Essential role of microglial transforming growth factor-β1 in antidepressant actions of (R)-ketamine and the novel antidepressant TGF-β1

(R)-ketamine as prophylactic and therapeutic drug for neurological disorders: beyond depression

Neurological disorders are the leading cause of disability and the second leading cause of death worldwide. The increasing social and economic burdens of neurological disorders are driven by global population growth and aging. Depression is a common psychiatric symptom in numerous neurological disorders. It is also a risk factor for Alzheimer's disease (AD) and other dementias, Parkinson's disease (PD), and stroke. The rapid-acting and sustained antidepressant actions of (R,S)-ketamine for severe depression was accidentally discovered. Interestingly, (R)-ketamine has greater potency and longer-lasting antidepressant-like effects than (S)-ketamine in rodents. Importantly, its side effects in rodents and humans are lower than those of (R,S)-ketamine and (S)-ketamine. Furthermore, (R)-ketamine could elicit beneficial actions in various rodent models of neurological disorders, including PD, multiple sclerosis (MS), and stroke. In this article, we review the potential of (R)-ketamine as a prophylactic or therapeutic drug for neurological disorders including AD and other dementias, PD, MS, and stroke.

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.

Repeated intermittent administration of (R)-ketamine during juvenile and adolescent stages prevents schizophrenia-relevant phenotypes in adult offspring after maternal immune activation: a role of TrkB signaling

Maternal immune activation (MIA) plays a role in the etiology of schizophrenia. MIA by prenatal exposure of polyinosinic:polycytidylic acid [poly(I:C)] in rodents caused behavioral and neurobiological changes relevant to schizophrenia in adult offspring. We investigated whether the novel antidepressant (R)-ketamine could prevent the development of psychosis-like phenotypes in adult offspring after MIA. We examined the effects of (R)-ketamine (10 mg/kg/day, twice weekly for 4 weeks) during juvenile and adolescent stages (P28-P56) on the development of cognitive deficits, loss of parvalbumin (PV)-immunoreactivity in the medial prefrontal cortex (mPFC), and decreased dendritic spine density in the mPFC and hippocampus from adult offspring after prenatal poly(I:C) exposure. Furthermore, we examined the role of TrkB in the prophylactic effects of (R)-ketamine. Repeated intermittent administration of (R)-ketamine during juvenile and adolescent stages significantly blocked the development of cognitive deficits, reduced PV-immunoreactivity in the prelimbic (PrL) of mPFC, and decreased dendritic spine density in the PrL of mPFC, CA3 and dentate gyrus of the hippocampus from adult offspring after prenatal poly(I:C) exposure. Furthermore, pretreatment with ANA-12 (TrkB antagonist: twice weekly for 4 weeks) significantly blocked the beneficial effects of (R)-ketamine on cognitive deficits of adult offspring after prenatal poly(I:C) exposure. These data suggest that repeated intermittent administration of (R)-ketamine during juvenile and adolescent stages could prevent the development of psychosis in adult offspring after MIA. Therefore, (R)-ketamine would be a potential prophylactic drug for young subjects with high-risk for psychosis.

Microglia as a Hub for Suicide Neuropathology: Future Investigation and Prevention Targets

Suicide is a complex public health challenge associated worldwide with one death every 40 s. Research advances in the neuropathology of suicidal behaviors (SB) have defined discrete brain changes which may hold the key to suicide prevention. Physiological differences in microglia, the resident immune cells of the brain, are present in post-mortem tissue samples of individuals who died by suicide. Furthermore, microglia are mechanistically implicated in the outcomes of important risk factors for SB, including early-life adversity, stressful life events, and psychiatric disorders. SB risk factors result in inflammatory and oxidative stress activities which could converge to microglial synaptic remodeling affecting susceptibility or resistance to SB. To push further this perspective, in this Review we summarize current areas of opportunity that could untangle the functional participation of microglia in the context of suicide. Our discussion centers around microglial state diversity in respect to morphology, gene and protein expression, as well as function, depending on various factors, namely brain region, age, and sex.

Microglial depletion and abnormalities in gut microbiota composition and short-chain fatty acids in mice after repeated administration of colony stimulating factor 1 receptor inhibitor PLX5622

PLX5622, a brain-penetrant highly specific inhibitor of the colony-stimulating factor 1 receptor (CSF1R), is used to eliminate microglia in the brain. Considering the role of microglia and gut microbiota in the brain homeostasis, this study was undertaken to investigate whether repeated intragastric administration of PLX5622 (65 mg/kg/day for consecutive 7 days) could affect the composition of gut microbiota and the concentration of short-chain fatty acids (SCFAs) in fresh feces of adult mice. Repeated administration of PLX5622 caused significant reductions of the expression of genes and proteins for microglial markers in the prefrontal cortex (PFC) and hippocampus compared to control mice although the elimination of brain's microglia was partial. There was a significant alteration in the β-diversity of intestine microbiota in the PLX5622-treated group. Linear discriminant analysis effect size identified eight significant enriched bacteria as microbial markers for PLX5622-treated group. Repeated administration of PLX5622 affected the relative abundance of several bacteria at the genus and species levels. Furthermore, repeated administration of PLX5622 caused a significant change in lactic acid compared to control group. Interestingly, we found significant correlations between microglial markers in the brain and the relative abundance of several bacteria, suggesting microbiome-microglia crosstalk through the brain-gut axis. These data demonstrate that repeated administration of PLX5622 leads to an abnormal composition of the gut microbiota and lactic acid in adult mice. Therefore, abnormalities in the composition of gut microbiota after repeated treatment of PLX5622 should be considered for behavioral and biological functions in animals treated with CSF1R inhibitors.

Is (R)-ketamine a Potential Therapeutic Agent for Treatment-Resistant Depression with Less Detrimental Side Effects? A Review of Molecular Mechanisms Underlying Ketamine and its Enantiomers

Approximately one-third of individuals with major depressive disorder are resistant to conventional antidepressants (i.e., monoamine-based therapies), and, even among respondents, a proper therapeutic effect may require weeks of treatment. Ketamine, a racemic mixture of the two enantiomers, (R)-ketamine and (S)-ketamine, is an N-methyl-d-aspartate receptor (NMDAR) antagonist and has been shown to have rapid-acting antidepressant properties in patients with treatment-resistant depression (TRD). Although (R)-ketamine has a lower affinity for NMDAR, it presents greater potency and longer-lasting antidepressant properties, with no major side effects, than racemic ketamine or (S)-ketamine in preclinical findings. Thereby, ketamine and its enantiomers have not only an antagonistic effect on NMDAR but also a strong synaptogenic-modulatory effect, which is impaired in TRD pathophysiology. In this review, we summarize the current evidence regarding the modulation of neurotransmission, neuroplasticity, and neural network activity as putative mechanisms of these rapid-acting antidepressants, highlighting differences on intracellular signaling pathways of synaptic proteins such as mammalian target of rapamycin (mTOR), extracellular signal-regulated kinase (ERK) and brain-derived neurotrophic factor (BDNF). In addition, we discuss probable mechanisms involved in the side effects of ketamine and its enantiomers.

Molecular mechanisms underlying the antidepressant actions of arketamine: beyond the NMDA receptor

The discovery of robust antidepressant actions exerted by the N-methyl-D-aspartate receptor (NMDAR) antagonist (R,S)-ketamine has been a crucial breakthrough in mood disorder research. (R,S)-ketamine is a racemic mixture of equal amounts of (R)-ketamine (arketamine) and (S)-ketamine (esketamine). In 2019, an esketamine nasal spray from Johnson & Johnson was approved in the United States of America and Europe for treatment-resistant depression. However, an increasing number of preclinical studies show that arketamine has greater potency and longer-lasting antidepressant-like effects than esketamine in rodents, despite the lower binding affinity of arketamine for the NMDAR. In clinical trials, non-ketamine NMDAR-related compounds did not exhibit ketamine-like robust antidepressant actions in patients with depression, despite these compounds showing antidepressant-like effects in rodents. Thus, the rodent data do not necessarily translate to humans due to the complexity of human psychiatric disorders. Collectively, the available studies indicate that it is unlikely that NMDAR plays a major role in the antidepressant action of (R,S)-ketamine and its enantiomers, although the precise molecular mechanisms underlying antidepressant actions of (R,S)-ketamine and its enantiomers remain unclear. In this paper, we review recent findings on the molecular mechanisms underlying the antidepressant actions of (R,S)-ketamine and its potent enantiomer arketamine. Furthermore, we discuss the possible role of the brain-gut-microbiota axis and brain-spleen axis in stress-related psychiatric disorders and in the antidepressant-like action of arketamine. Finally, we discuss the potential of arketamine as a treatment for cognitive impairment in psychiatric disorders, Parkinson's disease, osteoporosis, inflammatory bowel diseases, and stroke.

Microglial ERK-NRBP1-CREB-BDNF signaling in sustained antidepressant actions of (R)-ketamine

(R,S)-ketamine elicits rapid-acting and sustained antidepressant actions in treatment-resistant patients with depression. (R)-ketamine produces longer-lasting antidepressant effects than (S)-ketamine in rodents; however, the precise molecular mechanisms underlying antidepressant actions of (R)-ketamine remain unknown. Using isobaric Tag for Relative and Absolute Quantification, we identified nuclear receptor-binding protein 1 (NRBP1) that could contribute to different antidepressant-like effects of the two enantiomers in chronic social defeat stress (CSDS) model. NRBP1 was localized in the microglia and neuron, not astrocyte, of mouse medial prefrontal cortex (mPFC). (R)-ketamine increased the expression of NRBP1, brain-derived neurotrophic factor (BDNF), and phosphorylated cAMP response element binding protein (p-CREB)/CREB ratio in primary microglia cultures thorough the extracellular signal-regulated kinase (ERK) activation. Furthermore, (R)-ketamine could activate BDNF transcription through activation of CREB as well as MeCP2 (methyl-CpG binding protein 2) suppression in microglia. Single intracerebroventricular (i.c.v.) injection of CREB-DNA/RNA heteroduplex oligonucleotides (CREB-HDO) or BDNF exon IV-HDO blocked the antidepressant-like effects of (R)-ketamine in CSDS susceptible mice. Moreover, microglial depletion by colony-stimulating factor 1 receptor (CSF1R) inhibitor PLX3397 blocked the antidepressant-like effects of (R)-ketamine in CSDS susceptible mice. In addition, inhibition of microglia by single i.c.v. injection of mannosylated clodronate liposomes (MCLs) significantly blocked the antidepressant-like effects of (R)-ketamine in CSDS susceptible mice. Finally, single i.c.v. injection of CREB-HDO, BDNF exon IV-HDO or MCLs blocked the beneficial effects of (R)-ketamine on the reduced dendritic spine density in the mPFC of CSDS susceptible mice. These data suggest a novel ERK-NRBP1-CREB-BDNF pathways in microglia underlying antidepressant-like effects of (R)-ketamine.

miR-98-5p plays a critical role in depression and antidepressant effect of ketamine

Ketamine has been demonstrated to be a rapid-onset and long-lasting antidepressant, but its underlying molecular mechanisms remain unclear. Recent studies have emerged microRNAs as important modulators for depression treatment. In this study, we report that miR-98-5p is downregulated in the prefrontal cortex and hippocampus of mice subjected to chronic social stress, while overexpressing it by its agonist alleviates depression-like behaviors. More importantly, we demonstrate that miR-98-5p is upregulated by ketamine administration, while inhibition of it by its antagonist blocks the antidepressant effect of ketamine. Our data implicate a novel molecular mechanism underlying the antidepressant effect of ketamine, and that therapeutic strategies targeting miR-98-5p could exert beneficial effects for depression treatment.

Intranasal administration of transforming growth factor-β1 elicits rapid-acting antidepressant-like effects in a chronic social defeat stress model: A role of TrkB signaling

(R,S)-ketamine causes rapid-acting and sustained antidepressant effects in treatment-resistant patients with depression although the precise molecular mechanisms underlying its antidepressant action remain unclear. We recently reported that transforming growth factor (TGF)-β1 might contribute to the antidepressant-like effects of (R)-ketamine that is a more potent enantiomer in rodents. Although TrkB signaling plays a role in the antidepressant-like actions of (R,S)-ketamine and its enantiomers, the role of TrkB signaling in the antidepressant effects of TGF-β1 remains unclear. Using behavioral tests such as tail-suspension test (TST), forced swimming test (FST), and 1% sucrose preference test (SPT), we investigated whether a single intranasal administration of the recombinant TGF-β1 (1.5 and 3.0 μg/kg) causes rapid and sustained antidepressant-like effects in a chronic social defeat stress (CSDS) model. Both doses of TGF-β1 significantly attenuated the increased immobility time of TST and FST in the CSDS susceptible mice. High dose of TGF-β1, but not low dose, significantly ameliorated the decreased sucrose preference of SPT in the CSDS susceptible mice. Pretreatment with a TrkB antagonist ANA-12 (0.5 mg/kg) blocked the antidepressant-like effects of TGF-β1 in CSDS susceptible mice. The data suggest that intranasal administration of TGF-β1 could elicit rapid-acting antidepressant-like effects via TrkB stimulation in a CSDS model. Therefore, it is likely that intranasal administration of TGF-β1 would be a novel therapeutic approach for depression.

(R,S)-Ketamine Promotes Striatal Neurogenesis and Sensorimotor Recovery Through Improving Poststroke Depression–Mediated Decrease in Atrial Natriuretic Peptide

Background

Poststroke social isolation could worsen poststroke depression and dampen neurogenesis. (R,S)-ketamine has antidepressant and neuroprotective effects; however, its roles and mechanisms in social isolation–mediated depressive-like behaviors and sensorimotor recovery remain unclear.

Methods

Mice were subjected to transient middle cerebral artery occlusion, and then were pair-housed with ovariectomized female mice or were housed isolated (ISO) starting at 3 days postischemia. ISO mice received 2 weeks of (R,S)-ketamine treatment starting at 14 days postischemia. Primary ependymal epithelial cells and choroid plexus epithelial cells were cultured and treated with recombinant human atrial natriuretic peptide (ANP) protein.

Results

The poststroke social isolation model was successfully established using middle cerebral artery occlusion combined with poststroke isolation, as demonstrated by a more prominent depression-like phenotype in ISO mice compared with pair-housed mice. (R,S)-ketamine reversed ISO-mediated depressive-like behaviors and increased ANP levels in the atrium. The depression-like phenotype was negatively correlated with ANP levels in both the atrium and plasma. Atrial GLP-1 and GLP-1 receptor signaling was essential to the promoting effects of (R,S)-ketamine on the synthesis and secretion of ANP from the atrium in ISO mice. (R,S)-ketamine also increased ANP and TGF-β1 levels in the choroid plexus of ISO mice. Recombinant human ANP increased TGF-β1 levels in both the primarily cultured ependymal epithelial cells and choroid plexus epithelial cells. Furthermore, (R,S)-ketamine increased TGF-β1 levels in the ischemic hemisphere and promoted striatal neurogenesis and sensorimotor recovery via ANP in ISO mice.

Conclusions

(R,S)-ketamine alleviated poststroke ISO-mediated depressive-like behaviors and thus promoted striatal neurogenesis and sensorimotor recovery via ANP.

Effect of ketamine on gene expression in zebrafish embryos

Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist. Used as an anesthetic, potential neurotoxic and cardiotoxic effects of ketamine in animal models have been reported. The underlying mechanisms of ketamine-induced toxicity are not clear. The zebrafish is an ideal model for toxicity assays because of its predictive capability in chemical testing, which compares well with that of mammalian models. To gain insight into potential mechanisms of ketamine effects, we performed real-time quantitative polymerase chain reaction-based gene expression array analyses. Gene expression analysis was conducted for multiple genes (a total of 84) related to 10 major signaling pathways including the transforming growth factor β (TGFβ), Wingless and Int-1 (Wnt), nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB), Janus kinase/signal transducers and activators of transcription (JAK/STAT), p53, Notch, Hedgehog, peroxisome proliferator-activated receptor (PPAR), oxidative stress, and hypoxia pathways. Our results show that ketamine altered the expression of specific genes related to hypoxia, p53, Wnt, Notch, TGFβ, PPAR, and oxidative stress pathways. Thus, we can further focus on these specific pathways to elucidate the mechanisms by which ketamine elicits a toxic response.

Activation of liver X receptors prevents emotional and cognitive dysfunction by suppressing microglial M1-polarization and restoring synaptic plasticity in the hippocampus of mice

Depression is a long-lasting and persistent mood disorder in which the regulatory mechanisms of neuroinflammation are thought to play a contributing role to the physiopathology of the condition. Previous studies have shown that liver X receptors (LXRs) can regulate the activation of microglia and neuroinflammation. However, the role of LXRs in depression remains to be fully understood. In this study, we hypothesized that stress impairs the function of LXRs and that the LXRs agonist GW3965 plays a potential anti-depressive role by inhibiting neuroinflammation. The anti-depressive effects of GW3965 were evaluated in both chronic unpredictable mild stress (CUMS) and lipopolysaccharide (LPS) models. The LXRs antagonist GSK2033 was also employed to block LXRs. Behavioural tests were performed to measure depression-like phenotypes and learning abilities. Electrophysiological recordings and Golgi staining were used to measure the plasticity of the dentate gyrus synapse. The expression of synapse and neuroinflammation related proteins were evaluated by Western blotting and immunofluorescence. The activation of LXRs by GW3965 prevented emotional and cognitive deficits induced by either CUMS or LPS. GW3965 prevented the decreased level of LXR-β induced by CUMS. The activation of LXRs significantly improved the impairment of synaptic plasticity, prevented the up-regulation of inflammatory factors and inhibited NF-κB phosphorylation and microglial M1-polarization in both models. The antidepressive-like effects of GW3965 were blocked by GSK2033 in the CUMS and LPS models. Our data suggest that inhibition of the LXRs signalling pathway may be a key driver in the pathogenesis of neuroinflammation during depression and that LXRs agonists have a high potential in the treatment of depression.

Obesity Prevents S-Adenosylmethionine-Mediated Improvements in Age-Related Peripheral and Hippocampal Outcomes

Background: Age predisposes individuals to a myriad of disorders involving inflammation; this includes stress-related neuropsychiatric disorders such as depression and anxiety, and neurodegenerative diseases. Obesity can further exacerbate these effects in the brain. We investigated whether an inexpensive dietary supplement, s-adenosylmethionine (SAMe), could improve age- and/or obesity-related inflammatory and affective measures in the hippocampus. Methods: Mice were placed on their diets at six weeks of age and then aged to 14 months, receiving SAMe (0.1 g/kg of food) for the final six weeks of the experiment. Prior to tissue collection, mice were tested for anxiety-like behaviors in the open field test and for metabolic outcomes related to type 2 diabetes. Results: SAMe treatment significantly improved outcomes in aged control mice, where fasting glucose decreased, liver glutathione levels increased, and hippocampal microglia morphology improved. SAMe increased transforming growth factor β-1 mRNA in both control mice, potentially accounting for improved microglial outcomes. Obese mice demonstrated increased anxiety-like behavior, where SAMe improved some, but not all, open field measures. Conclusions: In summary, SAMe boosted antioxidant levels, improved diabetic measures, and hippocampal inflammatory and behavioral outcomes in aged mice. The effects of SAMe in obese mice were more subdued, but it could still provide some positive outcomes for obese individuals dealing with anxiety and having difficulty changing their behaviors to improve health outcomes.

Integrating Clinical and Genomic Analyses of Hippocampal-Prefrontal Circuit Disorder in Depression

Major depressive disorder (MDD) is a prevalent, devastating and recurrent mental disease. Hippocampus (HIP)-prefrontal cortex (PFC) neural circuit abnormalities have been confirmed to exist in MDD; however, the gene-related molecular features of this circuit in the context of depression remain unclear. To clarify this issue, we performed gene set enrichment analysis (GSEA) to comprehensively analyze the genetic characteristics of the two brain regions and used weighted gene correlation network analysis (WGCNA) to determine the main depression-related gene modules in the HIP-PFC network. To clarify the regional differences and consistency for MDD, we also compared the expression patterns and molecular functions of the key modules from the two brain regions. The results showed that candidate modules related to clinical MDD of HIP and PFC, which contained with 363 genes and 225 genes, respectively. Ninety-five differentially expressed genes (DEGs) were identified in the HIP candidate module, and 51 DEGs were identified in the PFC candidate module, with only 11 overlapping DEGs in these two regional modules. Combined with the enrichment results, although there is heterogeneity in the molecular functions in the HIP-PFC network of depression, the regulation of the MAPK cascade, Ras protein signal transduction and Ephrin signaling were significantly enriched in both brain regions, indicating that these biological pathways play important roles in MDD pathogenesis. Additionally, the high coefficient protein–protein interaction (PPI) network was constructed via STRING, and the top-10 coefficient genes were identified as hub genes via the cytoHubba algorithm. In summary, the present study reveals the gene expression characteristics of MDD and identifies common and unique molecular features and patterns in the HIP-PFC network. Our results may provide novel clues from the gene function perspective to explain the pathogenic mechanism of depression and to aid drug development. Further research is needed to confirm these findings and to investigate the genetic regulation mechanisms of different neural networks in depression.

Ketamine: A tale of two enantiomers

The discovery of the rapid antidepressant effects of the dissociative anaesthetic ketamine, an uncompetitive N-Methyl-D-Aspartate receptor antagonist, is arguably the most important breakthrough in depression research in the last 50 years. Ketamine remains an off-label treatment for treatment-resistant depression with factors that limit widespread use including its dissociative effects and abuse potential. Ketamine is a racemic mixture, composed of equal amounts of (S)-ketamine and (R)-ketamine. An (S)-ketamine nasal spray has been developed and approved for use in treatment-resistant depression in the United States and Europe; however, some concerns regarding efficacy and side effects remain. Although (R)-ketamine is a less potent N-Methyl-D-Aspartate receptor antagonist than (S)-ketamine, increasing preclinical evidence suggests (R)-ketamine may have more potent and longer lasting antidepressant effects than (S)-ketamine, alongside fewer side effects. Furthermore, a recent pilot trial of (R)-ketamine has demonstrated rapid-acting and sustained antidepressant effects in individuals with treatment-resistant depression. Research is ongoing to determine the specific cellular and molecular mechanisms underlying the antidepressant actions of ketamine and its component enantiomers in an effort to develop future rapid-acting antidepressants that lack undesirable effects. Here, we briefly review findings regarding the antidepressant effects of ketamine and its enantiomers before considering underlying mechanisms including N-Methyl-D-Aspartate receptor antagonism, γ-aminobutyric acid-ergic interneuron inhibition, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptor activation, brain-derived neurotrophic factor and tropomyosin kinase B signalling, mammalian target of rapamycin complex 1 and extracellular signal-regulated kinase signalling, inhibition of glycogen synthase kinase-3 and inhibition of lateral habenula bursting, alongside potential roles of the monoaminergic and opioid receptor systems.

Drug repositioning for treatment-resistant depression: Hypotheses from a pharmacogenomic study

About 20-30% of patients with major depressive disorder (MDD) develop treatment-resistant depression (TRD) and finding new effective treatments for TRD has been a challenge. This study aimed to identify new possible pharmacological options for TRD. Genes in pathways included in predictive models of TRD in a previous whole exome sequence study were compared with those coding for targets of drugs in any phase of development, nutraceuticals, proteins and peptides from Drug repurposing Hub, Drug-Gene Interaction database and DrugBank database. We tested if known gene targets were enriched in TRD-associated genes by a hypergeometric test. Compounds enriched in TRD-associated genes after false-discovery rate (FDR) correction were annotated and compared with those showing enrichment in genes associated with MDD in the last Psychiatric Genomics Consortium genome-wide association study. Among a total of 15,475 compounds, 542 were enriched in TRD-associated genes (FDR p < .05). Significant results included drugs which are currently used in TRD (e.g. lithium and ketamine), confirming the rationale of this approach. Interesting molecules included modulators of inflammation, renin-angiotensin system, proliferator-activated receptor agonists, glycogen synthase kinase 3 beta inhibitors and the rho associated kinase inhibitor fasudil. Nutraceuticals, mostly antioxidant polyphenols, were also identified. Drugs showing enrichment for TRD-associated genes had a higher probability of enrichment for MDD-associated genes compared to those having no TRD-genes enrichment (p = 6.21e-55). This study suggested new potential treatments for TRD using a in silico approach. These analyses are exploratory only but can contribute to the identification of drugs to study in future clinical trials.

Don't know what you got till it's gone: microglial depletion and neurodegeneration

In the central nervous system, immunologic surveillance and response are carried out, in large part, by microglia. These resident macrophages derive from myeloid precursors in the embryonic yolk sac, migrating to the brain and eventually populating local tissue prior to blood-brain barrier formation. Preserved for the duration of lifespan, microglia serve the host as more than just a central arm of innate immunity, also contributing significantly to the development and maintenance of neurons and neural networks, as well as neuroregeneration. The critical nature of these varied functions makes the characterization of key roles played by microglia in neurodegenerative disorders, especially Alzheimer's disease, of paramount importance. While genetic models and rudimentary pharmacologic approaches for microglial manipulation have greatly improved our understanding of central nervous system health and disease, significant advances in the selective and near complete in vitro and in vivo depletion of microglia for neuroscience application continue to push the boundaries of research. Here we discuss the research efficacy and utility of various microglial depletion strategies, including the highly effective CSF1R inhibitor models, noteworthy insights into the relationship between microglia and neurodegeneration, and the potential for therapeutic repurposing of microglial depletion and repopulation.

ATP-binding cassette transporter 13 mRNA expression level in schizophrenia patients

The objective of this study was to investigate the expression and clinical role of ATP-binding cassette transporter 13 (ABCA13) gene previously shown to be associated with schizophrenia (SZ) through Genome-wide association studies studies. Thirty-two first-episode drug-naive SZ patients and forty-eight age and gender-matched healthy controls were enrolled in this study. We measured ABCA13 mRNA expression levels using quantitative real-time PCR at baseline and 12 weeks after antipsychotic therapy. Moreover, clinical symptoms were measured by the Positive and Negative Syndrome Scale (PANSS) at baseline and 12-week follow-up. We found that ABCA13 mRNA levels were significantly lower in SZ patients compared with healthy controls at baseline. SZ patients’ symptoms were decreased, but ABCA13 mRNA levels were increased after 12 weeks antipsychotic therapy. In addition, there was a significant difference in ABCA13 mRNA levels among SZ patients at baseline and 12-week follow-up. The ABCA13 mRNA levels were not associated with age, BMI, years of education. Of the clinical symptoms measured, the ABCA13 mRNA levels were negatively associated with the PANSS scores at baseline and 12-week follow-up. The results indicated that the ABCA13 mRNA expression level is of interest, and upon further studies, it could be used as a biomarker for SZ treatment outcome.

Can Intraoperative Low-Dose R,S-Ketamine Prevent Depressive Symptoms After Surgery? The First Meta-Analysis of Clinical Trials

Background: Postoperative depression is a common complication after surgery that profoundly affects recovery and prognosis. New research indicates that (R,S)-ketamine is a potent antidepressant that exerts a rapid and sustained antidepressive effect. However, there is no consensus on whether intraoperative low-dose (R,S)-ketamine prevents postoperative depression. Objectives: This study aimed to investigate the safety, feasibility, and short-term complications of intraoperative low-dose (R,S)-ketamine in preventing postoperative depressive symptoms. Methods: The Web of Science, Cochrane, PubMed, and CNKI databases were systematically searched (last search February 28, 2020) to identify studies involving ketamine. Sensitivity and metaregression analyses were performed to identify potential confounders. The meta-analysis was performed using Review Manager 5.3. Results: A total of 13 studies (seven in Chinese and six in English) representing 1,148 cases of patients who were treated with (R,S)-ketamine and 874 cases of patients who received other treatments were included in the meta-analysis. Anesthesia duration and blood loss did not significantly differ between the two groups, demonstrating that (R,S)-ketamine was safe (odds ratio,OR: 0.27; 95% CI: -1.14 to 1.68; P = 0.71) for prophylactic treatment of postoperative depression. Blood loss (OR: -1.83; 95% CI: -8.34 to 4.68; P = 0.58), the number of postoperative depressive patients (95% CI: 0.8-1.07; P = 0.08; (R,S)-ketamine: control = 12.9%:15.8%), and postoperative complications (OR: 0.83, 95% CI: 0.44-1.58; P = 0.57; (R,S)-ketamine: control = 19.3%:19.3%) were all similar across groups. Intra-operative low-dose (R,S)-ketamine reduced extubation time (OR: -2.84; 95% CI: -5.48 to -0.21; P = 0.03). Conclusions: The prophylactic anti-depressant effect of (R,S)-ketamine did not significantly differ between the (R,S)-ketamine and control groups in patients undergoing general or spinal anesthesia. However, (R,S)-ketamine use led to a higher incidence of adverse reactions in patients under 40 years of age who underwent a Cesarean section under spinal anesthesia.

Microglia in depression: current perspectives

Major depressive disorder (MDD) is a prevalent psychiatric disease that involves malfunctions of different cell types in the brain. Accumulating studies started to reveal that microglia, the primary resident immune cells, play an important role in the development and progression of depression. Microglia respond to stress-triggered neuroinflammation, and through the release of proinflammatory cytokines and their metabolic products, microglia may modulate the function of neurons and astrocytes to regulate depression. In this review, we focused on the role of microglia in the etiology of depression. We discussed the dynamic states of microglia; the correlative and causal evidence of microglial abnormalities in depression; possible mechanisms of how microglia sense depression-related stress and modulate depression state; and how antidepressive therapies affect microglia. Understanding the role of microglia in depression may shed light on developing new treatment strategies to fight against this devastating mental illness.

Ingestion of Lactobacillus intestinalis and Lactobacillus reuteri causes depression- and anhedonia-like phenotypes in antibiotic-treated mice via the vagus nerve

Background

The brain–gut–microbiota axis plays a role in the pathogenesis of stress-related disorders such as depression. In this study, we examined the effects of fecal microbiota transplantation (FMT) in mice with antibiotic-treated microbiota depletion.

Methods

The fecal microbiota was obtained from mice subjected to chronic social defeat stress (CSDS) and control (no CSDS) mice. FMT from these two groups was performed to antibiotic-treated mice. 16S rRNA analysis was performed to examine the composition of gut microbiota. Furthermore, the effects of subdiaphragmatic vagotomy in depression-like phenotypes after ingestion of microbes were examined.

Results

The ingestion of fecal microbiota from CSDS-susceptible mice resulted in an anhedonia-like phenotype, higher plasma levels of interleukin-6 (IL-6), and decreased expression of synaptic proteins in the prefrontal cortex (PFC) in antibiotic-treated mice but not in water-treated mice. 16S rRNA analysis suggested that two microbes (Lactobacillus intestinalis and Lactobacillus reuteri) may be responsible for the anhedonia-like phenotype in antibiotic-treated mice after FMT. Ingestion of these two microbes for 14 days led to depression- and anhedonia-like phenotypes, higher plasma IL-6 levels, and decreased expression of synaptic proteins in the PFC of antibiotic-treated mice. Interestingly, subdiaphragmatic vagotomy significantly blocked the development of behavioral abnormalities, elevation of plasma IL-6 levels, and downregulation of synaptic proteins in the PFC after ingestion of these two microbes.

Conclusions

These findings suggest that microbiota depletion using an antibiotic cocktail is essential for the development of FMT-induced behavioral changes and that the vagus nerve plays a key role in behavioral abnormalities in antibiotic-treated mice after the ingestion of L. intestinalis and L. reuteri. Therefore, it is likely that the brain–gut–microbiota axis participates in the pathogenesis of depression via the vagus nerve.

Antidepressant Drugs and Physical Activity: A Possible Synergism in the Treatment of Major Depression?

Major depressive disorder (MDD) is a severe mental illness that affects 5–20% of the general population. Current antidepressant drugs exert only a partial clinical efficacy because approximately 30% of depressed patients failed to respond to these drugs and antidepressants produce remission only in 30% of patients. This can be explained by the fact that the complex pathophysiology of depression has not been completely elucidated, and treatments have been mainly developed following the “monoaminergic hypothesis” of depression without considering the key role of other factors involved in the pathogenesis of MDD, such as the role of chronic stress and neuroinflammation. Chronic stress acts as a risk factor for the development of MDD through the impairment of neurotrophins signaling such as brain-derived neurotrophic factor (BDNF) and transforming-growth-factor-β1 (TGF-β1). Stress-induced depressive pathology contributes to altered BDNF level and function in MDD patients and, thereby, an impairment of neuroplasticity at the regional and circuit level. Recent studies demonstrate that aerobic exercise strongly increases BDNF production and it may contribute as a non-pharmacological strategy to improve the treatment of cognitive and affective symptoms in MDD. Here we will provide a general overview on the possible synergism between physical activity and antidepressants in MDD. Physical activity can synergize with antidepressant treatment by rescuing neurotrophins signaling in MDD patients, promoting neuronal health and recovery of function in MDD-related circuits, finally enhancing pharmacotherapeutic response. This synergism might be particularly relevant in elderly patients with late-life depression, a clinical subgroup with an increased risk to develop dementia.