Forced swim test: What about females?

Sex differences in anxiety and depression: insights from adult rodent models of chronic stress and neural plasticity

The often co-morbid conditions of depression and anxiety are the most common mental illnesses and are more prevalent among females than males. Chronic stress paradigms in rodents serve as valuable preclinical models for investigating the factors contributing to these disorders and their neural underpinnings. A variety of chronic stressors are associated with the development of sexually differentiated effects on anxiety- and depressive-like responses in rodents. This review summarizes and discusses common behavioral tasks used to assess anxiety-like (e.g., elevated plus maze, open field) and depressive-like (e.g., sucrose preference, forced swim) behaviors in rodents and discusses evidence of sex differences in these responses. Preclinical chronic stress models also aid in identifying potential mechanisms underlying behavioral changes, including dendritic synaptic alterations in neural circuits affected by stress. Robust sex differences have been observed in stress-responsive brain regions such as the prefrontal cortex, hippocampus, and amygdala. Therefore, applying chronic stress paradigms and assessing their neural effects in rodents may provide crucial insights into the biological basis of sexually differentiated mental illnesses in humans.

Prolactin-Releasing Peptide System as a Potential Mechanism of Stress Coping: Studies in Male Rats

Prolactin-releasing peptide (PrRP) has a regulatory role in both acute and chronic stress, suggesting its potential contribution to stress-related disorders such as depression. However, not all individuals with depression respond equally to stressors. We aimed to determine whether the PrRP system could underlie stress coping, an important aspect of depression. The forced swim test was used both as a stressor and as a method to assess coping strategy. Based on immobility time, active coping and passive coping subgroups were identified, and 10 brain regions were studied using qPCR to measure the mRNA expression levels of PrRP and its receptors (specific: GPR10; non-specific: NPFFR2). Passive coping animals spent more time in an immobile posture and exhibited altered mRNA expression levels in the medullary A1 region, the habenula, and the arcuate nucleus than control or active coping rats. Additionally, we identified corticotropin-releasing hormone and vesicular glutamate transporter 2 positive neurons in the A1 medullary region that contained Prrp, suggesting a modulatory role of PrRP in these excitatory neurons involved in stress regulation. Our findings reinforce the hypothesis that PrRP plays a role in stress coping, a process closely linked to depression. However its effect is brain region-specific.

Neonatal maternal separation causes depressive-like behavior and potentiates memory impairment induced by amyloid-β oligomers in adult mice

BACKGROUND

Alzheimer's disease (AD) is characterized by memory decline and mood alterations. A growing body of evidence implicates stress and other social determinants of health as potential contributors to the progressive cerebral alterations that culminate in AD. In the current study, we investigated the impact of neonatal maternal separation (MS) on the susceptibility of male and female mice to AD-associated memory impairments and depressive-like behavior in adulthood, and on brain levels of pro-inflammatory cytokines and neurotransmitters.

METHODOLOGY

Male and female Swiss mice were exposed to MS for 180 min daily from post-natal day 1 to 10. Seventy days post-MS, mice received an intracerebroventricular infusion of amyloid-β oligomers (AβOs), and memory and mood were evaluated. Levels of TNF-α, IL-1β, serotonin, dopamine, and related metabolites were determined in the cortex and hippocampus.

RESULTS

Previous exposure to MS alone did not cause memory impairments in adult mice. Interestingly, however, MS increased the susceptibility of adult male mice to memory impairment and depressive-like behavior induced by AβOs, and potentiated the inhibitory impact of AβOs on memory in adult females. Females were more susceptible to depressive-like behavior caused by a low dose of AβOs, regardless of MS. No changes in IL-1β were found. A decrease in TNF-α was selectively found in females exposed to MS that received an infusion of 1 pmol AβOs. MS led to an increase in serotonin (5-HT) in the hippocampus of male mice, without influencing the levels of the serotonin metabolite, 5-HIAA. Changes in serotonin turnover were predominantly observed in the cortex of female mice. No changes in dopamine or its metabolites were induced by MS or AβOs in male or female mice.

CONCLUSIONS

Neonatal MS enhances the susceptibility of adult mice to AD-associated cognitive deficits and depressive-like behavior in a sex-specific manner. This suggests that early life stress may play a role in the development of AD.

L-type calcium channel blockade attenuates the anxiogenic-like effects of cocaine abstinence in female and male rats

Cocaine abstinence and withdrawal are linked to relapse and heightened anxiety. While L-type calcium channels (LTCCs) have been associated with cocaine use disorders in humans and drug-seeking in rodents, their role in mood-related symptoms during cocaine abstinence remains unclear. We addressed this by investigating the ability of LTCC blockade with isradipine to alter the mood-related behavioral phenotypes induced by cocaine abstinence. Female and male Sprague-Dawley rats were trained to self-administer cocaine or saline, followed by a 14-day period of abstinence. Subsequently, behavioral responses were examined using the sucrose preference test (SPT), elevated plus maze (EPM), and forced swim test (FST). Cocaine-abstinent rats showed decreased open arm time in the EPM and increased immobility time in the FST with no changes in the SPT. Isradipine (0.4 mg/kg or 1.2 mg/kg, i.p.), reversed the anxiogenic-like EPM behavior in female cocaine-abstinent rats, whereas only the higher dose (1.2 mg/kg, i.p.) was effective in male cocaine-abstinent rats. In the FST, the lower dose (0.4 mg/kg, i.p.) of isradipine reversed the increased immobility time observed in cocaine-abstinent female and male rats, with no isradipine effect in saline-abstinent rats. In contrast 1.2 mg/kg, i.p. isradipine decreased immobility time in both cocaine and saline abstinent female and male rats. In summary, isradipine administration reversed the anxiogenic and increased the FST immobility time associated with cocaine abstinence in a dose and sex-dependent manner. The data underscore the importance of further investigation of LTCC mechanisms and their therapeutic potential for mood disorders associated with cocaine use disorder.

Endocannabinoid involvement in beneficial effects of caloric restriction in a rodent model of comorbid depression and epilepsy

Clinically, patients with depression are at a heightened risk for developing epilepsy, and vice versa, suggesting shared mechanisms for this bidirectional comorbidity. Unfortunately, comorbid depression and epilepsy is associated with worsened quality of life and treatment refractoriness, highlighting the need for novel treatment targets and nonpharmacologic supplements to existing therapies. The present study used the Swim-Low Active rat, a well-validated model of depression and epilepsy comorbidity that was selectively bred based on forced swim test behavior, to assess the safety and efficacy of caloric restriction in treating this comorbidity. The study also investigated the role of endocannabinoids in the effects of caloric restriction on the behavioral endpoints and to determine whether there were any sex differences in these effects. Male rats restricted to approximately 80 % of their daily food intake for an acute 24-h period showed elevated struggling behavior in the Porsolt (Forced) Swim Test and increased latency to pilocarpine-induced seizure; this same caloric restriction yielded a significant increase in hippocampal anandamide levels compared to ad lib rats. These effects were not seen in female rats, although female rats did show anticonvulsant effects of chronic caloric restriction. Administration of 1 mg/kg SR141716 alongside an acute caloric restriction in male rats blocked the antidepressant-like effects of caloric restriction but did not affect seizure responses. Combined, these results suggest caloric restriction may be both safe and modestly effective in benefitting depression- and epilepsy-related behaviors in male SwLo rats, and that the endocannabinoid system may be a promising target for treating this comorbidity.

Could probiotics be used as a novel therapeutic approach to alleviate the reproductive and neurobehavioral side effects of sertraline? A study in male mice

There are still few studies that have investigated the impact of sertraline (SE) on fertility, as well as adjuvant treatments that alleviate its side effects. Thus, the present study aimed to investigate the impact of SE on reproductive and neurobehavior parameters and verify whether the probiotic Lactobacillus rhamnosus alleviates the side effects of SE. After carrying out a dose-response study with SE, experiment II was conducted. Thus, male mice were distributed into four experimental groups (n=8-9/group): control (CO)-received filtered water (vehicle); sertraline group (S)-received 20 mg/kg of SE, diluted in the vehicle; probiotic (P)-received the probiotic Lactobacillus rhamnosus (1×109 CFU) diluted in the vehicle; and SP group that received both probiotic and SE. The treatment occurred/lasted for 30 days. At the end of treatment, behavioral aspects were analyzed. After euthanasia, the organs were weighed, the histology of the testis and epididymis were analyzed, and the sperm quality and also natural fertility were verified. Complementarily, in vitro assays were carried out to verify whether sertraline could affect sperm capacitation and embryonic development. The results showed that the SP group, compared to S, did not reduce body weight and seminal gland weight and presented a lower number of resorptions. Notably, the rate of resorption in both the SP and S groups was similar to that of the control group. It was also observed that the S group was less exploratory and more anxious than the SP group. Thus, the present study demonstrated that SE has an impact on the reproductive system and neurobehavior. Therefore, for the first time, we demonstrate that the probiotic can alleviate the side effects of SE.

Applying the Research Domain Criteria to Rodent Studies of Sex Differences in Chronic Stress Susceptibility

Women have a 2-fold increased rate of stress-associated psychiatric disorders such as depression and anxiety, but the mechanisms that underlie this increased susceptibility remain incompletely understood. Historically, female subjects were excluded from preclinical studies and clinical trials. Additionally, chronic stress paradigms used to study psychiatric pathology in animal models were developed for use in males. However, recent changes in National Institutes of Health policy encourage inclusion of female subjects, and considerable work has been performed in recent years to understand biological sex differences that may underlie differences in susceptibility to chronic stress-associated psychiatric conditions. Here, we review the utility as well as current challenges of using the framework of the National Institute of Mental Health's Research Domain Criteria as a transdiagnostic approach to study sex differences in rodent models of chronic stress including recent progress in the study of sex differences in the neurobehavioral domains of negative valence, positive valence, cognition, social processes, and arousal.

Dual Approach to Depression: The Combined Efficacy of Intermittent Hypoxia and Fluoxetine in Modulating Behavioral and Inflammatory Responses

Background/Objectives: Mental disorders pose a significant public health challenge, affecting millions worldwide. Given the limitations of current therapies, many patients experience inadequate responses and adverse effects. Intermittent hypoxia (IH) has demonstrated anxiolytic, antidepressant, and neuroprotective properties in various protocols. This study investigated the effects of acute IH (13% O2, 1 h), fluoxetine (FLX) and their combination on depression-like behavior, serum corticosterone, and inflammatory cytokine levels induced by acute restraint stress in C57BL/6 female mice. Methods: Behavioral assessments included the tail suspension test, forced swim test, and open field test. Results: The combined IH + FLX treatment exhibited a synergistic effect, reducing immobility time and increasing latency time, respectively, in the tail suspension test (46%, p = 0.0014; 73%, p = 0.0033) and forced swim test (56%, p = 0.0082; 48%, p = 0.0322) compared to the ARS group. Biochemical analysis revealed that individual and combined treatments significantly reduced most inflammatory interleukins by up to 96%. Corticosterone levels were reduced by 30% only in the IH group. Conclusions: These findings highlight the potential of a one-hour IH session, particularly when combined with fluoxetine, to alleviate depressive-like behaviors and exert anti-inflammatory effects, suggesting a promising therapeutic approach for depression.

Prefrontal cortex-nucleus reuniens-hippocampus network exhibits sex-differentiated responses to stress and antidepressant treatment in rats

RATIONALE

Depression is a serious psychiatric disease, which is diagnosed twice as frequently in women than men. We have recently shown that lesioning or inactivation of the nucleus reuniens (RE), which interconnects the prefrontal cortex (PFC) and hippocampus, promoted resilience to stress in males, exerts an antidepressant effect in the Forced Swim Test (FST) and prevents the development of behavioral and neurobiological alterations induced by the chronic mild stress model of depression.

OBJECTIVES

In this study, we expand our findings on the FST in female rats and we investigate whether RE lesion presents sex differences following treatment with two distinct antidepressants, a selective serotonin reuptake inhibitor, i.e. sertraline and a tricyclic antidepressant, i.e. clomipramine.

METHODS

Male and female rats received either a surgical lesion of the RE or sham operation, then treated with vehicle, sertraline (10mg/kg) or clomipramine (10mg/kg) and were subjected to the FST. Activation of key brain areas of interest (PFC, Hippocampus and RE) were measured by c-Fos immunoreactivity.

RESULTS

RE lesion induced an antidepressant-like phenotype in both female and male rats, confirming its crucial role in the stress response. Similarly to RE lesion, sertraline treatment resulted in increased swimming and decreased immobility duration, as well as enhanced head shake frequency, in both sexes. Notably, climbing behavior was increased only following clomipramine treatment. RE area was less active in females compared to male rats and in clomipramine-treated males compared to their corresponding vehicle-group. Activation of the PFC and the CA1 hippocampal area was reduced in clomipramine-treated females, in comparison to vehicle-treated female rats. This effect was not evident in males, which exhibited less activation in the PFC and the hippocampus than females.

CONCLUSION

Re lesion proves equally effective in female and male rats, but sex is highlighted as a pivotal factor in behavioral and treatment response in FST, as well as in related circuit connectivity and activation.

Differential effects of high-fat diet on endocrine, metabolic and depressive-like behaviors in male and female rats

The complications of obesity extend beyond the periphery to the central nervous system (CNS) and include an increased risk of developing neuropsychiatric co-morbidities like depressive illness. Preclinical studies support this concept, including studies that have examined the effects of a high-fat diet (HFD) on depressive-like behaviors. Although women are approximately two-fold more likely to develop depressive illness compared to men, most preclinical studies have focused on the effects of HFD in male rodents. Accordingly, the goal of this study was to examine depressive-like behaviors in male and female rats provided access to a HFD. In agreement with prior studies, male and female rats provided a HFD segregate into an obesity phenotype (i.e., diet-induced obesity; DIO) or a diet resistant (DR) phenotype. Upon confirmation of the DR and DIO phenotypes, behavioral assays were performed in control chow, DR, and DIO rats. In the sucrose preference test, male DIO rats exhibited significant decreases in sucrose consumption (i.e., anhedonia) compared to male DR and male control rats. In the forced swim test (FST), male DIO rats exhibited increases in immobility and decreases in climbing behaviors in the pre-test sessions. Interestingly, male DR rats exhibited these same changes in both the pre-test and test sessions of the FST, suggesting that consumption of a HFD, even in the absence of the development of an obesity phenotype, has behavioral consequences. Female rats did not exhibit differences in sucrose preference, but female DIO rats exhibited increases in immobility exclusively in the test session of the FST, behavioral changes that were not affected by the stage of the estrous cycle. Collectively, these studies demonstrate that access to a HFD elicits different behavioral outcomes in male and female rats.

Cyclooxygenase-2 inhibitors alleviated depressive and anxious-like behaviors in mice exposed to lipopolysaccharide: Involvement of oxidative stress and neuroinflammation

Depression and anxiety disorders have their pathophysiologies linked to inflammation and oxidative stress. In this context, celecoxib (CLX) and etoricoxib (ETR) inhibit cyclooxygenase 2 (COX-2), an enzyme expressed by cells involved in the inflammatory process and found in the brain. Studies have been using CLX as a possible drug in the treatment of depression, although its mechanisms at the central nervous system level are not fully elucidated. In this study, the effects of CLX and ETR on behavioral, oxidative, and inflammatory changes induced by systemic exposure to Escherichia coli lipopolysaccharide (LPS) were evaluated in adult male swiss mice. For ten days, the animals received intraperitoneal injections of LPS at 0.5 mg/kg. From the sixth to the tenth day, one hour after LPS exposure, they were treated orally with CLX (15 mg/kg), ETR (10 mg/kg), or fluoxetine (FLU) (20 mg/kg). Twenty-four hours after the last oral administration, the animals underwent evaluation of locomotor activity (open field test), predictive tests for depressive-like behavior (forced swim and tail suspension tests), and anxiolytic-like effect (elevated plus maze and hole board tests). Subsequently, the hippocampus, prefrontal cortex and striatum were dissected for the measurement of oxidative and nitrosative parameters (malondialdehyde, nitrite, and glutathione) and quantification of pro-inflammatory cytokines (IL-1β and IL-6). LPS induced depressive and anxious-like behavior, and treatment with CLX or ETR was able to reverse most of the behavioral changes. It was evidenced that nitrosative stress and the degree of lipid peroxidation induced by LPS were reduced in different brain areas after treatment with the drugs, as well as the endogenous defense system against free radicals was strengthened. CLX and ETR also significantly reduced LPS-induced cytokine levels. These data are expected to expand information on the role of inflammation in depression and anxiety and provide insights into possible mechanisms of COX-2 inhibitors in psychiatric disorders with a neurobiological basis in inflammation and oxidative stress.

The Affective Bias Test and Reward Learning Assay: Neuropsychological Models for Depression Research and Investigating Antidepressant Treatments in Rodents

The Affective Bias Test (ABT) quantifies acute changes in affective state based on the affective biases they generate in an associative reward learning task. The Reward Learning Assay (RLA) provides a control assay for the ABT and reward-induced biases generated in this model are sensitive to changes in core affective state. Both tasks involve training animals to associate a specific digging substrate with a food reward. Animals learn to discriminate between two digging substrates placed in ceramic bowls, one rewarded and one unrewarded. In the ABT, the animal learns two independent substrate-reward associations with a fixed reward value following either an affective state or drug manipulation, or under control conditions. Affective biases generated are quantified in a choice test where the animals exhibit a bias (make more choices) for one of the substrates which is specifically related to affective state at the time of learning. The ABT is used to investigate biases generated during learning as well as modulation of biases associated with past experiences. The RLA follows a similar protocol, but the animal remains in the same affective state throughout and a reward-induced bias is generated by pairing one substrate with a higher value reward. The RLA provides a control to determine if drug treatments affect memory retrieval more generally. Studies in depression models and following environmental enrichment suggest that reward-induced biases are sensitive to core changes in affective state. Each task offers different insights into affective processing mechanisms and may help improve the translational validity of animal studies and benefit pre-clinical drug development. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Bowl digging and discrimination training Basic Protocol 2: The reward learning assay Basic Protocol 3: The affective bias test - new learning Basic Protocol 4: The affective bias test - modulation of affective biases associated with past experiences.

Antidepressant Effect of Sodium Butyrate is Accompanied by Brain Epigenetic Modulation in Rats Subjected to Early or Late Life Stress

BACKGROUND

Major depression has a complex and multifactorial etiology constituted by the interaction between genetic and environmental factors in its development.

OBJECTIVE

The aim of this study was to evaluate the effects of sodium butyrate (SD) on epigenetic enzyme alterations in rats subjected to animal models of depression induced by maternal deprivation (MD) or chronic mild stress (CMS).

METHODS

To induce MD, male Wistar rats were deprived of maternal care during the first 10 days of life. To induce CMS, rats were subjected to the CMS for 40 days. Adult rats were then treated with daily injections of SD for 7 days. Animals were subjected to the forced swimming test (FST), and then, histone deacetylase (HDAC), histone acetyltransferase (HAT), and DNA methyltransferase (DNMT) activities were evaluated in the brain.

RESULTS

MD and CMS increased immobility time in FST and increased HDAC and DNMT activity in the animal brains. SD reversed increased immobility induced by both animal models and the alterations in HDAC and DNMT activities. There was a positive correlation between enzyme activities and immobility time for both models. HDAC and DNMT activities also presented a positive correlation between themselves.

CONCLUSION

These results suggest that epigenetics can play an important role in major depression pathophysiology triggered by early or late life stress and its treatment.

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.

Synthesis, computational simulations and biological evaluation of new dual 5HT1A/5HT7 receptor ligands based on purine-2,6-dione scaffold

The new dual 5HT1A/5HT7 receptor ligands were designed based on the purine-2,6-dione scaffold with the fluorine atom. Twenty-one new derivatives were synthesized, and their structure-activity relationship was summarized. Compound 11 (7-(2-(3-fluorophenyl)-2-oxoethyl)-8-((4-(4-(2-methoxyphenyl)piperazin-1-yl)butyl)amino)-1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione) showed the highest affinity to 5HT1AR and 5HT7R, and was the most potent antagonist of 5-HT1AR (Kb = 0.26 ± 0.1 nM) which activity can be to reference compound NAN-190 (Kb = 0.26 ± 0.1 nM). The experimentally established physicochemical parameters of compound 11 showed that compound, as slightly ionized in the blood, could penetrate the blood-brain barrier. A molecular docking study showed that the fluorine substitution introduces additional stabilization effects on binding to 5HT1A/5HT7Rs. In animal assays of depression and anxiety, compound 11 revealed activity in terms of dosage compared to marketed psychotropics such as fluoxetine, citalopram, and sertraline.

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.

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.

Minimal influence of estrous cycle on studies of female mouse behaviors

Introduction

Sex bias has been an issue in many biomedical fields, especially in neuroscience. In rodent research, many scientists only focused on male animals due to the belief that female estrous cycle gives rise to unacceptable, high levels of variance in the experiments. However, even though female sexual behaviors are well known to be regulated by estrous cycle, which effects on other non-sexual behaviors were not always consistent in previous reports. Recent reviews analyzing published literature even suggested that there is no evidence for larger variation in female than male in several phenotypes.

Methods

To further investigate the impact of estrous cycle on the variability of female behaviors, we conducted multiple behavioral assays, including the open field test, forced swimming test, and resident-intruder assay to assess anxiety-, depression-like behaviors, as well as social interaction respectively. We compared females in the estrus and diestrus stages across four different mouse strains: C57BL/6, BALB/c, C3H, and DBA/2.

Results

Our results found no significant difference in most behavioral parameters between females in these two stages. On the other hand, the differences in behaviors among certain strains are relatively consistent in both stages, suggesting a very minimal effect of estrous cycle for detecting the behavioral difference. Last, we compared the behavioral variation between male and female and found very similar variations in most behaviors between the two sexes.

Discussion

While our study successfully identified behavioral differences among strains and between the sexes, we did not find solid evidence to support the notion that female behaviors are influenced by the estrous cycle. Additionally, we observed similar levels of behavioral variability between males and females. Female mice, therefore, have no reason to be excluded in future behavioral research.

Neural mechanism of acute stress regulation by trace aminergic signalling in the lateral habenula in male mice

Stress management is necessary for vertebrate survival. Chronic stress drives depression by excitation of the lateral habenula (LHb), which silences dopaminergic neurons in the ventral tegmental area (VTA) via GABAergic neuronal projection from the rostromedial tegmental nucleus (RMTg). However, the effect of acute stress on this LHb-RMTg-VTA pathway is not clearly understood. Here, we used fluorescent in situ hybridisation and in vivo electrophysiology in mice to show that LHb aromatic L-amino acid decarboxylase-expressing neurons (D-neurons) are activated by acute stressors and suppress RMTg GABAergic neurons via trace aminergic signalling, thus activating VTA dopaminergic neurons. We show that the LHb regulates RMTg GABAergic neurons biphasically under acute stress. This study, carried out on male mice, has elucidated a molecular mechanism in the efferent LHb-RMTg-VTA pathway whereby trace aminergic signalling enables the brain to manage acute stress by preventing the hypoactivity of VTA dopaminergic neurons.

The Track-by-Day Method for Monitoring the Rodent Estrous Cycle

The exclusion of female subjects from preclinical neuroscience research has traditionally been justified in part by concerns about potential effects of cycling ovarian hormones on brain function. There is evidence that some behavioral and neurobiological measures do change over the estrous cycle and, as the use of female subjects becomes increasingly routine, there is a greater demand for accessible cycle-tracking methods. Conventional estrous cycle staging requires expert training in the qualitative interpretation of vaginal cytology smears, which serves as a barrier for novice researchers. In addition, definitions and reporting practices are not standardized across laboratories, which makes it difficult to compare results across studies and likely contributes to a false perception of the cycle as ephemeral and inconsistent. Here, we describe a streamlined method for monitoring the estrous cycle in rats, which we term Track-by-Day. It is simple to implement and inherently produces consistent reporting. Our protocol should serve to demystify and facilitate adoption of cycle tracking for those new to the practice. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Collection and staining of vaginal smears Basic Protocol 2: Track-by-Day classification of vaginal smears Support Protocol: Preparation of gelatin-subbed slides.

The Greater Impact of Paternal, Compared to Maternal, Hereditary Background on Depressive-Like Behavior in Wistar Kyoto Rats with Different Amino Acid Metabolism in the Pup Brain

In the pathogenesis of depression, heredity is believed to be a major factor. However, the mechanism by which heredity contributes to the onset of depression is not fully understood. Wistar Kyoto (WKY) rats have been used as an animal model for depression because of their increased depression-like behavior compared to Wistar (WIS) rats. In the present study, pups crossbred from WKY × WIS rats were used to evaluate locomotor activity in an open field test (OFT) and depression-like behavior in a forced swimming test (FST), with a focus on amino acid metabolism. Pups in the WKY♂ × WKY♀ group showed lower locomotor activity in the OFT and higher depression-like behavior in the FST than those in the WIS♂ × WIS♀ group. In addition, multiple regression analysis showed that the paternal strain had a greater effect than the maternal strain on locomotor activity and depression-like behavior in OFT and FST, respectively. Several amino acids in the brainstem, hippocampus, and striatum were significantly decreased through the influence of the WKY paternal strain, but not the WKY maternal strain. Based on these data from comparing WKY and WIS rats, we hypothesize that the hereditary effects of the WKY paternal strain on behavioral tests are partially caused by dysregulation of the amino acid metabolism in the brain.

Cannabinoid Receptor 2 Blockade Prevents Anti-Depressive-like Effect of Cannabidiol Acid Methyl Ester in Female WKY Rats

The pathophysiology of major depressive disorder (MDD) is diverse and multi-factorial, yet treatment strategies remain limited. While women are twice as likely to develop the disorder as men, many animal model studies of antidepressant response rely solely on male subjects. The endocannabinoid system has been linked to depression in clinical and pre-clinical studies. Cannabidiolic Acid-Methyl Ester (CBDA-ME, EPM-301) demonstrated anti-depressive-like effects in male rats. Here, we explored acute effects of CBDA-ME and some possible mediating mechanisms, using a depressive-like genetic animal model, the Wistar-Kyoto (WKY) rat. In Experiment 1, Female WKY rats underwent the Forced swim test (FST) following acute CBDA-ME oral ingestion (1/5/10 mg/kg). In Experiment 2, Male and female WKY rats underwent the FST after injection of CB1 (AM-251) and CB2 (AM-630) receptor antagonists 30 min before acute CBDA-ME ingestion (1 mg/kg, males; 5 mg/kg, females). Serum levels of Brain-Derived Neurotrophic Factor (BDNF), numerous endocannabinoids and hippocampal Fatty Acid Amide Hydrolase (FAAH) levels were assessed. Results indicate that females required higher doses of CBDA-ME (5 and 10 mg/kg) to induce an anti-depressive-like effect in the FST. AM-630 blocked the antidepressant-like effect in females, but not in males. The effect of CBDA-ME in females was accompanied by elevated serum BDNF and some endocannabinoids and low hippocampal expression of FAAH. This study shows a sexually diverse behavioral anti-depressive response to CBDA-ME and possible underlying mechanisms in females, supporting its potential use for treating MDD and related disorders.

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.

Are cognitive aspects of defense a core feature of anxiety and depression?

Anxiety and depression are highly prevalent behavior disorders, particularly in women. Recent preclinical work using animal models has been suboptimal in predicting the efficacy of drugs targeted at these conditions, suggesting a potential discrepancy between such models and the human disorders. Notably female animals tend to be equal to, or less responsive than, males in these tasks. A number of analyses suggest that mammalian defense patterns are complex: In addition to relatively discrete and immediate fight, flight, and freezing responses, a risk assessment pattern may occur in response to threat stimuli or situations with ambiguous elements. This pattern combines defensiveness with a number of cognition-linked behaviors such as sensory attention and orientation, approach, contact, and investigation of the potential threat. Studies measuring elements of this pattern suggest that female rats, and perhaps female mice, show higher levels than equivalent males. Higher female involvement may also occur in tasks involving learning/generalization/extinction of defensiveness to conditioned stimuli. Such findings are consonant with recent analyses of "female survival strategies" based on differential adaptiveness of cognitive components of defensiveness in females, due to the necessity of female care of offspring until they are independent. These data suggest the value of additional behavioral and functional analyses of cognitive aspects of defensive behavior; contributing to both an understanding of their underlying mechanisms, and providing more sensitive measures of drug responsivity for use with animal models.

Role of 5-HT1A-mediated upregulation of brain indoleamine 2,3 dioxygenase 1 in the reduced antidepressant and antihyperalgesic effects of fluoxetine during maintenance treatment

The reduced antidepressant and antihyperalgesic effects of selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine during maintenance treatment has been reported, but little is known about the molecular mechanism of this phenomenon. In three comorbid pain and depression animal models (genetic predisposition, chronic social stress, arthritis), we showed that the fluoxetine's antidepressant and antihyperalgesic effects were reduced during the maintenance treatment. Fluoxetine exposure induced upregulation of the 5-hydroxytryptamine 1A (5-HT1A) auto-receptor and indoleamine 2,3 dioxygenase 1 (IDO1, a rate-limiting enzyme of tryptophan metabolism) in the brainstem dorsal raphe nucleus (DRN), which shifted the tryptophan metabolism away from the 5-HT biosynthesis. Mechanistically, IDO1 upregulation was downstream to fluoxetine-induced 5-HT1A receptor expression because 1) antagonism of the 5-HT1A receptor with WAY100635 or 5-HT1A receptor knockout blocked the IDO1 upregulation, and 2) inhibition of IDO1 activity did not block the 5-HT1A receptor upregulation following fluoxetine exposure. Importantly, inhibition of either the 5-HT1A receptor or IDO1 activity sustained the fluoxetine's antidepressant and antihyperalgesic effects, indicating that 5-HT1A-mediated IDO1 upregulation in the brainstem DRN contributed to the reduced antidepressant and antihyperalgesic effects of fluoxetine. These results suggest a new strategy to improving the therapeutic efficacy of SSRI during maintenance treatment.

Behavioral effects of environmental enrichment on male and female wistar rats with early life stress experiences

Exposure to adverse childhood experiences or early life stress experiences (ELSs) increase the risk of non-adaptive behaviors and psychopathology in adulthood. Environmental enrichment (EE) has been proposed to minimize these effects. The vast number of methodological variations in animal studies underscores the lack of systematicity in the studies and the need for a detailed understanding of how enrichment interacts with other variables. Here we evaluate the effects of environmental enrichment in male and female Wistar rats exposed to adverse early life experiences (prenatal, postnatal, and combined) on emotional (elevated plus maze), social (social interaction chamber), memory (Morris water maze) and flexibility tasks. Our results—collected from PND 51 to 64—confirmed: 1) the positive effect of environmental enrichment (PND 28–49) on anxiety-like behaviors in animals submitted to ELSs. These effects depended on type of experience and type of enrichment: foraging enrichment reduced anxiety-like behaviors in animals with prenatal and postnatal stress but increased them in animals without ELSs. This effect was sex-dependent: females showed lower anxiety compared to males. Our data also indicated that females exposed to prenatal and postnatal stress had lower anxious responses than males in the same conditions; 2) no differences were found for social interactions; 3) concerning memory, there was a significant interaction between the three factors: A significant interaction for males with prenatal stress was observed for foraging enrichment, while physical enrichment was positive for males with postnatal stress; d) regarding cognitive flexibility, a positive effect of EE was found in animals exposed to adverse ELSs: animals with combined stress and exposed to physical enrichment showed a higher index of cognitive flexibility than those not exposed to enrichment. Yet, within animals with no EE, those exposed to combined stress showed lower flexibility than those exposed to both prenatal stress and no stress. On the other hand, animals with prenatal stress and exposed to foraging-type enrichment showed lower cognitive flexibility than those with no EE. The prenatal stress-inducing conditions used here 5) did not induced fetal or maternal problems and 6) did not induced changes in the volume of the dentate gyrus of the hippocampus.

Sex- and age-dependent effects of chronic corticosterone exposure on depressive-like, anxiety-like, and fear-related behavior: Role of amygdala glutamate receptors in the rat

Persistent glucocorticoid elevation consistent with chronic stress exposure can lead to psychopathology, including mood and anxiety disorders. Women and stress-exposed adolescents are more likely to be diagnosed with mood disorders, suggesting that sex and age are important factors in determining vulnerability, though much remains to be determined regarding the mechanisms underlying this risk. Thus, the aim of the present experiments was to use the chronic corticosterone (CORT) exposure paradigm, a model of depression-like behavior that has previously been established primarily in adult males, to determine the mood-related effects of CORT in female and adolescent rats. Depression- and anxiety-like effects in adulthood were determined using the sucrose preference (SPT), the forced swim test (FST), the elevated plus maze, and fear conditioning. Basolateral amygdala (BLA) and medial prefrontal cortex (mPFC) glutamate receptor subunit levels were then measured. In a subsequent experiment, adult male and female rats were tested for the effects of pharmacological activation (via AMPA) or inhibition (via NBQX) of AMPA receptors in the BLA on behavior in the FST. Overall, females showed reduced anxiety- and depressive-like behaviors relative to males. However, females treated with CORT in adolescence, but not adulthood, had increased immobility in the FST, indicative of depression-like behavior. In contrast, CORT did not alter behavior in adolescent-treated males, though the previously reported depression-like effect of adult CORT exposure was observed. Control females had higher expression of the AMPA receptor subunits GluA1 and GluA2/3 selectively in the BLA relative to males. Adolescent CORT treatment, however, decreased BLA GluA1 and GluA2/3 expression in females, but increased expression in males, consistent with the direction of depression-like behavioral effects. Male and female rats also demonstrated opposing patterns of response to BLA AMPA receptor modulation in the FST, with AMPA infusion magnifying the sex difference of decreased immobility in females. Overall, these experiments show that increased glutamate receptor function in the BLA may decrease the risk of developing depressive-like behavior, further supporting efforts to target glutamatergic receptors for the treatment of stress-related psychiatric disorders. These findings also support further focus on sex as a biological variable in neuropsychiatric research.

Encore: Behavioural animal models of stress, depression and mood disorders

Animal studies over the past two decades have led to extensive advances in our understanding of pathogenesis of depressive and mood disorders. Among these, rodent behavioural models proved to be of highest informative value. Here, we present a comprehensive overview of the most popular behavioural models with respect to physiological, circuit, and molecular biological correlates. Behavioural stress paradigms and behavioural tests are assessed in terms of outcomes, strengths, weaknesses, and translational value, especially in the domain of pharmacological studies.

Sex hormone fluctuation and increased female risk for depression and anxiety disorders: From clinical evidence to molecular mechanisms

Women are at twice the risk for anxiety and depression disorders as men are, although the underlying biological factors and mechanisms are largely unknown. In this review, we address this sex disparity at both the etiological and mechanistic level. We dissect the role of fluctuating sex hormones as a critical biological factor contributing to the increased depression and anxiety risk in women. We provide parallel evidence in humans and rodents that brain structure and function vary with naturally-cycling ovarian hormones. This female-unique brain plasticity and associated vulnerability are primarily driven by estrogen level changes. For the first time, we provide a sex hormone-driven molecular mechanism, namely chromatin organizational changes, that regulates neuronal gene expression and brain plasticity but may also prime the (epi)genome for psychopathology. Finally, we map out future directions including experimental and clinical studies that will facilitate novel sex- and gender-informed approaches to treat depression and anxiety disorders.

Revisiting the antidepressant-like effects of desipramine in male and female adult rats: sex disparities in neurochemical correlates

Background

The preclinical antidepressant-like characterization of desipramine relied almost exclusively in male rodents, with only a few contradictory reports done in females. Given that most experiments assessed a single dose and/or timepoint of analysis after-treatment, this study evaluated potential sex-differences in the length of the antidepressant-like response induced by different doses of desipramine as well as the molecular underpinnings driving the different responses by sex.

Methods

Male and female Sprague–Dawley rats were treated (i.p.) with 3 pulses of desipramine (5, 10 or 20 mg/kg) or vehicle (0.9% NaCl) within 24 h. The antidepressant-like effects were evaluated in the forced-swim test 1-h, 1- and 3-day post-treatment. The rate of cell proliferation and the regulation of key neuroplasticity markers (FADD, Cdk5, p35, p25) involved in antidepressant-like responses in the hippocampus were evaluated 1-h, 1-day and 5-day post-treatment.

Results

Desipramine induced similar antidepressant-like effects in male and female rats (effective doses of 10 and 20 mg/kg, with effects that lasted up to 1-day post-treatment), without altering the rate of cell proliferation. However, some sex-differences emerged when evaluating neuroplasticity markers in the hippocampus, while no changes were observed for female rats, desipramine regulated FADD, Cdk-5 and p25 in males in a way that suggested neuroprotective actions.

Conclusions

Our findings imply that while desipramine induced similar antidepressant-like responses for male and female rats, some differences emerged in the regulation of certain neuroplasticity markers, suggesting that distinctive molecular mechanisms might be participating in the therapeutic response of desipramine for both sexes.

Exploring pharmacological options for adolescent depression: a preclinical evaluation with a sex perspective

There is an urgent need for developing novel pharmacological treatment options for adolescent depression, and to ensure an optimal translational outcome to the clinic, sex should be included as a biological variable in preclinical studies. In this context, the present study compared the antidepressant-like potential of ketamine and cannabidiol, with the clinical standard fluoxetine, in adolescent rats exposed to maternal deprivation (as a model of early-life stress), while including a sex perspective. Moreover, changes in drug efficacy over time were evaluated by re-exposing rats to the same dose regimens during adulthood. Antidepressant-like responses were scored through a battery of distinctive tests (forced-swim, novelty-suppressed feeding, and sucrose preference) across time. The main results proved an antidepressant-like potential for ketamine and cannabidiol in adolescent rats, although their efficacy was dependent on sex and prior stress exposure, as well as on treatment length and the behavioral feature analyzed. In general, while all tested antidepressants in male rats improved certain affective-like features, female rats were mainly unresponsive to the treatments performed (except for certain benefits induced by ketamine), demonstrating the need for further characterizing proper treatments for this particular sex. Moreover, when rats were re-exposed in adulthood to the same drug regimens as in adolescence, a drop in efficacy was observed. These findings may have translational ramifications in that ketamine or cannabidiol could be moved forward as antidepressants for the adolescent depressed population, but not before further characterizing their potential long-term safety and/or beneficial vs. harmful effects for both sexes.

Antidepressant-like activity of gestational administration of vitamin D is suppressed by prenatal overexposure to dexamethasone in female Wistar rats

Overexposure to glucocorticoids during gestation can lead to long-term mental disorders. Given the higher prevalence of depression in females, we investigated whether late gestational administration of dexamethasone could generate a depressive-like phenotype in the adult female offspring and if vitamin D could have a neuroprotective effect in this context. Pregnant rats received vitamin D (VitD, 500 IU/day) or vehicle (CTL) during gestation. Other pregnant rats received dexamethasone (Dex 0.1 mg/kg/ - 14th to the 19th gestational day) or dexamethasone + vitamin D (DexVitD). The offspring were tested for anhedonia (sucrose preference) and depressive-like behavior (forced swimming test) at postnatal months (PNM) 3, 6 and 12. Components of the serotonergic system, as well as glucocorticoids' receptors, were evaluated in the dorsal raphe nucleus at PNM 6 and 12. Prenatal vitamin D and dexamethasone increased sucrose preference at PNM 12. Prenatal vitamin D had an antidepressant-like effect at PNM 3 in rats overexposed to dexamethasone. However, at PNM 12, this effect was blunted in the DexVitD group. Prenatal dexamethasone reduced the protein content of SERT, TPH, and 5-HT_1A receptors in the dorsal raphe nucleus at 6 but not at 12 PNM. The glucocorticoids' receptors expression was similar in all groups. We concluded that prenatal overexposure to dexamethasone does not change emotional behaviors in females, but it blunts the antidepressant-like effect of gestational vitamin D in an age-dependent manner. The antidepressant-like activity of vitamin D in the offspring was not related either to alterations of the serotonergic system or the glucocorticoids' receptors expression in the dorsal raphe nucleus.

Neuropeptide Y, calcitonin gene-related peptide, and neurokinin A in brain regions of HAB rats correlate with anxiety-like behaviours

Anxiety disorders are pervasive psychiatric disorders causing great suffering. The high (HAB) and low (LAB) anxiety-related behaviour rats were selectively bred to investigate neurobiological correlates of anxiety. We compared the level of neuropeptides relevant for anxiety- and depression-related behaviours in selected brain regions of HAB and LAB rats. Increased anxiety and depression-like behaviours of male and female HAB rats in the elevated plus-maze and forced swim tests were accompanied by elevated levels of neuropeptide Y (NPY) in the prefrontal (PFC), frontal (FC) and cingulate cortex (CCx), the striatum, and periaqueductal grey (PAG). Moreover, HAB rats displayed sex-dependent, elevated levels of calcitonin gene-related peptide (CGRP) in PFC, FC, CCx, hippocampus, and PAG. Higher neurokinin A (NKA) levels were detected in CCx, striatum, and PAG in HAB males and in CCx and hypothalamus in HAB females. Increased neurotensin was detected in CCx and PAG in HAB males and in hypothalamus in HAB females. Elevated corticotropin-releasing hormone (CRH) levels appeared in female HAB hypothalamus. Significant correlations were found between anxiety-like behaviour and NPY, CGRP, NKA, and neurotensin, particularly with NPY in CCx and striatum, CGRP in FC and hippocampus, and NKA in entorhinal cortex. This is the first report of NPY, CGRP, NKA, Neurotensin, and CRH measurements in brain regions of HAB and LAB rats, which showed widespread NPY and CGRP alterations in cortical regions, with NKA and neurotensin changes localised in sub-cortical areas. The results may contribute to elucidate pathophysiological mechanisms underlying anxiety and depression and should facilitate identifying novel therapeutic targets.

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.

Sex Differences in Anxiety and Depression: What Can (and Cannot) Preclinical Studies Tell Us?

In recent years, the gender perspective in scientific research and sex differences in biological studies on emotional disorders have become increasingly important. However, sex bias in basic research on anxiety and depression is still far from being covered. This review addresses the study of sex differences in the field of anxiety and depression using animal models that consider this issue so far. What can preclinical studies tell us and what are their main limitations? First, we describe the behavioral tests most frequently used in preclinical research to assess depressive-like and anxiety-like behaviors in rodents. Then, we analyze the main findings, strengths, and weaknesses of rodent models of anxiety and depression, dividing them into three main categories: sex chromosome complement-biased sex differences; gonadal hormone-biased sex differences; environmental-biased sex differences. Regardless of the animal model used, none can reproduce all the characteristics of such complex and multifactorial pathologies as anxiety and depressive disorders; however, each animal model contributes to elucidating the bases that underlie these disorders. The importance is highlighted of considering sex differences in the responses that emerge from each model.

Imperatorin Influences Depressive-like Behaviors: A Preclinical Study on Behavioral and Neurochemical Sex Differences

Imperatorin, a naturally derived furanocoumarin, exerts promising neuropharmacological properties. Therefore, it might be applicable in the treatment of brain diseases such as depression. In the present project, we aimed to investigate the sex-dependent effects of imperatorin (1, 5, and 10 mg/kg) on behavior and neurochemistry associated with antidepressant effects. The depressive-like behaviors of male and female Swiss mice were investigated in a forced swim test (FST). Subsequently, High-Performance Liquid Chromatography (HPLC) was used to evaluate the level of serotonin, its metabolite, 5-HIAA, and noradrenaline, in mouse brains. The study revealed that only males responded to imperatorin (1 and 5 mg/kg) treatment and caused an antidepressant effect, such as with respect to depressive-like behaviors, lowering immobility time and increasing immobility latency. The HPLC analysis demonstrated that serotonin levels in the prefrontal cortex of females decreased with the middle dose of imperatorin (5 mg/kg), while in the male prefrontal cortex, the lower dose (1 mg/kg) boosted serotonin levels. There were no evident changes observed with respect to noradrenaline and serotonin metabolite levels in the male hippocampus. To conclude, we propose that imperatorin has antidepressant potential, seemingly only in males, influencing brain serotonin level, but the direct mechanism of action requires further investigation.

Folic acid supplementation during pregnancy alters behavior in male rat offspring: nitrative stress and neuroinflammatory implications

Pregnancy diet can impact offspring's neurodevelopment, metabolism, redox homeostasis, and inflammatory status. In pregnancy, folate demand is increased due to the requirement for one-carbon transfer reactions. The present study was proposed to investigate the effect of folic acid supplementation throughout pregnancy on a battery of behavior tests (olfactory preference, motor activity, exploratory capacity, habituation, memory, anxiety- and depression-like behavior). Redox homeostasis and neuroinflammatory status in cerebral cortex were also investigated. After pregnancy confirmation, the pregnant rats were randomly divided into two groups, according to the diet: group 1, (control) standard diet (2 mg/kg diet of folic acid) and group 2, supplemented diet with 4 mg/kg diet of folic acid. Throughout the gestational period, the pregnant rats received experimental diets. Results show that the supplemented diet with 4 mg/kg diet of folic acid throughout pregnancy impaired memory and motricity of the offspring when compared with control (standard diet). It was also observed an increase in anxiety- and depression-like behavior in this group. Nitrite levels increased in cerebral cortex of the offspring, when compared to control group. In contrast, iNOS expression and immunocontent were not altered. Moreover, we identify an increase in TNF-α, IL-1β, IL-6, IL-10, and MCP-1 gene expression in the cerebral cortex. In conclusion, our study showed that the supplemented diet with 4 mg/kg diet of folic acid throughout pregnancy may cause behavioral and biochemical changes in the male offspringGraphical abstract After pregnancy confirmation, the pregnant rats were randomly divided into two groups, according to the diet: group 1, (control) standard diet (2 mg/kg diet of folic acid) and group 2, supplemented diet with 4 mg/kg diet of folic acid. Throughout the gestational period, the pregnant rats received experimental diets. Results show that folic acid supplementation did not impair the mother-pup relationship. We showed that supplemented diet with 4 mg/kg diet of folic acid during pregnancy impairs memory and motricity of the offspring when compared with standard diet. It was also observed an increase in anxiety- and depression-like behavior in this group. Nitrative stress and neuroinflammation parameters were increased in the cerebral cortex of the offspring. ROS, reactive oxygen species.

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.

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.

Early life and adult stress promote sex dependent changes in hypothalamic miRNAs and environmental enrichment prevents stress-induced miRNA and gene expression changes in rats

BACKGROUND

The hypothalamus plays a key role in the stress response. While early life stress (ELS) increases susceptibility to psychiatric disorders including major depressive disorder (MDD), acute stress during adulthood can also precipitate MDD after ELS.

AIM

Here, we tested the expression of miRNAs following ELS and susceptibility to depression-like behavior and whether sex or acute stress exacerbates this response. We also tested whether environmental enrichment (Enr) promotes early life and adult behavioral stress resilience and its effect on hypothalamic miRNA and gene expression. Following rat maternal separation (MS) as an ELS model, Enr from weaning through adulthood, and restraint (RS) as acute adult stress, we tested both animal behavior and miRNA expression in the hypothalamus. Target genes and their enrichment and ontology were analyzed using bioinformatic tools. Target gene expression changes were tested using qPCR, and miRNA promoter methylation was studied using methylated-DNA immunoprecipitation qPCR.

RESULTS

MS, Enr, RS, and sex altered hypothalamic miRNAs, including several previously reported in MS literature: miRs-29, - 124, - 132, - 144, - 504. Sex had a significant effect on the greatest number of miRNAs. Also, Enr reversed downregulation of miR-29b-1-5p and -301b-3p in MS. qPCR showed that MAPK6 and MMP19, targets of miR-301b-3p, were upregulated in MS and reversed by Enr. Additionally, miR-219a was hypermethylated in MS coinciding with decreased miR-219a expression.

CONCLUSIONS

This study found that sex plays a critical role in the hypothalamic miRNA response to both ELS and acute stress, with males expressing greater changes following postnatal stress. Moreover, enrichment significantly altered behavior as well as hypothalamic miRNA expression and their gene targets. Because of its role as the initiator of the autonomic stress response and connection to hedonic and motivational behavior, the hypothalamic miRNA landscape may significantly alter both the short and long-term behavioral response to stress.

Early Pup Removal Leads to Social Dysfunction and Dopamine Deficit in Late Postpartum Rats: Prevention by Social Support

Offspring interaction is among the most highly motivated behaviors in maternal mammals and is mediated by mesolimbic dopamine (DA) system activation. Disruption or loss of significant social relationships is among the strongest individual predictors of affective dysregulation and depression onset in humans. However, little is known regarding the effects of disrupted mother–infant attachment (pup removal) in rat dams. Here, we tested the effects of permanent pup removal in rat dams, which were assigned to one of three groups on postpartum day (PD) 1: pups; pups removed, single-housed; or pups removed, co-housed with another dam who also had pups removed; and underwent a behavioral test battery during PD 21–23. In vivo electrophysiological recordings of ventral tegmental area (VTA) DA neurons were performed on PD 22 and 23 in a subset of animals. Pup removal did not impact sucrose consumption or anxiety-like behavior, but increased passive forced swim test (FST) coping responses. Pup-removal effects on social behavior and VTA activity were sensitive to social buffering: only single-housed dams exhibited reduced social motivation and decreased numbers of active DA neurons. Dams that had pups removed and were co-housed did not exhibit changes in social behavior or VTA function. Moreover, no changes in social behavior, FST coping, or VTA activity were found in socially isolated adult virgin females, indicating that effects observed in dams are specific to pup loss. This study showed that deprivation of species-expected social relationships (pups) during the postpartum precipitates an enduring negative affect state (enhanced passive coping, blunted social motivation) and attenuated VTA DA function in the dam, and that a subset of these effects is partially ameliorated through social buffering.

The forced swim test: Historical, conceptual and methodological considerations and its relationship with individual behavioral traits

The forced swim test (FST), developed by Porsolt and collaborators in 1977 to evaluate antidepressant (AD) treatments in rodents, has become extensively used for this purpose and to evaluate depression-like states. Despite its popularity, studies have raised important concerns regarding its theoretical and predictive validity. In my view and that of others, the FST mainly evaluates coping strategies in an inescapable situation. Although it is reasonable to assume that ADs act favoring active coping whereas negative affective states would favor passive coping, this does not mean that only ADs should enhance active coping or that a depression state has developed, respectively. Given its simplicity, proper interpretation of the FST behavior is critically dependent on how FST behavior relates to other behavioral traits. Unfortunately, this issue has been poorly discussed previously. Then, the present review, using a historical perspective, offers information needed to better understand the meaning and limitations of the FST, discusses critical methodological aspects and analyzes the relationship of FST behavior with classical behavioral traits in rodents.

Novel Antimuscarinic Antidepressant-like Compounds with Reduced Effects on Cognition

The cholinergic nervous system has been implicated in mood disorders, evident in the fast-onset antidepressant effects of scopolamine, a potent muscarinic antagonist, in clinical studies. One prominent disadvantage of the use of scopolamine in the treatment of depression is its detrimental effects on cognition, especially as such effects might aggravate cognitive deficits that occur with depression itself. Thus, the identification of antimuscarinic drugs that are free of such detrimental effects may provide an important avenue for the development of novel therapeutics for the management of depression. The present data in rats indicate that a historical muscarinic antagonist, L-687,306, and a muscarinic antagonist of our own design, CJ2100, were as or more effective than scopolamine in antagonizing both the bradycardic effects of the muscarinic agonist arecoline in cardiovascular studies and its discriminative stimulus and rate-decreasing effects in behavioral studies. Additionally, both novel muscarinic antagonists were as effective as scopolamine in decreasing immobility in the forced swim test, a preclinical indicator of potential antidepressant activity. However, at equieffective or even larger doses, they were considerably less disruptive than scopolamine in assays of cognition-related behavior. All three drugs displayed high specificity for the mAChRs with few off-target binding sites, and CJ2100 showed modest affinity across the mAChRs when compared with L-687,306 and scopolamine. These data emphasize the dissimilar pharmacological profiles that are evident across antimuscarinic compounds and the potential utility of novel antagonists for the improved treatment of depression. SIGNIFICANCE STATEMENT: Some clinical studies with the muscarinic antagonist scopolamine document its ability to produce antidepressant effects in patients with mood disorders; however, scopolamine also has well known adverse effects on both autonomic and centrally mediated physiological functions that limit its therapeutic use. This study characterizes the cardiovascular and discriminative stimulus effects of two novel muscarinic antagonists, L-687,306 and CJ2100, that produce antidepressant-like effects in a rodent model (forced swim test) without affecting touchscreen-based cognitive performance (titrating psychomotor vigilance and delayed matching-to-position).

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.

Forced swim stressor: Trends in usage and mechanistic consideration

The acquired immobility response during the “forced swim test (FST)” is not a rodent model of depression, but the test has some validity in predicting a compound's antidepressant potential. Nevertheless, 60% of the about 600 papers that were published annually the past 2 years label the rodent's immobility response as depression‐like behaviour, but the relative contribution per country is changing. When the Editors‐in‐Chief of 5 journals publishing most FST papers were asked for their point of view on labelling immobility as depression‐like behaviour and despair, they responded that they primarily rely on the reviewers regarding scientific merit of the submission. One Editor informs authors of the recent NIMH notice (https://grants.nih.gov/grants/guide/notice‐files/NOT‐MH‐19‐053.html) which encourages investigators to use animal models “for” addressing neurobiological questions rather than as model “of” specific mental disorders. The neurobiological questions raised by use of the FST fall in two categories. First, research on the role of endocrine and metabolic factors, with roots in the 1980s, and with focus on the bottom‐up action of glucocorticoids on circuits processing salient information, executive control and memory consolidation. Second, recent findings using novel technological and computational advances that have allowed great progress in charting top‐down control in the switch from active to passive coping with the inescapable stressor executed by neuronal ensembles of the medial prefrontal cortex via the peri‐aquaductal grey. It is expected that combining neural top‐down and endocrine bottom‐up approaches will provide new insights in the role of stress‐coping and adaptation in pathogenesis of mental disorders.

Stress Resilience is Associated with Hippocampal Synaptoprotection in the Female Rat Learned Helplessness Paradigm

The synaptogenic hypothesis of major depressive disorder implies that preventing the onset of depressive-like behavior also prevents the loss of hippocampal spine synapses. By applying the psychoactive drugs, diazepam and fluoxetine, we investigated whether blocking the development of helpless behavior by promoting stress resilience in the rat learned helplessness paradigm is associated with a synaptoprotective action in the hippocampus. Adult ovariectomized and intact female Sprague-Dawley rats (n = 297) were treated with either diazepam, fluoxetine, or vehicle, exposed to inescapable footshocks or sham stress, and tested in an active escape task to assess helpless behavior. Escape-evoked corticosterone secretion, as well as remodeling of hippocampal spine synapses at a timepoint representing the onset of escape testing were also analyzed. In ovariectomized females, treatment with diazepam prior to stress exposure prevented helpless behavior, blocked the loss of hippocampal spine synapses, and muted the corticosterone surge evoked by escape testing. Although fluoxetine stimulated escape performance and hippocampal synaptogenesis under non-stressed conditions, almost all responses to fluoxetine were abolished following exposure to inescapable stress. Only a much higher dose of fluoxetine was capable of partly reproducing the strong protective actions of diazepam. Importantly, these protective actions were retained in the presence of ovarian hormones. Our findings indicate that stress resilience is associated with the preservation of spine synapses in the hippocampus, raising the possibility that, besides synaptogenesis, hippocampal synaptoprotection is also implicated in antidepressant therapy.