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

Sex Steroid Hormone Receptor Content of Medial Preoptic Efferents to the Ventral Tegmental Area Is Sexually Dimorphic: Implications for Sex Differences in Mesolimbic Reward Processing

INTRODUCTION

The medial preoptic area (mPOA) is an important regulator of natural and drug-induced reward. However, despite the mPOA being implicated in sexually dimorphic reward responses, sex differences in medial preoptic efferents to the ventral tegmental area (VTA) have not been fully investigated.

METHODS

Two cohorts of male and female rats received unilateral injections of the tract-tracer Fluoro-Gold (FLG) into the VTA. Immunohistochemical staining was used to quantify co-labeled FLG-positive neurons with γ-aminobutyric acid (GABA), estrogen receptor α (ERα), and androgen receptors (AR).

RESULTS

Results revealed a pattern of VTA innervation that was comparable between males and females; more efferents emerged from the rostrocentral portions of the mPOA than caudal portions. Results also indicated that males and females had the same percentage of GABAergic mPOA-VTA projections. Differences emerged when investigating the hormone receptor profile of projections to the VTA, where females had a greater percentage of efferents expressing ERα and males had a greater percentage of efferents expressing AR, in the central portion of the mPOA. Lastly, FLG-positive cells were colocalized with GABA and ERα in cohort 1 and GABA and AR in cohort 2. The majority of AR-expressing cells colocalized with GABAergic efferents to the VTA, but only a portion of ERα-expressing cells colocalized with GABAergic efferents to the VTA.

CONCLUSION

Results indicate that sex differences are present in the sex-steroid hormone receptor content of mPOA-VTA projections, particularly among efferents arising from the central region of the mPOA. These sexually dimorphic connections may influence a wide range of sex differences in reward responses.

Sex differences in basal reelin levels in the paraventricular hypothalamus and in response to chronic stress induced by repeated corticosterone in rats

Repeated exposure to the stress hormone corticosterone results in depressive-like behaviours paralleled by the downregulation of hippocampal reelin expression. Reelin is expressed in key neural populations involved in the stress response, but whether its hypothalamic expression is sex-specific or involved in sex-specific vulnerability to stress is unknown. Female and male rats were treated with either daily vehicle or corticosterone injections (40 mg/kg) for 21 days. Thereafter, they were subjected to several behavioural tasks before being sacrificed to allow the analysis of reelin expression in hypothalamic nuclei. The basal density of reelin-positive cells in males was significantly higher in the paraventricular nucleus (19 %) and in the medial preoptic area (51 %) compared to females. Chronic corticosterone injections increased the immobility time in the forced swim test in males (107 %) and females (108 %) and decreased the exploration of the elevated plus maze in males (34 %). Corticosterone also caused a significant decrease in the density of reelin-positive cells in males, in both ventrodorsal (37 %) and ventrolateral (32 %) subdivisions of the paraventricular nucleus, while not affecting females. Moreover, in the paraventricular nucleus of males, 30 % of the basal reelin-positive cells co-expressed oxytocin while only 17.5 % did in females, showing a positive correlation between reelin and oxytocin levels. Chronic corticosterone did not significantly affect co-localization levels. For the first time, this study shows that there is a sexually dimorphic subpopulation of reelin-positive neurons in the paraventricular nucleus that can be differentially affected by chronic stress.

Age-dependent changes in hormonal stress reactivity following repeated restraint stress throughout adolescence in male rats

Stress-related psychological dysfunctions show a marked increase during adolescence, yet the mechanisms that mediate these vulnerabilities are unknown. Notably, however, adolescence is associated with changes in hormonal stress reactivity mediated by the hypothalamic-pituitary-adrenal (HPA) axis, which might contribute to these dysfunctions. Specifically, pre-adolescent animals display prolonged stress-induced HPA responses compared to adults. Previous experience with stressors further modify these changes in stress reactivity, such that repeated exposure to the same stressor results in an augmented HPA response prior to adolescence, but a habituated response in adulthood. It is unclear when during adolescence the habituated, adult-like response develops to a repeated stressor. Using male rats at various ages that span adolescence (30-70 days of age), we show that by mid-adolescence (i.e. 42 days of age), animals show neither a facilitated nor a habituated HPA hormonal response following four days of repeated restraint stress (4RS) compared to a single restraint session (1RS). We also show that the habituated HPA response to 4RS develops between late-adolescence and young adulthood (i.e. between 56 and 70 days of age, respectively). Further, we find age- and experience-dependent changes in progesterone and testosterone secretion, indicating that the interaction between development and experience affects stress-induced hormonal responses outside of canonical HPA-related hormones. Despite these hormonal differences mediated by age and experience, repeated restraint stress resulted in decreased fecal boli production at all four ages, suggesting dissociation between hormonal and autonomic reactivity during adolescence. These data indicate that HPA plasticity is significantly affected by adolescence and that a habituated hormonal response to homotypic stress does not occur until young adulthood. A greater appreciation of these changes in stress reactivity will contribute to our understanding of the psychological vulnerabilities often associated with stressful adolescence.

Effects of Sleep Deprivation by Olfactorily Induced Sexual Arousal Compared to Immobilization Stress and Manual Sleep Deprivation on Neuromessengers and Time Keeping Genes in the Suprachiasmatic Nuclei and Other Cerebral Entities of Syrian Hamsters-An Immunohistochemical Study

We investigated the effects of sexual arousal induced by olfactory stimuli on the expression of neuromodulators, neurotransmitters and sexual steroid receptors in the suprachiasmatic nucleus (SCN, the circadian pacemaker of mammals) and other cerebral entities of Syrian hamsters (Mesocricetus auratus) compared to manual sleep deprivation and immobilization stress. The hamsters kept under a 12:12 hours (h) light:dark cycle were deprived of sleep by sexual stimulation, gentle manual handling or immobilization stress for 1 h at the beginning of the light phase and subsequently sacrificed at zeitgeber time 01:00, respectively; for comparison, hamsters were manually sleep deprived for 6 or 20 h or sacrificed after completing a full sleep phase. As demonstrated by immunohistochemistry, apart from various alterations after manual sleep deprivation, sexual stimulation caused down-regulation of arginine-vasopressin (AVP), vasointestinal peptide (VIP), serotonin (5-HT), substance P (SP), and met-enkephalin (ME) in the SCN. Somatostatin (SOM) was diminished in the medial periventricular nucleus (MPVN). In contrast, an increase in AVP was observed in the PVN, that of oxytocin (OXY) in the supraoptic nucleus (SON), of tyrosine-hydroxylase (TH) in the infundibular nucleus (IN), and dopamine beta-hydroxylase (DBH) in the A7 neuron population of the brain stem (A7), respectively. Testosterone in plasma was increased. The results indicate that sexual arousal extensively influences the neuropeptide systems of the SCN, suggesting an involvement of the SCN in reproductive behavior.

Age-dependent regulation by androgens of gene expression in the anterior hypothalamus and stress-induced release of adrenal hormones in adolescent and adult male rats

Adolescents show greater and/or more prolonged activation of the hypothalamic-pituitary-adrenal axis in response to stressors than adults, although the basis for such an age difference is not understood. We investigated developmental shifts in the regulation of HPA function by testosterone using androgen replacement in orchiectomised (OCX) pre-pubertal and post-pubertal adolescent rats and in adults, as well as using inhibitors of testosterone synthesis in non-operated rats. The expected dampening effect of testosterone in adult OCX rats did not meet statistical significance in all of the three experiments. Nevertheless, in each, adolescents had higher post-stress concentrations of corticosterone compared to adults despite similar concentrations of testosterone. The effect of testosterone was in the opposite direction in post-pubertal adolescents compared to that in adults, with testosterone replacement leading to increased rather than lower corticosterone concentration. Testosterone replacement decreased arginine vasopressin and corticotrophin-releasing hormone immune-reactive cell counts in the paraventricular nucleus at all ages. In a fourth experiment, we provide evidence that the basis of the age difference in corticosterone release is because of a greater conversion of testosterone to oestradiol in adolescents and a greater conversion of testosterone to dihydrotestosterone in adults: aromatase inhibition had little effect in adults and attenuated the age difference by decreasing stress-induced corticosterone release in adolescents. By contrast, 5α-reductase inhibition or an androgen receptor antagonist had little effect in adolescents and attenuated the age difference by increasing stress-induced corticosterone release in adults. In the adrenal gland, adolescents had reduced 5α-reductase and androgen receptor gene expression. There also were age differences in the regulation of hypothalamic mRNA expression of androgen receptors, oestrogen receptors and aromatase by testosterone. In sum, the results suggest that developmental shifts in the synthesis of testosterone and the regulation of gene expression are factors with respect to age differences in corticosterone release in response to stressors.

Sex differences in the hypothalamic-pituitary-adrenal axis' response to stress: an important role for gonadal hormones

The hypothalamic-pituitary-adrenal (HPA) axis, a neuroendocrine network that controls hormonal responses to internal and external challenges in an organism's environment, exhibits strikingly sex-biased activity. In adult female rodents, acute HPA function following a stressor is markedly greater than it is in males, and this difference has largely been attributed to modulation by the gonadal hormones testosterone and estradiol. These gonadal hormones are produced by the hypothalamic-pituitary-gonadal (HPG) axis and have been shown to determine sex differences in adult HPA function after acute stress via their activational and organizational effects. Although these actions of gonadal hormones are well supported, the possibility that sex chromosomes similarly influence HPA activity is unexplored. Moreover, questions remain regarding sex differences in the activity of the HPA axis following chronic stress and the underlying contributions of gonadal hormones and sex chromosomes. The present review examines what is currently known about sex differences in the neuroendocrine response to stress, as well as outstanding questions regarding this sex bias. Although it primarily focuses on the rodent literature, a brief discussion of sex differences in the human HPA axis is also included.

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.

Rapid nonapeptide synthesis during a critical period of development in the prairie vole: plasticity of the paraventricular nucleus of the hypothalamus

Vasopressin (VP) and oxytocin (OT) are involved in modulating basic physiology and numerous social behaviors. Although the anatomical distributions of nonapeptide neurons throughout development have been described, the functional roles of VP and OT neurons during development are surprisingly understudied, and it is unknown whether they exhibit functional changes throughout early development. We utilized an acute social isolation paradigm to determine if VP and OT neural responses in eight nonapeptide cell groups differ at three different stages of early development in prairie voles. We tested pups at ages that are representative of the three rapid growth stages of the developing brain: postnatal day (PND)2 (closed eyes; poor locomotion), PND9 (eye opening; locomotion; peak brain growth spurt), and PND21 (weaning). Neural responses were examined in pups that (1) were under normal family conditions with their parents and siblings, (2) were isolated from their parents and siblings and then reunited, and (3) were isolated from their parents and siblings. We found that VP and OT neural activity (as assessed via Fos co-localization) did not differ in response to social condition across development. However, remarkably rapid VP and OT synthesis in response to social isolation was observed only in the paraventricular nucleus of the hypothalamus (PVN) and only in PND9 pups. These results suggest that PVN nonapeptide neurons exhibit distinct cellular properties during a critical period of development, allowing nonapeptide neurons to rapidly upregulate peptide production in response to stressors on a much shorter timescale than has been observed in adult animals.

The role of ΔfosB in the medial preoptic area: Differential effects of mating and cocaine history

The transcription factor deltaFosB (ΔFosB) is induced in the nucleus accumbens (NAc) by repeated exposure to drugs of abuse and natural rewards. Less is known about its role in other brain areas. Here, we compared the effects of mating versus cocaine history on induction of ΔFosB in the medial preoptic area (MPOA), an integral site for reproductive behavior, and in the NAc. ΔFosB immunoreactivity (ir) was increased in the MPOA of previously naïve and experienced male rats that mated the day before euthanasia, compared to unmated controls and experienced males with recent mating abstinence. Western immunoblots confirmed that the 35-37-kDa isoform of ΔFosB was increased more in recently mated males. Conversely, previous plus recent cocaine did not increase ΔFosB-ir in the MPOA, despite an increase in the NAc. Next, a viral vector expressing ΔFosB, its dominant negative antagonist ΔJunD, or green fluorescent protein (GFP) control, were microinjected bilaterally into the MPOA. ΔFosB overexpression impaired copulation and promoted female-directed aggression, compared to ΔJunD and control males. These data suggest that ΔFosB in the mPOA is expressed in an experience-dependent manner and affects systems that coordinate mating and aggression. (PsycINFO Database Record

Hypothalamic-pituitary-adrenal axis responsiveness to methamphetamine is modulated by gonadectomy in males

Sex differences in patterns of methamphetamine (MA) abuse have been reported with females (humans and rodents) showing an elevated addiction phenotype. Previous findings indicate MA-induced hypothalamic-pituitary-adrenal (HPA) axis activation is also sexually dimorphic with females exhibiting an elevated glucocorticoid release and differential neural activation patterns within HPA axis-associated brain regions. These effects may contribute to sex differences in abuse. To determine the role of gonadal hormones in mediating sex differences in MA-induced glucocorticoids, male and female C57BL/6J mice were gonadectomized or sham-operated, and following recovery, injected with MA (5mg/kg) and sacrificed 60min or 120min later. Blood was collected for corticosterone radioimmunoassay, and brains were used to assess c-Fos, and c-Fos co-localization with glucocorticoid receptor (GR). At 120min after MA injection, corticosterone levels were elevated in females compared to males and gonadectomy in males increased corticosterone to female levels. C-Fos was greater in females than males in the medial preoptic area, bed nucleus of the stria terminalis, basolateral amygdala, and central amygdala. Female gonadectomy had little effect on either corticosterone or c-Fos, while male gonadectomy elevated c-Fos in the central amygdala. Relative to sham males, gonadectomized males also showed decreased c-Fos/GR cell number in the CA3 hippocampal area compared to sham males, indicating a central site for attenuated negative feedback. Together, these findings indicate that androgens regulate MA-induced activation of the HPA axis, potentially by enhancing negative feedback. These sex and gonadal hormone effects on the HPA axis may contribute to sex differences in MA abuse patterns.

Distribution of corticotropin-releasing factor receptor 1 in the developing mouse forebrain: A novel sex difference revealed in the rostral periventricular hypothalamus

Corticotropin-releasing factor (CRF) signaling through CRF receptor 1 (CRFR1) regulates autonomic, endocrine and behavioral responses to stress and has been implicated in the pathophysiology of several disorders including anxiety, depression, and addiction. Using a validated CRFR1 reporter mouse line (bacterial artificial chromosome identified by green fluorescence protein (BAC GFP-CRFR1)), we investigated the distribution of CRFR1 in the developing mouse forebrain. Distribution of CRFR1 was investigated at postnatal days (P) 0, 4, and 21 in male and female mice. CRFR1 increased with age in several regions including the medial amygdala, arcuate nucleus, paraventricular hypothalamus, medial septum, CA1 hippocampal area, and the lateral habenula. Regions showing decreased CRFR1 expression with increased age include the intermediate portion of the periventricular hypothalamic nucleus, and CA3 hippocampal area. We report a sexually dimorphic expression of CRFR1 within the rostral portion of the anteroventral periventricular nucleus of the hypothalamus (AVPV/PeN), a region known to regulate ovulation, reproductive and maternal behaviors. Females had a greater number of CRFR1-GFP-ir cells at all time points in the AVPV/PeN and CRFR1-GFP-ir was nearly absent in males by P21. Overall, alterations in CRFR1-GFP-ir distribution based on age and sex may contribute to observed age- and sex-dependent differences in stress regulation.

Modifications of anxiety-like behavior in prenatally stressed male offspring with imbalance of androgens

Gonadal hormones have been well-known to affect brain regions known to be involved in the modulation of mood and affective-related behavior. Prenatal stress might alter hypothalamic-pituitary-gonadal axis, it could be a target for development of affective-related disorders in male offspring. The present study was designed to examine an anxiety-like behavior in the adult male offspring with low levels of endogenous androgens delivered from pregnant dams exposed to prenatal stress from gestation day 15 to gestation day 19. The non-stressed and prenatally stressed intact, gonadectomized (GDX) and GDX male offspring treated with oil solvent or testosterone propionate (TP, 0.5 mg/kg, s.c., 14 days, once daily) were used in all experiments. Anxiety-like behavior was assessed in the elevated plus maze (EPM) and the open field test (OFT), respectively. Also, testosterone levels in the blood serum were measured in all experimental groups of offspring. Prenatally stressed GDX offspring demonstrated a significant decrease for time spent into the open arms and increase for time spent into the closed arms as compared to the non-stressed offspring. Administration of TP to the prenatally stressed GDX offspring resulted in a more markedly decrease of the time spent into the open arms and significantly raised the time spent into the closed arms as compared to the non-stressed GDX offspring treated with TP, non-stressed/prenatally stressed GDX offspring. Prenatally stressed GDX offspring showed a significant increase of crossing, rearing, grooming and defecation as compared to the prenatally stressed control offspring. On the contrary, administration of TP to the prenatally stressed GDX offspring significantly decreased crossing behavior, frequency of rearing and grooming behavior as compared to the non-stressed GDX offspring treated with TP, non-stressed/prenatally stressed GDX offspring. Prenatally stressed GDX offspring demonstrated a significant decrease of testosterone levels as compared to the non-stressed/prenatally stressed intact offspring, as well as non-stressed GDX offspring. Administration of TP significantly increased testosterone levels when prenatally stressed GDX offspring were compared with the prenatally stressed intact offspring, non-stressed/prenatally stressed GDX offspring. Thus, the results of the study clearly suggest that gonadectomy and TP supplementation profoundly changed an anxiety-related behavior in prenatally stressed male offspring in the EPM. Our current findings suggest that androgen deficiency in the prenatally stressed male offspring produces the high anxiety level and induces a marked anxious-like state. TP supplementation provokes development of profoundly anxious-like state in the prenatally stressed male offspring, Furthermore, this is the first study to show anxiogenic-like effect of TP administration on anxiety-related states in prenatally stressed male offspring with androgen deficiency.

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.

Suprachiasmatic nucleus as the site of androgen action on circadian rhythms

Androgens act widely in the body in both central and peripheral sites. Prior studies indicate that in the mouse, suprachiasmatic nucleus (SCN) cells bear androgen receptors (ARs). The SCN of the hypothalamus in mammals is the locus of a brain clock that regulates circadian rhythms in physiology and behavior. Gonadectomy results in reduced AR expression in the SCN and in marked lengthening of the period of free-running activity rhythms. Both responses are restored by systemic administration of androgens, but the site of action remains unknown. Our goal was to determine whether intracranial androgen implants targeted to the SCN are sufficient to restore the characteristic free-running period in gonadectomized male mice. The results indicate that hypothalamic implants of testosterone propionate in or very near the SCN produce both anatomical and behavioral effects, namely increased AR expression in the SCN and restored period of free-running locomotor activity. The effect of the implant on the period of the free-running locomotor rhythm is positively correlated with the amount of AR expression in the SCN. There is no such correlation of period change with amount of AR expression in other brain regions examined, namely the preoptic area, bed nucleus of the stria terminalis and premammillary nucleus. We conclude that the SCN is the site of action of androgen effects on the period of circadian activity rhythmicity.

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 anxiety and depression: role of testosterone

Compelling evidence exists for pervasive sex differences in pathological conditions, including anxiety and depressive disorders, with females more than twice as likely to be afflicted. Gonadal hormones may be a major factor in this disparity, given that women are more likely to experience mood disturbances during times of hormonal flux, and testosterone may have protective benefits against anxiety and depression. In this review we focus on the effects of testosterone in males and females, revealed in both human and animal studies. We also present possible neurobiological mechanisms underlying testosterone's mostly protective benefits, including the brain regions, neural circuits, and cellular and molecular pathways involved. While the precise underlying mechanisms remain unclear, both activational and organizational effects of testosterone appear to contribute to these effects. Future clinical studies are necessary in order to better understand when and how testosterone therapy may be effective in both sexes.

Controlling feeding behavior by chemical or gene-directed targeting in the brain: what's so spatial about our methods?

Intracranial chemical injection (ICI) methods have been used to identify the locations in the brain where feeding behavior can be controlled acutely. Scientists conducting ICI studies often document their injection site locations, thereby leaving kernels of valuable location data for others to use to further characterize feeding control circuits. Unfortunately, this rich dataset has not yet been formally contextualized with other published neuroanatomical data. In particular, axonal tracing studies have delineated several neural circuits originating in the same areas where ICI injection feeding-control sites have been documented, but it remains unclear whether these circuits participate in feeding control. Comparing injection sites with other types of location data would require careful anatomical registration between the datasets. Here, a conceptual framework is presented for how such anatomical registration efforts can be performed. For example, by using a simple atlas alignment tool, a hypothalamic locus sensitive to the orexigenic effects of neuropeptide Y (NPY) can be aligned accurately with the locations of neurons labeled by anterograde tracers or those known to express NPY receptors or feeding-related peptides. This approach can also be applied to those intracranial "gene-directed" injection (IGI) methods (e.g., site-specific recombinase methods, RNA expression or interference, optogenetics, and pharmacosynthetics) that involve viral injections to targeted neuronal populations. Spatial alignment efforts can be accelerated if location data from ICI/IGI methods are mapped to stereotaxic brain atlases to allow powerful neuroinformatics tools to overlay different types of data in the same reference space. Atlas-based mapping will be critical for community-based sharing of location data for feeding control circuits, and will accelerate our understanding of structure-function relationships in the brain for mammalian models of obesity and metabolic disorders.

Basal regulation of HPA and dopamine systems is altered differentially in males and females by prenatal alcohol exposure and chronic variable stress

Effects of prenatal alcohol exposure (PAE) on central nervous system function include an increased prevalence of mental health problems, including substance use disorders (SUD). The hypothalamic-pituitary-adrenal (HPA) and dopamine (DA) systems have overlapping neurocircuitries and are both implicated in SUD. PAE alters both HPA and dopaminergic activity and regulation, resulting in increased HPA tone and an overall reduction in tonic DA activity. However, effects of PAE on the interaction between HPA and DA systems have not been investigated. The present study examined PAE effects on basal regulation of central stress and DA systems in key brain regions where these systems intersect. Adult Sprague-Dawley male and female offspring from prenatal alcohol-exposed (PAE), pairfed (PF), and ad libitum-fed control (C) groups were subjected to chronic variable stress (CVS) or remained as a no stress (non-CVS) control group. Corticotropin releasing hormone (CRH) mRNA, as well as glucocorticoid and DA receptor (DA-R) expression were measured under basal conditions 24h following the end of CVS. We show, for the first time, that regulation of basal HPA and DA systems, and likely, HPA-DA interactions, are altered differentially in males and females by PAE and CVS. PAE augmented the typical attenuation in weight gain during CVS in males and caused increased weight loss in females. Increased basal corticosterone levels in control, but not PAE, females suggest that PAE alters the profile of basal hormone secretion throughout CVS. CVS downregulated basal CRH mRNA in the prefrontal cortex and throughout the bed nucleus of the stria terminalis (BNST) in PAE females but only in the posterior BNST of control females. PAE males and females exposed to CVS exhibited more widespread upregulation of basal mineralocorticoid receptor mRNA throughout the hippocampus, and an attenuated decrease in DA-R expression throughout the nucleus accumbens and striatum compared to CVS-exposed control males and females. Overall, these findings enhance our understanding of PAE effects on the cross-talk between HPA and DA systems, and provide insight into possible mechanisms underlying mental health problems that are related to stress and DA signaling, including SUD, which have a high prevalence among individuals with FASD.

Central stress-integrative circuits: forebrain glutamatergic and GABAergic projections to the dorsomedial hypothalamus, medial preoptic area, and bed nucleus of the stria terminalis

Central regulation of hypothalamo-pituitary-adrenocortical (HPA) axis stress responses is mediated by a relatively circumscribed group of projections to the paraventricular hypothalamus (PVN). The dorsomedial hypothalamus (DMH), medial preoptic area (mPOA), and bed nucleus of the stria terminalis (BST) provide direct, predominantly inhibitory, innervation of the PVN. These PVN-projecting neurons are controlled by descending information from limbic forebrain structures, including the prefrontal cortex, amygdala, hippocampus, and septum. The neurochemical phenotype of limbic circuits targeting PVN relays has not been systematically analyzed. The current study combined retrograde tracing and immunohistochemistry/in situ hybridization to identify the specific sites of glutamatergic and GABAergic inputs to the DMH, mPOA, and BST. Following Fluoro-gold (FG) injections in the DMH, retrogradely labeled cells co-localized with vesicular glutamate transporter mRNA in the prefrontal cortex, ventral hippocampus, and paraventricular thalamus. Co-localization of FG and glutamic acid decarboxylase mRNA was present throughout the central and medial amygdaloid nuclei and septal area. In addition, the mPOA received predominantly GABAergic input from the septum, amygdala, and BST. The BST received glutamatergic projections from the hippocampus and basomedial amygdala, whereas, GABAergic inputs arose from central and medial amygdaloid nuclei. Thus, discrete sets of neurons in the hypothalamus and BST are positioned to summate limbic inputs into PVN regulation and may play a role in HPA dysfunction and stress-related illness.

The androgen metabolite, 5α-androstane-3β,17β-diol (3β-diol), activates the oxytocin promoter through an estrogen receptor-β pathway

Testosterone has been shown to suppress the acute stress-induced activation of the hypothalamic-pituitary-adrenal axis; however, the mechanisms underlying this response remain unclear. The hypothalamic-pituitary-adrenal axis is regulated by a neuroendocrine subpopulation of medial parvocellular neurons in the paraventricular nucleus of the hypothalamus (PVN). These neurons are devoid of androgen receptors (ARs). Therefore, a possibility is that the PVN target neurons respond to a metabolite in the testosterone catabolic pathway via an AR-independent mechanism. The dihydrotestosterone metabolite, 5α-androstane-3β,17β-diol (3β-diol), binds and activates estrogen receptor-β (ER-β), the predominant ER in the PVN. In the PVN, ER-β is coexpressed with oxytocin (OT). Therefore, we tested the hypothesis that 3β-diol regulates OT expression through ER-β activation. Treatment of ovariectomized rats with estradiol benzoate or 3β-diol for 4 days increased OT mRNA selectively in the midcaudal, but not rostral PVN compared with vehicle-treated controls. 3β-Diol treatment also increased OT mRNA in the hypothalamic N38 cell line in vitro. The functional interactions between 3β-diol and ER-β with the human OT promoter were examined using an OT promoter-luciferase reporter construct (OT-luc). In a dose-dependent manner, 3β-diol treatment increased OT-luc activity when cells were cotransfected with ER-β, but not ER-α. The 3β-diol-induced OT-luc activity was reduced by deletion of the promoter region containing the composite hormone response element (cHRE). Point mutations of the cHRE also prevented OT-luc activation by 3β-diol. These results indicate that 3β-diol induces OT promoter activity via ER-β-cHRE interactions.

Sex differences in activated corticotropin-releasing factor neurons within stress-related neurocircuitry and hypothalamic-pituitary-adrenocortical axis hormones following restraint in rats

Women may be more vulnerable to certain stress-related psychiatric illnesses than men due to differences in hypothalamic-pituitary-adrenocortical (HPA) axis function. To investigate potential sex differences in forebrain regions associated with HPA axis activation in rats, these experiments utilized acute exposure to a psychological stressor. Male and female rats in various stages of the estrous cycle were exposed to 30min of restraint, producing a robust HPA axis hormonal response in all animals, the magnitude of which was significantly higher in female rats. Although both male and female animals displayed equivalent c-fos expression in many brain regions known to be involved in the detection of threatening stimuli, three regions had significantly higher expression in females: the paraventricular nucleus of the hypothalamus (PVN), the anteroventral division of the bed nucleus of the stria terminalis (BSTav), and the medial preoptic area (MPOA). Dual fluorescence in situ hybridization analysis of neurons containing c-fos and corticotropin-releasing factor (CRF) mRNA in these regions revealed significantly more c-fos and CRF single-labeled neurons, as well as significantly more double-labeled neurons in females. Surprisingly, there was no effect of the estrous cycle on any measure analyzed, and an additional experiment revealed no demonstrable effect of estradiol replacement following ovariectomy on HPA axis hormone induction following stress. Taken together, these data suggest sex differences in HPA axis activation in response to perceived threat may be influenced by specific populations of CRF neurons in key stress-related brain regions, the BSTav, MPOA, and PVN, which may be independent of circulating sex steroids.

Sex, stress, and mood disorders: at the intersection of adrenal and gonadal hormones

The risk for neuropsychiatric illnesses has a strong sex bias, and for major depressive disorder (MDD), females show a more than 2-fold greater risk compared to males. Such mood disorders are commonly associated with a dysregulation of the hypothalamo-pituitary-adrenal (HPA) axis. Thus, sex differences in the incidence of MDD may be related with the levels of gonadal steroid hormone in adulthood or during early development as well as with the sex differences in HPA axis function. In rodents, organizational and activational effects of gonadal steroid hormones have been described for the regulation of HPA axis function and, if consistent with humans, this may underlie the increased risk of mood disorders in women. Other developmental factors, such as prenatal stress and prenatal overexposure to glucocorticoids can also impact behaviors and neuroendocrine responses to stress in adulthood and these effects are also reported to occur with sex differences. Similarly, in humans, the clinical benefits of antidepressants are associated with the normalization of the dysregulated HPA axis, and genetic polymorphisms have been found in some genes involved in controlling the stress response. This review examines some potential factors contributing to the sex difference in the risk of affective disorders with a focus on adrenal and gonadal hormones as potential modulators. Genetic and environmental factors that contribute to individual risk for affective disorders are also described. Ultimately, future treatment strategies for depression should consider all of these biological elements in their design.

Neuroendocrine control of maternal stress responses and fetal programming by stress in pregnancy

The major changes in highly dynamic neuroendocrine systems that are essential for establishing and maintaining pregnancy are outlined from studies on rodents. These changes optimise the internal environment to provide the life support system for the placenta, embryo and fetus. These include automatic prevention of further pregnancy, blood volume expansion, increased appetite and energy storage. The brain regulates these changes, in response to steroid (estrogens, progesterone) and peptide (lactogens, relaxin) hormone signals. Activation of inhibitory endogenous opioid mechanisms in the brain in late pregnancy restrains premature secretion of oxytocin, and attenuates hypothalamo-pituitary-adrenal (HPA) responses to stress. This opioid mechanism is activated by allopregnanolone, a neuroactive progesterone metabolite. The significance of reduced HPA axis responses in shifting maternal metabolic balance, and in protecting the fetuses from adverse programming of HPA axis stress responsiveness and anxious behaviour in later life is critically discussed. Experimental studies showing sex-dependent fetal programming by maternal stress or glucocorticoid exposure in late pregnancy are reviewed. The possibility of over-writing programming in offspring through neurosteroid administration is discussed. The impact of maternal stress on placental function is considered in the context of reconciling studies that show offspring programming by stress in very early or late pregnancy produce similar phenotypes in the offspring.

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.

Stress vulnerability during adolescent development in rats

Adolescent development is proposed to represent a time of increased susceptibility to stress. During adolescence, the brain demonstrates a high level of plasticity and can be positively or negatively affected by the environment. This study tests the hypothesis that adolescent development is a stage of enhanced vulnerability to chronic stress. Male Sprague-Dawley rats were exposed to our 14-d chronic variable stress (CVS) paradigm at three developmental stages: 1) early adolescence (35 d; age at initiation of CVS); 2) late adolescence (50 d); or 3) adulthood (80 d). We examined the effects of CVS on the following: 1) depression-like behavior; 2) somatic indices; 3) hypothalamic-pituitary-adrenal (HPA) axis activity; and 4) neuropeptide expression in the hypothalamus. Results show, regardless of age, CVS exposure: 1) decreased body weight; 2) increased adrenal size; 3) decreased fat weight; and 4) increased HPA response to stress. The somatic effects of CVS were exaggerated in late adolescent animals, and late adolescent animals were the only group where CVS decreased oxytocin expression and increased basal corticosterone. In response to CVS, adult animals increased immobility during the forced-swim test while early and late adolescent animals were resistant to the effects of chronic stress on depression-like behavior. Results show that adolescent animals were protected from the effect of chronic stress on depression-like behavior while late adolescent animals were more susceptible to the somatic, HPA axis, and neuropeptide effects of chronic stress. Thus, adolescent development is a unique window of vulnerabilities and protections to the effects of chronic stress.

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.