Is persistent ketamine use a valid model of the cognitive and oculomotor deficits in schizophrenia?

Exploring ketamine's reinforcement, cue-induced reinstatement, and nucleus accumbens cFos activation in male and female long evans rats

Ketamine (KET), a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, has rapid onset of antidepressant effects in Treatment-Resistant Depression patients and repeated infusions are required to sustain its antidepressant properties. However, KET is an addictive drug, and so more preclinical and clinical research is needed to assess the safety of recurring treatments in both sexes. Thus, the aim of this study was to investigate the reinforcing properties of various doses of KET (0-, 0.125-, 0.25-, 0.5 mg/kg/infusion) and assess KET's cue-induced reinstatement and neuronal activation in both sexes of Long Evans rats. Neuronal activation was assessed using the protein expression of the immediate early gene cFos in the nucleus accumbens (Nac), an important brain area implicated in reward, reinforcement and reinstatement to most drug-related cues. Our findings show that KET has reinforcing effects in both male and female rats, albeit exclusively at the highest two doses (0.25 and 0.5 mg/kg/infusion). Furthermore, we noted sex differences, particularly at the highest dose of ketamine, with female rats displaying a higher rate of self-administration. Interestingly, all groups that self-administered KET reinstated to drug-cues. Following drug cue-induced reinstatement test in rats exposed to KET (0.25 mg/kg/infusion) or saline, there was higher cFos protein expression in KET-treated animals compared to saline controls, and higher cFos expression in the core compared to the shell subregions of the Nac. As for reinstatement, there were no notable sex differences reported for cFos expression in the Nac. These findings reveal some sex and dose dependent effects in KET's reinforcing properties and that KET at all doses induced similar reinstatement in both sexes. This study also demonstrated that cues associated with ketamine induce comparable neuronal activation in the Nac of both male and female rats. This work warrants further research into the potential addictive properties of KET, especially when administered at lower doses which are now being used in the clinic for treating various psychopathologies.

Antisaccade error rates in first-episode psychosis, ultra-high risk for psychosis and unaffected relatives of schizophrenia: A systematic review and meta-analysis

BACKGROUND

Antisaccade, which is described as looking at the opposite location of the target, is an eye movements paradigm used for assessing cognitive functions in schizophrenia. Initiation and sustainment of saccades in antisaccade are managed by frontal and parietal cortical areas. Antisaccade abnormalities are well-established findings in schizophrenia. However, studies in the early phases of psychotic disorders and clinical/familial risk for psychosis reported inconsistent findings. The current systematic review aimed to review the results of studies investigating antisaccade error rates in first-episode psychosis (FEP), individuals with ultra-high-risk for psychosis (UHRP), and familial-high-risk for psychosis (FHRP) compared to healthy controls.

METHOD

A meta-analysis of 17 studies was conducted to quantitatively review antisaccade errors in FEP, UHR-P and FHRP. The error rate (Hedges'g) was compared between the total of 860 FEP, UHRP, FHRP, and 817 healthy controls. Hedges' g for effect size, I2 for estimating the percentage of variability, and publication bias were evaluated through the R software.

RESULTS

The outcomes of this meta-analysis suggested that FEP is associated with a robust deficit in the antisaccade error rate (g = 1.16, CI = 0.95-1.38). Additionally, both the clinical and familial high-risk groups showed small but significant increases in AS errors (g = 0.26, CI = 0.02-0.52 and g = 0.34, CI = 0.13-0.55, respectively).

CONCLUSION

The large effect size estimated for FEP was compatible with previously reported results in chronic schizophrenia patients. Additionally, relatives had abnormalities with small to medium effect sizes and significant differences. The current findings suggest that antisaccade errors might be a potential endophenotype for psychotic disorders.

The Kappa Opioid Receptor and the Sleep of Reason: Cortico-Subcortical Imbalance Following Salvinorin-A

BACKGROUND

The mechanisms through which kappa opioid receptor (KOR) agonists induce psychotomimetic effects are largely unknown, although the modulation of this receptor has attracted attention for its clinical use. In this work, we characterize the neuropharmacological effects of salvinorin-A, a highly selective KOR agonist.

METHODS

Changes in multimodal electroencephalography, single-photon emission computed tomography, and subjective effects following the acute administration of salvinorin-A are reported. The study included 2 sub-studies that employed a double-blind, crossover, randomized, placebo-controlled design.

RESULTS

The electroencephalography measures showed a marked increase in delta and gamma waves and a decrease in alpha waves while subjects were under the effect of salvinorin-A. Regarding single-photon emission computed tomography measures, significant decreases in regional cerebral blood flow were detected in multiple regions of the frontal, temporal, parietal, and occipital cortices. Significant regional cerebral blood flow increases were observed in some regions of the medial temporal lobe, including the amygdala, the hippocampal gyrus, and the cerebellum. The pattern of subjective effects induced by salvinorin-A was similar to those observed in relation to other psychotomimetic drugs but with an evidently dissociative nature. No dysphoric effects were reported.

CONCLUSION

The salvinorin-A-mediated KOR agonism induced dramatic psychotomimetic effects along with a generalized decrease in cerebral blood flow and electric activity within the cerebral cortex.

Harm related to recreational ketamine use and its relevance for the clinical use of ketamine. A systematic review and comparison study

BACKGROUNDS

Ketamine is a dissociative anesthetic that is currently considered for several new indications.

AIM

To deduce the safety of long-term ketamine treatment using the harm of heavy recreational (non-medical) ketamine use as a proxy for maximal possible harm of ketamine treatment.

METHODS

Systematic literature review according to PRISMA guidelines to identify controlled studies on ketamine-related harm in heavy recreational ketamine users. Results were compared with serious adverse events (SAEs) in patients treated with ketamine according to three systematic reviews considering dosing regimen and cumulative dose.

RESULTS

The systematic search yielded 25 studies. Heavy recreational ketamine use can escalate to ketamine dependency and was often dose-dependently associated with other SAEs, including cognitive and mental disorders, and gastrointestinal and urinary tract symptoms, which disappeared upon marked reduction of ketamine use. Heavy ketamine users have a much higher cumulative exposure to ketamine than ketamine treated patients (>90 times), which may explain why SAEs in the clinical context are mostly mild and reversible and why ketamine dependence was not reported in these patients.

CONCLUSION

Treatment of patients with ketamine is not associated with ketamine dependency or SAEs. However, caution is needed since data on long-term clinical ketamine use with a long-term follow-up is lacking.

Effects of ketamine on brain function during response inhibition

INTRODUCTION

The uncompetitive N-methyl-D-aspartate (NMDA) receptor (NMDAR) antagonist ketamine has been proposed to model symptoms of psychosis. Inhibitory deficits in the schizophrenia spectrum have been reliably reported using the antisaccade task. Interestingly, although similar antisaccade deficits have been reported following ketamine in non-human primates, ketamine-induced deficits have not been observed in healthy human volunteers.

METHODS

To investigate the effects of ketamine on brain function during an antisaccade task, we conducted a double-blind, placebo-controlled, within-subjects study on n = 15 healthy males. We measured the blood oxygen level dependent (BOLD) response and eye movements during a mixed antisaccade/prosaccade task while participants received a subanesthetic dose of intravenous ketamine (target plasma level 100 ng/ml) on one occasion and placebo on the other occasion.

RESULTS

While ketamine significantly increased self-ratings of psychosis-like experiences, it did not induce antisaccade or prosaccade performance deficits. At the level of BOLD, we observed an interaction between treatment and task condition in somatosensory cortex, suggesting recruitment of additional neural resources in the antisaccade condition under NMDAR blockage.

DISCUSSION

Given the robust evidence of antisaccade deficits in schizophrenia spectrum populations, the current findings suggest that ketamine may not mimic all features of psychosis at the dose used in this study. Our findings underline the importance of a more detailed research to further understand and define effects of NMDAR hypofunction on human brain function and behavior, with a view to applying ketamine administration as a model system of psychosis. Future studies with varying doses will be of importance in this context.

The effects of ketamine and risperidone on eye movement control in healthy volunteers

The non-competitive N-methyl-D-aspartate receptor antagonist ketamine leads to transient psychosis-like symptoms and impairments in oculomotor performance in healthy volunteers. This study examined whether the adverse effects of ketamine on oculomotor performance can be reversed by the atypical antipsychotic risperidone. In this randomized double-blind, placebo-controlled study, 72 healthy participants performed smooth pursuit eye movements (SPEM), prosaccades (PS) and antisaccades (AS) while being randomly assigned to one of four drug groups (intravenous 100 ng ml(-1) ketamine, 2 mg oral risperidone, 100  ng ml(-1) ketamine plus 2 mg oral risperidone, placebo). Drug administration did not lead to harmful adverse events. Ketamine increased saccadic frequency and decreased velocity gain of SPEM (all P < 0.01) but had no significant effects on PS or AS (all P > or = 0.07). An effect of risperidone was observed for amplitude gain and peak velocity of PS and AS, indicating hypometric gain and slower velocities compared with placebo (both P < or = 0.04). No ketamine by risperidone interactions were found (all P > or = 0.26). The results confirm that the administration of ketamine produces oculomotor performance deficits similar in part to those seen in schizophrenia. The atypical antipsychotic risperidone did not reverse ketamine-induced deteriorations. These findings do not support the cognitive enhancing potential of risperidone on oculomotor biomarkers in this model system of schizophrenia and point towards the importance of developing alternative performance-enhancing compounds to optimise pharmacological treatment of schizophrenia.

Psychological effects of ketamine: a research note

Purpose

Ketamine intoxication has been mooted as a model of some of the signs and symptoms of psychosis. However, little research has focused on the self‐report experience of ketamine users. The purpose of the current study is to quantify (the frequency of occurrence of) ketamine induced phenomenology in recreational users. The paper also seeks to meaningfully group these experiences into facets and their principal components.

Design/methodology/approach

Respondents completed a checklist of experiences, the Ketamine Experiences Questionnaire (KEQ). Two samples were recruited via opportunity and snowball sampling one in 2009 (n=52) and one in 2010/11 (n=35).

Findings

The “Q‐sort” and principal component analysis (PCA) indicate that there are two factors, factor one representing aversive ketamine experiences (accounting for 48.2 per cent of the variance) and factor two representing appetitive ketamine experiences (accounting for 20.1 per cent of the variance). Ketamine induces a raft of appetitive, aversive and transcendental experiences many of which are illustrated. The data suggest that a decision about whether to continue using ketamine (and if so, how often) depends in part on an intuitive cost‐benefit analysis of the phenomenology that it induces.

Research limitations/implications

There are some notable limitations to the current study; the small sample size to variable ratio necessitated a “Q‐sort” before PCA; the sampling procedure prohibited the generation of a representative sample; and there were no means of independently verifying ketamine use.

Originality/value

This study represents a novel exploration into ketamine phenomenology and the principal components of these experiences.

Interaction of mGlu2/3 agonism with clozapine and lurasidone to restore novel object recognition in subchronic phencyclidine-treated rats

RATIONALE

Subchronic administration to rodents of the N-methyl-D-aspartate non-competitive antagonist, phencyclidine (PCP), impairs novel object recognition (NOR). Atypical antipsychotic drugs (APDs) reverse the effects of subchronic PCP on NOR. The effect of metabotropic glutamate₂/₃ receptor (mGlu₂/₃) agonists upon NOR is unknown.

OBJECTIVES AND METHODS

We tested the hypotheses that the mGlu₂/₃ agonist, LY379268, by itself, or in combination with APDs or pimavanserin, a 5-HT(2A) inverse agonist, would reverse the deficit in NOR induced by subchronic treatment with PCP (2 mg/kg, b.i.d., for 7 days).

RESULTS

The mGlu₂/₃ agonist LY379268 (1 or 3 mg/kg) did not attenuate the PCP-induced NOR deficit. However, together with sub-effective dose of the atypical APDs, clozapine (0.1 mg/kg) or lurasidone (0.03 mg/kg), but not the typical APD, haloperidol (0.1 mg/kg), or pimavanserin (3 mg/kg), LY379268, 1 mg/kg, significantly reversed the PCP-induced NOR deficit. Moreover, the effect of clozapine was blocked by the mGlu₂/₃ antagonist, LY341495 (1 mg/kg).

CONCLUSIONS

These results indicate that mGlu₂/₃ agonism can potentiate the ability of atypical, but not typical APDs, to ameliorate the effect of subchronic PCP on NOR, that mGlu₂/₃ agonism may contribute to the ability of atypical APDs to acutely reverse the effect of subchronic PCP on NOR, but that by itself, mGlu₂/₃ agonism, is ineffective in this model of cognitive impairment in schizophrenia. These results suggest that mGlu₂/₃ receptor agonism should be investigated as an adjunctive treatment of cognitive impairment in schizophrenia rather than as monotherapy, which may be effective for control of psychosis, but not for cognitive impairment.

Clair DM, Benson PJ. Atypical scanpaths in schizophrenia: evidence of a trait- or state-dependent phenomenon?

The development of trait markers of schizophrenia would represent an important advance in understanding the genetic architecture of the disease. To date, no candidate markers have satisfied all of the trait marker criteria, and many are not specific to the schizophrenia spectrum. Abnormalities in visual scanpaths are frequently reported in patients with schizophrenia and are emerging as a novel candidate for a schizophrenia biomarker. Here we review the suitability of scanpath measures as a target for trait marker research in schizophrenia. Papers reporting scanpath patterns in patients with schizophrenia were identified by PubMed and Google Scholar searches and by scanning reference lists in relevant articles. Search terms included "schizophrenia," "psychosis," "scanpath," "scan path," "fixation," "saccade" and "eye movement." Scanpath abnormalities afford impressive sensitivity and specificity and appear largely independent of psychotropic medications. Scanpaths may demonstrate some fluctuation with symptomatology and may be useful in illuminating illness state or subtypes. However, there is evidence that viewing behaviours remain atypical regardless of symptom remission and may be present in unaffected relatives of individuals with schizophrenia. This research is in its early stages, and further investigation regarding patterns of inheritance is required. Our findings support scanpath measures as a favourable topic for further investigation as a trait marker.

Glutamatergic model psychoses: prediction error, learning, and inference

Modulating glutamatergic neurotransmission induces alterations in conscious experience that mimic the symptoms of early psychotic illness. We review studies that use intravenous administration of ketamine, focusing on interindividual variability in the profundity of the ketamine experience. We will consider this individual variability within a hypothetical model of brain and cognitive function centered upon learning and inference. Within this model, the brains, neural systems, and even single neurons specify expectations about their inputs and responding to violations of those expectations with new learning that renders future inputs more predictable. We argue that ketamine temporarily deranges this ability by perturbing both the ways in which prior expectations are specified and the ways in which expectancy violations are signaled. We suggest that the former effect is predominantly mediated by NMDA blockade and the latter by augmented and inappropriate feedforward glutamatergic signaling. We suggest that the observed interindividual variability emerges from individual differences in neural circuits that normally underpin the learning and inference processes described. The exact source for that variability is uncertain, although it is likely to arise not only from genetic variation but also from subjects' previous experiences and prior learning. Furthermore, we argue that chronic, unlike acute, NMDA blockade alters the specification of expectancies more profoundly and permanently. Scrutinizing individual differences in the effects of acute and chronic ketamine administration in the context of the Bayesian brain model may generate new insights about the symptoms of psychosis; their underlying cognitive processes and neurocircuitry.

Disruption of performance in the five-choice serial reaction time task induced by administration of N-methyl-D-aspartate receptor antagonists: relevance to cognitive dysfunction in schizophrenia

Schizophrenia patients suffer from cognitive impairments that are not satisfactorily treated by currently available medications. Cognitive dysfunction in schizophrenia encompasses deficits in several cognitive modalities that can be differentially responsive to different medications and are likely to be mediated by different neurobiological substrates. Translational animal models of cognitive deficits with relevance to schizophrenia are critical for gaining insights into the mechanisms underlying these impairments and developing more effective treatments. The five-choice serial reaction time task (5-CSRTT) is a cognitive task used in rodents that allows simultaneous assessment of several cognitive modalities, including attention, response inhibition, cognitive flexibility, and processing speed. Administration of N-methyl-D-aspartate (NMDA) glutamate receptor antagonists disrupts multiple 5-CSRTT performance measures in a way that mirrors various cognitive deficits exhibited by schizophrenia patients. Some of these disruptions are partially attenuated by antipsychotic medications that exhibit partial effectiveness on cognitive dysfunction in schizophrenia, suggesting that the model has predictive validity. Examination of the effects of pharmacological manipulations on 5-CSRTT performance disruptions induced by NMDA antagonists have implicated a range of brain regions, neurotransmitter systems, and specific receptor subtypes in schizophrenia-like impairment of different cognitive modalities. Thus, disruption of 5-CSRTT performance by NMDA antagonists represents a valuable tool for exploring the neurobiological bases of cognitive dysfunction in schizophrenia.

Frontal white matter abnormalities following chronic ketamine use: a diffusion tensor imaging study

Ketamine abuse has been shown to have a deleterious impact on brain function. However, the precise mechanisms of ketamine dependence-induced pathological change remain poorly understood. Although there is evidence for white matter changes in drug abuse, the presence of white matter abnormalities in chronic ketamine users has not been studied. White matter volumes were measured using in vivo diffusion tensor magnetic resonance imaging data in 41 ketamine-dependent subjects and 44 drug-free healthy volunteers. White matter changes associated with chronic ketamine use were found in bilateral frontal and left temporoparietal cortices. There was also evidence that frontal white matter fractional anisotropy correlated with the severity of drug use (as measured by estimated total ketamine consumption). We provide direct evidence for dose-dependent abnormalities of white matter in bilateral frontal and left temporoparietal regions following chronic ketamine use. The findings suggest a microstructural basis for the changes in cognition and experience observed with prolonged ketamine use. Moreover, the similarities of these changes to those observed in chronic schizophrenia have implications for the glutamate model of this illness.

Rapid development of tolerance to sub-anaesthetic dose of ketamine: an oculomotor study in macaque monkeys

BACKGROUND

Ketamine, a non-competitive N-methyl-D: -aspartic acid antagonist, has been widely used for anaesthetic purposes. At sub-anaesthetic dosage, it induces a dissociative state similar to schizophrenia. The discovery of this effect on dissociative state has led to its use as a pharmacological model of schizophrenia and has also been responsible for its illegal use as a recreational drug. Whereas the former has provided invaluable information, the latter has demonstrated that repeated administration of ketamine induces tolerance. Surprisingly, a review of the relevant literature shows that tolerance to sub-anaesthetic doses of ketamine is largely unreported in neuropharmacological studies.

METHODS

In order to investigate this caveat, we have performed a post hoc analysis of the behavioural effects induced by repeated injections of sub-anaesthetic doses of ketamine observed in five consecutive monkeys performing two oculomotor tasks. Ketamine effects were quantified by the animals' performances and latencies in a prosaccade and an antisaccade task, two oculomotor paradigms that are impaired after ketamine administration.

RESULTS

Although the result of the initial injections confirmed a clear behavioural effect of ketamine injections in all monkeys, subsequent administrations showed that a tolerance eventually appeared in all monkeys. The profile of this tolerance exhibited however a large inter-subject variability.

CONCLUSIONS

Psychopharmacological experiments using ketamine as a pharmacological model of psychosis should therefore consider the kinetic and time course of these effects in each individuals and take them into account in the design of experimental protocols.