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

Apoptosis-induced decline in hippocampal microglia mediates the development of depression-like behaviors in adult mice triggered by unpredictable stress during adolescence

Depression triggered by harmful stress during adolescence is a common problem that can affect mental health. To date, the mechanisms underlying this type of depression remain unclear. One mechanism for the promotion of depression by chronic stress in adulthood is the loss of hippocampal microglia. Since deleterious stress in adolescence also activates microglia, we investigated the dynamic changes of microglia in the hippocampus in mice exposed to chronic unpredictable stress (CUS) in adolescence. Our results showed that 12 days of CUS stimulation in adolescence induced typical depression-like behaviors in adult mice, which were accompanied by a significant decrease and dystrophy of microglia in the dentate gyrus of the hippocampus. Further analysis showed that this decrease in microglia was mediated by the initial response of microglia to unpredictable stress in the dentate gyrus of the hippocampus and their subsequent apoptosis. Blocking the initial response of microglia to unpredictable stress by pretreatment with minocycline was able to prevent apoptosis and microglial decline as well as the development of depression-like behaviors in adult mice induced by adolescent CUS. Moreover, administration of lipopolysaccharide (LPS) or macrophage-colony stimulatory factor (M-CSF), two drugs that reversed microglia decline in the dentate gyrus, ameliorated the depression-like behaviors induced by CUS stimulation in adolescence. These findings reveal a novel mechanism for the development of depression-like behaviors in animals triggered by deleterious stress in adolescence and suggest that reversing microglial decline in the hippocampus may be a hopeful strategy for the treatment of depression triggered by deleterious stress in adolescence.

Role of oxidative phosphorylation in the antidepressant effects of arketamine via the vagus nerve-dependent spleen-brain axis

Arketamine, the (R)-enantiomer of ketamine, exhibits antidepressant-like effects in mice, though the precise molecular mechanisms remain elusive. It has been shown to reduce splenomegaly and depression-like behaviors in the chronic social defeat stress (CSDS) model of depression. This study investigated whether the spleen contributes to the antidepressant-like effects of arketamine in the CSDS model. We found that splenectomy significantly inhibited arketamine's antidepressant-like effects in CSDS-susceptible mice. RNA-sequencing analysis identified the oxidative phosphorylation (OXPHOS) pathway in the prefrontal cortex (PFC) as a key mediator of splenectomy's impact on arketamine's effects. Furthermore, oligomycin A, an inhibitor of the OXPHOS pathway, reversed the suppressive effects of splenectomy on arketamine's antidepressant-like effects. Specific genes within the OXPHOS pathways, such as COX11, UQCR11 and ATP5e, may contribute to these inhibitory effects. Notably, transforming growth factor (TGF)-β1, along with COX11, appears to modulate the suppressive effects of splenectomy and contribute to arketamine's antidepressant-like effects. Additionally, SRI-01138, an agonist of the TGF-β1 receptor, alleviated the inhibitory effects of splenectomy on arketamine's antidepressant-like effects. Subdiaphragmatic vagotomy also counteracted the inhibitory effects of splenectomy on arketamine's antidepressant-like effects in CSDS-susceptible mice. These findings suggest that the OXPHOS pathway and TGF-β1 in the PFC play significant roles in the antidepressant-like effects of arketamine, mediated through the spleen-brain axis via the vagus nerve.

PLCβ4 driven by cadmium-exposure during gestation and lactation contributes to cognitive deficits by suppressing PIP2/PLCγ1/CREB/BDNF signaling pathway in male offspring

The fetus and infants are particularly vulnerable to Cadmium (Cd) due to the immaturity of the blood-brain barrier. In utero and early life exposure to Cd is associated with cognitive deficits. Although such exposure has attracted widespread attention, its gender-specificity remains controversial, and there are no reports disclosing the underlying mechanism of gender‑specific neurotoxicity. We extensively evaluated the learning and cognitive functions and synaptic plasticity of male and female rats exposed to maternal Cd. Maternal Cd exposure induced learning and memory deficits in male offspring rats, but not in female offspring rats. PLCβ4 was identified as a critical protein, which might be related to the gender‑specific cognitive deficits in male rats. The up-regulated PLCβ4 competed with PLCγ1 to bind to PIP2, which counteracted the hydrolysis of PIP2 by PLCγ1. The decreased activation of PLCγ1 inhibited the phosphorylation of CREB to reduce BDNF transcription, which consequently resulted in the damage of hippocampal neurons and cognitive deficiency. Moreover, the low level of BDNF promoted AEP activation to induce Aβ deposition in the hippocampus. These findings highlight that PLCβ4 might be a potential target for the therapy of learning and cognitive deficits caused by Cd exposure in early life.

From Perspective of Hippocampal Plasticity: Function of Antidepressant Chinese Medicine Xiaoyaosan

The hippocampus is one of the most commonly studied brain regions in the context of depression. The volume of the hippocampus is significantly reduced in patients with depression, which severely disrupts hippocampal neuroplasticity. However, antidepressant therapies that target hippocampal neuroplasticity have not been identified as yet. Chinese medicine (CM) can slow the progression of depression, potentially by modulating hippocampal neuroplasticity. Xiaoyaosan (XYS) is a CM formula that has been clinically used for the treatment of depression. It is known to protect Gan (Liver) and Pi (Spleen) function, and may exert its antidepressant effects by regulating hippocampal neuroplasticity. In this review, we have summarized the association between depression and aberrant hippocampal neuroplasticity. Furthermore, we have discussed the researches published in the last 30 years on the effects of XYS on hippocampal neuroplasticity in order to elucidate the possible mechanisms underlying its therapeutic action against depression. The results of this review can aid future research on XYS for the treatment of depression.

Study on the antidepressant activity of (2R,6R; 2S,6S)-Hydroxynorketamine (HNK) and its derivatives

OBJECTIVE

This study mainly explores (2R,6R; 2S,6S)-HNK and its compounds whether there are antidepressant effects.

METHODS

Four HNK compounds were obtained from 2-(Chlorophenyl) Cyclopentylmethanone. Forced swimming test, locomotor sensitization test, and conditioned location preference test were used to screen the antidepressant activity of the synthesized target compounds.

RESULTS

In the case of 10 mg HNK treatment, compared with saline, the immobile time of mice in the HNK group, I5 group and I6 group at 1 h and 7 days had statistical significance. In the case of 10 mg HNK treatment, compared with saline, the immobile time of compound C and D groups in the glass cylinder area was significantly different. In the locomotor sensitization test, the movement distance of compound C and D groups on day 15 and day 7 mice increased significantly compared with the first day. In the conditioned place preference experiment, compound C and compound D induced conditioned place preference in mice compared with the Veh group.

CONCLUSION

The results of the forced swimming test, locomotor sensitization test, and conditioned location preference test showed that compounds C and D may have certain anti-depressant activity. However, HNK exerts a rapid and significant antidepressant effect within 1 week, but the duration is short.

Melatonin Ameliorates Depressive-Like Behaviors in Ovariectomized Mice by Improving Tryptophan Metabolism via Inhibition of Gut Microbe Alistipes Inops

Melatonin (N-acetyl-5-methoxytryptamine) is reported to improve mood disorders in perimenopausal women and gut microbiome composition is altered during menopausal period. The possible role of microbiome in the treatment effect of melatonin on menopausal depression remains unknown. Here, it is shown that melatonin treatment reverses the gut microbiota dysbiosis and depressive-like behaviors in ovariectomy (OVX) operated mice. This effect of melatonin is prevented by antibiotic cocktails (ABX) treatment. Transferring microbiota harvested from adolescent female mice to OVX-operated mice is sufficient to ameliorate depressive-like behaviors. Conversely, microbiota transplantation from OVX-operated mice or melatonin-treated OVX-operated mice to naïve recipient mice exhibits similar phenotypes to donors. The colonization of Alistipes Inops, which is abundant in OVX-operated mice, confers the recipient with depressive-like behaviors. Further investigation indicates that the expansion of Alistipes Inops induced by OVX leads to the degradation of intestinal tryptophan, which destroys systemic tryptophan availability. Melatonin supplementation restores systemic tryptophan metabolic disorders by suppressing the growth of Alistipes Inops, which ameliorates depressive-like behaviors. These results highlight the previously unrecognized role of Alistipes Inops in the modulation of OVX-induced behavioral disorders and suggest that the application of melatonin to inhibit Alistipes Inops may serve as a potential strategy for preventing menopausal depressive symptoms.

Effects of perioperative application of esketamine on postpartum depression in cesarean section: A systematic review and meta-analysis

BACKGROUND

To evaluate the effect of perioperative esketamine administration on postpartum depression in pregnant women undergoing cesarean section.

METHODS

Data sources was PubMed, Embase, Web of Science, and Cochrane Library from inception to February 1, 2024. Randomized controlled trials in pregnant women undergoing cesarean section were selected and compared to the use of esketamine in the perioperative period. The primary outcome measure was the incidence of postpartum maternal depression. Preferred reporting items for systematic reviews and meta-analyses were used. Data pooled by random-effects models are presented as risk ratios (RR) (95% confidence intervals, 95% CI) or mean differences (95% CI). This review was registered in PROSPERO (ID: CRD42023431197).

RESULTS

We included 8 studies with a total of 1655 participants. The quality of the studies was rated high or unclear. Seven studies involving 1485 participants reported the incidence of postpartum depression. Compared with pregnant women undergoing cesarean section without the use of esketamine, those using esketamine in the perioperative period showed a 48% decreased risk of developing postpartum depression (RR: 0.52, 95% CI: 0.35-0.79) and a 1.43-point reduction in EPDS (Edinburgh Postnatal Depression Scale) (mean difference: -1.43, 95% CI: -2.32 to -0.54). For immediate intraoperative adverse reactions, the application of esketamine caused maternal nausea and vomiting (RR: 2.16, 95% CI: 1.22-3.81), dizziness (RR: 6.11, 95% CI: 1.49-24.98), and hallucinations (RR: 6.83, 95% CI: 1.57-29.68) compared to no esketamine use.

CONCLUSIONS

Perioperative use of esketamine in pregnant women undergoing cesarean section may reduce postpartum depression and increase intraoperative adverse reactions, but has no significant effect on postoperative adverse reactions.

Activation of 5-HT6 Receptors in the Ventrolateral Orbital Cortex Produces Anti-Anxiodepressive Effects in a Rat Model of Neuropathic Pain

The comorbidity of anxiety and depression frequently occurs in patients with neuropathic pain. The ventrolateral orbital cortex (VLO) plays a critical role in mediating neuropathic pain and anxiodepression in rodents. Previous studies suggested that 5-HT6 receptors in the VLO are involved in neuropathic pain. Strong evidence supports a close link between 5-HT6 receptors and affective disorders such as depression and anxiety disorders. However, it remains unclear whether the 5-HT6 receptors in the VLO are involved in neuropathic pain-induced anxiodepression. Using a rat neuropathic pain model of spared nerve injury (SNI), we demonstrated that rats exhibited significant anxiodepression-like behaviors and the expression of VLO 5-HT6 receptors obviously decreased four weeks after SNI surgery. Microinjection of the 5-HT6 receptor agonist EMD-386088 into the VLO or overexpression of VLO 5-HT6 receptors alleviated anxiodepression-like behaviors. These effects were blocked by pre-microinjection of a selective 5-HT6 receptor antagonist (SB-258585) or inhibitors of AC (SQ-22536), PKA (H89), and MEK1/2 (U0126) respectively. Meanwhile, the expression of p-ERK, p-CREB, and BDNF in the VLO decreased four weeks after SNI surgery. Furthermore, administration of EMD-386088 upregulated the expression of BDNF, p-ERK, and p-CREB in the VLO of SNI rats, which were reversed by pre-injection of SB-258585. These findings suggest that activating 5-HT6 receptors in the VLO has anti-anxiodepressive effects in rats with neuropathic pain via activating AC-cAMP-PKA-MERK-CREB-BDNF signaling pathway. Accordingly, 5-HT6 receptor in the VLO could be a potential target for the treatment of the comorbidity of neuropathic pain and anxiodepression.

(R)-(-)-Ketamine: The Promise of a Novel Treatment for Psychiatric and Neurological Disorders

NMDA receptor antagonists have potential for therapeutics in neurological and psychiatric diseases, including neurodegenerative diseases, epilepsy, traumatic brain injury, substance abuse disorder (SUD), and major depressive disorder (MDD). (S)-ketamine was the first of a novel class of antidepressants, rapid-acting antidepressants, to be approved for medical use. The stereoisomer, (R)-ketamine (arketamine), is currently under development for treatment-resistant depression (TRD). The compound has demonstrated efficacy in multiple animal models. Two clinical studies disclosed efficacy in TRD and bipolar depression. A study by the drug sponsor recently failed to reach a priori clinical endpoints but post hoc analysis revealed efficacy. The clinical value of (R)-ketamine is supported by experimental data in humans and rodents, showing that it is less sedating, does not produce marked psychotomimetic or dissociative effects, has less abuse potential than (S)-ketamine, and produces efficacy in animal models of a range of neurological and psychiatric disorders. The mechanisms of action of the antidepressant effects of (R)-ketamine are hypothesized to be due to NMDA receptor antagonism and/or non-NMDA receptor mechanisms. We suggest that further clinical experimentation with (R)-ketamine will create novel and improved medicines for some of the neurological and psychiatric disorders that are underserved by current medications.

Repurposing Ketamine in the Therapy of Depression and Depression-Related Disorders: Recent Advances and Future Potential

Depression represents a prevalent and enduring mental disorder of significant concern within the clinical domain. Extensive research indicates that depression is very complex, with many interconnected pathways involved. Most research related to depression focuses on monoamines, neurotrophic factors, the hypothalamic-pituitary-adrenal axis, tryptophan metabolism, energy metabolism, mitochondrial function, the gut-brain axis, glial cell-mediated inflammation, myelination, homeostasis, and brain neural networks. However, recently, Ketamine, an ionotropic N-methyl-D-aspartate (NMDA) receptor antagonist, has been discovered to have rapid antidepressant effects in patients, leading to novel and successful treatment approaches for mood disorders. This review aims to summarize the latest findings and insights into various signaling pathways and systems observed in depression patients and animal models, providing a more comprehensive view of the neurobiology of anxious-depressive-like behavior. Specifically, it highlights the key mechanisms of ketamine as a rapid-acting antidepressant, aiming to enhance the treatment of neuropsychiatric disorders. Moreover, we discuss the potential of ketamine as a prophylactic or therapeutic intervention for stress-related psychiatric disorders.

Ketamine's Amelioration of Fear Extinction in Adolescent Male Mice Is Associated with the Activation of the Hippocampal Akt-mTOR-GluA1 Pathway

Fear-related disorders, including post-traumatic stress disorder (PTSD), and anxiety disorders are pervasive psychiatric conditions marked by persistent fear, stemming from its dysregulated acquisition and extinction. The primary treatment for these disorders, exposure therapy (ET), relies heavily on fear extinction (FE) principles. Adolescence, a vulnerable period for developing psychiatric disorders, is characterized by neurobiological changes in the fear circuitry, leading to impaired FE and increased susceptibility to relapse following ET. Ketamine, known for relieving anxiety and reducing PTSD symptoms, influences fear-related learning processes and synaptic plasticity across the fear circuitry. Our study aimed to investigate the effects of ketamine (10 mg/kg) on FE in adolescent male C57 BL/6 mice at the behavioral and molecular levels. We analyzed the protein and gene expression of synaptic plasticity markers in the hippocampus (HPC) and prefrontal cortex (PFC) and sought to identify neural correlates associated with ketamine's effects on adolescent extinction learning. Ketamine ameliorated FE in the adolescent males, likely affecting the consolidation and/or recall of extinction memory. Ketamine also increased the Akt and mTOR activity and the GluA1 and GluN2A levels in the HPC and upregulated BDNF exon IV mRNA expression in the HPC and PFC of the fear-extinguished mice. Furthermore, ketamine increased the c-Fos expression in specific brain regions, including the ventral HPC (vHPC) and the left infralimbic ventromedial PFC (IL vmPFC). Providing a comprehensive exploration of ketamine's mechanisms in adolescent FE, our study suggests that ketamine's effects on FE in adolescent males are associated with the activation of hippocampal Akt-mTOR-GluA1 signaling, with the vHPC and the left IL vmPFC as the proposed neural correlates.

A role of gut-brain axis on prophylactic actions of arketamine in male mice exposed to chronic restrain stress

The gut-brain axis, which includes gut microbiota and microbiome-derived metabolites, might be implicated in depression. We reported the sustained prophylactic effects of a new antidepressant arketamine in chronic restrain stress (CRS) model of depression. In this study, we investigated the role of gut-brain axis on the prophylactic effects of arketamine in the CRS (7 days) model. Pretreatment with arketamine (10 mg/kg, 1 day prior to the CRS onset) significantly prevented CRS-induced body weight loss, increased immobility time of forced swimming test, decreased sucrose preference of sucrose preference test, and reduced expressions of synaptic proteins (GluA1 and PSD-95) in the prefrontal cortex (PFC) in the male mice. Gut microbiota analysis showed that pretreatment with arketamine might restore altered abundance of gut microbiota in CRS-exposed mice. An untargeted metabolomics analysis revealed four metabolites (e.g., L-leucine, N-acetyl-l-glutamine, 2-(2,4-dichlorophenyl)-3-[4-(dimethylamino)phenyl]acrylonitrile, L-threonine amide) that were altered between control and CRS group; however, there were found to be altered between the saline + CRS group and the arketamine + CRS group. Network analysis demonstrated correlations among synaptic proteins in the PFC and certain microbiota, and blood metabolites. These findings suggest that gut-brain axis, including its metabolites, might partially contribute to the persistent prophylactic effects of arketamine in the CRS model.

Effects of autotaxin and lysophosphatidic acid deficiencies on depression-like behaviors in mice exposed to chronic unpredictable mild stress

The involvement of lipids in the mechanism of depression has triggered extensive discussions. Earlier studies have identified diminished levels of lysophosphatidic acid (LPA) and autotaxin (ATX) in individuals experiencing depression. However, the exact significance of this phenomenon in relation to depression remains inconclusive. This study seeks to explore the deeper implications of these observations. We assessed alterations in ATX and LPA in both the control group and the chronic unpredictable mild stress (CUMS) model group. Additionally, the impact of ATX adeno-associated virus (AAV-ATX) injection into the hippocampus was validated through behavioral tests in CUMS-exposed mice. Furthermore, we probed the effects of LPA on synapse-associated proteins both in HT22 cells and within the mouse hippocampus. The mechanisms underpinning the LPA-triggered shifts in protein expression were further scrutinized. Hippocampal tissues were augmented with ATX to assess its potential to alleviate depression-like behavior by modulating synaptic-related proteins. Our findings suggest that the decrement in ATX and LPA levels alters the expression of proteins associated with synaptic plasticity in vitro and in vivo, such as synapsin-I (SYN), synaptophysin (SYP), and brain-derived neurotrophic factor (BDNF). Moreover, we discerned a role for the ERK/CREB signaling pathway in mediating the effects of ATX and LPA. Importantly, strategic supplementation of ATX effectively mitigated depression-like behaviors. This study indicates that the ATX-LPA pathway may influence depression-like behaviors by modulating synaptic plasticity in the brains of CUMS-exposed mice. These insights augment our understanding of depression's potential pathogenic mechanism in the context of lipid metabolism and propose promising therapeutic strategies for ameliorating the disease.

Ketamine and its enantiomers for depression: a bibliometric analysis from 2000 to 2023

Ketamine has demonstrated rapid and sustained antidepressant effects, marking its emergence as an innovative treatment of depression. Despite the growing number of preclinical and clinical studies exploring the antidepressant effects of ketamine and its enantiomers, a comprehensive bibliometric analysis in this field has yet to be conducted. This study employs bibliometric methods and visualization tools to examine the literature and identify key topics related to the antidepressant effects of ketamine and its enantiomers. We sourced publications on the antidepressant effects of ketamine and its enantiomers from the Web of Science Core Collection (WOSCC) database, covering the period from 2000 to 2023. Tools such as VOSviewer, CiteSpace and the R package "bibliometrix" were utilized for visual analysis. The study included 4,274 publications, with a notable increase in publications peaking in 2022. Co-occurrence analysis highlighted two primary research focal points: the efficacy and safety of ketamine and its enantiomers in treating depression, and the mechanisms behind their antidepressant effects. In conclusion, this analysis revealed a significant increase in research on the antidepressant effects of ketamine and its enantiomers over the past two decades, leading to the approval of esketamine nasal spray for treatment-resistant depression. The rapid antidepressant effects of ketamine have spurred further studies into its mechanisms of action and the search for new antidepressants with fewer side effects.

Cerebrospinal fluid metabolomes of treatment-resistant depression subtypes and ketamine response: a pilot study

Depression is a disorder with variable presentation. Selecting treatments and dose-finding is, therefore, challenging and time-consuming. In addition, novel antidepressants such as ketamine have sparse optimization evidence. Insights obtained from metabolomics may improve the management of patients. The objective of this study was to determine whether compounds in the cerebrospinal fluid (CSF) metabolome correlate with scores on questionnaires and response to medication. We performed a retrospective pilot study to evaluate phenotypic and metabolomic variability in patients with treatment-resistant depression using multivariate data compression algorithms. Twenty-nine patients with treatment-resistant depression provided fasting CSF samples. Over 300 metabolites were analyzed in these samples with liquid chromatography-mass spectrometry. Chart review provided basic demographic information, clinical status with self-reported questionnaires, and response to medication. Of the 300 metabolites analyzed, 151 were present in all CSF samples and used in the analyses. Hypothesis-free multivariate analysis compressed the resultant data set into two dimensions using Principal Component (PC) analysis, accounting for ~ 32% of the variance. PC1 accounted for 16.9% of the variance and strongly correlated with age in one direction and 5-methyltetrahydrofolate, homocarnosine, and depression and anxiety scores in the opposite direction. PC2 accounted for 15.4% of the variance, with one end strongly correlated with autism scores, male gender, and cognitive fatigue scores, and the other end with bipolar diagnosis, lithium use, and ethylmalonate disturbance. This small pilot study suggests that complex treatment-resistant depression can be mapped onto a 2-dimensional pathophysiological domain. The results may have implications for treatment selection for depression subtypes.

Exploring the multifaceted potential of (R)-ketamine beyond antidepressant applications

(R, S)- and (S)-ketamine have made significant progress in the treatment of treatment-resistant depression (TRD) and have become a research focus in recent years. However, they both have risks of psychomimetic effects, dissociative effects, and abuse liability, which limit their clinical use. Recent preclinical and clinical studies have shown that (R)-ketamine has a more efficient and lasting antidepressant effect with fewer side effects compared to (R, S)- and (S)-ketamine. However, a recent small-sample randomized controlled trial found that although (R)-ketamine has a lower incidence of adverse reactions in adult TRD treatment, its antidepressant efficacy is not superior to the placebo group, indicating its antidepressant advantage still needs further verification and clarification. Moreover, an increasing body of research suggests that (R)-ketamine might also have significant applications in the prevention and treatment of medical fields or diseases such as cognitive disorders, perioperative anesthesia, ischemic stroke, Parkinson's disease, multiple sclerosis, osteoporosis, substance use disorders, inflammatory diseases, COVID-19, and organophosphate poisoning. This article briefly reviews the mechanism of action and research on antidepressants related to (R)-ketamine, fully revealing its application potential and development prospects, and providing some references and assistance for subsequent expanded research.

The role of NMDARs in the anesthetic and antidepressant effects of ketamine

BACKGROUND

As a phencyclidine (PCP) analog, ketamine can generate rapid-onset and substantial anesthetic effects. Contrary to traditional anesthetics, ketamine is a dissociative anesthetic and can induce loss of consciousness in patients. Recently, the subanaesthetic dose of ketamine was found to produce rapid-onset and lasting antidepressant effects.

AIM

However, how different concentrations of ketamine can induce diverse actions remains unclear. Furthermore, the molecular mechanisms underlying the NMDAR-mediated anesthetic and antidepressant effects of ketamine are not fully understood.

METHOD

In this review, we have introduced ketamine and its metabolism, summarized recent advances in the molecular mechanisms underlying NMDAR inhibition in the anesthetic and antidepressant effects of ketamine, explored the possible functions of NMDAR subunits in the effects of ketamine, and discussed the future directions of ketamine-based anesthetic and antidepressant drugs.

RESULT

Both the anesthetic and antidepressant effects of ketamine were thought to be mediated by N-methyl-D-aspartate receptor (NMDAR) inhibition.

CONCLUSION

The roles of NMDARs have been extensively studied in the anaesthetic effects of ketamine. However, the roles of NMDARs in antidepressant effects of ketamine are complicated and controversial.

Natural product Kaji-ichigoside F1 exhibits rapid antidepression via activating the AMPA-BDNF-mTOR pathway and inhibiting the NMDAR-CaMKIIα pathway

BACKGROUND

Depression is a common and recurrent neuropsychiatric disorder. Recent studies have shown that the N-methyl-d-aspartate (NMDA) receptor (NMDAR) is involved in the pathophysiology of depression. Previous studies have found that Kaji-ichigoside F1 (KF1) has a protective effect against NMDA-induced neurotoxicity. However, the antidepressant mechanism of KF1 has not been confirmed yet.

PURPOSE

In the present study, we aimed to evaluate the rapid antidepressant activity of KF1 and explore the underlying mechanism.

STUDY DESIGN

First, we explored the effect of KF1 on NMDA-induced hippocampal neurons and the underlying mechanism. Second, depression was induced in C57BL/6 mice via chronic unpredictable mild stress (CUMS), and the immediate and persistent depression-like behavior was evaluated using the forced swimming test (FST) after a single administration of KF1. Third, the contributions of NMDA signaling to the antidepressant effect of KF1 were investigated using pharmacological interventions. Fourth, CUMS mice were treated with KF1 for 21 days, and then their depression-like behaviors and the underlying mechanism were further explored.

METHODS

The FST was used to evaluate immediate and persistent depression-like behavior after a single administration of KF1 with or without NMDA pretreatment. The effect of KF1 on depressive-like behavior was investigated in CUMS mice by treating them with KF1 once daily for 21 days through the sucrose preference test, FST, open field test, and tail suspension test. Then, the effects of KF1 on the morphology and molecular and functional phenotypes of primary neuronal cells and hippocampus of mice were investigated by hematoxylin-eosin staining, Nissl staining, propidium iodide staining, TUNEL staining, Ca2+ imaging, JC-1 staining, ELISA, immunofluorescence analysis, RT-PCR, and Western blot.

RESULTS

KF1 could effectively improve cellular viability, reduce apoptosis, inhibit the release of LDH and Ca2+, and increase the mitochondrial membrane potential and the number of dendritic spines numbers in hippocampal neurons. Moreover, behavioral tests showed that KF1 exerted acute and sustained antidepressant-like effects by reducing Glu-levels and ameliorating neuronal damage in the hippocampus. Additionally, in vivo and in vitro experiments revealed that PSD95, Syn1, α-amino-3‑hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and brain-derived neurotrophic factor (BDNF) were upregulated at the protein level, and BDNF and AMPA were upregulated at the mRNA level. NR1 and NR2A showed the opposite trend.

CONCLUSION

These results confirm that KF1 exerts rapid antidepressant effects mainly by activating the AMPA-BDNF-mTOR pathway and inhibiting the NMDAR-CaMKIIα pathway. This study serves as a new reference for discovering rapid antidepressants.

Targeting autophagy to counteract neuroinflammation: A novel antidepressant strategy

Depression is a common disease that affects physical and mental health and imposes a considerable burden on afflicted individuals and their families worldwide. Depression is associated with a high rate of disability and suicide. It causes a severe decline in productivity and quality of life. Unfortunately, the pathophysiological mechanisms underlying depression have not been fully elucidated, and the risk of its treatment is still presented. Studies have shown that the expression of autophagic markers in the brain and peripheral inflammatory mediators are dysregulated in depression. Autophagy-related genes regulate the level of autophagy and change the inflammatory response in depression. Depression is related to several aspects of immunity. The regulation of the immune system and inflammation by autophagy may lead to the development or deterioration of mental disorders. This review highlights the role of autophagy and neuroinflammation in the pathophysiology of depression, sumaries the autophagy-targeting small moleculars, and discusses a novel therapeutic strategy based on anti-inflammatory mechanisms that target autophagy to treat the disease.

Depression-like phenotypes in mice following common bile duct ligation: Insights into the gut-liver-brain axis via the vagus nerve

Depression frequently occurs in patients with liver cirrhosis, yet the reasons for this correlation are not fully understood. Dysbiosis of gut microbiota has been implicated in depression through the gut-brain axis via the vagus nerve. This study explored the potential role of the gut-liver-brain axis via the vagus nerve in depression-like phenotypes in mice with liver cirrhosis. These mice underwent common bile duct ligation (CBDL), a method used to stimulate liver cirrhosis. To assess depression-like behaviors, behavioral tests were conducted 10 days following either sham or CBDL surgeries. The mice with CBDL displayed symptoms such as splenomegaly, elevated plasma levels of interleukin-6 and tumor necrosis factor-α, depression-like behaviors, decreased levels of synaptic proteins in the prefrontal cortex (PFC), disrupted gut microbiota balance, and changes in blood metabolites (or lipids). Additionally, there were positive or negative correlations between the relative abundance of microbiome and behavioral data or blood metabolites (or lipids). Significantly, these changes were reversed in CBDL mice by performing a subdiaphragmatic vagotomy. Intriguingly, depression-like phenotypes in mice with CBDL were improved after a single injection of arketamine, a new antidepressant. These results suggest that CBDL-induced depression-like phenotypes in mice are mediated through the gut-liver-brain axis via the subdiaphragmatic vagus nerve, and that arketamine might offer a new treatment approach for depression in liver cirrhosis patients.

An integrative view on the cell-type-specific mechanisms of ketamine's antidepressant actions

Over the past six decades, the use of ketamine has evolved from an anesthetic and recreational drug to the first non-monoaminergic antidepressant approved for treatment-resistant major depressive disorder (MDD). Subanesthetic doses of ketamine and its enantiomer (S)-ketamine (esketamine) directly bind to several neurotransmitter receptors [including N-methyl-d-aspartic acid receptor (NMDAR), κ and μ opioid receptor (KOR and MOR)] widely distributed in the brain and across different cell types, implicating several potential molecular mechanisms underlying the action of ketamine as an antidepressant. This review examines preclinical studies investigating cell-type-specific mechanisms underlying the effects of ketamine on behavior and synapses. Cell-type-specific approaches are crucial for disentangling the critical mechanisms involved in the therapeutic effect of ketamine.

Are "mystical experiences" essential for antidepressant actions of ketamine and the classic psychedelics?

The growing interest in the rapid and sustained antidepressant effects of the dissociative anesthetic ketamine and classic psychedelics, such as psilocybin, is remarkable. However, both ketamine and psychedelics are known to induce acute mystical experiences; ketamine can cause dissociative symptoms such as out-of-body experience, while psychedelics typically bring about hallucinogenic experiences, like a profound sense of unity with the universe or nature. The role of these mystical experiences in enhancing the antidepressant outcomes for patients with depression is currently an area of ongoing investigation and debate. Clinical studies have shown that the dissociative symptoms following the administration of ketamine or (S)-ketamine (esketamine) are not directly linked to their antidepressant properties. In contrast, the antidepressant potential of (R)-ketamine (arketamine), thought to lack dissociative side effects, has yet to be conclusively proven in large-scale clinical trials. Moreover, although the activation of the serotonin 5-HT2A receptor is crucial for the hallucinogenic effects of psychedelics in humans, its precise role in their antidepressant action is still under discussion. This article explores the importance of mystical experiences in enhancing the antidepressant efficacy of both ketamine and classic psychedelics.

Exploring Novel Antidepressants Targeting G Protein-Coupled Receptors and Key Membrane Receptors Based on Molecular Structures

Major Depressive Disorder (MDD) is a complex mental disorder that involves alterations in signal transmission across multiple scales and structural abnormalities. The development of effective antidepressants (ADs) has been hindered by the dominance of monoamine hypothesis, resulting in slow progress. Traditional ADs have undesirable traits like delayed onset of action, limited efficacy, and severe side effects. Recently, two categories of fast-acting antidepressant compounds have surfaced, dissociative anesthetics S-ketamine and its metabolites, as well as psychedelics such as lysergic acid diethylamide (LSD). This has led to structural research and drug development of the receptors that they target. This review provides breakthroughs and achievements in the structure of depression-related receptors and novel ADs based on these. Cryo-electron microscopy (cryo-EM) has enabled researchers to identify the structures of membrane receptors, including the N-methyl-D-aspartate receptor (NMDAR) and the 5-hydroxytryptamine 2A (5-HT2A) receptor. These high-resolution structures can be used for the development of novel ADs using virtual drug screening (VDS). Moreover, the unique antidepressant effects of 5-HT1A receptors in various brain regions, and the pivotal roles of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) and tyrosine kinase receptor 2 (TrkB) in regulating synaptic plasticity, emphasize their potential as therapeutic targets. Using structural information, a series of highly selective ADs were designed based on the different role of receptors in MDD. These molecules have the favorable characteristics of rapid onset and low adverse drug reactions. This review offers researchers guidance and a methodological framework for the structure-based design of ADs.

Genetic Dissection of BDNF and TrkB Expression in Glial Cells

The brain-derived neurotrophic factor (BDNF) and its high-affinity receptor tropomyosin-related kinase receptor B (TrkB) are widely expressed in the central nervous system. It is well documented that neurons express BDNF and full-length TrkB (TrkB.FL) as well as a lower level of truncated TrkB (TrkB.T). However, there are conflicting reports regarding the expression of BDNF and TrkB in glial cells, particularly microglia. In this study, we employed a sensitive and reliable genetic method to characterize the expression of BDNF and TrkB in glial cells in the mouse brain. We utilized three Cre mouse strains in which Cre recombinase is expressed in the same cells as BDNF, TrkB.FL, or all TrkB isoforms, and crossed them to Cre-dependent reporter mice to label BDNF- or TrkB-expressing cells with soma-localized EGFP. We performed immunohistochemistry with glial cell markers to examine the expression of BDNF and TrkB in microglia, astrocytes, and oligodendrocytes. Surprisingly, we found no BDNF- or TrkB-expressing microglia in examined CNS regions, including the somatomotor cortex, hippocampal CA1, and spinal cord. Consistent with previous studies, most astrocytes only express TrkB.T in the hippocampus of adult brains. Moreover, there are a small number of astrocytes and oligodendrocytes that express BDNF in the hippocampus, the function of which is to be determined. We also found that oligodendrocyte precursor cells, but not mature oligodendrocytes, express both TrkB.FL and TrkB.T in the hippocampus of adult mice. These results not only clarify the expression of BDNF and TrkB in glial cells but also open opportunities to investigate previously unidentified roles of BDNF and TrkB in astrocytes and oligodendrocytes.

Changes in neurotrophic signaling pathways in brain areas of the chronic mild stress rat model of depression as a signature of ketamine fast antidepressant response/non-response

Major Depressive Disorder (MDD) is a highly debilitating disorder characterized by a persistent feeling of sadness and anhedonia. Traditional antidepressants have a delayed onset of action and lack of efficacy in up to one third of patients, leading to treatment resistant depression (TRD). Recent years have witnessed a revolutionary treatment of TRD with the introduction of the fast-acting antidepressant ketamine. However, ketamine's mechanisms of action are still poorly understood. Here, we used the chronic mild stress animal model of depression on male rats to investigate the involvement of neurotrophic signaling pathways in stress vulnerability/resilience and fast antidepressant response/non-response to acute subanesthetic ketamine. We performed our analysis on both the hippocampus and the prefrontal cortex, two brain areas implicated in stress-related disorders, considering different subcellular fractions. We measured the activation by phosphorylation of protein kinase B (AKT), extracellular signal-regulated kinases (ERKs), glycogen synthase kinase-3 beta (GSK3 β), mammalian target of rapamycin (mTOR), and eukaryotic elongation factor 2 (eEF2), key effectors in the regulation of neuroplasticity and glutamatergic transmission which were previously associated to ketamine's fast antidepressant effect. We showed here for the first time that both stress and ketamine induced brain area and subcellular fraction specific changes in these pathways. Our study represents the first attempt to identify molecular mechanisms underlying the response/non-response to ketamine in an animal model of depression. This approach could give a crucial contribution to the study of etiopathogenetic mechanisms as well as to the identification of novel targets for the development of innovative therapeutic strategies.

Exploring the memory: existing activity-dependent tools to tag and manipulate engram cells

The theory of engrams, proposed several years ago, is highly crucial to understanding the progress of memory. Although it significantly contributes to identifying new treatments for cognitive disorders, it is limited by a lack of technology. Several scientists have attempted to validate this theory but failed. With the increasing availability of activity-dependent tools, several researchers have found traces of engram cells. Activity-dependent tools are based on the mechanisms underlying neuronal activity and use a combination of emerging molecular biological and genetic technology. Scientists have used these tools to tag and manipulate engram neurons and identified numerous internal connections between engram neurons and memory. In this review, we provide the background, principles, and selected examples of applications of existing activity-dependent tools. Using a combination of traditional definitions and concepts of engram cells, we discuss the applications and limitations of these tools and propose certain developmental directions to further explore the functions of engram cells.

Ketamine - A New Antidepressant Drug with Anti-Inflammatory Properties

Ketamine is a new, potent and rapid-acting antidepressant approved for therapy of treatment-resistant depression, which has a different mechanism of action than currently-available antidepressant therapies. It owes its uniquely potent antidepressant properties to a complex mechanism of action, which currently remains unclear. However, it is thought that it acts by modulating the functioning of the glutamatergic system, which plays an important role in the process of neuroplasticity associated with depression. However, preclinical and clinical studies have also found ketamine to reduce inflammation, either directly or indirectly (by activating neuroprotective branches of the kynurenine pathway), among patients exhibiting higher levels of inflammation. Inflammation and immune system activation are believed to play key roles in the development and course of depression. Therefore, the present work examines the role of the antidepressant effect of ketamine and its anti-inflammatory properties in the treatment of depression. SIGNIFICANCE STATEMENT: The present work examines the relationship between the antidepressant effect of ketamine and its anti-inflammatory properties, and the resulting benefits in treatment-resistant depression (TRD). The antidepressant mechanism of ketamine remains unclear, and there is an urgent need to develop new therapeutic strategies for treatment of depression, particularly TRD.

Repurposing of pexidartinib for microglia depletion and renewal

Pexidartinib (PLX3397) is a small molecule receptor tyrosine kinase inhibitor of colony stimulating factor 1 receptor (CSF1R) with moderate selectivity over other members of the platelet derived growth factor receptor family. It is approved for treatment of tenosynovial giant cell tumors (TGCT). CSF1R is highly expressed by microglia, which are macrophages of the central nervous system (CNS) that defend the CNS against injury and pathogens and contribute to synapse development and plasticity. Challenged by pathogens, apoptotic cells, debris, or inflammatory molecules they adopt a responsive state to propagate the inflammation and eventually return to a homeostatic state. The phenotypic switch may fail, and disease-associated microglia contribute to the pathophysiology in neurodegenerative or neuropsychiatric diseases or long-lasting detrimental brain inflammation after brain, spinal cord or nerve injury or ischemia/hemorrhage. Microglia also contribute to the growth permissive tumor microenvironment of glioblastoma (GBM). In rodents, continuous treatment for 1-2 weeks via pexidartinib food pellets leads to a depletion of microglia and subsequent repopulation from the remaining fraction, which is aided by peripheral monocytes that search empty niches for engraftment. The putative therapeutic benefit of such microglia depletion or forced renewal has been assessed in almost any rodent model of CNS disease or injury or GBM with heterogeneous outcomes, but a tendency of partial beneficial effects. So far, microglia monitoring e.g. via positron emission imaging is not standard of care for patients receiving Pexidartinib (e.g. for TGCT), so that the depletion and repopulation efficiency in humans is still largely unknown. Considering the virtuous functions of microglia, continuous depletion is likely no therapeutic option but short-lasting transient partial depletion to stimulate microglia renewal or replace microglia in genetic disease in combination with e.g. stem cell transplantation or as part of a multimodal concept in treatment of glioblastoma appears feasible. The present review provides an overview of the preclinical evidence pro and contra microglia depletion as a therapeutic approach.

Ketamine and rapid antidepressant action: new treatments and novel synaptic signaling mechanisms

Ketamine is an open channel blocker of ionotropic glutamatergic N-Methyl-D-Aspartate (NMDA) receptors. The discovery of its rapid antidepressant effects in patients with depression and treatment-resistant depression fostered novel effective treatments for mood disorders. This discovery not only provided new insight into the neurobiology of mood disorders but also uncovered fundamental synaptic plasticity mechanisms that underlie its treatment. In this review, we discuss key clinical aspects of ketamine's effect as a rapidly acting antidepressant, synaptic and circuit mechanisms underlying its action, as well as how these novel perspectives in clinical practice and synapse biology form a road map for future studies aimed at more effective treatments for neuropsychiatric disorders.

The role of neurotrophic factors in novel, rapid psychiatric treatments

Neurotrophic factors are a family of growth factors that modulate cellular growth, survival, and differentiation. For many decades, it has been generally believed that a lack of neurotrophic support led to the decreased neuronal synaptic plasticity, death, and loss of non-neuronal supportive cells seen in neuropsychiatric disorders. Traditional psychiatric medications that lead to immediate increases in neurotransmitter levels at the synapse have been shown also to elevate synaptic neurotrophic levels over weeks, correlating with the time course of the therapeutic effects of these drugs. Recent advances in psychiatric treatments, such as ketamine and psychedelics, have shown a much faster onset of therapeutic effects (within minutes to hours). They have also been shown to lead to a rapid release of neurotrophins into the synapse. This has spurred a significant shift in understanding the role of neurotrophins and how the receptor tyrosine kinases that bind neurotrophins may work in concert with other signaling systems. In this review, this renewed understanding of synaptic receptor signaling interactions and the clinical implications of this mechanistic insight will be discussed within the larger context of the well-established roles of neurotrophic factors in psychiatric disorders and treatments.

The role of BDNF transcription in the antidepressant-like effects of 18β-glycyrrhetinic acid in a chronic social defeat stress model

BACKGROUND

Xiaoyaosan (XYS), a traditional Chinese medicine formulation, has been used in the treatment of depression. However, no studies have yet identified the active compounds responsible for its antidepressant effects in the brain.

STUDY DESIGN

We investigated the antidepressants effects of XYS and identified 18β-glycyrrhetinic acid (18β-GA) as the primary compound present in the brain following XYS injection. Furthermore, we explored the molecular mechanisms underlying the antidepressant-like effects of both XYS and 18β-GA.

METHODS

To investigate the antidepressant-like effects of XYS and elucidate the associated molecular mechanisms, we employed various methodologies, including cell cultures, the chronic social defeat stress (CSDS) model, behavioral tests, immunoprecipitation, quantitative PCR (qPCR) assays, Western blotting assays, luciferase assays, chromatin immunoprecipitation (ChIP) assays, immunofluorescence staining, and dendritic spine analysis.

RESULTS

We identified 18β-GA as the primary compound in the brain following XYS injection. In vitro, 18β-GA was found to bind with ERK (extracellular signal-regulated kinase), subsequently activating ERK kinase activity toward both c-Jun and cAMP response element binding protein (CREB). Moreover, 18β-GA activated brain-derived neurotrophic factor (BDNF) transcription by stimulating nuclear factor-erythroid factor 2-related factor 2 (Nrf2), c-Jun, and CREB, while also inhibiting methyl CpG binding protein 2 (MeCP2) both in vitro and in vivo. Chronic intraperitoneal (i.p.) administration of 18β-GA exhibited prophylactic antidepressant-like effects in a CSDS model, primarily by activating BDNF transcription in the medial prefrontal cortex (mPFC). Interestingly, a single i.p. injection of 18β-GA produced rapid and sustained antidepressant-like effects in CSDS-susceptible mice by engaging the BDNF-tropomyosin receptor kinase B (TrkB) signaling pathway in the mPFC.

CONCLUSION

These findings suggest that the activation of BDNF transcription in the mPFC underlies the antidepressant-like effects of 18β-GA, a key component of XYS in the brain.

β-glucan, a specific immuno-stimulant, produces rapid antidepressant effects by stimulating ERK1/2-dependent synthesis of BDNF in the hippocampus

A decline in microglia in the dentate gyrus of the hippocampus has recently been described as an important mechanism for the progression of depression. Reversal of this decline by innate immune system stimulants may represent a novel strategy to ameliorate the depressive phenotype in chronically stressed animals. β-glucan is a polysaccharide from Saccharomyces cerevisiae. It can efficiently stimulate microglia without inducing the production of pro-inflammatory cytokines. Therefore, β-glucan could be an ideal drug to ameliorate depressive phenotypes. In the present study, we found that a single injection of β-glucan reversed depression-like behaviors in mice induced by chronic unpredictable stress (CUS) in a dose-dependent manner, which was accompanied by a reversal of the CUS-induced decrease in brain-derived neurotrophic factor (BDNF) protein levels in the dentate gyrus. The crucial role of BDNF signaling in the antidepressant effect of β-glucan was demonstrated by experiments showing that infusion of an anti-BDNF antibody into dentate gyrus, construction of BDNF-Val68Met allele knock-in mice, or treatment with the BDNF receptor antagonist K252a abolished the antidepressant effect of β-glucan. The increased BDNF signaling induced by β-glucan was mediated by extracellular signal-regulated kinase1/2 (ERK1/2)-mediated BDNF synthesis, and inhibition of ERK1/2 by SL327 was able to abolish the antidepressant effect of β-glucan. Moreover, inhibition or depletion of microglia by minocycline or PLX3397 abolished the reversal effect of β-glucan on CUS-induced depression-like behaviors and CUS-induced impairment of ERK1/2-BDNF signaling. These results suggest that β-glucan exhibits antidepressant effects by stimulating microglia-mediated activation of ERK1/2 and synthesis of BDNF in the hippocampus.

Prophylactic effects of arketamine, but not hallucinogenic psychedelic DOI nor non-hallucinogenic psychedelic analog lisuride, in lipopolysaccharide-treated mice and mice exposed to chronic restrain stress

Anesthetic ketamine and classical psychedelics that act as 5-hydroxytryptamine-2A receptor (5-HT2AR) agonists demonstrated rapid and sustained antidepressant actions in patients with treatment-resistant depression. The new antidepressant arketamine is reported to cause long-lasting prophylactic effects in lipopolysaccharide (LPS)-treated mice and mice exposed to chronic restrain stress (CRS). However, no study has compared the prophylactic effects of DOI (2,5-dimethoxy-4-iodoamphetamine: a hallucinogenic psychedelic drug with potent 5-HT2AR agonism), lisuride (non-hallucinogenic psychedelic analog with 5-HT2AR and 5-HT1AR agonism), and arketamine on depression-like behaviors in mice. Saline (10 ml/kg), DOI (2.0 or 4.0 mg/kg), lisuride (1.0 or 2.0 mg/kg), or arketamine (10 mg/kg) was administered intraperitoneally (i.p.) to male mice 6 days before administration of LPS (1.0 mg/kg). Pretreatment with aketamine, but not DOI and lisuride, significantly ameliorated body weight loss, splenomegaly, the increased immobility time of forced swimming test (FST), and the decreased expression of PSD-95 in the prefrontal cortex (PFC) of LPS-treated mice. In another test, male mice received the same treatment one day before CRS (7 days). Pretreatment with aketamine, but not DOI and lisuride, significantly ameliorated the increased FST immobility time, the reduced sucrose preference in the sucrose preference test, and the decreased expression of PSD-95 in the PFC of CRS-exposed mice. These findings suggest that, unlike to arketamine, both DOI and lisuride did not exhibit long-lasting prophylactic effects in mouse models of depression.

Microglial stimulation triggered by intranasal lipopolysaccharide administration produces antidepressant-like effect through ERK1/2-mediated BDNF synthesis in the hippocampus

We recently reported that reversing the chronic stress-induced decline of microglia in the dentate gyrus (DG) of the hippocampus by intraperitoneal injection of a low dose of lipopolysaccharide (LPS) ameliorated depression-like behavior in chronically stressed mice. In this study, we found that a single intranasal administration of LPS dose-dependently improved depression-like behavior in mice treated with chronic unpredictable stress (CUS), as evidenced by the reduction of immobility time in the tail suspension test (TST) and forced swimming test (FST) and by the increase of sucrose uptake in the sucrose preference test (SPT). The antidepressant effects of intranasal administration of LPS could be abolished by inhibition of brain-derived neurotrophic factor (BDNF) signaling by infusion of an anti-BDNF antibody, by knock-in of the mutant BDNF Val68Met allele, or by the BDNF receptor antagonist K252a. In addition, intranasal administration of LPS was found to exert antidepressant effects in a BDNF-dependent manner via promotion of BDNF synthesis mediated by extracellular signal-regulated kinase 1/2 (ERK1/2) signaling but not protein kinase B (Akt)-mammalian target of rapamycin (mTOR) signaling in DG. Inhibition of microglia by minocycline or depletion of microglia by PLX3397 was able to abolish the reversal effect of intranasal LPS administration on CUS-induced depression-like behaviors as well as the CUS-induced decrease in phospho-ERK1/2 and BDNF protein levels in DG. These results demonstrate that stimulation of hippocampal microglia by intranasal LPS administration can induce antidepressant effects via ERK1/2-dependent synthesis of BDNF protein, providing hope for the development of new strategies for the treatment of depression.

Deep brain stimulation of ventromedial prefrontal cortex reverses depressive-like behaviors via BDNF/TrkB signaling pathway in rats

AIM

Deep brain stimulation (DBS) is currently under investigation as a potential therapeutic approach for managing major depressive disorder (MDD) and ventromedial prefrontal cortex (vmPFC) is recognized as a promising target region. Therefore, the present study aimed to investigate a preclinical paradigm of bilateral vmPFC DBS and examine the molecular mechanisms underlying its antidepressant-like effects using chronic unpredictable stress (CUS) model in rats.

MAIN METHODS

Male rats were subjected to stereotaxic surgery and deep brain stimulation paradigm in non-stressed and CUS rats respectively, and the therapeutic effect of DBS were assessed by a series of behavioral tests including sucrose preference test, open field test, elevated plus maze test, and forced swim test. The potential involvement of the BDNF/TrkB signaling pathway and its downstream effects in this process were also investigated using western blot.

KEY FINDINGS

We identified that a stimulation protocol consisting of 130 Hz, 200 μA, 90 μs pulses administered for 5 h per day over a period of 7 days effectively mitigated CUS-induced depressive-like and anxiety-like behaviors in rats. These therapeutic effects were associated with the enhancement of the BDNF/TrkB signaling pathway and its downstream ERK1/2 activity.

SIGNIFICANCE

These findings provide valuable insights into the potential clinical utility of vmPFC DBS as an approach of improving the symptoms experienced by individuals with MDD. This evidence contributes to our understanding of the neurobiological basis of depression and offers promise for the development of more effective treatments.

The role and mechanism of TGF-β1 in the antidepressant-like effects of tetrahydrocurcumin

Astrocytes and the activation of inflammatory factors are associated with depression. Tetrahydrocurcumin (THC), the principal metabolite of natural curcumin, is renowned for its anti-inflammatory properties. In this research, we explored the impact of THC on the expression of inflammatory factors, neurotrophins, and transforming growth factor β1 (TGF-β1) in the prefrontal cortex after chronic restraint stress (CRS) in mice and in lipopolysaccharide (LPS)-induced TNC1 astrocytes. Our findings indicated that THC mitigated the anxiety and depression-like behaviours observed in CRS mice. It also influenced the expression of TGF-β1, p-SMAD3/SMAD3, sirtuin 1 (SIRT1), brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), inducible nitric oxide synthase (iNOS), and tumour necrosis factor α (TNF-α). Specifically, THC augmented the expressions of TGF-β1, p-SMAD3/SMAD3, SIRT1, BDNF, and GDNF, whilst diminishing the expressions of iNOS and TNF-α in LPS-induced astrocytes. However, when pre-treated with SB431542, a TGF-β1 receptor inhibitor, it nullified the aforementioned effects of THC on astrocytes. Our results propose that THC delivers its anti-depressive effects through the activation of TGF-β1, enhancement of p-SMAD3/SMAD3 and SIRT1 expression, upregulation of BDNF and GDNF, and downregulation of iNOS and TNF-α. This research furnishes new perspectives on the anti-inflammatory mechanism that underpins the antidepressant-like impact of THC.

Storm on predictive brain: A neurocomputational account of ketamine antidepressant effect

For the past decade, ketamine, an N-methyl-D-aspartate receptor (NMDAr) antagonist, has been considered a promising treatment for major depressive disorder (MDD). Unlike the delayed effect of monoaminergic treatment, ketamine may produce fast-acting antidepressant effects hours after a single administration at subanesthetic dose. Along with these antidepressant effects, it may also induce transient dissociative (disturbing of the sense of self and reality) symptoms during acute administration which resolve within hours. To understand ketamine's rapid-acting antidepressant effect, several biological hypotheses have been explored, but despite these promising avenues, there is a lack of model to understand the timeframe of antidepressant and dissociative effects of ketamine. In this article, we propose a neurocomputational account of ketamine's antidepressant and dissociative effects based on the Predictive Processing (PP) theory, a framework for cognitive and sensory processing. PP theory suggests that the brain produces top-down predictions to process incoming sensory signals, and generates bottom-up prediction errors (PEs) which are then used to update predictions. This iterative dynamic neural process would relies on N-methyl-D-aspartate (NMDAr) and α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic receptors (AMPAr), two major component of the glutamatergic signaling. Furthermore, it has been suggested that MDD is characterized by over-rigid predictions which cannot be updated by the PEs, leading to miscalibration of hierarchical inference and self-reinforcing negative feedback loops. Based on former empirical studies using behavioral paradigms, neurophysiological recordings, and computational modeling, we suggest that ketamine impairs top-down predictions by blocking NMDA receptors, and enhances presynaptic glutamate release and PEs, producing transient dissociative symptoms and fast-acting antidepressant effect in hours following acute administration. Moreover, we present data showing that ketamine may enhance a delayed neural plasticity pathways through AMPAr potentiation, triggering a prolonged antidepressant effect up to seven days for unique administration. Taken together, the two sides of antidepressant effects with distinct timeframe could constitute the keystone of antidepressant properties of ketamine. These PP disturbances may also participate to a ketamine-induced time window of mental flexibility, which can be used to improve the psychotherapeutic process. Finally, these proposals could be used as a theoretical framework for future research into fast-acting antidepressants, and combination with existing antidepressant and psychotherapy.

Antidepressant effects of 70% ethanolic extract of Lonicerae japonicae flos and it contained chlorogenic acid via upregulation of BDNF-TrkB pathway in the hippocampus of mice

Lonicera japonica flos (LJF) is a common clinical herb with outstanding medicinal and nutritional value. This study aimed to evaluate the antidepressant effects of LJF's active extract and compound chlorogenic acid (CGA) around brain-derived neurotrophic factor(BDNF)-tropomyosin receptor kinase B (TrkB) pathway. The results showed that LJF's extracts and CGA had significant antidepressant effects, and the antidepressant effects of different extracts of LJF were highly positively correlated with the content of CGA (forced swimming test, r = 0.998; tail suspension test, r = 0.934). Moreover, LJF-70% ethanolic extract and CGA improved chronic unpredictable mild stress-induced depressive behavior, upregulated protein expression levels of BDNF and p-TrkB in the hippocampus, restored the damage of hippocampal neurons, and protected liver from damage. In summary, this study demonstrated for the first time that LJF-70% ethanolic extract was the active extract of LJF in antidepressant and CGA was its active compound, and the antidepressant mechanisms mainly involved the upregulation of BDNF-TrkB signaling pathway in the hippocampus of mice.

Mechanisms of the Beneficial Effects of Exercise on Brain-Derived Neurotrophic Factor Expression in Alzheimer's Disease

Brain-derived neurotrophic factor (BDNF) is a key molecule in promoting neurogenesis, dendritic and synaptic health, neuronal survival, plasticity, and excitability, all of which are disrupted in neurological and cognitive disorders such as Alzheimer's disease (AD). Extracellular aggregates of amyloid-β (Aβ) in the form of plaques and intracellular aggregates of hyperphosphorylated tau protein have been identified as major pathological insults in the AD brain, along with immune dysfunction, oxidative stress, and other toxic stressors. Although aggregated Aβ and tau lead to decreased brain BDNF expression, early losses in BDNF prior to plaque and tangle formation may be due to other insults such as oxidative stress and contribute to early synaptic dysfunction. Physical exercise, on the other hand, protects synaptic and neuronal structure and function, with increased BDNF as a major mediator of exercise-induced enhancements in cognitive function. Here, we review recent literature on the mechanisms behind exercise-induced BDNF upregulation and its effects on improving learning and memory and on Alzheimer's disease pathology. Exercise releases into the circulation a host of hormones and factors from a variety of peripheral tissues. Mechanisms of BDNF induction discussed here are osteocalcin, FNDC5/irisin, and lactate. The fundamental mechanisms of how exercise impacts BDNF and cognition are not yet fully understood but are a prerequisite to developing new biomarkers and therapies to delay or prevent cognitive decline.

Myelin-associated oligodendrocytic basic protein-dependent myelin repair confers the long-lasting antidepressant effect of ketamine

Ketamine exhibits rapid and sustained antidepressant effects. As decreased myelination has been linked to depression pathology, changes in myelination may be a pivotal mechanism underlying ketamine's long-lasting antidepressant effects. Although ketamine has a long-lasting facilitating effect on myelination, the precise roles of myelination in ketamine's sustained antidepressant effects remain unknown. In this study, we employed spatial transcriptomics (ST) to examine ketamine's lasting effects in the medial prefrontal cortex (mPFC) and hippocampus of mice subjected to chronic social defeat stress and identified several differentially expressed myelin-related genes. Ketamine's ability to restore impaired myelination in the brain by promoting the differentiation of oligodendrocyte precursor cells (OPCs) into mature oligodendrocytes was demonstrated. Moreover, we showed that inhibiting the expression of myelin-associated oligodendrocytic basic protein (Mobp) blocked ketamine's long-lasting antidepressant effects. We also illustrated that α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) signaling mediated ketamine's facilitation on myelination. In addition, we found that the (R)-stereoisomer of ketamine showed stronger effects on myelination than (S)-ketamine, which may explain its longer-lasting antidepressant effects. These findings reveal novel mechanisms underlying the sustained antidepressant effects of ketamine and the differences in antidepressant effects between (R)-ketamine and (S)-ketamine, providing new insights into the role of myelination in antidepressant mechanisms.

A synopsis of multitarget therapeutic effects of anesthetics on depression

Depression is a profound mental disorder that dampens the mood and undermines volition, which exhibited an increased incidence over the years. Although drug-based interventions remain the primary approach for depression treatment, the available medications still can't satisfy the patients. In recent years, the newly discovered therapeutic targets such as N-methyl-D-aspartate (NMDA) receptor, α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor, and tyrosine kinase B (TrkB) have brought new breakthroughs in the development of antidepressant drugs. Moreover, it has come to light that certain anesthetics possess pharmacological mechanisms intricately linked to the aforementioned therapeutic targets for depression. At present, numerous preclinical and clinical studies have explored the therapeutic effects of anesthetic drugs such as ketamine, isoflurane, N2O, and propofol, on depression. These investigations suggested that these drugs can swiftly ameliorate patients' depression symptoms and engender long-term effects. In this paper, we provide a comprehensive review of the research progress and potential molecular mechanisms of various anesthetic drugs for depression treatment. By shedding light on this subject, we aim to facilitate the development and clinical implementation of new antidepressant drugs based on anesthetic medications.

Roles of microglia in adult hippocampal neurogenesis in depression and their therapeutics

Adult hippocampal neurogenesis generates functional neurons from neural progenitor cells in the hippocampal dentate gyrus (DG) to complement and repair neurons and neural circuits, thus benefiting the treatment of depression. Increasing evidence has shown that aberrant microglial activity can disrupt the appropriate formation and development of functional properties of neurogenesis, which will play a crucial role in the occurrence and development of depression. However, the mechanisms of the crosstalk between microglia and adult hippocampal neurogenesis in depression are not yet fully understood. Therefore, in this review, we first introduce recent discoveries regarding the roles of microglia and adult hippocampal neurogenesis in the etiology of depression. Then, we systematically discuss the possible mechanisms of how microglia regulate adult hippocampal neurogenesis in depression according to recent studies, which involve toll-like receptors, microglial polarization, fractalkine-C-X3-C motif chemokine receptor 1, hypothalamic-pituitary-adrenal axis, cytokines, brain-derived neurotrophic factor, and the microbiota-gut-brain axis, etc. In addition, we summarize the promising drugs that could improve the adult hippocampal neurogenesis by regulating the microglia. These findings will help us understand the complicated pathological mechanisms of depression and shed light on the development of new treatment strategies for this disease.

Noteworthy perspectives on microglia in neuropsychiatric disorders

Microglia are so versatile that they not only provide immune surveillance for central nervous system, but participate in neural circuitry development, brain blood vessels formation, blood-brain barrier architecture, and intriguingly, the regulation of emotions and behaviors. Microglia have a profound impact on neuronal survival, brain wiring and synaptic plasticity. As professional phagocytic cells in the brain, they remove dead cell debris and neurotoxic agents via an elaborate mechanism. The functional profile of microglia varies considerately depending on age, gender, disease context and other internal or external environmental factors. Numerous studies have demonstrated a pivotal involvement of microglia in neuropsychiatric disorders, including negative affection, social deficit, compulsive behavior, fear memory, pain and other symptoms associated with major depression disorder, anxiety disorder, autism spectrum disorder and schizophrenia. In this review, we summarized the latest discoveries regarding microglial ontogeny, cell subtypes or state spectrum, biological functions and mechanistic underpinnings of emotional and behavioral disorders. Furthermore, we highlight the potential of microglia-targeted therapies of neuropsychiatric disorders, and propose outstanding questions to be addressed in future research of human microglia.

Arketamine for cognitive impairment in psychiatric disorders

Cognitive impairment has been observed in patients with various psychiatric disorders, including schizophrenia, major depressive disorder (MDD), and bipolar disorder (BD). Although modern therapeutic drugs can improve certain symptoms (i.e., psychosis, depression) in these patients, these drugs have not been found to improve cognitive impairment. The N-methyl-D-aspartate receptor antagonist (R,S)-ketamine has attracted attention as a rapidly acting antidepressant. In addition to its robust antidepressant effects, (R,S)-ketamine has been suggested to improve cognitive impairment in patients with MDD and BD, despite causing cognitive impairment in healthy control subjects. (R,S)-ketamine is a racemic mixture of equal amounts of (R)-ketamine (or arketamine) and (S)-ketamine (or esketamine). Arketamine has been found to have more potent antidepressant-like actions than esketamine in rodents. Interestingly, arketamine, but not esketamine, has been suggested to improve phencyclidine-induced cognitive deficits in mice. Furthermore, arketamine has been suggested to ameliorate cognitive deficits in rodent offspring after maternal immune activation. In the current article, it is proposed that arketamine has therapeutic potential for treating cognitive impairment in patients with psychiatric disorders. Additionally, the potential role of the gut-microbiome-brain axis in cognitive impairment in psychiatric disorders is discussed.

Activation of σ1-Receptors by R-Ketamine May Enhance the Antidepressant Effect of S-Ketamine

Ketamine is a racemic mixture composed of two enantiomers, S-ketamine and R-ketamine. In preclinical studies, both enantiomers have exhibited antidepressant effects, but these effects are attributed to distinct pharmacological activities. The S-enantiomer acts as an NMDA-channel blocker and as an opioid μ-receptor agonist, whereas the R-enantiomer binds to σ1-receptors and is believed to act as an agonist. As racemate, ketamine potentially triggers four biochemical pathways involving the AGC-kinases, PKA, Akt (PKB), PKC and RSK that ultimately lead to inhibitory phosphorylation of GSK3β in microglia. In patients with major depressive disorder, S-ketamine administered as a nasal spray has shown clear antidepressant activity. However, when compared to intravenously infused racemic ketamine, the response rate, duration of action and anti-suicidal activity of S-ketamine appear to be less pronounced. The σ1-protein interacts with μ-opioid and TrkB-receptors, whereas in preclinical experiments σ1-agonists reduce μ-receptor desensitization and improve TrkB signal transduction. TrkB activation occurs as a response to NMDA blockade. So, the σ1-activity of R-ketamine may not only enhance two pathways via which S-ketamine produces an antidepressant response, but it furthermore provides an antidepressant activity in its own right. These two factors could explain the apparently superior antidepressant effect observed with racemic ketamine compared to S-ketamine alone.

Marasmius androsaceus mitigates depression-exacerbated intestinal radiation injuries through reprogramming hippocampal miRNA expression

INTRODUCTION

Cancer patients commonly experience high levels of psychological stress, which poses significant risks to their well-being. Radiotherapy is a primary treatment modality for cancer; however, it often leads to intestinal injuries in these patients. Nevertheless, the impact of mental stress on radiotherapy-intertwined complications remains unclear.

METHODS

To induce intestinal injury, we employed total abdominal irradiation in our experimental model. We conducted high-throughput sequencing to analyze the expression profile of miRNAs in the hippocampus.

RESULTS

We observed that mice with depression exhibited more severe intestinal injuries following total abdominal irradiation. Remarkably, oral administration of Marasmius androsaceus not only alleviated the depressive phenotype but also mitigated radiation-induced intestinal toxicity. Notably, this radioprotective effect was not observed in mice without depression. Depression disrupted the hippocampal miRNA expression profile in mice subjected to local irradiation of the abdomen, leading to the accumulation of miR-139-5p and miR-184-3p in the hippocampus, serum, and small intestine tissues. However, treatment with Marasmius androsaceus reprogrammed the miRNA expression signature in mice with depression. Furthermore, intravenous injection of antagomirs targeting miR-139-5p and miR-184-3p ameliorated depression, up-regulated Spn expression, reduced radiation enteritis, and improved the integrity of the small intestine in irradiated mice.

CONCLUSION

Our findings demonstrate the efficacy of Marasmius androsaceus, a small mushroom, in alleviating depression-aggravated intestinal toxicity following radiotherapy by reprogramming hippocampal miRNA expression.

Molecular mechanisms of rapid-acting antidepressants: New perspectives for developing antidepressants

Major depressive disorder (MDD) is a chronic relapsing psychiatric disorder. Conventional antidepressants usually require several weeks of continuous administration to exert clinically significant therapeutic effects, while about two-thirds of the patients are prone to relapse of symptoms or are completely ineffective in antidepressant treatment. The recent success of the N-methyl-D-aspartic acid (NMDA) receptor antagonist ketamine as a rapid-acting antidepressant has propelled extensive research on the action mechanism of antidepressants, especially in relation to its role in synaptic targets. Studies have revealed that the mechanism of antidepressant action of ketamine is not limited to antagonism of postsynaptic NMDA receptors or GABA interneurons. Ketamine produces powerful and rapid antidepressant effects by affecting α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptors, adenosine A1 receptors, and the L-type calcium channels, among others in the synapse. More interestingly, the 5-HT2A receptor agonist psilocybin has demonstrated potential for rapid antidepressant effects in depressed mouse models and clinical studies. This article focuses on a review of new pharmacological target studies of emerging rapid-acting antidepressant drugs such as ketamine and hallucinogens (e.g., psilocybin) and briefly discusses the possible strategies for new targets of antidepressants, with a view to shed light on the direction of future antidepressant research.

Polygonum sibiricum polysaccharides exert the antidepressant-like effects in chronic unpredictable mild stress-induced depressive mice by modulating microbiota-gut-brain axis

Polygonum sibiricum polysaccharides (PSP) are one of the main active components of Polygonatum sibiricum, which is a traditional Chinese medicine with food and drug homologies. Recent studies have revealed the antidepressant-like effects of PSP. However, the precise mechanisms have not been clarified. Therefore, the present study was conducted to explore that whether PSP could exert the antidepressant-like effects via microbiota-gut-brain (MGB) axis in chronic unpredictable mild stress (CUMS)-induced depressive mice by transplantation of fecal microbiota (FMT) from PSP administration mice. FMT markedly reversed the depressive-like behaviors of CUMS-induced mice in the open field, the sucrose preference, the tail suspension, the forced swimming, and the novelty-suppressed feeding tests. FMT significantly increased the levels of 5-hydroxytryptamine and norepinephrine, decreased the levels of the pro-inflammatory cytokines in the hippocampus and reduced the levels of corticosterone, an adrenocorticotropic-hormone, in the serum of CUMS-induced mice. In addition, administration of PSP and FMT significantly increased the expressions of ZO-1 and occludin in the colon and decreased the levels of lipopolysaccharide and interferon-γ in the serum of CUMS-induced mice. Moreover, administration of PSP and FMT regulated the signaling pathways of PI3K/AKT/TLR4/NF-κB and ERK/CREB/BDNF. Taken together, these findings indicated that PSP exerted antidepressant-like effects via the MGB axis.

Lepidium meyenii Walp (Maca)-derived extracellular vesicles ameliorate depression by promoting 5-HT synthesis via the modulation of gut-brain axis

Depression is a common and debilitating condition for which effective treatments are needed. Lepidium meyenii Walp (Maca) is a plant with potential medicinal effects in treating depression. Recently, there has been growing interest in plant-derived extracellular vesicles (EVs) due to their low toxicity and ability to transport to human cells. Targeting the gut-brain axis, a novel strategy for depression management, may be achieved through the use of Maca-derived EVs (Maca-EVs). In this study, we successfully isolated Maca-EVs using gradient ultracentrifugation and characterized their shape, size, and markers (CD63 and TSG101). The in vivo imaging showed that the Dil-labeled Maca-EVs crossed the brain-blood barrier and accumulated in the brain. The behavioral tests revealed that Maca-EVs dramatically recovered the depression-like behaviors of unpredictable chronic mild stress (UCMS) mice. UCMS mice fecal were characterized by an elevated abundance of g_Enterococcus, g_Lactobacillus, and g_Escherichia_Shigella, which were significantly restored by administration of Maca-EVs. The effects of Maca-EVs on the altered microbial and fecal metabolites in UCMS mice were mapped to biotin, pyrimidine, and amino acid (tyrosine, alanine, aspartate, and glutamate) metabolisms, which were closely associated with the serotonin (5-HT) production. Maca-EVs were able to increase serum monoamine neurotransmitter levels in UCMS mice, with 5-HT showing the most significant changes. We further demonstrated that 5-HT improved the expression of brain-derived neurotrophic factor, a key regulator of neuronal plasticity, and its subsequent activation of TrkB/p-AKT signaling by regulating the GTP-Cdc42/ERK pathway. These findings suggest that Maca-EVs enhance 5-HT release, possibly by modulating the gut-brain axis, to improve depression behavior. Our study sheds light on a novel approach to depression treatment using plant-derived EVs.

Genetic dissection of BDNF and TrkB expression in glial cells

The brain-derived neurotrophic factor (BDNF) and its high-affinity receptor tropomyosin-related kinase receptor B (TrkB) are widely expressed in the central nervous system. It is well documented that neurons express BDNF and full-length TrkB (TrkB.FL), and a lower level of truncated TrkB (TrkB.T). With conflicting results, glial cells also have been reported to express BDNF and TrkB. In the current study, we employed a more sensitive and reliable genetic method to characterize the expression of BDNF and TrkB in glial cells in the mouse brain. We utilized three Cre mouse strains in which Cre recombinase is expressed in the same cells as BDNF, TrkB.FL, or all TrkB isoforms, and crossed them to Cre-dependent EGFP reporter mice to label BDNF- or TrkB- expressing cells. We performed immunohistochemistry with glial cell markers to examine the expression of BDNF and TrkB in microglia, astrocytes, and oligodendrocytes. Surprisingly, we found no BDNF- or TrkB- expressing microglia in the brain and spinal cord. Consistent with previous studies, most astrocytes only express TrkB.T in the adult brain. Moreover, there are a small number of astrocytes and oligodendrocytes that express BDNF, the function of which is to be determined. We also found that oligodendrocyte precursor cells, but not mature oligodendrocytes, express both TrkB.FL and TrkB.T in the adult brain. These results not only clarify the expression of BDNF and TrkB in glial cells, but also open opportunities to investigate previously unidentified roles of BDNF and TrkB in glial cells.