Attenuation of Antidepressant Effects of Ketamine by Opioid Receptor Antagonism

Investigating the network ties between affect, attachment, and psychopathology

OBJECTIVES

Recent years have seen an increased interest regarding theoretical and empirical associations of adult attachment security and primary affective traits concerning psychiatric disorders. In this study, network analysis technique is applied to dissect the links between both psychodynamic personality constructs and an array of psychopathological symptoms.

METHODS

A total sample of 921 (69.9 % female) participants from the general population was investigated. A regularized cross-sectional partial correlation network between attachment (Experiences in Close Relationships-Revised [ECR-RD8]), primary affective traits (Brief Affective Neuroscience Personality Scales [BANPS-GL]) and psychopathological symptoms (ICD-10-Symptom-Rating Questionnaire [ISR]) was estimated via the EBICglasso algorithm. Node centrality, predictability and bridge centrality were analyzed. To evaluate the stability of the network and evaluate the significance of differences, we employed bootstrap techniques.

RESULTS

The network was found to be stable, allowing reliable interpretations. We observed SADNESS, as well as depressive, PTSD and anxiety symptoms as the most influential nodes within the investigated network. Attachment AV and SADNESS were observed as nodes with the highest bridge centrality.

CONCLUSIONS

The results provide a data-driven in-depth look into the complex dynamics between psychopathological symptoms, attachment security and basic affective traits. Results underscore the critical interconnections between affect, attachment, and psychopathology, advocating for a psychodynamically informed systems approach in psychological research that considers the affective dimensions underlying human mental health.

Efficacy of ketamine versus esketamine in the treatment of perioperative depression: A review

Depression is a significant factor contributing to postoperative occurrences, and patients diagnosed with depression have a higher risk for postoperative complications. Studies on cardiovascular surgery extensively addresses this concern. Several studies report that people who undergo coronary artery bypass graft surgery have a 20% chance of developing postoperative depression. A retrospective analysis of medical records spanning 21 years, involving 817 patients, revealed that approximately 40% of individuals undergoing coronary artery bypass grafting (CABG) were at risk of perioperative depression. Patients endure prolonged suffering from illness because each attempt with standard antidepressants requires several weeks to be effective. In addition, multi-drug combination adjuvants or combination medication therapy may alleviate symptoms for some individuals, but they also increase the risk of side effects. Conventional antidepressants primarily modulate the monoamine system, whereas different therapies target the serotonin, norepinephrine, and dopamine systems. Esketamine is a fast-acting antidepressant with high efficacy. Esketamine is the S-enantiomer of ketamine, a derivative of phencyclidine developed in 1956. Esketamine exerts its effect by targeting the glutaminergic system the glutaminergic system. In this paper, we discuss the current depression treatment strategies with a focus on the pharmacology and mechanism of action of esketamine. In addition, studies reporting use of esketamine to treat perioperative depressive symptoms are reviwed, and the potential future applications of the drug are presented.

Ketamine-assisted buprenorphine initiation: a pilot case series

BACKGROUND

Many people with opioid use disorder who stand to benefit from buprenorphine treatment are unwilling to initiate it due to experience with or fear of both spontaneous and buprenorphine-precipitated opioid withdrawal (BPOW). An effective means of minimizing withdrawal symptoms would reduce patient apprehensiveness, lowering the barrier to buprenorphine initiation. Ketamine, approved by the FDA as a dissociative anesthetic, completely resolved BPOW in case reports when infused at a sub-anesthetic dose range in which dissociative symptoms are common. However, most patients attempt buprenorphine initiation in the outpatient setting where altered mental status is undesirable. We explored the potential of short-term use of ketamine, self-administered sublingually at a lower, sub-dissociative dose to assist ambulatory patients undergoing transition to buprenorphine from fentanyl and methadone.

METHODS

Patients prescribed ketamine were either (1) seeking transition to buprenorphine from illicit fentanyl and highly apprehensive of BPOW or (2) undergoing transition to buprenorphine from illicit fentanyl or methadone and experiencing BPOW. We prescribed 4-8 doses of sublingual ketamine 16 mg (each dose bioequivalent to 3-6% of an anesthetic dose), monitored patients daily or near-daily, and adjusted buprenorphine and ketamine dosing based on patient response and prescriber experience.

RESULTS

Over a period of 14 months, 37 patients were prescribed ketamine. Buprenorphine initiation was completed by 16 patients, representing 43% of the 37 patients prescribed ketamine, and 67% of the 24 who reported trying it. Of the last 12 patients who completed buprenorphine initiation, 11 (92%) achieved 30-day retention in treatment. Most of the patients who tried ketamine reported reduction or elimination of spontaneous opioid withdrawal symptoms. Some patients reported avoidance of severe BPOW when used prophylactically or as treatment of established BPOW. We developed a ketamine protocol that allowed four of the last patients to complete buprenorphine initiation over four days reporting only mild withdrawal symptoms. Two patients described cognitive changes from ketamine at a dose that exceeded the effective dose range for the other patients.

CONCLUSIONS

Ketamine at a sub-dissociative dose allowed completion of buprenorphine initiation in the outpatient setting in the majority of patients who reported trying it. Further research is warranted to confirm these results and develop reliable protocols for a range of treatment settings.

Update on the assessment of resistance to antidepressant treatment: Rationale for the Antidepressant Treatment History Form: Short Form-2 (ATHF-SF2)

All definitions of treatment-resistant depression (TRD) require that patients have experienced insufficient benefit from one or more adequate antidepressant trials. Thus, identifying "failed, adequate trials" is key to the assessment of TRD. The Antidepressant Treatment History Form (ATHF) was one of the first and most widely used instruments that provided objective criteria in making these assessments. The original ATHF was updated in 2018 to the ATHF-SF, changing to a checklist format for scoring, and including specific pharmacotherapy, brain stimulation, and psychotherapy interventions as potentially adequate antidepressant treatments. The ATHF-SF2, presented here, is based on the consensus of the ATHF workgroup about the novel interventions introduced since the last revision and which should/should not be considered effective treatments for major depressive episodes. This document describes the rationale for these choices and, for each intervention, the minimal criteria for determining the adequacy of treatment administration. The Supplementary Material that accompanies this article provide the Scoring Checklist, Data Collection Forms (current episode and composite of previous episodes), and Instruction Manual for the ATHF-SF2.

Repurposing General Anesthetic Drugs to Treat Depression: A New Frontier for Anesthesiologists in Neuropsychiatric Care

During the last 100 years, the role of anesthesiologists in psychiatry has focused primarily on facilitating electroconvulsive therapy and mitigating postoperative delirium and other perioperative neurocognitive disorders. The discovery of the rapid and sustained antidepressant properties of ketamine, and early results suggesting that other general anesthetic drugs (including nitrous oxide, propofol, and isoflurane) have antidepressant properties, has positioned anesthesiologists at a new frontier in the treatment of neuropsychiatric disorders. Moreover, shared interest in understanding the biologic underpinnings of anesthetic drugs as psychotropic agents is eroding traditional academic boundaries between anesthesiology and psychiatry. This article presents a brief overview of anesthetic drugs as novel antidepressants and identifies promising future candidates for the treatment of depression. The authors issue a call to action and outline strategies to foster collaborations between anesthesiologists and psychiatrists as they work toward the common goals of repurposing anesthetic drugs as antidepressants and addressing mood disorders in surgical patients.

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'.

Comparison of low-dose ketamine to methadone for postoperative pain in opioid addicts: a randomized clinical trial

BACKGROUND

Postoperative pain can lead to several complications. The effectiveness of different opioids in relieving pain after surgery has been widely studied. However, managing pain in patients with opioid addiction is still challenging. This study aimed to examine the impact of ketamine and methadone on postoperative pain in patients with addiction.

METHODS

This was a non-inferiority randomized clinical trial. All included patients were monitored for morphine use, pain scores, and vital signs every 3 h. The intervention group received 0.5 mg/kg ketamine administered intravenously every 6 h. The control group received 5 mg of methadone intramuscularly every 8 h. The patient received intravenous morphine if their visual analog scale was above 3. All side effects in each group were recorded.

RESULTS

Two hundred and twenty patients were included in this study. There were 127 men (57.7%) with an average age of 57.1 ± 19.5 and 93 women (42.3%) with an average age of 57.1 ± 21.0. There were no significant differences in demographic characteristics between the groups. There was no significant difference in the dose or frequency of morphine administration between groups. There was no significant difference between the groups in pain scores and vital signs at different time points. Drug side effects, including delirium and gastrointestinal symptoms, did not differ significantly between the methadone and ketamine groups.

CONCLUSIONS

Our clinical data support the hypothesis that ketamine is not inferior to methadone in patients with addiction. Future randomize clinical trials are needed to confirm these observations.

Low-dose ketamine infusion to facilitate opioid tapering in chronic non-cancer pain with opioid-use disorder: a historical cohort study

BACKGROUND

Long-term opioid use is associated with pharmacological tolerance, a risk of misuse and hyperalgesia in patients with chronic pain (CP). Tapering is challenging in this context, particularly with comorbid opioid-use disorder (OUD). The antihyperalgesic effect of ketamine, through N-methyl-D-aspartate (NMDA) antagonism, could be useful. We aimed to describe the changes in the dose of opioids consumed over 1 year after a 5-day hospitalisation with ketamine infusion for CP patients with OUD.

METHODS

We performed a historical cohort study using a medical chart from 1 January 2014 to 31 December 2019. Patients were long-term opioid users with OUD and CP, followed by the Pain Center of the University Hospital of Toulouse, for which outpatient progressive tapering failed. Ketamine was administered at a low dose to initiate tapering during a 5-day hospitalisation.

RESULTS

59 patients were included, with 64% of them female and a mean age of 48±10 years old. The most frequent CP aetiologies were back pain (53%) and fibromyalgia (17%). The baseline opioid daily dose was 207 mg (±128) morphine milligram equivalent (MME). It was lowered to 92±72 mg MME at discharge (p<0.001), 99±77 mg at 3 months (p<0.001) and 103±106 mg at 12 months. More than 50% tapering was achieved immediately for 40 patients (68%), with immediate cessation for seven patients (12%). 17 patients were lost to follow-up.

CONCLUSIONS

A 5-day hospitalisation with a low-dose ketamine infusion appeared useful to facilitate opioid tapering in long-term opioid users with CP and OUD. Ketamine was well tolerated, and patients did not present significant withdrawal symptoms. Prospective and comparative studies are needed to confirm our findings.

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.

Beyond the serotonin deficit hypothesis: communicating a neuroplasticity framework of major depressive disorder

The serotonin deficit hypothesis explanation for major depressive disorder (MDD) has persisted among clinicians and the general public alike despite insufficient supporting evidence. To combat rising mental health crises and eroding public trust in science and medicine, researchers and clinicians must be able to communicate to patients and the public an updated framework of MDD: one that is (1) accessible to a general audience, (2) accurately integrates current evidence about the efficacy of conventional serotonergic antidepressants with broader and deeper understandings of pathophysiology and treatment, and (3) capable of accommodating new evidence. In this article, we summarize a framework for the pathophysiology and treatment of MDD that is informed by clinical and preclinical research in psychiatry and neuroscience. First, we discuss how MDD can be understood as inflexibility in cognitive and emotional brain circuits that involves a persistent negativity bias. Second, we discuss how effective treatments for MDD enhance mechanisms of neuroplasticity-including via serotonergic interventions-to restore synaptic, network, and behavioral function in ways that facilitate adaptive cognitive and emotional processing. These treatments include typical monoaminergic antidepressants, novel antidepressants like ketamine and psychedelics, and psychotherapy and neuromodulation techniques. At the end of the article, we discuss this framework from the perspective of effective science communication and provide useful language and metaphors for researchers, clinicians, and other professionals discussing MDD with a general or patient audience.

Ketamine can produce oscillatory dynamics by engaging mechanisms dependent on the kinetics of NMDA receptors

Ketamine is an N-methyl-D-aspartate (NMDA)-receptor antagonist that produces sedation, analgesia, and dissociation at low doses and profound unconsciousness with antinociception at high doses. At high and low doses, ketamine can generate gamma oscillations (>25 Hz) in the electroencephalogram (EEG). The gamma oscillations are interrupted by slow-delta oscillations (0.1 to 4 Hz) at high doses. Ketamine's primary molecular targets and its oscillatory dynamics have been characterized. However, how the actions of ketamine at the subcellular level give rise to the oscillatory dynamics observed at the network level remains unknown. By developing a biophysical model of cortical circuits, we demonstrate how NMDA-receptor antagonism by ketamine can produce the oscillatory dynamics observed in human EEG recordings and nonhuman primate local field potential recordings. We have identified how impaired NMDA-receptor kinetics can cause disinhibition in neuronal circuits and how a disinhibited interaction between NMDA-receptor-mediated excitation and GABA-receptor-mediated inhibition can produce gamma oscillations at high and low doses, and slow-delta oscillations at high doses. Our work uncovers general mechanisms for generating oscillatory brain dynamics that differs from ones previously reported and provides important insights into ketamine's mechanisms of action as an anesthetic and as a therapy for treatment-resistant depression.

New Advances in the Pharmacology and Toxicology of Lithium: A Neurobiologically Oriented Overview

Over the last six decades, lithium has been considered the gold standard treatment for the long-term management of bipolar disorder due to its efficacy in preventing both manic and depressive episodes as well as suicidal behaviors. Nevertheless, despite numerous observed effects on various cellular pathways and biologic systems, the precise mechanism through which lithium stabilizes mood remains elusive. Furthermore, there is recent support for the therapeutic potential of lithium in other brain diseases. This review offers a comprehensive examination of contemporary understanding and predominant theories concerning the diverse mechanisms underlying lithium's effects. These findings are based on investigations utilizing cellular and animal models of neurodegenerative and psychiatric disorders. Recent studies have provided additional support for the significance of glycogen synthase kinase-3 (GSK3) inhibition as a crucial mechanism. Furthermore, research has shed more light on the interconnections between GSK3-mediated neuroprotective, antioxidant, and neuroplasticity processes. Moreover, recent advancements in animal and human models have provided valuable insights into how lithium-induced modifications at the homeostatic synaptic plasticity level may play a pivotal role in its clinical effectiveness. We focused on findings from translational studies suggesting that lithium may interface with microRNA expression. Finally, we are exploring the repurposing potential of lithium beyond bipolar disorder. These recent findings on the therapeutic mechanisms of lithium have provided important clues toward developing predictive models of response to lithium treatment and identifying new biologic targets. SIGNIFICANCE STATEMENT: Lithium is the drug of choice for the treatment of bipolar disorder, but its mechanism of action in stabilizing mood remains elusive. This review presents the latest evidence on lithium's various mechanisms of action. Recent evidence has strengthened glycogen synthase kinase-3 (GSK3) inhibition, changes at the level of homeostatic synaptic plasticity, and regulation of microRNA expression as key mechanisms, providing an intriguing perspective that may help bridge the mechanistic gap between molecular functions and its clinical efficacy as a mood stabilizer.

Expectancy Effects in Psychedelic Trials

Clinical trials of psychedelic compounds like psilocybin, lysergic acid diethylamide (LSD), and N,N-dimethyltrptamine (DMT) have forced a reconsideration of how nondrug factors, such as participant expectations, are measured and controlled in mental health research. As doses of these profoundly psychoactive substances increase, so does the difficulty in concealing the treatment condition in the classic double-blind, placebo-controlled trial design. As widespread public enthusiasm for the promise of psychedelic therapy grows, so do questions regarding whether and how much trial results are biased by positive expectancy. First, we review the key concepts related to expectancy and its measurement. Then, we review expectancy effects that have been reported in both micro- and macrodose psychedelic trials from the modern era. Finally, we consider expectancy as a discrete physiological process that can be independent of, or even interact with, the drug effect. Expectancy effects can be harnessed to improve treatment outcomes and can also be actively managed in controlled studies to enhance the rigor and generalizability of future psychedelic trials.

Ketamine can produce oscillatory dynamics by engaging mechanisms dependent on the kinetics of NMDA receptors

Ketamine is an NMDA-receptor antagonist that produces sedation, analgesia and dissociation at low doses and profound unconsciousness with antinociception at high doses. At high and low doses, ketamine can generate gamma oscillations (>25 Hz) in the electroencephalogram (EEG). The gamma oscillations are interrupted by slow-delta oscillations (0.1-4 Hz) at high doses. Ketamine's primary molecular targets and its oscillatory dynamics have been characterized. However, how the actions of ketamine at the subcellular level give rise to the oscillatory dynamics observed at the network level remains unknown. By developing a biophysical model of cortical circuits, we demonstrate how NMDA-receptor antagonism by ketamine can produce the oscillatory dynamics observed in human EEG recordings and non-human primate local field potential recordings. We have discovered how impaired NMDA-receptor kinetics can cause disinhibition in neuronal circuits and how a disinhibited interaction between NMDA-receptor-mediated excitation and GABA-receptor-mediated inhibition can produce gamma oscillations at high and low doses, and slow-delta oscillations at high doses. Our work uncovers general mechanisms for generating oscillatory brain dynamics that differs from ones previously reported, and provides important insights into ketamine's mechanisms of action as an anesthetic and as a therapy for treatment-resistant depression.

Ketamine's mechanism of action with an emphasis on neuroimmune regulation: can the complement system complement ketamine's antidepressant effects?

Over 300 million people worldwide suffer from major depressive disorder (MDD). Unfortunately, only 30-40% of patients with MDD achieve complete remission after conventional monoamine antidepressant therapy. In recent years, ketamine has revolutionized the treatment of MDD, with its rapid antidepressant effects manifesting within a few hours as opposed to weeks with conventional antidepressants. Many research endeavors have sought to identify ketamine's mechanism of action in mood disorders; while many studies have focused on ketamine's role in glutamatergic modulation, several studies have implicated its role in regulating neuroinflammation. The complement system is an important component of the innate immune response vital for synaptic plasticity. The complement system has been implicated in the pathophysiology of depression, and studies have shown increases in complement component 3 (C3) expression in the prefrontal cortex of suicidal individuals with depression. Given the role of the complement system in depression, ketamine and the complement system's abilities to modulate glutamatergic transmission, and our current understanding of ketamine's anti-inflammatory properties, there is reason to suspect a common link between the complement system and ketamine's mechanism of action. This review will summarize ketamine's anti- inflammatory roles in the periphery and central nervous system, with an emphasis on complement system regulation.

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.

Rethinking ketamine as a panacea: adverse effects on oxygenation and postoperative outcomes

Ketamine is receiving renewed interest in perioperative medicine as an anaesthetic adjunct and a treatment for chronic conditions, including depression. Ketamine's complex pharmacologic profile results not only in several desirable effects, such as anaesthesia and analgesia, but also multiple adverse effects affecting the central nervous, cardiovascular, and respiratory systems. In addition to defining patient-centred outcomes in future clinical studies on the perioperative uses of ketamine, careful monitoring for its numerous adverse effects will be paramount.

Opioid receptor expressing neurons of the central amygdala gate behavioral effects of ketamine in mice

Ketamine has anesthetic, analgesic, and antidepressant properties which may involve multiple neuromodulatory systems. In humans, the opioid receptor (OR) antagonist naltrexone blocks the antidepressant effect of ketamine. It is unclear whether naltrexone blocks a direct effect of ketamine at ORs, or whether normal functioning of the OR system is required to realize the full antidepressant effects of treatment. In mice, the effect of ketamine on locomotion, but not analgesia or the forced swim test, was sensitive to naltrexone and was therefore used as a behavioral readout to localize the effect of naltrexone in the brain. We performed whole-brain imaging of cFos expression in ketamine-treated mice, pretreated with naltrexone or vehicle, and identified the central amygdala (CeA) as the area with greatest difference in cFos intensity. CeA neurons expressing both μOR (MOR) and PKCμ were strongly activated by naltrexone but not ketamine, and selectively interrupting MOR function in the CeA either pharmacologically or genetically blocked the locomotor effects of ketamine. These data suggest that MORs expressed in CeA neurons gate behavioral effects of ketamine but are not direct targets of ketamine.

Treatment of dissociative identity disorder: leveraging neurobiology to optimize success

INTRODUCTION

Dissociative identity disorder (DID) is a treatable mental health condition that is associated with a range of psychobiological manifestations. However, historical controversy, modern day misunderstanding, and lack of professional education have prevented accurate treatment information from reaching most clinicians and patients. These obstacles also have slowed empirical efforts to improve treatment outcomes for people with DID. Emerging neurobiological findings in DID provide essential information that can be used to improve treatment outcomes.

AREAS COVERED

In this narrative review, the authors discuss symptom characteristics of DID, including dissociative self-states. Current treatment approaches are described, focusing on empirically supported psychotherapeutic interventions for DID and pharmacological agents targeting dissociative symptoms in other conditions. Neurobiological correlates of DID are reviewed, including recent research aimed at identifying a neural signature of DID.

EXPERT OPINION

Now is the time to move beyond historical controversy and focus on improving DID treatment availability and efficacy. Neurobiological findings could optimize treatment by reducing shame, aiding assessment, providing novel interventional brain targets and guiding novel pharmacologic and psychotherapeutic interventions. The inclusion of those with lived experience in the design, planning and interpretation of research investigations is another powerful way to improve health outcomes for those with DID.

The rapid antidepressant effectiveness of repeated dose of intravenous ketamine and intranasal esketamine: A post-hoc analysis of pooled real-world data

INTRODUCTION

Intravenous ketamine (KET-IV) and intranasal esketamine (ESK-NS) are effective in the acute treatment of Treatment-Resistant Depression (TRD). Studies comparing KET-IV and ESK-NS concerning their action, safety, and tolerability are currently lacking.

MATERIALS AND METHODS

We combined patients' data from two unipolar TRD cohorts that received KET-IV (n = 171) at the Canadian Rapid Treatment Center of Excellence in Toronto, Canada, or ESK-NS (n = 140) at several TRD clinics in Italy. The Quick Inventory for Depression Symptomatology-Self-Report-16/QIDS-SR16 in the KET-IV group and Montgomery-Åsberg Depression Rating Scale/MADRS in the ESK-NS group measured depressive symptoms at baseline (T0) and after the acute treatment phase (T1) (i.e., four infusions of KET-IV and eight administrations of ESK-NS). As different scales were used, the primary outcome was to compare the improvement in depression severity in the two cohorts by measuring effect sizes, response and remission rates. Finally, we compare side effects and discontinuation rates.

RESULTS

At T1, KET-IV and ESK-NS significantly reduced depressive symptoms (respectively: QIDS-SR16 mean reduction = 5.65, p < 0.001; MADRS mean reduction = 11.41, p = 0.025). KET-IV showed larger effect sizes compared to ESK-NS (1.666 vs. 1.244). KET-IV had higher response rates (36 % vs. 25 %; p = 0.042) but not superior remission rates (13 % vs. 12 %; p = 0.845) than ESK-NS at T1. Despite more reported side effects, KET-IV did not cause more discontinuations for adverse events (4.6 % vs. 2.12 %; p = 0.228) than ESK-NS.

CONCLUSION

KET-IV showed a higher short-term antidepressant effect, whereas ESK-NS exhibited lower side effects. Both were generally well tolerated. Future head-to-head studies should consider the long-term efficacy of these treatments.

Unique pharmacodynamic properties and low abuse liability of the µ-opioid receptor ligand (S)-methadone

(R,S)-methadone ((R,S)-MTD) is a µ-opioid receptor (MOR) agonist comprised of (R)-MTD and (S)-MTD enantiomers. (S)-MTD is being developed as an antidepressant and is considered an N-methyl-D-aspartate receptor (NMDAR) antagonist. We compared the pharmacology of (R)-MTD and (S)-MTD and found they bind to MORs, but not NMDARs, and induce full analgesia. Unlike (R)-MTD, (S)-MTD was a weak reinforcer that failed to affect extracellular dopamine or induce locomotor stimulation. Furthermore, (S)-MTD antagonized motor and dopamine releasing effects of (R)-MTD. (S)-MTD acted as a partial agonist at MOR, with complete loss of efficacy at the MOR-galanin Gal1 receptor (Gal1R) heteromer, a key mediator of the dopaminergic effects of opioids. In sum, we report novel and unique pharmacodynamic properties of (S)-MTD that are relevant to its potential mechanism of action and therapeutic use. One-sentence summary: (S)-MTD, like (R)-MTD, binds to and activates MORs in vitro, but (S)-MTD antagonizes the MOR-Gal1R heteromer, decreasing its abuse liability.

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.

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.

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.

Sex dependence of opioid-mediated responses to subanesthetic ketamine in rats

Subanesthetic ketamine is increasingly used for the treatment of varied psychiatric conditions, both on- and off-label. While it is commonly classified as an N-methyl D-aspartate receptor (NMDAR) antagonist, our picture of ketamine's mechanistic underpinnings is incomplete. Recent clinical evidence has indicated, controversially, that a component of the efficacy of subanesthetic ketamine may be opioid dependent. Using pharmacological functional ultrasound imaging in rats, we found that blocking opioid receptors suppressed neurophysiologic changes evoked by ketamine, but not by a more selective NMDAR antagonist, in limbic regions implicated in the pathophysiology of depression and in reward processing. Importantly, this opioid-dependent response was strongly sex-dependent, as it was not evident in female subjects and was fully reversed by surgical removal of the male gonads. We observed similar sex-dependent effects of opioid blockade affecting ketamine-evoked postsynaptic density and behavioral sensitization, as well as in opioid blockade-induced changes in opioid receptor density. Together, these results underscore the potential for ketamine to induce its affective responses via opioid signaling, and indicate that this opioid dependence may be strongly influenced by subject sex. These factors should be more directly assessed in future clinical trials.

Ketamine: Pro or antiepileptic agent? A systematic review

Purpose

of Review: This evidence-based systematic review evaluated the safety of ketamine as regard the potential to provoke epilepsy to help better guide anesthesiologists in their practice.

Recent findings

Ketamine, originally developed as a dissociative anesthetic, has gained attention for its potential therapeutic applications in various medical conditions, including epilepsy. Ketamine is generally well-tolerated and widely used in anesthesia, however, conflicting data are confusing the anesthesiologists regarding the potential risk of seizures associated with its use. The literature that claimed the proepileeptic property are inconsistent and the mechanism of action is unclear. Moreover, the case reports had been in same certain contexts, such as procedural sedation where ketamine was used as a single agent. On the other hand, the retrospective data analysis confirmed the positive role ketamine plays as antiepileptic agent.

Summary

Many studies have shown promising results for the use of ketamine as antiepileptic agent. In case of epileptic patients, there is no contraindication for using ketamine, however, combining with benzodiazepine or propofol may enhance the safety.

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.

I like therefore I can, and I can therefore I like: the role of self-efficacy and affect in active inference of allostasis

Active inference (AIF) is a theory of the behavior of information-processing open dynamic systems. It describes them as generative models (GM) generating inferences on the causes of sensory input they receive from their environment. Based on these inferences, GMs generate predictions about sensory input. The discrepancy between a prediction and the actual input results in prediction error. GMs then execute action policies predicted to minimize the prediction error. The free-energy principle provides a rationale for AIF by stipulating that information-processing open systems must constantly minimize their free energy (through suppressing the cumulative prediction error) to avoid decay. The theory of homeostasis and allostasis has a similar logic. Homeostatic set points are expectations of living organisms. Discrepancies between set points and actual states generate stress. For optimal functioning, organisms avoid stress by preserving homeostasis. Theories of AIF and homeostasis have recently converged, with AIF providing a formal account for homeo- and allostasis. In this paper, we present bacterial chemotaxis as molecular AIF, where mutual constraints by extero- and interoception play an essential role in controlling bacterial behavior supporting homeostasis. Extending this insight to the brain, we propose a conceptual model of the brain homeostatic GM, in which we suggest partition of the brain GM into cognitive and physiological homeostatic GMs. We outline their mutual regulation as well as their integration based on the free-energy principle. From this analysis, affect and self-efficacy emerge as the main regulators of the cognitive homeostatic GM. We suggest fatigue and depression as target neurocognitive phenomena for studying the neural mechanisms of such regulation.

Ketamine Produces Antidepressant Effects by Inhibiting Histone Deacetylases and Upregulating Hippocampal Brain-Derived Neurotrophic Factor Levels in a Diisopropyl Fluorophosphate-Based Rat Model of Gulf War Illness

Approximately one-third of Gulf War veterans suffer from Gulf War Illness (GWI), which encompasses mood disorders and depressive symptoms. Deployment-related exposure to organophosphate compounds has been associated with GWI development. Epigenetic modifications have been reported in GWI veterans. We previously showed that epigenetic histone dysregulations were associated with decreased brain-derived neurotrophic factor (BDNF) expression in a GWI rat model. GWI has no effective therapies. Ketamine (KET) has recently been approved by the Food and Drug Administration for therapy-resistant depression. Interestingly, BDNF upregulation underlies KET's antidepressant effect in GWI-related depression. Here, we investigated whether KET's effect on histone mechanisms signals BDNF upregulations in GWI. Male Sprague-Dawley rats were injected once daily with diisopropyl fluorophosphate (DFP; 0.5 mg/kg, s.c., 5 days). At 6 months following DFP exposure, KET (10 mg/kg, i.p.) was injected, and brains were dissected 24 hours later. Western blotting was used for protein expression, and epigenetic studies used chromatin immunoprecipitation methods. Dil staining was conducted for assessing dendritic spines. Our results indicated that an antidepressant dose of KET inhibited the upregulation of histone deacetylase (HDAC) enzymes in DFP rats. Furthermore, KET restored acetylated histone occupancy at the Bdnf promoter IV and induced BDNF protein expression in DFP rats. Finally, KET treatment also increased the spine density and altered the spine diversity with increased T-type and decreased S-type spines in DFP rats. Given these findings, we propose that KET's actions involve the inhibition of HDAC expression, upregulation of BDNF, and dendritic modifications that together ameliorates the pathologic synaptic plasticity and exerts an antidepressant effect in DFP rats. SIGNIFICANCE STATEMENT: This study offers evidence supporting the involvement of epigenetic histone pathways in the antidepressant effects of ketamine (KET) in a rat model of Gulf War Illness (GWI)-like depression. This effect is achieved through the modulation of histone acetylation at the Bdnf promoter, resulting in elevated brain-derived neurotrophic factor expression and subsequent dendritic remodeling in the hippocampus. These findings underscore the rationale for considering KET as a potential candidate for clinical trials aimed at managing GWI-related depression.

A systematic review of the incidence of medical serious adverse events in sub-anesthetic ketamine treatment of psychiatric disorders

BACKGROUND

Limited published data exists that collates serious adverse outcomes involving ketamine as a psychiatric intervention. This systematic review assesses the reported incidence of medical serious adverse events (MSAEs), including but not limited to cardiovascular events, in patients receiving sub-anesthetic doses of ketamine for psychiatric disorders to guide practitioners during treatment planning, risk-benefit analyses, and the informed consent process.

METHODS

Pubmed database was searched for clinical trials of sub-anesthetic ketamine for psychiatric disorders in non-pregnant adult patients. Of the 2275 articles identified, 93 met inclusion criteria, over half of which were published in 2017 or later. Only studies that reported adverse events were included, and the incidence of MSAEs was calculated.

RESULTS

Of the 3756 participants who received at least one sub-anesthetic dose of ketamine, four participants experienced a MSAE, resulting in an incidence of approximately 0.1 % of individuals. The four MSAEs resolved without reported sequelae. Eighty-three percent of studies reported screening for medical illness and exclusion of high-risk patients. There were no serious cardiac adverse events or deaths observed in any participants; however, most trials' study designs excluded those with high cardiovascular complication risk.

LIMITATIONS

Most studies were small, underpowered for detecting rare MSAEs, at potential high-risk of bias of non-report of MSAEs, and limited mostly to intranasal and intravenous routes.

CONCLUSIONS

Findings suggest that with basic medical screening there is a very low incidence of MSAEs including adverse cardiac or cerebrovascular events in individuals receiving sub-anesthetic ketamine for psychiatric disorders.

Use of ketamine for treatment resistant depression: updated review of literature and practical applications to a community ketamine program in Edmonton, Alberta, Canada

Background

Though intravenous (IV) ketamine and intranasal (IN) esketamine are noted to be efficacious for treatment-resistant depression (TRD), access to each of these treatments within healthcare systems is limited due to cost, availability, and/or monitoring requirements. IV ketamine has been offered at two public hospital sites in Edmonton, Canada since 2015. Since then, demand for maintenance ketamine treatments has grown. This has required creative solutions for safe, accessible, evidence-based patient care.

Objectives

Aims of this paper are twofold. First, we will provide a synthesis of current knowledge with regards to the clinical use of ketamine for TRD. Consideration will be given regarding; off-label racemic ketamine uses versus FDA-approved intranasal esketamine, populations treated, inclusion/exclusion criteria, dosing, assessing clinical response, concomitant medications, and tolerability/safety. Second, this paper will describe our experience as a community case study in applying evidence-based treatment. We will describe application of the literature review to our clinical programming, and in particular focus on cost-effective maintenance treatments, long-term safety concerns, routes of ketamine administration other than via intravenous, and cautious prescribing of ketamine outside of clinically monitored settings.

Methodology

We conducted a literature review of the on the use of ketamine for TRD up to June 30, 2023. Key findings are reviewed, and we describe their application to our ketamine program.

Conclusion

Evidence for the use of ketamine in resistant depression has grown in recent years, with evolving data to support and direct its clinical use. There is an increasing body of evidence to guide judicious use of ketamine in various clinical circumstances, for a population of patients with a high burden of suffering and morbidity. While large-scale, randomized controlled trials, comparative studies, and longer-term treatment outcomes is lacking, this community case study illustrates that currently available evidence can be applied to real-world clinical settings with complex patients. As cost is often a significant barrier to accessing initial and/or maintenance IV or esketamine treatments, public ketamine programs may incorporate SL or IN ketamine to support a sustainable and accessible treatment model. Three of such models are described.

The why, when, where, how, and so what of so-called rapidly acting antidepressants

Developing antidepressants that are not only more effective but are rapidly acting is the Holy Grail for psychiatry. We review multiple issues that arise in determining rapid responses in antidepressant trials. The current status of purportedly rapid acting agents is first reviewed. Then, a number of key questions/issues are addressed: Is there a unifying definition for rapid response across studies? Should rapid response criteria be based on required measurable effects on overall improvement? On specific symptoms such as psychomotor retardation, depressed mood, or anhedonia? In associated symptoms such as anxiety or insomnia? When should onset be considered rapid-by Day 3? Day7? Day 14? If there is a rapid response, for how long should the effects be maintained? Is maintenance of effect dependent on continuing the medication? Is rapid response associated with specific mechanisms of action? Do the mechanisms of action suggest possible risk for drug abuse? How important is rapid response really in an often chronic or recurrent depressive disorder? In which types of patients could rapid response be particularly important? What are the study design issues that need to be considered for assessing rapid response, including: selection of specific types of depressed patients, multiple doses of drug studied, designation of primary and secondary outcome measures, specific time points at which to determine efficacy, requirements for demonstrating durability, etc. A framework for approaching this complex area is developed for both researchers and clinicians.

Opioid Mechanisms and the Treatment of Depression

Opioid receptors are widely expressed in the brain, and the opioid system has a key role in modulating mood, reward processing and stress responsivity. There is mounting evidence that the endogenous opioid system may be dysregulated in depression and that drug treatments targeting mu, delta and kappa opioid receptors may show antidepressant potential. The mechanisms underlying the therapeutic effects of opioid system engagement are complex and likely multi-factorial. This chapter explores various pathways through which the modulation of the opioid system may influence depression. These include impacts on monoaminergic systems, the regulation of stress and the hypothalamic-pituitary-adrenal axis, the immune system and inflammation, brain-derived neurotrophic factors, neurogenesis and neuroplasticity, social pain and social reward, as well as expectancy and placebo effects. A greater understanding of the diverse mechanisms through which opioid system modulation may improve depressive symptoms could ultimately aid in the development of safe and effective alternative treatments for individuals with difficult-to-treat depression.

Treatment of Posttraumatic Stress Disorder: A State-of-the-art Review

This narrative state-of-the-art review paper describes the progress in the understanding and treatment of Posttraumatic Stress Disorder (PTSD). Over the last four decades, the scientific landscape has matured, with many interdisciplinary contributions to understanding its diagnosis, etiology, and epidemiology. Advances in genetics, neurobiology, stress pathophysiology, and brain imaging have made it apparent that chronic PTSD is a systemic disorder with high allostatic load. The current state of PTSD treatment includes a wide variety of pharmacological and psychotherapeutic approaches, of which many are evidence-based. However, the myriad challenges inherent in the disorder, such as individual and systemic barriers to good treatment outcome, comorbidity, emotional dysregulation, suicidality, dissociation, substance use, and trauma-related guilt and shame, often render treatment response suboptimal. These challenges are discussed as drivers for emerging novel treatment approaches, including early interventions in the Golden Hours, pharmacological and psychotherapeutic interventions, medication augmentation interventions, the use of psychedelics, as well as interventions targeting the brain and nervous system. All of this aims to improve symptom relief and clinical outcomes. Finally, a phase orientation to treatment is recognized as a tool to strategize treatment of the disorder, and position interventions in step with the progression of the pathophysiology. Revisions to guidelines and systems of care will be needed to incorporate innovative treatments as evidence emerges and they become mainstream. This generation is well-positioned to address the devastating and often chronic disabling impact of traumatic stress events through holistic, cutting-edge clinical efforts and interdisciplinary research.

Accelerated TMS - moving quickly into the future of depression treatment

Accelerated TMS is an emerging application of Transcranial Magnetic Stimulation (TMS) aimed to reduce treatment length and improve response time. Extant literature generally shows similar efficacy and safety profiles compared to the FDA-cleared protocols for TMS to treat major depressive disorder (MDD), yet accelerated TMS research remains at a very early stage in development. The few applied protocols have not been standardized and vary significantly across a set of core elements. In this review, we consider nine elements that include treatment parameters (i.e., frequency and inter-stimulation interval), cumulative exposure (i.e., number of treatment days, sessions per day, and pulses per session), individualized parameters (i.e., treatment target and dose), and brain state (i.e., context and concurrent treatments). Precisely which of these elements is critical and what parameters are most optimal for the treatment of MDD remains unclear. Other important considerations for accelerated TMS include durability of effect, safety profiles as doses increase over time, the possibility and advantage of individualized functional neuronavigation, use of biological readouts, and accessibility for patients most in need of the treatment. Overall, accelerated TMS appears to hold promise to reduce treatment time and achieve rapid reduction in depressive symptoms, but at this time significant work remains to be done. Rigorous clinical trials combining clinical outcomes and neuroscientific measures such as electroencephalogram, magnetic resonance imaging and e-field modeling are needed to define the future of accelerated TMS for MDD.

Ketamine for Major Depressive Disorder

Major Depressive Disorder (MDD) is a leading cause of disability worldwide. Conventional antidepressant treatment is characterised by a significant time to onset of therapeutic action (approximately 2 weeks) and fails to achieve a stable remission of symptoms in one-third of subjects with MDD. In the last 20 years the discovery of antidepressant effects of the N-methyl-d-aspartate (NMDA) receptor antagonist ketamine as a rapid acting (within hours) and sustained (up to 7 days) antidepressant has represented a major paradigm shift in the field.The present chapter reviews the pharmacology, safety, and efficacy of ketamine as a novel therapeutic agent for MDD and specifically for subjects who did not respond to conventional antidepressant (treatment resistant depression). The impact of ketamine on suicidal ideation, the availability of brain biomarkers of ketamine treatment response and the association of ketamine and psychotherapy are considered.

Understanding the role of the NMDA receptor subunit, GluN2D, in mediating NMDA receptor antagonist-induced behavioral disruptions in male and female mice

Noncompetitive NMDA receptor (NMDAR) antagonists like phencyclidine (PCP) and ketamine cause psychosis-like symptoms in healthy humans, exacerbate schizophrenia symptoms in people with the disorder, and disrupt a range of schizophrenia-relevant behaviors in rodents, including hyperlocomotion. This is negated in mice lacking the GluN2D subunit of the NMDAR, suggesting the GluN2D subunit mediates the hyperlocomotor effects of these drugs. However, the role of GluN2D in mediating other schizophrenia-relevant NMDAR antagonist-induced behavioral disturbances, and in both sexes, is unclear. This study aimed to investigate the role of the GluN2D subunit in mediating schizophrenia-relevant behaviors induced by a range of NMDA receptor antagonists. Using both male and female GluN2D knockout (KO) mice, we examined the effects of the NMDAR antagonist's PCP, the S-ketamine enantiomer (S-ket), and the ketamine metabolite R-norketamine (R-norket) on locomotor activity, anxiety-related behavior, and recognition and short-term spatial memory. GluN2D-KO mice showed a blunted locomotor response to R-norket, S-ket, and PCP, a phenotype present in both sexes. GluN2D-KO mice of both sexes showed an anxious phenotype and S-ket, R-norket, and PCP showed anxiolytic effects that were dependent on sex and genotype. S-ket disrupted spatial recognition memory in females and novel object recognition memory in both sexes, independent of genotype. This datum identifies a role for the GluN2D subunit in sex-specific effects of NMDAR antagonists and on the differential effects of the R- and S-ket enantiomers.

Mechanisms of SSRI Therapy and Discontinuation

SSRIs are one of the most widely used drug therapies in primary care and psychiatry, and central to the management of the most common mental health problems in today's society. Despite this, SSRIs suffer from a slow onset of therapeutic effect and relatively poor efficacy as well as adverse effects, with recent concerns being focused on a disabling SSRI discontinuation syndrome. The mechanism underpinning their therapeutic effect has long shifted away from thinking that SSRIs act simply by increasing 5-HT in the synapse. Rather, a current popular view is that increased 5-HT is just the beginning of a series of complex downstream signalling events, which trigger changes in neural plasticity at the functional and structural level. These changes in plasticity are then thought to interact with neuropsychological processes to enhance re-learning of emotional experiences that ultimately brings about changes in mood. This compelling view of SSRI action is underpinning attempts to understand fast-acting antidepressants, such as ketamine and psychedelic drugs, and aid the development of future therapies. An important gap in the theory is evidence that changes in plasticity are causally linked to relevant behavioural effects. Also, predictions that the SSRI-induced neural plasticity might have applicability in other areas of medicine have not yet been borne out. In contrast to the sophisticated view of the antidepressant action of SSRIs, the mechanism underpinning SSRI discontinuation is little explored. Nevertheless, evidence of rebound increases in 5-HT neuron excitability immediately on cessation of SSRI treatment provide a starting point for future investigation. Indeed, this evidence allows formulation of a mechanistic explanation of SSRI discontinuation which draws on parallels with the withdrawal states of other psychotropic drugs.

[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.

The Psychedelic Future of Post-Traumatic Stress Disorder Treatment

Post-traumatic stress disorder (PTSD) is a mental health condition that can occur following exposure to a traumatic experience. An estimated 12 million U.S. adults are presently affected by this disorder. Current treatments include psychological therapies (e.g., exposure-based interventions) and pharmacological treatments (e.g., selective serotonin reuptake inhibitors (SSRIs)). However, a significant proportion of patients receiving standard-of-care therapies for PTSD remain symptomatic, and new approaches for this and other trauma-related mental health conditions are greatly needed. Psychedelic compounds that alter cognition, perception, and mood are currently being examined for their efficacy in treating PTSD despite their current status as Drug Enforcement Administration (DEA)- scheduled substances. Initial clinical trials have demonstrated the potential value of psychedelicassisted therapy to treat PTSD and other psychiatric disorders. In this comprehensive review, we summarize the state of the science of PTSD clinical care, including current treatments and their shortcomings. We review clinical studies of psychedelic interventions to treat PTSD, trauma-related disorders, and common comorbidities. The classic psychedelics psilocybin, lysergic acid diethylamide (LSD), and N,N-dimethyltryptamine (DMT) and DMT-containing ayahuasca, as well as the entactogen 3,4-methylenedioxymethamphetamine (MDMA) and the dissociative anesthetic ketamine, are reviewed. For each drug, we present the history of use, psychological and somatic effects, pharmacology, and safety profile. The rationale and proposed mechanisms for use in treating PTSD and traumarelated disorders are discussed. This review concludes with an in-depth consideration of future directions for the psychiatric applications of psychedelics to maximize therapeutic benefit and minimize risk in individuals and communities impacted by trauma-related conditions.

Ketamine and the neurobiology of depression: Toward next-generation rapid-acting antidepressant treatments

Ketamine has emerged as a transformative and mechanistically novel pharmacotherapy for depression. Its rapid onset of action, efficacy for treatment-resistant symptoms, and protection against relapse distinguish it from prior antidepressants. Its discovery emerged from a reconceptualization of the neurobiology of depression and, in turn, insights from the elaboration of its mechanisms of action inform studies of the pathophysiology of depression and related disorders. It has been 25 y since we first presented our ketamine findings in depression. Thus, it is timely for this review to consider what we have learned from studies of ketamine and to suggest future directions for the optimization of rapid-acting antidepressant treatment.

Oral ketamine may offer a solution to the ketamine conundrum

Ketamine has received considerable attention for its rapid and robust antidepressant response over the past decade. Current evidence, in clinical populations, predominantly relates to parenterally administered ketamine, which is reported to produce significant undesirable side effects, with additional concerns regarding long-term safety and abuse potential. Attempts to produce a similar drug to ketamine, without the psychotomimetic side effects, have proved elusive. Orally administered ketamine has a different pharmacological profile to parentally administered ketamine, suggesting it may be a viable alternative. Emerging evidence regarding the efficacy and tolerability of oral ketamine suggests that it may be a favourable route of administration, as it appears to obtain similarly beneficial treatment effects, but without the cost and medical resources required in parenteral dosing. The pharmacological effects may be due to the active metabolite norketamine, which has been found to be at substantially higher levels via oral dosing, most likely due to first-pass clearance. Despite bioavailability and peak plasma concentrations both being lower than when administered parenterally, evidence suggests that low-dose oral ketamine is clinically effective in treating pain. This may also be due to the actions of norketamine and therefore, its relevance to the mental health context is explored in this narrative review.

Online news media reporting of ketamine as a treatment for depression from 2000 to 2017

OBJECTIVES

Since the first reporting of ketamine's antidepressant effects in 2000, there has been growing public interest in this novel rapid-acting treatment for depression despite its abuse potential. Online media is an increasingly popular way for the general public to source information. Our objective was to examine how online news outlets have portrayed ketamine as an antidepressant by ascertaining the volume and content of relevant articles and trends over time.

METHODS

In this semi-quantitative study, we identified articles regarding ketamine's use in depression from the 30 most popular English-language online news-generating sources over 18 years (2000-2017). Articles were then blindly assessed by 2 independent raters, who analysed the texts by quantifying the presence/absence of 12 content items.

RESULTS

We identified 97 articles, the number of which has increased since the first online news report in 2006. Most (69%) came from the USA and nearly all correctly stated the indications for ketamine. About half of the most recent articles mentioned abuse potential and 27% of articles referred to risks of unregulated use of ketamine. Just under 20% of articles referred to the lack of evidence regarding direct comparisons between ketamine and other currently available antidepressants. There was no difference in the overall level of detail within the articles during the study time period.

CONCLUSIONS

Online news media articles have been generally positive about ketamine for treating depression but need to be interpreted with caution as many of them did not discuss negative aspects of ketamine and made unsubstantiated claims about ketamine.

[Interest and mechanisms of action of ketamine in alcohol addiction- A review of clinical and preclinical studies]

Alcohol Use Disorder (AUD) is a psychiatric condition characterized by chronic and excessive drinking despite negative consequences on overall health and social or occupational functioning. There are currently limited treatment options available for AUD, and the effects size and the response rates to these treatments are often low to moderate. The World Health Organization has identified the development of medications to treat AUD as one of its 24 priorities. This past decade was marked by a renewed interest in psychedelic use in psychiatry. At the centre of this renaissance, ketamine, an atypical psychedelic already used in the treatment of major depression, is an NMDA receptor antagonist that exists as a racemic compound made of two enantiomers, S-ketamine, and R-ketamine. Each form can be metabolized into different metabolites, some of which having antidepressant properties. In this article, we review both clinical and preclinical studies on ketamine and its metabolites in the treatment of AUD. Preclinical as well as clinical studies have revealed that ketamine is effective in reducing withdrawal symptoms and alcohol craving. Convergent data showed that antidepressant properties of ketamine largely contribute to the decreased likelihood of alcohol relapse, especially in patients undergoing ketamine-assisted psychotherapies. Its effectiveness is believed to be linked with its ability to regulate the glutamatergic pathway, enhance neuroplasticity, rewire brain resting state network functional connectivity and decrease depressive-like states. However, it remains to further investigate (i) why strong differences exist between male and female responses in preclinical studies and (ii) the respective roles of each of the metabolites in the ketamine effects in both genders. Interestingly, current studies are also focusing on ketamine addiction and the comorbidity between alcohol addiction and depression occurring more frequently in females.

Courtes A, Jones G, Soares JC, Machado-Vieira R. Pharmacotherapies Targeting GABA-Glutamate Neurotransmission for Treatment-Resistant Depression

Treatment-resistant depression (TRD) is a term used to describe a particular type of major depressive disorder (MDD). There is no consensus about what defines TRD, with various studies describing between 1 and 4 failures of antidepressant therapies, with or without electroconvulsive therapy (ECT). That is why TRD is such a growing concern among clinicians and researchers, and it explains the necessity for investigating novel therapeutic targets beyond conventional monoamine pathways. An imbalance between two primary central nervous system (CNS) neurotransmitters, L-glutamate and γ-aminobutyric acid (GABA), has emerged as having a key role in the pathophysiology of TRD. In this review, we provide an evaluation and comprehensive review of investigational antidepressants targeting these two systems, accessing their levels of available evidence, mechanisms of action, and safety profiles. N-methyl-D-aspartate (NMDA) receptor antagonism has shown the most promise amongst the glutamatergic targets, with ketamine and esketamine (Spravato) robustly generating responses across trials. Two specific NMDA-glycine site modulators, D-cycloserine (DCS) and apimostinel, have also generated promising initial safety and efficacy profiles, warranting further investigation. Combination dextromethorphan-bupropion (AXS-05/Auvelity) displays a unique mechanism of action and demonstrated positive results in particular applicability in subpopulations with cognitive dysfunction. Currently, the most promising GABA modulators appear to be synthetic neurosteroid analogs with positive GABAA receptor modulation (such as brexanolone). Overall, advances in the last decade provide exciting perspectives for those who do not improve with conventional therapies. Of the compounds reviewed here, three are approved by the Food and Drug Administration (FDA): esketamine (Spravato) for TRD, Auvelity (dextromethorphan-bupropion) for major depressive disorder (MDD), and brexanolone (Zulresso) for post-partum depression (PPD). Notably, some concerns have arisen with esketamine and brexanolone, which will be detailed in this study.

Randomized trial of ketamine masked by surgical anesthesia in patients with depression

Ketamine may have antidepressant properties, but its acute psychoactive effects complicate successful masking in placebo-controlled trials. We present a single-center, parallel-arm, triple-masked, randomized, placebo-controlled trial assessing the antidepressant efficacy of intravenous ketamine masked by surgical anesthesia (ClinicalTrials.gov, NCT03861988). Forty adult patients with major depressive disorder who were scheduled for routine surgery were randomized to a single infusion of ketamine (0.5 mg/kg) or placebo (saline) during usual anesthesia. All participants, investigators, and direct patient care staff were masked to treatment allocation. The primary outcome was depression severity measured by the Montgomery-Åsberg Depression Rating Scale (MADRS) at 1, 2, and 3 days post-infusion. After all follow-up visits, participants were asked to guess which intervention they received. A mixed-effects model showed no evidence of effect of treatment assignment on the primary outcome (-5.82, 95% CI -13.3 to 1.64, p=0.13). 36.8% of participants guessed their treatment assignment correctly; both groups allocated their guesses in similar proportions. In conclusion, a single dose of intravenous ketamine delivered during surgical anesthesia had no greater effect than placebo in acutely reducing the severity of depressive symptoms in adults with major depressive disorder. This trial successfully masked treatment allocation in moderate-to-severely depressed patients using surgical anesthesia. Although this masking strategy is impractical for most placebo-controlled trials, future studies of novel antidepressants with acute psychoactive effects should make efforts to fully mask treatment assignment in order to minimize subject-expectancy bias.

Effects of different doses of esketamine intervention on postpartum depressive symptoms in cesarean section women: A randomized, double-blind, controlled clinical study

BACKGROUND

The optimal dosage and method of esketamine for postpartum depressive symptoms (PDS) are unclear. We conducted a randomized controlled trial (RCT) to investigate the effect of different doses of esketamine on PDS in women undergoing cesarean section, with evidence of prenatal depression.

METHODS

The three groups were high- (2 mg kg-1) and low-dose (1 mg kg-1) esketamine via patient controlled intravenous analgesia (PCIA), following an initial intravenous infusion of 0.25 mg kg-1 esketamine, compared to placebo (0.9 % saline infusion). All groups also received the sufentanil (2.2 μg kg-1). The primary outcome was the incidence of PDS at 7 and 42 days postpartum. The secondary outcomes were: the remission from depression and total EPDS scores at 7 days and 42 days postpartum; mean change from baseline in the EPDS score; postoperative analgesia.

RESULTS

i). 0.25 mg kg-1 of esketamine intravenous infusion combined with 1 mg kg-1 (n = 99) or 2 mg kg-1 (n = 99) esketamine PCIA reduces PDS incidence at 7 days postpartum (p < 0.05), with high-dose esketamine PCIA also reduces PDS incidence 42 days postpartum (p < 0.05), compared to placebo (n = 97). ii). Low- and high-dose esketamine PCIA lowers NRS scores at rest within 48 h postoperatively (p < 0.01), with high-dose esketamine also reducing the NRS score during movement at 48 h postoperatively (p = 0.018). iii). Neither high- nor low-dose esketamine PCIA increased postoperative adverse reactions (p > 0.05).

CONCLUSIONS

Esketamine (0.25 mg kg-1) intravenous infusion combined with 1 mg kg-1 or 2 mg kg-1 esketamine PCIA seems safe and with few adverse effects in the management of PDS and pain in women undergoing cesarean section.

LIMITATIONS

The tolerability and safety of esketamine requires further investigation based on more specific scales; the transient side effects of esketamine could have biased the staff and patients.

TRIAL REGISTRATION

ChiCTR-ROC-2000039069.

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.