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

The potential of food-derived peptides in alleviating depressed mood: Function, evaluation and mechanism

Food-derived peptides offer a promising approach to alleviating depressive symptoms due to their safety and natural origin, avoiding the adverse side effects of conventional pharmacological treatments. This review aims to explore their potential in mitigating depressive symptoms. Antidepressant peptides from both animal and plant sources have been reviewed, while the animal models and evaluation methods used to assess their efficacy have been summarized. The review highlights four major mechanisms underlying their effects, namely modulation of gut microbiota and production of neuroactive metabolites, alteration of molecules associated with nervous system, normalization of hypothalamic-pituitary-adrenal axis dysregulation to reduce cortisol production, and suppression of pro-inflammatory cytokines linked to neuroinflammation. It also highlights the role of gut-brain axis in mediating the mechanisms, which has been insufficiently elucidated. However, the efficacy of antidepressant peptides for clinical use has not been established. The present review provides a reference for developing dietary interventions with food-derived peptides to supplement current therapeutic approaches.

Non-aversive handling in laboratory animals and its effects on depressive-like and anxiety-related behaviors: A scoping review

Stress is an adaptive response to environmental demands, but increased intensity and frequency can lead to impaired adaptive functions. Stress is considered a risk factor for Major Depressive Disorder, a multifactorial disorder that often coexists with anxiety. Picking up laboratory mice by the tail is the most common method for animal capture and may create background stress. Non-aversive handling (NAH) includes capturing the animal with the help of a tunnel or by capturing the animal with cupped hands. Given the importance of stress-induced models in the investigation of depressive-like and anxiety-related behaviors, we conducted a literature review to investigate the current knowledge on the behavioral effects of NAH in laboratory animals. While the ability of NAH to counteract depressive-like behavior has yielded mixed results, its ability to induce anxiolytic-like effects in mice has been confirmed by several studies. Some of the studies also investigated the impact of NAH on stress-related molecules (e.g. corticosterone) and physiological parameters (i.e. adrenal gland mass and body weight). The anxiolytic-like effect elicited by NAH seems to be well established in the literature, but little is known about the biochemical pathways underlying it and its antidepressant potential.

Development of a TBK1 and ALK dual inhibitor for alleviating depressive behavior via anti-inflammatory effects

Polypharmacology offers innovative strategies for treating immune and inflammatory dysregulation in complex diseases. Here, we identified ALS-04, a dual inhibitor of TANK-binding kinase 1 (TBK1) and anaplastic lymphoma kinase (ALK), which are closely linked to stimulator of interferon genes (STING)-mediated immune responses. ALS-04 effectively suppressed 2'3'-cyclic GMP-AMP (cGAMP)- and lipopolysaccharide (LPS)-induced type I interferon and pro-inflammatory responses by targeting the STING-TBK1 and STING-ALK pathways. Furthermore, ALS-04 significantly alleviated depressive symptoms, including anhedonia and behavioral despair, in an LPS-induced mouse model of depression. These findings highlight the therapeutic potential of dual TBK1 and ALK inhibition in depression by modulating immune and inflammatory pathways.

Coadministration of scopolamine and mGlu2 receptor negative allosteric modulator VU6001966 as a potential therapeutic approach for depression: Rat frontal cortex neurochemistry and behavior

Clinical studies provide evidence that scopolamine, a nonselective antagonist of muscarinic cholinergic receptors, exerts rapid and prolonged antidepressant effects. However, its use as a psychiatric drug has been limited due to its significant adverse effects. A therapeutic option that could help reduce the adverse effects of scopolamine is its coadministration at lower doses with other substances with similar antidepressant properties. To address this issue, we have investigated the effect of a single acute coadministration of scopolamine and a negative allosteric modulator of the mGlu2 receptor VU6001966 on rat behavior using a forced swim test (FST) and locomotor activity test. The effect of given compounds on the extracellular levels of neurotransmitters in the rat frontal cortex (FCX) was examined using microdialysis in freely moving rats. Both scopolamine and VU6001966 induced dose-dependent antidepressant-like effects in the FST test without affecting locomotor activity. Furthermore, VU6001966 enhanced extracellular dopamine and serotonin levels while lowering glutamate, without affecting GABA level. Both scopolamine alone or in combination with VU6001966 increased dopamine, serotonin, and glutamate levels in the FCX, without affecting GABA levels. Our results suggest that coadministration of scopolamine with mGlu2 NAM might be a promising alternative to using scopolamine alone in depression therapy, potentially allowing for a lower therapeutically effective dose. The common mechanism underlying the observed behavioral effects of the tested drugs may be associated with the modulation of the serotoninergic, glutamatergic, and dopaminergic systems.

Chronic stress induces behavioural changes through increased kynurenic acid by downregulation of kynurenine-3-monooxygenase with microglial decline

BACKGROUND AND PURPOSE

Alterations in tryptophan-kynurenine (TRP-KYN) pathway are implicated in major depressive disorder (MDD). α7 nicotinic acetylcholine (α7nACh) receptor regulates the hypothalamic-pituitary-adrenal (HPA) axis. We have shown that deficiency of kynurenine 3-monooxygenase (KMO) induces depression-like behaviour via kynurenic acid (KYNA; α7nACh antagonist). In this study, we investigated the involvement of the TRP-KYN pathway in stress-induced behavioural changes and the regulation of the HPA axis.

EXPERIMENTAL APPROACH

Mice were exposed to chronic unpredictable mild stress (CUMS) and subjected to behavioural tests. We measured TRP-KYN metabolites and the expression of their enzymes in the hippocampus. KMO heterozygous mice were used to investigate stress vulnerability. We also evaluated the effect of nicotine (s.c.) on CUMS-induced behavioural changes and an increase in serum corticosterone (CORT) concentration.

KEY RESULTS

CUMS decreased social interaction time but increased immobility time under tail suspension associated with increased serum corticosterone concentration. CUMS increased KYNA levels via KMO suppression with microglial decline in the hippocampus. Kmo+/- mice were vulnerable to stress: they exhibited social impairment and increased serum corticosterone concentration even after short-term CUMS. Nicotine attenuated CUMS-induced behavioural changes and increased serum corticosterone concentration by inhibiting the increase in corticotropin-releasing hormone. Methyllycaconitine (α7nACh antagonist) inhibited the attenuating effect of nicotine.

CONCLUSIONS AND IMPLICATIONS

CUMS-induced behavioural changes and the HPA axis dysregulation could be induced by the increased levels of KYNA via KMO suppression. KYNA plays an important role in the pathophysiology of MDD as an α7nACh antagonist. Therefore, α7nACh receptor is an attractive therapeutic target for MDD.

Utilization of Medicinal Plants in Mental Disorders: Neuroplasticity and Neuroprotection in Biomodels

BACKGROUND/OBJECTIVES

Mental disorders such as anxiety, schizophrenia, and depression are linked to alterations in neuroplasticity and neuroprotection within the central nervous system. While conventional drugs are widely used, medicinal plants are emerging as a promising alternative due to their potential therapeutic effects on neuronal function. This study aimed to explore and analyze the impact of medicinal plants on neuroplasticity and neuroprotection in relation to mental disorders using biomodels.

METHODS

Data were collected from Scopus, Dimensions, and PubMed by using the search terms "Medicinal plants", "Neuronal Plasticity", and "Mental Disorder" in accordance with the guidelines of the PRISMA checklist.

RESULTS

A total of twenty-three relevant studies were selected to investigate the association between medicinal plants and mental disorders, focusing on factors such as administered doses and the modulation of neurotransmitters in the context of neuroplasticity and neuroprotection. This review highlights the complexity of study designs, target populations, and methodologies. Of the studies, 86% investigated depression, while 13% focused on anxiety. Regarding neurotransmitter modulation, 47% found that medicinal plants influenced serotonin levels, followed by 27% which found that they affected dopamine; according to the remaining studies, medicinal plants impacted norepinephrine, GABA, and acetylcholine. These findings emphasize the importance of precise dosing and neurotransmitter modulation, suggesting that targeted interactions with neural systems may help clarify the specific effects of these plants on mental health.

CONCLUSIONS

Research on the effects of medicinal plants on psychiatric disorders in animal models suggests their potential to support neuroplasticity and neuroprotection. Positive impacts on mental health are indicated through the modulation of cytokines, neurotransmitters, and specific signaling pathways.

Thymus ad astra, or spaceflight-induced thymic involution

Spaceflight imposes a constellation of physiological challenges-cosmic radiation, microgravity, disrupted circadian rhythms, and psychosocial stress-that critically compromise astronaut health. Among the most vulnerable organs is the thymus, a cornerstone of immune system functionality, tasked with generating naive T cells essential for adaptive immunity. The thymus is particularly sensitive to spaceflight conditions, as its role in maintaining immune homeostasis is tightly regulated by a balance of systemic and local factors easily disrupted in space. Cosmic radiation, an omnipresent hazard beyond Earth's magnetosphere, accelerates DNA damage and cellular senescence in thymic epithelial cells, impairing thymopoiesis and increasing the risk of immune dysregulation. Microgravity and circadian rhythm disruption exacerbate this by altering immune cell migration patterns and stromal support, critical for T-cell development. Psychosocial stressors, including prolonged isolation and mission-induced anxiety, further compound thymic atrophy by elevating systemic glucocorticoid levels. Ground-based analogs simulating cosmic radiation and microgravity have been instrumental in elucidating mechanisms of thymic involution and its downstream effects on immunity. These models reveal that long-duration missions result in diminished naive T-cell output, leaving astronauts vulnerable to infections and possibly at high risk for developing neoplasia. Advances in countermeasures, such as pharmacological interventions targeting thymic regeneration and bioengineering approaches to protect thymic architecture, are emerging as vital strategies to preserve immune resilience during prolonged space exploration. Focusing on the thymus as a central hub of immune vulnerability underscores its pivotal role in spaceflight-induced health risks. Understanding these dynamics will not only enhance the safety of human space missions but also provide critical insights into thymus biology under extreme conditions.

Insights for the Next Generation of Ketamine for the Treatment of Depressive Disorder

Treatment-resistant depression responds quickly to ketamine. As an N-methyl-d-aspartate receptor (NMDAR) antagonist, ketamine may affect prefrontal cortex (PFC) neurons. Recent investigations reveal that the (R)-enantiomer is the most effective and least abuseable antidepressant. The Food and Drug Administration approves only the (S)-enantiomer for medical usage. (2R,6R)-Hydroxynorketamine (HNK) inhibits mGlu2, linked to a Gi, in presynaptic glutamatergic neurons, increasing brain-derived neurotrophic factor (BDNF) release, which autocrinely activates Tropomyosin receptor kinase B (TrkB) and promotes synaptogenesis. Ketamine, originally an anesthetic, has garnered attention for its many pharmacological effects, including its potential as a rapid-acting antidepressant and recreational use. In this Perspective, we explore the synthesis, pharmacology, metabolism, and effects of ketamine and its metabolites in animal and human studies to explain the difference in the biological activity between the enantiomers.

Oxidative and Excitatory Neurotoxic Stresses in CRISPR/Cas9-Induced Kynurenine Aminotransferase Knockout Mice: A Novel Model for Despair-Based Depression and Post-Traumatic Stress Disorder

BACKGROUNDS

Memory and emotion are especially vulnerable to psychiatric disorders such as post-traumatic stress disorder (PTSD), which is linked to disruptions in serotonin (5-HT) metabolism. Over 90% of the 5-HT precursor tryptophan (Trp) is metabolized via the Trp-kynurenine (KYN) metabolic pathway, which generates a variety of bioactive molecules. Dysregulation of KYN metabolism, particularly low levels of kynurenic acid (KYNA), appears to be linked to neuropsychiatric disorders. The majority of KYNA is produced by the aadat (kat2) gene-encoded mitochondrial kynurenine aminotransferase (KAT) isotype 2. Little is known about the consequences of deleting the KYN enzyme gene.

METHODS

In CRISPR/Cas9-induced aadat knockout (kat2-/-) mice, we examined the effects on emotion, memory, motor function, Trp and its metabolite levels, enzyme activities in the plasma and urine of 8-week-old males compared to wild-type mice.

RESULTS

Transgenic mice showed more depressive-like behaviors in the forced swim test, but not in the tail suspension, anxiety, or memory tests. They also had fewer center field and corner entries, shorter walking distances, and fewer jumping counts in the open field test. Plasma metabolite levels are generally consistent with those of urine: antioxidant KYNs, 5-hydroxyindoleacetic acid, and indole-3-acetic acid levels were lower; enzyme activities in KATs, kynureninase, and monoamine oxidase/aldehyde dehydrogenase were lower, but kynurenine 3-monooxygenase was higher; and oxidative stress and excitotoxicity indices were higher. Transgenic mice displayed depression-like behavior in a learned helplessness model, emotional indifference, and motor deficits, coupled with a decrease in KYNA, a shift of Trp metabolism toward the KYN-3-hydroxykynurenine pathway, and a partial decrease in the gut microbial Trp-indole pathway metabolite.

CONCLUSIONS

This is the first evidence that deleting the aadat gene induces depression-like behaviors uniquely linked to experiences of despair, which appear to be associated with excitatory neurotoxic and oxidative stresses. This may lead to the development of a double-hit preclinical model in despair-based depression, a better understanding of these complex conditions, and more effective therapeutic strategies by elucidating the relationship between Trp metabolism and PTSD pathogenesis.

Differential effects of chronic unpredictable stress on behavioral and molecular (cortisol and microglia-related neurotranscriptomic) responses in adult leopard (leo) zebrafish

Stress plays a key role in mental, neurological, endocrine, and immune disorders. The zebrafish (Danio rerio) is rapidly gaining popularity as s model organism in stress physiology and neuroscience research. Although the leopard (leo) fish are a common outbred zebrafish strain, their behavioral phenotypes and stress responses remain poorly characterized. Here, we examined the effects of a 5-week chronic unpredictable stress (CUS) exposure on adult leo zebrafish behavior, cortisol levels, and brain gene expression. Compared to their unstressed control leo counterparts, CUS-exposed fish showed paradoxically lower anxiety-like, but higher whole-body cortisol levels and altered expression of multiple pro- and anti-inflammatory brain genes. Taken together, these findings suggest that behavioral and physiological (endocrine and genomic) responses to CUS do differ across zebrafish strains. These findings add further complexity to systemic effects of chronic stress in vivo and also underscore the importance of considering the genetic background of zebrafish in stress research.

Effectiveness of positive allosteric modulators of metabotropic glutamate receptor 2/3 (mGluR2/3) in animal models of schizophrenia

Schizophrenia (SZ) is a deleterious brain disorder characterised by its heterogeneity and complex symptomatology consisting of positive, negative and cognitive deficits. Current antipsychotic drugs ameliorate the positive symptomatology, but are inefficient in treating the negative symptomatology and cognitive deficits. The neurodevelopmental glutamate hypothesis of SZ has opened new avenues in the development of drugs targeting the glutamatergic system. One of these new therapies involves the positive allosteric modulators (PAMs) of metabotropic glutamate receptors, mainly types 2/3 (mGluR2/3). mGluR2/3 PAMs are selective for the receptor, present high tolerability and can modulate the activity of the receptor for long periods. There is not much research in clinical trials regarding mGluR2/3 PAMs. However, several lines of evidence from animal models have indicated the efficiency of mGluR2/3 PAMs. In this review, focusing on in vivo animal studies, we will specifically discuss the utilization of SZ animal models and the various methods employed to assess animal behaviour before summarising the evidence obtained to date in the field of mGluR2/3 PAMs. By doing so, we aim to deepen our understanding of the underlying mechanisms and the potential efficiency of mGluR2/3 PAMs in treating SZ. Overall, mGluR2/3 PAMs have demonstrated efficiency in attenuating SZ-like behavioural and molecular deficits in animal models and could be useful for the early management of the disorder or to treat specific subsets of patients.

Recognising depression in non-human primates: a narrative review of reported signs of depression

Major depressive disorder (depression) is a highly heterogenous human mental disorder that may have equivalents in non-human animals. Research into non-human depression teaches us about human depression and can contribute to enhance welfare of non-human animals. Here, we narratively review how signs of depression in non-human primates (NHPs) can be observed based on symptoms of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). Furthermore, we propose diagnostic criteria of NHP depression and we review reports on signs of depression in NHPs. We diagnose an NHP with depression when it shows a core sign (depressed mood or anhedonia) alongside at least three other DSM-5-derived signs of depression. Results show that four out of six observable signs of depression are present in NHPs, occasionally lasting for months. However, only a group of six NHPs in one study met our proposed criteria for a diagnosis of depression. We call for more research into the co-occurrence of depressive symptoms in individual NHPs to establish the prevalence of depression in NHPs.

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.

Brain region-specific roles of brain-derived neurotrophic factor in social stress-induced depressive-like behavior

Brain-derived neurotrophic factor is a key factor in stress adaptation and avoidance of a social stress behavioral response. Recent studies have shown that brain-derived neurotrophic factor expression in stressed mice is brain region-specific, particularly involving the corticolimbic system, including the ventral tegmental area, nucleus accumbens, prefrontal cortex, amygdala, and hippocampus. Determining how brain-derived neurotrophic factor participates in stress processing in different brain regions will deepen our understanding of social stress psychopathology. In this review, we discuss the expression and regulation of brain-derived neurotrophic factor in stress-sensitive brain regions closely related to the pathophysiology of depression. We focused on associated molecular pathways and neural circuits, with special attention to the brain-derived neurotrophic factor-tropomyosin receptor kinase B signaling pathway and the ventral tegmental area-nucleus accumbens dopamine circuit. We determined that stress-induced alterations in brain-derived neurotrophic factor levels are likely related to the nature, severity, and duration of stress, especially in the above-mentioned brain regions of the corticolimbic system. Therefore, BDNF might be a biological indicator regulating stress-related processes in various brain regions.

Natural products that alleviate depression: The putative role of autophagy

Major depressive disorder (MDD) is a common mental disorder that severely disrupts psychosocial function and decreases the quality of life. Although the pathophysiological mechanism underlying MDD is complex and remains unclear, emerging evidence suggests that autophagy dysfunction plays a role in MDD occurrence and progression. Natural products serve as a major source of drug discovery and exert tremendous potential in developing antidepressants. Recently published reports are paying more attention on the autophagy regulatory effect of antidepressant natural products. In this review, we comprehensively discuss the abnormal changes occurred in multiple autophagy stages in MDD patients, and animal and cell models of depression. Importantly, we emphasize the regulatory mechanism of antidepressant natural products on disturbed autophagy, including monomeric compounds, bioactive components, crude extracts, and traditional Chinese medicine formulae. Our comprehensive review suggests that enhancing autophagy might be a novel approach for MDD treatment, and natural products restore autophagy homeostasis to facilitate the renovation of mitochondria, impede neuroinflammation, and enhance neuroplasticity, thereby alleviating depression.

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.

Nighttime-specific differential gene expression in suprachiasmatic nucleus and habenula is associated with resilience to chronic social stress

The molecular mechanisms that link stress and biological rhythms still remain unclear. The habenula (Hb) is a key brain region involved in regulating diverse types of emotion-related behaviours while the suprachiasmatic nucleus (SCN) is the body's central clock. To investigate the effects of chronic social stress on transcription patterns, we performed gene expression analysis in the Hb and SCN of stress-naïve and stress-exposed mice. Our analysis revealed a large number of differentially expressed genes and enrichment of synaptic and cell signalling pathways between resilient and stress-naïve mice at zeitgeber 16 (ZT16) in both the Hb and SCN. This transcriptomic signature was nighttime-specific and observed only in stress-resilient mice. In contrast, there were relatively few differences between the stress-susceptible and stress-naïve groups across time points. Our results reinforce the functional link between circadian gene expression patterns and differential responses to stress, thereby highlighting the importance of temporal expression patterns in homoeostatic stress responses.

Comparative Efficacy of Animal Depression Models and Antidepressant Treatment: A Systematic Review and Meta-Analysis

BACKGROUND

Animal models are critical tools in the study of psychiatric disorders; however, none of the current models fully reflect human stress-related disorders, even though most of the knowledge about the mechanisms of depression comes from animal studies. Animal studies are useful in pharmacological research, whereby we can obtain results that translate into patient treatment by controlling environmental factors, especially in behavioural research. The authors systematically reviewed this issue since medical databases provide access to many primary studies.

METHODS

A systematic review and meta-analysis were conducted based on 25 primary studies. The studies were identified in databases such as PubMed, Embase, and Web of Science (December 2022) according to the inclusion and exclusion criteria established at the beginning of the research and published in the form of a protocol, following the PRISMA and Cochrane Collaboration methodology for secondary studies and CAMARADES (CAMARADES Berlin, QUEST-BIH Charité) for secondary studies on animals. Forest plot analyses were performed (data presented as Mean Difference, Random Model, Inverse Variance), Risk of Bias assessment (Systematic Review Center for Laboratory animal Experimentation (SYRCLE) evaluation), quality assessment of included studies (Animal research: Reporting of In Vivo Experiments (ARRIVE)), and a range of data from source publications were compiled in tabular form. The study analysed the popularity of both animal depression models (ADM) and rat strains used in pharmacological research to test the efficacy of antidepressant drugs based on the immobility time (IT) factor (Forced Swimming Test). The study examined selective serotonin reuptake inhibitors, namely fluoxetine, sertraline, paroxetine, citalopram, and escitalopram. Additionally, the study addressed issues concerning the "data availability statement" because precise IT data analysis was impossible in the case of 212 papers.

RESULTS

Our data confirm that the Chronic Unpredictable Mild Stress (CUMS) model is the most popular and versatile model used in preclinical depression research, while the two most popular rat strains were Wistar and Sprague-Dawley. The quality of included papers based on the ARRIVE assessment showed a ratio value equal to 0.63, meaning that studies were of intermediate overall quality. The Risk of Bias assessment based on the SYRCLE tool revealed a high risk related to the blinding and the random outcome assessment. In the meta-analysis, the results indicate that all analysed drugs demonstrated efficacy in reducing IT, and the most analysed drug was fluoxetine (confirmed based on 17 studies (19 models)). The analysis of the efficacy of ADMs showed that the most effective models were CUMS, Flinders Sensitive Line (genetic model), Social Isolation, Restraint Stress, and Low-dose Lipopolysaccharide (pharmacological model). Only 2.35% (5 out of 212) of corresponding authors responded to our data request.

CONCLUSIONS

The study highlights the dominance of the CUMS model and the Wistar and Sprague-Dawley rat strains in preclinical depression research, affirming the efficacy of SSRIs, particularly fluoxetine, in reducing IT. The findings underscore the need for better data availability and methodological improvements despite intermediate overall study quality and notable bias risks. Enhanced transparency and rigorous assessment standards are essential for advancing the reliability of animal models in depression research.

Loss of Sigma-2 Receptor/TMEM97 Is Associated with Neuropathic Injury-Induced Depression-Like Behaviors in Female Mice

Previous studies have shown that ligands that bind to sigma-2 receptor/TMEM97 (s2R/TMEM97), a transmembrane protein, have anxiolytic/antidepressant-like properties and relieve neuropathic pain-like effects in rodents. Despite medical interest in s2R/TMEM97, little affective and pain behavioral characterization has been done using transgenic mice, which limits the development of s2R/TMEM97 as a viable therapeutic target. Using wild-type (WT) and global Tmem97 knock-out (KO) mice, we sought to identify the contribution of Tmem97 in modulating affective and pain-like behaviors using a battery of affective and pain assays, including open field, light/dark preference, elevated plus maze, forced swim test, tail suspension test, and the mechanical sensitivity tests. Our results demonstrate that female Tmem97 KO mice show less anxiety-like and depressive-like behaviors in light/dark preference and tail suspension tests but not in an open field, elevated plus maze, and forced swim tests at baseline. We next performed spared nerve injury in WT and Tmem97 KO mice to assess the role of Tmem97 in neuropathic pain-induced anxiety and depression. WT mice, but not Tmem97 KO mice, developed a prolonged neuropathic pain-induced depressive-like phenotype when tested 10 weeks after nerve injury in females. Our results show that Tmem97 plays a role in modulating anxiety-like and depressive-like behaviors in naive animals with a significant change in the presence of nerve injury in female mice. Overall, these data demonstrate that Tmem97 could be a target to alleviate affective comorbidities of pain disorders.

Differential effects of allopregnanolone and diazepam on social behavior through modulation of neural oscillation dynamics in basolateral amygdala and medial prefrontal cortex

Effective treatments for major depressive disorder (MDD) have long been needed. One hypothesis for the mechanism of depression involves a decrease in neuroactive steroids such as allopregnanolone, an endogenous positive allosteric modulator of the γ-aminobutyric acid-gated chloride channel (GABAA) receptor. In our previous study, we discovered that allopregnanolone, not diazepam, exhibited antidepressant-like effects in the social interaction test (SIT) of social defeat stress (SDS) model mice. However, the dynamics of neuronal activity underlying the antidepressant-like effect remain unknown. In the current study, we conducted local field potentials (LFPs) recordings from the basolateral amygdala (BLA) and the medial prefrontal cortex (mPFC) during the SIT to elucidate the relationship between the antidepressant-like effect and neuronal oscillation. We discovered that allopregnanolone has antidepressant-like effects in the SIT of SDS model mice by decreasing intervals of repetitive social interaction (inter-event intervals), resulting in increase of total social interaction time. We also found that theta and beta oscillation increased in BLA at the onset of social interaction following administration of allopregnanolone, which differed from the effects of diazepam. Theta and beta power in BLA within the social interaction zone exhibited a positive correlation with interaction time. This increase of theta and beta power was negatively correlated with inter-event intervals. Regarding theta-band coordinated activity between the BLA and mPFC, theta power correlation decreased at the onset of social interaction with the administration of allopregnanolone. These findings suggest that theta activity in BLA following social interaction and the reduced theta-band coordinated activity between the BLA and mPFC are implicated in social interaction, which is one of the antidepressant behaviors. These differences in neural activity could elucidate the distinctive mechanism underlying antidepressant-like effects of neuroactive steroids, as opposed to benzodiazepines.

A scoping review of the effects of mushroom and fungus extracts in rodent models of depression and tests of antidepressant activity

One of the most important developments in psychopharmacology in the past decade has been the emergence of novel treatments for mood disorders, such as psilocybin for treatment-resistant depression. Psilocybin is most commonly found in different species of mushroom; however, the literature on mushroom and fungus extracts with potential antidepressant activity extends well beyond just psilocybin-containing mushrooms, and includes both psychedelic and non-psychedelic species. In the current review, we systematically review the preclinical literature on mushroom and fungus extracts, and their effects of animal models of depression and tests of antidepressant activity. The PICO structure, PRISMA checklist and the Cochrane Handbook for systematic reviews of intervention were used to guide the search strategy. A scoping search was conducted in electronic databases PubMed, CINAHL, Embase and Web of Science. The literature search identified 50 relevant and suitable published studies. These included 19 different species of mushrooms, as well as seven different species of other fungi. Nearly all studies reported antidepressant-like effects of treatment with extracts. Treatments were most commonly delivered orally, in both acute and chronically administered studies to predominantly male rodents. Multiple animal models of depression were used, the most common being unpredictable chronic mild stress, while the tail suspension test and forced swim test were most frequently used as standalone antidepressant screens. Details on each experiment with mushroom and fungus species are discussed in detail, while an evaluation is provided of the strengths and weaknesses of these studies.

Animal models to study cognitive impairment of chronic kidney disease

Mild cognitive impairment (MCI) is common in people with chronic kidney disease (CKD), and its prevalence increases with progressive loss of kidney function. MCI is characterized by a decline in cognitive performance greater than expected for an individual age and education level but with minimal impairment of instrumental activities of daily living. Deterioration can affect one or several cognitive domains (attention, memory, executive functions, language, and perceptual motor or social cognition). Given the increasing prevalence of kidney disease, more and more people with CKD will also develop MCI causing an enormous disease burden for these individuals, their relatives, and society. However, the underlying pathomechanisms are poorly understood, and current therapies mostly aim at supporting patients in their daily lives. This illustrates the urgent need to elucidate the pathogenesis and potential therapeutic targets and test novel therapies in appropriate preclinical models. Here, we will outline the necessary criteria for experimental modeling of cognitive disorders in CKD. We discuss the use of mice, rats, and zebrafish as model systems and present valuable techniques through which kidney function and cognitive impairment can be assessed in this setting. Our objective is to enable researchers to overcome hurdles and accelerate preclinical research aimed at improving the therapy of people with CKD and MCI.

Understanding Why Homeopathic Medicines are Used for Menopause: Searching for Insights into Neuroendocrine Features

BACKGROUND

Menopause is a physiological event that marks the end of a woman's reproductive stage in life. Vasomotor symptoms and changes in mood are among its most important effects. Homeopathy has been used for many years in treating menopausal complaints, though clinical and pre-clinical research in this field is limited. Homeopathy often bases its prescription on neuropsychiatric symptoms, but it is unknown if homeopathic medicines (HMs) exert a neuroendocrine effect that causes an improvement in vasomotor symptoms and mood during menopause.

OBJECTIVES

The study's objectives were to address the pathophysiological changes of menopause that could help in the understanding of the possible effect of HMs at a neuroendocrine level, to review the current evidence for two of the most frequently prescribed HMs for menopause (Lachesis mutus and Sepia officinalis), and to discuss the future directions of research in this field.

METHODS

An extensive literature search for the pathophysiologic events of menopause and depression, as well as for the current evidence for HMs in menopause and depression, was performed.

RESULTS

Neuroendocrine changes are involved in the pathophysiology of vasomotor symptoms and changes in mood during menopause. Gonadal hormones modulate neurotransmitter systems. Both play a role in mood disorders and temperature regulation. It has been demonstrated that Gelsemium sempervirens, Ignatia amara and Chamomilla matricaria exert anxiolytic effects in rodent models. Lachesis mutus and Sepia officinalis are frequently prescribed for important neuropsychiatric and vasomotor symptoms. Dopamine, a neurotransmitter involved in mood, is among the constituents of the ink of the common cuttlefish, Sepia officinalis.

CONCLUSION

Based on all the pathophysiologic events of menopause and the improvement in menopausal complaints that certain HMs show in daily practice, these medicines might have a direct or indirect neuroendocrine effect in the body, possibly triggered via an as-yet unidentified biological mechanism. Many unanswered questions in this field require further pre-clinical and clinical research.

NADPH-oxidases as potential pharmacological targets for thrombosis and depression comorbidity

There is a complex interrelationship between the nervous system and the cardiovascular system. Comorbidities of cardiovascular diseases (CVD) with mental disorders, and vice versa, are prevalent. Adults with mental disorders such as anxiety and depression have a higher risk of developing CVD, and people with CVD have an increased risk of being diagnosed with mental disorders. Oxidative stress is one of the many pathways associated with the pathophysiology of brain and cardiovascular disease. Nicotinamide adenine dinucleotide phosphate oxidase (NOX) is one of the major generators of reactive oxygen species (ROS) in mammalian cells, as it is the enzyme that specifically produces superoxide. This review summarizes recent findings on the consequences of NOX activation in thrombosis and depression. It also discusses the therapeutic effects and pharmacological strategies of NOX inhibitors in CVD and brain disorders. A better comprehension of these processes could facilitate the development of new therapeutic approaches for the prevention and treatment of the comorbidity of thrombosis and depression.

TRPC4 deletion elicits behavioral defects in sociability by dysregulating expression of microRNA-138-2

To investigate whether the defects in transient receptor potential canonical 4 (TRPC4), which is strongly expressed in the hippocampus, are implicated in ASD, we examined the social behaviors of mice in which Trpc4 was deleted (Trpc4-/-). Trpc4-/- mice displayed the core symptoms of ASD, namely, social disability and repetitive behaviors. In microarray analysis of the hippocampus, microRNA (miR)-138-2, the precursor of miR-138, was upregulated in Trpc4-/- mice. We also found that binding of Matrin3 (MATR3), a selective miR-138-2 binding nuclear protein, to miR-138-2 was prominently enhanced, resulting in the downregulation of miR-138 in Trpc4-/- mice. Some parameters of the social defects and repetitive behaviors in the Trpc4-/- mice were rescued by increased miR-138 levels following miR-138-2 infusion in the hippocampus. Together, these results suggest that Trpc4 regulates some signaling components that oppose the development of social behavioral deficits through miR-138 and provide a potential therapeutic strategy for ASD.

Distinct mechanisms of allopregnanolone and diazepam underlie neuronal oscillations and differential antidepressant effect

The rapid relief of depressive symptoms is a major medical requirement for effective treatments for major depressive disorder (MDD). A decrease in neuroactive steroids contributes to the pathophysiological mechanisms associated with the neurological symptoms of MDD. Zuranolone (SAGE-217), a neuroactive steroid that acts as a positive allosteric modulator of synaptic and extrasynaptic δ-subunit-containing GABAA receptors, has shown rapid-onset, clinically effective antidepressant action in patients with MDD or postpartum depression (PPD). Benzodiazepines, on the other hand, act as positive allosteric modulators of synaptic GABAA receptors but are not approved for the treatment of patients with MDD. It remains unclear how differences in molecular mechanisms contribute to the alleviation of depressive symptoms and the regulation of associated neuronal activity. Focusing on the antidepressant-like effects and neuronal activity of the basolateral amygdala (BLA) and medial prefrontal cortex (mPFC), we conducted a head-to-head comparison study of the neuroactive steroid allopregnanolone and the benzodiazepine diazepam using a mouse social defeat stress (SDS) model. Allopregnanolone but not diazepam exhibited antidepressant-like effects in a social interaction test in SDS mice. This antidepressant-like effect of allopregnanolone was abolished in extrasynaptic GABAA receptor δ-subunit knockout mice (δko mice) subjected to the same SDS protocol. Regarding the neurophysiological mechanism associated with these antidepressant-like effects, allopregnanolone but not diazepam increased theta oscillation in the BLA of SDS mice. This increase did not occur in δko mice. Consistent with this, allopregnanolone potentiated tonic inhibition in BLA interneurons via δ-subunit-containing extrasynaptic GABAA receptors. Theta oscillation in the mPFC of SDS mice was also increased by allopregnanolone but not by diazepam. Finally, allopregnanolone but not diazepam increased frontal theta activity in electroencephalography recordings in naïve and SDS mice. Neuronal network alterations associated with MDD showed decreased frontal theta and beta activity in depressed SDS mice. These results demonstrated that, unlike benzodiazepines, neuroactive steroids increased theta oscillation in the BLA and mPFC through the activation of δ-subunit-containing GABAA receptors, and this change was associated with antidepressant-like effects in the SDS model. Our findings support the notion that the distinctive mechanism of neuroactive steroids may contribute to the rapid antidepressant effects in MDD.

Administering a Behavioral Test Battery in Rodents

Although animal models cannot broadly represent uniquely human psychiatric or psychological syndromes such as anxiety, depression, or schizophrenia, behavioral testing in rodents can be extremely helpful to investigate specific disease aspects and symptoms. Animal behavioral test batteries allow researchers to reveal specific behavioral changes in genetically modified mice or following targeted treatments or in response to environmental interventions. Examples of types of behaviors that can be combined in a test battery include anxiety-like behavior, learning and memory, depression-relevant behavior, social interaction, and locomotor hyperactivity. Here, we describe several commonly used and relatively simple behavioral tests which can be combined in the same cohort of animals.

Neuroinflammation, memory, and depression: new approaches to hippocampal neurogenesis

As one of most common and severe mental disorders, major depressive disorder (MDD) significantly increases the risks of premature death and other medical conditions for patients. Neuroinflammation is the abnormal immune response in the brain, and its correlation with MDD is receiving increasing attention. Neuroinflammation has been reported to be involved in MDD through distinct neurobiological mechanisms, among which the dysregulation of neurogenesis in the dentate gyrus (DG) of the hippocampus (HPC) is receiving increasing attention. The DG of the hippocampus is one of two niches for neurogenesis in the adult mammalian brain, and neurotrophic factors are fundamental regulators of this neurogenesis process. The reported cell types involved in mediating neuroinflammation include microglia, astrocytes, oligodendrocytes, meningeal leukocytes, and peripheral immune cells which selectively penetrate the blood-brain barrier and infiltrate into inflammatory regions. This review summarizes the functions of the hippocampus affected by neuroinflammation during MDD progression and the corresponding influences on the memory of MDD patients and model animals.

Distinct latent symptom profiles in late-onset depressive symptoms in community-dwelling older adults

OBJECTIVES

To examine the symptom profiles of late-onset depressive symptoms in a sample of older adults.

METHOD

The sample included 1,192 participants from the National Alzheimer's Coordinating Center Data Set. Participants were ≥65 years old, community-dwelling, and without cognitive impairment or a prior history of depression. Depressive symptoms were assessed using the Geriatric Depression Scale, 15-item (GDS-15). Latent class analysis (LCA) was used to identify and group participants based on profiles of depressive symptoms.

RESULTS

LCA revealed three distinct symptom profiles: (1) an Anhedonia/Amotivation profile with a higher probability of endorsing a combination of low positive emotion and amotivation (6%), (2) an Amotivation/Withdrawal profile with a high probability of endorsing only amotivational depressive symptoms (35%), and (3) an asymptomatic profile with no probability of endorsing any depressive symptoms (59%). Amotivational depressive symptoms were observed across both symptomatic profiles, while depressed mood (e.g. sadness) did not predominantly characterize any profile in this sample. There were also significant differences among symptom profiles in terms of demographic and clinical characteristics.

CONCLUSIONS

Findings highlight the importance of understanding depression at the symptom pattern level. A profile-based diagnostic approach may help improve the recognition of depressive symptoms in older adults.

The Effects of Ethanol and Acetic acid on Behaviour of Extranidal Workers of the Narrow-Headed Ant Formica exsecta (Hymenoptera, Formicidae) during a Field Experiment

Ethanol addiction belongs to the most important problems encountered in the domain of human mental health. The research on the behavioural effects of exposure to/consumption of ethanol are investigated largely with the help of animal models that also include insects, mainly fruit flies and honeybees. The effects of ethanol on ant behaviour remain, however, little known. In the present field study, we investigated the behaviour of workers of the narrow-headed ant (Formica exsecta) displayed in the vicinity of cotton pads soaked in water or in water solutions of ethanol or acetic acid during 5 min tests (n = 30 tests in each group). Both ethanol and acetic acid induced significant modifications of ant locomotion, exploratory behaviour, self-grooming behaviour, and aggressive social behaviour. We confirmed that acetic acid is aversive for the ants, but ethanol enhances their exploratory behaviour. We also found out that field studies may document more types of responses to experimental compounds than laboratory ones, as the tested animals may also escape from aversive substances. Our findings documented a wide spectrum of behavioural effects of exposure to ethanol and acetic acid in a highly social animal species and broadened the general knowledge about behavioural responses to these compounds encountered in animals.

Efficacy, Tolerability, and Safety of Toludesvenlafaxine for the Treatment of Major Depressive Disorder-A Narrative Review

The estimated rate of treatment-resistant major depressive disorder (TRD) remains higher than 30%, even after the discovery of multiple classes of antidepressants in the last 7 decades. Toludesvenlafaxine (ansofaxine, LY03005, or LPM570065) is a first-in-class triple monoaminergic reuptake inhibitor (TRI) that has reached clinical use. The objective of this narrative review was to summarize clinical and preclinical evidence about the efficacy, tolerability, and safety of toludesvenlafaxine. Based on the results of 17 reports retrieved in the literature, the safety and tolerability profiles of toludesvenlafaxine were good in all clinical trials, and the pharmacokinetic parameters were well described in the phase 1 trials. The efficacy of toludesvenlafaxine was demonstrated in one phase 2 and one phase 3 trial, both on primary and secondary outcomes. In conclusion, this review highlights the favorable clinical results of toludesvenlafaxine in only two short-term trials that enrolled patients with major depressive disorder (MDD) (efficacy and tolerability were good for up to eight weeks), indicating the need for more good quality, larger-sample, and longer-term trials. Exploring new antidepressants, such as TRI, can be considered a priority for clinical research due to the high rates of TRD, but also due to the significant percentages of relapse in patients with MDD.