Sexual dimorphism of glucocorticoid binding in rat brain

Expression of mineralocorticoid and glucocorticoid receptor mRNA in the human hippocampus

The genomic effects of corticosteroids in the brain are mediated through two receptors with a high affinity for cortisol: the glucocorticoid and mineralocorticoid receptor (GR/MR). We used competitive reverse transcription-polymerase chain reaction to quantify the amount of MR and GR mRNA in hippocampal tissue obtained from patients with temporal lobe epilepsy. MR and GR mRNA were expressed at approximately the same levels as in tissues known for high glucocorticoid/mineralocorticoid sensitivity, i.e. liver or kidney. MR mRNA concentrations were significantly higher in the hippocampus of women (0.24+/-0.04 aU, arbitrary units; mean+/-SEM) than in men (0.14+/-0.01 aU, P<0.006) or children (0.09+/-0.02, P<0. 007). No such differences were observed for GR mRNA expression.

Contribution of sex and cellular context in the regulation of brain corticosteroid receptors following restraint stress

The two subtypes of corticosterone receptors in the rat brain play a pivotal role in the modulation of the stress response. Appropriate control of their gene expression is therefore critical for the maintenance of cellular and organism homeostasis. In this study, we investigated the contribution of gender and of the cellular environment of certain brain areas to the expression of both types of corticosteroid receptors, following restraint stress. Adult Wistar rats of both sexes were subjected to acute, chronic or to a combined chronic plus acute stress regimen, and the expression of glucocorticoid and mineralocorticoid receptors was evaluated in their hippocampus, hypothalamus, pituitary and frontal cortex, by using Northern blot analysis. Significant sex differences were observed in the first three brain areas examined as to the stress-induced expression of corticosteroid receptors. Among these, females showed a distinct mechanism of regulating glucocorticoid/mineralocorticoid receptor ratio in the hippocampus upon chronic stress, while the female hypothalamus was more prone than the male to changing corticosteroid receptor expression in response to restraint stress. In another set of experiments, we assessed the influence of ovarian steroids on stress-induced corticosteroid receptor expression in the above brain areas by analyzing ovariectomized rats exposed to short-term restraint. Our results showed that although ovarian steroids affect the stress-induced expression of receptor genes in a region-specific manner, their elimination does not appear to lead to the male pattern of expression. These findings provide further evidence for the existence of both regional and gender specificity in the regulation of brain and pituitary corticosteroid receptors following stress, and support the hypothesis of a distinct male and female neuroendocrine axis in response to stress.

Responses of serum corticosterone and corticosteroid-binding globulin to acute and prolonged stress in the rat

Responses of serum corticosterone (B) and corticosteroid-binding globulin (CBG) to ether anesthesia (a "classic" acute stress) and to a number of stressors influencing metabolic homeostasis--fasting, physical exercise, cold exposure, and water deprivation--were studied in male and female rats. Metabolic stressors included placing in an ice bath, physical exercise (swimming), fasting for 2 d, swimming after fasting for 2 d, cold-room (4 degrees C) exposure for 2 d, fasting in combination with cold-room exposure for 1 d, and water deprivation for 2 d. The study demonstrated clear differences between males and females in basal B levels and B responses to some stressors. Only ether anesthesia and fasting resulted in similar B levels in males and females whereas in control and all other groups serum B levels were higher in females. Serum CBG was considerably higher in females. In females, ether, swimming, swimming after fasting, fasting, and fasting during cold exposure resulted in a decrease in circulating CBG. Ice bathing and cold exposure did not influence CBG, and water deprivation elevated serum CBG. In males, animals subjected to fasting and fasting during cold exposure had CBG levels lower than control animals. Other groups did not differ from the control. Higher CBG levels in females counterbalanced higher total B in setting circulating free B: significant sex differences in free B were observed only after swimming or fasting during cold exposure. Stress-responsive changes in CBG levels seem to contribute little to changes in free B; the main contributing factor is the rise in total B. However, CBG may play a special role, independent of the functions of corticosteroids. It is proposed that the need for substantial mobilization of spare fuel (as it takes place during physical exercise or fasting) is critical in involving CBG in the stress response.

Functional sex differences ('sexual diergism') of central nervous system cholinergic systems, vasopressin, and hypothalamic-pituitary-adrenal axis activity in mammals: a selective review

Sexual dimorphism of the mammalian central nervous system (CNS) has been widely documented. Morphological sex differences in brain areas underlie sex differences in function. To distinguish sex differences in physiological function from underlying sexual dimorphisms, we use the term, sexual diergism, to encompass differences in function between males and females. Whereas the influence of sex hormones on CNS morphological characteristics and function of the hypothalamic-pituitary-gonadal axis has been well-documented, little is known about sexual diergism of CNS control of the hypothalamic-pituitary-adrenal (HPA) axis. Many studies have been conducted on both men and women but have not reported comparisons between them, and many animal studies have used males or females, but not both. From a diergic standpoint, the CNS cholinergic system appears to be more responsive to stress and other stimuli in female than in male mammals; but from a dimorphic standpoint, it is anatomically larger, higher in cell density, and more stable with age in males than in females. Dimorphism often produces diergism, but age, hormones, environment and genetics contribute differentially. This review focuses on the sexual diergism of CNS cholinergic and vasopressinergic systems and their relationship to the HPA axis, with resulting implications for the study of behavior, disease, and therapeutics.

Relationships among cortisol (CRT), dehydroepiandrosterone-sulfate (DHEAS), and memory in a longitudinal study of healthy elderly men and women

At test times 18 months apart (Time 1 and Time 2), men (n Time 1 = 31, Time 2 = 23), women estrogen-users (n Time 1 = 14, Time 2 = 10), and women estrogen non-users (n Time 1 = 41, Time 2 = 27), whose average age was 72.1 and 73.4 years at Time 1 and Time 2, respectively, were tested with a battery of neuropsychological tests measuring verbal memory, visual memory, concentration/attention, language fluency and semantic memory. Plasma levels of CRT and DHEAS were assayed by radioimmunoassay at both test times. The men had higher DHEAS levels than both groups of women at both test times (p < 0.001) and also had a higher DHEAS/CRT ratio compared to the estrogen non-users (p < 0.05). Although there were no group differences in CRT levels at either time, CRT levels increased in the estrogen non-using women from Time 1 to Time 2 (p < 0.001). Subjects with lower CRT levels performed better than those with higher levels on several tests of declarative memory (p < 0.05). Men and estrogen-users had higher Digit Span scores compared to female estrogen non-users at both test times (p < 0.01), and women estrogen-users also had higher Backward Digit Span scores than non-users (p < 0.05). Both groups of women performed better than men on Category Retrieval (p < 0.01). These findings suggest that higher CRT levels in elderly men and women are associated with poorer explicit memory functioning; however, these results failed to provide any evidence that DHEAS is protective against declarative memory decline with aging.

Luteinizing hormone-releasing hormone is a primary signaling molecule in the neuroimmune network

The brain-pituitary-reproductive axis and the brain thymus-lymphoid axis are linked by an array of internal mechanisms of communication that use similar signals (neurotransmitters, peptides, growth factors, hormones) acting on similar recognition targets. Moreover, such communication networks form the basis and control each step and every level of reproductive physiology. This presentation highlights the extent to which endocrine, neural, glial, or immunologically competent cells may achieve their specific functions using common mechanisms, but employing them to different degrees. In particular, this work will focus on LHRH, the chief hormone orchestrating reproductive events. Within the thymus LHRH plays a unique role of immunomodulator, contributing to the sex-dependent changes in immune responsiveness during the estrous-menstrual cycle as well as pregnancy. From the recent cloning and sequencing of lymphocyte LHRH, the expression of LHRH receptor mRNA in lymphocyte, the transduction mechanisms involved, and the steroidogenic sensitivity of the intralymphocyte LHRH system. It would appear that this peptide may act as an immunological response modifier in the brain-pituitary-lymphoid-gonadal axis. The interplay between neuronal, endocrine, and immune compartments is further emphasized in the study of LHRH-astroglial interactions. Astrocytes are able to manufacture a wide variety of signaling agents and can secrete immunoregulatory molecules that influence immune cells, as well as the glial cells themselves. Astroglia and the immortalized hypothalamic LHRH (GT1-1) neurons communicate with an array of mechanisms, via soluble mediators as well as cell-to-cell contacts. Manipulation of astroglial-derived cytokines and nitric oxide (NO) in GT1-1 neuron-astroglia cocultures, underscores a potential cross-talk between different intra/inter-cellular mediators in the dynamic control of LHRH release. Further studies aimed to disclose at a biochemical and a molecular level such bidirectional, informative network will give us new insights into more general issues concerned with the malfunction of the neuroendocrine-immune axis.

Gender specificity in the neural regulation of the response to stress: new leads from classical paradigms

Pronounced gender-related differences are observable in the regulation of the limbic-hypothalamic-pituitary-adrenal (LHPA) activity under basal and stress-related conditions, and by circulating glucocorticoid levels. This article reviews recent studies that have unequivocally demonstrated that these differences emerge from the organizational effects of gonadal steroids during early brain development. Although largely masked by the dominating role of glucocorticoids in maintaining feedback thresholds, gonadal steroids continue to exert gender-specific activational effects on the LHPA axis through adulthood. The importance of these modulatory effects of gonadal steroids may be reflected in gender differences in the incidence of psychopathologies that are accompanied by symptoms of LHPA dysregulation. One goal of this review is to highlight the need for further investigations into the (still elusive) cellular and molecular mechanisms underlying the activational effects of sex steroids, which may provide leads for neuroprotective hormone replacement strategies.

Sex differences in pain-induced effects on the septo-hippocampal system

In addition to its role in the modulation of functions such as arousal and attention, learning and memory, the limbic system has repeatedly been described to be involved in the regulation of several behavioral aspects concerning the adaptation to aversive situations, including pain. A key role in these processes seems to be played by the septo-hippocampal system. This paper, far from being a comprehensive review of all the data available about the limbic system, describes some of the circuits participating in the septo-hippocampal system, with the aim of contributing to an understanding of the sex differences in the behavioral, hormonal and neuronal responses to aversive stimuli. It will appear that the complex anatomical and functional interactions between the different neurotransmitters acting at this level prevent one from indicating a certain substance as more important than others in determining a difference between the two sexes. This leads to the conclusion that the septo-hippocampal formation in toto plays a key role in determining the sex differences in the 'pain experience'.

Influence of gonadal steroids on brain corticosteroid receptors: a minireview

Sex differences exist in the functioning of the two brain corticosteroid receptor systems. Ovarian steroid replacement alters receptor mRNA expression, receptor binding capacities, and receptor affinity. The abundance of both mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) message can be reduced by estrogen. Progesterone is able to partially antagonize the action of estrogen and to induce MR transcription. The effect of estrogen on receptor binding capacity is more modest than its transcriptional actions. Estrogen decreases MR binding more reliably than it does GR. Progesterone has high affinity for the MR and can substantially reduce MR affinity for corticoids. Androgen apparently regulates corticoid receptor transcription but may not affect binding capacity. Estrogen and androgen are both more potent in regulating pituitary-adrenal function than would be suggested by their actions on receptor binding parameters.

Gonadal steroids exert facilitating and "buffering" effects on glucocorticoid-mediated transcriptional regulation of corticotropin-releasing hormone and corticosteroid receptor genes in rat brain

Gonadal steroids profoundly influence several brain functions and are apparently responsible for gender-specific differences in the regulation of hypothalamic-pituitary-adrenal (HPA) secretions. In this study, we examined the so-called "activational" effects of gonadal steroids on the glucocorticoid-mediated regulation of the gene transcription of corticotropin-releasing hormone (CRH) and corticosteroid receptors in brain areas of relevance for the control of pituitary-adrenal secretion. The efficacy of adrenalectomy (ADX) and chronic treatment with high doses of corticosterone (B) to regulate the gene transcription of CRH and corticosteroid receptors in the hypothalamic paraventricular nucleus (PVN) and hippocampus was studied in male and female rats under the conditions of deprivation of gonadectomy (GDX) and replacement with different gonadal steroids, such as estradiol (E2), progesterone (P), and dihydrotestosterone (DHT). In both sexes, ADX alone or in combination with GDX increased, and B treatment suppressed, the steady-state levels of CRH and corticosteroid receptor mRNAs, whereas GDX alone failed to affect any of the parameters studied. Administration of gonadal hormones to steroid-deprived (ADX/GDX) animals partially attenuated the upregulation of mRNAs encoding corticosteroid receptors in the hippocampus. Supplementation with gonadal steroids modified the effects of B on the gene transcription of CRH and corticosteroid receptors. Whereas P alone or in combination with E2 counteracted the B-induced downregulation of GR and CRH gene transcription in females, DHT and E2 administration further potentiated the effects of B on these parameters in a sex-specific manner. Taken together, the results indicate that gonadal steroids have minor influence on MR, GR, and CRH gene transcription under basal conditions, exert "glucocorticoid-like" effects on the transcription of corticosteroid receptors in the hippocampus of steroid-deprived animals, and interact with glucocorticoid-mediated mechanisms of regulation in the HPA axis through gender-specific "buffering" and "potentiating" effects.

No sex difference occurs in hippocampus, food-storing, or memory for food caches in black-capped chickadees

A number of recent studies have described sex differences in the relative size of the hippocampus that are associated with sex differences in the use of space. Voles, kangaroo rats, and cowbirds all exhibit a sex difference in relative size of the hippocampal formation that is correlated with a sex difference in spatial behaviour. We wished to determine whether sex differences in the size of the hippocampus occur in the absence of a difference in the use of space, and whether the previously described correlations could be adventitious. Relative hippocampal size was determined in wild-caught black-capped chickadees (Parus atricapillus) following behavioural observations of food caching and spatial memory for cache sites. There was no indication of a sex difference in either relative size of the hippocampus or in food-caching behaviour and memory for cache sites. These results show that sex differences in relative size of the hippocampus do not occur as a matter of course, and are consistent with the hypothesis that sex differences in spatial behaviour and spatial ability are predictive of sex differences in the relative size of the hippocampus.

Sex differentiation of rat hippocampal GABAergic neurons

In order to analyse mechanisms of sex differentiation of the hippocampus at the cellular level, the differentiation of hippocampal GABAergic neurons was studied in vitro. Serum-supplemented and serum-free dissociated cell cultures were raised from the hippocampus of embryonic day 17 male and female rat embryos for up to 14 days in vitro. This time period roughly corresponds to the critical phase for sex differentiation of the rat brain as determined in vivo. Serum-free cultures were treated with testosterone and/or 17 beta-oestradiol for the entire culture period. Control cultures from male donors contained twice as many GABA-immunoreactive neurons as those from female donors, while there was no sex difference in overall counts of neurons stained for microtubule-associated protein 5. Measurements of high-affinity uptake of [3H]GABA essentially confirmed this sex difference. The development of the sex difference could not be influenced by long-term treatment with androgen or oestrogen. It is concluded that sex differentiation of a specific subpopulation of hippocampal neurons may take place independently of the environment provided by gonadal steroids and in the absence of extrinsic connections with the hypothalamus or other relays of the limbic circuit.

Chronic corticosterone treatment elicits dose-dependent changes in mouse brain alpha-bungarotoxin binding

Previous studies have shown that adrenalectomy results in a small increase in hippocampal alpha-bungarotoxin binding, whereas seven days of chronic treatment with high doses of corticosterone results in decreases in alpha-bungarotoxin binding in several brain regions. The studies reported here examined the effects of different doses of corticosterone on brain alpha-bungarotoxin binding. C3H mice were adrenalectomized and treated with corticosterone-containing pellets (0.5-60%) for four days. Alpha-Bungarotoxin binding was measured in eight brain regions. Chronic treatment with corticosterone resulted in plasma corticosterone levels ranging from the low levels observed in an unstressed mouse during the daytime to levels significantly above those observed in mice during the night or as a result of stress. Adrenalectomy resulted in small increases in binding in hippocampus which was reversed by low dose corticosterone treatment. Chronic high-dose corticosterone treatment resulted in significant decreases in binding in four of the eight brain regions examined. Similar, but not identical, results were obtained in two other mouse strains (C57BL and DBA/2). These results argue that corticosterone levels play an important role in modulating the level of the brain nicotinic receptors that bind alpha-bungarotoxin with high affinity.

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.

Fetal ethanol exposure alters pituitary-adrenal sensitivity to dexamethasone suppression

The present study investigated the hypothesis that a deficit in feedback inhibition of the hypothalamic-pituitary-adrenal (HPA) axis may underlie the hormonal hyperresponsiveness seen in fetal ethanol-exposed rats. Male and female Sprague-Dawley rats from prenatal ethanol (E), pair-fed (PF) and ad lib-fed control (C) treatment groups were tested in adulthood. The effects of dexamethasone (DEX) blockade on basal and stress corticosterone (CORT) levels and stress adrenocorticotropin (ACTH) levels were examined over a 36-h period. Stress CORT and ACTH levels after DEX administration at the trough (AM) and peak (PM) of the CORT circadian rhythm were compared. DEX administration significantly suppressed both resting and stress levels of CORT and ACTH in all animals, regardless of prenatal treatment. Importantly, E animals did not differ from PF and C animals in basal CORT. However, E males and females had significantly higher stress levels of CORT and/or ACTH than PF and C animals, and further, showed differential responsiveness following DEX administration depending on the time of day when testing occurred. At the trough of the CORT circadian rhythm. E males did not differ from PF and C males, whereas E females had increased stress levels of CORT compared to PF and C females. In contrast, at the peak of the circadian rhythm, E males showed increased stress levels of CORT but not ACTH, whereas E females showed increased stress levels of both CORT and ACTH compared to males and females in respective control groups. These data support the hypothesis that E animals may exhibit deficits in HPA feedback inhibition compared to controls and suggest a sex-specific difference in sensitivity of the mechanism underlying HPA hyperresponsiveness.

Roles of steroid hormones and their receptors in structural organization in the nervous system

Due to their chemical properties, steroid hormones cross the blood-brain barrier where they have profound effects on neuronal development and reorganization both in invertebrates and vertebrates, including humans mediated through their receptors. Steroids play a crucial role in the organizational actions of cellular differentiation representing sexual dimorphism and apoptosis, and in the activational effects of phenotypic changes in association with structural plasticity. Their sites of action are primarily the genes themselves but some are coupled with membrane-bound receptor/ion channels. The effects of steroid hormones on gene transcription are not direct, and other cellular components interfere with their receptors through cross-talk and convergence of the signaling pathways in neurons. These genomic and non-genomic actions account for the divergent effects of steroid hormones on brain function as well as on their structure. This review looks again at and updates the tremendous advances made in recent decades on the study of the role of steroid (gonadal and adrenal) hormones and their receptors on developmental processes and plastic changes in the nervous system.

Neuroendocrineimmunology (NEI) at the turn of the century: towards a molecular understanding of basic mechanisms and implications for reproductive physiopathology

The interactions between the nervous, endocrine and immune systems require a complex communication network. The central nervous system (CNS) affects the immune system through endocrine, paracrine and neuronal mechanisms. Evidence that this bidirectional communication plays a vital role in the regulation of physiological homeostatic mechanisms while a disfunction of the neuroendocrineimmune balance favors the susceptibility to a number of diseases is derived largely by animal models but also by an increasing number of clinical studies in different fields, including endocrinology, reproductive physiology, pediatrics, oncology, neurology and psychiatry. An increasing number of endocrine hormones, neurotransmitters and neuropeptides are expressed in immune tissues and cells and are actively involved in the physiological regulation of immunity. Conversely, the endocrine and nervous systems harbor receptors for a wide variety of immunologically-derived substances, suggesting potential regulatory feedback loops between the three major integrative bodily systems. Major implications for the reproductive endocrinology field are that psychoneuroendocrine processes may alter fertility via immunomodulation, and that events that occur as part of immune responses influence the neuroendocrine axes, which in turn counter-regulate immune function. In the present article, some features of reproductive-immune interactions will be described, and the neuroendocrineimmune dialogue via the chief reproductive hormone, luteinizing hormone-releasing hormone (LHRH), will be summarized as prototype of intersystem crosstalk. A particular emphasis will be given to the cytokine-LHRH interrelationships both at central (i.e. especially with the astroglial compartment) and peripheral levels. The surprisingly similar communication network systems used by the gonads and the thymus will be summarized, and the sexually-driven dimorphisms dictating female versus male reproductive and immunological capacities reviewed. Evidence that neural, endocrine and immune systems work together as a single unit are emphasized in animal models and human pathologies where interruption of NEI feedback loops results in long lasting pathological consequences for the nervous, endocrine and immune functions.

Estradiol abolishes autologous down regulation of glucocorticoid receptors in brain

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

Contribution of stress and gender to exploratory preferences for familiar versus unfamiliar conspecifics

An apparatus for measuring the exploratory preferences of rats for familiar and unfamiliar conspecifics in a novel environment was designed. The exploratory behavior of males and females was compared and contrasted to that elicited in response to an acute aversive event. Sprague-Dawley male and female rats were exposed to restraint and 60, 1 s, 1 mA tailshocks and returned to their home cage. Either 2 or 24 h later, they were placed in a novel environment with a familiar cage-mate and an unfamiliar conspecific of the same sex. Relative to unstressed controls and females, males stressed 2 h previously decreased the exploration of the unfamiliar conspecific, exhibiting a rapid decrease over the course of the trial. In response to the stressor, however both sexes, however, decreased the exploration of the familiar conspecific, decreased their overall activity, and returned preferentially to their starting quadrant. None of these stress-induced effects were evident 24 h later upon the first or second exposure to the apparatus. Thus, exposure to the stressor transiently increased perseveration and decreased activity in males and females, but only decreased the exploration of novel conspecifics in males. These results indicate that a number of behavioral responses to stressors are conserved across gender, but those relating to novelty are more pronounced in males.

Treatment of major depression with metyrapone and hydrocortisone

Eight inpatients with Major Depression were treated with metyrapone and hydrocortisone in a balanced order placebo-controlled single-blind cross-over study. The hydrocortisone dose (30 mg daily) was a physiological replacement dose and the metyrapone dose was titrated against plasma cortisol in order to keep cortisol within physiological limits. The treatment resulted in a significant reduction in depressive symptoms. This placebo-controlled study replicates the results of several uncontrolled studies but leaves open for further study the mechanism by which the combined administration of metyrapone and hydrocortisone might exert its antidepressant effect.

Growth hormone responses to dexamethasone in healthy females throughout the menstrual cycle

OBJECTIVE

In health, acute administration of dexamethasone (DEX) leads to growth hormone release. As sex steroids have a profound influence on the somatotrophic axis, we decided to investigate the effects of DEX on GH release throughout the menstrual cycle.

DESIGN

A within subjects, randomized double-blind counter-balanced design was employed.

METHODOLOGY

Baseline levels of GH, oestradiol and progesterone were taken at three time points in two consecutive menstrual cycles, after which 4 mg of oral DEX or placebo was administered. Plasma samples for GH estimation were taken at 60, 180, 240 and 300 minutes. Each woman was tested 6 times, 3 times with placebo and 3 times with DEX.

SUBJECTS

Six women with regular menstrual cycles were studied.

MEASUREMENTS

Plasma GH, oestradiol and progesterone were measured by radioimmunoassay.

RESULTS

When expressed as maximum change from base line (delta GH) mean GH responses to DEX increased incrementally from early (12.2 +/- 2.5 mU/l), through mid (25.6 +/- 3.3 mU/l) to late (37.2 +/- 3.5 mU/l) cycle. This represents a significant effect of cycle phase on GH responses to DEX (P < 0.05). GH responses at both the mid-cycle and the luteal time points are different from those during the follicular phase (P < 0.05) and difference between mid-cycle and luteal phases just fail to reach significance (P < 0.15). Responses to placebo did not vary from baseline. Plasma oestradiol values were significantly correlated with GH responsivity to active drug throughout the cycle (P < 0.05); the same was not true of progesterone.

CONCLUSION

Our study has demonstrated that dexamethasone-mediated GH release shows a stepwise increase throughout the menstrual cycle.

In vitro studies of glucocorticoid effects on neurons and astrocytes

Studies using immunocytochemistry and RNase protection assay demonstrate that glucocorticoid and mineralocorticoid receptors (GR, MR) and their corresponding mRNAs are co-expressed in hippocampal neurons cultured in serum-free, defined medium and at lower levels in cultured astrocytes. Addition of serum or medium conditioned by astrocytes increases the levels of MR mRNA, but has little effect on the levels of GR mRNA. Cellular levels of both GR mRNA and MR mRNA are upregulated by growth of embryonic hippocampal neurons in corticosterone. This is in distinct contrast to regulation of receptor expression in vivo where mRNAs for these receptors are downregulated in the rat hippocampus by corticosterone treatment of the adult adrenalectomized rat. However, in cultured astrocytes, GR and MR mRNAs are also downregulated by corticosterone. To begin to define the role of glucocorticoids in gene expression in astrocytes, we have used giant two-dimensional (2D) gel electrophoresis to separate astrocyte cellular proteins and translation products synthesized in vitro from astrocyte poly A+ RNA. Analysis of approximately 1,500 in vitro translation products by giant 2D gel electrophoresis reveals 11 protein inductions and 1 repression that occur at the level of mRNA in the absence of protein synthesis following treatment of astrocytes with corticosterone. Interestingly, these changes appear to be mediated by GR, but not by MR. The in vitro studies described here are relevant to identifying the role of GR and MR in gene expression in specific cell types in the hippocampus.

The neurosteroid tetrahydroprogesterone counteracts corticotropin-releasing hormone-induced anxiety and alters the release and gene expression of corticotropin-releasing hormone in the rat hypothalamus

The ring-A-reduced progesterone derivative 5 alpha-pregnan-3 alpha-ol-20-one (tetrahydroprogesterone) is synthesized under normal physiological conditions in the brain and is a potent modulator of the GABA receptor. This neurosteroid has significant sedative and anxiolytic properties. Corticotropin-releasing hormone plays a major role in stress-induced activation of the hypothalamo-pituitary-adrenal axis, and sustained hyperactivity of hypothalamic corticotropin-releasing hormone-producing neurons may be causally related to both, increased pituitary-adrenal secretion and behavioural symptoms observed in anxiety and affective disorders. We investigated the effect of tetrahydroprogesterone on corticotropin-releasing hormone-induced anxiety, the basal and methoxamine-stimulated release of corticotropin-releasing hormone from hypothalamic organ explants in vitro, and adrenalectomy-induced up-regulation of the gene expression of corticotropin-releasing hormone in the hypothalamic paraventricular nucleus in rats. At doses of 5 and 10 micrograms i.c.v., tetrahydroprogesterone counteracted the anxiogenic action of 0.5 microgram of corticotropin-releasing hormone. Tetrahydroprogesterone did not alter the basal release of corticotropin-releasing hormone in vitro, but suppressed the stimulatory effect of the alpha 1-adrenergic agonist methoxamine on this parameter. Measurements of the steady-state levels of mRNA coding for corticotropin-releasing hormone by quantitative in situ-hybridization histochemistry revealed that tetrahydroprogesterone was equipotent with corticosterone in preventing adrenalectomy-induced up-regulation of peptide gene expression. Systemic administration of tetrahydroprogesterone also restrained adrenalectomy-induced thymus enlargement. These results demonstrate that tetrahydroprogesterone has anxiolytic effects that are mediated through interactions with hypothalamic corticotropin-releasing hormone in both, genomic and non-genomic fashions.

Development of mRNAs for glucocorticoid and mineralocorticoid receptors in rat hippocampus

The hippocampus plays an important role in mediating glucocorticoid effects on the brain. Glucocorticoids are also implicated in neurogenesis and age-related neuronal death in the hippocampus. The effects of glucocorticoids in the hippocampus are elicited through two receptors with high-affinity for corticosterone, the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). In this study, we used a sensitive RNase protection assay to quantify the ontogeny of GR mRNA and MR mRNA in hippocampus from embryonic day 18 (E18) to postnatal day 60 (P60). GR mRNA and MR mRNA are expressed at approximately equal levels in the E18 hippocampus. However, by birth, the level of MR mRNA is three-fold that of GR mRNA and remains elevated up to P60. The levels of both mRNAs increase gradually during the period of postnatal neurogenesis after which they markedly increase to adult levels. In addition, the levels of hippocampal MR mRNA are the same in male and female rats, whereas the levels of GR mRNA are significantly higher in the P60 female rat hippocampus, but not in younger female rats. Our data on the development of mRNA levels do not parallel the levels of glucocorticoid and mineralocorticoid receptors as reported in a number of binding studies. Therefore, our studies, when considered together with previous reports, suggest that posttranscriptional mechanisms play a major role in regulating the levels of glucocorticoid-binding sites in the hippocampus.

AF64A-induced brain damage and its relation to dementia

Several data obtained in the AF64A-model are of particular relevance for our understanding of the pathogenesis and progression of Alzheimer's disease. The AF64A-induced withdrawal of cholinergic function in the rat hippocampus was associated with reversible functional changes in other neurotransmitters, including noradrenaline, serotonin, somatostatin and glutamate, thereby mimicking changes in Alzheimer's disease. Identical changes in markers for synaptic vesicles were found in Alzheimer's disease and AF64A-model. A study on the role of gender revealed a higher susceptibility to the neurotoxic action of AF64A in female rats. The cholinergic deficit was also responsible for a disinhibition of the negative feedback regulation of glucocorticoids. Increased exposure to glucocorticoids, however, enhanced the vulnerability of hippocampal cholinergic neurons to AF64A. These data indicate that the AF64A-induced cholinergic deficit in the rat brain represents a reliable tool to study several mechanisms possibly involved in Alzheimer's disease.

Sex differences and estrous cycle-variations in the AF64A-induced cholinergic deficit in the rat hippocampus

The influence of gender and stage of the estrous cycle on the levels of acetylcholine, serotonin, and noradrenaline in the hippocampus and on the susceptibility of the cholinergic septo-hippocampal pathway to the neurotoxic effect of ethylcholine aziridinium (AF64A) was investigated in the rat. Levels of acetylcholine and serotonin were consistently higher in female rats during the stage of diestrus and proestrus than in age-matched male rats (p < 0.05). Across the estrous cycle the highest levels of acetylcholine and serotonin, coinciding with the lowest levels of noradrenaline, were measured on proestrus. Eight to 10 days after the bilateral intracerebroventricular injection of a submaximal dose of AF64A (1 nmol/ventricle) the decrease of acetylcholine in hippocampus was larger in females than in male rats. The reduction of acetylcholine was most pronounced in female rats that had received submaximal doses of AF64A on proestrus (42.7 +/- 3.4%), whereas in male rats, the corresponding decrease was 25.9 +/- 5.1% (p < 0.05). At a maximal dose of AF64A (2 nmole/ventricle), the sex-specific or cycle-dependent difference in the cholinotoxicity of AF64A vanished. The dose-dependent loss of acetylcholine was associated with a secondary dose-dependent decrease in the levels of serotonin and noradrenaline, but significant differences between male and female rats or stages of estrous cycle were not apparent. The present data provide evidence that adult female rats in general, and particularly females on proestrus, are more susceptible to the neurotoxic action of submaximal doses of AF64A than age-matched male rats.

Estradiol increases glucocorticoid binding and glucocorticoid induction of ornithine decarboxylase in the rat spinal cord

Previous results demonstrated that estradiol (E2) treatment of ovariectomized-adrenalectomized (OVX-ADX) rats increased glucocorticoid (GC) binding in brain regions. The experimental protocol was extended to the spinal cord, a GC target tissue in which ornithine decarboxylase (ODC) is markedly induced by GC treatment. First, we measured GC binding to type I and type II receptors in ventral horn, dorsal horn and lateral funiculus of OVX-ADX rats treated during 4 days with E2 or vehicle. In E2-treated rats, type II receptors increased solely in dorsal horn, whereas type I sites remained unchanged. Second, in a group of OVX-ADX rats receiving dexamethasone (DEX), pretreatment with E2 superinduced ODC in ventral horn and lateral funiculus, but not in dorsal horn. Third, we found that the dorsal horn was relatively enriched in E2 receptors compared to other areas. Therefore, E2 stimulation of GC binding to type II sites may be mediated through E2 receptors localized in the dorsal horn. We suggest that combined treatment with E2 and DEX employs a transsynaptic mechanism for ODC induction at the ventral horn and lateral funiculus, with hormonal interaction taking place at the dorsal horn level.

Sex differences in the binding of type I and type II corticosteroid receptors in rat hippocampus

Binding parameters of soluble Type I and Type II receptors were assessed in hippocampus of adult, adrenalectomized, male and female rats. No sex differences in the number of either Type I or Type II receptors could be demonstrated between gonadally intact animals. When females treated with 17 beta-estradiol benzoate (10 micrograms/day) were compared with males, a statistically significant reduction in Type II receptors was observed in the females; progesterone produced no further decrease in receptor numbers. The amount of tissue-associated corticosteroid-binding globulin in gonadally intact animals (perfused with dextran-saline) was twice as great in females as males. Sex-dependent differences in these gonadally intact rats were found in the affinity, measured as the dissociation constant (Kd), of both the Type I and Type II receptors. For both receptors, affinity in cytosols from females was reduced. The difference for the Type II receptor was slight, but the Kd value of the Type I receptor was several-fold higher in females. The difference in affinity was evident with both natural and synthetic steroid ligands. There appears to be little, if any, difference in affinity between the hippocampal Type I and the Type II receptors in females. This suggests that the occupancy of Type I receptors in females is substantially less than that of males at low circulating concentrations of corticosteroids.

Prenatal ethanol effects: sex differences in offspring stress responsiveness

Previous studies have shown that offspring prenatally exposed to ethanol are hyperresponsive to stressors in adulthood, and have suggested that females are typically more affected than males. The present study was undertaken to investigate further this apparent sex difference in prenatal ethanol effects on stress responsiveness. Male and female offspring from prenatal ethanol-exposed (E), pair-fed (PF), and ad lib-fed control (C) conditions were tested in adulthood to determine adrenocortical responses to a prolonged (4-h) restraint stress. There were no significant differences in corticoid responsiveness among females from the three treatment groups. All females showed a marked increase in plasma corticosterone at 30 min, and corticoid levels remained elevated through 150-min restraint. By 180 min, all females showed a significant corticoid decrease, although corticosterone remained elevated over basal levels throughout the 240-min stress period. For males, in contrast, there were significant differences among groups. All males showed a significant corticoid increase over basal levels at 30 min, and corticoids remained significantly elevated through 90-min restraint. By 120 min, PF and C males showed a significant corticoid decrease although corticoids never returned to basal levels during the 240-min restraint period. E males, however, showed no significant decrease from peak corticosterone levels throughout the 240-min restraint stress. These data indicate that pituitary-adrenal hyperresponsiveness is not limited to fetal ethanol-exposed females, but may be demonstrated in fetal ethanol-exposed males under appropriate conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex differences in neurochemical and behavioural effects of 8-hydroxy-2-(di-n-propylamino) tetralin

A number of neurochemical investigations have shown that 5-hydroxytryptamine (5-HT) metabolism and turnover is greater in females than male rats. However increased 5-HT metabolism does not necessarily imply greater 5-HT release at the functional post-synaptic sites. Pharmacological research based on 5-HT receptor stimulation therefore gained attention. Studies of this type are complicated because of the multiplicity of 5-HT receptors in the central nervous system. Chemical ligands may not have sufficient selectivity, to specifically bind to a single receptor population. Moreover, both the density and distribution of 5-HT receptors may follow a different pattern in male and female rats. 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) is a centrally acting 5-HT agonist with a ligand binding profile showing selectivity towards 5-HT-1A receptor sites. The present article integrates research on neurochemical and behavioural effects of 8-OH-DPAT in male and female rats, in order to investigate sex-related differences in 5-HT-1A receptor dependent functions.

Effects of prenatal ethanol exposure on glucocorticoid receptors in rat hippocampus

Animals exposed to ethanol in utero are typically hyperresponsive to stressors in adulthood as indicated by increased adrenocortical activation and/or deficits in response inhibition or recovery following stress. In the present study we reasoned that a deficit in feedback control of pituitary-adrenal activity might underlie this hyperresponsiveness in fetal ethanol-exposed (FEE) animals. Further, we hypothesized that a long-term decrease in hippocampal glucocorticoid receptor concentration, induced by prenatal ethanol exposure, might mediate such a deficit in pituitary-adrenal feedback regulation. Male and female Sprague-Dawley rats from prenatal ethanol (E), pair-fed (PF), and control (C) treatment groups were tested in adulthood for determination of cytosolic hippocampal glucocorticoid receptor binding. No significant differences in specific binding (Bmax) or binding affinity (Kd) of either type I or type II glucocorticoid receptors were found among animals from E, PF, and C conditions. There were, however, significant sex differences in receptor concentration and binding affinity; females showed significantly greater maximal binding and significantly lower binding affinity than males. These data do not support the hypothesis that prenatal ethanol exposure induces a long-term decrease in hippocampal glucocorticoid receptors in animals tested under basal nonstressed conditions. However, these data do not preclude the possibility that receptor binding capacity may be differentially affected in E, PF, and C animals during stress.

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

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

Antidepressant and other centrally acting drugs regulate glucocorticoid receptor messenger RNA levels in rat brain

The effect of imipramine, desipramine, ketanserin and lithium on Type II glucocorticoid receptor (GR) mRNA levels was studied in rat brain regions involved in the control of the hypothalamo-pituitary-adrenal (HPA) axis, the dysregulation of which has been implicated in the pathophysiology of major depression. Northern blot analysis of Type II GR mRNA showed that treatment of male rats with either desipramine or imipramine increased hypothalamic and hippocampal GR mRNA levels. Upregulation of GR mRNA following administration of imipramine was found in brain regions of female rats, while desipramine had no effect. Ketanserin increased levels of GR mRNA in hippocampus of male, but not female, rats. Lithium also was able to induce important increases rat brain GR mRNA; this effect was particularly marked in females. We conclude that desipramine, imipramine, ketanserin and lithium can modulate GR mRNA in regions of rat brain involved in the control of the HPA axis and may have a common mechanism of action at the level of the GR gene. Sexual dimorphism for drug regulation of brain GR mRNA content was shown and may be related to sex differences in the prevalence of certain affective disorders.

Transient elevation of estrogen receptors in the neonatal rat hippocampus

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

Oestrogens down-regulate type I but not type II adrenal corticoid receptors in rat anterior pituitary

We have studied type I and type II adrenal cortical steroid receptors in the anterior (AL), intermediate (IL) and posterior (PL) lobes of the pituitary and in the hippocampus of ovariectomized-adrenalectomized female rats and in castrated-adrenalectomized male animals, with or without oestrogen treatment. Using [3H]dexamethasone as ligand and conditions suitable for determination of its binding to type I and type II receptors, we found that 4 or 15 days of oestrogen reduced type I receptors in AL by 50-60% without changes in IL, PL or hippocampus, or in type II sites in any of the four neuroendocrine tissues studied. This down-regulatory effect was seen only in female rats and no change was found for males. The reduction in type I sites in AL in oestrogenized female rats was confirmed by labelling type I sites with the synthetic antimineralocorticoid [3H]ZK 91587. Saturation analysis with [3H]ZK 91587 demonstrated that the reduction was due to a reduction in Bmax without change in Kd. We conclude that: (a) type I receptors in the anterior pituitary are under oestrogenic control; (b) there is a sex difference in the response to oestrogen of AL type I sites; and (c) this demonstration may be useful in determining the role of type I receptors in neuroendocrine regulation of the anterior pituitary by hormones derived from the adrenal cortex, and the participation of sex hormones in this process.

Hippocampal 5-hydroxytryptamine synthesis is greater in female rats than in males and more decreased by the 5-HT1A agonist 8-OH-DPAT

Brain regional 5-hydroxytryptamine (5-HT) and/or 5-hydroxyindoleacetic acid (5-HIAA) concentrations tended to be slightly higher in female rats than in males but differences were substantial only in the hippocampus where female values were 34% and 36% higher respectively. These findings were consistent with the synthesis rates of 5-HT as this was 53% greater in the female than in the male hippocampi. Other regions did not show significant sex differences. The 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT, 1 mg/kg sc) caused comparable decreases of 5-HT synthesis rate in both sexes and in all regions studied except the hippocampus where the percentage decrease was twice as large in the females (-64%) as in the males (-32%) so that the sex difference in 5-HT synthesis in this region largely disappeared. The results are discussed in relation to sex differences in behaviour and hippocampal function.

Sex difference in glucocorticoid binding in rat pituitary is estrogen dependent

Sex-dependent differences in corticosteroid binding were assessed in individual pituitaries from adult male and female rats that had been adrenalectomized 12 h before sacrifice. Soluble binding was assayed in duplicate on LH-20 columns. Gonadally intact females showed significantly less 3H-dexamethasone binding than did intact males (p less than 0.01). This difference was confirmed in a second study (p less than .001). However, when ovariectomized females were compared with gondadectomized males, there was no difference in receptor concentration. Estrogen was able to reverse the effect of ovariectomy: ovariectomized females receiving estrogen (10 micrograms/rat/day) had significantly fewer receptors than intact males; p less than 0.01). Progesterone (500 micrograms/rat/day) did not antagonize the effect of estrogen in the pituitary. A sex difference was also found in the Type I (mineralocorticoid) receptor subpopulation which comprised approximately 10% of the total receptors, with females having fewer receptors than males. These results demonstrate that in the pituitary, the level of functional corticosteroid receptors is subject to a 20% down-regulation by circulating levels of estrogen. This raises the possibility that the lower number of receptors in females may act to reduce their sensitivity to the negative feedback effects of glucocorticoids at the level of the pituitary.

Sex differences in aversive and appetitive conditioning in two strains of rats

In order to examine sex differences in non sexual behavior, 40 rats of each sex from two strains (gray, A x C and albino, Sprague-Dawley) were trained, using different experimental procedures. In Experiment I, aversive conditioning in a one-way (easy task) and a two-way (difficult task) active avoidance task was examined. Results consistently showed that males of both strains were inferior to females in the acquisition of the two-way avoidance task. A significant interaction between sex of both strains and the difficulty of the task was found. In Experiment II, rats were trained in a Sutherland Apparatus in an easy (black vs. white) and a difficult (horizontal vs. vertical) visual discrimination task, using appetitive reinforcement; no differences between sexes were observed. A significant interaction, however, was found between strain and task, indicating a lower performance of the A x C strain in the difficult task. The results are discussed within the theoretical framework of the Yerkes-Dodson Law, which states a relationship between drive level, performance and different degrees of task difficulty.

Exposure of rats to ethanol from postnatal days 4 to 8: alterations of cholinergic neurochemistry in the hippocampus and cerebellum at day 20

Brief neonatal ethanol exposure (3.0 g/kg/dose, twice daily; postnatal day (PN) 4 to PN8) resulted in cholinergic neurochemical alterations in the cerebellum, but not the hippocampus of rats assayed on PN20. Analysis revealed that the binding affinity of cerebellar muscarinic receptors for [3H]quinuclidinyl benzilate was decreased by ethanol, but only in female pups. Other gender-specific but treatment-independent cerebellar differences were identified as well, including lower levels of choline acetyltransferase activity and S1-level (1,000 x g) crude protein in males and females, respectively. No evidence of ethanol-induced cholinergic change was noted in the hippocampus of the same pups on PN20. However, collapsed across treatment, male hippocampi were found to contain less S1-level protein than their female counterparts. Neither muscarinic receptor density nor acetyl cholinesterase activity were found to differ between treatments or genders, in either brain region. Consistent with the developmental timetables for regional cholinergic synaptogenesis in the rat, observations on PN20 confirm a hypothesis of cerebellar cholinergic vulnerability and hippocampal cholinergic resilience to neonatal ethanol insult.

8-OH-DPAT increases corticosterone but not other 5-HT1A receptor-dependent responses more in females

The 5-HT1A receptor subtype agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) (50-1000 micrograms/kg s.c.) dose dependently increased rat plasma corticosterone. Tube restraint for 30 min also increased plasma corticosterone; this effect was completely blocked by (-)-pindolol (1 mg/kg i.p.). Increases of corticosterone following either 8-OH-DPAT injection or restraint were significantly greater in female animals. The restraint stress-induced changes but not those due to 8-OH-DPAT were decreased by pretreatment with the tranquiliser chlordiazepoxide (10 mg/kg i.p.). In anaesthetized rats, restraint no longer significantly affected corticosterone levels but 8-OH-DPAT caused increases which (though much attenuated) were significantly greater in the females. Dose-dependent increases of plasma corticosterone also resulted on infusing 8-OH-DPAT (500-1500 ng) into the paraventricular nucleus of the hypothalamus; increases were significantly greater in the females. As mentioned in the discussion, these results may be relevant to the greater incidents of depression in women and the possible role of adrenal corticoids in the illness.

The dendritic morphology of pyramidal neurons in the rat hippocampal CA3 area. II. Effects of gender and the environment

Sex differences in the dendritic structure of hippocampal CA3 pyramidal neurons were studied in Golgi-stained tissue from hooded rats that had been raised in either a relatively complex or an isolated environment from weaning for one month. Pyramidal neurons were sampled from both the short-shaft and long-shaft neuron categories as described by Fitch et al. The pattern of sex differences varies in different parts of the apical dendritic tree. In the apical tree proximal to the soma, females had more dendritic material than males. This pattern was attributable to the sex differences in the short-shaft neurons of rats from the more complex environment. The direction of sex differences was reversed in the distal apical dendritic tree where males had more dendritic material than females. As in the proximal dendritic tree, this pattern of sex differences stemmed from the short-shaft neurons of rats from the more complex environment. There were no sex differences in the basilar dendritic tree. Thus sex differences in the pyramidal neurons of hippocampal area CA3 vary with the portion of the dendritic tree examined, the type of pyramidal neuron, and the rearing environment of the animal.

Maternal adrenalectomy and adult offspring in a conflict situation in the rat

The effects of the absence of maternal adrenals during pregnancy (P), during lactation (L), during pregnancy and lactation (PL) were studied on pain suppressed behavior (punished drinking test) of the adult offspring in comparison with controls (C). The female L offspring showed a lower responsiveness to the anxiogenic stimulus, as demonstrated by increased water intake, decreased percentage of ineffective licks, and decreased time to perform 300 licks compared to C. The male L behavior was not affected. Reduced growth was not responsible for the reduced anxiogenic reactivity because also both male and female PL offspring had lower weight than C, but did not show any significant effect. Pain threshold in the tail flick test was the same in all types of offspring. Thus, absence of maternal adrenals, specifically during lactation, significantly affects behavior of female offspring. It is discussed whether this is due to the lack of a physiological influence of maternal adrenal hormones on brain ontogenesis (hippocampal glucocorticoid receptors), or on the development of the brain-pituitary-adrenal system during neonatal life of the offspring.

Dexamethasone effects on vascular volume and tissue hematocrit in experimental RG-2 gliomas and adjacent brain

We have studied the effects of dexamethasone, a corticosteroid commonly used to treat brain tumors, on vascular volume and tissue hematocrit in RG-2 experimental rat gliomas. 125I-RISA (radioiodinated serum albumin) was used to measure tissue plasma vascular volume (Vp) and 51Cr labeled red cells were used to measure tissue red cell volume (Vrbc). Quantitative autoradiography was used to obtain local measurements of Vp and Vrbc in different brain and tumor regions. From these experimentally measured values, we calculated the tissue vascular volume (Vv), tissue hematocrit (THct) and systemic arterial hematocrit (AHct). The value reported primarily reflect capillary and small vessel volumes since blood drained from larger vessels during tissue processing and large vascular structures were avoided during analysis of the autoradiographic images. A total of 110 tumors were studied in 29 animals. There was a consistent trend for Vp and Vv to be reduced in all tumor regions after dexamethasone treatment, although a significant decrease was seen only in tumor center. Dexamethasone did not affect Vp or Vv in tumor-free brain regions. Dexamethasone appeared to have little effect on Vrbc in any brain or tumor region. THct was consistently, although not significantly, higher in tumors after treatment with dexamethasone; THct in tumor-free brain regions was unaffected by dexamethasone treatment.

Adaptation of female rats to stress: shift to male pattern by inhibition of corticosterone synthesis

In a previous study, male rats showed behavioural deficits after a single restraint stress but not after 5 daily restraint periods (i.e. adaptation had developed): female rats although less affected by single restraint failed to adapt over the same time course. This sex difference was associated with the male but not the female rats showing enhanced behavioural responses to the 5-HT agonist 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) after 5 restraint periods. In the present study, the role of the greater increases of plasma corticosterone in stressed females in these sex differences was studied. The corticosterone synthesis inhibitor metyrapone (75 mg/kg i.p.) was given to attenuate the rise of corticosterone to a level typical of stressed males. This resulted in the behavioural deficits of the female rats being shifted in the direction of the male pattern. Thus, their deficits in open field activity and food intake after single and repeated stresses were potentiated and opposed respectively. The latter effect was associated with increased responses to 5-MeODMT. Metyrapone alone was without significant effect. Brain regional 5-HT metabolism was unaffected. The results are consistent with corticosterone facilitating adaptation to single restraint but impairing adaptation to repeated restraint. As failure to adapt to repeated stress is an animal model of depression, results as a whole suggest that increased corticoid levels and decreased 5-HT functional activity may have a role in the development of the illness and its greater incidence in women.

Steroid hormones and the brain: linking "nature" and "nurture"

Contrary to earlier belief, the genetic constitution of each cell of the body ("nature") is subject to modulation by environmental factors ("nurture") which act throughout the life of the organism to shape the individual characteristics. The nervous system adapts and changes with the environment that the organism experiences through genomic activity controlled by chemical messengers from other nerve cells and from endocrine secretions. The nervous system expresses receptors for a number of circulating hormones, and the location of these hormone receptors has revealed a great deal about the neuroanatomy of neuroendocrine and behavioral control processes. The brain controls the endocrine system through the hypothalamus and pituitary gland, and it responds to circulating hormones throughout each stage of life. These effects begin during early development (eg., sexual differentiation of the brain; effects of maternal or neonatal stress). They continue in adult life in response to cyclic events (eg., season of year; time of day, controlling reproduction and daily activity-sleep rhythms of behavior); and they also include the behavior of other animals which alters hormone output. Hormones also operate during the aging process and under conditions which induce neural damage such as hypoxia and stress. This overview summarizes involvement of steroid hormones of gonads and adrenals in many of these processes and also examines the features of the genomic activity which is modified by these hormones. This area of research is fruitful because it brings together molecular, anatomical, physiological and behavioral approaches in an attempt to understand the long-term plasticity of the nervous system.