Organizational effects of testosterone, estradiol, and dihydrotestosterone on vasopressin mRNA expression in the bed nucleus of the stria terminalis

Adolescent exposure to bisphenol-a antagonizes androgen regulation of social behavior in male mice

Social behavior is sexually dimorphic, which is regulated by gonadal hormones in the brain. Our recent study found that exposure to low doses of bisphenol-A (BPA) during adolescence, permanently alters social behavior in adult male mice, but the underlying mechanisms remain unclear. Using adolescent gonadectomy (GDX) male mice with testosterone propionate (TP, 0.5 mg/kg) supplement (TP-GDX), this study showed that BPA antagonized promoting effects of TP on social interaction, sexual behavior, and aggression in GDX mice. BPA eliminated the reversal effects of TP on GDX-induced decrease in the number of immunoreactive to arginine vasopressin (AVP-ir) neurons in the medial amygdala (MeA) and the levels of AVP receptor 1a (V1aR) in the MeA and the nucleus accumbens (NAc). In addition, BPA removed down-regulation in the levels of dopamine (DA) transporter (DAT) and DA receptor 1 (DR1) in the NAc of TP-GDX mice. BPA exposure reduced testosterone (T) levels in the brain and serum and the expression of androgen receptor (AR) protein in the amygdala and striatum of sham-operated and TP-GDX males. These results suggest that adolescent exposure to BPA inhibits regulation of androgen in AVP and DA systems of the brain regions associated with social behavior, and thus alters social behaviors of adult male mice.

Four-week intranasal oxytocin administration reduces attachment avoidance in older women

The neuropeptide oxytocin (OT) serves as a critical modulator of social cognition and social behavior. Adult attachment is an affiliative process crucial for social interaction across adulthood. Insecure adult attachment comprises two broad dimensions, attachment anxiety and attachment avoidance. Both these dimensions of attachment are currently understudied regarding OT modulation, and especially in older adults. The present study determined the effects of chronic intranasal OT administration on adult attachment in generally healthy older women and men (aged 55-95 years). Embedded in a larger project, participants were randomly assigned to self-administer 24 international units of either OT or a placebo (P) intranasally twice daily for four weeks. The Experiences in Close Relationships Scale assessed adult attachment (anxiety and avoidance) pre- and post-treatment. There was no significant pre- to post-treatment change in attachment avoidance overall, but the treatment x timepoint x sex interaction was significant, in that women (but not men) in the OT (vs. P) group reported decreased attachment avoidance. No comparable effects were observed for attachment anxiety. Results suggest that older women may benefit from chronic intranasal OT treatment by experiencing less attachment avoidance in their adult relationships.

Oxytocin and testosterone administration amplify viewing preferences for sexual images in male rhesus macaques

Social stimuli, like faces, and sexual stimuli, like genitalia, spontaneously attract visual attention in both human and non-human primates. Social orienting behaviour is thought to be modulated by neuropeptides as well as sex hormones. Using a free viewing task in which paired images of monkey faces and anogenital regions were presented simultaneously, we found that male rhesus macaques overwhelmingly preferred to view images of anogenital regions over faces. They were more likely to make an initial gaze shift towards, and spent more time viewing, anogenital regions compared with faces, and this preference was accompanied by relatively constricted pupils. On face images, monkeys mostly fixated on the forehead and eyes. These viewing preferences were found for images of both males and females. Both oxytocin (OT), a neuropeptide linked to social bonding and affiliation, and testosterone (TE), a sex hormone implicated in mating and aggression, amplified the pre-existing orienting bias for female genitalia over female faces; neither treatment altered the viewing preference for male anogenital regions over male faces. Testosterone but not OT increased the probability of monkeys making the first gaze shift towards female anogenital rather than face pictures, with the strongest effects on anogenital images of young and unfamiliar females. Finally, both OT and TE promoted viewing of the forehead region of both female and male faces, which display sexual skins, but decreased the relative salience of the eyes of older males. Together, these results invite the hypothesis that both OT and TE regulate reproductive behaviours by acting as a gain control on the visual orienting network to increase attention to mating-relevant signals in the environment.

This article is part of the theme issue ‘Interplays between oxytocin and other neuromodulators in shaping complex social behaviours’.

Exocrine scent marking: Coordinative role of arginine vasopressin in the systemic regulation of social signaling behaviors

Arginine vasopressin (AVP) is a neurohypophysial hormone that coordinatively regulates central socio-emotional behavior and peripheral control of antidiuretic fluid homeostasis. Most mammals, including rodents, utilize exocrine or urine-contained scent marking as a social signaling tool that facilitates social adaptation. The exocrine scent marking behavior is postulated to fine-tune sensory and cognitive abilities to recognize key social features via exocrine/urinary olfactory cues and subsequently control exocrine deposition or urinary marking through the mediation of osmotic fluid balance. AVP is implicated as a major player in controlling both recognition and signaling responses. This review provides constructive hypotheses on the coordinative processes of the AVP neurohypophysial circuits in the systemic regulations of fluid control and social-communicative behavior, via the expression of exocrine scent marking, and further emphasizes a potential role of AVP in a common mechanism underlying social communication in rodents.

Neuroendocrine underpinning of social recognition in males and females

Social recognition is an essential skill for the expression of appropriate behaviors towards conspecifics in most social species. Several studies point to oxytocin (OT) and arginine vasopressin (AVP) as key mediators of social recognition in males and females. However, sex differences in social cognitive behaviors highlight an important interplay between OT, AVP and the sex steroids. Estrogens facilitate social recognition by regulating OT action in the hypothalamus and that of OT receptor in the medial amygdala. The role of OT in these brain regions appears to be essential for social recognition in both males and females. Conversely, social recognition in male rats and mice is more dependent on AVP release in the lateral septum than in females. The AVP system comprises a series of highly sexually dimorphic brain nuclei, including the bed nucleus of the stria terminalis, the amygdala and the lateral septum. Various studies suggest that testosterone and its metabolites, including estradiol, influence social recognition in males by modulating the activity of the AVP at V1a receptor. Intriguingly, both estrogens and androgens can affect social recognition very rapidly, through non-genomic mechanisms. In addition, the androgen metabolites, namely 3α-diol and 3β-diol, may also have an impact on social behaviors either by interacting with the estrogen receptors or through other mechanisms. Overall, the regulation of OT and AVP by sex steroids fine tunes social recognition and the behaviors that depend upon it (e.g., social bond, hierarchical organization, aggression) in a sex-dependent manner. Elucidating the sex-dependent interaction between sex steroids and neuroendocrine systems is essential for understanding sex differences in the normal and abnormal expression of social behaviors.

Pubertal exposure to bisphenol-A affects social recognition and arginine vasopressin in the brain of male mice

Social recognition is an ability of animals to identify and distinguish conspecifics, which is essential for nearly all social species to establish social relationships. Social recognition provides the basis for a variety of social behaviors. Because of modulated by gonadal hormones, it is possible that social cognition is affected by environmental endocrine disruptors (EEDs). In the present study, after being pubertal exposed to bisphenol A (BPA, 0.04, 0.4, and 4 mg/kg) for 18 days, adult male mice did not show significant dishabituation to a novel female stimulus in habituation-dishabituation task. The capacity for discriminating the odors between familiar and novel female urine or between male and female urine was suppressed in BPA-exposed male. In addition, BPA (0.4, 4 mg/kg) decreased the number of immunoreaction of AVP (AVP-ir) neurons in both the bed nucleus of the stria terminalis (BNST) and the medial amygdala (MeA), and BPA (0.04, 0.4, 4 mg/kg) reduced the level of V1αR in the lateral septum (LS) of adult male. Further, BPA decreased the levels of testosterone (T) in the brain and androgens receptor (AR) in the LS, the amygdala, and BNST, as well the levels of estrogen receptor α and β (ERα/β) in the amygdala and BNST. These results indicate that pubertal exposure to BPA affected the actions of both androgens and estrogens in the brain and inhibited AVP system of social circuits, and these alterations may be associated with impaired social recognition of adult male mice.

Centromedial amygdala is more relevant for phobic confrontation relative to the bed nucleus of stria terminalis in patients with spider phobia

Recent studies indicate differential involvement of the centromedial amygdala (CM) and the bed nucleus of the stria terminalis (BNST) during processing (anticipation and confrontation) of threat stimuli. Here, temporal predictability was shown to be a relevant factor. In this study, we want to investigate the relevance of these effects, which were found in healthy subjects, for anxiety disorders. Therefore, we investigated the differential involvement of CM and BNST in the anticipation and confrontation of phobic stimuli under variation of temporal predictability in spider phobia. 21 patients with spider phobia and 21 healthy controls underwent a temporally predictable/unpredictable phobic and neutral anticipation and confrontation paradigm using functional magnetic resonance imaging (fMRI) and ROI analyses. During the anticipation phase, healthy controls showed higher CM and BNST activity during the predictable compared with the unpredictable condition compared with the anxiety patients. During a confrontation phase that followed the anticipation phase, CM was more activated than BNST during the phobic compared with the neutral confrontation. While this effect was independent of threat predictability in patients, healthy controls showed higher activation in the CM compared with the BNST only during the predictable spider confrontation compared with the predictable bird confrontation. The results contribute to a better understanding of the separate roles of the CM and BNST during phobic processes. The CM was found to be more relevant to phobic confrontation in patients with spider phobia compared with the BNST.

Binge ethanol drinking associated with sex-dependent plasticity of neurons in the insula that project to the bed nucleus of the stria terminalis

Modifications in brain regions that govern reward-seeking are thought to contribute to persistent behaviors that are heavily associated with alcohol-use disorder (AUD) including binge ethanol drinking. The bed nucleus of the stria terminalis (BNST) is a critical node linked to both alcohol consumption and the onset, maintenance and progression of adaptive anxiety and stress-related disorders. Differences in anatomy, connectivity and receptor subpopulations, make the BNST a sexually dimorphic region. Previous work indicates that the ventral BNST (vBNST) receives input from the insular cortex (IC), a brain region involved in processing the body's internal state. This IC-vBNST projection has also been implicated in emotional and reward-seeking processes. Therefore, we examined the functional properties of vBNST-projecting, IC neurons in male and female mice that have undergone short-term ethanol exposure and abstinence using a voluntary Drinking in the Dark paradigm (DID) paired with whole-cell slice electrophysiology. First we show that IC neurons projected predominantly to the vBNST. Next, our data show that short-term ethanol exposure and abstinence enhanced excitatory synaptic strength onto vBNST-projecting, IC neurons in both sexes. However, we observed diametrically opposing modifications in excitability across sexes. In particular, short-term ethanol exposure resulted in increased intrinsic excitability of vBNST-projecting, IC neurons in females but not in males. Furthermore, in females, abstinence decreased the excitability of these same neurons. Taken together these findings show that short-term ethanol exposure, as well as the abstinence cause sex-related adaptations in BNST-projecting, IC neurons.

Corticotropin-releasing factor neurons in the bed nucleus of the stria terminalis exhibit sex-specific pain encoding in mice

The bed nucleus of the stria terminalis (BNST) plays an emerging role in pain regulation. Pharmacological studies have found that inhibiting corticotropin-releasing factor (CRF) signaling in the BNST can selectively mitigate the sensory and affective-motivational components of pain. However, mechanistic insight on the source of CRF that drives BNST responses to these harmful experiences remains unknown. In the present study, we used a series of genetic approaches to show that CRF in the BNST is engaged in the processing and modulation of pain. We conducted cell-type specific in vivo calcium imaging in CRF-Cre mice and found robust and synchronized recruitment of BNSTCRF neurons during acute exposures to noxious heat. Distinct patterns of recruitment were observed by sex, as the magnitude and timing of heat responsive activity in BNSTCRF neurons differed for male and female mice. We then used a viral approach in Floxed-CRF mice to selectively reduce CRF expression in the BNST and found it decreased nociceptive sensitivity for both sexes and increased paw attending for females. Together, these findings reveal that CRF in the BNST influences multiple facets of the pain experience to impact the sex-specific expression of pain-related behaviors.

Anxious to see you: Neuroendocrine mechanisms of social vigilance and anxiety during adolescence

Social vigilance is a behavioral strategy commonly used in adverse or changing social environments. In animals, a combination of avoidance and vigilance allows an individual to evade potentially dangerous confrontations while monitoring the social environment to identify favorable changes. However, prolonged use of this behavioral strategy in humans is associated with increased risk of anxiety disorders, a major burden for human health. Elucidating the mechanisms of social vigilance in animals could provide important clues for new treatment strategies for social anxiety. Importantly, during adolescence the prevalence of social anxiety increases significantly. We hypothesize that many of the actions typically characterized as anxiety behaviors begin to emerge during this time as strategies for navigating more complex social structures. Here, we consider how the social environment and the pubertal transition shape neural circuits that modulate social vigilance, focusing on the bed nucleus of the stria terminalis and prefrontal cortex. The emergence of gonadal hormone secretion during adolescence has important effects on the function and structure of these circuits, and may play a role in the emergence of a notable sex difference in anxiety rates across adolescence. However, the significance of these changes in the context of anxiety is still uncertain, as not enough studies are sufficiently powered to evaluate sex as a biological variable. We conclude that greater integration between human and animal models will aid the development of more effective strategies for treating social anxiety.

Neuroendocrine-Immune Crosstalk Shapes Sex-Specific Brain Development

Sex is an essential biological variable that significantly impacts multiple aspects of neural functioning in both the healthy and diseased brain. Sex differences in brain structure and function are organized early in development during the critical period of sexual differentiation. While decades of research establish gonadal hormones as the primary modulators of this process, new research has revealed a critical, and perhaps underappreciated, role of the neuroimmune system in sex-specific brain development. The immune and endocrine systems are tightly intertwined and share processes and effector molecules that influence the nervous system. Thus, a natural question is whether endocrine-immune crosstalk contributes to sexual differentiation of the brain. In this mini-review, we first provide a conceptual framework by classifying the major categories of neural sex differences and review the concept of sexual differentiation of the brain, a process occurring early in development and largely controlled by steroid hormones. Next, we describe developmental sex differences in the neuroimmune system, which may represent targets or mediators of the sexual differentiation process. We then discuss the overwhelming evidence in support of crosstalk between the neuroendocrine and immune systems and highlight recent examples that shape sex differences in the brain. Finally, we review how early life events can perturb sex-specific neurodevelopment via aberrant immune activation.

Sex differences in the hypothalamic-pituitary-adrenal axis: An obstacle to antidepressant drug development?

Hypothalamic-pituitary-adrenal (HPA) axis dysfunction has long been implicated in the pathophysiology of depression, and HPA axis-based compounds have served as potential new therapeutic targets, but with no success. This review details sex differences from animal and human studies in the function of HPA axis elements (glucocorticoids, corticotropin releasing factor, and vasopressin) and related compounds tested as candidate antidepressants. We propose that sex differences contribute to the failure of novel HPA axis-based drugs in clinical trials. Compounds studied preclinically in males were tested in clinical trials that recruited more, if not exclusively, women, and did not control, but rather adjusted, for potential sex differences. Indeed, clinical trials of antidepressants are usually not stratified by sex or other important factors, although preclinical and epidemiological data support such stratification. In conclusion, we suggest that clinical testing of HPA axis-related compounds creates an opportunity for targeted, personalized antidepressant treatments based on sex. LINKED ARTICLES: This article is part of a themed section on The Importance of Sex Differences in Pharmacology Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.21/issuetoc.

Sex-Dependent Modulation of Anxiety and Fear by 5-HT1A Receptors in the Bed Nucleus of the Stria Terminalis

Serotonin (5-hydroxytryptamine; 5-HT) coordinates behavioral responses to stress through a variety of presynaptic and postsynaptic receptors distributed across functionally diverse neuronal networks in the central nervous system. Efferent 5-HT projections from the dorsal raphe nucleus (DRN) to the bed nucleus of the stria terminalis (BNST) are generally thought to enhance anxiety and aversive learning by activating 5-HT_2C receptor (5-HT_2CR) signaling in the BNST, although an opposing role for postsynaptic 5-HT_1A receptors has recently been suggested. In the present study, we sought to delineate a role for postsynaptic 5-HT_1A receptors in the BNST in aversive behaviors using a conditional knockdown of the 5-HT_1A receptor. Both males and females were tested to dissect out sex-specific effects. We found that male mice have significantly reduced fear memory recall relative to female mice and inactivation of 5-HT_1A receptor in the BNST increases contextual fear conditioning in male mice so that they resemble the females. This coincided with an increase in neuronal excitability in males, suggesting that 5-HT_1A receptor deletion may enhance contextual fear recall by disinhibiting fear memory circuits in the BNST. Interestingly, 5-HT_1A receptor knockdown did not significantly alter anxiety-like behavior in male or female mice, which is in agreement with previous findings that anxiety and fear are modulated by dissociable circuits in the BNST. Overall, these results suggest that BNST 5-HT_1A receptors do not significantly alter behavior under basal conditions, but can act as a molecular brake that buffer against excessive activation of aversive circuits in more threatening contexts.

Comparing vasopressin and oxytocin fiber and receptor density patterns in the social behavior neural network: Implications for cross-system signaling

Vasopressin (AVP) and oxytocin (OXT) regulate social behavior by binding to their canonical receptors, the vasopressin V1a receptor (V1aR) and oxytocin receptor (OTR), respectively. Recent studies suggest that these neuropeptides may also signal via each other's receptors. The extent to which such cross-system signaling occurs likely depends on anatomical overlap between AVP/OXT fibers and V1aR/OTR expression. By comparing AVP/OXT fiber densities with V1aR/OTR binding densities throughout the rat social behavior neural network (SBNN), we propose the potential for cross-system signaling in four regions: the medial amygdala (MeA), bed nucleus of the stria terminalis (BNSTp), medial preoptic area, and periaqueductal grey. We also discuss possible implications of corresponding sex (higher in males versus females) and age (higher in adults versus juveniles) differences in AVP fiber and OTR binding densities in the MeA and BNSTp. Overall, this review reveals the need to unravel the consequences of potential cross-system signaling between AVP and OXT systems in the SBNN for the regulation of social behavior.

Neural Regulation of Paternal Behavior in Mammals: Sensory, Neuroendocrine, and Experiential Influences on the Paternal Brain

Across the animal kingdom, parents in many species devote extraordinary effort toward caring for offspring, often risking their lives and exhausting limited resources. Understanding how the brain orchestrates parental care, biasing effort over the many competing demands, is an important topic in social neuroscience. In mammals, maternal care is necessary for offspring survival and is largely mediated by changes in hormones and neuropeptides that fluctuate massively during pregnancy, parturition, and lactation (e.g., progesterone, estradiol, oxytocin, and prolactin). In the relatively small number of mammalian species in which parental care by fathers enhances offspring survival and development, males also undergo endocrine changes concurrent with birth of their offspring, but on a smaller scale than females. Thus, fathers additionally rely on sensory signals from their mates, environment, and/or offspring to orchestrate paternal behavior. Males can engage in a variety of infant-directed behaviors that range from infanticide to avoidance to care; in many species, males can display all three behaviors in their lifetime. The neural plasticity that underlies such stark changes in behavior is not well understood. In this chapter we summarize current data on the neural circuitry that has been proposed to underlie paternal care in mammals, as well as sensory, neuroendocrine, and experiential influences on paternal behavior and on the underlying circuitry. We highlight some of the gaps in our current knowledge of this system and propose future directions that will enable the development of a more comprehensive understanding of the proximate control of parenting by fathers.

Stress, sex, and motivated behaviors

Stress is a major risk factor for development of psychiatric disorders such as depression and development of substance use disorder. Although there are important sex differences in the prevalence of these disorders, most preclinical models used to study stress-induced disorders have used males only. Social defeat stress is a commonly used method to induce stress in an ethologically relevant way but has only recently begun to be used in female rodents. Using these new female models, recent studies have examined how social defeat stress affects males and females differently at the behavioral, circuit, and molecular levels. This Mini-Review discusses sex differences in the effects of social defeat stress on social behavior and drug-seeking behavior as well as its impact on the mesolimbic dopamine system and the highly connected region of the bed nucleus of the stria terminalis. © 2016 Wiley Periodicals, Inc.

Sex-specific mechanisms for responding to stress

Posttraumatic stress disorder and major depression share stress as an etiological contributor and are more common in women than in men. Traditionally, preclinical studies investigating the neurobiological underpinnings of stress vulnerability have used only male rodents; however, recent studies that include females are finding sex-specific mechanisms for responding to stress. This Mini-Review examines recent literature using a framework developed by McCarthy and colleagues (2012; J Neurosci 32:2241-2247) that highlights different types of sex differences. First, we detail how learned fear responses in rats are sexually dimorphic. Then, we contrast this finding with fear extinction, which is similar in males and females at the behavioral level but at the circuitry level is associated with sex-specific cellular changes and, thus, exemplifies a sex convergence. Next, sex differences in stress hormones are detailed. Finally, the effects of stress on learning, attention, and arousal are used to highlight the concept of a sex divergence in which the behavior of males and females is similar at baseline but diverges following stressor exposure. We argue that appreciating and investigating the diversity of sex differences in stress response systems will improve our understanding of vulnerability and resilience to stress-related psychiatric disorders and likely lead to the development of novel therapeutics for better treatment of these disorders in both men and women. © 2016 Wiley Periodicals, Inc.

Gonadal Hormone-Dependent Sexual Differentiation of a Female-Biased Sexually Dimorphic Cell Group in the Principal Nucleus of the Bed Nucleus of the Stria Terminalis in Mice

We recently reported a female-biased sexually dimorphic area in the mouse brain in the boundary region between the preoptic area and the bed nucleus of the stria terminalis (BNST). We reexamined this area and found that it is a ventral part of the principal nucleus of the BNST (BNSTp). The BNSTp is a male-biased sexually dimorphic nucleus, but the ventral part of the BNSTp (BNSTpv) exhibits female-biased sex differences in volume and neuron number. The volume and neuron number of the BNSTpv were increased in males by neonatal orchiectomy and decreased in females by treatment with testosterone, dihydrotestosterone, or estradiol within 5 days after birth. Sex differences in the volume and neuron number of the BNSTpv emerged before puberty. These sex differences became prominent in adulthood with increasing volume in females and loss of neurons in males during the pubertal/adolescent period. Prepubertal orchiectomy did not affect the BNSTpv, although prepubertal ovariectomy reduced the volume increase and induced loss of neurons in the female BNSTpv. In contrast, the volume and neuron number of male-biased sexually dimorphic nuclei that are composed of mainly calbindin neurons and are located in the preoptic area and BNST were decreased by prepubertal orchiectomy but not affected by prepubertal ovariectomy. Testicular testosterone during the postnatal period may defeminize the BNSTpv via binding directly to the androgen receptor and indirectly to the estrogen receptor after aromatization, although defeminization may proceed independently of testicular hormones in the pubertal/adolescent period. Ovarian hormones may act to feminize the BNSTpv during the pubertal/adolescent period.

Increased vasopressin expression in the BNST accompanies paternally induced territoriality in male and female California mouse offspring

While developmental consequences of parental investment on species-typical social behaviors has been extensively characterized in same-sex parent-offspring interactions, the impact of opposite-sex relationships is less clear. In the bi-parental California mouse (Peromyscus californicus), paternal retrieval behavior induces territorial aggression and the expression of arginine vasopressin (AVP) in adult male offspring. Although similar patterns of territorially emerge among females, the sexually dimorphic AVP system has not been considered since it is generally thought to regulate male-typical behavior. However, we recently demonstrated that male and female P. californicus offspring experience increases in plasma testosterone following paternal retrieval. Since AVP expression is androgen-dependent during development, we postulate that increases in AVP expression may accompany territoriality in female, as well as male offspring. To explore this aim, adult P. californicus offspring that received either high or low levels of paternal care (retrievals) during early development were tested for territoriality and immunohistochemical analysis of AVP within the bed nucleus of the stria terminalis (BNST), paraventricular nucleus (PVN), and supraoptic nucleus (SON). Consistent with previous studies, high care offspring were more aggressive than low care offspring. Moreover, high care offspring had significantly more AVP immunoreactive (AVP-ir) cells within the BNST than low care offspring. This pattern was observed within female as well as male offspring, suggesting an equally salient role for paternal care on female offspring physiology. Regardless of early social experience, sex differences in AVP persisted in the BNST, with males having greater expression than females.

Neuroimmunology and neuroepigenetics in the establishment of sex differences in the brain

The study of sex differences in the brain is a topic of neuroscientific study that has broad reaching implications for culture, society and biomedical science. Recent research in rodent models has led to dramatic shifts in our views of the mechanisms underlying the sexual differentiation of the brain. These include the surprising discoveries of a role for immune cells and inflammatory mediators in brain masculinization and a role for epigenetic suppression in brain feminization. How and to what degree these findings will translate to human brain development will be questions of central importance in future research in this field.

Quantitative mapping reveals age and sex differences in vasopressin, but not oxytocin, immunoreactivity in the rat social behavior neural network

The neuropeptides vasopressin (AVP) and oxytocin (OT) have been implicated in the regulation of numerous social behaviors in adult and juvenile animals. AVP and OT signaling predominantly occur within a circuit of interconnected brain regions known collectively as the "social behavior neural network" (SBNN). Importantly, AVP and OT signaling within the SBNN has been shown to differentially regulate diverse social behaviors, depending on the age and/or sex of the animal. We hypothesized that variation in the display of these behaviors is due in part to age and sex differences in AVP and OT synthesis within the SBNN. However, a thorough characterization of AVP and OT-immunoreactive (ir) fibers and cell bodies across age and sex within the SBNN has been lacking in rats. We therefore quantified AVP- and OT-ir fibers and cell bodies in 22 subregions of the forebrain SBNN in juvenile and adult, male and female rats. We found numerous age (16 subregions) and sex (10 subregions) differences in AVP-ir fiber fractional areas, and AVP-ir cell body numbers, which were mainly observed in the medial amygdala/bed nucleus of the stria terminalis to lateral septum circuit. In contrast to AVP, we observed no age or sex differences in OT-ir fiber fractional areas or cell bodies in any of the 22 subregions of the forebrain SBNN. Thus, unlike the static pattern observed for OT, AVP innervation of the forebrain SBNN appears to undergo developmental changes, and is highly sexually dimorphic, which likely has significant functional consequences for the regulation of social behavior.

The effects of long-term estradiol treatment on social behavior and gene expression in adult female rats

This study tested the effects of long-term estradiol (E₂) replacement on social behavior and gene expression in brain nuclei involved in the regulation of these social behaviors in adult female rats. We developed an ultrasonic vocalization (USV) test and a sociability test to examine communications, social interactions, and social preference, using young adult female cagemates. All rats were ovariectomized (OVX) and implanted with a Silastic capsule containing E₂ or vehicle, and housed in same-treatment pairs for a 3-month period. Then, rats were behaviorally tested, euthanized, and 5 nuclei in the brain's social decision-making circuit were selected for neuromolecular profiling by a multiplex qPCR method. Our novel USV test proved to be a robust tool to measure numbers and types of calls emitted by cagemates that had been reintroduced after a 1-week separation. Results also showed that E₂-treated OVX rats had profoundly decreased numbers of USV calls compared to vehicle-treated OVX rats. In a test of sociability, in which a female was allowed to choose between her cagemate or a same-treatment novel rat, we found few effects of E₂ compared to vehicle, although interestingly, rats chose the cagemate over an unfamiliar conspecific. Gene expression results revealed that the supraoptic nucleus had the greatest number of gene changes caused by E₂: Oxt, Oxtr and Avp were increased, and Drd2, Htr1a, Grin2b, and Gabbr1 were decreased, by E₂. No genes were affected in the prefrontal cortex, and 1-4 genes were changed in paraventricular nucleus (Pgr), bed nucleus of the stria terminalis (Oxtr, Esr2, Dnmt3a), and medial amygdala (Oxtr, Ar, Foxp1, Tac3). Thus, E₂ changes communicative interactions between adult female rats, together with selected expression of genes in the brain, especially in the supraoptic nucleus.

Multi- and Transgenerational Consequences of Bisphenol A on Sexually Dimorphic Cell Populations in Mouse Brain

Bisphenol A (BPA) is an endocrine-disrupting compound used to manufacture plastics; it is present in linings of food cans, bottles, thermal receipts, and many other everyday items and is detectable in human urine and blood. Exposure to BPA during development can disrupt sexual differentiation of some brain regions. Moreover, BPA can have transgenerational effects on gene expression and behaviors. Here, we used a diet and breeding regimen that produces transgenerational effects on behaviors. C57BL/6J mice consumed control or BPA-containing diets during pregnancy. We examined vasopressin (AVP) and estrogen receptor α (ERα) immunoreactivity (ir) in sexually dimorphic brain regions from first-generation (F1) offspring and transgenerational effects of BPA in third-generation offspring. In all but one brain region examined, the expected sex differences were noted in both generations of control mice. In F1 mice, a diet by sex interaction was present for AVP-ir in the lateral septum and posterodorsal medial amygdala. In both regions, BPA exposure reduced immunoreactivity in male brains. An interaction between diet and sex for ERα-ir in the ventromedial hypothalamus was caused by reduced immunoreactivity in BPA-exposed females. Of interest, BPA had transgenerational effects on ERα-ir in the anteroventral periventricular nucleus and bed nucleus of the stria terminalis. Our data show that BPA produces immunoreactive differences in ERα-ir generations after exposure to BPA. We speculate that actions of BPA in utero on ERα-ir in brain have long-term consequences for reproduction and social behavior.

Endocrine Disruption of Vasopressin Systems and Related Behaviors

Endocrine disrupting chemicals (EDCs) are chemicals that interfere with the organizational or activational effects of hormones. Although the vast majority of the EDC literature focuses on steroid hormone signaling related impacts, growing evidence from a myriad of species reveals that the nonapeptide hormones vasopressin (AVP) and oxytocin (OT) may also be EDC targets. EDCs shown to alter pathways and behaviors coordinated by AVP and/or OT include the plastics component bisphenol A (BPA), the soy phytoestrogen genistein (GEN), and various flame retardants. Many effects are sex specific and likely involve action at nuclear estrogen receptors. Effects include the elimination or reversal of well-characterized sexually dimorphic aspects of the AVP system, including innervation of the lateral septum and other brain regions critical for social and other non-reproductive behaviors. Disruption of magnocellular AVP function has also been reported in rats, suggesting possible effects on hemodynamics and cardiovascular function.

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.

Testing the critical window of estradiol replacement on gene expression of vasopressin, oxytocin, and their receptors, in the hypothalamus of aging female rats

The current study tested the "critical window" hypothesis of menopause that postulates that the timing and duration of hormone treatment determine their potential outcomes. Our focus was genes in the rat hypothalamus involved in social and affiliative behaviors that change with aging and/or estradiol (E2): Avp, Avpr1a, Oxt, Oxtr, and Esr2 in the paraventricular nucleus (PVN) and supraoptic nucleus (SON). Rats were reproductively mature or aging adults, ovariectomized, given E2 or vehicle treatment of different durations, with or without a post-ovariectomy delay. Our hypothesis was that age-related changes in gene expression are mitigated by E2 treatments. Contrary to this, PVN Oxtr increased with E2, and Avpr1a increased with age. In the SON, Avpr1a increased with age, Oxtr with age and timing, and Avp was altered by duration. Thus, chronological age and E2 have independent actions on gene expression, with the "critical window" hypothesis supported by the observed timing and duration effects.

Species, sex and individual differences in the vasotocin/vasopressin system: relationship to neurochemical signaling in the social behavior neural network

Arginine-vasotocin (AVT)/arginine vasopressin (AVP) are members of the AVP/oxytocin (OT) superfamily of peptides that are involved in the regulation of social behavior, social cognition and emotion. Comparative studies have revealed that AVT/AVP and their receptors are found throughout the "social behavior neural network (SBNN)" and display the properties expected from a signaling system that controls social behavior (i.e., species, sex and individual differences and modulation by gonadal hormones and social factors). Neurochemical signaling within the SBNN likely involves a complex combination of synaptic mechanisms that co-release multiple chemical signals (e.g., classical neurotransmitters and AVT/AVP as well as other peptides) and non-synaptic mechanisms (i.e., volume transmission). Crosstalk between AVP/OT peptides and receptors within the SBNN is likely. A better understanding of the functional properties of neurochemical signaling in the SBNN will allow for a more refined examination of the relationships between this peptide system and species, sex and individual differences in sociality.

Implications of prenatal steroid perturbations for neurodevelopment, behavior, and autism

The prenatal brain develops under the influence of an ever-changing hormonal milieu that includes endogenous fetal gonadal and adrenal hormones, placental and maternal hormones, and exogenous substances with hormonal activity that can cross the placental barrier. This review discusses the influences of endogenous fetal and maternal hormones on normal brain development and potential consequences of pathophysiological hormonal perturbations to the developing brain, with particular reference to autism. We also consider the effects of hormonal pharmaceuticals used for assisted reproduction, the maintenance of pregnancy, the prevention of congenital adrenal hypertrophy, and hormonal contraceptives continued into an unanticipated pregnancy, among others. These treatments, although in some instances life-saving, may have unintended consequences on the developing fetuses. Additional concern is raised by fetal exposures to endocrine-disrupting chemicals encountered universally by pregnant women from food/water containers, contaminated food, household chemicals, and other sources. What are the potential outcomes of prenatal steroid perturbations on neurodevelopmental and behavioral disorders, including autism-spectrum disorders? Our purposes here are 1) to summarize some consequences of steroid exposures during pregnancy for the development of brain and behavior in the offspring; 2) to summarize what is known about the relationships between exposures and behavior, including autism spectrum disorders; 3) to discuss the molecular underpinnings of such effects, especially molecular epigenetic mechanisms of prenatal steroid manipulations, a field that may explain effects of direct exposures, and even transgenerational effects; and 4) for all of these, to add cautionary notes about their interpretation in the name of scientific rigor.

Sex dimorphism in seizure-controlling networks

Males and females show a different predisposition to certain types of seizures in clinical studies. Animal studies have provided growing evidence for sexual dimorphism of certain brain regions, including those that control seizures. Seizures are modulated by networks involving subcortical structures, including thalamus, reticular formation nuclei, and structures belonging to the basal ganglia. In animal models, the substantia nigra pars reticulata (SNR) is the best studied of these areas, given its relevant role in the expression and control of seizures throughout development in the rat. Studies with bilateral infusions of the GABA(A) receptor agonist muscimol have identified distinct roles of the anterior or posterior rat SNR in flurothyl seizure control, that follow sex-specific maturational patterns during development. These studies indicate that (a) the regional functional compartmentalization of the SNR appears only after the third week of life, (b) only the male SNR exhibits muscimol-sensitive proconvulsant effects which, in older animals, is confined to the posterior SNR, and (c) the expression of the muscimol-sensitive anticonvulsant effects become apparent earlier in females than in males. The first three postnatal days are crucial in determining the expression of the muscimol-sensitive proconvulsant effects of the immature male SNR, depending on the gonadal hormone setting. Activation of the androgen receptors during this early period seems to be important for the formation of this proconvulsant SNR region. We describe molecular/anatomical candidates underlying these age- and sex-related differences, as derived from in vitro and in vivo experiments, as well as by [(14)C]2-deoxyglucose autoradiography. These involve sex-specific patterns in the developmental changes in the structure or physiology or GABA(A) receptors or of other subcortical structures (e.g., locus coeruleus, hippocampus) that may affect the function of seizure-controlling networks.

Sex differences in stress-induced social withdrawal: role of brain derived neurotrophic factor in the bed nucleus of the stria terminalis

Depression and anxiety disorders are more common in women than men, and little is known about the neurobiological mechanisms that contribute to this disparity. Recent data suggest that stress-induced changes in neurotrophins have opposing effects on behavior by acting in different brain networks. Social defeat has been an important approach for understanding neurotrophin action, but low female aggression levels in rats and mice have limited the application of these methods primarily to males. We examined the effects of social defeat in monogamous California mice (Peromyscus californicus), a species in which both males and females defend territories. We demonstrate that defeat stress increases mature brain-derived neurotrophic factor (BDNF) protein but not mRNA in the bed nucleus of the stria terminalis (BNST) in females but not males. Changes in BDNF protein were limited to anterior subregions of the BNST, and there were no changes in the adjacent nucleus accumbens (NAc). The effects of defeat on social withdrawal behavior and BDNF were reversed by chronic, low doses of the antidepressant sertraline. However, higher doses of sertraline restored social withdrawal and elevated BDNF levels. Acute treatment with a low dose of sertraline failed to reverse the effects of defeat. Infusions of the selective tyrosine-related kinase B receptor (TrkB) antagonist ANA-12 into the anterior BNST specifically increased social interaction in stressed females but had no effect on behavior in females naïve to defeat. These results suggest that stress-induced increases in BDNF in the anterior BNST contribute to the exaggerated social withdrawal phenotype observed in females.

Sensitive periods for hormonal programming of the brain

During sensitive periods, information from the external and internal environment that occurs during particular phases of development is relayed to the brain to program neural development. Hormones play a central role in this process. In this review, we first discuss sexual differentiation of the brain as an example of hormonal programming. Using sexual differentiation, we define sensitive periods, review cellular and molecular processes that can explain their restricted temporal window, and discuss challenges in determining the precise timing of the temporal window. We then briefly review programming effects of other hormonal systems and discuss how programming of these systems interact with sexual differentiation.

Epigenetic mechanisms may underlie the aetiology of sex differences in mental health risk and resilience

In this review, we propose that experiential and hormonal influences on biological sex during development may produce differences in the epigenome, and that these differences play an important role in gating risk or resilience to a number of neurological and psychiatric disorders. One intriguing hypothesis is that the framework belying sex differences in the brain creates differences in methylation and demethylation patterns, and these in turn confer risk and resilience to mental health disorders. Here, we discuss these concepts with regard to social behaviour in rodent models and briefly discuss their possible relevance to human disease.

Effects of neural androgen receptor disruption on aggressive behavior, arginine vasopressin and galanin systems in the bed nucleus of stria terminalis and lateral septum

In the present study, we investigated the role of the androgen receptor (AR) in the nervous system in the regulation of aggressive behavior and arginine vasopressin and galanin systems by testosterone. For this purpose, we used a conditional mouse line selectively lacking AR gene in the nervous system, backcrossed onto the C57BL/6J strain. Adult males were gonadectomized and supplemented with similar amounts of testosterone. When tested on two consecutive days in the resident intruder paradigm, fewer males of the mutant group exhibited aggressive behavior compared to their control littermates. In addition, a high latency to the first offensive attack was observed for the few animals that exhibited fighting behavior. This alteration was associated with a normal anogenital chemoinvestigation of intruder males. In olfactory discrimination tasks, sexual experience enhanced preference towards female-soiled bedding rather than male-soiled bedding and estrus females rather than intact males, regardless of genotype. This indicated that the behavioral alteration induced by neural AR mutation occurs in brain areas located downstream from the olfactory bulb. Quantification of the sexually dimorphic cell populations expressing preprovasopressin and galanin mRNAs in the bed nucleus of stria terminalis (BNST) and vasopressin-neurophysin 2 and galanin immunoreactivity in the lateral septum showed no significant differences between the two genotypes. The present findings indicate that the neural AR is required in the expression of aggressive behavior but not in the sexual differentiation of AVP and galanin cell number in the BNST and fiber immunoreactivity in the lateral septum. They also suggest that AR in the nervous system could mediate activational effects of testosterone in the regulation of aggressive behavior during adulthood.

Effects of perinatal daidzein exposure on subsequent behavior and central estrogen receptor α expression in the adult male mouse

Daidzein is one of the most important isoflavones present in soy and it is unique as it can be further metabolized to equol, a compound with greater estrogenic activity than other isoflavones. The potential role of daidzein in the prevention of some chronic diseases has drawn public attention and increased its consumption in human, including in pregnant women and adolescent. It is unclear whether perinatal exposure to daidzein through maternal diets affects subsequent behavior and central estrogen receptor α (ERα) expression in male adults. Following developmental exposure to daidzein through maternal diets during perinatal period, subsequent anxiety-like behavior, social behavior, spatial learning and memory of male mice at adulthood were assessed using a series of tests. The levels of central ER α expression were also examined using immunocytochemistry. Compared with the controls, adult male mice exposed to daidzein during the perinatal period showed significantly less exploration, higher levels of anxiety and aggression. They also displayed more social investigation for females and a tendency to improve spatial learning and memory. The mice with this early daidzein treatment demonstrated significantly higher levels of ERα expression in several brain regions such as the bed nucleus of the stria terminalis, medial preoptic, arcuate hypothalamic nucleus and central amygdaloid mucleus, but decreased it in the lateral septum. Our results indicated that perinatal exposure to daidzein enhanced masculinization on male behaviors which is assocciated with alterations in ERα expression levels led by perinatal daidzein exposure.

Sex differences in stress-induced social withdrawal: independence from adult gonadal hormones and inhibition of female phenotype by corncob bedding

There is compelling evidence for important sex differences in behavioral and hormonal responses to psychosocial stress. Here we examined the effects of gonadal hormones on behavioral responses to social defeat stress in monogamous California mice (Peromyscus californicus). Three episodes of social defeat induced social withdrawal in intact females but not males. Gonadectomy blocked corticosterone responses to defeat in females and sensitized male corticosterone responses. However, gonadectomy had no effects on social interaction behavior, suggesting that social withdrawal is not dependent on gonadal hormones in the adult California mouse. In contrast, defeat reduced exploratory behavior in the open field test for intact but not castrated males. We also examined the effects of social defeat on social interaction behavior when California mice were raised on corncob bedding, which has estrogenic properties. In this dataset of over 300 mice, we observed that social defeat did not induce social withdrawal when females were raised on corncob bedding. This finding suggests that the use of corncob in rodent studies could mask important sex differences in the effects of stress on brain and behavior. Although gonadal hormones do not affect social withdrawal behavior in adults, our data suggest that hormones may act earlier in development to induce a more resilient social phenotype.

Characterisation of human oestrogen receptor beta (ERβ) splice variants in neuronal cells

Oestrogen receptor (ER)α and ERβ are members of the ligand-activated superfamily of nuclear receptors and mediate most facets of oestrogen signalling. Several naturally occurring splice variants of each ER have been identified in the human brain, yet the biological significance of these splice variants in the brain remains unknown. In the present study, we exploit the unique structural differences of the human ERβ splice variants to determine the functional significance of individual ER domains in the brain. We previously established that full-length rodent ERβ (i.e. rERβ1) has constitutive transcriptional activity in neuronal cells in the absence of ligand. By contrast to the rodent splice variants, the human ERβ splice variants used in the present study contain varying length truncations of exon 8, which encodes for the E/F domains. Our results reveal that, in neuronal cells, each human-specific ERβ splice variant constitutively activated promoters mediated by a canonical oestrogen response element and repressed promoters mediated by activator protein-1 sites via p38 activity. From these data, we conclude that the C-terminus, encoding the AF-2 region and F domain, is not essential for the constitutive properties of human ERβ. Taken together, these studies show that human-specific ERβ variants are constitutively active and also provide novel insight into the contributions of the functional domains of ERβ towards mediating constitutive transcription at various promoters in neuronal cells.

Location, location, location: genetic regulation of neural sex differences

Sex differences in many behaviors such as cognition, mood, and motor skills are well-documented in animals and humans and are regulated by many neural circuits. Sexual dimorphisms within cell populations in these circuits play critical roles in the production of these behavioral dichotomies. Here we focus on three proteins that have well described sexual dimorphisms; calbindin-D28k, a calcium binding protein, tyrosine hydroxylase, the rate limiting enzyme involved in dopamine synthesis and vasopressin, a neuropeptide with central and peripheral sites of action. We describe the sex differences in subpopulations of these proteins, with particular emphasis on laboratory mice. Our thrust is to examine genetic bases of sex differences and how the use of genetically modified models has advanced our understanding of this topic. Regional sex differences in the expression of these three proteins are driven by sex chromosome complement, steroid receptors or in some instances both. While studies of sex differences attributable to sex chromosome genes are still few in number it is exciting to note that this variable factors into expression differences for all three of these proteins. Different genetic mechanisms, which elaborate sex differences, may be employed stochastically in different cell populations. Alternately, general patterns involving the timing of differentiation of the sex differences, relative to the "critical period" in hormonal differences between males and female neonates may emerge. In conclusion, future directions in this area should include examination of the importance of location, timing, steroidal receptor/sex chromosome gene synergy and epigenetics in molding neural sex differences.

Neonatal MeCP2 is important for the organization of sex differences in vasopressin expression

Several neurodevelopmental disorders are marked by atypical Methyl-CpG-binding protein 2 (MeCP2) expression or function; however, the role of MeCP2 is complex and not entirely clear. Interestingly, there are sex differences in some of these disorders, and it appears that MeCP2 has sex-specific roles during development. Specifically, recent data indicate that a transient reduction in MeCP2 within developing amygdala reduces juvenile social play behavior in males to female-typical levels. These data suggest that MeCP2 within the amygdala is involved in programming lasting sex differences in social behavior. In the present study, we infused MeCP2 or control siRNA into the amygdala of male and female rats during the first three days of postnatal life in order to assess the impact of a transient reduction in MeCP2 on arginine vasopressin (AVP), a neural marker that is expressed differentially between males and females and is linked to a number of social behaviors. The expression of AVP, as well as several other genes, was measured in two-week old and adult animals. Two-week old males expressed more AVP and galanin mRNA in the amygdala than females, and a transient reduction in MeCP2 eliminated this sex difference by reducing the expression of both gene products in males. A transient reduction in MeCP2 also decreased androgen receptor (AR) mRNA in two-week old males. In adulthood, control males had more AVP-immunoreactive (AVP-ir) cells than females in the centromedial amygdala (CMA), bed nucleus of the stria terminalis (BST) and in the fibers that project from these cells to the lateral septum (LS). A transient reduction in MeCP2 eliminated this sex difference. Interestingly, there were no lasting differences in galanin or AR levels in adulthood. Reducing MeCP2 levels during development did not alter estrogen receptorα, neurofilament or Foxg1. We conclude that a transient reduction in MeCP2 expression in the developing male amygdala has a transient impact on galanin and AR expression but a lasting impact on AVP expression, highlighting the importance of MeCP2 in organizing sex differences in the amygdala.

Sexually dimorphic effects of a prenatal immune challenge on social play and vasopressin expression in juvenile rats

Background

Infectious diseases and inflammation during pregnancy increase the offspring’s risk for behavioral disorders. However, how immune stress affects neural circuitry during development is not well known. We tested whether a prenatal immune challenge interferes with the development of social play and with neural circuits implicated in social behavior.

Methods

Pregnant rats were given intraperitoneal injections of the bacterial endotoxin lipopolysaccharide (LPS – 100 μg /kg) or saline on the 15th day of pregnancy. Offspring were tested for social play behaviors between postnatal days 26–40. Brains were harvested on postnatal day 45 and processed for arginine vasopressin (AVP) mRNA in situ hybridization.

Results

In males, LPS treatment reduced the frequency of juvenile play behavior and reduced AVP mRNA expression in the medial amygdala and bed nucleus of the stria terminalis. These effects were not found in females. LPS treatment did not change AVP mRNA expression in the suprachiasmatic nucleus, paraventricular nucleus, or supraoptic nucleus of either sex, nor did it affect the sex difference in the size of the sexually dimorphic nucleus of the preoptic area.

Conclusions

Given AVP’s central role in regulating social behavior, the sexually dimorphic effects of prenatal LPS treatment on male AVP mRNA expression may contribute to the sexually dimorphic effect of LPS on male social play and may, therefore, increase understanding of factors that contribute to sex differences in social psychopathology.

A comparative, developmental, and clinical perspective of neurobehavioral sexual dimorphisms

Women and men differ in a wide variety of behavioral traits and in their vulnerability to developing certain mental disorders. This review endeavors to explore how recent preclinical and clinical research findings have enhanced our understanding of the factors that underlie these disparities. We start with a brief overview of some of the important genetic, molecular, and hormonal determinants that contribute to the process of sexual differentiation. We then discuss the importance of animal models in studying the mechanisms responsible for sex differences in neuropsychiatric disorders (e.g., drug dependence) - with a special emphasis on experimental models based on the neurodevelopmental and "three hits" hypotheses. Next, we describe the most common brain phenotypes observed in vivo with magnetic resonance imaging. We discuss the challenges in interpreting these phenotypes vis-à-vis the underlying neurobiology and revisit the known sex differences in brain structure from birth, through adolescence, and into adulthood. This is followed by a presentation of pertinent clinical and epidemiological data that point to important sex differences in the prevalence, course, and expression of psychopathologies such as schizophrenia, and mood disorders including major depression and posttraumatic stress disorder. Recent evidence implies that mood disorders and psychosis share some common genetic predispositions and neurobiological bases. Therefore, modern research is emphasizing dimensional representation of mental disorders and conceptualization of schizophrenia and major depression as a continuum of cognitive deficits and neurobiological abnormalities. Herein, we examine available evidence on cerebral sexual dimorphism to verify if sex differences vary quantitatively and/or qualitatively along the psychoses-depression continuum. Finally, sex differences in the prevalence of posttraumatic disorder and drug abuse have been described, and we consider the genomic and molecular data supporting these differences.

Sex differences in molecular and cellular substrates of stress

Women are twice as likely as men to suffer from stress-related psychiatric disorders, like unipolar depression and post-traumatic stress disorder. Although the underlying neural mechanisms are not well characterized, the pivotal role of stress in the onset and severity of these diseases has led to the idea that sex differences in stress responses account for this sex bias. Corticotropin-releasing factor (CRF) orchestrates stress responses by acting both as a neurohormone to initiate the hypothalamic-pituitary-adrenal (HPA) axis and as a neuromodulator in the brain. One target of CRF modulation is the locus coeruleus (LC)-norepinephrine system, which coordinates arousal components of the stress response. Hypersecretion of CRF and dysregulation of targets downstream from CRF, such as the HPA axis and LC-norepinephrine system, are characteristic features of many stress-related psychiatric diseases, suggesting a causal role for CRF and its targets in the development of these disorders. This review will describe sex differences in CRF and the LC-norepinephrine system that can increase stress sensitivity in females, making them vulnerable to stress-related disorders. Evidence for gonadal hormone regulation of hypothalamic CRF is discussed as an effect that can lead to increased HPA axis activity in females. Sex differences in the structure of LC neurons that create the potential for hyperarousal in response to emotional stimuli are described. Finally, sex differences at the molecular level of the CRF(1) receptor that make the LC-norepinephrine system more reactive in females are reviewed. The implications of these sex differences for the treatment of stress-related psychiatric disorders also will be discussed.

Acute effects of steroid hormones and neuropeptides on human social-emotional behavior: a review of single administration studies

Steroids and peptides mediate a diverse array of animal social behaviors. Human research is restricted by technical-ethical limitations, and models of the neuroendocrine regulation of social-emotional behavior are therefore mainly limited to non-human species, often under the assumption that human social-emotional behavior is emancipated from hormonal control. Development of acute hormone administration procedures in human research, together with the advent of novel non-invasive neuroimaging techniques, have opened up opportunities to systematically study the neuroendocrinology of human social-emotional behavior. Here, we review all placebo-controlled single hormone administration studies addressing human social-emotional behavior, involving the steroids testosterone and estradiol, and the peptides oxytocin and vasopressin. These studies demonstrate substantial hormonal control over human social-emotional behavior and give insights into the underlying neural mechanisms. Finally, we propose a theoretical model that synthesizes detailed knowledge of the neuroendocrinology of social-emotional behavior in animals with the recently gained data from humans described in our review.

Endocrine disrupters: a review of some sources, effects, and mechanisms of actions on behaviour and neuroendocrine systems

Some environmental contaminants interact with hormones and may exert adverse consequences as a result of their actions as endocrine disrupting chemicals (EDCs). Exposure in people is typically a result of contamination of the food chain, inhalation of contaminated house dust or occupational exposure. EDCs include pesticides and herbicides (such as dichlorodiphenyl trichloroethane or its metabolites), methoxychlor, biocides, heat stabilisers and chemical catalysts (such as tributyltin), plastic contaminants (e.g. bisphenol A), pharmaceuticals (i.e. diethylstilbestrol; 17α-ethinylestradiol) or dietary components (such as phytoestrogens). The goal of this review is to address the sources, effects and actions of EDCs, with an emphasis on topics discussed at the International Congress on Steroids and the Nervous System. EDCs may alter reproductively-relevant or nonreproductive, sexually-dimorphic behaviours. In addition, EDCs may have significant effects on neurodevelopmental processes, influencing the morphology of sexually-dimorphic cerebral circuits. Exposure to EDCs is more dangerous if it occurs during specific 'critical periods' of life, such as intrauterine, perinatal, juvenile or puberty periods, when organisms are more sensitive to hormonal disruption, compared to other periods. However, exposure to EDCs in adulthood can also alter physiology. Several EDCs are xenoestrogens, which can alter serum lipid concentrations or metabolism enzymes that are necessary for converting cholesterol to steroid hormones. This can ultimately alter the production of oestradiol and/or other steroids. Finally, many EDCs may have actions via (or independent of) classic actions at cognate steroid receptors. EDCs may have effects through numerous other substrates, such as the aryl hydrocarbon receptor, the peroxisome proliferator-activated receptor and the retinoid X receptor, signal transduction pathways, calcium influx and/or neurotransmitter receptors. Thus, EDCs, from varied sources, may have organisational effects during development and/or activational effects in adulthood that influence sexually-dimorphic, reproductively-relevant processes or other functions, by mimicking, antagonising or altering steroidal actions.

Effects of neonatal treatment with valproic acid on vasopressin immunoreactivity and olfactory behaviour in mice

Recent findings demonstrate that epigenetic modifications are required for the sexual differentiation of the brain. For example, neonatal administration of the histone deacetylase inhibitor, valproic acid, blocks masculinisation of cell number in the principal nucleus of the bed nucleus of the stria terminalis (BNST). In the present study, we examined the effects of valproic acid on neurochemistry and behaviour, focusing on traits that are sexually dimorphic and linked to the BNST. Newborn mice were treated with saline or valproic acid and the effect on vasopressin immunoreactivity and olfactory preference behaviour was examined in adulthood. As expected, males had more vasopressin immunoreactive fibres than females in the lateral septum and medial dorsal thalamus, which are two projection sites of BNST vasopressin neurones. Neonatal valproic acid increased vasopressin fibre density specifically in females in the lateral septum, thereby reducing the sex difference, and increased vasopressin fibres in both sexes in the medial dorsal thalamus. The effects were not specific to BNST vasopressin projections, however, because valproic acid also significantly increased vasopressin immunoreactivity in the anterior hypothalamic area in both sexes. Subtle sex-specific effects of neonatal valproic acid treatment were observed on olfactory behaviour. As predicted, males showed a preference for investigating female-soiled bedding, whereas females showed a preference for male-soiled bedding. Valproic acid did not significantly alter olfactory preference, per se, although it increased the number of visits females made to female-soiled bedding and the overall time females spent investigating soiled versus clean bedding. Taken together, these results suggest that a transient disruption of histone deacetylation at birth does not have generalised effects on sexual differentiation, although it does produce lasting effects on brain neurochemistry and behaviour.

Neuropeptides and enzymes are targets for the action of endocrine disrupting chemicals in the vertebrate brain

Endocrine-disrupting chemicals (EDC) are molecules that interfere with endocrine signaling pathways and produce adverse consequences on animal and human physiology, such as infertility or behavioral alterations. Some EDC act through binding to androgen or/and estrogen receptors primarily operating through a genomic mechanism regulating gene expression. This mechanism of action may induce profound developmental adverse effects, and the major targets of the EDC action are the gene products, i.e., mRNAs inducing the synthesis of various peptidic molecules, which include neuropeptides and enzymes related to neurotransmitters syntheses. Available immunohistochemical data on some of the systems that are affected by EDC in lower and higher vertebrates are detailed in this review.

Sex differences in the cerebellum and frontal cortex: roles of estrogen receptor alpha and sex chromosome genes

Most neurobehavioral diseases are sexually dimorphic in their incidence, and sex differences in the brain may be key for understanding and treating these diseases. Calbindin (Calb) D28K is used as a biomarker for the well-studied sexually dimorphic nucleus, a hypothalamic structure that is larger in males than in females. In the current study weanling C56BL/6J mice were used to examine sex differences in the Calb protein and message focusing on regions outside of the hypothalamus. A robust sex difference was found in Calb in the frontal cortex (FC) and cerebellum (CB; specifically in Purkinje cells); mRNA and protein were higher in females than in males. Using 2 mouse lines, i.e. one with a complete deletion of estrogen receptor alpha (ERα) and the other with uncoupled gonads and sex chromosomes, we probed the mechanisms that underlie sexual dimorphisms. In the FC, deletion of ERα reduced Calb1 mRNA in females compared to males. In addition, females with XY sex chromosomes had levels of Calb1 equal to those of males. Thus, both ERα and the sex chromosome complement regulate Calb1 in the FC. In the CB, ERα knockout mice of both sexes had reduced Calb1 mRNA, yet sex differences were retained. However, the sex chromosome complement, regardless of gonadal sex, dictated Calb1 mRNA levels. Mice with XX chromosomes had significantly greater Calb1 than did XY mice. This is the first study demonstrating that sex chromosome genes are a driving force producing sex differences in the CB and FC, which are neuoranatomical regions involved in many normal functions and in neurobehavioral diseases.