Abnormalities in white matter microstructure associated with chronic ketamine use

Neurotoxicity mechanisms and clinical implications of six common recreational drugs

The recreational abuse of addictive drugs poses considerable challenges to public health, leading to widespread neurotoxicity and neurological dysfunction. This review comprehensively examines the neurotoxic mechanisms, clinical manifestations, and treatment strategies associated with six commonly abused substances: methamphetamine, cocaine, synthetic cathinones, ketamine, nitrous oxide and heroin. Despite their diverse pharmacological properties, these drugs converge on shared neurotoxic pathways, including oxidative stress, mitochondrial dysfunction, excitotoxicity, and neuroinflammation. Psychostimulants, such as methamphetamine, cocaine and synthetic cathinones, disrupt monoaminergic neurotransmission, causing cognitive impairment, psychiatric disturbances, and neurovascular damage. Dissociative anesthetics, including ketamine and nitrous oxide, impair glutamatergic transmission and mitochondrial function, thereby exacerbating excitotoxicity and neuronal apoptosis. Opioids, such as heroin, primarily target the brain's reward system and induce oxidative stress, neuroinflammation, and cerebrovascular complications. Treatment strategies remain limited, focusing on symptomatic management, neuroprotective interventions, and behavioral therapies. Emerging approaches, such as antioxidants, NMDA receptor modulators, and cognitive rehabilitation, show promise but require further validation. By highlighting the underlying mechanisms and therapeutic challenges, this review provides a foundation for developing targeted interventions and advancing research on drug-induced neurotoxicity.

The immune regulatory mechanism of ketamine-induced psychiatric disorders: A new perspective on drug-induced psychiatric symptoms

Ketamine, a psychoactive substance strictly regulated by international drug conventions, is classified as a "new type drug" due to its excitatory, hallucinogenic, or inhibitory effects. The etiology of ketamine-induced psychiatric symptoms is multifaceted, with the immune regulatory mechanism being the most prominent among several explanatory theories. In recent years, the interaction between the immune system and nervous system have garnered significant attention in neuropsychiatric disorder research. Notably, the infiltration of peripheral lymphocytes into the central nervous system has emerged as an early hallmark of certain neuropsychiatric disorders. However, a notable gap exists in the current literature, regarding the immune regulatory mechanisms, specifically the peripheral immune alterations, associated with ketamine-induced psychiatric symptoms. To address this void, this article endeavors to provide a comprehensive overview of the pathophysiological processes implicated in psychiatric disorders or symptoms, encompassing those elicited by ketamine. This analysis delves into aspects such as nerve damage, alterations within the central immune system, and the regulation of the peripheral immune system. By emphasizing the intricate crosstalk between the peripheral immune system and the central nervous system, this study sheds light on their collaborative role in the onset and progression of psychiatric diseases or symptoms. This insight offers fresh perspectives on the underlying mechanisms, diagnosis and therapeutic strategies for mental disorders stemming from drug abuse.

KETAMINE: Neural- and network-level changes

Ketamine is a widely used clinical drug that has several functional and clinical applications, including its use as an anaesthetic, analgesic, anti-depressive, anti-suicidal agent, among others. Among its diverse behavioral effects, it influences short-term memory and induces psychedelic effects. At the neural level across different brain areas, it modulates neural firing rates, neural tuning, brain oscillations, and modularity, while promoting hypersynchrony and random connectivity between neurons. In our recent studies we demonstrated that topical application of ketamine on the visual cortex alters neural tuning and promotes vigorous connectivity between neurons by decreasing their firing variability. Here, we begin with a brief review of the literature, followed by results from our lab, where we synthesize a dendritic model of neural tuning and network changes following ketamine application. This model has potential implications for focused modulation of cortical networks in clinical settings. Finally, we identify current gaps in research and suggest directions for future studies, particularly emphasizing the need for more animal experiments to establish a platform for effective translation and synergistic therapies combining ketamine with other protocols such as training and adaptation. In summary, investigating ketamine's broader systemic effects, not only provides deeper insight into cognitive functions and consciousness but also paves the way to advance therapies for neuropsychiatric disorders.

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.

Adolescent substance use initiation and long-term neurobiological outcomes: insights, challenges and opportunities

The increased frequency of risk taking behavior combined with marked neuromaturation has positioned adolescence as a focal point of research into the neural causes and consequences of substance use. However, little work has provided a summary of the links between adolescent initiated substance use and longer-term brain outcomes. Here we review studies exploring the long-term effects of adolescent-initiated substance use with structural and microstructural neuroimaging. A quarter of all studies reviewed conducted repeated neuroimaging assessments. Long-term alcohol use, as well as tobacco use were consistently associated with smaller frontal cortices and altered white matter microstructure. This association was mostly observed in the ACC, insula and subcortical regions in alcohol users, and for the OFC in tobacco users. Long-term cannabis use was mostly related to altered frontal cortices and hippocampal volumes. Interestingly, cannabis users scanned more years after use initiation tended to show smaller measures of these regions, whereas those with fewer years since initiation showed larger measures. Long-term stimulant use tended to show a similar trend as cannabis in terms of years since initiation in measures of the putamen, insula and frontal cortex. Long-term opioid use was mostly associated with smaller subcortical and insular volumes. Of note, null findings were reported in all substance use categories, most often in cannabis use studies. In the context of the large variety in study designs, substance use assessment, methods, and sample characteristics, we provide recommendations on how to interpret these findings, and considerations for future studies.

Aberrant sense of agency induced by delayed prediction signals in schizophrenia: a computational modeling study

Aberrant sense of agency (SoA, a feeling of control over one's own actions and their subsequent events) has been considered key to understanding the pathology of schizophrenia. Behavioral studies have demonstrated that a bidirectional (i.e., excessive and diminished) SoA is observed in schizophrenia. Several neurophysiological and theoretical studies have suggested that aberrancy may be due to temporal delays (TDs) in sensory-motor prediction signals. Here, we examined this hypothesis via computational modeling using a recurrent neural network (RNN) expressing the sensory-motor prediction process. The proposed model successfully reproduced the behavioral features of SoA in healthy controls. In addition, simulation of delayed prediction signals reproduced the bidirectional schizophrenia-pattern SoA, whereas three control experiments (random noise addition, TDs in outputs, and TDs in inputs) demonstrated no schizophrenia-pattern SoA. These results support the TD hypothesis and provide a mechanistic understanding of the pathology underlying aberrant SoA in schizophrenia.

Comorbidity of ketamine dependence with major depressive disorder increases the vulnerability to neuroaxonal pathology

We recently demonstrated that patients with ketamine dependence (KD) have increased serum levels of neurofilament light chain (NfL), a novel marker of active neuroaxonal pathology, with NfL levels being significantly higher in those KD patients comorbid with major depressive disorder (MDD). However, considering that NfL elevation has been associated with both ketamine-related brain pathology and MDD, we could not determine whether the observed elevation of NfL levels was driven by an interaction of KD with MDD or by MDD itself. Therefore, we compared serum NfL levels between 35 patients with MDD without ketamine use (MDD group), 23 with KD without MDD (KD without MDD group), 30 KD with MDD (KD with MDD group), and 86 healthy controls (HC group). Using a 2*2 (KD*MDD) generalized linear model controlling for age, sex, body mass index, and smoking status, we found that KD and KD*MDD interactions, but not MDD factor, significantly affected NfL levels. Posthoc tests showed that the KD with MDD group had significantly higher NfL levels than all other groups. The KD without MDD group also showed higher NfL levels than the MDD and, as shown before, HC groups. The levels in MDD group were not different from the HC group. These results suggest that the interaction of KD with MDD, but not MDD alone, results in increased vulnerability to neuroaxonal pathology.

White matter alterations in chronic MDMA use: Evidence from diffusion tensor imaging and neurofilament light chain blood levels

3,4-Methylenedioxymethamphetamine (MDMA, "Ecstasy") is a serotonin- and noradrenaline-releasing substance, currently among the most widely used illicit substances worldwide. In animal studies, repeated exposure to MDMA has been associated with dendritic but also axonal degeneration in the brain. However, translation of the axonal findings, specifically, to humans has been repeatedly questioned and the few existing studies investigating white matter alterations in human chronic MDMA users have yielded conflicting findings. In this study, we combined whole-brain diffusion tensor imaging and neurofilament light chain (NfL) analysis in blood to reveal potential MDMA-induced axonal neuropathology. To this end, we assessed 39 chronic MDMA users and 39 matched MDMA-naïve healthy controls. MDMA users showed increased fractional anisotropy in several white matter tracts, most prominently in the corpus callosum as well as corticospinal tracts, with these findings partly related to MDMA use intensity. However, the NfL levels of MDMA users were not significantly different from those of controls. We conclude that MDMA use is not associated with significant white matter lesions due to the absence of reduced fractional anisotropy and increased NfL levels commonly observed in conditions associated with white matter lesions, including stimulant and ketamine use disorders. Hence, the MDMA-induced axonal degradation demonstrated in animal models was not observed in this human study of chronic MDMA users.

Ketamine plus Alcohol: What We Know and What We Can Expect about This

Drug abuse has become a public health concern. The misuse of ketamine, a psychedelic substance, has increased worldwide. In addition, the co-abuse with alcohol is frequently identified among misusers. Considering that ketamine and alcohol share several pharmacological targets, we hypothesize that the consumption of both psychoactive substances may synergically intensify the toxicological consequences, both under the effect of drugs available in body systems and during withdrawal. The aim of this review is to examine the toxicological mechanisms related to ketamine plus ethanol co-abuse, as well the consequences on cardiorespiratory, digestive, urinary, and central nervous systems. Furthermore, we provide a comprehensive discussion about the probable sites of shared molecular mechanisms that may elicit additional hazardous effects. Finally, we highlight the gaps of knowledge in this area, which deserves further research.

Ketamine use disorder: preclinical, clinical, and neuroimaging evidence to support proposed mechanisms of actions

Ketamine, a noncompetitive NMDA receptor antagonist, has been exclusively used as an anesthetic in medicine and has led to new insights into the pathophysiology of neuropsychiatric disorders. Clinical studies have shown that low subanesthetic doses of ketamine produce antidepressant effects for individuals with depression. However, its use as a treatment for psychiatric disorders has been limited due to its reinforcing effects and high potential for diversion and misuse. Preclinical studies have focused on understanding the molecular mechanisms underlying ketamine's antidepressant effects, but a precise mechanism had yet to be elucidated. Here we review different hypotheses for ketamine's mechanism of action including the direct inhibition and disinhibition of NMDA receptors, AMPAR activation, and heightened activation of monoaminergic systems. The proposed mechanisms are not mutually exclusive, and their combined influence may exert the observed structural and functional neural impairments. Long term use of ketamine induces brain structural, functional impairments, and neurodevelopmental effects in both rodents and humans. Its misuse has increased rapidly in the past 20 years and is one of the most common addictive drugs used in Asia. The proposed mechanisms of action and supporting neuroimaging data allow for the development of tools to identify 'biotypes' of ketamine use disorder (KUD) using machine learning approaches, which could inform intervention and treatment.

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.

Neurofilament light chain as novel blood biomarker of disturbed neuroaxonal integrity in patients with ketamine dependence

OBJECTIVES

Chronic and heavy ketamine use has been associated with persistent neurocognitive impairment and structural brain abnormalities. Blood levels of neurofilament light chain (NFL) was recently proposed as a measure of axonal integrity in several neuropsychiatric disorders. We aimed to characterise the axonal neurotoxicity of chronic ketamine use and its relationship to relevant clinical outcomes.

METHODS

We enrolled 65 treatment-seeking ketamine-dependent patients (55 males and 10 females) and 60 healthy controls (51 males and 9 females). Blood NFL levels measured by single molecule array (SiMoA) immunoassay. We compared NFL levels between groups and used regression analyses to identify clinical variables related to NFL levels.

RESULTS

Ketamine-dependent patients had significantly higher NFL levels compared to controls (p < 0.001). A multivariate regression showed that age (p < 0.05) and lifetime history of major depressive disorder (MDD) (p < 0.01) predicted high NFL blood levels in patients. Subsequent group comparisons showed that specifically ketamine-dependent patients with a lifetime history of MDD had significantly increased NFL levels than those without (p < 0.05).

CONCLUSIONS

These results suggest substantial neuroaxonal alterations following chronic and heavy ketamine use. The pronounced increase of NFL levels in the MDD subgroup warrants further investigation of a potential neuroaxonal vulnerability of depressed patients to ketamine.

Chronic administration of ketamine induces cognitive deterioration by restraining synaptic signaling

The discovery of the rapid antidepressant effects of ketamine has arguably been the most important advance in depression treatment. Recently, it was reported that repeated long-term ketamine administration is effective in preventing relapse of depression, which may broaden the clinical use of ketamine. However, long-term treatment with ketamine produces cognitive impairments, and the underlying molecular mechanisms for these impairments are largely unknown. Here, we found that chronic in vivo exposure to ketamine for 28 days led to decreased expression of the glutamate receptor subunits GluA1, GluA2, GluN2A, and GluN2B; decreased expression of the synaptic proteins Syn and PSD-95; decreased dendrite spine density; impairments in long-term potentiation (LTP) and synaptic transmission in the hippocampal CA1 area; and deterioration of learning and memory in mice. Furthermore, the reduced glutamate receptor subunit and synaptic protein expression and the LTP deficits were still observed on day 28 after the last injection of ketamine. We found that the expression and phosphorylation of CaMKIIβ, ERK1/2, CREB, and NF-κB were inhibited by ketamine. The reductions in glutamate receptor subunit expression and dendritic spine density and the deficits in LTP, synaptic transmission, and cognition were alleviated by overexpression of CaMKIIβ. Our study indicates that inhibition of CaMKIIβ-ERK1/2-CREB/NF-κB signaling may mediate chronic ketamine use-associated cognitive impairments by restraining synaptic signaling. Hypofunction of the glutamatergic system might be the underlying mechanism accounting for chronic ketamine use-associated cognitive impairments. Our findings may suggest possible strategies to alleviate ketamine use-associated cognitive deficits and broaden the clinical use of ketamine in depression treatment.

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.

Metabolic effects of repeated ketamine administration in the rat brain

Ketamine is a popular recreational drug used in club and dance music settings. Evidence suggests that chronic or repeated ketamine use could induce neurological and psychological harm, while the mechanisms underlying ketamine's effects on the nervous system are still unclear. The aim of this study was to explore the metabolic changes that occur in the prefrontal cortex (PFC), hippocampus (Hip) and striatum of rats with repeated ketamine exposure and withdrawal intervention and to identify the potential metabolic pathways influenced by ketamine. An untargeted ultra-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry (UPLC-Q-TOF-MS)-based metabolomics method coupled with multivariate and univariate statistical analysis was applied to analyze the metabolic profiles of the PFC, Hip, and striatum and to identify metabolite alterations. The pathway analysis tool in MetaboAnalyst was subsequently applied for pathway predictions. A total of 79, 54 and 58 changed metabolites were identified in the PFC, Hip and striatum, respectively, after repeated ketamine exposure. Pathway analysis indicated that purine metabolism and glycerophospholipid metabolism were the main pathways disturbed by ketamine in all three brain regions. After one week of withdrawal intervention, most changed metabolites in the Hip and striatum had been restored to control levels, while the metabolite alterations in the PFC were persistent. These results revealed that repeated ketamine exposure significantly changed purine metabolism and glycerophospholipid metabolism in the PFC, Hip and striatum, which might be involved in the neurotoxic effects of ketamine. Additionally, this study also identified that the PFC, rather than the Hip or striatum, was more likely to be the target region of the long-term effects of ketamine.

Ketamine metabolite pilot study in a suicidal depression trial

Ketamine shows promise as a rapidly-acting treatment for depression and suicidal ideation, but side effects and abuse potential limit its use. Understanding its mechanism of action could help develop analogous but safer drugs. This post hoc study explored relationships of ketamine and metabolites, including hydroxynorketamine enantiomers, (2S,6S)- and (2R,6R)-HNK, to clinical response in a subgroup from a published trial in suicidal depression. Depressed adults with clinically significant suicidal ideation were randomized to double-blind infusion of sub-anesthetic ketamine or midazolam. Ketamine and metabolites were measured after infusion (N = 53). Plasma (2R,6R)-HNK was associated with change (higher levels correlated with less clinical improvement) from baseline to 24 h post-infusion of depression (HDRS-24: Spearman r = 0.37, p = 0.009) and suicidal thoughts (SSI: Spearman r = 0.29, p = 0.041). There were similar correlations with weekly follow-up clinical rating scores for both HNK enantiomers and dehydronorketamine (DHNK). Ketamine and norketamine were not associated with change in depression or suicidal ideation (unadjusted p > 0.28).

Global brain volume reductions in a sub-chronic phencyclidine animal model for schizophrenia and their relationship to recognition memory

BACKGROUND

Cognitive deficits and structural brain changes co-occur in patients with schizophrenia. Improving our understanding of the relationship between these is important to develop improved therapeutic strategies. Back-translation of these findings into rodent models for schizophrenia offers a potential means to achieve this goal.

AIMS

The purpose of this study was to determine the extent of structural brain changes and how these relate to cognitive behaviour in a sub-chronic phencyclidine rat model.

METHODS

Performance in the novel object recognition task was examined in female Lister Hooded rats at one and six weeks after sub-chronic phencyclidine (2 mg/kg intra-peritoneal, n=15) and saline controls (1 ml/kg intra-peritoneal, n=15). Locomotor activity following acute phencyclidine challenge was also measured. Brain volume changes were assessed in the same animals using ex vivo structural magnetic resonance imaging and computational neuroanatomical analysis at six weeks.

RESULTS

Female sub-chronic phencyclidine-treated Lister Hooded rats spent significantly less time exploring novel objects (p<0.05) at both time-points and had significantly greater locomotor activity response to an acute phencyclidine challenge (p<0.01) at 3-4 weeks of washout. At six weeks, sub-chronic phencyclidine-treated Lister Hooded rats displayed significant global brain volume reductions (p<0.05; q<0.05), without apparent regional specificity. Relative volumes of the perirhinal cortex however were positively correlated with novel object exploration time only in sub-chronic phencyclidine rats at this time-point.

CONCLUSION

A sustained sub-chronic phencyclidine-induced cognitive deficit in novel object recognition is accompanied by global brain volume reductions in female Lister Hooded rats. The relative volumes of the perirhinal cortex however are positively correlated with novel object exploration, indicating some functional relevance.

Neurocognitive performance and repeated-dose intravenous ketamine in major depressive disorder

OBJECTIVE

Ketamine has demonstrated a rapid antidepressant and antisuicidal effect in patients with major depressive disorder (MDD), but the neurocognitive effects of ketamine are relatively unknown. This study aims to examine the neurocognitive effects of six ketamine infusions and the association of baseline neurocognitive function and the change in severity of depressive symptoms after the last infusions.

METHODS

Sixty-four patients with MDD completed six intravenous infusions of ketamine (0.5 mg/kg over 40 min) administered over a 12-day period (Monday-Wednesday-Friday), and were followed by a 2-week observational period. Four domains of neurocognitive function (including speed of processing, working memory, visual learning and verbal learning) were assessed using the MATRICS Consensus Cognitive Battery (MCCB) at 0, 13 and 26 days.

RESULTS

In linear mixed model, significant improvements were found in terms of speed of processing (F = 20.7, p < 0.001) and verbal learning (F = 11.1, p < 0.001). The Sobel test showed the improvement of speed of processing (Sobel test = 2.8, p < 0.001) and verbal learning (Sobel test = 3.6, p < 0.001) were significantly mediated by change in depressive symptoms. Other two neurocognitive domains showed no significant changes over time. Correlation analysis showed no significant association of change in depressive symptoms with neurocognitive function at baseline.

CONCLUSION

Our findings suggest that six ketamine infusions were associated with the improvement of speed of processing and verbal learning, which were partly accounted for by improvement in the severity of depression symptoms over time.

Expression of heat shock protein HSP-70 in the retrosplenial cortex of rat brain after administration of (R,S)-ketamine and (S)-ketamine, but not (R)-ketamine

The N-methyl-d-aspartate receptor (NMDAR) antagonist (R,S)-ketamine has robust antidepressant effects in depressed patients although it has detrimental side effects such as psychotomimetic and dissociative symptoms. (R,S)-Ketamine is known to cause the expression of heat shock protein HSP-70 (a marker for neuronal injury) in the retrosplenial cortex of rat brain, suggesting that the neuropathological changes may play a role in the detrimental side effects of (R,S)-ketamine. This study was undertaken to examine whether (R,S)-ketamine and its two enantiomers, (R)-ketamine and (S)-ketamine, causes the expression of HSP-70 in the rat retrosplenial cortex after a single administration. The HSP-70 immunohistochemistry in the rat brain was performed 24 h after intraperitoneal administration of saline (1 ml/kg), (+)-MK-801 (or dizocilpine: 1.0 mg/kg), (R,S)-ketamine (100 mg/kg), (S)-ketamine (25, 50, or 75, mg/kg), or (R)-ketamine (25, 50, or 75 mg/kg). Marked expression of HSP-70 immunoreactivity in the retrosplenial cortex was detected after administration of dizocilpine or (R,S)-ketamine (100 mg/kg). Higher does (50 and 75 mg/kg) of (S)-ketamine, but not low dose (25 mg/kg), caused expression of HSP-70 in this region. In contrast, all doses of (R)-ketamine did not induce the expression of HSP-70 in this region. These findings suggest that marked expression of HSP-70 in the retrosplenial cortex after a single dose of (R,S)-ketamine or (S)-ketamine may have detrimental side effects in the rat brain. Therefore, it is likely that (R)-ketamine is a safer compound in humans than (R,S)-ketamine and (S)-ketamine.

Cue-Induced Brain Activation in Chronic Ketamine-Dependent Subjects, Cigarette Smokers, and Healthy Controls: A Task Functional Magnetic Resonance Imaging Study

BACKGROUND

Observations of drug-related cues may induce craving in drug-dependent patients, prompting compulsive drug-seeking behavior. Sexual dysfunction is common in drug users. The aim of the study was to examine regional brain activation to drug (ketamine, cigarette smoking) associated cues and natural (sexual) rewards.

METHODS

A sample of 129 [40 ketamine use smokers (KUS), 45 non-ketamine use smokers (NKUS) and 44 non-ketamine use non-smoking healthy controls (HC)] participants underwent functional magnetic resonance imaging (fMRI) while viewing ketamine use related, smoking and sexual films.

RESULTS

We found that KUS showed significant increased activation in anterior cingulate cortex and precuneus in response to ketamine cues. Ketamine users (KUS) showed lower activation in cerebellum and middle temporal cortex compared with non-ketamine users (NKUS and HC) in response to sexual cues. Smokers (KUS and NKUS) showed higher activation in the right precentral frontal cortex in response to smoking cues. Non-ketamine users (NKUS and HC) showed significantly increased activation of cerebellum and middle temporal cortex while viewing sexual cues.

CONCLUSION

These findings clearly show the engagement of distinct neural circuitry for drug-related stimuli in chronic ketamine users. While smokers (both KUS and NKUS) showed overlapping differences in activation for smoking cues, the former group showed a specific neural response to relevant (i.e., ketamine-related) cues. In particular, the heightened response in anterior cingulate cortex may have important implications for how attentionally salient such cues are in this group. Ketamine users (KUS) showed lower activation in response to sexual cues may partly reflect the neural basis of sexual dysfunction.

ZL006, a small molecule inhibitor of PSD-95/nNOS interaction, does not induce antidepressant-like effects in two genetically predisposed rat models of depression and control animals

N-methyl-D-aspartate receptor (NMDA-R) antagonists and nitric oxide inhibitors have shown promising efficacy in depression but commonly induce adverse events. To circumvent these, a more indirect disruption of the nitric oxide synthase/postsynaptic density protein 95 kDa complex at the NMDA-R has been proposed. This disruption can be achieved using small molecule inhibitors such as ZL006, which has attracted attention as ischemic stroke therapy in rodents and has been proposed as a potential novel treatment for depression. Based on this, our aim was to translate these findings to animal models of depression to elucidate antidepressant-like properties in more detail. In the present study, we administered ZL006 to two established animal models of depression and control rodents. Following treatment, we measured locomotion in the Open Field and depressive-like behavior in the Forced Swim Test and Tail Suspension Test. Our experimental designs included the use of different species (rats, mice), strains (Flinders Sensitive Line rats, Flinders Resistant Line rats, Wistar Kyoto rats, Wistar Hanover rats, Sprague Dawley rats, B6NTac mice), routes of administration (intraperitoneal, intracerebroventricular), times of administration (single injection, repeated injections), treatment regimens (acute, sustained), and doses (5, 10, 15, 50 mg/kg). ZL006 did not affect behavior in any of the described settings. On a molecular level, ZL006 significantly reduced total nitrate/nitrite concentrations in the cerebellum, supporting that it is capable of reducing nitric oxide metabolites in the brain. Future studies using different experimental parameters are needed to further investigate the behavioral profile of ZL006.

Classics in Chemical Neuroscience: Ketamine

Ketamine, a molecule of many faces, has contributed immeasurably to numerous realms of clinical practice and scientific inquiry. From anesthesia and analgesia to depression and schizophrenia, it continues to shed light on the molecular underpinnings of pain, consciousness, and the pathophysiology of neuropsychiatric disorders. In particular, research on ketamine's mechanism of action is providing new hope in the search for therapies for treatment-resistant depression and affords insights into disorders of glutamatergic dysfunction. In this Review, we will cover aspects of ketamine's synthesis, manufacturing, metabolism, pharmacology, approved and off-label indications, and adverse effects. We will also discuss the captivating history of this molecule, its influence on neuropsychiatry, and its potential to advance the fields of chemical neuroscience and neuropharmacology.

Chronic Ketamine Exposure Causes White Matter Microstructural Abnormalities in Adolescent Cynomolgus Monkeys

Acute and repeated exposures to ketamine mimic aspects of positive, negative, and cognitive symptoms of schizophrenia in humans. Recent studies by our group and others have shown that chronicity of ketamine use may be a key element for establishing a more valid model of cognitive symptoms of schizophrenia. However, current understanding on the long-term consequences of ketamine exposure on brain circuits has remained incomplete, particularly with regard to microstructural changes of white matter tracts that underpin the neuropathology of schizophrenia. Thus, the present study aimed to expand on previous investigations by examining causal effects of repeated ketamine exposure on white matter integrity in a non-human primate model. Ketamine or saline (control) was administered intravenously for 3 months to male adolescent cynomolgus monkeys (n = 5/group). Diffusion tensor imaging (DTI) experiments were performed and tract-based spatial statistics (TBSS) was used for data analysis. Fractional anisotropy (FA) was quantified across the whole brain. Profoundly reduced FA on the right side of sagittal striatum, posterior thalamic radiation (PTR), retrolenticular limb of the internal capsule (RLIC) and superior longitudinal fasciculus (SLF), and on the left side of PTR, middle temporal gyrus and inferior frontal gyrus were observed in the ketamine group compared to controls. Diminished white matter integrity found in either fronto-thalamo-temporal or striato-thalamic connections with tracts including the SLF, PTR, and RLIC lends support to similar findings from DTI studies on schizophrenia in humans. This study suggests that chronic ketamine exposure is a useful pharmacological paradigm that might provide translational insights into the pathophysiology and treatment of schizophrenia.

Cognitive dysfunction in major depression and Alzheimer's disease is associated with hippocampal-prefrontal cortex dysconnectivity

Cognitive dysfunction is prevalent in psychiatric disorders. Deficits are observed in multiple domains, including working memory, executive function, attention, and information processing. Disability caused by cognitive dysfunction is frequently as debilitating as the prominent emotional disturbances. Interactions between the hippocampus and the prefrontal cortex are increasingly appreciated as an important link between cognition and emotion. Recent developments in optogenetics, imaging, and connectomics can enable the investigation of this circuit in a manner that is relevant to disease pathophysiology. The goal of this review is to shed light on the contributions of this circuit to cognitive dysfunction in neuropsychiatric disorders, focusing on Alzheimer's disease and depression.

Imaging the neuroplastic effects of ketamine with VBM and the necessity of placebo control

In the last years a plethora of studies have investigated morphological changes induced by behavioural or pharmacological interventions using structural T1-weighted MRI and voxel-based morphometry (VBM). Ketamine is thought to exert its antidepressant action by restoring neuroplasticity. In order to test for acute impact of a single ketamine infusion on grey matter volume we performed a placebo-controlled, double-blind investigation in healthy volunteers using VBM. 28 healthy individuals underwent two MRI sessions within a timeframe of 2 weeks, each consisting of two structural T1-weighted MRIs within a single session, one before and one 45min after infusion of S-ketamine (bolus of 0.11mg/kg, followed by an maintenance infusion of 0.12mg/kg) or placebo (0.9% NaCl infusion) using a crossover design. In the repeated-measures ANOVA with time (post-infusion/pre-infusion) and medication (placebo/ketamine) as factors, no significant effect of interaction and no effect of medication was found (FWE-corrected). Importantly, further post-hoc t-tests revealed a strong "decrease" of grey matter both in the placebo and the ketamine condition over time. This effect was evident mainly in frontal and temporal regions bilaterally with t-values ranging from 4.95 to 5.31 (FWE-corrected at p<0.05 voxel level). The vulnerabilities of VBM have been repeatedly demonstrated, with reports of influence of blood flow, tissue water and direct effects of pharmacological compounds on the MRI signal. Here again, we highlight that the relationship between intervention and VBM results is apparently subject to a number of physiological influences, which are partly unknown. Future studies focusing on the effects of ketamine on grey matter should try to integrate known influential factors such as blood flow into analysis. Furthermore, the results of this study highlight the importance of a carefully performed placebo condition in pharmacological fMRI studies.

Efficacy of ketamine in the rapid treatment of major depressive disorder: a meta-analysis of randomized, double-blind, placebo-controlled studies

BACKGROUND

An increasing number of studies are reporting that ketamine could be treated as a novel antidepressant for major depressive disorder (MDD). Therefore, we performed this meta-analysis to comprehensively and systematically assess the efficacy of ketamine for treating patients with MDD.

METHOD

Randomized, double-blind, placebo-controlled studies on ketamine versus placebo for treating MDD were searched up to April 2016 in medical databases (PubMed, CCTR, Web of Science, Embase, CBM-disc, and CNKI). Three treatment time points (24 and 72 h, and day 7) were chosen. Response and remission rates were the main outcomes. The random effects model was used. An intention-to-treat analysis was conducted.

RESULTS

Nine high-quality studies that included 368 patients were selected to compare the efficacy of ketamine to placebo. The therapeutic effects of ketamine at 24 and 72 h, and day 7 were found to be significantly better than placebo. Response and remission rates in the ketamine group at 24 and 72 h, and day 7 were 52.2% and 20.6%; 47.9% and 23.8%; and 39.8% and 26.2%, respectively. No significant heterogeneity existed, and the Egger's test showed no publication bias.

CONCLUSION

These results indicated that ketamine could yield a good efficacy in the rapid treatment of MDD. Future large-scale clinical studies are needed to confirm our results and investigate the mid- and long-term efficacy of ketamine in treating MDD.

Role of glutamate receptors and glial cells in the pathophysiology of treatment-resistant depression

Treatment-resistant depression (TRD) causes substantial socioeconomic burden. Although a consensus on the definition of TRD has not yet been reached, it is certain that classic monoaminergic antidepressants are ineffective for TRD. One decade ago, many researchers found ketamine, an N-methyl-d-aspartate receptor (NMDAR) antagonist, to be an alternative to classic monoaminergic antidepressants. The major mechanisms of action of ketamine rapidly induce synaptogenesis in the brain-derived neurotrophic factor (BDNF) pathway. Although excessive glutamatergic neurotransmission and consequent excitotoxicity were considered a major cause of TRD, recent evidence suggests that the extrasynaptic glutamatergic receptor signal pathway mainly contributes to the detrimental effects of TRD. Glial cells such as microglia and astrocytes, early life adversity, and glucocorticoid receptor dysfunction participate in complex cross-talk. An appropriate reuptake of glutamate at the astrocyte is crucial for preventing 'spill-over' of synaptic glutamate and binding to the extrasynaptic NMDA receptor. Excessive microglial activation and the inflammatory process cause astrocyte glutamatergic dysfunction, which in turn activates microglial function. Early life adversity and glucocorticoid receptor dysfunction result in vulnerability to stress in adulthood. A maladaptive response to stress leads to increased glutamatergic release and pro-inflammatory cytokines, which then activate microglia. However, since the role of inflammatory mediators such as pro-inflammatory cytokines is not specific for depression, more disease-specific mechanisms should be identified. Last, although much research has focused on ketamine as an alternative antidepressant for TRD, its long-lasting effectiveness and adverse events have not been rigorously demonstrated. Additionally, evidence suggests that substantial brain abnormalities develop in ketamine abusers. Thus, more investigations for ketamine and other novel glutamatergic agents are needed.

Disrupted salience network functional connectivity and white-matter microstructure in persons at risk for psychosis: findings from the LYRIKS study

BACKGROUND

Salience network (SN) dysconnectivity has been hypothesized to contribute to schizophrenia. Nevertheless, little is known about the functional and structural dysconnectivity of SN in subjects at risk for psychosis. We hypothesized that SN functional and structural connectivity would be disrupted in subjects with At-Risk Mental State (ARMS) and would be associated with symptom severity and disease progression.

METHOD

We examined 87 ARMS and 37 healthy participants using both resting-state functional magnetic resonance imaging and diffusion tensor imaging. Group differences in SN functional and structural connectivity were examined using a seed-based approach and tract-based spatial statistics. Subject-level functional connectivity measures and diffusion indices of disrupted regions were correlated with CAARMS scores and compared between ARMS with and without transition to psychosis.

RESULTS

ARMS subjects exhibited reduced functional connectivity between the left ventral anterior insula and other SN regions. Reduced fractional anisotropy (FA) and axial diffusivity were also found along white-matter tracts in close proximity to regions of disrupted functional connectivity, including frontal-striatal-thalamic circuits and the cingulum. FA measures extracted from these disrupted white-matter regions correlated with individual symptom severity in the ARMS group. Furthermore, functional connectivity between the bilateral insula and FA at the forceps minor were further reduced in subjects who transitioned to psychosis after 2 years.

CONCLUSIONS

Our findings support the insular dysconnectivity of the proximal SN hypothesis in the early stages of psychosis. Further developed, the combined structural and functional SN assays may inform the prognosis of persons at-risk for psychosis.

Practical application of the neuroregenerative properties of ketamine: real world treatment experience

While controversial, ketamine has emerged as an effective treatment for refractory depression. Serial infusions have been performed 3 times per week, but our practical experience has challenged this precept concerning infusion frequency. Depression is associated with neuron loss, reduced synapse numbers, and dearborization of dendrites. Ketamine appears to potently induce mechanisms which reverse these neurodegenerative processes. Ketamine not only blocks the glutamate receptor, it activates eukaroyotic elongation factor 2 (eEF2). This, in turn, activates brain-derived neurotrophic factor (BDNF) protein synthesis. This is thought to underlie ketamine's enduring benefits. In addition, ketamine alters glycogen synthase kinase-3 (GSK-3) phosphorylation, probably responsible for its rapid antidepressant effect. Notably, inhibition of the BDNF receptor does not block the immediate benefits of ketamine, but does prevent the enduring effects. Neuro-Luminance Ketamine Infusion Centers have been treating patients with serial ketamine infusions for over three years. Our methods differ from what is often reported, as we perform infusions only once per week and generally do not perform more than five infusions. Data from 100 patients showed that 80% of the patients responded. The baseline Quick Inventory of Depressive Symptomatology-Self Report (QIDS-SR) score was 17.8 ± 2.8. Responders to ketamine showed a drop in QIDS-SR score of 10.8 ± 3.5, while non-responders showed a 0.8 ± 1.8 change. Moreover, they often had persistent benefits over several months. Recently, it was proposed that psychotomimetic effects are necessary during a ketamine infusion to yield effective antidepressant benefits. Yet, only one patient in our clinic has experienced hallucinations in three years. Nevertheless, 80% of our patients show clinical improvement. Further studies of clinical methods for ketamine infusion therapy are encouraged.

Oral ketamine for the treatment of pain and treatment-resistant depression†

BACKGROUND

Recent studies with intravenous (i.v.) application of ketamine show remarkable but short-term success in patients with MDD. Studies in patients with chronic pain have used different ketamine applications for longer time periods. This experience may be relevant for psychiatric indications.

AIMS

To review the literature about the dosing regimen, duration, effects and side-effects of oral, intravenous, intranasal and subcutaneous routes of administration of ketamine for treatment-resistant depression and pain.

METHOD

Searches in PubMed with the terms 'oral ketamine', 'depression', 'chronic pain', 'neuropathic pain', 'intravenous ketamine', 'intranasal ketamine' and 'subcutaneous ketamine' yielded 88 articles. We reviewed all papers for information about dosing regimen, number of individuals who received ketamine, number of ketamine days per study, results and side-effects, as well as study quality.

RESULTS

Overall, the methodological strength of studies investigating the antidepressant effects of ketamine was considered low, regardless of the route of administration. The doses for depression were in the lower range compared with studies that investigated analgesic use. Studies on pain suggested that oral ketamine may be acceptable for treatment-resistant depression in terms of tolerability and side-effects.

CONCLUSIONS

Oral ketamine, given for longer time periods in the described doses, appears to be well tolerated, but few studies have systematically examined the longer-term negative consequences. The short- and longer-term depression outcomes as well as side-effects need to be studied with rigorous randomised controlled trials.

The myelinated fiber loss in the corpus callosum of mouse model of schizophrenia induced by MK-801

Previous magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) investigations have shown that the white matter volume and fractional anisotropy (FA) were decreased in schizophrenia (SZ), which indicated impaired white matter integrity in SZ. However, the mechanism underlying these abnormalities has been less studied. The current study was designed to investigate the possible reasons for white matter abnormalities in the mouse model of SZ induced by NMDA receptor antagonist using the unbiased stereological methods and transmission electron microscope technique. We found that the mice treated with MK-801 demonstrated a series of schizophrenia-like behaviors including hyperlocomotor activity and more anxiety. The myelinated fibers in the corpus callosum (CC) of the mice treated with MK-801 were impaired with splitting lamellae of myelin sheaths and segmental demyelination. The CC volume and the total length of the myelinated fibers in the CC of the mice treated with MK-801 were significantly decreased by 9.4% and 16.8% when compared to those of the mice treated with saline. We further found that the loss of the myelinated fibers length was mainly due to the marked loss of the myelinated nerve fibers with the diameter of 0.4-0.5 μm. These results indicated that the splitting myelin sheaths, demyelination and the loss of myelinated fibers with small diameter might provide one of the structural bases for impaired white matter integrity of CC in the mouse model of SZ. These results might also provide a baseline for further studies searching for the treatment of SZ through targeting white matter.

Neurocognitive effects of ketamine and association with antidepressant response in individuals with treatment-resistant depression: a randomized controlled trial

The glutamate N-methyl-D-aspartate (NMDA) receptor antagonist ketamine displays rapid antidepressant effects in patients with treatment-resistant depression (TRD); however, the potential for adverse neurocognitive effects in this population has not received adequate study. The current study was designed to investigate the delayed neurocognitive impact of ketamine in TRD and examine baseline antidepressant response predictors in the context of a randomized controlled trial. In the current study, 62 patients (mean age = 46.2 ± 12.2) with TRD free of concomitant antidepressant medication underwent neurocognitive assessments using components of the MATRICS Consensus Cognitive Battery (MCCB) before and after a single intravenous infusion of ketamine (0.5 mg/kg) or midazolam (0.045 mg/kg). Participants were randomized to ketamine or midazolam in a 2:1 fashion under double-blind conditions and underwent depression symptom assessments at 24, 48, 72 h, and 7 days post treatment using the Montgomery-Asberg Depression Rating Scale (MADRS). Post-treatment neurocognitive assessment was conducted once at 7 days. Neurocognitive performance improved following the treatment regardless of treatment condition. There was no differential effect of treatment on neurocognitive performance and no association with antidepressant response. Slower processing speed at baseline uniquely predicted greater improvement in depression at 24 h following ketamine (t = 2.3, p = 0.027), while controlling for age, depression severity, and performance on other neurocognitive domains. In the current study, we found that ketamine was devoid of adverse neurocognitive effects at 7 days post treatment and that slower baseline processing speed was associated with greater antidepressant response. Future studies are required to further define the neurocognitive profile of ketamine in clinical samples and to identify clinically useful response moderators.

Affected connectivity organization of the reward system structure in obesity

With the prevalence of obesity rapidly increasing worldwide, understanding the processes leading to excessive eating behavior becomes increasingly important. Considering the widely recognized crucial role of reward processes in food intake, we examined the white matter wiring and integrity of the anatomical reward network in obesity. Anatomical wiring of the reward network was reconstructed derived from diffusion weighted imaging in 31 obese participants and 32 normal-weight participants. Network wiring was compared in terms of the white matter volume as well as in terms of white matter microstructure, revealing lower number of streamlines and lower fiber integrity within the reward network in obese subjects. Specifically, the orbitofrontal cortex and striatum nuclei including accumbens, caudate and putamen showed lower strength and network clustering in the obesity group as compared to healthy controls. Our results provide evidence for obesity-related disruptions of global and local anatomical connectivity of the reward circuitry in regions that are key in the reinforcing mechanisms of eating-behavior processes.

Preliminary analysis of positive and negative syndrome scale in ketamine-associated psychosis in comparison with schizophrenia

OBJECTIVE

Studies of the effects of the N-methyl-d-aspartate (NMDA) glutamate receptor antagonist, ketamine, have suggested similarities to the symptoms of schizophrenia. Our primary goal was to evaluate the dimensions of the Positive and Negative Syndrome Scale (PANSS) in ketamine users (acute and chronic) compared to schizophrenia patients (early and chronic stages).

METHOD

We conducted exploratory factor analysis for the PANSS from four groups: 135 healthy subject administrated ketamine or saline, 187 inpatients of ketamine abuse; 154 inpatients of early course schizophrenia and 522 inpatients of chronic schizophrenia. Principal component factor analyses were conducted to identify the factor structure of the PANSS.

RESULTS

Factor analysis yielded five factors for each group: positive, negative, cognitive, depressed, excitement or dissociation symptoms. The symptom dimensions in two schizophrenia groups were consistent with the established five-factor model (Wallwork et al., 2012). The factor structures across four groups were similar, with 19 of 30 symptoms loading on the same factor in at least 3 of 4 groups. The factors in the chronic ketamine group were more similar to the factors in the two schizophrenia groups rather than to the factors in the acute ketamine group. Symptom severities were significantly different across the groups (Kruskal-Wallis χ(2)(4) = 540.6, p < 0.0001). Symptoms in the two ketamine groups were milder than in the two schizophrenia groups (Cohen's d = 0.7).

CONCLUSION

Our results provide the evidence of similarity in symptom dimensions between ketamine psychosis and schizophrenia psychosis. The interpretations should be cautious because of potential confounding factors.

Approaching a network connectivity-driven classification of the psychosis continuum: a selective review and suggestions for future research

Brain changes in schizophrenia evolve along a dynamic trajectory, emerging before disease onset and proceeding with ongoing illness. Recent investigations have focused attention on functional brain interactions, with experimental imaging studies supporting the disconnection hypothesis of schizophrenia. These studies have revealed a broad spectrum of abnormalities in brain connectivity in patients, particularly for connections integrating the frontal cortex. A critical point is that brain connectivity abnormalities, including altered resting state connectivity within the fronto-parietal (FP) network, are already observed in non-help-seeking individuals with psychotic-like experiences. If we consider psychosis as a continuum, with individuals with psychotic-like experiences at the lower and psychotic patients at the upper ends, individuals with psychotic-like experiences represent a key population for investigating the validity of putative biomarkers underlying the onset of psychosis. This paper selectively addresses the role played by FP connectivity in the psychosis continuum, which includes patients with chronic psychosis, early psychosis, clinical high risk, genetic high risk, as well as the general population with psychotic experiences. We first discuss structural connectivity changes among the FP pathway in each domain in the psychosis continuum. This may provide a basis for us to gain an understanding of the subsequent changes in functional FP connectivity. We further indicate that abnormal FP connectivity may arise from glutamatergic disturbances of this pathway, in particular from abnormal NMDA receptor-mediated plasticity. In the second part of this paper we propose some concepts for further research on the use of network connectivity in the classification of the psychosis continuum. These concepts are consistent with recent efforts to enhance the role of data in driving the diagnosis of psychiatric spectrum diseases.

Pathophysiology of depression and innovative treatments: remodeling glutamatergic synaptic connections

Despite the complexity and heterogeneity of mood disorders, basic and clinical research studies have begun to elucidate the pathophysiology of depression and to identify rapid, efficacious antidepressant agents. Stress and depression are associated with neuronal atrophy, characterized by loss of synaptic connections in key cortical and limbic brain regions implicated in depression. This is thought to occur in part via decreased expression and function of growth factors, such as brain-derived neurotrophic factor (BDNF), in the prefrontal cortex (PFC) and hippocampus. These structural alterations are difficult to reverse with typical antidepressants. However, recent studies demonstrate that ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist that produces rapid antidepressant actions in treatment-resistant depressed patients, rapidly increases spine synapses in the PFC and reverses the deficits caused by chronic stress. This is thought to occur by disinhibition of glutamate transmission, resulting in a rapid but transient burst of glutamate, followed by an increase in BDNF release and activation of downstream signaling pathways that stimulate synapse formation. Recent work demonstrates that the rapid-acting antidepressant effects of scopolamine, a muscarinic receptor antagonist, are also associated with increased glutamate transmission and synapse formation. These findings have resulted in testing and identification of additional targets and agents that influence glutamate transmission and have rapid antidepressant actions in rodent models and in clinical trials. Together these studies have created tremendous excitement and hope for a new generation of rapid, efficacious antidepressants.

Three months of methoxetamine administration is associated with significant bladder and renal toxicity in mice

CONTEXT.: Methoxetamine is a ketamine analogue that has recently emerged as a novel psychoactive substance. Chronic ketamine use is associated with significant bladder and renal toxicity. Methoxetamine has been marketed as "bladder friendly", but there is no data to be able to substantiate this claim.

OBJECTIVE

To characterise the patterns of bladder and renal toxicity associated with 3 months of methoxetamine administration in an animal model.

MATERIALS AND METHODS

Two-month-old Institute of Cancer Research mice were administered 30 mg/kg methoxetamine intraperitoneally (n = 5) or saline (n = 3 control) for 3 months. The animals were then sacrificed and histological examination, immuno-cytochemistry using polyclonal anti-CD4 antibodies and sirius-red staining for collagen were performed.

RESULTS

The kidneys of methoxetamine-treated animals showed inflammatory cell infiltration, tubular cell necrosis and glomerular damage (1.9 ± 0.3% shrunken glomeruli in control, 9.8 ± 0.8% in methoxetamine-treated mice (p < 0.0001); 2.9 ± 0.3% tubular cell degeneration in control, 20.4 ± 1.1% in methoxetamine-treated mice (p < 0.0001)). There was a greater density of mononuclear cells in the bladder lamina propria and submucosa in methoxetamine-treated mice (43.0 ± 2.1 per 250 × 250 μm) than controls (7.1 ± 1.2 per 250 × 250 μm), p < 0.001. CD4-positive staining was seen in the bladder submucosa and lamina propria of all methoxetamine-treated mice and muscle-layer of two methoxetamine-treated mice; these changes were not seen in the control mice. There was an increase in sirius-red collagen in the bladder sub-mucosa and muscle-layer in the methoxetamine-treated mice compared with control mice.

DISCUSSION

This study has shown that 3 months of daily 30 mg/kg intra-peritoneal methoxetamine results in significant bladder and renal toxicity in mice. Changes in the bladder included inflammatory changes with subsequent fibrosis and changes in the kidney were seen at both a tubular and glomerular level. These changes are similar to those seen in comparable animal models of chronic ketamine administration. Further work is required to determine the time course of the onset of these effects and whether the effects are reversible with methoxetamine cessation.