by 1.9-fold above placebo/placebo. Te/dutasteride and Te/anastrozole reduced stimulated DHT and E(2) by 89 and 86%, respectively. Stepwise forward-selection regression analysis revealed that 1) Te positively determines mean (P = 0.017) and peak (P < 0.001) GH concentrations, basal GH secretion (P = 0.015), and pulsatile GH secretion stimulated by GHRP-2 (P < 0.001); 2) Te and E(2) jointly predict GH responses to the triple stimulus (positively for Te, P = 0.006, and negatively for E(2), P = 0.031); and 3) DHT correlates positively with pulsatile GH secretion during SS infusion (P = 0.011). These effects persisted when abdominal visceral fat was included in the regression.

CONCLUSION

The present outcomes suggest a tetrapartite model of GH regulation in men, in which systemic concentrations of Te, DHT, and E(2) along with abdominal visceral fat determine the selective actions of GH secretagogues and SS.

Spatiotemporal dynamics of the expression of estrogen receptors in the postnatal mouse brain

This study reports on the spatiotemporal dynamics of the expression of estrogen receptors (ERs) in the mouse central nervous system (CNS) during the early postnatal and the peripubertal period. At postnatal day 7 (P7), neurons with strong nuclear immunostaining for both ERalpha and ERbeta1 were widely distributed throughout the brain. Sucrose density gradient sedimentation followed by western blotting supported the histochemical evidence for high levels of both ERs at P7. Over the following 2 days, there was a rapid downregulation of ERs. At P9, ERalpha expression was visible only in the hypothalamic area. Decline in ERbeta1 expression was slower than that of ERalpha, and ERalpha-negative, ERbeta1-positive cells were observed in the dentate gyrus and walls of third ventricle. Between P14 and P35, ERs were undetectable except for the hypothalamic area. As before P7, the ovary does not produce estrogen but does produce 5alpha-androstane-3beta, 17beta-diol (3betaAdiol), an estrogenic metabolite of dihydrotestosterone, we examined the effects of high levels of 3betaAdiol in the postnatal period. We used CYP7B1 knockout mice which cannot hydroxylate and inactivate 3betaAdiol. The brains of these mice are abnormally large with reduced apoptosis. In the early postnatal period, there was 1-week delay in the timing of the reduction in ER expression in the brain. These data reveal that the time when ERs might be activated in the brain is limited to the first 8 postnatal days. In addition, the importance of aromatase has to be reconsidered as the alternative estrogen, 3betaAdiol, is important in neuronal function in the postnatal brain.

Effects of a 5-day treatment with vinclozolin on the hypothalamo-pituitary-gonadal axis in male rats

Vinclozolin (VZ), a potent antiandrogenic fungicide, is known to interfere with male reproductive function. Little data are currently available regarding possible impacts of VZ on brain function, particularly neuroendocrine activity and regulation of the hypothalamo-pituitary-gonadal (HPG) axis. Therefore, we examined the effects of VZ on gene expression in the brain (MBH/ME, MPOA/AH, striatum, hippocampus), pituitary, prostate, seminal vesicles, and epididymis of 4-month-old male rats treated daily by gavage for 5 days with VZ (150 mg/kg body weight/day). Alterations in levels of serum hormones and gene expression were determined by RIA and qRT-PCR, respectively. Our results revealed that (i) VZ decreases epididymis weights, increases serum levels of LH and T, and decreases serum TSH and total T(4) levels; (ii) VZ affects the hypothalamic expression of both estrogen receptor (ERs) subtypes, ERalpha and ERbeta; (iii) in the extrahypothalamic brain areas, VZ alters expression of ERs and androgen receptor (AR); (iv) in the pituitary, VZ up-regulates expression of the GnRH receptor, LHbeta, alpha-subunit, and TERP-1/-2; (v) in the ventral prostate, VZ increases and decreases levels of AR and ERbeta mRNA, respectively; (vi) in the seminal vesicles, VZ increases levels of AR and ERalpha mRNA expressions; (vii) in the epididymis, VZ up-regulates AR and ERbeta mRNA expression. These results indicate that in vivo VZ is not a 'pure' antiandrogen, since it exerts mixed AR antagonistic/ERs agonistic actions observed at the levels of mRNA expression of selected androgen- and estrogen-regulated genes in the CNS, pituitary, and male accessory sex organs.

Hypothalamus region-specific global gene expression profiling in early stages of central endocrine disruption in rat neonates injected with estradiol benzoate or flutamide

To identify genes linked to early stages of disruption of brain sexual differentiation, hypothalamic region-specific microarray analyses were performed using a microdissection technique with neonatal rats exposed to endocrine-acting drugs. To validate the methodology, the expression fidelity of microarrays was first examined with two-round amplified antisense RNAs (aRNAs) from methacarn-fixed paraffin-embedded tissue (PET) in comparison with expression in unfixed frozen tissue (UFT). Decline of expression fidelity when compared with the 1x-amplified aRNAs from UFTs was found as a result of the preferential amplification of the 3' side of mRNAs in the second round in vitro transcription. However, expression patterns for the 2x-amplified aRNAs were mostly identical between methacarn-fixed PET and UFT, suggesting no obvious influence of methacarn fixation and subsequent paraffin embedding on expression levels. Next, in the main experiment, neonatal rats at birth were treated subcutaneously either with estradiol benzoate (EB; 10 microg/pup) or flutamide (FA; 250 microg/pup), and medial preoptic area (MPOA)-specific microarray analysis was performed 24 h later using 2x-amplified aRNAs from methacarn-fixed PET. Numbers of genes showing constitutively high expression in the MPOA predominated in males, implying a link with male-type growth supported by perinatal testosterone. Around 60% of genes showing sex differences in expression demonstrated altered levels after EB treatment in females, suggesting an involvement of genes necessary for brain sexual differentiation. When compared with EB, FA affected a rather small number of genes, but fluctuation was mostly observed in females, as with EB. Moreover, many selected genes common to EB and FA showed down-regulation in females with both drugs, suggesting a common mechanism for endocrine center disruption in females, at least at early stages of post-natal development.

Sexually dimorphic gene regulation in brain as a target for endocrine disrupters: developmental exposure of rats to 4-methylbenzylidene camphor

The developing neuroendocrine brain represents a potential target for endocrine active chemicals. The UV filter 4-methylbenzylidene camphor (4-MBC) exhibits estrogenic activity, but also interferes with the thyroid axis. We investigated effects of pre- and postnatal exposure to 4-MBC in the same rat offspring at brain and reproductive organ levels. 4-MBC (7, 24, 47 mg/kg/day) was administered in chow to the parent generation before mating, during gestation and lactation, and to the offspring until adulthood. mRNA of estrogen target genes involved in control of sexual behavior and gonadal functions was measured by real-time RT-PCR in ventromedial hypothalamic nucleus (VMH) and medial preoptic area (MPO) of adult offspring. 4-MBC exposure affected mRNA levels of ER alpha, progesterone receptor (PR), preproenkephalin (PPE) and insulin-like growth factor-I (IGF-I) in a sex- and region-specific manner. In order to assess possible changes in sensitivity of target genes to estrogens, offspring were gonadectomized on day 70, injected with estradiol (E2, 10 or 50 microg/kg s.c.) or vehicle on day 84, and sacrificed 6 h later. The acute induction of PR mRNA, and repression (at 6 h) of PPE mRNA by E2 was enhanced by 4-MBC in male and female VMH and female MPO, whereas male MPO exhibited reduced responsiveness of both genes. Steroid receptor coactivator SRC-1 mRNA levels were increased in female VMH and MPO. The data indicate profound sex- and region-specific alterations in the regulation of estrogen target genes at brain level. Effect patterns in baseline and E2-induced gene expression differ from those in uterus and prostate.

Persistent sex-reversal and oviducal agenesis in adult Xenopus (Silurana) tropicalis frogs following larval exposure to the environmental pollutant ethynylestradiol

It is known that estrogen-like environmental pollutants can feminise gonadal differentiation in frogs resulting in female-biased sex-ratios at metamorphosis. The long-term effects on reproductive function in frogs following larval exposure to pollutants are less known. Amphibian test systems which allow life-cycle studies are therefore needed. The aim of the present study was to characterise long-term estrogenic effects on the reproductive system of the emerging model species Xenopus (Silurana) tropicalis following larval exposure to ethynylestradiol (EE(2)). EE(2) is a synthetic estrogen that has been detected in sewage effluents and in surface waters. Newly hatched tadpoles (Niewkoop Faber (NF) stage 48) were exposed to the nominal EE(2) concentrations 0 (control), 1, 10, and 100 nM (with analytical chemistry support) until complete metamorphosis (NF stage 66). Effects on the reproductive organs were determined in juveniles (1 month after metamorphosis) and in 9-month-old frogs. Larval exposure to EE(2) caused female-biased phenotypic sex-ratios in both juvenile and adult frogs, which is in agreement with previous work on other frog species. Nearly all (97%) of the 63 EE(2)-exposed 9-month-old frogs had ovaries. Histological evaluation of the gonads of the 9-month-old frogs showed that they were sexually mature. Among the adult frogs with ovaries there was a dose-dependent increase in the frequency of individuals lacking oviducts. Adult frogs exposed to 100 nM EE(2) that had ovaries but no oviducts had lower levels of estrogen receptor alpha (ERalpha) mRNA in the brain than control animals and those exposed to 100 nM EE(2) that had ovaries as well as oviducts. EE(2) exposure did not cause any significant changes in ERalpha mRNA levels in the ovaries of the adult frogs. The reduced level of ERalpha mRNA in the brain of individuals with ovaries lacking oviducts suggests an organizing effect of EE(2) on the central nervous system. The results show that transient early life-stage exposure to an environmental pollutant can induce effects on the reproductive organs and the central nervous system that persist into adulthood. Overall, our data suggest that X. tropicalis, which has a shorter generation time than the well-established model species Xenopus laevis, is a suitable model organism for research on developmental reproductive toxicity in anuran species.

Seminiferous cord formation and germ-cell programming: epigenetic transgenerational actions of endocrine disruptors

The molecular and cellular control of embryonic testis development was investigated through an analysis of the embryonic testis transcriptome to identify potential regulatory factors for male sex determination and testis morphogenesis. One critical factor identified is neurotropin 3 (NT3). At the onset of male sex determination, Sertoli cells initiate differentiation and express NT3 to act as a chemotactic factor for mesonephros cells to migrate and associate with Sertoli-germ cell aggregates to promote cord formation. Promoter analysis suggests that NT3 may be an initial downstream gene to SRY and helps promote testis morphogenesis. Endocrine disruptors were used to potentially interfere with embryonic testis development and further investigate this biological process. The estrogenic pesticide methoxychlor and antiandrogenic fungicide vinclozolin were used. Previous studies have shown that methoxychlor and vinclozolin both interfere with embryonic testis cord formation and cause increased spermatogenic cell apoptosis in the adult testis. Interestingly, transient in vivo exposure to endocrine disruptors at the time of male sex determination caused a transgenerational phenotype (F1-F4) of spermatogenic cell apoptosis and subfertility. This apparent epigenetic mechanism involves altered DNA methylation and permanent re-programming of the male germ-line. A series of genes with altered DNA methylation and imprinting are being identified. Observations reviewed demonstrate that a transient embryonic in utero exposure to an endocrine disruptor influences the embryonic testis transcriptome and through epigenetic effects (e.g., DNA methylation) results in abnormal germ-cell differentiation that subsequently influences adult spermatogenic capacity and male fertility, and that this phenotype is transgenerational through the germ-line. The novel observations of transgenerational epigenetic endocrine disruptor actions on male reproduction critically impact the potential hazards of these compounds as environmental toxins. The literature reviewed provides insight into the molecular and cellular control of embryonic testis development, male sex determination, and the programming of the male germ-line.

Two estrogen replacement therapies differentially regulate expression of estrogen receptors alpha and beta in the hippocampus and cortex of ovariectomized rat

As estrogens have been implicated in altered cognitive function associated with menopause, the purpose of the present study was to determine the regulatory effects of different estrogen preparations on the expression of estrogen receptor subtypes in the hippocampus and cortex of ovariectomized rats. The expression of estrogen receptor mRNA and protein was determined with RT-PCR and immunohistochemistry, respectively. Two estrogen reagents, Premarin and Progynova, were used in the present study. Premarin, a conjugated equine estrogen, down-regulated ER alpha expression in the hippocampus and cortex of ovariectomized rats and had no effect on levels of ER beta expression in the same two regions. However, Progynova (valerate estradiol) was shown to up-regulate ER beta expression in the hippocampus and cortex and had no effect on the levels of ER alpha expression. Our present data suggest that different estrogen reagents used in estrogen replacement therapy could have different regulatory effects on the expression of estrogen receptor subtypes, which might, at least in part, explain why clinically, different estrogen preparations have distinct estrogenic effects on target organs.

Is the brain hormonally imprintable?

Hormonal imprinting develops at the first encounter between the target hormone and its developing receptor in the perinatal critical period. This determines the binding and response capacity of the receptor-signal transduction system and hormone production of cells for life. Molecules similar to the hormone and excess or absence of the target hormone cause faulty imprinting with lifelong consequences. Prenatal or neonatal imprinting with opiates, other drugs and prenatal stress have harmful consequences on the adult brain. Perinatal imprinting with endorphin or serotonin decreases the serotonin level of the brain while increasing sexual activity and (as in the case of endorphin) aggression. Endorphin or serotonin antagonist treatment at weaning (late imprinting) also significantly reduces the serotonin content of the brain. Backed by literary data, these observations are discussed, and the possible consequences of medical treatments are shown. The paper concludes that an excess of molecules produced by the brain itself can provoke perinatal imprinting, and it points to the possibility of late imprinting of the brain by receptor level acting agents, including a brain product (endorphin).

Infantile 4-tert-octylphenol exposure transiently inhibits rat ovarian steroidogenesis and steroidogenic acute regulatory protein (StAR) expression

Phenolic compounds, such as 4-tert-octylphenol (OP), have been shown to interfere with rat ovarian steroidogenesis. However, little is known about steroidogenic effects of infantile OP exposure on immature ovary. The aim of the present study was to investigate the effects of infantile OP exposure on plasma FSH, LH, estradiol, and progesterone levels in 14-day-old female rats. The effect on ovarian steroidogenic acute regulatory protein (StAR) and FSH receptor (FSHr) expression was analyzed by Western blotting. Ex vivo analysis was carried out for follicular estradiol, progesterone, testosterone, and cAMP production. Sprague-Dawley rats were given OP (0, 10, 50, or 100 mg/kg) subcutaneously on postnatal days 6, 8, 10, and 12. On postnatal day 14, plasma FSH was decreased and progesterone increased significantly at a dose of 100 mg OP/kg. In addition, the highest OP dose advanced the time of vaginal opening in puberty. OP had no effect on infantile LH and estradiol levels or ovarian FSHr content. Ovarian StAR protein content and ex vivo hormone and cAMP production were decreased at all OP doses compared to controls. However, hormone levels recovered independent on FSH and even increased above the control level during a prolonged culture. On postnatal day 35, no statistically significant differences were seen between control and OP-exposed animals in plasma FSH, LH, estradiol, and progesterone levels, or in ovarian StAR protein content. The results indicate that the effect of OP on the infantile ovary is reversible, while more permanent effects in the hypothalamus and pituitary, as described earlier, are involved in the reduction of circulating FSH levels and premature vaginal opening.

Suppressive effect of neonatal treatment with a phytoestrogen, coumestrol, on lordosis and estrous cycle in female rats

The neural control systems for the ovulatory cycle and lordosis behavior are sexually differentiated by estrogen during the perinatal period in rats. In the present study, the effects of a single neonatal injection with the phytoestrogen, coumestrol, on female reproductive functions were investigated. Female rats were injected subcutaneously with 1 or 3mg coumestrol (CM1, CM3), 1mg genistein (GS1), 1mg estradiol (E2), or oil at day 5 after birth (birth day=day 1) and an estrous cycle check and lordosis behavior test were performed. As a result, vaginal opening was advanced in CM1-, CM3- or E2-treated females. A vaginal smear check indicated that oil- or GS1-treated females showed a constant 4- or 5-day estrous cycle, whereas CM1-, CM3- or E2-treated rats showed a persistent or prolonged estrus. Ovariectomy was performed in all females at 60 days of age. The ovary weights in the CM1-, CM3- or E2-treated groups were lower than those in the oil- and GS1-treated groups and no corpora lutea were found in any rats of these three groups, except for two E2-treated rats. Behavioral tests were carried out after implantation of E2-tubes. All rats in the CM1-, GS1-treated groups showed a high lordosis quotient (LQ), being comparable to that in the oil-treated females. On the other hand, LQs in the CM3, E2 or male groups were lower than that in the control female group. These results suggest that a single neonatal injection of 3 mg coumestrol was effective in suppressing the functions of ovulation-inducing mechanisms and the induction of lordosis, but 1mg coumestrol was effective in only the estrous cycle of female rats.

Neurosteroid synthesis in the hippocampus: Role in synaptic plasticity

Neurosteroids are still found in the brain after steroidogenic glands were removed, indicating that they are synthesized either de novo or from endogenous precursors by enzymes present in the CNS. In fact, steroidogenic acute regulatory protein, and aromatase, two molecules essential for estrogen synthesis, are expressed in the hippocampus. We recently showed, for the first time, that estrogens are synthesized de novo in hippocampal neurons and that these hippocampus-derived estrogens are essential for synaptic plasticity. Both estrogen receptor isoforms, estrogen receptor alpha and estrogen receptor beta, are expressed in the hippocampus, and estradiol treatment of the cultures leads to an upregulation of estrogen receptor alpha. This finding confirmed the presence of functional estrogen receptors in hippocampal neurons and showed the responsiveness of the cultured hippocampal neurons to estradiol. By using letrozole, an inhibitor of aromatase, estradiol levels in hippocampal dispersion cultures as well as in hippocampal slice cultures were significantly suppressed which in turn led to a downregulation of estrogen receptor alpha. Letrozole treatment was followed by a significant decrease in the density of spines and spine synapses and in the number of presynaptic boutons. Quantitative immunohistochemistry revealed a dose-dependent downregulation of spinophilin, a spine marker, and of synaptophysin, a presynaptic marker, and of growth-associated protein 43 after letrozole treatment. Our data provide strong evidence for estrogens being potent modulators of structural synaptic plasticity and point to a paracrine rather than endocrine mechanism of estrogen action in the hippocampus.

Developmental and hormonally regulated messenger ribonucleic acid expression of KiSS-1 and its putative receptor, GPR54, in rat hypothalamus and potent luteinizing hormone-releasing activity of KiSS-1 peptide

The gonadotropic axis is centrally controlled by a complex regulatory network of excitatory and inhibitory signals that is activated at puberty. Recently, loss of function mutations of the gene encoding G protein-coupled receptor 54 (GPR54), the putative receptor for the KiSS-1-derived peptide metastin, have been associated with lack of puberty onset and hypogonadotropic hypogonadism. Yet the pattern of expression and functional role of the KiSS-1/GPR54 system in the rat hypothalamus remain unexplored to date. In the present work, expression analyses of KiSS-1 and GPR54 genes were conducted in different physiological and experimental settings, and the effects of central administration of KiSS-1 peptide on LH release were assessed in vivo. Persistent expression of KiSS-1 and GPR54 mRNAs was detected in rat hypothalamus throughout postnatal development, with maximum expression levels at puberty in both male and female rats. Hypothalamic expression of KiSS-1 and GPR54 genes changed throughout the estrous cycle and was significantly increased after gonadectomy, a rise that was prevented by sex steroid replacement both in males and females. Moreover, hypothalamic expression of the KiSS-1 gene was sensitive to neonatal imprinting by estrogen. From a functional standpoint, intracerebroventricular administration of KiSS-1 peptide induced a dramatic increase in serum LH levels in prepubertal male and female rats as well as in adult animals. In conclusion, we provide novel evidence of the developmental and hormonally regulated expression of KiSS-1 and GPR54 mRNAs in rat hypothalamus and the ability of KiSS-1 peptide to potently stimulate LH secretion in vivo. Our current data support the contention that the hypothalamic KiSS-1/GPR54 system is a pivotal factor in central regulation of the gonadotropic axis at puberty and in adulthood.

EXPRESSION OF ESTROGEN RECEPTOR α AND PROGESTERONE RECEPTOR IN CHILDREN WITH UNDESCENDED TESTICLE PREVIOUSLY TREATED WITH HUMAN CHORIONIC GONADOTROPIN

PURPOSE

The aim of this study was to investigate expression of estrogen receptor alpha (ERalpha) and progesterone receptor (PR) in paratesticular tissues obtained from boys with undescended testes.

MATERIALS AND METHODS

A total of 65 boys with unilateral cryptorchidism and failed human chorionic gonadotropion treatment underwent orchiopexy. A small sample of gubernaculum, cremasteric muscle and processus vaginalis was obtained. A total of 57 boys who underwent inguinal hernia repair served as the control group. All boys in the control group had testes in the scrotum. The expression of estrogen receptor alpha and progesterone receptor was measured by counting the number of ERalpha or PR positive cells detected by immunohistochemical analysis.

RESULTS

ERalpha and PR density was higher in cremasteric muscle and processus vaginalis obtained from boys with undescended testes than in the control group. Density of progesterone receptor in the examined groups was lower than the density of estrogen receptor.

CONCLUSIONS

ERalpha and PR are expressed in paratesticular tissues important for normal testicular descent. ERalpha was over expressed in cremasteric muscle and processus vaginalis in boys with undescended testes previously treated with human chorionic gonadotropin.

Regulation of Estrogen Receptor (ER) Isoform Messenger RNA Expression by Different ER Ligands in Female Rat Pituitary1

Net estrogen sensitivity in target tissues critically depends on the regulated expression of full-length and alternately processed estrogen receptor (ER) isoforms. However, the molecular mechanisms for the control of pituitary responsiveness to estrogen remain partially unknown. In the present communication, we report the ability of different ligands, with distinct agonistic or antagonistic properties at the ER, to modulate the expression of the transcripts encoding ERalpha and ERbeta isoforms, as well as those for the truncated ERalpha product (TERP), and the variant ERbeta2, in pituitaries from ovariectomized rats, i.e., a background devoid of endogenous estrogen. Compared with expression levels at the morning of proestrus, ovariectomy (OVX) resulted in increased pituitary expression of ERbeta and ERbeta2 mRNAs, whereas it decreased TERP-1 and -2 levels without affecting those of ERalpha. Administration of estradiol benzoate (as potent agonist for alpha and beta forms of ER) or the selective ERalpha agonist, propyl pyrazole triol, fully reversed the responses to OVX, while the ERbeta ligand, diarylpropionitrile, failed to induce any significant effect except for a partial stimulation of TERP-1 and -2 mRNA expression levels. To note, the ERbeta agonist was also ineffective in altering pituitary expression of progesterone receptor-B mRNA, i.e., a major estrogen-responsive target. In all parameters tested, tamoxifen, a selective ER modulator with mixed agonist/antagonist activity, behaved as ERalpha agonist, although the magnitude of tamoxifen effects was significantly lower than those of the ERalpha ligand, except for TERP induction. In contrast, the pure antiestrogen RU-58668 did not modify the expression of any of the targets under analysis. Overall, our results indicate that endogenous estrogen differentially regulates pituitary expression of the mRNAs encoding several ER isoforms with distinct functional properties, by a mechanism that is mostly conducted through ERalpha. Differential regulation of ER isoforms may represent a relevant system for the self-tuning of estrogen responsiveness in female pituitary.

What pharmacologists can learn from recent advances in estrogen signalling

The discovery of the second estrogen receptor (ER) in 1995 surprised many endocrinologists and resulted in some scepticism regarding its physiological importance. However, 8 years later, it is clear that the multiple actions of estrogen in the body are mediated by two receptors that, although similar, are distinct gene products with non-overlapping functions. This clear delineation of the functions of the two receptors in such a short time was made possible by the development of ER alpha and ER beta knockout mice. The distinct patterns of tissue distribution of these two receptors has heightened interest in novel estrogen targets in the body and has led to awareness of new sites for pharmacological intervention in diseases such as depression, prostate dysfunction, leukaemia, inflammatory bowel disease and colon cancer.

Effects of neonatal treatment with phytoestrogens, genistein and daidzein, on sex difference in female rat brain function: estrous cycle and lordosis

It is well known that neonatal exposure to estrogen induces masculinization or defeminization of the brain. In this study, the effects of neonatal treatment with two kinds of soybean isoflavone aglycone, genistein (GS) and daidzein (DZ), on the estrous cycle and lordosis behavior were investigated. Female rats were injected subcutaneously with 1 mg GS, 1 mg DZ, 100 microg estradiol (E2), or oil daily for 5 days from birth. As a result, vaginal opening was advanced in GS- or E2-treated females. A vaginal smear check indicated that oil- or DZ-treated females showed a constant 4- or 5-day estrous cycle, whereas GS- or E2-treated rats showed a persistent or prolonged estrus. Ovariectomy was performed in all females at 60 days of age. The ovaries in the GS- or E2-treated groups were smaller than those in the oil- and DZ-treated groups and contained no corpora lutea. In the DZ group, although corpora lutea were seen, ovaries were smaller than that of control females. Behavioral tests were carried out after implantation of E2-tubes. All of the oil- or DZ-treated females showed lordosis with a high lordosis quotient (LQ). On the other hand, as male rats, LQs were extremely low in the E2-treated group, when compared to the oil-treated group. In the GS-treated group, the mean LQ was lower than that in the oil-treated group, but higher than those in the E2-treated female or male groups. These results suggest that genistein acts as an estrogen in the sexual differentiation of the brain and causes defeminization of the brain in regulating lordosis and the estrous cycle in rats. In addition, neonatal daidzein also has some influence on ovarian function.

Update on estrogen signaling

Our understanding of estrogen signaling has undergone a true paradigm shift over recent years, following the discovery in 1995 of a second estrogen receptor, estrogen receptor beta (ERbeta). In many contexts ERbeta appears to antagonize the actions of ERalpha (yin/yang relationship) although there also exist genes that are specifically regulated by one of the two receptors. Studies of ERbeta knockout mice have shown that ERbeta exerts important functions in the ovary, central nervous system, mammary gland, prostate gland, hematopoiesis, immune system, vessels and bone. The use of ERbeta-specific ligands against certain forms of cancer represents one of the many pharmaceutical possibilities that have been created thanks to the discovery of ERbeta.

Para/autocrine regulation of estrogen receptors in hippocampal neurons

Previous studies have shown that estrogens, originating from ovaries, have a wide variety of estrogen receptor (ER)-mediated effects in the hippocampus. In the present study, we have investigated whether estrogens, which are synthesized in the hippocampus, could induce these effects as well. As a parameter, we used ER expression in response to estrogen synthesis, because estrogen receptors are ligand-inducible transcription factors. The experiments were carried out with cultures of isolated adult rat hippocampal cells, which contained about 95% neurons and about 5% oligodendrocytes in serum-free and steroid-free medium. Hippocampal neurons express both estrogen receptor isoforms (ERalpha and ERbeta), as shown by reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization. The release of estrogens by hippocampal neurons was quantified by radioimmunoassay (RIA). The ER isoforms (alpha and beta) were studied by semiquantitative immunocytochemical image analysis. Hippocampal cells precultured for 4 days were found to synthesize 17beta-estradiol for the next 8 days. This synthesis was completely inhibited by letrozol, an aromatase inhibitor. Inhibition of estrogen synthesis by letrozol induced a significant decrease in ERalpha expression, but an increase in ERbeta. As a control, supplementation of the medium with 17beta-estradiol resulted in a significant increase of ERalpha expression, whereas ERbeta was downregulated. Our findings provide evidence for a de novo synthesis of estrogens in the hippocampus, differential regulation of estrogen receptor isoforms by estrogen and consequently for a para/autocrine loop of estrogen action in the hippocampus.

Estrogen receptor-beta immunoreactivity in the midbrain of adult rats: regional, subregional, and cellular localization in the A10, A9, and A8 dopamine cell groups

Estrogen modulates dopamine synthesis, release, and metabolism in corticolimbic and striatal targets of midbrain dopamine neurons. The relevant sites of receptor-mediated action, however, had been elusive, because all available evidence suggested a paucity of intracellular estrogen receptors in the A8, A9, and A10 dopamine regions and their afferent targets. More recent evidence of a relative abundance of the beta isoform of the estrogen receptor (ER) in the substantia nigra and ventral tegmental area (VTA), however, suggests that this newly described receptor may be important in estrogen's stimulation of midbrain DA systems. It is unknown, however, precisely how ERbeta is distributed with respect to the functionally and neurochemically diverse cell populations of the ventral midbrain. To address these issues, this study used single- and double-label immunocytochemistry to detail the regional, subregional, and cellular distributions of ERbeta immunoreactivity in and around midbrain dopamine-containing cell groups in hormonally intact adult male and female rats. These analyses revealed that ERbeta-immunoreactive nuclei were found only in neurons, more specifically, within subsets of both dopaminergic and nondopaminergic neurons in the dorsal VTA, the parabrachial pigmented nucleus, the substantia nigra pars lateralis, the retrorubral fields, and to a lesser extent the linear midline nuclei. These regional and cellular receptor distributions thus place the ERbeta isoform in anatomical register with midbrain dopamine systems known to participate in a spectrum of motor, cognitive, and affective functions.

Oestrogen receptors, receptor variants and oestrogen actions in the hypothalamic-pituitary axis

Information on oestrogen action has grown exponentially in the past decade, and recent studies have begun to define the mechanism of ligand-dependent activation and cell-specific effects. Oestrogen-mediated gene transcription in a specific tissue depends on several factors, the most important of which is the presence of at least one of the two nuclear oestrogen receptor (ER) isoforms, ER(alpha) and ERbeta. The presence and levels of specific ER isoform variants, along with receptor coactivator, corepressor and integrator proteins, directly modulate overall nuclear ER activity. The structure of the ligand, including both physiological oestrogens and synthetic oestrogen receptor modulators, influences ER interactions with these other proteins and thus determines the biological response. Furthermore, peptide and neurotransmitter-stimulated intracellular signalling pathways activate specific enzyme cascades and may modify the receptors and their interacting proteins, resulting in either independent or ligand-enhanced ER-mediated responses. Finally, several rapid effects of oestrogen probably occur at the membrane through nongenomic pathways that may or may not require the same ER proteins that are found in the nucleus. This review concentrates on the pituitary-hypothalamic axis and the genomic effects of oestrogen, and discusses the current knowledge of each of these factors in determining oestrogen actions in the neuroendocrine system.

Selective estrogen receptor modulator effects in the rat brain

The effects in the brain of selective estrogen receptor modulators (SERMs) such as tamoxifen and raloxifene have not yet been fully elucidated. Based upon the hypothesis that serotonin (5-HT)-steroid hormone interactions are important in mood regulation, we have compared six SERMs (tamoxifen, raloxifene, levormeloxifene, NNC 45-0781, NNC 45-0320, NNC 45-1506) with 17beta-estradiol (E(2)) in terms of their ability to regulate mRNA levels of estrogen receptor (ER)alpha, ER beta, 5-HT(1A) receptor, and 5-HT reuptake transporter (SERT) in the midbrain, amygdala, and hypothalamus of ovariectomized (OVX) rats. Female rats (n = 6/group, 8 groups total) were OVX and allowed to recover for 2 weeks. During the third post-OVX week, rats were injected subcutaneously with E(2) (0.1 mg/kg) or one of the SERMs (5 mg/kg) once per day for 7 days. Twenty-four hours after the last injection, tissue was collected for the determination of mRNA levels by ribonuclease protection assay (RPA). E(2) treatment significantly decreased mRNA levels for ER alpha, ER beta, and SERT in midbrain and ER alpha in hypothalamus. Tamoxifen increased ER beta mRNA levels in hypothalamus, while raloxifene increased ER beta mRNA levels in amygdala. NNC 45-0320 decreased ER alpha mRNA in hypothalamus and decreased ER beta mRNA in amygdala. These results suggest that while SERMs are not full estrogen receptor agonists in the brain, the agonist/antagonist profiles for individual SERMs may differ among brain areas. This raises the possibility of developing new SERMs for selective functions in specific brain areas.

Differential neonatal imprinting and regulation by estrogen of estrogen receptor subtypes alpha and beta and of the truncated estrogen receptor product (TERP-1) mRNA expression in the male rat pituitary

Two distinct nuclear estrogen receptors (ERs) have been identified, the classical one, renamed ERalpha, and the more recently cloned ERbeta. In a variety of tissues, gene expression of both receptor subtypes results in the generation of multiple transcripts encoding the full-length as well as several alternately spliced isoforms. In the rat pituitary, a truncated, tissue-specific variant of ERalpha, called TERP-1, has been identified and found able to modulate ERalpha and ERbeta activity. So far, its pattern of expression and hormonal regulation have been mostly studied in females. The present study was designed to analyze the pattern of expression of TERP-1 mRNA in the male rat pituitary at different stages of postnatal development, and to evaluate the impact of neonatal imprinting and estrogen treatment upon TERP-1 expression in the male pituitary. Assessment of TERP-1 mRNA levels by semi-quantitative RT-PCR, using a variant-specific primer pair, revealed that TERP-1 is also expressed in the male rat pituitary. Relative mRNA expression levels changed markedly during postnatal development, with moderate expression of the TERP-1 transcript at birth, barely detectable levels during the infantile-prepubertal period, and maximal values in adulthood. Expression of TERP-1 was sensitive to neonatal estrogen exposure, which resulted in a significant, persistent increase in mRNA levels from the infantile period until puberty. This phenomenon was not mimicked by neonatal blockade of endogenous GnRH. In addition, estrogen was able to acutely up-regulate pituitary TERP-1 mRNA expression levels in prepubertal (30-day-old) and adult (75-day-old) males. Interestingly, neonatal imprinting as well as acute estrogen treatment resulted in opposite effects on TERP-1 and full-length ERalpha and ERbeta transcripts, the latter being decreased under both conditions. In conclusion, our data indicate that TERP-1 mRNA is expressed in a developmentally regulated manner in the male rat pituitary, and is affected by neonatal estrogen imprinting and acute estrogen treatment. Regulation of TERP-1 expression by neonatal or acute estrogen treatment may thus represent an additional tuning mechanism for estrogen actions in the male rat pituitary.