The genetics of sex differences in brain and behavior

Is Male Androphilia a Context-Dependent Cross-Cultural Universal?

The cross-cultural ethnographic literature has traditionally used the label male "homosexuality" to describe sexual relationships between biological males without considering whether or not the concept encompasses primary sexual attraction to adult males. Although male androphilia seems to be found in all national populations, its universal existence in tribal populations has been questioned. Our goal is to review previous cross-cultural classifications and surveys of male same sex behavior to present a system that does justice to its varied expressions, especially as it is informed by contemporary sexuality research. Previous comparative research does not effectively distinguish male same sex behavior from male androphilia. Using the standard cross-cultural sample (SCCS) as a sampling frame and the ethnographic sources in the human relations area files and elsewhere, we present distributional data on various forms of male same sex behavior. The SCCS is useful because it is designed to be representative of all historically known social formations and the sample is designed to reduce similarities as a consequence of common descent or historical origin as well as reduce the probability of diffusion of sociocultural practices from one culture to another. Our results show that male same sex behavior as well as male androphilia is much more common than previously estimated in the SCCS. With our findings, we make an argument that male androphilia is a context-dependent cross-cultural universal.

Enduring, Sexually Dimorphic Impact of In Utero Exposure to Elevated Levels of Glucocorticoids on Midbrain Dopaminergic Populations

Glucocorticoid hormones (GCs) released from the fetal/maternal glands during late gestation are required for normal development of mammalian organs and tissues. Accordingly, synthetic glucocorticoids have proven to be invaluable in perinatal medicine where they are widely used to accelerate fetal lung maturation when there is risk of pre-term birth and to promote infant survival. However, clinical and pre-clinical studies have demonstrated that inappropriate exposure of the developing brain to elevated levels of GCs, either as a result of clinical over-use or after stress-induced activation of the fetal/maternal adrenal cortex, is linked with significant effects on brain structure, neurological function and behaviour in later life. In order to understand the underlying neural processes, particular interest has focused on the midbrain dopaminergic systems, which are critical regulators of normal adaptive behaviours, cognitive and sensorimotor functions. Specifically, using a rodent model of GC exposure in late gestation (approximating human brain development at late second/early third trimester), we demonstrated enduring effects on the shape and volume of the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) (origins of the mesocorticolimbic and nigrostriatal dopaminergic pathways) on the topographical organisation and size of the dopaminergic neuronal populations and astrocytes within these nuclei and on target innervation density and neurochemical markers of dopaminergic transmission (receptors, transporters, basal and amphetamine-stimulated dopamine release at striatal and prefrontal cortical sites) that impact on the adult brain. The effects of antenatal GC treatment (AGT) were both profound and sexually-dimorphic, not only in terms of quantitative change but also qualitatively, with several parameters affected in the opposite direction in males and females. Although such substantial neurobiological changes might presage marked behavioural effects, in utero GC exposure had only a modest or no effect, depending on sex, on a range of conditioned and unconditioned behaviours known to depend on midbrain dopaminergic transmission. Collectively, these findings suggest that apparent behavioural normality in certain tests, but not others, arises from AGT-induced adaptations or compensatory mechanisms within the midbrain dopaminergic systems, which preserve some, but not all functions. Furthermore, the capacities for molecular adaptations to early environmental challenge are different, even opponent, in males and females, which may account for their differential resilience or failure to perform adequately in behavioural tests. Behavioural "normality" is thus achieved by the midbrain dopaminergic network operating outside its normal limits (in a state of allostasis), rendering it at greater risk to malfunction when challenged in later life. Sex-specific neurobiological programming of midbrain dopaminergic systems may, therefore, have psychopathological relevance for the sex bias commonly found in brain disorders associated with these systems, and which have a neurodevelopmental component, including schizophrenia, ADHD (attention/deficit hyperactivity disorders), autism, depression and substance abuse.

Sex-Specific Effects of Testosterone on the Sexually Dimorphic Transcriptome and Epigenome of Embryonic Neural Stem/Progenitor Cells

The mechanisms by which sex differences in the mammalian brain arise are poorly understood, but are influenced by a combination of underlying genetic differences and gonadal hormone exposure. Using a mouse embryonic neural stem cell (eNSC) model to understand early events contributing to sexually dimorphic brain development, we identified novel interactions between chromosomal sex and hormonal exposure that are instrumental to early brain sex differences. RNA-sequencing identified 103 transcripts that were differentially expressed between XX and XY eNSCs at baseline (FDR = 0.10). Treatment with testosterone-propionate (TP) reveals sex-specific gene expression changes, causing 2854 and 792 transcripts to become differentially expressed on XX and XY genetic backgrounds respectively. Within the TP responsive transcripts, there was enrichment for genes which function as epigenetic regulators that affect both histone modifications and DNA methylation patterning. We observed that TP caused a global decrease in 5-methylcytosine abundance in both sexes, a transmissible effect that was maintained in cellular progeny. Additionally, we determined that TP was associated with residue-specific alterations in acetylation of histone tails. These findings highlight an unknown component of androgen action on cells within the developmental CNS, and contribute to a novel mechanism of action by which early hormonal organization is initiated and maintained.

Midbrain functional connectivity and ventral striatal dopamine D2-type receptors: link to impulsivity in methamphetamine users

Stimulant use disorders are associated with deficits in striatal dopamine receptor availability, abnormalities in mesocorticolimbic resting-state functional connectivity (RSFC) and impulsivity. In methamphetamine-dependent research participants, impulsivity is correlated negatively with striatal D2-type receptor availability, and mesocorticolimbic RSFC is stronger than that in controls. The extent to which these features of methamphetamine dependence are interrelated, however, is unknown. This question was addressed in two studies. In Study 1, 19 methamphetamine-dependent and 26 healthy control subjects underwent [¹⁸F]fallypride positron emission tomography to measure ventral striatal dopamine D2-type receptor availability, indexed by binding potential (BP_ND), and functional magnetic resonance imaging (fMRI) to assess mesocorticolimbic RSFC, using a midbrain seed. In Study 2, an independent sample of 20 methamphetamine-dependent and 18 control subjects completed the Barratt Impulsiveness Scale in addition to fMRI. Study 1 showed a significant group by ventral striatal BP_ND interaction effect on RSFC, reflecting a negative relationship between ventral striatal BP_ND and RSFC between the midbrain and striatum, orbitofrontal cortex and insula in methamphetamine-dependent participants, but a positive relationship in the control group. In Study 2, an interaction of the group with RSFC on impulsivity was observed. Methamphetamine-dependent users exhibited a positive relationship of midbrain RSFC to the left ventral striatum with cognitive impulsivity, whereas a negative relationship was observed in healthy controls. The results indicate that ventral striatal D2-type receptor signaling may affect the system-level activity within the mesocorticolimbic system, providing a functional link that may help explain high impulsivity in methamphetamine-dependent individuals.

Neuroimaging studies in people with gender incongruence

The current review gives an overview of brain studies in transgender people. First, we describe studies into the aetiology of feelings of gender incongruence, primarily addressing the sexual differentiation hypothesis: does the brain of transgender individuals resemble that of their natal sex, or that of their experienced gender? Findings from neuroimaging studies focusing on brain structure suggest that the brain phenotypes of trans women (MtF) and trans men (FtM) differ in various ways from control men and women with feminine, masculine, demasculinized and defeminized features. The brain phenotypes of people with feelings of gender incongruence may help us to figure out whether sex differentiation of the brain is atypical in these individuals, and shed light on gender identity development. Task-related imaging studies may show whether brain activation and task performance in transgender people is sex-atypical. Second, we review studies that evaluate the effects of cross-sex hormone treatment on the brain. This type of research provides knowledge on how changes in sex hormone levels may affect brain structure and function.

Sex biology contributions to vulnerability to Alzheimer's disease: A think tank convened by the Women's Alzheimer's Research Initiative

More than 5 million Americans are living with Alzheimer's disease (AD) today, and nearly two-thirds of Americans with AD are women. This sex difference may be due to the higher longevity women generally experience; however, increasing evidence suggests that longevity alone is not a sufficient explanation and there may be other factors at play. The Alzheimer's Association convened an expert think tank to focus on the state of the science and level of evidence around gender and biological sex differences for AD, including the knowledge gaps and areas of science that need to be more fully addressed. This article summarizes the think tank discussion, moving forward a research agenda and funding program to better understand the biological underpinnings of sex- and gender-related disparities of risk for AD.

Experimental elevation of wildlife testosterone using silastic tube implants

Testosterone (T) is a key androgen that mediates vertebrate molecular, cellular, and behavioral processes. Its manipulation is therefore of interest to a vast number of researchers studying animal behavior and reproduction, among others. Here, the usage of silastic implants across wildlife species is reviewed, and a method to manipulate rock hyrax (Procavia capensis) testosterone levels using silastic implants is presented. Using a series of in-vitro and in-vivo experiments, the secretion patterns of silastic tubes and silastic glue were tested and were surprisingly found to be similar. In addition, we studied endogenous T levels in wild-captured rock hyraxes (Procavia capensis), and using T implants succeeded in elevating T to the maximal physiological concentrations recorded during the mating period. The number of implants that were inserted was the only predictor of T levels, and seven 20mm implants were found to be the optimal dose. Implants induced sexual behaviors in the non-reproductive period. The duration of time that the implants were in the hyrax was the only significant factor that influenced the amount of T left over in the implant once it was removed. All together we affirm that T implants may offer a versatile tool for wildlife behavioral research by elevating T levels in the non-breeding period to maximal breeding levels.

Civil liability: characterization of the demand for lawsuits against dentists

In light of the fact that dentists may be held civilly liable for their practice, it is important to understand the current situation of lawsuits filed against these professionals by studying current legal decisions and the literature. The objective of this study was to analyze the case law of the Court of Justice of São Paulo, Brazil, relative to the profile of patients and professionals, the most commonly involved specialties, the amounts litigated and the court decisions pertaining to civil liability lawsuits against dentists. In an inductive approach, a single researcher screened and collected civil liability rulings by accessing the Court's website, and following a statistical-descriptive procedure and an indirect observation technique. The most frequently involved specialty was prosthodontics. However, oral and maxillofacial surgery was related to a higher incidence of damages awarded to settle claims and to higher damage amounts. The dentist was found guilty in 44.32% of the cases researched. Pecuniary damages ranged between R$ 485.50 and R$ 12,530.00, and non-pecuniary damages ranged between R$ 2,500.00 and R$ 70,000.00. Most lawsuits were filed by women against male dentists. An increase in the relative number of lawsuits against companies versus individuals was observed.

Reward-based plasticity of spatial priority maps: Exploiting inter-subject variability to probe the underlying neurobiology

Recent evidence indicates that the attentional priority of objects and locations is altered by the controlled delivery of reward, reflecting reward-based attentional learning. Here, we take an approach hinging on intersubject variability to probe the neurobiological bases of the reward-driven plasticity of spatial priority maps. Specifically, we ask whether an individual's susceptibility to the reward-based treatment can be accounted for by specific predictors, notably personality traits that are linked to reward processing (along with more general personality traits), but also gender. Using a visual search protocol, we show that when different target locations are associated with unequal reward probability, different priorities are acquired by the more rewarded relative to the less rewarded locations. However, while males exhibit the expected pattern of results, with greater priority for locations associated with higher reward, females show an opposite trend. Critically, both the extent and the direction of reward-based adjustments are further predicted by personality traits indexing reward sensitivity, indicating that not only male and female brains are differentially sensitive to reward, but also that specific personality traits further contribute to shaping their learning-dependent attentional plasticity. These results contribute to a better understanding of the neurobiology underlying reward-dependent attentional learning and cross-subject variability in this domain.

Hypobaric hypoxia induces depression-like behavior in female Sprague-Dawley rats, but not in males

Rates of depression and suicide are higher in people living at altitude, and in those with chronic hypoxic disorders like asthma, chronic obstructive pulmonary disorder (COPD), and smoking. Living at altitude exposes people to hypobaric hypoxia, which can lower rat brain serotonin levels, and impair brain bioenergetics in both humans and rats. We therefore examined the effect of hypobaric hypoxia on depression-like behavior in rats. After a week of housing at simulated altitudes of 20,000 ft, 10,000 ft, or sea level, or at local conditions of 4500 ft (Salt Lake City, UT), Sprague Dawley rats were tested for depression-like behavior in the forced swim test (FST). Time spent swimming, climbing, or immobile, and latency to immobility were measured. Female rats housed at altitude display more depression-like behavior in the FST, with significantly more immobility, less swimming, and lower latency to immobility than those at sea level. In contrast, males in all four altitude groups were similar in their FST behavior. Locomotor behavior in the open field test did not change with altitude, thus validating immobility in the FST as depression-like behavior. Hypobaric hypoxia exposure therefore induces depression-like behavior in female rats, but not in males.

Sexual Orientation, Controversy, and Science

Summary

Ongoing political controversies around the world exemplify a long-standing and widespread preoccupation with the acceptability of homosexuality. Nonheterosexual people have seen dramatic surges both in their rights and in positive public opinion in many Western countries. In contrast, in much of Africa, the Middle East, the Caribbean, Oceania, and parts of Asia, homosexual behavior remains illegal and severely punishable, with some countries retaining the death penalty for it. Political controversies about sexual orientation have often overlapped with scientific controversies. That is, participants on both sides of the sociopolitical debates have tended to believe that scientific findings—and scientific truths—about sexual orientation matter a great deal in making political decisions. The most contentious scientific issues have concerned the causes of sexual orientation—that is, why are some people heterosexual, others bisexual, and others homosexual? The actual relevance of these issues to social, political, and ethical decisions is often poorly justified, however.

Roads Less Traveled: Sexual Dimorphism and Mast Cell Contributions to Migraine Pathology

Migraine is a common, little understood, and debilitating disease. It is much more prominent in women than in men (~2/3 are women) but the reasons for female preponderance are not clear. Migraineurs frequently experience severe comorbidities, such as allergies, depression, irritable bowel syndrome, and others; many of the comorbidities are more common in females. Current treatments for migraine are not gender specific, and rarely are migraine and its comorbidities considered and treated by the same specialist. Thus, migraine treatments represent a huge unmet medical need, which will only be addressed with greater understanding of its underlying pathophysiology. We discuss the current knowledge about sex differences in migraine and its comorbidities, and focus on the potential role of mast cells (MCs) in both. Sex-based differences in pain recognition and drug responses, fluid balance, and the blood–brain barrier are recognized but their impact on migraine is not well studied. Furthermore, MCs are well recognized for their prominent role in allergies but much less is known about their contributions to pain pathways in general and migraine specifically. MC-neuron bidirectional communication uniquely positions these cells as potential initiators and/or perpetuators of pain. MCs can secrete nociceptor sensitizing and activating agents, such as serotonin, prostaglandins, histamine, and proteolytic enzymes that can also activate the pain-mediating transient receptor potential vanilloid channels. MCs express receptors for both estrogen and progesterone that induce degranulation upon binding. Furthermore, environmental estrogens, such as Bisphenol A, activate MCs in preclinical models but their impact on pain pathways or migraine is understudied. We hope that this discussion will encourage scientists and physicians alike to bridge the knowledge gaps linking sex, MCs, and migraine to develop better, more comprehensive treatments for migraine patients.

Personality and gender differences in global perspective

Men's and women's personalities appear to differ in several respects. Social role theories of development assume gender differences result primarily from perceived gender roles, gender socialization and sociostructural power differentials. As a consequence, social role theorists expect gender differences in personality to be smaller in cultures with more gender egalitarianism. Several large cross-cultural studies have generated sufficient data for evaluating these global personality predictions. Empirically, evidence suggests gender differences in most aspects of personality-Big Five traits, Dark Triad traits, self-esteem, subjective well-being, depression and values-are conspicuously larger in cultures with more egalitarian gender roles, gender socialization and sociopolitical gender equity. Similar patterns are evident when examining objectively measured attributes such as tested cognitive abilities and physical traits such as height and blood pressure. Social role theory appears inadequate for explaining some of the observed cultural variations in men's and women's personalities. Evolutionary theories regarding ecologically-evoked gender differences are described that may prove more useful in explaining global variation in human personality.

Sex differences in partner preferences in humans and animals

A large number of morphological, physiological and behavioural traits are differentially expressed by males and females in all vertebrates including humans. These sex differences, sometimes, reflect the different hormonal environment of the adults, but they often remain present after subjects of both sexes are placed in the same endocrine conditions following gonadectomy associated or not with hormonal replacement therapy. They are then the result of combined influences of organizational actions of sex steroids acting early during development, or genetic differences between the sexes, or epigenetic mechanisms differentially affecting males and females. Sexual partner preference is a sexually differentiated behavioural trait that is clearly controlled in animals by the same type of mechanisms. This is also probably true in humans, even if critical experiments that would be needed to obtain scientific proof of this assertion are often impossible for pragmatic or ethical reasons. Clinical, epidemiological and correlative studies provide, however, converging evidence strongly suggesting, if not demonstrating, that endocrine, genetic and epigenetic mechanisms acting during the pre- or perinatal life control human sexual orientation, i.e. homosexuality versus heterosexuality. Whether they interact with postnatal psychosexual influences remains, however, unclear at present.

The importance of having two X chromosomes

Historically, it was thought that the number of X chromosomes plays little role in causing sex differences in traits. Recently, selected mouse models have been used increasingly to compare mice with the same type of gonad but with one versus two copies of the X chromosome. Study of these models demonstrates that mice with one X chromosome can be strikingly different from those with two X chromosomes, when the differences are not attributable to confounding group differences in gonadal hormones. The number of X chromosomes affects adiposity and metabolic disease, cardiovascular ischaemia/reperfusion injury and behaviour. The effects of X chromosome number are likely the result of inherent differences in expression of X genes that escape inactivation, and are therefore expressed from both X chromosomes in XX mice, resulting in a higher level of expression when two X chromosomes are present. The effects of X chromosome number contribute to sex differences in disease phenotypes, and may explain some features of X chromosome aneuploidies such as in Turner and Klinefelter syndromes.

How Early Hormones Shape Gender Development

Many important psychological characteristics show sex differences, and are influenced by sex hormones at different developmental periods. We focus on the role of sex hormones in early development, particularly the differential effects of prenatal androgens on aspects of gender development. Increasing evidence confirms that prenatal androgens have facilitative effects on male-typed activity interests and engagement (including child toy preferences and adult careers), and spatial abilities, but relatively minimal effects on gender identity. Recent emphasis has been directed to the psychological mechanisms underlying these effects (including sex differences in propulsive movement, and androgen effects on interest in people versus things), and neural substrates of androgen effects (including regional brain volumes, and neural responses to mental rotation, sexually arousing stimuli, emotion, and reward). Ongoing and planned work is focused on understanding the ways in which hormones act jointly with the social environment across time to produce varying trajectories of gender development, and clarifying mechanisms by which androgens affect behaviors. Such work will be facilitated by applying lessons from other species, and by expanding methodology. Understanding hormonal influences on gender development enhances knowledge of psychological development generally, and has important implications for basic and applied questions, including sex differences in psychopathology, women's underrepresentation in science and math, and clinical care of individuals with variations in gender expression.

Decoding the non-coding genome: elucidating genetic risk outside the coding genome

Current evidence emerging from genome-wide association studies indicates that the genetic underpinnings of complex traits are likely attributable to genetic variation that changes gene expression, rather than (or in combination with) variation that changes protein-coding sequences. This is particularly compelling with respect to psychiatric disorders, as genetic changes in regulatory regions may result in differential transcriptional responses to developmental cues and environmental/psychosocial stressors. Until recently, however, the link between transcriptional regulation and psychiatric genetic risk has been understudied. Multiple obstacles have contributed to the paucity of research in this area, including challenges in identifying the positions of remote (distal from the promoter) regulatory elements (e.g. enhancers) and their target genes and the underrepresentation of neural cell types and brain tissues in epigenome projects - the availability of high-quality brain tissues for epigenetic and transcriptome profiling, particularly for the adolescent and developing brain, has been limited. Further challenges have arisen in the prediction and testing of the functional impact of DNA variation with respect to multiple aspects of transcriptional control, including regulatory-element interaction (e.g. between enhancers and promoters), transcription factor binding and DNA methylation. Further, the brain has uncommon DNA-methylation marks with unique genomic distributions not found in other tissues - current evidence suggests the involvement of non-CG methylation and 5-hydroxymethylation in neurodevelopmental processes but much remains unknown. We review here knowledge gaps as well as both technological and resource obstacles that will need to be overcome in order to elucidate the involvement of brain-relevant gene-regulatory variants in genetic risk for psychiatric disorders.

Zebrafish sexual behavior: role of sex steroid hormones and prostaglandins

Background

Mating behavior differ between sexes and involves gonadal hormones and possibly sexually dimorphic gene expression in the brain. Sex steroids and prostaglandin E₂ (PGE₂) have been shown to regulate mammalian sexual behavior. The present study was aimed at determining whether exposure to sex steroids and prostaglandins could alter zebrafish sexual mating behavior.

Methods

Mating behavior and successful spawning was recorded following exposure to 17β-estradiol (E2), 11-ketotestosterone (11-KT), prostaglandin D₂ (PGD₂) and PGE₂ via the water. qRT-PCR was used to analyze transcript levels in the forebrain, midbrain, and hindbrain of male and female zebrafish and compared to animals exposed to E2 via the water.

Results

Exposure of zebrafish to sex hormones resulted in alterations in behavior and spawning when male fish were exposed to E2 and female fish were exposed to 11-KT. Exposure to PGD_2, and PGE₂ did not alter mating behavior or spawning success. Determination of gene expression patterns of selected genes from three brain regions using qRT-PCR analysis demonstrated that the three brain regions differed in gene expression pattern and that there were differences between the sexes. In addition, E2 exposure also resulted in altered gene transcription profiles of several genes.

Conclusions

Exposure to sex hormones, but not prostaglandins altered mating behavior in zebrafish. The expression patterns of the studied genes indicate that there are large regional and gender-based differences in gene expression and that E2 treatment alter the gene expression pattern in all regions of the brain.

Electronic supplementary material

The online version of this article (doi:10.1186/s12993-015-0068-6) contains supplementary material, which is available to authorized users.

Pathophysiology and Treatments of Oxidative Injury in Ischemic Stroke: Focus on the Phagocytic NADPH Oxidase 2

SIGNIFICANCE

Phagocytes play a key role in promoting the oxidative stress after ischemic stroke occurrence. The phagocytic NADPH oxidase (NOX) 2 is a membrane-bound enzyme complex involved in the antimicrobial respiratory burst and free radical production in these cells.

RECENT ADVANCES

Different oxidants have been shown to induce opposite effects on neuronal homeostasis after a stroke. However, several experimental models support the detrimental effects of NOX activity (especially the phagocytic isoform) on brain recovery after stroke. Therapeutic strategies selectively targeting the neurotoxic ROS and increasing neuroprotective oxidants have recently produced promising results.

CRITICAL ISSUES

NOX2 might promote carotid plaque rupture and stroke occurrence. In addition, NOX2-derived reactive oxygen species (ROS) released by resident and recruited phagocytes enhance cerebral ischemic injury, activating the inflammatory apoptotic pathways. The aim of this review is to update evidence on phagocyte-related oxidative stress, focusing on the role of NOX2 as a potential therapeutic target to reduce ROS-related cerebral injury after stroke.

FUTURE DIRECTIONS

Radical scavenger compounds (such as Ebselen and Edaravone) are under clinical investigation as a therapeutic approach against stroke. On the other hand, NOX inhibition might represent a promising strategy to prevent the stroke-related injury. Although selective NOX inhibitors are not yet available, nonselective compounds (such as apocynin and fasudil) provided encouraging results in preclinical studies. Whereas additional studies are needed to better evaluate this therapeutic potential in human beings, the development of specific NOX inhibitors (such as monoclonal antibodies, small-molecule inhibitors, or aptamers) might further improve brain recovery after stroke.

The gestational foundation of sex differences in development and vulnerability

Despite long-standing interest in the role of sex on human development, the functional consequences of fetal sex on early development are not well-understood. Here we explore the gestational origins of sex as a moderator of development. In accordance with the focus of this special issue, we examine evidence for a sex differential in vulnerability to prenatal and perinatal risks. Exposures evaluated include those present in the external environment (e.g., lead, pesticides), those introduced by maternal behaviors (e.g., alcohol, opioid use), and those resulting from an adverse intrauterine environment (e.g., preterm birth). We also provide current knowledge on the degree to which sex differences in fetal neurobehavioral development (i.e., cardiac and motor patterns) are present prior to birth. Also considered are contemporaneous and persistent sex of fetus effects on the pregnant woman. Converging evidence confirms that infant and early childhood developmental outcomes of male fetuses exposed to prenatal and perinatal adversities are more highly impaired than those of female fetuses. In certain circumstances, male fetuses are both more frequently exposed to early adversities and more affected by them when exposed than are female fetuses. The mechanisms through which biological sex imparts vulnerability or protection on the developing nervous system are largely unknown. We consider models that implicate variation in maturation, placental functioning, and the neuroendocrine milieu as potential contributors. Many studies use sex as a control variable, some analyze and report main effects for sex, but those that report interaction terms for sex are scarce. As a result, the true scope of sex differences in vulnerability is unknown.

Bisphenol A Interaction With Brain Development and Functions

Brain development is an organized, but constantly adaptive, process in which genetic and epigenetic signals allow neurons to differentiate, to migrate, and to develop correct connections. Gender specific prenatal sex hormone milieu participates in the dimorphic development of many neuronal networks. Environmental cues may interfere with these developmental programs, producing adverse outcomes. Bisphenol A (BPA), an estrogenic/antiandrogenic endocrine disruptor widely diffused in the environment, produces adverse effects at levels below the acceptable daily intake. This review analyzes the recent literature on the consequences of perinatal exposure to BPA environmental doses on the development of a dimorphic brain. The BPA interference with the development and function of the neuroendocrine hypothalamus and of the nuclei controlling energy balance, and with the hippocampal memory processing is also discussed. The detrimental action of BPA appears complex, involving different hormonal and epigenetic pathways activated, often in a dimorphic way, within clearcut susceptibility windows. To date, discrepancies in experimental approaches and in related outcomes make unfeasible to translate the available information into clear dose-response models for human risk assessment. Evaluation of BPA brain levels in relation to the appearance of adverse effects in future basic studies will certainly give better definition of the warning threshold for human health.

Biological factors underlying sex differences in neurological disorders

The prevalence, age of onset, pathophysiology, and symptomatology of many neurological and neuropsychiatric conditions differ significantly between males and females. Females suffer more from mood disorders such as depression and anxiety, whereas males are more susceptible to deficits in the dopamine system including Parkinson's disease (PD), attention-deficit hyperactivity disorder (ADHD), schizophrenia, and autism spectrum disorders (ASD). Until recently, these sex differences have been explained solely by the neuroprotective actions of sex hormones in females. Emerging evidence however indicates that the sex chromosome genes (i.e. X- and Y-linked genes) also contribute to brain sex differences. In particular, the Y-chromosome gene, SRY (Sex-determining Region on the Y chromosome) is an interesting candidate as it is expressed in dopamine-abundant brain regions, where it regulates dopamine biosynthesis and dopamine-mediated functions such as voluntary movement in males. Furthermore, SRY expression is dysregulated in a toxin-induced model of PD, suggesting a role for SRY in the pathogenesis of dopamine cells. Taken together, these studies highlight the importance of understanding the interplay between sex-specific hormones and sex-specific genes in healthy and diseased brain. In particular, better understanding of regulation and function of SRY in the male brain could provide entirely novel and important insights into genetic factors involved in the susceptibility of men to neurological disorders, as well as development of novel sex-specific therapies.

Y genetic variation and phenotypic diversity in health and disease

Sexually dimorphic traits arise through the combined effects of sex hormones and sex chromosomes on sex-biased gene expression, and experimental mouse models have been instrumental in determining their relative contribution in modulating sex differences. A role for the Y chromosome (ChrY) in mediating sex differences outside of development and reproduction has historically been overlooked due to its unusual genetic composition and the predominant testes-specific expression of ChrY-encoded genes. However, ample evidence now exists supporting ChrY as a mediator of other physiological traits in males, and genetic variation in ChrY has been linked to several diseases, including heart disease, cancer, and autoimmune diseases in experimental animal models, as well as humans. The genetic and molecular mechanisms by which ChrY modulates phenotypic variation in males remain unknown but may be a function of copy number variation between homologous X-Y multicopy genes driving differential gene expression. Here, we review the literature identifying an association between ChrY polymorphism and phenotypic variation and present the current evidence depicting the mammalian ChrY as a member of the regulatory genome in males and as a factor influencing paternal parent-of-origin effects in female offspring.

Sex differences in ischemic stroke sensitivity are influenced by gonadal hormones, not by sex chromosome complement

Epidemiologic studies have shown sex differences in ischemic stroke. The four core genotype (FCG) mouse model, in which the testes determining gene, Sry, has been moved from Y chromosome to an autosome, was used to dissociate the effects of sex hormones from sex chromosome in ischemic stroke outcome. Middle cerebral artery occlusion (MCAO) in gonad intact FCG mice revealed that gonadal males (XXM and XYM) had significantly higher infarct volumes as compared with gonadal females (XXF and XYF). Serum testosterone levels were equivalent in adult XXM and XYM, as was serum estrogen in XXF and XYF mice. To remove the effects of gonadal hormones, gonadectomized FCG mice were subjected to MCAO. Gonadectomy significantly increased infarct volumes in females, while no change was seen in gonadectomized males, indicating that estrogen loss increases ischemic sensitivity. Estradiol supplementation in gonadectomized FCG mice rescued this phenotype. Interestingly, FCG male mice were less sensitive to effects of hormones. This may be due to enhanced expression of the transgene Sry in brains of FCG male mice. Sex differences in ischemic stroke sensitivity appear to be shaped by organizational and activational effects of sex hormones, rather than sex chromosomal complement.

Gene expression profile of the neonatal female mouse brain after administration of testosterone propionate

INTRODUCTION

Clinical care decisions for peripubertal adolescents with gender dysphoria (GD) should be made carefully. Furthermore, the identification of biomarkers is very important for rapid and accurate diagnosis of GD in young people.

AIM

The aim of this study was to investigate gene expression profiles during masculinization of the neonatal female mouse brain by testosterone and to identify biomarkers related to GD.

METHODS

Microarray analysis was performed using RNAs extracted from the brains of neonatal mice treated by intraperitoneal injection of testosterone propionate during the sexual determination period. Sequence motif enrichment analysis for sex hormone receptor responsive elements was performed for the flanking regions of genes that showed significant expression changes following administration of testosterone propionate.

MAIN OUTCOME MEASURES

We revealed a gene set with marked changes in expression during brain masculinization of neonatal female mice following administration of testosterone propionate.

RESULTS

We identified 334 genes that showed differential expression in the masculinized neonatal female brain after testosterone propionate treatment. Interestingly, most of these genes are not reported to be expressed in a sexually dimorphic manner. Moreover, sequence motif enrichment analysis suggested that masculinization of the neonatal female brain by testosterone was controlled more by estrogen receptors than androgen receptors.

CONCLUSIONS

Differences in genes that are expressed differentially following administration of testosterone injection from known sexually dimorphic genes suggest that many GD-related genes are upregulated during female brain masculinization. The gene set identified in this study provides a basis to better understand the mechanisms of GD and delineate its associated biomarkers.

Human homosexuality: a paradigmatic arena for sexually antagonistic selection?

Sexual conflict likely plays a crucial role in the origin and maintenance of homosexuality in our species. Although environmental factors are known to affect human homosexual (HS) preference, sibling concordances and population patterns related to HS indicate that genetic components are also influencing this trait in humans. We argue that multilocus, partially X-linked genetic factors undergoing sexually antagonistic selection that promote maternal female fecundity at the cost of occasional male offspring homosexuality are the best candidates capable of explaining the frequency, familial clustering, and pedigree asymmetries observed in HS male proband families. This establishes male HS as a paradigmatic example of sexual conflict in human biology. HS in females, on the other hand, is currently a more elusive phenomenon from both the empirical and theoretical standpoints because of its fluidity and marked environmental influence. Genetic and epigenetic mechanisms, the latter involving sexually antagonistic components, have been hypothesized for the propagation and maintenance of female HS in the population. However, further data are needed to truly clarify the evolutionary dynamics of this trait.

Sex-dependent diversity in ventral tegmental dopaminergic neurons and developmental programing: A molecular, cellular and behavioral analysis

The knowledge that diverse populations of dopaminergic neurons within the ventral tegmental area (VTA) can be distinguished in terms of their molecular, electrophysiological and functional properties, as well as their differential projections to cortical and subcortical regions has significance for key brain functions, such as the regulation of motivation, working memory and sensorimotor control. Almost without exception, this understanding has evolved from landmark studies performed in the male sex. However, converging evidence from both clinical and pre-clinical studies illustrates that the structure and functioning of the VTA dopaminergic systems are intrinsically different in males and females. This may be driven by sex differences in the hormonal environment during adulthood ('activational' effects) and development (perinatal and/or pubertal 'organizational' effects), as well as genetic factors, especially the SRY gene on the Y chromosome in males, which is expressed in a sub-population of adult midbrain dopaminergic neurons. Stress and stress hormones, especially glucocorticoids, are important factors which interact with the VTA dopaminergic systems in order to achieve behavioral adaptation and enable the individual to cope with environmental change. Here, also, there is male/female diversity not only during adulthood, but also in early life when neurobiological programing by stress or glucocorticoid exposure differentially impacts dopaminergic developmental trajectories in male and female brains. This may have enduring consequences for individual resilience or susceptibility to pathophysiological change induced by stressors in later life, with potential translational significance for sex bias commonly found in disorders involving dysfunction of the mesocorticolimbic dopaminergic systems. These findings highlight the urgent need for a better understanding of the sexual dimorphism in the VTA if we are to improve strategies for the prevention and treatment of debilitating conditions which differentially affect men and women in their prevalence and nature, including schizophrenia, attention/deficit hyperactivity disorder, autism spectrum disorders, anxiety, depression and addiction.

(Patho)physiology of cross-sex hormone administration to transsexual people: the potential impact of male-female genetic differences

There is a limited body of knowledge of desired and undesired effects of cross-sex hormones in transsexual people. Little attention has been given to the fact that chromosomal configurations, 46,XY in male-to-female transsexuals subjects (MtoF) and 46,XX in female-to-male transsexual subjects (FtoM), obviously, remain unchanged. These differences in their genomes cause sex differences in the functions of cells. This study reviews sex differences in metabolism/cardiovascular pathology, immune mechanisms, bone (patho)physiology and brain functions and examines whether they are, maybe partially, determined by genetic mechanisms rather than by (cross-sex) hormones. There do not appear to be major genetic impacts on the changes in bone physiology. Also immune functions are rather unaffected and the evidence for an increase of autoimmune disease in MtoF is preliminary. Brain functions of transsexuals may have differed from controls before cross-sex hormones; they do undergo shifts upon cross-sex hormone treatment, but there is no evidence for changes in sex-specific brain disease. The prevalence of cardiovascular disease is higher in MtoF receiving oestrogens than in FtoM receiving androgens. While type of oestrogen and route of administration might be significant, it is reasonable to speculate that nonhormonal/genetic factors play a role.

Separate effects of sex hormones and sex chromosomes on brain structure and function revealed by high-resolution magnetic resonance imaging and spatial navigation assessment of the Four Core Genotype mouse model

Males and females exhibit several differences in brain structure and function. To examine the basis for these sex differences, we investigated the influences of sex hormones and sex chromosomes on brain structure and function in mice. We used the Four Core Genotype (4CG) mice, which can generate both male and female mice with XX or XY sex chromosome complement, allowing the decoupling of sex chromosomes from hormonal milieu. To examine whole brain structure, high-resolution ex vivo MRI was performed, and to assess differences in cognitive function, mice were trained on a radial arm maze. Voxel-wise and volumetric analyses of MRI data uncovered a striking independence of hormonal versus chromosomal influences in 30 sexually dimorphic brain regions. For example, the bed nucleus of the stria terminalis and the parieto-temporal lobe of the cerebral cortex displayed steroid-dependence while the cerebellar cortex, corpus callosum, and olfactory bulbs were influenced by sex chromosomes. Spatial learning and memory demonstrated strict hormone-dependency with no apparent influence of sex chromosomes. Understanding the influences of chromosomes and hormones on brain structure and function is important for understanding sex differences in brain structure and function, an endeavor that has eventual implications for understanding sex biases observed in the prevalence of psychiatric disorders.

On the validity of popular masculinity rating scales with gay men

During the past decade, greater quantitative attention has been given to how gay men's lives are affected by traditional notions of masculinity. Consequently, it is important that masculinity-related measures that are often used in research are valid for use with gay men. This study examined the factor structures, loadings, and psychometric properties of three commonly used masculinity-related measures: the Gender Role Conflict Scale, the Conformity to Masculine Norms Inventory, and the Reference Group Identity Dependence Scale. Data were collected via an online survey of 920 self-identified gay men (M(age) = 32.48 years, SD = 11.73). Confirmatory factor analyses indicated that while the goodness of fit statistics did not always indicate the model fit, there were similar endorsements of items across the three masculinity scales and subscale factor loadings consistent with published studies using mostly heterosexual male samples. Implications for future masculinity scale research on gay men are discussed.

Habituation responses to external stimuli: is the habituation of preterm infants at a postconceptual age of 40 weeks equal to that of term infants?

OBJECTIVE

Compare the habituation responses to external stimuli between preterm infants at the postconceptual age of 40 weeks and term infants in the first days of life, and evaluate the habituation responses of the preterm infants until the age of 40 postconceptual weeks.

METHODS

Prospective cohort study of preterm infants aged <32 weeks. The habituation responses to light, rattle, bell and tactile stimuli of preterm infants were assessed at 32, 34, 36 and 38-40 postconceptual weeks. External stimuli were presented and responses were scored according to Lester and Tronik (2004). Habituation scores were compared between preterm and term infants, matched by sex, using t test. Repeated measures ANOVA was used to compare the responses between the different postconceptual gestational ages. Contrast models were used to verify the differences between the habituation responses according to the type of stimulus and the postconceptual ages.

RESULTS

51 preterm infants were studied (gestational age 29.4±2.4w; birth weight 1230±323 g). The scores for the habituation responses to the four stimuli progressively increased with advancing postconceptual age. At the age of 40 postconceptual weeks, the preterm infants were habituated to external stimuli similarly to the 51 studied term infants. The preterm infants showed higher habituation response scores for the rattle and bell stimuli than for the light and tactile stimuli.

CONCLUSIONS

Preterm infants improve their habituation responses to external stimuli as their postconceptual age increases, and, at 40 weeks of corrected age, they have similar responses to those exhibited by full-term infants in the first days of life.

Feminized behavior and brain gene expression in a novel mouse model of Klinefelter Syndrome

Klinefelter Syndrome (KS) is the most common sex chromosome aneuploidy in men and is characterized by the presence of an additional X chromosome (XXY). In some Klinefelter males, certain traits may be feminized or shifted from the male-typical pattern towards a more female-typical one. Among them might be partner choice, one of the most sexually dimorphic traits in the animal kingdom. We investigated the extent of feminization in XXY male mice (XXYM) in partner preference and gene expression in the bed nucleus of the stria terminalis/preoptic area and the striatum in mice from the Sex Chromosome Trisomy model. We tested for partner preference using a three-chambered apparatus in which the test mouse was free to choose between stimulus animals of either sex. We found that partner preference in XXYM was feminized. These differences were likely due to interactions of the additional X chromosome with the Y. We also discovered genes that differed in expression in XXYM versus XYM. Some of these genes are feminized in their expression pattern. Lastly, we also identified genes that differed only between XXYM versus XYM and not XXM versus XYM. Genes that are both feminized and unique to XXYM versus XYM represent strong candidates for dissecting the molecular pathways responsible for phenotypes present in KS/XXYM but not XXM. In sum, our results demonstrated that investigating behavioral and molecular feminization in XXY males can provide crucial information about the pathophysiology of KS and may aid our understanding of sex differences in brain and behavior.

Sex differences in Parkinson's disease

Parkinson's disease (PD) displays a greater prevalence and earlier age at onset in men. This review addresses the concept that sex differences in PD are determined, largely, by biological sex differences in the NSDA system which, in turn, arise from hormonal, genetic and environmental influences. Current therapies for PD rely on dopamine replacement strategies to treat symptoms, and there is an urgent, unmet need for disease modifying agents. As a significant degree of neuroprotection against the early stages of clinical or experimental PD is seen, respectively, in human and rodent females compared with males, a better understanding of brain sex dimorphisms in the intact and injured NSDA system will shed light on mechanisms which have the potential to delay, or even halt, the progression of PD. Available evidence suggests that sex-specific, hormone-based therapeutic agents hold particular promise for developing treatments with optimal efficacy in men and women.

Sex chromosome complement influences operant responding for a palatable food in mice

The procurement and consumption of palatable, calorie-dense foods is influenced by the nutritional and hedonic value of foods. Although many factors can influence the control over behavior by foods rich in sugar and fat, emerging evidence indicates that biological sex may play a particularly crucial role in the types of foods individuals seek out, as well as the level of motivation individuals will exert to obtain those foods. However, a systematic investigation of food-seeking and consumption that disentangles the effects of the major sex-biasing factors, including sex chromosome complement and organizational and activational effects of sex hormones, has yet to be conducted. Using the four core genotypes mouse model system, we separated and quantified the effects of sex chromosome complement and gonadal sex on consumption of and motivation to obtain a highly palatable solution [sweetened condensed milk (SCM)]. Gonadectomized mice with an XY sex chromosome complement, compared with those with two X chromosomes, independent of gonadal sex, appeared to be more sensitive to the reward value of the SCM solution and were more motivated to expend effort to obtain it, as evidenced by their dramatically greater expended effort in an instrumental task with progressively larger response-to-reward ratios. Gonadal sex independently affected free consumption of the solution but not motivation to obtain it. These data indicate that gonadal and chromosomal sex effects independently influence reward-related behaviors, contributing to sexually dimorphic patterns of behavior related to the pursuit and consumption of rewards.

The effects of perinatal testosterone exposure on the DNA methylome of the mouse brain are late-emerging

Background

The biological basis for sex differences in brain function and disease susceptibility is poorly understood. Examining the role of gonadal hormones in brain sexual differentiation may provide important information about sex differences in neural health and development. Permanent masculinization of brain structure, function, and disease is induced by testosterone prenatally in males, but the possible mediation of these effects by long-term changes in the epigenome is poorly understood.

Methods

We investigated the organizational effects of testosterone on the DNA methylome and transcriptome in two sexually dimorphic forebrain regions—the bed nucleus of the stria terminalis/preoptic area and the striatum. To study the contribution of testosterone to both the establishment and persistence of sex differences in DNA methylation, we performed genome-wide surveys in male, female, and female mice given testosterone on the day of birth. Methylation was assessed during the perinatal window for testosterone's organizational effects and in adulthood.

Results

The short-term effect of testosterone exposure was relatively modest. However, in adult animals the number of genes whose methylation was altered had increased by 20-fold. Furthermore, we found that in adulthood, methylation at a substantial number of sexually dimorphic CpG sites was masculinized in response to neonatal testosterone exposure. Consistent with this, testosterone's effect on gene expression in the striatum was more apparent in adulthood.

Conclusion

Taken together, our data imply that the organizational effects of testosterone on the brain methylome and transcriptome are dramatic and late-emerging. Our findings offer important insights into the long-term molecular effects of early-life hormonal exposure.

Triple comorbid trajectories of tobacco, alcohol, and marijuana use as predictors of antisocial personality disorder and generalized anxiety disorder among urban adults

OBJECTIVES

We modeled triple trajectories of tobacco, alcohol, and marijuana use from adolescence to adulthood as predictors of antisocial personality disorder (ASPD) and generalized anxiety disorder (GAD).

METHODS

We assessed urban African American and Puerto Rican participants (n = 816) in the Harlem Longitudinal Development Study, a psychosocial investigation, at 4 time waves (mean ages = 19, 24, 29, and 32 years). We used Mplus to obtain the 3 variable trajectories of tobacco, alcohol, and marijuana use from time 2 to time 5 and then conducted logistic regression analyses.

RESULTS

A 5-trajectory group model, ranging from the use of all 3 substances (23%) to a nonuse group (9%), best fit the data. Membership in the trajectory group that used all 3 substances was associated with an increased likelihood of both ASPD (adjusted odds ratio [AOR] = 6.83; 95% CI = 1.14, 40.74; P < .05) and GAD (AOR = 4.35; 95% CI = 1.63, 11.63; P < .001) in adulthood, as compared with the nonuse group, with control for earlier proxies of these conditions.

CONCLUSIONS

Adults with comorbid tobacco, alcohol, and marijuana use should be evaluated for use of other substances and for ASPD, GAD, and other psychiatric disorders. Treatment programs should address the use of all 3 substances to decrease the likelihood of comorbid psychopathology.

Measurement of androgen and estrogen concentrations in cord blood: accuracy, biological interpretation, and applications to understanding human behavioral development

Accurately measuring hormone exposure during prenatal life presents a methodological challenge and there is currently no "gold standard" approach. Ideally, circulating fetal hormone levels would be measured at repeated time points during pregnancy. However, it is not currently possible to obtain fetal blood samples without significant risk to the fetus, and therefore surrogate markers of fetal hormone levels must be utilized. Umbilical cord blood can be readily obtained at birth and largely reflects fetal circulation in late gestation. This review examines the accuracy and biological interpretation of the measurement of androgens and estrogens in cord blood. The use of cord blood hormones to understand and investigate human development is then discussed.

Influence of the X-chromosome on neuroanatomy: evidence from Turner and Klinefelter syndromes

Studies of sex effects on neurodevelopment have traditionally focused on animal models investigating hormonal influences on brain anatomy. However, more recent evidence suggests that sex chromosomes may also have direct upstream effects that act independently of hormones. Sex chromosome aneuploidies provide ideal models to examine this framework in humans, including Turner syndrome (TS), where females are missing one X-chromosome (45X), and Klinefelter syndrome (KS), where males have an additional X-chromosome (47XXY). As these disorders essentially represent copy number variants of the sex chromosomes, investigation of brain structure across these disorders allows us to determine whether sex chromosome gene dosage effects exist. We used voxel-based morphometry to investigate this hypothesis in a large sample of children in early puberty, to compare regional gray matter volumes among individuals with one (45X), two (typically developing 46XX females and 46XY males), and three (47XXY) sex chromosomes. Between-group contrasts of TS and KS groups relative to respective sex-matched controls demonstrated highly convergent patterns of volumetric differences with the presence of an additional sex chromosome being associated with relatively decreased parieto-occipital gray matter volume and relatively increased temporo-insular gray matter volumes. Furthermore, z-score map comparisons between TS and KS cohorts also suggested that this effect occurs in a linear dose-dependent fashion. We infer that sex chromosome gene expression directly influences brain structure in children during early stages of puberty, extending our understanding of genotype-phenotype mechanisms underlying sex differences in the brain.

Gender-specific association of the SLC6A4 and DRD2 gene variants in bipolar disorder

Findings on the association between the risk for developing bipolar disorder and the functions of the serotonin transporter-linked polymorphic region gene (5-HTTLPR) and dopamine D2 receptor gene (DRD2) variants are contradictory. One explanation for this is that a gender difference may exist for genetic contributions. We compared the gender-related main effects and the gene-to-gene interaction between serotonin transporter gene (SLC6A4) and DRD2 in adult male and female patients with bipolar I (BP-I) and bipolar II (BP-II) disorder. Patients with BP-I (n = 400) and BP-II (n = 493), and healthy controls (n = 442) were recruited from Taiwan's Han Chinese population. The genotypes of the 5-HTTLPR and DRD2 Taq-IA polymorphisms were determined using polymerase chain reaction-restriction fragment length polymorphism analysis. Logistic regression analysis showed a significant gender-specific association of the DRD2 A1/A1 and the 5-HTTLPR S/S, S/LG , and LG/LG (S+) (p = 0.01) genotypes in men with BP-I (p = 0.002 and 0.01, respectively) and BP-II (p = 0.001 and 0.007, respectively), but not in women. A significant interaction for the DRD2 A1/A1 and 5-HTTLPR S+ polymorphisms was also found only in men with BP-I and BP-II (p = 0.003 and 0.001, respectively). We provide preliminary evidence for a gender-specific effect of the SLC6A4 and DRD2 gene variants for the risk of BP-I and of BP-II. We also found gender-specific interaction between 5-HTTLPR and DRD2 Taq-IA polymorphisms in patients with bipolar disorder.