Growth of white matter in the adolescent brain: role of testosterone and androgen receptor

Investigating the shared genetic architecture between schizophrenia and sex hormone traits

Sex hormones are involved in schizophrenia pathogenesis; however, their direction and genetic overlap remain unknown. By leveraging summary statistics from large-scale genome-wide association studies, we quantified the shared genetic architecture between schizophrenia and four sex hormone traits. Linkage disequilibrium score regression and bivariate causal mixture modeling strategies showed significant positive correlations between sex hormone-binding globulin (SHBG), total testosterone, and schizophrenia, while bioavailable testosterone and schizophrenia were negatively correlated. Estradiol showed a weak positive correlation with schizophrenia, with little polygenic overlap. The conjunctional false discovery rate method identified 303 lead single-nucleotide polymorphisms (SNPs) in jointly shared genomic loci between schizophrenia and SHBG, with 130, 52, and 9 SNPs shared between schizophrenia and total testosterone, bioavailable testosterone, and estradiol, respectively. Functional annotation suggests that mitotic sister chromatid segregation and N-glycan biosynthesis may be involved in common mechanisms underlying sex hormone regulation and schizophrenia onset. In conclusion, this study clarified the inherent relationships between schizophrenia and sex hormone traits, highlighted the roles of mitotic sister chromatid segregation and N-glycan biosynthesis in the pathogenesis of schizophrenia, and delivered potential targets for further validation.

Critical menarche age for late-life dementia and the role of education and socioeconomic status

Estrogen exposure during menstrual years has been associated with late-life neuroprotection. We explored the presence of an age-sensitive menarche window for cognition in old age and the impact of socioeconomic status and education. We compared neuropsychological performance of 1082 older women [MeanAGE = 72.69 (5.48)] with menarche in childhood, early-, mid-, and late-adolescence and dementia prevalence, severity, and type, including the effects of education and socioeconomic status. Adjusting for covariates, menarche at 11-14 years of age was associated with better memory, executive and global cognitive functioning in old age, and stronger positive effects of education and socioeconomic status on cognition than those with menarche at 15-17 years. We found a critical age window for the neuroprotective effects of estrogens during early adolescence, putting women with later menarche at higher risk for cognitive decline. Effects of socioeconomic status and education in adulthood should be a focus of future research.

White Matter Microstructure Among Straight and Gay Cisgender Men, Sao Praphet Song, and Straight Cisgender Women in Thailand

White matter (WM) microstructure is differentiated in relation to sex/gender, psychosexuality, and, among transgender people, gender-affirming hormone (GAH) use. Prior research focused on Western samples, which limits generalizability to other populations. Here, diffusion tensor imaging (DTI) was used to assess WM microstructure in a Thai sample (N = 128) of straight cisgender men, straight cisgender women, gay cisgender men, and sao praphet song (i.e., transfeminine individuals assigned male at birth and sexually attracted to cisgender men). Sao praphet song were further grouped by GAH use. Groups were compared on fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) using whole-brain tract-based spatial statistics (TBSS). FA, AD, and RD were further examined via multivariate analysis to assess covariance across WM microstructural indices and participant groups. A significant multivariate pattern differentiated the feminine- from masculine-identifying groups irrespective of sex assigned at birth and suggested WM tissue organization was greater among the latter in the bilateral cingulum, anterior corona radiata, left corpus callosum, and right superior longitudinal fasciculus, forceps minor, and corticospinal tracts. TBSS analyses reinforced that WM differed by gender identity in various regions. Among sao praphet song, GAH use was associated with lower regional FA, suggesting less WM organization bilaterally in the corpus callosum, cingulum, and anterior corona radiata. The findings aligned with prior studies in Western samples, indicating cross-population generalizability of WM microstructural differentiation in relation to sex/gender, psychosexuality, and GAH use.

Sex-differences in brain multimodal estimates of white matter microstructure during early adolescence: Sex-specific associations with biological factors

Adolescence is marked by significant maturation of brain white matter microstructure, with evidence for sex-specific maturational trajectory. Most studies have examined conventional diffusion tensor imaging (DTI) metrics, which lack specificity to the underlying tissue modifications. In this study, we characterized sex-differences in white matter microstructure cross-sectionally using DTI, advanced diffusion spectrum imaging (DSI) and diffusion kurtosis imaging (DKI), as well as the white matter tract integrity-Watson (WMTI-W) biophysical model. We also aimed to explore the effect of age and biological systems undergoing sex-specific changes during adolescence, namely pubertal hormones, hypothalamic-pituitary-adrenal (HPA)-axis function, and glutathione-redox cycle homeostasis. The results indicate widespread sex-differences in all the white matter derived metrics, suggesting more advanced maturation in females compared to males as well as distinct tissue modifications underlying white matter maturation between males and females during this narrow developmental period. Additionally, the three biological factors explored appeared to be associated with indices of white matter maturation in females specifically, emphasizing this period as critical in female white matter development and sensitivity to environmental factors.

Causal influences of testosterone on brain structure change rate: A sex-stratified Mendelian randomization study

The impact of testosterone levels on changes in brain structure has been reported. However, it is still unclear which specific brain region could be affected. This study approached Mendelian randomization method to reveal the causal relationship between testosterone levels and the rate of longitudinal structural changes in the brain. The testosterone-related GWAS data were determined from 425,097 European participants. The GWAS data on the rate of longitudinal structural changes in the brain came from the ENIGMA consortium, which included 15,640 all-age participants from 40 longitudinal cohorts. The inverse variance weighted was considered as the main estimate, MR Egger and weighted median methods were used to supplement IVW. A positive correlation was found between total testosterone levels and bioavailable testosterone levels in women and age-independent longitudinal changes in cerebral WM and surface area. The sex hormone-binding globulin levels were found a negative correlation with age-dependent longitudinal structural changes of cortical GM in men. Additionally, we also found that the bioavailable testosterone level in males was negatively associated with the quadratic age-dependent longitudinal change rate in the globus pallidum. We also found estradiol levels and sex hormone-binding globulin levels were negatively associated with the quadratic age-dependent longitudinal change rate of total brain in men. Moreover, we found a positive correlation between total testosterone levels and linear age-dependent longitudinal changes in the hippocampus in both males and females. The testosterone levels in different genders may have varying degrees of causal effects on the structural changes of brain regions. These findings provide evidence for the influence of the brain glandular axis on brain structure, particularly during female brain development.

Epigenetic programming for obesity and noncommunicable disease: From womb to tomb

Several epidemiological, clinical and experimental studies in recent decades have shown the relationship between exposure to stressors during development and health outcomes later in life. The characterization of these susceptible phases, such as preconception, gestation, lactation and adolescence, and the understanding of factors that influence the risk of an adult individual for developing obesity, metabolic and cardiovascular diseases, is the focus of the DOHaD (Developmental Origins of Health and Disease) research line. In this sense, advancements in molecular biology techniques have contributed significantly to the understanding of the mechanisms underlying the observed phenotypes, their morphological and physiological alterations, having as a main driving factor the epigenetic modifications and their consequent modulation of gene expression. The present narrative review aimed to characterize the different susceptible phases of development and associated epigenetic modifications, and their implication in the development of non-communicable diseases. Additionally, we provide useful insights into interventions during development to counteract or prevent long-term programming for disease susceptibility.

White matter microstructure in transmasculine and cisgender adolescents: A multiparametric and multivariate study

Adolescence is a sensitive developmental period for neural sex/gender differentiation. The present study used multiparametric mapping to better characterize adolescent white matter (WM) microstructure. WM microstructure was investigated using diffusion tensor indices (fractional anisotropy; mean, radial, and axial diffusivity [AD]) and quantitative T1 relaxometry (T1) in hormone therapy naïve adolescent cisgender girls, cisgender boys, and transgender boys (i.e., assigned female at birth and diagnosed with gender dysphoria). Diffusion indices were first analyzed for group differences using tract-based spatial statistics, which revealed a group difference in AD. Thus, two multiparametric and multivariate analyses assessed AD in conjunction with T1 relaxation time, and with respect to developmental proxy variables (i.e., age, serum estradiol, pubertal development, sexual attraction) thought to be relevant to adolescent brain development. The multivariate analyses showed a shared pattern between AD and T1 such that higher AD was associated with longer T1, and AD and T1 strongly related to all five developmental variables in cisgender boys (10 significant correlations, r range: 0.21-0.73). There were fewer significant correlations between the brain and developmental variables in cisgender girls (three correlations, r range: -0.54-0.54) and transgender boys (two correlations, r range: -0.59-0.77). Specifically, AD related to direction of sexual attraction (i.e., gynephilia, androphilia) in all groups, and T1 related to estradiol inversely in cisgender boys compared with transgender boys. These brain patterns may be indicative of less myelination and tissue density in cisgender boys, which corroborates other reports of protracted WM development in cisgender boys. Further, these findings highlight the importance of considering developmental trajectory when assessing the subtleties of neural structure associated with variations in sex, gender, and sexual attraction.

Association between cortical thickness and cognitive ability in very preterm school-age children

Very preterm children, born before 32 weeks of gestation, are at risk for impaired cognitive function, mediated by several risk factors. Cognitive impairment can be measured by various neurodevelopmental assessments and is closely associated with structural alterations of brain morphometry, such as cortical thickness. However, the association between structural alterations and high-order cognitive function remains unclear. This study aimed to investigate the neurodevelopmental associations between brain structural changes and cognitive abilities in very preterm and full-term children. Cortical thickness was assessed in 37 very preterm and 24 full-term children aged 6 years. Cortical thickness analysis of structural T1-weighted images was performed using Advanced Normalization Tools. Associations between cortical thickness and the Wechsler Intelligence Scale for Children were evaluated by regression analysis based on ordinary least square estimation. Compared with full-term children, very preterm children showed significant differences in cortical thickness, variously associated with cognitive abilities in several brain regions. Perceptual reasoning indices were broadly correlated with cortical thickness in very preterm and full-term children. These findings provide important insights into neurodevelopment and its association with cortical thickness, which may serve as a biomarker in predictive models for neurodevelopmental diagnosis of high-order cognitive function.

Sex and Gender in Population Neuroscience

To understand psychiatric and neurological disorders and the structural and functional properties of the human brain, it is essential to consider the roles of sex and gender. In this chapter, I first define sex and gender and describe studies of sex differences in non-human animals. In humans, I describe the sex differences in behavioral and clinical phenotypes and neuroimaging-derived phenotypes, including whole-brain measures, regional subcortical and cortical measures, and structural and functional connectivity. Although structural whole-brain sex differences are large, regional effects (adjusting for whole-brain volumes) are typically much smaller and often fail to replicate. Nevertheless, while an individual neuroimaging feature may have a small effect size, aggregating them in a "maleness/femaleness" score or machine learning multivariate paradigm may prove to be predictive and informative of sex- and gender-related traits. Finally, I conclude by summarizing emerging investigations of gender norms and gender identity and provide methodological recommendations to incorporate sex and gender in population neuroscience research.

Development and Maturation of the Human Brain, from Infancy to Adolescence

This chapter describes basic principles and key findings regarding the development and maturation of the human brain, the former referring to the pre-natal and early post-natal periods and the latter concerning childhood and adolescence. In both cases, we focus on brain structure as revealed in vivo with multi-modal magnetic resonance imaging (MRI). We begin with a few numbers about the human brain and its cellular composition and a brief overview of a number of MRI-based metrics used to characterize age-related variations in grey and white matter. We then proceed with synthesizing current knowledge about developmental and maturational changes in the cerebral cortex (its thickness, surface area, and intra-cortical myelination) and the underlying white matter (volume and structural properties). To facilitate biological interpretations of MRI-derived metrics, we introduce the concept of virtual histology. We conclude the chapter with a few notes about future directions in the study of factors shaping the human brain from conception onwards.

Sex steroids and the female brain across the lifespan: insights into risk of depression and Alzheimer's disease

Despite widespread sex differences in prevalence and presentation of numerous illnesses affecting the human brain, there has been little focus on the effect of endocrine ageing. Most preclinical studies have focused on males only, and clinical studies often analyse data by covarying for sex, ignoring relevant differences between the sexes. This sex- (and gender)-neutral approach is biased and contributes to the absence of targeted treatments and services for all sexes (and genders). Female health has been historically understudied, with grave consequences for their wellbeing and health equity. In this Review, we spotlight female brain health across the lifespan by informing on the role of sex steroids, particularly oestradiol, on the female brain and on risk for diseases more prevalent in females, such as depression and Alzheimer's disease.

In vivo evidence of microstructural hypo-connectivity of brain white matter in 22q11.2 deletion syndrome

22q11.2 deletion syndrome, or 22q11.2DS, is a genetic syndrome associated with high rates of schizophrenia and autism spectrum disorders, in addition to widespread structural and functional abnormalities throughout the brain. Experimental animal models have identified neuronal connectivity deficits, e.g., decreased axonal length and complexity of axonal branching, as a primary mechanism underlying atypical brain development in 22q11.2DS. However, it is still unclear whether deficits in axonal morphology can also be observed in people with 22q11.2DS. Here, we provide an unparalleled in vivo characterization of white matter microstructure in participants with 22q11.2DS (12-15 years) and those undergoing typical development (8-18 years) using a customized magnetic resonance imaging scanner which is sensitive to axonal morphology. A rich array of diffusion MRI metrics are extracted to present microstructural profiles of typical and atypical white matter development, and provide new evidence of connectivity differences in individuals with 22q11.2DS. A recent, large-scale consortium study of 22q11.2DS identified higher diffusion anisotropy and reduced overall diffusion mobility of water as hallmark microstructural alterations of white matter in individuals across a wide age range (6-52 years). We observed similar findings across the white matter tracts included in this study, in addition to identifying deficits in axonal morphology. This, in combination with reduced tract volume measurements, supports the hypothesis that abnormal microstructural connectivity in 22q11.2DS may be mediated by densely packed axons with disproportionately small diameters. Our findings provide insight into the in vivo white matter phenotype of 22q11.2DS, and promote the continued investigation of shared features in neurodevelopmental and psychiatric disorders.

An intracellular isotropic diffusion signal is positively associated with pubertal development in white matter

Puberty is a key event in adolescent development that involves significant, hormone-driven changes to many aspects of physiology including the brain. Understanding how the brain responds during this time period is important for evaluating neuronal developments that affect mental health throughout adolescence and the adult lifespan. This study examines diffusion MRI scans from the cross-sectional ABCD Study baseline cohort, a large multi-site study containing thousands of participants, to describe the relationship between pubertal development and brain microstructure. Using advanced, 3-tissue constrained spherical deconvolution methods, this study is able to describe multiple tissue compartments beyond only white matter (WM) axonal qualities. After controlling for age, sex, brain volume, subject handedness, scanning site, and sibling relationships, we observe a positive relationship between an isotropic, intracellular diffusion signal fraction and pubertal development across a majority of regions of interest (ROIs) in the WM skeleton. We also observe regional effects from an intracellular anisotropic signal fraction compartment and extracellular isotropic free water-like compartment in several ROIs. This cross-sectional work suggests that changes in pubertal status are associated with a complex response from brain tissue that cannot be completely described by traditional methods focusing only on WM axonal properties.

Effects of Androgens on the Thickness of Retinal Layers in Transgender Men and in Women with Polycystic Ovarian Syndrome

Purpose

This study aimed to evaluate the relationship between androgens and the retinal thickness by comparing the macular thickness (MT), retinal nerve fiber layer (RNFL), and ganglion cell complex (GCC) thickness of female-to-male transgender men (TGM), women with polycystic ovary syndrome (PCOS), and cisgender women (CW).

Methods

Thirty-four eyes of 34 TGM, 34 eyes of 34 women with PCOS, and 45 eyes of 45 CW were evaluated by optical coherence tomography. One-way analysis of variance and body mass index (BMI)-adjusted one-way analysis of covariance were conducted to test the differences between groups for statistical evaluation.

Results

The parafoveal MT in TGM was significantly higher than women with PCOS and CW (p<0.001 and p=0.022, respectively). After adjusting for BMI, the perifoveal MT in TGM was significantly higher than women with PCOS and CW (p=0.041 and p=0.021, respectively). The nasal RNFL thickness in TGM was significantly higher than women with PCOS and CW (p=0.021 and p=0.009, respectively). The means of average and inferior RNFL, fovea, and the mean of all GCC values were higher in the TGM group than women with PCOS and CW, but these results were not statistically significant.

Conclusions

In this study, there was a significant difference between the TGM group and the CW group for the thickness of the nasal RNFL and parafoveal and perifoveal macular area. Androgens may have the potential to increase retinal thickness in TGM; however, there is a need for validation in larger study groups. Clinical Trial Registration Number: HNEAH-KAEK 2021/4.

Puberty differentially predicts brain maturation in male and female youth: A longitudinal ABCD Study

Research has demonstrated associations between pubertal development and brain maturation. However, existing studies have been limited by small samples, cross-sectional designs, and inconclusive findings regarding directionality of effects and sex differences. We examined the longitudinal temporal coupling of puberty status assessed using the Pubertal Development Scale (PDS) and magnetic resonance imaging (MRI)-based grey and white matter brain structure. Our sample consisted of 8896 children and adolescents at baseline (mean age = 9.9) and 6099 at follow-up (mean age = 11.9) from the Adolescent Brain and Cognitive Development (ABCD) Study cohort. Applying multigroup Bivariate Latent Change Score (BLCS) models, we found that baseline PDS predicted the rate of change in cortical thickness among females and rate of change in cortical surface area for both males and females. We also found a correlation between baseline PDS and surface area and co-occurring changes over time in males. Diffusion tensor imaging (DTI) analyses revealed correlated change between PDS and fractional anisotropy (FA) for both males and females, but no significant associations for mean diffusivity (MD). Our results suggest that pubertal status predicts cortical maturation, and that the strength of the associations differ between sex. Further research spanning the entire duration of puberty is needed to understand the extent and contribution of pubertal development on the youth brain.

Distinct developmental trajectories for risky and impulsive decision-making in chimpanzees

Human adolescence is characterized by a suite of changes in decision-making and emotional regulation that promote risky and impulsive behavior. Accumulating evidence suggests that behavioral and physiological shifts seen in human adolescence are shared by some primates, yet it is unclear if the same cognitive mechanisms are recruited. We examined developmental changes in risky choice, intertemporal choice, and emotional responses to decision outcomes in chimpanzees, our closest-living relatives. We found that adolescent chimpanzees were more risk-seeking than adults, as in humans. However, chimpanzees showed no developmental change in intertemporal choice, unlike humans, although younger chimpanzees did exhibit elevated emotional reactivity to waiting compared to adults. Comparisons of cortisol and testosterone indicated robust age-related variation in these biomarkers, and patterns of individual differences in choices, emotional reactivity, and hormones also supported a developmental dissociation between risk and choice impulsivity. These results show that some but not all core features of human adolescent decision-making are shared with chimpanzees. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

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.

Novel insights into axon diameter and myelin content in late childhood and adolescence

White matter microstructural development in late childhood and adolescence is driven predominantly by increasing axon density and myelin thickness. Ex vivo studies suggest that the increase in axon diameter drives developmental increases in axon density observed with pubertal onset. In this cross-sectional study, 50 typically developing participants aged 8-18 years were scanned using an ultra-strong gradient magnetic resonance imaging scanner. Microstructural properties, including apparent axon diameter $({d}_a)$, myelin content, and g-ratio, were estimated in regions of the corpus callosum. We observed age-related differences in ${d}_a$, myelin content, and g-ratio. In early puberty, males had larger ${d}_a$ in the splenium and lower myelin content in the genu and body of the corpus callosum, compared with females. Overall, this work provides novel insights into developmental, pubertal, and cognitive correlates of individual differences in apparent axon diameter and myelin content in the developing human brain.

The role of puberty on physical and brain development: A longitudinal study in male Rhesus Macaques

This study examined the role of male pubertal maturation on physical growth and development of neurocircuits that regulate stress, emotional and cognitive control using a translational nonhuman primate model. We collected longitudinal data from male macaques between pre- and peri-puberty, including measures of physical growth, pubertal maturation (testicular volume, blood testosterone -T- concentrations) and brain structural and resting-state functional MRI scans to examine developmental changes in amygdala (AMY), hippocampus (HIPPO), prefrontal cortex (PFC), as well as functional connectivity (FC) between those regions. Physical growth and pubertal measures increased from pre- to peri-puberty. The indexes of pubertal maturation -testicular size and T- were correlated at peri-puberty, but not at pre-puberty (23 months). Our findings also showed ICV, AMY, HIPPO and total PFC volumetric growth, but with region-specific changes in PFC. Surprisingly, FC in these neural circuits only showed developmental changes from pre- to peri-puberty for HIPPO-orbitofrontal FC. Finally, testicular size was a better predictor of brain structural maturation than T levels -suggesting gonadal hormones-independent mechanisms-, whereas T was a strong predictor of functional connectivity development. We expect that these neural circuits will show more drastic pubertal-dependent maturation, including stronger associations with pubertal measures later, during and after male puberty.

The effects of puberty and sex on adolescent white matter development: A systematic review

Adolescence, the transition between childhood and adulthood, is characterized by rapid brain development in white matter (WM) that is attributed in part to rising levels in adrenal and gonadal hormones. The extent to which pubertal hormones and related neuroendocrine processes explain sex differences in WM during this period is unclear. In this systematic review, we sought to examine whether there are consistent associations between hormonal changes and morphological and microstructural properties of WM across species and whether these effects are sex-specific. We identified 90 (75 human, 15 non-human) studies that met inclusion criteria for our analyses. While studies in human adolescents show notable heterogeneity, results broadly demonstrate that increases in gonadal hormones across pubertal development are associated with macro- and microstructural changes in WM tracts that are consistent with the sex differences found in non-human animals, particularly in the corpus callosum. We discuss limitations of the current state of the science and recommend important future directions for investigators in the field to consider in order to advance our understanding of the neuroscience of puberty and to promote forward and backward translation across model organisms.

Patterns of risk-Using machine learning and structural neuroimaging to identify pedophilic offenders

Background

Child sexual abuse (CSA) has become a focal point for lawmakers, law enforcement, and mental health professionals. With high prevalence rates around the world and far-reaching, often chronic, individual, and societal implications, CSA and its leading risk factor, pedophilia, have been well investigated. This has led to a wide range of clinical tools and actuarial instruments for diagnosis and risk assessment regarding CSA. However, the neurobiological underpinnings of pedosexual behavior, specifically regarding hands-on pedophilic offenders (PO), remain elusive. Such biomarkers for PO individuals could potentially improve the early detection of high-risk PO individuals and enhance efforts to prevent future CSA.

Aim

To use machine learning and MRI data to identify PO individuals.

Methods

From a single-center male cohort of 14 PO individuals and 15 matched healthy control (HC) individuals, we acquired diffusion tensor imaging data (anisotropy, diffusivity, and fiber tracking) in literature-based regions of interest (prefrontal cortex, anterior cingulate cortex, amygdala, and corpus callosum). We trained a linear support vector machine to discriminate between PO and HC individuals using these WM microstructure data. Post hoc, we investigated the PO model decision scores with respect to sociodemographic (age, education, and IQ) and forensic characteristics (psychopathy, sexual deviance, and future risk of sexual violence) in the PO subpopulation. We assessed model specificity in an external cohort of 53 HC individuals.

Results

The classifier discriminated PO from HC individuals with a balanced accuracy of 75.5% (sensitivity = 64.3%, specificity = 86.7%, P ₅₀₀₀ = 0.018) and an out-of-sample specificity to correctly identify HC individuals of 94.3%. The predictive brain pattern contained bilateral fractional anisotropy in the anterior cingulate cortex, diffusivity in the left amygdala, and structural prefrontal cortex-amygdala connectivity in both hemispheres. This brain pattern was associated with the number of previous child victims, the current stance on sexuality, and the professionally assessed risk of future sexual violent reoffending.

Conclusion

Aberrant white matter microstructure in the prefronto-temporo-limbic circuit could be a potential neurobiological correlate for PO individuals at high-risk of reoffending with CSA. Although preliminary and exploratory at this point, our findings highlight the general potential of MRI-based biomarkers and particularly WM microstructure patterns for future CSA risk assessment and preventive efforts.

Adolescent sleep and the foundations of prefrontal cortical development and dysfunction

Modern life poses many threats to good-quality sleep, challenging brain health across the lifespan. Curtailed or fragmented sleep may be particularly damaging during adolescence, when sleep disruption by delayed chronotypes and societal pressures coincides with our brains preparing for adult life via intense refinement of neural connectivity. These vulnerabilities converge on the prefrontal cortex, one of the last brain regions to mature and a central hub of the limbic-cortical circuits underpinning decision-making, reward processing, social interactions and emotion. Even subtle disruption of prefrontal cortical development during adolescence may therefore have enduring impact. In this review, we integrate synaptic and circuit mechanisms, glial biology, sleep neurophysiology and epidemiology, to frame a hypothesis highlighting the implications of adolescent sleep disruption for the neural circuitry of the prefrontal cortex. Convergent evidence underscores the importance of acknowledging, quantifying and optimizing adolescent sleep's contributions to normative brain development and to lifelong mental health.

Linking Puberty and the Gut Microbiome to the Pathogenesis of Neurodegenerative Disorders

Puberty is a critical period of development marked by the maturation of the central nervous system, immune system, and hypothalamic-pituitary-adrenal axis. Due to the maturation of these fundamental systems, this is a period of development that is particularly sensitive to stressors, increasing susceptibility to neurodevelopmental and neurodegenerative disorders later in life. The gut microbiome plays a critical role in the regulation of stress and immune responses, and gut dysbiosis has been implicated in the development of neurodevelopmental and neurodegenerative disorders. The purpose of this review is to summarize the current knowledge about puberty, neurodegeneration, and the gut microbiome. We also examine the consequences of pubertal exposure to stress and gut dysbiosis on the development of neurodevelopmental and neurodegenerative disorders. Understanding how alterations to the gut microbiome, particularly during critical periods of development (i.e., puberty), influence the pathogenesis of these disorders may allow for the development of therapeutic strategies to prevent them.

Effects of androgen deprivation on white matter integrity and processing speed in prostate cancer patients

Studies have associated chemotherapy-elicited changes in cognitive function with impaired white matter integrity in cancer patients. Androgen deprivation therapy (ADT) may lead to cognitive deficits in prostate cancer patients; however, whether ADT influences white matter integrity has never been investigated. In a prospective study, 15 men with non-metastatic prostate cancer receiving ADT and 15 not receiving ADT (controls or CON), comparable in age and years of education, participated in N-back task, flankers' task, and quality-of-life (QoL) assessments. All participants underwent diffusion tensor imaging of the brain at baseline and at 6 months. Imaging data were processed with published routines. The results of a paired t-test of 6-month follow-up vs. baseline were evaluated at a corrected threshold for the whole brain each in ADT and CON. ADT patients showed significantly worse 1-back accuracy during follow-up, but the two groups did not differ in 2-back accuracy, 1- or 2-back reaction time (RT), flankers' task RT or QoL across time points. In ADT, significantly reduced fractional anisotropy (FA) was noted in the corpus callosum, forceps minor/anterior thalamic radiation, superior and posterior corona radiata. The differences in FA correlated significantly with changes in 2-back and flankers' task RT. No significant FA changes were noted during follow-up in CON. Six-month ADT affects white matter integrity, and the deficits were associated with slower processing speed. These findings add to the literature supporting the deleterious effects of androgen deprivation on the brain and cognition in prostate cancer patients.

Immune signaling as a node of interaction between systems that sex-specifically develop during puberty and adolescence

Adolescence is pivotal for neural and behavioral development across species. During this period, maturation occurs in several biological systems, the most well-recognized being activation of the hypothalamic-pituitary-gonadal axis marking pubertal onset. Increasing comparative studies of sex differences have enriched our understanding of systems integration during neurodevelopment. In recent years, immune signaling has emerged as a key node of interaction between a variety of biological signaling processes. Herein, we review the age- and sex-specific changes that occur in neural, hypothalamic-pituitary, and microbiome systems during adolescence. We then describe how immune signaling interacts with these systems, and review recent preclinical evidence indicating that immune signaling may play a central role in integrating changes in their typical and atypical development during adolescence. Finally, we discuss the translational relevance of these preclinical studies to human health and wellness.

Nuclear hormone receptors in demyelinating diseases

Demyelination results from the pathological loss of myelin and is a hallmark of many neurodegenerative diseases. Despite the prevalence of demyelinating diseases, there are no disease modifying therapies that prevent the loss of myelin or promote remyelination. This review aims to summarize studies in the field that highlight the importance of nuclear hormone receptors in the promotion and maintenance of myelination and the relevance of nuclear hormone receptors as potential therapeutic targets for demyelinating diseases. These nuclear hormone receptors include the estrogen receptor, progesterone receptor, androgen receptor, vitamin D receptor, thyroid hormone receptor, peroxisome proliferator-activated receptor, liver X receptor, and retinoid X receptor. Pre-clinical studies in well-established animal models of demyelination have shown a prominent role of these nuclear hormone receptors in myelination through their promotion of oligodendrocyte maturation and development. The activation of the nuclear hormone receptors by their ligands also promotes the synthesis of myelin proteins and lipids in mouse models of demyelination. There are limited clinical studies that focus on how the activation of these nuclear hormone receptors could alleviate demyelination in patients with diseases such as multiple sclerosis (MS). However, the completed clinical trials have reported improved clinical outcome in MS patients treated with the ligands of some of these nuclear hormone receptors. Together, the positive results from both clinical and pre-clinical studies point to nuclear hormone receptors as promising therapeutic targets to counter demyelination.

Mediating role of the default mode network on parental acceptance/warmth and psychopathology in youth

Humans are reliant on their caregivers for an extended period of time, offering numerous opportunities for environmental factors, such as parental attitudes and behaviors, to impact brain development. The default mode network is a neural system encompassing the medial prefrontal cortex, posterior cingulate cortex, precuneus, and temporo-parietal junction, which is implicated in aspects of cognition and psychopathology. Delayed default mode network maturation in children and adolescents has been associated with greater general dimensional psychopathology, and positive parenting behaviors have been suggested to serve as protective mechanisms against atypical default mode network development. The current study aimed to extend the existing research by examining whether within- default mode network resting-state functional connectivity would mediate the relation between parental acceptance/warmth and youth psychopathology. Data from the Adolescent Brain and Cognitive Development study, which included a community sample of 9,366 children ages 8.9-10.9 years, were analyzed to test this prediction. Results demonstrated a significant mediation, where greater parental acceptance/warmth predicted greater within- default mode network resting-state functional connectivity, which in turn predicted lower externalizing, but not internalizing symptoms, at baseline and 1-year later. Our study provides preliminary support for the notion that positive parenting behaviors may reduce the risk for psychopathology in youth through their influence on the default mode network.

Adolescent Alcohol and Stress Exposure Rewires Key Cortical Neurocircuitry

Human adolescence is a period of development characterized by wide ranging emotions and behavioral risk taking, including binge drinking (Konrad et al., 2013). These behavioral manifestations of adolescence are complemented by growth in the neuroarchitecture of the brain, including synaptic pruning (Spear, 2013) and increases in overall white matter volume (Perrin et al., 2008). During this period of profound physiological maturation, the adolescent brain has a unique vulnerability to negative perturbations. Alcohol consumption and stress exposure, both of which are heightened during adolescence, can individually and synergistically alter these neurodevelopmental trajectories in positive and negative ways (conferring both resiliency and susceptibility) and influence already changing neurotransmitter systems and circuits. Importantly, the literature is rapidly changing and evolving in our understanding of basal sex differences in the brain, as well as the interaction between biological sex and life experiences. The animal literature provides the distinctive opportunity to explore sex-specific stress- and alcohol- induced changes in neurocircuits on a relatively rapid time scale. In addition, animal models allow for the investigation of individual neurons and signaling molecules otherwise inaccessible in the human brain. Here, we review the human and rodent literature with a focus on cortical development, neurotransmitters, peptides, and steroids, to characterize the field's current understanding of the interaction between adolescence, biological sex, and exposure to stress and alcohol.

Adolescence as a sensitive period for neurotoxicity: Lifespan developmental effects of methylmercury

Neurotoxicity resulting from the environmental contaminant, methylmercury (MeHg), is a source of concern for many human populations that rely heavily on the consumption of fish and rice as stable ingredients in the diet. The developmental period of exposure is important both to the qualitative effects of MeHg and to the dose required to produce those effects. MeHg exposure during the sensitive prenatal period causes deleterious and long-lasting changes in neurodevelopment at particularly low doses. The effects include a wide host of cognitive and behavioral outcomes expressed in adulthood and sometimes not until aging. However, neurotoxic outcomes of methylmercury when exposure occurs during adolescence are only recently revealing impacts on human populations and animal models. This review examines the current body of work and showcases the sensitivity of adolescence, a period that straddles early development and adulthood, to methylmercury neurotoxicity and the implications such toxicity has in our understanding of methylmercury's effects in human populations and animal models.

Raging Hormones: Why Age-Based Etiological Conceptualizations of the Development of Antisocial Behavior Are Insufficient

Developmental science, particularly developmental neuroscience, has substantially influenced the modern legal system. However, this science has typically failed to consider the role of puberty and pubertal hormones on development when considering antisocial behavior. This review describes major theoretical positions on the developmental neuroscience of antisocial behavior and highlights where basic developmental neuroscience suggests that the role of puberty and pubertal hormones should be considered. The implications of the current state of the science with respect to developmental neuroscience is considered, particularly what is known in light of development beyond puberty. This review shows that development continues to an older age for many youth than the legal system typically acknowledges. The plasticity of the brain that this continued development implies has implications for the outcome of interventions in the legal system in ways that have not been explored. Future directions for both developmental scientists and legal professions are recommended.

Associations between testosterone, estradiol, and androgen receptor genotype with amygdala subregions in adolescents

Much is known about the development of the whole amygdala, but less is known about its structurally and functionally diverse subregions. One notable distinguishing feature is their wide range of androgen and estrogen receptor densities. Given the rise in pubertal hormones during adolescence, sex steroid levels as well as receptor sensitivity could influence age-related subregion volumes. Therefore, our goal was to evaluate the associations between the total amygdala and its subregion volumes in relation to sex hormones - estradiol and free testosterone (FT) - as a function of age and genetic differences in androgen receptor (AR) sensitivity in a sample of 297 adolescents (46% female). In males, we found small effects of FT-by-age interactions in the total amygdala, portions of the basolateral complex, and the cortical and medial nuclei (CMN), with the CMN effects being moderated by AR sensitivity. For females, small effects were seen with increased genetic AR sensitivity relating to smaller basolateral complexes. However, none of these small effects passed multiple comparisons. Future larger studies are necessary to replicate these small, yet possibly meaningful effects of FT-by-age associations and modulation by AR sensitivity on amygdala development to ultimately determine if they contribute to known sex differences in emotional neurodevelopment.

Developmental cascades and educational attainment

Developmental cascades describe how systems of development interact and influence one another to shape human development across the lifespan. Despite its popularity, developmental cascades are commonly used to understand the developmental course of psychopathology, typically in the context of risk and resilience. Whether this framework can be useful for studying children's educational outcomes remains underexplored. Therefore, in this chapter, we provide an overview of how developmental cascades can be used to study children's academic development, with a particular focus on the biological, cognitive, and contextual pathways to educational attainment. We also provide a summary of contemporary statistical methods and highlight existing data sets that can be used to test developmental cascade models of educational attainment from birth through adulthood. We conclude the chapter by discussing the challenges of this research and explore important future directions of using developmental cascades to understand educational attainment.

Adolescent Brain Development and Contextual Influences: A Decade in Review

Adolescence is a developmental period characterized by substantial psychological, biological, and neurobiological changes. This review discusses the past decade of research on the adolescent brain, as based on the overarching framework that development is a dynamic process both within the individual and between the individual and external inputs. As such, this review focuses on research showing that the development of the brain is influenced by multiple ongoing and dynamic elements. It highlights the implications this body of work on behavioral development and offers areas of opportunity for future research in the coming decade.

Age related sex differences in maladaptive regulatory responses to sadness: A study of youths at high and low familial risk for depression

Offspring of parents with depression histories are at increased risk of developing depression and also report maladaptive ways of self-regulating sadness. Maladaptive regulation of sadness tends to be more prevalent among females than males and has been proposed as one explanation of sex differences in depression rates that emerge around mid-adolescence. However, there is scant information about the age at which the sex differences in maladaptive regulatory responses become evident and whether such age-related sex differences vary depending on depression risk. The present study examined two samples aged 8-18 years: 86 offspring of emotionally healthy parents and 98 offspring of parents with depression histories. Subjects were clinically assessed and provided self-reports of maladaptive responses to sadness. In the combined samples, sex differences in maladaptive responses were significant at age 12.5 years and older ages (i.e., chronologically earlier than the documented emergence of sex differences in depression). While in the high-risk group, sex differences in maladaptive regulatory responses were significant at 12.11 years of age and older, in the low-risk group there was no age at which sex differences were significant. Our findings support the possible mechanistic role of maladaptive emotion regulation in the emergence of sex disparities in depression rates and have implications for prevention.

Altered Connectivity of the Frontoparietal Network During Attention Processing in Prolactinomas

Prolactinomas have been reported for the failure of cognitive functions. However, the electrophysiological mechanisms of attention processing in prolactinomas remain unclear. In a visual mission, we monitored the scalp electroencephalography (EEG) of the participants. Compared with the healthy controls (HCs), larger frontoparietal theta and alpha coherence were found in the patients, especially in the right-lateralized hemisphere, which indicated a deficit in attention processing. Moreover, the frontoparietal coherence was positively correlated with altered prolactin (PRL) levels, implying the significance of PRL for adaptive brain compensation in prolactinomas. Taken together, this research showed the variations in attention processing between the HCs and prolactinomas. The coherence between frontal and parietal regions may be one of the possible electrophysiological biomarkers for detecting deficient attention processing in prolactinomas.

Brain microstructural changes in mice persist in adulthood and are modulated by the palmitoyl acyltransferase ZDHHC7

For a long time, mice have been classified as adults with completely mature brains at 8 weeks of age, but recent research suggests that developmental brain changes occur for up to 6 months. In particular, adolescence coincides with dramatic changes of neuronal structure and function in the brain that influence the connectivity between areas like hippocampus and medial prefrontal cortex (mPFC). Neuronal development and plasticity are regulated in part by the palmitoyl acyltransferase ZDHHC7, which modulates structural connectivity between hippocampus and mPFC. The aim of the current study was to investigate whether developmental changes take place in hippocampus and mPFC microstructure even after 8 weeks of age and whether deficiency of ZDHHC7 impacts such age-dependent alterations. Altogether, 46 mice at 11, 14 or 17 weeks of age with a genetic Zdhhc7 knockout (KO) or wild type (WT) were analysed with neuroimaging and diffusion tensor-based fibre tractography. The hippocampus and mPFC regions were compared regarding fibre metrics, supplemented by volumetric and immunohistological analyses of the hippocampus. In WT animals, we identified age-dependent changes in hippocampal fibre lengths that followed a U-shaped pattern, whereas in mPFC, changes were linear. In Zdhhc7-deficient animals, the fibre statistics were reduced in both regions, whereas the hippocampus volume and the intensities of myelin and neurofilament were higher in 11-week-old KO mice compared to WTs. Our results confirmed ongoing changes of microstructure in mice up to 17 weeks old and demonstrate that deleting the Zdhhc7 gene impairs fibre development, suggesting that palmitoylation is important in this process.

Developmental variation in testosterone:cortisol ratio alters cortical- and amygdala-based cognitive processes

Testosterone (T) and cortisol (C) are the end products of neuroendocrine axes that interact with the process of shaping brain structure and function. Relative levels of T:C (TC ratio) may alter prefrontal-amygdala functional connectivity in adulthood. What remains unclear is whether TC-related effects are rooted to childhood and adolescence. We used a healthy cohort of 4-22-year-olds to test for associations between TC ratios, brain structure (amygdala volume, cortical thickness (CTh), and their coordinated growth), as well as cognitive and behavioral development. We found greater TC ratios to be associated with the growth of specific brain structures: 1) parietal CTh; 2) covariance of the amygdala with CTh in visual and somatosensory areas. These brain parameters were in turn associated with lower verbal/executive function and higher spatial working memory. In sum, individual TC profiles may confer a particular brain phenotype and set of cognitive strengths and vulnerabilities, prior to adulthood.

Shifting gradients of macroscale cortical organization mark the transition from childhood to adolescence

The transition from childhood to adolescence is marked by pronounced shifts in brain structure and function that coincide with the development of physical, cognitive, and social abilities. Prior work in adult populations has characterized the topographical organization of the cortex, revealing macroscale functional gradients that extend from unimodal (somatosensory/motor and visual) regions through the cortical association areas that underpin complex cognition in humans. However, the presence of these core functional gradients across development as well as their maturational course have yet to be established. Here, leveraging 378 resting-state functional MRI scans from 190 healthy individuals aged 6 to 17 y old, we demonstrate that the transition from childhood to adolescence is reflected in the gradual maturation of gradient patterns across the cortical sheet. In children, the overarching organizational gradient is anchored within the unimodal cortex, between somatosensory/motor and visual territories. Conversely, in adolescence, the principal gradient of connectivity transitions into an adult-like spatial framework, with the default network at the opposite end of a spectrum from primary sensory and motor regions. The observed gradient transitions are gradually refined with age, reaching a sharp inflection point in 13 and 14 y olds. Functional maturation was nonuniformly distributed across cortical networks. Unimodal networks reached their mature positions early in development, while association regions, in particular the medial prefrontal cortex, reached a later peak during adolescence. These data reveal age-dependent changes in the macroscale organization of the cortex and suggest the scheduled maturation of functional gradient patterns may be critically important for understanding how cognitive and behavioral capabilities are refined across development.

Effects of testosterone on intraocular pressure, thicknesses of retinal nerve fiber layer, ganglion cell complex, macula and on ocular blood flow in female-to-male transgender persons

PURPOSE

To compare the effects of testosterone on intraocular pressure (IOP), thicknesses of retinal nerve fiber layer (RNFL), ganglion cell complex (GCC), macula and on ocular blood flow between female-to-male transgender (FMT) persons who use testosterone and healthy women and healthy men.

METHOD

The study included 39 eyes of 20 FMT(Group 1), 40 eyes of 20 healthy women (Group 2), and 42 eyes of 21 healthy men (Group 3). In all subjects, RNFL, GCC and, macular thicknesses (MT) were measured by optical coherence tomography (OCT). Ocular blood flow was measured by Color Doppler Ultrasonography in all subjects.

RESULTS

IOP levels in FMT were significantly higher than men (p = 0.025). Superior (Sup), inferior (Inf) thicknesses of parafovea, and nasal thickness of perifovea in FMT were significantly higher than the Group 2 (p = 0.024, p = 0.037, p = 0.018). Sup thickness of perifovea in FMT was significantly higher than Group 3 (p = 0.011). Inf thickness of perifovea in FMT was significantly higher than Group 2 and 3 (p = 0.038, p = 0.002). Mean thickness of RNFL Inf in FMT was significantly higher than the Group 2 and 3 (p = 0.039, p = 0.032). Avg and Inf thicknesses of GCC in FMT were significantly higher than group 2 (p = 0.02, p = 0.005). In correlation test, systole/diastole ratio(S/D) in ophthalmic artery (OA) (r = 0.504, p = 0.028) and Inf thickness of perifovea (r = 0.485, p = 0.035) were positively correlated with the serum levels of testosterone in FMT.

CONCLUSIONS

We found that the use of supraphysiologic testosterone dose increased IOP and the thicknesses of macula, RNFL, and GCC in FMT. Serum testosterone level was positively correlated with S/D ratio in the OA.

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.

Epigenetics of the developing and aging brain: Mechanisms that regulate onset and outcomes of brain reorganization

Brain development is a life-long process that encompasses several critical periods of transition, during which significant cognitive changes occur. Embryonic development, puberty, and reproductive senescence are all periods of transition that are hypersensitive to environmental factors. Rather than isolated episodes, each transition builds upon the last and is influenced by consequential changes that occur in the transition before it. Epigenetic marks, such as DNA methylation and histone modifications, provide mechanisms by which early events can influence development, cognition, and health outcomes. For example, parental environment influences imprinting patterns in gamete cells, which ultimately impacts gene expression in the embryo which may result in hypersensitivity to poor maternal nutrition during pregnancy, raising the risks for cognitive impairment later in life. This review explores how epigenetics induce and regulate critical periods, and also discusses how early environmental interactions prime a system towards a particular health outcome and influence susceptibility to disease or cognitive impairment throughout life.

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.

Impact of gonadectomy on maturational changes in brain volume in adolescent macaques

Adolescence is a transitional period between childhood and adulthood characterized by significant changes in global and regional brain tissue volumes. It is also a period of increasing vulnerability to psychiatric illness. The relationship between these patterns and increased levels of circulating sex steroids during adolescence remains unclear. The objective of the current study was to determine whether gonadectomy, prior to puberty, alters adolescent brain development in male rhesus macaques. Ninety-six structural MRI scans were acquired from 12 male rhesus macaques (8 time points per animal over a two-year period). Six animals underwent gonadectomy and 6 animals underwent a sham operation at 29 months of age. Mixed-effects models were used to determine whether gonadectomy altered developmental trajectories of global and regional brain tissue volumes. We observed a significant effect of gonadectomy on the developmental trajectory of prefrontal gray matter (GM), with intact males showing peak volumes around 3.5 years of age with a subsequent decline. In contrast, prefrontal GM volumes continued to increase in gonadectomized males until the end of the study. We did not observe a significant effect of gonadectomy on prefrontal white matter or on any other global or regional brain tissue volumes, though we cannot rule out that effects might be detected in a larger sample. Results suggest that the prefrontal cortex is more vulnerable to gonadectomy than other brain regions.

Shaping of the Female Human Brain by Sex Hormones: A Review

Traditionally sex hormones have been associated with reproductive and developmental processes only. Since the 1950s we know that hormones can have organizational effects on the developing brain and initiate hormonal transition periods such as puberty. However, recent evidence shows that sex hormones additionally structure the brain during important hormonal transition periods across a woman's life including short-term fluctuations during the menstrual cycle. However, a comprehensive review focusing on structural changes during all hormonal transition phases of women is still missing. Therefore, in this review structural changes across hormonal transition periods (i.e., puberty, menstrual cycle, oral contraceptive intake, pregnancy and menopause) were investigated in a structured way and correlations with sex hormones evaluated. Results show an overall reduction in grey matter and region-specific decreases in prefrontal, parietal and middle temporal areas during puberty. Across the menstrual cycle grey matter plasticity in the hippocampus, the amygdala as well as temporal and parietal regions were most consistently reported. Studies reporting on pre- and post-pregnancy measurements revealed volume reductions in midline structures as well as prefrontal and temporal cortices. During perimenopause, the decline in sex hormones was paralleled with a reduction in hippocampal and parietal cortex volume. Brain volume changes were significantly correlated with estradiol, testosterone and progesterone levels in some studies, but directionality remains inconclusive between studies. These results indicate that sex hormones play an important role in shaping women's brain structure during different transition periods and are not restricted to specific developmental periods.

Sex-Related Differences in White Matter Asymmetry and Its Implications for Verbal Working Memory in Psychosis High-Risk State

Objective: Sexual dimorphism has been investigated in schizophrenia, although sex-specific differences among individuals who are at clinical high-risk (CHR) for developing psychosis have been inconclusive. This study aims to characterize sexual dimorphism of language areas in the brain by investigating the asymmetry of four white matter tracts relevant to verbal working memory in CHR patients compared to healthy controls (HC). HC typically show a leftward asymmetry of these tracts. Moreover, structural abnormalities in asymmetry and verbal working memory dysfunctions have been associated with neurodevelopmental abnormalities and are considered core features of schizophrenia. Methods: Twenty-nine subjects with CHR (17 female/12 male) for developing psychosis and twenty-one HC (11 female/10 male) matched for age, sex, and education were included in the study. Two-tensor unscented Kalman filter tractography, followed by an automated, atlas-guided fiber clustering approach, were used to identify four fiber tracts related to verbal working memory: the superior longitudinal fasciculi (SLF) I, II and III, and the superior occipitofrontal fasciculus (SOFF). Using fractional anisotropy (FA) of tissue as the primary measure, we calculated the laterality index for each tract. Results: There was a significantly greater right>left asymmetry of the SLF-III in CHR females compared to HC females, but no hemispheric difference between CHR vs. HC males. Moreover, the laterality index of SLF-III for CHR females correlated negatively with Backward Digit Span performance, suggesting a greater rightward asymmetry was associated with poorer working memory functioning. Conclusion: This study suggests increased rightward asymmetry of the SLF-III in CHR females. This finding of sexual dimorphism in white matter asymmetry in a language-related area of the brain in CHR highlights the need for a deeper understanding of the role of sex in the high-risk state. Future work investigating early sex-specific pathophysiological mechanisms, may lead to the development of novel personalized treatment strategies aimed at preventing transition to a more chronic and difficult-to-treat disorder.

Size Matters: The CAG Repeat Length of the Androgen Receptor Gene, Testosterone, and Male Adolescent Depression Severity

There is a distinct increase in the prevalence of depression with the onset of puberty. The role of peripubertal testosterone levels in boys in this context is insufficiently understood and may be modulated by a functional polymorphism of the androgen receptor gene (AR), a variable number of CAG repeats. Moreover, there is preliminary evidence that the relationship between testosterone, CAG repeat length, and the severity of depressive symptoms may differ between subclinical and overt depression, but this has neither been studied in a clinical sample of adolescents with depression nor compared between subclinical and overt depression in an adequately powered study. To investigate the relationship between free testosterone, CAG repeat length of the AR, depression status (subclinical vs. overt), and the severity of depressive symptoms, 118 boys treated as in- or daycare patients at a single psychiatric hospital were studied. Of these, 73 boys had at least mild depressive symptoms according to the Beck Depression Inventory-II (BDI-II > 13). Higher-order moderation analysis in the multiple regression framework revealed a constant relationship between free testosterone and depression severity irrespective of the number of CAG repeats in adolescents with a BDI-II score ≤ 13. In adolescents with a BDI-II score > 13, however, there was a significant negative relationship between free testosterone and BDI-II score in patients with <19 CAG repeats and a significant positive relationship regarding free testosterone and BDI-II score in those with more than 28 CAG repeats, even when considering important covariates. These results suggest that the effects of testosterone on mood in male adolescents with depression depend on the genetic make-up of the AR as well as on depression status. This complex relationship should be considered by future studies addressing mental health issues against an endocrine background and may, moreover, contribute to tailored treatment concepts in psychiatric medicine, especially in adults.

White matter microstructure correlates of age, sex, handedness and motor ability in a population-based sample of 3031 school-age children

Understanding the development of white matter microstructure in the general population is an imperative precursor to identifying its involvement in psychopathology. Previous studies have reported changes in white matter microstructure associated with age and different developmental patterns between boys and girls. Handedness has also been related to white matter in adults. Motor performance, tightly dependent on overall neuronal myelination, has been related to the corpus callosum. However, the association between motor performance and global white matter microstructure has not been reported in the literature. In general, these age, sex, handedness, and motor performance associations have been observed using small and poorly representative samples. We examined the relationships between age, sex, handedness, and motor performance, measured with a finger tapping task, and white matter microstructure in the forceps major and minor and in 5 tracts bilaterally (cingulum, corticospinal, inferior and superior longitudinal fasciculi, and uncinate) in a population-based sample of 3031 children between 8 and 12 years of age. Diffusion tensor imaging (DTI) data were acquired using a single, study-dedicated 3 Tesla scanner. We extracted and quantified features of white matter microstructure for each tract. We computed global DTI metrics by combining scalar values across multiple tracts into single latent factors using a confirmatory factor analysis. The adjusted linear regression models indicated that age was associated with global fractional anisotropy (FA), global mean diffusivity (MD), and almost all the tracts. Further, girls showed lower global MD than boys, while FA values differed by tract, and no age-sex interactions were found. No differences were observed in white matter microstructure between right- and left-handed children. We observed that FA in forceps major was associated with right-hand finger tapping performance. White matter FA in association tracts was only related to motor function before multiple testing correction. Our findings do not provide evidence for a relationship between finger tapping task performance and global white matter microstructure.