Chronic mild stress paradigm as a rat model of depression: facts, artifacts, and future perspectives

Drosophila model of depression-like behavior: systematic investigation of external stress parameters and intrinsic susceptibility

Currently, Drosophila is widely used to study brain diseases. Unfortunately, Drosophila still lacks a mature and stable model for research on depression. This study addressed this issue by systematically exploring external stress and intrinsic susceptibility factors (Drosophila strains, adult/larval forms) that may influence the establishment and reproducibility of the stress-induced model. On this basis, the parameters are optimized. The results indicate Drosophila strains and forms are critical factors influencing model establishment, while external stress is the primary cause affecting the model's mortality rate. Compared with the other four strains, Canton-S are the most susceptible to chronic unpredictable mild stress (CUMS). Larval forms exhibit lower reactivity to external stress compared to adults. Parameter variations greatly influence model mortality rates from cold/heat/starvation stress. The model methodology validation study conducted subsequently through assessments of face, construct, and predictive validity demonstrates that the model exhibits face (neurobehavioral differences), structural (neurotransmitter changes in the Drosophila brain), and predictive (behavioral changes after fluoxetine treatment) validity. Additionally, spatial behavior experiments in Drosophila provide more realistic activity patterns compared to planar behavior, minimizing potential errors in interpreting lateral movements of the Drosophila, and it is recommended that this metric be included in model evaluation. This study presents a comprehensive set of methods for establishing and evaluating a depression-like behavior model and offers greater convenience for research on the pathogenesis of depression, as well as the screening, efficacy evaluation, and mechanistic studies of antidepressant drugs.

A comprehensive pharmacology study reveals the molecular mechanisms underlying the antidepressant effects of Gastrodiae Rhizoma

BACKGROUND

Gastrodiae Rhizoma (GR) and its extract have been widely used in the treatment of depression, but the underlying mechanism of its antidepressant effects is unclear due to its numerous components.

PURPOSE

Revealing the cellular and molecular mechanisms underlying the antidepressant effects of GR through a comprehensive pharmacology-based in vivo and in vitro investigation.

METHODS

A mouse model of depression was established using chronic mild stress (CMS) procedure, and the antidepressant effects of GR were evaluated using systematic behavior. Metabolites in GR decoction and in mouse brain were identified by UPLC-QTOF-MS technology. Core components and targets of GR against MDD were screened based on network pharmacology analysis and molecular docking. The mechanism through which GR mitigated MDD was explored using transcriptome analysis, immunohistochemistry and western blotting in vitro and in vivo.

RESULTS

A total of 273 components were identified in the GR decoction, out of which 15 were detected in the brain of depressed mice treated with the GR decoction. We further identified nine key active ingredients, six essential targets, and fifth signaling pathways associated with the therapeutic effects of GR against MDD. We confirmed that the active ingredients of GR can target the neural stem/precursor cells (NSPCs) in the hippocampus of depressed mice to promote neurogenesis, as evidenced by a significant increase in the numbers of DCX+ cells, BrdU+ cells, BrdU+-DCX+ cells, and BrdU+-NeuN+ cells within the hippocampus of GR-treated mice compared to salinetreated mice under CMS exposure. Moreover, we have identified that the key active constituents of GR, namely gastrodin and parishin C, exert a targeted effect on EGFR to activate PI3K-Akt signaling in NSPCs, thereby facilitating proliferation and differentiation of NSPCs.

CONCLUSION

The antidepressant effect of GR involves the facilitation of PI3K/Akt-mediated neurogenesis through gastrodin and parishin C targeting EGFR in NSPCs.

A review on the validity of animal models for neuropsychiatric disorders: an exploration of anhedonia

Despite major advances in neuroscience, there has been limited progress in improving pharmacological treatment for neuropsychiatric disorders. Neuropsychiatric disorders are heterogeneous with variance in symptoms within disorders and partial overlap in symptoms between disorders, leading to symptoms that remain untreated. To improve treatment outcomes, neuroscience has shifted to examining the neurobiological mechanisms underlying individual components, or dysfunctions, across disorders. Anhedonia, a decreased capacity to experience pleasure from positive stimuli or rewards, is a prominent symptom associated with poor functional outcome across neuropsychiatric disorders. This article reflects on Professor Paul Willner's contributions to the field of behavioural neuroscience, specifically his promotion of validity in animal models of neuropsychiatric disorders. Research can build upon Willner's scholarship by continuing to refine and explore the validity of animal models as our understanding of neuropsychiatric disorders improves. To exemplify this, we discuss current understanding of the neurobiological basis and clinical presentation of the two domains of anhedonia: anticipation and consumption. We argue for the examination of anticipatory anhedonia and consummatory anhedonia within a single paradigm to improve understanding of these domains, aligning animal models to the clinical reality in humans.

Early maternal separation potentiates the impact of later social isolation in inducing depressive-like behavior via oxidative stress in adult rats

RATIONALE

Individuals who have experienced early life stress (ELS) are more vulnerable to later life stress induced depression, which might attribute to ELS potentiated impact of later life stress. The presumption and neurobiological mechanisms involved require further validation and elucidation.

OBJECTIVES

To investigate impact of pre-weaning maternal separation (MS) on post-weaning social isolation (SI) in inducing depressive-like behavior, and involvement of central oxidative stress, glutamatergic and brain-derived neurotrophic factor (BDNF)/tyrosine kinase receptor B (TrkB) signaling in the process.

METHODS

Male offspring were exposed to MS, SI or maternal separation and social isolation (MSSI) stress, respectively. Subjects were treated with saline, antioxidant diallyl disulfide (DADS) (30 mg/kg, i.g.) or antidepressant fluoxetine (10 mg/kg, i.p.), for two weeks before behavioral tests in adolescents or adults. Depressive-like behavior was assessed with sucrose preference, forced swim and tail suspension tests. Concentrations of 4-hydroxynonenal (4-HNE), glutathione and superoxide dismutase in hippocampus and serum, and hippocampal protein expressions of glutamate transporter 1 (GLT-1), BDNF and TrkB were assessed by western blotting analysis.

RESULTS

MSSI, rather than MS or SI, induced significant depressive-like behavior, in adults but not adolescents. Consistently, only MSSI significantly elevated 4-HNE, whereas inhibited GLT-1, BDNF and TrkB in adult hippocampus. MSSI induced behavioral and biochemical abnormalities in adults were reversed by DADS or fluoxetine treatment.

CONCLUSIONS

Early MS age-dependently potentiates later SI impact in inducing depressive-like behavior in male rats, through elevating oxidative stress and interrupting glutamatergic and BDNF/TrkB signaling in the brain. Results further suggest antioxidant treatment as a promising anti-depressant avenue.

Sex-dependent changes induced by combined low-level systemic inflammation and chronic mild unpredictable stress in rats are partially attenuated by positive modulation of α5 GABAA receptors

The response to prolonged mild stress is dichotomous, has been associated with depression, anxiety and cognitive impairment, and may be modulated by various factors such as sex or GABA-ergic transmission. We investigated in rats the sex-dependent effects of four doses of lipopolysaccharide (LPS) in one week, followed by four weeks of chronic unpredictable mild stress (CUMS), on behavioral parameters assessed in the weekly sucrose preference test and spontaneous locomotor activity, as well as in the behavioral battery (elevated-plus-maze test, resident-intruder test, three-chamber test and forced-swim test) conducted after 7 days of treatment with GL-II-73, a positive allosteric modulator selective for α5 GABAA receptors (LPS/CUMS-GL-II-73), or with solvent (LPS/CUMS-SOL), beginning after the third week of CUMS. At the end of stress, sucrose intake was significantly increased in LPS/CUMS-SOL compared to male controls (CRTL); in females, LPS/CUMS-GL-II-73 showed a significantly higher preference for sucrose than CTRL-SOL. In males, forced swimming time was significantly longer in LPS/CUMS-SOL compared to CTRL-SOL. Social play in the resident-intruder test was reduced in female LPS/CUMS-SOL, and GL-II-73 and GL-II-73 tended to reversed this stress effect. LPS/CUMS-GL-II-73 males showed no significant social recognition in the three-chamber test. Ex vivo tests showed an increase in Gabra5 gene expression in the ventral hippocampus in LPS/CUMS-GL-II-73 compared to CTRL-SOL. The subtle changes in the measured parameters suggest that the clinical benefit of positive modulation of α5 GABAA receptors may result from focusing on the sex-specific niches of behavioral domains affected by prolonged stressors.

Genetic, Epigenetic, and Hormonal Regulation of Stress Phenotypes in Major Depressive Disorder: From Maladaptation to Resilience

Major Depressive Disorder (MDD) is a complex psychiatric disorder with varied molecular mechanisms underlying its aetiology, diagnosis, and treatment. This review explores the crucial roles of stress, genetics, epigenetics, and hormones in shaping susceptibility and resilience to mood disorders. We discuss how acute stress can be beneficial, while prolonged stress disrupts brain function, leading to MDD. The review also highlights the significance of various animal models in understanding depression pathophysiology, including zebrafish, mice, and rats, which exhibit distinct sex differences in stress responses. Furthermore, we delve into the molecular bases of susceptible and resilient phenotypes, focusing on genetic aspects such as gene polymorphisms, mutations, and telomere length alterations. The review also examines epigenetic aspects including DNA methylation, histone acetylation and deacetylation, histone methylation and HMTs, and miRNA, which contribute to the development of MDD. Additionally, we explore the role of hormones such as estrogen, progesterone, and prolactin in modulating stress responses and influencing MDD susceptibility and resilience. Finally, we discuss the clinical implications of these findings, including recent clinical methods for determining MDD susceptibility and resiliency phenotypes. By consolidating the current knowledge and insights, this review aims to provide a comprehensive understanding of the molecular basis of susceptibility and resilience in mood disorders, contributing to the ongoing efforts in combating this debilitating disorder.

Neuropharmacological potential of Mimosa tenuiflora in adult zebrafish: An integrated approach to GABAergic and serotonergic neuromodulation

Mimosa tenuiflora ("jurema-preta") is traditionally used in folk medicine for various diseases. The study investigated the neuropharmacological potential of Mimosa tenuiflora bark fraction (FATEM) in adult zebrafish. This included the acute toxicity (LC50) of FATEM (0.01; 0.05; 0.1; 0.5; 1.0 and 5.0 mg/mL; i.p.) and the effects on behavioral tests, such as open field, light & dark and zebrafish tail immobilization test (ZTI). The anxiolytic response induced by alcohol withdrawal and the seizure induced by pentylenetetrazole were also tested. The possible mechanisms of anxiolytic and antidepressant actions of FATEM were evaluated through the administration of specific antagonists (Flumazenil, Cyproheptadine, Pizotifen or Granisetron). Furthermore, the study investigated the ADME profile and molecular docking simulations of the major FATEM compound, Benzyloxyamine, with GABAergic and serotonergic receptors. FATEM did not present acute toxicity and caused a reduction in locomotor activity (p < 0.0001 vs. Control) similar (p< 0.0001) to Diazepam, indicating a sedative/anxiolytic effect. The anxiolytic activity in the light & dark test was similar to Diazepam (p < 0.0001), prevented by GABA and serotonergic antagonists. FATEM also prevented anxious behaviors induced by alcohol withdrawal and exhibited an antidepressant effect in the ZTI (p < 0.0001 vs. Control) similar (p < 0.0001) to the effect of Fluoxetine, which was reversed by serotonergic antagonists. In silico evaluations indicated favorable pharmacokinetic properties and affinity of FATEM with GABAergic and serotonergic receptors. The study reveals that FATEM has adequate physicochemical characteristics to act on the CNS with specific affinity for GABAA and serotonergic receptors, indicating its potential as a treatment for anxiety and depression.

Activation of SIRT1 by Hydroxysafflor Yellow A Attenuates Chronic Unpredictable Mild Stress-Induced Microglia Activation and Iron Death in Depressed Rats

BACKGROUND

Hydroxysafflor yellow A (HSYA), the main active ingredient in safflower, possesses antioxidant and anti-inflammatory activities. We confirmed in our previous study that HSYA exerts antidepressant effects, but further investigation is needed to uncover the exact mechanism. Herein, we aimed to explore the antidepressant effects of HSYA based on microglial activation and ferroptosis studies.

METHODS

The chronic unpredictable mild stress (CUMS) procedure was used to establish a depression model in rats. Behavioral tests were conducted on rats after HSYA administration. Iba-1 immunostaining was used to determine the activation of microglia in the hippocampus. We examined the iron ion level using a colorimetric method. Assayed by western blot for protein expression.

RESULTS

Rats receiving HSYA showed enhanced spatial learning and memory abilities, as well as improvements in depression-like behaviors. HSYA administration reduced Iba-1 expression in CUMS rats' hippocampus, indicating that HSYA suppressed microglial activation. HSYA inhibited CUMS-induced Fe2+ concentration and promoted ferroptosis-related protein GPX4 and SLC7A11 expression. HSYA treatment also elevated SIRT1 and Nrf2 protein levels, while p-p65 protein levels decreased in the hippocampus of CUMS rats.

CONCLUSION

HSYA exerts an antidepressant-like effect by inhibiting microglia activation in the hippocampus and inducing SIRT1/Nrf2/NF-kB signaling.

Models developed to explain the effects of stress on brain and behavior

There is an integral relationship between stress, brain function and behavior. Over the year's extensive research has led to the development of various models to explain the intricate intersection between brain and stress. This chapter delves into some of the theoretical frameworks that explains the neurobiological and behavioral responses to stress using key models of stress such as the allostatic load model, which is the most common model that describes how chronic stress affect brain structure and function resulting in long-term changes in regions such as the hippocampus, amygdala, and prefrontal cortex which phenotypically express as cognitive impairments, emotional dysfunction seen in various forms of neurological disorder. The neuro-endocrine model, follows the glucocorticoid cascade hypothesis, that associates prolonged stress exposure to hippocampal damage and cognitive decline via alteration in the hypothalamic-pituitary-adrenal (HPA) axis and the overproduction of stress hormones like cortisol which can induce hippocampal atrophy, impair learning and memory, and promote depressive-like behaviors. The neurobiological stress model addresses the role of the hypothalamic-pituitary-adrenal (HPA) axis and stress-related neurotransmitters in shaping behavioral responses, emphasizing alterations in neuroplasticity and synaptic function. These models demonstrate how chronic stress can alter neural plasticity, neurotransmitter systems, and synaptic connectivity, affecting behavior and cognitive function. Hence by integrating molecular, neurobiological, and behavioral perspectives, these models offer a comprehensive understanding of how stress alters brain activity and behavior. The chapter further showcase how these models direct the development of medical interventions, shedding light on potential therapies that target the underlying molecular mechanisms of stress-induced brain changes.

Chronic stress induces depression-like behavior in rats through affecting brain mitochondrial function and inflammation

Chronic stress is involved in pathophysiology of depression, and causes some neurochemical alterations in brain. Both mitochondrial dysfunction and neuroinflammation are implicated in mediating the depression-like behavior. The objectives of present study were, at first, to confirm that chronic unpredictable mild stress (CUMS) induces depression-like behavior and alters mitochondrial function and inflammatory responses within the brain, and then to explore the role of mitochondria in the development of this depression-like behavior. It has been found that CUMS exposure induced depression-like behavior, mitochondrial dysfunction, increased IL-1, IL-6, IFN-γ and TNF-α levels in hippocampus and PFC. Moreover, the level of ATP, the key index of mitochondrial function, was inversely correlated with the levels of proinflammatory cytokine. Intracerebroventricular (ICV) injection of the mitochondrial targeted antioxidant MnTBAP significantly alleviated depression-like behavior in CUMS group. These findings suggested that CUMS results in depression-like behavior, mitochondrial dysfunction as well as neuroinflammation, and mitochondria dysfunction contributes to depression-like behavior caused by CUMS.

Tryptophan-induced effects on the behavior and physiology of aging in tryptophan hydroxylase-2 heterozygous mice C57BL/6N

Background and Aim

Tryptophan (Trp), a precursor of serotonin, plays a critical role in cognitive and emotional processes. Its metabolism through serotonin and kynurenine pathways impacts neuropsychiatric functions and lipid metabolism. This study investigates Trp's effects on the behavioral, physiological, and molecular parameters of aging female wild-type (WT) and heterozygous tryptophan hydroxylase-2 (HET) mice.

Materials and Methods

A 68-day experiment was conducted on 13-month-old WT and HET mice. Groups received either distilled water or Trp supplementation (400 mg/kg/day). Behavioral tests (Open Field, Elevated Zero Maze, Forced Swim, and Extrapolation Escape Task) assessed locomotion, anxiety, and cognition. Physiological assessments included body composition through NMR relaxometry, lipid histology, serotonin content in the brain (ELISA), and serotonergic gene expression (RT-PCR). Blood biochemistry and organ weights were also analyzed.

Results

Trp supplementation reduced growth rates and adipose tissue while increasing muscle mass in both genotypes, more markedly in HET mice. Behavioral tests revealed a decrease in anxiety and enhanced cognitive performance in HET+Trp mice but an increase in immobility. Trp increased brain serotonin content in HET mice and altered serotonergic gene expression. Histological studies showed hepatoprotective effects in HET+Trp mice, reducing liver lipid infiltration compared to WT+Trp mice.

Conclusion

Trp exhibited genotype-specific effects, with HET mice showing anabolic, hepatoprotective, and neuropsychiatric changes. These findings highlight Trp's potential in neuro-nutrition for conditions like depression and cognitive decline. Further studies are needed to explore Trp's metabolic pathways and their implications for personalized dietary interventions.

The Utility of Prolonged Chronic Unpredictable Stress to Study the Effects of Chronic Fluoxetine, Eicosapentaenoic Acid, and Lipopolysaccharide on Anxiety-Like Behavior and Hippocampal Transcriptomic Responses in Male Rats

Chronic stress is a common trigger of multiple neuropsychiatric illnesses. Animal models are widely used to study stress-induced brain disorders and their interplay with neuroinflammation and other neuroimmune processes. Here, we apply the prolonged 12-week chronic unpredictable stress (PCUS) model to examine rat behavioral and hippocampal transcriptomic responses to stress and to chronic 4-week treatment with a classical antidepressant fluoxetine, an anti-inflammatory agent eicosapentaenoic acid (EPA), a pro-inflammatory agent lipopolysaccharide and their combinations. Overall, PCUS evoked anxiety-like behavioral phenotype in rats, corrected by chronic fluoxetine (alone or combined with other drugs), and EPA. PCUS also evoked pronounced transcriptomic responses in rat hippocampi, involving > 200 differentially expressed genes. While pharmacological manipulations did not affect hippocampal gene expression markedly, Gpr6, Drd2 and Adora2a were downregulated in stressed rats treated with fluoxetine, EPA and fluoxetine + EPA, suggesting their respective protein products (G protein-coupled receptor 6, dopamine D2 receptor and adenosine A2A receptor) as potential evolutionarily conserved targets under chronic stress. Overall, these findings support the validity of rat PCUS paradigm as a useful model to study stress-related anxiety pathogenesis, and call for further research probing how various conventional and novel drugs may (co)modulate behavioral and neurotranscriptomic biomarkers of chronic stress.

Mitochondrial Transplantation in Animal Models of Psychiatric Disorders: A Novel Approach to Psychiatric Treatment

Mitochondria are essential for brain function, and accumulating evidence from postmortem brain studies, neuroimaging, and basic research indicates mitochondrial impairments in patients with psychiatric disorders. Restoring mitochondrial function therefore represents a promising therapeutic strategy for these conditions. Mitochondrial transplantation, an innovative approach that uses functional mitochondria to repair damaged cells, has demonstrated efficacy through various delivery methods in cell, animal, and animal disease models. This review explores the critical link between mitochondria and psychiatric disorders and provides an overview of mitochondrial transplantation as a therapeutic intervention. It highlights recent advances in mitochondrial transplantation in animal models of psychiatric disorders, focusing on delivery methods, the timing of administration, and the integration of exogenous mitochondria into brain cells. The potential therapeutic effects and the mechanisms that underlie these effects are discussed. Additionally, this review evaluates the clinical relevance, challenges, and future strategies for the application of mitochondrial transplantation in the treatment of psychiatric disorders.

Bridging animal models and humans: neuroimaging as intermediate phenotypes linking genetic or stress factors to anhedonia

BACKGROUND

Intermediate phenotypes, such as characteristic neuroimaging patterns, offer unique insights into the genetic and stress-related underpinnings of neuropsychiatric disorders like depression. This study aimed to identify neuroimaging intermediate phenotypes associated with depression, bridging etiological factors to behavioral manifestations and connecting insights from animal models to diverse clinical populations.

METHODS

We analyzed datasets from both rodents and humans. The rodent studies included a genetic model (P11 knockout) and an environmental stress model (chronic unpredictable mild stress), while the human data comprised 748 participants from three cohorts. Using the amplitude of low-frequency fluctuations, we identified neuroimaging patterns in rodent models. We then applied a machine-learning approach to cluster neuroimaging subtypes of depression. To assess the genetic predispositions and stress-related changes associated with these subtypes, we analyzed genotype and metabolite data. Linear regression was employed to determine which neuroimaging features predicted core depression symptoms across species.

RESULTS

The genetic and environmental stress models exhibited distinct neuroimaging patterns in subcortical and sensorimotor regions. Consistent patterns emerged in two neuroimaging subtypes identified across three independent depressed cohorts. The subtype resembling P11 knockout demonstrated higher genetic susceptibility, with enriched expression of risk genes in brain tissues and abnormal metabolites linked to tryptophan metabolism. In contrast, the stress animal-like subtype did not show changes in genetic risk scores but exhibited enriched risk gene expression in somatic and endocrine tissues, along with mitochondrial dysfunction in the antioxidant stress system. Notably, these distinct subcortical-sensorimotor neuroimaging patterns predicted anhedonia, a core symptom of depression, in both rodent models and depressed subtypes.

CONCLUSIONS

This cross-species validation suggests that these neuroimaging patterns may serve as robust intermediate phenotypes, linking etiology to anhedonia and facilitating the translation of findings from animal models to humans with depression and other psychiatric disorders.

Sex in aging matters: exercise and chronic stress differentially impact females and males across the lifespan

Assessing sex as a biological variable is critical to determining the influence of environmental and lifestyle risks and protective factors mediating behavior and neuroplasticity across the lifespan. We investigated sex differences in affective behavior, memory, and hippocampal neurogenesis following short- or long-term exposure to exercise or chronic mild stress in young and aged mice. Male and female mice were assigned control, running, or chronic stress rearing conditions for 1 month (young) or for 15 months (aged), then underwent a behavioral test battery to assess activity, affective behavior, and memory. Stress exposure into late-adulthood increased hyperactivity in both sexes, and enhanced anxiety-like and depressive-like behavior in aged female, but not male, mice. One month of stress or running had no differential effects on behavior in young males and females. Running increased survival of BrdU-labelled hippocampal cells in both young and aged mice, and enhanced spatial memory in aged mice. These findings highlight the importance of considering sex when determining how aging is differently impacted by modifiable lifestyle factors across the lifespan.

Unveiling the Mechanisms of a Remission in Major Depressive Disorder (MDD)-like Syndrome: The Role of Hippocampal Palmitoyltransferase Expression and Stress Susceptibility

Post-translational modifications of proteins via palmitoylation, a thioester linkage of a 16-carbon fatty acid to a cysteine residue, reversibly increases their affinity for cholesterol-rich lipid rafts in membranes, changing their function. Little is known about how altered palmitoylation affects function at the systemic level and contributes to CNS pathology. However, recent studies suggested a role for the downregulation of palmitoyl acetyltransferase (DHHC) 21 gene expression in the development of Major Depressive Disorder (MDD)-like syndrome. Here, we sought to investigate how susceptibility (sucrose preference below 65%) or resilience (sucrose preference > 65%) to stress-induced anhedonia affects DHHC gene expression in the hippocampus of C57BL/6J mice during the phase of spontaneous recovery from anhedonia. Because MDD is a recurrent disorder, it is important to understand the molecular mechanisms underlying not only the symptomatic phase of the disease but also a state of temporary remission. Indeed, molecular changes associated with the application of pharmacotherapy at the remission stage are currently not well understood. Therefore, we used a mouse model of chronic stress to address these questions. The stress protocol consisted of rat exposure, social defeat, restraint stress, and tail suspension. Mice from the stress group were not treated, received imipramine via drinking water (7 mg/kg/day), or received intraperitoneal injections of dicholine succinate (DS; 25 mg/kg/day) starting 7 days prior to stress and continuing during a 14-day stress procedure. Controls were either untreated or treated with either of the two drugs. At the 1st after-stress week, sucrose preference, forced swim, novel cage, and fear-conditioning tests were carried out; the sucrose test and 5-day Morris water maze test followed by a sacrifice of mice on post-stress day 31 for all mice were performed. Transcriptome Illumina analysis of hippocampi was carried out. Using the RT-PCR, the hippocampal gene expression of Dhhc3, Dhhc7, Dhhc8, Dhhc13, Dhhc14, and Dhhc21 was studied. We found that chronic stress lowered sucrose preference in a subgroup of mice that also exhibited prolonged floating behavior, behavioral invigoration, and impaired contextual fear conditioning, while auditory conditioning was unaltered. At the remission phase, no changes in the sucrose test were found, and the acquisition of the Morris water maze was unchanged in all groups. In anhedonic, but not resilient animals, Dhhc8 expression was lowered, and the expression of Dhhc14 was increased. Antidepressant treatment with either drug partially preserved gene expression changes and behavioral abnormalities. Our data suggest that Dhhc8 and Dhhc14 are likely to be implicated in the mechanisms of depression at the remission stage, serving as targets for preventive therapy.

Effect of Withania somnifera on Expression of Selected Genes in Hippocampus of Male Wistar Rats Subjected to Chronic Unpredictable Mild Stress

Background

Depression affects millions globally, with existing treatments having many side effects. Withania somnifera (WS) shows potential as an antidepressant and neuroprotective agent, possibly by influencing brain-derived neurotrophic factor (BDNF)-related pathways.

Aim

This study evaluated the effect of WS alone and in combination with fluoxetine on neuritin, NARP, and BDNF Exon-III gene expression in the hippocampus of male Wistar rats subjected to chronic unpredictable mild stress (CUMS).

Materials and Methods

Thirty male Wistar rats were divided into five groups (n = 6 each): normal group (NG), disease control (DC), standard treatment (ST), WS, and combination group of fluoxetine and WS (FW). Depression was induced using CUMS, except in the NG. The sucrose preference test confirmed depression at the end of 3rd week and assessed treatment effects at the end of 7th week. Gene expression in the hippocampus was analyzed through real-time PCR at the end of 7th week.

Results

After 7 weeks, the ST, WS, and FW groups showed a significant increase in sucrose preference compared to the DC group. The ST and FW groups showed significant upregulation of all three genes selected in the present study. Comparison between NG and FW groups showed no significant difference in gene expression.

Conclusion

This study highlights the antidepressant effects of WS by demonstrating its effect on BDNF-associated gene expression. Fluoxetine combined with WS demonstrated additive effects which proves an adjuvant role of WS in the treatment of depression. Further studies involving human subjects are essential to validate the antidepressant effects of WS and its additive effects with fluoxetine.

Rat Models in Post-Traumatic Stress Disorder Research: Strengths, Limitations, and Implications for Translational Studies

Post-Traumatic Stress Disorder (PTSD) is a multifaceted psychiatric disorder triggered by traumatic events, leading to prolonged psychological distress and varied symptoms. Rat models have been extensively used to explore the biological, behavioral, and neurochemical underpinnings of PTSD. This review critically examines the strengths and limitations of commonly used rat models, such as single prolonged stress (SPS), stress-re-stress (S-R), and predator-based paradigms, in replicating human PTSD pathology. While these models provide valuable insights into neuroendocrine responses, genetic predispositions, and potential therapeutic targets, they face challenges in capturing the full complexity of PTSD, particularly in terms of ethological relevance and translational validity. We assess the degree to which these models mimic the neurobiological and behavioral aspects of human PTSD, highlighting areas where they succeed and where they fall short. This review also discusses future directions in refining these models to improve their utility for translational research, aiming to bridge the gap between preclinical findings and clinical applications.

Antidepressant-like and antistress effects of the ACTH(4-10) synthetic analogs Semax and Melanotan II on male rats in a model of chronic unpredictable stress

Current antidepressant therapy shows substantial limitations, and there is an urgent need for the development of new treatment strategies for depression. Stressful events and hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis play an important role in the pathogenesis of depression. HPA axis activity is self-regulated by negative feedback at several levels including adrenocorticotropic hormone (ACTH)-mediated feedback. Here, we investigated whether noncorticotropic synthetic analogs of the ACTH(4-10) fragment, ACTH(4-7)-Pro-Gly-Pro (Semax) and Ac-Nle4-cyclo[Asp5-His6-D-Phe7-Arg8-Trp9-Lys10]ACTH(4-10)-NH2 (Melanotan II (MTII), a potent agonist of melanocortin receptors), have potential antidepressant activity in a chronic unpredictable stress (CUS) rat model of depression. Stressed and control male adult Sprague-Dawley rats received daily intraperitoneal injections of saline or a low dose (60 nmol/kg of body weight (BW)) of Semax or MTII. Rats were monitored for BW and hedonic status, as measured in the sucrose preference test. We found that chronic treatment with Semax and MTII reversed or substantially attenuated CUS-induced anhedonia, BW gain suppression, adrenal hypertrophy and a decrease in the hippocampal levels of BDNF. In the forced swim test, no effects of the CUS procedure or peptides on the duration of rat immobility were detected. Our findings show that in the CUS paradigm, systemically administered ACTH(4-10) analogs Semax and MTII exert antidepressant-like effects on anhedonia and hippocampal BDNF levels, and attenuate markers of chronic stress load, at least in male rats. The results support the argument that ACTH(4-10) analogs and other noncorticotropic melanocortins may have promising therapeutic potential for the treatment and prevention of depression and other stress-related pathologies.

Methane-rich saline ameliorates depressive-like behaviors during chronic unpredictable mild stress (CUMS)

Depression, considered the most prevalent neuropsychiatric disorder, is multifactorial and complex. Oxidative stress and inflammation significantly contribute to its etiology. Conversely, methane, a novel therapeutic gas, has demonstrated efficacy in enhancing tissue resilience against ischemic injuries and inflammation. In this study, we investigated the effect of methane-rich saline (MRS) on depression using the chronic unpredictable mild stress (CUMS) model. Depressed rats received MRS treatment, and depression-like behaviors and cognitive function were assessed through sucrose preference, open field, forced swimming, and Morris water maze tests. Additionally, we measured serum corticosterone levels, antioxidant enzyme activity, hippocampal malondialdehyde (MDA), and TNFα levels, and investigated histological changes in the hippocampus. Our findings revealed that MRS significantly ameliorated Depressive-like behaviors and cognitive impairment. Furthermore, MRS administration regulated serum corticosterone levels and also MRS reduced hippocampal lipid peroxidation, TNFα, and hippocampus tissue damage. MRS likely exerts its effects by reducing oxidative stress and inflammatory factors and modulating the function of the hypothalamus-pituitary-adrenal (HPA) axis. These results demonstrate the protective effects of MRS on the hippocampus in CUMS animals.

The chronic unpredictable mild stress (CUMS) Paradigm: Bridging the gap in depression research from bench to bedside

Depression is a complicated neuropsychiatric condition with an incompletely understoodetiology, making the discovery of effective therapies challenging. Animal models have been crucial in improving our understanding of depression and enabling antidepressant medication development. The CUMS model has significant face validity since it induces fundamental depression symptoms in humans, such as anhedonia, behavioral despair, anxiety, cognitive impairments, and changes in sleep, food, and social behavior. Its construct validity is demonstrated by the dysregulation of neurobiological systems involved in depression, including monoaminergic neurotransmission, the hypothalamic-pituitary-adrenal axis, neuroinflammatory processes, and structural brain alterations. Critically, the model's predictive validity is demonstrated by the reversal of CUMS-induced deficits following treatment with clinically effective antidepressants such as selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, tricyclic antidepressants, and monoamine oxidase inhibitors. This review comprehensivelyassesses the multifarious depressive-like phenotypes in the CUMS model using behavioral paradigms like sucrose preference, forced swim, tail suspension, elevated plus maze, and novel object recognition tests. It investigates the neurobiological mechanisms that underlie CUMS-induced behaviors, including signaling pathways involving tumor necrosis factor-alpha, brain-derived neurotrophic factor and its receptor TrkB, cyclooxygenase-2, glycogen synthase kinase-3 beta, and the kynurenine pathway. This review emphasizes the CUMS model's importance as a translationally relevant tool for unraveling the complex mechanisms underlying depression and facilitating the development of improved and targeted interventions for this debilitating neuropsychiatric disorder by providing a comprehensive overview of its validity, behavioral assessments, and neurobiological underpinnings.

Prolactin mitigates chronic stress-induced maladaptive behaviors and physiology in ovariectomized female rats

Stress is a major risk factor for several neuropsychiatric disorders in women, including postpartum depression. During the postpartum period, diminished ovarian hormone secretion increases susceptibility to developing depressive symptoms. Pleiotropic peptide hormones, like prolactin, are markedly released during lactation and suppress hypothalamic-pituitary-adrenal axis responses in women and acute stress-induced behavioral responses in female rodents. However, the effects of prolactin on chronic stress-induced maladaptive behaviors remain unclear. Here, we used chronic variable stress to induce maladaptive physiology in ovariectomized female rats and concurrently administered prolactin to assess its effects on several depression-relevant behavioral, endocrine, and neural characteristics. We found that chronic stress increased sucrose anhedonia and passive coping in saline-treated, but not prolactin-treated rats. Prolactin treatment did not alter stress-induced thigmotaxis, corticosterone (CORT) concentrations, hippocampal cell activation or survival. However, prolactin treatment reduced basal CORT concentrations and increased dopaminergic cells in the ventral tegmental area. Further, prolactin-treated rats had reduced microglial activation in the ventral hippocampus following chronic stress exposure. Together, these data suggest prolactin mitigates chronic stress-induced maladaptive behaviors and physiology in hypogonadal females. Moreover, these findings imply neuroendocrine-immune mechanisms by which peptide hormones confer stress resilience during periods of low ovarian hormone secretion.

Looking Back to Move Forward: Research in Stress, Behavior, and Immune Function

BACKGROUND

From the original studies investigating the effects of adrenal gland secretion to modern high-throughput multidimensional analyses, stress research has been a topic of scientific interest spanning just over a century.

SUMMARY

The objective of this review was to provide historical context for influential discoveries, surprising findings, and preclinical models in stress-related neuroimmune research. Furthermore, we summarize this work and present a current understanding of the stress pathways and their effects on the immune system and behavior. We focus on recent work demonstrating stress-induced immune changes within the brain and highlight studies investigating stress effects on microglia. Lastly, we conclude with potential areas for future investigation concerning microglia heterogeneity, bone marrow niches, and sex differences.

KEY MESSAGES

Stress is a phenomenon that ties together not only the central and peripheral nervous system, but the immune system as well. The cumulative effects of stress can enhance or suppress immune function, based on the intensity and duration of the stressor. These stress-induced immune alterations are associated with neurobiological changes, including structural remodeling of neurons and decreased neurogenesis, and these contribute to the development of behavioral and cognitive deficits. As such, research in this field has revealed important insights into neuroimmune communication as well as molecular and cellular mediators of complex behaviors relevant to psychiatric disorders.

Morphological Differences in Hippocampal Microglia in C57BL/6N Mice with Liver Injury and Depressive-Like Behavior

INTRODUCTION

Microglia, one of the most important cells of the central nervous system, undergo specific changes depending on the pathology. It has been reported that both depressive disorders and liver diseases generate hippocampal changes and neuroinflammation. However, the combined effects of the two pathologies on microglia morphology in the hippocampus have not been sufficiently explored.

MATERIAL AND METHODS

In this study, we analyzed the morphological changes of the hippocampal microglia using confocal microscopy and a semi-manual method of quantification. We focused on total branch length, the branch number and the mean branch length. C57BL/6N mice were used and subjected to a methionine and choline deficient diet (MCD) to induce liver damage, and a chronic unpredictable mild stress (CUMS) procedure for depressive-like behavior.

RESULTS

We were able to show that CUMS protocol and MCD diet led to a reduction in total branch length, branch number and mean branch length. Also, CUMS alone was associated with a decrease in the number of secondary and terminal branches.

CONCLUSION

Our study showed that depressive-like behavior and liver damage influence microglial morphology in the hippocampus, and it may be considered in future research of these intricate pathologies.

Sucrose binge-eating and increased anxiety-like behavior in Sprague-Dawley rats exposed to repeated LPS administration followed by chronic mild unpredictable stress

Exposure to persistent mild stress is a frequently encountered chronic challenge in a rapidly evolving society. Depending on various factors including sex, the response to stressors varies and is closely linked to the phenomenon of resilience. Depression and anxiety can be considered maladaptive responses to such stress. In this rat study, we investigated the sex-dependent effects of low-grade systemic inflammation during 1 week in combination with chronic unpredictable mild stress during the following 4 weeks on anxiety-like behavior and episodic feeding behavior. Increased anxiety-like behavior and increased sucrose intake were identified in stressed compared to control animals regardless of sex. Interestingly, two nearly equally distributed subpopulations were found in the stressed groups within each sex at the end of the 5-week protocol of combined stress exposure: the resistant and the susceptible, which were characterized by unchanged and increased sucrose intake, respectively. This difference in susceptibility to protracted combined mild stress and ensuing response to a sucrose eating binge demonstrates the complexity of the underlying regulatory mechanisms associated with emotional hyperreactivity. This model carries the potential for further investigation of the molecular basis of resilience and susceptibility to combined stressors and for testing treatments with potential preventive or therapeutic effects.

Preventive and therapeutic effect of vitamin D on depression-like behavior in a mouse adolescent depression model and its association with BDNF protein expression

Introduction

Previous studies in different populations have shown that vitamin D supplementation may reduce depression levels. In adolescents, vitamin D deficiency has been identified as a factor contributing to the onset of depression. This study aimed to establish a model of adolescent depression in mice by using the scientific unpredictable chronic mild stress (UCMS) model and to preliminarily evaluate the effect of vitamin D on the occurrence and development of depression and whether it is related to the protein expression of the BDNF pathway.

Methods

The UCMS method was used to establish a model of adolescent depression in 4-week-old C57BL/6 male mice, randomly divided into five groups: Control group, Stress group, Stress+ low-dose group, Stress+ medium-dose group, Stress+ high-dose group. At the same time as chronic stress, the administration groups were given intramuscular injections of different doses of vitamin D. After 8 weeks, behavioral tests, including the forced swimming test (FST) and open field test (OFT), were performed on each group of mice, along with recording of indicators, blood vitamin D level detection, and brain tissue western blot analysis.

Results

The results showed a significant difference in vitamin D levels among mice in different groups after 8 weeks (P=0.012). The results of behavioral testing showed a significant difference in the static time of forced swimming among the groups (P<0.001). Compared with the UCMS group, the static time of mice with vitamin D injection was significantly reduced (P<0.001). The total number of times mice entered the central area, the total distance of movement, and the time spent in the central area significantly increased after vitamin D injection compared with the UCMS-only group (all P<0.001). There was no significant difference in the expression of BDNF in the brain tissues of experimental mice (P>0.05).

Discussion

In conclusion, in the mouse adolescent depression model, appropriate vitamin D supplementation can reduce the occurrence of stress-induced depression. Furthermore, vitamin D deficiency may also serve as a potential risk factor for depression.

The cycle of stress: A systematic review of the impact of chronic psychological stress models on the rodent estrous cycle

Stress is known to impair reproduction through interactions between the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes. However, while it is well accepted that stress can alter estrous cycle regularity, a key indicator of female's HPG axis function, effects of different types of psychological stress have been inconsistent. This systematic review evaluated the impact of rodent models of psychological stress on estrous cyclicity, while reporting biological parameters pertaining to HPA or HPG axis function assessed within these studies. We performed a systematic database search and included articles that implemented a psychological stress model in rodents and reported estrous cyclicity for at least two cycles after initiation of stress. Of the 32 studies included, 62.5% reported post-stress alterations to estrous cyclicity, with Chronic Mild Stress (CMS) models showing the most conclusive effects. Twenty-five studies measured HPG or HPA axis markers, with cycle disruptions being commonly observed in parallel with altered estradiol and increased corticosterone levels. Our review highlights gaps in reporting estrous cyclicity assessments and makes recommendations to improve comparability between studies.

Omega-3 alleviates behavioral and molecular changes in a mouse model of stress-induced juvenile depression

Introduction

Depression is increasingly diagnosed in adolescence, necessitating specific prevention and treatment methods. However, there is a lack of animal models mimicking juvenile depression. This study explores a novel model using ultrasound (US) stress in juvenile mice.

Methods

We employed the US stress model in one-month-old C57/BL6 mice, exposing them to alternating ultrasound frequencies (20-25 kHz and 25-45 kHz) for three weeks. These frequencies correspond to negative and neutral emotional states in rodents and can induce a depressive-like syndrome. Concurrently, mice received either an omega-3 food supplement (FS) containing eicosapentaenoic acid (EPA; 0.55 mg/kg/day) and docosahexaenoic acid (DHA; 0.55 mg/kg/day) or a vehicle. Post-stress, we evaluated anxiety- and depressive-like behaviors, blood corticosterone levels, brain expression of pro-inflammatory cytokines, and conducted metabolome analysis of brain, liver and blood plasma.

Results

US-exposed mice treated with vehicle exhibited decreased sucrose preference, a sign of anhedonia, a key feature of depression, increased anxiety-like behavior, elevated corticosterone levels, and enhanced TNF and IL-1β gene expression in the brain. In contrast, US-FS mice did not display these changes. Omega-3 supplementation also reduced anxiety-like behavior in non-stressed mice. Metabolomic analysis revealed US-induced changes in brain energy metabolism, with FS increasing brain sphingomyelin. Liver metabolism was affected by both US and FS, while plasma metabolome changes were exclusive to FS. Brain glucose levels correlated positively with activity in anxiety tests.

Conclusion

Chronic omega-3 intake counteracted depressive- and anxiety-like behaviors in a US model of juvenile depression in mice. These effects likely stem from the anti-inflammatory properties of the supplement, suggesting potential therapeutic applications in juvenile depression.

Prevalence of post-traumatic stress disorder and depressive symptoms among civilians residing in armed conflict-affected regions: a systematic review and meta-analysis

Background

Globally, populations afflicted by armed conflict are known to have high rates of mental health disorders.

Aims

This meta-analysis aims to estimate the prevalence of post-traumatic stress disorder (PTSD) and depressive symptoms among civilians residing in armed conflict-affected regions.

Methods

This meta-analysis was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. A literature search employing MEDLINE(R), Embase Classic+Embase, APA PsycINFO, Ovid Healthstar, Journal@Ovid Full Text, Cochrane, PTSDpubs and CINAHL was conducted from inception until 19 March 2024 to identify relevant studies. Quality assessment was performed using the Joanna Briggs Institute Critical Appraisal Checklist for Prevalence Studies, and a Comprehensive Meta-Analysis was used to conduct the statistical analysis.

Results

The search yielded 38 595 articles, of which 57 were considered eligible for inclusion. The included studies comprised data from 64 596 participants. We estimated a prevalence of 23.70% (95% CI 19.50% to 28.40%) for PTSD symptoms and 25.60% (95% CI 20.70% to 31.10%) for depressive features among war-afflicted civilians. The subgroup analysis based on time since the war and the country's economic status revealed the highest prevalence for both PTSD and depressive symptoms was present during the years of war and in low/middle-income countries.

Conclusions

The results of this study provide conclusive evidence of the detrimental impacts of armed conflict on mental health outcomes. Hence, it is crucial to emphasise the significance of both physical and mental health in the aftermath of war and take appropriate humanistic measures to overcome challenges in the management of psychiatric illnesses.

PROSPERO registration number

CRD42023416096.

Antidepressant effects of esketamine via the BDNF/AKT/mTOR pathway in mice with postpartum depression and their offspring

Postpartum depression (PPD) is a serious mental health problem that can negatively affect future generations. BDNF/AKT/mTOR signaling in the frontal lobe and hippocampus in mice is associated with depression, but its role in mice with PPD and their offspring is unknown. This study was aimed at investigating the effects of esketamine (ESK), a drug approved for treatment of refractory depression, on the BDNF/AKT/mTOR pathway in mice with PPD and their offspring. A model of chronic unpredictable mild stress with pregnancy was used. ESK was injected into postpartum mice, and behavioral tests were conducted to predict the severity of symptoms at the end of lactation and in the offspring after adulthood. Both mice with PPD and their offspring showed significant anxiety- and depression-like behaviors that were ameliorated with the ESK intervention. ESK enhanced exploratory behavior in unfamiliar environments, increased the preference for sucrose, and ameliorated the impaired BDNF/AKT/mTOR signaling in the frontal and hippocampal regions in mice. Thus, ESK may have great potential in treating PPD and decreasing the incidence of depression in offspring.

Ciprofol ameliorates ECS-induced learning and memory impairment by modulating aerobic glycolysis in the hippocampus of depressive-like rats

Electroconvulsive shock (ECS) is utilized to treat depression but may cause learning/memory impairments, which may be ameliorated by anesthetics through the modulation of hippocampal synaptic plasticity. Given that synaptic plasticity is governed by aerobic glycolysis, it remains unclear whether anesthetics modulate aerobic glycolysis to enhance learning and memory function. Depression-like behavior in rats was induced by chronic mild unpredictable stress (CUMS), with anhedonia assessed via sucrose preference test (SPT). Depressive-like behaviors and spatial learning/memory were assessed with forced swim test (FST), open field test (OFT), and Morris water maze (MWM) test. Changes in aerobic glycolysis and synaptic plasticity in the hippocampal region of depressive-like rats post-ECS were documented using immunofluorescence analysis, Western blot, Lactate Assay Kit and transmission electron microscopy. Both the OFT and FST indicated that ECS was effective in alleviating depressive-like behaviors. The MWM test demonstrated that anesthetics were capable of attenuating ECS-induced learning and memory deficits. Immunofluorescence analysis, Western blot, Lactate Assay Kit and transmission electron microscopy revealed that the decline in learning and memory abilities in ECS-induced depressive-like rats was correlated with decreased aerobic glycolysis, and that the additional use of ciprofol or propofol ameliorated these alterations. Adding the glycolysis inhibitor 2-DG diminished the ameliorative effects of the anesthetic. No significant difference was observed between ciprofol and propofol in enhancing aerobic glycolysis in astrocytes and synaptic plasticity after ECS. These findings may contribute to understanding the mechanisms by which anesthetic drugs modulate learning and memory impairment after ECS in depressive-like behavior rats.

Pathological Changes and Metabolic Adaptation in the Myocardium of Rats in Response to Chronic Variable Mild Stress

Chronic variable mild stress (CVS) in rats is a well-established paradigm for inducing depressive-like behaviors and has been utilized extensively to explore potential therapeutic interventions for depression. While the behavioral and neurobiological effects of CVS have been extensively studied, its impact on myocardial function remains largely unexplored. To induce the CVS model, rats were exposed to various stressors over 40 days. Behavioral assessments confirmed depressive-like behavior. Biochemical analyses revealed alterations in myocardial metabolism, including changes in NAD+ and NADP+, and NADPH concentrations. Free amino acid analysis indicated disturbances in myocardial amino acid metabolism. Evaluation of oxidative DNA damage demonstrated an increased number of abasic sites in the DNA of rats exposed to CVS. Molecular analysis showed significant changes in gene expression associated with glucose metabolism, oxidative stress, and cardiac remodeling pathways. Histological staining revealed minor morphological changes in the myocardium of CVS-exposed rats, including increased acidophilicity of cells, collagen deposition surrounding blood vessels, and glycogen accumulation. This study provides novel insights into the impact of chronic stress on myocardial function and metabolism, highlighting potential mechanisms linking depression and cardiovascular diseases. Understanding these mechanisms may aid in the development of targeted therapeutic strategies to mitigate the adverse cardiovascular effects of depression.

Jnk1 and downstream signalling hubs regulate anxiety-like behaviours in a zebrafish larvae phenotypic screen

Current treatments for anxiety and depression show limited efficacy in many patients, indicating the need for further research into the underlying mechanisms. JNK1 has been shown to regulate anxiety- and depressive-like behaviours in mice, however the effectors downstream of JNK1 are not known. Here we compare the phosphoproteomes from wild-type and Jnk1-/- mouse brains and identify JNK1-regulated signalling hubs. We next employ a zebrafish (Danio rerio) larvae behavioural assay to identify an antidepressant- and anxiolytic-like (AA) phenotype based on 2759 measured stereotypic responses to clinically proven antidepressant and anxiolytic (AA) drugs. Employing machine learning, we classify an AA phenotype from extracted features measured during and after a startle battery in fish exposed to AA drugs. Using this classifier, we demonstrate that structurally independent JNK inhibitors replicate the AA phenotype with high accuracy, consistent with findings in mice. Furthermore, pharmacological targeting of JNK1-regulated signalling hubs identifies AKT, GSK-3, 14-3-3 ζ/ε and PKCε as downstream hubs that phenocopy clinically proven AA drugs. This study identifies AKT and related signalling molecules as mediators of JNK1-regulated antidepressant- and anxiolytic-like behaviours. Moreover, the assay shows promise for early phase screening of compounds with anti-stress-axis properties and for mode of action analysis.

Circular RNA expression profiles and functional predication after restraint stress in the amygdala of rats

Prolonged or repeated exposure to stress elevates the risk of various psychological diseases, many of which are characterized by central nervous system dysfunction. Recent studies have demonstrated that circular RNAs (circRNAs) are highly abundant in the mammalian brain. Although their precise expression and function remain unknown, they have been hypothesized to regulate transcriptional and post-transcriptional gene expression. In this investigation, we comprehensively analyzed whether restraint stress for 2 days altered the circRNA expression profile in the amygdala of male rats. The impact of restraint stress on behavior was evaluated using an elevated plus maze and open field test. Serum corticosterone levels were measured using an enzyme-linked immunosorbent assay. A total of 10,670 circRNAs were identified using RNA sequencing. Ten circRNAs were validated by reverse transcription and quantitative polymerase chain reaction analysis. Gene ontology and Kyoto encyclopedia of genes and genomes pathway analyzes supported the notion that genes associated with differentially expressed circRNAs are primarily implicated in neuronal activity and neurotransmitter transport. Moreover, the three differentially expressed circRNAs showed high specificity in the amygdala. Overall, these findings indicate that differentially expressed circRNAs are highly enriched in the amygdala and offer a potential direction for further research on restraint stress.

Differential effect of chronic mild stress on anxiety and depressive-like behaviors in three strains of male and female laboratory mice

Major depressive disorder is the most common psychiatric disorder worldwide. To understand mechanisms and search for new approaches to treating depression, animal models are crucial. Chronic mild stress (CMS) is the most used animal model of depression. Although CMS is considered a robust model of depression, conflicting results have been reported for emotion-related behaviors, which the intrinsic characteristics of each rodent strain could explain. To further shed light on the impact of genetic background on the relevant parameters commonly addressed in depression, we examined the effect of 4-weeks CMS on anxiety and depression-related behaviors and body weight gain in three strain mice (BALB/c, C57BL/6, and CD1) of both sexes. CMS reduced body weight gain in C57BL/6NCrl and CD1 male mice. C57BL/6 animals exhibited a more pronounced anxious-like behavior than CD1 and BALB/c mice in the light-dark box (LDB) and the elevated plus maze (EPM) tests, whereas BALB/c animals exhibited the more robust depressive-like phenotype in the splash test (ST), tail suspension test (TST) and forced-swimming test (FST). Under CMS, exposure did not affect anxiety-related behaviors in any strain but induced depression-like behaviors strain-dependently. CMS C57BL/6 and CD1 mice of both sexes showed depression-like behaviors, and CMS BALB/c male mice exhibited reduced depressive behaviors in the FST. These results suggest a differential effect of stress, with the C57BL/6 strain being more vulnerable to stress than the CD1 and BALB/c strain mice. Furthermore, our findings emphasize the need for researchers to consider mouse strains and behavioral tests in their CMS experimental designs.

Effects of pre-gestational exposure to the stressors and perinatal bupropion administration on the firing activity of serotonergic neurons and anxiety-like behavior in rats

Exposure by women to stressors before pregnancy increases their risk of contracting prenatal depression, a condition which typically may require antidepressant treatment. And even though such perinatal antidepressant treatment is generally considered to be safe. For the mother, its effects on the development and functioning of the offspring`s brain remain unknown. In this study, we aimed to investigate the effects of pregestational chronic unpredictable stress (CUS) and perinatal bupropion on the anxiety behavior and firing activity of the dorsal raphe nucleus (DRN) serotonin (5-HT) neurons. Female rats underwent CUS for three weeks before mating. Bupropion was administered to them from gestation day ten until their offspring were weaned. Behavioral (elevated plus maze or EPM test) and neurophysiological (single-unit in vivo electrophysiology) assessments were performed on offspring who reached the age of 48-56 days. We found that maternal CUS and perinatal bupropion, as separate factors on their own, did not change offspring behavior. There was, however, an interaction between their effects on the number of entries to the open arms and time spent in the intersection: maternal CUS tended to decrease these values, and perinatal bupropion tended to diminish CUS effect. Maternal CUS increased the firing activity of 5-HT neurons in males, but not females. Perinatal bupropion did not alter the firing activity of 5-HT neurons but tended to potentiate the maternal CUS-induced increase in 5-HT neuronal firing activity. The CUS-induced increase in firing activity of 5-HT neurons might be a compensatory mechanism that diminishes the negative effects of maternal stress. Perinatal bupropion does not alter the offspring`s anxiety and firing activity of 5-HT, but it does intervene in the effects of maternal stress.

HIF-1A regulates cognitive deficits of post-stroke depressive rats

Post-stroke depression (PSD) is a serious neuropsychiatric complication post stroke and leads to cognitive deficits. This study was conducted to explore the molecular mechanism of hypoxia-inducible factor-1α (HIF-1A) in cognitive dysfunction in rats with PSD. The rat model of PSD was established by middle cerebral artery occlusion, followed by 3 weeks of treatment with chronic unpredictable mild stress. The levels of miR-582-5p, HIF-1A, and neighbor of Brca1 gene (NBR1) in brain tissues were determined using RT-qPCR. The behaviors and cognitive capacity of rats were evaluated by various behavioral tests. PSD rats were injected with HIF-1A/miR-582-5p lowexpression vectors or NBR1 overexpression vectors via stereotactic method. The binding of HIF-1A to NBR1 or miR-582-5p was analyzed by chromatin immunoprecipitation and dual-luciferase assay. HIF-1A and NBR1 were highly expressed while miR-582-5p was poorly expressed in the brain of PSD rats. HIF-1A inhibition alleviated cognitive dysfunction of PSD rats. miR-582-5p was the upstream miRNA of HIF-1A, and HIF-1A specifically interacted with the NBR1 promoter to enhance NBR1 expression. miR-582-5p downregulation and NBR1 upregulation reversed the alleviative role of HIF-1A inhibition in cognitive dysfunction of PSD rats. In summary, HIF-1A inhibition may be a therapeutic target for cognitive dysfunction post PSD.

Validation of Wistar-Kyoto rats kept in solitary housing as an animal model for depression using voxel-based morphometry

Major depressive disorder is a common psychiatric condition often resistant to medication. The Wistar-Kyoto (WKY) rat has been suggested as an animal model of depression; however, it is still challenging to translate results from animal models into humans. Solitary housing is a mild stress paradigm that can simulate the environment of depressive patients with limited social activity due to symptoms. We used voxel-based morphometry to associate the solitary-housed WKY (sWKY) rat model with data from previous human studies and validated our results with behavioural studies. As a result, atrophy in sWKY rats was detected in the ventral hippocampus, caudate putamen, lateral septum, cerebellar vermis, and cerebellar nuclei (p < 0.05, corrected for family-wise error rate). Locomotor behaviour was negatively correlated with habenula volume and positively correlated with atrophy of the cerebellar vermis. In addition, sWKY rats showed depletion of sucrose consumption not after reward habituation but without reward habituation. Although the application of sWKY rats in a study of anhedonia might be limited, we observed some similarities between the regions of brain atrophy in sWKY rats and humans with depression, supporting the translation of sWKY rat studies to humans.

Behavioural characteristics and sex differences of a treatment-resistant depression model: Chronic mild stress in the Wistar-Kyoto rat

Depression affects 20% of the general population and is a leading cause of disability worldwide, with a strong female prevalence. Current pharmacotherapies have significant limitations, and one third of patients are unresponsive. Male Wistar-Kyoto rats exposed to chronic mild stress (CMS) were recently proposed as a model to study antidepressant resistance. However, sex differences and interindividual vulnerability to stress are yet unexplored in this model. We aimed to investigate these in the context of the behavioural impact of CMS in the sucrose preference test, elevated plus maze (EPM), forced swim test (FST), open field test and daily locomotor activity rhythms, in male and female WKY rats exposed or not to a 4-week CMS protocol. CMS-exposed animals were clustered through K-means into subgroups based on the EPM and FST results. In both sexes, one subgroup behaved similarly to non-stressed animals and was labelled stress-non vulnerable; the second exhibited less open arms exploration in the EPM and higher immobility in the FST and was named stress-vulnerable. Vulnerable males presented phase delay in daily locomotor activity following CMS, but no significant rhythm could be determined in females. CMS-exposed males of both groups showed hyperlocomotion in reaction to novelty and slower weight gain through the course of CMS, while CMS-exposed females showed smaller sucrose intake. Unexpectedly, CMS did not affect sucrose preference. Our findings strengthen the view that in models of psychiatric pathologies based on stress exposure it is important to consider the effect of sex and to differentiate the non vulnerable and vulnerable subpopulations.

Microglia-Dependent Reversal of Depression-Like Behaviors in Chronically Stressed Mice by Administration of a Specific Immuno-stimulant β-Glucan

In recent years, the decline of microglia in the hippocampus has been shown to play a role in the development of depression, and its reversal shows marked antidepressant-like effects. β-glucan is a polysaccharide from Saccharomyces cerevisiae and has numerous beneficial effects on the nervous system, including improving axon regeneration and cognition. Considering its immuno-stimulatory activities in cultured microglia and brain tissues, we hypothesize that β-glucan may be a potential candidate to correct the functional deficiency of microglia and thereby alleviate depression-like behaviors in chronically stressed animals. An expected, our results showed that a single injection of β-glucan 5 h before behavioral tests at a dose of 10 or 20 mg/kg, but not at a dose of 5 mg/kg, reversed the depression-like behavior induced by chronic stress in mice in the tail suspension test, forced swimming test, and sucrose preference test. The effect of β-glucan (20 mg/kg) also showed time-dependent properties that were statistically significant 5 and 8, but not 3, hours after drug injection and persisted for at least 7 days. Fourteen days after β-glucan injection, no antidepressant-like effect was observed anymore. However, this effect was overcome by a second β-glucan injection (20 mg/kg) 14 days after the first β-glucan injection. Stimulation of microglia appeared to mediate the antidepressant-like effect of β-glucan, because both inhibition of microglia and their depletion prevented the antidepressant-like effect of β-glucan. Based on these effects of β-glucan, β-glucan administration could be developed as a new strategy for the treatment of depression.

Of Mice and Men: The Inter-individual Variability of the Brain's Response to Drugs

Biological variation is ubiquitous in nature. Despite highly standardized breeding and husbandry under controlled environmental conditions, phenotypic diversity exists in laboratory mice and rats just as it does in humans. The resulting inter-individual variability affects various characteristics of animal disease models, including the responsiveness to drugs. Thus, the common practice of averaging data within an experimental group can lead to misinterpretations in neuroscience and other research fields. In this commentary, the impact of inter-individual variation in drug responsiveness is illustrated by examples from the testing of antiseizure medications in rodent temporal lobe epilepsy models. Individual mice and rats rendered epileptic by treatment according to standardized protocols fall into groups that either do or do not respond to antiseizure medications, thus mimicking the clinical situation in patients with epilepsy. Population responses are not normally distributed, and divergent responding is concealed in averages subjected to parametric statistical tests. Genetic, epigenetic, and environmental factors are believed to contribute to inter-individual variation in drug response but the specific molecular and physiological causes are not well understood. Being aware of inter-individual variability in rodents allows an improved interpretation of both behavioral phenotypes and drug effects in a pharmacological experiment.

SYK-623, a δ Opioid Receptor Inverse Agonist, Mitigates Chronic Stress-Induced Behavioral Abnormalities and Disrupted Neurogenesis

The δ opioid receptor (DOR) inverse agonist has been demonstrated to improve learning and memory impairment in mice subjected to restraint stress. Here, we investigated the effects of SYK-623, a new DOR inverse agonist, on behavioral, immunohistochemical, and biochemical abnormalities in a mouse model of imipramine treatment-resistant depression. Male ddY mice received daily treatment of adrenocorticotropic hormone (ACTH) combined with chronic mild stress exposure (ACMS). SYK-623, imipramine, or the vehicle was administered once daily before ACMS. After three weeks, ACMS mice showed impaired learning and memory in the Y-maze test and increased immobility time in the forced swim test. SYK-623, but not imipramine, significantly suppressed behavioral abnormalities caused by ACMS. Based on the fluorescent immunohistochemical analysis of the hippocampus, ACMS induced a reduction in astrocytes and newborn neurons, similar to the reported findings observed in the postmortem brains of depressed patients. In addition, the number of parvalbumin-positive GABA neurons, which play a crucial role in neurogenesis, was reduced in the hippocampus, and western blot analysis showed decreased glutamic acid decarboxylase protein levels. These changes, except for the decrease in astrocytes, were suppressed by SYK-623. Thus, SYK-623 mitigates behavioral abnormalities and disturbed neurogenesis caused by chronic stress.

Changes in neurotrophic signaling pathways in brain areas of the chronic mild stress rat model of depression as a signature of ketamine fast antidepressant response/non-response

Major Depressive Disorder (MDD) is a highly debilitating disorder characterized by a persistent feeling of sadness and anhedonia. Traditional antidepressants have a delayed onset of action and lack of efficacy in up to one third of patients, leading to treatment resistant depression (TRD). Recent years have witnessed a revolutionary treatment of TRD with the introduction of the fast-acting antidepressant ketamine. However, ketamine's mechanisms of action are still poorly understood. Here, we used the chronic mild stress animal model of depression on male rats to investigate the involvement of neurotrophic signaling pathways in stress vulnerability/resilience and fast antidepressant response/non-response to acute subanesthetic ketamine. We performed our analysis on both the hippocampus and the prefrontal cortex, two brain areas implicated in stress-related disorders, considering different subcellular fractions. We measured the activation by phosphorylation of protein kinase B (AKT), extracellular signal-regulated kinases (ERKs), glycogen synthase kinase-3 beta (GSK3 β), mammalian target of rapamycin (mTOR), and eukaryotic elongation factor 2 (eEF2), key effectors in the regulation of neuroplasticity and glutamatergic transmission which were previously associated to ketamine's fast antidepressant effect. We showed here for the first time that both stress and ketamine induced brain area and subcellular fraction specific changes in these pathways. Our study represents the first attempt to identify molecular mechanisms underlying the response/non-response to ketamine in an animal model of depression. This approach could give a crucial contribution to the study of etiopathogenetic mechanisms as well as to the identification of novel targets for the development of innovative therapeutic strategies.

Resilience and Vulnerability to Stress-Induced Anhedonia: Unveiling Brain Gene Expression and Mitochondrial Dynamics in a Mouse Chronic Stress Depression Model

The role of altered brain mitochondrial regulation in psychiatric pathologies, including Major Depressive Disorder (MDD), has attracted increasing attention. Aberrant mitochondrial functions were suggested to underlie distinct inter-individual vulnerability to stress-related MDD syndrome. In this context, insulin receptor sensitizers (IRSs) that regulate brain metabolism have become a focus of recent research, as their use in pre-clinical studies can help to elucidate the role of mitochondrial dynamics in this disorder and contribute to the development of new antidepressant treatment. Here, following 2-week chronic mild stress (CMS) using predation, social defeat, and restraint, MDD-related behaviour and brain molecular markers have been investigated along with the hippocampus-dependent performance and emotionality in mice that received the IRS dicholine succinate (DS). In a sucrose test, mice were studied for the key feature of MDD, a decreased sensitivity to reward, called anhedonia. Based on this test, animals were assigned to anhedonic and resilient-to-stress-induced-anhedonia groups, using a previously established criterion of a decrease in sucrose preference below 65%. Such assignment was based on the fact that none of control, non-stressed animals displayed sucrose preference that would be smaller than this value. DS-treated stressed mice displayed ameliorated behaviours in a battery of assays: sucrose preference, coat state, the Y-maze, the marble test, tail suspension, and nest building. CMS-vulnerable mice exhibited overexpression of the inflammatory markers Il-1β, tnf, and Cox-1, as well as 5-htt and 5-ht2a-R, in various brain regions. The alterations in hippocampal gene expression were the closest to clinical findings and were studied further. DS-treated, stressed mice showed normalised hippocampal expression of the plasticity markers Camk4, Camk2, Pka, Adcy1, Creb-ar, Nmda-2r-ar, and Nmda-2r-s. DS-treated and non-treated stressed mice who were resilient or vulnerable to anhedonia were compared for hippocampal mitochondrial pathway regulation using Illumina profiling. Resilient mice revealed overexpression of the mitochondrial complexes NADH dehydrogenase, succinate dehydrogenase, cytochrome bc1, cytochrome c oxidase, F-type and V-type ATPases, and inorganic pyrophosphatase, which were decreased in anhedonic mice. DS partially normalised the expression of both ATPases. We conclude that hippocampal reduction in ATP synthesis is associated with anhedonia and pro-inflammatory brain changes that are ameliorated by DS.

Lipopolysaccharide triggers exacerbated microglial activation, excessive cytokine release and behavioural disturbances in mice with truncated Fused-in-Sarcoma Protein (FUS)

CNS inflammation, including microglial activation, in response to peripheral infections are known to contribute to the pathology of both familial and sporadic neurodegenerative disease. The relationship between Fused-in-Sarcoma Protein (FUS)-mediated disease in the transgenic FUS[1-359] animals and the systemic inflammatory response have not been explored. Here, we investigated microglial activation, inflammatory gene expression and the behavioural responses to lipopolysaccharide-induced (LPS; 0.1 mg/kg) systemic inflammation in the FUS[1-359] transgenic mice. The pathology of these mice recapitulates the key features of mutant FUS-associated familial frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). Here, pre-symptomatic 8-week-old mutant or wild type controls were challenged with LPS or with saline and sucrose intake, novel cage exploration, marble burying and swimming behaviours were analyzed. The level of pro-inflammatory gene expression was also determined, and microglial activation was evaluated. In chronic experiments, to discover whether the LPS challenge would affect the onset of ALS-like paralysis, animals were evaluated for clinical signs from 5 to 7 weeks post-injection. Compared to controls, acutely challenged FUS[1-359]-tg mice exhibited decreased sucrose intake and increased floating behaviours. The FUS[1-359]-tg mice exhibited an increase in immunoreactivity for Iba1-positive cells in the prefrontal cortex and ventral horn of the spinal cord, which was accompanied by increased expression of interleukin-1β, tumour necrosis factor, cyclooxygenase-(COX)-1 and COX-2. However, the single LPS challenge did not alter the time to development of paralysis in the FUS[1-359]-tg mice. Thus, while the acute inflammatory response was enhanced in the FUS mutant animals, it did not have a lasting impact on disease progression.

Activation of the basolateral or the central amygdala dampened the incentive motivation for food reward on high fixed-ratio schedules

The amygdala plays crucial roles in emotional processing, motivated behaviors, and stress responses. It receives sensory information and modulates fear- and anxiety-related behaviors. Neuronal activations are induced in the basolateral complex of the amygdala (BLA) and the central nucleus of the amygdala (CeA) when exposing to acute stress, leading to increased alertness and proper behavioral adaptation. Previous studies have shown that animals displayed a decrease in appetitive motivated behaviors under stress conditions. However, whether the hyperactive amygdala is responsible for the decrease in appetitive motivated behaviors remains unknown. In this study, we aimed to examine the role of BLA or CeA activation in effort-based motivated behavior. We pharmacologically activated the BLA or the CeA with N-methyl-D-aspartate (NMDA) before the lever-pressing for food reward test on different fixed-ratio (FR) schedules (FR1, FR16, or FR32) in male Long-Evans rats. Our data showed that activation of either the BLA or the CeA with NMDA (0.05 μg in 0.5 μl per site) decreased the lever-pressing behavior on higher FR schedules of FR16 and FR32, but not on the FR1 test. Importantly, locomotor activity and free-feeding food intake were intact under amygdala activation, suggesting that the decrease in lever-pressing behavior was not due to motor disablement or decreased appetite. These results suggested that activation of the BLA or the CeA negatively impaired the effort-based motivated behavior that the animals were less willing to work for food reward.

Atomoxetine and escitalopram migrate the derangement of the temporomandibular joint morphologic and histologic changes in rats exposed to stress-induced depression

PURPOSE

The purpose of this in vivo study was to determine the effects of stress-induced depression and antidepressants on depressive-like behavior, microstructure, and histomorphology of the temporomandibular joint (TMJ) using rats.

METHODS

Experimentally induced depression in rats was created before being treated with two antidepressants; escitalopram (selective-serotonin-reuptake inhibitors) and atomoxetine (norepinephrine-reuptake inhibitors). Micro-computed tomography (Micro-CT) was performed to measure the change in bone volume and bone porosity of the condyle. Further histological evaluation of the condylar cartilage was performed.

RESULTS

Micro-CT scanning revealed a decrease in bone volume in the depression group. The bone porosity percentage significantly increased in both the escitalopram and atomoxetine groups compared with the control group and the depression group. Histopathological analysis showed increased thickness of cartilage layers in the depression group. In the atomoxetine group, there was a significant increase in the pre-hypertrophic and hypertrophic layer thickness and cell count, but a significant decrease in proteoglycans.

CONCLUSION

The present study findings indicated the change in TMJ characteristics, especially on the superficial part of the condylar head in the depression group. Concerning the applicability of the different antidepressants, depression with the treatment of atomoxetine has the most disadvantages due to bone porosity and cartilaginous condyle changes.

Molecular signature of excessive female aggression: study of stressed mice with genetic inactivation of neuronal serotonin synthesis

Aggression is a complex social behavior, critically involving brain serotonin (5-HT) function. The neurobiology of female aggression remains elusive, while the incidence of its manifestations has been increasing. Yet, animal models of female aggression are scarce. We previously proposed a paradigm of female aggression in the context of gene x environment interaction where mice with partial genetic inactivation of tryptophan hydroxylase-2 (Tph2+/- mice), a key enzyme of neuronal 5-HT synthesis, are subjected to predation stress resulting in pathological aggression. Using deep sequencing and the EBSeq method, we studied the transcriptomic signature of excessive aggression in the prefrontal cortex of female Tph2+/- mice subjected to rat exposure stress and food deprivation. Challenged mutants, but not other groups, displayed marked aggressive behaviors. We found 26 genes with altered expression in the opposite direction between stressed groups of both Tph2 genotypes. We identified several molecular markers, including Dgkh, Arfgef3, Kcnh7, Grin2a, Tenm1 and Epha6, implicated in neurodevelopmental deficits and psychiatric conditions featuring impaired cognition and emotional dysregulation. Moreover, while 17 regulons, including several relevant to neural plasticity and function, were significantly altered in stressed mutants, no alteration in regulons was detected in stressed wildtype mice. An interplay of the uncovered pathways likely mediates partial Tph2 inactivation in interaction with severe stress experience, thus resulting in excessive female aggression.

Maternal Chronic Ultrasound Stress Provokes Immune Activation and Behavioral Deficits in the Offspring: A Mouse Model of Neurodevelopmental Pathology

Neurodevelopmental disorders stemming from maternal immune activation can significantly affect a child's life. A major limitation in pre-clinical studies is the scarcity of valid animal models that accurately mimic these challenges. Among the available models, administration of lipopolysaccharide (LPS) to pregnant females is a widely used paradigm. Previous studies have reported that a model of 'emotional stress', involving chronic exposure of rodents to ultrasonic frequencies, induces neuroinflammation, aberrant neuroplasticity, and behavioral deficits. In this study, we explored whether this model is a suitable paradigm for maternal stress and promotes neurodevelopmental abnormalities in the offspring of stressed females. Pregnant dams were exposed to ultrasound stress for 21 days. A separate group was injected with LPS on embryonic days E11.5 and E12.5 to mimic prenatal infection. The behavior of the dams and their female offspring was assessed using the sucrose test, open field test, and elevated plus maze. Additionally, the three-chamber sociability test and Barnes maze were used in the offspring groups. ELISA and qPCR were used to examine pro-inflammatory changes in the blood and hippocampus of adult females. Ultrasound-exposed adult females developed a depressive-like syndrome, hippocampal overexpression of GSK-3β, IL-1β, and IL-6 and increased serum concentrations of IL-1β, IL-6, IL-17, RANTES, and TNFα. The female offspring also displayed depressive-like behavior, as well as cognitive deficits. These abnormalities were comparable to the behavioral changes induced by LPS. The ultrasound stress model can be a promising animal paradigm of neurodevelopmental pathology associated with prenatal 'emotional stress'.