Insulin-like growth factor 2 mitigates depressive behavior in a rat model of chronic stress

Neuroprotective Role of Selenium Nanoparticles Against Behavioral, Neurobiochemical and Histological Alterations in Rats Subjected to Chronic Restraint Stress

Chronic stress induces changes in the prefrontal cortex and hippocampus. Selenium nanoparticles (SeNPs) showed promising results in several neurological animal models. The implementation of SeNPs in chronic restraint stress (CRS) remains to be elucidated. This study was done to determine the possible protective effects of selenium nanoparticles on behavioral changes and brain oxidative stress markers in a rat model of CRS. 50 rats were divided into three groups; control group (n = 10), untreated CRS group (n = 10) and CRS-SeNPs treated group (n = 30). Restraint stress was performed 6 h./day for 21 days. Rats of CRS-SeNPs treated group received 1, 2.5 or 5 mg/kg SeNPs (10 rats each) by oral gavage for 21 days. Rats were subjected to behavioral assessments and then sacrificed for biochemical and histological analysis of the prefrontal cortex and hippocampus. Prefrontal cortical and hippocampal serotonin levels, oxidative stress markers including malondialdehyde (MDA), reduced glutathione (GSH) and glutathione peroxidase (GPx), tumor necrosis factor alpha (TNF-α) and caspase-3 were assessed. Accordingly, different doses of SeNPs showed variable effectiveness in ameliorating disease parameters, with 2.5 mg/kg dose of SeNPs showing the best improving results in all studied parameters. The present study exhibited the neuroprotective role of SeNPs in rats subjected to CRS and proposed their antioxidant, anti-inflammatory and anti-apoptotic effects as the possible mechanism for increased prefrontal cortical and hippocampal serotonin level, ameliorated anxiety-like and depressive-like behaviors and improved prefrontal cortical and hippocampal histological architecture.

Plasma IGFBP-3 and IGFBP-5 levels are decreased during acute manic episodes in bipolar disorder patients

Introduction: Bipolar disorder (BD) is a recurrent and disabling psychiatric disorder related to low-grade peripheral inflammation and altered levels of the members of the insulin-like growth factor (IGF) family. The aim of this study was to evaluate the plasma levels of IGF-2, insulin-like growth factor-binding protein 1 (IGFBP-1), IGFBP-3, IGFBP-5, IGFBP-7, and inflammatory markers such as tumor necrosis factor α (TNF-α), monocyte chemoattractant protein 1 (MCP-1), and macrophage inflammatory protein 1β (MIP-1β). Methods: We used the Young Mania Rating Scale (YMRS) to determine the severity of the symptomatology, while proteins were measured by enzyme-linked immunosorbent assay (ELISA). We included 20 patients with BD who suffered a manic episode and 20 controls. Some BD patients (n = 10) were evaluated after a period (17 ± 8 days) of pharmacological treatment. Results: No statistical difference was found in IGF-2, IGFBP-1, IGFBP-7, TNF-α, and MIP-1β levels. However, IGFBP-3 and IGFBP-5 levels were found to be statistically decreased in BD patients. Conversely, the MCP-1 level was significantly increased in BD patients, but their levels were normalized after treatment. Intriguingly, only IGFBP-1 levels were significantly decreased after treatment. No significant correlation was found between the YMRS and any of the proteins studied either before or after treatment or between IGF proteins and inflammatory markers. Discussion: To some extent, IGFBP-3 and IGFBP-5 might be further explored as potential indicators of treatment responsiveness or diagnosis biomarkers in BD.

Lower serum insulin-like growth factor 2 level in patients with bipolar disorder is associated with the severity of manic symptoms during manic episodes

Objective

Accumulating evidence has indicated that neurodevelopmental defects may underlie the pathophysiology of bipolar disorder (BD). Insulin-like growth factors (IGFs) are a family of neurotrophic factors that are essential for the survival and development of neurons. The present study aims to investigate whether IGF-2 signaling is implicated in the pathophysiological processes of BD.

Method

50 healthy controls and 78 patients with BD, including 23 patients who diagnosed acute depressive episode and 55 patients who diagnosed acute manic episode, were recruited in this study. The 17-item Hamilton Depression Rating Scale (HAMD-17) and the Young Mania Rating Scale (YMRS) were used to assess the severity of the depressive and manic symptoms, respectively. The serum IGF-2 level was determined by an enzyme-linked immunosorbent assay (ELISA). The Kolmogorov-Smirnov and Mann-Whitney U tests were used for between-group comparisons and spearman analysis was used to analyze correlations.

Results

Patients with BD had lower serum IGF-2 levels (66.08 ± 21.22 ng/ml) when compared to healthy controls (88.72 ± 31.55 ng/ml). BD patients were divided into manic episode and depressive episode subgroups. We found that serum IGF-2 levels were reduced in both the mania and depression subgroups (mania: 67.19 ± 21.52 ng/ml, depression: 63.43 ± 20.67 ng/ml; P < 0.001), while no significant difference was observed between two groups (P > 0.05). Spearman correlation analyses revealed that the levels of serum IGF-2 were negatively correlated with the YMRS scores in BD patients (r = -0.522, P < 0.001). Furthermore, IGF-2 was found to be an independent contributor to the severity of symptoms in patients with manic episodes (B = -0.610, t = -5.299, P < 0.001).

Conclusion

Lower serum IGF-2 levels were found in BD patients and correlated with the severity of the manic symptoms in these patients during manic episodes. These results suggest that reduced IGF-2 levels might be involved in the pathophysiology of BD, and serum IGF-2 could be a peripheral biomarker for the evaluation of the severity of manic symptoms in BD patients.

Protein Plasma Levels of the IGF Signalling System Are Altered in Major Depressive Disorder

The Insulin-like growth factor 2 (IGF-2) has been recently proven to alleviate depressive-like behaviors in both rats and mice models. However, its potential role as a peripheral biomarker has not been evaluated in depression. To do this, we measured plasma IGF-2 and other members of the IGF family such as Binding Proteins (IGFBP-1, IGFBP-3, IGFBP-5 and IGFBP-7) in a depressed group of patients (n = 51) and in a healthy control group (n = 48). In some of these patients (n = 15), we measured these proteins after a period (19 ± 6 days) of treatment with antidepressants. The Hamilton Depressive Rating Scale (HDRS) and the Self-Assessment Anhedonia Scale (SAAS) were used to measure depression severity and anhedonia, respectively. The general cognition state was assessed by the Mini-Mental State Examination (MMSE) test and memory with the Free and Cued Selective Reminding Test (FCSRT). The levels of both IGF-2 and IGFBP-7 were found to be significantly increased in the depressed group; however, only IGF-2 remained significantly elevated after correction by age and sex. On the other hand, the levels of IGF-2, IGFBP-3 and IGFBP-5 were significantly decreased after treatment, whereas only IGFBP-7 was significantly increased. Therefore, peripheral changes in the IGF family and their response to antidepressants might represent alterations at the brain level in depression.

IGF2 inhibits hippocampal over-activated microglia and alleviates depression-like behavior in LPS- treated male mice

Over-activated microglia and inflammatory mediators are found in patients with depression, while manipulation of the microglia function might represent a potential therapeutic strategy. Insulin-like growth factor 2 (IGF2) has been implicated in bacterial infections and autoimmune disorders, but the role of IGF2 on the active phenotype of microglia and neuroinflammation has not been well established. IGF2 influences in modulating microglia responding to neuroinflammation induced by lipopolysaccharide（LPS）challenge will be carefully examined. In the current study, we verified that systemic IGF2 treatment could produce an anti-depression effect in LPS-treated mice. Particularly, we found that systemic IGF2 treatment inhibited microglia over-activation and prevented its transformation to a pro-inflammatory phenotype, thereby protecting hippocampal neurogenesis. Since microglia reactive to neuroinflammation is a common feature of neuropsychiatric disorders, the discoveries from the present study may provide therapeutic innovation for these diseases.

Electroconvulsive Stimulation in Rats Induces Alterations in the Hippocampal miRNome: Translational Implications for Depression

MicroRNAs (miRNAs) may contribute to the development of depression and its treatment. Here, we used the hypothesis-neutral approach of next-generation sequencing (NGS) to gain comprehensive understanding of the effects of a course of electroconvulsive stimulation (ECS), the animal model equivalent of electroconvulsive therapy (ECT), on rat hippocampal miRNAs. Significant differential expression (p < 0.001) of six hippocampal miRNAs was noted following NGS, after correcting for multiple comparisons. Three of these miRNAs were upregulated (miR-132, miR-212, miR-331) and three downregulated (miR-204, miR-483, miR-301a). qRT-PCR confirmed significant changes in four of the six miRNAs (miR-132, miR-212, miR-204, miR-483). miR-483 was also significantly reduced in frontal cortex, though no other significant alterations were noted in frontal cortex, cerebellum, or whole blood. Assessing the translatability of the results, miR-132 and miR-483 were significantly reduced in whole blood samples from medicated patients with depression (n = 50) compared to healthy controls (n = 45), though ECT had no impact on miRNA levels. Notably, pre-ECT miR-204 levels moderately positively correlated with depression severity at baseline and moderately negatively correlated with mood score reduction post-ECT. miRNAs were also examined in cerebrospinal fluid and serum from a separate cohort of patients (n = 8) treated with ECT; no significant changes were noted post-treatment. However, there was a large positive correlation between changes in miR-212 and mood score post-ECT in serum. Though replication studies using larger sample sizes are required, alterations in miRNA expression may be informative about the mechanism of action of ECS/ECT and in turn might give insight into the neurobiology of depression.

Role of neurotrophic and growth factors in the rapid and sustained antidepressant actions of ketamine

The neurotrophic hypothesis of depression proposes that reduced levels of brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) contribute to neuronal atrophy or loss in the prefrontal cortex (PFC) and hippocampus and impaired hippocampal adult neurogenesis, which are associated with depressive symptoms. Chronic, but acute, treatment with typical monoaminergic antidepressants can at least partially reverse these deficits, in part via induction of BDNF and/or VEGF expression, consistent with their delayed onset of action. Ketamine, an N-methyl-d-aspartate receptor antagonist, exerts rapid and sustained antidepressant effects. Rodent studies have revealed that ketamine rapidly increases BDNF and VEGF release and/or expression in the PFC and hippocampus, which in turn increases the number and function of spine synapses in the PFC and hippocampal neurogenesis. Ketamine also induces the persistent release of insulin-like growth factor 1 (IGF-1) in the PFC of male mice. These neurotrophic effects of ketamine are associated with its rapid and sustained antidepressant effects. In this review, we first provide an overview of the neurotrophic hypothesis of depression and then discuss the role of BDNF, VEGF, IGF-1, and other growth factors (IGF-2 and transforming growth factor-β1) in the antidepressant effects of ketamine and its enantiomers. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

Hyperactivation of TRPV4 causes the hippocampal pyroptosis pathway and results in cognitive impairment in LPS-treated mice

Pyroptosis, a newly discovered proinflammatory programmed cell death, is involved in the regulation of cognitive dysfunction, such as Alzheimer's disease. Exploring potential drug targets that prevent pyroptotic procedures might benefit the development of a cure for these diseases. In the present study, we explored whether the transient receptor potential vanilloid 4 (TRPV4) blocker HC067047 and knockdown of TRPV4 in the hippocampus could improve cognitive behavior through the inhibition of pyroptosis in a mouse model developed using systemic administration of lipopolysaccharide (LPS). We found that systemic administration of HC067047 or knockdown of hippocampal TRPV4 prevented the activation of canonical and noncanonical pyroptosis in the hippocampus of LPS-treated mice. Consistent with the inhibition of the hippocampal pyroptosis pathway, a knockdown of hippocampal TRPV4 lowered expression of TNF-α, IL-1β, IL-18, and IL-6. Furthermore, we verified that the main pyroptosis cell type might be a neuron, indicated by reduced neuronal marker expression. Mechanically, we also found that knockdown of hippocampal TRPV4 might inhibit phosphorylation of CamkⅡα which results in NFκb mediated inflammasome reduction in the hippocampus of LPS-treated mice. More interestingly, mice intraperitoneally injected with HC067047 or the hippocampus injected with TRPV4 shRNA showed improved cognitive behavior, as indicated by the enhanced discrimination ratio in the NORT, NOPT, and SNPT. Collectively, we consider that HC067047 might be a small molecular drug that prevents pyroptosis, and TRPV4 could be an effective therapeutic target for preventing pyroptosis-induced cognitive dysfunction.

CRS induces depression-like behavior after MCAO in rats possibly by activating p38 MAPK

Post-stroke depression (PSD) is a common neuropsychiatric complication of stroke, which seriously affects the quality of life and prognosis of patients. Nevertheless, the pathogenesis of PSD remains unclear. In our study, a PSD rat model was established by chronic restraint stress (CRS) combined with middle cerebral artery occlusion (MCAO). Depressive and anxiety-like behaviors were tested, as well as Neuronal loss and Apoptosis. The expression of synapse and p38 MAPK signaling pathway -relevant proteins was detected. Our data indicated that CRS combined with MCAO could induce depression-like and anxiety-like behaviors, which led to neuronal damage, apoptosis, and cellular loss in the left parietal cortex and left hippocampus. Furthermore, CRS combined with MCAO decreased synaptic plasticity in the parietal cortex and left hippocampus. We found that CRS combined with MCAO had activated the p38 MAPK signaling pathway, and decreased the expression of pathway-related proteins MKK6 and MKK3. These results suggested that CRS combined with MCAO could lead to depression-like behavior via neuronal damage, apoptosis and reduced synaptic plasticity, which might be related to the activation of the p38 MAPK pathway. Therefore, it provides novel ideas for the research on the intervention and prevention mechanisms of PSD.

Validity of chronic restraint stress for modeling anhedonic-like behavior in rodents: a systematic review and meta-analysis

BACKGROUND

Chronic restraint stress (CRS) is widely used to recapitulate depression phenotypes in rodents but is frequently criticized for a perceived lack of efficacy. The aim of this study was to evaluate anhedonic-like behavior in the CRS model in rodents by performing a meta-analysis of studies that included sucrose preference tests.

METHODS

This meta-analysis was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) recommendations. We comprehensively searched for eligible studies published before June 2021 in the PubMed, Embase, Medline, and Web of Science databases. We chose sucrose preference ratio as the indicative measure of anhedonia because it is a core symptom of depression in humans.

RESULTS

Our pooled analysis included 34 articles with 57 studies and seven rodent species/strains and demonstrated decreased sucrose preference in the stress group compared with controls. The duration of CRS differentially affected the validity of anhedonic-like behavior in the models. Rats exhibited greater susceptibility to restraint stress than mice, demonstrating inter-species variability.

CONCLUSIONS

Our meta-analysis of studies that used the CRS paradigm to evaluate anhedonic-like behavior in rodents was focused on a core symptom of depression (anhedonia) as the main endpoint of the model and identified species-dependent susceptibility to restraint stress.

Circulating hsa-let-7e-5p and hsa-miR-125a-5p as Possible Biomarkers in the Diagnosis of Major Depression and Bipolar Disorders

Background. Evidence shows that microRNAs (miRNAs) could play a key role in the homeostasis and development of major depressive disorder and bipolar disorder. The present study is aimed at investigating the changes in circulating miRNA expression profiles in a plasma of patients suffering from major depressive disorder (MDD) and bipolar disorder (BD) to distinguish and evaluate these molecules as biomarkers for mood disorders. Methods. A study enrolled a total of 184 subjects: 74 controls, 84 MDD patients, and 26 BD patients. Small RNA sequencing revealed 11 deregulated circulating miRNAs in MDD and BD plasma, of which expression of 5, hsa-miR-139-3p, miRNAs hsa-let-7e-5p, hsa-let-7f-5p, hsa-miR-125a-5p, and hsa-miR-483-5p, were further verified using qPCR. miRNA gene expression data was evaluated alongside the data from clinical assessment questionnaires. Results. hsa-let-7e-5p and hsa-miR-125a-5p were both confirmed upregulated: 0.75-fold and 0.25-fold, respectively, in the MDD group as well as 1.36-fold and 0.68-fold in the BD group. Receiver operating curve (ROC) analysis showed mediocre diagnostic sensitivity and specificity of both hsa-let-7e-5p and hsa-miR-125a-5p with approximate area under the curve (AOC) of 0.66. ROC analysis of combined miRNA and clinical assessment data showed that hsa-let-7e-5p and hsa-miR-125a-5p testing could improve MDD and BD diagnostic accuracy by approximately 10%. Conclusions. Circulating hsa-let-7e-5 and hsa-miR-125a-5p could serve as additional peripheral biomarkers for mood disorders; however, suicidal ideation remains the major diagnostic factor for MDD and BD.

Pharmahuasca and DMT Rescue ROS Production and Differentially Expressed Genes Observed after Predator and Psychosocial Stress: Relevance to Human PTSD

Post-traumatic stress disorder (PTSD) is associated with cognitive deficits, oxidative stress, and inflammation. Animal models have recapitulated features of PTSD, but no comparative RNA sequencing analysis of differentially expressed genes (DEGs) in the brain between PTSD and animal models of traumatic stress has been carried out. We compared DEGs from the prefrontal cortex (PFC) of an established stress model to DEGs from the dorsolateral PFC (dlPFC) of humans. We observed a significant enrichment of rat DEGs in human PTSD and identified 20 overlapping DEGs, of which 17 (85%) are directionally concordant. N,N-dimethyltryptamine (DMT) is a known indirect antioxidant, anti-inflammatory, and neuroprotective compound with antidepressant and plasticity-facilitating effects. We tested the capacity of DMT, the monoamine oxidase inhibitor (MAOI) harmaline, and "pharmahuasca" (DMT + harmaline) to reduce reactive oxygen species (ROS) production and inflammatory gene expression and to modulate neuroplasticity-related gene expression in the model. We administered DMT (2 mg/kg IP), harmaline (1.5 mg/kg IP), pharmahuasca, or vehicle every other day for 5 days, following a 30 day stress regiment. We measured ROS production in the PFC and hippocampus (HC) by electron paramagnetic resonance spectroscopy and sequenced total mRNA in the PFC. We also performed in vitro assays to measure the affinity and efficacy of DMT and harmaline at 5HT_2AR compared to 5-HT. DMT and pharmahuasca reduced ROS production in the PFC and HC, while harmaline had mixed effects. Treatments normalized 9, 12, and 14 overlapping DEGs, and pathway analysis implicated that genes were involved in ROS production, inflammation, growth factor signaling, neurotransmission, and neuroplasticity.

The Mechanisms Behind Rapid Antidepressant Effects of Ketamine: A Systematic Review With a Focus on Molecular Neuroplasticity

The mechanism of action underlying ketamine's rapid antidepressant effects in patients with depression, both suffering from major depressive disorder (MDD) and bipolar disorder (BD), including treatment resistant depression (TRD), remains unclear. Of the many speculated routes that ketamine may act through, restoring deficits in neuroplasticity may be the most parsimonious mechanism in both human patients and preclinical models of depression. Here, we conducted a literature search using PubMed for any reports of ketamine inducing neuroplasticity relevant to depression, to identify cellular and molecular events, relevant to neuroplasticity, immediately observed with rapid mood improvements in humans or antidepressant-like effects in animals. After screening reports using our inclusion/exclusion criteria, 139 publications with data from cell cultures, animal models, and patients with BD or MDD were included (registered on PROSPERO, ID: CRD42019123346). We found accumulating evidence to support that ketamine induces an increase in molecules involved in modulating neuroplasticity, and that these changes are paired with rapid antidepressant effects. Molecules or complexes of high interest include glutamate, AMPA receptors (AMPAR), mTOR, BDNF/TrkB, VGF, eEF2K, p70S6K, GSK-3, IGF2, Erk, and microRNAs. In summary, these studies suggest a robust relationship between improvements in mood, and ketamine-induced increases in molecular neuroplasticity, particularly regarding intracellular signaling molecules.

TRPV4 inhibitor HC067047 produces antidepressant-like effect in LPS-induced depression mouse model

Inflammation is a crucial component that contributes to the pathogenesis of major depressive disorder. It has been revealed that the nonselective cation channel transient receptor potential vanilloid 4 (TRPV4) profoundly affects a variety of physiological processes, including inflammation. However, its roles and mechanisms in LPS-induced depression are still unclear. Here, for the first time, we found that there was a significant increase in TRPV4 in the hippocampus in a depression mouse model induced by LPS. TRPV4 inhibitor HC067047 or knockdown the hippocampal TRPV4 with TRPV4 shRNA could effectively rescue the aberrant behaviors. Furthermore, TRPV4 inhibitor HC067047 reduced the activation of astrocyte and microglia, decreased expression of CaMKII-NLRP3 inflammasome and increased the expression of neurogenesis marker DCX in the hippocampus. In addition, enhanced neuroinflammation in the serum was also reversed by TRPV4 inhibitor HC067047. Thus, we consider that TRPV4 has an important role in contributing to the depression-like behavior following LPS-induced systemic inflammation.

Neuropeptides as the Shared Genetic Crosstalks Linking Periodontitis and Major Depression Disorder

Background

The aim of this study was at investigating the association between major depressive disorder (MDD) and periodontitis based on crosstalk genes and neuropeptides.

Methods

Datasets for periodontitis (GSE10334, GSE16134, and GSE23586) and MDD (GSE38206 and GSE39653) were downloaded from GEO. Following batch correction, a differential expression analysis was applied (MDD: ∣log2FC | >0 and periodontitis ∣log2FC | ≥0.5, p < 0.05). The neuropeptide data were downloaded from NeuroPep and NeuroPedia. Intersected genes were potential crosstalk genes. The correlation between neuropeptides and crosstalk genes in MDD and periodontitis was analyzed with Pearson correlation coefficient. Subsequently, regression analysis was performed to calculate the differentially regulated link. Cytoscape was used to map the pathways of crosstalk genes and neuropeptides and to construct the protein-protein interaction network. Lasso regression was applied to screen neuropeptides, whereby boxplots were created, and receiver operating curve (ROC) analysis was conducted.

Results

The MDD dataset contained 30 case and 33 control samples, and the periodontitis dataset contained 430 case and 139 control samples. 35 crosstalk genes were obtained. A total of 102 neuropeptides were extracted from the database, which were not differentially expressed in MDD and periodontitis and had no intersection with crosstalk genes. Through lasso regression, 9 neuropeptides in MDD and 43 neuropeptides in periodontitis were obtained. Four intersected neuropeptide genes were obtained, i.e., ADM, IGF2, PDYN, and RETN. The results of ROC analysis showed that IGF2 was highly predictive in MDD and periodontitis. ADM was better than the other three genes in predicting MDD disease. A total of 13 crosstalk genes were differentially coexpressed with four neuropeptides, whereby FOSB was highly expressed in MDD and periodontitis.

Conclusion

The neuropeptide genes ADM, IGF2, PDYN, and RETN were intersected between periodontitis and MDD, and FOSB was a crosstalk gene related to these neuropeptides on the transcriptomic level. These results are a basis for future research in the field, needing further validation.

Defining Valid Chronic Stress Models for Depression With Female Rodents

Women are twice as likely to experience depression than men, yet until recently, preclinical studies in rodents have focused almost exclusively on males. As interest in sex differences and sex-specific mechanisms of stress susceptibility increases, chronic stress models for inducing depression-relevant behavioral and physiological changes in male rodents are being applied to females, and several new models have emerged to include both males and females, yet not all models have been systematically validated in females. An increasing number of researchers seek to include female rodents in their experimental designs, asking the question "what is the ideal chronic stress model for depression in females?" We review criteria for assessing female model validity in light of key research questions and the fundamental distinction between studying sex differences and studying both sexes. In overviewing current models, we explore challenges inherent to establishing an ideal female chronic stress model, with particular emphasis on the need for standardization and adoption of validated behavioral tests sensitive to stress effects in females. Taken together, these considerations will empower female chronic stress models to provide a better understanding of stress susceptibility and allow the development of efficient sex-specific treatments.

Hippocampal LASP1 ameliorates chronic stress-mediated behavioral responses in a mouse model of unpredictable chronic mild stress

Substantial evidence has revealed that abnormalities in synaptic plasticity play important roles during the process of depression. LASP1 (LIM and SH3 domain protein 1), a member of actin-binding proteins, has been shown to be associated with the regulation of synaptic plasticity. However, the role of LASP1 in the regulation of mood is still unclear. Here, using an unpredictable chronic mild stress (UCMS) paradigm, we found that the mRNA and protein levels of LASP1 were decreased in the hippocampus of stressed mice and that UCMS-induced down-regulation of LASP1 was abolished by chronic administration of fluoxetine. Adenosine-associated virus-mediated hippocampal LASP1 overexpression alleviated the UCMS-induced behavioral results of forced swimming test and sucrose preference test in stressed mice. It also restored the dendritic spine density, elevated the levels of AKT (a serine/threonine protein kinase), phosphorylated-AKT, insulin-like growth factor 2, and postsynaptic density protein 95. These findings suggest that LASP1 alleviates UCMS-provoked behavioral defects, which may be mediated by an enhanced dendritic spine density and more activated AKT-dependent LASP1 signaling, pointing to the antidepressant role of LASP1.

Associations between disordered gut microbiota and changes of neurotransmitters and short-chain fatty acids in depressed mice

Mounting evidence suggests that gut microbiota can play an important role in pathophysiology of depression, but its specific molecular mechanisms are still unclear. This study was conducted to explore the associations between changes in neurotransmitters and short-chain fatty acids (SCFAs) and altered gut microbiota in depressed mice. Here, the chronic restraint stress (CRS) model of depression was built. The classical behavioral tests were conducted to assess the depressive-like behaviors of mice. The 16S rRNA gene sequence extracted from fecal samples was used to assess the gut microbial composition. Liquid and gas chromatography mass spectroscopy were used to identify neurotransmitters in hypothalamus and SCFAs in fecal samples, respectively. Finally, 29 differential bacteria taxa between depressed mice and control mice were identified, and the most differentially abundant bacteria taxa were genus Allobaculum and family Ruminococcaceae between the two groups. The acetic acid, propionic acid, pentanoic acid, norepinephrine, 5-HIAA and 5-HT were significantly decreased in depressed mice compared to control mice. Genus Allobaculum was found to be significantly positively correlated with acetic acid and 5-HT. Taken together, these results provided novel microbial and metabolic frameworks for understanding the role of microbiota-gut-brain axis in depression, and suggested new insights to pave the way for novel therapeutic methods.

Mechanisms of Stress-Induced Spermatogenesis Impairment in Male Rats Following Unpredictable Chronic Mild Stress (uCMS)

The negative association between psychological stress and male fertility has been known for many years. This study was aimed at (i) identifying spermatogenesis impairment induced by psychological stress in rats and (ii) exploring the role of glucocorticoid receptor (GR) signaling in these adverse effects (if they exist). Male Sprague Dawley rats were exposed to a six-week period of unpredictable chronic mild stress (uCMS) along with cotreatment of GR antagonist RU486 (1 mg/kg/day). Testicular damage was assessed by testicular pathological evaluation, epididymal sperm concentration, serum testosterone levels, testicular apoptotic cell measurements, and cell cycle progression analyses. Rats in the uCMS group had decreased levels of serum testosterone and decreased epididymal sperm concentration. The uCMS-treated rats also had decreased numbers of spermatids and increased levels of apoptotic seminiferous tubules; additionally, cell cycle progression of spermatogonia was arrested at the G₀/G₁ phase. Furthermore, uCMS exposure caused an increase in serum corticosterone level and activated GR signaling in the testes including upregulated GR expression. RU486 treatment suppressed GR signaling and alleviated the damaging effects of stress, resulting in an increased epididymal sperm concentration. Overall, this work demonstrated for the first time that the activation of GR signaling mediates stress-induced spermatogenesis impairment and that this outcome is related to cell apoptosis and cell cycle arrest in germ cells.

Abnormalities in FGF family members and their roles in modulating depression-related molecules

The role of the fibroblast growth factor (FGF) system in depression has received considerable attention in recent years. To understand the role of this system, it is important to identify the specific members of the FGF family that have been implicated and the various mechanisms that they modulated. Here, we review the role of FGFs in depression and integrate evidence from clinical and basic research. These data suggest that changes in the FGF family are involved in depression and possibly in a wider range of psychiatric disorders. We analyse the abnormalities of FGF family members in depression and their roles in modulating depression-related molecules. The role of the FGF family in depression and related disorders needs to be studied in more detail.

The ERK Pathway: Molecular Mechanisms and Treatment of Depression

Major depressive disorder is a chronic debilitating mental illness. Its pathophysiology at cellular and molecular levels is incompletely understood. Increasing evidence supports a pivotal role of the mitogen-activated protein kinase (MAPK), in particular the extracellular signal-regulated kinase (ERK) subclass of MAPKs, in the pathogenesis, symptomatology, and treatment of depression. In humans and various chronic animal models of depression, the ERK signaling was significantly downregulated in the prefrontal cortex and hippocampus, two core areas implicated in depression. Inhibiting the ERK pathway in these areas caused depression-like behavior. A variety of antidepressants produced their behavioral effects in part via normalizing the downregulated ERK activity. In addition to ERK, the brain-derived neurotrophic factor (BDNF), an immediate upstream regulator of ERK, the cAMP response element-binding protein (CREB), a transcription factor downstream to ERK, and the MAPK phosphatase (MKP) are equally vulnerable to depression. While BDNF and CREB were reduced in their activity in the prefrontal cortex and hippocampus of depressed animals, MKP activity was enhanced in parallel. Chronic antidepressant treatment readily reversed these neurochemical changes. Thus, ERK signaling in the depression-implicated brain regions was disrupted during the development of depression, which contributes to the long-lasting and transcription-dependent neuroadaptations critical for enduring depression-like behavior and the therapeutic effect of antidepressants.

Combined Fluoxetine and Metformin Treatment Potentiates Antidepressant Efficacy Increasing IGF2 Expression in the Dorsal Hippocampus

An increasing number of studies show that selective serotonin reuptake inhibitors (SSRIs) exert their therapeutic action, at least in part, by amplifying the influence of the living environment on mood. As a consequence, when administered in a favorable environment, SSRIs lead to a reduction of symptoms, but in stressful conditions, they show limited efficacy. Therefore, novel therapeutic approaches able to neutralize the influence of the stressful environment on treatment are needed. The aim of our study was to test whether, in a mouse model of depression, the combined administration of SSRI fluoxetine and metformin, a drug able to improve the metabolic profile, counteracts the limited efficacy of fluoxetine alone when administered in stressful conditions. Indeed, metabolic alterations are associated to both the onset of major depression and the antidepressant efficacy. To this goal, adult C57BL/6 male mice were exposed to stress for 6 weeks; the first two weeks was aimed at generating a mouse model of depression. During the remaining 4 weeks, mice received one of the following treatments: vehicle, fluoxetine, metformin, or a combination of fluoxetine and metformin. We measured liking- and wanting-type anhedonia as behavioral phenotypes of depression and assessed the expression levels of selected genes involved in major depressive disorder and antidepressant response in the dorsal and ventral hippocampus, which are differently involved in the depressive symptomatology. The combined treatment was more effective than fluoxetine alone in ameliorating the depressive phenotype after one week of treatment. This was associated to an increase in IGF2 mRNA expression and enhanced long-term potentiation, specifically in the dorsal hippocampus, at the end of treatment. Overall, the present results show that, when administered in stressful conditions, the combined fluoxetine and metformin treatment may represent a more effective approach than fluoxetine alone in a short term. Finally, our findings highlight the relevance of polypharmacological strategy as effective interventions to increase the efficacy of the antidepressant drugs currently available.

Insulin growth factor 2 (IGF2) as an emergent target in psychiatric and neurological disorders. Review

Insulin-like growth factor 2 (IGF2) is abundantly expressed in the central nervous system (CNS). Recent evidence highlights the role of IGF2 in the brain, sustained by data showing its alterations as a common feature across a variety of psychiatric and neurological disorders. Previous studies emphasize the potential role of IGF2 in psychiatric and neurological conditions as well as in memory impairments, targeting IGF2 as a pro-cognitive agent. New research on animal models supports that upcoming investigations should explore IGF2's strong promising role as a memory enhancer. The lack of effective treatments for cognitive disturbances as a result of psychiatric diseases lead to further explore IGF2 as a promising target for the development of new pharmacology for the treatment of memory dysfunctions. In this review, we aim at gathering all recent relevant studies and findings on the role of IGF2 in the development of psychiatric diseases that occur with cognitive problems.

γ-oryzanol ameliorates the acute stress induced by behavioral anxiety testing in mice

We evaluated the anxiolytic effect of γ-oryzanol (GORZ) and elucidated the molecular mechanisms involved in its inhibition of behavioral test-induced anxiety. Behavioral tests were conducted on day 13, and mice were subjected to 30 min of acute restraint stress treatment (ARST) before sacrifice on day 16. In other group, behavioral tests were conducted on day 13 and 14 after ARST. 0.5% GORZ significantly weakened the effect of behavioral stress, but not the effect of strong ARST. GORZ downregulated ARST-induced cFos levels in the cerebral cortex. In conclusion, GORZ has potential ant-anxiety effect in the treatment of weak behavioral test-induced stress.

The Role of miR-150 in Stress-Induced Anxiety-Like Behavior in Mice

Stress plays a crucial role in several psychiatric disorders, including anxiety. However, the underlying mechanisms remain poorly understood. Here, we used acute stress (AS) and chronic restraint stress (CRS) models to develop anxiety-like behavior and investigate the role of miR-150 in the hippocampi of mice. Corticosterone levels as well as glutamate receptors in the hippocampus were evaluated. We found that anxiety-like behavior was induced after either AS or CRS, as determined by the open-field test (OFT) and elevated plus-maze test (EPM). Increased corticosterone levels were observed in the blood of AS and CRS groups, while the expression of miR-150 mRNA in the hippocampus was significantly decreased. The expressions of GluN2A, GluR1, GluR2, and V-Glut2 in the hippocampus were decreased after either AS or CRS. Hippocampal GAD67 expression was increased by AS but not CRS, and GluN2B expression was decreased by CRS but not AS. Adult miR-150 knockout mice showed anxiety-like behavior, as assessed by the OFT and EPM. The expressions of GluN2A, GluN2B, GluR1, and GluR2 were also downregulated, but the expression of V-Glut2 was upregulated in the hippocampi of miR-150 knockout mice compared with wild-type mice. Interestingly, we found that the miR-150 knockout mice showed decreased dendrite lengths, dendrite branchings, and numbers of dendrite spines in the hippocampus compared with wild-type mice. These results suggest that miR-150 may influence the synaptic plasticity of the hippocampus and play a significant role in stress-induced anxiety-like behavior in adult mice.

Knockdown of BACE1-AS by siRNA improves memory and learning behaviors in Alzheimer's disease animal model

Alzheimer's disease (AD) is a devastating neurodegenerative disease that causes progressive damage to neurons. Emerging evidence has demonstrated that long non-coding RNAs (lncRNAs) serve an important role in many neurological diseases, such as AD. β-secretase 1 (BACE1)-antisense transcript (BACE1-AS) was identified as a conserved non-coding antisense BACE1. Previous reports stated that BACE1-AS positively regulated BACE1 mRNA and subsequently BACE1 protein expression in vitro and in vivo. However, whether BACE1-AS is able to regulate memory and learning behaviors remains to be elucidated. In the present study, the role of lncRNA BACE1-AS on memory and learning was investigated. It was demonstrated that lncRNA BACE1-AS expression was highly expressed in blood samples from AD patients, and also upregulated in peripheral blood samples and hippocampi from an AD animal model. Knockdown of BACE1-AS by short interfering RNA increased the primary hippocampal neurons proliferation in vitro. Knockdown of BACE1-AS mediated by lentivirus in vivo improved the memory and learning behaviors of SAMP8 mice, inhibited BACE1 and amyloid precursor protein production, and phosphorylation of tau protein in hippocampi. Therefore, the present findings suggested that BACE1-AS may be a potential target for management of memory loss related diseases, such as AD.

Premature hippocampus-dependent memory decline in middle-aged females of a genetic rat model of depression

Aging and major depressive disorder are risk factors for dementia, including Alzheimer's Disease (AD), but the mechanism(s) linking depression and dementia are not known. Both AD and depression show greater prevalence in women. We began to investigate this connection using females of the genetic model of depression, the inbred Wistar Kyoto More Immobile (WMI) rat. These rats consistently display depression-like behavior compared to the genetically close control, the Wistar Kyoto Less Immobile (WLI) strain. Hippocampus-dependent contextual fear memory did not differ between young WLI and WMI females, but, by middle-age, female WMIs showed memory deficits compared to same age WLIs. This deficit, measured as duration of freezing in the fear provoking-context was not related to activity differences between the strains prior to fear conditioning. Hippocampal expression of AD-related genes, such as amyloid precursor protein, amyloid beta 42, beta secretase, synucleins, total and dephosphorylated tau, and synaptophysin, did not differ between WLIs and WMIs in either age group. However, hippocampal transcript levels of catalase (Cat) and hippocampal and frontal cortex expression of insulin-like growth factor 2 (Igf2) and Igf2 receptor (Igf2r) paralleled fear memory differences between middle-aged WLIs and WMIs. This data suggests that chronic depression-like behavior that is present in this genetic model is a risk factor for early spatial memory decline in females. The molecular mechanisms of this early memory decline likely involve the interaction of aging processes with the genetic components responsible for the depression-like behavior in this model.

Brain-Derived Neurotrophic Factor Precursor in the Hippocampus Regulates Both Depressive and Anxiety-Like Behaviors in Rats

Depression and anxiety are two affective disorders that greatly threaten the mental health of a large population worldwide. Previous studies have shown that brain-derived neurotrophic factor precursor (proBDNF) is involved in the development of depression. However, it is still elusive whether proBDNF is involved in anxiety, and if so, which brain regions of proBDNF regulate these two affective disorders. The present study aims to investigate the role of proBDNF in the hippocampus in the development of depression and anxiety. Rat models of an anxiety-like phenotype and depression-like phenotype were established by complete Freund's adjuvant intra-plantar injection and chronic restraint stress, respectively. Both rat models developed anxiety-like behaviors as determined by the open field test and elevated plus maze test. However, only rats with depression-like phenotype displayed the lower sucrose consumption in the sucrose preference test and a longer immobility time in the forced swimming test. Sholl analysis showed that the dendritic arborization of granule cells in the hippocampus was decreased in rats with depression-like phenotype but was not changed in rats with anxiety-like phenotype. In addition, synaptophysin was downregulated in the rats with depression-like phenotype but upregulated in the rats with anxiety-like phenotype. In both models, proBDNF was greatly increased in the hippocampus. Intra-hippocampal injection anti-proBDNF antibody greatly ameliorated the anxiety-like and depressive behaviors in the rats. These findings suggest that despite some behavioral and morphological differences between depression and anxiety, hippocampal proBDNF is a common mediator to regulate these two mental disorders.

Changes of the brain activities after chronic restraint stress in rats: A study based on 18F-FDG PET

As a prevalent disease all over the world, changed functional activities and/or structures in many brain regions have been found in depression. In this study, 5-week chronic restraint stress (CRS) was performed to establish depression rat models, and ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) was used to detect brain functional activities. Our study found that CRS induced depressive behaviors and increased the expression of serum IL-6. After exposure to CRS, rats showed decreased glucose metabolism in the whole-brain and brain regions including left medial prefrontal and auditory cortices; right amygdala, cingulate cortex, olfactory and AcbCore/Shell; bilateral caudate putamen, dorsal hippocampi, insular and entorhinal cortices. Expression of serum IL-6 and glucose metabolism in most of the above brain regions were significantly correlated with the severity of some CRS-induced depressive behaviors. In conclusion, the increased peripheral inflammatory response and decreased brain functional activities might be the important pathogenesis of experimental depression induced by CRS, and could reflect the severity of depression to some extent.

Anti-Anxiety Effect of (-)-Syringaresnol-4-O-β-d-apiofuranosyl-(1→2)-β-d-glucopyranoside from Albizzia julibrissin Durazz (Leguminosae)

Albizzia julibrissin Durazz, a Chinese Medicine, is commonly used for its anti-anxiety effects. (−)-syringaresnol-4-O-β-d-apiofuranosyl-(1→2)-β-d-glucopyranoside (SAG) is the main ingredient of Albizzia julibrissin Durazz. The present study investigated the anxiolytic effect and potential mechanisms on the HPA axis and monoaminergic systems of SAG on acute restraint-stressed rats. The anxiolytic effect of SAG was examined through an open field test and an elevated plus maze test. The concentration of CRF, ACTH, and CORT in plasma was examined by an enzyme-linked immune sorbent assay (ELISA) kit while neurotransmitters in the cerebral cortex and hippocampus of the brain were examined by High Performance Liquid Chromatography (HPLC). We show that repeated treatment with SAG (3.6 mg/kg, p.o.) significantly increased the number and time spent on the central entries in the open-field test when compared to the vehicle/stressed group. In the elevated plus maze test, 3.6 mg/kg SAG could increase the percentage of entries into and time spent on the open arms of the elevated plus maze. In addition, the concentration of CRF, ACTH, and CORT in plasma and neurotransmitters (NE, 5-HT, DA and their metabolites 5-HIAA, DOPAC, and HVA) in the cerebral cortex and hippocampus of the brain were decreased after SAG treatment, as compared to the repeated acute restraint-stressed rats. These results suggest that SAG is a potential anti-anxiety drug candidate.

Genome-wide transcriptome analysis of hippocampus in rats indicated that TLR/NLR signaling pathway was involved in the pathogenisis of depressive disorder induced by chronic restraint stress

Data from clinical investigations and laboratory fundings have provided preliminary evidence for the effectiveness and safety of acupuncture therapy in depression. However, the mechanisms underlying the antidepressant response of acupuncture are not fully elucidated. To elucidate the potential effects of acupuncture for depression on the hippocampal genome-wide transcriptome at the molecular level, we evaluated the transcriptomic profile of depression rats under treatment of acupuncture, and fluoxetine. We identified a very significant effect of acupucture intervention, with 107 genes differentially expressed in acupuncture vs. model group; while 41 genes between fluoxetine vs. model group. Notably, the 54 differentially expressed genes between acupuncture and fluoxetine showed the significantly different effect between acupuncture and fluoxetine. Through GO (gene ontology) functional term and KEGG (kyoto encyclopedia of genes and genomes) pathway analysis, we identified that the upregulation of gene sets were related to inflammatory response, innate immunity and immune response. We found that toll-like receptor signalling pathway and NOD like receptor signalling pathway were associated with the function of inflammatory response, innate immunity and immune response. Importantly, acupuncture reversed the upregulation of gene sets that were related to inflammatory response, innate immunity and immune response (including toll-like receptor signalling pathway and NOD like receptor signalling pathway), which might be critical for the pathogenesis of depression and provide evidence for the antidepressive effects of acupuncture by regulating inflammatory response, innate immunity and immune response via toll-like receptor signalling pathway and NOD like receptor signalling pathway.

The behavioral deficits and cognitive impairment are correlated with decreased IGF-II and ERK in depressed mice induced by chronic unpredictable stress

AIM

To investigate the behavioral deficits, cognitive impairment and possible mechanisms induced by chronic unpredictable stress (CUS) in mice of different ages.

METHODS

The behaviors and cognition were tested using the open field test, tail suspension test and the Morris water maze. The changes in the insulin-like growth factor II (IGF-II) and the extracellular signal-regulated kinase (ERK) and phosphorylation (p-ERK) in the hippocampus (HP) and prefrontal cortex (PFC) were evaluated by immunohistochemistry.

RESULTS

The 15-month-old mice revealed a significant decline in spontaneous behavior and the learning-memory function and showed a decrease in IGF-II and p-ERK expression levels in HP and PFC. Four weeks of CUS exposure induced significant anxiety- and depression-like behavior and learning-memory function impairment in 3- to 15-month-old mice, and reduced IGF-II and p-ERK expression levels in HP and PFC, compared with control group mice, respectively.

CONCLUSIONS

The behavioral deficits and cognitive impairment induced by CUS and aging in mice could be associated with the down-regulated expression of IGF-II and p-ERK in HP and PFC. This role seems to be dependent on the intracellular ERK pathway.

Mechanisms Underlying the Antidepressant Response of Acupuncture via PKA/CREB Signaling Pathway

Protein kinase A (PKA)/cAMP response element-binding (CREB) protein signaling pathway, contributing to impaired neurogenesis parallel to depressive-like behaviors, has been identified as the crucial factor involved in the antidepressant response of acupuncture. However, the molecular mechanisms associated with antidepressant response of acupuncture, neurogenesis, and depressive-like behaviors ameliorating remain unexplored. The objective was to identify the mechanisms underlying the antidepressant response of acupuncture through PKA signaling pathway in depression rats by employing the PKA signaling pathway inhibitor H89 in in vivo experiments. Our results indicated that the expression of hippocampal PKA-α and p-CREB was significantly downregulated by chronic unpredicted mild stress (CUMS) procedures. Importantly, acupuncture reversed the downregulation of PKA-α and p-CREB. The expression of PKA-α was upregulated by fluoxetine, but not p-CREB. No significant difference was found between Acu and FLX groups on the expression of PKA-α and p-CREB. Interestingly, H89 inhibited the effects of acupuncture or fluoxetine on upregulating the expression of p-CREB, but not PKA-α. There was no significant difference in expression of CREB among the groups. Conclusively, our findings further support the hypothesis that acupuncture could ameliorate depressive-like behaviors by regulating PKA/CREB signaling pathway, which might be mainly mediated by regulating the phosphorylation level of CREB.

The hippocampal transcriptomic signature of stress resilience in mice with microglial fractalkine receptor (CX3CR1) deficiency

Clinical studies suggest that key genetic factors involved in stress resilience are related to the innate immune system. In the brain, this system includes microglia cells, which play a major role in stress responsiveness. Consistently, mice with deletion of the CX3CR1 gene (CX3CR1^-/- mice), which in the brain is expressed exclusively by microglia, exhibit resilience to chronic stress. Here, we compared the emotional, cognitive, neurogenic and microglial responses to chronic unpredictable stress (CUS) between CX3CR1^-/- and wild type (WT) mice. This was followed by hippocampal whole transcriptome (RNA-seq) analysis. We found that following CUS exposure, WT mice displayed reduced sucrose preference, impaired novel object recognition memory, and reduced neurogenesis, whereas CX3CR1^-/- mice were completely resistant to these effects of CUS. CX3CR1^-/- mice were also resilient to the memory-suppressive effect of a short period of unpredictable stress. Microglial somas were larger in CX3CR1^-/- than in WT, but in both genotypes CUS induced a similar decline in hippocampal microglial density and processes length. RNA sequencing and pathway analysis revealed basal strain differences, particularly reduced expression of interferon (IFN)-regulated and MHC class I gene transcripts in CX3CR1^-/- mice. Furthermore, while CUS exposure similarly altered neuronal gene transcripts (e.g. Arc, Npas4) in both strains, transcripts downstream of hippocampal estrogen receptor signaling (particularly Igf2 and Igfbp2) were altered only in CX3CR1^-/- mice. These findings indicate that emotional and cognitive stress resilience involves CX3CR1-dependent basal and stress-induced alterations in hippocampal transcription, implicating inhibition of CX3CR1 signaling as a novel approach for promoting stress resilience.

Paeoniflorin ameliorates interferon-alpha-induced neuroinflammation and depressive-like behaviors in mice

Long-term treatment with high-dose Interferon-alpha (IFN-α) has resulted in depression in 30-50% of the patients. Paeoniflorin may ameliorate the IFN-α-induced depression; however, the underlying mechanism is less studied. Here, we investigated the prophylactic antidepressant and anti-neuroinflammatory effects of paeoniflorin on the behaviors and specific emotion-related regions of the brain in mice with IFN-α-induced depression. A series of behavior assessments were conducted to identify the depressive state after subcutaneously IFN-α injections and with or without intragastrically paeoniflorin administration in C57BL/6J mice. Levels of many inflammatory-related cytokines in serum, mPFC, vHi and amygdala were determined by cytokine array analysis. Furthermore, microglia and astrocyte activation in these three regions were evaluated by immunohistochemistry. We found that the mice which were subcutaneously injected IFN-α 15×106 IU/kg for 4 successive weeks to mimic an IFN-α-induced depression model had distinct inflammatory changes in the amygdala. Interestingly, 4-week 20 mg/kg or 40 mg/kg paeoniflorin pretreatments reversed the depressive-like behaviors and the abnormal inflammatory cytokine levels in the serum, mPFC, vHi and amygdala. These cytokines were not limited to the commonly reported IL-6, IL-1β and TNF-α, but also IL-9, IL-10, IL-12, and MCP-1. Besides, the increased density of microglia in IFN-α-treated mice was reversed by paeoniflorin in these three brain areas. Taken together, our data suggest that paeoniflorin can reverse the long-term, high-dose IFN-α-induced depressive-like behaviors that were associated with local distinct neuroinflammation in the mPFC, vHi and particularly the amygdala. Paeoniflorin might have a preventive therapeutic potential in IFN-α-induced depression.

Early-Life Social Isolation-Induced Depressive-Like Behavior in Rats Results in Microglial Activation and Neuronal Histone Methylation that Are Mitigated by Minocycline

Early-life stress is a potent risk factor for development of psychiatric conditions such as depression. The underlying mechanisms remain poorly understood. Here, we used the early-life social isolation (ESI) model of early-life stress in rats to characterize development of depressive-like behavior, the role of microglia, levels of histone methylation, as well as expression of glutamate receptor subunits in the hippocampus. We found that depressive-like behavior was induced after ESI as determined by sucrose preference and forced swimming tests. Increased expression of microglial activation marker, Iba1, was observed in the hippocampus of the ESI group, while expression of the microglial CD200 receptor, which promotes microglial quiescence, significantly decreased. In addition, increased levels of proinflammatory cytokines, interleukin 1β (IL-1β), interleukin 6 (IL-6), and tumor necrosis factor-alpha (TNF-α) were observed in the hippocampus of the ESI group. Moreover, ESI increased levels of neuronal H3K9me2 (a repressive marker of transcription) and its associated "writer" enzymes, G9a and G9a-like protein, in the hippocampus. ESI also decreased expression of hippocampal NMDA receptor subunits, NR1, and AMPA receptor subunits, GluR1 and GluR2, which are involved in synaptic plasticity, but it did not affect expression of PSD95 and NR2B. Interestingly, treatment with minocycline to block microglial activation induced by ESI inhibited increases in hippocampal microglia and prevented ESI-induced depressive-like behavior as well as increases in IL-1β, IL-6, and TNF-α. Notably, minocycline also triggered downregulation of H3K9me2 expression and restored expression of NR1, GluR1, and GluR2. These results suggest that ESI induces depressive-like behavior, which may be mediated by microglial signaling.

Up-regulation of insulin-like growth factor 2 by ketamine requires glycogen synthase kinase-3 inhibition

An antidepressant dose of the rapidly-acting ketamine inhibits glycogen synthase kinase-3 (GSK3) in mouse hippocampus, and this inhibition is required for the antidepressant effect of ketamine in learned helplessness depression-like behavior. Here we report that treatment with an antidepressant dose of ketamine (10mg/kg) increased expression of insulin-like growth factor 2 (IGF2) in mouse hippocampus, an effect that required ketamine-induced inhibition of GSK3. Ketamine also inhibited hippocampal GSK3 and increased expression of hippocampal IGF2 in mice when administered after the induction of learned helplessness. Treatment with the specific GSK3 inhibitor L803-mts was sufficient to up-regulate hippocampal IGF2 expression. Administration of IGF2 siRNA reduced ketamine's antidepressant effect in the learned helplessness paradigm. Mice subjected to the learned helplessness paradigm were separated into two groups, those that were resilient (non-depressed) and those that were susceptible (depressed). Non-depressed resilient mice displayed higher expression of IGF2 than susceptible mice. These results indicate that IGF2 contributes to ketamine's antidepressant effect and that IGF2 may confer resilience to depression-like behavior.

The exercise-glucocorticoid paradox: How exercise is beneficial to cognition, mood, and the brain while increasing glucocorticoid levels

Exercise is known to have beneficial effects on cognition, mood, and the brain. However, exercise also activates the hypothalamic-pituitary-adrenal axis and increases levels of the glucocorticoid cortisol (CORT). CORT, also known as the "stress hormone," is considered a mediator between chronic stress and depression and to link various cognitive deficits. Here, we review the evidence that shows that while both chronic stress and exercise elevate basal CORT levels leading to increased secretion of CORT, the former is detrimental to cognition/memory, mood/stress coping, and brain plasticity, while the latter is beneficial. We propose three preliminary answers to the exercise-CORT paradox. Importantly, the elevated CORT, through glucocorticoid receptors, functions to elevate dopamine in the medial prefrontal cortex under chronic exercise but not chronic stress, and the medial prefrontal dopamine is essential for active coping. Future inquiries may provide further insights to promote our understanding of this paradox.

New Perspectives on Genomic Imprinting, an Essential and Multifaceted Mode of Epigenetic Control in the Developing and Adult Brain

Mammalian evolution entailed multiple innovations in gene regulation, including the emergence of genomic imprinting, an epigenetic regulation leading to the preferential expression of a gene from its maternal or paternal allele. Genomic imprinting is highly prevalent in the brain, yet, until recently, its central roles in neural processes have not been fully appreciated. Here, we provide a comprehensive survey of adult and developmental brain functions influenced by imprinted genes, from neural development and wiring to synaptic function and plasticity, energy balance, social behaviors, emotions, and cognition. We further review the widespread identification of parental biases alongside monoallelic expression in brain tissues, discuss their potential roles in dosage regulation of key neural pathways, and suggest possible mechanisms underlying the dynamic regulation of imprinting in the brain. This review should help provide a better understanding of the significance of genomic imprinting in the normal and pathological brain of mammals including humans.

Retrograde fibroblast growth factor 22 (FGF22) signaling regulates insulin-like growth factor 2 (IGF2) expression for activity-dependent synapse stabilization in the mammalian brain

Communication between pre- and postsynaptic cells promotes the initial organization of synaptic specializations, but subsequent synaptic stabilization requires transcriptional regulation. Here we show that fibroblast growth factor 22 (FGF22), a target-derived presynaptic organizer in the mouse hippocampus, induces the expression of insulin-like growth factor 2 (IGF2) for the stabilization of presynaptic terminals. FGF22 is released from CA3 pyramidal neurons and organizes the differentiation of excitatory nerve terminals formed onto them. Local application of FGF22 on the axons of dentate granule cells (DGCs), which are presynaptic to CA3 pyramidal neurons, induces IGF2 in the DGCs. IGF2, in turn, localizes to DGC presynaptic terminals and stabilizes them in an activity-dependent manner. IGF2 application rescues presynaptic defects of Fgf22(-/-) cultures. IGF2 is dispensable for the initial presynaptic differentiation, but is required for the following presynaptic stabilization both in vitro and in vivo. These results reveal a novel feedback signal that is critical for the activity-dependent stabilization of presynaptic terminals in the mammalian hippocampus.

The identification of metabolic disturbances in the prefrontal cortex of the chronic restraint stress rat model of depression

Major depressive disorder, with serious impairment in cognitive and social functioning, is a complex psychiatric disorder characterized by pervasive and persistent low mood and a loss of interest or pleasure. However, the underlying molecular mechanisms of depression remain largely unknown. In this study, we used a non-targeted metabolomics approach based on gas chromatography-mass spectrometry of the prefrontal cortex in chronic restraint stress (CRS)-treated rats. CRS was induced in the stress group by restraining rats in a plastic restrainer for 6h every day. This stress paradigm continued for 21 days. Body weight measurement and behavior tests were applied, including the sucrose preference test for anhedonia, the forced swimming test for despair-like behavior, and open field test and the elevated plus-maze to test for anxiety-like behaviors in rats after CRS. Differentially expressed metabolites associated with CRS-treated rats were identified by combining multivariate and univariate statistical analysis and corrected for multiple testing using the Benjamini-Hochberg procedure. A heat map of differential metabolites was constructed using Matlab. Ingenuity Pathways Analysis was applied to identify the predicted pathways and biological functions relevant to the bio-molecules of interest. Our findings showed that CRS induces depression-like behaviors and not anxiety-like behaviors. Thirty-six metabolites were identified as potential depression biomarkers involved in amino acid metabolism, energy metabolism and lipid metabolism, as well as a disturbance in neurotransmitters. Consequently, this study provides useful insights into the molecular mechanisms of depression.

Forced swimming sabotages the morphological and synaptic maturation of newborn granule neurons and triggers a unique pro-inflammatory milieu in the hippocampus

Recent experimental data suggest that mood disorders are related to inflammatory phenomena and have led to the "inflammatory hypothesis of depression". Given that the hippocampus is one of the most affected areas in these disorders, we used a model of acute stress (the Porsolt test) to evaluate the consequences of forced swimming on two crucial events related to the pathophysiology of major depression: the functional maturation of newborn granule neurons; and the hippocampal inflammatory milieu. Using PSD95:GFP-expressing retroviruses, we found that forced swimming selectively alters the dendritic morphology of newborn neurons and impairs their connectivity by reducing the number and volume of their postsynaptic densities. In addition, acute stress triggered a series of morphological changes in microglial cells, together with an increase in microglial CD68 expression, thus suggesting the functional and morphological activation of this cell population. Furthermore, we observed an intriguing change in the hippocampal inflammatory milieu in response to forced swimming. Importantly, the levels of several molecules affected by acute stress (such as Interleukin-6 and eotaxin) have been described to also be altered in patients with depression and other mood disorders.

Dendritic Spines in Depression: What We Learned from Animal Models

Depression, a severe psychiatric disorder, has been studied for decades, but the underlying mechanisms still remain largely unknown. Depression is closely associated with alterations in dendritic spine morphology and spine density. Therefore, understanding dendritic spines is vital for uncovering the mechanisms underlying depression. Several chronic stress models, including chronic restraint stress (CRS), chronic unpredictable mild stress (CUMS), and chronic social defeat stress (CSDS), have been used to recapitulate depression-like behaviors in rodents and study the underlying mechanisms. In comparison with CRS, CUMS overcomes the stress habituation and has been widely used to model depression-like behaviors. CSDS is one of the most frequently used models for depression, but it is limited to the study of male mice. Generally, chronic stress causes dendritic atrophy and spine loss in the neurons of the hippocampus and prefrontal cortex. Meanwhile, neurons of the amygdala and nucleus accumbens exhibit an increase in spine density. These alterations induced by chronic stress are often accompanied by depression-like behaviors. However, the underlying mechanisms are poorly understood. This review summarizes our current understanding of the chronic stress-induced remodeling of dendritic spines in the hippocampus, prefrontal cortex, orbitofrontal cortex, amygdala, and nucleus accumbens and also discusses the putative underlying mechanisms.

MeCP2 controls hippocampal brain-derived neurotrophic factor expression via homeostatic interactions with microRNA‑132 in rats with depression

Major depressive disorder (MDD) is a considerable public health concern, which affects patients worldwide. MDD is associated with psychosocial impairment, poor quality of life, and significant disability, morbidity and mortality. Stress is a major factor in depression, which impairs the structural and functional plasticity of the hippocampus. Previous studies have demonstrated that chronic unpredictable mild stress is able to downregulate the expression of brain‑derived neurotrophic factor (BDNF) and methyl‑CpG‑binding protein 2 (MeCP2), and alter the expression levels of certain microRNAs (miR). The aim of the present study was to investigate the regulatory association between BDNF, MeCP2 and miR-132 in an animal model of chronic stress‑induced depression. ELISA, western blot and qPCR were used to detect the expression levels of BDNF, MeCP2 and miR-132 in the peripheral blood samples of patients with MDD and in the hippocampi of depressed animals. In addition, a dual luciferase reporter gene system was used to determine whether miR-132 directly targets BDNF or MeCP2. The present study demonstrated that, as compared with normal subjects, miR‑132 expression was increased in the peripheral blood samples of patients with MDD, whereas the expression of MeCP2 and BDNF was decreased; thus, the expression levels of MeCP2 and BDNF were negatively correlated with those of miR‑132. In addition, in an animal model of chronic stress‑induced depression, increased expression levels of miR‑132, and decreased levels of MeCP2 and BDNF were detected in the hippocampi. Furthermore, knockdown of MeCP2 expression in primary hippocampal neurons increased the expression of miR‑132 and decreased the expression levels of BDNF. The results of the present study demonstrated that miR‑132 may directly target MeCP2, but not BDNF, and control its expression at the transcriptional and translational level. miR‑132 was also shown to negatively regulate BDNF expression. The reduced expression levels of BDNF, as induced by MeCP2 knockdown, were enhanced by miR‑132 mimics, and were rescued by miR‑132 inhibitors. These results suggested that homeostatic interactions between MeCP2 and miR‑132 may regulate hippocampal BDNF levels, which may have a role in the pathogenesis of MDD.

Flupirtine attenuates chronic restraint stress-induced cognitive deficits and hippocampal apoptosis in male mice

Chronic restraint stress (CRS) causes hippocampal neurodegeneration and hippocampus-dependent cognitive deficits. Flupirtine represents neuroprotective effects and we have previously shown that flupirtine can protect against memory impairment induced by acute stress. The present study aimed to investigate whether flupirtine could alleviate spatial learning and memory impairment and hippocampal apoptosis induced by CRS. CRS mice were restrained in well-ventilated Plexiglass tubes for 6h daily beginning from 10:00 to 16:00 for 21 consecutive days. Mice were injected with flupirtine (10mg/kg and 25mg/kg) or vehicle (10% DMSO) 30min before restraint stress for 21 days. After stressor cessation, the spatial learning and memory, dendritic spine density, injured neurons and the levels of Bcl-2, Bax, p-Akt, p-GSK-3β, p-Erk1/2 and synaptophysin of hippocampal tissues were examined. Our results showed that flupirtine significantly prevented spatial learning and memory impairment induced by CRS in the Morris water maze. In addition, flupirtine (10mg/kg and 25mg/kg) treatment alleviated neuronal apoptosis and the reduction of dendritic spine density and synaptophysin expression in the hippocampal CA1 region of CRS mice. Furthermore, flupirtine (10mg/kg and 25mg/kg) treatment significantly decreased the expression of Bax and increased the p-Akt and p-GSK-3β, and flupirtine (25mg/kg) treatment up-regulated the p-Erk1/2 in the hippocampus of CRS mice. These results suggested that flupirtine exerted protective effects on the CRS-induced cognitive impairment and hippocampal neuronal apoptosis, which is possibly associated with the activation of Akt/GSK-3β and Erk1/2 signaling pathways.

Genome-wide methylation study on depression: differential methylation and variable methylation in monozygotic twins

Depressive disorders have been shown to be highly influenced by environmental pathogenic factors, some of which are believed to exert stress on human brain functioning via epigenetic modifications. Previous genome-wide methylomic studies on depression have suggested that, along with differential DNA methylation, affected co-twins of monozygotic (MZ) pairs have increased DNA methylation variability, probably in line with theories of epigenetic stochasticity. Nevertheless, the potential biological roots of this variability remain largely unexplored. The current study aimed to evaluate whether DNA methylation differences within MZ twin pairs were related to differences in their psychopathological status. Data from the Illumina Infinium HumanMethylation450 Beadchip was used to evaluate peripheral blood DNA methylation of 34 twins (17 MZ pairs). Two analytical strategies were used to identify (a) differentially methylated probes (DMPs) and (b) variably methylated probes (VMPs). Most DMPs were located in genes previously related to neuropsychiatric phenotypes. Remarkably, one of these DMPs (cg01122889) was located in the WDR26 gene, the DNA sequence of which has been implicated in major depressive disorder from genome-wide association studies. Expression of WDR26 has also been proposed as a biomarker of depression in human blood. Complementarily, VMPs were located in genes such as CACNA1C, IGF2 and the p38 MAP kinase MAPK11, showing enrichment for biological processes such as glucocorticoid signaling. These results expand on previous research to indicate that both differential methylation and differential variability have a role in the etiology and clinical manifestation of depression, and provide clues on specific genomic loci of potential interest in the epigenetics of depression.