Chronic Mild Stress Mice Research Articles

Sodium-Glucose Co-Transporter-2 Inhibitors Act as AMPK Activators and Ameliorate the Depressive Symptoms Induced by Unpredictable Chronic Mild Stress in Mice

Depression is a prevalent disorder of mental health with a highly multifaceted pathogenesis thus finding an effective therapy for it remains a challenge. Depression is associated with downregulation of AMPK signaling pathways and lowers AMP/ATP and ADP/ATP ratios. Brain AMPK pathway malfunction and metabolic imbalances induce depression. The Unpredictable Chronic Mild Stress (UCMS) model was created centered on the predisposition of the stress-associated assumption of depression. SGLT2 inhibitor drugs canagliflozin and remogliflozin enhance brain AMPK signaling, reduce oxidative stress, increase neurotransmitters, and improve metabolism. SGLT2 inhibitor drugs have promising anti-depressant effects. Thus, in this investigation, we examined Sodium-glucose co-transporter-2 inhibitors to ameliorate depression symptoms in mice induced by unpredictable chronic mild stress by improving AMPK signaling. Seven groups of male mice (Swiss albino) were divided into (n=6). The disease groups received different stressors (unpredictable chronic mild stress model) for one week to produce depression, while normal control groups got 0.5% w/v Saline (orally). The standard group received Fluoxetine (10 mg/kg, orally), while the treatment groups were given canagliflozin (15 and 30 mg/kg, orally) and remogliflozin (10 and 30 mg/kg, orally). Behavioral parameters were assessed for induction of depression. Treatment with SGLT2 inhibitors showed significant (p < 0.05) antidepressant effects on behavioral, oxidative stress, neurotransmitter, brain histopathology, and gene expression evaluation of AMPK, mTOR, BNDF, and TNF-α levels. The current study found that SGLT2 inhibitor drugs have the potential to improve the AMPK signaling pathway and alleviate depression.

β-arrestin2 is indispensable for the antidepressant effects of fluoxetine via inhibiting astrocytic pyroptosis in chronic mild stress mouse model for depression

β-arrestin2 is a versatile protein for signaling transduction in brain physiology and pathology. Herein, we investigated the involvement of β-arrestin2 in pharmacological effects of fluoxetine for depression. A chronic mild stress (CMS) model was established using wild-type (WT) and β-arrestin2−/− mice. Behavioral results demonstrated that CMS mice showed increased immobility time in the tail suspension test and forced swimming test, elevated concentrations of pro-inflammatory factors in peripheral blood, increased expression of pyroptosis-related proteins, and increased co-labeling of glial fibrillary acidic protein and Caspase1 p10 in the hippocampus compared to the CON group. Treatment with fluoxetine (FLX) ameliorated these conditions. However, compared with the β-arrestin2−/− CMS group, these results of the β-arrestin2−/− CMS + FLX group showed no significant changes. These results suggested that the above effects of FLX could be eliminated by knocking out β-arrestin2. Mass spectrometry implying that FLX promoted the binding of β-arrestin2 to the NLRP2 inflammasome of depressed mice. Subsequently, the results of the cellular experiments suggested that the 5HT2B receptor antagonist may attenuate L-kynurenine + ATP-induced cell pyroptosis by attenuating NLRP2 binding to β-arrestin2. We further found that the lack of β-arrestin2 eliminated the anti-pyroptosis effect of fluoxetine. In conclusion, β-arrestin2 is an essential protein for fluoxetine to alleviate pyroptosis in the hippocampal astrocytes of CMS mice. Mechanistically, we found that the 5-HT2BR-β-arrestin2-NLRP2 axis is vital for maintaining the antidepressant effects of fluoxetine.

Possible Mechanisms for the Prevention of Anxiety and Depressive-Like Behavior in a Chronic Mild Stress Mouse Model by the Thai Herbal Medicine with Nelumbo nucifera, Centella asiatica, and Piper nigrum

Possible Mechanisms for the Prevention of Anxiety and Depressive-Like Behavior in a Chronic Mild Stress Mouse Model by the Thai Herbal Medicine with Nelumbo nucifera, Centella asiatica, and Piper nigrum

Fast-onset effects of Pseudospondias microcarpa (A. Rich) Engl. (Anacardiaceae) hydroethanolic leaf extract on behavioral alterations induced by chronic mild stress in mice.

Pseudospondias microcarpa (Anacardiaceae) is a plant widely used traditionally for treating various central nervous system disorders. A previous study in our laboratory confirmed that the hydroethanolic leaf extract (PME) of the plant produces an antidepressant-like effect in rodent models of behavioral despair. However, its effect on depressive-like behavior induced by chronic mild stress (CMS) and its time course of action are still unknown. In this context, the long-term effects of PME on cognitive function and depressive- and anxiety-like behavior caused by CMS were assessed. Male ICR mice were exposed to CMS for nine weeks and anhedonia was evaluated by monitoring sucrose intake (SIT) weekly. PME (30, 100, or 300 mg kg-1) or fluoxetine (FLX) (3, 10, or 30 mg kg-1) was administered to the mice during the last six weeks of CMS. Behavioral tests-coat state, splash test, forced swimming test (FST), tail suspension test (TST), elevated plus maze (EPM), open field test (OFT), novelty suppressed feeding (NSF), EPM transfer latency, and Morris water maze (MWM)-were performed after the nine-week CMS period. When the mice were exposed to CMS, their SIT and grooming behavior reduced (splash test), their coat status was poor, they became more immobile (FST and TST), more anxious (OFT, EPM, and NSF), and their cognitive function was compromised (EPM transfer latency and MWM tests). Chronic PME treatment, however, was able to counteract these effects. Additionally, following two (2) weeks of treatment, PME significantly boosted SIT in stressed mice (30 mg kg-1, P<0.05; 100 mg kg-1, P<0.05; and 300 mg kg-1, P<0.001), as compared to four (4) weeks of treatment with FLX. The present findings demonstrate that PME produces a rapid and sustained antidepressant-like action and reverses behavioral changes induced by chronic exposure to mild stressors.

Morinda officinalis oligosaccharides mitigate chronic mild stress-induced inflammation and depression-like behaviour by deactivating the MyD88/PI3K pathway via E2F2

Morinda officinalis oligosaccharides (MOs) are natural herbal extracts that have been shown to exert antidepressant effects. However, the mechanism of this effect remains unclear. Here, we explored the mechanism by which MOs improved experimental depression. Using a chronic mild stress (CMS) murine model, we examined whether MOs could protect against depressive-like behaviour. Lipopolysaccharide (LPS)- and ATP-treated BV2 cells were used to examine the potential mechanism by which MOs mediate the inflammatory response. We found that MOs prevented the CMS-induced reduction in the sucrose preference ratio in the sucrose preference test (SPT) and shortened the immobility durations in both the tail suspension test (TST) and forced swim test (FST). We also noticed that MOs suppressed inflammatory effects by deactivating the MyD88/PI3K pathway via E2F2 in CMS mice or LPS- and ATP-stimulated BV2 cells. Furthermore, overexpression of E2F2 blunted the beneficial effects of MOs in vitro. Collectively, these data showed that MOs exerted antidepressant effects in CMS mice by targeting E2F2-mediated MyD88/PI3K signalling pathway.

Negative air ion exposure ameliorates depression-like behaviors induced by chronic mild stress in mice

The presence of negative air ions (NAI) is suggested to be a beneficial factor in improving psychological status and used in treating depression as an alternative approach. However, more biological evidence from animal models is needed to ensure the effects of NAI on the mood regulation, through which can facilitate identification of possible underlying mechanisms. In this study, the chronic mild stress (CMS) protocol was used to induce depressive-like behaviors in mice, and the effects of NAI exposure on CMS-induced depression-like behaviors were examined. Thirty-day NAI exposure prevented the CMS-induced depression-like behaviors as shown by the restoration of sucrose preference and reduced immobility time in the tail suspension test. In addition, the elevation of serous corticosterone was present in CMS-treated mice but not existed in those with the NAI exposure. Furthermore, we observed altered ratios of some cytokines secreted by type 1 T helper (Th1) cells and Th2 cells in CMS-treated mice, but it could be restored after NAI exposure. In conclusion, NAI intervention is able to ameliorate CMS-induced depression-like behaviors in mice, and this effect is associated with the alteration of corticosterone and functional rebalance between Th1 and Th2 cells.

Abstract TP17: Activation Of Erk1/2 Signaling Drives Cardiac Hypertrophy During Chronic Mild Stress-induced Depression In Mice

Background: Major depressive disorder (MDD) is one of the fastest-growing disability disorders in the US and worldwide. Extensive clinical data suggest that MDD is associated with an increased risk of hypertension, coronary heart disease, and other cardiovascular diseases. A close relation between cardiovascular and cerebrovascular diseases and clinical evidence presents a potential link between depression and stroke. MDD when combined with other comorbidities, makes the prognosis worse. Dysregulation of the sympathetic nervous system, impaired hypothalamic-pituitary-adrenal axis, and increased inflammatory response are plausible mechanisms that have been linked to depression-induced cardio- and cerebrovascular complications. In the current study, we investigated cardiac structural and functional alterations in a mouse model of chronic mild stress (CMS) exhibiting depression-like behavior. Methods and Results: The mice were divided into control (CT) and CMS groups. The CMS mice were subjected to various mild, unpredictable stressors for 7 weeks. Depression-like traits were confirmed in the CMS group by analyses of behavioral changes using open field and forced swim tests and a decrease in hippocampal brain-derived neurotrophic factor (BDNF) protein level. To evaluate depression-associated neuronal damage and neuronal plasticity, Fluoro-Jade C staining and expression of microtubule-associated protein 2 were examined. However, we did not observe neuronal damage in the CMS mice as compared to the CT mice. We also observed a decrease in cardiac BDNF expression and upregulation of IL-6 in the CMS mice compared to the CT group. Echocardiographic and histological analyses showed an increase in ventricular wall thickness with increased cardiomyocyte size in the CMS group. However, we did not find changes in fetal gene expression or fibrosis markers. Investigation of underlying mechanisms showed a significant upregulation in ERK1/2 signaling in the left ventricles of the CMS mice as compared to the control group, with no changes in phospho-p38, NFATc3, or JNK levels. Conclusion: In conclusion, these data suggest that ERK1/2 signaling might have an important role in cardiac hypertrophic response during the CMS-induced depression in mice.

Fluoxetine inhibited the activation of A1 reactive astrocyte in a mouse model of major depressive disorder through astrocytic 5-HT2BR/\u03b2-arrestin2 pathway

BackgroundFluoxetine, a selective serotonin reuptake inhibitor, has been reported to directly bind with 5-HT2B receptor (5-HT2BR), but the precise mechanisms, whereby fluoxetine confers the anti-depressive actions via 5-HT2BR is not fully understood. Although neuroinflammation-induced A1 astrocytes are involved in neurodegenerative diseases, the role of A1 astrocyte in the pathogenesis and treatment of major depressive disorder (MDD) remains unclear.MethodsMice were subjected to chronic mild stress (CMS) for 6 weeks and subsequently treated with fluoxetine for 4 weeks. The depressive-like and anxiety-like behaviors and the activation of A1 reactive astrocyte in hippocampus and cortex of mice were measured. Primary astrocytes were stimulated with A1 cocktail (tumor necrosis factor (TNF)-α, interleukin (IL)-1α and C1q), activated (LPS) microglia-conditioned medium (MCM) or IL-6 for 24 h and the expression of A1-special and A2-special markers were determined using RT-qPCR and western blot. The role of 5-HT2BR in the effects of fluoxetine on A1 reactive astrocyte was measured using 5-HT2BR inhibitor and siRNA in vitro and AAVs in vivo. The functions of downstream signaling Gq protein and β-arrestins in the effects of fluoxetine on the activation of A1 astrocyte were determined using pharmacological inhibitor and genetic knockout, respectively.ResultsIn this study, we found that fluoxetine inhibited the activation of A1 reactive astrocyte and reduced the abnormal behaviors in CMS mice, as well as ameliorated A1 astrocyte reactivity under three different stimulators in primary astrocytes. We also showed that astrocytic 5-HT2BR was required in the inhibitory effects of fluoxetine on A1 reactive astrocyte in MDD in vivo and in vitro. We further found that the functions of fluoxetine in the activation of A1 astrocyte were independent of either Gq protein or β-arrestin1 in vitro. β-arrestin2 pathway was the downstream signaling of astrocytic 5-HT2BR mediated the inhibitory effects of fluoxetine on A1 astrocyte reactivity in primary astrocytes and CMS mice, as well as the improved roles of fluoxetine in behavioral impairments of CMS mice.ConclusionsThese data demonstrate that fluoxetine restricts reactive A1 astrocyte via astrocytic 5-HT2BR/β-arrestin2 pathway in a mouse model of MDD and provide a novel therapeutic avenue for MDD.

Models of Depression: Unpredictable Chronic Mild Stress in Mice.

Major depression is a complex psychiatric disorder characterized by affective, cognitive, and physiological impairments that lead to maladaptive behavior. The high lifetime prevalence of this disabling condition, coupled with limitations of existing medications, make necessary the development of improved therapeutics. This requires animal models that allow investigation of key biological correlates of the disorder. Described in this article is the unpredictable chronic mild stress mouse model that can be used to screen for antidepressant drug candidates. Originally designed for rats, this model has been adapted for mice to capitalize on the advantages of this species as an experimental model, including inter-strain variability, which permits an exploration of the contribution of genetic background; the ability to create transgenic animals; and lower cost. Thus, because it combines genetic features and socio-environmental chronic stressful events, the unpredictable chronic mild stress model in mice is a relevant and valuable paradigm to gain insight into the etiological and developmental components of major depression, as well as to identify novel treatments for this condition. © 2021 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Unpredictable Chronic Mild Stress (UCMS) Test in Mice Basic Protocol 2: Assessment Of Self-Directed Activity And Anhedonia in Mice.

Pain sensitivity increases with sleep disturbance under predictable chronic mild stress in mice

Even though it has been well documented that stress can lead to the development of sleep disorders and the intensification of pain, their relationships have not been fully understood. The present study was aimed at investigating the effects of predictable chronic mild stress (PCMS) on sleep–wake states and pain threshold, using the PCMS rearing conditions of mesh wire (MW) and water (W) for 21 days. Exposure to PCMS decreased the amount of non-rapid eye movement (NREM) sleep during the dark phase. Moreover, the chronicity of PCMS decreased slow-wave activity (SWA) during NREM sleep in the MW and W groups in both the light and dark phases. Mechanical and aversively hot thermal hyperalgesia were more intensified in the PCMS groups than the control. Higher plasma corticosterone levels were seen in mice subjected to PCMS, whereas TNF-α expression was found higher in the hypothalamus in the W and the trigeminal ganglion in the MW group. The W group had higher expression levels of IL-6 in the thalamus as well. The PCMS paradigm decreased SWA and may have intensified mechanical and thermal hyperalgesia. The current study also suggests that rearing under PCMS may cause impaired sleep quality and heightened pain sensation to painful mechanical and aversively hot thermal stimuli.

Saikosaponin D Rescues Deficits in Sexual Behavior and Ameliorates Neurological Dysfunction in Mice Exposed to Chronic Mild Stress.

Often associated with sexual dysfunction (SD), chronic stress is the main contributing risk factor for the pathogenesis of depression. Radix bupleuri had been widely used in traditional Chinese medicine formulation for the regulation of emotion and sexual activity. As the main active component of Radix bupleuri, saikosaponin D (SSD) has a demonstrated antidepressant effect in preclinical studies. Herein, we sought to investigate the effect of SSD to restore sexual functions in chronically stressed mice and elucidate the potential brain mechanisms that might underly these effects. SSD was gavage administered for three weeks during the induction of chronic mild stress (CMS), and its effects on emotional and sexual behaviors in CMS mice were observed. The medial posterodorsal amygdala (MePD) was speculated to be involved in the manifestation of sexual dysfunctions in CMS mice. Our results revealed that SSD not only alleviated CMS-induced depressive-like behaviors but also rescued CMS-induced low sexual motivation and poor sexual performance. CMS destroyed astrocytes and activated microglia in the MePD. SSD treatment reversed the changes in glial pathology and inhibited neuroinflammatory and oxidative stress in the MePD of CMS mice. The neuronal morphological and functional deficits in the MePD were also alleviated by SSD administration. Our results provide insights into the central mechanisms involving the brain associated with sexual dysfunction. These findings deepen our understanding of SSD in light of the psychopharmacology of stress and sexual disorders, providing a theoretical basis for its potential clinical application.

Chronic stress induces significant gene expression changes in the prefrontal cortex alongside alterations in adult hippocampal neurogenesis.

Adult hippocampal neurogenesis is involved in stress-related disorders such as depression, posttraumatic stress disorders, as well as in the mechanism of antidepressant effects. However, the molecular mechanisms involved in these associations remain to be fully explored. In this study, unpredictable chronic mild stress in mice resulted in a deficit in neuronal dendritic tree development and neuroblast migration in the hippocampal neurogenic niche. To investigate molecular pathways underlying neurogenesis alteration, genome-wide gene expression changes were assessed in the prefrontal cortex, hippocampus and the hypothalamus alongside neurogenesis changes. Cluster analysis showed that the transcriptomic signature of chronic stress is much more prominent in the prefrontal cortex compared to the hippocampus and the hypothalamus. Pathway analyses suggested huntingtin, leptin, myelin regulatory factor, methyl-CpG binding protein and brain-derived neurotrophic factor as the top predicted upstream regulators of transcriptomic changes in the prefrontal cortex. Involvement of the satiety regulating pathways (leptin) was corroborated by behavioural data showing increased food reward motivation in stressed mice. Behavioural and gene expression data also suggested circadian rhythm disruption and activation of circadian clock genes such as Period 2. Interestingly, most of these pathways have been previously shown to be involved in the regulation of adult hippocampal neurogenesis. It is possible that activation of these pathways in the prefrontal cortex by chronic stress indirectly affects neuronal differentiation and migration in the hippocampal neurogenic niche via reciprocal connections between the two brain areas.

NNOS-CAPON blockers produce anxiolytic effects by promoting synaptogenesis in chronic stress-induced animal models of anxiety.

Anxiety disorder is a common mental health disorder. However, there are few safe and fast-acting anxiolytic drugs available that can treat anxiety disorder. We previously demonstrated that the interaction of neuronal NOS (nNOS) with its carboxy-terminal PDZ ligand (CAPON) is involved in regulating anxiety-related behaviours. Here, we further investigated the anxiolytic effects of nNOS-CAPON disruptors in chronic stress-induced anxiety in animals. Mice were intravenously treated with nNOS-CAPON disruptors, ZLc-002 or Tat-CAPON12C, at the last week of chronic mild stress (CMS) exposure. We also infused corticosterone (CORT) into the hippocampus of mice to model anxiety behaviours and also delivered ZLc-002 or Tat-CAPON12C on the last week of chronic CORT treatment via pre-implanted cannula. Anxiety-related behaviours were examined using elevated plus maze, open field, novelty-suppressed feeding and light-dark (LD) tests. The level of nNOS-CAPON interaction was determined by co-immunoprecipitation (CO-IP) and proximity ligation assay (PLA). The neural mechanisms underlying the behavioural effects of nNOS-CAPON uncoupling in anxiety animal models were assessed by western blot, immunofluorescence and Golgi-Cox staining. ZLc-002 and Tat-CAPON12C reversed CMS- or CORT-induced anxiety-related behaviours. ZLc-002 and Tat-CAPON12C increased synaptogenesis along with improved dendritic remodelling in CMS mice or CORT-treated cultured neurons. Meanwhile, blocking nNOS-CAPON interaction significantly activated the cAMP response element-binding protein (CREB)-brain-derived neurotrophic factor (BDNF) pathway, which is associated with synaptic plasticity. Collectively, these results provide evidence for the anxiolytic effects of nNOS-CAPON uncouplers and their underlying mechanisms in anxiety disorders.

NK cell-derived exosomes carry miR-207 and alleviate depression-like symptoms in mice

BackgroundDepression is a common mental disease that mainly manifests as bad mood, decreased interest, pessimism, slow thinking, lack of initiative, poor diet and sleep. Patients with severe depression have suicidal tendencies. Exosomes are small vesicles released by the fusion of a multivesicular body and membranes, and they contain specific proteins, nucleic acids, and lipids related to the cells from which they originate. MicroRNAs (miRNAs) are 20–24 nt RNAs that can be packaged into exosomes and can play important regulatory roles. Astrocytes are the most abundant cell population in the central nervous system and have a close link to depression. Astrocyte activation could result in the release of inflammatory cytokines, including IL-1β, IL-6, and TNF-α, which could promote the symptoms of depression. In previous research, our team confirmed that NK cells regulate depression in mice. Here, we propose that miRNA in the exosomes from NK cells performs this antidepressant function.MethodsExosomes from NK cells were shown by in vivo and in vitro experiments to alleviate symptoms of chronic mild stress in mice and decrease pro-inflammatory cytokines release from astrocytes. The production of pro-inflammatory cytokines was assessed by ELISA. Microarray analysis was used to identify critical miRNAs. Luciferase reporter assays, qPCR, and other experiments were used to prove that exosomal miR-207 has an important role in alleviating the symptoms of stress in mice.ResultsMiRNA-containing exosomes from NK cells could alleviate symptoms of chronic mild stress in mice. In vivo experiments showed that these exosomes decreased the levels of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) released by astrocytes. By microarray analysis of exosome miRNA profiles, miR-207 was found to be overexpressed in exosomes derived from unstressed mice. Experiments confirmed that miR-207 directly targets TLR4 interactor with leucine-rich repeats (Tril) and inhibits NF-κB signaling in astrocytes. MiR-207 could decrease the release of pro-inflammatory cytokines and inhibit expression of Tril in vitro. In vivo experiments revealed that exosomes with low miR-207 levels showed decreased antidepressant activity.ConclusionCollectively, our findings revealed that exosomal miR-207 alleviated symptoms of depression in stressed mice by targeting Tril to inhibit NF-κB signaling in astrocytes.

Pharmacokinetics of oral and intravenous cannabidiol and its antidepressant-like effects in chronic mild stress mouse model

Cannabidiol (CBD) exhibits significant efficacy in mental and inflammatory diseases. Several studies have recently reported on the rapid antidepressant-like effects of CBD, suggesting that CBD is a potential anti-depressant or anti-stress drug. However, CBD is mainly administered orally or by inhalation with poor bioavailability, resulting in high costs. We aim to explore the efficacy of long-term periodic administration of CBD in chronic mild stress (CMS) via two routes and its pharmacokinetics. We treated ICR mice with CBD administered orally and intravenously and then determined the kinetic constants. A single bolus intravenous injection of CBD resulted in a half-life of 3.9 h, mean residence time of 3.3 h, and oral bioavailability of about 8.6%. The antidepressant-like effects of periodically administered CBD on the chronic mild stress mouse model are evaluated. Results demonstrated that such treatment at a high dose of 100 mg/kg CBD (p.o.) or a low dose of 10 mg/kg CBD (i.v.), elicited significant antidepressant-like behavioral effects in forced swim test, following increased mRNA expression of brain-derived neurotrophic factor (BDNF) and synaptophysin in the prefrontal cortex and the hippocampus. Our findings are expected to provide a reference for the development of intravenous antidepressant formulations of CBD.

Exploring the involvement of Tac2 in the mouse hippocampal stress response through gene networking

Tachykinin 2 (Tac2) is expressed in a number of areas throughout the brain, including the hippocampus. However, knowledge about its function has been only well explored in the hypothalamus in the context of reproductive health. In this study, we identified and validated increased hippocampal Tac2 mRNA expression in response to chronic mild stress in mice. Expression quantitative trait locus (eQTL) analysis showed Tac2 is cis-regulated in the hippocampus. Using a systems genetics approach, we constructed a Tac2 co-expression network to better understand the relationship between Tac2 and the hippocampal stress response. Our network identified 69 total genes associated with Tac2, several of which encode major neuropeptides involved in hippocampal stress signaling as well as critical genes for producing neural plasticity, indicating that Tac2 is involved in these processes. Pathway analysis for the member of Tac2 gene network revealed a strong connection between Tac2 and neuroactive ligand-receptor interaction, calcium signaling pathway, as well as cardiac muscle contraction. In addition, we also identified 46 stress-related phenotypes, specifically fear conditioning response, that were significantly correlated with Tac2 expression. Our results provide evidence for Tac2 as a strong candidate gene who likely plays a role in hippocampal stress processing and neural plasticity.

Oral Probiotics Ameliorate the Behavioral Deficits Induced by Chronic Mild Stress in Mice via the Gut Microbiota-Inflammation Axis

In recent years, a burgeoning body of research has revealed links between depression and the gut microbiota, leading to the therapeutic use of probiotics for stress-related disorders. In this study, we explored the potential antidepressant efficacy of a multi-strain probiotics treatment (Lactobacillus helveticus R0052, Lactobacillus plantarum R1012, and Bifidobacterium longum R0175) in a chronic mild stress (CMS) mouse model of depression and determined its probable mechanism of action. Our findings revealed that mice subjected to CMS exhibited anxiety- and depressive-like behaviors in the sucrose preference test, elevated plus maze, and forced swim test, along with increased interferon-γ, tumor necrosis factor-α, and indoleamine 2,3-dioxygenase-1 levels in the hippocampus. Moreover, the microbiota distinctly changed from the non-stress group and was characterized by highly diverse bacterial communities associated with significant reductions in Lactobacillus species. Probiotics attenuated CMS-induced anxiety- and depressive-like behaviors, significantly increased Lactobacillus abundance, and reversed the CMS-induced immune changes in the hippocampus. Thus, the possible mechanism involved in the antidepressant-like activity of probiotics is correlated with Lactobacillus species via the gut microbiota-inflammation-brain axis.

Magnolol abrogates chronic mild stress-induced depressive-like behaviors by inhibiting neuroinflammation and oxidative stress in the prefrontal cortex of mice

Magnolol, the main constituent of Magnolia officinalis, has been shown to produce antidepressant-like effect in rodents. Growing evidence shows that neuroinflammation, oxidative stress and neuroendocrine contribute to the pathogenesis of major depression. Here, the aim of this present study was to determine whether magnolol affected these systems in mice exposed to chronic mild stress (CMS). The ameliorative effect of magnolol on depressive-like symptoms was investigated through behavioral tests, including the classical sucrose preference and forced swimming tests. The behavioral evaluation showed that magnolol reversed the depressive-like deficits both in sucrose preference test and forced swimming test. The elevation of prefrontal cortex pro-inflammatory cytokines such as interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) was decreased by magnolol. Consistently, the microglia activation by CMS was also alleviated by magnolol. In addition, the hyperactivity of the hypothalamic–pituitary–adrenal (HPA) axis induced by CMS was attenuated by magnolol. Moreover, the increased lipid peroxidation such as malonaldehyde (MDA) and decreased antioxidant defense enzymes including superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) induced by CMS were also reversed by magnolol. These findings suggest that administration of magnolol could alleviate depressive-like behaviors in CMS mice that are mediated by suppressing neuroinflammation and oxidative stress in the prefrontal cortex.

Antidepression action of BDNF requires and is mimicked by Gαi1/3 expression in the hippocampus

Stress-related alterations in brain-derived neurotrophic factor (BDNF) expression, a neurotrophin that plays a key role in synaptic plasticity, are believed to contribute to the pathophysiology of depression. Here, we show that in a chronic mild stress (CMS) model of depression the Gαi1 and Gαi3 subunits of heterotrimeric G proteins are down-regulated in the hippocampus, a key limbic structure associated with major depressive disorder. We provide evidence that Gαi1 and Gαi3 (Gαi1/3) are required for the activation of TrkB downstream signaling pathways. In mouse embryonic fibroblasts (MEFs) and CNS neurons, Gαi1/3 knockdown inhibited BDNF-induced tropomyosin-related kinase B (TrkB) endocytosis, adaptor protein activation, and Akt-mTORC1 and Erk-MAPK signaling. Functional studies show that Gαi1 and Gαi3 knockdown decreases the number of dendrites and dendritic spines in hippocampal neurons. In vivo, hippocampal Gαi1/3 knockdown after bilateral microinjection of lentiviral constructs containing Gαi1 and Gαi3 shRNA elicited depressive behaviors. Critically, exogenous expression of Gαi3 in the hippocampus reversed depressive behaviors in CMS mice. Similar results were observed in Gαi1/Gαi3 double-knockout mice, which exhibited severe depressive behaviors. These results demonstrate that heterotrimeric Gαi1 and Gαi3 proteins are essential for TrkB signaling and that disruption of Gαi1 or Gαi3 function could contribute to depressive behaviors.

Brain-derived neurotrophic factor-mediated projection-specific regulation of depressive-like and nociceptive behaviors in the mesolimbic reward circuitry.

Increasing evidence suggests that the mesolimbic reward system plays critical roles in the regulation of depression and nociception; however, its circuitry and cellular mechanisms remain unclear. In this study, we investigated the output-specific regulatory roles of dopaminergic (DA) neurons within the ventral tegmental area (VTA) in depressive-like and nociceptive behaviors in mice subjected to unpredictable chronic mild stress (CMS), using the projection-specific electrophysiological recording, pharmacological manipulation, behavioral test, and molecular biology technologies. We demonstrated that CMS decreased the firing activity in VTA projecting to medial prefrontal cortex (VTA → mPFC), but not in VTA to nucleus accumbens (VTA → NAc), DA neurons. However, both VTA → mPFC and VTA → NAc DA neurons showed increased firing activity in response to morphine perfusion in CMS mice. Behavioral results showed that intra-VTA microinjection of morphine (25.5 ng/0.15 μL) relieved depressive-like behaviors, intriguingly, accompanied by a thermal hyperalgesia. Furthermore, the relief of depressive-like behaviors induced by intra-VTA injection of morphine in CMS mice could be prevented by blocking brain-derived neurotrophic factor (BDNF) signaling and mimicked by the administration of exogenous BDNF in mPFC rather than in NAc shell. Nociceptive responses induced by the activation of VTA DA neurons with morphine in CMS mice could be prevented by blocking BDNF signaling or mimicked by administration of exogenous BDNF in NAc shell, but not in mPFC. These results reveal projection-specific regulatory mechanisms of depression and nociception in the mesolimbic reward circuitry and provide new insights into the neural circuits involved in the processing of depressive and nociceptive information.