Brain-derived neurotrophic factor-estrogen interactions in the hippocampal mossy fiber pathway: implications for normal brain function and disease.

The neurotrophin brain-derived neurotrophic factor (BDNF) and the steroid hormone estrogen exhibit potent effects on hippocampal neurons during development and in adulthood. BDNF and estrogen have also been implicated in the etiology of diverse types of neurological disorders or psychiatric illnesses, or have been discussed as potentially important in treatment. Although both are typically studied independently, it has been suggested that BDNF mediates several of the effects of estrogen in the hippocampus, and that these interactions play a role in the normal brain as well as disease. Here we focus on the mossy fiber (MF) pathway of the hippocampus, a critical pathway in normal hippocampal function, and a prime example of a location where numerous studies support an interaction between BDNF and estrogen in the rodent brain. We first review the temporal and spatially regulated expression of BDNF and estrogen in the MFs, as well as their receptors. Then we consider the results of studies that suggest that 17ß-estradiol alters hippocampal function by its influence on BDNF expression in the MF pathway. We also address the hypothesis that estrogen influences the hippocampus by mechanisms related not only to the mature form of BDNF, acting at trkB receptors, but also by regulating the precursor, proBDNF, acting at p75NTR. We suggest that the interactions between BDNF and 17ß-estradiol in the MFs are potentially important in the normal function of the hippocampus, and have implications for sex differences in functions that depend on the MFs and in diseases where MF plasticity has been suggested to play an important role, Alzheimer's disease, epilepsy and addiction.

Chronic stress and neural function: accounting for sex and age.

Cognitive responses to stress follow the temporally dependent pattern originally established by Selye (1) wherein short-term stressors elicit adaptive responses whereas continued stress (chronic) results in maladaptive changes--deleterious effects on physiological systems and impaired cognition. However, this pattern for cognitive effects appears to apply to only half the population (males) and, more specifically, to young, adult males. Females show different cognitive responses to stress. In contrast to impaired cognition in males after chronic stress, female rodents show enhanced performance on the same memory tasks after the same stress. Not only cognition, but anxiety, shows sex-dependent changes following chronic stress--stress is anxiolytic in males and anxiogenic in females. Moreover, behavioral responses to chronic stress are different in developing as well as aging subjects (both sexes) as compared to adults. In aged rats, chronic stress enhances recognition memory in both sexes, does not alter spatial memory, and anxiety effects are opposite to young adults. When pregnant dams are exposed to chronic stress, at adulthood the offspring display yet different consequences of stress on anxiety and cognition, and, in contrast to adulthood when the behavioral effects of stress are reversible, prenatal stress effects appear enduring. Changing levels of estradiol in the sexes over the lifespan appear to contribute to the differences in response to stress. Thus, theories of stress dependent modulations in CNS function--developed solely in male models, focused on peripheral physiological processes and tested in adults--may require revision when applied to a more diverse population (age- and sex-wise) at least in relation to the neural functions of cognition and anxiety. Moreover, these results suggest that other stressors and neural functions should be investigated to determine whether age, sex and gonadal hormones also have an impact.

Androgen modulation of hippocampal synaptic plasticity.

This review briefly summarizes recent developments in our understanding of the role of androgens in maintaining normal hippocampal structure. Studies in rats and vervet monkeys have demonstrated that removal of the testes reduces the density of synaptic contacts on dendritic spines of cornu ammonis 1 (CA1) pyramidal neurons. This effect is rapidly reversed by treatment with either testosterone or the non-aromatizable androgen dihydrotestosterone, suggesting that maintenance of normal synaptic density is androgen-dependent, via a mechanism that does not require intermediate estrogen biosynthesis. Similar effects of these androgens are observed in ovariectomized female rats, except that in the female the actions of testosterone include a substantial contribution from estrogen formation. The ability to stimulate hippocampal spine synapse density is not directly related to systemic androgenic potency: thus, weak androgens such as dehydroepiandrosterone exert effects that are comparable to those of dihydrotestosterone; while partial agonist responses are observed after injection of the synthetic antiandrogen, flutamide. These data provide a morphological counterpart to observations that androgens enhance cognitive function and mood state, suggesting that these effects may result at least in part from hippocampal neurotrophic responses. The unusual specificity of these responses raises the possibility that effects of androgens on the brain may be mediated via different mechanisms than the masculinizing actions of these steroids in non-neural androgen target organs.

Synaptic remodeling induced by gonadal hormones: neuronal plasticity as a mediator of neuroendocrine and behavioral responses to steroids.

During recent decades, it has become a generally accepted view that structural neuroplasticity is remarkably involved in the functional adaptation of the CNS. Thus, cellular morphology in the brain is in continuous transition throughout the life span, as a response to environmental stimuli. The effects of the environment on neuroplasticity are mediated by, to some extent, the changing levels of circulating gonadal steroid hormones. Today, it is clear that the function of gonadal steroids in the brain extends beyond simply regulating reproductive and/or neuroendocrine events. In addition, or even more importantly, gonadal steroids participate in the shaping of the developing brain, while their actions during adult life are implicated in higher brain functions such as cognition, mood and memory. A large body of evidence indicates that gonadal steroid-induced functional changes are accompanied by alterations in neuron and synapse numbers, as well as in dendritic and synaptic morphology. These structural modifications are believed to serve as a morphological basis for changes in behavior and cellular activity. Due to their growing functional and clinical significance, the specificity, timeframe, as well as the molecular and cellular mechanisms of hormone-induced neuroplasticity have become the focus of many studies. In this review, we briefly summarize current knowledge and the most significant recent discoveries from our laboratories on estrogen- and dehydroepiandrosterone-induced synaptic remodeling in the hypothalamus and hippocampus, two important brain areas heavily involved in autonomic and cognitive operations, respectively.

Effects of testosterone on hippocampal CA1 spine synaptic density in the male rat are inhibited by fimbria/fornix transection.

This study investigated the contribution of sub-cortical afferent input to the effects of testosterone (T) on spine synapse density in the CA1 subfield of the hippocampus, in adult male rats. Gonadectomized (GDX) male rats exhibited a considerably lower density of spine synapses in the CA1 region than control, intact males. The effects of GDX were reversed by treatment with testosterone propionate (TP; 500 microg/day, for 2 days). Transection of the fimbria/fornix (FF) had no significant effect on the synaptic density in non-GDX males. However, FF transection partially inhibited the responses to TP in GDX animals. These data suggest that the effects of T on spine synapse density in the CA1 region of the male rat hippocampus are partially, but not completely, dependent on afferent sub-cortical input.

Ovarian steroids reduce apoptosis induced by trophic insufficiency in nerve growth factor-differentiated PC12 cells and axotomized rat facial motoneurons.

Previous studies have demonstrated that ovarian steroids exert neuroprotective effects in a variety of in vitro and in vivo systems. The mechanisms underlying these effects remain poorly understood. In the present study, the neuroprotective effects of estradiol (E(2)) and progesterone (P) were examined in two models of apoptosis induced by growth factor insufficiency: partially nerve growth factor (NGF)-differentiated PC12 cells, after serum and NGF withdrawal; and axotomized immature rat facial motor motoneurons. E(2) and P both increased the survival of trophically withdrawn NGF-differentiated PC12 cells, at physiologically relevant concentrations. However, neither steroid had a significant effect on the survival of PC12 cells that had not been NGF treated. Exposure to NGF had no effect on the expression of estrogen receptor (ER)beta, but markedly increased the levels of ERalpha and altered the expression of the progesterone receptor (PR) from predominantly PR-B in NGF naive cells, to predominantly PR-A after NGF. The survival promoting effects of E(2) and P were blocked by the specific steroid receptor antagonists Faslodex (ICI 182780) and onapristone (ZK98299), respectively. Inhibitors of RNA (actinomycin D) or protein (cycloheximide) synthesis also abrogated the protective effects of both steroids. In immature rats, E(2) and P both significantly increased the numbers of surviving facial motor neurons at 21 days after axotomy. These data demonstrate significant protective effects of E(2) and P in two well-characterized models of apoptosis induced by trophic withdrawal and suggest that, at least in PC12 cells, the effects of the steroids are mediated via interaction with nuclear steroid receptor systems. The lack of steroid responsiveness in NGF-naive PC12 cells despite the presence of abundant ERbeta and PR-B are consistent with the view that ERalpha and PR-A may be particularly important as mediators of the neuroprotective effects of their corresponding hormonal ligands.

Gonadectomy unmasks an inhibitory effect of progesterone on amygdala kindling in male rats.

Previous studies have suggested that the effects of progesterone on kindling in rats may be sexually differentiated, significant effects of physiological levels of progesterone being observed only in females. The present study demonstrates that this difference results from the hormones secreted by the testes. Thus, in orchidectomized males, progesterone induces a delay in the onset of amygdala-kindled seizures similar to that observed in females.

The effect of seizures and kindling on reproductive hormones in the rat.

Reproductive dysfunction and endocrine disorders are common among both women and men with epilepsy, and, in particular, with temporal lobe epilepsy. In clinical studies, it is hard to separate the effects of seizures from the effects of medication and life style. Studies in rodents, however, suggest that seizures per se can contribute to reproductive dysfunction. In female rats, generalized seizures disrupt normal ovarian cyclicity in adults, and repeated electroshock seizures delay the onset of puberty in juveniles. Right amygdala kindling in adult female rats causes acyclicity, the development of polycystic ovaries and premature aging of the hypothalamic-pituitary neuroendocrine axis, leading to chronic anovulation and continuous estrogen exposure. In adult male rats, repeated electroshock seizures result in transient hypogonadism, characterized by decreased serum testosterone levels and lowered gonadal tissue weight. In contrast, right amygdala kindling increases serum testosterone, estradiol levels and gonadal weight. These findings suggest that reproductive dysfunction in women and men with epilepsy may result from recurrent seizure activity, due to seizure-related interference with the normal functions of the hypothalamic-pituitary-gonadal axis.

Neuroendocrine function and response to stress in mice with complete disruption of glucagon-like peptide-1 receptor signaling.

Glucagon-like peptide-1 (GLP-1), a potent regulator of glucose homeostasis, is also produced in the central nervous system, where GLP-1 has been implicated in the neuroendocrine control of hypothalamic-pituitary function, food intake, and the response to stress. The finding that intracerebroventricular GLP-1 stimulates LH, TSH, corticosterone, and vasopressin secretion in rats prompted us to assess the neuroendocrine consequences of disrupting GLP-1 signaling in mice in vivo. Male GLP-1 receptor knockout (GLP-1R-/-) mice exhibit reduced gonadal weights, and females exhibit a slight delay in the onset of puberty; however, male and female GLP-1R-/- animals reproduce successfully and respond appropriately to fluid restriction. Although adrenal weights are reduced in GLP-1R-/- mice, hypothalamic CRH gene expression and circulating levels of corticosterone, thyroid hormone, testosterone, estradiol, and progesterone are normal in the absence of GLP-1R-/- signaling. Intriguingly, GLP-1R-/- mice exhibit paradoxically increased corticosterone responses to stress as well as abnormal responses to acoustic startle that are corrected by glucocorticoid treatment. These findings suggest that although GLP-1R signaling is not essential for development and basal function of the murine hypothalamic-pituitary-adrenal axis, abrogation of GLP-1 signaling is associated with impairment of the behavioral and neuroendocrine responses to stress.

Partial and generalized seizures affect reproductive physiology differentially in the male rat.

PURPOSE: Reproductive dysfunction and endocrine disorders occur frequently among men with epilepsy. This study tested the hypothesis that focal limbic seizures and generalized seizures may both contribute to reproductive dysfunction. METHODS: The rat kindling model was used to mimic focal limbic seizures. Kindling electrodes were placed in the basolateral amygdala. Male rats were either intact, gonadectomized (GDX) or GDX + testosterone (T) replaced and then kindled. Controls were left intact and sham-kindled. Maximal electroconvulsive shock (MES) treatment was used to model generalized seizures, by using eight stimulations, one every other day, for 2.5 weeks. Animals were killed either 3 h or 6 weeks after MES treatment to determine short- and long-term effects. RESULTS: Kindled seizures resulted in an increase in serum testosterone, estradiol, and prolactin in intact males, accompanied by a significant increase in testis, epididymis, and pituitary weight, as well as a significant decrease in prostate weight. MES treatment caused a short-term reduction in serum testosterone and testis, epididymis, and prostate weight. All parameters were restored to control values within 6 weeks of the last MES seizure, with the exception of pituitary weight and serum prolactin, which remained significantly elevated 6 weeks after MES treatment. CONCLUSIONS: Our results indicate that both focal limbic (amygdaloid) seizures and generalized MES seizures disturb normal reproductive physiology in the male rat. Amygdaloid-kindled seizures have mixed effects on different parameters of reproductive function, whereas MES seizures induce a transient hypogonadal state. These results suggest that reproductive dysfunction in men with epilepsy may result from seizure-related interference with the normal functions of the hypothalamic-pituitary-testicular axis.

Limbic seizures alter reproductive function in the female rat.

PURPOSE: Reproductive dysfunction and endocrine disorders are common among women with temporal lobe epilepsy. This study used the kindled rat model to test the hypothesis that limbic seizures directly contribute to reproductive dysfunction. METHODS: Kindling electrodes were implanted in the basolateral amygdala in adult female rats. Females were kindled by either brief, daily, suprathreshold stimulations with a bipolar electrode or sham-kindled (controls). Electrographic and behavioral seizures were monitored. Estrous cycles also were monitored with daily vaginal smears. RESULTS: Seizures arrested ovarian cyclicity in all (n = 42) kindled animals, the rats exhibiting persistent vaginal cornification (PVC). In these animals PVC was associated with high serum estradiol, increased pituitary weight, and polyfollicular ovaries consisting of many cystic follicles, as well as follicles in various stages of growth and atresia. In 93% of females, this effect occurred after the development of stage 5 motor seizures, when focal seizures had secondarily generalized. In contrast, only five (21%) of 24 sham-kindled controls exhibited PVC. A single injection of progesterone (P4) temporarily restored cyclicity in five (18%) of 28 kindled females exhibiting PVC. In contrast, P4 administration restored cyclicity in all five sham-kindled controls that had spontaneously stopped cycling. P4 treatment to kindled females in PVC resulted in a different endocrine profile than that in non-P4-treated, kindled rats in PVC. P4-treated rats had high serum estradiol, testosterone, and prolactin levels; they showed an increase in pituitary weight; and their ovaries contained numerous corpora lutea and cystic follicles surrounded by markedly overdeveloped thecal cell layers. CONCLUSIONS: Seizures initiated in the amygdala result in impairment of the hypothalamic-pituitary axis, resulting in loss of ovarian cyclicity.

Steroid hormones affect limbic afterdischarge thresholds and kindling rates in adult female rats.

UNLABELLED: Catamenial epileptics show particular vulnerability to seizures during menstruation and at the time of ovulation, when circulating estradiol (E(2))/progesterone (P(4)) ratios are high. The present study tested the hypothesis that alterations in neuronal excitability induced by E(2) and P(4) affect thresholds and the development of secondary generalization in kindled rats. METHODS: The effects of endogenous hormones secreted during the estrous cycle, and of exogenous exposure to E(2) and P(4) after ovariectomy (OVX), with and without adrenalectomy (ADX), were tested. Kindling electrodes were implanted in the basolateral amygdala or dorsal hippocampus in adult female rats. The anticonvulsive effects of P(4) on amygdala kindled seizures were also determined in intact subjects. RESULTS: In intact females, afterdischarge thresholds (ADTs) in the amygdala were significantly lower (306+/-48 microA; peak to peak) at mid-day proestrus, just prior to ovulation, when serum E(2) is elevated. ADTs were more than twofold higher (808+/-95 microA) during metestrus, coincident with peak ovarian P(4) secretion. In OVX females, amygdala thresholds were lowest with E(2) replacement and highest with P(4) replacement. Hippocampal ADT was unaffected by hormone replacement after OVX. The rates of both amygdala and hippocampal kindling were significantly accelerated by E(2) and slowed by P(4). E(2) replacement significantly increased serum corticosterone (CORT) levels. In ADX rats, CORT replacement increased kindling rates, synergizing with the effects of E(2). In fully kindled animals, P(4) administration suppressed motor seizures in approximately 60% of cases. CONCLUSIONS: E(2) lowers amygdala ADTs and facilitates kindling. This effect may involve both direct E(2) effects and indirect effects mediated via increased levels of circulating corticosterone. P(4) raises amygdala ADTs, slows kindling development and suppresses fully kindled seizures. Hence, P(4) may have potential therapeutic value for women with catamenial epilepsy.

Testosterone and its metabolites affect afterdischarge thresholds and the development of amygdala kindled seizures.

UNLABELLED: In boys with epilepsy, pubertal increases in seizure frequency may be associated with rising androgen levels. The present study tested the hypothesis that testosterone (T) and/or its metabolites might affect amygdala seizure thresholds and the development of secondary generalization from amygdala foci (kindling). Afterdischarge thresholds and kindling rate were measured in gonadectomized (GDX) male rats, with or without T replacement therapy. Drugs that block either androgen or estradiol (E(2)) receptor-mediated responses were also tested. METHODS: Kindling electrodes were implanted in the basolateral amygdala of adult male Wistar rats. In Experiment 1, subjects were GDX and implanted with a silastic capsule containing either: cholesterol (control); T; 5% E(2) in cholesterol; or 5alpha-dihydrotestosterone (DHT). In Experiment 2, intact subjects were treated with daily injections of vehicle (control); daily injections of flutamide (an androgen receptor antagonist); or Silastic implants containing 1,4,9-androstatriene 3,17-dione (ATD; an aromatase inhibitor). RESULTS: In Experiment 1, initial afterdischarge (AD) thresholds were significantly lowered by E(2) treatment, as compared to cholesterol controls, and remained low throughout the kindling paradigm. In T replaced males, AD threshold significantly decreased over the kindling period, a response that was not observed in DHT treated rats. Rates of kindling were significantly faster as a result of T, E(2) and DHT treatment, as compared to cholesterol controls. E(2) treated males kindled the fastest of all 3 groups. In Experiment 2, initial AD thresholds were significantly lowered by flutamide treatment, as compared to cholesterol controls, and remained low throughout the kindling paradigm. AD threshold significantly decreased over the kindling period in intact males, a response that was blocked by ATD treatment. Both flutamide and ATD significantly slowed the rate of kindling, as compared to intact controls. ATD had the most dramatic inhibitory effect on kindling rate. CONCLUSIONS: In males, T and its two metabolites, E(2) and DHT, all appear to enhance the development of amygdala-kindled seizures. E(2) has the most potent epileptogenic effect. Antagonism of E(2) mediated effects in the brain may have potential therapeutic value for males with epilepsy.

Hormonal interactions in the effects of halogenated aromatic hydrocarbons on the developing brain.

Halogenated arylhydrocarbons (HAHs) exert a wide range of effects on the developing brain. These effects result in altered patterns of neuroendocrine function and behavior in adulthood, as well as changes in cognitive function. The underlying mechanisms have not yet been clearly defined. This paper briefly reviews the effects of HAHs on brain development, and proposes the hypothesis that interactions between different hormone-sensitive systems may contribute to the broad spectrum of responses observed after fetal or early postnatal HAH exposure. Physiological interactions between the effects of sex steroids, corticosteroids, and thyroid hormone are known to influence the development of the central nervous system (CNS). Since the biosynthesis and/or action of each of these hormones is sensitive to developmental HAH exposure, it is suggested that convergent effects of HAHs on different endocrine pathways may underlie some of the disruptive effects of these chemicals on CNS differentiation. Data are presented indicating that the disruptive effects of low dose dioxin exposure on sexual differentiation of the rat brain are probably not mediated through blockade of estrogen responses, but may instead involve subtle developmental changes in other endocrine systems, perhaps also affecting the feedback control of adrenocortical function. The potential for interactive endocrine effects illustrates the need for a fuller understanding of the range of biological activities of HAHs in the brain, so that the potential risks of low dose developmental exposure to these environmental toxicants can be predicted with greater certainty.

Sex and the developing brain: suppression of neuronal estrogen sensitivity by developmental androgen exposure.

The developmental effects of androgen play a central role in sexual differentiation of the mammalian central nervous system. The cellular mechanisms responsible for mediating these effects remain incompletely understood. A considerable amount of evidence has accumulated indicating that one of the earliest detectable events in the mechanism of sexual differentiation is a selective and permanent reduction in estrogen receptor concentrations in specific regions of the brain. Using quantitative autoradiographic methods, it has been possible to precisely map the regional distribution of estrogen receptors in the brains of male and female rats, as well as to study the development of sexual dimorphisms in receptor distribution. Despite previous data suggesting that the left and right sides of the brain may be differentially responsive to early androgen exposure, there is no significant right-left asymmetry in estrogen receptor distribution, in either sex. Significant sex differences in receptor density are, however, observed in several regions of the preoptic area, the bed nucleus of the stria terminalis and the ventromedial nucleus of the hypothalamus, particularly in its most rostral and caudal aspects. In the periventricular preoptic area of the female, highest estrogen receptor density occurs in the anteroventral periventricular region: binding in this region is reduced by approximately 50% in the male, as compared to the female. These data are consistent with the hypothesis that androgen-induced defeminization of feminine behavioral and neuroendocrine responses to estrogen may involve selective reductions in the estrogen sensitivity of critical components of the neural circuitry regulating these responses, mediated in part through a reduction in estrogen receptor biosynthesis.

Effects of different estrogen and progestin regimens on the mechanical properties of rat femur.

The purpose of this study was to examine the effects of estrogen replacement, in concert with three different progestin regimens, on the mechanical properties of rat femoral cortical bone. Ninety-two 11-month-old female Sprague-Dawley rats were randomly divided into six groups and were treated for a duration of 6 months. Group-1 rats were intact controls, group-2 rats were ovariectomized controls, and groups 3-6 were ovariectomized and given continuous doses of estrogen with 5% estradiol 17B silicone-rubber implants. Groups 4, 5, and 6 were also given different doses of progestin (norethindrone): group 4 received a continuous dose of 3 micrograms per animal per day, group 5 received a cyclic dose of 6 micrograms per animal per day for 14 days of a 28-day cycle, and group 6 received an interrupted dose of 3 micrograms per animal per day for 3 days of a 6-day cycle. Femurs from each group were mechanically tested. Bending stiffness was measured by nondestructive three-point bending tests and maximum torque capacity, by destructive torsion tests. Geometrical properties and apparent density of cortical bone were also measured. The significant differences were: the increases in elastic modulus (measured from the three-point bending stiffness) of group 5 (cyclic norethindrone) compared with those of group 2 (ovariectomized controls) and group 3 (estrogen only); the increases in the size represented by the moment of inertia, the moment of the area, and medial-lateral width of group 2 compared with those of group 5; and the increases in apparent density and decreases in moment of inertia of group 6 (interrupted norethindrone) compared with those of group 2. Cyclic or interrupted treatment of progestin along with continuous treatment of estrogen after ovariectomy likely improves material properties of cortical bone, increases its density, and reduces the size of the bone compared with ovariectomized rats.

Rationale for estrogen with interrupted progestin as a new low-dose hormonal replacement therapy.

OBJECTIVE: This review outlines the basic principles of a novel interrupted progestin hormone replacement therapy (HRT) regimen in which estrogen is given continuously but the progestin is administered in a 3-days-on and 3-days-off schedule. The rationale for this regimen is to prevent receptor down-regulation and allow estrogen to increase estrogen and progestin sensitivity during the progestin-free periods. METHODS: The reasons for poor patient acceptance of HRT are reviewed. The association of HRT with breast and endometrial cancer is discussed, as are the potential benefits of HRT on the skeleton and the cardiovascular system. Basic research studies in the rat are described that provide supporting evidence for the interrupted progestin regimen. Clinically, we review a pilot study examining symptom control, bleeding rates, and safety of the interrupted progestin regimen as well as preliminary results of the usefulness of this regimen for add-back therapy in GnRH agonist-treated patients. RESULTS: Estrogen and progestin receptor measurements in the rat uterus demonstrate a clear up- and down-regulation in response to estrogen and interrupted progestin but not to the continuous administration of estrogen and progestin or estrogen alone. In addition, we found a significant beneficial effect of a low-dose interrupted HRT regimen on bone mineral content and density in an aged rat model of osteopenia, compared with continuous estrogen and progestin or estrogen alone. These results support the hypothesis that the interrupted progestin HRT increases tissue sensitivity to both estrogen and progestin. Clinical studies demonstrated good symptom control, low bleeding rates, endometrial protection, and excellent patient acceptance. CONCLUSION: The combination of continuous estrogen with interrupted progestin appears to result in increased sensitivity to estrogen and progestin in estrogen-responsive tissues. As a result, lower doses of estrogen and progestin may be used for HRT with good biological effects. Further clinical studies, preferably in prospective randomized trials, are required to demonstrate reduced bleeding and improved patient acceptance of this new regimen compared to continuous combined HRT.

Sex differences in estrogen receptor and progestin receptor induction in the guinea pig hypothalamus and preoptic area.

Quantitative in vitro autoradiography was used to determine if regional sex differences in estrogen receptor (ER) content and/or estrogen responsiveness, as indicated by an increase in progestin receptor (PR), are present in the adult guinea pig brain. Adult male and female guinea pigs were gonadectomized 1 week before subcutaneous injection of 25 micrograms estradiol benzoate (EB)/kg body wt or the sesame oil vehicle. Animals were killed by decapitation 44 h after injection. Unoccupied PRs, and unoccupied and occupied ERs, were measured in discrete brain regions by quantitative in vitro autoradiography using [3H]R5020 and [3H]estradiol as ligands, respectively. In vehicle-injected controls, a higher level of ER was found in the arcuate nucleus (ARC), dorsal medial nucleus (DMN) and ventrolateral nucleus (VLN) of females as compared to males. At 44 h after EB injection, 32-55% of the ERs were occupied; however, EB treatment caused a marked down-regulation of total receptor (calculated as occupied+ unoccupied receptor) in most of the brain regions examined, including the periventricular preoptic area (PVP), medial preoptic area (MPO), bed nucleus of the stria terminalis, paraventricular nucleus, ARC, ventrolateral hypothalamus (VLH), VLN, and DMN. In EB-treated animals, PR binding was detectable in the PVP, MPO, ARC, VLH, and VLN, with higher levels of binding observed in the PVP, MPO, and VLN of the female as compared to the male. No PR binding was observed in oil-injected control animals. These results demonstrate region-specific sex differences in ER as well as estrogen-induced regulation of progestin and ERs in the guinea pig brain. The discordance between the regional distributions of sex differences in ER and estrogen-induced PR implies that sex differences in ER and estrogen-induced PR implies that sex differences in estrogen response may not be clearly linked to a sex difference in receptor number. Instead, sex differences in response may involve differences in receptor number within specific subpopulations of estrogen target cells or may involve differences in ER dynamics.

Embryonic human leukocyte antigen-G expression: possible implications for human preimplantation development.

OBJECTIVE: To investigate further the association between human leukocyte antigen G (HLA-G) expression in human embryos and other factors known to influence IVF pregnancy outcome. SETTING: A university-based tertiary referral center (The Toronto Hospital). INTERVENTIONS: Nontransferred embryos at the two- to four-cell stage were obtained from patients undergoing IVF and were cultured in Ham's F-10 medium supplemented with 10% human sera or cocultured with ovarian cancer cells in the same medium. Embryos that reached blastocyst stage (n = 148) were analyzed by reverse transcriptase-polymerase chain reaction for HLA-G and beta 2 microglobulin (beta 2m) expression. Statistical analysis was performed to identify possible factors associated with variability of expression. RESULTS: Approximately 40% of studied blastocysts had detectable expression of both HLA-G and beta 2m messenger RNA. In 46% of blastocysts, beta 2m alone was observed. Interestingly, sibling embryos from patients that became pregnant were significantly more likely to express HLA-G than embryos from patients that did not conceive as a result of their IVF cycles. No association was found between HLA-G expression and culture conditions, patients age, or infertility diagnosis. CONCLUSION: The population of embryos obtained through IVF is heterogeneous in expression of HLA-G and beta 2m, which may reflect overall health of the embryos. Blastocysts showing positive HLA-G expression may have increased viability and implantation potential, although the underlying mechanisms remain to be elucidated.

Sex differences in corticosteroid binding in the rat brain: an in vitro autoradiographic study.

Several previous studies have raised the possibility of sex differences in the distribution of corticosteroid receptors in the brain. The direction and magnitude of these differences have, however, remained controversial. In the present study, we have re-examined the concentrations of mineralocorticoid (MR) and glucocorticoid (GR) receptors in the brains of male and female rats at varying times (1 to 6 days) after combined gonadectomy (GDX) and adrenalectomy (ADX). Cytosol binding assays confirmed the presence of higher MR levels in short-term (3-day) GDX-ADX males. This difference disappeared by 6 days after surgery, as receptor levels in females rose to be equivalent to those in males. Using an improved in vitro autoradiographic method, the distribution of MR and GR was studied in males and females 3 days after GDX-ADX. The distribution of MR and GR in the brains of these rats was similar in the two sexes. MR binding in the male, however, was significantly greater than that in the female throughout the principal cell fields of the hippocampus. Measurements of circulating corticosterone levels at the time of GDX-ADX suggest that this sex difference may reflect a more rapid recovery of the MR system in males than in females following the stress-induced rise in corticosterone secretion occurring at the time of surgery.