Intrahypothalamic estradiol modulates hypothalamus-pituitary-adrenal-axis activity in female rats

Network analysis of comorbid depression, suicidality and biomarkers on HPA axis among mood disorder patients to psychiatric emergency services

Rapid assessment and intervention of suicide risk are common and challenging in psychiatric emergency departments (PED). It is unclear whether distinct pathophysiological processes exist among depressive patients with suicidality. This study examined the network structures of biomarkers on Hypothalamic-Pituitary-Adrenal (HPA) axis, such as Adrenocorticotropic hormone (ACTH) and Corticosterone (Cort), as well as suicidality and depressive symptoms in mood disorder patients in PED. Mood disorder patients in PED were assessed with the measurements of suicidality and depressive symptoms, respectively. A network analysis was performed to identify central symptoms and bridge symptoms of this network and their links to ACTH and Cort. Network stability was examined using the case-dropping procedure. The Network Comparison Test (NCT) was conducted to evaluate whether network characteristics differed by gender. A total of 1815 mood disorder patients were recruited. The prevalence of SI was 31.2% (95% CI: 28.15-34.21%), SP was 30.4% (95% CI: 27.39-33.41%), SA was 30.62% (95% CI: 27.61-33.64%) among psychiatric outpatients. The mean score of HAMD-24 was 13.87 ± 8.02. Network analysis revealed that 'Somatic anxiety' had the highest expected centrality, followed by 'Hopelessness' and 'Suicide attempt'. 'Corticosterone' and 'Retardation' may be the main bridge symptoms between depressive symptoms and the suicidality community. The network model showed a high degree of stability. Gender did not significantly influence the network structure. The central symptoms and key bridge symptoms identified could be potential targets for interventions of the HPA axis, which is designed for regular screening of a range of suicidal activity. In the light of this, timely treatment should be provided for psychiatric emergency care.

Alterations in the activation of corticotropin-releasing factor neurons in the paraventricular nucleus following a single or multiple days of sleep restriction

Sleep disturbances are common among disorders associated with hypothalamic pituitary-adrenal (HPA) axis dysfunction, such as depression and anxiety. This comorbidity may partly be the result of the intersection between the role of the HPA axis in mediating the stress response and its involvement in sleep-wake cyclicity. Our previous work has shown that following 20 h of sleep restriction, mice show a blunting of the HPA axis in response to an acute stressor. Furthermore, these responses differ in a sex-dependent manner. This study sought to examine the effect of sleep restriction on corticotropin-releasing factor (CRF)-containing neurons in the paraventricular nucleus (PVN) of the hypothalamus. Male and female Crf-IRES-Cre: Ai14 (Tdtomato) reporter mice were sleep restricted for 20 h daily for either a single or three consecutive days using the modified multiple platform method. These mice allowed the visualization of CRF+ neurons throughout the brain. Animals were subjected to acute restraint stress, and their brains were collected to assess PVN neuronal activation via c-Fos immunohistochemistry. Analyses of cell counts revealed an ablation of the restraint-induced increase in both CRF/c-Fos colocalization and overall c-Fos expression in female mice following both a single day and three days of sleep restriction. Males showed an overall decrease in restraint-induced c-Fos levels following a single day of sleep restriction. However, male mice examined after three days of sleep restriction showed a recovery in PVN-CRF and overall PVN neuronal activation. These data suggest the sex dependent dysregulation in CRF function following sleep restriction.

Longitudinal association of maternal dietary patterns with antenatal depression: Evidence from the Chinese Pregnant Women Cohort Study

BACKGROUND

Limited evidence to show the longitudinal associations between maternal dietary patterns and antenatal depression (AD) from cohort studies across the entire gestation period.

METHODS

Data came from the Chinese Pregnant Women Cohort Study. The qualitative food frequency questionnaire (Q-FFQ) and Edinburgh Postnatal Depression Scale (EPDS) were used to collect diet and depression data. Dietary patterns were derived by using factor analysis. Generalized estimating equation models were used to analyze the association between diet and AD.

RESULTS

A total of 4139 participants finishing 3-wave of follow-up were finally included. Four constant diets were identified, namely plant-based, animal-protein, vitamin-rich and oily-fatty patterns. The prevalence of depression was 23.89%, 21.12% and 22.42% for the first, second and third trimesters. There were reverse associations of plant-based pattern (OR:0.85, 95%CI:0.75-0.97), animal-protein pattern (OR:0.85, 95%CI:0.74-0.99) and vitamin-rich pattern (OR:0.58, 95%CI:0.50-0.67) with AD, while a positive association between oily-fatty pattern and AD (OR:1.47, 95%CI:1.29-1.68). Except for the plant-based pattern, other patterns had linear trend relationships with AD (P_trend < 0.05). Moreover, a 1-SD increase in vitamin-rich pattern scores was associated with a 20% lower AD risk (OR:0.80, 95%CI:0.76-0.84), while a 1-SD increase in oily-fatty pattern scores was associated with a 19% higher risk (OR:1.19, 95%CI:1.13-1.24). Interactions between dietary patterns and lifestyle habits were observed.

LIMITATIONS

The self-reported Q-FFQ and EPDS may cause recall bias.

CONCLUSIONS

There are longitudinal associations between maternal dietary patterns and antenatal depression. Our findings are expected to provide evidence for a dietary therapy strategy to improve or prevent depression during pregnancy.

The hypothalamic paraventricular nucleus as a central hub for the estrogenic modulation of neuroendocrine function and behavior

Estradiol and hypothalamic paraventricular nucleus (PVN) help coordinate reproduction with body physiology, growth and metabolism. PVN integrates hormonal and neural signals originating in the periphery, generating an output mediated both by its long-distance neuronal projections, and by a variety of neurohormones produced by its magnocellular and parvocellular neurosecretory cells. Here we review the cyto-and chemo-architecture, the connectivity and function of PVN and the sex-specific regulation exerted by estradiol on PVN neurons and on the expression of neurotransmitters, neuromodulators, neuropeptides and neurohormones in PVN. Classical and non-classical estrogen receptors (ERs) are expressed in neuronal afferents to PVN and in specific PVN interneurons, projecting neurons, neurosecretory neurons and glial cells that are involved in the input-output integration and coordination of neurohormonal signals. Indeed, PVN ERs are known to modulate body homeostatic processes such as autonomic functions, stress response, reproduction, and metabolic control. Finally, the functional implications of the estrogenic modulation of the PVN for body homeostasis are discussed.

Determinants of Chronic Biological Stress, Measured as Hair Cortisol Concentration, in a General Population of Adolescents: From Individual and Household Characteristics to Neighborhood Urbanicity

Chronic biological stress may adversely affect adolescents' physical and mental health, but insight in the personal and environmental factors that determine chronic stress is limited. We measured 3-month cumulative hair cortisol concentration (HCC) in 419 adolescents, participating in the Flemish Environment and Health Study. Adolescents' health and lifestyle characteristics, household and neighborhood socio-economic status as well as neighborhood urbanicity were assessed as potential determinants of HCC, using multiple linear regression models. We additionally explored heterogeneity of our results by sex. HCC were significantly higher in boys from densely populated neighborhoods, the association was not significant in girls. Accordingly, boys living outside cities had significantly lower HCC than boys, living in cities. HCC was significantly lower in adolescents with an optimal vitality, a measure of a positive mental health status. In adolescent girls, menarcheal status (pre-/postmenarche) was a significant determinant of HCC. Our findings are the first to suggest that residential urbanicity may have an impact on chronic biological stress in a general population of adolescent boys.

Developmental stress has sex-specific effects on contextual and cued fear conditioning in adulthood

Stress-induced deviations in central nervous system development has long-term effects on adult mental health. Previous research in humans demonstrates that prenatal or adolescent stress increases the risk for psychiatric disorders. Animal models investigating the effects of stress during prenatal or adolescent development produces behavioral outcomes analogous to those observed in humans. However, whether adolescent stress exposure potentiates the effects of prenatal stress is currently unknown. Thus, the current study tested whether adolescent stress increases the impact of prenatal stress on contextual and cued fear memory in adulthood. Male and female Sprague Dawley rats were exposed to a chronic variable stress schedule during the last week of gestation, during adolescence, or during both developmental periods before undergoing fear conditioning training in adulthood. Our hypothesis predicted that the combined effects of prenatal and adolescent stress on contextual and cued fear memory would be greater than the effects of stress during either time period alone. In contrast to our hypothesis, however, we found independent effects of prenatal and adolescent stress on contextual and cued fear memory in both sexes, with no additional combined impact of stress exposure during both developmental phases. In males, developmental stress increased freezing behavior during contextual and cued testing regardless of whether stress exposure was prenatal, adolescent, or combined prenatal and adolescent stress exposure. In contrast, the effects of developmental stress in females were both test- and ovarian hormone status-dependent. During cued testing, nonstressed female freezing behavior depended on estrous cycle phase, whereas freezing behavior in stressed females did not, suggesting that developmental stress interferes with hormone-dependent cued fear memory. No effects of developmental stress or estrous cycle phase were observed for contextual fear memory in females. The results of the current study suggest that the effects of prenatal and adolescent stress on contextual and cued fear memory are not cumulative, but the effects of developmental stress on associative memory differ between males and females.

Intranasal oxytocin compensates for estrus cycle-specific reduction of conditioned safety memory in rats: Implications for psychiatric disorders

Stress and anxiety disorder patients frequently fail to benefit from psychotherapies which often consist of inhibitory fear learning paradigms. One option to improve the therapy outcome is medication-enhanced psychotherapy. Research in humans and laboratory rodents has demonstrated that oxytocin (OT) reduces fear and facilitates fear extinction. However, the role of OT in conditioned safety learning, an understudied but highly suitable type of inhibitory fear learning, remains to be investigated. The present study aimed at investigating the effect of intranasal OT on conditioned safety. To test this, Sprague Dawley rats (♂n = 57; ♀n = 72) were safety conditioned. The effects of pre-training or pre-testing intranasal OT on conditioned safety and contextual fear, both measured by the acoustic startle response, and on corticosterone plasma levels were assessed. Furthermore, the involvement of the estrous cycle was analyzed. The present data show that intranasal OT administration before the acquisition or recall sessions enhanced conditioned safety memory in female rats while OT had no effects in male rats. Further analysis of the estrus cycle revealed that vehicle-treated female rats in the metestrus showed reduced safety memory which was compensated by OT-treatment. Moreover, all vehicle-treated rats, regardless of sex, expressed robust contextual fear following conditioning. Intranasal OT-treated rats showed a decrease in contextual fear, along with reduced plasma corticosterone levels. The present data demonstrate that intranasal OT has the capacity to compensate deficits in safety learning, along with a reduction in contextual fear and corticosterone levels. Therefore, add-on treatment with intranasal OT could optimize the therapy of anxiety disorders.

Sex differences in vulnerability to addiction

This article reviews evidence for sex differences in vulnerability to addiction with an emphasis on the neural mechanisms underlying these differences. Sex differences in the way that the gonadal hormone, estradiol, interacts with the ascending telencephalic dopamine system results in sex differences in motivated behaviors, including drug-seeking. In rodents, repeated psychostimulant exposure enhances incentive sensitization to a greater extent in females than males. Estradiol increases females' motivation to attain psychostimulants and enhances the value of drug related cues, which ultimately increases their susceptibility towards spontaneous relapse. This, along with females' dampened ability to alter decisions regarding risky behaviors, enhances their vulnerability for escalation of drug use. In males, recent evidence suggests that estradiol may be protective against susceptibility towards drug-preference. Sex differences in the actions of estradiol are reviewed to provide a foundation for understanding how future research might enhance understanding of the mechanisms of sex differences in addiction-related behaviors, which are dependent on estradiol receptor (ER) subtype and the region of the brain they are acting in. A comprehensive review of the distribution of ERα, ERβ, and GPER1 throughout the rodent brain are provided along with a discussion of the possible ways in which these patterns differentially regulate drug-taking between the sexes. The article concludes with a brief discussion of the actions of gonadal hormones on the circuitry of the stress system, including the hypothalamic pituitary adrenal axis and regulation of corticotropin-releasing factor. Sex differences in the stress system can also contribute to females' enhanced vulnerability towards addiction.

Sex-Bias in Irritable Bowel Syndrome: Linking Steroids to the Gut-Brain Axis

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that is more common in females. Despite its high global incidence, the disease mechanism is still unclear and therapeutic options remain limited. The sexual dimorphism in IBS incidence suggests that sex steroids play a role in disease onset and symptoms severity. This review considers sex steroids and their involvement in IBS symptoms and the underlying disease mechanisms. Estrogens and androgens play important regulatory roles in IBS symptomology, including visceral sensitivity, gut motility and psychological conditions, possibly through modulating the gut-brain axis. Steroids are regulators of hypothalamic-pituitary-adrenal activity and autonomic nervous system function. They also modulate gut microbiota and enteric nervous systems, impacting serotonin and mast cell signaling. Sex steroids also facilitate bidirectional cross-talk between the microbiota and host following bacterial transformation and recycling of steroids by the intestine. The sex-specific interplay between sex steroids and the host provides neuroendocrinology insight into the pathophysiology, epigenetics and treatment of IBS patients.

Pro-social and anxiolytic-like behavior following a single 24-h exposure to 17β-estradiol in adult male zebrafish

Estradiol (17β-estradiol, E₂) is a crucial estrogen hormone that regulates sexual, cognitive, social and affective behaviors in various species. However, complex central nervous system (CNS) effects of E₂, including its activity in males, remain poorly understood. The zebrafish (Danio rerio) is rapidly becoming a powerful novel model system in translational neuroscience research. Here, we evaluate the effects of a single 24-h exposure to 20 μg/L of E₂ on behavioral and endocrine (cortisol) responses in adult male zebrafish. Overall, E₂ exerted pro-social effect in the social preference test, reduced whole-body cortisol levels, elevated exploration in the novel tank test and increased the shoal size in the shoaling test, indicative of an anxiolytic-like profile of this hormone in male zebrafish. Supporting mounting human and rodent evidence on the role of E₂ in behavioral regulation, the observed pro-social and anxiolytic-like effects of E₂ in male zebrafish reinforce the use of this aquatic organism in studying steroid-mediated CNS mechanisms of complex affective and social behaviors.

Antidepressive Effects of Kamishoyosan through 5-HT1AReceptor and PKA-CREB-BDNF Signaling in the Hippocampus in Postmenopausal Depression-Model Mice

Females are well known to suffer disproportionately more than males from stress-related neuropsychiatric disorders, especially during perimenopausal and postmenopausal periods. In addition to a decline in serum estradiol levels, environmental stress and social stress likely contribute to the development of neuropsychiatric symptoms in perimenopausal and postmenopausal women. Kamishoyosan (KSS) is a traditional Japanese Kampo medicine, composed of a specified mixture of 10 crude compounds derived from plant sources, widely used for various neuropsychiatric symptoms in perimenopausal and postmenopausal women. However, the molecular mechanisms underlying KSS-mediated attenuation of neuropsychological symptoms and stress-response behaviors in perimenopausal and postmenopausal women remain unknown. In the present study, we first established a mouse model for postmenopausal depression-like signs using chronic water-immersion and restraint-stressed ovariectomized (OVX) mice to investigate the underlying molecular mechanism of KSS. We found that continuous administration of KSS to these mice normalized the activation of the hypothalamic-pituitary-adrenal (HPA) axis, ameliorated stress-induced depressive behavior, and prevented a decrease of neurogenesis in the hippocampus. As previous studies have implicated dysfunction of the hippocampal 5-HT1A receptor (5-HT1AR) in depressive disorders, we also evaluated the effect of KSS on 5-HT1AR expression and the protein kinase A- (PKA-) cAMP response element-binding- (CREB-) brain-derived neurotrophic factor (BDNF) signaling pathway in the hippocampus in this model. The level of 5-HT1AR in the hippocampus decreased in chronic stress-exposed OVX mice, while KSS treatment normalized the stress-induced decrease in 5-HT1AR expression in the hippocampus of chronic stress-exposed OVX mice. Furthermore, we found that KSS treatment upregulated the expression levels of phosphorylated PKA (p-PKA), phosphorylated CREB (p-CREB), and BDNF in the hippocampus in chronic stress-exposed OVX mice. These results suggest that KSS improves neuropsychiatric symptoms through 5-HT1AR and PKA-CREB-BDNF signaling in the hippocampus in postmenopausal women.

An alternative theory for hormone effects on sex differences in PTSD: The role of heightened sex hormones during trauma

Women are at least twice as susceptible to developing post-traumatic stress disorder (PTSD) compared to men. Although most research seeking to explain this discrepancy has focussed on the role of oestradiol during fear extinction learning, the role of progesterone has been overlooked, despite relatively consistent findings being reported concerning the role of progesterone during consolidation of emotional and intrusive memories. In this review article, we outline literature supporting the role of progesterone on memory formation, with particular emphasis on potential memory-enhancing properties of progesterone when subjects are placed under stress. It is possible that progesterone directly and indirectly exerts memory-enhancing effects at the time of trauma, which is an effect that may not be necessarily captured during non-stressful paradigms. We propose a model whereby progesterone's steroidogenic relationship to cortisol and brain-derived neurotrophic factor in combination with elevated oestradiol may enhance emotional memory consolidation during trauma and therefore present a specific vulnerability to PTSD formation in women, particularly during the mid-luteal phase of the menstrual cycle.

Hypothalamic-pituitary-adrenal axis responsivity to an acute novel stress in female rats subjected to the chronic mild stress paradigm

The chronic mild stress (CMS) paradigm is the most frequently investigated animal model for major depression. The hypothalamic-pituitary-adrenal (HPA) axis participates in the generation of depressive symptomatology. We examined whether the depression-like state induced by CMS is associated with immediate changes in HPA axis activation in response to a novel acute stress and whether this response could be modified by hormonal status. Adult female Wistar rats were ovariectomized and received estrogen or vehicle pellets. After 2 weeks, rats were subjected to CMS (or control) conditions for 2.5 or 4.5 weeks. Rats were subsequently subjected to restraint stress for 1 h, and plasma corticosterone (CT) levels were determined before (2:00 p.m.) and after acute stress induction (3:00 and 4:00 p.m.). CT levels and FOS expression were measured in the medial parvocellular subdivision of the PVN (PaMP), central (CeA) and medial amygdala (MeA) and ventral subiculum of the hippocampus (vSub). Plasma CT levels in animals treated with 6.5 weeks of estrogen were elevated before and 1 h after restraint stress induction. Results indicate that the estrogen chronicity and CMS exposure impacted CT secretion. Neuronal PaMP, CeA, MeA and vSub activity decreased after 4.5 weeks of CMS in all groups. No differences were detected between CMS and non-CMS groups. These data suggest that the HPA central hyporesponsiveness observed in the experimental groups subjected to a longer protocol period was independent to CMS paradigm and estrogen treatment restored partially its activity. These data suggest that additional stressors could be responsible for the observed alterations of the HPA axis.

The impact of oxytocin on stress: the role of sex

Accumulating research indicates oxytocin plays a significant role in regulating the behavioral and neurobiological responses to stress. Evidence from preclinical models suggests the effect of oxytocin on stress-responsivity appears to be dependent on individual characteristics, including sex. Although the interaction between oxytocinergic and stress systems has been widely studied in rodents, recent efforts have been made to examine the interface between these two systems in humans. This brief review examines how administration of oxytocin can influence the neuroendocrine, behavioral, and neural responses to stress, explores how sex may impact these effects, and provides considerations for future work.

The effects of ovarian hormones on stressor-induced hormonal responses, glucocorticoid receptor expression and translocation, and genes related to receptor signaling in adult female rats

Estradiol potentiates hypothalamic-pituitary-adrenal activity and delays the return of glucocorticoid secretion to baseline after a stressor exposure in female rats; we investigated whether estradiol effects involve actions on glucocorticoid receptor (GR) translocation and expression of receptor co-chaperones. In Experiment 1 intact females and ovariectomized (OVX) females were treated for four days with vehicle (VEH), 17β-estradiol benzoate (EB), or EB and progesterone (EB + P). Samples were taken from rats in the home cage (baseline) or after 30 min of restraint stress in a plastic restrainer (post-restraint) (n = 10/group). OVX-VEH treatment reduced baseline and post-restraint plasma concentrations of corticosterone versus all other treatments. Western blots indicated that OVX-VEH treated rats had greater hippocampal cytosolic GR expression than other treatments. Stress increased hippocampal nuclear GR expression, but without treatment differences. In Experiment 2 OVX rats were treated daily with VEH, EB, or EB + P (n = 8/group). OVX-VEH rats showed a lower stimulation of corticosterone secretion by restraint stress than other treatments and OVX-EB + P treated rats had lower concentrations than the OVX-EB group, suggesting progesterone mitigated estradiol effects. Quantitative polymerase chain reaction experiments indicated that stress increased Fkbp5 mRNA in the ventral hippocampus, with no effect of stress or treatment on Nr3c1 (GR), Nr3c2 (MR), Fkbp4, Bag1, or Ncoa1 (SRC-1) expression. Thus, the hypothesis is that estradiol effects on negative feedback are mediated by altered expression of receptor co-chaperones or co-modulators in the hippocampus was not supported. Estradiol may blunt feedback by limiting the availability of cytosolic GR protein.

Oxytocin and Steroid Actions

Biosynthesis and secretion of the hypothalamic nonapeptide oxytocin largely depends on steroid hormones. Estradiol, corticosterone, and vitamin D seem to be the most prominent actors. Due to their lipophilic nature, systemic steroids are thought to be capable of crossing the blood-brain barrier, thus mediating central functions including neuroendocrine and behavioral control. The actual mode of action of steroids in hypothalamic circuitry is still unknown: Most of the oxytocinergic perikarya lack nuclear steroid receptors but express proteins suspected to be membrane receptors for steroids. Oxytocin expressing neurons contain enzymes important for intrinsic steroid metabolism. Furthermore, they produce and probably liberate specific steroid-binding globulins. Rapid responses to steroid hormones may involve these binding proteins and membrane-associated receptors, rather than classic nuclear receptors and genomic pathways. Neuroendocrine regulation, reproductive behaviors, and stress response seem to depend on these mechanisms.

Psychological stress in aged female mice causes acute hypophagia independent of central serotonin 2C receptor activation

Sex differences exist in the activation of the hypothalamic–pituitary–adrenal axis following exposure to stress, and the stress response is further affected by aging. This study was conducted to elucidate the mechanism of hypophagia in aged female mice exposed to stress. Immediately after a stress load, aged female mice exhibited acute hypophagia and a rise in plasma corticosterone levels. The administration of a serotonin 2C receptor (5-HT_2CR) antagonist suppressed plasma corticosterone but did not affect the reduction in food intake. In contrast, an endogenous ghrelin enhancer, rikkunshito (RKT), significantly inhibited the reduction in food intake. An increase in peripheral acylated ghrelin levels during fasting, which occurs in young mice, was not observed in aged female mice. Moreover, in these mice, significantly increased levels of ghrelin and gastric preproghrelin mRNA expression were observed in the fed status. Moreover, plasma ghrelin levels were elevated by RKT and not by the 5-HT_2CR antagonist. In female mice, the hypothalamic non-edited (INI) and partially edited mRNA 5-HT_2CR isoforms (VNV, VNI, VSV or VSI) decreased with age, while in male mice, the editing isoform was unchanged by aging or stress. Estrogen receptor α (ERα)-positive cell counts in the arcuate nucleus of young male mice exposed to stress and control aged male mice were increased compared with those in young control mice. In aged male mice exposed to stress, the number of ERα-expressing cells in the paraventricular nucleus were significantly increased compared with those in aged control mice; in female mice, there was no increase in the number of ERα-positive cells. Hypophagia in aged female mice exposed to stress may be independent of 5-HT_2CR activation. It seems likely that the mechanisms may be caused by sex dependent, differential regulation in 5-HT_2CR mRNA expression, peripheral acylated ghrelin secretion and/or hypothalamic ERα expression.

17β-estradiol regulates the RNA-binding protein Nova1, which then regulates the alternative splicing of estrogen receptor β in the aging female rat brain

Alternative RNA splicing results in the translation of diverse protein products arising from a common nucleotide sequence. These alternative protein products are often functional and can have widely divergent actions from the canonical protein. Studies in humans and other vertebrate animals have demonstrated that alternative splicing events increase with advanced age, sometimes resulting in pathological consequences. Menopause represents a critical transition for women, where the beneficial effects of estrogens are no longer evident; therefore, factors underlying increased pathological conditions in women are confounded by the dual factors of aging and declining estrogens. Estrogen receptors (ERs) are subject to alternative splicing, the spliced variants increase following menopause, and they fail to efficiently activate estrogen-dependent signaling pathways. However, the factors that regulate the alternative splicing of ERs remain unknown. We demonstrate novel evidence supporting a potential biological feedback loop where 17β-estradiol regulates the RNA-binding protein Nova1, which, in turn, regulates the alternative splicing of ERβ. These data increase our understanding of ER alternative splicing and could have potential implications for women taking hormone replacement therapy after menopause.

Gq Protein-Coupled Membrane-Initiated Estrogen Signaling Rapidly Excites Corticotropin-Releasing Hormone Neurons in the Hypothalamic Paraventricular Nucleus in Female Mice

CRH neurons in the hypothalamic paraventricular nucleus (PVN) play a central role in regulating the hypothalamus-pituitary-adrenal (HPA) axis and are directly influenced by 17β-estradiol (E2). Although compelling evidence has suggested the existence of membrane-associated estrogen receptors (mERs) in hypothalamic and other central nervous system neurons, it remains unknown whether E2 impacts CRH neuronal excitability through this mechanism. The purpose of the current study is to examine the existence and function of mER signaling in PVN CRH neurons. Whole-cell recordings were made from CRH neurons identified by Alexa Fluor 594 labeling and post hoc immunostaining in ovariectomized female mice. E2 (100nM) rapidly suppressed the M-current (a voltage-dependent K(+) current) and potentiated glutamatergic excitatory postsynaptic currents. The putative Gq-coupled mER (Gq-mER) characterized in hypothalamic proopiomelanocortin neurons initiates a phospholipase C-protein kinase C-protein kinase A pathway; therefore, we examined the involvement of this pathway using selective inhibitors. Indeed, the ER antagonist ICI 182780 and inhibitors of Gq-phospholipase C-protein kinase C-protein kinase A blocked E2's actions, suggesting dependence on the Gq-mER. Furthermore, STX, a selective ligand for the Gq-mER, mimicked E2's actions. Finally, to examine the in vivo effect of Gq-mER activation, E2 or STX injection increased c-fos expression in CRH neurons in the PVN, suggesting CRH neuronal activation. This corresponded to an increase in plasma corticosterone. We conclude that the Gq-mER plays a critical role in the rapid regulation of CRH neuronal activity and the HPA axis. Our findings provide a potential underlying mechanism for E2's involvement in the pathophysiology of HPA-associated mood disorders.

Sex and stress steroids in adolescence: Gonadal regulation of the hypothalamic-pituitary-adrenal axis in the rat

This review provides an overview of the current understanding of the role of the hypothalamic-pituitary-gonadal (HPG) axis in regulating the hypothalamic-pituitary-adrenal (HPA) axis response to stressors. HPA function is influenced by both organizational (programming) and activational effects of gonadal hormones. Typically, in adult rats, estradiol increases and androgens decrease the HPA response to stressors, thereby contributing to sex differences in HPA function, and sensitivity of the HPA axis to gonadal steroids is in part determined by exposure to these hormones in early development. Although developmental differences in HPA function are well characterized, the extent to which gonadal steroids contribute to age differences in HPA function is not well understood. Deficits in the understanding of the relationships between the HPA and HPG axes are greatest for the adolescent period of development. The critical outstanding questions are, when do gonadal hormones begin to regulate HPA function in adolescence, and what mechanisms precipitate change in sensitivity of the HPA axis to the HPG axis at this stage of life.

Histories of abuse predict stronger within-person covariation of ovarian steroids and mood symptoms in women with menstrually related mood disorder

OBJECTIVE

Individual differences in sensitivity to cyclical changes in ovarian steroids estradiol (E2) and progesterone (P4) have been implicated in the pathophysiology of menstrually related mood disorder (MRMD). However, no prospective studies have investigated psychosocial risk factors for sensitivity to hormone effects on mood in MRMD. Using a repeated measures approach and multilevel models, we tested the hypothesis that a history of abuse provides a context in which within-person elevations of E2 and P4 prospectively predict daily symptoms.

METHOD

66 women with prospectively-confirmed MRMD recruited for a trial of oral contraceptives provided 1 month of baseline hormone and mood data prior to randomization. Lifetime physical and sexual abuse experiences were assessed. Across one cycle, women completed daily measures of symptoms and provided blood samples on 5 days across the menstrual cycle. Current E2 and P4 were centered within person (CWP) such that higher values represented cyclical elevations in hormones.

RESULTS

Rates of physical (27%) and sexual (29%) abuse were high, consistent with previous work documenting a link between trauma and MRMD. In women with a history of physical abuse, cyclical increases in P4 predicted greater mood and interpersonal symptoms on the three days following that sample. In women with a history of sexual abuse, cyclical increases in E2 predicted greater anxiety symptoms on the three days following that sample.

CONCLUSIONS

Results inform further inquiry into the role of severe life stressors and stress response systems in MRMD. We discuss areas for future research on the psychosocial and physiological pathways through which abuse may influence the link between hormones and symptoms.

Chronic retinoic acid treatment suppresses adult hippocampal neurogenesis, in close correlation with depressive-like behavior

Clinical studies have highlighted an association between retinoid treatment and depressive symptoms. As we had shown before that chronic application of all-trans retinoic acid (RA) potently activated the hypothalamus-pituitary-adrenal (HPA) stress axis, we here questioned whether RA also induced changes in adult hippocampal neurogenesis, a form of structural plasticity sensitive to stress and implicated in aspects of depression and hippocampal function. RA was applied intracerebroventricularly (i.c.v.) to adult rats for 19 days after which animals were subjected to tests for depressive-like behavior (sucrose preference) and spatial learning and memory (water maze) performance. On day 27, adult hippocampal neurogenesis and astrogliosis was quantified using BrdU (newborn cell survival), PCNA (proliferation), doublecortin (DCX; neuronal differentiation), and GFAP (astrocytes) as markers. RA was found to increase retinoic acid receptor-α (RAR-α) protein expression in the hippocampus, suggesting an activation of RA-induced signaling mechanisms. RA further potently suppressed cell proliferation, newborn cell survival as well as neurogenesis, but not astrogliosis. These structural plasticity changes were significantly correlated with scores for anhedonia, a core symptom of depression, but not with water maze performance. Our results suggest that RA-induced impairments in hippocampal neurogenesis correlate with depression-like symptoms but not with spatial learning and memory in this design. Thus, manipulations aimed to enhance neurogenesis may help ameliorate emotional aspects of RA-associated mood disorders. © 2016 Wiley Periodicals, Inc.

Estrogen alters baseline and inflammatory-induced cytokine levels independent from hypothalamic-pituitary-adrenal axis activity

Although estrogen reduces inflammatory-mediated pain responses, the mechanisms behind its effects are unclear. This study investigated if estrogen modulates inflammatory signaling by reducing baseline or inflammation-induced cytokine levels in the injury-site, serum, dorsal root ganglia (DRG) and/or spinal cord. We further tested whether estrogen effects on cytokine levels are in part mediated through hypothalamic-pituitary-adrenal (HPA) axis activation. Lumbar DRG, spinal cord, serum, and hind paw tissue were analyzed for cytokine levels in 17β-estradiol-(20%) or vehicle-(100% cholesterol) treated female rats following ovariectomy/sham adrenalectomy (OVX), adrenalectomy/sham ovariectomy (ADX) or ADX+OVX operation at baseline and post formalin injection. Formalin significantly increased pro-inflammatory interleukin (IL)-6 levels in the paw, as well as pro- and anti-inflammatory cytokine levels in the DRG, spinal cord and serum in comparison to naïve conditions. Estrogen replacement significantly increased anti-inflammatory IL-10 levels in the DRG. Centrally, estradiol significantly decreased pro-inflammatory tumor necrosis factor (TNF)-α and IL-1β levels, as well as IL-10 levels, in the spinal cord in comparison to cholesterol treatment. At both sites, most estradiol modulatory effects occurred irrespective of pain or surgical condition. Estradiol alone had no influence on cytokine release in the paw or serum, indicating that estrogen effects were site-specific. Although cytokine levels were altered between surgical conditions at baseline and following formalin administration, ADX operation did not significantly reverse estradiol's modulation of cytokine levels. These results suggest that estrogen directly regulates cytokines independent of HPA axis activity in vivo, in part by reducing cytokine levels in the spinal cord.

Membrane-initiated non-genomic signaling by estrogens in the hypothalamus: cross-talk with glucocorticoids with implications for behavior

The estrogen receptor and glucocorticoid receptor are members of the nuclear receptor superfamily that can signal using both non-genomic and genomic transcriptional modes. Though genomic modes of signaling have been well characterized and several behaviors attributed to this signaling mechanism, the physiological significance of non-genomic modes of signaling has not been well understood. This has partly been due to the controversy regarding the identity of the membrane ER (mER) or membrane GR (mGR) that may mediate rapid, non-genomic signaling and the downstream signaling cascades that may result as a consequence of steroid ligands binding the mER or the mGR. Both estrogens and glucocorticoids exert a number of actions on the hypothalamus, including feedback. This review focuses on the various candidates for the mER or mGR in the hypothalamus and the contribution of non-genomic signaling to classical hypothalamically driven behaviors and changes in neuronal morphology. It also attempts to categorize some of the possible functions of non-genomic signaling at both the cellular level and at the organismal level that are relevant for behavior, including some behaviors that are regulated by both estrogens and glucocorticoids in a potentially synergistic manner. Lastly, it attempts to show that steroid signaling via non-genomic modes may provide the organism with rapid behavioral responses to stimuli.

The effect of ghrelin and estradiol on mean concentration of thyroid hormones

BACKGROUND

Ghrelin is a novel peptide hormone that has GH releasing activity and also other endocrine and metabolic functions. It can also increase food intake and decrease T3 and T4 concentrations. Several parameters of hypothalamic-pituitary-thyroid (HPT) axis function are modulated by 17β-estradiol (E2).

OBJECTIVES

The purpose of this study was to investigate the effect of interactions between ghrelin and estradiol (injected via ICV route) on plasma T3 and T4 concentrations in female rats.

MATERIALS AND METHODS

Eighteen Wistar female rats (bodyweight, 200-250 g) were randomly divided into three groups. Group 1 received estradiol, Group 2 received ghrelin and Group 3 received ghrelin and estradiol. Plasma samples were used to assess T3 and T4 concentration by RIA.

RESULTS

The results indicated that ghrelin significantly decreased thyroid hormone concentrations, whereas estradiol increased these concentrations. The simultaneous injection of ghrelin and estradiol significantly decreased the inhibitory effect of ghrelin on thyroid hormone concentrations (P < 0.05).

CONCLUSIONS

According to the results of this study, both ghrelin and estradiol affect the concentration of thyroid hormone but in opposite directions. This difference might be due to different underlying hormonal mechanisms such as HPA and/or HPT axis melanocyte stimulating hormone (MSH) systems could be suggested.

Oxytocin and Estrogen Receptor β in the Brain: An Overview

Oxytocin (OT) is a neuropeptide synthesized primarily by neurons of the paraventricular and supraoptic nuclei of the hypothalamus. These neurons have axons that project into the posterior pituitary and release OT into the bloodstream to promote labor and lactation; however, OT neurons also project to other brain areas where it plays a role in numerous brain functions. OT binds to the widely expressed OT receptor (OTR), and, in doing so, it regulates homeostatic processes, social recognition, and fear conditioning. In addition to these functions, OT decreases neuroendocrine stress signaling and anxiety-related and depression-like behaviors. Steroid hormones differentially modulate stress responses and alter OTR expression. In particular, estrogen receptor β activation has been found to both reduce anxiety-related behaviors and increase OT peptide transcription, suggesting a role for OT in this estrogen receptor β-mediated anxiolytic effect. Further research is needed to identify modulators of OT signaling and the pathways utilized and to elucidate molecular mechanisms controlling OT expression to allow better therapeutic manipulations of this system in patient populations.

Estrogen signaling in metabolic inflammation

There is extensive evidence supporting the interference of inflammatory activation with metabolism. Obesity, mainly visceral obesity, is associated with a low-grade inflammatory state, triggered by metabolic surplus where specialized metabolic cells such as adipocytes activate cellular stress initiating and sustaining the inflammatory program. The increasing prevalence of obesity, resulting in increased cardiometabolic risk and precipitating illness such as cardiovascular disease, type 2 diabetes, fatty liver, cirrhosis, and certain types of cancer, constitutes a good example of this association. The metabolic actions of estrogens have been studied extensively and there is also accumulating evidence that estrogens influence immune processes. However, the connection between these two fields of estrogen actions has been underacknowledged since little attention has been drawn towards the possible action of estrogens on the modulation of metabolism through their anti-inflammatory properties. In the present paper, we summarize knowledge on the modification inflammatory processes by estrogens with impact on metabolism and highlight major research questions on the field. Understanding the regulation of metabolic inflammation by estrogens may provide the basis for the development of therapeutic strategies to the management of metabolic dysfunctions.

The influence of the HPG axis on stress response and depressive-like behaviour in a transgenic mouse model of Huntington's disease

Huntington's disease (HD) is an autosomal dominant, neurodegenerative disease caused by a CAG tandem repeat mutation encoding a polyglutamine tract expansion in the huntingtin protein. Depression is among the most common affective symptoms in HD but the pathophysiology is unclear. We have previously discovered sexually dimorphic depressive-like behaviours in the R6/1 transgenic mouse model of HD at a pre-motor symptomatic age. Interestingly, only female R6/1 mice display this phenotype. Sexual dimorphism has not been explored in the human HD population despite the well-established knowledge that the clinical depression rate in females is almost twice that of males. Female susceptibility suggests a role of sex hormones, which have been shown to modulate stress response. There is evidence suggesting that the gonads are adversely affected in HD patients, which could alter sex hormone levels. The present study examined the role sex hormones play on stress response in the R6/1 mouse model of HD, in particular, its modulatory effect on the hypothalamic-pituitary-adrenal (HPA) axis and depression-like behaviour. We found that the gonads of female R6/1 mice show atrophy at an early age. Expression levels of gonadotropin-releasing hormone (GnRH) were decreased in the hypothalamus of female HD mice, relative to wild-type female littermates, as were serum testosterone levels. Female serum estradiol levels were not significantly changed. Gonadectomy surgery reduced HPA-axis activity in female mice but had no effect on behavioural phenotypes. Furthermore, expression of the oestrogen receptor (ER) α gene was found to be higher in the adrenal cells of female HD mice. Finally, administration of an ERβ agonist diarylpropionitrile (DPN) rescued depressive-like behaviour in the female HD mice. Our findings provide new insight into the pathogenesis of sexually dimorphic neuroendocrine, physiological and behavioural endophenotypes in HD, and suggest a new avenue for therapeutic intervention.

Characterization of neural estrogen signaling and neurotrophic changes in the accelerated ovarian failure mouse model of menopause

Accelerated ovarian failure (AOF) can be induced in young mice with low doses of 4-vinylcyclohexene diepoxide (VCD), modeling the hormone changes observed across menopause. We assessed markers of synaptic plasticity in the hippocampus, anxiety-like behavior, and spatial learning longitudinally at 4 time points across the AOF model: premenopause, early perimenopause, late perimenopause, and postmenopause (POST). As others have shown, VCD administration decreased ovarian follicle counts and increased acyclicity as the model progressed to POST but with no impact on organ or body weights. The morphology of Iba1 immunoreactive microglia did not differ between vehicle- and VCD-administered mice. Hippocampal postsynaptic density 95 levels were minimally altered across the AOF model but decreased at POST in CA3b 24 hours after exogenous estradiol benzoate (EB). In contrast, hippocampal phosphorylated AKT levels transiently decreased in premenopause but increased at POST after 24 hours of EB in select subregions. Electron microscopy revealed fewer estrogen receptor α containing dendritic spines and terminals in CA1 stratum radiatum at POST. mRNA levels of most brain-derived neurotrophic factor exons (except V and VI) were lower in POST compared with ovariectomized mice. Exon V was sensitive to 24 hours of EB administration in POST-VCD. Anxiety-like behavior was unaffected at any menopause phase. Spatial learning was unaffected in all groups, but POST-VCD mice performed below chance. Our results suggest that the AOF model is suitable for longitudinal studies of neurobiological changes across the menopause transition in mice. Our findings also point to complex interactions between estrogen receptors and pathways involved in synaptic plasticity.

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.

All-trans retinoic acid-induced hypothalamus-pituitary-adrenal hyperactivity involves glucocorticoid receptor dysregulation

Clinical reports have highlighted a role for retinoids in the etiology of mood disorders. Although we had shown that recruitment of the nuclear receptor retinoic acid receptor-α (RAR-α) to corticotropin-releasing hormone (CRH) promoter is implicated in activation of the hypothalamus-pituitary-adrenal (HPA) axis, further insight into how retinoids modulate HPA axis activity is lacking. Here we show that all-trans retinoic acid (RA)-induced HPA activation involves impairments in glucocorticoid receptor (GR) negative feedback. RA was applied to rats chronically through intracerebroventricular injection. A 19-day RA exposure induced potent HPA axis activation and typical depression-like behavior. Dexamethasone failed to suppress basal corticosterone (CORT) secretion, which is indicative of a disturbed GR negative feedback. In the hypothalamic paraventricular nucleus, increased CRH⁺ and c-fos⁺ cells were found while a negative R-2⁺/ER⁺ correlation was present between the number of RAR-α⁺ and GR⁺ cells. This was paralleled by increased RAR-α and decreased GR protein expression in the hypothalamus. Additional in vitro studies confirmed that RA abolished GR-mediated glucocorticoid-induced suppression of CRH expression, indicating a negative cross-talk between RAR-α and GR signaling pathways. Finally, the above changes could be rapidly normalized by treatment with GR antagonist mifepristone. We conclude that in addition to the 'classic' RAR-α-mediated transcriptional control of CRH expression, disturbances in GR negative feedback constitute a novel pathway that underlies RA-induced HPA axis hyperactivity. The rapid normalization by mifepristone may be of potential clinical interest in this respect.

V. Gender determines ACTH recovery from hypercortisolemia in healthy older humans

OBJECTIVE

Available clinical data raise the possibility that stress-adaptive mechanisms differ by gender. However, this notion has not been rigorously tested in relation to cortisol-mediated negative feedback.

MATERIALS/METHODS

Degree of ACTH inhibition during and recovery from an experimental cortisol clamp was tested in 20 healthy older subjects (age 60±2.2 y). Volunteers received oral placebo or ketoconazole (KTCZ) to inhibit adrenal steroidogenesis along with i.v. infusions of saline or a low vs high physiological dose of cortisol in a prospectively randomized double-blind, placebo-controlled design. ACTH and cortisol concentrations were measured every 10 min during the feedback-clamp phase and thereafter (recovery or escape phase). Corticosteroid-binding globulin (CBG) was measured, and free cortisol concentrations were calculated.

RESULTS

Gender did not determine mean ACTH concentrations during the saline or cortisol feedback-clamp phases per se. However, women had markedly impaired ACTH recovery after stopping both low- and high-dose cortisol infusions compared with men (P=0.005, KTCZ/low-dose cortisol arm; and P=0.006, KTCZ/high-dose cortisol arm). Decreased ACTH recovery in women was accompanied by lower total and free cortisol concentrations, pointing to heightened feedback inhibition of hypothalamo-pituitary drive of ACTH secretion as the main mechanism.

CONCLUSIONS

In summary, gender or a factor related to gender, such as sex steroids or body composition, determines recovery of ACTH secretion from cortisol-enforced negative feedback. Attenuated ACTH recovery in post-menopausal women may have relevance to sex differences in stress-related adaptations.

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.

Early life adversity as a risk factor for visceral pain in later life: importance of sex differences

A history of early life adversity (ELA) has health-related consequences that persist beyond the initial maltreatment and into adulthood. Childhood adversity is associated with abnormal glucocorticoid signaling within the hypothalamic-pituitary-adrenal (HPA) axis and the development of functional pain disorders such as the irritable bowel syndrome (IBS). IBS and many adult psychopathologies are more frequently diagnosed in women, and ovarian hormones have been shown to modulate pain sensitivity. Therefore, the sexually dimorphic effects of ELA and the role of ovarian hormones in visceral pain perception represent critical research concepts to enhance our understanding of the etiology of IBS. In this review, we discuss current animal models of ELA and the potential mechanisms through which ovarian hormones modulate the HPA axis to alter nociceptive signaling pathways and induce functionally relevant changes in pain behaviors following ELA.