Behavioral sexual dimorphism in models of anxiety and depression due to changes in HPA axis activity

Maternal immune activation induces sex-dependent behavioral differences in a rat model of schizophrenia

Background

Maternal immune activation (MIA) is a mature means to construct a schizophrenia model. However, some preclinical studies have reported that a MIA-induced schizophrenia model seemed to have gender heterogeneity in behavioral phenotype. On the other hand, the MIA's paradigms were diverse in different studies, and many details could affect the effect of MIA. To some extent, it is not credible and scientific to directly compare the gender differences of different MIA programs. Therefore, it is necessary to study whether the sex of the exposed offspring leads to behavioral differences on the premise of maintaining a consistent MIA mode.

Methods

An animal model of schizophrenia was established by the administration of 10 mg/kg Poly (I: C) when dams were on day 9 of gestation. Then, a number of female and male offspring completed a series of behavioral tests during postnatal days 61-75.

Results

Compared with the female control group (n = 14), female MIA offspring (n = 12) showed a longer movement distance (d = 1.07, p < 0.05) and higher average speed (d = 1.08, p < 0.05) in the open field test (OFT). In the Y maze test, the percentage of entering the novel arm of female MIA offspring was lower (d = 0.92, p < 0.05). Compared with the male control group (n = 14), male MIA offspring (n = 13) displayed less movement distance (d = 0.93, p < 0.05) and a lower average speed (d = 0.94, p < 0.05) in the OFT. In the Y maze test, the proportion of exploration time in the novel arm of male MIA offspring was lower (d = 0.96, p < 0.05). In the EPM, male MIA offspring showed less time (d = 0.85, p < 0.05) and a lower percentage of time spent in the open arms (d = 0.85, p < 0.05). Male MIA offspring also had a lower PPI index (76 dB + 120 dB, d = 0.81, p < 0.05; 80 dB + 120 dB, d = 1.45, p < 0.01).

Conclusions

Our results showed that the behavioral phenotypes induced by prenatal immune activation were highly dependent on the sex of the offspring.

Enduring sex-dependent implications of pubertal stress on the gut-brain axis and mental health

The gut-brain axis (GBA) is a network responsible for the bidirectional communication between the central nervous system and the gastrointestinal tract. This multifaceted system is comprised of a complex microbiota, which may be altered by both intrinsic and extrinsic factors. During critical periods of development, these intrinsic and extrinsic factors can cause long-lasting sex-dependent changes in the GBA, which can affect brain structure and function. However, there is limited understanding of how the GBA is altered by stress and how it may be linked to the onset of mental illness during puberty. This article reviews current literature on the relationships between the GBA, the effects of stress during puberty, and the implications for mental health.

Influencing factors of life satisfaction among medical staff of rehabilitation departments based on a structural equation model

Life satisfaction (LS) exhibited gender differences and was associated with age, income, and negative emotions. There is no research on the relationship between professional values and LS, although professional values are essential for medical staff and correlate with negative emotions. This study aimed to explore the relationship between professional values and LS, the action mechanism of influencing factors of LS, and gender differences among medical staff of rehabilitation departments in China. A total of 284 participants (108 men and 176 women) completed the questionnaires. Data were analyzed using SPSS19.0 and Amos21.0. Age, length of service, and anxiety differed significantly between genders. Professional values had a direct effect on LS and an indirect effect on LS via anxiety and depression. Therefore, enhancing professional values and reducing anxiety and depression could increase the medical staff's LS. Moreover, the LS of female medical staff improved with age.

Practical solutions for including sex as a biological variable (SABV) in preclinical neuropsychopharmacological research

Recently, many funding agencies have released guidelines on the importance of considering sex as a biological variable (SABV) as an experimental factor, aiming to address sex differences and avoid possible sex biases to enhance the reproducibility and translational relevance of preclinical research. In neuroscience and pharmacology, the female sex is often omitted from experimental designs, with researchers generalizing male-driven outcomes to both sexes, risking a biased or limited understanding of disease mechanisms and thus potentially ineffective therapeutics. Herein, we describe key methodological aspects that should be considered when sex is factored into in vitro and in vivo experiments and provide practical knowledge for researchers to incorporate SABV into preclinical research. Both age and sex significantly influence biological and behavioral processes due to critical changes at different timepoints of development for males and females and due to hormonal fluctuations across the rodent lifespan. We show that including both sexes does not require larger sample sizes, and even if sex is included as an independent variable in the study design, a moderate increase in sample size is sufficient. Moreover, the importance of tracking hormone levels in both sexes and the differentiation between sex differences and sex-related strategy in behaviors are explained. Finally, the lack of robust data on how biological sex influences the pharmacokinetic (PK), pharmacodynamic (PD), or toxicological effects of various preclinically administered drugs to animals due to the exclusion of female animals is discussed, and methodological strategies to enhance the rigor and translational relevance of preclinical research are proposed.

Sex Differences in Stress Response: Classical Mechanisms and Beyond

Neuropsychiatric disorders, which are associated with stress hormone dysregulation, occur at different rates in men and women. Moreover, nowadays, preclinical and clinical evidence demonstrates that sex and gender can lead to differences in stress responses that predispose males and females to different expressions of similar pathologies. In this curated review, we focus on what is known about sex differences in classic mechanisms of stress response, such as glucocorticoid hormones and corticotrophin-releasing factor (CRF), which are components of the hypothalamicpituitary- adrenal (HPA) axis. Then, we present sex differences in neurotransmitter levels, such as serotonin, dopamine, glutamate and GABA, as well as indices of neurodegeneration, such as amyloid β and Tau. Gonadal hormone effects, such as estrogens and testosterone, are also discussed throughout the review. We also review in detail preclinical data investigating sex differences caused by recentlyrecognized regulators of stress and disease, such as the immune system, genetic and epigenetic mechanisms, as well neurosteroids. Finally, we discuss how understanding sex differences in stress responses, as well as in pharmacology, can be leveraged into novel, more efficacious therapeutics for all. Based on the supporting evidence, it is obvious that incorporating sex as a biological variable into preclinical research is imperative for the understanding and treatment of stress-related neuropsychiatric disorders, such as depression, anxiety and Alzheimer's disease.

A Survey on the Knowledge, Attitudes, Behaviors and Influencing Factors of Caregivers for Newborns With COVID-19 in Chongqing, China

OBJECTIVE

This study aimed to investigate the healthcare knowledge, attitudes, and behaviors of primary caregivers of newborns with coronavirus disease 2019 (COVID-19) during the pandemic in Chongqing, China, and analyze the influencing factors.

METHODS

 The study included primary caregivers of COVID-19 newborns hospitalized in our institution from December 2022 to January 2023. A questionnaire survey was initiated to assess the caregivers' health-care knowledge, attitudes, and behaviors for COVID-19 and the influencing factors. The data were analyzed statistically.

RESULTS

A total of 195 caregivers were included, one for each infant with COVID-19. The questionnaire consisted of three dimensions. For the knowledge dimension, the top scoring items were wearing masks in public spaces (4.92 ± 0.087), strengthening hand hygiene (4.83 ± 0.164), and frequent ventilation in living environment (4.62 ± 0.331) in order; for the attitude dimension, the top three scoring items were wearing masks in public spaces (4.85 ± 0.353), strengthening hand washing and disinfection (4.72 ± 0.450), and regular ventilation (4.49 ± 0.501). For the behavior dimension, the top three were confidence in winning the challenge of the pandemic (4.71 ± 0.480), standardized wearing of masks in public spaces/confined spaces (4.68 ± 0.589), and high satisfaction with community epidemic prevention measures (4.67 ± 0.496). Among the influencing factors, fear of COVID-19 was the independent risk indicator for the caregivers' anxiety (OR = 38.085, 95% CI = 14.383-100.664) and fear of COVID-19 (OR = 8.170, 95%CI = 2.156-30.957) and fever (OR = 10.213, 95% CI = 1.972-52.892) were the independent risk indicators for depression.

CONCLUSION

 The study shows a key link between caregiver knowledge, attitudes, behaviors, and neonatal COVID-19 infection, with a gap between knowledge, attitudes, and behaviors. Caregivers, especially those dealing with premature infants, worried about mother-to-child transmission and experienced multiple births, face significant psychological stress during this phase of the pandemic.

A systematic mapping review of the evolution of the rat Forced Swim Test: Protocols and outcome parameters

As depression is projected to become the leading mental disease burden globally by 2030, understanding the underlying pathology, as well as screening potential anti-depressants with a higher efficacy, faster onset of action, and/or fewer side-effects is essential. A commonly used test for screening novel antidepressants and studying depression-linked aspects in rodents is the Porsolt Forced Swim Test. The present systematic mappping review gives a comprehensive overview of the evolution and of the most prevalently used set-ups of this test in rats, including the choice of animals (strain, sex, and age), technical aspects of protocol and environment, as well as reported outcome measures. Additionally, we provide an accessible list of all existing publications, to support informed decision-making for procedural and technical aspects of the test, to thereby enhance reproducibility and comparability. This should further contribute to reducing the number of unnecessarily replicated experiments, and consequently, reduce the number of animals used in future.

Sex and hormonal status influence the anxiolytic-like effect of oxytocin in mice

Anxiety and depression are highly prevalent psychiatric disorders, affecting approximately 18% of the United States population. Evidence indicates that central oxytocin mediates social cognition, social bonding, and social anxiety. Although it is well-established that oxytocin ameliorates social deficits, less is known about the therapeutic effects of oxytocin in non-social contexts. We hypothesized that positive effects of oxytocin in social contexts are attributable to intrinsic effects of oxytocin on neural systems that are related to emotion regulation. The present study investigated the effect of intracerebroventricular (ICV) oxytocin administration (i.e., central action) on anxiety- and depression-like behavior in C57Bl/6J mice using non-social tests. Male and female mice received an ICV infusion of vehicle or oxytocin (100, 200, or 500 ng), then were tested in the elevated zero maze (for anxiety-like behavior) and the tail suspension test (for depression-like behavior). Oxytocin dose-dependently increased open zone occupancy and entries in the elevated zero maze and reduced immobility duration in the tail suspension test in both sexes. Oxytocin decreased anxiety and depression-like behavior in male and female mice. The observed effect of oxytocin on anxiolytic-like behavior appeared to be driven by the males. Given the smaller anxiolytic-like effect of oxytocin in the female mice and the established interaction between oxytocin and reproductive hormones (estrogen and progesterone), we also explored whether oxytocin sensitivity in females varies across estrous cycle phases and in ovariectomized females that were or were not supplemented with estrogen or progesterone. Oxytocin reduced anxiety-like behavior in female mice in proestrus/estrus, ovariectomized females (supplemented or not with estrogen or progesterone), but not females in metestrus/diestrus. Additionally, oxytocin reduced depression-like behavior in all groups tested with slight differences across the various hormonal statuses. These results suggest that the effect of oxytocin in depression- and anxiety-like behavior in mice can be influenced by sex and hormonal status.

Effects of the dopamine depleting agent tetrabenazine in tests evaluating different components of depressive-like behavior in mice: sex-dependent response to antidepressant drugs with SERT and DAT blocker profiles

BACKGROUND

Depression is a disorder twice as common in women than in men. There are sex differences in the symptomatology and treatment response to this disorder. Impairments in behavioral activation (i.e. anergia, fatigue) are often seen in people with depression and are highly resistant to treatment. The role of mesolimbic dopamine (DA) in regulating behavioral activation has been extensively studied in male rodents, but little is known in female rodents.

OBJECTIVE

The present studies assessed potential sex differences in rodent paradigms used to study different components of depressive-like behavior, and in the treatment response to antidepressants with different mechanisms of action.

METHODS

Male and female CD1 mice received Tetrabenazine (TBZ), a VMAT-2 blocker that depletes DA and induces depressive symptoms in humans. Mice were tested on the Forced Swim Test, (FST), the Dark-Light box (DL), the elevated plus maze (EPM), Social Interaction (SI) test, and sucrose preference and consumption using the two bottles test. In addition, bupropion (a DA reuptake inhibitor) or fluoxetine (a serotonin reuptake inhibitor) were used to reverse TBZ-induced anergia.

RESULTS

In the FST, bupropion reversed TBZ effects in both sexes but fluoxetine was only effective in female mice. DA depletion did not affect other aspects of depression such as anxiety, sociability or sucrose consumption, and there was no interaction with bupropion on these parameters. In TBZ treated-females SERT-blockers may be effective at reversing anergia in aversive contexts (FST), and potentiating avoidance of anxiogenic stimuli.

CONCLUSIONS

Pro-dopaminergic antidepressants seem more efficacious at improving anergia in both sexes than SERT-blockers.

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.

The Wistar Kyoto Rat: A Model of Depression Traits

There is an ongoing debate about the value of animal research in psychiatry with valid lines of reasoning stating the limits of individual animal models compared to human psychiatric illnesses. Human depression is not a homogenous disorder; therefore, one cannot expect a single animal model to reflect depression heterogeneity. This limited review presents arguments that the Wistar Kyoto (WKY) rats show intrinsic depression traits. The phenotypes of WKY do not completely mirror those of human depression but clearly indicate characteristics that are common with it. WKYs present despair- like behavior, passive coping with stress, comorbid anxiety, and enhanced drug use compared to other routinely used inbred or outbred strains of rats. The commonly used tests identifying these phenotypes reflect exploratory, escape-oriented, and withdrawal-like behaviors. The WKYs consistently choose withdrawal or avoidance in novel environments and freezing behaviors in response to a challenge in these tests. The physiological response to a stressful environment is exaggerated in WKYs. Selective breeding generated two WKY substrains that are nearly isogenic but show clear behavioral differences, including that of depression-like behavior. WKY and its substrains may share characteristics of subgroups of depressed individuals with social withdrawal, low energy, weight loss, sleep disturbances, and specific cognitive dysfunction. The genomes of the WKY and WKY substrains contain variations that impact the function of many genes identified in recent human genetic studies of depression. Thus, these strains of rats share characteristics of human depression at both phenotypic and genetic levels, making them a model of depression traits.

The sex-dependent response to psychosocial stress and ischaemic heart disease

Stress is an important risk factor for modern chronic diseases, with distinct influences in males and females. The sex specificity of the mammalian stress response contributes to the sex-dependent development and impacts of coronary artery disease (CAD). Compared to men, women appear to have greater susceptibility to chronic forms of psychosocial stress, extending beyond an increased incidence of mood disorders to include a 2- to 4-fold higher risk of stress-dependent myocardial infarction in women, and up to 10-fold higher risk of Takotsubo syndrome-a stress-dependent coronary-myocardial disorder most prevalent in post-menopausal women. Sex differences arise at all levels of the stress response: from initial perception of stress to behavioural, cognitive, and affective responses and longer-term disease outcomes. These fundamental differences involve interactions between chromosomal and gonadal determinants, (mal)adaptive epigenetic modulation across the lifespan (particularly in early life), and the extrinsic influences of socio-cultural, economic, and environmental factors. Pre-clinical investigations of biological mechanisms support distinct early life programming and a heightened corticolimbic-noradrenaline-neuroinflammatory reactivity in females vs. males, among implicated determinants of the chronic stress response. Unravelling the intrinsic molecular, cellular and systems biological basis of these differences, and their interactions with external lifestyle/socio-cultural determinants, can guide preventative and therapeutic strategies to better target coronary heart disease in a tailored sex-specific manner.

The Effectiveness of Interventions for the Prevention or Treatment of Paternal Perinatal Anxiety: A Systematic Review

Background: The worldwide prevalence of paternal perinatal anxiety (PPA) ranges between 3.4% and 25.0% antenatally, and 2.4% and 51.0% postnatally. Experiencing PPA can adversely impact the individual, partners, and infants. Research concerning PPA is lagging and fragmented compared to research for new mothers. Objectives: To establish the effectiveness of prevention or treatment interventions for PPA in adults identifying as male. Data sources: We completed searches of Medline, EMBASE, PsycINFO and Web of Science from inception to 2 December 2021, as well as hand searches of references from relevant papers. Search selection and data extraction: Randomised controlled trials delivering prevention or treatment interventions and reporting anxiety outcomes for new/expectant fathers in the perinatal mental health period were included. Our review follows the PRISMA reporting guidelines. One reviewer independently screened 5170 titles/abstracts; second reviewers screened 50%. Two reviewers independently screened full text, extracted data, and conducted risk of bias assessments. Synthesis: Cochrane's collaboration tool 2 was used to assess quality. Primarily results are synthesised narratively, a post-hoc sub-group analysis was completed on four studies using the same outcome measure. Main results: Twelve of the 5170 studies fulfilled the inclusion criteria. Studies used psychoeducational or practical skills interventions. Interventions mostly involved couple-dyads and three studies assessed PPA as a primary outcome. Included interventions were prevention-based; no treatment interventions were found. Father-only interventions consistently reported a significant reduction of PPA. Conclusions: Systematic searching yielded no treatment interventions, highlighting a substantial gap in the evidence base. Within a limited and heterogenous sample, no studies targeted diagnosed PPA. Evidence suggested father-focused interventions may be effective in preventing PPA, regardless of the intervention delivery mode or intervention content. However, consistency between study design and options within the field are lacking compared to interventions available for mothers.

Investigating the role of environmental enrichment initiated in adolescence against the detrimental effects of chronic unpredictable stress in adulthood: Sex-specific differences in behavioral and neuroendocrinological findings

Environmental Enrichment (EE) improves cognitive function and enhances brain plasticity, while chronic stress increases emotionality, impairs learning and memory, and has adverse effects on brain anatomy and biochemistry. We explored the beneficial role of environmental enrichment initiated in adolescence against the negative outcomes of Chronic Unpredictable Stress (CUS) during adulthood on emotional behavior, cognitive function, as well as somatic and neuroendocrine markers in both sexes. Adolescent Wistar rats housed either in enriched or standard housing conditions for 10 weeks. On postnatal day 66, a subgroup from each housing condition was daily exposed to a 4-week stress protocol. Following stress, adult rats underwent behavioral testing to evaluate anxiety, exploration/locomotor activity, depressive-like behavior and spatial learning/memory. Upon completion of behavioral testing, animals were exposed to a 10-m stressful event to test the neuroendocrine response to acute stress. CUS decreased body weight gain and increased adrenal weight. Some stress-induced behavioral adverse effects were sex-specific since learning impairments were limited to males while depressive-like behavior to females. EE housing protected against CUS-related behavioral deficits and body weight loss. Exposure to CUS affected the neuroendocrine response of males to acute stress as revealed by the increased corticosterone levels. Our findings highlight the significant role of EE in adolescence as a protective factor against the negative effects of stress and underline the importance of inclusion of both sexes in animal studies.

Sex Differences in Depression-Like Behaviors in Adult Mice Depend on Endophenotype and Strain

Depression affects women nearly twice as frequently as men. In contrast, rodent models of depression have shown inconsistent results regarding sex bias, often reporting more depression-like behaviors in males. This sex discrepancy in rodents modeling depression may rely on differences in the baseline activity of males and females in depression-related behavioral tests. We previously showed that the baseline despair and anhedonia behaviors, major endophenotypes of depression, are not sex biased in young adolescent wild-type mice of C57BL/6N, DBA/2, and FVB/N strains. Since the prevalence of depression in women peaks in their reproductive years, we here investigated sex differences of the baseline depression-like behaviors in adult mice using these three strains. Similar to the results in young mice, no difference was found between adult male and female mice in behavioral tests measuring despair in both tail suspension and forced swim tests, and anhedonia in the sucrose preference test. We then extended our study and tested apathy, another endophenotype of depression, using the splash test. Adult male and female mice showed significantly different results in the baseline apathy-like behaviors depending on the investigated strain. This study dissects the complex sex effects of different depression endophenotypes, stresses the importance of considering strain, and puts forward a hypothesis of the inconsistency of results between different laboratories investigating rodent models of depression.

Female-specific role of ciliary neurotrophic factor in the medial amygdala in promoting stress responses

Ciliary neurotrophic factor (CNTF) is produced by astrocytes which have been implicated in regulating stress responses. We found that CNTF in the medial amygdala (MeA) promotes despair or passive coping, i.e., immobility in an acute forced swim stress, in female mice, while having no effect in males. Neutralizing CNTF antibody injected into the MeA of wildtype females reduced activation of downstream STAT3 (Y705) 24 and 48 h later. In concert, the antibody reduced immobility in the swim test in females and only after MeA injection, but not when injected in the central or basolateral amygdala. Antibody injected into the male MeA did not affect immobility. These data reveal a unique role of CNTF in female MeA in promoting despair or passive coping behavior. Moreover, 4 weeks of chronic unpredictable stress (CUS) increased immobility in the swim test and reduced sucrose preference in wildtype CNTF+/+, but not CNTF−/− littermate, females. Following CUS, 10 min of restraint stress increased plasma corticosterone levels only in CNTF+/+ females. In males, the CUS effects were present in both genotypes. Further, CUS increased CNTF expression in the MeA of female, but not male, mice. CUS did not alter CNTF in the female hippocampus, hypothalamus and bed nucleus of stria terminalis. This suggests that MeA CNTF has a female-specific role in promoting CUS-induced despair or passive coping, behavioral anhedonia and neuroendocrine responses. Compared to CNTF+/+ mice, CNTF−/− mice did not show differences in CUS-induced anxiety-like behavior and sensorimotor gating function as measured by elevated T-Maze, open field and pre-pulse inhibition of the acoustic startle response. Together, this study reveals a novel CNTF-mediated female-specific mechanism in stress responses and points to opportunities for developing treatments for stress-related disorders in women.

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CNTF in the MeA promotes despair or passive coping behavior in female mice only.

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Chronic stress upregulates CNTF in female but not male MeA.

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CNTF contributes to chronic stress-induced despair or passive coping, anhedonia and neuroendocrine responses in females only.

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CNTF does not affect anxiety-like behavior and sensorimotor gating function.

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These data reveal a novel CNTF-mediated female-specific mechanism in stress responses.

High-fat diet induces depression-like phenotype via astrocyte-mediated hyperactivation of ventral hippocampal glutamatergic afferents to the nucleus accumbens

Comorbidity exists between metabolic disorders and depressive syndrome with unclear mechanisms. To characterize the causal relationship, we adopted a 12-week high-fat diet (HFD) to induce metabolic disorder and depressive phenotypes in mice. Initially, we identified an enhanced glutamatergic input in the nucleus accumbens of HFD mice. Retrograde tracing and chemogenetic inhibition showed that the hyperactive ventral hippocampal glutamatergic afferents to the nucleus accumbens determined the exhibition of depression-like behavior in HFD mice. Using lentiviral knockdown and overexpression approaches, we proved that HFD-induced downregulation of glial glutamate transporters, GLAST and GLT-1, contributed to the observed circuit maladaptations and subsequent depression-like behaviors. Finally, we identified a potential therapeutic agent, riluzole, which could mitigate the HFD-induced behavioral deficits by normalizing the expressions of GLAST and GLT-1 and ventral hippocampal glutamatergic afferents to the nucleus accumbens. Overall, astrocyte-mediated disturbance in glutamatergic transmission underlies the metabolic disorder-related depressive syndrome and represents a therapeutic target for this subtype of depressive mood disorders.

Juvenile Stress Exerts Sex-independent Effects on Anxiety, Antidepressant-like Behaviours and Dopaminergic Innervation of the Prelimbic Cortex in Adulthood and Does Not Alter Hippocampal Neurogenesis

Stress, particularly during childhood, is a major risk factor for the development of depression. Depression is twice as prevalent in women compared to men, which suggests that that biological sex also contributes to depression susceptibility. However, the neurobiology underpinning sex differences in the long-term consequences of childhood stress remains unknown. Thus, the aim of this study was to determine whether stress applied during the prepubertal juvenile period (postnatal day 27-29) in rats induces sex-specific changes in anxiety-like behaviour, anhedonia, and antidepressant-like behaviour in adulthood in males and females. The impact of juvenile stress on two systems in the brain associated with these behaviours and that develop during the juvenile period, the mesocorticolimbic dopaminergic system and hippocampal neurogenesis, were also investigated. Juvenile stress altered escape-oriented behaviours in the forced swim test in both sexes, decreased latency to drink a palatable substance in a novel environment in the novelty-induced hypophagia test in both sexes, and decreased open field supported rearing behavior in females. These behavioural changes were accompanied by stress-induced increases in tyrosine hydroxylase immunoreactivity in the prefrontal cortex of both sexes, but not other regions of the mesocorticolimbic dopaminergic system. Juvenile stress did not impact anhedonia in adulthood as measured by the saccharin preference test and had no effect hippocampal neurogenesis across the longitudinal axis of the hippocampus. These results suggest that juvenile stress has long-lasting impacts on antidepressant-like and reward-seeking behaviour in adulthood and these changes may be due to alterations to catecholaminergic innervation of the medial prefrontal cortex.

High fat diet-induced obesity leads to depressive and anxiety-like behaviors in mice via AMPK/mTOR-mediated autophagy

Depression is one of the most common mental illnesses in modern society. In recent years, several studies show that there are disturbances in lipid metabolism in depressed patients. High-fat diet may lead to anxiety and depression, but the mechanisms involved remain unclear. In our study, we found that 8 weeks of high-fat feeding effectively induced metabolic disorders, including obesity and hyperlipidemia in mice. Interestingly, the mice also showed depressive and anxiety-like behaviors. We further found activated microglia and astrocyte, increased neuroinflammation, decreased autophagy and BDNF levels in mice after high-fat feeding. Besides, high-fat feeding can also inhibit AMPK phosphorylation and induce mTOR phosphorylation. After treating with the mTOR inhibitor rapamycin, autophagy and BDNF levels were elevated. The number of activated microglia and astrocyte, and pro-inflammation levels were reduced. Besides, rapamycin can also reduce the body weight and serum lipid level in high fat feeding mice. Depressive and anxiety-like behaviors were also ameliorated to some extent after rapamycin treatment. In summary, these results suggest that high-fat diet-induced obesity may lead to depressive and anxiety-like behaviors in mice by inhibiting AMPK phosphorylation and promoting mTOR shift to phosphorylation to inhibit autophagy. Therefore, improving lipid metabolism or enhancing autophagy through the AMPK/mTOR pathway could be potential targets for the treatment of obesity depression.

Differential chronic social stress models in male and female mice

Chronic stress creates an allostatic overload that may lead to mood disorders such as anxiety and depression. Modern causes of chronic stress in humans are mostly social in nature, relating to work and relationship stress. Research into neural and molecular mechanisms of vulnerability and resilience following chronic social stress (CSS) is ongoing and uses animal models to discover efficient prevention strategies and treatments. To date, most CSS studies have neglected the female sex and used male-focused aggression-based animal models such as chronic social defeat stress (CSDS). Accumulating evidence on sex differences suggests differences in the stress response, the prevalence of stress-related illness and in response to treatment, indicating that researchers should expand CSS investigation to include female-focused protocols alongside the popular CSDS protocols. Here, we describe a novel female mouse model of CSS and a parallel modified male mouse model of CSDS in C57BL/6 mice. These new models enable the investigation of vulnerability, coping and downstream effectors mediating short-term and long-term consequences of CSS in both sexes. Our data demonstrate differential effects on male and female mice during, soon after, and many weeks after CSS. Female mice are more prone to body weight loss during CSS and hyperactive anxious behaviour following CSS. Both sexes show reduced social interaction, but only stressed male mice show long-term changes in emotional memory and neuroendocrine function. We further discuss future avenues of research using these models to investigate mechanisms pertaining to sensitivity to CSS and treatment response profiles, in a sex-appropriate manner.

Effect of Estrous Cycle on Behavior of Females in Rodent Tests of Anxiety

Anxiety disorders are more prevalent in women than in men. In women the menstrual cycle introduces another variable; indeed, some conditions e.g., premenstrual syndrome, are menstrual cycle specific. Animal models of fear and anxiety, which form the basis for research into drug treatments, have been developed almost exclusively, using males. There remains a paucity of work using females and the available literature presents a confusing picture. One confound is the estrous cycle in females, which some authors consider, but many do not. Importantly, there are no accepted standardized criteria for defining cycle phase, which is important given the rapidly changing hormonal profile during the 4-day cycle of rodents. Moreover, since many behavioral tests that involve a learning component or that consider extinction of a previously acquired association require several days to complete; the outcome may depend on the phase of the cycle on the days of training as well as on test days. In this article we consider responsiveness of females compared to males in a number of commonly used behavioral tests of anxiety and fear that were developed in male rodents. We conclude that females perform in a qualitatively similar manner to males in most tests although there may be sex and strain differences in sensitivity. Tests based on unconditioned threatening stimuli are significantly influenced by estrous cycle phase with animals displaying increased responsiveness in the late diestrus phase of the cycle (similar to the premenstrual phase in women). Tests that utilize conditioned fear paradigms, which involve a learning component appear to be less impacted by the estrous cycle although sex and cycle-related differences in responding can still be detected. Ethologically-relevant tests appear to have more translational value in females. However, even when sex differences in behavior are not detected, the same outward behavioral response may be mediated by different brain mechanisms. In order to progress basic research in the field of female psychiatry and psychopharmacology, there is a pressing need to validate and standardize experimental protocols for using female animal models of anxiety-related states.

Sex differences shape zebrafish performance in a battery of anxiety tests and in response to acute scopolamine treatment

Sex differences influence human and animal behavioral and pharmacological responses. The zebrafish (Danio rerio) is a powerful, popular model system in neuroscience and drug screening. However, the impact of zebrafish sex differences on their behavior and drug responses remains poorly understood. Here, we evaluate baseline anxiety-like behavior in adult male and female zebrafish, and its changes following an acute 30-min exposure to 800-μM scopolamine, a common psychoactive anticholinergic drug. Overall, we report high baseline anxiety-like behavior and more individual variability in locomotion in female zebrafish, as well as distinct, sex-specific (anxiolytic-like in females and anxiogenic-like in males) effects of scopolamine. Collectively, these findings reinforce the growing importance of zebrafish models for studying how both individual and sex differences shape behavioral and pharmacological responses.

Antidepressants' effects on testosterone and estrogens: What do we know?

Various antidepressants are commonly used to treat depression and anxiety disorders, and sex differences have been identified in their efficacy and side effects. Steroids, such as estrogens and testosterone, both in the periphery and locally in the brain, are regarded as important modulators of these sex differences. This review presents published data from preclinical and clinical studies that measure testosterone and estrogen level changes during and/or after acute or chronic administration of different antidepressants. The majority of studies show an interaction between sex hormones and antidepressants on sexual function and behavior, or in depressive symptom alleviation. However, most of the studies omit to investigate antidepressants' effects on circulating levels of gonadal hormones. From data reviewed herein, it is evident that most antidepressants can influence testosterone and estrogen levels. Still, the evidence is conflicting with some studies showing an increase, others decrease or no effect. Most studies are conducted in male animals or humans, underscoring the importance of considering sex as an important variable in such investigations, especially as depression and anxiety disorders are more common in women than men. Therefore, research is needed to elucidate the extent to which antidepressants can influence both peripheral and brain levels of testosterone and estrogens, in males and females, and whether this impacts the effectiveness or side effects of antidepressants.

Antidepressant-like effects of acupuncture via modulation of corticosterone, sex hormones, and hippocampal BDNF expression in male rats

BACKGROUND

Post-weaning social isolated rodents exhibit pathophysiological changes associated with depression including adrenal axis hyperactivity, gonadal hormone level disturbances, molecular alterations in hippocampus, and immobility behavior in the forced swimming test (FST). Although acupuncture by absorbable thread implantation (acu-catgut, AC) elicits antidepressant-like effects in social isolated rats, AC effects on neuroendocrine and hippocampal molecular alterations have been less characterized.

OBJECTIVE

To investigate the participation of gonadal hormones, corticosterone, and brain-derived neurotrophic factor (BDNF) hippocampal expression, on the AC antidepressant-like effects in social isolated male rats.

METHODS

Sprague-Dawley male rats were raised in social isolation (SI) or standard conditions, for 11 weeks. AC (on Baihui (Du20), Yintang (E X-HN3), Shenshu (BL 23), Pishu (BL 20), Ganshu (BL 18), Xinshu (BL 15) and Guanyuan (Ren 4)), or Sham-AC (puncturing of acupoints without embedding the thread), was applied during the last three weeks of isolation period. Rats were evaluated in the FST; hormones plasmatic levels and hippocampal BDNF content were quantified by ELISA and Western blotting, respectively.

RESULTS

Social isolated rats showed more immobility in the FST and had lower testosterone and estradiol levels, higher corticosterone levels, and reduced hippocampal BDNF content than controls. BDNF level in hippocampus inversely correlated to depression-like behavior. AC but not sham-AC normalized immobility behavior, steroid hormone levels, and BDNF content, as in rats raised in a social environment.

CONCLUSIONS

AC antidepressant effect could be related to an improvement of hippocampal BDNF protein expression, as well as corticosterone and sex hormones disturbances associated with prolonged exposure to stress caused by social isolation. Present findings have implications for depression treatment in individuals early exposed to stress.

Early estradiol exposure masculinizes disease-relevant behaviors in female mice

Most psychiatric disorders show a sex bias in incidence, symptomatology, and/or response to treatment. Males are more susceptible to neurodevelopmental disorders including autism spectrum disorder and attention-deficit activity disorder, while women are more prone to major depressive disorder and anxiety disorders after puberty. A striking difference between males and females in humans and other mammals is that males undergo a process of brain masculinization due to the early exposure to gonadal hormones. In rodents, this developmental organization of the brain is essential for adult males to express the appropriate sexual behaviors in the presence of a receptive female. Our goal was to determine whether this process of brain masculinization influences behaviors relevant to psychiatric disorders. To this aim, we studied sex differences and the effect of neonatal 17β-estradiol benzoate treatment of female mice on different disease-relevant behaviors. Our analysis includes postnatal behavior, juvenile play, and adult tests for sociability, repetitive behaviors, anxiety, and depression. Our results show that the sex differences observed in exploration, repetitive behaviors, and depression-related behaviors are largely reduced when females are neonatally treated with 17β-estradiol benzoate. These results suggest a role of neonatal sex steroids in the development of disease-relevant behaviors and provide evidence supporting a role for perinatal exposure to estrogens and androgens on the development and manifestation of psychiatric disorders.

Neurobiology of resilience in depression: immune and vascular insights from human and animal studies

Major depressive disorder (MDD) is a chronic and recurrent psychiatric condition characterized by depressed mood, social isolation and anhedonia. It will affect 20% of individuals with considerable economic impacts. Unfortunately, 30-50% of depressed individuals are resistant to current antidepressant treatments. MDD is twice as prevalent in women and associated symptoms are different. Depression's main environmental risk factor is chronic stress, and women report higher levels of stress in daily life. However, not every stressed individual becomes depressed, highlighting the need to identify biological determinants of stress vulnerability but also resilience. Based on a reverse translational approach, rodent models of depression were developed to study the mechanisms underlying susceptibility vs resilience. Indeed, a subpopulation of animals can display coping mechanisms and a set of biological alterations leading to stress resilience. The aetiology of MDD is multifactorial and involves several physiological systems. Exacerbation of endocrine and immune responses from both innate and adaptive systems are observed in depressed individuals and mice exhibiting depression-like behaviours. Increasing attention has been given to neurovascular health since higher prevalence of cardiovascular diseases is found in MDD patients and inflammatory conditions are associated with depression, treatment resistance and relapse. Here, we provide an overview of endocrine, immune and vascular changes associated with stress vulnerability vs. resilience in rodents and when available, in humans. Lack of treatment efficacy suggests that neuron-centric treatments do not address important causal biological factors and better understanding of stress-induced adaptations, including sex differences, could contribute to develop novel therapeutic strategies including personalized medicine approaches.

Xanthotoxin affects depression-related behavior and neurotransmitters content in a sex-dependent manner in mice

The present study aimed to evaluate xanthotoxin's influence on male and female Swiss mice's depression-like behaviors and investigate the potential mechanism of this effect. Naturally derived furanocoumarin (the Apiaceae family), xanthotoxin, administered acutely (12.5 mg/kg), diminished the immobility level in the forced swim test only in males. The immobility level was lower in females than males, which may be associated with a higher serotonin level in the female prefrontal cortex. A dose-dependent increase of serotonin and noradrenaline was reported in the reverse-phase ion-pair liquid chromatography in the female prefrontal cortex but not in the hippocampus. We suggest that xanthotoxin may exert antidepressant properties and affect males and females differently. The increasing level of serotonin in the male and female prefrontal cortex may underlie this effect.

Behavioral and Neurochemical Effects of Extra Virgin Olive Oil Total Phenolic Content and Sideritis Extract in Female Mice

The aim of this study was to determine the cognitive and behavioral effects of extra virgin olive oil total phenolic content (TPC) and Sideritis (SID) extracts in female mice, and identify the associated neurochemical changes in the hippocampus and the prefrontal cortex. All animals received intraperitoneal low or high doses of TPC, SID or vehicle treatment for 7 days and were subjected to the Open Field (OF), Novel Object Recognition (NOR) and Tail Suspension Test (TST). The prefrontal cortex and hippocampus were dissected for analysis of neurotransmitters and aminoacids with high performance liquid chromatography with electrochemical detection (HPLC-ED). Both TPC doses enhanced vertical activity and center entries in the OF, which could indicate an anxiolytic-like effect. In addition, TPC enhanced non-spatial working memory and, in high doses, exerted antidepressant effects. On the other hand, high SID doses remarkably decreased the animals’ overall activity. Locomotor and exploratory activities were closely associated with cortical increases in serotonin turnover induced by both treatments. Cognitive performance was linked to glutamate level changes. Furthermore, TPC reduced cortical taurine levels, while SID reduced cortical aspartate levels. TPC seems to have promising cognitive, anxiolytic and antidepressant effects, whereas SID has sedative effects in high doses. Both extracts act in the brain, but their specific actions and properties merit further exploration.

Psychoactive properties of BNN27, a novel neurosteroid derivate, in male and female rats

RATIONALE

Νeurosteroids, like dehydroepiandrosterone (DHEA), play an important role in neurodegeneration and neural protection, but they are metabolized in androgens, estrogens, or other active metabolites. A newly developed synthetic DHEA analog, BNN27 ((20R)-3β,21-dihydroxy-17R,20-epoxy-5-pregnene), exerts neurotrophic and neuroprotective actions without estrogenic or androgenic effects.

OBJECTIVES

This study aimed to investigate potential anxiolytic or antidepressant properties of BNN27.

METHODS

Male and female adult Wistar rats were treated with BNN27 (10, 30, or 90 mg/kg, i.p.) and subjected to behavioral tests measuring locomotion, exploration, and "depressive-like" behavior (open field, light/dark box, hole-board, and forced swim tests). The hippocampus and prefrontal cortex were collected for glutamate and GABA measurements, and trunk blood was collected for gonadal hormone analysis.

RESULTS

Acute high-dose BNN27 reduced locomotion and exploratory behavior in both sexes. Intermediate acute doses (30 mg/kg) of BNN27 reduced exploration and testosterone levels only in males, and enhanced progesterone levels in both sexes. Notably, with the present design, BNN27 had neither anxiolytic nor antidepressant effects and did not affect estrogen levels. Interestingly, acute administration of a low BNN27 dose (10 mg/kg) increased glutamate turnover, GABA, and glutamine levels in the hippocampus. The same dose also enhanced glutamate levels in the prefrontal cortex of males only. Sex differences were apparent in the basal levels of behavioral, hormonal, and neurochemical parameters, as expected.

CONCLUSIONS

BNN27 affects locomotion, progesterone, and testosterone levels, as well as the glutamatergic and GABAergic systems of the hippocampus and prefrontal cortex in a sex-dependent way.

Do corticosterone levels predict female depressive-like behavior in rodents?

Dysregulation of the hypothalamus-pituitary-adrenal (HPA) axis is often linked to the neurobiology of depression, though the presence and type of this dysregulation is not a consistent finding. Meanwhile, significant sex differences exist regarding depression and the HPA axis. Animal models of depression simulate certain aspects of the human disease and aim to advance our knowledge regarding its neurobiology and discover new antidepressant treatments. Most animal models of depression induce a depressive-like phenotype taking advantage of stressful experimental conditions, that also increase corticosterone, the main stress hormone in rodents. In this review we present inconsistent results in male and female rodents regarding the interaction between the depressive-like behavioral phenotype and corticosterone. In commonly used models, the female depressive-like phenotype in rodents seems significantly less dependent on the stress hormone corticosterone, whereas the male behavioral response is more evident and associates with variations of corticosterone. Further research and clarification of this sex-dependent interaction will have significant ramifications on the improvement of the validity of animal models of depression.

Corticosterone Induces Depressive-Like Behavior in Female Peri-Pubescent Rats, but Not in Pre-Pubescent Rats

Background

There are no data on the effect of exogenous corticosterone on depressive-like behavior in juvenile rats. Furthermore, it has not been tested whether the effects of corticosterone in female rats is different before or after puberty.

Objective

We tested the effect of corticosterone treatment on female pre- and peri-pubescent juvenile rats on depressive-like behavior.

Methods

Female juvenile rats were divided into pre-pubescent (post-natal day 7–27) or peri-pubescent (post-natal day 28–48) groups and administered daily corticosterone (40 mg kg⁻¹day⁻¹) for 21 days. Depressive-like behavior was assessed using a modified forced swim test and the sucrose preference test. After behavioral assessment, brains were analyzed to determine if there were changes in cell proliferation and newborn neuron survival in the dentate gyrus of the dorsal hippocampus.

Results

Chronic corticosterone treatment did not affect behavior or neurogenesis in female pre-pubescent juvenile rats. However, female peri-pubescent rats injected with corticosterone showed increased depressive-like behavior as well as a decrease in cell proliferation in the subgranular zone. Furthermore, there was an inverse correlation between time spent immobile in the forced swim test and cell proliferation in the granule cell layer in peri-pubescent rats.

Conclusions

Corticosterone induces depressive-like behavior in peri-pubescent, but not in pre-pubescent female rats. Finally, our results suggest that depressive-like behavior may be associated with a decrease in hippocampal cell proliferation in female peri-pubescent rats.

Type 3 adenylyl cyclase in the main olfactory epithelium participates in depression-like and anxiety-like behaviours

BACKGROUND

Deficiency of olfaction is thought to be associated with depression, and type 3 adenylyl cyclase (AC₃) genetic knockout and forebrain knockout mice show depression-like behaviours. AC₃ is expressed in the main olfactory epithelium (MOE) and hippocampus, which plays an important role in olfactory signal transduction. However, it is unclear whether AC₃ in the MOE also plays a role in the pathogenesis of depression. Thus, we aimed to study the relationship between AC₃ in the MOE and the pathogenesis of depression.

METHODS

We obtained anosmic mice by intranasal perfusion of zinc sulphate (ZnSO₄) (ZnSO₄ mice), and distinctively knocked down AC₃ in the MOE (AC_3KD/MOE mice) by CRISPR/cas9 technology. Behavioural tests related to depression and anxiety were employed to evaluate the depression- and anxiety-like behaviours of mice. The mRNA and protein expressions of tyrosine hydroxylase (TH), dopamine receptors (Drds), and N-Methyl D-aspartate receptor subunit 2B (GluN2B) in the hippocampus of mice were investigated by qPCR and western blotting to explore the mechanism of depression and anxiety caused by AC₃ in the MOE, preliminarily.

RESULTS

Compared with NaCl mice, ZnSO₄ mice exhibited depression-like behaviours in tail suspension tests (TST), forced swimming tests, and social (FST) interaction tests (SIT), but showed no anxiety-like behaviours in anxiety-related behavioural tests. The mRNA and protein expressions of Drd3 and GluN2B in the hippocampus of ZnSO₄ mice were significantly downregulated. Compared with the negative control mice (NC mice), AC_{3KD / MOE} mice showed depression-like behaviours in TST, FST, and SIT tests, anxiety-like behaviours in light/dark transition test, elevated-plus maze test, and novelty-suppressed feeding test. The protein expressions of Drd3, TH, and GluN2B were significantly downregulated in the hippocampus.

LIMITATIONS

We did not further demonstrate that AC₃ in the MOE causes depression through the dopaminergic nervous system with dopamine or dopamine receptor agonists.

CONCLUSIONS

Our data demonstrate that intranasal infusion of ZnSO₄ can cause depression-like behaviours and has no effect on anxiety-like behaviours. Specific knockdown of AC₃ in the MOE can cause depression-like and anxiety-like behaviours. The behavioural changes caused by intranasal ZnSO₄ and specific knockdown of AC₃ in the MOE can be related to the significant downregulation of dopaminergic system and GluN2B expressions in the hippocampus of mice.

Thymol reverses depression-like behaviour and upregulates hippocampal BDNF levels in chronic corticosterone-induced depression model in female mice

Objectives

Based on this, the central therapeutic effects of thymol were verified in the neurotrophic pathway.

Methods

Female swiss mice were divided into four groups: control, corticosterone (Cort), thymol (Cort + thymol) and fluvoxamine (Cort + Flu). The administration of corticosterone was used to induce depressive symptoms for 23 days. After the treatment, the animals were exposed the behavioural tests, such as forced swimming test, tail suspension test, sucrose preference test, light/dark test, social interaction test, Y-maze test, plus-maze test and hole-board test. The hippocampus was also removed, and BDNF was measured by ELISA and Western blot.

Key findings

As a result, thymol and fluvoxamine were able to reverse the depressive symptoms, as well as to improve the anxious frame. The anhedonic and short-term memory was restored with the treatment. In the neurochemical tests, both thymol and fluvoxamine restored BDNF levels, improving the depressive condition.

Conclusions

This work opens up new investigations aiming at the use of this molecule as a therapeutic alternative for treating depression disorders.

Social instability is an effective chronic stress paradigm for both male and female mice

Despite stress-associated disorders having a higher incidence rate in females, preclinical research mainly focuses on males. Chronic stress paradigms, such as chronic social defeat and chronic corticosterone (CORT) administration, were mainly designed and validated in males and subsequent attempts to use these paradigms in females has demonstrated sex differences in the behavioral and HPA axis response to stress. Here, we assessed the behavioral response to chronic CORT exposure and developed a social stress paradigm, social instability stress (SIS), which exposes adult mice to unstable social hierarchies every 3 days for 7 weeks. Sex differences in response to chronic CORT emerged, with negative valence behaviors induced in CORT treated males, not females. SIS effectively induces negative valence behaviors in the open field, light dark, and novelty suppressed feeding tests, increases immobility in the forced swim test, and activates the hypothalamus-pituitary-adrenal (HPA) axis in both males and females. Importantly, while there were effects of estrous cycle on behavior, this variability did not impact the overall effects of SIS on behavior, suggesting estrous does not need to be tracked while utilizing SIS. Furthermore, the effects of SIS on negative valence behaviors were also reversed following chronic antidepressant treatment with fluoxetine (FLX) in both males and females. SIS also reduced adult hippocampal neurogenesis in female mice, while chronic FLX treatment increased adult hippocampal neurogenesis in both males and females. Overall, these data demonstrate that the SIS paradigm is an ethologically valid approach that effectively induces chronic stress in both adult male and adult female mice.

Minocycline inhibits microglial activation and alleviates depressive-like behaviors in male adolescent mice subjected to maternal separation

Exposure to early adversity increases vulnerability to psychiatric disorders in later life. Microglia-mediated inflammation has been linked to psychopathology, so such inflammation may be a target for treating depression. Using a model of depression involving adolescent male C57BL/6J mice subjected to maternal separation, we explored whether using minocycline to mitigate inflammation can alleviate depression-like behaviors. Between postnatal days 1 and 14, male mice were separated from their mothers for 3 h per day. Minocycline (20 mg/kg) was administered intraperitoneally once daily for 2 weeks starting one week after weaning. Then the male mice were subjected to a second stress for 2 weeks. Results from the sucrose preference test, forced swimming test, and open field test showed that maternal separation did not obviously alter behavior of the male mice, but it did increase the risk of depression-like behaviors following a second stress. This increased risk disappeared if minocycline was given preemptively before the second stress. Maternal separation and second stress up-regulated pro-inflammatory markers and down-regulated anti-inflammatory markers in the hippocampus, and they activated microglia and promoted pro-inflammatory transitions in microglia. All these effects were reversed by minocycline. These changes in inflammatory processes correlated with changes in neurogenesis and BDNF expression in the hippocampus. Our results in this mouse model suggest the potential of minocycline for treating psychiatric disorders induced by early adversity.

Stressor during Early Adolescence in Hyperreactive Female Wistar Kyoto Rats Induces a 'Double Hit' Manifested by Variation in Neurobehaviors and Brain Monoamines

Stress is an additive factor in the development of depressive-like profiles that mainly onsets during adolescence. However, effects of early post-weaning stress on developing brain neurochemical pathways in inducing anxiety- and depressive-like profiles in vulnerable females have not been extensively studied. The Wistar Kyoto (WKY) rat, a putative model of adolescent depression and stress-sensitivity could elucidate the pathophysiology of stress-related depression in vulnerability. Through such an approach, links between inherent risk for predisposition to depression and homotypic stress, as in a 'double hit' would unravel endocrine regulation, interference in developing neural pathways and neurobehaviors. Here, early adolescent WKY female rats were subjected to 1-h physical restraint over 7 days followed by neurobehavioral testing in the elevated plus maze (EPM) and forced swim test (FST). The stressor's effectiveness was assayed by plasma corticosterone (CORT) and altered functioning in depression-implicated brain areas by assaying monoamines/metabolites. Homotypic stress induced an anxiolytic-like response in the EPM with learned helplessness and reduced struggling behavior in FST. Significant elevation in CORT levels (p < 0.05) indicated an upregulated HPA axis. Medial prefrontal cortex, a still maturing brain area, exhibited increased serotonin (5-HT) metabolite (p < 0.01) and turnover rates (p < 0.01) indicative of altered/maladaptive serotonergic functioning. Nucleus accumbens (p < 0.05) and dorsal striatum (p < 0.01) also depicted increased 5-HT metabolite, with the latter also demonstrating reduced Dopamine turnover (p < 0.01) as a result of homotypic stress. Hence, female WKY rats could constitute a diathesis-stress model to study underlying mechanisms of stress-related depression.

Sex differences in the hypothalamic-pituitary-adrenal axis: An obstacle to antidepressant drug development?

Hypothalamic-pituitary-adrenal (HPA) axis dysfunction has long been implicated in the pathophysiology of depression, and HPA axis-based compounds have served as potential new therapeutic targets, but with no success. This review details sex differences from animal and human studies in the function of HPA axis elements (glucocorticoids, corticotropin releasing factor, and vasopressin) and related compounds tested as candidate antidepressants. We propose that sex differences contribute to the failure of novel HPA axis-based drugs in clinical trials. Compounds studied preclinically in males were tested in clinical trials that recruited more, if not exclusively, women, and did not control, but rather adjusted, for potential sex differences. Indeed, clinical trials of antidepressants are usually not stratified by sex or other important factors, although preclinical and epidemiological data support such stratification. In conclusion, we suggest that clinical testing of HPA axis-related compounds creates an opportunity for targeted, personalized antidepressant treatments based on sex. LINKED ARTICLES: This article is part of a themed section on The Importance of Sex Differences in Pharmacology Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.21/issuetoc.

What do we know about sex differences in depression: A review of animal models and potential mechanisms

Clinical studies have shown that women are more susceptible to depression than men. Sex differences in depression have been associated with social, cultural, as well as biological factors. In spite of extensive preclinical studies in animal models for depression that have been used for understanding the mechanisms of the disease as well as for new drug development, a substantive lack of attention on sex-specific phenotypes in depression might mask the effect of sex on the outcome. In this review article, we summarize findings on the influence of sex on behavior in the most commonly used animal models for depression. We also discuss the potential underlying mechanisms of such sex-dependent variation in the phenotype, particularly in the neuroendocrine system.

Neuroplasticity-related correlates of environmental enrichment combined with physical activity differ between the sexes

Environmental enrichment (EE), comprising positive physical (exercise) and cognitive stimuli, influences neuronal structure and usually improves brain function. The promise of EE as a preventative strategy against neuropsychiatric disease is especially high during early postnatal development when the brain is still amenable to reorganization. Despite the fact that male and female brains differ in terms of connectivity and function that may reflect early life experiences, knowledge of the neural substrates and mechanisms by which such changes arise remains limited. This study compared the impact of EE combined with physical activity on neuroplasticity and its functional consequences in adult male and female rats; EE was provided during the first 3 months of life and our analysis focused on the hippocampus, an area implicated in cognitive behavior as well as the neuroendocrine response to stress. Both male and female rats reared in EE displayed better object recognition memory than their control counterparts. Interestingly, sex differences were revealed in the effects of EE on time spent exploring the objects during this test. Independently of sex, EE increased hippocampal turnover rates of dopamine and serotonin and reduced expression of 5-HT_1A receptors; in addition, EE upregulated expression of synaptophysin, a presynaptic protein, in the hippocampus. As compared to their respective controls, EE-exposed males exhibited parallel increases in phosphorylated Tau and the GluN2B receptor, whereas females responded to EE with reduced hippocampal levels of glutamate and GluN2B. Together, these observations provide further evidence on the differential effects of EE on markers of hippocampal neuroplasticity in males and females.

Could a blood test for PTSD and depression be on the horizon?

INTRODUCTION

Depression and posttraumatic stress disorder (PTSD) are two complex and debilitating psychiatric disorders that result in poor life and destructive behaviors against self and others. Currently, diagnosis is based on subjective rather than objective determinations leading to misdiagnose and ineffective treatments. Advances in novel neurobiological methods have allowed assessment of promising biomarkers to diagnose depression and PTSD, which offers a new means of appropriately treating patients. Areas covered: Biomarkers discovery in blood represents a fundamental tool to predict, diagnose, and monitor treatment efficacy in depression and PTSD. The potential role of altered HPA axis, epigenetics, NPY, BDNF, neurosteroid biosynthesis, the endocannabinoid system, and their function as biomarkers for mood disorders is discussed. Insofar, we propose the identification of a biomarker axis to univocally identify and discriminate disorders with large comorbidity and symptoms overlap, so as to provide a base of support for development of targeted treatments. We also weigh in on the feasibility of a future blood test for early diagnosis. Expert commentary: Potential biomarkers have already been assessed in patients' blood and need to be further validated through multisite large clinical trial stratification. Another challenge is to assess the relation among several interdependent biomarkers to form an axis that identifies a specific disorder and secures the best-individualized treatment. The future of blood-based tests for PTSD and depression is not only on the horizon but, possibly, already around the corner.

Differential effects of chronic 17β-oestradiol treatment on rat behaviours relevant to depression

Sex differences are a prominent feature of the pathophysiology of psychiatric disorders, such as major depressive disorder, which affects women at a higher incidence than men. Research suggests that the most potent endogenous oestrogen, 17β-oestradiol, may have therapeutic potential in treating depression. However, preclinical studies have produced mixed results, likely as a result of various methodological factors such as treatment duration. The present study aimed to investigate the effects of ovariectomy and chronic 17β-oestradiol treatment via a s.c. silastic implant on behaviours relevant to depression in adult female Sprague-Dawley rats. Rats were assessed in the forced swim test, saccharin preference test and novel object recognition memory test, as well as for possible confounding behaviours, including locomotion and anxiety (open field test) and motivation and anxiety (novelty suppressed feeding test). Treatment effects were verified using body and uterus weight, as well as serum concentrations of 17β-oestradiol, progesterone and testosterone. Compared to ovariectomised rats, chronic 17β-oestradiol treatment enhanced saccharin preference and novel object recognition performance. There were no group differences in passive or active coping behaviour when assayed using the forced swim test. Taken together, these results support an antidepressant-like action of oestrogens but highlight that the beneficial effects of chronic 17β-oestradiol treatment may be related to specific depression-related symptoms, particularly anhedonia and memory.

Evaluation of antidepressant activity of methanolic extract of Saraca asoca bark in a chronic unpredictable mild stress model

It is well established that chronic exposure to stressful events plays an important role in the etiology of depression. Saraca asoca (Roxb.), De. wild, or Saraca indica, belonging to family Fabaceae, is endogenous to India. The flowers, seeds, bark, and leaves of the plant have been used widely in Ayurveda medicine. The bark extract of S. asoca has shown chemoprotection, myeloprotection, and antioxidant potential. Owing to the above-mentioned properties of the plant, the present study sought to evaluate the effect of a methanolic extract of S. asoca bark in rats exposed to chronic unpredictable mild stress (CUMS) daily for 8 weeks using a forced-swim test, an open-field test, and a sucrose-preference test. The effect of the extract on endogenous antioxidant levels in the brain was also assessed using catalase activity, superoxide dismutase activity, reduced glutathione levels, and malondialdehyde levels in the brain. Male Sprague-Dawley rats received 100 mg/kg (oral) of the extract daily 1 h before daily stress exposure for 8 weeks. The extract showed a significant reduction in the immobility time in the forced-swim test, increased the total number of line crossing, rearing, and grooming in the open-field test, and increased the sucrose consumption as well as the levels of endogenous antioxidants significantly in comparison with the CUMS control group. Therefore, S. asoca might be a useful agent for the treatment or alleviation of symptoms associated with depression possibly by reducing CUMS-induced oxidative stress and reactive oxygen species in the brain.

Deciphering sex differences in the immune system and depression

Certain mood disorders and autoimmune diseases are predominately female diseases but we do not know why. Here, we explore the relationship between depression and the immune system from a sex-based perspective. This review characterizes sex differences in the immune system in health and disease. We explore the contribution of gonadal and stress hormones to immune function at the cellular and molecular level in the brain and body. We propose hormonal and genetic sex specific immune mechanisms that may contribute to the etiology of mood disorders.

Repeated forced-swimming test in intact female rats: behaviour, oestrous cycle and enriched environment

Psychopharmacology used animal models to study the effects of drugs on brain and behaviour. The repeated forced-swimming test (rFST), which is used to assess the gradual effects of antidepressants on rat behaviour, was standardized only in males. Because of the known sex differences in rats, experimental conditions standardized for males may not apply to female rats. Therefore, the present work aimed to standardize experimental and housing conditions for the rFST in female rats. Young or adult Wistar female rats were housed in standard or enriched environments for different experimental periods. As assessed in tested and nontested females, all rats had reached sexual maturity by the time behavioural testing occurred. The rFST consisted of a 15-min session of forced swimming (pretest), followed by 5-min sessions at 1 (test), 7 (retest 1) and 14 days (retest 2) later. The oestrous cycle was registered immediately before every behavioural session. All sessions were videotaped for further analysis. The immobility time of female rats remained similar over the different sessions of rFST independent of the age, the phase of the oestrous cycle or the housing conditions. These data indicate that rFST in female Wistar rats may be reproducible in different experimental conditions.

The Effect of Gentle Handling on Depressive-Like Behavior in Adult Male Mice: Considerations for Human and Rodent Interactions in the Laboratory

Environmental factors play a significant role in well-being of laboratory animals. Regulations and guidelines recommend, if not require, that stressors such as bright lighting, smells, and noises are eliminated or reduced to maximize animal well-being. A factor that is often overlooked is handling and how researchers interact with their animals. Researchers, lab assistants, and husbandry staff in animal facilities may use inconsistent handling methods when interacting with rodents, but humans should be considered a part of the animal's social environment. This study examined the effects of different handling techniques on depressive-like behavior, measured by the Porsolt forced swim test, in adult C57BL/6J male mice. The same two researchers handled the mice in a gentle, aggressive, or minimal (control) fashion over approximately two weeks prior to testing. The results demonstrated a beneficial effect of gentle handling: gentle handling reduced swimming immobility in the forced swim test compared to mice that were aggressively or minimally handled. We argue that gentle handling, rather than methodical handling, can foster a better relationship between the handlers and rodents. Although handling is not standardized across labs, consistent gentle handling allows for less challenging behavioral testing, better data collection, and overall improved animal welfare.

Sex differences in behavioral and neurochemical effects of gonadectomy and aromatase inhibition in rats

Aromatase inhibitors, which are widely used for the treatment of estrogen-dependent cancers, have been associated with psychiatric side effects ranging from mania to depression. In the present study, we investigated sex differences in the behavioral and neurochemical effects of aromatase inhibition on male and female, sham-operated or gonadectomized adult rats. Three weeks after surgery, rats received chronic treatment with the aromatase inhibitor letrozole or vehicle and were then subjected to the open field test, which assesses general activity. Half of the subjects were subsequently exposed to the stressful procedure of the forced swim test (FST), which is also a test of antidepressant activity. Aromatase activity was analyzed in the hypothalamus and testosterone and corticosterone were assayed in the blood serum of all rats. The hippocampus and prefrontal cortex (PFC) were analyzed for monoamine (noradrenaline, dopamine and serotonin), as well as amino acid (GABA, glutamate, glycine, taurine, alanine and histidine) levels. The observed decrease in hypothalamic aromatase activity confirmed the efficacy of letrozole treatment in both sexes. Moreover, letrozole enhanced testosterone levels in sham-operated females. In the open field test, females were overall more active and explorative than males and gonadectomy eliminated this sex difference. In the FST, females exhibited overall higher immobility than males and gonadectomy further enhanced this passive behavior in both sexes. However, sustained aromatase inhibition had no effect on open field and FST behaviors. Head shakes during FST, which were fewer in females than in males, were reduced by castration in males and by letrozole treatment in ovariectomized females, suggesting a role of testosterone and extra-gonadal estrogens in the expression of this behavior. Sustained aromatase inhibition also decreased noradrenaline and the dopaminergic turnover rates [DOPAC/DA, HVA/DA] in the hippocampus and PFC of male and female rats, irrespectively of gonadectomy. Moreover, letrozole treatment enhanced the serotonergic turnover [5HIAA/5HT] rate in the hippocampus of males and females, irrespectively of gonadectomy. Amino acid levels were not influenced by letrozole, but sex differences were demonstrated with higher levels in the PFC of females vs. males. Present findings suggest that the neuropsychiatric effects of aromatase inhibition can be attributed to the inhibition of extragonadal estrogen synthesis, presumably in the brain, and could be further associated with serotonergic and catecholaminergic changes in brain regions involved in mood and cognition. Importantly, present data could be linked with the neurobiology of affective side-effects in post-menopausal women receiving aromatase inhibitors.

The nucleus reuniens: a key node in the neurocircuitry of stress and depression

The hippocampus and prefrontal cortex (PFC) are connected in a reciprocal manner: whereas the hippocampus projects directly to the PFC, a polysynaptic pathway that passes through the nucleus reuniens (RE) of the thalamus relays inputs from the PFC to the hippocampus. The present study demonstrates that lesioning and/or inactivation of the RE reduces coherence in the PFC-hippocampal pathway, provokes an antidepressant-like behavioral response in the forced swim test and prevents, but does not ameliorate, anhedonia in the chronic mild stress (CMS) model of depression. Additionally, RE lesioning before CMS abrogates the well-known neuromorphological and endocrine correlates of CMS. In summary, this work highlights the importance of the reciprocal connectivity between the hippocampus and PFC in the establishment of stress-induced brain pathology and suggests a role for the RE in promoting resilience to depressive illness.