Cellular mechanisms underlying the antidepressant effects of ketamine: role of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors

Is the antidepressant effect of ketamine separate from its psychotomimetic effect? A review of rodent models

Ketamine is an NMDA (N-methyl-d-aspartate) glutamate receptor antagonist, which has a myriad of dose-dependent pharmacological and behavioral effects, including anesthetic, sedative, amnestic, analgesic, and anti-inflammatory properties. Intriguingly, ketamine at subanesthetic doses displays a relevant profile both in mimicking symptoms of schizophrenia and also as the first fast-acting treatment for depression. Here, we present an overview of the state-of-the-art knowledge about ketamine as an antidepressant as well as a pharmacological model of schizophrenia in animal models and human participants. Ketamine's dual effect appears to arise from its mechanism of action involving NMDA receptors, with both immediate and downstream consequences being triggered as a result. Finally, we discuss the feasibility of a unified approach linking the glutamatergic hypothesis of schizophrenia to the promising preclinical and clinical success of ketamine in the treatment of refractory depression.

Combinatorial therapy with sub-effective Ro25-6981 and ZL006 ameliorates depressive-like behavior in single or combined stressed male mice

Major depression is a severe neuropsychiatric disorder that poses a significant challenge to health. However, development of an effective therapy for the disease has long been difficult. Here, we investigate the efficacy of a novel combinatorial treatment employing sub-effective doses of Ro25-6981, an antagonist targeting GluN2B-containing NMDA receptors, in conjunction with ZL006, an inhibitor of the PSD95/nNOS, on mouse models of depression. We employed social isolation, chronic restraint stress, or a combination of both to establish a depressed mouse model. Treatment with the drug combination reduced depressive-like behaviors without affecting locomotor activity in mice subjected to social isolation or chronic restraint stress. Furthermore, the combination therapy ameliorated depressive-like behaviors induced by combined stress of chronic restraint followed by social isolation. Mechanistic studies revealed that the combined treatment downregulated the hippocampal nitric oxide level. However, the therapeutic benefits of this combination were negated by the activation of NMDA receptors with a low dose of NMDA or by increasing nitric oxide levels with l-arginine. Moreover, the combinatorial treatment had negligible effects on object memory and contextual fear memory. Our data establish a combined therapy paradigm, providing a potential strategy targeting major depression.

Shared effects of electroconvulsive shocks and ketamine on neuroplasticity: A systematic review of animal models of depression

Electroconvulsive shocks (ECS) and ketamine are antidepressant treatments with a relatively fast onset of therapeutic effects compared to conventional medication and psychotherapy. While the exact neurobiological mechanisms underlying the antidepressant response of ECS and ketamine are unknown, both interventions are associated with neuroplasticity. Restoration of neuroplasticity may be a shared mechanism underlying the antidepressant efficacy of these interventions. In this systematic review, literature of animal models of depression is summarized to examine the possible role of neuroplasticity in ECS and ketamine on a molecular, neuronal, synaptic and functional level, and specifically to what extent these mechanisms are shared between both interventions. The results highlight that hippocampal neurogenesis and brain-derived neurotrophic factor (BDNF) levels are consistently increased after ECS and ketamine. Moreover, both interventions positively affect glutamatergic neurotransmission, astrocyte and neuronal morphology, synaptic density, vasculature and functional plasticity. However, a small number of studies investigated these processes after ECS. Understanding the shared fundamental mechanisms of fast-acting antidepressants can contribute to the development of novel therapeutic approaches for patients with severe depression.

Efficacy and safety of add-on sarcosine in patients with major depressive disorder: A randomized controlled trial

The main hurdles with current therapies for major depressive disorder (MDD) include lack of efficacy, therapeutic latency, and adverse drug reactions. Add-on therapy to conventional antidepressants may result in better therapeutic outcomes to overcome these obstacles. Sarcosine (N-methyl glycine), an endogenous amino acid that acts by modulating the NMDA receptor, is available as a dietary supplement. So, the present study was planned to evaluate the efficacy and safety of add-on sarcosine to SSRIs in MDD. In the present randomized, double-blind clinical trial (NCT04975100), 60 eligible participants with MDD were randomly assigned to either the test group (SSRI + sarcosine) or the control group (SSRI + placebo). Clinical and biochemical parameters like MADRS, CGI, serum BDNF, and serum glycine were assessed at baseline and eight weeks. The mean reduction in MADRS score was significant in both the control (-8.7, 95% CI: -11.0 to -6.4, p < 0.001) and the test group (-13.3, 95% CI: -14.9 to -11.7, p < 0.001), but the change in the test group was significantly greater (-4.6, 95% CI: -7.5 to -1.7, p = 0.003). The test group had a significantly higher response rate (p = 0.007) and remission rate (p = 0.038) compared to the control group. There was a significant increase in serum BDNF in both groups; however, the change in the test group was significantly higher than in the control group (p = 0.041). Similarly, the test group had a significantly higher increase in serum glycine than the control group (p < 0.001). Sarcosine may be considered an efficacious and safe add-on therapy to standard SSRIs in the management of MDD. ClinicalTrial.gov IdentifierNCT04975100.

The Antidepressant- and Anxiolytic-Like Effects of the Phosphodiesterase Type-5 Inhibitor Tadalafil are Associated with the Modulation of the Gut-Brain Axis During CNS Autoimmunity

Multiple Sclerosis (MS) is a debilitating disease that severely affects the central nervous system (CNS). Apart from neurological symptoms, it is also characterized by neuropsychiatric comorbidities, such as anxiety and depression. Phosphodiesterase-5 inhibitors (PDE5Is) such as Sildenafil and Tadalafil have been shown to possess antidepressant-like effects, but the mechanisms underpinning such effects are not fully characterized. To address this question, we used the EAE model of MS, behavioral tests, immunofluorescence, immunohistochemistry, western blot, and 16 S rRNA sequencing. Here, we showed that depressive-like behavior in Experimental Autoimmune Encephalomyelitis (EAE) mice is due to neuroinflammation, reduced synaptic plasticity, dysfunction in glutamatergic neurotransmission, glucocorticoid receptor (GR) resistance, increased blood-brain barrier (BBB) permeability, and immune cell infiltration to the CNS, as well as inflammation, increased intestinal permeability, and immune cell infiltration in the distal colon. Furthermore, 16 S rRNA sequencing revealed that behavioral dysfunction in EAE mice is associated with changes in the gut microbiota, such as an increased abundance of Firmicutes and Saccharibacteria and a reduction in Proteobacteria, Parabacteroides, and Desulfovibrio. Moreover, we detected an increased abundance of Erysipelotrichaceae and Desulfovibrionaceae and a reduced abundance of Lactobacillus johnsonii. Surprisingly, we showed that Tadalafil likely exerts antidepressant-like effects by targeting all aforementioned disease aspects. In conclusion, our work demonstrated that anxiety- and depressive-like behavior in EAE is associated with a plethora of neuroimmune and gut microbiota-mediated mechanisms and that Tadalafil exerts antidepressant-like effects probably by targeting these mechanisms. Harnessing the knowledge of these mechanisms of action of Tadalafil is important to pave the way for future clinical trials with depressed patients.

Glutamatergic Modulators for Major Depression from Theory to Clinical Use

Major depressive disorder (MDD) is a chronic, burdensome, highly prevalent disease that is characterized by depressed mood and anhedonia. MDD is especially burdensome as approved monoamine antidepressant treatments have weeks-long delays before clinical benefit and low remission rates. In the past 2 decades, a promising target emerged to improve patient outcomes in depression treatment: glutamatergic signaling. This narrative review provides a high-level overview of glutamate signaling in synaptogenesis and neural plasticity and the implications of glutamate dysregulation in depression. Based on this preclinical evidence implicating glutamate in depression and the rapid improvement of depression with ketamine treatment in a proof-of-concept trial, a range of N-methyl-D-aspartate (NMDA)-targeted therapies have been investigated. While an array of treatments has been investigated in registered phase 2 or 3 clinical trials, the development of most of these agents has been discontinued. Multiple glutamate-targeted antidepressants are actively in development, and two are approved. Nasal administration of esketamine (Spravato®) was approved by the US Food and Drug Administration (FDA) in 2019 to treat adults with treatment-resistant depression and in 2020 for adults with MDD with acute suicidal ideation or behavior. Oral combination dextromethorphan-bupropion (AXS-05, Auvelity® extended-release tablet) was FDA approved in 2022 for the treatment of MDD in adults. These approvals bolster the importance of glutamate in depression and represent an exciting breakthrough in contemporary psychiatry, providing new avenues of treatment for patients as first-line therapy or with either poor response or unacceptable side effects to monoaminergic antidepressants.

Novel insight into astrocyte-mediated gliotransmission modulates the synaptic plasticity in major depressive disorder

Major depressive disorder (MDD) is a form of glial cell-based synaptic dysfunction disease in which glial cells interact closely with neuronal synapses and perform synaptic information processing. Glial cells, particularly astrocytes, are active components of the brain and are responsible for synaptic activity through the release gliotransmitters. A reduced density of astrocytes and astrocyte dysfunction have both been identified the brains of patients with MDD. Furthermore, gliotransmission, i.e., active information transfer mediated by gliotransmitters between astrocytes and neurons, is thought to be involved in the pathogenesis of MDD. However, the mechanism by which astrocyte-mediated gliotransmission contributes to depression remains unknown. This review therefore summarizes the alterations in astrocytes in MDD, including astrocyte marker, connexin 43 (Cx43) expression, Cx43 gap junctions, and Cx43 hemichannels, and describes the regulatory mechanisms of astrocytes involved in synaptic plasticity. Additionally, we investigate the mechanisms acting of the glutamatergic, gamma-aminobutyric acidergic, and purinergic systems that modulate synaptic function and the antidepressant mechanisms of the related receptor antagonists. Further, we summarize the roles of glutamate, gamma-aminobutyric acid, d-serine, and adenosine triphosphate in depression, providing a basis for the identification of diagnostic and therapeutic targets for MDD.

A novel framework for ketamine-assisted couple therapy

Intimate relationship distress is prevalent and is associated with poorer health, mental health, and mortality outcomes. Evidence-based couple therapies target cognitive, behavioral, and emotional processes that underlie relationship dysfunction. Increasing research and clinical evidence supports the efficacy of ketamine-assisted psychotherapy (KAP) for addressing clinical mental health concerns, including depression, anxiety disorders, posttraumatic stress disorder, and more. The purported mechanisms of KAP are also likely to improve psychosocial and relational functioning for patients and may be useful for supporting change mechanisms in couple therapy. This paper reviews the current evidence for therapeutic ketamine and KAP and outlines how the mechanisms of ketamine therapy may also augment the cognitive, behavioral, and emotional interventions in the most commonly used evidence-based couple therapies. Key mechanisms include increased neuroplasticity, changes in functional connectivity, adaptive dissociation, decreased inhibition, and reduced avoidance. Given the reciprocal interaction between relationship dysfunction and mental health problems, ketamine may also help alleviate relationship distress by directly treating clinical mental health symptoms. We then outline a proposed framework for ketamine-assisted couple therapy, addressing the application of KAP preparation, dosing, and integration to a dyadic intervention framework in a way that can be applied to different couple therapy modalities. This clinical framework for couples' KAP may be useful for clinicians and researchers working to improve the efficacy of couple therapy, particularly when one or both partners has accompanying mental health concerns.

Brain region-specific action of ketamine as a rapid antidepressant

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

The N-methyl-d-aspartate receptor hypothesis of ketamine's antidepressant action: evidence and controversies

Substantial clinical evidence has unravelled the superior antidepressant efficacy of ketamine: in comparison to traditional antidepressants targeting the monoamine systems, ketamine, as an N-methyl-d-aspartate receptor (NMDAR) antagonist, acts much faster and more potently. Surrounding the antidepressant mechanisms of ketamine, there is ample evidence supporting an NMDAR-antagonism-based hypothesis. However, alternative arguments also exist, mostly derived from the controversial clinical results of other NMDAR inhibitors. In this article, we first summarize the historical development of the NMDAR-centred hypothesis of rapid antidepressants. We then classify different NMDAR inhibitors based on their mechanisms of inhibition and evaluate preclinical as well as clinical evidence of their antidepressant effects. Finally, we critically analyse controversies and arguments surrounding ketamine's NMDAR-dependent and NMDAR-independent antidepressant action. A better understanding of ketamine's molecular targets and antidepressant mechanisms should shed light on the future development of better treatment for depression. This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.

Challenges and rewards of in vivo synaptic density imaging, and its application to the study of depression

The development of novel radiotracers for Positron Emission Tomography (PET) imaging agents targeting the synaptic vesicle glycoprotein 2 A (SV2A), an integral glycoprotein present in the membrane of all synaptic vesicles throughout the central nervous system, provides a method for the in vivo quantification of synaptic density. This is of particular interest in neuropsychiatric disorders given that synaptic alterations appear to underlie disease progression and symptom severity. In this review, we briefly describe the development of these SV2A tracers and the evaluation of quantification methods. Next, we discuss application of SV2A PET imaging to the study of depression, including a review of our findings demonstrating lower SV2A synaptic density in people with significant depressive symptoms and the use of a ketamine drug challenge to examine synaptogenesis in vivo. We then highlight the importance of performing translational PET imaging in animal models in conjunction with clinical imaging. We consider the ongoing challenges, possible solutions, and present preliminary findings from our lab demonstrating the translational benefit and potential of in vivo SV2A imaging in animal models of chronic stress. Finally, we discuss methodological improvements and future directions for SV2A imaging, potentially in conjunction with other neural markers.

Behaviorally conditioned effects of psychoactive drugs in experimental animals: What we have learned from nearly a century of research and what remains to be learned

Continuous treatment with drugs is a crucial requirement for managing various clinical conditions, including chronic pain and neuropsychiatric disorders such as depression or schizophrenia. Associative learning processes, i.e. Pavlovian conditioning, can play an important role for the effects of drugs and could open new avenues for optimizing patient treatment. In this narrative literature review, we summarize available data in experimental animals regarding the behaviorally conditioned effects of psychostimulants such as d-amphetamine and cocaine, the dopamine receptor agonist apomorphine, the dopamine receptor antagonist haloperidol, morphine and antidepressant drugs. In each section, the drug under discussion is briefly introduced, followed by a detailed examination of conditioning features, including doses and dosing regimens, characteristics of the conditioning process such as test environments or specific conditioned stimuli, testing and conditioned response characteristics, possible extinction or reconditioning or reversal training, neural mechanisms, and finally, the potential clinical relevance of the research area related to the drug. We focus on key outcomes, delve into methodical issues, identify gaps in current knowledge, and suggest future research directions.

The role of mGluR5 on the therapeutic effects of ketamine in Wistar rats

RATIONALE

Ketamine produces dissociative, psychomimetic, anxiolytic, antidepressant, and anesthetic effects in a dose dependent manner. It has a complex mechanism of action that involve alterations in other glutamate receptors. The metabotropic glutamate receptor 5 (mGluR5) has been investigated in relation to the psychotic and anesthetic properties of ketamine, while its role in mediating the therapeutic effects of ketamine remains unknown.

OBJECTIVES

We investigated the role of mGluR5 on the antidepressant, anxiolytic and fear memory-related effects of ketamine in adult male Wistar rats.

METHODS

Two sets of experiments were conducted. We first utilized the positive allosteric modulator CDPPB to investigate how acute mGluR5 activation regulates the therapeutic effects of ketamine (10 mg/kg). We then tested the synergistic antidepressant effect of mGluR5 antagonism and ketamine by combining MTEP with a sub-effective dose of ketamine (1 mg/kg). Behavioral despair, locomotor activity, anxiety-like behavior, and fear memory were respectively assessed in the forced swim test (FST), open field test (OFT), elevated plus maze (EPM), and auditory fear conditioning.

RESULTS

Enhancing mGluR5 activity via CDPPB occluded the antidepressant effect of ketamine without changing locomotor activity. Furthermore, concomitant administration of MTEP and ketamine exhibited a robust synergistic antidepressant effect. The MTEP + ketamine treatment, however, blocked the anxiolytic effect observed by sole administration of MTEP or the low dose ketamine.

CONCLUSIONS

These findings suggest that suppressed mGluR5 activity is required for the antidepressant effects of ketamine. Consequently, the antagonism of mGluR5 enhances the antidepressant effectiveness of low dose ketamine, but eliminates its anxiolytic effects.

Environmental enrichment enhances the antidepressant effect of ketamine and ameliorates spatial memory deficits in adult rats

Ketamine is a rapid-acting antidepressant associated with various cognitive side effects. To mitigate these side effects while enhancing efficacy, it can be co-administered with other antidepressants. In our study, we adopted a similar strategy by combining ketamine with environmental enrichment, a potent sensory-motor paradigm, in adult male Wistar rats. We divided the animals into four groups based on a combination of housing conditions and ketamine versus vehicle injections. The groups included those housed in standard cages or an enriched environment for 50 days, which encompassed a 13-day-long behavioral testing period. Each group received either two doses of ketamine (20 mg/kg, IP) or saline as a vehicle. We tested the animals in the novel object recognition test (NORT), forced swim test (FST), open field test (OFT), elevated plus maze (EPM), and Morris water maze (MWM), which was followed by ex vivo c-Fos immunohistochemistry. We observed that combining environmental enrichment with ketamine led to a synergistic antidepressant effect. Environmental enrichment also ameliorated the spatial memory deficits caused by ketamine in the MWM. There was enhanced neuronal activity in the habenula of the enrichment only group following the probe trial of the MWM. In contrast, no differential activity was observed in enriched animals that received ketamine injections. The present study showed how environmental enrichment can enhance the antidepressant properties of ketamine while reducing some of its side effects, highlighting the potential of combining pharmacological and sensory-motor manipulations in the treatment of mood disorders.

The dynamic strategy shifting task: Optimisation of an operant task for assessing cognitive flexibility in rats

Introduction

Although schizophrenia is associated with a broad range of symptoms including hallucinations, delusions, and reduced motivation, measures of cognitive dysfunction, including cognitive flexibility and executive function, are the strongest predictors of functional outcomes. Antipsychotic medications are useful for reducing psychotic symptoms, but they are ineffective at improving cognitive deficits. Despite extensive investment by industry, the transition from preclinical to clinical trials has not been successful for developing precognitive medications for individuals with schizophrenia. Here, we describe the optimisation of a novel dynamic strategy shifting task (DSST) using standard operant chambers to investigate the optimal stimuli required to limit the extensive training times required in previous tasks.

Methods

We determined that optimal learning by male and female Sprague Dawley rats for the flexibility task incorporated dynamic strategy shifts between spatial rules, such as following a visual cue or responding at one location, and non-spatial rules, such as responding to a central visual or auditory cue. A minimum of 6 correct consecutive responses were required to make a within-session change in the behavioural strategies. As a proof of concept, we trained and tested 84 Sprague Dawley rats on the DSST, and then assessed their cognitive flexibility using a within-subject design after an acute dose of ketamine (0, 3, 10 mg/kg). Rats made fewer premature and more perseverant responses to initiate a trial following ketamine. The effects of ketamine on trials to criterion was dependent on the rule.

Results

Ketamine induced a significant improvement on the reversal of a non-spatial visual discrimination rule. There was no significant effect of ketamine on the spatial visual or response discrimination rules.

Discussion

The DSST is a novel assay for studying distinct forms of cognitive flexibility and offers a rapid and adaptable means of assessing the ability to shift between increasingly challenging rule conditions. The DSST has potential utility in advancing our understanding of cognitive processes and the underlying neurobiological mechanisms related to flexibility in neuropsychiatric and neurological conditions where executive dysfunctions occur.>.

Ketamine induced synaptic plasticity operates independently of long-term potentiation

Synaptic plasticity occurs via multiple mechanisms to regulate synaptic efficacy. Homeostatic and Hebbian plasticity are two such mechanisms by which neuronal synapses can be altered. Although these two processes are mechanistically distinct, they converge on downstream regulation of AMPA receptor activity to modify glutamatergic neurotransmission. However, much remains to be explored regarding how these two prominent forms of plasticity interact. Ketamine, a rapidly acting antidepressant, increases glutamatergic transmission via pharmacologically-induced homeostatic plasticity. Here, we demonstrate that Hebbian plasticity mechanisms are still intact in synapses that have undergone homeostatic scaling by ketamine after either systemic injection or perfusion onto hippocampal brain slices. We also investigated this relationship in the context of stress induced by chronic exposure to corticosterone (CORT) to better model the circumstances under which ketamine may be used as an antidepressant. We found that CORT induced an anhedonia-like behavioral phenotype in mice but did not impair long-term potentiation (LTP) induction. Furthermore, corticosterone exposure does not impact the intersection of homeostatic and Hebbian plasticity mechanisms, as synapses from CORT-exposed mice also demonstrated intact ketamine-induced plasticity and LTP in succession. These results provide a mechanistic explanation for how ketamine used for the treatment of depression does not impair the integrity of learning and memory processes encoded by mechanisms such as LTP.

Targeting inflammasome complexes as a novel therapeutic strategy for mood disorders

INTRODUCTION

Inflammasome complexes, especially NLRP3, have gained great attention as a potential therapeutic target in mood disorders. NLRP3 triggers a caspase 1-dependent release of the inflammatory cytokines IL-1β and IL-18, and seems to interact with purinergic and kynurenine pathways, all of which are implicated in mood disorders development and progression.

AREAS COVERED

Emerging evidence supports NLRP3 inflammasome as a promising pharmacological target for mood disorders. We discussed the available evidence from animal models and human studies and provided a reflection on drawbacks and perspectives for this novel target.

EXPERT OPINION

Several studies have supported the involvement of NLRP3 inflammasome in MDD. However, most of the evidence comes from animal models. The role of NLRP3 inflammasome in BD as well as its anti-manic properties is not very clear and requires further exploration. There is evidence of anti-manic effects of P2×R7 antagonists associated with reduction in the brain levels of IL-1β and TNF-α in a murine model of mania. The involvement of other NLRP3 inflammasome expressing cells besides microglia, like astrocytes, and of other inflammasome complexes in mood disorders also deserves further investigation. Preclinical and clinical characterization of NLRP3 and other inflammasomes in mood disorders is needed before considering translational approaches, including clinical trials.

Effects of ketamine and esketamine on preventing postpartum depression after cesarean delivery: A meta-analysis

BACKGROUND

Ketamine and esketamine has been suggested to have potential efficacy in preventing postpartum depression (PPD) recent years. The aim of this meta-analysis was to evaluate the effectiveness of ketamine and esketamine on PPD after cesarean delivery.

METHODS

We systematically searched PubMed, Embase, and the Cochrane Library for studies investigating the efficacy of ketamine and esketamine in preventing PPD. The primary outcomes of this study were risk ratios (RRs) and EPDS scores (Edinburgh Postnatal Depression Scale) in relation to PPD after ketamine and esketamine. The second outcomes were the postoperative adverse events.

RESULTS

Thirteen randomized controlled trials (RCTs) and one retrospective study including 2916 patients were analyzed, including six on the use of ketamine and eight on the use of esketamine. The risk ratios and EPDS scores of PPD were significantly decreased in the ketamine/esketamine group compared to those in the control group in one week and four weeks postoperative periods. Subgroup analyses showed that high dosage, administrated in patient controlled intravenous analgesia (PCIA) method and only esketamine exhibited a significant reduction in the incidence and EPDS scores of PPD in one week and four week postoperative. However, the incidences of postoperative adverse events, such as dizziness, diplopia, hallucination, and headache were significantly higher in the ketamine/esketamine group than that in the control group.

CONCLUSION

Ketamine and esketamine appear to be effective in preventing PPD in the one week and four week postoperative periods after cesarean delivery with moderate certainty of evidence. But they can also lead to some short-term complications too. Future high-quality studies are needed to confirm the efficacy of ketamine and esketamine in different countries.

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.

Psychedelics for alzheimer's disease-related dementia: Unveiling therapeutic possibilities and pathways

Psychedelics have traditionally been used for spiritual and recreational purposes, but recent developments in psychotherapy have highlighted their potential as therapeutic agents. These compounds, which act as potent 5-hydroxytryptamine (5HT) agonists, have been recognized for their ability to enhance neural plasticity through the activation of the serotoninergic and glutamatergic systems. However, the implications of these findings for the treatment of neurodegenerative disorders, particularly dementia, have not been fully explored. In recent years, studies have revealed the modulatory and beneficial effects of psychedelics in the context of dementia, specifically Alzheimer's disease (AD)-related dementia, which lacks a definitive cure. Psychedelics such as N,N-dimethyltryptamine (DMT), lysergic acid diethylamide (LSD), and Psilocybin have shown potential in mitigating the effects of this debilitating disease. These compounds not only target neurotransmitter imbalances but also act at the molecular level to modulate signalling pathways in AD, including the brain-derived neurotrophic factor signalling pathway and the subsequent activation of mammalian target of rapamycin and other autophagy regulators. Therefore, the controlled and dose-dependent administration of psychedelics represents a novel therapeutic intervention worth exploring and considering for the development of drugs for the treatment of AD-related dementia. In this article, we critically examined the literature that sheds light on the therapeutic possibilities and pathways of psychedelics for AD-related dementia. While this emerging field of research holds great promise, further studies are necessary to elucidate the long-term safety, efficacy, and optimal treatment protocols. Ultimately, the integration of psychedelics into the current treatment paradigm may provide a transformative approach for addressing the unmet needs of individuals living with AD-related dementia and their caregivers.

Targeting metaplasticity mechanisms to promote sustained antidepressant actions

The discovery that subanesthetic doses of (R, S)-ketamine (ketamine) and (S)-ketamine (esketamine) rapidly induce antidepressant effects and promote sustained actions following drug clearance in depressed patients who are treatment-resistant to other therapies has resulted in a paradigm shift in the conceptualization of how rapidly and effectively depression can be treated. Consequently, the mechanism(s) that next generation antidepressants may engage to improve pathophysiology and resultant symptomology are being reconceptualized. Impaired excitatory glutamatergic synapses in mood-regulating circuits are likely a substantial contributor to the pathophysiology of depression. Metaplasticity is the process of regulating future capacity for plasticity by priming neurons with a stimulation that alters later neuronal plasticity responses. Accordingly, the development of treatment modalities that specifically modulate the duration, direction, or magnitude of glutamatergic synaptic plasticity events such as long-term potentiation (LTP), defined here as metaplastogens, may be an effective approach to reverse the pathophysiology underlying depression and improve depression symptoms. We review evidence that the initiating mechanisms of pharmacologically diverse rapid-acting antidepressants (i.e., ketamine mimetics) converge on consistent downstream molecular mediators that facilitate the expression/maintenance of increased synaptic strength and resultant persisting antidepressant effects. Specifically, while the initiating mechanisms of these therapies may differ (e.g., cell type-specificity, N-methyl-D-aspartate receptor (NMDAR) subtype-selective inhibition vs activation, metabotropic glutamate receptor 2/3 antagonism, AMPA receptor potentiation, 5-HT receptor-activating psychedelics, etc.), the sustained therapeutic mechanisms of putative rapid-acting antidepressants will be mediated, in part, by metaplastic effects that converge on consistent molecular mediators to enhance excitatory neurotransmission and altered capacity for synaptic plasticity. We conclude that the convergence of these therapeutic mechanisms provides the opportunity for metaplasticity processes to be harnessed as a druggable plasticity mechanism by next-generation therapeutics. Further, targeting metaplastic mechanisms presents therapeutic advantages including decreased dosing frequency and associated diminished adverse responses by eliminating the requirement for the drug to be continuously present.

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.

Psychedelic Therapy: A Primer for Primary Care Clinicians-Ketamine

BACKGROUND

Ketamine, an arylcyclohexylamine dissociative anesthetic agent, has evolved into a versatile therapeutic. It has a rapid-onset, well-understood cardiovascular effects and a favorable safety profile in clinical use. Its enantiomeric compound, esketamine, was approved by the Food and Drug Administration in 2019 for both treatment-resistant depression and major depressive disorder with suicidal ideation.

AREAS OF UNCERTAINTY

Research indicates dose-dependent impacts on cognition, particularly affecting episodic and working memory following both acute administration and chronic use, albeit temporarily for the former and potentially persistent for the latter. Alongside acute risks to cardiovascular stability, ketamine use poses potential liver toxicity concerns, especially with prolonged or repeated exposure within short time frames. The drug's association with "ketamine cystitis," characterized by bladder inflammation, adds to its profile of physiological risks.

THERAPEUTIC ADVANCES

Data demonstrate a single intravenous infusion of ketamine exhibits antidepressant effects within hours (weighted effect size averages of depression scores (N = 518) following a single 0.5 mg/kg infusion of ketamine is d = 0.96 at 24 hours). Ketamine is also effective at reducing posttraumatic stress disorder (PTSD) symptom severity following repeated infusions (Clinician-Administered PTSD Scale scores: -11.88 points compared with midazolam control). Ketamine also decreased suicidal ideation in emergency settings (Scale for Suicidal Ideation scores: -4.96 compared with midazolam control). Through its opioid-sparing effect, ketamine has revolutionized postoperative pain management by reducing analgesic consumption and enhancing recovery.

LIMITATIONS

Many studies indicate that ketamine's therapeutic effects may subside within weeks. Repeated administrations, given multiple times per week, are often required to sustain decreases in suicidality and depressive symptoms.

CONCLUSIONS

Ketamine's comprehensive clinical profile, combined with its robust effects on depression, suicidal ideation, PTSD, chronic pain, and other psychiatric conditions, positions it as a substantial contender for transformative therapeutic application.

Ketamine causes poor maternal care in rats with postpartum depression and leads to few behavioral and neurochemical alterations on male offspring

Ketamine is an anesthetic drug that also has antidepressant properties, with quick action. Despite the great number of studies showing its effectiveness as a treatment for major depression, there is little information about its effects on postpartum depression, as pharmacological treatments bring risks to the health of both mother and child. Thus, this study aimed to evaluate the effects of prolonged treatment with subanesthetic doses of ketamine in a rat model of postpartum depression. Female dams were induced to postpartum depression by the maternal separation model from lactating day (LD) 2-12. They were divided into four groups: one control and three experimental groups, which were treated with different doses of ketamine (5, 10 or 20 mg/kg) from LD 2-21 i.p. Maternal studies were conducted from LD5 to LD21 and the offspring studies from postnatal day 2 through 90. Ketamine causes poor maternal care, with few neurochemical alterations. However, the highest dose used in this study had an antidepressant effect. Regarding the male offspring, indirect exposure to ketamine through breast milk caused few behavioral changes during infancy, but they were not permanent, as they faded in adulthood. Nevertheless, this exposure was able to cause alterations in their monoaminergic neurotransmission systems that were found in both infancy and adulthood periods.

The endogenous opioid system in the medial prefrontal cortex mediates ketamine's antidepressant-like actions

Recent studies have implicated the endogenous opioid system in the antidepressant actions of ketamine, but the underlying mechanisms remain unclear. We used a combination of pharmacological, behavioral, and molecular approaches in rats to test the contribution of the prefrontal endogenous opioid system to the antidepressant-like effects of a single dose of ketamine. Both the behavioral actions of ketamine and their molecular correlates in the medial prefrontal cortex (mPFC) are blocked by acute systemic administration of naltrexone, a competitive opioid receptor antagonist. Naltrexone delivered directly into the mPFC similarly disrupts the behavioral effects of ketamine. Ketamine treatment rapidly increases levels of β-endorphin and the expression of the μ-opioid receptor gene (Oprm1) in the mPFC, and the expression of gene that encodes proopiomelanocortin, the precursor of β-endorphin, in the hypothalamus, in vivo. Finally, neutralization of β-endorphin in the mPFC using a specific antibody prior to ketamine treatment abolishes both behavioral and molecular effects. Together, these findings indicate that presence of β-endorphin and activation of opioid receptors in the mPFC are required for the antidepressant-like actions of ketamine.

The mechanistic basis for the rapid antidepressant-like effects of ketamine: From neural circuits to molecular pathways

Conventional antidepressants that target monoaminergic receptors require several weeks to be efficacious. This lag represents a significant problem in the currently available treatments for serious depression. Ketamine, acting as an N-methyl-d-aspartate receptor antagonist, was shown to have rapid antidepressant-like effects, marking a significant advancement in the study of mood disorders. However, serious side effects and adverse reactions limit its clinical use. Considering the limitations of ketamine, it is crucial to further define the network targets of ketamine. The rapid action of ketamine an as antidepressant is thought to be mediated by the glutamate system. It is believed that synaptic plasticity is essential for the rapid effects of ketamine as an antidepressant. Other mechanisms include the involvement of the γ-aminobutyric acidergic (GABAergic), 5-HTergic systems, and recent studies have linked astrocytes to ketamine's rapid antidepressant-like effects. The interactions between these systems exert a synergistic rapid antidepressant effect through neural circuits and molecular mechanisms. Here, we discuss the neural circuits and molecular mechanisms underlying the action of ketamine. This work will help explain how molecular and neural targets are responsible for the effects of rapidly acting antidepressants and will aid in the discovery of new therapeutic approaches for major depressive disorder.

Ketamine: Mechanisms and Relevance to Treatment of Depression

Major depressive disorder (MDD) is a leading cause of suicide in the world. Monoamine-based antidepressant drugs are a primary line of treatment for this mental disorder, although the delayed response and incomplete efficacy in some patients highlight the need for improved therapeutic approaches. Over the past two decades, ketamine has shown rapid onset with sustained (up to several days) antidepressant effects in patients whose MDD has not responded to conventional antidepressant drugs. Recent preclinical studies have started to elucidate the underlying mechanisms of ketamine's antidepressant properties. Herein, we describe and compare recent clinical and preclinical findings to provide a broad perspective of the relevant mechanisms for the antidepressant action of ketamine.

Hydroxynorketamine, but not ketamine, acts via α7 nicotinic acetylcholine receptor to control presynaptic function and gene expression

Ketamine is clinically used fast-acting antidepressant. Its metabolite hydroxynorketamine (HNK) shows a robust antidepressant effect in animal studies. It is unclear, how these chemically distinct compounds converge on similar neuronal effects. While KET acts mostly as N-methyl-d-aspartate receptor (NMDAR) antagonist, the molecular target of HNK remains enigmatic. Here, we show that KET and HNK converge on rapid inhibition of glutamate release by reducing the release competence of synaptic vesicles and induce nuclear translocation of pCREB that controls expression of neuroplasticity genes connected to KET- and HNK-mediated antidepressant action. Ro25-6981, a selective antagonist of GluN2B, mimics effect of KET indicating that GluN2B-containing NMDAR might mediate the presynaptic effect of KET. Selective antagonist of α7 nicotinic acetylcholine receptors (α7nAChRs) or genetic deletion of Chrna7, its pore-forming subunit, fully abolishes HNK-induced synaptic and nuclear regulations, but leaves KET-dependent cellular effects unaffected. Thus, KET or HNK-induced modulation of synaptic transmission and nuclear translocation of pCREB can be mediated by selective signaling via NMDAR or α7nAChRs, respectively. Due to the rapid metabolism of KET to HNK, it is conceivable that subsequent modulation of glutamatergic and cholinergic neurotransmission affects circuits in a cell-type-specific manner and contributes to the therapeutic potency of KET. This finding promotes further exploration of new combined medications for mood disorders.

Optimizing the use of ketamine to reduce chronic postsurgical pain in women undergoing mastectomy for oncologic indication: study protocol for the KALPAS multicenter randomized controlled trial

BACKGROUND

Mastectomies are commonly performed and strongly associated with chronic postsurgical pain (CPSP), more specifically termed postmastectomy pain syndrome (PMPS), with 25-60% of patients reporting pain 3 months after surgery. PMPS interferes with function, recovery, and compliance with adjuvant therapy. Importantly, it is associated with chronic opioid use, as a recent study showed that 1 in 10 patients continue to use opioids at least 3 months after curative surgery. The majority of PMPS patients are women, and, over the past 10 years, women have outpaced men in the rate of growth in opioid dependence. Standard perioperative multimodal analgesia is only modestly effective in prevention of CPSP. Thus, interventions to reduce CPSP and PMPS are urgently needed. Ketamine is well known to improve pain and reduce opioid use in the acute postoperative period. Additionally, ketamine has been shown to control mood in studies of anxiety and depression. By targeting acute pain and improving mood in the perioperative period, ketamine may be able to prevent the development of CPSP.

METHODS

Ketamine analgesia for long-lasting pain relief after surgery (KALPAS) is a phase 3, multicenter, randomized, placebo-controlled, double-blind trial to study the effectiveness of ketamine in reducing PMPS. The study compares continuous perioperative ketamine infusion vs single-dose ketamine in the postanesthesia care unit vs placebo for reducing PMPS. Participants are followed for 1 year after surgery. The primary outcome is pain at the surgical site at 3 months after the index surgery as assessed with the Brief Pain Inventory-short form pain severity subscale.

DISCUSSION

This project is part of the NIH Helping to End Addiction Long-term (HEAL) Initiative, a nationwide effort to address the opioid public health crisis. This study can substantially impact perioperative pain management and can contribute significantly to combatting the opioid epidemic.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05037123. Registered on September 8, 2021.

Serotonin 2A Receptor (5-HT2AR) Agonists: Psychedelics and Non-Hallucinogenic Analogues as Emerging Antidepressants

Psychedelics make up a group of psychoactive compounds that induce hallucinogenic effects by activating the serotonin 2A receptor (5-HT2AR). Clinical trials have demonstrated the traditional psychedelic substances like psilocybin as a class of rapid-acting and long-lasting antidepressants. However, there is a pressing need for rationally designed 5-HT2AR agonists that possess optimal pharmacological profiles in order to fully reveal the therapeutic potential of these agonists and identify safer drug candidates devoid of hallucinogenic effects. This Perspective provides an overview of the structure-activity relationships of existing 5-HT2AR agonists based on their chemical classifications and discusses recent advancements in understanding their molecular pharmacology at a structural level. The encouraging clinical outcomes of psychedelics in depression treatment have sparked drug discovery endeavors aimed at developing novel 5-HT2AR agonists with improved subtype selectivity and signaling bias properties, which could serve as safer and potentially nonhallucinogenic antidepressants. These efforts can be significantly expedited through the utilization of structure-based methods and functional selectivity-directed screening.

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.

[Ketamine and suicidal behavior: Contribution of animal models of aggression-impulsivity to understanding its mechanism of action]

More than two-thirds of suicides occur during a major depressive episode. Acting out prevention measures and therapeutic options to manage the suicidal crisis are limited. The impulsive-aggressive dimensions are vulnerability factors associated with suicide in patients suffering from a characterized depressive episode: this can be a dimension involved in animals. Impulsive and aggressive rodent models can help analyze, at least in part, the neurobiology of suicide and the beneficial effects of treatments. Ketamine, a glutamatergic antagonist, by rapidly improving the symptoms of depressive episodes, would help reduce suicidal thoughts in the short term. Animal models share with humans impulsive and aggressive endophenotypes modulated by the serotonergic system (5-HTB receptor, MAO-A enzyme), neuroinflammation or the hypothalamic-pituitary-adrenal axis and stress. Significant effects of ketamine on these endophenotypes remain to be demonstrated.

Cerebrospinal fluid exploratory proteomics and ketamine metabolite pharmacokinetics in human volunteers after ketamine infusion

Ketamine is a treatment for both refractory depression and chronic pain syndromes. In order to explore ketamine's potential mechanism of action and whether ketamine or its metabolites cross the blood brain barrier, we examined the pharmacokinetics of ketamine and its metabolites-norketamine (NK), dehydronorketamine (DHNK), and hydroxynorketamines (HNKs)-in cerebrospinal fluid (CSF) and plasma, as well as in an exploratory proteomic analysis in the CSF of nine healthy volunteers who received ketamine intravenously (0.5 mg/kg IV). We found that ketamine, NK, and (2R,6R;2S,6S)-HNK readily crossed the blood brain barrier. Additionally, 354 proteins were altered in the CSF in at least two consecutive timepoints (p < 0.01). Proteins in the classes of tyrosine kinases, cellular adhesion molecules, and growth factors, including insulin, were most affected, suggesting an interplay of altered neurotransmission, neuroplasticity, neurogenesis, synaptogenesis, and neural network functions following ketamine administration.

Enhanced TARP-γ8-PSD-95 coupling in excitatory neurons contributes to the rapid antidepressant-like action of ketamine in male mice

Ketamine produces rapid antidepressant effects at sub-anesthetic dosage through early and sustained activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), however, the exact molecular mechanism still remains unclear. Transmembrane AMPAR regulatory protein-γ8 (TARP-γ8) is identified as one of AMPAR auxiliary subunits, which controls assemblies, surface trafficking and gating of AMPARs. Here, we show that ketamine rescues both depressive-like behaviors and the decreased AMPARs-mediated neurotransmission by recruitment of TARP-γ8 at the postsynaptic sites in the ventral hippocampus of stressed male mice. Furthermore, the rapid antidepressant effects of ketamine are abolished by selective blockade of TARP-γ8-containing AMPAR or uncoupling of TARP-γ8 from PSD-95. Overexpression of TARP-γ8 reverses chronic stress-induced depressive-like behaviors and attenuation of AMPARs-mediated neurotransmission. Conversely, knockdown of TARP-γ8 in excitatory neurons prevents the rapid antidepressant effects of ketamine.

Promising new pharmacological targets for depression: The search for efficacy

Pharmacological treatment of major depressive disorder (MDD) still relies on the use of serotonergic drugs, despite their limited efficacy. A few mechanistically new drugs have been developed in recent years, but many fail in clinical trials. Several hypotheses have been proposed to explain MDD pathophysiology, indicating that physiological processes such as neuroplasticity, circadian rhythms, and metabolism are potential targets. Here, we review the current state of pharmacological treatments for MDD, as well as the preclinical and clinical evidence for an antidepressant effect of molecules that target non-serotonergic systems. We offer some insights into the challenges facing the development of new antidepressant drugs, and the prospect of finding more effectiveness for each target discussed.

Evaluating the effects of S-ketamine on postoperative delirium in elderly patients following total hip or knee arthroplasty under intraspinal anesthesia: a single-center randomized, double-blind, placebo-controlled, pragmatic study protocol

Introduction

Postoperative delirium (POD) is an acute, transient brain disorder associated with decreased postoperative quality of life, dementia, neurocognitive changes, and mortality. A small number of trials have explored the role of S-ketamine in the treatment of POD due to its neuroprotective effects. Surprisingly, these trials have failed to yield supportive results. However, heterogeneity in delirium assessment methodologies, sample sizes, and outcome settings as well as deficiencies in S-ketamine use methods make the evidence provided by these studies less persuasive. Given the severe impact of POD on the health of elderly patients and the potential for S-ketamine to prevent it, we believe that designing a large sample size, and rigorous randomized controlled trial for further evaluation is necessary.

Methods

This is a single-center, randomized, double-blind, placebo-controlled, pragmatic study. Subjects undergoing total hip or knee arthroplasty will be randomized in a 1:1 ratio to intervention (n = 186) and placebo (n = 186) groups. This trial aims to explore the potential role of S-ketamine in the prevention of POD. Its primary outcome is the incidence of POD within 3 postoperative days. Secondary outcomes include the number of POD episodes, the onset and duration of POD, the severity and subtype of POD, pain scores and opioid consumption, sleep quality, clinical outcomes, and safety outcomes.

Discussion

To our knowledge, this is the first pragmatic study that proposes to use S-ketamine to prevent POD. We reviewed a large body of literature to identify potential preoperative confounding variables that may bias associations between the intervention and primary outcome. We will use advanced statistical methods to correct potential confounding variables, improving the test's power and external validity of test results. Of note, the patient population included in this trial will undergo intraspinal anesthesia. Although large, multicenter, randomized controlled studies have found no considerable difference in the effects of regional and general anesthesia on POD, patients receiving intraspinal anesthesia have less exposure to at-risk drugs, such as sevoflurane, propofol, and benzodiazepines, than patients receiving general anesthesia. At-risk drugs have been shown to negatively interfere with the neuroprotective effects of S-ketamine, which may be the reason for the failure of a large number of previous studies. There is currently a lack of randomized controlled studies evaluating S-ketamine for POD prevention, and our trial helps to fill a gap in this area.Trial registration: http://www.chictr.org.cn, identifier ChiCTR2300075796.

[Ketamine: a neuropsychotropic drug with an innovative mechanism of action]

Ketamine, a non-competitive antagonist of the N-methyl-D-aspartate-glutamate receptor (R-NMDA), has a rapid (from 24 h post-dose) and prolonged (up to one week) antidepressant effect in treatment resistant depression and in rodent models of anxiety/depression. Arguments regarding its cellular and molecular mechanisms underlying its antidepressant activity mainly come from animal studies. However, debates still persist on the structural remodeling of frontocortical/hippocampal neurons and the role of excitatory/inhibitory neurotransmitters involved in its behavioral effect. Neurochemical and behavioral changes are maintained 24 h after administration of ketamine, well beyond its plasma elimination half-life. The glutamatergic pyramidal cells of the medial prefrontal cortex are primarily implicated in the therapeutic effects of ketamine. Advances in knowledge of the consequences of R-NMDA blockade allowed to specify the underlying mechanisms involving the activation of AMPA glutamate receptors, which triggers a cascade of intracellular events dependent on the mechanistic target of rapamycin, brain-derived neurotrophic factor, and synaptic protein synthesis facilitating synaptic plasticity (number of dendritic spines, synaptogenesis). This review focuses on abnormalities of neurotransmitter systems involved in major depressive disorders, their potential impact on neural circuitry and beneficial effects of ketamine. Recent preclinical data pave the way for future studies to better clarify the mechanism of action of fast-acting antidepressant drugs for the development of novel, more effective therapies.

Low-dose ketamine improves animals' locomotor activity and decreases brain oxidative stress and inflammation in ammonia-induced neurotoxicity

Ammonium ion (NH4 + ) is the major suspected molecule responsible for neurological complications of hepatic encephalopathy (HE). No specific pharmacological action for NH4 + -induced brain injury exists so far. Excitotoxicity is a well-known phenomenon in the brain of hyperammonemic cases. The hyperactivation of the N-Methyl- d-aspartate (NMDA) receptors by agents such as glutamate, an NH4 + metabolite, could cause excitotoxicity. Excitotoxicity is connected with events such as oxidative stress and neuroinflammation. Hence, utilizing NMDA receptor antagonists could prevent neurological complications of NH4 + neurotoxicity. In the current study, C57BL6/J mice received acetaminophen (APAP; 800 mg/kg, i.p) to induce HE. Hyperammonemic animals were treated with ketamine (0.25, 0.5, and 1 mg/kg, s.c) as an NMDA receptor antagonist. Animals' brain and plasma levels of NH4 + were dramatically high, and animals' locomotor activities were disturbed. Moreover, several markers of oxidative stress were significantly increased in the brain. A significant increase in brain tissue levels of TNF-α, IL-6, and IL-1β was also detected in hyperammonemic animals. It was found that ketamine significantly normalized animals' locomotor activity, improved biomarkers of oxidative stress, and decreased proinflammatory cytokines. The effects of ketamine on oxidative stress biomarkers and inflammation seem to play a key role in its neuroprotective mechanisms in the current study.

The 5-HT1A receptor biased agonists, NLX-204 and NLX-101, display ketamine-like RAAD and anti-TRD activities in rat CMS models

OBJECTIVES

NLX-101 and NLX-204 are highly selective serotonin 5-HT1A 'biased' agonists, displaying potent and efficacious antidepressant-like activity upon acute administration in models such as the forced swim test.

METHODS

we compared the effects of repeated administration of NLX-101, NLX-204 and ketamine in the chronic mild stress (CMS) model of depression, considered to have high translational potential, on sucrose consumption (anhedonia measure), novel object recognition (NOR; working memory measure) and elevated plus maze (EPM; anxiety measure) in male Wistar and Wistar-Kyoto rats (the latter being resistant to classical antidepressants).

RESULTS

in Wistar rats, NLX-204 and NLX-101 (0.08-0.16 mg/kg i.p.), like ketamine (10 mg/kg i.p.) dose-dependently reversed CMS-induced sucrose intake deficit from treatment Day 1, with nearly full reversal observed at the higher dose at Days 8 and 15. These effects persisted for 3 weeks following treatment cessation. In the NOR test, both doses of NLX-101/NLX-204, and ketamine, rescued the deficit in discrimination index caused by CMS on Days 3 and 17; all three compounds increased time spent in open arms (EPM) but only NLX-204 achieved statistical significance on Days 2 and 16. In Wistar-Kyoto rats, all 3 compounds were also active in the sucrose test and, to a lesser extent, in the NOR and EPM. In non-stressed rats (both strains), the three compounds produced no significant effects in all tests.

CONCLUSIONS

these observations further strengthen the hypothesis that biased agonism at 5-HT1A receptors constitutes a promising strategy to achieve rapid-acting/sustained antidepressant effects combined with activity against TRD, in addition to providing beneficial effects against memory deficit and anxiety in depressed patients.

A Comprehensive Review of the Current Status of the Cellular Neurobiology of Psychedelics

Psychedelic substances have gained significant attention in recent years for their potential therapeutic effects on various psychiatric disorders. This review delves into the intricate cellular neurobiology of psychedelics, emphasizing their potential therapeutic applications in addressing the global burden of mental illness. It focuses on contemporary research into the pharmacological and molecular mechanisms underlying these substances, particularly the role of 5-HT2A receptor signaling and the promotion of plasticity through the TrkB-BDNF pathway. The review also discusses how psychedelics affect various receptors and pathways and explores their potential as anti-inflammatory agents. Overall, this research represents a significant development in biomedical sciences with the potential to transform mental health treatments.

Trace Elements Levels in Major Depressive Disorder-Evaluation of Potential Threats and Possible Therapeutic Approaches

The multifactorial etiology of major depressive disorder (MDD) includes biological, environmental, genetic, and psychological aspects. Recently, there has been an increasing interest in metallomic studies in psychiatry, aiming to evaluate the role of chosen trace elements in the MDD etiology as well as the progression of symptoms. This narrative review aims to summarize the available literature on the relationship between the concentration of chosen elements in the serum of patients with MDD and the onset and progression of this psychiatric condition. The authors reviewed PubMed, Web of Science, and Scopus databases searching for elements that had been investigated so far and further evaluated them in this paper. Ultimately, 15 elements were evaluated, namely, zinc, magnesium, selenium, iron, copper, aluminium, cadmium, lead, mercury, arsenic, calcium, manganese, chromium, nickel, and phosphorus. The association between metallomic studies and psychiatry has been developing dynamically recently. According to the results of current research, metallomics might act as a potential screening tool for patients with MDD while at the same time providing an assessment of the severity of symptoms. Either deficiencies or excessive amounts of chosen elements might be associated with the progression of depressive symptoms or even the onset of the disease among people predisposed to MDD.

The endogenous opioid system in the medial prefrontal cortex mediates ketamine's antidepressant-like actions

Recent studies have implicated the endogenous opioid system in the antidepressant actions of ketamine, but the underlying mechanisms remain unclear. We used a combination of pharmacological, behavioral, and molecular approaches in rats to test the contribution of the prefrontal endogenous opioid system to the antidepressant-like effects of a single dose of ketamine. Both the behavioral actions of ketamine and their molecular correlates in the medial prefrontal cortex (mPFC) were blocked by acute systemic administration of naltrexone, a competitive opioid receptor antagonist. Naltrexone delivered directly into the mPFC similarly disrupted the behavioral effects of ketamine. Ketamine treatment rapidly increased levels of β-endorphin and the expression of the μ-opioid receptor gene (Oprm1) in the mPFC, and the expression of the gene that encodes proopiomelanocortin, the precursor of β-endorphin, in the hypothalamus, in vivo. Finally, neutralization of β-endorphin in the mPFC using a specific antibody prior to ketamine treatment abolished both behavioral and molecular effects. Together, these findings indicate that presence of β-endorphin and activation of opioid receptors in the mPFC are required for the antidepressant-like actions of ketamine.

Sustained antidepressant effect of ketamine through NMDAR trapping in the LHb

Ketamine, an N-methyl-D-aspartate receptor (NMDAR) antagonist1, has revolutionized the treatment of depression because of its potent, rapid and sustained antidepressant effects2-4. Although the elimination half-life of ketamine is only 13 min in mice5, its antidepressant activities can last for at least 24 h6-9. This large discrepancy poses an interesting basic biological question and has strong clinical implications. Here we demonstrate that after a single systemic injection, ketamine continues to suppress burst firing and block NMDARs in the lateral habenula (LHb) for up to 24 h. This long inhibition of NMDARs is not due to endocytosis but depends on the use-dependent trapping of ketamine in NMDARs. The rate of untrapping is regulated by neural activity. Harnessing the dynamic equilibrium of ketamine-NMDAR interactions by activating the LHb and opening local NMDARs at different plasma ketamine concentrations, we were able to either shorten or prolong the antidepressant effects of ketamine in vivo. These results provide new insights into the causal mechanisms of the sustained antidepressant effects of ketamine. The ability to modulate the duration of ketamine action based on the biophysical properties of ketamine-NMDAR interactions opens up new opportunities for the therapeutic use of ketamine.

Esketamine Inhibits Cocaine-Seeking Behaviour Subsequent to Various Abstinence Conditions in Rats

BACKGROUND

Cocaine use disorder (CUD) is a relapsing brain disease caused by a chronic drug intake that involves neural mechanisms and psychological processes, including depression. Preclinical and clinical studies have demonstrated the promise of pharmacological drugs in controlling the reinstatement of cocaine by targeting the N-methyl-D-aspartate (NMDA) receptor. Recent evidence has revealed that esketamine, a (S) enantiomer of ketamine, shows a high affinity to NMDA receptors and has been used in clinical trials to treat moderate-to-severe depression.

METHODS

In the present paper, we investigated the effects of esketamine in regulating cocaine-seeking behaviour induced through the use of cocaine (10 mg/kg) or the cocaine-associated conditioned cue after a short (10 days)-lasting period of drug abstinence with extinction training, home cage or enrichment environment conditions in male rats. Furthermore, we investigated the acute effects of esketamine on locomotor activity in drug-naïve animals.

RESULTS

Esketamine (2.5-10 mg/kg) administered peripherally attenuated the reinstatement induced with cocaine priming or the drug-associated conditioned cue after different conditions of abstinence.

CONCLUSIONS

These results seem to support esketamine as a candidate for the pharmacological management of cocaine-seeking and relapse prevention; however, further preclinical and clinical research is needed to better clarify esketamine's actions in CUD.

HCN channel inhibitor induces ketamine-like rapid and sustained antidepressant effects in chronic social defeat stress model

Repeated, long-term (weeks to months) exposure to standard antidepressant medications is required to achieve treatment efficacy. In contrast, acute ketamine quickly improves mood for an extended time. Recent work implicates that hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are involved in mediating ketamine's antidepressant effects. In this study, we directly targeted HCN channels and achieved ketamine-like rapid and sustained antidepressant efficacy. Our in vitro electrophysiological recordings first showed that HCN inhibitor DK-AH 269 (also called cilobradine) decreased the pathological HCN-mediated current (Ih) and abnormal hyperactivity of ventral tegmental area (VTA) dopamine (DA) neurons in a depressive-like model produced by chronic social defeat stress (CSDS). Our in vivo studies further showed that acute intra-VTA or acute systemic administration of DK-AH 269 normalized social behavior and rescued sucrose preference in CSDS-susceptible mice. The single-dose of DK-AH 269, both by intra-VTA microinfusion and intraperitoneal (ip) approaches, could produce an extended 13-day duration of antidepressant-like efficacy. Animals treated with acute DK-AH 269 spent less time immobile than vehicle-treated mice during forced swim test. A social behavioral reversal lasted up to 13 days following the acute DK-AH 269 ip injection, and this rapid and sustained antidepressant-like response is paralleled with a single-dose treatment of ketamine. This study provides a novel ion channel target for acutely acting, long-lasting antidepressant-like effects.

Clinical specificity profile for novel rapid acting antidepressant drugs

Mood disorders are recurrent/chronic diseases with variable clinical remission rates. Available antidepressants are not effective in all patients and often show a relevant response latency, with a range of adverse events, including weight gain and sexual dysfunction. Novel rapid agents were developed with the aim of overcoming at least in part these issues. Novel drugs target glutamate, gamma-aminobutyric acid, orexin, and other receptors, providing a broader range of pharmacodynamic mechanisms, that is, expected to increase the possibility of personalizing treatments on the individual clinical profile. These new drugs were developed with the aim of combining a rapid action, a tolerable profile, and higher effectiveness on specific symptoms, which were relatively poorly targeted by standard antidepressants, such as anhedonia and response to reward, suicidal ideation/behaviours, insomnia, cognitive deficits, and irritability. This review discusses the clinical specificity profile of new antidepressants, namely 4-chlorokynurenine (AV-101), dextromethorphan-bupropion, pregn-4-en-20-yn-3-one (PH-10), pimavanserin, PRAX-114, psilocybin, esmethadone (REL-1017/dextromethadone), seltorexant (JNJ-42847922/MIN-202), and zuranolone (SAGE-217). The main aim is to provide an overview of the efficacy/tolerability of these compounds in patients with mood disorders having different symptom/comorbidity patterns, to help clinicians in the optimization of the risk/benefit ratio when prescribing these drugs.

The Role of Glutamate Underlying Treatment-resistant Depression

The monoamine hypothesis has significantly improved our understanding of mood disorders and their treatment by linking monoaminergic abnormalities to the pathophysiology of mood disorders. Even 50 years after the monoamine hypothesis was established, some patients do not respond to treatments for depression, including selective serotonin reuptake drugs. Accumulating evidence shows that patients with treatment-resistant depression (TRD) have severe abnormalities in the neuroplasticity and neurotrophic factor pathways, indicating that different treatment approaches may be necessary. Therefore, the glutamate hypothesis is gaining attention as a novel hypothesis that can overcome monoamine restrictions. Glutamate has been linked to structural and maladaptive morphological alterations in several brain areas associated with mood disorders. Recently, ketamine, an N-methyl-D-aspartate receptor (NMDAR) antagonist, has shown efficacy in TRD treatment and has received the U.S. Food and Drug Administration approval, revitalizing psychiatry research. However, the mechanism by which ketamine improves TRD remains unclear. In this review, we re-examined the glutamate hypothesis, bringing the glutamate system onboard to join the modulation of the monoamine systems, emphasizing the most prominent ketamine antidepressant mechanisms, such as NMDAR inhibition and NMDAR disinhibition in GABAergic interneurons. Furthermore, we discuss the animal models used in preclinical studies and the sex differences in the effects of ketamine.

Changes in social, sexual, and hedonic behaviors in rats in response to stress and restoration by a negative allosteric modulator of α5-subunit containing GABA receptor

Major depressive disorder (MDD) is a debilitating and costly human condition. Treatment for MDD relies heavily on the use of antidepressants that are slow to produce mood-related changes and are not effective in all patients, such as selective serotonin reuptake inhibitors (SSRIs). Several novel compounds, including negative allosteric modulators of GABA-A receptors containing the α5-subunit (GABA-NAMs), are under investigation for potential fast acting therapeutic use in MDD. Preclinical evidence that these compounds produce a rapid antidepressant-like response comes primarily from simple tests of escape behavior and preference for rewarding stimuli after chronic stress. To increase the ethological relevance of these compounds, we tested the hypothesis that the GABA-NAM, L-655,708, would produce an antidepressant-like response in more complex stress-sensitive social and sex behaviors, which are of relevance to the symptoms of human depression. In male rats subjected to chronic restraint stress, injection of L-655,708 increased reward in a sexual conditioned place preference task, increased male sexual activity with a receptive female, and re-established male social dominance hierarchies within 24 h. We also report increased sucrose preference in the social defeat stress (SDS) model of depression following GABA-NAM administration, demonstrating that its antidepressant-like actions are independent of the type of chronic stress administered. This work extends the impact of GABA-NAMs beyond traditional tests of anhedonia and further supports the development of alpha5 subunit-selective GABA-NAMs as a potential fast-acting therapeutic approach for treating human MDD.

A Multifunctional Nanocarrier System for Highly Efficient and Targeted Delivery of Ketamine to NMDAR Sites for Improved Treatment of Depression

Ketamine (KA), commonly used as an anesthetic, is now widely studied as an antidepressant for the treatment of depression. However, due to its side effects, such as addiction and cognitive impairment, the dosage and frequency of (S)-ketamine approved by the FDA for the treatment of refractory depression is very low, which limits its efficacy. Here, a new multifunctional nanocarrier system (AC-RM@HA-MS) with specific targeting capabilities is developed to improve the efficacy of KA treatment. KA-loaded NPs (AC-RM@HA-MS-KA) are constructed with a multilayer core-shell structure. KA-loaded mesoporous silica NPs are prepared, conjugated with hyaluronic acid (HA) as pore gatekeepers, and sheathed with an RBC-membrane (RM) for camouflage. Finally, the surface is tagged with bifunctional peptides (Ang-2-Con-G, AC) to achieve specific targeting. One peptide (Ang-2) is acted as a guide to facilitate the crossing of the blood-brain barrier (BBB), while the other (Con-G) is functioned as a ligand for the targeted delivery of KA to the N-methyl-D-aspartate receptor sites. Animal experiments reveal that AC-RM@HA-MS-KA NPs effectively cross the BBB and directionally accumulate in the curing areas, thereby alleviating the depressive symptoms and improving the cognitive functions of depressed mice. After treatment, the depressed mice almost completely return to normal without obvious symptoms of addiction.