Androgens alter corticotropin releasing hormone and arginine vasopressin mRNA within forebrain sites known to regulate activity in the hypothalamic-pituitary-adrenal axis

The adipose tissue keeps the score: priming of the adrenal-adipose tissue axis by early life stress predisposes women to obesity and cardiometabolic risk

Adverse Childhood Experiences (ACEs) refer to early life stress events, including abuse, neglect, and other psychosocial childhood traumas that can have long-lasting effects on a wide range of physiological functions. ACEs provoke sex-specific effects, whereas women have been shown to display a strong positive correlation with obesity and cardiometabolic disease. Notably, rodent models of chronic behavioral stress during postnatal life recapitulate several effects of ACEs in a sex-specific fashion. In this review, we will discuss the potential mechanisms uncovered by models of early life stress that may explain the greater susceptibility of females to obesity and metabolic risk compared with their male counterparts. We highlight the early life stress-induced neuroendocrine shaping of the adrenal-adipose tissue axis as a primary event conferring sex-dependent heightened sensitivity to obesity.

Cellular and serotonergic correlates of habituated neuroendocrine responses in male and female rats

Male and females appear equally capable of showing habituated hypothalamic-pituitary-adrenal (HPA) axis output responses to repeated exposures of the same challenge. Whether this reflects, within males and females, common mechanisms of decreased neuronal activity within stress responding, afferents to the paraventricular hypothalamic nucleus (PVH), the final common pathway to the HPA axis, has not been examined. Here we compared in adult male and female rats the extent to which declines in HPA axis responses to repeated restraint are met by habituated cellular (Fos) responses, in addition to changes in serotonin (5-hydroxytryptamine; 5-HT) expression and signaling, which normally stimulates the HPA axis. Thus, alterations in this component of HPA axis drive could provide an underlying basis for sex differences in adaptive responses. Males and females showed reliable declines in ACTH and corticosterone responses after 10 daily episodes of repeated restraint, recapitulated, in largest part, by similar regional patterns of Fos habituation, including within the PVH, several stress sensitive cell groups of the limbic forebrain, as well as within the raphe nucleus. Serotonin staining in the dorsal raphe and terminal profiles in the forebrain continued to reflect a higher pre-synaptic capacity for the 5-HT system in females. The sexual dimorphism encountered within the lateral septum and medial preoptic area of control animals was less distinguished in the repeat condition, however, whereas 5-HT varicosities in the PVH increased after repeated restraint only in females. Relative to their singly restrained counterparts, males displayed an increase in 5-HT 1 A receptor expression in the raphe nucleus after repeated restraint, whereas females showed a decrease in 5-HT 1 A mRNA levels in the hippocampus and in the zona incerta, representing the most proximal of cell groups expressing the 5-HT 1 A receptor in the vicinity of the PVH. In conclusion, similar regional profiles of cellular habituation in males and females suggest common CNS substrates of neuroendocrine adaptation. However, this process may be met by underlying sex differences in serotonergic control, given the respective roles for pre- and postsynaptic 5-HT 1 A receptors in mediating serotonin availability and signal transfer.

Androgens and Their Role in Regulating Sex Differences in the Hypothalamic/Pituitary/Adrenal Axis Stress Response and Stress-Related Behaviors

Androgens play a pivotal role during development. These gonadal hormones and their receptors exert organizational actions that shape brain morphology in regions controlling the stress regulatory systems in a male-specific manner. Specifically, androgens drive sex differences in the hypothalamic/pituitary/adrenal (HPA) axis and corresponding hypothalamic neuropeptides. While studies have examined the role of estradiol and its receptors in sex differences in the HPA axis and associated behaviors, the role of androgens remains far less studied. Androgens are generally thought to modulate the HPA axis through the activation of androgen receptors (ARs). They can also impact the HPA axis through reduction to estrogenic metabolites that can bind estrogen receptors in the brain and periphery. Such regulation of the HPA axis stress response by androgens can often result in sex-biased risk factors for stress-related disorders, such as anxiety and depression. This review focuses on the biosynthesis pathways and molecular actions of androgens and their nuclear receptors. The impact of androgens on hypothalamic neuropeptide systems (corticotropin-releasing hormone, arginine vasopressin, oxytocin, dopamine, and serotonin) that control the stress response and stress-related disorders is discussed. Finally, this review discusses potential therapeutics involving androgens (androgen replacement therapies, selective AR modulator therapies) and ongoing clinical trials.

The Hypothalamic-Pituitary-Adrenal Axis: Development, Programming Actions of Hormones, and Maternal-Fetal Interactions

The hypothalamic-pituitary-adrenal axis is a complex system of neuroendocrine pathways and feedback loops that function to maintain physiological homeostasis. Abnormal development of the hypothalamic-pituitary-adrenal (HPA) axis can further result in long-term alterations in neuropeptide and neurotransmitter synthesis in the central nervous system, as well as glucocorticoid hormone synthesis in the periphery. Together, these changes can potentially lead to a disruption in neuroendocrine, behavioral, autonomic, and metabolic functions in adulthood. In this review, we will discuss the regulation of the HPA axis and its development. We will also examine the maternal-fetal hypothalamic-pituitary-adrenal axis and disruption of the normal fetal environment which becomes a major risk factor for many neurodevelopmental pathologies in adulthood, such as major depressive disorder, anxiety, schizophrenia, and others.

Developmental conditions promote individual differentiation of endocrine axes and behavior in a tropical pinniped

Between-individual variation in behavior can emerge through complex interactions between state-related mechanisms, which include internal physiological constraints or feedback derived from the external environment. State-related conditions can be especially influential during early life, when parental effort and exposure to social stress may canalize consistent differences in offspring hormonal profiles and foster specific behavioral strategies. Here, we unravel how relevant state variables, including sex, somatic condition, local population density, and maternal traits, contribute to within-cohort differences in stress, sex, and thyroid hormone axes in dependent Galapagos sea lions with the primary goal of understanding downstream effects on boldness, docility, habitat use, and activity. Pups within denser natal sites had higher levels of cortisol and thyroid T4, a prohormone and proxy for metabolic reserves, likely as an adaptive physiological response after exposure to increased numbers of conspecific interactions. Furthermore, considering maternal effects, mothers in better body condition produced pups with higher testosterone yet downregulated basal cortisol and thyroid T4. This hormonal profile was correlated with increased boldness toward novel objects and attenuated stress responsiveness during capture. Intriguingly, pups with increased thyroid T3, the biologically active form, maintained faster somatic growth and were observed to have increased activity and extensively explored surrounding habitats. Collectively, these findings provide comprehensive evidence for several links to hormone-mediated behavioral strategies, highlighted by variation in socio-environmental and maternally derived input during a foundational life stage.

Roles for androgens in mediating the sex differences of neuroendocrine and behavioral stress responses

Estradiol and testosterone are powerful steroid hormones that impact brain function in numerous ways. During development, these hormones can act to program the adult brain in a male or female direction. During adulthood, gonadal steroid hormones can activate or inhibit brain regions to modulate adult functions. Sex differences in behavioral and neuroendocrine (i.e., hypothalamic pituitary adrenal (HPA) axis) responses to stress arise as a result of these organizational and activational actions. The sex differences that are present in the HPA and behavioral responses to stress are particularly important considering their role in maintaining homeostasis. Furthermore, dysregulation of these systems can underlie the sex biases in risk for complex, stress-related diseases that are found in humans. Although many studies have explored the role of estrogen and estrogen receptors in mediating sex differences in stress-related behaviors and HPA function, much less consideration has been given to the role of androgens. While circulating androgens can act by binding and activating androgen receptors, they can also act by metabolism to estrogenic molecules to impact estrogen signaling in the brain and periphery. This review focuses on androgens as an important hormone for modulating the HPA axis and behaviors throughout life and for setting up sex differences in key stress regulatory systems that could impact risk for disease in adulthood. In particular, impacts of androgens on neuropeptide systems known to play key roles in HPA and behavioral responses to stress (corticotropin-releasing factor, vasopressin, and oxytocin) are discussed. A greater knowledge of androgen action in the brain is key to understanding the neurobiology of stress in both sexes.

Effect of Yokukansan and Yokukansankachimpihange on Aggressive Behavior, 5-HT Receptors and Arginine Vasopressin Expression in Social Isolation-Reared Mice

The traditional herbal medicines yokukansan (YKS) and yokukansankachimpihange (YKSCH) are prescribed for neurosis, insomnia or night crying and irritability in children. YKSCH comprises YKS and two additional herbs, a chimpi and a hange, and is used to treat digestive function deficiencies. However, the differences between the effects of YKS and YKSCH on brain function are unclear. The present study examined the effects of YKS and YKSCH on aggressive behavior in mice reared under a social isolation (SI) condition. Mice were housed individually for 6 weeks. YKS and YKSCH were administered orally for 2 weeks before aggression tests. SI increased aggressive behavior against naïve mice, and YKS, but not YKSCH, significantly attenuated this aggressive behavior. Because serotonin (5-HT)_2A and 5-HT_3A receptor antagonists are reported to have anti-aggressive effects, the mRNA levels of these receptors were examined. YKS attenuated the SI-induced increase in 5-HT_2A and 5-HT_3A receptor mRNA in the amygdala. On the other hand, YKSCH attenuated the SI-induced increase in 5-HT_1A receptor mRNA. YKS and YKSCH did not affect 5-HT and its metabolite 5-hydroxyindoleacetic acid content in the amygdala. However, YKSCH increased the mRNA level of arginine vasopressin (AVP), which is a neuropeptide that has been implicated in aggression, in the amygdala. These results suggest that YKS ameliorates aggressive behavior by decreasing 5-HT_2A and 5-HT_3A receptor expression. The YKSCH-induced increase in AVP may disrupt the anti-aggressive effect of YKS. YKS may be more effective than YKSCH for treating irritability if digestive function deficiencies are not considered.

Sex-dependent effects of chronic variable stress on discrete corticotropin-releasing factor receptor 1 cell populations

Anxiety and depression are strikingly more prevalent in women compared with men. Dysregulation of corticotropin-releasing factor (CRF) binding to its cognate receptor (CRFR1) is thought to play a critical role in the etiology of these disorders. In the present study, we investigated whether there were sex differences in the effects of chronic variable stress (CVS) on CRFR1 cells using CRFR1-GFP reporter mice experiencing a 9-day CVS paradigm. Brains were collected from CVS and stress naïve female and male mice following exposure to the open field test. This CVS paradigm effectively increased anxiety-like behavior in female and male mice. In addition, we assessed changes in activation of CRFR1 cells (co-localization with c-Fos and phosphorylated CREB (pCREB)) in stress associated brain structures, including two sexually dimorphic CRFR1 cell groups in the anteroventral periventricular nucleus (AVPV/PeN; F>M) and paraventricular hypothalamus (PVN; M>F). CVS increased CRFR1-GFP cell number as well as the number of CRFR1/pCREB co-expressing cells in the female but not male AVPV/PeN. In the PVN, the number of CRFR1/pCREB co-expressing cells was overall greater in males regardless of treatment and CVS resulted in a male-specific reduction of CRFR1/c-Fos cells. In addition, CVS induced a female-specific reduction in CRFR1/c-Fos cells within the anteroventral bed nucleus of the stria terminalis and both sexes exhibited a reduction in CRFR1/c-Fos co-expressing cells following CVS within the ventral basolateral amygdala. Overall, these sex-specific effects of CVS on CRFR1 populations may have implications for sex differences in stress-induction of mood disorders.

Androgens Drive Sex Biases in Hypothalamic Corticotropin-Releasing Hormone Gene Expression After Adrenalectomy of Mice

Although prominent sex differences exist in the hypothalamic-pituitary-adrenal axis's response to stressors, few studies of its regulation in the hypothalamic paraventricular nucleus (PVN) have compared both male and female subjects. In this study, we sought to explore sex differences in the acute regulation of PVN neuropeptide expression following glucocorticoid (GC) removal and the underlying role of gonadal hormones. We first examined the effects of short-term adrenalectomy (ADX) on PVN Crh and arginine vasopressin (Avp) expression in mice using in situ hybridization. ADX increased PVN AVP mRNA levels in both sexes. In contrast, PVN CRH mRNA was increased by 2 days after ADX in males only. Both sexes showed increases in CRH mRNA after 4 days. To determine if gonadal hormones contributed to this sex bias, we examined adrenalectomized (ADX'd) and gonadectomized (GDX'd) mice with or without gonadal hormone replacement. Unlike the pattern in intact animals, 2 days following ADX/gonadectomy, CRH mRNA levels did not increase in either sex. When males were given DHT propionate, CRH mRNA levels increased in ADX'd/GDX'd males similar to those observed following ADX alone. To determine a potential mechanism, we examined the coexpression of androgen receptor (AR) immunoreactivity and CRH neurons. Abundant colocalization was found in the anteroventral bed nucleus of the stria terminalis but not the PVN. Thus, our findings reveal a sex difference in PVN Crh expression following the removal of GC-negative feedback that may depend on indirect AR actions in males.

Testosterone-cortisol dissociation in children exposed to prenatal maternal stress, and relationship with aggression: Project Ice Storm

Prenatal maternal stress (PNMS) has been associated with postnatal behavioral alterations that may be partly explained by interactions between the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes. Yet it remains unclear whether PNMS leads to enduring HPA-HPG alterations in the offspring, and whether HPA-HPG interactions can impact behavior during development, in particular levels of aggression in childhood. Here we investigated the relationship between a marker for HPG axis function (baseline testosterone) and a marker for HPA axis response (cortisol area under the curve) in 11½-year-olds whose mothers were exposed to the 1998 Quebec ice storm during pregnancy (n = 59 children; 31 boys, 28 girls). We examined (a) whether the degree of objective or subjective PNMS regulates the testosterone-cortisol relationship at age 11½, and (b) whether this testosterone-cortisol relationship is associated with differences in aggressive behavior. We found that, at lower levels of subjective PNMS, baseline testosterone and cortisol reactivity were positively correlated; in contrast, there was no relationship between these hormones at higher levels of subjective PNMS. Cortisol response moderated the relationship between testosterone and aggression. These results support the notion PNMS may explain variance in fetal HPA-HPG interactions, and that these interactions may be associated with aggressive behavior in late childhood.

Chronic Variable Stress Induces Sex-Specific Alterations in Social Behavior and Neuropeptide Expression in the Mouse

Chronic exposure to stressors impairs the function of multiple organ systems and has been implicated in increased disease risk. In the rodent, the chronic variable stress (CVS) paradigm has successfully modeled several stress-related illnesses. Despite striking disparities between men and women in the prevalence and etiology of disorders associated with chronic stress, most preclinical research examining chronic stressor exposure has focused on male subjects. One potential mediator of the consequences of CVS is oxytocin (OT), a known regulator of stress neurocircuitry and behavior. To ascertain the sex-specific effects of CVS in the C57BL/6 mouse on OT and the structurally similar neuropeptide arginine vasopressin (AVP), the numbers of immunoreactive and mRNA-containing neurons in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) were determined using immunohistochemistry and in situ hybridization, respectively. In addition, the mice underwent a battery of behavioral tests to determine whether CVS affects social behaviors known to be regulated by OT and AVP. Six weeks of CVS increased sociability in the female mouse and decreased PVN OT immunoreactivity (ir) and AVP mRNA. In the male mice, CVS decreased PVN OT mRNA but had no effect on social behavior, AVP, or OT-ir. CVS also increased the soma volume for PVN OT neurons. In contrast, OT and AVP neurons in the SON were unaffected by CVS treatment. These findings demonstrate clear sex differences in the effects of CVS on neuropeptides in the mouse, suggest a pathway through which CVS alters sociability and stress-coping responses in females and reveals a vulnerability to CVS in the C57BL/6 mouse strain.

Gonadal hormones modulate the HPA-axis and the SNS in response to psychosocial stress

Exposure to stress activates both the hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS). A growing body of research points to the contribution of sex hormones (testosterone, estrogen, and progesterone), the end products of the hypothalamus-pituitary-gonadal (HPG) axis, in modulating stress reactivity. The present study aimed at investigating the potential modulating role of sex hormones on HPA and SNS reactivity to psychosocial stress. The reactivity, induced by the Trier Social Stress Test, was analyzed by measuring the levels of cortisol and alpha-amylase (markers for SNS activity) in four saliva samples each of 21 men and 37 women (17 not using oral contraceptives and in their luteal phase, and 20 women using oral contraceptives). In addition, basal sex hormones were sampled prior to the psychosocial stress exposure. Results revealed that controlling for testosterone, estrogen, and progesterone diminished the impact of stress on cortisol reactivity and on alpha-amylase reactivity. Moreover, controlling for sex hormones also diminished the differential pattern of cortisol reactivity in each experimental group among responders. Furthermore, correlation analyses revealed differences between groups in the association between sex hormones and alpha-amylase. The present findings indicate a modulatory role for sex hormones in HPA and SNS reactivity and emphasize the need for control of sex hormone fluctuations when examining cortisol and alpha-amylase reactivity to stress.

Stress Response to Physical Exercise in Rats with Alimentary Obesity

Stress response to physical exercise was studied in rats with alimentary obesity with and without caloric diet restriction. Daily excretion of corticosterone, progesterone, and testosterone, weights of internal organs, and serum levels of glucose, free fatty acids, triglycerides, corticosterone, and testosterone were estimated. Stress response to moderate exercise in rats with alimentary obesity was associated with predominance of anabolic influence of testosterone over the catabolic effects of corticosterone, which promoted the increase in the weight of reproductive organs. Exposure to physical loads against the background of restricted ration potentiated the response of the adrenocortical system and reduced the concentration and anabolic effects of testosterone.

Assessment of Cardiac Vegetative Control during Acute Graduated Exogenous Normobaric Hypoxia in Rats

The effects of exogenous normobaric hypoxic hypoxia on vegetative control of the heart and BP were examined in Wistar rats. The reference ranges of variation pulsometry parameters were determined in rats with normoxemia for 3 physiological variants of autonomic homeostasis: eutony, sympathicotony, and vagotony. Most rats (80%) demonstrated autonomic eutony. The study showed that saturation of arterial blood with oxygen is the most adequate assessment of severity of acute exogenous normobaric hypoxic hypoxia progressing within a closed hypoxic chamber, which standardizes this method and minimizes inaccuracies resulting from individual sensitivity to hypoxic stress. The changes in functional activity of systems that control the heart rhythm closely correlated with the drop in arterial blood oxygenation. While a small arterial hypoxemia activated the ergotropic elements of autonomic nervous system central subdivision accompanied by elevation of systolic BP, the moderate hypoxemia augmented the cholinergic influences and moderated the adrenergic ones under maintaining mobilization of the central autonomic nervous system-control loop and normotension. Severe hypoxemia was manifested by augmented influences from autonomic nervous system central subdivisions on the heart rate, disadaptation of the control systems, and systolic-diastolic arterial hypotension.

Effects of Sex Steroids in the Human Brain

Sex steroids are thought to play a critical developmental role in shaping both cortical and subcortical structures in the human brain. Periods of profound changes in sex steroids invariably coincide with the onset of sex differences in mental health vulnerability, highlighting the importance of sex steroids in determining sexual differentiation of the brain. Yet, most of the evidence for the central effects of sex steroids relies on non-human studies, as several challenges have limited our understanding of these effects in humans: the lack of systematic assessment of the human sex steroid metabolome, the different developmental trajectories of specific sex steroids, the impact of genetic variation and epigenetic changes, and the plethora of interactions between sex steroids, sex chromosomes, neurotransmitters, and other hormonal systems. Here we review how multimodal strategies may be employed to bridge the gap between the basic and clinical understanding of sex steroid-related changes in the human brain.

Down, But Not Out: Partial Elimination of Androgen Receptors in the Male Mouse Brain Does Not Affect Androgenic Regulation of Anxiety or HPA Activity

We previously found that androgen receptor (AR) activity mediates two effects of T in adult male mice: reduction of anxiety-like behaviors and dampening of the hypothalamic-pituitary-adrenal response to stress. To determine whether brain ARs mediate these effects, we used the Cre/loxP technology seeking to disable AR throughout the central nervous system (CNS). Female mice carrying the floxed AR allele (ARlox) were crossed with males carrying cre recombinase transgene controlled by the nestin promoter (NesCre), producing cre in developing neurons and glia. Among male offspring, four genotypes resulted: males carrying ARlox and NesCre (NesARko), and three control groups (wild types, NesCre, and ARlox). Reporter mice indicated ubiquitous Cre expression throughout the CNS. Nevertheless, AR immunocytochemistry in NesARko mice revealed efficient knockout (KO) of AR in some brain regions (hippocampus and medial prefrontal cortex [mPFC]), but not others. Substantial AR protein was seen in the amygdala and hypothalamus among other regions, whereas negligible AR remained in others like the bed nucleus of the stria terminalis and dorsal periaqueductal gray. This selective KO allowed for testing the role of AR in hippocampus and mPFC. Males were castrated and implanted with T at postnatal day 60 before testing on postnatal day 90-100. In contrast with males with global KO of AR, T still modulated anxiety-related behavior and hypothalamic-pituitary-adrenal activity in NesARko males. These results leave open the possibility that AR acting in the CNS mediates these effects of T, but demonstrate that AR is not required in the hippocampus or mPFC for T's anxiolytic effects.

Overshadowed by the amygdala: the bed nucleus of the stria terminalis emerges as key to psychiatric disorders

The bed nucleus of the stria terminalis (BNST) is a center of integration for limbic information and valence monitoring. The BNST, sometimes referred to as the extended amygdala, is located in the basal forebrain and is a sexually dimorphic structure made up of between 12 and 18 sub-nuclei. These sub-nuclei are rich with distinct neuronal subpopulations of receptors, neurotransmitters, transporters and proteins. The BNST is important in a range of behaviors such as: the stress response, extended duration fear states and social behavior, all crucial determinants of dysfunction in human psychiatric diseases. Most research on stress and psychiatric diseases has focused on the amygdala, which regulates immediate responses to fear. However, the BNST, and not the amygdala, is the center of the psychogenic circuit from the hippocampus to the paraventricular nucleus. This circuit is important in the stimulation of the hypothalamic-pituitary-adrenal axis. Thus, the BNST has been largely overlooked with respect to its possible dysregulation in mood and anxiety disorders, social dysfunction and psychological trauma, all of which have clear gender disparities. In this review, we will look in-depth at the anatomy and projections of the BNST, and provide an overview of the current literature on the relevance of BNST dysregulation in psychiatric diseases.

Sex differences in the HPA axis

The hypothalamic-pituitary-adrenal (HPA) axis is a major component of the systems that respond to stress, by coordinating the neuroendocrine and autonomic responses. Tightly controlled regulation of HPA responses is critical for maintaining mental and physical health, as hyper- and hypo-activity have been linked to disease states. A long history of research has revealed sex differences in numerous components of the HPA stress system and its responses, which may partially form the basis for sex disparities in disease development. Despite this, many studies use male subjects exclusively, while fewer reports involve females or provide direct sex comparisons. The purpose of this article is to present sex comparisons in the functional and molecular aspects of the HPA axis, through various phases of activity, including basal, acute stress, and chronic stress conditions. The HPA axis in females initiates more rapidly and produces a greater output of stress hormones. This review focuses on the interactions between the gonadal hormone system and the HPA axis as the key mediators of these sex differences, whereby androgens increase and estrogens decrease HPA activity in adulthood. In addition to the effects of gonadal hormones on the adult response, morphological impacts of hormone exposure during development are also involved in mediating sex differences. Additional systems impinging on the HPA axis that contribute to sex differences include the monoamine neurotransmitters norepinephrine and serotonin. Diverse signals originating from the brain and periphery are integrated to determine the level of HPA axis activity, and these signals are, in many cases, sex-specific.

Sex differences in neurosteroid and hormonal responses to metyrapone in posttraumatic stress disorder

RATIONALE

Mechanisms contributing to sex differences in the regulation of acute stress responsivity and their effect on the increased incidence of posttraumatic stress disorder (PTSD) in women are poorly understood. The reproductive hormone, progesterone, through conversion to allopregnanolone (ALLO), suppresses the hypothalamic pituitary adrenal (HPA) axis and has potent anxiolytic effects. The potential that progesterone and allopregnanolone reactivity modulate HPA axis responses and account for sex differences in PTSD has not been previously examined.

OBJECTIVE

The present study examined the effects of sex and PTSD on adrenocorticotropic hormone (ACTH), progesterone, and allopregnanolone responses to metyrapone and whether progesterone and allopregnanolone reactivity could affect the ACTH response in PTSD.

METHODS

Healthy medication-free male and premenopausal follicular phase female participants with chronic PTSD (n = 43; 49 % female) and controls (n = 42; 50 % female) completed an overnight metyrapone challenge and ACTH, progesterone, and allopregnanolone were obtained by repeated blood sampling.

RESULTS

The increase in ACTH response to metyrapone was higher in PTSD subjects compared to controls and in women compared to men. Contrary to our initial prediction of an inverse relationship, progesterone and allopregnanolone were positively associated with ACTH. Progesterone and allopregnanolone partially mediated the relationship between PTSD and ACTH.

CONCLUSIONS

Our findings of increased ACTH to metyrapone in PTSD and in women may reflect heightened hypothalamic CRF hypersecretion. Progesterone and allopregnanolone partially mediated the ACTH response in PTSD. Further characterizing sex differences in these processes will advance our understanding of the pathophysiology of PTSD, and may ultimately lead to better-targeted, more effective treatment.

Gonadal steroid hormones and the hypothalamo-pituitary-adrenal axis

The hypothalamo-pituitary-adrenal (HPA) axis represents a complex neuroendocrine feedback loop controlling the secretion of adrenal glucocorticoid hormones. Central to its function is the paraventricular nucleus of the hypothalamus (PVN) where neurons expressing corticotropin releasing factor reside. These HPA motor neurons are a primary site of integration leading to graded endocrine responses to physical and psychological stressors. An important regulatory factor that must be considered, prior to generating an appropriate response is the animal's reproductive status. Thus, PVN neurons express androgen and estrogen receptors and receive input from sites that also express these receptors. Consequently, changes in reproduction and gonadal steroid levels modulate the stress response and this underlies sex differences in HPA axis function. This review examines the make up of the HPA axis and hypothalamo-pituitary-gonadal (HPG) axis and the interactions between the two that should be considered when exploring normal and pathological responses to environmental stressors.

Effects of testosterone and estradiol on stress-induced adrenal and hippocampal weight changes in female rats

OBJECTIVE

To examine the impact of circulating testosterone (T) and the T/Estradiol (T/Ediol) ratio on chronic stress-induced changes of adrenal and hippocampal weight during proestrus (PE) and estrus (E) in female rats.

DESIGN

Stress was composed of repeated vaginal smear screening (VSS) and measured by the emotional reactivity score (ERS). Adrenal and hippocampal weight and the T, Ediol and T/Ediol ratio were assessed in PE and E controls as well as 20 h after sham or left adrenalectomy performed on diestrus-2 (DE-2) and PE, respectively. T was measured in ovariectomized (OVX) rats treated with estradiol benzoate (EB) or vehicle (VEH) and in non-OVX EB-treated rats.

RESULTS

In OVX rats EB treatment increased adrenal weight and T levels. After separation of VEH- and EB-treated rats into the low and high T-range (below and above the mean, respectively), it was observed that higher T was accompanied by higher adrenal weight in EB- compared to VEH-treated rats only in the low T-range. Non-OVX EB-treated rats with high T had lower adrenal weight compared to low T. Cycling rats assigned to the high T-range presented higher T/Ediol ratio but similar ERS and Ediol levels compared to rats in the low T-range, and were characterized by reduced adrenal weight, higher hippocampal weight and prevalence of PE versus E.

CONCLUSIONS

High T and high T/Ediol ratios are prominent in PE compared to E and exert a protective effect on hippocampal neuronal degeneration after similar chronic stress through T-mediated lessening of stress response thus counteracting the stress-promoting effects of Ediol.

Sex difference in urocortin production is contributory to the gender disparity in a rat model of vasculitis induced by sodium laurate

Cardiovascular diseases, the most common leading death diseases, occur more in men than women of the same ages. Increasing evidence shows that urocortin (Ucn1), an autocrine or paracrine pro-inflammatory factor, can be regulated by sex hormones. The purpose of the study is to investigate the role of Ucn1 in gender disparity in a sodium laurate-induced vasculitis model. Rats exhibited visible signs of vasculitis on the 14th day after sodium laurate injection. Inflammatory states of the rat femoral artery were observed by histological examination. Significant gender disparity, with the symptoms much grosser in males than females, was seen. In males, the serum levels of Ucn1, prostaglandin estradiol, and soluble intercellular adhesion molecule-1 and the expressions of Ucn1, cyclooxygenase-2, and intercellular adhesion molecule-1 in femoral artery were higher than those in females. Orchidectomy significantly ameliorated the symptoms of vasculitis accompanied with a decrease in the plasma Ucn1 level. However, estradiol supplement after orchidectomy failed to improve the inflammatory states further. In females, ovariectomy and/or dihydrotestosterone supplement significantly increased Ucn1 level and exacerbated symptoms of vasculitis. Furthermore, ip administration of rabbit antiserum to Ucn1 almost abolished the gender differences in vasculitis. These results demonstrated that vasculitis of this model is androgen-responsive and hormonal manipulation by surgical orchidectomy could substantially attenuate the symptoms of vasculitis. Moreover, Ucn1 is a contributory factor to the gender disparity in vasculitis and dihydrotestosterone-promoted Ucn1 secretion exacerbated the development of vasculitis.

Age-dependent and gender-dependent regulation of hypothalamic-adrenocorticotropic-adrenal axis

Tightly regulated output of glucocorticoids is critical to maintaining immune competence, the structure of neurons, muscle, and bone, blood pressure, glucose homeostasis, work capacity, and vitality in the human and experimental animal. Age, sex steroids, gender, stress, body composition, and disease govern glucocorticoid availability through incompletely understood mechanisms. According to an ensemble concept of neuroendocrine regulation, successful stress adaptations require repeated incremental signaling adjustments among hypothalamic corticotropin-releasing hormone and arginine vasopressin, pituitary adrenocorticotropic hormone, and adrenal corticosteroids. Signals are transduced via (positive) feedforward and (negative) feedback effects. Age and gonadal steroids strongly modulate stress-adaptive glucocorticoid secretion by such interlinked pathways.

Glucocorticoids regulation of FosB/ΔFosB expression induced by chronic opiate exposure in the brain stress system

Chronic use of drugs of abuse profoundly alters stress-responsive system. Repeated exposure to morphine leads to accumulation of the transcription factor ΔFosB, particularly in brain areas associated with reward and stress. The persistent effects of ΔFosB on target genes may play an important role in the plasticity induced by drugs of abuse. Recent evidence suggests that stress-related hormones (e.g., glucocorticoids, GC) may induce adaptations in the brain stress system that is likely to involve alteration in gene expression and transcription factors. This study examined the role of GC in regulation of FosB/ΔFosB in both hypothalamic and extrahypothalamic brain stress systems during morphine dependence. For that, expression of FosB/ΔFosB was measured in control (sham-operated) and adrenalectomized (ADX) rats that were made opiate dependent after ten days of morphine treatment. In sham-operated rats, FosB/ΔFosB was induced after chronic morphine administration in all the brain stress areas investigated: nucleus accumbens(shell) (NAc), bed nucleus of the stria terminalis (BNST), central amygdala (CeA), hypothalamic paraventricular nucleus (PVN) and nucleus of the solitary tract noradrenergic cell group (NTS-A(2)). Adrenalectomy attenuated the increased production of FosB/ΔFosB observed after chronic morphine exposure in NAc, CeA, and NTS. Furthermore, ADX decreased expression of FosB/ΔFosB within CRH-positive neurons of the BNST, PVN and CeA. Similar results were obtained in NTS-A(2) TH-positive neurons and NAc pro-dynorphin-positive neurons. These data suggest that neuroadaptation (estimated as accumulation of FosB/ΔFosB) to opiates in brain areas associated with stress is modulated by GC, supporting the evidence of a link between brain stress hormones and addiction.

Central vasopressin V1A receptor blockade impedes hypothalamic-pituitary-adrenal habituation to repeated restraint stress exposure in adult male rats

Previous studies suggest that central arginine vasopressin (AVP) signaling can inhibit the hypothalamic-pituitary-adrenal (HPA) axis. To test a role for the AVP V1A receptor in stress HPA axis habituation, adult male rats were exposed to 5 consecutive days of 3 h restraint with or without continuous intracerebroventricular infusion of the V1A receptor antagonist d(CH2)5Tyr(Me)AVP (10 μg/day). Assessment of neuropeptide expression and HPA output under basal conditions revealed no effects of V1A receptor antagonism in stress naive animals. Between the first and last day of restraint exposure, controls showed marked declines in ACTH and corticosterone responses, and maintained plasma concentrations of testosterone. In contrast, V1A receptor antagonized animals displayed significantly smaller declines in ACTH and corticosterone responses, and a decrease in plasma testosterone. Despite their reduced expression of HPA axis habituation, antagonized animals continued to show stress-induced increases in AVP mRNA in the hypothalamic paraventricular nucleus and bed nucleus of the stria terminalis, and even higher levels of AVP expression in the medial amygdala relative to controls. The data leave open the nature and extent to which these and other AVP-containing pathways are recruited during repeated restraint, but nevertheless reveal a critical role for central V1A receptors in stress adaptation. As the effects of V1A receptor antagonism were restricted to the repeated restraint condition, we conclude that normal adaptation to stress involves a shift toward enhanced AVP utilization and/or V1A receptor signaling.

Social subordination impairs hypothalamic-pituitary-adrenal function in female rhesus monkeys

Linear dominance hierarchies organize and maintain stability in female rhesus macaque (Macaca mulatta) social groups regardless of group size. As a consequence of their low social status, subordinate females suffer from an array of adverse outcomes including reproductive compromise, impaired immune function, and poor cardiovascular health. However, data that differentiate limbic-hypothalamic-pituitary-adrenal axis (LHPA) parameters between dominant from subordinate female monkeys are inconsistent, bringing into question whether social subordination alters the LHPA axis in female macaques. One difficulty in examining LHPA function in macaques may be the confounding effects of cycling ovarian steroids that are known to modulate LHPA activity. The current study used ovariectomized dominant and subordinate female rhesus monkeys to examine the effect that social subordination has on LHPA function by measuring morning and diurnal serum cortisol levels, dexamethasone (Dex) suppression of cortisol, metabolic clearance of Dex, and ACTH stimulation of adrenal cortisol release and cortisol response following exposure to acute social isolation. Compared to dominant females, subordinate females showed diminished morning peak cortisol secretion, weakened glucocorticoid negative feedback, and decreased adrenal cortisol response to an ACTH challenge as well as a restrained cortisol response following social isolation. However, the metabolism of Dex did not account for differences in Dex suppression between dominant and subordinate females. These results indicate that the ability to mount and limit glucocorticoid release is significantly reduced by psychosocial stress in female rhesus macaques, suggesting a hyporesponsive LHPA phenotype which resembles that observed in several human psychopathologies.

Dihydrotestosterone differentially modulates the cortisol response of the hypothalamic-pituitary-adrenal axis in male and female rhesus macaques, and restores circadian secretion of cortisol in females

Here we used a within-subject design to evaluate hypothalamic-pituitary-adrenal (HPA) activity following replacement of low and high physiological levels of testosterone (T) to adult, gonadally-suppressed, male rhesus macaques, and replacement with sex-specific low and high physiological doses of dihydrotestosterone (DHT) in the same adult males as well as in adult, gonadally-suppressed, female rhesus macaques. As indexes of HPA axis activation following T and DHT replacement, serum levels of cortisol (CORT) were measured before and following dexamethasone (DEX) inhibition, and corticotrophin-releasing factor (CRF) induced activation. Female monkeys were assessed for differences in response associated with dominant (DOM) and subordinate (SUB) social status. Data show that the high physiological dose of DHT significantly decreased basal CORT in both male and female monkeys irrespective of social status, but reduced CRF-stimulated CORT only in males. SUB female monkeys showed a trend towards increased CRF-stimulated CORT release under high-dose DHT replacement compared to DOM females or males given the same treatment, indicating that androgens likely have no influence on reducing HPA activation under chronic psychosocial stress in females. The normal circadian rhythm of CORT release was absent in placebo-replaced SUB and DOM females and was restored with low-dose DHT replacement. These results indicate that DHT significantly reduces CRF-stimulated CORT release only in male monkeys, and plays a role in maintaining circadian changes in CORT release in female monkeys.

Stress and glucocorticoids regulated corticotropin releasing factor in rat prefrontal cortex

Corticotropin releasing factor (CRF) is considered as the central driving force in the stress response and plays a key role in the pathogenesis of depression. CRF neurons have been identified to locate in most regions of the prefrontal cortex (PFC), a brain region that is highly associated with the control of emotion and cognition. However, little is known on the regulation of CRF in this region. In this study, we aimed to identify the regulatory effect of acute restraint stress and glucocorticoid on PFC CRF and characterize the possible function of CRF in the PFC. We found that acute restraint stress increased and glucocorticoid decreased PFC CRF mRNA expression. The expression of glucocorticoid receptor (GR) was found to colocalize with CRF neurons in the PFC. In addition, recruitment of GR by the CRF promoter was observed in vivo. Specific attention was paid to the effect of CRF on CRF receptor 1 (CRFR1) expression in primary PFC cultures. The results showed that CRF increased CRFR1 expression through the MEK-ERK1/2 pathway. In summary, this study may contribute to the better understanding of CRF functions in the PFC.

Androgen receptors in the posterior bed nucleus of the stria terminalis increase neuropeptide expression and the stress-induced activation of the paraventricular nucleus of the hypothalamus

The posterior bed nuclei of the stria terminalis (BST) are important neural substrate for relaying limbic influences to the paraventricular nucleus (PVN) of the hypothalamus to inhibit hypothalamic-pituitary-adrenal (HPA) axis responses to emotional stress. Androgen receptor-expressing cells within the posterior BST have been identified as projecting to the PVN region. To test a role for androgen receptors in the posterior BST to inhibit PVN motor neurons, we compared the effects of the non-aromatizable androgen dihydrotestosterone (DHT), the androgen receptor antagonist hydroxyflutamide (HF), or a combination of both drugs implanted unilaterally within the posterior BST. Rats bearing unilateral implants were analyzed for PVN Fos induction in response to acute-restraint stress and relative levels of corticotrophin-releasing hormone and arginine vasopressin (AVP) mRNA. Glutamic acid decarboxylase (GAD) 65 and GAD 67 mRNA were analyzed in the posterior BST to test a local involvement of GABA. There were no changes in GAD expression to support a GABA-related mechanism in the BST. For PVN neuropeptide expression and Fos responses, basic effects were lateralized to the sides of the PVN ipsilateral to the implants. However, opposite to our expectations of an inhibitory influence of androgen receptors in the posterior BST, PVN AVP mRNA and stress-induced Fos were augmented in response to DHT and attenuated in response to HF. These results suggest that a subset of androgen receptor-expressing cells within the posterior BST region may be responsible for increasing the biosynthetic capacity and stress-induced drive of PVN motor neurons.

A role for the androgen metabolite, 5alpha androstane 3beta, 17beta diol (3β-diol) in the regulation of the hypothalamo-pituitary-adrenal axis

Activation of the hypothalamo-pituitary-adrenal (HPA) axis is a basic reaction of animals to environmental perturbations that threaten homeostasis. These responses are ultimately regulated by neurons residing within the paraventricular nucleus (PVN) of the hypothalamus. Within the PVN, corticotrophin-releasing hormone (CRH), vasopressin (AVP), and oxytocin (OT) expressing neurons are critical as they can regulate both neuroendocrine and autonomic responses. Estradiol (E2) and testosterone (T) are well known reproductive hormones; however, they have also been shown to modulate stress reactivity. In rodent models, evidence shows that under some conditions E2 enhances stress activated adrenocorticotropic hormone (ACTH) and corticosterone secretion. In contrast, T decreases the gain of the HPA axis. The modulatory role of testosterone was originally thought to be via 5 alpha reduction to the potent androgen dihydrotestosterone (DHT) and its subsequent binding to the androgen receptor, whereas E2 effects were thought to be mediated by estrogen receptors alpha (ERalpha) and beta (ERbeta). However, DHT has been shown to be metabolized to the ERbeta agonist, 5α- androstane 3β, 17β Diol (3β-Diol). The actions of 3β-Diol on the HPA axis are mediated by ERbeta which inhibits the PVN response to stressors. In gonadectomized rats, ERbeta agonists reduce CORT and ACTH responses to restraint stress, an effect that is also present in wild-type but not ERbeta-knockout mice. The neurobiological mechanisms underlying the ability of ERbeta to alter HPA reactivity are not currently known. CRH, AVP, and OT have all been shown to be regulated by estradiol and recent studies indicate an important role of ERbeta in these regulatory processes. Moreover, activation of the CRH and AVP promoters has been shown to occur by 3β-Diol binding to ERbeta and this is thought to occur through alternate pathways of gene regulation. Based on available data, a novel and important role of 3β-Diol in the regulation of the HPA axis is suggested.

The medial preoptic nucleus integrates the central influences of testosterone on the paraventricular nucleus of the hypothalamus and its extended circuitries

Testosterone contributes to sex differences in hypothalamic-pituitary-adrenal (HPA) function in humans and rodents, but the central organization of this regulation remains unclear. The medial preoptic nucleus (MPN) stands out as an important candidate in this regard because it contains androgen receptors and projects to forebrain nuclei integrating cognitive-affective information and regulating HPA responses to homeostatic threat. These include the HPA effector neurons of the paraventricular nucleus (PVN) of the hypothalamus, medial amygdala, and lateral septum. To test the extent to which androgen receptors in the MPN engage these cell groups, we compared in adult male rats the effects of unilateral microimplants of testosterone and the androgen receptor antagonist hydroxyflutamide into the MPN on acute restraint induced activation and/or neuropeptide expression levels. The basic effects of these implants were lateralized to the sides of the nuclei ipsilateral to the implants. Testosterone, but not hydroxyflutamide implants, decreased stress-induced Fos and arginine vasopressin (AVP) heteronuclear RNA expression in the PVN, as well as Fos expression in the lateral septum. In unstressed animals, AVP mRNA expression in the PVN decreased and increased in response to testosterone and hydroxflutamide MPN implants, respectively. The differential influences of these implants on AVP mRNA expression were opposite in the medial amygdala. These results confirm a role for androgen receptors in the MPN to concurrently modulate neuropeptide expression and activational responses in the PVN and its extended circuitries. This suggests that the MPN is capable of bridging converging limbic influences to the HPA axis with changes in gonadal status.

Follicle growth and oocyte development after ovary transplantation into back muscle of immune-intact adult castrated male mice

Ovary grafting is not only a method of investigating follicle and oocyte development, but also a useful model to explore the possibility of the re-establishment of the reproductive axis in male-to-female sexual reversal. This study investigated ovary survival and follicle development after mouse ovaries were transplanted into immune-intact castrated male mice. Ten-day-old mouse ovaries were transplanted into the back muscle of adult outbred castrated male mice treated with immunosuppressants. Twenty-two days later, the ovary structure and the number of follicles present was examined by hematoxylin and eosin staining. The oocytes were harvested, and then used for in vitro maturation (IVM) and IVF. The results showed that primordial and antral follicles were mainly found in the grafts, and there were obvious differences compared with 32-day-old fresh ovaries (P<0.05). Embryos were derived from collected oocytes after IVM and IVF with a 72.4% cleavage rate and 7.9% blastocyst rate; 12 live pups were generated by embryo transfer. The hormone assay showed that plasma concentrations of both estrogen and progesterone increased after ovarian transplantation (P<0.01). In conclusion, immune-intact adult castrated male mice can support ovary survival and further development of follicles with endocrine function after ovarian transplantation.

Estrogen receptor beta activation prevents glucocorticoid receptor-dependent effects of the central nucleus of the amygdala on behavior and neuroendocrine function

Neuropsychiatric disorders such as anxiety and depression have formidable economic and societal impacts. A dysregulation of the hypothalamo-pituitary-adrenal (HPA) axis leading to elevated endogenous glucocorticoid levels is often associated with such disorders. Chronically high glucocorticoid levels may act upon the central nucleus of the amygdala (CeA) to alter normally adaptive responses into those that are maladaptive and detrimental. In addition to glucocorticoids, other steroid hormones such as estradiol and androgens can also modify hormonal and behavioral responses to threatening stimuli. In particular, estrogen receptor beta (ERbeta) agonists have been shown to be anxiolytic. Consequently, these experiments addressed the hypothesis that the selective stimulation of glucocorticoid receptor (GR) in the CeA would increase anxiety-like behaviors and HPA axis reactivity to stress, and further, that an ERbeta agonist could modulate these effects. Young adult female Sprague-Dawley rats were ovariectomized and bilaterally implanted via stereotaxic surgery with a wax pellet containing the selective GR agonist RU28362 or a blank pellet, to a region just dorsal to the CeA. Four days later, animals were administered the ERbeta agonist S-DPN or vehicle (with four daily sc injections). Anxiety-type behaviors were measured using the elevated plus maze (EPM). Central RU28362 implants caused significantly higher anxiety-type behaviors in the EPM and greater plasma CORT levels than controls given a blank central implant. Moreover, S-DPN treated animals, regardless of type of central implant, displayed significantly lower anxiety-type behaviors and post-EPM plasma CORT levels than vehicle treated controls or vehicle treated animals implanted with RU28362. These results indicate that selective activation of GR within the CeA is anxiogenic, and peripheral administration of an ERbeta agonist can overcome this effect. These data suggest that estradiol signaling via ERbeta prevents glucocorticoid-dependent effects of the CeA on behavior and neuroendocrine function.

Salivary testosterone, cortisol, and progesterone: two-week stability, interhormone correlations, and effects of time of day, menstrual cycle, and oral contraceptive use on steroid hormone levels

With salivary assessment of steroid hormones increasing, more work is needed to address fundamental properties of steroid hormone levels in humans. Using a test-retest design and radioimmunoassay assessment of salivary steroids, we tested the reliability of testosterone, cortisol, and progesterone levels across two weeks, as well as the effects of oral contraceptives, menstrual cycle phase, and time of day on steroid hormone levels. Testosterone and cortisol were found to be highly reliable in both sexes. Progesterone was found to be reliable after collapsing across sex. Oral contraceptive use was associated with lower levels of testosterone, but did not affect cortisol. Contrary to expectations, oral contraceptives also did not affect progesterone. Menstrual cycle was found to affect levels of progesterone, but not testosterone or cortisol. Time of day had an effect on cortisol, on progesterone only at one testing time, and no effect on testosterone. We explored the interhormone correlations among testosterone, progesterone, and cortisol. All three hormones were positively correlated with one another in men. In women, progesterone was positively correlated with testosterone and cortisol, but testosterone and cortisol were uncorrelated.

A comparison of two repeated restraint stress paradigms on hypothalamic-pituitary-adrenal axis habituation, gonadal status and central neuropeptide expression in adult male rats

The available evidence continues to illustrate an inhibitory influence of male gonadal activity on the hypothalamic-pituitary-adrenal (HPA) axis under acute stress. However, far less is known about how these systems interact during repeated stress. Because HPA output consistently declines across studies examining repeated restraint, the potential mechanisms mediating this habituation are often inferred as being equivalent, even though these studies use a spectrum of restraint durations and exposures. To test this generalisation, as well as to emphasise a potential influence of the male gonadal axis on the process of HPA habituation, we compared the effects of two commonly used paradigms of repeated restraint in the rodent: ten daily episodes of 0.5 h of restraint and five daily episodes of 3 h of restraint. Both paradigms produced comparable declines in adrenocorticotrophic hormone and corticosterone between the first and last day of testing. However, marked differences in testosterone levels, as well as corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) expression, occurred between the two stress groups. Plasma testosterone levels remained relatively higher in animals exposed to 0.5 h of restraint compared to 3 h of restraint, whereas forebrain gonadotrophin-releasing hormone (GnRH) cell counts increased in both groups. AVP mRNA was increased after 3 h, but not after 0.5 h of repeated restraint, in the medial parvicellular paraventricular nucleus and in the posterior bed nucleus of the stria terminalis (BST), and increased with 0.5 h of repeated restraint in the medial amygdala. CRH mRNA was increased after 3 h, but not after 0.5 h of repeated restraint, in the central amygdala and anterior BST. The data obtained illustrate that, despite comparable declines in HPA responses, the pathways recruited for stress adaptation appear to be distinct between restraint groups. Given the extreme sensitivity of limbic AVP to testosterone, and conversely CRH to circulating glucocorticoids, whether differences in endocrine profiles might explain these neuropeptide differences remains to be seen. Nonetheless, the present study provides several new entry points for testing gonadal influences on stress-specific HPA habituation.

Role of testosterone in mediating prenatal ethanol effects on hypothalamic-pituitary-adrenal activity in male rats

Prenatal ethanol (E) exposure programs the fetal hypothalamic-pituitary-adrenal (HPA) and -gonadal (HPG) axes such that E rats show HPA hyperresponsiveness to stressors and altered HPG and reproductive function in adulthood. Importantly, prenatal ethanol may differentially alter stress responsiveness in adult male and female offspring compared to their control counterparts. To test the hypothesis that alterations in HPA activity in E males are mediated, at least in part, by ethanol-induced changes in the capacity of testosterone to regulate HPA activity, we explored dose-related effects of testosterone on HPA and HPG function in adult male offspring from prenatal E, pair-fed (PF) and ad libitum-fed control (C) dams. Our data suggest that E males show changes in both HPA and HPG regulation, as well as altered sensitivity to the inhibitory effects of testosterone. While gonadectomy (GDX) reduced weight gain in all animals, low testosterone replacement restored body weights in PF and C but not E males. Further, sensitivity of the thymus and adrenal to circulating testosterone was reduced in E rats. In addition, stress-induced corticosterone (CORT) levels were increased in PF and C but not E males following GDX, and while low dose testosterone replacement restored CORT levels for PF and C, high testosterone levels were needed to normalize CORT levels for E males. A negative correlation between pre-stress testosterone and post-stress CORT levels in C but not in E and PF males further supports the finding of reduced sensitivity to testosterone. Importantly, testosterone appeared to have reduced effects on central corticotrophin releasing hormone (CRH) pathways in E, but greater effects on central arginine vasopressin (AVP) pathways in E and/or PF compared to C males. Testosterone also had less of an inhibitory effect on stress-induced luteinizing hormone increases in E than in PF and C males following GDX. In addition, androgen receptor mRNA levels in the medial preoptic nucleus and the principal nucleus of posterior bed nucleus of the stria terminalis were lower in E and PF compared to C males under intact conditions. Together, these data support our previous work suggesting altered sensitivity to testosterone in E males. Furthermore, differential effects of testosterone on the complex balance between central CRH and central AVP pathways may play a role in the HPA alterations observed. That some findings were similar in E and PF males suggest that nutritional effects of diet may have played a role in mediating at least some of the changes seen in E animals.

Naturally occurring variations in defensive burying behavior are associated with differences in vasopressin, oxytocin, and androgen receptors in the male rat

Largely ignored in tests of defensive burying is the capacity for individual animals to display marked variations in active coping behaviors. To expose the neurobiological correlates of this behavioral differentiation rats were exposed to a mousetrap that was remotely triggered upon approach to remove the quality of pain. Relative to animals showing no significant levels of defensive burying activity, rats showing sustained elevations in defensive burying displayed higher levels of arginine vasopressin (AVP) mRNA and increased numbers of androgen receptor positive cells in the medial amygdala and posterior bed nuclei of the stria terminalis, brain regions that integrate emotional appraisal and sensory information. In contrast, animals showing little to no defensive burying responses displayed relatively higher levels of AVP and oxytocin (OT) mRNA within the supraoptic nucleus and subregions of the paraventricular nucleus of the hypothalamus responsible for neuroendocrine and autonomic function. Finally, animals showing sustained levels of burying also displayed increased levels of testosterone and pituitary-adrenal hormones under stress conditions. These findings implicate roles for central AVP and OT in mediating differential avoidance behaviors and demonstrate the utility of using a pain-free test of defensive burying as a framework for exploring naturally occurring differences in coping style and neuroendocrine capacity.

Dihydrotestosterone modulates spatial working-memory performance in male mice

Androgens affect cognitive processes in both humans and animals. The effects of androgens may be limited to certain cognitive domains, specifically spatial memory, but this hypothesis remains elusive. Here, we tested castrated and sham-operated mice in various behavioral tasks to ask whether androgens affect multiple or specific cognitive domains in male mice. Castration impaired spatial working memory performance in the delayed matching to place water maze task following a 1-h, but not a 1-min, retention interval, as has been reported for rats. In contrast, castration had no effect on novel object recognition memory, spatial reference memory in the water maze, motor coordination, or passive avoidance memory. Castration increased anxiety-like behavior in the open field test, but not the elevated zero maze. Finally, we assessed the effects of androgen replacement with non-aromatizable dihydrotestosterone on spatial working memory following various retention intervals. Dihydrotestosterone recovered spatial memory performance following a 24-h, but not a 1-h retention interval, and had no effect at other retention intervals. These data support that in male mice androgens specifically affect spatial working memory performance, and that the neurobiological processes underlying spatial memory formation may be differentially affected by androgens.

HPA-axis regulation at in-patient admission is associated with antidepressant therapy outcome in male but not in female depressed patients

A concatenation of data implicates a hyperactivity of the hypothalamus pituitary adrenal (HPA)-axis in the pathogenesis of depression and its normalization as a necessary predecessor of clinical response to antidepressant drugs. In addition, regulation of the HPA-axis has been shown to be dependent on sex hormones. We therefore investigated gender differences in HPA-axis regulation in depression and its normalization during remission of clinical symptoms. We used the combined dexamethasone suppression/CRH stimulation (Dex-CRH) test to evaluate the degree of HPA-axis dysregulation in 194 in-patients with unipolar depression from the Munich Antidepressant Response Signature (MARS) study at both admission and discharge. The Hamilton Depression (HAM-D) Rating Scale was used to monitor clinical response to antidepressant treatment. For both genders, we observed a normalization of HPA-axis dysregulation in remitters but not in non-remitters, both after 5 weeks of treatment and at discharge. The pattern of HPA-axis normalization with remission of depressive symptoms, however, showed gender-specific differences. In male patients, remission after 5 weeks of in-patient treatment was associated with a significantly higher cortisol response in the Dex-CRH test at admission. In female patients, 5-week remitters and non-remitters had a comparable cortisol response at admission. Cortisol response at admission was not correlated with gonadal steroid levels at this time point and the results were similar for pre-menopausal women vs. post-menopausal women. Gender-associated biological characteristics, likely independent of circulating gonadal steroids, thus seem to influence HPA-axis regulation in depression. In male patients, a single measure of HPA-axis dysregulation at admission may serve as a predictor of response to antidepressant treatment in addition to the previously reported repeated measure of the Dex-CRH test.

Selective contributions of the medial preoptic nucleus to testosterone-dependant regulation of the paraventricular nucleus of the hypothalamus and the HPA axis

Previous data have consistently demonstrated an inhibitory effect of androgens on stress-induced hypothalamic-pituitary-adrenal (HPA) responses. Several brain regions may influence androgen-mediated inhibition of the HPA axis, including the medial preoptic area. To test the role of the medial preoptic nucleus (MPN) specifically, we examined in high- and low-testosterone-replaced gonadectomized rats bearing discrete bilateral lesions of the MPN basal and stress-induced indexes of HPA function, and the relative levels of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) mRNA in the amygdala. High testosterone replacement decreased plasma adrenocorticotropin hormone (ACTH) and paraventricular nucleus (PVN) Fos responses to restraint exposure in sham- but not in MPN-lesioned animals. AVP-, but not CRH-immunoreactivity staining in the external zone of the median eminence was increased by testosterone in sham animals, and MPN lesions blocked this increment in AVP. A similar interaction between MPN lesions and testosterone occurred on AVP mRNA levels in the medial nucleus of the amygdala. These findings support an involvement of MPN projections in mediating the AVP response to testosterone in both the medial parvocellular PVN and medial amygdala. We conclude that the MPN forms part of an integral circuit that mediates the central effects of gonadal status on neuroendocrine and central stress responses.

Neonatal gonadectomy and adult testosterone replacement suggest an involvement of limbic arginine vasopressin and androgen receptors in the organization of the hypothalamic-pituitary-adrenal axis

Testosterone exposure during critical periods of development exerts major organizing effects on the hypothalamic-pituitary-adrenal (HPA) axis. Here we examined how neonatal gonadectomy (GDX) with or without testosterone treatment during the first week of life alters the HPA response to adult testosterone replacement in 65-d-old male rats. As adults, neonatal GDX rats showed higher levels of plasma corticosterone and Fos activation in medial parvocellular part of the paraventricular nucleus of the hypothalamus under basal conditions and during 30 min of restraint exposure. These responses were normalized with testosterone treatment on postnatal d 1-5 but were not restored with adult testosterone replacement. As adults, neonatal GDX rats also showed a decrease in the number of androgen receptor and arginine vasopressin-positive cells in the bed nucleus of the stria terminalis and in the medial nucleus of the amygdala, and both of these responses were reversed with postnatal testosterone treatment. In stressed and unstressed animals, the number of androgen receptors and arginine vasopressin-expressing neurons in both of these nuclei correlated negatively with corticosterone concentrations in plasma and Fos levels in the paraventricular nucleus. Taken together, our findings suggest that testosterone exposure during the neonatal period primes the adult HPA response to testosterone by altering androgen receptor levels and function within afferent mediators of basal and stress-related input to the HPA axis.

Prenatal alcohol exposure: foetal programming, the hypothalamic-pituitary-adrenal axis and sex differences in outcome

Prenatal exposure to alcohol has adverse effects on offspring neuroendocrine and behavioural functions. Alcohol readily crosses the placenta, thus directly affecting developing foetal endocrine organs. In addition, alcohol-induced changes in maternal endocrine function can disrupt the normal hormonal interactions between the pregnant female and foetal systems, altering the normal hormone balance and, indirectly, affecting the development of foetal metabolic, physiological and endocrine functions. The present review focuses on the adverse effects of prenatal alcohol exposure on offspring neuroendocrine function, with particular emphasis on the hypothalamic-pituitary-adrenal (HPA) axis, a key player in the stress response. The HPA axis is highly susceptible to programming during foetal and neonatal development. Here, we review data demonstrating that alcohol exposure in utero programmes the foetal HPA axis such that HPA tone is increased throughout life. Importantly, we show that, although alterations in HPA responsiveness and regulation are robust phenomena, occurring in both male and female offspring, sexually dimorphic effects of alcohol are frequently observed. We present updated findings on possible mechanisms underlying differential effects of alcohol on male and female offspring, with special emphasis on effects at different levels of the HPA axis, and on modulatory influences of the hypothalamic-pituitary-gonadal hormones and serotonin. Finally, possible mechanisms underlying foetal programming of the HPA axis, and the long-term implications of increased exposure to endogenous glucocorticoids for offspring vulnerability to illnesses or disorders later in life are discussed.

Androgen receptor expressing neurons that project to the paraventricular nucleus of the hypothalamus in the male rat

Androgen receptors are distributed throughout the central nervous system and are contained by a variety of nuclei that are known to project to or regulate the paraventricular nucleus (PVN) of the hypothalamus, the final common pathway by which the brain regulates the hypothalamic-pituitary-adrenal (HPA) response to homeostatic threat. Here we characterized androgen receptor staining within cells identified as projecting to the PVN in male rats bearing iontophoretic or crystalline injections of the retrograde tracer FluoroGold aimed at the caudal two-thirds of the nucleus, where corticotropin-releasing hormone-expressing neurons are amassed. Androgen receptor (AR) and FluoroGold (FG) double labeling was revealed throughout the limbic forebrain, including scattered numbers of cells within the anterior and posterior subdivisions of the bed nuclei of the stria terminalis; the medial zone of the hypothalamus, including large numbers of AR-FG-positive cells within the anteroventral periventricular and medial preoptic cell groups. Strong and consistent colabeling was also revealed throughout the hindbrain, predominantly within the periaqueductal gray and the lateral parabrachial nucleus, and within various medullary cell groups identified as catecholaminergic, predominantly C1 and A1 neurons of the ventral medulla. These connectional data predict that androgens can act on a large assortment of multimodal inputs to the PVN, including those involved with the processing of various types of sensory and limbic information, and provide an anatomical framework for understanding how gonadal status could contribute to individual differences in HPA function.

Estrogen receptor-beta mediates dihydrotestosterone-induced stimulation of the arginine vasopressin promoter in neuronal cells

Arginine vasopressin (AVP) is a neuropeptide involved in the regulation of fluid balance, stress, circadian rhythms, and social behaviors. In the brain, AVP is tightly regulated by gonadal steroid hormones in discrete regions with gonadectomy abolishing and testosterone replacement restoring normal AVP expression in adult males. Previous studies demonstrated that 17beta-estradiol, a primary metabolite of testosterone, is responsible for restoring most of the AVP expression in the brain after castration. However, 5alpha-dihydrotestosterone (DHT) has also been shown to play a role in the regulation of AVP expression, thus implicating the involvement of both androgen and estrogen receptors (ER). Furthermore, DHT, through its conversion to 5alpha-androstane-3beta,17beta-diol, has been shown to modulate estrogen response element-mediated promoter activity through an ER pathway. The present study addressed two central hypotheses: 1) that androgens directly modulate AVP promoter activity and 2) the effect is mediated by an estrogen or androgen receptor pathway. To that end, we overexpressed androgen receptor, ERbeta, and ERbeta splice variants in a neuronal cell line and measured AVP promoter activity using a firefly luciferase reporter assay. Our results demonstrate that DHT and its metabolite 5alpha-androstane-3beta,17beta-diol stimulate AVP promoter activity through ERbeta in a neuronal cell line.

Estrogen receptor beta in the brain: from form to function

Estrogens have numerous effects on the brain, both in adulthood and during development. These actions of estrogen are mediated by two distinct estrogen receptor (ER) systems, ER alpha (ERalpha) and ER beta (ERbeta). In brain, ERalpha plays a critical role in regulating reproductive neuroendocrine function and behavior, however, a definitive role for ERbeta in any neurobiological function has been slow in forthcoming. Clues to the function of ERbeta in the central nervous system can be gleaned from the neuroanatomical distribution of ERbeta and the phenotypes of neurons that express ERbeta. ERbeta immunoreactivity has been found in populations of GnRH, CRH, vasopressin, oxytocin and prolactin containing neurons in the hypothalamus. Utilizing subtype-selective estrogen receptor agonists can help determine the roles for ERbeta in non-reproductive behaviors in rat models. ERbeta-selective agonists exert potent anxiolytic activity when animals were tested in a number of behavioral paradigms. Consistent with this, ERbeta-selective agonists also inhibited the ACTH and corticosterone response to stress. In contrast, ERalpha selective agonists were found to be anxiogenic and correspondingly increased the hormonal stress response. Taken together, our studies implicate ERbeta as an important modulator of some non-reproductive neurobiological systems. The molecular and neuroanatomical targets of estrogen that are mediated by ERbeta remain to be determined. A number of splice variants of ERbeta mRNA have been reported in brain tissue. Imaging of eGFP labeled chimeric receptor proteins transfected into cell lines shows that ERbeta splice variation can alter trafficking patterns and function. The originally described ERbeta (herein termed ERbeta1) is characterized by possessing a high affinity for estradiol. Similar to ERalpha, it is localized in the nucleus and is trafficked to nuclear sites termed "hyperspeckles" following ligand binding. In contrast, ERbeta2 contains an 18 amino acid insert within the ligand-binding domain and as a result can be best described as a low affinity form of ERbeta. A delta3 (delta3) variant of ERbeta has a deletion of the 3rd exon (coding for the second half of the DNA-binding domain) and as a result does not bind an estrogen response element in DNA. delta3 variants are trafficked to a unique low abundance and larger nuclear site following ligand binding. A delta4 (delta4) variant lacks exon 4 and as a result is localized to the cytoplasm. The amount of individual splice variant mRNAs varies depending upon brain region. Examination of neuropeptide promoter regulation by ERbeta splice variants demonstrates that ERbeta functions as a constitutively active transcription factor. Moreover, it appears that splice variation of ERbeta alters its ability to regulate transcription in a promoter-dependent and ligand-dependent fashion.

HPA function in adolescence: Role of sex hormones in its regulation and the enduring consequences of exposure to stressors

The hypothalamic-pituitary-adrenal (HPA) axis is one of the physiological systems involved in coping with stressors. There are functional shifts in the HPA axis and its regulation by sex hormones over the lifespan that allow the animal to meet the challenges of the internal and external environment that are specific to each stage of development. Sex differences in HPA function emerge over adolescence, a phenomenon reflecting the concomitant initiation of regulatory effects of sex hormones. The focus of this review is recent research on differences between adolescents and adults in HPA function and the enduring effects of exposure to stressors in adolescence. During adolescence, HPA function is characterized by a prolonged activation in response to stressors compared to adulthood, which may render ongoing development of the brain vulnerable. Although research has been scarce, there is a growing evidence that exposure to stressors in adolescence may alter behavioural responses to drugs and cognitive performance in adulthood. However, the effects reported appear to be stressor-specific and sex-specific. Such research may contribute toward understanding the increased risk for drug abuse and psychopathology that occurs over adolescence in people.

Cortisol moderates the relationship between testosterone and aggression in delinquent male adolescents

BACKGROUND

In animals, strong evidence exists for an association between testosterone and aggression. In humans, and particularly in children and adolescents, findings have been less consistent. Previous research has suggested that this may partly be due to moderating effects of other factors, e.g., hormones. This study aims to investigate the moderating effect of cortisol on the relationship between testosterone and subtypes of aggression in delinquent male adolescents.

METHODS

Participants were 103 boys (mean age 13.7) referred to a delinquency diversion program. Testosterone and cortisol levels were determined from saliva samples collected during resting conditions and related to self-report scores on overt and covert aggression.

RESULTS

Linear regression analyses revealed a significant interaction between cortisol and testosterone in relation to overt aggression, with a significant positive relationship between testosterone and overt aggression in subjects with low cortisol levels but not in subjects with high cortisol levels. Using the same model for covert aggression, no significant effects of testosterone, cortisol, or testosterone x cortisol interaction were found.

CONCLUSIONS

These results indicate a moderating effect of cortisol on the relationship between testosterone and overt aggression in delinquent male adolescents. Implications and directions for future research are discussed.

Glucocorticoids, chronic stress, and obesity

Glucocorticoids either inhibit or sensitize stress-induced activity in the hypothalamo-pituitary-adrenal (HPA) axis, depending on time after their administration, the concentration of the steroids, and whether there is a concurrent stressor input. When there are high glucocorticoids together with a chronic stressor, the steroids act in brain in a feed-forward fashion to recruit a stress-response network that biases ongoing autonomic, neuroendocrine, and behavioral outflow as well as responses to novel stressors. We review evidence for the role of glucocorticoids in activating the central stress-response network, and for mediation of this network by corticotropin-releasing factor (CRF). We briefly review the effects of CRF and its receptor antagonists on motor outflows in rodents, and examine the effects of glucocorticoids and CRF on monoaminergic neurons in brain. Corticosteroids stimulate behaviors that are mediated by dopaminergic mesolimbic "reward" pathways, and increase palatable feeding in rats. Moreover, in the absence of corticosteroids, the typical deficits in adrenalectomized rats are normalized by providing sucrose solutions to drink, suggesting that there is, in addition to the feed-forward action of glucocorticoids on brain, also a feedback action that is based on metabolic well being. Finally, we briefly discuss the problems with this network that normally serves to aid in responses to chronic stress, in our current overindulged, and underexercised society.

The effect of gonadal hormones and gender on anxiety and emotional learning

Disorders of anxiety and fear dysregulation are highly prevalent. These disorders affect women approximately 2 times more than they affect men, occur predominately during a woman's reproductive years, and are especially prevalent at times of hormonal flux. This implies that gender differences and sex steroids play a key role in the regulation of anxiety and fear. However, the underlying mechanism by which these factors regulate emotional states in either sex is still largely unknown. This review discusses animal studies describing sex-differences in and gonadal steroid effects on affect and emotional learning. The effects of gonadal hormones on the modulation of anxiety, with particular emphasis on progesterone's ability to reduce the responsiveness of female rats to corticotropin releasing factor and the sex-specific effect of testosterone in the reduction of anxiety in male rats, is discussed. In addition, gonadal hormone and gender modulation of emotional learning is considered and preliminary data are presented showing that estrogen (E2) disrupts fear learning in female rats, probably through the antagonistic effect of ERalpha and ERbeta activation.

Prenatal ethanol exposure alters the effects of gonadectomy on hypothalamic-pituitary-adrenal activity in male rats

Prenatal ethanol exposure has marked effects on development of the hypothalamic-pituitary-adrenal (HPA) and -gonadal (HPG) axes. In adulthood, ethanol-treated rats show altered gonadal hormone responses and reproductive function, and increased HPA responsiveness to stressors. Importantly, prenatal ethanol differentially alters stress responsiveness in adult males and females, raising the possibility that the gonadal hormones play a role in mediating prenatal ethanol effects on HPA function. To examine a possible testicular influence on HPA activity in males, we compared the effects of gonadectomy on HPA stress responses of adult male offspring from ethanol, pair-fed (PF) and ad libitum-fed control dams. Intact ethanol-treated rats showed increased adrenocorticotrophic hormone (ACTH) but blunted testosterone and luteinising hormone (LH) responses to restraint stress, and no stress-induced elevation in arginine vasopressin (AVP) mRNA levels compared to those observed in PF and/or control rats. Gonadectomy: (i) significantly increased ACTH responses to stress in control but not ethanol-treated and PF males; (ii) eliminated differences among groups in plasma ACTH and AVP mRNA levels; and (iii) altered LH and gonadotrophin-releasing hormone responses in ethanol-treated males. Taken together, these findings suggest that central regulation of both the HPA and HPG axes are altered by prenatal ethanol exposure, with normal testicular influences on HPA function markedly reduced in ethanol-treated animals. A decreased sensitivity to inhibitory effects of androgens could contribute to the HPA hyperresponsiveness typically observed in ethanol-treated males.