Depression-like Mice Research Articles

Apple Polyphenol Extracts Attenuated Depressive-Like Behaviors of High-Sucrose Diet Feeding Mice by Farnesoid X Receptor-Mediated Modulation of Bile Acid Circulation within the Liver-Gut-Brain Axis.

Although the association between high-sugar diets and depression has been verified, few studies have explored the antidepressant mechanisms of apple polyphenol extracts (APE). Therefore, fifty-four C57BL/6 male mice aged 5 weeks were randomly assigned into five groups: the control group with the standard diet (CON), the constant high-sucrose diet group (HSD), the "2 + 5" alternate diet group (A-HSD), and the 500 mg/(kg·bw) APE treatment for the HSD group (APE) and the A-HSD group (A-APE), respectively. The data of hypothalamic-pituitary-adrenal (HPA) axis function and behavioral experiments confirmed the success in the establishment of depression-like mouse models in both HSD and A-HSD groups, which were significantly alleviated after APE treatment. Meanwhile, APE reduced serum levels of corticosterone and adrenocorticotrophic hormone, alleviated histopathological damage of the liver, colon, and brain, respectively, elevated the protein expressions of Occludin, ZO-1, and MUC-2, and decreased Firmicutes/Bacteroidota ratio and Dubosiella abundance with the increased microbiota of Tannerellaceae_unclassified, Muribaculum, and Lachnospiraceae_unclassified. Moreover, APE treatment reduced Farnesoid X receptor (FXR) protein levels along with the increased expressions of CYP7A1 and TGR5, lowered the contents of serum and fecal total bile acids, and modulated fecal BA compositions, particularly glycocholic acid (GCA) and isolithocholic acid (ILCA). Thus, both the constant and alternate high-sucrose diets successfully induced depression-like behaviors in mice, and APE might be a potential nutraceutical to attenuate high-sucrose diet-induced depression by regulating BAs circulation within the liver-gut-brain axis mediated by FXR.

Central effects of <i>ex vivo</i> caffeine-modulated immune cells in the mechanisms of editing depressive-like behavior

Depression is a serious medical and social problem due to its high prevalence, involvement of people of working age and lack of highly effective therapy. Social stressors contribute to the prevalence of depression. The COVID-19 pandemic and the associated rules of social distancing, military clashes, and a deteriorating economic situation can lead to a painful “breakdown” of socio-biological adaptation mechanisms and contribute to an increase in the prevalence of depressive disorders, which, according to WHO forecasts, may take second place in the world by 2030, which leads to interest in studying this problem and finding new effective approaches to therapy. Decreased cognitive function in depressive disorders is caused by neuroinflammatory and neurodegenerative changes. The latter are predominantly recorded in the hippocampus, numerous changes in the plasticity of which have been observed both in patients with clinical depression and in rodent models of depression. There is also a sufficient amount of data on the significant role of immune cells and their cytokines in depression, including in the development of behavioral phenotype. We have previously shown that spleen cells of depressive-like mice after ex vivo treatment with caffeine, a psychoactive drug with a wide range of immunomodulatory properties, change their functional activity and, after intravenous administration to syngeneic depressive-like recipients, have editing depressive-like behavior effect. The purpose of this work was to investigate the central effects of caffeine-modulated spleen cells in the mechanisms of editing depressive-like behavior. It was found that in depressive-like recipients after transplantation of syngeneic caffeine-modulated splenocytes, there is an increase in the density of neurons in the CA1 and CA3 zones of the hippocampus, accompanied by BDNF level increase in the hippocampus and prefrontal cortex against the background of a decrease of a number of pro-inflammatory (IL-1β, IL-6, IFNγ and TNFα) and increased of anti-inflammatory (IL-10 and IL-4) cytokines in brain structures pathogenetically significant for the state of depression. The mechanisms of the identified structural and functional changes in the recipient’s brain after the caffeine-modulated splenocytes transplantation are discussed, including their possible direct influence, confirmed by visualization of transplanted cells in the brain parenchyma of depressed-like recipients.

Brain region-specific action of ketamine as a rapid antidepressant.

Ketamine has been found to have rapid and potent antidepressant activity. However, despite the ubiquitous brain expression of its molecular target, the N-methyl-d-aspartate receptor (NMDAR), it was not clear whether there is a selective, primary site for ketamine's antidepressant action. We found that ketamine injection in depressive-like mice specifically blocks NMDARs in lateral habenular (LHb) neurons, but not in hippocampal pyramidal neurons. This regional specificity depended on the use-dependent nature of ketamine as a channel blocker, local neural activity, and the extrasynaptic reservoir pool size of NMDARs. Activating hippocampal or inactivating LHb neurons swapped their ketamine sensitivity. Conditional knockout of NMDARs in the LHb occluded ketamine's antidepressant effects and blocked the systemic ketamine-induced elevation of serotonin and brain-derived neurotrophic factor in the hippocampus. This distinction of the primary versus secondary brain target(s) of ketamine should help with the design of more precise and efficient antidepressant treatments.

Depression-related testosterone deficiency is linked to reduced cholesterol levels in Leydig cells of CUMS mice.

Male reproductive problems under psychological stress were widely studied. Using chronically unpredictable mild stress-treated mice, we found that reduced serum testosterone levels were related to the low level of cholesterol in the Leydig cells. Testosterone deficiency in humans can be caused by depressive symptoms; however, the causes of this deficiency are incompletely understood. This study demonstrates that male mice with depression-like symptoms due to chronic unpredictable mild stress (CUMS) show reduced serum testosterone levels and disrupted sexual behaviors. However, the observed testosterone reductions were not caused by apoptosis of Leydig cells. Oil red O staining revealed that lipid droplets were dramatically decreased in Leydig cells, suggesting that defects in cholesterol uptake might be related to testosterone deficiency in depression-like mice. To investigate the potential mechanism, lipid homeostasis was examined by liquid chromatography-tandem mass spectrometry. The results revealed that higher levels of sphingomyelins (SM 8:0;2O/28:1, 18:0;2O/22:2, 33:0;3O, 33:1;2O) were linked to decreased cholesterol levels. Further investigation indicated that testosterone biosynthesis from cholesterol in Leydig cells was impaired by the downregulation of Ldlr, Srb1, Lhr, and P450scc. Elevated levels of interferon signaling-associated pathways in depression-like mice testes may also contribute to decreased testosterone levels. Taken together, these findings provide a novel understanding of male reproductive problems under psychological stress and suggest that cholesterol uptake might be a causal factor in reduced testosterone production in depression-like mice.

Antidepressant Effect and Mechanism of Picea mariana Essential Oil on Reserpine-Induced Depression Model Mice.

The disturbance of brain biochemical substances serves as a primary cause and aggravating factor of depression. This study aimed to investigate the principal components of Picea mariana and its effect on reserpine-induced depression mice,w ith its relationship with brain central transmitters and related proteins. The main constituents of P. mariana essential oil (PMEO) were analyzed by GC-MS spectrometry. The quiescent time in the tail suspension test (TST) and forced swim test (FST), along with the weight change of the mice was detected. The number of normal neurons was quantified through Nissl staining. Immunohistochemistry was employed to determine the levels of 5HT-1A and 5HT-2A in the brain. Western blotting was utilized to detect 5HT-2A, CRF and TrkB protein levels. RT-qPCR was used to detect the mRNA levels of 5HT-1A, 5HT-2A, TrkB, CRF, and BDNF. The main active ingredients of PMEOs were (-) -bornyl acetate (44.95%), γ-Terpinene (14.17%), and β-Pinene (10.12%). PMEOs effectively improved the retardation and weight loss due to anorexia in depression-like mice. This improvement was associated with an increase in the number of normal neurons. After administering different doses of PMEOs, the levels of 5HT-1A, 5HT-2A, CRF, and TrkB were found to be increased in brain tissue. RT-qPCR revealed that the mRNA levels of CRF, 5HT-1A, and 5HT-2A were generally upregulated, whereas TrkB and BDNF were downregulated. PMEO can effectively alleviate depression induced by reserpine, which may be attributed to its regulation of 5HT-1A, 5HT-2A, CRF and TrkB protein expression, thus reducing brain nerve injury.

Astrocyte-specific activation of sigma-1 receptors in mPFC mediates the faster onset antidepressant effect by inhibiting NF-κB-induced neuroinflammation

Major depressive disorder (MDD) is a global health burden characterized by persistent low mood, deprivation of pleasure, recurrent thoughts of death, and physical and cognitive deficits. The current understanding of the pathophysiology of MDD is lacking, resulting in few rapid and effective antidepressant therapies. Recent studies have pointed to the sigma-1 (σ-1) receptor as a potential rapid antidepressant target; σ-1 agonists have shown promise in a variety of preclinical depression models. Hypidone hydrochloride (YL-0919), an independently developed antidepressant by our institute with faster onset of action and low rate of side effects, has recently emerged as a highly selective σ-1 receptor agonist; however, its underlying astrocyte-specific mechanism is unknown. In this study, we investigated the effect of YL-0919 treatment on gene expression in the prefrontal cortex of depressive-like mice by single-cell RNA sequencing. Furthermore, we knocked down σ-1 receptors on astrocytes in the medial prefrontal cortex of mice to explore the effects of YL-0919 on depressive-like behavior and neuroinflammation in mice. Our results demonstrated that astrocyte-specific knockdown of σ-1 receptor resulted in depressive-like behavior in mice, which was reversed by YL-0919 administration. In addition, astrocytic σ-1 receptor deficiency led to activation of the NF-κB inflammatory pathway, and crosstalk between reactive astrocytes and activated microglia amplified neuroinflammation, exacerbating stress-induced neuronal apoptosis. Furthermore, the depressive-like behavior induced by astrocyte-specific knockdown of the σ-1 receptor was improved by a selective NF-κB inhibitor, JSH-23, in mice. Our study not only reaffirms the σ-1 receptor as a key target of the faster antidepressant effect of YL-0919, but also contributes to the development of astrocytic σ-1 receptor-based novel drugs.

TNF-α/TNFR1 activated astrocytes exacerbate depression-like behavior in CUMS mice

Neuroinflammation is considered to be a significant mechanism contributing to depression. Several studies have reported that A1 astrocytes were highly prevalent in human neuroinflammatory and neurodegenerative diseases. However, the precise mechanism by which A1 astrocytes contribute to depression remains unclear. Clinical studies have suggested a correlation between TNF-α, an activator of A1 astrocytes, and the severity of depression. Based on these findings, we hypothesized that TNF-α might worsen depression by activating A1 astrocytes. Our previous studies indicated that Rhodomyrtone (Rho) has the potential to improve depression-like behavior in mice. However, the exact mechanism for this effect has not been fully elucidated. Importantly, it was reported that Rho alleviated skin inflammation in a mouse model of psoriasis by inhibiting the expression of TNF-α. Based on this finding, we hypothesized that rhodomyrtone may exert antidepressant effects by modulating the TNF-α pathway. However, further research is required to investigate and validate these hypotheses, shedding light on the relationships between neuroinflammation, A1 astrocytes, TNF-α, and depression. By obtaining a deeper understanding of the underlying mechanisms, these findings could lead to the development of novel antidepressant strategies that target the TNF-α pathway in the context of neuroinflammation. In vivo, based on the established chronic unpredictable mild stress (CUMS) mouse depression model, we characterized the mechanism of TNF-α and Rho during depression by using several behavioral assays, adeno-associated virus(AAV) transfection, western blotting, immunofluorescence, and other experimental methods. In vitro, we characterized the effect of Rho on inflammation in TNF-α-treated primary astrocytes. TNFR1 expression was significantly increased in the hippocampus of depression-like mice, with increased astrocytes activation and neuronal apoptosis. These processes were further enhanced with increasing levels of TNF-α in the cerebrospinal fluid of mice. However, this process was attenuated by knockdown of TNFR1 and infliximab (Inf; a TNF-α antagonist). Injection of rhodomyrtone decreased the expressions of TNFR1 and TNF-α, resulting in significant improvements in mouse depression-like behaviors and reduction of astrocyte activation. TNF-α could be involved in the pathophysiological process of depression, through mediating astrocytes activation by binding to TNFR1. By blocking this pathway, Rho may be a novel antidepressant.

M2 macrophage-derived soluble factors enhance neuronal density in the frontal cortex of depression-like mice

IntroductionChronic inflammation in depression is associated with decreased levels of neurotrpohic factors and suppressed neurogenesis. We have previously shown that intranasal therapy with soluble factors from M2 macrophages polarized by interaction with apoptotic cells in serum deprivation conditions (M2(LS); LS - low serum) and characterized by anti-inflammatory and pro-regenerative activity leads to the correction of the behavioral pattern in mice with a depression-like state.ObjectivesThe present study focuses on the effect of M2(LS) macrophages on neuronal density in the frontal cortex and hippocampus of depression-like mice.MethodsDepressive-like state was formed in passive male mice (CBAxC57Bl/6)F1) as a result of repeated experience of defeat in agonistic interactions with aggressive partner during 20 days (the sensory contact model). Depression-like mice were then treated intranasally with M2(LS) macrophages conditioned medium for 7 days. After that, the number of mature neurons in the frontal cortex and hippocampus was assessed using Nissl staining.ResultsThe neuronal density in the pyramidal layer of the frontal cortex was significantly lower in depression-like mice than that in the intact control group of mice (p=0,047). At the same time, the number of neurons in the experimental group of mice that received soluble M2(LS) factors, was higher than that in depressive-like untreated control mice (p=0,003) and was comparable to that in the intact group of mice. At the same time the neuronal density in the CA1 and CA3 hippocampal areas did not change in depression-like mice following intranasal treatment with conditioned medium of M2(LS) macrophages.ConclusionsThe data obtained may indicate the neuroprotective effect of M2(LS) macrophages in the stress-induced depression model, which is realized through soluble factors and manifests itself in an increase of the pyramidal neurons density in the frontal cortex.Disclosure of InterestNone Declared

Dihydroartemisinin Protects Mice from CUMS-induced Depression-like Behaviors by Regulating Gut Microbes

Depression is one of the most common forms of psychopathology, which is associated with gut microbiota dysfunction. Dihydroartemisinin (DHA) has been shown to regulate gut microbiota and ameliorate neuropathies, but whether it can be used to treat depression remains unclear. Our study found that DHA treatment raised the preference for sugar water in chronic unpredictable mild stress (CUMS)-induced mice and reduced the immobility time in open field, forced swimming and tail suspension experiments, and promoted doublecortin expression. Additionally, DHA up-regulated the diversity and richness of intestinal microbiota in depression-like mice, and restored the abnormal abundance of microbiota induced by CUMS, such as Turicibacter, Lachnospiraceae, Erysipelotrichaceae, Erysipelatoclostridium, Eubacterium, Psychrobacter, Atopostipes, Ileibacterium, Coriobacteriacea, Alistipes, Roseburia, Rikenella, Eggerthellaceae, Ruminococcus, Tyzzerella, and Clostridia. Furthermore, KEGG pathway analysis revealed that gut microbiota involved in the process of depression may be related to glucose metabolism, energy absorption and transport, and AMPK signaling pathway. These results indicated that DHA may play a protective role in CUMS-induced depression by mediating gut-microbiome.

TGR5-mediated lateral hypothalamus-dCA3-dorsolateral septum circuit regulates depressive-like behavior in male mice

Although bile acids play a notable role in depression, the pathological significance of the bile acid TGR5 membrane-type receptor in this disorder remains elusive. Using depression models of chronic social defeat stress and chronic restraint stress in male mice, we found that TGR5 in the lateral hypothalamic area (LHA) predominantly decreased in GABAergic neurons, the excitability of which increased in depressive-like mice. Upregulation of TGR5 or inhibition of GABAergic excitability in LHA markedly alleviated depressive-like behavior, whereas down-regulation of TGR5 or enhancement of GABAergic excitability facilitated stress-induced depressive-like behavior. TGR5 also bidirectionally regulated excitability of LHA GABAergic neurons via extracellular regulated protein kinases-dependent Kv4.2 channels. Notably, LHA GABAergic neurons specifically innervated dorsal CA3 (dCA3) CaMKIIα neurons for mediation of depressive-like behavior. LHA GABAergic TGR5 exerted antidepressant-like effects by disinhibiting dCA3 CaMKIIα neurons projecting to the dorsolateral septum (DLS). These findings advance our understanding of TGR5 and the LHAGABA→dCA3CaMKIIα→DLSGABA circuit for the development of potential therapeutic strategies in depression.

Effects of chronic unpredictable mild stress on gut microbiota and fecal amino acid and short-chain fatty acid pathways in mice

Depression is a serious disease that has a significant impact on social functioning. However, the exact causes of depression are still not fully understood. Therefore, it is necessary to explore new pathways leading to depression. In this study, we used 16 S rDNA to examine changes in gut microbiota and predict related pathways in depression-like mice. Additionally, we employed liquid chromatography-mass spectrometry (LC-MS) to identify changes in amino acids and gas chromatography-mass spectrometry (GC-MS) to identify changes in short-chain fatty acids (SCFAs) in fecal samples. We conducted Pearson/Spearman correlation analysis to investigate the associations between changes in amino acids/SCFAs and behavioral outcomes. The 16 S rDNA sequencing revealed significant alterations in gut microbiota at the phylum and genus levels in mice subjected to chronic unpredictable mild stress (CUMS). The relative abundances of Bacteroidetes, Proteobacteria, Bacteroides, and Alloprevotella were increased, while Firmicutes, Verrucomicrobia, Actinobacteria, Lactobacillus, Akkermansia, Lachnospirillum, and Enterobacter were decreased in the CUMS mice. We used PICRUSt software to annotate the kyoto encyclopedia of genes and genomes (KEGG) pathway function related to depression-like behavior in mice. Our analysis identified sixty functional pathways associated with the gut microbiota of mice exhibiting depression-like behavior. In the amino acid concentration analysis, we observed decreased levels of hydroxyproline and tryptophan, and increased levels of alanine in CUMS mice. In the SCFAs concentration assay, we found decreased levels of butyric acid and valeric acid, and increased levels of acetic acid in CUMS mice. Some of these changes were significantly correlated with depressive-like behaviors. Our study contributes to the understanding of the mechanism of the gut-brain axis in the occurrence and development of depression.

Niuhuang Qingxin Wan ameliorates depressive-like behaviors and improves hippocampal neurogenesis through modulating TrkB/ERK/CREB signaling pathway in chronic restraint stress or corticosterone challenge mice.

Introduction: Chronic stress-associated hormonal imbalance impairs hippocampal neurogenesis, contributing to depressive and anxiety behaviors. Targeting neurogenesis is thus a promising antidepressant therapeutic strategy. Niuhuang Qingxin Wan (NHQXW) is an herbal formula for mental disorders in Traditional Chinese Medicine (TCM) practice, but its anti-depressant efficacies and mechanisms remain unverified. Methods: In the present study, we tested the hypothesis that NHQXW could ameliorate depressive-like behaviors and improve hippocampal neurogenesis by modulating the TrkB/ERK/CREB signaling pathway by utilizing two depression mouse models including a chronic restraint stress (CRS) mouse model and a chronic corticosterone (CORT) stress (CCS) induced mouse model. The depression-like mouse models were orally treated with NHQXW whereas fluoxetine was used as the positive control group. We evaluated the effects of NHQXW on depressive- and anxiety-like behaviors and determined the effects of NHQXW on inducing hippocampal neurogenesis. Results: NHQXW treatment significantly ameliorated depressive-like behaviors in those chronic stress mouse models. NHQXW significantly improved hippocampal neurogenesis in the CRS mice and CCS mice. The potential neurogenic mechanism of NHQXW was identified by regulating the expression levels of BDNF, TrkB, p-ERK (T202/T204), p-MEK1/2 (S217/221), and p-CREB (S133) in the hippocampus area of the CCS mice. NHQXW revealed its antidepressant and neurogenic effects that were similar to fluoxetine. Moreover, NHQXW treatment revealed long-term effects on preventing withdrawal-associated rebound symptoms in the CCS mice. Furthermore, in a bioactivity-guided quality control study, liquiritin was identified as one of the bioactive compounds of NHQXW with the bioactivities of neurogenesis-promoting effects. Discussion: Taken together, NHQXW could be a promising TCM formula to attenuate depressive- and anxiety-like behaviors against chronic stress and depression. The underlying anti-depressant mechanisms could be correlated with its neurogenic activities by stimulating the TrkB/ERK/CREB signaling pathway.

The physicochemical characteristics and antidepressant-like effects of a polysaccharide-rich fraction from Schisandra chinensis (Turcz.) Baill in behavioral despair mice and olfactory bulbectomy-induced depression-like mice

Ethnopharmacological relevanceThe dried fruit of Schisandra chinensis (Turcz.) Baill (S. chinensis) is widely used in treating central nervous system disorders. Increasing evidence has suggested that alcohol-soluble extracts and lignans from S. chinensis could significantly ameliorate depression-like behaviors in animal models, while there was little research on the potential of alcohol-insoluble polysaccharides as a candidate in the treatment of depression. Aim of the studyOur research was designed to explore both the physicochemical characteristics and antidepressant-like effects of an alcohol-insoluble polysaccharide-rich fraction named SCP from S. chinensis. Simultaneously, the underlying mechanisms were elucidated in the study. Materials and methodsThe physicochemical characteristics were accomplished by colorimetric assays, CE, HPGPC, and FT-IR. Behavioral despair testing accompanied by LAT were processed to promptly assess the antidepressant-like effects of SCP in mice. Then OBX-induced mice were established to explore the impacts of chronic co-treatments with SCP. Furthermore, effects of SCP on the HPA axis, oxidant/antioxidant system, neurotrophic and synaptic factors, and gut microbiota in OBX-induced mice were detected through ELISA and 16S rDNA (V3 + V4 regions) gene sequencing. ResultsSCP is a polysaccharide-rich fraction mainly comprised of xylose, glucose, rhamnose, galactose, mannose, and galacturonic acid in ratios of 0.27, 5.09, 0.24, 1.00, 0.63, and 2.86, of which the MW distribution ranges from 681 to 3232 Da. Acute pre-treatment with SCP (200 mg/kg, i.g.) remarkably reduced mice’s immobility in the FST without motor stimulation. Prolonged pre-treatments effectively enhanced the effects of SCP on the behavioral despair testing in mice. Chronic co-treatments with SCP (50, 200, and 800 mg/kg, i.g.) could ameliorate the slow increase of body weight and behavioral abnormality of OBX-induced mice in systemic behavioral testing. SCP (200 mg/kg) also successfully restored hyperactivity of the HPA axis, oxidative damage in the liver, neurotrophic disturbance and abnormal synaptic plasticity in the hippocampus, and dysregulation of gut microbiota in OBX-induced mice. ConclusionSCP exerts noteworthy antidepressant-like impacts on behavioral despair mice and OBX-induced mice via multiple targets, indicating a potential therapeutic candidate in depression therapy.

NEDD4 like E3 ubiquitin protein ligase represses astrocyte activation and aggravates neuroinflammation in mice with depression via paired box 6 ubiquitination.

Astrocytes are implicated in stress-induced neuroinflammatory responses in depression. This paper was to explore the molecular mechanism of the E3 ubiquitin ligase NEDD4L (NEDD4 like E3 ubiquitin protein ligase) in depressed mice by regulating astrocyte activation, and to find a new target for depression. A mouse model of depression was established by CUMS (chronic mild unpredictable stress) in 48 6-week male C57BL/6 mice and injected with sh-NEDD4L vector for testing behavioral and cognitive abilities, histopathological changes, and the number of GFAP-positive cells. The mRNA and protein levels of NEDD4L, PAX6 (paired box 6) and P2X7R (purinergic ligand-gated ion channel 7 receptor) were measured. Inflammation model was established by lipopolysaccharide treatment of mouse astrocyte line C8-D1A and infected with sh-NEDD4L. After CUMS induction, mice showed depression-like symptoms, increased inflammatory infiltration, decreased glial fibrillary acidic protein (GFAP)-positive cells in brain tissue, and increased NEDD4L protein levels. NEDD4L inhibition increased GFAP-positive cells, increased PAX6 protein levels and decreased P2X7R mRNA and protein levels, and decreased inflammatory factor secretion in brain tissue and in vitro cells. PAX6 knockdown or P2X7R overexpression partially reversed the effects of NEDD4L inhibition on astrocyte activation and neuroinflammation. To conclude, highly-expressed NEDD4L in depression-like mouse brain inhibits astrocyte activation and exacerbates neuroinflammation by ubiquitinating PAX6 and promoting P2X7R level.

The PrLGlu→avBNSTGABA circuit rapidly modulates depression-like behaviors in male mice

Depression is a global disease with a high prevalence. Here, we examine the role of the circuit from prelimbic mPFC (PrL) to the anterior ventral bed nucleus of the stria terminalis (avBNST) in depression-like mice through behavioral tests, immunofluorescence, chemogenetics, optogenetics, pharmacology, and fiber photometry. Mice exposed to chronic restraint stress with individual housing displayed depression-like behaviors. Optogenetic or chemogenetic activation of the avBNST-projecting glutamatergic neurons in the PrL had an antidepressant effect. Moreover, we found that α-amino-3-hydroxy-5-methyl-4-isoxazole-propionicacid receptors (AMPARs) play a dominant role in this circuit. Systemic administration of ketamine profoundly alleviated depression-like behaviors in the mice and rapidly rescued the decreased activity in the PrLGlu→avBNSTGABA circuit. Furthermore, the fast-acting effect of ketamine on depressive behaviors was diminished when the circuit was inhibited. To summarize, activating the PrLGlu→avBNSTGABA circuit quickly ameliorated depression-like behaviors. Thus, we propose the PrLGlu→avBNSTGABA circuit as a target for fast regulation of depression.

The connexin hemichannel inhibitor D4 produces rapid antidepressant-like effects in mice.

Depression is a common mood disorder characterized by a range of clinical symptoms, including prolonged low mood and diminished interest. Although many clinical and animal studies have provided significant insights into the pathophysiology of depression, current treatment strategies are not sufficient to manage this disorder. It has been suggested that connexin (Cx)-based hemichannels are candidates for depression intervention by modifying the state of neuroinflammation. In this study, we investigated the antidepressant-like effect of a recently discovered selective Cx hemichannel inhibitor, a small organic molecule called D4. We first showed that D4 reduced hemichannel activity following systemic inflammation after LPS injections. Next, we found that D4 treatment prevented LPS-induced inflammatory response and depressive-like behaviors. These behavioral effects were accompanied by reduced astrocytic activation and hemichannel activity in depressive-like mice induced by repeated low-dose LPS challenges. D4 treatment also reverses depressive-like symptoms in mice subjected to chronic restraint stress (CRS). To test whether D4 broadly affected neural activity, we measured c-Fos expression in depression-related brain regions and found a reduction in c-Fos+ cells in different brain regions. D4 significantly normalized CRS-induced hypoactivation in several brain regions, including the hippocampus, entorhinal cortex, and lateral septum. Together, these results indicate that blocking Cx hemichannels using D4 can normalize neuronal activity and reduce depressive-like symptoms in mice by reducing neuroinflammation. Our work provides evidence of the antidepressant-like effect of D4 and supports glial Cx hemichannels as potential therapeutic targets for depression.

Structural changes of the frontal cortex in depressed mice are associated with decreased expression of brain-derived neurotrophic factor

To investigate the changes in gray matter volume in depressive-like mice and explore the possible mechanism. Twenty-four 6-week-old C57 mice were randomized equally into control group and model group, and the mice in the model group were subjected to chronic unpredictable mild stimulation (CUMS) for 35 days. Magnetic resonance imaging was performed to examine structural changes of the grey matter volume in depressive-like mice. The expression of brain-derived neurotrophic factor (BDNF) in the grey matter of the mice was detected using Western blotting and immunofluorescence staining. Compared with the control mice, the mice with CUMS showed significantly decreased central walking distance in the open field test (P < 0.05) and increased immobile time in forced swimming test (P < 0.05). Magnetic resonance imaging showed that the volume of the frontal cortex was significantly decreased in CUMS mice (P < 0.001, when the mass level was greater than or equal to 10 756, the FDRc was corrected with P=0.05). Western blotting showed that the expression of mature BDNF in the frontal cortex was significantly decreased in CUMS mice (P < 0.05), and its expression began to decrease after the exposure to CUMS as shown by immunofluorescence staining. The volume of different clusters obtained by voxel-based morphometry (VBM) analysis was correlated with the expression level of mature BDNF detected by Western blotting (P < 0.05). The decrease of frontal cortex volume after CUMS is related with the reduction of mature BDNF expression in the frontal cortex.

Identification of paeoniflorin from Paeonia lactiflora pall. As an inhibitor of tryptophan 2,3-dioxygenase and assessment of its pharmacological effects on depressive mice

Ethnopharmacological relevanceThe radix of Paeonia lactiflora Pall. (PaeR) is a traditional Chinese medicine (TCM) clinically used for treating depression. Although it has been established that PaeR can protect the liver and alleviate depressive-like behaviors, its bioactive chemicals and antidepressant mechanism remain unclear. Our pilot study showed that PaeR reduced the expression of the L-tryptophan- catabolizing enzyme tryptophan 2,3-dioxygenase (TDO) in the livers of stress-induced depression-like mice. Aim of the studyThis study aimed to screen potential TDO inhibitors from PaeR and investigate the potential therapeutic use of TDO inhibition for treating depression. Materials and methodsMolecular docking, magnetic ligand fishing, and secrete-pair dual luminescence assay were conducted for in vitro ligand discovery and high-throughput screening of TDO inhibitors. Stable TDO overexpression was achieved in HepG2 cell lines to evaluate the TDO inhibitory activities of drugs in vitro by RT-PCR and Western blot analyses of TDO at mRNA and protein levels. In vivo validation of TDO inhibitory potency and evaluation of TDO inhibition as a potential therapeutic strategy for major depressive disorder (MDD) were performed using mice subjected to “3 + 1″ combined stresses for at least 30 days to induce depression-like behaviors. A well-known TDO inhibitor, LM10, was evaluated in parallel. ResultsThe PaeR extract significantly ameliorated depressive-like behaviors of stressed mice, attributed to inhibition of TDO expression and tryptophan modulation metabolism. After a comprehensive analysis of molecular docking, ligand fishing, and luciferase assay, paeoniflorin was screened as a TDO inhibitor from the PaeR extract. This compound, structurally different from LM10, potently inhibited human and mouse TDO in cell- and animal-based assays. The effects of TDO inhibitors on MDD symptoms were evaluated in a stress-induced depression-like mouse model. In mice, both inhibitors had beneficial effects on stress-induced depressive-like behavioral despair and unhealthy physical status. Moreover, both inhibitors increased the liver serotonin/tryptophan ratio and decreased the kynurenine/tryptophan ratio after oral administration, demonstrating in vivo inhibition of TDO activity. Our data substantiated the potential of TDO inhibition as a therapeutic strategy to improve behavioral activity and decrease despair symptoms in major depressive disorder. ConclusionsThis study introduced a hitherto undocumented comprehensive screening strategy to identify TDO inhibitors in PaeR extract. Our findings also highlighted the potential of PaeR as a source of antidepressant constituents and pinpointed the inhibition of TDO as a promising therapeutic approach for managing major depressive disorder.

Effect of soluble factors of macrophages polarized by efferocytosis on neuronal density in the frontal cortex and hippocampus of mice in a model of stress-induced depression

Recently, there has been a steady increase in depressive disorders, which occupy an important place in the structure of the causes of disability. In the pathogenesis of depression, an important role is played by neuroinflammation, which is associated with impaired adult neurogenesis. Notably, neuroinflammation is partially reversible, and the leading role in the initiation and regulation of neuroregeneration is given to macrophages. Opposite states of macrophage activation are classically activated M1 and alternatively activated M2 macrophages, characterized, respectively, by pro- and anti-inflammatory activity. A balance shift towards M2 macrophages has been considered as a new therapeutic strategy of psycho-neurological disorders. One of the inducers of the M2 phenotype is the efferocytosis. We have previously developed an original protocol for the generation of human macrophages under conditions of deficiency of growth / serum factors, in which M2 phenotype is formed through efferocytosis. Macrophages (M2(LS), LS – Low Serum) obtained according to this protocol express M2-associated markers, and are characterized by high production of growth and pro- angiogenic factors (IGF-1, VEGF, BDNF, EGF, FGF-basic, etc.), which can suppress inflammation and stimulate neuroregeneration / neuroplasticity. In the model of stress-induced depression, the antidepressant effect of soluble factors of M2(LS) macrophages was shown, accompanied by a decrease in the level of pro- inflammatory cytokines in certain brain structures. However, the effect of M2(LS) factors on neurogenesis remained unexplored. In the present work, which is a continuation of the aforementioned study, we analyzed the effect of intranasal administration of M2(LS) soluble factors on neuronal density in different brain areas – the frontal cortex and hippocampus – of depression-like mice. The results obtained showed that neuronal density in the frontal cortex, CA1 and CA3 zones of the hippocampus, was significantly higher in mice with intranasal administration of M2(LS) conditioned medium than in depression-like mice, and reached the level of neuronal density in intact animals. These results may indicate the neuroregenerative activity of M2(LS) macrophages in the model of stress-induced depression, which is mediated through soluble factors and manifests itself in an increase in the density of neurons in the brain.

Loganin improves chronic unpredictable mild stress-induced depressive-like behaviors and neurochemical dysfunction.

Cornus officinalis Sieb. et Zucc., is a valuable herb commonly used in Chinese medicine clinics. Loganin is a major iridoid glycoside obtained from the traditional Chinese herb Corni Fructus. Loganin, which has been shown to improve depression-like behavior in mice exposed to acute stress, is probably a potential antidepressant candidate. Loganin was evaluated for its effect on chronic unpredictable mild stress (CUMS) induced depressive-like mice, and its action mechanisms were explored. ICR mice were subjected to the CUMS stimulation method to induce depression. The therapeutic effect of loganin on depressive-like behavior was evaluated by a series of behavioral tests such as sucrose preference test (SPT), forced swim test (FST), tail suspension test (TST) and open-field test (OFT). In addition, the serum levels of adrenocorticotropic hormone (ACTH) and corticosterone (CORT) were measured using ELISA. The levels of monoamine neurotransmitters were detected by high performance liquid chromatography-electrochemical detection (HPLC-ECD). The levels of brain-derived neurotrophic factor (BDNF) in the hippocampus were measured using western blot analysis. The results showed that CUMS induced depressive-like behaviors in mice, as indicated by behavioral tests. Administration of loganin increased the sucrose preference in SPT, as well as decreased the immobility time in FST and TST. Loganin could also improve food intake, and increased crossing times in the OFT. In mechanism, loganin restored the secretion of monoamine neurotransmitters, ACTH and CORT to normal levels. In addition, loganin elevated the expression of BDNF in the hippocampus. In conclusion, loganin exerts antidepressant-like effects in CUMS model mice through modulating monoamine neurotransmitters, ACTH, CORT and BDNF. Loganin effectively ameliorated depressive-like symptoms in CUMS-exposed mice by increasing 5-hydroxytryptamine (5-HT) and dopamine (DA) levels, alleviating hypothalamic-pituitary-adrenal (HPA) axis dysfunction, and increasing BDNF expression. In conclusion, the findings of the current study extensive evidence for the application of loganin in stress-associated disorders, specifically targeting depression.