Changes in the arginine-vasopressin immunoreactive systems in male mice lacking a functional aromatase gene

Social regulation of arginine vasopressin and oxytocin systems in a wild group-living fish

The neuropeptides arginine vasopressin (AVP) and oxytocin (OXT) are key regulators of social behaviour across vertebrates. However, much of our understanding of how these neuropeptide systems interact with social behaviour is centred around laboratory studies which fail to capture the social and physiological challenges of living in the wild. To evaluate relationships between these neuropeptide systems and social behaviour in the wild, we studied social groups of the cichlid fish Neolamprologus pulcher in Lake Tanganyika, Africa. We first used SCUBA to observe the behaviour of focal group members and then measured transcript abundance of key components of the AVP and OXT systems across different brain regions. While AVP is often associated with male-typical behaviours, we found that dominant females had higher expression of avp and its receptor (avpr1a2) in the preoptic area of the brain compared to either dominant males or subordinates of either sex. Dominant females also generally had the highest levels of leucyl-cystinyl aminopeptidase (lnpep)-which inactivates AVP and OXT-throughout the brain, potentially indicating greater overall activity (i.e., production, release, and turnover) of the AVP system in dominant females. Expression of OXT and its receptors did not differ across social ranks. However, dominant males that visited the brood chamber more often had lower preoptic expression of OXT receptor a (oxtra) suggesting a negative relationship between OXT signalling and parental care in males of this species. Overall, these results advance our understanding of the relationships between complex social behaviours and neuroendocrine systems under natural settings.

The role of androgens and estrogens in social interactions and social cognition

Gonadal hormones are becoming increasingly recognized for their effects on cognition. Estrogens, in particular, have received attention for their effects on learning and memory that rely upon the functioning of various brain regions. However, the impacts of androgens on cognition are relatively under investigated. Testosterone, as well as estrogens, have been shown to play a role in the modulation of different aspects of social cognition. This review explores the impact of testosterone and other androgens on various facets of social cognition including social recognition, social learning, social approach/avoidance, and aggression. We highlight the relevance of considering not only the actions of the most commonly studied steroids (i.e., testosterone, 17β-estradiol, and dihydrotestosterone), but also that of their metabolites and precursors, which interact with a plethora of different receptors and signalling molecules, ultimately modulating behaviour. We point out that it is also essential to investigate the effects of androgens, their precursors and metabolites in females, as prior studies have mostly focused on males. Overall, a comprehensive analysis of the impact of steroids such as androgens on behaviour is fundamental for a full understanding of the neural mechanisms underlying social cognition, including that of humans.

Amygdala AVPR1A mediates susceptibility to chronic social isolation in females

Females are more sensitive to social exclusion, which could contribute to their heightened susceptibility to anxiety disorders. Chronic social isolation stress (CSIS) for at least 7 weeks after puberty induces anxiety-related behavioral adaptations in female mice. Here, we show that Arginine vasopressin receptor 1a ( Avpr1a )-expressing neurons in the central nucleus of the amygdala (CeA) mediate these sex-specific effects, in part, via projections to the caudate putamen. Loss of function studies demonstrate that AVPR1A signaling in the CeA is required for effects of CSIS on anxiety-related behaviors in females but has no effect in males or group housed females. This sex-specificity is mediated by AVP produced by a subpopulation of neurons in the posterodorsal medial nucleus of the amygdala that project to the CeA. Estrogen receptor alpha signaling in these neurons also contributes to preferential sensitivity of females to CSIS. These data support new therapeutic applications for AVPR1A antagonists in women.

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.

The role of vasopressin in olfactory and visual processing

Neural vasopressin is a potent modulator of behaviour in vertebrates. It acts at both sensory processing regions and within larger regulatory networks to mediate changes in social recognition, affiliation, aggression, communication and other social behaviours. There are multiple populations of vasopressin neurons within the brain, including groups in olfactory and visual processing regions. Some of these vasopressin neurons, such as those in the main and accessory olfactory bulbs, anterior olfactory nucleus, piriform cortex and retina, were recently identified using an enhanced green fluorescent protein-vasopressin (eGFP-VP) transgenic rat. Based on the interconnectivity of vasopressin-producing and sensitive brain areas and in consideration of autocrine, paracrine and neurohormone-like actions associated with somato-dendritic release, we discuss how these different neuronal populations may interact to impact behaviour.

Impact of aromatase absence on murine intraocular pressure and retinal ganglion cells

We hypothesize that aromatase, an enzyme that regulates estrogen production, plays a significant role in the control of intraocular pressure (IOP) and retinal ganglion cells (RGCs). To begin to test our hypothesis, we examined the impact of aromatase absence, which completely eliminates estrogen synthesis, in male and female mice. Studies were performed with adult, age-matched wild type (WT) and aromatase knockout (ArKO) mice. IOP was measured in a masked fashion in both eyes of conscious mice at 12 and 24 weeks of age. Retinas were obtained and processed for RGC counting with a confocal microscope. IOP levels in both 12- and 24-week old female ArKO mice were significantly higher than those of age- and sex-matched WT controls. The mean increase in IOP was 7.9% in the 12-week-, and 19.7% in the 24-week-old mice, respectively. These changes were accompanied by significant 9% and 7% decreases in RGC numbers in the ArKO female mice, relative to controls, at 12- and 24-weeks, respectively. In contrast, aromatase deficiency did not lead to an increased IOP in male mice. There was a significant reduction in RGC counts in the 12-, but not 24-, week-old male ArKO mice, as compared to their age- and sex-matched WT controls. Overall, our findings show that aromatase inhibition in females is associated with elevated IOP and reduced RGC counts.

Kisspeptin innervation of the hypothalamic paraventricular nucleus: sexual dimorphism and effect of estrous cycle in female mice

The hypothalamic paraventricular nucleus (PVN) is the major autonomic output area of the hypothalamus and a critical regulatory center for energy homeostasis. The organism's energetic balance is very important for both the regular onset of puberty and regulation of fertility. Several studies have suggested a relationship among neural circuits controlling food intake, energy homeostasis and the kisspeptin peptide. The kisspeptin system is clustered in two main groups of cell bodies [the anterior ventral periventricular region (AVPV) and the arcuate nucleus (ARC)] projecting mainly to gonadotropin-releasing hormone (GnRH) neurons and to a few other locations, including the PVN. In the present study, we investigated the distribution of the kisspeptin fibers within the PVN of adult CD1 mice. We observed a significant sexual dimorphism for AVPV and ARC, as well as for the PVN innervation. Kisspeptin fibers showed a different density within the PVN, being denser in the medial part than in the lateral one; moreover, in female, the density changed, according to different phases of the estrous cycle (the highest density being in estrus phase). The presence of a profound effect of estrous cycle on the kisspeptin immunoreactivity in AVPV (with a higher signal in estrus) and ARC, and the strong co-localization between kisspeptin and NkB only in ARC and not in PVN suggested that the majority of the kisspeptin fibers found in the PVN might arise directly from AVPV.

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.

Hypothalamic Vasopressinergic Projections Innervate Central Amygdala GABAergic Neurons: Implications for Anxiety and Stress Coping

The arginine-vasopressin (AVP)-containing hypothalamic magnocellular neurosecretory neurons (VPMNNs) are known for their role in hydro-electrolytic balance control via their projections to the neurohypophysis. Recently, projections from these same neurons to hippocampus, habenula and other brain regions in which vasopressin infusion modulates contingent social and emotionally-affected behaviors, have been reported. Here, we present evidence that VPMNN collaterals also project to the amygdaloid complex, and establish synaptic connections with neurons in central amygdala (CeA). The density of AVP innervation in amygdala was substantially increased in adult rats that had experienced neonatal maternal separation (MS), consistent with our previous observations that MS enhances VPMNN number in the paraventricular (PVN) and supraoptic (SON) nuclei of the hypothalamus. In the CeA, V1a AVP receptor mRNA was only observed in GABAergic neurons, demonstrated by complete co-localization of V1a transcripts in neurons expressing Gad1 and Gad2 transcripts in CeA using the RNAscope method. V1b and V2 receptor mRNAs were not detected, using the same method. Water-deprivation (WD) for 24 h, which increased the metabolic activity of VPMNNs, also increased anxiety-like behavior measured using the elevated plus maze (EPM) test, and this effect was mimicked by bilateral microinfusion of AVP into the CeA. Anxious behavior induced by either WD or AVP infusion was reversed by CeA infusion of V1a antagonist. VPMNNs are thus a newly discovered source of CeA inhibitory circuit modulation, through which both early-life and adult stress coping signals are conveyed from the hypothalamus to the amygdala.

Adult exposure to tributyltin affects hypothalamic neuropeptide Y, Y1 receptor distribution, and circulating leptin in mice

Tributyltin (TBT), a pesticide used in antifouling paints, is toxic for aquatic invertebrates. In vertebrates, TBT may act in obesogen- inducing adipogenetic gene transcription for adipocyte differentiation. In a previous study, we demonstrated that acute administration of TBT induces c-fos expression in the arcuate nucleus. Therefore, in this study, we tested the hypothesis that adult exposure to TBT may alter a part of the nervous pathways controlling animal food intake. In particular, we investigated the expression of neuropeptide Y (NPY) immunoreactivity. This neuropeptide forms neural circuits dedicated to food assumption and its action is mediated by Y1 receptors that are widely expressed in the hypothalamic nuclei responsible for the regulation of food intake and energy homeostasis. To this purpose, TBT was orally administered at a dose of 0.025 mg/kg/day/body weight to adult animals [male and female C57BL/6 (Y1-LacZ transgenic mice] for 4 weeks. No differences were found in body weight and fat deposition, but we observed a significant increase in feed efficiency in TBT-treated male mice and a significant decrease in circulating leptin in both sexes. Computerized quantitative analysis of NPY immunoreactivity and Y1-related β-galactosidase activity demonstrated a statistically significant reduction in NPY and Y1 transgene expression in the hypothalamic circuit controlling food intake of treated male mice in comparison with controls. In conclusion, the present results indicate that adult exposure to TBT is profoundly interfering with the nervous circuits involved in the stimulation of food intake.

Neuropeptide Arginine Vasotocin Positively Affects Neurosteroidogenesis in the Early Brain of Grouper, Epinephelus coioides

The neuropeptide arginine vasotocin (AVT) has versatile physiological functions in non-mammalian vertebrates. However, the functional association between AVT and neurosteroidogenesis in the early brain of teleosts remains elusive. We thus studied the developmental expression patterns of the avt gene and their V1 type receptor (avt-rv1 ) at various stages of development [90-150 days after hatching (dah)] in relation to neurosteroidogenesis and oestrogen signalling in the early brain of the orange-spotted grouper (Epinephelus coioides). avt and avt-rv1 mRNAs displayed a significantly increase in expression at 110 dah in the telencephalon and diencephalon. Further, avt mRNAs were localised in three magnocellular neuronal populations of the preoptic area, such as parvocellular, magnocellular and gigantocellular preoptic neurones. Intriguingly, the avt transcripts in those neurones were more abundant in 110 dah compared to other ages. Subsequently, dual fluorescence in situ hybridisation analysis showed that the avt and avt-rv1 genes were highly coexpressed with cyp11a1, hsd3b1, cyp17a1, erα, erβ and gpr30, which indicates their potential for functional association. Cyp19a1b-immunoreactive positive fibres were found in close proximity to avt-expressing neurones. Moreover, our results showed that exogenous Avt caused a significant increase in the cellular and gene levels of steroidogenic enzymes and oestrogen receptors (ers), whereas the administration of an Avt-rv1 antagonist caused a decrease in the expression of both steroidogenic enzymes and ers genes in the brain. Furthermore, exogenous oestradiol (E2 ) strongly up-regulated avt mRNAs in the grouper brain. Taken together, the present studies suggest that avt and steroidogenesis may positively work together to increase both E2 biosynthesis and early brain development.

Chronic unpredictable stress and long-term ovariectomy affect arginine-vasopressin expression in the paraventricular nucleus of adult female mice

Arginine-Vasopressin (AVP) may regulate the hypothalamic-pituitary-adrenal axis (HPA) and its effects on depressive responses. In a recent study, we demonstrated that Chronic Unpredictable Stress (CUS) depressive effects are enhanced by long-term ovariectomy (a model of post-menopause). In the present study, we investigated the effects of long-term ovariectomy and CUS on AVP expression in different subdivision of the paraventricular nucleus (PVN) of female mice. Both long-term ovariectomy and CUS affect AVP immunoreactivity in some of the PVN subnuclei of adult female mice. In particular, significant changes on AVP immunoreactivity were observed in magnocellular subdivisions, the paraventricular lateral magnocellular (PaLM) and the paraventricular medial magnocellular (PaMM), the 2 subnuclei projecting to the neurohypophysis for the hormonal regulation of body homeostasis. AVP immunoreactivity was decreased in the PaLM by both the long-term deprivation of ovarian hormones and the CUS. In contrast, AVP immunoreactivity was increased in the PaMM by CUS, whereas it was decreased by ovariectomy. Therefore, present results suggest morphological and functional differences among the PVN's subnuclei and complex interactions among CUS, gonadal hormones and AVP immunoreactivity.

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.

Species differences in the immunoreactive expression of oxytocin, vasopressin, tyrosine hydroxylase and estrogen receptor alpha in the brain of Mongolian gerbils (Meriones unguiculatus) and Chinese striped hamsters (Cricetulus barabensis)

Species differences in neurochemical expression and activity in the brain may play an important role in species-specific patterns of social behavior. In the present study, we used immunoreactive (ir) labeling to compare the regional density of cells containing oxytocin (OT), vasopressin (AVP), tyrosine hydroxylase (TH), or estrogen receptor alpha (ERα) staining in the brains of social Mongolian gerbils (Meriones unguiculatus) and solitary Chinese striped hamsters (Cricetulus barabensis). Multiple region- and neurochemical-specific species differences were found. In the anterior hypothalamus (AH), Mongolian gerbils had higher densities of AVP-ir and ERα-ir cells than Chinese striped hamsters. In the lateral hypothalamus (LH), Mongolian gerbils also had higher densities of AVP-ir and TH-ir cells, but a lower density of OT-ir cells, than Chinese striped hamsters. Furthermore, in the anterior nucleus of the medial preoptic area (MPOAa), Mongolian gerbils had higher densities of OT-ir and AVP-ir cells than Chinese striped hamsters, and an opposite pattern was found in the posterior nucleus of the MPOA (MPOAp). Some sex differences were also observed. Females of both species had higher densities of TH-ir cells in the MPOAa and of OT-ir cells in the intermediate nucleus of the MPOA (MPOAi) than males. Given the role of these neurochemicals in social behaviors, our data provide additional evidence to support the notion that species-specific patterns of neurochemical expression in the brain may be involved in species differences in social behaviors associated with different life strategies.

Extending the socio-sexual brain: arginine-vasopressin immunoreactive circuits in the telencephalon of mice

Quantitative analysis of the immunoreactivity for arginine-vasopressin (AVP-ir) in the telencephalon of male (intact and castrated) and female CD1 mice allows us to precisely locate two sexually dimorphic (more abundant in intact than castrated males and females) AVP-ir cell groups in the posterior bed nucleus of the stria terminalis (BST) and the amygdala. Chemoarchitecture (NADPH diaphorase) reveals that the intraamygdaloid AVP-ir cells are located in the intra-amygdaloid BST (BSTIA) rather than the medial amygdala (Me), as previously thought. Then, we have used for the first time tract tracing (combined with AVP immunofluorescence) and fiber-sparing lesions of the BST to analyze the projections of the telencephalic AVP-ir cell groups. The results demonstrate that the posterior BST originates the sexually dimorphic innervation of the lateral septum, the posterodorsal Me and a substance P-negative area in the medioventral striato-pallidum (mvStP).The BSTIA may also contribute to some of these terminal fields. Our material also reveals non-dimorphic AVP-ir processes in two locations of the amygdala. First, the ventral Me shows dendrite-like AVP-ir processes apparently belonging supraoptic neurons, whose possible functions are discussed. Second, the Ce shows sparse, thick AVP-ir axons with high individual variability in density and distribution, whose possible influence on stress coping in relation to the affiliative or agonistic behaviors mediated by the Me are discussed. Finally, we propose that the region of the mvStP showing sexually dimorphic AVP-ir innervation is part of the brain network for socio-sexual behavior, in which it would mediate motivational aspects of chemosensory-guided social interactions.

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.

Sexually dimorphic effects of melatonin on brain arginine vasotocin immunoreactivity in green treefrogs (Hyla cinerea)

Arginine vasotocin (AVT) and its mammalian homologue, arginine vasopressin (AVP), regulate a variety of social and reproductive behaviors, often with complex species-, sex- and context-dependent effects. Despite extensive evidence documenting seasonal variation in brain AVT/AVP, relatively few studies have investigated the environmental and/or hormonal factors mediating these seasonal changes. In the present study, we investigated whether the pineal hormone melatonin alters brain AVT immunoreactivity in green treefrogs (Hyla cinerea). Reproductively active male and female frogs were collected during the summer breeding season and a melatonin-filled or blank silastic capsule was surgically implanted subcutaneously. The duration of hormone treatment was 4 weeks, at which time frogs were eutha-nized and the brains and blood collected and processed for AVT immunohistochemistry and steroid hormone assay. We quantified AVT-immunoreactive (AVT-ir) cell bodies in the nucleus accumbens (NAcc), caudal striatum and amygda- la (AMG), anterior preoptic area, suprachiasmatic nucleus (SCN) and infundibular region of the ventral hypothalamus. Sex differences in AVT-ir cell number were observed in all brain regions except in the anterior preoptic area and ventral hypothalamus, with males having more AVT-ir cells than females in the NAcc, amygdala and SCN. Brain AVT was sensitive to melatonin signaling during the breeding season, and the effects of melatonin varied significantly with both region and sex. Treatment with melatonin decreased AVT immunoreactivity in both the NAcc and SCN in male H. cinerea. In contrast, brain AVT was relatively insensitive to melatonin signaling in females, indicating that the regulation of the AVT/AVP neuropeptide system by melatonin may be sexually dimorphic. Finally, melatonin did not significantly influence testosterone or estradiol concentrations of male or female frogs, respectively, suggesting that the effects of melatonin on AVT immunoreactivity are independent of changes in gonadal sex steroid hormones. Collectively, our results indicate that the AVT/AVP neuronal system may be an important target for melatonin in facilitating seasonal changes in reproductive physiology and social behavior.

Estrogenic involvement in social learning, social recognition and pathogen avoidance

Sociality comes with specific cognitive skills that allow the proper processing of information about others (social recognition), as well as of information originating from others (social learning). Because sociality and social interactions can also facilitate the spread of infection among individuals the ability to recognize and avoid pathogen threat is also essential. We review here various studies primarily from the rodent literature supporting estrogenic involvement in the regulation of social recognition, social learning (socially acquired food preferences and mate choice copying) and the recognition and avoidance of infected and potentially infected individuals. We consider both genomic and rapid estrogenic effects involving estrogen receptors α and β, and G-protein coupled estrogen receptor 1, along with their interactions with neuropeptide systems in the processing of social stimuli and the regulation and expression of these various socially relevant behaviors.

Implication of the VGF-derived peptide TLQP-21 in mouse acute and chronic stress responses

The impact of stress is widely recognized in the etiology of multiple disorders. In particular, psychological stress may increase the risk of cardiovascular, metabolic, immune, and mood disorders. Several genes are considered potential candidates to account for the deleterious consequences of stress and recent data point to role of Vgf. VGF mRNA is abundantly expressed in the hypothalamus, where it has been involved in metabolism and energy homeostasis; more recently a link between VGF-derived peptides and mood disorders has been highlighted. The following experiments were performed to address the contribution of the VGF-system to stress induced changes in mice: the distribution of VGF immuno-reactivity in hypothalamic nuclei and its modulation by social stress; the role of VGF-derived peptide TLQP-21 in plasma catecholamine release induced by acute restraint stress (RS); the efficacy of chronic TLQP-21 in a mouse model of chronic subordination stress (CSS). VGF fibers were found in high density in arcuate, dorsomedial, and suprachiasmatic and, at lower density, in lateral, paraventricular, and ventromedial hypothalamic nuclei. Central administration of either 2 or 4 mM TLQP-21 acutely altered the biphasic serum epinephrine release and decreased norepinephrine serum levels in response to RS. Finally, 28-day of 40 μg/day TLQP-21 treatment increased CSS-induced social avoidance of an unfamiliar conspecific. Overall these data support a role for TLQP-21 in stress responses providing a promising starting point to further elucidate its role as a player in stress-related human pathologies.

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.

Milestones on Steroids and the Nervous System: 10 years of basic and translational research

During the last 10 years, the conference on 'Steroids and Nervous System' held in Torino (Italy) has been an important international point of discussion for scientists involved in this exciting and expanding research field. The present review aims to recapitulate the main topics that have been presented through the various meetings. Two broad areas have been explored: the impact of gonadal hormones on brain circuits and behaviour, as well as the mechanism of action of neuroactive steroids. Relationships among steroids, brain and behaviour, the sexual differentiation of the brain and the impact of gonadal hormones, the interactions of exogenous steroidal molecules (endocrine disrupters) with neural circuits and behaviour, and how gonadal steroids modulate the behaviour of gonadotrophin-releasing hormone neurones, have been the topics of several lectures and symposia during this series of meetings. At the same time, many contributions have been dedicated to the biosynthetic pathways, the physiopathological relevance of neurosteroids, the demonstration of the cellular localisation of different enzymes involved in neurosteroidogenesis, the mechanisms by which steroids may exert some of their effects, both the classical and nonclassical actions of different steroids, the role of neuroactive steroids on neurodegeneration, neuroprotection, and the response of the neural tissue to injury. In these 10 years, this field has significantly advanced and neuroactive steroids have emerged as new potential therapeutic tools to counteract neurodegenerative events.

Appetitive and consummatory sexual and agonistic behaviour elicits FOS expression in aromatase and vasotocin neurones within the preoptic area and bed nucleus of the stria terminalis of male domestic chickens

Some components of male sexual and agonistic behaviours are considered to be regulated by the same neurocircuitry in the medial preoptic nucleus (POM) and the medial portion of bed nucleus of the stria terminalis (BSTM). To better understand this neurocircuitry, numbers of aromatase- (ARO) or arginine vasotocin- (AVT) immunoreactive (ir) neurones expressing immediate early gene protein FOS were compared in the POM and BSTM of male chickens following sexual or agonistic behaviours. Observations were made on males showing: (i) appetitive (courtship) and consummatory (copulation) sexual behaviours; (ii) only appetitive sexual behaviour, or (iii) displaying agonistic behaviour toward other males. Control males were placed on their own in the observation pen, or only handled. In the POM, appetitive sexual behaviour increased ARO+FOS colocalisation, whereas agonistic behaviour decreased the number of visible ARO-ir cells. In the dorsolateral subdivision of BSTM (BSTM1), appetitive sexual behaviour also increased ARO+FOS colocalisation, although the numbers of visible ARO-ir and AVT-ir cells were not altered by sexual or agonistic behaviours. In the ventromedial BSTM (BSTM2), appetitive sexual behaviour increased ARO+FOS and AVT+FOS colocalisation, and all behaviours decreased the number of visible ARO-ir cells, particularly in males expressing consummatory sexual behaviour. Positive correlations were found between numbers of cells with ARO+FOS and AVT+FOS colocalisation in both subdivisions of the BSTM. Waltzing frequency was positively correlated with ARO+FOS colocalisation in the lateral POM, and in both subdivisions of the BSTM in males expressing sexual behaviour. Waltzing frequency in males expressing agonistic behaviour was negatively correlated with the total number of visible ARO-ir cells in the lateral POM and BSTM2. These observations suggest a key role for ARO and AVT neurones in BSTM2 in the expression of appetitive sexual behaviour, and differential roles for ARO cells in the POM and BSTM in the regulation of components of sexual and agonistic behaviours.

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.

Effects of aromatase or estrogen receptor gene deletion on masculinization of the principal nucleus of the bed nucleus of the stria terminalis of mice

The principal nucleus of the bed nucleus of the stria terminalis (BNSTp) is a sexually dimorphic nucleus, and the male BNSTp is larger and has more neurons than the female BNSTp. To assess the roles of neuroestrogen synthesized from testicular androgen by brain aromatase in masculinization of the BNSTp, we performed morphometrical analyses of the adult BNSTp in aromatase knockout (ArKO), estrogen receptor-α knockout (αERKO), and estrogen receptor-β knockout (βERKO) mice and their respective wild-type littermates. In wild-type littermates, the BNSTp of males had a larger volume and greater numbers of neuronal and glial cells than did that of females. The volume and neuron number of the BNSTp in ArKO and αERKO males and glial cell number of the BNSTp in αERKO males were significantly smaller than those of wild-type male littermates, and they were not significantly different from those in female mice with either gene knockout. In contrast, there was no significant morphological difference in the BNSTp between βERKO and wild-type mice. Next, we examined the BNSTp of ArKO males subcutaneously injected with estradiol benzoate (EB) on postnatal days 1, 2, and 3 (1.5 μg/day). EB-treated ArKO males had a significantly greater number of BNSTp neurons than did oil-treated ArKO males. The number of BNSTp neurons in EB-treated ArKO males was comparable to that in wild-type males. These findings suggested that masculinization of the BNSTp in mice involves the actions of neuroestrogen that was synthesized by aromatase and that this estrogen mostly binds to ERα during the postnatal period.

Salivary testosterone and a trinucleotide (CAG) length polymorphism in the androgen receptor gene predict amygdala reactivity in men

In studies employing functional magnetic resonance imaging (fMRI), reactivity of the amygdala to threat-related sensory cues (viz., facial displays of negative emotion) has been found to correlate positively with interindividual variability in testosterone levels of women and young men and to increase on acute administration of exogenous testosterone. Many of the biological actions of testosterone are mediated by intracellular androgen receptors (ARs), which exert transcriptional control of androgen-dependent genes and are expressed in various regions of the brain, including the amygdala. Transactivation potential of the AR decreases (yielding relative androgen insensitivity) with expansion a polyglutamine stretch in the N-terminal domain of the AR protein, as encoded by a trinucleotide (CAG) repeat polymorphism in exon 1 of the X-chromosome AR gene. Here we examined whether amygdala reactivity to threat-related facial expressions (fear, anger) differs as a function of AR CAG length variation and endogenous (salivary) testosterone in a mid-life sample of 41 healthy men (mean age=45.6 years, range: 34-54 years; CAG repeats, range: 19-29). Testosterone correlated inversely with participant age (r=-0.39, p=0.012) and positively with number of CAG repeats (r=0.45, p=0.003). In partial correlations adjusted for testosterone level, reactivity in the ventral amygdala was lowest among men with largest number of CAG repeats. This inverse association was seen in both the right (r(p)=-0.34, p<0.05) and left (r(p)=-0.32, p<0.05) hemisphere. Activation of dorsal amygdala, correlated positively with individual differences in salivary testosterone, also in right (r=0.40, p<0.02) and left (r=0.32, p<0.05) hemisphere, but was not affected by number of CAG repeats. Hence, androgenic influences on threat-related reactivity in the ventral amygdala may be moderated partially by CAG length variation in the AR gene. Because individual differences in salivary testosterone also predicted dorsal amygdala reactivity and did so independently of CAG repeats, it is suggested that androgenic influences within this anatomically distinct region may be mediated, in part, by non-genomic or AR-independent mechanisms.

Neuroactive steroids: an update of their roles in central and peripheral nervous system

After five editions, the congress on "Steroids and Nervous System" held in Torino, Italy, represents an important international event for researchers involved in this field aimed to recapitulate mechanisms, physiological and pharmacological effects of neuroactive steroids. The present review introduces manuscripts collected in this supplement issue which are based on new interesting findings such as the influence of sex steroids on cannabinoid-regulated biology, the role of steroids in pain, the importance of co-regulators in steroidal mechanisms and the understanding of new non classical mechanism, the emerging role of vitamin D as a neuroactive steroid and the pathogenetic mechanisms mediated by glucocorticoid receptors. Finally, we have integrated these aspects with an update on some of the several and important observations recently published on this hot topic.

The bed nucleus of the stria terminalis in the Syrian hamster (Mesocricetus auratus): absence of vasopressin expression in standard and wild-derived hamsters and galanin regulation by seasonal changes in circulating sex steroids

The bed nucleus of the stria terminalis (BNST) is a nucleus of the forebrain highly sensitive to sex steroids and containing vasopressin neurons implicated in several social- and reproduction-related behaviours such as scent-marking, aggression, pair bonding and parental behaviour. Sexually dimorphic vasopressin expression in BNST neurons has been reported in almost all rodents, with the notable exception of the Syrian hamster. In this species, vasopressin expression is completely absent in the BNST. Because almost all Syrian hamsters used in research are derived from a very small breeding stock captured in 1930, we compared commercially available Syrian hamsters with a recently captured, wild-derived breeding stock. We checked for vasopressin expression using in situ hybridization and immunohistochemistry. Vasopressin expression in BNST neurons was completely absent in both breeding stocks, confirming the absence of BNST vasopressin expression in Mesocricetus auratus and ruling out a breeding artefact. Because vasopressin expression in BNST neurons appears to be strictly dependent on circulating sex steroids, the absence of vasopressin expression in Syrian hamster BNST neurons might be due to an insensitivity of these neurons to sex steroids. BNST vasopressin neurons also express galanin. Although galanin expression in the BNST is not sexually dimorphic in the Syrian hamster, it appears to be regulated by sex steroids. In the Djungarian hamster, photoperiodically driven seasonal variations of circulating sex steroids result in a seasonal rhythm of galanin expression in BNST neurons. We analysed the sex steroid dependence of galanin expression in the Syrian hamster. Castration and short photoperiod-induced sexual quiescence both resulted in downregulation of galanin mRNA in cell bodies (BNST) and immunoreactivity in the fibres (lateral septum). Testosterone supplementation of short photoperiod-adapted animals was able to restore galanin expression. Thus Syrian hamster BNST neurons respond to circulating sex steroids and their seasonal variations as observed in other rodent species.

Neuroendocrinology of social information processing in rats and mice

We reviewed oxytocin (OT), arginine-vasopressin (AVP) and gonadal hormone involvement in various modes of social information processing in mice and rats. Gonadal hormones regulate OT and AVP mediation of social recognition and social learning. Estrogens foster OT-mediated social recognition and the recognition and avoidance of parasitized conspecifics via estrogen receptor (ER) alpha (ERalpha) and ERbeta. Testosterone and its metabolites, including estrogens, regulate social recognition in males predominantly via the AVP V1a receptor. Both OT and AVP are involved in the social transmission of food preferences and ERalpha has inhibitory, while ERbeta has enhancing, roles. OT also enhances mate copying by females. ERalpha mediates the sexual, and ERbeta the recognition, aspects of the risk-taking enhancing effects of females on males. Thus, androgens and estrogens control social information processing by regulating OT and AVP. This control is finely tuned for different forms of social information processing.

Neurosteroid biosynthesis: enzymatic pathways and neuroendocrine regulation by neurotransmitters and neuropeptides

Neuroactive steroids synthesized in neuronal tissue, referred to as neurosteroids, are implicated in proliferation, differentiation, activity and survival of nerve cells. Neurosteroids are also involved in the control of a number of behavioral, neuroendocrine and metabolic processes such as regulation of food intake, locomotor activity, sexual activity, aggressiveness, anxiety, depression, body temperature and blood pressure. In this article, we summarize the current knowledge regarding the existence, neuroanatomical distribution and biological activity of the enzymes responsible for the biosynthesis of neurosteroids in the brain of vertebrates, and we review the neuronal mechanisms that control the activity of these enzymes. The observation that the activity of key steroidogenic enzymes is finely tuned by various neurotransmitters and neuropeptides strongly suggests that some of the central effects of these neuromodulators may be mediated via the regulation of neurosteroid production.

Absence of progestin receptors alters distribution of vasopressin fibers but not sexual differentiation of vasopressin system in mice

Perinatal estrogens increase the number of vasopressin-expressing cells and the density of vasopressin-immunoreactive fibers observed in adult male rodents. The mechanism of action of estrogens on sexual differentiation of the extra-hypothalamic vasopressin system is unknown. We hypothesized that the sexually dimorphic expression of progestin receptors (PRs) during development would masculinize vasopressin expression in mice. We compared the number of vasopressin-expressing cells in the bed nucleus of the stria terminalis (BNST) and medial amygdala and the density of vasopressin-immunoreactive fibers in several brain regions of male and female wild type and PRKO mice using in situ hybridization and immunohistochemistry. As expected, sex differences in vasopressin cell number were observed in the BNST and medial amygdaloid nucleus. Vasopressin-immunoreactive fiber density was sexually dimorphic in the lateral septum, lateral habenular nucleus, medial amygdaloid nucleus, and mediodorsal thalamus. Sex differences were also observed in the principal nucleus of the BNST and medial preoptic area but not in the dorsomedial hypothalamus, which are thought to receive vasopressin innervation from the suprachiasmatic nucleus. Deletion of PRs did not alter the sex difference in vasopressin mRNA expression and vasopressin fiber immunoreactivity in any area examined. However, deletion of PRs increased the density of vasopressin fiber immunoreactivity in the lateral habenular nucleus. Our data suggest that PRs modulate vasopressin levels, but not sexual differentiation of vasopressin innervation in mice.

Activational effects of estradiol and dihydrotestosterone on social recognition and the arginine-vasopressin immunoreactive system in male mice lacking a functional aromatase gene

In rodents, parts of the arginine-vasopressin (AVP) neuronal system are sexually dimorphic with males having more AVP-immunoreactive cells/fibers than females. This neuropeptide neuronal system is highly sensitive to steroids and has been proposed to play an important role in the processing of olfactory cues critical to the establishment of a social memory. We demonstrate here that gonadally intact male aromatase knockout (ArKO) mice, which cannot aromatize androgens into estrogens due to a targeted mutation in the aromatase gene, showed severe deficits in social recognition as well as a reduced AVP-immunoreactivity in several brain regions. To determine whether this reduction is due to a lack of organizational or activational effects of estrogens, we assessed social recognition abilities and AVP-immunoreactivity in male ArKO and wild-type (WT) mice when treated with estradiol benzoate (EB) in association with dihydrotestosterone propionate (DHTP) in adulthood. Adult treatment with EB and DHTP restored social recognition abilities in castrated ArKO males since they showed normal female-oriented ultrasonic vocalizations and were able to recognize an unfamiliar female using a habituation-dishabituation paradigm. Furthermore, adult treatment also restored AVP-immunoreactivity in the lateral septum of ArKO males to levels observed in intact WT males. These results suggest that social recognition in adulthood and stimulation of AVP expression in the adult mouse forebrain depend predominantly on the estrogenic metabolite of testosterone. Furthermore, our results are in line with the idea that the organization of the AVP system may depend on androgen or sex chromosomes rather than estrogens.

Role for estradiol in female-typical brain and behavioral sexual differentiation

The importance of estrogens in controlling brain and behavioral sexual differentiation in female rodents is an unresolved issue in the field of behavioral neuroendocrinology. Whereas, the current dogma states that the female brain develops independently of estradiol, many studies have hinted at possible roles of estrogen in female sexual differentiation. Accordingly, it has been proposed that alpha-fetoprotein, a fetal plasma protein that binds estrogens with high affinity, has more than a neuroprotective role and specifically delivers estrogens to target brain cells to ensure female differentiation. Here, we review new results obtained in aromatase and alpha-fetoprotein knockout mice showing that estrogens can have both feminizing and defeminizing effects on the developing neural mechanisms that control sexual behavior. We propose that the defeminizing action of estradiol normally occurs prenatally in males and is avoided in fetal females because of the protective actions of alpha-fetoprotein, whereas the feminizing action of estradiol normally occurs postnatally in genetic females.

Estrogen receptors: their roles in regulation of vasopressin release for maintenance of fluid and electrolyte homeostasis

Long standing interest in the impact of gonadal steroid hormones on fluid and electrolyte balance has led to a body of literature filled with conflicting reports about gender differences, the effects of gonadectomy, hormone replacement, and reproductive cycles on plasma vasopressin (VP), VP secretion, and VP gene expression. This reflects the complexity of gonadal steroid hormone actions in the body resulting from multiple sites of action that impact fluid and electrolyte balance (e.g. VP target organs, afferent pathways regulating the VP neurons, and the VP secreting neurons themselves). It also reflects involvement of multiple types of estrogen receptors (ER) in these diverse sites including ERs that act as transcription factors regulating gene expression (i.e. the classic ERalpha as well as the more recently discovered ERbeta) and potentially G-protein coupled, membrane localized ERs that mediate rapid non-genomic actions of estrogen. Furthermore, altered expression of these receptors in physiologically diverse conditions of fluid and electrolyte balance contributes to the difficulty of using simplistic approaches such as gender comparisons, gonadectomy, and hormone replacement to assess the role of gonadal steroids in regulation of VP secretion for maintenance of fluid and electrolyte homeostasis. This review catalogs these inconsistencies and provides a frame work for understanding them by describing: (1) the effect of gonadal steroids on target organ responsiveness to VP; (2) the expression of multiple types of estrogen receptors in the VP neurons and in brain regions monitoring feedback signals from the periphery; and (3) the impact of dehydration and hyponatremia on expression of these receptors.

Estrogenic regulation of gene and protein expression within the amygdala of female mice

Estrogens exert important actions on fear and anxiety in both humans and non-humans. Currently, the mechanisms underlying estrogenic modulation of fear are not known. However, evidence suggests that estrogens may exert their influence on fear and anxiety within the amygdala. The purpose of the present study was to examine the genomic effects of estrogens within the amygdala of female mice using high-density oligonucleotide microarrays. We examined the effects of estrogens on gene expression at 2 and 24 h after an acute subcutaneous injection. Data from the microarrays revealed that 2 h following an acute injection of estradiol, 44 genes were significantly up- or downregulated, and at 24 h, 13 transcripts were significantly up- or downregulated. One interesting estrogen-regulated gene, (CaMKIIalpha), was downregulated ninefold 2 h following an acute estradiol injection but was not altered 24 h after injection. We further examined estrogen regulation of CaMKIIalpha, as well as CaMKIIbeta and CaMKIV within the amygdala using quantitative PCR and western blot analysis. The data indicate that estrogen decreases CaMKIIalpha and CaMKIV but not CaMKIIbeta gene expression within the amygdala. However, CaMKII protein levels were not different, and CaMKIV protein levels increased 2 h post-EB treatment. These results indicate that estrogen regulates CaMK gene expression and protein levels within the amygdala.

Modulation of neuropeptide Y and Y1 receptor expression in the amygdala by fluctuations in the brain content of neuroactive steroids during ethanol drinking discontinuation in Y1R/LacZ transgenic mice

Previous studies have shown that GABAergic neuroactive steroids increase Y1 receptor (Y1R) gene expression in the amygdala of Y1R/LacZ transgenic mice, harbouring the murine Y1R gene promoter linked to a LacZ reporter gene. As ethanol is known to increase GABAergic neuroactive steroids, we investigated the relationship between fluctuations in the brain content of neuroactive steroids induced by chronic voluntary ethanol consumption or ethanol discontinuation and both the level of neuropeptide Y (NPY) immunoreactivity and Y1R gene expression in the amygdala of Y1R/LacZ transgenic mice. Ethanol discontinuation (48 h) after voluntary consumption of consecutive solutions of 3%, 6%, 10% and 20% (v/v) ethanol over 4 weeks produced an anxiety-like behaviour as measured by elevated plus maze. Voluntary ethanol intake increased the cerebrocortical concentration of the progesterone metabolite 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-TH PROG) that returned to control level 48 h after discontinuation of ethanol intake. Ethanol discontinuation significantly decreased NPY immunoreactivity and concomitantly increased Y1R/LacZ transgene expression in the amygdala, whereas chronic ethanol intake failed to affect these parameters. The 5alpha-reductase inhibitor finasteride prevented both the increase in the cerebrocortical concentration of 3alpha,5alpha-TH PROG apparent after 4 weeks of ethanol intake and the changes in NPY immunoreactivity and transgene expression induced by ethanol discontinuation. Data suggest that 3alpha,5alpha-TH PROG plays an important role in the changes in NPY-Y1R signalling in the amygdala during ethanol discontinuation.

Loss of aromatase cytochrome P450 function as a risk factor for Parkinson's disease?

The final step in the physiological synthesis of 17beta estradiol (E(2)) is aromatization of precursor testosterone by a CYP19 gene product, cytochrome P450 estrogen aromatase in the C19 steroid metabolic pathway. Within the central nervous system (CNS) the presence, distribution, and activity of aromatase have been well characterized. Developmental stage and injury are known modulators of brain enzyme activity, where both neurons and glial cells reportedly have the capability to synthesize this key estrogenic enzyme. The gonadal steroid E(2) is a critical survival, neurotrophic and neuroprotective factor for dopaminergic neurons of the substantia nigra pars compacta (SNpc), the cells that degenerate in Parkinson's disease (PD). In previous studies we underlined a crucial role for the estrogenic status at the time of injury in dictating vulnerability to the parkinsonian neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Our ongoing studies address the contribution of brain aromatase and extragonadal E(2) as vulnerability factors for PD pathology in female brain, by exposing aromatase knockout (ArKO, -/-) female mice which are unable to synthesize estrogens to MPTP. Our initial results indicate that aromatase deficiency from early embryonic life significantly impairs the functional integrity of SNpc tyrosine hydroxylase-positive neurons and dopamine transporter innervation of the caudate-putamen in adulthood. In addition, ArKO females exhibited a far greater vulnerability to MPTP-induced nigrostriatal damage as compared to their Wt type gonadally intact and gonadectomized counterparts. Characterization of this novel implication of P450 aromatase as determining factor for PD vulnerability may unravel new avenues for the understanding and development of novel therapeutic approaches for Parkinson's disease.

Aromatase immunoreactivity in the bluehead wrasse brain, Thalassoma bifasciatum: immunolocalization and co-regionalization with arginine vasotocin and tyrosine hydroxylase

Sex steroid hormones regulate various neural functions that control vertebrate sociosexual behavior. A number of sex steroids can be synthesized de novo in the brain, including estrogens by the enzyme aromatase. Aromatase, the neuropeptides arginine vasotocin/vasopressin, and the monoamine neurotransmitter dopamine have all been implicated in the control of male sexual and aggressive behavior in a variety of vertebrates. This study examined the expression of brain aromatase in the bluehead wrasse (Thalassoma bifasciatum), a teleost fish that exhibits socially controlled behavioral and gonadal sex change. We used immunocytochemistry (ICC) to characterize distributions of aromatase-immunoreactive (ir) cells, and to examine their relationship with AVT-ir neurons and tyrosine hydroxylase-ir (TH-ir) neurons in key sensory and integrative areas of the brain of this species. Aromatase-ir appeared to be in glial cell populations, and was found in the dorsal and ventral telencephalon, the preoptic area of the hypothalamus, and the lateral recess of the third ventricle, among other brain areas. Aromatase-ir fibers are closely associated with AVT-ir neurons throughout the preoptic area, indicating the potential for functional interactions. Aromatase-ir cell bodies and fibers were also co-regionalized with TH-ir neurons, suggesting possible interaction between the dopaminergic system and neural estrogen production. The presence of aromatase in brain regions important in the regulation of sexual and aggressive behavior suggests that local estrogen synthesis could regulate sex change through effects on signaling systems that subserve reproductive behavior and function.

Estrogen receptor-alpha distribution in male rodents is associated with social organization

It has been hypothesized that site-specific reduction of estrogen receptor-alpha (ERalpha) is associated with the expression of male prosocial behaviors. Specifically, highly social males are predicted to express significantly lower levels of ERalpha than females and less social males in brain regions associated with prosocial behavior including the bed nucleus of the stria terminalis (BST) and the medial amygdala (MeA). This hypothesis was tested by comparing ERalpha immunoreactivity (IR) in three species of microtines, the polygynous montane (Microtus montanus) and meadow (M. pennsylvanicus) voles and the monogamous pine vole (M. pinetorum), and two species of cricetines that differ in the extent of social pair-bond formation, Siberian (Phodopus sungorus) and Djungarian (P. campbelli) hamsters. As predicted, ERalpha-IR was sexually dimorphic in the BST and MeA of the highly social species, with females expressing more ERalpha-IR cells than males. Male and female montane voles did not differ. Male and female meadow voles differed in the ventromedial hypothalamus, with females expressing more ERalpha-IR cells. Male pine voles expressed lower levels of ERalpha-IR in the MeA than male montane and meadow voles and in the BST relative to montane males. Male Djungarian hamsters, which show higher levels of parental care, had fewer ERalpha-IR cells in the BST than male Siberian hamsters. Results indicate that the distribution of ERalpha differs relative to the continuum of species-typical affiliative behavior and supports the hypothesis that ERalpha has a significant role in regulating species-specific social organization.

Of mice and men: the evolving phenotype of aromatase deficiency

We are rapidly becoming aware of the importance of estrogen in maintaining virtually all facets of male health. In order for estrogens to be synthesized endogenously, the enzyme responsible for their synthesis from androgens, aromatase, must be functional. The seven known men in whom aromatase is nonfunctional all have a mutation in either exon V or IX of the CYP19 gene, which encodes aromatase. Collectively, these men are reported to have undetectable estrogen; normal to high levels of testosterone and gonadotropins; tall stature with delayed skeletal maturation and epiphyseal closure; osteoporosis; impaired lipid and insulin metabolism; and impaired reproductive function. The aromatase knockout mouse presents with a phenotype that is similar in many aspects and provides a valuable tool with which to examine and manipulate the actions of estrogen. By studying the naturally occurring aromatase-deficient humans, together with studies of the aromatase-knockout mouse, we are expanding our understanding of the essential role of estrogen in male physiology.

Alpha-fetoprotein protects the developing female mouse brain from masculinization and defeminization by estrogens

Two clearly opposing views exist on the function of alpha-fetoprotein (AFP), a fetal plasma protein that binds estrogens with high affinity, in the sexual differentiation of the rodent brain. AFP has been proposed to either prevent the entry of estrogens or to actively transport estrogens into the developing female brain. The availability of Afp mutant mice (Afp(-/-)) now finally allows us to resolve this longstanding controversy concerning the role of AFP in brain sexual differentiation, and thus to determine whether prenatal estrogens contribute to the development of the female brain. Here we show that the brain and behavior of female Afp(-/-) mice were masculinized and defeminized. However, when estrogen production was blocked by embryonic treatment with the aromatase inhibitor 1,4,6-androstatriene-3,17-dione, the feminine phenotype of these mice was rescued. These results clearly demonstrate that prenatal estrogens masculinize and defeminize the brain and that AFP protects the female brain from these effects of estrogens.

Sexual differentiation of central vasopressin and vasotocin systems in vertebrates: different mechanisms, similar endpoints

Vasopressin neurons in the bed nucleus of the stria terminalis and amygdala and vasotocin neurons in homologous areas in non-mammalian vertebrates show some of the most consistently found neural sex differences, with males having more cells and denser projections than females. These projections have been implicated in social and reproductive behaviors but also in autonomic functions. The sex differences in these projections may cause as well as prevent sex differences in these functions. This paper discusses the anatomy, steroid dependency, and sexual differentiation of these neurons. Although the final steps in sexual differentiation of vasopressin/vasotocin expression may be similar across vertebrate species, what triggers differentiation may vary dramatically. For example, during development, estrogen masculinizes vasopressin expression in rats but feminizes its counterpart in Japanese quail. Apparently, nature consistently finds a way of maintaining sex differences in vasopressin and vasotocin pathways, suggesting that the function of these differences is important enough that it was conserved during evolution.

The paleoamygdala: cytoarchitectonics, organization, and the cytological characteristics of its neurons

The aim of the present work was to compare the cytoarchitectonics, neuronal organization, and cytological characteristics of the dorsomedial, posterior medial, and posterior cortical nuclei of the amygdaloid body (AB) of the rat brain. Series of frontal brain sections stained with cresyl violet and silver nitrate impregnation by the Golgi method were studied. The results showed that rearrangements of the nuclear principle of organization of the gray matter of the nervous system into the screened organization occur within the territory of this complex of nuclei; it consists of a sparsely branched neuron system and contains neuroendocrine cells. It is concluded that this complex of nuclei is unique in terms of its structural organization and the mechanism of development of this part of the AB, which forms in the earliest stages of AB development; it is termed the "paleoamygdala."

Neurosecretory cells of the amygdaloid complex during estrous cycle

Ultrastructure of neurosecretory cells of the dorsomedial nucleus of the cerebral amygdaloid complex (one of the main zones of sexual dimorphism) was studied in different phases of the estrous cycle. The characteristics of the "light" and "dark" cells change depending on the concentrations of sex steroids during estrus and metestrus.

Estrogen receptor alpha and vasopressin in the paraventricular nucleus of the hypothalamus in Peromyscus

The purpose of this study was to determine the presence of estrogen receptor alpha (ERalpha) and the relationship between neurons that express ERalpha and produce vasopressin (AVP) in the paraventricular nucleus of the hypothalamus (PVN) in new world mice of the genus Peromyscus. Brains were collected from male and female Peromyscus californicus, Peromyscus leucopus, Peromyscus maniculatus, and Peromyscus polionotus, and double labeled for the expression of ERalpha and AVP immunoreactivity (IR). The number of cells expressing ERalpha-IR and AVP-IR was determined in the medial and posterior region of the PVN. The results indicate that Peromyscus is the first taxonomic group reported to have ERalpha widely distributed in the PVN, occurring in both medial and posterior regions of the PVN. While estrogen can regulate the production of AVP, AVP and ERalpha were rarely colocalized. There was, however, a significant inverse relationship between the number of cells that expressed ERalpha-IR and the number expressing AVP-IR. There were no sex differences in the expression of ERalpha-IR or AVP-IR.

Distribution of estrogen receptor alpha mRNA in the brain and inner ear of a vocal fish with comparisons to sites of aromatase expression

Among vertebrates, teleost fish have the greatest capacity for estrogen production in the brain. Previously, we characterized the distribution of the estrogen-synthesizing enzyme aromatase in the brain of the midshipman fish. Here, we investigated the distribution of estrogen receptor alpha (ERalpha). A partial cDNA of ERalpha was cloned and used to generate midshipman-specific primers for RT and real-time PCR which identified transcripts in liver and ovary, the CNS, and the sensory epithelium of the main auditory endorgan (sacculus). In situ hybridization revealed abundant expression throughout the preoptic area, a vocal-acoustic site in the hypothalamus, amygdala homologs of the dorsal pallium, the pineal organ, the inner ear, the pituitary, and the ovary. Weaker expression was found in the midbrain's nucleus of the medial longitudinal fasciculus and in the dimorphic vocal motor nucleus. ERalpha expression in the pineal, gonad, and pituitary axis may function to time seasonal abiotic cues to reproductive state, while expression in the vocal motor and auditory systems support neurophysiological evidence for estrogen as a modulator of vocal motor and auditory encoding mechanisms in midshipman fish. While ERalpha is restricted to specific nuclei, aromatase expression is abundant in glial cells throughout the entire forebrain, and high in midbrain and hindbrain - spinal vocal regions. The only site of aromatase-containing neurons is in the peripheral auditory system, where it is localized to ganglion cells in the auditory nerve. Estrogen production proximal to ERalpha-positive neurons may provide for focal sites of estrogen effects on reproductive-, vocal-, and auditory-related neurons.

Aggression and arginine vasopressin immunoreactivity regulation by androgen receptor and estrogen receptor alpha

In the following study, we asked which steroid receptors regulate aggression and arginine vasopressin (AVP) immunoreactivity (-ir) in several limbic regions. Using spontaneous mutant and knockout mice, we generated a novel cross of mice whose offspring lacked estrogen receptor alpha (ER alpha), androgen receptor (AR) or both ER alpha and AR. The wild-type (WT) males and females were compared with ER alpha knockout (ER alphaKO) male, mutated AR (Tfm) male and ER alphaKO/Tfm (double knockout; DKO) male littermates. Animals were gonadectomized and treated with 17beta-estradiol (E2) prior to resident-intruder aggression tests. WT and Tfm males showed aggression whereas WT females, ER alphaKO and DKO males did not. In the lateral septum, WT and Tfm male brains had significantly denser AVP-ir as compared with WT females and DKO males. ER alphaKO male brains were intermediate in the amount of AVP-ir present. In the medial amygdala, brains from all genotypes had equivalent AVP-ir, except DKO males, which had significantly less AVP-ir. Overall, the expression of aggressive behavior coincided with AVP-ir in WT, Tfm and DKO males. However, in ER alphaKO males and WT females, the amount of AVP-ir was not associated with resident-intruder aggression. In sum we have shown that E2 acts via ER alpha to regulate aggression in male mice. In contrast both ER alpha and AR contribute to AVP-ir in limbic brain regions.