Antidepressant-Like Activity of Myelophil via Attenuation of Microglial-Mediated Neuroinflammation in Mice Undergoing Unpredictable Chronic Mild Stress

Evaluating myelophil, a 30% ethanol extract of Astragalus membranaceus and Salvia miltiorrhiza, for alleviating fatigue in long COVID: a real-world observational study

Background

Persistent post-infectious symptoms, predominantly fatigue, characterize Long COVID. This study investigated the efficacy of Myelophil (MYP), which contains metabolites extracted from Astragalus membranaceus and Salvia miltiorrhiza using 30% ethanol, in alleviating fatigue among subjects with Long COVID.

Methods

In this prospective observational study, we enrolled subjects with significant fatigue related to Long COVID, using criteria of scores of 60 or higher on the modified Korean Chalder Fatigue scale (mKCFQ11), or five or higher on the Visual Analog Scale (VAS) for brain fog. Utilizing a single-arm design, participants were orally administered MYP (2,000 mg daily) for 4 weeks. Changes in fatigue severity were assessed using mKCFQ11, Multidimensional Fatigue Inventory (MFI-20), and VAS for fatigue and brain fog. In addition, changes in quality of life using the short form 12 (SF-12) were also assessed along with plasma cortisol levels.

Results

A total of 50 participants (18 males, 32 females) were enrolled; 49 were included in the intention-to-treat analysis with scores of 66.9 ± 11.7 on mKCFQ11 and 6.3 ± 1.5 on the brain fog VAS. After 4 weeks of MYP administration, there were statistically significant improvements in fatigue levels: mKCFQ11 was measured at 34.8 ± 17.1 and brain fog VAS at 3.0 ± 1.9. Additionally, MFI-20 decreased from 64.8 ± 9.8 to 49.3 ± 10.8, fatigue VAS dropped from 7.4 ± 1.0 to 3.4 ± 1.7, SF-12 scores rose from 53.3 ± 14.9 to 78.6 ± 14.3, and plasma cortisol levels also elevated from 138.8 ± 50.1 to 176.9 ± 62.0 /mL. No safety concerns emerged during the trial.

Conclusion

Current findings underline MYP's potential in managing Long COVID-induced fatigue. However, comprehensive studies remain imperative.

Clinical Trial Registration

https://cris.nih.go.kr, identifier KCT0008948.

PINK1 deficiency with Ca2+ changes in the hippocampus exacerbates septic encephalopathy in mice

PTEN-induced putative kinase 1 (PINK1) is a mitochondrial kinase that protects against oxidative stress-induced cellular death. PINK1 deletion, on the other hand, disrupts mitochondrial calcium (Ca²⁺) homeostasis in various brain disorders. This study looked at how PINK1 affects hippocampal intracellular Ca²⁺ changes in mice with septic encephalopathy. Mice were injected intraperitoneally with lipopolysaccharide (LPS, 5 mg/kg) to induce septic encephalopathy; then, fiber photometry was used to record hippocampal Ca²⁺ transients during behavioral tests in freely moving mice. Basal cytoplasmic Ca²⁺ levels were detected under a fluorescent microscope. LPS induced PINK1 expression and neuronal loss in the hippocampus of mice, whereas no difference in neuronal counts was shown between PINK1 knockout LPS mice and WT LPS mice. PINK1 deficiency led to inhibited Ca²⁺ transients and increased intracellular Ca²⁺ levels in the hippocampus of mice, thus, significantly aggravating the cognitive dysfunction in septic mice. An analysis of Parkin and PLC-γ1, downstream effectors of PINK1, showed that they are associated with the effects of PINK1. These results demonstrate that PINK1 deficiency disrupts intracellular Ca²⁺ homeostasis and exacerbates septic encephalopathy. This observation suggests a protective role of PINK1 in septic encephalopathy.

Animal Inflammation-Based Models of Neuropsychiatric Disorders

Mounting evidence links psychiatric disorders to central and systemic inflammation. Experimental (animal) models of psychiatric disorders are important tools for translational biopsychiatry research and CNS drug discovery. Current experimental models, most typically involving rodents, continue to reveal shared fundamental pathological pathways and biomarkers underlying the pathogenetic link between brain illnesses and neuroinflammation. Recent data also show that various proinflammatory factors can alter brain neurochemistry, modulating the levels of neurohormones and neurotrophins in neurons and microglia. The role of "active" glia in releasing a wide range of proinflammatory cytokines also implicates glial cells in various psychiatric disorders. Here, we discuss recent animal inflammation-related models of psychiatric disorders, focusing on their translational perspectives and the use of some novel promising model organisms (zebrafish), to better understand the evolutionally conservative role of inflammation in neuropsychiatric conditions.

Enriched Environment Attenuates Enhanced Trait Anxiety in Association with Normalization of Aberrant Neuro-Inflammatory Events

Neuroinflammation is discussed to play a role in specific subgroups of different psychiatric disorders, including anxiety disorders. We have previously shown that a mouse model of trait anxiety (HAB) displays enhanced microglial density and phagocytic activity in key regions of anxiety circuits compared to normal-anxiety controls (NAB). Using minocycline, we provided causal evidence that reducing microglial activation within the dentate gyrus (DG) attenuated enhanced anxiety in HABs. Besides pharmacological intervention, "positive environmental stimuli", which have the advantage of exerting no side-effects, have been shown to modulate inflammation-related markers in human beings. Therefore, we now investigated whether environmental enrichment (EE) would be sufficient to modulate upregulated neuroinflammation in high-anxiety HABs. We show for the first time that EE can indeed attenuate enhanced trait anxiety, even when presented as late as adulthood. We further found that EE-induced anxiolysis was associated with the attenuation of enhanced microglial density (using Iba-1 as the marker) in the DG and medial prefrontal cortex. Additionally, EE reduced Iba1 + CD68+ microglia density within the anterior DG. Hence, the successful attenuation of trait anxiety by EE was associated in part with the normalization of neuro-inflammatory imbalances. These results suggest that pharmacological and/or positive behavioral therapies triggering microglia-targeted anti-inflammatory effects could be promising as novel alternatives or complimentary anxiolytic therapeutic approaches in specific subgroups of individuals predisposed to trait anxiety.

Microglia in depression: an overview of microglia in the pathogenesis and treatment of depression

Major depressive disorder is a highly debilitating psychiatric disorder involving the dysfunction of different cell types in the brain. Microglia are the predominant resident immune cells in the brain and exhibit a critical role in depression. Recent studies have suggested that depression can be regarded as a microglial disease. Microglia regulate inflammation, synaptic plasticity, and the formation of neural networks, all of which affect depression. In this review, we highlighted the role of microglia in the pathology of depression. First, we described microglial activation in animal models and clinically depressed patients. Second, we emphasized the possible mechanisms by which microglia recognize depression-associated stress and regulate conditions. Third, we described how antidepressants (clinical medicines and natural products) affect microglial activation. Thus, this review aimed to objectively analyze the role of microglia in depression and focus on potential antidepressants. These data suggested that regulation of microglial actions might be a novel therapeutic strategy to counteract the adverse effects of devastating mental disorders.

Therapeutic effect of Thymoquinone on behavioural response to UCMS and neuroinflammation in hippocampus and amygdala in BALB/c mice model

RATIONALE

Major depressive disorder is the leading cause of disability worldwide. The corticolimbic system plays a critical role in the emotional and cognitive aspects of major depressive disorder. Owing to the unsatisfactory efficacy of conventional antidepressants, there is a need to explore novel therapies.

OBJECTIVES

The current study aimed to explore the antidepressant potential of thymoquinone, a natural compound with anti-inflammatory activity, and propose its underlying mechanism of action in the unpredictable chronic mild stress (UCMS) mouse model.

METHODS

Coat state, forced swim test, elevated plus maze test, novelty suppressed feeding test and social interaction test were performed to quantify the behavioural shift induced by UCMS and the effect of thymoquinone and fluoxetine treatment. In addition, messenger RNA (mRNA) expression levels of inflammatory cytokines (IL-1β, IL-6 and TNF-α) and BDNF and NeuN were analysed by a quantitative real-time polymerase chain reaction in the hippocampus and amygdala of experimental and control groups.

RESULTS

UCMS significantly deteriorated coat state. Thymoquinone reinstated the resignation behaviour and latency to feed affected by UCMS. UCMS induced an increase in inflammatory cytokines (IL-1β, IL-6 and TNF-α) in the hippocampus and amygdala, which was decreased by thymoquinone. UCMS caused an increase in BDNF and NeuN mRNA levels in the amygdala while a decrease in the hippocampus. This opposite effect on BDNF was also compensated by thymoquinone; however, thymoquinone did not significantly change Ki67 and NeuN mRNA levels in the hippocampus.

CONCLUSIONS

Thymoquinone restored the behavioural changes induced by UCMS. In addition, the antidepressant effect of thymoquinone is in line with changes in inflammatory parameters and changes in BDNF in the hippocampus and amygdala.

Screening of potential biomarkers in peripheral blood of patients with depression based on weighted gene co-expression network analysis and machine learning algorithms

BACKGROUND

The prevalence of depression has been increasing worldwide in recent years, posing a heavy burden on patients and society. However, the diagnostic and therapeutic tools available for this disease are inadequate. Therefore, this research focused on the identification of potential biomarkers in the peripheral blood of patients with depression.

METHODS

The expression dataset GSE98793 of depression was provided by the Gene Expression Omnibus (GEO) (https://www.ncbi.nlm.nih.gov/gds). Initially, differentially expressed genes (DEGs) were detected in GSE98793. Subsequently, the most relevant modules for depression were screened according to weighted gene co-expression network analysis (WGCNA). Finally, the identified DEGs were mapped to the WGCNA module genes to obtain the intersection genes. In addition, Gene Ontology (GO), Disease Ontology (DO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment analyses were conducted on these genes. Moreover, biomarker screening was carried out by protein-protein interaction (PPI) network construction of intersection genes on the basis of various machine learning algorithms. Furthermore, the gene set enrichment analysis (GSEA), immune function analysis, transcription factor (TF) analysis, and the prediction of the regulatory mechanism were collectively performed on the identified biomarkers. In addition, we also estimated the clinical diagnostic ability of the obtained biomarkers, and performed Mfuzz expression pattern clustering and functional enrichment of the most potential biomarkers to explore their regulatory mechanisms. Finally, we also perform biomarker-related drug prediction.

RESULTS

Differential analysis was used for obtaining a total of 550 DEGs and WGCNA for obtaining 1,194 significant genes. Intersection analysis of the two yielded 140 intersection genes. Biological functional analysis indicated that these genes had a major role in inflammation-related bacterial infection pathways and cardiovascular diseases such as atherosclerosis. Subsequently, the genes S100A12, SERPINB2, TIGIT, GRB10, and LHFPL2 in peripheral serum were identified as depression biomarkers by using machine learning algorithms. Among them, S100A12 is the most valuable biomarker for clinical diagnosis. Finally, antidepressants, including disodium selenite and eplerenone, were predicted.

CONCLUSION

The genes S100A12, TIGIT, SERPINB2, GRB10, and LHFPL2 in peripheral serum are viable diagnostic biomarkers for depression. and contribute to the diagnosis and prevention of depression in clinical practice.

Merging the Multi-Target Effects of Kleeb Bua Daeng, a Thai Traditional Herbal Formula in Unpredictable Chronic Mild Stress-Induced Depression

Major depressive disorder (MDD) is a common and debilitating psychiatric disease characterized by persistent low mood, lack of energy, hypoactivity, anhedonia, decreased libido, and impaired cognitive and social functions. However, the multifactorial etiology of MDD remains largely unknown due the complex interaction between genetics and environment involved. Kleeb Bua Daeng (KBD) is a Thai traditional herbal formula that has been used to promote brain health. It consists of a 1:1:1 ratio of the aerial part of Centella asiatica, Piper nigrum fruit, and the petals of Nelumbo nucifera. According to the pharmacological activities of the individual medicinal plants, KBD has good potential as a treatment for MDD. The present study investigated the antidepressant activity of KBD in an unpredictable chronic mild stress (UCMS) mouse model. Daily administration of KBD to UCMS mice ameliorated both anhedonia, by increasing 2% sucrose intake, and hopeless behavior, by reducing immobility times in the forced swimming test (FST) and tail suspension test (TST) without any effect on locomotor activity. The mechanism of KBD activity was multi-modal. KBD promoted neurogenesis by upregulation of brain-derived neurotrophic factor (BDNF) and cyclic AMP-responsive element binding (CREB) mRNA expression in the frontal cortex and hippocampus. Daily treatment with KBD significantly reversed UCMS-induced HPA axis dysregulation by upregulating the glucocorticoid receptor (GR) while downregulating serum- and glucocorticoid-inducible kinase 1 (SGK1) and FK506 binding protein 5 (FKBP5) mRNA expression. KBD treatment also normalized proinflammatory cytokine expression including tumor necrosis factor-alpha (TNF-α), and interleukin (IL)-1β and IL-6. KBD and its component extracts also exhibited an inhibitory effect in vitro on monoamine oxidase (MAO) A and B. The multiple antidepressant actions of KBD emphasize its potential as an effective, novel treatment for MDD.

Do changes in microglial status underlie neurogenesis impairments and depressive-like behaviours induced by psychological stress? A systematic review in animal models

Stress may have a negative effect on mental health and is the primary environmental risk factor in the aetiology of depression. Nevertheless, the neurobiological mechanisms underlying this mood disorder remain poorly characterized. The hippocampus is a target structure of the adverse effects of stress, and hippocampal neurogenesis plays a crucial role. However, we do not know the mechanisms by which stress impacts neurogenesis. Recent studies indicate that changes in neuroinflammation, primarily via microglial cells, may play an essential role in this process. However, the relationship between stress, microglial changes, and alterations in neurogenesis and their involvement in the development of depression is poorly characterized. For this reason, this systematic review aims to synthesise and evaluate current studies that have investigated the relationship between these variables. Taken together, the revised data, although not entirely conclusive, seem to suggest that microglial changes induced by psychological stress regulate neurogenesis and in turn may be responsible for the development of depressive-like behaviours, but other factors that influence these stressful experiences should not be dismissed.

High Fructose Corn Syrup-Moderate Fat Diet Potentiates Anxio-Depressive Behavior and Alters Ventral Striatal Neuronal Signaling

The neurobiological mechanisms that mediate psychiatric comorbidities associated with metabolic disorders such as obesity, metabolic syndrome and diabetes remain obscure. High fructose corn syrup (HFCS) is widely used in beverages and is often included in food products with moderate or high fat content that have been linked to many serious health issues including diabetes and obesity. However, the impact of such foods on the brain has not been fully characterized. Here, we evaluated the effects of long-term consumption of a HFCS-Moderate Fat diet (HFCS-MFD) on behavior, neuronal signal transduction, gut microbiota, and serum metabolomic profile in mice to better understand how its consumption and resulting obesity and metabolic alterations relate to behavioral dysfunction. Mice fed HFCS-MFD for 16 weeks displayed enhanced anxiogenesis, increased behavioral despair, and impaired social interactions. Furthermore, the HFCS-MFD induced gut microbiota dysbiosis and lowered serum levels of serotonin and its tryptophan-based precursors. Importantly, the HFCS-MFD altered neuronal signaling in the ventral striatum including reduced inhibitory phosphorylation of glycogen synthase kinase 3β (GSK3β), increased expression of ΔFosB, increased Cdk5-dependent phosphorylation of DARPP-32, and reduced PKA-dependent phosphorylation of the GluR1 subunit of the AMPA receptor. These findings suggest that HFCS-MFD-induced changes in the gut microbiota and neuroactive metabolites may contribute to maladaptive alterations in ventral striatal function that underlie neurobehavioral impairment. While future studies are essential to further evaluate the interplay between these factors in obesity and metabolic syndrome-associated behavioral comorbidities, these data underscore the important role of peripheral-CNS interactions in diet-induced behavioral and brain function. This study also highlights the clinical need to address neurobehavioral comorbidities associated with obesity and metabolic syndrome.

Jianpi Jieyu Decoction, An Empirical Herbal Formula, Exerts Psychotropic Effects in Association With Modulation of Gut Microbial Diversity and GABA Activity

Background: Recent studies suggest that gut microbiota was associated with the bidirectional gut-brain axis which could modulate neuropsychological functions of the central nervous system. Gut microbiota could produce gamma aminobutyric acid (GABA) that could modulate the gut-brain axis response. Jianpi Jieyu (JPJY) decoction, a traditional Chinese formula, is mainly composed of Astragalus membranaxeus and Radix Pseudostellariae. Although the JPJY decoction has been used to treat the depression in China, the potential action of its antidepressant has not been well understood. Thus this study was aim to investigate the role of JPJY improve gut microbiota homeostasis in the chronic stress induced depressive mice. Methods: The antidepressant effect of JPJY on chronic unpredictable mild stress (CUMS) mice was evaluated by using sucrose preference test, tail suspension test and forced swim test. Fatigue-like behaviors were evaluated using degree of redness, grip strength test, and exhaustive swimming test. The new object recognition test was used to evaluate cognition performance. Fecal samples were collected and taxonomical analysis of intestinal microbial distribution was conducted with 16S rDNA. Serum level of GABA was measured using high performance liquid chromatography (HPLC). The expression of GluR1 and p-Tau protein in the hippocampus was determined using Western blotting. Results: The dose of 9.2 g/kg JPJY produced antidepressant-like effects. JPJY and its major components also modulated gut microbiota diversity in the CUMS mice. Serum level of GABA and the expressions of hippocampal GluR1 and p-Tau were reversed after the administration of JPJY in CUMS mice. Conclusion: JPJY regulates gut microbiota to produce antidepressant-like effect and improve cognition deficit in depressive mice while its molecular mechanism possibly be enhanced NR1 and Tau expression in hippocampus and increased GABA in serum.

Isoliquiritin ameliorates depression by suppressing NLRP3-mediated pyroptosis via miRNA-27a/SYK/NF-κB axis

Background

The NLRP3-mediated pyroptosis, which could be regulated by miRNA-27a, is a key player in the development of depression. Isoliquiritin is a phenolic flavonoid compound that has been demonstrated to suppress NLRP3-mediated pyroptosis. However, it is still unknown whether isoliquiritin could confer antidepressant activity via decreasing NLRP3-mediated pyroptosis by stimulating miRNA-27a. Thus, in the current study, we explored the antidepressant activity of isoliquiritin and its underlying mechanism.

Methods

Expression of miRNA-27a in depressed patients or mice was measured using qRT-PCR. Luciferase reporter assay was performed to illustrate the link between miRNA-27a and SYK. Lipopolysaccharide (LPS) and chronic social defeat stress (CSDS) depression models were established to investigate the antidepressant actions of isoliquiritin. Changes in miRNA-27a/SYK/NF-κB axis and NLRP3-mediated pyroptosis were also examined. The role of miRNA-27a in isoliquiritin-related antidepressant effect was further investigated by using miRNA-27a inhibitors and mimics of miRNA-27a.

Results

Our results showed the miRNA-27a expression was downregulated in the serum of depressed patients, and decreased serum and hippocampus expression of miRNA-27a were observed in rodent models of depression. SYK gene expression was significantly reduced by miRNA-27a mimic incubation. Isoliquiritin profoundly attenuated LPS or CSDS-induced depressive symptoms, as well as CSDS-induced anxiety behavior. In the hippocampus, LPS and CSDS decreased miRNA-27a mRNA expression; increased the protein levels of SYK, p-NF-κB, and NLRP3: cleaved Caspase-1, IL-1β, and GSDMD-N: and elevated the concentration of IL-1β, IL-6, and TNF-α, which were all restored by isoliquiritin administration. Meanwhile, isoliquiritin upregulated the hippocampal NeuN protein level, improved the survival and morphology of neurons, and decreased pyroptosis-related neuronal cell death. Moreover, isoliquiritin protected primary microglia against LPS and adenosine triphosphate (ATP) elicited NLRP3 inflammasome activation in vitro, evidenced by declined protein levels of p-NF-κB, NLRP3; cleaved Caspase-1, IL-1β, and GSDMD-N; upregulated miRNA-27a mRNA expression; and decreased the mRNA and protein levels of SYK. Nevertheless, miRNA-27a inhibitors significantly reversed isoliquiritin-generated therapeutic efficacy in CSDS mice and in vitro. Furthermore, the cytoprotective effect of isoliquiritin was similar to that of miRNA-27a mimics in LPS and ATP-treated primary microglia.

Taken together, these findings suggest that isoliquiritin possesses potent antidepressant property, which requires miRNA-27a/SYK/NF-κB axis controlled decrease of pyroptosis via NLRP3 cascade.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-020-02040-8.

Neuroinflammatory alterations in trait anxiety: modulatory effects of minocycline

High trait anxiety is a substantial risk factor for developing anxiety disorders and depression. While neuroinflammation has been identified to contribute to stress-induced anxiety, little is known about potential dysregulation in the neuroinflammatory system of genetically determined pathological anxiety or high trait anxiety individuals. We report microglial alterations in various brain regions in a mouse model of high trait anxiety (HAB). In particular, the dentate gyrus (DG) of the hippocampus of HABs exhibited enhanced density and average cell area of Iba1+, and density of phagocytic (CD68+/Iba1+) microglia compared to normal anxiety (NAB) controls. Minocycline was used to assess the capacity of a putative microglia 'inhibitor' in modulating hyperanxiety behavior of HABs. Chronic oral minocycline indeed reduced HAB hyperanxiety, which was associated with significant decreases in Iba1+ and CD68+Iba1+ cell densities in the DG. Addressing causality, it was demonstrated that longer (10 days), but not shorter (5 days), periods of minocycline microinfusions locally into the DG of HAB reduced Iba-1+ cell density and attenuated hyperanxiety-related behavior, indicating that neuroinflammation in the DG is at least partially involved in the maintenance of pathological anxiety. The present data reveal evidence of disturbances in the microglial system of individuals with high trait anxiety. Minocycline attenuated HAB hyperanxiety, likely by modulation of microglial activity within the DG. Thus, the present data suggest that drugs with microglia-targeted anti-inflammatory properties could be promising as novel alternative or complimentary anxiolytic therapeutic approaches in specific subgroups of individuals genetically predisposed to hyperanxiety.

Ketamine contributes to the alteration of Ca2+ transient evoked by behavioral tests in the prelimbic area of mPFC: A study on chronic CORT-induced depressive mice

Recent studies have showed that ketamine is a rapid and efficient antidepressant, but the mechanism of its antidepressant effect is not fully clear. It is still lack of the research investigating the relation between depressive-like behaviors and neuronal activities in specific brain area after administration of ketamine in vivo. Medial prefrontal cortex (mPFC) involved in the pathogenesis of depression. As a result of effective assessments after behavioral test, most studies lack of direct evidence of the relation between efficacy and the activity of specific brain area. Therefore, we used fiber photometry to explore the alteration of Ca²⁺ transient in the prelimbic (PrL) area of mPFC during behavioral tests in freely moving mice. Our results showed that the chronic corticosterone (CORT) protocol induced depressive-like behaviors. Administration of ketamine reversed these effects. The activation of Ca²⁺ transients was associated with some behaviors during behavioral tests. Struggling, rearing and exploring evoked strong Ca²⁺ transients, but moving and grooming did not. The Ca²⁺ transients amplitude reductions of struggling, rearing and exploring induced by CORT were reversed by ketamine. The results indicated that ketamine ameliorated depressive-like behaviors via mediating neural activation in PrL.

FGF21 Attenuated LPS-Induced Depressive-Like Behavior via Inhibiting the Inflammatory Pathway

Major depressive disorder is a serious neuropsychiatric disorder with high rates of recurrence and mortality. Many studies have supported that inflammatory processes play a central role in the etiology of depression. Fibroblast growth factor 21 (FGF21), a member of the fibroblast growth factors (FGFs) family, regulates a variety of pharmacological activities, including energy metabolism, glucose and lipid metabolism, and insulin sensitivity. In addition, recent studies showed that the administration of FGF21, a regulator of metabolic function, had therapeutic effects on mood stabilizers, indicating that FGF21 could be a common regulator of the mood response. However, few studies have highlighted the antidepressant effects of FGF21 on lipopolysaccharide (LPS)-induced mice, and the anti-inflammatory mechanism of FGF21 in depression has not yet been elucidated. The purpose of the current study was to determine the antidepressant effects of recombinant human FGF21 (rhFGF21). The effects of rhFGF21 on depression-like behaviors and the inflammatory signaling pathway were investigated in both an LPS-induced mouse model and primary microglia in vitro. The current study demonstrated that LPS induced depressive-like behaviors, upregulated proinflammatory cytokines, and activated microglia in the mouse hippocampus and activated the inflammatory response in primary microglia, while pretreatment with rhFGF21 markedly improved depression-like behavior deficits, as shown by an increase in the total distance traveled and number of standing numbers in the open field test (OFT) and a decrease in the duration of immobility in the tail suspension test (TST) and forced swimming test (FST). Furthermore, rhFGF21 obviously suppressed expression levels of the proinflammatory cytokines interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) and inhibited microglial activation and the nuclear factor-κB (NF-κB) signing pathway. Moreover, coadministration of rhFGF21 with the fibroblast growth factor receptor 1 (FGFR1) inhibitor PD173074 significantly reversed these protective effects, indicating that the antidepressant effects of rhFGF21 occur through FGFR1 activation. Taken together, the results of the current study demonstrated for the first time that exogenous rhFGF21 ameliorated LPS-induced depressive-like behavior by inhibiting microglial expression of proinflammatory cytokines through NF-κB suppression. This new discovery suggests rhFGF21 as a new therapeutic candidate for depression treatment.