Understanding the epigenetic basis of sex differences in depression

Sex-specific neurobehavioral and biochemical effects of developmental exposure to Malathion in offspring mice

Malathion is an organophosphate pesticide (OP) commonly used in agriculture, industry, and veterinary medicine. Sex is a crucial factor in responding to neurotoxicants, yet the sex-specific effects of OP exposure, particularly neurological impairments following chronic low-level exposure remains limited. Our study aims to evaluate the neurobehavioral and biochemical effects of developmental exposure to Malathion across sexes. Pregnant mice were exposed to a low oral dose of Malathion from gestation up to the weaning of the pups, which were individually gavaged with a similar dose regimen until postnatal day 70. Our results show that Malathion decreased body weight and food intake, reduced locomotor activity and recognition memory. Motor coordination and special memory were only altered in females, whereas we found a male-specific effect of Malathion on social behavior and marble burying. These alterations were accompanied by increased malondialdehyde (MDA), decreased brain acetylcholinesterase activity (AChE), and disrupted brain redox homeostasis. Our findings about the effects of Malathion exposure across sexes may, in part, contribute to understanding the dimorphic susceptibilities observed in neurological disorders.

Profiling Small RNA From Brain Extracellular Vesicles in Individuals With Depression

BACKGROUND

Major depressive disorder (MDD) is a leading cause of disability with significant mortality risk. Despite progress in our understanding of the etiology of MDD, the underlying molecular changes in the brain remain poorly understood. Extracellular vesicles (EVs) are lipid-bound particles that can reflect the molecular signatures of the tissue of origin. We aimed to optimize a streamlined EV isolation protocol from postmortem brain tissue and determine whether EV RNA cargo, particularly microRNAs (miRNAs), have an MDD-specific profile.

METHODS

EVs were isolated from postmortem human brain tissue. Quality was assessed using western blots, transmission electron microscopy, and microfluidic resistive pulse sensing. EV RNA was extracted and sequenced on Illumina platforms. Functional follow-up was performed in silico.

RESULTS

Quality assessment showed an enrichment of EV markers, as well as a size distribution of 30 to 200 nm in diameter, and no contamination with cellular debris. Small RNA profiling indicated the presence of several RNA biotypes, with miRNAs and transfer RNAs being the most prominent. Exploring miRNA levels between groups revealed decreased expression of miR-92a-3p and miR-129-5p, which was validated by qPCR and was specific to EVs and not seen in bulk tissue. Finally, in silico functional analyses indicate potential roles for these 2 miRNAs in neurotransmission and synaptic plasticity.

CONCLUSION

We provide a streamlined isolation protocol that yields EVs of high quality that are suitable for molecular follow-up. Our findings warrant future investigations into brain EV miRNA dysregulation in MDD.

Mental Health Needs of Adolescent and Young Adult PrEP Users in South Africa: Implications for Sexual and Reproductive Health Programming

PURPOSE

Poor mental health is associated with sexual and reproductive health (SRH) risks, including human immunodeficiency virus (HIV) and pre-exposure prophylaxis discontinuation. Adolescents and young people (AYP) are vulnerable to HIV and depression. This paper describes the prevalence and severity of depression and associated factors in AYP accessing SRH services in South Africa.

METHODS

A cross-sectional analysis of enrollment data (January 2019 to December 2021) from a cohort of individuals receiving pre-exposure prophylaxis services at eight clinics in three provinces in South Africa was conducted. Females (n = 1,074) and males (n = 231) aged 15-24 years were included. Interviewer-administered questionnaires were conducted, and the prevalence and severity of depression assessed using the Patient Health Questionnaire-9. Multivariate analysis was used to identify factors associated with depression.

RESULTS

Over 40% of participants had experienced any depression symptoms (43.7% of females, 38.5% of males). For males, experiencing intimate partner violence was the only predictor of depression symptoms (adjusted odds ratio (AOR) 8.81, 95% confidence intervals (CI) 1.03-75.44). For females, living with both parents (AOR 1.70, 95% CI 1.15-2.51), having transactional sex (AOR 1.63, 95% CI 1.00-2.65), experiencing any intimate partner violence (AOR 1.96, 95% CI 1.34-2.89), and using drugs (AOR 1.78, 95% CI 1.03-3.11) were all positively associated with depression symptoms. Resilience was a protective factor against depression symptoms for both sexes (males: AOR 0.96, 95% CI 0.93-0.98; females: AOR 0.96, 95% CI 0.95-0.97).

DISCUSSION

There is a high burden of depression among AYP accessing SRH services in South Africa. Mental health screening should be integrated into SRH and HIV prevention programs for AYP.

A commentary on "Don't mind the gap: Why we do not care about the gender gap in mental health?" by P. Patalay and O. Demkowicz

In their article, Drs. Patalay and Demkowicz raise important questions about research regarding the sex/gender gap in depression rates. However, their perspective on this topic is rather polarizing and yields statements of questionable accuracy. In this Commentary, I respond to several statements in the Article, which I consider potentially misleading. My goal is to present a broader perspective on sex/gender and depression and encourage further discussion of this important topic.

A sex-specific genome-wide association study of depression phenotypes in UK Biobank

There are marked sex differences in the prevalence, phenotypic presentation and treatment response for major depression. While genome-wide association studies (GWAS) adjust for sex differences, to date, no studies seek to identify sex-specific markers and pathways. In this study, we performed a sex-stratified genome-wide association analysis for broad depression with the UK Biobank total participants (N = 274,141), including only non-related participants, as well as with males (N = 127,867) and females (N = 146,274) separately. Bioinformatics analyses were performed to characterize common and sex-specific markers and associated processes/pathways. We identified 11 loci passing genome-level significance (P < 5 × 10-8) in females and one in males. In both males and females, genetic correlations were significant between the broad depression GWA and other psychopathologies; however, correlations with educational attainment and metabolic features including body fat, waist circumference, waist-to-hip ratio and triglycerides were significant only in females. Gene-based analysis showed 147 genes significantly associated with broad depression in the total sample, 64 in the females and 53 in the males. Gene-based analysis revealed "Regulation of Gene Expression" as a common biological process, but suggested sex-specific molecular mechanisms. Finally, sex-specific polygenic risk scores (PRSs) for broad depression outperformed total and the opposite sex PRSs in the prediction of broad major depressive disorder. These findings provide evidence for sex-dependent genetic pathways for clinical depression as well as for health conditions comorbid with depression.

Differential effects of the stress peptides PACAP and CRF on sleep architecture in mice

Stress produces profound effects on behavior, including persistent alterations in sleep patterns. Here we examined the effects of two prototypical stress peptides, pituitary adenylate cyclase-activating polypeptide (PACAP) and corticotropin-releasing factor (CRF), on sleep architecture and other translationally-relevant endpoints. Male and female mice were implanted with subcutaneous transmitters enabling continuous measurement of electroencephalography (EEG) and electromyography (EMG), as well as body temperature and locomotor activity, without tethering that restricts free movement, body posture, or head orientation during sleep. At baseline, females spent more time awake (AW) and less time in slow wave sleep (SWS) than males. Mice then received intracerebral infusions of PACAP or CRF at doses producing equivalent increases in anxiety-like behavior. The effects of PACAP on sleep architecture were similar in both sexes and resembled those reported in male mice after chronic stress exposure. Compared to vehicle infusions, PACAP infusions decreased time in AW, increased time in SWS, and increased rapid eye movement sleep (REM) time and bouts on the day following treatment. In addition, PACAP effects on REM time remained detectable a week after treatment. PACAP infusions also reduced body temperature and locomotor activity. Under the same experimental conditions, CRF infusions had minimal effects on sleep architecture in either sex, causing only transient increases in SWS during the dark phase, with no effects on temperature or activity. These findings suggest that PACAP and CRF have fundamentally different effects on sleep-related metrics, and provide new insights into the mechanisms by which stress disrupts sleep.

Methylome changes associated with functional movement/conversion disorder: Influence of biological sex and childhood abuse exposure

Epigenetic changes, such as DNA methylation (DNAm), may represent an important mechanism implicated in the etiopathogenesis of functional movement/conversion disorder (FMD). Here, we aimed to identify methylomic variations in a case-control cohort of FMD and to uncover specific epigenetic signatures associated with female sex and childhood abuse, two key risk factors for FMD and other functional neurological disorders. Genome-wide DNAm analysis was performed from peripheral blood in 57 patients with FMD and 47 healthy controls with and without childhood abuse. Using principal component analysis, we examined the association of principal components with FMD status in abused and non-abused individuals, in the entire study sample and in female subjects only. Next, we used enrichment pathway analysis to investigate the biological significance of DNAm changes and explored differences in methylation levels of genes annotated to the top enriched biological pathways shared across comparisons. We found that FMD was associated with DNAm variation across the genome and identified a common epigenetic 'signature' enriched for biological pathways implicated in chronic stress and chronic pain. However, methylation levels of genes included in the top two shared pathways hardly overlapped, suggesting that transcriptional profiles may differ as a function of childhood abuse exposure and sex among subjects with FMD. This study is unique in providing genome-wide evidence of DNAm changes in FMD and in indicating a potential mechanism linking childhood abuse exposure and female sex to differences in FMD pathophysiology. Future studies are needed to replicate our findings in independent cohorts.

Sex Differences in Depression and Anxiety

Depression and anxiety disorders carry a tremendous worldwide burden and emerge as a significant cause of disability among western societies. Both disorders are known to disproportionally affect women, as they are twice more likely to be diagnosed and moreover, they are also prone to suffer from female-specific mood disorders. Importantly, the prevalence of these affective disorders has notably risen after the COVID pandemic, especially in women. In this chapter, we describe factors that are possibly contributing to the expression of such sex differences in depression and anxiety. For this, we overview the effect of transcriptomic and genetic factors, the immune system, neuroendocrine aspects, and cognition. Furthermore, we also provide evidence of sex differences in antidepressant response and their causes. Finally, we emphasize the importance to consider sex as a biological variable in preclinical and clinical research, which may facilitate the discovery and development of new and more efficacious antidepressant and anxiolytic pharmacotherapies for both women and men.

Astroglia in the Vulnerability to and Maintenance of Stress-Mediated Neuropathology and Depression

Significant stress exposure and psychiatric depression are associated with morphological, biochemical, and physiological disturbances of astrocytes in specific brain regions relevant to the pathophysiology of those disorders, suggesting that astrocytes are involved in the mechanisms underlying the vulnerability to or maintenance of stress-related neuropathology and depression. To understand those mechanisms a variety of studies have probed the effect of various modalities of stress exposure on the metabolism, gene expression and plasticity of astrocytes. These studies have uncovered the participation of various cellular pathways, such as those for intracellular calcium regulation, neuroimmune responses, extracellular ionic regulation, gap junctions-based cellular communication, and regulation of neurotransmitter and gliotransmitter release and uptake. More recently epigenetic modifications resulting from exposure to chronic forms of stress or to early life adversity have been suggested to affect not only neuronal mechanisms but also gene expression and physiology of astrocytes and other glial cells. However, much remains to be learned to understand the specific role of those and other modifications in the astroglial contribution to the vulnerability to and maintenance of stress-related disorders and depression, and for leveraging that knowledge to achieve more effective psychiatric therapies.

Auditing the Editor: A Review of Key Translational Issues in Epigenetic Editing

Currently, most advances in site-specific epigenetic editing for human use are concentrated in basic research, yet, there is considerable interest to translate this technology beyond the bench. This review highlights recent developments with epigenetic editing technology in comparison with the canonical CRISPR-Cas genome editing, as well as the epistemic and ethical considerations with preemptive translation of epigenetic editing into clinical or commercial use in humans. Key considerations in safety, equity, and access to epigenetic editing are highlighted, with a spotlight on the ethical, legal, and social issues of this technology in the context of global health equity.

Lipoic acid prevents mirtazapine-induced weight gain in mice without impairs its antidepressant-like action in a neuroendocrine model of depression

Mirtazapine (MIRT) is a multi-target antidepressant used in treatment of severe depression with promising efficacy, but also with important side effects, mainly sedation and weight gain. Thus, the present study aimed to test the effects of the neuroprotective antioxidant lipoic acid (ALA) in the reversal of weight and metabolic changes induced by MIRT in corticosterone-induced depression model in mice, as well as proposed mechanisms for their association antidepressant and pro-cognitive effects. To do these male Swiss mice received Tween 80 (control), corticosterone (CORT 20 mg / kg), MIRT (3 mg / kg) and ALA (100 or 200 mg / kg), alone or associated for 21 days. After this, the animals were subjected to behavioral tests for affective and cognitive domains. Daily weight changes, blood cholesterol fractions and corticosterone were measured. Also, hippocampus (HC) protein expression of the serotonin transporter (SERT), synaptophysin, protein kinase B-Akt (total and phosphorylated) and the cytokines IL-4 and IL-6 were investigated. CORT induced a marked depression-like behavior, memory deficits, metabolic changes (total cholesterol and LDL) and increased serum corticosterone. Also, CORT increased SERT expression in the HC. MIRT alone or combined with ALA sustained its antidepressant-like effect, as well as reversed CORT-induced impairment in spatial recognition memory. Additionally, the association MIRT+ALA200 reversed the weight gain induced by the former antidepressant, as well as reduced serum corticosterone levels and SERT expression in the HC. ALA alone induced significant weight loss and reduced total cholesterol and HDL fraction. Our findings provide promising evidence about the ALA potential to prevent metabolic and weight changes associated to MIRT, without impair its antidepressant and pro-cognition actions. Therefore, ALA+MIRT combination could represent a new therapeutic strategy for treating depression with less side effects.

DNA Epigenetics in Addiction Susceptibility

Addiction is a chronically relapsing neuropsychiatric disease that occurs in some, but not all, individuals who use substances of abuse. Relatively little is known about the mechanisms which contribute to individual differences in susceptibility to addiction. Neural gene expression regulation underlies the pathogenesis of addiction, which is mediated by epigenetic mechanisms, such as DNA modifications. A growing body of work has demonstrated distinct DNA epigenetic signatures in brain reward regions that may be associated with addiction susceptibility. Furthermore, factors that influence addiction susceptibility are also known to have a DNA epigenetic basis. In the present review, we discuss the notion that addiction susceptibility has an underlying DNA epigenetic basis. We focus on major phenotypes of addiction susceptibility and review evidence of cell type-specific, time dependent, and sex biased effects of drug use. We highlight the role of DNA epigenetics in these diverse processes and propose its contribution to addiction susceptibility differences. Given the prevalence and lack of effective treatments for addiction, elucidating the DNA epigenetic mechanism of addiction vulnerability may represent an expeditious approach to relieving the addiction disease burden.

Translating the Transcriptome: Sex Differences in the Mechanisms of Depression and Stress, Revisited

The past decade has produced a plethora of studies examining sex differences in the transcriptional profiles of stress and mood disorders. As we move forward from accepting the existence of extensive molecular sex differences in the brain to exploring the purpose of these sex differences, our approach must become more systemic and less reductionist. Earlier studies have examined specific brain regions and/or cell types. To use this knowledge to develop the next generation of personalized medicine, we need to comprehend how transcriptional changes across the brain and/or the body relate to each other. We provide an overview of the relationships between baseline and depression/stress-related transcriptional sex differences and explore contributions of preclinically identified mechanisms and their impacts on behavior.

A Review on Epigenetic Inheritance of Experiences in Humans

If genetics defines the inheritance of DNA, epigenetics aims to regulate and make it adaptable. Epigenetic alterations include DNA methylation, chromatin remodelling, post-translational modifications of histone proteins and activity of non-coding RNAs. Several studies, especially in animal models, have reported transgenerational inheritance of epigenetic marks. However, evidence of transgenerational inheritance in humans via germline in the absence of any direct exposure to the driving external stimulus remains controversial. Most of the epimutations exist in relation with genetic variants. The present review looks at intergenerational and transgenerational inheritance in humans, (both father and mother) in response to diet, exposure to chemicals, stress, exercise, and disease status. If not transgenerational, at least intergenerational human studies could help to understand early processes of inheritance. In humans, female and male germline development follow separate paths of epigenetic events and both oocyte and sperm possess their own unique epigenomes. While DNA methylation alterations are reset during epigenetic reprogramming, non-coding RNAs via human sperm provide evidence of being reliable carriers for transgenerational inheritance. Human studies reveal that one mechanism of epigenetic inheritance cannot be applied to the complete human genome. Multiple factors including time, type, and tissue of exposure determine if the modified epigenetic mark could be transmissible and till which generation. Population-specific differences should also be taken into consideration while associating inheritance to an environmental exposure. A longitudinal study targeting one environmental factor, but different population groups should be conducted at a specific geographical location to pinpoint heritable epigenetic changes.

Sex/gender differences in the brain are not trivial-A commentary on Eliot et al. (2021)

In this commentary to the comprehensive review by Eliot et al. (2021), we fully comply with rejecting the 'sexual dimorphism' concept in its extreme, binary form. However, we criticise the authors' extreme position and argue that sex/gender differences in the brain are far from being 'trivial' and 'unlikely to be meaningful'. Our key arguments refer to the importance of small effects which can have meaningful behavioural consequences, and to several non-binary sex/gender-related factors which might explain individual differences better than sex/gender per se and which have shown to play important roles as risk factors in the aetiology of many mental and neurodevelopmental disorders. We conclude that the biopsychosocial approach is key to understanding sex/gender differences in the brain better than we currently do.

Life With Corona: Increased Gender Differences in Aggression and Depression Symptoms Due to the COVID-19 Pandemic Burden in Germany

Gender differences (GD) in mental health have come under renewed scrutiny during the COVID-19 pandemic. While rapidly emerging evidence indicates a deterioration of mental health in general, it remains unknown whether the pandemic will have an impact on GD in mental health. To this end, we investigate the association of the pandemic and its countermeasures affecting everyday life, labor, and households with changes in GD in aggression, anxiety, depression, and the somatic symptom burden. We analyze cross-sectional data from 10,979 individuals who live in Germany and who responded to the online survey "Life with Corona" between October 1, 2020 and February 28, 2021. We estimate interaction effects from generalized linear models. The analyses reveal no pre-existing GD in aggression but exposure to COVID-19 and COVID-19 countermeasures is associated with sharper increases in aggression in men than in women. GD in anxiety decreased among participants with children in the household (with men becoming more anxious). We also observe pre-existing and increasing GD with regards to the severity of depression, with women presenting a larger increase in symptoms during the hard lockdown or with increasing stringency. In contrast to anxiety, GD in depression increased among participants who lived without children (women > men), but decreased for individuals who lived with children; here, men converged to the levels of depression presented by women. Finally, GD in somatic symptoms decreased during the hard lockdown (but not with higher stringency), with men showing a sharper increase in symptoms, especially when they lived with children or alone. Taken together, the findings indicate an increase in GD in mental health as the pandemic unfolded in Germany, with rising female vulnerability to depression and increasing male aggression. The combination of these two trends further suggests a worrying mental health situation for singles and families. Our results have important policy implications for the German health system and public health policy. This public health challenge requires addressing the rising burden of pandemic-related mental health challenges and the distribution of this burden between women and men, within families and for individuals who live alone.

The effect of sex on the mouse lens transcriptome

The transcriptome of mammalian tissues differs between males and females, and these differences can change across the lifespan, likely regulating known sexual dimorphisms in disease prevalence and severity. Cataract, the most prevalent disease of the ocular lens, occurs at similar rates in young individuals, but its incidence is elevated in older women compared to men of the same age. However, the influence of sex on the lens transcriptome was unknown. RNAseq based transcriptomic profiling of young adult C57BL/6J mouse lens epithelial and fiber cells revealed that few genes are differentially expressed between the sexes. In contrast, lens cells from aged (24 month old) male and female C57BL/6J mice differentially expressed many genes, including several whose expression is lens preferred. Like cataracts, posterior capsular opacification (PCO), a major sequela of cataract surgery, may also be more prevalent in women. Lens epithelial cells isolated from mouse eyes 24 h after lens fiber cell removal exhibited numerous transcriptomic differences between the sexes, including genes implicated in complement cascades and extracellular matrix regulation, and these differences are much more pronounced in aged mice than in young mice. These results provide an unbiased basis for future studies on how sex affects the lens response to aging, cataract development, and cataract surgery.

Environmental enrichment improves lifelong persistent behavioral and epigenetic changes induced by early-life stress

This study aimed to evaluate the effects of environmental enrichment (EE) in Wistar rats subjected to maternal deprivation (MD). MD was performed in the first post-natal days (PND) ten for 3 h/day. The groups were: control; deprived without EE; and deprived with EE. The EE was applied for 3 h/day. Forced swimming test (FST) and open field test were performed, and histone deacetylase (HDAC) and DNA methyltransferase (DNMT) activities in the prefrontal cortex (PFC) and hippocampus were evaluated on 31, 41, and 61 PND. MD altered spontaneous locomotor activity and immobility time in FST, but the effects were sex- and developmental period dependent. In deprived females at PND 31, 41, and 61, HDAC and DNMT increased in the PFC and hippocampus. In females exposed to EE for 20 days, there was a decrease of HDAC in the hippocampus and DNMT in the PFC and hippocampus. Exposure of females to EE for 40 days can reverse HDAC and DNMT increase in all brain areas. In deprived males at PND 31, 41, and 61, HDAC and DNMT increased in the hippocampus, and in the group exposed to EE for 40 days, there was a decrease in hippocampal activity. In PFC of male deprived rats at PND 61 and EE for 40 days, there was a reduction of HDAC and DNMT. MD induced lifelong persistent behavioral and epigenetic changes, and such effects were more evident in female than male rats. EE can be considered an essential non-pharmacological strategy to treat long-term trauma-induced early life changes.

Synaptic Microenvironment in Depressive Disorder: Insights from Synaptic Plasticity

Depression is a major disease that can affect both mental and physical health, limits psychosocial functioning and diminishes the quality of life. But its complex pathogenesis remains poorly understood. The dynamic changes of synaptic structure and function, known as synaptic plasticity, occur with the changes of different cellular microenvironment and are closely related to learning and memory function. Accumulating evidence implies that synaptic plasticity is integrally involved in the pathological changes of mood disorders, especially in depressive disorder. However, the complex dynamic process of synaptic plasticity is influenced by many factors. Here, we reviewed and discussed various factors affecting synaptic plasticity in depression, and proposed a specific framework named synaptic microenvironment, which may be critical for synaptic plasticity under pathological conditions. Based on this concept, we will show how we understand the balance between the synaptic microenvironment and the synaptic plasticity network in depression. Finally, we point out the clinical significance of the synaptic microenvironment in depression.

Fatores de risco e proteção e sintomas de depressão na adolescência

Avaliou-se a relação fatores de proteção e risco e sintomas depressivos na adolescência. Foi realizado um estudo transversal com amostra de 388 adolescentes de Sergipe, estudantes do ensino médio. Utilizaram-se um questionário sociodemográfico/escolar e as escalas da Bateria de Avaliação de Indicadores de Depressão Infantojuvenil (BAID-IJ). Os dados foram analisados por meio do teste de Regressão Logística Multinomial. Observou-se que o sexo feminino (OR = 6,1) e ter idade igual ou superior a 16 anos (OR = 3,3) aumentaram consideravelmente as chances de os adolescentes pontuarem no estrato de elevada pontuação quanto à sintomatologia depressiva. Baixa pontuação em autoconceito (OR = 5,7), elevado desamparo (OR = 12,3), elevada solidão (OR = 7,0) e elevada desesperança (OR = 2,8) exibiram impacto significativo para a presença de sintomas de depressão. Acredita-se tais achados podem auxiliar na elaboração de intervenções eficazes frente aos sintomas depressivos na adolescência.

Depression and substance use disorders: Clinical comorbidity and shared neurobiology

Mood disorders, including major depressive disorder (MDD), are the most prevalent psychiatric illnesses, and pose an incredible burden to society, both in terms of disability and in terms of costs associated with medical care and lost work time. MDD has extremely high rates of comorbidity with substance use disorders (SUD) as many of the same neurobiological circuits and molecular mechanisms regulate the reward pathways disrupted in both conditions. MDD may induce SUDs, SUD may contribute to MDD development, or underlying vulnerabilities and common life experience may confer risk to developing both conditions. In this chapter we explore theories of MDD and SUD comorbidity, the neurobiological underpinnings of depression, overlapping cellular and molecular pathways for both conditions, and current treatment approaches for these comorbid conditions.

An Overview of the Heterogeneity of Major Depressive Disorder: Current Knowledge and Future Prospective

Major depressive disorder (MDD) is estimated to impose maximum debilitating effects on the society by 2030, with its critical effects on health, functioning, quality of life and concomitant high levels of morbidity and mortality. Yet, the disease is inadequately understood, diagnosed and treated. Moreover, with the recent drastic rise in the pace of life, stress has materialized as one of the most potent environmental factors for depression. In this scenario, it is important to understand the modern pathogenetic hypotheses and mechanisms, and possibly try to shift from the traditional approaches in depression therapy. These include the elaboration of pathophysiological changes in heterogeneous systems such as genetic, epigenetic, serotonergic, noradrenergic, gamma-aminobutyric acid, glutamatergic and endocannabinoid systems, neurotrophic factors, HPA axis, immune system as well as cellular stress mechanisms. These components interact with each other in a complex matrix and further elucidation of their mechanism and cascade pathways are needed. This might aid in the identification of MDD subtypes as well as the development of sophisticated biomarkers. Further, characterization might also aid in developing multitargeted therapies that hold much promise as compared to the conventional monoamine based treatment. New candidate pharmacons, refined psychotherapeutic modalities, advanced neuro-surgical and imaging techniques as well as the implementation of pharmacokinetic, pharmacogenetic prescribing guidelines constitute the emerging expanses of MDD treatment.

miR-218 in Adolescence Predicts and Mediates Vulnerability to Stress

BACKGROUND

Adolescence is a period of increased vulnerability to psychiatric disorders, including depression. Discovering novel biomarkers to identify individuals who are at high risk is very much needed. Our previous work shows that the microRNA miR-218 mediates susceptibility to stress and depression in adulthood by targeting the netrin-1 guidance cue receptor gene Dcc in the medial prefrontal cortex (mPFC).

METHODS

Here, we investigated whether miR-218 regulates Dcc expression in adolescence and could serve as an early predictor of lifetime stress vulnerability in male mice.

RESULTS

miR-218 expression in the mPFC increases from early adolescence to adulthood and correlates negatively with Dcc levels. In blood, postnatal miR-218 expression parallels changes occurring in the mPFC. Notably, circulating miR-218 levels in adolescence associate with vulnerability to social defeat stress in adulthood, with high levels associated with social avoidance severity. Indeed, downregulation of miR-218 in the mPFC in adolescence promotes resilience to stress in adulthood.

CONCLUSIONS

miR-218 expression in adolescence may serve both as a marker of risk and as a target for early interventions.

Animal models built for women's brain health: Progress and potential

Women and men have different levels of risk for a variety of brain disorders. Despite this well-known epidemiological finding, preclinical work utilizing animal models has historically only included male animals. The policies of funders to require consideration of sex as a biological variable has shifted the momentum to include female animals in preclinical neuroscience and to report findings by sex. However, there are many biological questions related to brain health that go beyond sex differences and are indeed specific to women. Here, the focus is on why animal models should be utilized in the pursuit of understanding women's brain health, a brief overview of what they have provided thus far, and why they still hold tremendous promise. This review concludes with a set of suggestions for how to begin to pursue translational animal models in a way that facilitates rapid success and harnesses the most powerful aspects of animal models.

The impact of sex and gender on heart-brain axis dysfunction: current concepts and novel perspectives

The heart-brain axis (HBA) recapitulates all the circuits that regulate bidirectional flow of communication between heart and brain. Several mechanisms may underlie the interdependent relationship involving heterogeneous tissues at rest and during specific target organ injury such as myocardial infarction, heart failure, arrhythmia, stroke, mood disorders, or dementia. In-depth translational studies of the HBA dysfunction under single-organ injury should include both male and female animals to develop sex- and gender-oriented prevention, diagnosis, and treatment strategies. Indeed, sex and gender are determining factors as females and males exhibit significant differences in terms of susceptibility to risk factors, age of onset, severity of symptoms, and outcome. Despite most studies having focused on the male population, we have conducted a careful appraisal of the literature investigating HBA in females. In particular, we have (i) analyzed sex-related heart and brain illnesses, (ii) recapitulated the most significant studies simultaneously conducted on cardio- and cerebro-vascular systems in female populations, and (iii) hypothesized future perspectives for the development of a gender-based approach to HBA dysfunction. Although sex- and gender-oriented research is at its infancy, the impact of sex on HBA dysfunction is opening unexpected new avenues for managing the health of female subjects exposed to risk of lifestyle multi-organ disease.

Stress and signaling pathways regulating autophagy: From behavioral models to psychiatric disorders

Autophagy is a process of degradation and recycling of cytoplasmatic components by the lysosomes. In the central nervous system (CNS), autophagy is involved in cell surveillance, neuroinflammation, and neuroplasticity. Neuropsychiatric conditions are associated with functional disturbances at molecular and cellular levels, causing significant impairments in cell homeostasis. Additionally, emerging evidence supports that dysfunctions in autophagy contribute to the pathophysiology of neurological diseases. However, the studies on autophagy in psychiatric disorders are highly heterogeneous and have several limitations, mainly to assess causality and determine the autophagy flux in animals and human samples. Besides, the role of this mechanism in non-neuronal cells in the CNS is only recently being explored. Thus, this review summarizes and discusses the changes in the autophagy pathway in animal models of psychiatric disorders and the limitations underlying the significant findings. Moreover, we compared these findings with clinical studies. Understanding the involvement of autophagy in psychiatric conditions, and the limitation of our current models may contribute to the development of more effective research approaches and possibly pharmacological therapies.

New insights on brain-derived neurotrophic factor epigenetics: from depression to memory extinction

Advances in characterizing molecular profiles provide valuable insights and opportunities for deciphering the neuropathology of depression. Although abnormal brain-derived neurotrophic factor (BDNF) expression in depression has gained much support from preclinical and clinical research, how it mediates behavioral alterations in the depressed state remains largely obscure. Environmental factors contribute significantly to the onset of depression and produce robust epigenetic changes. Epigenetic regulation of BDNF, as one of the most characterized gene loci in epigenetics, has recently emerged as a target in research on memory and psychiatric disorders. Specifically, epigenetic alterations of BDNF exons are heavily involved in mediating memory functions and antidepressant effects. In this review, we discuss key research on stress-induced depression from both preclinical and clinical studies, which revealed that differential epigenetic regulation of specific BDNF exons is associated with depression pathophysiology. Considering that BDNF has a central role in depression, we argue that memory extinction, an adaptive response to fear exposure, is dependent on BDNF modulation and holds promise as a prospective target for alleviating or treating depression and anxiety disorders.

Epigenetics, Gender, and Sex in the Diagnosis of Depression

Background :

A marked sexual dimorphism exists in psychiatric diagnoses. Culture derived gender bias in diagnostic criteria is one explanation. Adverse childhood events, including sexual and physical abuse, are more reliable and consistent predictors of later psychiatric diagnoses, including depression and post-traumatic stress disorder. Some interesting interactions between genes and experience have been uncovered, but the primary effect appears to be epigenetic with life experience altering gene expression and being transmitted to subsequent generations.

Objectives :

To determine if reconceptualizing depression as encompassing both internalizing and externalizing strategies would eliminate gender differences in the diagnosis of depression

Methods :

We reviewed 74 life stories of patients, collected during a study of the effect of physicians’ knowing patients’ life stories on the quality of the doctor-patient relationship. Looking at diagnoses, the prevalence of women to men was 2.9 to 1. We redefined depression as a response to being in a seemingly hopeless situation accompanied by despair, either externalizing ((more often diagnosed as substance use disorders, impulse control disorders, antisocial personality disorder, or bipolar disorder) or internalizing (the more standard diagnosis of depression). Then we reviewed these life stories from that perspective to determine how many would be diagnosed as depressed.

Results :

With this reconceptualization of depression, the sex ratio changed to 1.2 to 1.

Conclusions:

From this perspective, men and women are equally likely to respond to hopelessness, though men are more socialized to externalize and women to internalize. Considering depression in this way may help to better identify men at risk for suicide.

Unraveling the epigenetic landscape of depression: focus on early life stress

Depression is a devastating psychiatric disorder caused by a combination of genetic predisposition and life events, mainly exposure to stress. Early life stress (ELS) in particular is known to "scar" the brain, leading to an increased susceptibility to developing depression later in life via epigenetic mechanisms. Epigenetic processes lead to changes in gene expression that are not due to changes in DNA sequence, but achieved via modulation of chromatin modifications, DNA methylation, and noncoding RNAs. Here we review common epigenetic mechanisms including the enzymes that take part in reading, writing, and erasing specific epigenetic marks. We then describe recent developments in understanding how ELS leads to changes in the epigenome that are manifested in increased susceptibility to depression-like abnormalities in animal models. We conclude with highlighting the need for future studies that will potentially enable the utilisation of the understanding of epigenetic changes linked to ELS for the development of much-needed novel therapeutic strategies and biomarker discovery.
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CYP19A1 rs2470152 polymorphism increases susceptibility to depression in Chinese Han population

Estrogen plays a vital role in the pathogenesis of depression. The cytochrome p450 (CYP) 19A1 gene encodes aromatase, which is responsible for a key step in estrogen production. Previous studies suggested that CYP19A1 polymorphisms increase the risk of depression in the Japanese population. The current study aimed to investigate the correlation between the CYP19A1 rs2470152 polymorphism and the risk of depression in Chinese Han population. In total, 1006 Chinese Han subjects were recruited in this case-control study, including 502 patients diagnosed with depression and 504 healthy gender- and age-matched (from 18-65 years) controls. Genotyping was performed using multiplex PCR and high-throughput sequencing to assess the effects of the CYP19A1 rs2470152 (G > A) polymorphism on the risk of depression in the entire cohort and the subjects were further stratified by gender. No significant differences were observed in allele and genotype frequencies of CYP19A1 rs2470152 between total cases and controls (P > 0.05). However, the CYP19A1 rs2470152 polymorphism in the recessive model (AA vs. GG + GA) was associated with increased risk of depression (χ² = 4.077, P = 0.043, OR = 1.347, 95% CI = 1.008-1.798). After subjects stratification by gender, neither genotypes nor genetic models showed significant differences between cases and controls (all P > 0.05). The results indicated that the CYP19A1 rs2470152 (G > A) polymorphism in the recessive model (AA vs. GG + GA) was correlated with increased risk of depression in Chinese Han population.

Paternal transgenerational epigenetic mechanisms mediating stress phenotypes of offspring

Depression and anxiety risk are highly influenced by both genetic and environmental factors. Recently, it has been proposed that epigenetic mechanisms may also contribute to the transmission of both depression- and anxiety-related behaviors across multiple generations. This review highlights long-lasting epigenetic alterations observed in offspring of fathers, including some distinct effects on male and female offspring, in animal models. Available evidence emphasizes how both the developmental time point and the type of paternal stress (social vs. asocial) influence the complex transmission patterns of these phenotypes to future generations. This research is critical in understanding the factors that influence risk for depression and anxiety disorders and has the potential to contribute to the development of innovative treatments that can more precisely target vulnerable populations.

Placebo mechanisms in depression: An experimental investigation of the impact of expectations on sadness in female participants

INTRODUCTION

We aimed to examine whether drug-associated expectations have an impact on the experience of sadness. We hypothesized that participants who received an active placebo nasal spray (but were told that it was an antidepressant that would protect them from experiencing negative emotions) would become less sad than the control groups.

METHODS

128 healthy female participants were randomly allocated to one of four groups: the experimental group, which received an active placebo and the expectancy-modifying instructions ("Protection: the spray protects from experiencing negative emotions", n = 32), or one of three different control groups ("Sensitization": the spray sensitizes to negative emotions", n = 31; "Placebo: the spray is a placebo", n = 32; and "Control: no nasal spray", n = 32) RESULTS: In line with our hypotheses, the experimental group experienced significantly less sadness after having watched a sadness provoking film sequence compared to the three control groups, with medium- to large effect sizes (Hedge´s gs 0.59-0.87).

DISCUSSION

Our results suggest that sadness can be significantly influenced by placebos in the short-term. Our study further suggests that knowledge about the effect of placebos on depressive symptoms should be utilized in clinical practice. However, depression is a complex disorder and antidepressants address a wide range of symptoms associated with depression such as suicidal thoughts, disturbed sleep and loss of energy. Further research on the placebo effects associated with the antidepressant treatment is needed.

LIMITATIONS

concern generalizability to treatment because sadness is only one potential symptom of depression and antidepressants often also address other symptoms.

Prenatal Dexamethasone Exposure Induced Alterations in Neurobehavior and Hippocampal Glutamatergic System Balance in Female Rat Offspring

Epidemiological investigations have suggested that periodic use of dexamethasone during pregnancy is a risk factor for abnormal behavior in offspring, but the potential mechanism remains unclear. In this study, we investigated the changes in the glutamatergic system and neurobehavior in female offspring with prenatal dexamethasone exposure (PDE) to explore intrauterine programing mechanisms. Compared with the control group, rat offspring with PDE exhibited spatial memory deficits and anxiety-like behavior. The expression of hippocampal glucocorticoid receptors (GR) and histone deacetylase 2 (HDAC2) increased, whereas histone H3 lysine 14 acetylation (H3K14ac) of brain-derived neurotrophic factor (BDNF) exon IV (BDNF IV) and expression of BDNF decreased. The glutamatergic system also changed. We further observed that changes in the fetal hippocampus were consistent with those in adult offspring. In vitro, the administration of 0.5 μM dexamethasone to the H19-7 fetal hippocampal neuron cells directly led to a cascade of changes in the GR/HDAC2/BDNF pathway, whereas the GR antagonist RU486 and the HDAC2 inhibitor romidepsin (Rom) reversed changes caused by dexamethasone to the H3K14ac level of BDNF IV and to the expression of BDNF. The increase in HDAC2 can be reversed by RU486, and the changes in the glutamatergic system can be partially reversed after supplementation with BDNF. It is suggested that PDE increases the expression of HDAC2 by activating GR, reducing the H3K14ac level of BDNF IV, inducing alterations in neurobehavior and hippocampal glutamatergic system balance. The findings suggest that BDNF supplementation and glutamatergic system improvement are potential therapeutic targets for the fetal origins of abnormal neurobehavior.

Sex Differences in the Epigenome: A Cause or Consequence of Sexual Differentiation of the Brain?

Females and males display differences in neural activity patterns, behavioral responses, and incidence of psychiatric and neurological diseases. Sex differences in the brain appear throughout the animal kingdom and are largely a consequence of the physiological requirements necessary for the distinct roles of the two sexes in reproduction. As with the rest of the body, gonadal steroid hormones act to specify and regulate many of these differences. It is thought that transient hormonal signaling during brain development gives rise to persistent sex differences in gene expression via an epigenetic mechanism, leading to divergent neurodevelopmental trajectories that may underlie sex differences in disease susceptibility. However, few genes with a persistent sex difference in expression have been identified, and only a handful of studies have employed genome-wide approaches to assess sex differences in epigenomic modifications. To date, there are no confirmed examples of gene regulatory elements that direct sex differences in gene expression in the brain. Here, we review foundational studies in this field, describe transcriptional mechanisms that could act downstream of hormone receptors in the brain, and suggest future approaches for identification and validation of sex-typical gene programs. We propose that sexual differentiation of the brain involves self-perpetuating transcriptional states that canalize sex-specific development.

DNA methylation studies of depression with onset in the peripartum: A critical systematic review

OBJECTIVE

Major depression with peripartum onset (MDP) has been associated with multiple adverse offspring health outcomes. The biological mechanisms underlying this relationship remain unclear, but DNA methylation (DNAm) represents a plausible mechanism for mediating MDP exposures and changes in offspring development, behavior, and health. Advances in DNAm research necessitate reevaluating the MDP-DNAm literature to determine how well past studies conform with current best practices.

METHOD

Five databases were searched to identify studies of prenatal-onset MDP and DNAm. Quality scores were assigned to each article independently by two raters using a novel scale specific for MDP-DNAm research.

RESULTS

Nineteen studies met inclusion criteria. Quality scores ranged from 10 to 17 out of 24 points (M = 12.8; SD = 1.9), with higher scores indicating increased study rigor. Poor covariate reporting was the most significant contributor to lower scores.

CONCLUSION

No longitudinal MDP-DNAm studies exist. Earlier MDP-DNAm studies should be interpreted with caution, and future research must commit to sharing methodology and data to facilitate cross-study comparisons and maximize dataset utility.

Depression and neuroticism decrease among women but not among men between 1976 and 2016 in Swedish septuagenarians

OBJECTIVES

We evaluated birth-cohort differences in depressive symptom burden, prevalence of depression diagnoses, and neuroticism, among Swedish 70-year-olds examined between 1976 and 2016.

METHODS

We used a repeated cross-sectional design examining four representative population samples of Swedish 70-year-olds (total n = 2279) with identical methods in 1976-77 (n = 392), 1992-93 (n = 226), 2000-02 (n = 487), and 2014-16 (n = 1166). Depressive symptom burden was rated with the Montgomery Åsberg Depression Rating Scale. Major depression was diagnosed according to DSM-5, and minor depression according to DSM-IV-TR research criteria. Neuroticism was rated with the Eysenck Personality Inventory.

RESULTS

For women in 2014-16, MADRS score (4.4 vs. 6.1 vs. 5.8; P < 0.05) and neuroticism (6.6 vs. 7.7 vs. 9.2; P < 0.05) were lower compared with 1992-93 and 1976-77, and the prevalence of any depression was lower compared with 2000-02 and 1992-93 (10.9% vs. 16.9% vs. 18.1%; P < 0.05). For men, we observed no birth-cohort differences in depression, while neuroticism was found to be lower in 2014-16 compared with 1976-77 among men without depression (5.1 vs. 5.9; P < 0.01). The sex difference for MADRS and neuroticism declined between 1976-77 and 2014-16 (cohort*sex P < 0.05).

CONCLUSIONS

Depressive burden and neuroticism decreased in 70-year-old women between 1976 and 2016.

Environmental Programming of Susceptibility and Resilience to Stress in Adulthood in Male Mice

Epidemiological evidence identifies early life adversity as a significant risk factor for the development of mood disorders. Much evidence points to the role of early life experience in susceptibility and, to a lesser extent, resilience, to stress in adulthood. While many models of these phenomena exist in the literature, results are often conflicting and a systematic comparison of multiple models is lacking. Here, we compare effects of nine manipulations spanning the early postnatal through peri-adolescent periods, both at baseline and following exposure to chronic social defeat stress in adulthood, in male mice. By applying rigorous criteria across three commonly used measures of depression- and anxiety-like behavior, we identify manipulations that increase susceptibility to subsequent stress in adulthood and other pro-resilient manipulations that mitigate the deleterious consequences of adult stress. Our findings point to the importance of timing of early life stress and provide the foundation for future studies to probe the neurobiological mechanisms of risk and resilience conferred by variation in the early life environment.

Sex differences in depression: Insights from clinical and preclinical studies

Depression represents a global mental health concern, and disproportionally affects women as they are twice more likely to be diagnosed than men. In this review, we provide a summary of evidence to support the notion that differences in depression between men and women span multiple facets of the disease, including epidemiology, symptomology, treatment, and pathophysiology. Through a lens of biological sex, we overview depression-related transcriptional patterns, changes in neuroanatomy and neuroplasticity, and immune signatures. We acknowledge the unique physiological and behavioral demands of pregnancy and motherhood by devoting special attention to depression occurring in the peripartum period. Specifically, we discuss issues surrounding the presentation, time course, treatment, and neurobiology of peripartum depression. We write this review with the intention of highlighting the encouraging advancements in our understanding of sex differences in depression, while underscoring the gaps that remain. A more systematic consideration of biological sex as a variable in depression research will be critical in the discovery and development of pharmacotherapies that are efficacious for both men and women.

Prenatal and postnatal experiences associated with epigenetic changes in the adult mouse brain

To analyze the influences of early-life history on the brain epigenome, the offspring of mouse dams kept in an enriched or standard environment were exposed postnatally to enriched, standard, or adverse conditions. The methylation patterns of 7 candidate genes (9 loci) involved in developmental programming of stress vulnerability/resilience and psychiatric disease were analyzed in 6 brain regions of adult male and female mice. Exposure to an enriched prenatal environment was associated with widespread epigenetic changes (all of small effect size), affecting 29 of 324 (9%) gene/region-specific methylation patterns. The effects of either adverse or enriched postnatal conditions were tested separately in the two prenatal cohorts. Significant changes were observed in 2 of 324 (0.6%) loci in offspring of dams in a standard environment and 6 of 324 (1.9%) loci in animals that were exposed prenatally to an enriched environment. Prenatal life experiences appear to have a bigger effect on the adult brain epigenome than postnatal experiences. Positive prenatal life experiences may increase epigenetic plasticity of the brain later in life. All observed between-group differences were sex-specific, consistent with largely different developmental trajectories of the male and female brain. Multiple changes of small effect size are consistent with a multifactorial model of developmental programming of adult behavior and disease susceptibility.

Gene regulatory mechanisms underlying sex differences in brain development and psychiatric disease

The sexual differentiation of the mammalian nervous system requires the precise coordination of the temporal and spatial regulation of gene expression in diverse cell types. Sex hormones act at multiple developmental time points to specify sex-typical differentiation during embryonic and early development and to coordinate subsequent responses to gonadal hormones later in life by establishing sex-typical patterns of epigenetic modifications across the genome. Thus, mutations associated with neuropsychiatric conditions may result in sexually dimorphic symptoms by acting on different neural substrates or chromatin landscapes in males and females. Finally, as stress hormone signaling may directly alter the molecular machinery that interacts with sex hormone receptors to regulate gene expression, the contribution of chronic stress to the pathogenesis or presentation of mental illness may be additionally different between the sexes. Here, we review the mechanisms that contribute to sexual differentiation in the mammalian nervous system and consider some of the implications of these processes for sex differences in neuropsychiatric conditions.

Brain inflammasomes in stroke and depressive disorders: Regulation by oestrogen

Neuroinflammation is a devastating pathophysiological process that results in brain damage and neuronal death. Pathogens, cell fragments and cellular dysfunction trigger inflammatory responses. Irrespective of the cause, inflammasomes are key intracellular multiprotein signalling platforms that sense neuropathological conditions. The activation of inflammasomes leads to the auto-proteolytic cleavage of caspase-1, resulting in the proteolysis of the pro-inflammatory cytokines interleukin (IL)1β and IL18 into their bioactive forms. It also initiates pyroptosis, a type of cell death. The two cytokines contribute to the pathogenesis in acute and chronic brain diseases and also play a central role in human aging and psychiatric disorders. Sex steroids, in particular oestrogens, are well-described neuroprotective agents in the central nervous system. Oestrogens improve the functional outcome after ischaemia and traumatic brain injury, reduce neuronal death in Parkinson's and Alzheimer's disease, as well as in amyotrophic lateral sclerosis, attenuate glutamate excitotoxicity and the formation of radical oxygen species, and lessen the spread of oedema after damage. Moreover, oestrogens alleviate menopause-related depressive symptoms and have a positive influence on depressive disorders probably by influencing growth factor production and serotonergic brain circuits. Recent evidence also suggests that inflammasome signalling affects anxiety- and depressive-like behaviour and that oestrogen ameliorates depression-like behaviour through the suppression of inflammasomes. In the present review, we highlight the most recent findings demonstrating that oestrogens selectively suppress the activation of the neuroinflammatory cascade in the brain in acute and chronic brain disease models. Furthermore, we aim to describe putative regulatory signalling pathways involved in the control of inflammasomes. Finally, we consider that psychiatric disorders such as depression also contain an inflammatory component that could be modulated by oestrogen.

Investigation of variants in estrogen receptor genes and perinatal depression

OBJECTIVES

Depressive symptoms are common during pregnancy and after childbirth. Estrogen levels fluctuate greatly during the course of pregnancy and may contribute to mood instability. The first aim of this case-control study was to investigate whether variants in the two estrogen receptor genes might contribute to the genetic susceptibility to pregnancy-related depression using controls that were screened for postnatal depression. The second aim was to uncover new variants in the two estrogen receptor genes.

PATIENTS AND METHODS

Our study sample comprised 554 control subjects who had Edinburgh Postnatal Depression Scale (EPDS) scores below 7 at postnatal screening, and 159 patients with clinically diagnosed pregnancy-related depression. They were genotyped for four single-nucleotide polymorphisms (SNPs) and a dinucleotide repeat in the two genes: estrogen receptor α (ESR1) and estrogen receptor β (ESR2). Fifty-six cases with personal and/or family history of depression of psychiatric disorders were selected for resequencing of the two genes.

RESULTS

There was no statistically significant association with perinatal depression for all five variants. However, there was a trend toward higher frequencies of the genotypes associated with higher risk of depression for rs2077647 and rs4986938 in the case group. From resequencing, two novel ESR1 variants were identified from two different patients.

CONCLUSION

Our study that used screened controls with low EPDS scores and cases with clinically diagnosed pregnancy-related depression could not replicate the association with depression for any of the SNPs for both genotype and allele frequencies. Two novel SNPs were identified and could be further investigated in a larger sample set.

Evidence of sexual dimorphism of HTR1B gene on major adult ADHD comorbidities

Attention-deficit/hyperactivity disorder (ADHD) is a very common psychiatric disorder across the life cycle and frequently presents comorbidities. Since ADHD is highly heritable, several studies have focused in the underlying genetic factors involved in its etiology. One of the major challenges in this search is the phenotypic heterogeneity, which could be partly attributable to the sexual dimorphism frequently seen in psychiatric disorders. Taking into account the well-known sexual dimorphic effect observed in serotonergic system characteristics, we differentially tested the influence of HTR1B SNPs (rs11568817, rs130058, rs6296 and rs13212041) on ADHD susceptibility and on its major comorbidities according to sex. The sample comprised 564 adults with ADHD diagnosed according to DSM-IV criteria and 635 controls. There was no association of any HTR1B SNPs tested in relation to ADHD susceptibility. As for the comorbidities evaluated, after correction for multiple tests, significant associations were observed for both rs11568817 and rs130058 with substance use disorders (P_corr = 0.009 and P_corr = 0.018, respectively) and for rs11568817 with nicotine dependence (P_corr = 0.025) in men with ADHD. In women with ADHD, the same rs11568817 was associated with generalized anxiety disorder (P_corr = 0.031). The observed effects of rs11568817 G allele presence conferring risk to either substance use disorders or generalized anxiety disorder according to sex, suggest an overall scenario where a higher transcriptional activity of HTR1B, resulting from the presence of this allele, is related to externalizing behaviors in men and internalizing behaviors in women. These results are consistent with and expand previous evidence of sexual dimorphism of the serotoninergic system.