Long-lasting masculinizing effects of postnatal androgens on myelin governed by the brain androgen receptor

Disrupted Maturation of White Matter Microstructure After Concussion Is Associated With Internalizing Behavior Scores in Female Children

BACKGROUND

Some children who experience concussions, particularly females, develop long-lasting emotional and behavioral problems. Establishing the potential contribution of preexisting behavioral problems and disrupted white matter maturation has been challenging due to a lack of preinjury data.

METHODS

From the Adolescent Brain Cognitive Development cohort, 239 (90 female) children age 12.1 ± 0.6 years who experienced a concussion after study entry at 10.0 ± 0.6 years were compared to 6438 (3245 female) children without head injuries who were age 9.9 ± 0.6 years at baseline and 12.0 ± 0.6 years at follow-up. The Child Behavior Checklist was used to assess internalizing and externalizing behavior at study entry and follow-up. In the children with magnetic resonance imaging data available (concussion n = 134, comparison n = 3520), deep and superficial white matter was characterized by neurite density from restriction spectrum image modeling of diffusion magnetic resonance imaging. Longitudinal ComBat harmonization removed scanner effects. Linear regressions modeled 1) behavior problems at follow-up controlling for baseline behavior, 2) impact of concussion on white matter maturation, and 3) contribution of deviations in white matter maturation to postconcussion behavior problems.

RESULTS

Only female children with concussion had higher internalizing behavior problem scores. The youngest children with concussion showed less change in superficial white matter neurite density over 2 years than children with no concussion. In females with concussion, less change in superficial white matter neurite density was correlated with increased internalizing behavior problem scores.

CONCLUSIONS

Concussions in female children are associated with emotional problems beyond preinjury levels. Injury to superficial white matter may contribute to persistent internalizing behavior problems in females.

Within-person biological mechanisms of mood variability in childhood and adolescence

Mood variability, the day-to-day fluctuation in mood, differs between individuals and develops during adolescence. Because adolescents show higher mood variability and average mood than children and adults, puberty might be a potential biological mechanism underlying this increase. The goal of this preregistered developmental study was to examine the neural and hormonal underpinnings of adolescent-specific within-person changes in mood variability, with a specific focus on testosterone, cortisol, pubertal status, and resting-state functional brain connectivity. Data from two longitudinal cohorts were used: the L-CID twin study (aged 7-13, N at the first timepoint = 258) and the accelerated Leiden Self-Concept study (SC; aged 11-21, N at the first timepoint = 138). In both studies resting-state functional magnetic resonance imaging (rs-fMRI) data was collected, as well as daily mood. Additionally, in the SC study self-reported puberty testosterone and cortisol were collected. Random intercept cross-lagged panel models (RI-CLPM) were used to study the within-person relations between these biological measures and mood variability and average mood. Mood variability and average mood peaked in adolescence and testosterone levels and self-reported puberty also showed an increase. Connectivity between prefrontal cortex (dlPFC and vmPFC) and subcortical regions (caudate, amygdala) decreased across development. Moreover, higher testosterone predicted average negative mood at the next time point, but not vice versa. Further, stronger vmPFC-amygdala functional connectivity predicted decreases in mood variability. Here, we show that brain connectivity during development is an important within-person biological mechanism of the development of mood in adolescents. PRACTITIONER POINTS: Mood variability peaks in adolescence. Within-person changes in testosterone predict within-person changes in mood. Within-person changes in vmPFC-amygdala connectivity predict within-person changes in mood variability.

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.

Testosterone Reduces Myelin Abnormalities in the Wobbler Mouse Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal motoneuron degenerative disease that is associated with demyelination. The Wobbler (WR) mouse exhibits motoneuron degeneration, gliosis and myelin deterioration in the cervical spinal cord. Since male WRs display low testosterone (T) levels in the nervous system, we investigated if T modified myelin-relative parameters in WRs in the absence or presence of the aromatase inhibitor, anastrozole (A). We studied myelin by using luxol-fast-blue (LFB) staining, semithin sections, electron microscopy and myelin protein expression, density of IBA1+ microglia and mRNA expression of inflammatory factors, and the glutamatergic parameters glutamine synthetase (GS) and the transporter GLT1. Controls and WR + T showed higher LFB, MBP and PLP staining, lower g-ratios and compact myelin than WRs and WR + T + A, and groups showing the rupture of myelin lamellae. WRs showed increased IBA1+ cells and mRNA for CD11b and inflammatory factors (IL-18, TLR4, TNFαR1 and P2Y12R) vs. controls or WR + T. IBA1+ cells, and CD11b were not reduced in WR + T + A, but inflammatory factors' mRNA remained low. A reduction of GS+ cells and GLT-1 immunoreactivity was observed in WRs and WR + T + A vs. controls and WR + T. Clinically, WR + T but not WR + T + A showed enhanced muscle mass, grip strength and reduced paw abnormalities. Therefore, T effects involve myelin protection, a finding of potential clinical translation.

Interplay between androgen and CXCR4 chemokine signaling in myelin repair

In men, reduced levels of testosterone are associated with the prevalence and progression of multiple sclerosis (MS), a chronic and disabling demyelinating disorder. Testosterone has been shown to promote myelin repair. Here, we demonstrate that the cooperation between testosterone and CXCR4 signaling involving astrocytes is required for myelin regeneration after focal demyelination produced in the ventral mouse spinal cord by the infusion of lysolecithin. The testosterone-dependent remyelination of axons by oligodendrocytes was accompanied by an increase in astrocytes expressing CXCR4, its ligand CXCL12 and the androgen receptor (AR) within the demyelinated area. Depriving males of their testosterone or pharmacological inhibition of CXCR4, with the selective antagonist AMD3100, prevented the appearance of astrocytes expressing CXCR4, CXCL12 and AR within the demyelinated area and the concomitant recruitment of myelin forming oligodendrocytes. Conditional genetic ablation of either CXCR4 or AR in astrocytes also completely blocked the formation of new myelin by oligodendrocytes. Interestingly, the gain of function mutation in CXCR4 causing WHIM syndrome allows remyelination to take place, even in the absence of testosterone, but its potentiating effects remained observable. After testosterone deprivation or CXCR4 inhibition, the absence of astrocytes within the demyelinated area led to the incursion of Schwann cells, most likely derived from spinal nerves, and the formation of peripheral nerve type myelin. In patients with progressive MS, astrocytes expressing CXCR4 and AR surrounded myelin lesions, and their presence opposed the incursion of Schwann cells. These results highlight a mechanism of promyelinating testosterone signaling and the importance of normalizing its levels in combined myelin repair therapies.

Differential induction of C6 glioma apoptosis and autophagy by 3β-hydroxysteroid-indolamine conjugates

In a previous work, we reported the synthesis of four novel indole steroids and their effect on rat C6 glioma proliferation in vitro. The steroid derived from dehydroepiandrosterone and tryptamine (IS-1) was the most active (52 % inhibition at 10 µM), followed by one of the epimers derived from pregnenolone and tryptamine (IS-3, 36 % inhibition at 10 µM). By contrast, the steroid derived from estrone and tryptamine (IS-2) showed negligible activity at 10 µM. No necrosis, increase in intracellular calcium or ROS levels was observed. In this work, the effect of compounds on C6 glioma apoptosis and autophagy is examined by fluorimetry and fluorescent microscopy. The IS-3 epimers disrupt the mitochondrial membrane potential and induce apoptosis in vitro moderately whereas IS-1 and IS-2 do not. However, IS-1 produces a large increase in monodansylcadaverine-positive autophagic vesicles over 24 h. The antiproliferative effect of indole steroids is ameliorated by autophagy inhibitor hydroxychloroquine, suggesting an autophagy-dependent mechanism of cell death.

Sex, myelin, and clinical characteristics of Parkinson's disease

Objective

To determine if there are sex differences in myelin in Parkinson's disease, and whether these explain some of the previously-described sex differences in clinical presentation.

Methods

Thirty-three subjects (23 males, 10 females) with Parkinson's disease underwent myelin water fraction (MWF) imaging, an MRI scanning technique of in vivo myelin content. MWF of 20 white matter regions of interest (ROIs) were assessed. Motor symptoms were assessed using the Unified Parkinson's Disease Rating Scale (UPDRS). Principal component analysis, logistic and multiple linear regressions, and t-tests were used to determine which white matter ROIs differed between sexes, the clinical features associated with these myelin changes, and if overall MWF and MWF laterality differed between males and females.

Results

Consistent with prior reports, tremor and bradykinesia were more likely seen in females, whereas rigidity and axial symptoms were more likely seen in males in our cohort. MWF of the thalamic radiation, cingulum, cingulum hippocampus, inferior fronto-occipital fasciculi, inferior longitudinal fasciculi, and uncinate were significant in predicting sex. Overall MWF and asymmetry of MWF was greater in males. MWF differences between sexes were associated with tremor symptomatology and asymmetry of motor performance.

Conclusion

Sex differences in myelin are associated with tremor and asymmetry of motor presentation. While preliminary, our results suggest that further investigation of the role of biological sex in myelin pathology and clinical presentation in Parkinson's disease is warranted.

Cortical Structure Differences in Relation to Age, Sexual Attractions, and Gender Dysphoria in Adolescents: An Examination of Mean Diffusivity and T1 Relaxation Time

Recent research found that the combination of masculine gender identity and gynephilia was associated with cortical T1 relaxation time, which is considered to reflect gray matter density. We hypothesized that mean diffusivity (MD), a diffusion tensor imaging metric that reflects the degree to which water movement is free versus constrained, in combination with T1 relaxation time would provide further insight regarding cortical tissue characteristics. MD and T1 relaxation time were measured in 76 cortical regions in 15 adolescents assigned female at birth who experience gender dysphoria (GD AFAB) and were not receiving hormone therapy, 17 cisgender girls, and 14 cisgender boys (ages 12-17 years). Sexual orientation was represented by the degree of androphilia-gynephilia and the strength of sexual attraction. In multivariate analyses, cortical T1 relaxation time showed a weak but statistically significant positive association with MD across the cortex, suggesting that macromolecule-rich cortical tissue also tends to show water movement that is somewhat more constrained. In further multivariate analyses, in several left frontal, parietal, and temporal regions, the combination of shorter T1 relaxation time and faster MD was associated with older age and greater gynephilia in GD AFAB individuals and cisgender boys and with stronger attractions in cisgender boys only. Thus, for these cortical regions in these groups, older age, gynephilia, and stronger attractions (cisgender boys only) were associated with macromolecule-rich tissue in which water movement was freer-a pattern that some prior research suggests is associated with greater cell density and size. Overall, this study indicates that investigating T1 relaxation time and MD together can further inform how cortical gray matter tissue characteristics relate to age and psychosexuality.

Sex differences in the effects of high fat diet on underlying neuropathology in a mouse model of VCID

BACKGROUND

Damage to the cerebral vasculature can lead to vascular contributions to cognitive impairment and dementia (VCID). A reduction in blood flow to the brain leads to neuropathology, including neuroinflammation and white matter lesions that are a hallmark of VCID. Mid-life metabolic disease (obesity, prediabetes, or diabetes) is a risk factor for VCID which may be sex-dependent (female bias).

METHODS

We compared the effects of mid-life metabolic disease between males and females in a chronic cerebral hypoperfusion mouse model of VCID. C57BL/6J mice were fed a control or high fat (HF) diet starting at ~ 8.5 months of age. Three months after diet initiation, sham or unilateral carotid artery occlusion surgery (VCID model) was performed. Three months later, mice underwent behavior testing and brains were collected to assess pathology.

RESULTS

We have previously shown that in this VCID model, HF diet causes greater metabolic impairment and a wider array of cognitive deficits in females compared to males. Here, we report on sex differences in the underlying neuropathology, specifically white matter changes and neuroinflammation in several areas of the brain. White matter was negatively impacted by VCID in males and HF diet in females, with greater metabolic impairment correlating with less myelin markers in females only. High fat diet led to an increase in microglia activation in males but not in females. Further, HF diet led to a decrease in proinflammatory cytokines and pro-resolving mediator mRNA expression in females but not males.

CONCLUSIONS

The current study adds to our understanding of sex differences in underlying neuropathology of VCID in the presence of a common risk factor (obesity/prediabetes). This information is crucial for the development of effective, sex-specific therapeutic interventions for VCID.

Potential biological contributers to the sex difference in multiple sclerosis progression

Multiple sclerosis (MS) is an immune-mediated disease that targets the myelin sheath of central nervous system (CNS) neurons leading to axon injury, neuronal death, and neurological progression. Though women are more highly susceptible to developing MS, men that develop this disease exhibit greater cognitive impairment and accumulate disability more rapidly than women. Magnetic resonance imaging and pathology studies have revealed that the greater neurological progression seen in males correlates with chronic immune activation and increased iron accumulation at the rims of chronic white matter lesions as well as more intensive whole brain and grey matter atrophy and axon loss. Studies in humans and in animal models of MS suggest that male aged microglia do not have a higher propensity for inflammation, but may become more re-active at the rim of white matter lesions as a result of the presence of pro-inflammatory T cells, greater astrocyte activation or iron release from oligodendrocytes in the males. There is also evidence that remyelination is more efficient in aged female than aged male rodents and that male neurons are more susceptible to oxidative and nitrosative stress. Both sex chromosome complement and sex hormones contribute to these sex differences in biology.

Biological underpinnings of sex differences in neurological disorders

The importance of sex differences in neurological disorders has been increasingly acknowledged in recent clinical and basic research studies, but the complex biology and genetics underlying sex-linked biological heterogeneity and its brain-to-body impact remained incompletely understood. Men and women differ substantially in their susceptibility to certain neurological diseases, in the severity of symptoms, prognosis as well as the nature and efficacy of their response to treatments. The detailed mechanisms underlying these differences, especially at the molecular level, are being addressed in many studies but leave a lot to be further revealed. Here, we provide an overview of recent advances in our understanding of how sex differences in the brain and brain-body signaling contribute to neurological disorders and further present some future prospects entailed in terms of diagnostics and therapeutics.

Remyelination therapies for multiple sclerosis: optimizing translation from animal models into clinical trials

Introduction: Multiple sclerosis (MS) is the most common inflammatory disease of the central nervous system (CNS). Demyelination, the main pathology in MS, contributes to clinical symptoms and long-term neurological deficits if left untreated. Remyelination, the natural repair of damaged myelin by cells of the oligodendrocyte lineage, occurs in MS, but eventually fails in most patients as they age. Encouraging timely remyelination can restore axon conduction and minimize deficits.Areas covered: We discuss and correlate human MS pathology with animal models, propose methods to deplete resident oligodendrocyte progenitor cells (OPCs) to determine whether mature oligodendrocytes support remyelination, and review remyelinating agents, mechanisms of action, and available clinical trial data.Expert opinion: The heterogeneity of human MS may limit successful translation of many candidate remyelinating agents; some patients lack the biological targets necessary to leverage current approaches. Development of therapeutics for remyelination has concentrated almost exclusively on mobilization of innate OPCs. However, mature oligodendrocytes appear an important contributor to remyelination in humans. Limiting the contribution of OPC mediated repair in models of MS would allow the evaluation of remyelination-promoting agents on mature oligodendrocytes. Among remyelinating reagents reviewed, only rHIgM22 targets both OPCs and mature oligodendrocytes.

Coming of age in the frontal cortex: The role of puberty in cortical maturation

Across species, adolescence is a period of growing independence that is associated with the maturation of cognitive, social, and affective processing. Reorganization of neural circuits within the frontal cortex is believed to contribute to the emergence of adolescent changes in cognition and behavior. While puberty coincides with adolescence, relatively little is known about which aspects of frontal cortex maturation are driven by pubertal development and gonadal hormones. In this review, we highlight existing work that suggests puberty plays a role in the maturation of specific cell types in the medial prefrontal cortex (mPFC) of rodents, and highlight possible routes by which gonadal hormones influence frontal cortical circuit development.

Pubertal Testosterone and the Structure of the Cerebral Cortex in Young Men

Adolescence is a period of brain maturation that may involve a second wave of organizational effects of sex steroids on the brain. Rodent studies suggest that, overall, organizational effects of gonadal steroid hormones decrease from the prenatal/perinatal period to adulthood. Here we used multimodal magnetic resonance imaging to investigate whether 1) testosterone exposure during adolescence (9-17 years) correlates with the structure of cerebral cortex in young men (n = 216, 19 years of age); 2) this relationship is modulated by the timing of testosterone surge during puberty. Our results showed that pubertal testosterone correlates with structural properties of the cerebral cortex, as captured by principal component analysis of T1 and T2 relaxation times, myelin water fraction, magnetization transfer ratio, fractional anisotropy and mean diffusivity. Many of the correlations between pubertal testosterone and the cortical structure were stronger in individuals with earlier (vs. later) testosterone surge. We also demonstrated that the strength of the relationship between pubertal testosterone and cortical structure across the cerebral cortex varies as a function of inter-regional profiles of gene expression specific to dendrites, axonal cytoskeleton, and myelin. This finding suggests that the cellular substrate underlying the relationships between pubertal testosterone and cerebral cortex involves both dendritic arbor and axon.

Role of glial cells in the generation of sex differences in neurodegenerative diseases and brain aging

Diseases and aging-associated alterations of the nervous system often show sex-specific characteristics. Glial cells play a major role in the endogenous homeostatic response of neural tissue, and sex differences in the glial transcriptome and function have been described. Therefore, the possible role of these cells in the generation of sex differences in pathological alterations of the nervous system is reviewed here. Studies have shown that glia react to pathological insults with sex-specific neuroprotective and regenerative effects. At least three factors determine this sex-specific response of glia: sex chromosome genes, gonadal hormones and neuroactive steroid hormone metabolites. The sex chromosome complement determines differences in the transcriptional responses in glia after brain injury, while gonadal hormones and their metabolites activate sex-specific neuroprotective mechanisms in these cells. Since the sex-specific neuroprotective and regenerative activity of glial cells causes sex differences in the pathological alterations of the nervous system, glia may represent a relevant target for sex-specific therapeutic interventions.

Developmental expression of genes involved in progesterone synthesis, metabolism and action during the post-natal cerebellar myelination

Progesterone is involved in dendritogenesis, synaptogenesis and maturation of cerebellar Purkinge cells, major sites of steroid synthesis in the brain. To study a possible time-relationship between myelination, neurosteroidogenesis and steroid receptors during development of the postnatal mouse cerebellum, we determined at postnatal days 5 (P5),18 (P18) and 35 (P35) the expression of myelin basic protein (MBP), components of the steroidogenic pathway, levels of endogenous steroids and progesterone's classical and non-classical receptors. In parallel with myelin increased expression during development, P18 and P35 mice showed higher levels of cerebellar progesterone and its reduced derivatives, higher expression of steroidogenic acute regulatory protein (StAR) mRNA, cholesterol side chain cleavage enzyme (P450scc) and 5α-reductase mRNA vs. P5 mice. Other steroids such as corticosterone and its reduced derivatives and 3β-androstanodiol (ADIOL) showed a peak increase at P18 compared to P5. Progesterone membrane receptors and binding proteins (PGRMC1, mPRα, mPRβ, mPRγ, and Sigma1 receptors) mRNAs levels increased during development while that of classical progesterone receptors (PR) remained invariable. PRKO mice showed similar MBP levels than wild type. Thus, these data suggests that progesterone and its neuroactive metabolites may play a role in postnatal cerebellar myelination.

Hormonal Regulation of Oligodendrogenesis I: Effects across the Lifespan

The brain’s capacity to respond to changing environments via hormonal signaling is critical to fine-tuned function. An emerging body of literature highlights a role for myelin plasticity as a prominent type of experience-dependent plasticity in the adult brain. Myelin plasticity is driven by oligodendrocytes (OLs) and their precursor cells (OPCs). OPC differentiation regulates the trajectory of myelin production throughout development, and importantly, OPCs maintain the ability to proliferate and generate new OLs throughout adulthood. The process of oligodendrogenesis, the creation of new OLs, can be dramatically influenced during early development and in adulthood by internal and environmental conditions such as hormones. Here, we review the current literature describing hormonal regulation of oligodendrogenesis within physiological conditions, focusing on several classes of hormones: steroid, peptide, and thyroid hormones. We discuss hormonal regulation at each stage of oligodendrogenesis and describe mechanisms of action, where known. Overall, the majority of hormones enhance oligodendrogenesis, increasing OPC differentiation and inducing maturation and myelin production in OLs. The mechanisms underlying these processes vary for each hormone but may ultimately converge upon common signaling pathways, mediated by specific receptors expressed across the OL lineage. However, not all of the mechanisms have been fully elucidated, and here, we note the remaining gaps in the literature, including the complex interactions between hormonal systems and with the immune system. In the companion manuscript in this issue, we discuss the implications of hormonal regulation of oligodendrogenesis for neurological and psychiatric disorders characterized by white matter loss. Ultimately, a better understanding of the fundamental mechanisms of hormonal regulation of oligodendrogenesis across the entire lifespan, especially in vivo, will progress both basic and translational research.

Functional cooperation of the hedgehog and androgen signaling pathways during developmental and repairing myelination

Hedgehog morphogens control fundamental cellular processes during tissue development and regeneration. In the central nervous system (CNS), Hedgehog signaling has been implicated in oligodendrocyte and myelin production, where it functions in a concerted manner with other pathways. Since androgen receptor (AR) plays a key role in establishing the sexual phenotype of myelin during development and is required for spontaneous myelin regeneration in the adult CNS, we hypothesized the existence of a possible coordination between Hedgehog and androgen signals in oligodendrocyte and myelin production. Here, we report complementary activities of both pathways during early postnatal oligodendrogenesis further revealing that persistent Hedgehog signaling activation impedes myelin production. The data also uncover prominent pro-myelinating activity of testosterone and involvement of AR in the control of neural stem cell commitment toward the oligodendroglial lineage. In the context of CNS demyelination, we provide evidence for the functional cooperation of the pathways leading to acceleration of myelin regeneration that might be related to their respective role on microglial and astroglial responses, higher preservation of axonal integrity, lower neuroinflammation, and functional improvement of animals in an immune model of CNS demyelination. Strong decreases of deleterious cytokines in the CNS (GM-CSF, TNF-α, IL-17A) and spleen (IL-2, IFN-γ) stand as unique features of the combined drugs while the potent therapeutic activity of testosterone on peripheral immune cells contributes to increase tolerogenic CD11c⁺ dendritic cells, reduce the clonal expansion of conventional CD4⁺ T cells and increase CD4⁺ Foxp3⁺ regulatory T cells. Altogether, these data might open promising perspectives for demyelinating diseases.

A Multi-Modal MRI Analysis of Cortical Structure in Relation to Gender Dysphoria, Sexual Orientation, and Age in Adolescents

Gender dysphoria (GD) is characterized by distress due to an incongruence between experienced gender and sex assigned at birth. Sex-differentiated brain regions are hypothesized to reflect the experienced gender in GD and may play a role in sexual orientation development. Magnetic resonance brain images were acquired from 16 GD adolescents assigned female at birth (AFAB) not receiving hormone therapy, 17 cisgender girls, and 14 cisgender boys (ages 12–17 years) to examine three morphological and microstructural gray matter features in 76 brain regions: surface area (SA), cortical thickness (CT), and T1 relaxation time. Sexual orientation was represented by degree of androphilia-gynephilia and sexual attraction strength. Multivariate analyses found that cisgender boys had larger SA than cisgender girls and GD AFAB. Shorter T1, reflecting denser, macromolecule-rich tissue, correlated with older age and stronger gynephilia in cisgender boys and GD AFAB, and with stronger attractions in cisgender boys. Thus, cortical morphometry (mainly SA) was related to sex assigned at birth, but not experienced gender. Effects of experienced gender were found as similarities in correlation patterns in GD AFAB and cisgender boys in age and sexual orientation (mainly T1), indicating the need to consider developmental trajectories and sexual orientation in brain studies of GD.

Effects of endocrine disrupting chemicals on myelin development and diseases

In the central and peripheral nervous systems, myelin is essential for efficient conduction of action potentials. During development, oligodendrocytes and Schwann cells differentiate and ensure axon myelination, and disruption of these processes can contribute to neurodevelopmental disorders. In adults, demyelination can lead to important disabilities, and recovery capacities by remyelination often decrease with disease progression. Among environmental chemical pollutants, endocrine disrupting chemicals (EDCs) are of major concern for human health and are notably suspected to participate in neurodevelopmental and neurodegenerative diseases. In this review, we have combined the current knowledge on EDCs impacts on myelin including several persistent organic pollutants, bisphenol A, triclosan, heavy metals, pesticides, and nicotine. Besides, we presented several other endocrine modulators, including pharmaceuticals and the phytoestrogen genistein, some of which are candidates for treating demyelinating conditions but could also be deleterious as contaminants. The direct impacts of EDCs on myelinating cells were considered as well as their indirect consequences on myelin, particularly on immune mechanisms associated with demyelinating conditions. More studies are needed to describe the effects of these compounds and to further understand the underlying mechanisms in relation to the potential for endocrine disruption.

Progesterone and fetal-neonatal neuroprotection

The role of progesterone goes beyond the maintenance of pregnancy. The hormone, indeed, protects the developing fetal brain and influences its maturation. Metabolomes analyzed by mass spectrometric methods have revealed the great diversity of steroids in maternal plasma and fetal fluids, but their developmental significance remains to be investigated. Progesterone and its metabolites reach highest levels during the third trimester, when the brain growth spurt occurs: its volume triples, synaptogenesis is particularly active, and axons start to be myelinated. This developmental stage coincides with a period of great vulnerability. Studies in sheep have shown that progesterone and its metabolite allopregnanolone protect the vulnerable fetal brain. Work in rats and mice have demonstrated that progesterone plays an important role in myelin formation. These experimental studies are discussed in relation to preterm birth. Influences of progesterone on very early stages of neural development at the beginning of pregnancy are yet to be explored.

Endogenous opioid peptides and brain development: Endomorphin-1 and Nociceptin play a sex-specific role in the control of oligodendrocyte maturation and brain myelination

The generation of fully functional oligodendrocytes, the myelinating cells of the central nervous system, is preceded by a complex maturational process. We previously showed that the timing of oligodendrocyte differentiation and rat brain myelination were altered by perinatal exposure to buprenorphine and methadone, opioid analogs used for the management of pregnant addicts. Those observations suggested the involvement of the μ-opioid receptor (MOR) and the nociceptin/orphanin FQ receptor (NOR). However, it remained to be determined if these receptors and their endogenous ligands could indeed control the timing of myelination under normal physiological conditions of brain development. We now found that the endogenous MOR ligand endomorphin-1 (EM-1) exerts a striking stimulatory action on cellular and morphological maturation of rat pre-oligodendrocytes, but unexpectedly, these effects appear to be restricted to the cells from the female pups. Critically, this stimulation is abolished by coincubation with the endogenous NOR ligand nociceptin. Furthermore, NOR antagonist treatment of 9-day-old female pups results in accelerated brain myelination. Interestingly, the lack of sex-dependent differences in developmental brain levels of EM-1 and nociceptin, or oligodendroglial expression of MOR and NOR, suggests that the observed sex-specific responses may be highly dependent on important intrinsic differences between the male and female oligodendrocytes. The discovery of a significant effect of EM-1 and nociceptin in the developing female oligodendrocytes and brain myelination, underscores the need for further studies investigating brain sex-related differences and their implications in opioid use and abuse, pain control, and susceptibility and remyelinating capacity in demyelinating disease as multiple sclerosis.

Androgens' effects on cerebrovascular function in health and disease

Androgens affect the cerebral vasculature and may contribute to sex differences in cerebrovascular diseases. Men are at a greater risk for stroke and vascular contributions to cognitive impairment and dementia (VCID) compared to women throughout much of the lifespan. The cerebral vasculature is a target for direct androgen actions, as it expresses several sex steroid receptors and metabolizing enzymes. Androgens’ actions on the cerebral vasculature are complex, as they have been shown to have both protective and detrimental effects, depending on factors such as age, dose, and disease state. When administered chronically, androgens are shown to be pro-angiogenic, promote vasoconstriction, and influence blood-brain barrier permeability. In addition to these direct effects of androgens on the cerebral vasculature, androgens also influence other vascular risk factors that may contribute to sex differences in cerebrovascular diseases. In men, low androgen levels have been linked to metabolic and cardiovascular diseases including hypertension, diabetes, hyperlipidemia, and obesity, which greatly increase the risk of stroke and VCID. Thus, a better understanding of androgens’ interactions with the cerebral vasculature under physiological and pathological conditions is of key importance.

Roles of Progesterone, Testosterone and Their Nuclear Receptors in Central Nervous System Myelination and Remyelination

Progesterone and testosterone, beyond their roles as sex hormones, are neuroactive steroids, playing crucial regulatory functions within the nervous system. Among these, neuroprotection and myelin regeneration are important ones. The present review aims to discuss the stimulatory effects of progesterone and testosterone on the process of myelination and remyelination. These effects have been demonstrated in vitro (i.e., organotypic cultures) and in vivo (cuprizone- or lysolecithin-induced demyelination and experimental autoimmune encephalomyelitis (EAE)). Both steroids stimulate myelin formation and regeneration by acting through their respective intracellular receptors: progesterone receptors (PR) and androgen receptors (AR). Activation of these receptors results in multiple events involving direct transcription and translation, regulating general homeostasis, cell proliferation, differentiation, growth and myelination. It also ameliorates immune response as seen in the EAE model, resulting in a significant decrease in inflammation leading to a fast recovery. Although natural progesterone and testosterone have a therapeutic potential, their synthetic derivatives—the 19-norprogesterone (nestorone) and 7α-methyl-nortestosterone (MENT), already used as hormonal contraception or in postmenopausal hormone replacement therapies, may offer enhanced benefits for myelin repair. We summarize here a recent advancement in the field of myelin biology, to treat demyelinating disorders using the natural as well as synthetic analogs of progesterone and testosterone.

Effects of 17β-trenbolone exposure on sex hormone synthesis and social behaviours in adolescent mice

17β-Trenbolone (17β-TBOH) is an endocrine disruptor that has been widely reported in aquatic organisms. However, little is known about the effect of 17β-TBOH on mammals, particularly on the development of adolescents. Through a series of behavioural experiments, exposure to at 80 μg kg ^-1 d ^-1 and 800 μg kg ^-1 d ^-1 17β-TBOH during puberty (from PND 28 to 56, male mice) increased anxiety-like behaviours. Exposure to the low dose of 80 μg kg ^-1 d ^-1 resulted in a clear social avoidance behaviour in mice. The two doses affected testicular development and endogenous androgen synthesis in male mice. In addition, 17β-TBOH exposure altered the differentiation of oligodendrocytes and the formation of the myelin sheath in the medial prefrontal cortex (mPFC). These results reveal the effects of 17β-TBOH on the behaviours, gonadal and neurodevelopment of adolescent mammals. In addition, the inhibition of the secretion of endogenous hormones and decrease in the formation of the myelin sheath in mPFC may be associated with the 17β-TBOH-induced behavioural changes in mice.

Sex differences in steroid levels and steroidogenesis in the nervous system: Physiopathological role

The nervous system, in addition to be a target for steroid hormones, is the source of a variety of neuroactive steroids, which are synthesized and metabolized by neurons and glial cells. Recent evidence indicates that the expression of neurosteroidogenic proteins and enzymes and the levels of neuroactive steroids are different in the nervous system of males and females. We here summarized the state of the art of neuroactive steroids, particularly taking in consideration sex differences occurring in the synthesis and levels of these molecules. In addition, we discuss the consequences of sex differences in neurosteroidogenesis for the function of the nervous system under healthy and pathological conditions and the implications of neuroactive steroids and neurosteroidogenesis for the development of sex-specific therapeutic interventions.

Why considering sexual differences is necessary when studying encephalopathy of prematurity through rodent models

Preterm birth is a high-risk factor for the development of gray and white matter abnormalities, referred to as "encephalopathy of prematurity," that may lead to life-long motor, cognitive, and behavioral impairments. The prevalence and clinical outcomes of encephalopathy of prematurity differ between sexes, and elucidating the underlying biological basis has become a high-priority challenge. Human studies are often limited to assessment of brain region volumes by MRI, which does not provide much information about the underlying mechanisms of lesions related to very preterm birth. However, models using KO mice or pharmacological manipulations in rodents allow relevant observations to help clarify the mechanisms of injury sustaining sex-differential vulnerability. This review focuses on data obtained from mice aged P1-P5 or rats aged P3 when submitted to cerebral damage such as hypoxia-ischemia, as their brain lesions share similarities with lesion patterns occurring in very preterm human brain, before 32 gestational weeks. We first report data on the mechanisms underlying the development of sexual brain dimorphism in rodent, focusing on the hippocampus. In the second part, we describe sex specificities of rodent models of encephalopathy of prematurity (RMEP), focusing on mechanisms underlying differences in hippocampal vulnerability. Finally, we discuss the relevance of these RMEP. Together, this review highlights the need to systematically search for potential effects of sex when studying the mechanisms underlying deficits in RMEP in order to design effective sex-specific medical interventions in human preterms.

The biological basis of sexual orientation: How hormonal, genetic, and environmental factors influence to whom we are sexually attracted

Humans develop relatively stable attractions to sexual partners during maturation and present a spectrum of sexual orientation from homosexuality to heterosexuality encompassing varying degrees of bisexuality, with some individuals also displaying asexuality. Sexual orientation represents a basic life phenomenon for humans. However, the molecular mechanisms underlying these diverse traits of sexual orientation remain highly controversial. In this review, we systematically discuss recent advancements in sexual orientation research, including those related to measurements and associated brain regions. Current findings regarding sexual orientation modulation by hormonal, genetic, maternal immune system, and environmental factors are summarized in both human and model systems. We also emphasize that future studies should recognize the differences between males and females and pay more attention to minor traits and the epigenetic regulation of sexual orientation. A comprehensive view of sexual orientation may promote our understanding of the biological basis of sex, and that of human reproduction, and evolution.

Maternal high-fat diet impairs leptin signaling and up-regulates type-1 cannabinoid receptor with sex-specific epigenetic changes in the hypothalamus of newborn rats

Maternal nutritional imbalances trigger developmental adaptations involving early epigenetic mechanisms associated with adult chronic disease. Maternal high-fat (HF) diet promotes obesity and hypothalamic leptin resistance in male rat offspring at weaning and adulthood. Leptin resistance is associated with over activation of the endocannabinoid system (ECS). The ECS mainly consists of endocannabinoids derived from n-6 fatty acids and cannabinoid receptors (CB1 coded by Cnr1 and CB2 coded by Cnr2). The CB1 activation in hypothalamus stimulates feeding and appetite for fat while CB2 activation seems to play an immunomodulatory role. We demonstrated that maternal HF diet increases hypothalamic CB1 in male offspring while increases CB2 in female offspring at birth, prior to obesity development. However, the molecular mechanisms behind these changes remain unexplored. We hypothesized that maternal HF diet would down-regulate leptin signaling and up-regulate Cnr1 mRNA levels in the hypothalamus of the offspring at birth, associated with sex-specific changes in epigenetic markers and sex steroid signaling. To test our hypothesis, we used progenitor female rats that received control diet (C, 9% fat) or isocaloric high-fat diet (HF, 28% fat) from 8 weeks before mating until delivery. Blood, hypothalamus and carcass from C and HF male and female offspring were collected for biochemical and molecular analyses at birth. Maternal HF diet down-regulated the transcriptional factor STAT3 in the hypothalamus of male and female offspring, but induced hypoleptinemia only in males and decreased phosphorylated STAT3 only in female offspring. Because leptin acts through STAT3 pathway to inhibit central ECS, our results suggest that leptin pathway impairment might contribute to increased levels of Crn1 mRNA in hypothalamus of both sex offspring. Besides, maternal HF diet increased the histone acetylation percentage of Cnr1 promoter in male offspring and increased the androgen receptor binding to the Cnr1 promoter, which can contribute to higher expression of Cnr1 in newborn HF offspring. Maternal HF diet increased plasma n6 to n3 fatty acid ratio in male offspring, which is an important risk factor to metabolic diseases and might indicate an over activation of endocannabinoid signaling. Thus, although maternal HF diet programs a similar phenotype in adult offspring of both sexes (obesity, hyperphagia and higher preference for fat), here we showed that molecular mechanisms involving leptin signaling, ECS, epigenetic markers and sex hormone signaling were modified prior to obesity development and can differ between newborn male and female offspring. These observations may provide molecular insights into sex-specific targets for anti-obesity therapies.

Changes in neurosteroidogenesis during demyelination and remyelination in cuprizone-treated mice

Changes of neurosteroids may be involved in the pathophysiology of multiple sclerosis (MS). The present study investigated whether changes of neurosteroidogenesis also occurred in the grey and white matter regions of the brain in mice subjected to cuprizone-induced demyelination. Accordingly, we compared the expression of neurosteroidogenic proteins, including steroidogenic acute regulatory protein (StAR), voltage-dependent anion channel (VDAC) and 18 kDa translocator protein (TSPO), as well as neurosteroidogenic enzymes, including the side chain cleavage enzyme (P450scc), 3β-hydroxysteroid dehydrogenase/isomerase and 5α-reductase (5α-R), during the demyelination and remyelination periods. Using immunohistochemistry and a quantitative polymerase chain reaction, we demonstrated a decreased expression of StAR, P450scc and 5α-R with respect to an increase astrocytic and microglial reaction and elevated levels of tumor necrosis factor (TNF)α during the cuprizone demyelination period in the hippocampus, cortex and corpus callosum. These parameters, as well as the glial reaction, were normalised after 2 weeks of spontaneous remyelination in regions containing grey matter. Conversely, persistent elevated levels of TNFα and low levels of StAR and P450scc were observed during remyelination in corpus callosum white matter. We conclude that neurosteroidogenesis/myelination status and glial reactivity are inversely related in the hippocampus and neocortex. Establishing a cause and effect relationship for the measured variables remains a future challenge for understanding the pathophysiology of MS.

Effects of Estrogens on Central Nervous System Neurotransmission: Implications for Sex Differences in Mental Disorders

Nearly one of every five US individuals aged 12 years old or older lives with certain types of mental disorders. Men are more likely to use various types of substances, while women tend to be more susceptible to mood disorders, addiction, and eating disorders, all of which are risks associated with suicidal attempts. Fundamental sex differences exist in multiple aspects of the functions and activities of neurotransmitter-mediated neural circuits in the central nervous system (CNS). Dysregulation of these neural circuits leads to various types of mental disorders. The potential mechanisms of sex differences in the CNS neural circuitry regulating mood, reward, and motivation are only beginning to be understood, although they have been largely attributed to the effects of sex hormones on CNS neurotransmission pathways. Understanding this topic is important for developing prevention and treatment of mental disorders that should be tailored differently for men and women. Studies using animal models have provided important insights into pathogenesis, mechanisms, and new therapeutic approaches of human diseases, but some concerns remain to be addressed. The purpose of this chapter is to integrate human and animal studies involving the effects of the sex hormones, estrogens, on CNS neurotransmission, reward processing, and associated mental disorders. We provide an overview of existing evidence for the physiological, behavioral, cellular, and molecular actions of estrogens in the context of controlling neurotransmission in the CNS circuits regulating mood, reward, and motivation and discuss related pathology that leads to mental disorders.