Gene regulation by gonadal hormone receptors underlies brain sex differences

Synaptic proteome perturbations after maternal immune activation: Identification of embryonic and adult hippocampal changes

BACKGROUND

Maternal immune activation (MIA) triggers neurobiological changes in offspring, potentially reshaping the molecular synaptic landscape, with the hippocampus being particularly vulnerable. However, critical details regarding developmental timing of these changes and whether they differ between males and females remain unclear.

METHODS

We induced MIA in C57BL/6J mice on gestational day nine using the viral mimetic poly(I:C) and performed mass spectrometry-based proteomic analyses on hippocampal synaptoneurosomes of embryonic (E18) and adult (20 ± 1 weeks) MIA offspring.

RESULTS

In the embryonic synaptoneurosomes, MIA led to lipid, polysaccharide, and glycoprotein metabolism pathway disruptions. In the adult synaptic proteome, we observed a dynamic shift toward transmembrane trafficking, intracellular signalling cascades, including cell death and growth, and cytoskeletal organisation. In adults, many associated pathways overlapped between males and females. However, we found distinct sex-specific enrichment of dopaminergic and glutamatergic pathways. We identified 50 proteins altered by MIA in both embryonic and adult samples (28 with the same directionality), mainly involved in presynaptic structure and synaptic vesicle function. We probed human phenome-wide association study data in the cognitive and psychiatric domains, and 49 of the 50 genes encoding these proteins were significantly associated with the investigated phenotypes.

CONCLUSIONS

Our data emphasise the dynamic effects of viral-like MIA on developing and mature hippocampi and provide novel targets for study following prenatal immune challenges. The 22 proteins that changed directionality from the embryonic to adult hippocampus, suggestive of compensatory over-adaptions, are particularly attractive for future investigations.

Microglia signaling in health and disease - Implications in sex-specific brain development and plasticity

Microglia, the intrinsic neuroimmune cells residing in the central nervous system (CNS), exert a pivotal influence on brain development, homeostasis, and functionality, encompassing critical roles during both aging and pathological states. Recent advancements in comprehending brain plasticity and functions have spotlighted conspicuous variances between male and female brains, notably in neurogenesis, neuronal myelination, axon fasciculation, and synaptogenesis. Nevertheless, the precise impact of microglia on sex-specific brain cell plasticity, sculpting diverse neural network architectures and circuits, remains largely unexplored. This article seeks to unravel the present understanding of microglial involvement in brain development, plasticity, and function, with a specific emphasis on microglial signaling in brain sex polymorphism. Commencing with an overview of microglia in the CNS and their associated signaling cascades, we subsequently probe recent revelations regarding molecular signaling by microglia in sex-dependent brain developmental plasticity, functions, and diseases. Notably, C-X3-C motif chemokine receptor 1 (CX3CR1), triggering receptors expressed on myeloid cells 2 (TREM2), calcium (Ca2+), and apolipoprotein E (APOE) emerge as molecular candidates significantly contributing to sex-dependent brain development and plasticity. In conclusion, we address burgeoning inquiries surrounding microglia's pivotal role in the functional diversity of developing and aging brains, contemplating their potential implications for gender-tailored therapeutic strategies in neurodegenerative diseases.

Adult sex change leads to extensive forebrain reorganization in clownfish

BACKGROUND

Sexual differentiation of the brain occurs in all major vertebrate lineages but is not well understood at a molecular and cellular level. Unlike most vertebrates, sex-changing fishes have the remarkable ability to change reproductive sex during adulthood in response to social stimuli, offering a unique opportunity to understand mechanisms by which the nervous system can initiate and coordinate sexual differentiation.

METHODS

This study explores sexual differentiation of the forebrain using single nucleus RNA-sequencing in the anemonefish Amphiprion ocellaris, producing the first cellular atlas of a sex-changing brain.

RESULTS

We uncover extensive sex differences in cell type-specific gene expression, relative proportions of cells, baseline neuronal excitation, and predicted inter-neuronal communication. Additionally, we identify the cholecystokinin, galanin, and estrogen systems as central molecular axes of sexual differentiation. Supported by these findings, we propose a model of sexual differentiation in the conserved vertebrate social decision-making network spanning multiple subtypes of neurons and glia, including neuronal subpopulations within the preoptic area that are positioned to regulate gonadal differentiation.

CONCLUSIONS

This work deepens our understanding of sexual differentiation in the vertebrate brain and defines a rich suite of molecular and cellular pathways that differentiate during adult sex change in anemonefish.

Sex-biasing influence of autism-associated Ube3a gene overdosage at connectomic, behavioral, and transcriptomic levels

Genomic mechanisms enhancing risk in males may contribute to sex bias in autism. The ubiquitin protein ligase E3A gene (Ube3a) affects cellular homeostasis via control of protein turnover and by acting as transcriptional coactivator with steroid hormone receptors. Overdosage of Ube3a via duplication or triplication of chromosomal region 15q11-13 causes 1 to 2% of autistic cases. Here, we test the hypothesis that increased dosage of Ube3a may influence autism-relevant phenotypes in a sex-biased manner. We show that mice with extra copies of Ube3a exhibit sex-biasing effects on brain connectomics and autism-relevant behaviors. These effects are associated with transcriptional dysregulation of autism-associated genes, as well as genes differentially expressed in 15q duplication and in autistic people. Increased Ube3a dosage also affects expression of genes on the X chromosome, genes influenced by sex steroid hormone, and genes sex-differentially regulated by transcription factors. These results suggest that Ube3a overdosage can contribute to sex bias in neurodevelopmental conditions via influence on sex-differential mechanisms.

Gender differences in gliomas: From epidemiological trends to changes at the hormonal and molecular levels

Gender plays a crucial role in the occurrence and development of cancer, as well as in the metabolism of nutrients and energy. Men and women display significant differences in the incidence, prognosis, and treatment response across various types of cancer, including certain sex-specific tumors. It has been observed that male glioma patients have a higher incidence and worse prognosis than female patients, but there is currently a limited systematic evaluation of sex differences in gliomas. The purpose of this study is to provide an overview of the association between fluctuations in sex hormone levels and changes in their receptor expression with the incidence, progression, treatment, and prognosis of gliomas. Estrogen may have a protective effect on glioma patients, while exposure to androgens increases the risk of glioma. We also discussed the specific genetic and molecular differences between genders in terms of the malignant nature and prognosis of gliomas. Factors such as TP53, MGMT methylation status may play a crucial role. Therefore, it is essential to consider the gender of patients while treating glioma, particularly the differences at the hormonal and molecular levels. This approach can help in the adoption of an individualized treatment strategy.

Androgen receptor alpha deficiency impacts aromatase expression in the female cichlid brain

Steroid hormones bind to specific receptors that act as transcription factors to modify gene expression in the brain to regulate physiological and behavioural processes. The specific genes controlled by steroid hormones in the brain are not fully known. Identifying these genes is integral to establishing a comprehensive understanding of how hormones impact physiology and behaviour. A popular organism for answering this question is the cichlid fish Astatotilapia burtoni. Recently, CRISPR/Cas9 was used to engineer A. burtoni that lack functional androgen receptor (AR) genes encoding ARα. ARα mutant male A. burtoni produced fewer aggressive displays and possessed reduced expression of the gene encoding brain-specific aromatase, cyp19a1, in the ventromedial hypothalamus (VMH), an aggression locus. As a follow-up, we investigated whether ARα deficiency affected cyp19a1 expression in female A. burtoni using the same genetic line. We find that female A. burtoni possessing one or two non-functional ARα alleles had much higher expression of cyp19a1 in the preoptic area (POA), while females with one non-functional ARα allele possessed lower expression of cyp19a1 in the putative fish homologue of the bed nucleus of the stria terminalis (BNST). Thus, ARα may have a sex-specific role in modifying cyp19a1 expression in the teleost POA and BNST, regions that underlie sex differences across vertebrates.

Sex mechanisms as nonbinary influences on cognitive diversity

Essentially all neuropsychiatric diagnoses show some degree of sex and/or gender differences in their etiology, diagnosis, or prognosis. As a result, the roles of sex-related variables in behavior and cognition are of strong interest to many, with several lines of research showing effects on executive functions and value-based decision making in particular. These findings are often framed within a sex binary, with behavior of females described as less optimal than male "defaults"-- a framing that pits males and females against each other and deemphasizes the enormous overlap in fundamental neural mechanisms across sexes. Here, we propose an alternative framework in which sex-related factors encompass just one subset of many sources of valuable diversity in cognition. First, we review literature establishing multidimensional, nonbinary impacts of factors related to sex chromosomes and endocrine mechanisms on cognition, focusing on value- based decision-making tasks. Next, we present two suggestions for nonbinary interpretations and analyses of sex-related data that can be implemented by behavioral neuroscientists without devoting laboratory resources to delving into mechanisms underlying sex differences. We recommend (1) shifting interpretations of behavior away from performance metrics and towards strategy assessments to avoid the fallacy that the performance of one sex is worse than another; and (2) asking how much variance sex explains in measures and whether any differences are mosaic rather than binary, to avoid assuming that sex differences in separate measures are inextricably correlated. Nonbinary frameworks in research on cognition will allow neuroscience to represent the full spectrum of brains and behaviors.

Androgen regulation of behavioral stress responses and the hypothalamic-pituitary-adrenal axis

Testosterone is a powerful steroid hormone that can impact the brain and behavior in various ways, including regulating behavioral and neuroendocrine (hypothalamic-pituitary-adrenal (HPA) axis) stress responses. Early in life androgens can act to alter development of brain regions associated with stress regulation, which ultimately impacts the display of stress responses later in life. Adult circulating androgens can also influence the expression of distinct genes and proteins that regulate stress responses. These changes in the brain are hypothesized to underlie the potent effects of androgens in regulating behaviors related to stress and stress-induced activation of the HPA axis. Androgens can induce alterations in these functions through direct binding to the androgen receptor (AR) or following conversion to estrogens and subsequent binding to estrogen receptors including estrogen receptor alpha (ERα), beta (ERβ), and G protein-coupled estrogen receptor 1 (GPER1). In this review, we focus on the role of androgens in regulating behavioral and neuroendocrine stress responses at different stages of the lifespan and the sex hormone receptors involved in regulating these effects. We also review the specific brain regions and cell phenotypes upon which androgens are proposed to act to regulate stress responses with an emphasis on hypothalamic and extended amygdala subregions. This knowledge of androgen effects on these neural systems is critical for understanding how sex hormones regulate stress responses.

Unveiling the potential of estrogen: Exploring its role in neuropsychiatric disorders and exercise intervention

Neuropsychiatric disorders shorten human life spans through multiple ways and become major threats to human health. Exercise can regulate the estrogen signaling, which may be involved in depression, Alzheimer's disease (AD) and Parkinson's disease (PD), and other neuropsychiatric disorders as well in their sex differences. In nervous system, estrogen is an important regulator of cell development, synaptic development, and brain connectivity. Therefore, this review aimed to investigate the potential of estrogen system in the exercise intervention of neuropsychiatric disorders to better understand the exercise in neuropsychiatric disorders and its sex specific. Exercise can exert a protective effect in neuropsychiatric disorders through regulating the expression of estrogen and estrogen receptors, which are involved in neuroprotection, neurodevelopment, and neuronal glucose homeostasis. These processes are mediated by the downstream factors of estrogen signaling, including N-myc downstream regulatory gene 2 (Ndrg2), serotonin (5-HT), delta like canonical Notch ligand 1 (DLL1), NOD-like receptor thermal protein domain associated protein 3 (NLRP3), etc. In addition, exercise can act on the estrogen response element (ERE) fragment in the genes of estrogenic downstream factors like β-amyloid precursor protein cleavase 1 (BACE1). However, there are few studies on the relationship between exercise, the estrogen signaling pathway, and neuropsychiatric disorders. Hence, we review how the estrogen signaling mediates the mechanism of exercise intervention in neuropsychiatric disorders. We aim to provide a theoretical perspective for neuropsychiatric disorders affecting female health and provide theoretical support for the design of exercise prescriptions.

Decoding the epigenetic mechanism of mammalian sex determination

Sex determination embodies a dynamic and intricate developmental process wielding significant influence over the destiny of bipotential gonads, steering them towards male or female gonads. Gonadal differentiation and the postnatal manifestation of the gonadal phenotype involve a sophisticated interplay of transcription factors such as SOX9 and FOXL2. Central to this interplay are chromatin modifiers regulating the mutual antagonism during this interplay. In this review, the key findings and knowledge gaps in DNA methylation, histone modification, and non-coding RNA-mediated control throughout mammalian gonadal development are covered. Furthermore, it explores the role of the developing brain in playing a pivotal role in the initiation of gonadogenesis and the subsequent involvement of gonadal hormone/hormone receptor in fine-tuning sexual differentiation. Based on promising facts, the role of the developing brain through the hypothalamic pituitary gonadal axis is explained and suggested as a novel hypothesis. The article also discusses the potential impact of ecological factors on the human epigenome in relation to sex determination and trans-generational epigenetics in uncovering novel genes and mechanisms involved in sex determination and gonadal differentiation. We have subtly emphasized the disruptions in epigenetic regulations contributing to sexual disorders, which further allows us to raise certain questions, decipher approaches for handling these questions and setting up the direction of future research.

Sexually dimorphic phenotypes and the role of androgen receptors in UBE3A-dependent autism spectrum disorder

Autism spectrum disorders (ASDs) are characterized by social, communication, and behavioral challenges. UBE3A is one of the most common ASD genes. ASDs display a remarkable sex difference with a 4:1 male to female prevalence ratio; however, the underlying mechanism remains largely unknown. Using the UBE3A-overexpressing mouse model for ASD, we studied sex differences at behavioral, genetic, and molecular levels. We found that male mice with extra copies of Ube3A exhibited greater impairments in social interaction, repetitive self-grooming behavior, memory, and pain sensitivity, whereas female mice with UBE3A overexpression displayed greater olfactory defects. Social communication was impaired in both sexes, with males making more calls and females preferring complex syllables. At the molecular level, androgen receptor (AR) levels were reduced in both sexes due to enhanced degradation mediated by UBE3A. However, AR reduction significantly dysregulated AR target genes only in male, not female, UBE3A-overexpressing mice. Importantly, restoring AR levels in the brain effectively normalized the expression of AR target genes, and rescued the deficits in social preference, grooming behavior, and memory in male UBE3A-overexpressing mice, without affecting females. These findings suggest that AR and its signaling cascade play an essential role in mediating the sexually dimorphic changes in UBE3A-dependent ASD.

Sexually dimorphic control of affective state processing and empathic behaviors

Recognizing the affective states of social counterparts and responding appropriately fosters successful social interactions. However, little is known about how the affective states are expressed and perceived and how they influence social decisions. Here, we show that male and female mice emit distinct olfactory cues after experiencing distress. These cues activate distinct neural circuits in the piriform cortex (PiC) and evoke sexually dimorphic empathic behaviors in observers. Specifically, the PiC → PrL pathway is activated in female observers, inducing a social preference for the distressed counterpart. Conversely, the PiC → MeA pathway is activated in male observers, evoking excessive self-grooming behaviors. These pathways originate from non-overlapping PiC neuron populations with distinct gene expression signatures regulated by transcription factors and sex hormones. Our study unveils how internal states of social counterparts are processed through sexually dimorphic mechanisms at the molecular, cellular, and circuit levels and offers insights into the neural mechanisms underpinning sex differences in higher brain functions.

Mechanisms of sex differences in Alzheimer's disease

Alzheimer's disease (AD) and the mechanisms underlying its etiology and progression are complex and multifactorial. The higher AD risk in women may serve as a clue to better understand these complicated processes. In this review, we examine aspects of AD that demonstrate sex-dependent effects and delve into the potential biological mechanisms responsible, compiling findings from advanced technologies such as single-cell RNA sequencing, metabolomics, and multi-omics analyses. We review evidence that sex hormones and sex chromosomes interact with various disease mechanisms during aging, encompassing inflammation, metabolism, and autophagy, leading to unique characteristics in disease progression between men and women.

Dietary restriction reveals sex-specific expression of the mTOR pathway genes in Japanese quails

Limited resources affect an organism's physiology through the conserved metabolic pathway, the mechanistic target of rapamycin (mTOR). Males and females often react differently to nutritional limitation, but whether it leads to differential mTOR pathway expression remains unknown. Recently, we found that dietary restriction (DR) induced significant changes in the expression of mTOR pathway genes in female Japanese quails (Coturnix japonica). We simultaneously exposed 32 male and female Japanese quails to either 20%, 30%, 40% restriction or ad libitum feeding for 14 days and determined the expression of six key genes of the mTOR pathway in the liver to investigate sex differences in the expression patterns. We found that DR significantly reduced body mass, albeit the effect was milder in males compared to females. We observed sex-specific liver gene expression. DR downregulated mTOR expression more in females than in males. Under moderate DR, ATG9A and RPS6K1 expressions were increased more in males than in females. Like females, body mass in males was correlated positively with mTOR and IGF1, but negatively with ATG9A and RS6K1 expressions. Our findings highlight that sexes may cope with nutritional deficits differently and emphasise the importance of considering sexual differences in studies of dietary restriction.

InSpectro-Gadget: A Tool for Estimating Neurotransmitter and Neuromodulator Receptor Distributions for MRS Voxels

Magnetic resonance spectroscopy (MRS) is widely used to estimate concentrations of glutamate and γ -aminobutyric acid (GABA) in specific regions of the living human brain. As cytoarchitectural properties differ across the brain, interpreting these measurements can be assisted by having knowledge of such properties for the MRS region(s) studied. In particular, some knowledge of likely local neurotransmitter receptor patterns can potentially give insights into the mechanistic environment GABA- and glutamatergic neurons are functioning in. This may be of particular utility when comparing two or more regions, given that the receptor populations may differ substantially across them. At the same time, when studying MRS data from multiple participants or timepoints, the homogeneity of the sample becomes relevant, as measurements taken from areas with different cytoarchitecture may be difficult to compare. To provide insights into the likely cytoarchitectural environment of user-defined regions-of-interest, we produced an easy to use tool - InSpectro-Gadget - that interfaces with receptor mRNA expression information from the Allen Human Brain Atlas. This Python tool allows users to input masks and automatically obtain a graphical overview of the receptor population likely to be found within. This includes comparison between multiple masks or participants where relevant. The receptors and receptor subunit genes featured include GABA- and glutamatergic classes, along with a wide range of neuromodulators. The functionality of the tool is explained here and its use is demonstrated through a set of example analyses. The tool is available at https://github.com/lizmcmanus/Inspectro-Gadget .

Role of estrogen in sex differences in memory, emotion and neuropsychiatric disorders

Estrogen regulates a wide range of neuronal functions in the brain, such as dendritic spine formation, remodeling of synaptic plasticity, cognition, neurotransmission, and neurodevelopment. Estrogen interacts with intracellular estrogen receptors (ERs) and membrane-bound ERs to produce its effect via genomic and non-genomic pathways. Any alterations in these pathways affect the number, size, and shape of dendritic spines in neurons associated with psychiatric diseases. Increasing evidence suggests that estrogen fluctuation causes changes in dendritic spine density, morphology, and synapse numbers of excitatory and inhibitory neurons differently in males and females. In this review, we discuss the role of estrogen hormone in rodents and humans based on sex differences. First, we explain estrogen role in learning and memory and show that a high estrogen level alleviates the deficits in learning and memory. Secondly, we point out that estrogen produces a striking difference in emotional memories in men and women, which leads them to display sex-specific differences in underlying neuronal signaling. Lastly, we discuss that fluctuations in estrogen levels in men and women are related to neuropsychiatric disorders, including schizophrenia, autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), bipolar disorder (BPD), major depressive disorder (MDD), substance use disorder (SUD), and anxiety disorders.

Let's talk about sex: Mechanisms of neural sexual differentiation in Bilateria

In multicellular organisms, sexed gonads have evolved that facilitate release of sperm versus eggs, and bilaterian animals purposefully combine their gametes via mating behaviors. Distinct neural circuits have evolved that control these physically different mating events for animals producing eggs from ovaries versus sperm from testis. In this review, we will describe the developmental mechanisms that sexually differentiate neural circuits across three major clades of bilaterian animals-Ecdysozoa, Deuterosomia, and Lophotrochozoa. While many of the mechanisms inducing somatic and neuronal sex differentiation across these diverse organisms are clade-specific rather than evolutionarily conserved, we develop a common framework for considering the developmental logic of these events and the types of neuronal differences that produce sex-differentiated behaviors. This article is categorized under: Congenital Diseases > Stem Cells and Development Neurological Diseases > Stem Cells and Development.

Estrogen-mediated individual differences in female rat voluntary running behavior

Regular exercise has numerous health benefits, but the human population displays significant variability in exercise participation. Rodent models, such as voluntary wheel running (VWR) in rats, can provide insight into the underlying mechanisms of exercise behavior and its regulation. In this study, we focused on the role of estrogen on VWR in female rats. Female rats run more than males, and we aimed to determine to what extent running levels in females were regulated by estrogen signaling. The running behavior of rats (duration, speed, and total distance run) was measured under normal physiological conditions, ovariectomy (OVX), and estrogen replacement in an OVX background. Results show cyclic variations in running linked to the estrous cycle. Ovariectomy markedly reduced running and eliminated the cyclic pattern. Estrogen replacement through estradiol benzoate (EB) injections and osmotic minipumps reinstated running activity to pre-OVX levels and restored the cyclic pattern. Importantly, individual differences and ranking are preserved such that high versus low runners before OVX remain high and low runners after treatment. Further analysis revealed that individual variation in running distance was primarily caused by rats running different speeds, but rats also varied in running duration. However, it is noteworthy that this model also displays features distinct from estrogen-driven running behavior under physiological conditions, notably a delayed onset and a broader duration of running activity. Collectively, this estrogen causality VWR model presents a unique opportunity to investigate sex-specific mechanisms that control voluntary physical activity.NEW & NOTEWORTHY This study investigates estrogen's role in voluntary wheel running (VWR) behavior in female rats. Female rats exhibit greater running than males, with estrogen signaling regulating this activity. The estrous cycle influences running, whereas ovariectomy reduces it, and estrogen replacement restores it, maintaining individual differences under all conditions. Both running speed and duration contribute to VWR variations. These findings emphasize individual estrogen regulation in female exercise and provide an estrogen replacement animal model for investigating neurobiological underpinnings that drive voluntary exercise behavior.

Region-specific transcriptomic responses to obesity and diabetes in macaque hypothalamus

The hypothalamus plays a crucial role in the progression of obesity and diabetes; however, its structural complexity and cellular heterogeneity impede targeted treatments. Here, we profiled the single-cell and spatial transcriptome of the hypothalamus in obese and sporadic type 2 diabetic macaques, revealing primate-specific distributions of clusters and genes as well as spatial region, cell-type-, and gene-feature-specific changes. The infundibular (INF) and paraventricular nuclei (PVN) are most susceptible to metabolic disruption, with the PVN being more sensitive to diabetes. In the INF, obesity results in reduced synaptic plasticity and energy sensing capability, whereas diabetes involves molecular reprogramming associated with impaired tanycytic barriers, activated microglia, and neuronal inflammatory response. In the PVN, cellular metabolism and neural activity are suppressed in diabetic macaques. Spatial transcriptomic data reveal microglia's preference for the parenchyma over the third ventricle in diabetes. Our findings provide a comprehensive view of molecular changes associated with obesity and diabetes.

Comparative analysis of gonadal hormone receptor expression in the postnatal house mouse, meadow vole, and prairie vole brain

The socially monogamous prairie vole (Microtus ochrogaster) and promiscuous meadow vole (Microtus pennsylvanicus) are closely related, but only prairie voles display long-lasting pair bonds, biparental care, and selective aggression towards unfamiliar individuals after pair bonding. These social behaviors in mammals are largely mediated by steroid hormone signaling in the social behavior network (SBN) of the brain. Hormone receptors are reproducible markers of sex differences that can provide more information than anatomy alone and can even be at odds with anatomical dimorphisms. We reasoned that behaviors associated with social monogamy in prairie voles may emerge in part from unique expression patterns of steroid hormone receptors in this species, and that these expression patterns would be more similar across males and females in prairie than in meadow voles or the laboratory mouse. To obtain insight into steroid hormone signaling in the developing prairie vole brain, we assessed expression of estrogen receptor alpha (Esr1), estrogen receptor beta (Esr2), and androgen receptor (Ar) within the SBN, using in situ hybridization at postnatal day 14 in mice, meadow, and prairie voles. We found species-specific patterns of hormone receptor expression in the hippocampus and ventromedial hypothalamus, as well as species differences in the sex bias of these markers in the principal nucleus of the bed nucleus of the stria terminalis. These findings suggest the observed differences in gonadal hormone receptor expression may underlie species differences in the display of social behaviors.

Adult sex change leads to extensive forebrain reorganization in clownfish

Sexual differentiation of the brain occurs in all major vertebrate lineages but is not well understood at a molecular and cellular level. Unlike most vertebrates, sex-changing fishes have the remarkable ability to change reproductive sex during adulthood in response to social stimuli, offering a unique opportunity to understand mechanisms by which the nervous system can initiate and coordinate sexual differentiation. This study explores sexual differentiation of the forebrain using single nucleus RNA-sequencing in the anemonefish Amphiprion ocellaris, producing the first cellular atlas of a sex-changing brain. We uncover extensive sex differences in cell type-specific gene expression, relative proportions of cells, baseline neuronal excitation, and predicted inter-neuronal communication. Additionally, we identify the cholecystokinin, galanin, and estrogen systems as central molecular axes of sexual differentiation. Supported by these findings, we propose a model of neurosexual differentiation in the conserved vertebrate social decision-making network spanning multiple subtypes of neurons and glia, including neuronal subpopulations within the preoptic area that are positioned to regulate gonadal differentiation. This work deepens our understanding of sexual differentiation in the vertebrate brain and defines a rich suite of molecular and cellular pathways that differentiate during adult sex change in anemonefish.

Multiomic analysis implicates nuclear hormone receptor signalling in clustering epilepsy

Clustering Epilepsy (CE) is an epileptic disorder with neurological comorbidities caused by heterozygous variants of the X chromosome gene Protocadherin 19 (PCDH19). Recent studies have implicated dysregulation of the Nuclear Hormone Receptor (NHR) pathway in CE pathogenesis. To obtain a comprehensive overview of the impact and mechanisms of loss of PCDH19 function in CE pathogenesis, we have performed epigenomic, transcriptomic and proteomic analysis of CE relevant models. Our studies identified differential regulation and expression of Androgen Receptor (AR) and its targets in CE patient skin fibroblasts. Furthermore, our cell culture assays revealed the repression of PCDH19 expression mediated through ERα and the co-regulator FOXA1. We also identified a protein-protein interaction between PCDH19 and AR, expanding upon the intrinsic link between PCDH19 and the NHR pathway. Together, these results point to a novel mechanism of NHR signaling in the pathogenesis of CE that can be explored for potential therapeutic options.

Sensory Input, Sex, and Function Shape Hypothalamic Cell Type Development

Mammalian behavior and physiology undergo dramatic changes in early life. Young animals rely on conspecifics to meet their homeostatic needs, until weaning and puberty initiate nutritional independence and sex-specific social interactions, respectively. How neuronal populations regulating homeostatic functions and social behaviors develop and mature during these transitions remains unclear. We used paired transcriptomic and chromatin accessibility profiling to examine the developmental trajectories of neuronal populations in the hypothalamic preoptic region, where cell types with key roles in physiological and behavioral control have been identified1-6. These data reveal a remarkable diversity of developmental trajectories shaped by the sex of the animal, and the location and behavioral or physiological function of the corresponding cell types. We identify key stages of preoptic development, including the perinatal emergence of sex differences, postnatal maturation and subsequent refinement of signaling networks, and nonlinear transcriptional changes accelerating at the time of weaning and puberty. We assessed preoptic development in various sensory mutants and find a major role for vomeronasal sensing in the timing of preoptic cell type maturation. These results provide novel insights into the development of neurons controlling homeostatic functions and social behaviors and lay ground for examining the dynamics of these functions in early life.

Epigenetic mechanisms underlying sex differences in the brain and behavior

Sex differences are found across brain regions, behaviors, and brain diseases. Sexual differentiation of the brain is initiated prenatally but it continues throughout life, as a result of the interaction of three major factors: gonadal hormones, sex chromosomes, and the environment. These factors are thought to act, in part, via epigenetic mechanisms which control chromatin and transcriptional states in brain cells. In this review, we discuss evidence that epigenetic mechanisms underlie sex-specific neurobehavioral changes during critical organizational periods, across the estrous cycle, and in response to diverse environments throughout life. We further identify future directions for the field that will provide novel mechanistic insights into brain sex differences, inform brain disease treatments and women's brain health in particular, and apply to people across genders.

Sex diversity in the 21st century: Concepts, frameworks, and approaches for the future of neuroendocrinology

Sex is ubiquitous and variable throughout the animal kingdom. Historically, scientists have used reductionist methodologies that rely on a priori sex categorizations, in which two discrete sexes are inextricably linked with gamete type. However, this binarized operationalization does not adequately reflect the diversity of sex observed in nature. This is due, in part, to the fact that sex exists across many levels of biological analysis, including genetic, molecular, cellular, morphological, behavioral, and population levels. Furthermore, the biological mechanisms governing sex are embedded in complex networks that dynamically interact with other systems. To produce the most accurate and scientifically rigorous work examining sex in neuroendocrinology and to capture the full range of sex variability and diversity present in animal systems, we must critically assess the frameworks, experimental designs, and analytical methods used in our research. In this perspective piece, we first propose a new conceptual framework to guide the integrative study of sex. Then, we provide practical guidance on research approaches for studying sex-associated variables, including factors to consider in study design, selection of model organisms, experimental methodologies, and statistical analyses. We invite fellow scientists to conscientiously apply these modernized approaches to advance our biological understanding of sex and to encourage academically and socially responsible outcomes of our work. By expanding our conceptual frameworks and methodological approaches to the study of sex, we will gain insight into the unique ways that sex exists across levels of biological organization to produce the vast array of variability and diversity observed in nature.

Precise Therapeutic Targeting of Distinct NRXN1+/- Mutations

As genetic studies continue to identify risk loci that are significantly associated with risk for neuropsychiatric disease, a critical unanswered question is the extent to which diverse mutations--sometimes impacting the same gene-- will require tailored therapeutic strategies. Here we consider this in the context of rare neuropsychiatric disorder-associated copy number variants (2p16.3) resulting in heterozygous deletions in NRXN1, a pre-synaptic cell adhesion protein that serves as a critical synaptic organizer in the brain. Complex patterns of NRXN1 alternative splicing are fundamental to establishing diverse neurocircuitry, vary between the cell types of the brain, and are differentially impacted by unique (non-recurrent) deletions. We contrast the cell-type-specific impact of patient-specific mutations in NRXN1 using human induced pluripotent stem cells, finding that perturbations in NRXN1 splicing result in divergent cell-type-specific synaptic outcomes. Via distinct loss-of-function (LOF) and gain-of-function (GOF) mechanisms, NRXN1+/- deletions cause decreased synaptic activity in glutamatergic neurons, yet increased synaptic activity in GABAergic neurons. Stratification of patients by LOF and GOF mechanisms will facilitate individualized restoration of NRXN1 isoform repertoires; towards this, antisense oligonucleotides knockdown mutant isoform expression and alters synaptic transcriptional signatures, while treatment with β-estradiol rescues synaptic function in glutamatergic neurons. Given the increasing number of mutations predicted to engender both LOF and GOF mechanisms in brain disease, our findings add nuance to future considerations of precision medicine.

Sex and interspecies differences in ESR2-expressing cell distributions in mouse and rat brains

BACKGROUND

ESR2, a nuclear estrogen receptor also known as estrogen receptor β, is expressed in the brain and contributes to the actions of estrogen in various physiological phenomena. However, its expression profiles in the brain have long been debated because of difficulties in detecting ESR2-expressing cells. In the present study, we aimed to determine the distribution of ESR2 in rodent brains, as well as its sex and interspecies differences, using immunohistochemical detection with a well-validated anti-ESR2 antibody (PPZ0506).

METHODS

To determine the expression profiles of ESR2 protein in rodent brains, whole brain sections from mice and rats of both sexes were subjected to immunostaining for ESR2. In addition, to evaluate the effects of circulating estrogen on ESR2 expression profiles, ovariectomized female mice and rats were treated with low or high doses of estrogen, and the resulting numbers of ESR2-immunopositive cells were analyzed. Welch's t-test was used for comparisons between two groups for sex differences, and one-way analysis of variance followed by the Tukey-Kramer test were used for comparisons among multiple groups with different estrogen treatments.

RESULTS

ESR2-immunopositive cells were observed in several subregions of mouse and rat brains, including the preoptic area, extended amygdala, hypothalamus, mesencephalon, and cerebral cortex. Their distribution profiles exhibited sex and interspecies differences. In addition, low-dose estrogen treatment in ovariectomized female mice and rats tended to increase the numbers of ESR2-immunopositive cells, whereas high-dose estrogen treatment tended to decrease these numbers.

CONCLUSIONS

Immunohistochemistry using the well-validated PPZ0506 antibody revealed a more localized expression of ESR2 protein in rodent brains than has previously been reported. Furthermore, there were marked sex and interspecies differences in its distribution. Our histological analyses also revealed estrogen-dependent changes in ESR2 expression levels in female brains. These findings will be helpful for understanding the ESR2-mediated actions of estrogen in the brain.

Evaluating the interplay between estrous cyclicity and flurothyl-induced seizure susceptibility in Scn2a K1422E mice

Recently, we demonstrated that Scn2a K1422E female mice showed a distinct distribution of flurothyl-induced seizure thresholds. To evaluate whether the estrous cycle contributes to this effect, estrous cycle monitoring was performed in mice that had undergone ovariectomy, sham surgery, or no treatment prior to seizure induction. Ovariectomy did not affect the non-unimodal distribution of flurothyl seizure thresholds observed in Scn2a K1422E females. Additionally, seizure thresholds were not associated with estrous cycle stage in mice that underwent sham surgery or in non-surgerized (intact) mice. Interestingly, intact Scn2a K1422E females showed evidence of disrupted estrous cyclicity, an effect not previously described in a genetic epilepsy model.

Minding the Gap: Exploring Neuroinflammatory and Microglial Sex Differences in Alzheimer's Disease

Research into Alzheimer's Disease (AD) describes a link between AD and the resident immune cells of the brain, the microglia. Further, this suspected link is thought to have underlying sex effects, although the mechanisms of these effects are only just beginning to be understood. Many of these insights are the result of policies put in place by funding agencies such as the National Institutes of Health (NIH) to consider sex as a biological variable (SABV) and the move towards precision medicine due to continued lackluster therapeutic options. The purpose of this review is to provide an updated assessment of the current research that summarizes sex differences and the research pertaining to microglia and their varied responses in AD.

Steroid hormone-mediated regulation of sexual and aggressive behaviour by non-genomic signalling

Sex and aggression are well studied examples of social behaviours that are common to most animals and are mediated by an evolutionary conserved group of interconnected nuclei in the brain called the social behaviour network. Though glucocorticoids and in particular estrogen regulate these social behaviours, their effects in the brain are generally thought to be mediated by genomic signalling, a slow transcriptional regulation mediated by nuclear hormone receptors. In the last decade or so, there has been renewed interest in understanding the physiological significance of rapid, non-genomic signalling mediated by steroids. Though the identity of the membrane hormone receptors that mediate this signalling is not clearly understood and appears to be different in different cell types, such signalling contributes to physiologically relevant behaviours such as sex and aggression. In this short review, we summarise the evidence for this phenomenon in the rodent, by focusing on estrogen and to some extent, glucocorticoid signalling. The use of these signals, in relation to genomic signalling is manifold and ranges from potentiation of transcription to the possible transduction of environmental signals.

Using Animal Models for Gender-Affirming Hormone Therapy

We have recently proposed experimental design guidelines and areas of study for preclinical rodent models of gender-affirming hormone therapy in neuroscience. These guidelines also apply to any field subject to the influences of gonadal steroid hormones, including metabolism and growth, cancer, and physiology. This perspective briefly describes our suggestions for these fields. Studying the effects of exogenous steroid hormones will have translational benefits for the community. We also discuss the need for equitable practices for cisgender scientists who wish to implement these guidelines and engage with the community. It is necessary that community-informed practices are implemented in preclinical research to maximize the benefit to transgender, nonbinary, and/or gender diverse (TNG) healthcare, which is currently in jeopardy in the United States, Europe, and across the globe.

Sexual dimorphic distribution of G protein-coupled receptor 30 in pain-related regions of the mouse brain

Sex differences in pain sensitivity have contributed to the fact that medications for curing chronic pain are unsatisfactory. However, the underlying mechanism remains to be elucidated. Brain-derived estrogen participates in modulation of sex differences in pain and related emotion. G protein-coupled receptor 30 (GPR30), identified as a novel estrogen receptor with a different distribution than traditional receptors, has been proved to play a vital role in regulating pain affected by estrogen. However, the contribution of its distribution to sexually dimorphic pain-related behaviors has not been fully explored. In the current study, immunofluorescence assays were applied to mark the neurons expressing GPR30 in male and female mice (in metestrus and proestrus phase) in pain-related brain regions. The neurons that express CaMKIIα or VGAT were also labeled to observe overlap with GPR30. We found that females had more GPR30-positive (GPR30+ ) neurons in the primary somatosensory (S1) and insular cortex (IC) than males. In the lateral habenula (LHb) and the nucleus tractus solitarius (NTS), males had more GPR30+ neurons than females. Moreover, within the LHb, the expression of GPR30 varied with estrous cycle phase; females in metestrus had fewer GPR30+ neurons than those in proestrus. In addition, females had more GPR30+ neurons, which co-expressed CaMKIIα in the medial preoptic nucleus (mPOA) than males, while males had more than females in the basolateral complex of the amygdala (BLA). These findings may partly explain the different modulatory effects of GPR30 in pain and related emotional phenotypes between sexes and provide a basis for comprehension of sexual dimorphism in pain related to estrogen and GPR30, and finally provide new targets for exploiting new treatments of sex-specific pain.

Sexual differentiation of neural mechanisms of stress sensitivity during puberty

Anxiety disorders are a major public health concern and current treatments are inadequate for many individuals. Anxiety is more common in women than men and this difference arises during puberty. Sex differences in physiological stress responses may contribute to this variability. During puberty, gonadal hormones shape brain structure and function, but the extent to which these changes affect stress sensitivity is unknown. We examined how pubertal androgens shape behavioral and neural responses to social stress in California mice (Peromyscus californicus), a model species for studying sex differences in stress responses. In adults, social defeat reduces social approach and increases social vigilance in females but not males. We show this sex difference is absent in juveniles, and that prepubertal castration sensitizes adult males to social defeat. Adult gonadectomy does not alter behavioral responses to defeat, indicating that gonadal hormones act during puberty to program behavioral responses to stress in adulthood. Calcium imaging in the medioventral bed nucleus of the stria terminalis (BNST) showed that social threats increased neural activity and that prepubertal castration generalized these responses to less threatening social contexts. These results support recent hypotheses that the BNST responds to immediate threats. Prepubertal treatment with the nonaromatizable androgen dihydrotestosterone acts in males and females to reduce the effects of defeat on social approach and vigilance in adults. These data indicate that activation of androgen receptors during puberty is critical for programming behavioral responses to stress in adulthood.

Nuclear lncRNA NORSF reduces E2 release in granulosa cells by sponging the endogenous small activating RNA miR-339

BACKGROUND

Functioning as a competing endogenous RNA (ceRNA) is the main action mechanism of most cytoplasmic lncRNAs. However, it is not known whether this mechanism of action also exists in the nucleus.

RESULTS

We identified four nuclear lncRNAs that are presented in granulosa cells (GCs) and were differentially expressed during sow follicular atresia. Notably, similar to cytoplasmic lncRNAs, these nuclear lncRNAs also sponge miRNAs in the nucleus of GCs through direct interactions. Furthermore, NORSF (non-coding RNA involved in sow fertility), one of the nuclear lncRNA acts as a ceRNA of miR-339. Thereby, it relieves the regulatory effect of miR-339 on CYP19A1 encoding P450arom, a rate-limiting enzyme for E2 synthesis in GCs. Interestingly, miR-339 acts as a saRNA that activates CYP19A1 transcription and enhances E2 release by GCs through altering histone modifications in the promoter by directly binding to the CYP19A1 promoter. Functionally, NORSF inhibited E2 release by GCs via the miR-339 and CYP19A1 axis.

CONCLUSIONS

Our findings highlight an unappreciated mechanism of nuclear lncRNAs and show it acts as a ceRNA, which may be a common lncRNA function in the cytoplasm and nucleus. We also identified a potential endogenous saRNA for improving female fertility and treating female infertility.

Molecular and cellular origins of behavioral sex differences: a tiny little fly tells a lot

Behavioral sex differences primarily derive from the sexually dimorphic organization of neural circuits that direct the behavior. In Drosophila melanogaster, the sex-determination genes fruitless (fru) and doublesex (dsx) play pivotal roles in producing the sexual dimorphism of neural circuits for behavior. Here we examine three neural groups expressing fru and/or dsx, i.e., the P1 cluster, aSP-f and aSP-g cluster pairs and aDN cluster, in which causal relationships between the dimorphic behavior and dimorphic neural characteristics are best illustrated. aSP-f, aSP-g and aDN clusters represent examples where fru or dsx switches cell-autonomously their neurite structures between the female-type and male-type. Processed sensory inputs impinging on these neurons may result in outputs that encode different valences, which culminate in the execution of distinct behavior according to the sex. In contrast, the P1 cluster is male-specific as its female counterpart undergoes dsx-driven cell death, which lowers the threshold for the induction of male-specific behaviors. We propose that the products of fru and dsx genes, as terminal selectors in sexually dimorphic neuronal wiring, induce and maintain the sex-typical chromatin state at postembryonic stages, orchestrating the transcription of effector genes that shape single neuron structures and govern cell survival and death.

Estrogen administration and withdrawal in a model of hormone-simulated pregnancy lead to alterations in behavior and gene expression but do not induce depression-like phenotypes in mice

Pregnancy and the post-partum period are associated with substantial fluctuations in hormone levels and are frequently associated with significant stress. Many individuals also experience affective disturbances during the peri‑partum period, including anxiety, the 'baby blues,' and post-partum depression. However, the extent to which these affective changes result from rapidly altering hormone levels, increased stress, or the combination of both remains largely unknown. The current study sought to evaluate the consequences of pregnancy-like hormonal changes on behavior and gene expression in c57BL/6 mice in the absence of stress using a hormone-simulated pregnancy model. Our results reveal that animals receiving hormone injections to simulate the high levels of estrogen observed in late pregnancy and animals withdrawn from estrogen to mimic the rapid decline in this hormone following parturition both exhibit increased anxiety-like behavior compared to ovariectomized controls in the novel open field test. However, no other significant anxiety- or depression-like alterations were observed in either hormone-treated group compared to ovariectomized controls. Both hormone administration and estrogen withdrawal were shown to induce several significant alterations in gene expression in the bed nucleus of the stria terminalis and the paraventricular nucleus of the hypothalamus. In contrast to the estrogen withdrawal hypothesis of post-partum depression, our results suggest that this method estrogen withdrawal following hormone-simulated pregnancy in the absence of stress does not induce phenotypes consistent with post-partum depression in c57BL/6 mice. However, given that estrogen withdrawal does lead to significant gene expression changes in two stress-sensitive brain regions, it remains possible that estrogen withdrawal could still contribute to affective dysregulation in the peri-partum period by influencing susceptibility to stress. Future research is required to evaluate this possibility.

Distribution and length of muscle spindles and their 3D visualisation in the medial gastrocnemius of male and female rats

The spatial distribution of the medial gastrocnemius muscle spindles of 10 male and 10 female rats was analysed under a light microscope, and for the first time, visualised using a 3D model of the muscle. Serial cross-sections of the medial gastrocnemius muscles were separated into 10 divisions along with the proximo-distal axis. The muscle spindles of the rat medial gastrocnemius were predominantly distributed on the proximo-medial divisions of the muscle. There were no sex-related differences in the distribution of the studied receptors. A single division contained an average of 2.71 receptors for animals of both sexes. Moreover, the calculated lengths of male and female rat muscle spindles were comparable, and average lengths did not significantly differ (3.30 ± 1.47 mm for male and 3.26 ± 1.32 mm for female rats). Therefore, the present results fill gaps in recent observations concerning similarities in muscle spindle numbers between male and female animals, despite significant differences in muscle mass and size.

Celf4 controls mRNA translation underlying synaptic development in the prenatal mammalian neocortex

Abnormalities in neocortical and synaptic development are linked to neurodevelopmental disorders. However, the molecular and cellular mechanisms governing initial synapse formation in the prenatal neocortex remain poorly understood. Using polysome profiling coupled with snRNAseq on human cortical samples at various fetal phases, we identify human mRNAs, including those encoding synaptic proteins, with finely controlled translation in distinct cell populations of developing frontal neocortices. Examination of murine and human neocortex reveals that the RNA binding protein and translational regulator, CELF4, is expressed in compartments enriched in initial synaptogenesis: the marginal zone and the subplate. We also find that Celf4/CELF4-target mRNAs are encoded by risk genes for adverse neurodevelopmental outcomes translating into synaptic proteins. Surprisingly, deleting Celf4 in the forebrain disrupts the balance of subplate synapses in a sex-specific fashion. This highlights the significance of RNA binding proteins and mRNA translation in evolutionarily advanced synaptic development, potentially contributing to sex differences.

Sex Differences in the Neurobiology of Stress

This review highlights the existing knowledge and data that explain the physiologic impacts of stress, especially pertaining to neurobiology, and how these impacts differ by sex. Furthermore, this review explains the benefits of interventions aimed at preventing or mitigating the adverse effects of stress, because of both the significant toll of stress on the body and the disproportionate impact of these changes experienced by women.

Pheromone Perception in Fish: Mechanisms and Modulation by Internal Status

Pheromones are chemical signals that facilitate communication between animals, and most animals use pheromones for reproduction and other forms of social behavior. The identification of key ligands and olfactory receptors used for pheromonal communication provides insight into the sensory processing of these important cues. An individual's responses to pheromones can be plastic, as physiological status modulates behavioral outputs. In this review, we outline the mechanisms for pheromone sensation and highlight physiological mechanisms that modify pheromone-guided behavior. We focus on hormones, which regulate pheromonal communication across vertebrates including fish, amphibians, and rodents. This regulation may occur in peripheral olfactory organs and the brain, but the mechanisms remain unclear. While this review centers on research in fish, we will discuss other systems to provide insight into how hormonal mechanisms function across taxa.

Estrogen-responsive neural circuits governing male and female mating behavior in mice

Decades of knockout analyses have highlighted the crucial involvement of estrogen receptors and downstream genes in controlling mating behaviors. More recently, advancements in neural circuit research have unveiled a distributed subcortical network comprising estrogen-receptor or estrogen-synthesis-enzyme-expressing cells that transforms sensory inputs into sex-specific mating actions. This review provides an overview of the latest discoveries on estrogen-responsive neurons in various brain regions and the associated neural circuits that govern different aspects of male and female mating actions in mice. By contextualizing these findings within previous knockout studies of estrogen receptors, we emphasize the emerging field of "circuit genetics", where identifying mating behavior-related neural circuits may allow for a more precise evaluation of gene functions within these circuits. Such investigations will enable a deeper understanding of how hormone fluctuation, acting through estrogen receptors and downstream genes, influences the connectivity and activity of neural circuits, ultimately impacting the manifestation of innate mating actions.

Sex differences in alpha-synucleinopathies: a systematic review

Background

Past research indicates a higher prevalence, incidence, and severe clinical manifestations of alpha-synucleinopathies in men, leading to a suggestion of neuroprotective properties of female sex hormones (especially estrogen). The potential pathomechanisms of any such effect on alpha-synucleinopathies, however, are far from understood. With that aim, we undertook to systematically review, and to critically assess, contemporary evidence on sex and gender differences in alpha-synucleinopathies using a bench-to-bedside approach.

Methods

In this systematic review, studies investigating sex and gender differences in alpha-synucleinopathies (Rapid Eye Movement (REM) Behavior Disorder (RBD), Parkinson's Disease (PD), Dementia with Lewy Bodies (DLB), Multiple System Atrophy (MSA)) from 2012 to 2022 were identified using electronic database searches of PubMed, Embase and Ovid.

Results

One hundred sixty-two studies were included; 5 RBD, 6 MSA, 20 DLB and 131 PD studies. Overall, there is conclusive evidence to suggest sex-and gender-specific manifestation in demographics, biomarkers, genetics, clinical features, interventions, and quality of life in alpha-synucleinopathies. Only limited data exists on the effects of distinct sex hormones, with majority of studies concentrating on estrogen and its speculated neuroprotective effects.

Conclusion

Future studies disentangling the underlying sex-specific mechanisms of alpha-synucleinopathies are urgently needed in order to enable novel sex-specific therapeutics.

Neural Control of Sexually Dimorphic Social Behavior: Connecting Development to Adulthood

Rapid advances in the neural control of social behavior highlight the role of interconnected nodes engaged in differential information processing to generate behavior. Many innate social behaviors are essential to reproductive fitness and therefore fundamentally different in males and females. Programming these differences occurs early in development in mammals, following gonadal differentiation and copious androgen production by the fetal testis during a critical period. Early-life programming of social behavior and its adult manifestation are separate but yoked processes, yet how they are linked is unknown. This review seeks to highlight that gap by identifying four core mechanisms (epigenetics, cell death, circuit formation, and adult hormonal modulation) that could connect developmental changes to the adult behaviors of mating and aggression. We further propose that a unique social behavior, adolescent play, bridges the preweaning to the postpubertal brain by engaging the same neural networks underpinning adult reproductive and aggressive behaviors.

Embryonic and adult synaptic proteome perturbations after maternal immune activation: Identification of persistent changes relevant for early intervention

Maternal infections during pregnancy pose an increased risk for neurodevelopmental psychiatric disorders (NPDs) in the offspring. Here, we examined age- and sex-dependent dynamic changes of the hippocampal synaptic proteome after maternal immune activation (MIA) in embryonic and adult mice. Adult male and female MIA offspring exhibited social deficits and sex-specific depression-like behaviours, among others, validating the model. Furthermore, we observed dose-, age-, and sex-dependent synaptic proteome differences. Analysis of the embryonic synaptic proteome implicates sphingolipid and ketoacid metabolism pathway disruptions during neurodevelopment for NPD-pertinent sequelae. In the embryonic hippocampus, prenatal immune activation also led to changes in neuronal guidance, glycosphingolipid metabolism important for signalling and myelination, and post-translational modification of proteins that regulate intercellular interaction and developmental timing. In adulthood, the observed changes in synaptoneurosomes revealed a dynamic shift toward transmembrane trafficking, intracellular signalling cascades, and hormone-mediated metabolism. Importantly, 68 of the proteins with differential abundance in the embryonic brains of MIA offspring were also altered in adulthood, 75% of which retained their directionality. These proteins are involved in synaptic organisation, neurotransmitter receptor regulation, and the vesicle cycle. A cluster of persistently upregulated proteins, including AKT3, PAK1/3, PPP3CA, formed a functional network enriched in the embryonic brain that is involved in cellular responses to environmental stimuli. To infer a link between the overlapping protein alterations and cognitive and psychiatric traits, we probed human phenome-wise association study data for cognitive and psychiatric phenotypes and all, but PORCN were significantly associated with the investigated domains. Our data provide insights into the dynamic effects of an early prenatal immune activation on developing and mature hippocampi and highlights targets for early intervention in individuals exposed to such immune challenges.

Esr1+ hypothalamic-habenula neurons shape aversive states

Excitatory projections from the lateral hypothalamic area (LHA) to the lateral habenula (LHb) drive aversive responses. We used patch-sequencing (Patch-seq) guided multimodal classification to define the structural and functional heterogeneity of the LHA-LHb pathway. Our classification identified six glutamatergic neuron types with unique electrophysiological properties, molecular profiles and projection patterns. We found that genetically defined LHA-LHb neurons signal distinct aspects of emotional or naturalistic behaviors, such as estrogen receptor 1-expressing (Esr1⁺) LHA-LHb neurons induce aversion, whereas neuropeptide Y-expressing (Npy⁺) LHA-LHb neurons control rearing behavior. Repeated optogenetic drive of Esr1⁺ LHA-LHb neurons induces a behaviorally persistent aversive state, and large-scale recordings showed a region-specific neural representation of the aversive signals in the prelimbic region of the prefrontal cortex. We further found that exposure to unpredictable mild shocks induced a sex-specific sensitivity to develop a stress state in female mice, which was associated with a specific shift in the intrinsic properties of bursting-type Esr1⁺ LHA-LHb neurons. In summary, we describe the diversity of LHA-LHb neuron types and provide evidence for the role of Esr1⁺ neurons in aversion and sexually dimorphic stress sensitivity.

Temporal transitions in the postembryonic nervous system of the nematode Caenorhabditis elegans: Recent insights and open questions

After the generation, differentiation and integration into functional circuitry, post-mitotic neurons continue to change certain phenotypic properties throughout postnatal juvenile stages until an animal has reached a fully mature state in adulthood. We will discuss such changes in the context of the nervous system of the nematode C. elegans, focusing on recent descriptions of anatomical and molecular changes that accompany postembryonic maturation of neurons. We summarize the characterization of genetic timer mechanisms that control these temporal transitions or maturational changes, and discuss that many but not all of these transitions relate to sexual maturation of the animal. We describe how temporal, spatial and sex-determination pathways are intertwined to sculpt the emergence of cell-type specific maturation events. Finally, we lay out several unresolved questions that should be addressed to move the field forward, both in C. elegans and in vertebrates.

Sex and Brain: The Role of Sex Chromosomes and Hormones in Brain Development and Parkinson's Disease

Sex hormones and genes on the sex chromosomes are not only key factors in the regulation of sexual differentiation and reproduction but they are also deeply involved in brain homeostasis. Their action is crucial for the development of the brain, which presents different characteristics depending on the sex of individuals. The role of these players in the brain is fundamental in the maintenance of brain function during adulthood as well, thus being important also with respect to age-related neurodegenerative diseases. In this review, we explore the role of biological sex in the development of the brain and analyze its impact on the predisposition toward and the progression of neurodegenerative diseases. In particular, we focus on Parkinson's disease, a neurodegenerative disorder that has a higher incidence in the male population. We report how sex hormones and genes encoded by the sex chromosomes could protect from the disease or alternatively predispose toward its development. We finally underline the importance of considering sex when studying brain physiology and pathology in cellular and animal models in order to better understand disease etiology and develop novel tailored therapeutic strategies.

Distribution of estrogen receptors alpha and beta in the brain of male rats with same-sex preference

Two distinct estrogen receptors (ERs) exist, ERα and ERβ. Both receptors participate in the sexual differentiation of the rat brain and likely participate in the regulation of adult sexual orientation (i.e. partner preference). This last idea was investigated herein by examining males treated with the aromatase inhibitor, letrozole, administered prenatally (0.56 μg/kg G10-22). This treatment usually provokes same-sex preference in 1-2 males per litter. Vehicle-treated males (with female preference) and females in spontaneous proestrus (with male preference) were included as controls. ERα and ERβ expression was analyzed by immunohistochemistry in brain areas known to control masculine sexual behavior and partner preference, like the medial preoptic area (MPOA), bed nucleus of the stria terminalis (BNST), medial amygdala (MeA) and ventromedial hypothalamic nucleus (VMH), as well as other brain regions suspected to participate in these processes. In addition, serum levels of estradiol were determined in all male groups. Letrozole-treated male rats that preferred sexually experienced males (LPM) showed over-expressed ERα in the hippocampal cornu Ammonis (CA 1, 3, 4) and dentate gyrus. The LPM group showed up-regulated ERβ expression in the CA2 and reticular thalamic nucleus. The levels of estradiol did not differ between the groups. The higher expression of ERs in these males was different than their expression in females, with male sex-preference. This suggests that males with same-sex preference showed a unique brain, this sui generis steroid receptor expression probably participates in the biological underpinnings of sexual preference.

Evaluating the interplay between estrous cyclicity and induced seizure susceptibility in Scn2aK1422E mice

Pathogenic variants in SCN2A are associated with a range of neurodevelopmental disorders (NDD). SCN2A-related NDD show wide phenotypic heterogeneity, suggesting that modifying factors must be considered in order to properly elucidate the mechanisms of pathogenic variants. Recently, we characterized neurological phenotypes in a mouse model of the variant SCN2A-p.K1422E. We demonstrated that heterozygous Scn2aK1422E female mice showed a distinct, reproducible distribution of flurothyl-induced seizure thresholds. Women with epilepsy often show a cyclical pattern of altered seizure susceptibility during specific phases of the menstrual cycle which can be attributed to fluctuations in hormones and corresponding changes in neurosteroid levels. Rodent models have been used extensively to examine the relationship between the estrous (menstrual) cycle, steroid hormones, and seizure susceptibility. However, the effects of the estrous cycle on seizure susceptibility have not been evaluated in the context of an epilepsy-associated genetic variant. To determine whether the estrous cycle affects susceptibility to flurothyl-induced seizures in Scn2aK1422E female mice, estrous cycle monitoring was performed in mice that had undergone ovariectomy (OVX), sham surgery, or no treatment prior to seizure induction. Removing the influence of circulating sex hormones via OVX did not affect the non-unimodal distribution of flurothyl seizure thresholds observed in Scn2aK1422E females. Additionally, flurothyl seizure thresholds were not associated with estrous cycle stage in mice that underwent sham surgery or were untreated. These data suggest that variation in Scn2aK1422E flurothyl seizure threshold is not significantly influenced by the estrous cycle and, by extension, fluctuations in ovarian hormones. Interestingly, untreated Scn2aK1422E females showed evidence of disrupted estrous cyclicity, an effect not previously described in a genetic epilepsy model. This unexpected result highlights the importance of considering sex specific effects and the estrous cycle in support of more inclusive biomedical research.