Effects of chronic ketamine use on frontal and medial temporal cognition

Ketamine-dependent patients with persistent psychosis have higher neurofilament light chain levels than patients with schizophrenia

OBJECTIVES

Ketamine can induce persisting psychosis in a subset of individuals who use it chronically and heavily. Previously, we found that the psychopathology and cognitive impairments in patients with ketamine dependence (KD) exhibiting persistent psychosis (KPP) bear resemblances with schizophrenia, albeit with less severity in those with no persistent psychosis (KNP). Furthermore, we also showed that patients with KD had higher blood levels of neurofilament light chain (NFL), a biomarker for neuroaxonal injury, compared to healthy controls. In this study, we aimed to investigate the differences in NFL levels between patients with KPP and KNP while comparing the levels of individuals with schizophrenia and healthy controls.

METHODS

We enrolled 64 treatment-seeking ketamine-dependent patients (53 with KNP and 11 with KPP), 37 medication-free patients with schizophrenia, and 80 healthy controls. Blood NFL levels were measured by single molecule array immunoassay.

RESULTS

NFL levels were highest in the KPP subgroup, followed by the KNP subgroup, and then the schizophrenia and control groups (mean ± SD: 24.5 ± 24.7, 12.9 ± 10.9, 9.2 ± 12.2, and 6.2 ± 2.2 pg/mL, respectively), with no significant difference observed between the schizophrenia and control groups.

CONCLUSIONS

We found that KD is associated with higher NFL levels compared to schizophrenia, with the KPP subgroup showing the most consistent alterations. The observation of accentuated neuroaxonal pathology in individuals with KPP implies that this clinical manifestation is associated with a specific neurobiological phenotype, despite prior evidence suggesting syndromal similarity between schizophrenia and KPP.

Abnormal resting-state functional connectivity of the right anterior cingulate cortex in chronic ketamine users and its correlation with cognitive impairments

BACKGROUND

Chronic ketamine use leads to cognitive impairments, however, the neural mechanisms underpinning these impairments are still unclear.

AIMS

Many studies showed Anterior cingulate cortex (ACC)is strongly involved in cognition and drug addiction, as supported by our previous studies. The objective of this study was to assess the variations in resting-state functional connectivity (FC) changes in the right anterior cingulate cortex (ACC) of chronic ketamine users (CKUs) and their relationship with cognitive performance.

METHODS

The study enrolled 28 chronic ketamine users (CKUs) and 30 healthy controls (HCs). Resting-state functional magnetic resonance imaging (fMRI) data were gathered from both groups. Cognitive functions were evaluated using the MATRICS Consensus Cognitive Battery (MCCB).

RESULTS

CKUs demonstrated significantly poorer cognitive performance than HCs in various cognitive domains, including Visual Learning, Speed of Processing, Working Memory, and the composite score of MCCB. Group-level comparisons revealed that CKUs exhibited enhanced functional connectivity between the right ACC and the right postcentral gyrus (PCG) compared to HCs. There was a positive relationship between the connectivity of right ACC-PCG and reasoning and problem-solving score, but there was no significant association with the characteristics of ketamine use.

CONCLUSION

CKUs showed enhanced connectivity between the right ACC and the right PCG. This enhanced functional connectivity may indicate functional compensation for cognitive deficits in CKUs, especially for reasoning and problem-solving impairments in CKUs.

The clinical toxicology of ketamine

INTRODUCTION

Ketamine is a pharmaceutical drug possessing both analgesic and anaesthetic properties. As an anaesthetic, it induces anaesthesia by producing analgesia with a state of altered consciousness while maintaining airway tone, respiratory drive, and hemodynamic stability. At lower doses, it has psychoactive properties and has gained popularity as a recreational drug.

OBJECTIVES

To review the epidemiology, mechanisms of toxicity, pharmacokinetics, clinical features, diagnosis and management of ketamine toxicity.

METHODS

Both OVID MEDLINE (January 1950-April 2023) and Web of Science (1900-April 2023) databases were searched using the term "ketamine" in combination with the keywords "pharmacokinetics", "kinetics", "poisoning", "poison", "toxicity", "ingestion", "adverse effects", "overdose", and "intoxication". Furthermore, bibliographies of identified articles were screened for additional relevant studies. These searches produced 5,268 non-duplicate citations; 185 articles (case reports, case series, pharmacokinetic studies, animal studies pertinent to pharmacology, and reviews) were considered relevant. Those excluded were other animal investigations, therapeutic human clinical investigations, commentaries, editorials, cases with no clinical relevance and post-mortem investigations.

EPIDEMIOLOGY

Following its introduction into medical practice in the early 1970s, ketamine has become a popular recreational drug. Its use has become associated with the dance culture, electronic and dubstep dance events.

MECHANISM OF ACTION

Ketamine acts primarily as a non-competitive antagonist on the glutamate N-methyl-D-aspartate receptor, causing the loss of responsiveness that is associated with clinical ketamine dissociative anaesthesia.

PHARMACOKINETICS

Absorption of ketamine is rapid though the rate of uptake and bioavailability is determined by the route of exposure. Ketamine is metabolized extensively in the liver. Initially, both isomers are metabolized to their major active metabolite, norketamine, by CYP2B6, CYP3A4 and CYP2C9 isoforms. The hydroxylation of the cyclohexan-1-one ring of norketamine to the three positional isomers of hydroxynorketamine occurs by CYP2B6 and CYP2A6. The dehydronorketamine metabolite occurs either by direct dehydrogenation from norketamine via CYP2B6 metabolism or non-enzymatic dehydration of hydroxynorketamine. Norketamine, the dehydronorketamine isomers, and hydroxynorketamine have pharmacological activity. The elimination of ketamine is primarily by the kidneys, though unchanged ketamine accounts for only a small percentage in the urine. The half-life of ketamine in humans is between 1.5 and 5 h.

CLINICAL FEATURES

Acute adverse effects following recreational use are diverse and can include impaired consciousness, dizziness, irrational behaviour, hallucinations, abdominal pain and vomiting. Chronic use can result in impaired verbal information processing, cystitis and cholangiopathy.

DIAGNOSIS

The diagnosis of acute ketamine intoxication is typically made on the basis of the patient's history, clinical features, such as vomiting, sialorrhea, or laryngospasm, along with neuropsychiatric features. Chronic effects of ketamine toxicity can result in cholangiopathy and cystitis, which can be confirmed by endoscopic retrograde cholangiopancreatography and cystoscopy, respectively.

MANAGEMENT

Treatment of acute clinical toxicity is predominantly supportive with empiric management of specific adverse effects. Benzodiazepines are recommended as initial treatment to reduce agitation, excess neuromuscular activity and blood pressure. Management of cystitis is multidisciplinary and multi-tiered, following a stepwise approach of pharmacotherapy and surgery. Management of cholangiopathy may require pain management and, where necessary, biliary stenting to alleviate obstructions. Chronic effects of ketamine toxicity are typically reversible, with management focusing on abstinence.

CONCLUSIONS

Ketamine is a dissociative drug employed predominantly in emergency medicine; it has also become popular as a recreational drug. Its recreational use can result in acute neuropsychiatric effects, whereas chronic use can result in cystitis and cholangiopathy.

Activation of ventral hippocampal CB1 receptors inhibits ketamine-induced anxiogenic-like behavior: Alteration of BDNF/c-Fos levels in the mouse hippocampus

Considering the increasing usage of ketamine as a recreational drug with hallucinogenic properties and also scarce studies about receptor systems responsible for its effects, in the present study we aimed to investigate whether the activation of the ventral hippocampal (VH) CB1 cannabinoid receptors affects the anxiety-like behaviors induced by ketamine. Also, the levels of BDNF and c-Fos proteins in the mouse hippocampus were measured following the treatments. For this purpose, male NMRI mice were cannulated bilaterally in the VH with a stereotaxic apparatus. Anxiety properties and protein changes were measured using elevated plus-maze (EPM) and western blotting respectively. The results revealed that intraperitoneal (i.p.) administration of ketamine (5-20 mg/kg) significantly decreased the percentage of open arm time (%OAT) and open arm entry (%OAE) in the EPM with no alteration in the locomotor activity suggesting an anxiogenic-like behavior to ketamine. Furthermore, ketamine administration (10 mg/kg, i.p.) increased BDNF and c-Fos levels in the hippocampus. Interestingly, activation of the VH CB1 receptors by ACPA (0.5-4 ng/mouse) inhibited the anxiogenic-like behaviors produced by ketamine, whereas the microinjection of the same doses of ACPA into VH by itself had no effect on the EPM parameters. Hippocampal levels of BDNF and c-Fos decreased after treatment with combined ketamine with ACPA. These results suggest the therapeutic potency of cannabinoid receptor agonists for ketamine-induced anxiogenic-related responses. This effect might be at least partially mediated by the alteration of BDNF and c-Fos signaling in the hippocampus.

Tau protein plays a role in the mechanism of cognitive disorders induced by anesthetic drugs

Cognitive disorders are mental health disorders that can affect cognitive ability. Surgery and anesthesia have been proposed to increase the incidence of cognitive dysfunction, including declines in memory, learning, attention and executive function. Tau protein is a microtubule-associated protein located in the axons of neurons and is important for microtubule assembly and stability; its biological function is mainly regulated by phosphorylation. Phosphorylated tau protein has been associated with cognitive dysfunction mediated by disrupting the stability of the microtubule structure. There is an increasing consensus that anesthetic drugs can cause cognitive impairment. Herein, we reviewed the latest literature and compared the relationship between tau protein and cognitive impairment caused by different anesthetics. Our results substantiated that tau protein phosphorylation is essential in cognitive dysfunction caused by anesthetic drugs, and the possible mechanism can be summarized as "anesthetic drugs-kinase/phosphatase-p-Tau-cognitive impairment".

Abnormal fractional Amplitude of Low-Frequency Fluctuation in chronic ketamine users

BACKGROUND

Ketamine has become a major substance of abuse worldwide. Nevertheless, The long-term effects of ketamine use on intrinsic spontaneous neural activity remain unknown.

OBJECTIVES

In the present study, rs-fMRI was used to explore whether chronic ketamine use changes the intrinsic spontaneous neural activity, and whether the intrinsic spontaneous neural activity changes in chronic ketamine users(CKUs) are associated with cognitive impairments observed in chronic ketamine users.

METHODS

28 CKUs and 30 healthy controls(HC) were enrolled. The fractional amplitude of low-frequency fluctuations (fALFF) was measured to evaluate the intrinsic spontaneous neural activity in multiple brain regions. Cognitive alterations were assessed using MATRICS Consensus Cognitive Battery (MCCB).

RESULTS

CKUs showed higher fALFF in the right parahippocampal gyrus(PHG), right anterior cingulate cortex(ACC), left cerebellar vermis, left posterior cingulate cortex(PCC), bilateral caudate, and lower fALFF in the right middle occipital gyrus(MOG), left cuneus, right precuneus. The fALFF in the right PHG, left cerebellar vermis, bilateral caudate, right ACC of CKUs presented a negative correlation with the average quantity of ketamine use/day(g) and estimated total ketamine consumption. The fALFF in left PCC had a negative correlation with the average quantity of ketamine use/day(g). Speed of processing on MCCB presented a negative correlation with the fALFF in the right MOG.

CONCLUSION

Our study found abnormal fALFF in multiple brain areas in CKUs, which indicated the changes of intrinsic spontaneous neural activity in multiple brain areas. The changes of fALFF were associated with the severity of ketamine use and cognitive impairment in CKUs.

Astrocyte Activation, but not Microglia, Is Associated with the Experimental Mouse Model of Schizophrenia Induced by Chronic Ketamine

Ketamine is a noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptors. Many experimental studies have shown that ketamine can induce cognitive impairments and schizophrenia-like symptoms. While much data have demonstrated that glial cells are associated with the pathophysiology of psychiatric disorders, including schizophrenia, the response of glial cells to ketamine and its significance to schizophrenia are not clear. The present study was intended to explore whether chronic ketamine treatment would induce behavioral and glial changes in mice. First, ketamine was used to stimulate behavioral abnormalities similar to schizophrenia evaluated by the open field test, elevated plus-maze test, Y maze test, novel object recognition test, and tail suspension test. Secondly, histopathology and Nissl staining were performed. Meanwhile, immunofluorescence was used to evaluate the expression levels of IBA-1 (a microglial marker) and GFAP (an astrocyte marker) in the mouse hippocampus for any change. Then, ELISA was used to analyze proinflammatory cytokine levels for any change. Our results showed that ketamine (25 mg/kg, i.p., qid, 12 days) induced anxiety, recognition deficits, and neuronal injury in the hippocampus. Moreover, chronic ketamine treatment enhanced GFAP expression in CA1 and DG regions of the hippocampus but did not influence the expression of IBA-1. Ketamine also increased the levels of IL-1β, IL-6, and TNF-α in the mouse hippocampus. Our study created a new procedure for ketamine administration, which successfully induce negative symptoms and cognitive-behavioral defects in schizophrenia by chronic ketamine. This study further revealed that an increase in astrocytosis, but not microglia, is associated with the mouse model of schizophrenia caused by ketamine. In summary, hippocampal astrocytes may be involved in the pathophysiology of ketamine-induced schizophrenia-like phenotypes through reactive transformation and regulation of neuroinflammation.

Translational control by ketamine and its implications for comorbid cognitive deficits in depressive disorders

Ketamine has shown antidepressant effects in patients with major depressive disorder (MDD) resistant to first-line treatments and approved for use in this patient population. Ketamine induces several forms of synaptic plasticity, which are proposed to underlie its antidepressant effects. However, the molecular mechanism of action directly responsible for ketamine's antidepressant effects remains under active investigation. It was recently demonstrated that the effectors of the mammalian target of rapamycin complex 1 (mTORC1) signalling pathway, namely, eukaryotic initiation factor 4E (eIF4E) binding proteins 1 and 2 (4E-BP1 and 4E-BP2), are central in mediating ketamine-induced synaptic plasticity and behavioural antidepressant-like effect. 4E-BPs are a family of messenger ribonucleic acid (mRNA) translation repressors inactivated by mTORC1. We observed that their expression in inhibitory interneurons mediates ketamine's effects in the forced swim and novelty suppressed feeding tests and the long-lasting inhibition of GABAergic neurotransmission in the hippocampus. In addition, another effector pathway that regulates translation elongation downstream of mTORC1, the eukaryotic elongation factor 2 kinase (eEF2K), has been implicated in ketamine's behavioural effects. We will discuss how ketamine's rapid antidepressant effect depends on the activation of neuronal mRNA translation through 4E-BP1/2 and eEF2K. Furthermore, given that these pathways also regulate cognitive functions, we will discuss the evidence of ketamine's effect on cognitive function in MDD. Overall, the data accrued from pre-clinical research have implicated the mRNA translation pathways in treating mood symptoms of MDD. However, it is yet unclear whether the pro-cognitive potential of subanesthetic ketamine in rodents also engages these pathways and whether such an effect is consistently observed in the treatment-resistant MDD population.

Brain Changes Associated With Long-Term Ketamine Abuse, A Systematic Review

Recently, the abuse of ketamine has soared. Therefore, it is of great importance to study its potential risks. The effects of prolonged ketamine on the brain can be observationally studied in chronic recreational users. We performed a systematic review of studies reporting functional and structural brain changes after repeated ketamine abuse. We searched the following electronic databases: Medline, Embase and PsycINFO We screened 11,438 records and 16 met inclusion criteria, totaling 440 chronic recreational ketamine users (2–9.7 years; mean use 2.4 g/day), 259 drug-free controls and 44 poly-drug controls. Long-term recreational ketamine use was associated with lower gray matter volume and less white matter integrity, lower functional thalamocortical and corticocortical connectivity. The observed differences in both structural and functional neuroanatomy between ketamine users and controls may explain some of its long-term cognitive and psychiatric side effects, such as memory impairment and executive functioning. Given the effect that long-term ketamine exposure may yield, an effort should be made to curb its abuse.

Neurocognitive effects of repeated ketamine infusion treatments in patients with treatment resistant depression: a retrospective chart review

BACKGROUND

Ketamine has emerged as a rapid-acting antidepressant in treatment-resistant depression (TRD) increasingly used in non-research, clinical settings. Few studies, however, have examined neurocognitive effects of repeated racemic ketamine infusion treatments in patients with TRD. In an effort to identify potential effects after serial infusions, we conducted a retrospective chart review to identify statistically significant changes in cognition in patient undergoing serial intravenous infusions; concomitantly, we examined baseline cognition as potential predictor of anti-depressant potential.

METHODS

Twenty-two patients with TRD were examined after they finished the induction phase of 8-10 repeated intravenous ketamine infusions and completed the assessments of their depressive symptoms (measured by the 16-item Quick Inventory of Depressive Symptomatology-Self Report Scale: QIDS-SR16) and cognitive function (measured by the Montreal Cognitive Assessment: MoCA) before the first and the last ketamine treatments.

RESULTS

Repeated ketamine infusions administered through an escalating dose protocol with 8-10 infusion sessions produced a 47.2% reduction response in depression; there was no evidence of impairment as reflected in MoCA testing. There was a moderate association between baseline cognition and antidepressant response with a Pearson correlation of 0.453.

CONCLUSION

In this naturalistic sample of patients with TRD in our clinical service, repeated ketamine infusions significantly decreased depression symptoms without impairing cognitive performance. The baseline cognition may positively predict antidepressant responses of repeated ketamine treatment.

Ketamine for Depression: Advances in Clinical Treatment, Rapid Antidepressant Mechanisms of Action, and a Contrast with Serotonergic Psychedelics

The approval of ketamine for treatment-resistant depression has created a model for a novel class of rapid-acting glutamatergic antidepressants. Recent research into other novel rapid-acting antidepressants - most notably serotonergic psychedelics (SPs) - has also proven promising. Presently, the mechanisms of action of these substances are under investigation to improve these novel treatments, which also exhibit considerable side effects such as dissociation. This chapter lays out the historical development of ketamine as an antidepressant, outlines its efficacy and safety profile, reviews the evidence for ketamine's molecular mechanism of action, and compares it to the proposed mechanism of SPs. The evidence suggests that although ketamine and SPs act on distinct primary targets, both may lead to rapid restoration of synaptic deficits and downstream network reconfiguration. In both classes of drugs, a glutamate surge activates α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) throughput and increases in brain-derived neurotrophic factor (BDNF) levels. Taken together, these novel antidepressant mechanisms may serve as a framework to explain the rapid and sustained antidepressant effects of ketamine and may be crucial for developing new rapid-acting antidepressants with an improved side effect profile.

A Multiscale View of the Mechanisms Underlying Ketamine's Antidepressant Effects: An Update on Neuronal Calcium Signaling

Major depressive disorder (MDD) is a debilitating disease characterized by depressed mood, loss of interest or pleasure, suicidal ideation, and reduced motivation or hopelessness. Despite considerable research, mechanisms underlying MDD remain poorly understood, and current advances in treatment are far from satisfactory. The antidepressant effect of ketamine is among the most important discoveries in psychiatric research over the last half-century. Neurobiological insights into the ketamine’s effects have shed light on the mechanisms underlying antidepressant efficacy. However, mechanisms underlying the rapid and sustained antidepressant effects of ketamine remain controversial. Elucidating such mechanisms is key to identifying new therapeutic targets and developing therapeutic strategies. Accumulating evidence demonstrates the contribution of the glutamatergic pathway, the major excitatory neurotransmitter system in the central nervous system, in MDD pathophysiology and antidepressant effects. The hypothesis of a connection among the calcium signaling cascade stimulated by the glutamatergic system, neural plasticity, and epigenetic regulation of gene transcription is further supported by its associations with ketamine’s antidepressant effects. This review briefly summarizes the potential mechanisms of ketamine’s effects with a specific focus on glutamatergic signaling from a multiscale perspective, including behavioral, cellular, molecular, and epigenetic aspects, to provide a valuable overview of ketamine’s antidepressant effects.

Craving for Ketamine and Its Relationship With Clinical Outcome Indicators in Males With Ketamine Use Disorder

Background: Craving is considered a hallmark of substance use disorder and is one of the criteria of substance use disorder. The Desires for Drug Questionnaire (DDQ) is a widely used questionnaire to assess craving for heroin. This study aimed to examine the psychometric properties of the ketamine version of the DDQ (DDQ-K) and the associations between craving for ketamine as measured using the DDQ-K and clinical outcome indicators in individuals with ketamine use disorder. Methods: In total, 651 individuals with ketamine use disorder completed the DDQ-K and the Visual Analog Craving Scale (VACS). Demographic data, severity of ketamine use, money spent on ketamine, positive/negative aspects of ketamine use, and readiness to change ketamine use were also recorded. We examined the reliability (internal consistency), construct validity (factor structure), and concurrent validity of the DDQ-K. Multiple regression analysis was used to examine the relationships of craving measured using the DDQ-K with clinical outcome indicators, including money spent on ketamine, severity of ketamine use, positive/negative aspects of ketamine use, and readiness to change ketamine use. Results: The original three-factor model of the DDQ-K was acceptable for use in individuals with ketamine use disorder according to confirmatory factor analysis. The subscales of Desire and Intention and Negative Reinforcement of the DDQ-K, but not the subscale of Control, were of acceptable concurrent validity. The score on the Desire and Intention subscale was positively associated with the level of ketamine dependence, money spent on ketamine use, and positive/negative aspects of ketamine use and negatively associated with readiness to change ketamine use. Conclusion: This study supported the use of the Desire and Intention and Negative Reinforcement subscales of the DDQ-K to assess craving in patients with ketamine use.

Acute cognitive effects of single-dose intravenous ketamine in major depressive and posttraumatic stress disorder

Intravenous (IV) subanesthetic doses of ketamine have been shown to reduce psychiatric distress in both major depressive (MDD) and posttraumatic stress disorder (PTSD). However, the effect of ketamine on cognitive function in these disorders is not well understood. To address this gap, we examined the effect of a single dose of IV ketamine on cognition in individuals with MDD and/or PTSD relative to healthy controls (HC). Psychiatric (n = 29; 15 PTSD, 14 MDD) and sex- age- and IQ matched HC (n = 29) groups were recruited from the community. A single subanesthetic dose of IV ketamine was administered. Mood and cognitive measures were collected prior to, 2 h and 1 day post-ketamine administration. MDD/PTSD individuals evidenced a large-magnitude improvement in severity of depressive symptoms at both 2-hours and 1 day post-ketamine administration (p's < .001, Cohen d's = 0.80-1.02). Controlling for baseline performance and years of education, IV ketamine induced declines in attention (ATTN), executive function (EF), and verbal memory (VM) 2 h post-administration, all of which had resolved by 1 day post-ketamine across groups. The magnitude of cognitive decline was significantly larger in MDD/PTSD relative to HC on attention only (p = .012, d = 0.56). Ketamine did not affect working memory (WM) performance. Cognitive function (baseline, change from baseline to post-ketamine) was not associated with antidepressant response to ketamine. Results suggest that while ketamine may have an acute deleterious effect on some cognitive domains in both MDD/PTSD and HC individuals, most notably attention, this reduction is transient and there is no evidence of ketamine-related cognitive dysfunction at 1 day post-administration.

Cortical Thickness Changes in Chronic Ketamine Users

Background: Previous studies have examined the effects of long-term ketamine use on gray matter volume. But it is unclear whether chronic ketamine use alters cortical thickness and whether cortical thickness changes in chronic ketamine users are associated with cognitive deficits observed in chronic ketamine users. Methods: Here, 28 chronic ketamine users and 30 healthy controls (HCs) were recruited. Cortical morphometry based on Computational Anatomy Toolbox (CAT12) was used to measure cortical thickness. Cognitive performance was measured by MATRICS Consensus Cognitive Battery (MCCB). Two-sample t-test was used to assess differences in cortical thickness and cognitive performance between the two groups. Partial correlation analysis was used for assessing correlations between cortical thickness changes and clinical characteristics, cognitive performance in chronic ketamine users. Results: Chronic ketamine users exhibited significantly reduced cortical thickness in frontal, parietal, temporal, and occipital lobes compared to HC [false discovery rate (FDR) corrected at p < 0.05]. In chronic ketamine users, the average quantity (g) of ketamine use/day was negatively correlated with cortical thickness in the left superior frontal gyrus (SFG), right caudal middle frontal gyrus (MFG), and right paracentral lobule. The frequency of ketamine use (days per week) was negatively correlated with cortical thickness in the left isthmus cingulate cortex. Duration of ketamine use (month) was negatively correlated with cortical thickness in the left precentral gyrus. The chronic ketamine users showed significantly poorer cognitive performance on the working memory (P = 0.009), visual learning (P = 0.009), speed of processing (P < 0.000), and Matrics composite (P = 0.01). There was no correlation between scores of domains of MCCB and reduced cortical thickness. Conclusion: The present study observed reduced cortical thickness in multiple brain areas, especially in the prefrontal cortex (PFC) in chronic ketamine users. Dose, frequency, and duration of ketamine use was negatively correlated with cortical thickness of some brain areas. Our results suggest that chronic ketamine use may lead to a decrease of cortical thickness. But the present study did not observe any correlation between reduced cortical thickness and decreased cognitive performance in chronic ketamine users.

Effects of Single-Dose and Long-Term Ketamine Administration on Tau Phosphorylation-Related Enzymes GSK-3β, CDK5, PP2A, and PP2B in the Mouse Hippocampus

Ketamine is a recreational drug that causes emotional and cognitive impairments, but its specific mechanisms of action are still unclear. Recent evidence suggests that Tau protein phosphorylation and targeted delivery to the postsynaptic area are closely related to its neurotoxicity, and our recent studies have shown that long-term ketamine administration causes excessive Tau protein phosphorylation. However, the regulatory mechanism of Tau protein phosphorylation induced by ketamine has not been clarified. In the present study, we administered a single ketamine injection and long-term (6 months) ketamine injections in C57BL/6 mice, to investigate the effects of different doses of ketamine on the expression levels of Tau protein and its phosphorylation, the expression levels and activities of the related protein phosphokinases GSK-3β and CDK5, and the expression levels and activities of the related protein phosphatases PP2A and PP2B in the mouse hippocampus. Our results showed that both single-dose and long-term ketamine administration induced excessive phosphorylation of the Tau protein at ser202/thr205 and ser396. A single ketamine administration caused an increase in the activity of GSK-3β (at high doses) and a decrease in the activity of PP2A. On the other hand, long-term ketamine administration resulted in an increase in the activities of GSK-3β (at high doses) and CDK5, and a decrease in the activity of PP2A. Our results indicate that GSK-3β, CDK5, and PP2A may be involved in ketamine-induced Tau protein phosphorylation.

Effects of early ketamine exposure on cerebral gray matter volume and functional connectivity

Ketamine has been used for medical purposes, most typically as an anesthetic, and recent studies support its use in the treatment of depression. However, ketamine tends to be abused by adolescents and young adults. In the current study, we examined the effects of early ketamine exposure on brain structure and function. We employed MRI to assess the effects of ketamine abuse on cerebral gray matter volume (GMV) and functional connectivity (FC) in 34 users and 19 non-users, employing covariates. Ketamine users were categorized as adolescent-onset and adult-onset based on when they were first exposed to ketamine. Imaging data were processed by published routines in SPM and AFNI. The results revealed lower GMV in the left precuneus in ketamine users, with a larger decrease in the adolescent-onset group. The results from a seed-based correlation analysis show that both ketamine groups had higher functional connectivity between left precuneus (seed) and right precuneus than the control group. Compared to controls, ketamine users showed decreased GMV in the right insula, left inferior parietal lobule, left dorsolateral prefrontal cortex/superior frontal gyrus, and left medial orbitofrontal cortex. These preliminary results characterize the effects of ketamine misuse on brain structure and function and highlight the influence of earlier exposure to ketamine on the development of the brain. The precuneus, a structure of central importance to cerebral functional organization, may be particularly vulnerable to the influences of early ketamine exposure. How these structural and functional brain changes may relate to the cognitive and affective deficits remains to be determined with a large cohort of participants.

Hydroxynorketamine Blocks N-Methyl-d-Aspartate Receptor Currents by Binding to Closed Receptors

Ketamine, a dissociative anesthetic, is experiencing a clinical resurgence as a fast-acting antidepressant. In the central nervous system, ketamine acts primarily by blocking NMDA receptor currents. Although it is generally safe in a clinical setting, it can be addictive, and several of its derivatives are being investigated as preferable alternatives. 2R,6R-Hydroxynorketamine (HNK), a ketamine metabolite, reproduces some of the therapeutic effects of ketamine and appears to lack abuse liability. Here, we report a systematic investigation of the effects of HNK on macroscopic responses elicited from recombinant NMDA receptors expressed in human embryonic kidney 293 cells. We found that, like ketamine, HNK reduced NMDA receptor currents in a dose-, pH-, and voltage-dependent manner. Relative to ketamine, it had 100-fold-lower potency (46 µM at pH 7.2), 10-fold-slower inhibition onset, slower apparent dissociation rate, weaker voltage dependence, and complete competition by magnesium. Notably, HNK inhibition was fully effective when applied to resting receptors. These results revealed unexpected properties of hydroxynorketamine that warrant its further investigation as a possible therapeutic in pathologies associated with NMDA receptor dysfunction. SIGNIFICANCE STATEMENT: NMDA receptors are excitatory ion channels with fundamental roles in synaptic transmission and plasticity, and their dysfunction associates with severe neuropsychiatric disorders. 2R,6R-Hydroxynorketamine, a metabolite of ketamine, mimics some of the neuroactive properties of ketamine and may lack its abuse liability. Results show that 2R,6R-hydroxynorketamine blocks NMDA receptor currents with low affinity and weak voltage dependence and is effective when applied to resting receptors. These properties highlight its effectiveness to a subset of NMDA receptor responses and recommend it for further investigation.

Ketamine as an antidepressant: overview of its mechanisms of action and potential predictive biomarkers

Ketamine, a drug introduced in the 1960s as an anesthetic agent and still used for that purpose, has garnered marked interest over the past two decades as an emerging treatment for major depressive disorder. With increasing evidence of its efficacy in treatment-resistant depression and its potential anti-suicidal action, a great deal of investigation has been conducted on elucidating ketamine's effects on the brain. Of particular interest and therapeutic potential is the ability of ketamine to exert rapid antidepressant properties as early as several hours after administration. This is in stark contrast to the delayed effects observed with traditional antidepressants, often requiring several weeks of therapy for a clinical response. Furthermore, ketamine appears to have a unique mechanism of action involving glutamate modulation via actions at the N-methyl-D-aspartate (NMDA) and α -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, as well as downstream activation of brain-derived neurotrophic factor (BDNF) and mechanistic target of rapamycin (mTOR) signaling pathways to potentiate synaptic plasticity. This paper provides a brief overview of ketamine with regard to pharmacology/pharmacokinetics, toxicology, the current state of clinical trials on depression, postulated antidepressant mechanisms and potential biomarkers (biochemical, inflammatory, metabolic, neuroimaging sleep-related and cognitive) for predicting response to and/or monitoring of therapeutic outcome with ketamine.

Repeated intravenous infusions of ketamine: Neurocognition in patients with anxious and nonanxious treatment-resistant depression

BACKGROUND

Recent studies have suggested that neurocognition is changed after repeated infusions of ketamine in patients with treatment-resistant depression (TRD). The objective of this study was to investigate whether differences existed in the neurocognitive effect of six ketamine infusions in patients with anxious and nonanxious TRD and to determine the association between baseline neurocognition and changes in symptoms after the infusions.

METHOD

Patients with anxious (n = 30) and nonanxious TRD (n = 20) received six intravenous infusions of ketamine (0.5 mg/kg over 40 min) over 12 days. Speed of processing (SOP), working memory (WM), verbal learning and memory (VBM), visual learning and memory (VSM) and the severity of depressive and anxious symptoms were assessed at baseline, one day after the last infusion (day 13) and two weeks after the completion of the serial infusions (day 26). A linear mixed model was used to determine whether the neurocognitive changes differed between the two groups. Pearson correlation analysis was used to determine the relationship between baseline neurocognition and the changes in the symptomatic scores.

RESULTS

Patients with anxious TRD had significant increases in SOP on day 13 and day 26 (both p < 0.001), and in VBM on day 13 (p = 0.028). However, no significant increase in any neurocognitive domain was found in patients with nonanxious TRD. Faster SOP at baseline was associated with greater improvement of anxious symptoms in patients with anxious TRD, and better VSM at baseline was associated with greater improvement of depressive symptoms in patients with nonanxious TRD.

LIMITATION

The major limitation of this study is the open-label design.

CONCLUSION

After six ketamine infusions, neurocognitive improvement was observed in patients with anxious TRD but not in patients with nonanxious TRD.

Long-term ketamine administration causes Tau protein phosphorylation and Tau protein-dependent AMPA receptor reduction in the hippocampus of mice

As a recreational drug of abuse and an injectable anesthetic, ketamine has been shown to cause cognitive dysfunction and induce psychotic states. Although the specific mechanism is still unclear, it may be linked to synaptic receptors, including the α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor. Recent evidence suggests that Tau protein phosphorylation and targeted delivery to the postsynaptic area is involved in maintaining neuronal plasticity, indicating that the neurotoxicity induced by ketamine may be related to the transfer of Tau protein after phosphorylation. In this study, we established a model of long-term (6 months) ketamine administration in wild-type (C57BL/6) and Tau knockout mice to investigate the effects of different doses of ketamine administration on Tau protein expression and phosphorylation in the mouse hippocampus. We also investigated changes in AMPA receptor expression in the synaptic membrane of wild-type and Tau knockout mice. Our results showed that long-term ketamine administration led to excessive Tau protein phosphorylation at Ser202/Thr205 and Ser396, but not at Ser199, Ser262 and Ser404. Most importantly, long-term ketamine administration decreased AMPA receptor levels in the hippocampal cell membrane in a Tau protein-dependent manner. Our results reveal the role of Tau protein phosphorylation in the mechanism of ketamine neurotoxicity, suggesting that the changes of membrane AMPA receptor and synaptic function induced by ketamine are mediated by abnormal phosphorylation of Tau protein at specific sites.

MTOR-Mediated Autophagy Is Involved in the Protective Effect of Ketamine on Allergic Airway Inflammation

Unresolved inflammation underpins the pathogenesis of allergic airway diseases, such as asthma. Ketamine, accepted as a promising therapy for resistant asthma, has been demonstrated to attenuate allergic airway inflammation. However, the anti-inflammatory mechanism by ketamine in this setting is largely unknown. We aimed to investigate whether autophagy was involved in the protective effect of ketamine on allergic airway inflammation. Female C57BL/6 mice were sensitized to ovalbumin (OVA) and treated with ketamine at 25, 50, or 100 mg/kg prior to OVA challenge. In this model, the pulmonary morphological findings and airway inflammation were significantly inhibited at 50 mg/kg but not at 25 or 100 mg/kg. Moreover, 50 mg/kg ketamine abrogated the increased concentrations of inflammatory cytokines in bronchoalveolar lavage fluid (BALF) of allergic mice, as well as activated the expression of phosphorylated mammalian target of rapamycin (p-MTOR) and inhibited autophagy in allergic mice. To confirm whether the effect of 50 mg/kg ketamine on asthma was mediated by inhibiting autophagy, rapamycin was administered to mice sensitized to OVA and exposed to 50 mg/kg ketamine. All of the effect of 50 mg/kg ketamine was reversed by rapamycin treatment, including increased p-MTOR and decreased autophagy. Taken together, the present study demonstrates that 50 mg/kg ketamine inhibits allergic airway inflammation by suppressed autophagy, and this effect is mediated by the activation of MTOR in the lungs of allergic mice.

Neurocognitive effects of six ketamine infusions and the association with antidepressant response in patients with unipolar and bipolar depression

BACKGROUND

Ketamine has proven to have rapid, robust antidepressant effects on treatment-resistant depression. However, whether repeated ketamine infusions would cause short-and long-term neurocognitive impairments was not clear. Our aims were to investigate the neurocognitive effects of six ketamine infusions and to examine the association between these infusions and the antidepressant response in patients with unipolar and bipolar depression.

METHODS

Six intravenous infusions of ketamine (0.5 mg/kg) over a 12-day period were administered to 84 patients with unipolar and bipolar depression. Severity of depressive symptoms and four domains of neurocognition, including speed of processing, working memory, visual learning and verbal learning, were assessed at baseline, one day following the last infusion and again two weeks post-infusion.

RESULTS

Significant improvements were found on speed of processing ( F=9.344, p<0.001) and verbal learning ( F=5.647, p=0.004) in a linear mixed model. The Sobel test showed significant indirect effects between time and improvement in speed of processing (Sobel test=3.573, p<0.001) as well as improvement in verbal learning (Sobel test=6.649, p<0.001), which were both significantly mediated by change in depressive symptoms. Logistic regression analysis showed ketamine responders had better visual learning at baseline than non-responders (B=0.118, p<0.001).

CONCLUSIONS

Our findings suggest that neurocognitive function would not deteriorate after six ketamine infusions, while verbal learning and speed of processing improved over 13 days and 26 days of observation, respectively. However, this change was mainly accounted for by improvements in severity of depressive symptoms over time. Greater baseline visual learning predicted an antidepressant response over six ketamine infusions.

The profile of cognitive impairments in chronic ketamine users

The aim of this study was to examine the cognitive function in chronic ketamine users. Factors correlated to cognition impairments were analyzed. Sixty-three chronic ketamine users and 65 healthy subjects were recruited. Cognitive function was assessed by using immediate/delayed visual reproduction (IVR/DVR) tasks, immediate/delayed logical memory (ILM/DLM) tasks, Stroop test, Wisconsin card sorting test (WCST), and continuous performance test (CPT). Psychopathological symptoms were assessed with the Positive and Negative Syndrome Scale (PANSS), Beck Depression Inventory (BDI) and Beck Anxiety Inventory (BAI). Ketamine users performed worse than controls on the IVR, ILM, DLM, Stroop and auditory CPT tests. IVR and DVR, color-naming and color-interference-reading scores were positively correlated with education level. In ketamine users ILM scores were negatively correlated with the negative subscale of PANSS. DLM score was positively correlated with average dose of ketamine use. Word-reading score was positively correlated with education level, and negatively correlated with duration of ketamine use. False hits in auditory CPT was positively correlated with duration of ketamine use. Number of trials to complete the first category and perseverative errors on WCST were positively correlated with the duration between the test and last ketamine use. Chronic ketamine users had cognitive impairments across multiple domains.

Cognitive profile of ketamine-dependent patients compared with methamphetamine-dependent patients and healthy controls

BACKGROUND

Ketamine has emerged as a major substance of abuse worldwide and has been listed with methamphetamine (METH) as two of the most widely available illicit substances in Taiwan. Only a few studies have examined the long-term consequences of chronic and heavy ketamine abuse. We compared the cognitive function of ketamine-dependent patients with that of METH-dependent patients and healthy controls.

METHODS

We recruited 165 participants (58 ketamine-dependent and 49 METH-dependent patients who sought treatment and 58 healthy controls) and evaluated them by using a cognitive test battery, the Brief Assessment of Cognition in Schizophrenia, with scores being estimated in reference to normative data in general population.

RESULTS

The ketamine-dependent patients had significantly poorer performance than did the controls in many cognitive tests, including verbal memory, motor speed, verbal fluency, and attention and processing speed, and the battery as a whole. METH-dependent patients exhibited poorer function in motor speed, verbal fluency, and attention and processing speed. The ketamine group performed poorer than did METH group in the domains of verbal memory, working memory, and attention and processing speed and the composite battery scores. A previous experience of ketamine-induced psychotomimetic symptoms, using higher doses of ketamine, and longer abstinence appeared to be associated with performance in some tests; however, the significance disappeared after multiple comparison correction.

CONCLUSIONS

The ketamine-dependent patients had impaired cognitive function, and METH-dependent patients exhibited intermediate performance between ketamine-dependent patients and healthy controls. Given the growing population of ketamine abusers, public education on the cognitive consequences should be provided.

Other drug use does not impact cognitive impairments in chronic ketamine users

BACKGROUND

Ketamine abuse causes cognitive impairments, which negatively impact on users' abstinence, prognosis, and quality of life.

RESULTS

of cognitive impairments in chronic ketamine users have been inconsistent across studies, possibly due to the small sample sizes and the confounding effects of concomitant use of other illicit drugs. This study investigated the cognitive impairment and its related factors in chronic ketamine users with a large sample size and explored the impact of another drug use on cognitive functions.

METHODS

Cognitive functions, including working, verbal and visual memory and executive functions were assessed in ketamine users: 286 non-heavy other drug users and 279 heavy other drug users, and 261 healthy controls. Correlations between cognitive impairment and patterns of ketamine use were analysed.

RESULTS

Verbal and visual memory were impaired, but working memory and executive functions were intact for all ketamine users. No significant cognitive differences were found between the two ketamine groups. Greater number of days of ketamine use in the past month was associated with worse visual memory performance in non-heavy other drug users. Higher dose of ketamine use was associated with worse short-term verbal memory in heavy other drug users.

CONCLUSION

Verbal and visual memory are impaired in chronic ketamine users. Other drug use appears to have no impact on ketamine users' cognitive performance.

Outcome Evaluation of a Short-Term Hospitalization and Community Support Program for People Who Abuse Ketamine

Ketamine is a popular recreational drug among young people in Hong Kong. Long-term abuse of ketamine can lead to acute urological and medical issues, which often require immediate care at emergency rooms. Many patients require short-term hospitalization for medical management. This opens a brief time window, within which mental health professionals could engage young people who abuses ketamine in psychosocial, functional, and lifestyle interventions. The Crisis Accommodation Program (CAP) is a short-term hospitalization and community support program that addresses the health care needs of young people who abuse ketamine. During short-term hospitalization, the patient participates in a range of cognitive and psychosocial assessments, motivational interviewing, emotions management, and lifestyle re-design interventions. Upon discharge, social work professionals of non-government agencies continue to work with the patients on their action plans in the community. This evaluation study uses a quasi-experimental non-equivalent group design, in which the outcomes of the treatment group (n = 84) are compared with a comparison group (n = 34) who have a history of ketamine abuse but who have not joined the treatment program. The results confirm that the treatment group showed significant increases in motivation for treatment, reduction in drug use, improvement in cognitive screening tests, healthy lifestyle scores, and self-efficacy in avoidance of drugs over 13 weeks. When compared with the comparison group, the treatment group had significant decreases in anxiety and treatment needs and had moved from pre-contemplation to the contemplation or preparation stage. However, there were no significant changes in outcome measures covering lifestyle or self-efficacy in drug avoidance. Overall, the CAP is effective in reducing drug use, anxiety, and helping patients to move from pre-contemplation to the contemplation or preparation stage of change. The study results suggest that health care professionals can successfully engage young people who abuse ketamine to participate in a package of psychosocial interventions, motivational interviewing, and lifestyle re-design during their hospital stay for management of urological problems. The CAP also highlights the importance of collaboration between hospitals and community social services in the management of addiction.

Distinct retrosplenial cortex cell populations and their spike dynamics during ketamine-induced unconscious state

Ketamine is known to induce psychotic-like symptoms, including delirium and visual hallucinations. It also causes neuronal damage and cell death in the retrosplenial cortex (RSC), an area that is thought to be a part of high visual cortical pathways and at least partially responsible for ketamine's psychotomimetic activities. However, the basic physiological properties of RSC cells as well as their response to ketamine in vivo remained largely unexplored. Here, we combine a computational method, the Inter-Spike Interval Classification Analysis (ISICA), and in vivo recordings to uncover and profile excitatory cell subtypes within layers 2&3 and 5&6 of the RSC in mice within both conscious, sleep, and ketamine-induced unconscious states. We demonstrate two distinct excitatory principal cell sub-populations, namely, high-bursting excitatory principal cells and low-bursting excitatory principal cells, within layers 2&3, and show that this classification is robust over the conscious states, namely quiet awake, and natural unconscious sleep periods. Similarly, we provide evidence of high-bursting and low-bursting excitatory principal cell sub-populations within layers 5&6 that remained distinct during quiet awake and sleep states. We further examined how these subtypes are dynamically altered by ketamine. During ketamine-induced unconscious state, these distinct excitatory principal cell subtypes in both layer 2&3 and layer 5&6 exhibited distinct dynamics. We also uncovered different dynamics of local field potential under various brain states in layer 2&3 and layer 5&6. Interestingly, ketamine administration induced high gamma oscillations in layer 2&3 of the RSC, but not layer 5&6. Our results show that excitatory principal cells within RSC layers 2&3 and 5&6 contain multiple physiologically distinct sub-populations, and they are differentially affected by ketamine.

Effects of Ketamine on Levels of Inflammatory Cytokines IL-6, IL-1β, and TNF-α in the Hippocampus of Mice Following Acute or Chronic Administration

Ketamine is an injectable anesthetic and recreational drug of abuse commonly used worldwide. Many experimental studies have shown that ketamine can impair cognitive function and induce psychotic states. Neuroinflammation has been suggested to play an important role in neurodegeneration. Meanwhile, ketamine has been shown to modulate the levels of inflammatory cytokines. We hypothesized that the effects of ketamine on the central nervous system are associated with inflammatory cytokines. Therefore, we set out to establish acute and chronic ketamine administration models in C57BL/6 mice, to evaluate spatial recognition memory and emotional response, to analyze the changes in the levels of the inflammatory cytokines interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) in the mouse hippocampus, employing behavioral tests, Western blot, quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and immunohistochemistry. Our results showed that ketamine at the dose of 60 mg/kg induced spatial recognition memory deficit and reduced anxiety-like behaviors in mice after chronic administration. Moreover, we found that ketamine increased the hippocampal levels of IL-6 and IL-1β after single, multiple and long-term administration in a dose-dependent manner. However, the expression level of TNF-α differed in the mouse hippocampus under different conditions. Single administration of ketamine increased the level of TNF-α, whereas multiple and long-term administration decreased it significantly. We considered that TNF-α expression could be controlled by a bi-directional regulatory pathway, which was associated with the dose and duration of ketamine administration. Our results suggest that the alterations in the levels of inflammatory cytokines IL-6, IL-1β, and TNF-α may be involved in the neurotoxicity of ketamine.

Decreased Thalamocortical Connectivity in Chronic Ketamine Users

Disintegration in thalamocortical integration suggests its role in the mechanistic 'switch' from recreational to dysregulated drug seeking/addiction. In this study, we aimed to address whether thalamic nuclear groups show altered functional connectivity within the cerebral cortex in chronic ketamine users. One hundred and thirty subjects (41 ketamine users and 89 control subjects) underwent rsfMRI (resting-state functional Magnetic Resonance Imaging). Based on partial correlation functional connectivity analysis we partitioned the thalamus into six nuclear groups that correspond well with human histology. Then, in the area of each nuclear group, the functional connectivity differences between the chronic ketamine user group and normal control group were investigated. We found that the ketamine user group showed significantly less connectivity between the thalamic nuclear groups and the cortical regions-of-interest, including the prefrontal cortex, the motor cortex /supplementary motor area, and the posterior parietal cortex. However, no increased thalamic connectivity was observed for these regions as compared with controls. This study provides the first evidence of abnormal thalamocortical connectivity of resting state brain activity in chronic ketamine users. Further understanding of pathophysiological mechanisms of the thalamus in addiction (ketamine addiction) may facilitate the evaluation of much-needed novel pharmacological agents for improved therapy of this complex disease.

Changes in hippocampal AMPA receptors and cognitive impairments in chronic ketamine addiction models: another understanding of ketamine CNS toxicity

Ketamine has been reported to impair human cognitive function as a recreational drug of abuse. However, chronic effects of ketamine on central nervous system need to be further explored. We set out to establish chronic ketamine addiction models by giving mice a three or six month course of daily intraperitoneal injections of ketamine, then examined whether long-term ketamine administration induced cognition deficits and changed hippocampal post-synaptic protein expression in adult mice. Behavior tests results showed that mice exhibited dose- and time-dependent learning and memory deficits after long-term ketamine administration. Western blot results showed levels of GluA1, p-S845 and p-S831 proteins demonstrated significant decline with ketamine 60 mg/kg until six months administration paradigm. But levels of p-S845 and p-S831 proteins exhibited obvious increase with ketamine 60 mg/kg three months administration paradigm. NR1 protein levels significantly decrease with ketamine 60 mg/kg three and six months administration paradigm. Our results indicate that reduced expression levels and decreased phosphorylation levels of hippocampal post-synaptic membrane GluA1- containing AMPA receptors maybe involved in cognition impairment after long-term ketamine administration. These findings provide further evidence for the cognitive damage of chronic ketamine addiction as a recreational drug.

N,N-dimethylglycine differentially modulates psychotomimetic and antidepressant-like effects of ketamine in mice

Ketamine, a dissociative anesthetic, produces rapid and sustained antidepressant effects at subanesthtic doses. However, it still inevitably induces psychotomimetic side effects. N,N-dimethylglycine (DMG) is a derivative of the amino acid glycine and is used as a dietary supplement. Recently, DMG has been found acting at glycine binding site of the N-methyl-d-aspartate receptor (NMDAR). As blockade of NMDARs is one of the main mechanisms responsible for the action of ketamine on central nervous system, DMG might modulate the behavioral responses to ketamine. The present study determined the effects of DMG on the ketamine-induced psychotomimetic, anesthetic and antidepressant-like effects in mice. DMG pretreatment reversed the ketamine-induced locomotor hyperactivity and impairment in the rotarod performance, novel location and novel object recognition tests, and prepulse inhibition. In addition, DMG alone exhibited antidepressant-like effects in the forced swim test and produced additive effects when combined with ketamine. However, DMG did not affect ketamine-induced anesthesia. These results reveal that DMG could antagonize ketamine's psychotomimetic effects, yet produce additive antidepressant-like effects with ketamine, suggesting that DMG might have antipsychotic potential and be suitable as an add-on therapy to ketamine for patients with treatment-resistant depression.

The similarities and differences in impulsivity and cognitive ability among ketamine, methadone, and non-drug users

The study aimed to identify similarities and differences among ketamine, methadone users, and non-drug-using controls, on impulsivity, antisocial personality, and related cognitive abilities. A case-control observational design was used to compare the impulsivity and cognitive function of ketamine users (n = 51), methadone users (n=59), and controls (n=60). Antisocial personality traits and emotion states were also measured. One-way ANOVAs and planned post hoc pair-wise tests were used to analyze the data. Compared to non-drug-using controls, ketamine and methadone users had elevated scores on BIS and Pd scale of the MMPI, poorer performance on 2-back task, Stop-signal task, and Stroop test. Ketamine users performed the worst in the 2-back accuracy and Stop miss rate compared to methadone users and controls. There were no significant differences between the groups on the Iowa Gambling Task. Ketamine users did not show deficits in decision-making but exhibited strong impulsivity, antisocial personality, and poor response inhibition and working memory at levels similar to methadone users. These deficits may reflect vulnerability to addiction. This suggests that future treatment programs for ketamine users could address drug users' impulsive cognition and psychopathic deviance.

The Effects of Long-Term Ketamine Treatment on Cognitive Function in Complex Regional Pain Syndrome: A Preliminary Study

OBJECTIVE

This preliminary study aimed to investigate the effects of long-term frequent ketamine treatment on cognitive function in [AQ-A] CRPS patients.

DESIGN

A total of 30 CRPS patients were divided into two groups based on both the duration and frequency of ketamine treatment; the long-term frequent ketamine treatment (LF) group (N = 14) and the Non-LF group (N = 16). Participants were asked to complete a questionnaire packet including demographic and clinical characteristics and potential variables affecting cognitive function. Then, they performed the neuropsychological test.

RESULTS

Results indicated that the LF group performed significantly poorer than the Non-LF group on the digit span, digit symbol, Controlled Oral Word Association Test, and Trail Making Test, but not the Stroop task.

CONCLUSIONS

Patients with CRPS receiving long-term frequent ketamine treatment showed impairment in cognitive function (specifically executive function) compared with those who do not. These findings may have implications for clinical assessment and rehabilitation of cognitive function in CRPS patients.

Serum metabolomics in rats models of ketamine abuse by gas chromatography-mass spectrometry

This study aims to evaluate the effect of ketamine on rats by examining the differences in serum metabolites between ketamine abuse group (Ket-group) and control group (Con-group). Compared to the Con-group, the level of phosphate, propanoic acid, ribitol and d-fructose of the Ket-group increased after continuous intraperitoneal administration of ketamine for 7 days, while the level of alanine, glycine, butanoic acid, valine, l-serine, l-proline, mannonic acid, octadecanoic acid and cholesterol decreased. After 14 days' administration, the level of alanine, butanoic acid, valine, l-leucine, phosphate, l-serine, l-threonine, propanetricarboxylic acid, hexadecanoic acid and oleic acid of the ketamine group increased while the level of mannonic acid, octadecanoic acid and cholesterol decreased. After stopping ketamine administration for 2 days, the level of butanoic acid, phosphate, aminomalonic acid, gluconic acid, hexadecanoic acid, oleic acid and arachidonic acid of Ket-group increased, while the level of glycine, l-lysine and cholesterol decreased. This study can provide invaluable information for the metabolites changes due to ketamine abuse.

Validation of the Chinese version of Addenbrooke's cognitive examination-revised for screening mild Alzheimer's disease and mild cognitive impairment

BACKGROUND/AIMS

As a suitable test to screen for Alzheimer's disease (AD) or mild cognitive impairment (MCI), studies to validate the Chinese version of Addenbrooke's Cognitive Examination-Revised (ACE-R) are rare.

METHODS

A total of 151 subjects were recruited and the neuropsychological assessments were employed. One-way analysis of variance and Bonferroni correction were used to compare scores of different psychometric scales. Intraclass correlation coefficient (ICC) and Cronbach's coefficient α were used to evaluate the reliability of psychometric scales. The validity of ACE-R to screen for mild AD and amnestic subtype of MCI (a-MCI) was assessed by receiver operating characteristic (ROC) curves.

RESULTS

The Chinese ACE-R had good reliability (inter-rater ICC = 0.994; test-retest ICC = 0.967) as well as reliable internal consistency (Cronbach's coefficient α = 0.859). With its cutoff of 67/68, the sensitivity (0.920) and specificity (0.857) were lower than for the Mini-Mental State Examination (MMSE) cutoff (sensitivity 1.000 and specificity 0.937) to screen for mild AD. However, the sensitivity of ACE-R to screen for a-MCI was superior to the MMSE with a cutoff of 85/86. The specificity of ACE-R was lower than that of the MMSE to screen for a-MCI. The area under the ROC curve of ACE-R was much larger than that of the MMSE (0.836 and 0.751) for detecting a-MCI rather than mild AD.

CONCLUSION

The Chinese ACE-R is a reliable assessment tool for cognitive impairment. It is more sensitive and accurate in screening for a-MCI rather than for AD compared to the MMSE.

Efficacy and safety of oral ketamine for the relief of intractable chronic pain: A retrospective 5-year study of 51 patients

BACKGROUND

This work summarizes the efficiency, failures and adverse effects of oral administration of ketamine at home for intractable pain.

METHODS

This 5-year retrospective study involved testing ketamine by intravenous in-hospital administration, then a conversion to an oral route, or oral treatment directly administered at home. The daily intravenous dose was increased by steps of 0.5 mg/kg to attain an effective daily dose of 1.5-3.0 mg/kg. Pain was evaluated on a numeric scale from 0 to 10, and evidence of adverse effects was collected every day. The effective daily dose was delivered orally (three to four intakes). If effective, ketamine was continued for 3 months. Short infusions or direct oral treatment began with a 0.5-mg/kg dose, then the daily ketamine dose was increased in 15- to 20-mg increments.

RESULTS

Among 55 cases (51 patients, neuropathic pain 60%), the mean effective oral dose was 2 mg/kg. Ketamine was effective in 24 patients (44%, mean pain reduction 67 ± 17%), partially effective in 20% (mean pain reduction 30 ± 11%), with a mean opioid sparing of 63 ± 32%, and failure in 22%. Half of the patients experienced adverse effects, but only eight had to stop treatment. For patients with opioid therapy, failure of ketamine was less frequent (7% vs. 36%; p < 0.02), with fewer adverse effects (33% vs. 68%; p < 0.01).

CONCLUSIONS

Pain was reduced or abolished in two-thirds of patients under ketamine therapy; ketamine was effective for patients taking opioids and resulted in few adverse effects.