In vivo and ex vivo evidence for ketamine-induced hyperglutamatergic activity in the cerebral cortex of the rat: Potential relevance to schizophrenia

Microglia heterogeneity in health and disease

Microglia, the resident immune cells of the central nervous system (CNS), have received significant attention due to their critical roles in maintaining brain homeostasis and mediating cerebral immune responses. Understanding the origin of microglia has been a subject of great interest, and emerging evidence suggests that microglia consist of multiple subpopulations with unique molecular and functional characteristics. These subpopulations of microglia may exhibit specialized roles in response to different environmental cues as in disease conditions. The newfound understanding of microglial heterogeneity has significant implications for elucidating their roles in both physiological and pathological conditions. In the context of disease, microglia have been studied rigorously as they play a very important role in neuroinflammation. Dysregulated microglial activation and function contribute to chronic inflammation. Further exploration of microglial heterogeneity and their interactions with other cell types in the CNS will undoubtedly pave the way to novel therapeutic strategies targeting microglia-mediated pathologies. In this review, we discuss the latest advances in the field of microglia research, focusing specifically on the origin and subpopulations of microglia, the populations of microglia types in the brains of patients with neurodegenerative diseases, and how microglia are regulated in the healthy CNS.

Erbb4 Deletion From Inhibitory Interneurons Causes Psychosis-Relevant Neuroimaging Phenotypes

BACKGROUND AND HYPOTHESIS

Converging lines of evidence suggest that dysfunction of cortical GABAergic inhibitory interneurons is a core feature of psychosis. This dysfunction is thought to underlie neuroimaging abnormalities commonly found in patients with psychosis, particularly in the hippocampus. These include increases in resting cerebral blood flow (CBF) and glutamatergic metabolite levels, and decreases in ligand binding to GABAA α5 receptors and to the synaptic density marker synaptic vesicle glycoprotein 2A (SV2A). However, direct links between inhibitory interneuron dysfunction and these neuroimaging readouts are yet to be established. Conditional deletion of a schizophrenia susceptibility gene, the tyrosine kinase receptor Erbb4, from cortical and hippocampal inhibitory interneurons leads to synaptic defects, and behavioral and cognitive phenotypes relevant to psychosis in mice.

STUDY DESIGN

Here, we investigated how this inhibitory interneuron disruption affects hippocampal in vivo neuroimaging readouts. Adult Erbb4 conditional mutant mice (Lhx6-Cre;Erbb4F/F, n = 12) and their wild-type littermates (Erbb4F/F, n = 12) were scanned in a 9.4T magnetic resonance scanner to quantify CBF and glutamatergic metabolite levels (glutamine, glutamate, GABA). Subsequently, we assessed GABAA receptors and SV2A density using quantitative autoradiography.

RESULTS

Erbb4 mutant mice showed significantly elevated ventral hippccampus CBF and glutamine levels, and decreased SV2A density across hippocampus sub-regions compared to wild-type littermates. No significant GABAA receptor density differences were identified.

CONCLUSIONS

These findings demonstrate that specific disruption of cortical inhibitory interneurons in mice recapitulate some of the key neuroimaging findings in patients with psychosis, and link inhibitory interneuron deficits to non-invasive measures of brain function and neurochemistry that can be used across species.

Dysregulated Signaling at Postsynaptic Density: A Systematic Review and Translational Appraisal for the Pathophysiology, Clinics, and Antipsychotics' Treatment of Schizophrenia

Emerging evidence from genomics, post-mortem, and preclinical studies point to a potential dysregulation of molecular signaling at postsynaptic density (PSD) in schizophrenia pathophysiology. The PSD that identifies the archetypal asymmetric synapse is a structure of approximately 300 nm in diameter, localized behind the neuronal membrane in the glutamatergic synapse, and constituted by more than 1000 proteins, including receptors, adaptors, kinases, and scaffold proteins. Furthermore, using FASS (fluorescence-activated synaptosome sorting) techniques, glutamatergic synaptosomes were isolated at around 70 nm, where the receptors anchored to the PSD proteins can diffuse laterally along the PSD and were stabilized by scaffold proteins in nanodomains of 50-80 nm at a distance of 20-40 nm creating "nanocolumns" within the synaptic button. In this context, PSD was envisioned as a multimodal hub integrating multiple signaling-related intracellular functions. Dysfunctions of glutamate signaling have been postulated in schizophrenia, starting from the glutamate receptor's interaction with scaffolding proteins involved in the N-methyl-D-aspartate receptor (NMDAR). Despite the emerging role of PSD proteins in behavioral disorders, there is currently no systematic review that integrates preclinical and clinical findings addressing dysregulated PSD signaling and translational implications for antipsychotic treatment in the aberrant postsynaptic function context. Here we reviewed a critical appraisal of the role of dysregulated PSD proteins signaling in the pathophysiology of schizophrenia, discussing how antipsychotics may affect PSD structures and synaptic plasticity in brain regions relevant to psychosis.

Ketamine administration in idiopathic epileptic and healthy control dogs: Can we detect differences in brain metabolite response with spectroscopy?

Introduction

In recent years ketamine has increasingly become the focus of multimodal emergency management for epileptic seizures. However, little is known about the effect of ketamine on brain metabolites in epileptic patients. Magnetic resonance spectroscopy (MRS) is a non-invasive technique to estimate brain metabolites in vivo. Our aim was to measure the effect of ketamine on thalamic metabolites in idiopathic epileptic (IE) dogs using 3 Tesla MRS. We hypothesized that ketamine would increase the glutamine-glutamate (GLX)/creatine ratio in epileptic dogs with and without antiseizure drug treatment, but not in control dogs. Furthermore, we hypothesized that no different responses after ketamine administration in other measured brain metabolite ratios between the different groups would be detected.

Methods

In this controlled prospective experimental trial IE dogs with or without antiseizure drug treatment and healthy client-owned relatives of the breeds Border Collie and Greater Swiss Mountain Dog, were included. After sedation with butorphanol, induction with propofol and maintenance with sevoflurane in oxygen and air, a single voxel MRS at the level of the thalamus was performed before and 2 min after intravenous administration of 1 mg/kg ketamine. An automated data processing spectral fitting linear combination model algorithm was used to estimate all commonly measured metabolite ratios. A mixed ANOVA with the independent variables ketamine administration and group allocation was performed for all measured metabolites. A p < 0.05 was considered statistically significant.

Results

Twelve healthy control dogs, 10 untreated IE and 12 treated IE dogs were included. No significant effects for GLX/creatine were found. However, increased glucose/creatine ratios were found (p < 0.001) with no effect of group allocation. Furthermore, increases in the GABA/creatine ratio were found in IEU dogs.

Discussion

MRS was able to detect changes in metabolite/creatine ratios after intravenous administration of 1 mg/kg ketamine in dogs and no evidence was found that excitatory effects are induced in the thalamus. Although it is beyond the scope of this study to investigate the antiseizure potential of ketamine in dogs, results of this research suggest that the effect of ketamine on the brain metabolites could be dependent on the concentrations of brain metabolites before administration.

Niacin mitigates blood-brain barrier tight junctional proteins dysregulation and cerebral inflammation in ketamine rat model of psychosis: Role of GPR109A receptor

Dysregulated inflammatory responses and blood-brain barrier (BBB) dysfunction are recognized as central factors in the development of psychiatric disorders. The present study was designed to evaluate the effect of niacin on BBB integrity in ketamine-induced model of psychosis. Meanwhile, mepenzolate bromide (MPN), a GPR109A receptor blocker, was used to investigate the role of this receptor on the observed niacin's effect. Male Wistar rats received ketamine (30 mg/kg/day, i.p) for 5 consecutive days and then niacin (40 mg/kg/day, p.o), with or without MPN (5 mg/kg/day, i.p), was given for the subsequent 15 days. Three days before the end of experiment, rats were behaviorally tested using open field, novel object recognition, social interaction, and forced swimming tests. Niacin significantly ameliorated ketamine-induced behavioral deficits, amended gamma aminobutyric acid and glutamate concentration, decreased tumor necrosis factor-α and matrix metallopeptidase 9 levels, and increased netrin-1 contents in the hippocampus of rats. Niacin also augmented the hippocampal expression of ZO-1, occludin, and claudin-5 proteins, indicating the ability of niacin to restore the BBB integrity. Moreover, the histopathologic changes in hippocampal neurons were alleviated. Since all the beneficial effects of niacin in the present investigation were partially abolished by the co-administration of MPN; GPR109A receptor was proven to partially mediate the observed antipsychotic effects of niacin. These data revealed that GPR109A-mediated signaling pathways might represent potential targets for therapeutic interventions to prevent or slow the progression of psychosis.

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.

Context-Specific Tolerance and Pharmacological Changes in the Infralimbic Cortex-Nucleus Accumbens Shell Pathway Evoked by Ketamine

Like other drugs, ketamine is abused due to its ability to act as a positive reinforcer in the control of behavior, just as natural reinforcers do. Besides, through Pavlovian conditioning, tolerance to drug effects can become conditioned to specific contextual cues showing that environmental stimuli can act as powerful mediators of craving and relapse. In the present study, we shall investigate the effects of long-term ketamine administration and withdrawal on behavioral measures and emotionality, the drug-context-specific influence on the tolerance to the sedative effects of an anesthetic dose of ketamine, and the neuropharmacological events underlying this phenomenon, in rats conditioned with 10 mg/kg of ketamine and later challenged with a dose of ketamine of 80 mg/kg in a familiar and non-familiar environment. Variations in dopamine and serotonin efflux in the infralimbic cortex-nucleus accumbens shell circuitry (IL-NAcSh) was further recorded in the same conditions. Our results highlight that besides its well-known reinforcing properties, ketamine also shares the ability to induce behavioral and pharmacological conditioned tolerance, associated with increases in cortical (IL), and decreases in striatal (NAcSh) dopamine release. To our knowledge, we are presenting the first set of behavioral and neurochemical data showing that, like other drugs of abuse, ketamine can induce learned context-specific tolerance.

Reproducing the dopamine pathophysiology of schizophrenia and approaches to ameliorate it: a translational imaging study with ketamine

Patients with schizophrenia show increased striatal dopamine synthesis capacity in imaging studies. The mechanism underlying this is unclear but may be due to N-methyl-D-aspartate receptor (NMDAR) hypofunction and parvalbumin (PV) neuronal dysfunction leading to disinhibition of mesostriatal dopamine neurons. Here, we develop a translational mouse model of the dopamine pathophysiology seen in schizophrenia and test approaches to reverse the dopamine changes. Mice were treated with sub-chronic ketamine (30 mg/kg) or saline and then received in vivo positron emission tomography of striatal dopamine synthesis capacity, analogous to measures used in patients. Locomotor activity was measured using the open-field test. In vivo cell-type-specific chemogenetic approaches and pharmacological interventions were used to manipulate neuronal excitability. Immunohistochemistry and RNA sequencing were used to investigate molecular mechanisms. Sub-chronic ketamine increased striatal dopamine synthesis capacity (Cohen's d = 2.5) and locomotor activity. These effects were countered by inhibition of midbrain dopamine neurons, and by activation of PV interneurons in pre-limbic cortex and ventral subiculum of the hippocampus. Sub-chronic ketamine reduced PV expression in these cortical and hippocampal regions. Pharmacological intervention with SEP-363856, a novel psychotropic agent with agonism at trace amine receptor 1 (TAAR1) and 5-HT1A receptors but no appreciable action at dopamine D2 receptors, significantly reduced the ketamine-induced increase in dopamine synthesis capacity. These results show that sub-chronic ketamine treatment in mice mimics the dopaminergic alterations in patients with psychosis, that this requires activation of midbrain dopamine neurons, and can be ameliorated by activating PV interneurons and by a TAAR1/5-HT1A agonist. This identifies novel therapeutic approaches for targeting presynaptic dopamine dysfunction in patients with schizophrenia and effects of ketamine relevant to its therapeutic use for  treating major depression.

The potential of 1H-MRS in CNS drug development

RATIONALE

Proton magnetic resonance spectroscopy (¹H-MRS) is a cross-species neuroimaging technique that can measure concentrations of several brain metabolites, including glutamate and GABA. This non-invasive method has promise in developing centrally acting drugs, as it can be performed repeatedly within-subjects and be used to translate findings from the preclinical to clinical laboratory using the same imaging biomarker.

OBJECTIVES

This review focuses on the utility of single-voxel ¹H-MRS in developing novel glutamatergic or GABAergic drugs for the treatment of psychiatric disorders and includes research performed in rodent models, healthy volunteers and patient cohorts.

RESULTS

Overall, these studies indicate that ¹H-MRS is able to detect the predicted pharmacological effects of glutamatergic or GABAergic drugs on voxel glutamate or GABA concentrations, although there is a shortage of studies examining dose-related effects. Clinical studies have applied ¹H-MRS to better understand drug therapeutic mechanisms, including the glutamatergic effects of ketamine in depression and of acamprosate in alcohol dependence. There is an emerging interest in identifying patient subgroups with 'high' or 'low' brain regional ¹H-MRS glutamate levels for more targeted drug development, which may require ancillary biomarkers to improve the accuracy of subgroup discrimination.

CONCLUSIONS

Considerations for future research include the sensitivity of single-voxel ¹H-MRS in detecting drug effects, inter-site measurement reliability and the interpretation of drug-induced changes in ¹H-MRS metabolites relative to the known pharmacological molecular mechanisms. On-going technological development, in single-voxel ¹H-MRS and in related complementary techniques, will further support applications within CNS drug discovery.

Glutamate and GABA Homeostasis and Neurometabolism in Major Depressive Disorder

Major depressive disorder (MDD) is a leading cause of distress, disability, and suicides. As per the latest WHO report, MDD affects more than 260 million people worldwide. Despite decades of research, the underlying etiology of depression is not fully understood. Glutamate and γ-aminobutyric acid (GABA) are the major excitatory and inhibitory neurotransmitters, respectively, in the matured central nervous system. Imbalance in the levels of these neurotransmitters has been implicated in different neurological and psychiatric disorders including MDD. ¹H nuclear magnetic resonance (NMR) spectroscopy is a powerful non-invasive method to study neurometabolites homeostasis in vivo. Additionally, ¹³C-NMR spectroscopy together with an intravenous administration of non-radioactive ¹³C-labeled glucose or acetate provides a measure of neural functions. In this review, we provide an overview of NMR-based measurements of glutamate and GABA homeostasis, neurometabolic activity, and neurotransmitter cycling in MDD. Finally, we highlight the impact of recent advancements in treatment strategies against a depressive disorder that target glutamate and GABA pathways in the brain.

Serum and CSF Anti-NMDAR Antibody Testing in Psychiatry

OBJECTIVE

The authors examined and compared the clinical presentation of CSF positive and negative N-methyl-d-aspartate receptor (NMDAR) antibody.

METHODS

The investigators performed a retrospective chart review of NMDAR-antibody-positive cases (serum or CSF) involving patients presenting to psychiatric services from 2010 to 2018 in Queensland, Australia. Presentation, progress, investigations, and efficacy of treatment are detailed.

RESULTS

There were 24 serum or CSF NMDAR-antibody-positive cases and three equivocal serum results. High rates of prodromal cognitive deficits, catatonia, speech disturbance, and antipsychotic sensitivity were observed in the 16 CSF NMDAR-antibody-positive case patients and two CSF NMDAR-antibody-negative case patients, all evident before neurological deterioration with seizures, movement disorder, and autonomic disturbance occurring in the weeks following admission. The majority of these patients (N=17) were treated successfully with immunomodulatory therapy. The nine remaining patients, who were CSF NMDAR antibody negative or equivocal, did not demonstrate any of these features and improved with psychiatric care alone.

CONCLUSIONS

These findings suggest that traditional psychiatric care may be appropriate for patients with isolated psychiatric symptoms who have positive serum NMDAR testing when CSF is negative and there are no key clinical features such as cognitive deficits, catatonia, speech disturbance, and antipsychotic sensitivity. However, if these key features are present, a trial of immunomodulatory treatment should be considered with repeated examination of CSF for neuronal antibodies.

The Role of Zebrafish and Laboratory Rodents in Schizophrenia Research

Schizophrenia is a severe disorder characterized by positive, negative and cognitive symptoms, which are still not fully understood. The development of efficient antipsychotics requires animal models of a strong validity, therefore the aims of the article were to summarize the construct, face and predictive validity of schizophrenia models based on rodents and zebrafish, to compare the advantages and disadvantages of these models, and to propose future directions in schizophrenia modeling and indicate when it is reasonable to combine these models. The advantages of rodent models stem primarily from the high homology between rodent and human physiology, neurochemistry, brain morphology and circuitry. The advantages of zebrafish models stem in the high fecundity, fast development and transparency of the embryo. Disadvantages of both models originate in behavioral repertoires not allowing specific symptoms to be modeled, even when the models are combined. Especially modeling the verbal component of certain positive, negative and cognitive symptoms is currently impossible.

Assessment of Relationship of Ketamine Dose With Magnetic Resonance Spectroscopy of Glx and GABA Responses in Adults With Major Depression: A Randomized Clinical Trial

IMPORTANCE

A single subanesthetic dose of ketamine produces an antidepressant response in patients with major depressive disorder (MDD) within hours, but the mechanism of antidepressant effect is uncertain.

OBJECTIVE

To evaluate whether ketamine dose and brain glutamate and glutamine (Glx) and γ-aminobutyric acid (GABA) level responses to ketamine are related to antidepressant benefit and adverse effects.

DESIGN, SETTING, AND PARTICIPANTS

This randomized, parallel-group, triple-masked clinical trial included 38 physically healthy, psychotropic medication-free adult outpatients who were in a major depressive episode of MDD but not actively suicidal. The trial was conducted at Columbia University Medical Center. Data were collected from February 2012 to May 2015. Data analysis was conducted from January to March 2020.

INTERVENTION

Participants received 1 dose of placebo or ketamine (0.1, 0.2, 0.3, 0.4, or 0.5 mg/kg) intravenously during 40 minutes of a proton magnetic resonance spectroscopy scan that measured ventro-medial prefrontal cortex Glx and GABA levels in 13-minute data frames.

MAIN OUTCOMES AND MEASURES

Clinical improvement was measured using a 22-item version of the Hamilton Depression Rating Scale (HDRS-22) 24 hours after ketamine was administered. Ketamine and metabolite blood levels were measured after the scan.

RESULTS

A total of 38 individuals participated in the study, with a mean (SD) age of 38.6 (11.2) years, 23 (60.5%) women, and 25 (65.8%) White patients. Improvement in HDRS-22 score at 24 hours correlated positively with ketamine dose (t36 = 2.81; P = .008; slope estimate, 19.80 [95% CI, 5.49 to 34.11]) and blood level (t36 = 2.25; P = .03; slope estimate, 0.070 [95% CI, 0.007 to 0.133]). The lower the Glx response, the better the antidepressant response (t33 = -2.400; P = .02; slope estimate, -9.85 [95% CI, -18.2 to -1.50]). Although GABA levels correlated with Glx (t33 = 8.117; P < .001; slope estimate, 0.510 [95% CI, 0.382 to 0.638]), GABA response did not correlate with antidepressant effect. When both ketamine dose and Glx response were included in a mediation analysis model, ketamine dose was no longer associated with antidepressant effect, indicating that Glx response mediated the relationship. Adverse effects were related to blood levels in men only (t5 = 2.606; P = .048; estimated slope, 0.093 [95% CI, 0.001 to 0.186]), but Glx and GABA response were not related to adverse effects.

CONCLUSIONS AND RELEVANCE

In this study, intravenous ketamine dose and blood levels correlated positively with antidepressant response. The Glx response correlated inversely with ketamine dose and with antidepressant effect. Future studies are needed to determine whether the relationship between Glx level and antidepressant effect is due to glutamate or glutamine.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01558063.

Anterior Cingulate Cortex Glutamate Levels Are Related to Response to Initial Antipsychotic Treatment in Drug-Naive First-Episode Schizophrenia Patients

The glutamatergic system has previously been shown to be involved in the pathophysiology of schizophrenia and the mechanisms of action of antipsychotic treatment. The present study aimed to investigate the relationship between the levels of glutamate (Glu) or Glu/total creatine (Glu/Cr+PCr) in the anterior cingulate cortex (ACC) and psychiatric symptoms as well as the response to antipsychotic treatment. We performed proton magnetic resonance spectroscopy (¹H-MRS) to measure Glu and Glu/Cr+PCr in the ACC of 35 drug-naïve first-episode schizophrenia (FES) patients and 40 well-matched healthy controls (HCs). After scanning, we treated the patients with risperidone for eight weeks. Remission status was based on the Positive and Negative Syndrome Scale (PANSS) scores at week 8. At baseline, there were no significant differences in the levels of Glu or Glu/Cr+PCr in the ACC between drug-naïve FES patients and HCs. Lower baseline levels of Glu/Cr+PCr but not Glu in the ACC were associated with more severe negative symptoms of schizophrenia. Compared to the remission group (RM), the non-remission group (NRM) had lower baseline ACC Glu levels (P < 0.05). Our results suggest that ACC Glu levels may be related to the severity of symptoms in the early stages of schizophrenia and therefore may be a marker with which to evaluate the treatment effect of antipsychotics in schizophrenia patients.

Gallic acid prevents ketamine-induced oxidative damages in brain regions and liver of rats

INTRODUCTION

Ketamine (KET) is an anesthetic agent widely used in human and veterinary medicine. According to studies, KET is associated to direct neutorotoxic damages due to its capacity to induce oxidative stress. Because of the free radical generation in the organism and its relation with diseases' development, there is a growing interest to study antioxidant molecules, such as gallic acid (GA), a natural phenolic compound.

AIM

Evaluate the GA antioxidant potential for the prevention of oxidative damage in the brain and liver tissue of rats exposed to acute KET administration.

MATERIAL AND METHODS

32 Wistar male rats received GA (by gavage, 13.5 mg/kg) for three consecutive days, 24 h after the last GA dose, animals were anesthetized with KET (50 mg/kg, i.m.). All animals were euthanized by decapitation 60 min after KET administration. The liver, brain cortex and hippocampus were removed and homogenized for biochemical analysis.

RESULTS

In brain cortex, KET increased reactive species (RS) generation, protein carbonyls (PC) levels and reduced non-protein thiols (NPSH) levels, while GA pre-treatment reduced PC and increased NPSH levels. KET increased PC and decreased NPSH levels in the hippocampus, and GA reduced PC and NPSH levels. In the liver, no difference was observed in the RS generation, while KET induced and increase of PC levels and decreased NPSH levels, while GA pre-treatment prevented it.

CONCLUSION

GA administration can prevent oxidative damage caused by acute KET administration and minimize its noxious effects. Further studies are needed to evidence GA antioxidant properties regarding KET chronic use.

Ketamine effects on default mode network activity and vigilance: A randomized, placebo-controlled crossover simultaneous fMRI/EEG study

In resting‐state functional connectivity experiments, a steady state (of consciousness) is commonly supposed. However, recent research has shown that the resting state is a rather dynamic than a steady state. In particular, changes of vigilance appear to play a prominent role. Accordingly, it is critical to assess the state of vigilance when conducting pharmacodynamic studies with resting‐state functional magnetic resonance imaging (fMRI) using drugs that are known to affect vigilance such as (subanesthetic) ketamine. In this study, we sought to clarify whether the previously described ketamine‐induced prefrontal decrease of functional connectivity is related to diminished vigilance as assessed by electroencephalography (EEG). We conducted a randomized, double‐blind, placebo‐controlled crossover study with subanesthetic S‐Ketamine in N = 24 healthy, young subjects by simultaneous acquisition of resting‐state fMRI and EEG data. We conducted seed‐based default mode network functional connectivity and EEG power spectrum analyses. After ketamine administration, decreased functional connectivity was found in medial prefrontal cortex whereas increased connectivities were observed in intraparietal cortices. In EEG, a shift of energy to slow (delta, theta) and fast (gamma) wave frequencies was seen in the ketamine condition. Frontal connectivity is negatively related to EEG gamma and theta activity while a positive relationship is found for parietal connectivity and EEG delta power. Our results suggest a direct relationship between ketamine‐induced functional connectivity changes and the concomitant decrease of vigilance in EEG. The observed functional changes after ketamine administration may serve as surrogate end points and provide a neurophysiological framework, for example, for the antidepressant action of ketamine (trial name: 29JN1556, EudraCT Number: 2009‐012399‐28).

The effects of sub-anesthetic ketamine plus ethanol on behaviors and apoptosis in the prefrontal cortex and hippocampus of adolescent rats

Ketamine has become increasingly popular in adolescent drug abusers worldwide. Meanwhile, alcohol is usually used by ketamine users. However, little work has been conducted to examine the chronic combined effects of ketamine and ethanol on adolescent brain. Here we probed into the effects of chronic administration of ketamine at recreational doses alone or combined with ethanol on behaviors and neuron damage in an adolescent rat model. 28-day old rats were treated with either 20 or 30 mg/kg ketamine plus or not plus 10% ethanol daily for 21 days. Depressive like behaviors, anxiety like behavior and memory impairment were tested using open field test, forced swimming test, elevated plus maze and Morris water maze. Apoptosis in prefrontal cortex (PFC) and hippocampus (HIP) were determined by the TdT-mediated dUTP Nick-End Labeling (TUNEL) and protein and mRNA levels of caspase-3, Bax and Bcl-2. Results show that co-application of ketamine and ethanol significantly increased immobility time in the forced swimming test, up-regulated TUNEL positive cells and both protein and mRNA expressions of caspase-3 and Bax, compared with the control group and ketamine and ethanol use alone groups in the PFC, but not in the HIP. Our study suggests that chronic co-administration of ketamine and ethanol results in depressive-like behavior and the caspase-dependent apoptosis in the PFC of adolescent rats' brains.

Age-dependent effects of (+)-MK801 treatment on glutamate release and metabolism in the rat medial prefrontal cortex

NMDAR antagonist treatments in adolescent/young adult rodents are associated with augmented glutamate (Glu) release and perturbed Glu/glutamine (Gln) metabolism in the medial prefrontal cortex (mPFC) resembling those found in first-episode schizophrenia. Few studies, however, investigated NMDAR antagonist-induced changes in the adult mPFC and whether there is an age-dependence to this end. In this study, the effects of acute/repeated (+)-MK801 treatment on Glu release/metabolism were measured in the mPFC of male adolescent (postnatal day 30) and adult (14 weeks) rats. Acute (+)-MK801 treatment at 0.5 mg/kg body weight induced an approximately 4-fold increase of extracellular Glu concentration in the adolescent rats, and repeated treatment for 6 consecutive days significantly increased the levels of Glu + Gln (Glx) and glial metabolites 7 days after the last dose. Histologically (+)-MK801 treatments induced reactive astrocytosis and elevated oxidative stress in the mPFC of adolescent rats, without causing evident neuronal degeneration in the region. All (+)-MK801-induced changes observed in the mPFC of adolescent rats were not present or evident in the adult rats, suggesting that the treatments might have caused less disinhibition in the adult mPFC than in the adolescent mPFC. In conclusion, the effects of (+)-MK801 treatments on the Glu release/metabolism in the mPFC were found to be age-dependent; and the adult mPFC is likely equipped with more robust neurobiological mechanisms to preserve excitatory-inhibitory balance in response to NMDAR hypofunction.

Neuro-metabolite profiles of rodent models of psychiatric dysfunctions characterised by MR spectroscopy

Neuroimaging endophenotypes in animal models provide an objective and translationally-relevant alternative to cognitive/behavioral traits in human psychopathologies. Metabolic alterations, such as those involved in the glutamate-cycle, have been proposed to play a preponderant role in both depression and schizophrenia. Chronic Mild Unpredictable Stress (CMUS) and sub-chronic administration of NMDA receptor antagonist generate animal models of depression and schizophrenia, respectively. The models are based on etiologically-relevant factors related to the induction and support of these psychopathologies. To test metabolic alterations within the glutamate-cycle and in other major neurochemicals, single-voxel Magnetic Resonance Spectroscopy was recorded within the hippocampus in both rat models and control animals. Surprisingly, altered glutamate-related metabolites were observed in the CMUS model, but not NMDA-based model, as indicated by decreased glutamine and increased GABA levels. However, both models presented elevated total visible choline and inositol levels relative to controls. These results indicate the presence cell membrane metabolic alterations and inflammatory processes shared in both models, comparable to evidence presented in schizophrenia and depression and other comparable animal models. These translationally-relevant biomarkers may thus form the basis for drug-development targets in both psychopathologies.

Genetics of Alcohol Use Disorder: A Role for Induced Pluripotent Stem Cells?

Alcohol use disorder (AUD) affects millions of people and costs nearly 250 billion dollars annually. Few effective FDA-approved treatments exist, and more are needed. AUDs have a strong heritability, but only a few genes have been identified with a large effect size on disease phenotype. Genomewide association studies (GWASs) have identified common variants with low effect sizes, most of which are in noncoding regions of the genome. Animal models frequently fail to recapitulate key molecular features of neuropsychiatric disease due to the polygenic nature of the disease, partial conservation of coding regions, and significant disparity in noncoding regions. By contrast, human induced pluripotent stem cells (hiPSCs) derived from patients provide a powerful platform for evaluating genes identified by GWAS and modeling complex interactions in the human genome. hiPSCs can be differentiated into a wide variety of human cells, including neurons, glia, and hepatic cells, which are compatible with numerous functional assays and genome editing techniques. In this review, we focus on current applications and future directions of patient hiPSC-derived central nervous system cells for modeling AUDs in addition to highlighting successful applications of hiPSCs in polygenic neuropsychiatric diseases.

In Vivo Brain Glycine and Glutamate Concentrations in Patients With First-Episode Psychosis Measured by Echo Time-Averaged Proton Magnetic Resonance Spectroscopy at 4T

BACKGROUND

Accumulating evidence suggests the involvement of abnormal glutamateric neurotransmission and N-methyl-D-aspartate receptor hypofunction in the pathophysiology of psychotic disorders. The purpose of this study was to quantify in vivo glutamate (Glu) and glycine (Gly) levels in patients with first-episode psychosis as well as age-matched healthy control subjects with magnetic resonance spectroscopy (MRS).

METHODS

The subjects were 46 patients with first-episode psychosis (20 with a schizophrenia spectrum disorder, 26 with bipolar disorder) and 50 age-matched healthy control subjects. Glu and Gly levels were measured in vivo in the anterior cingulate cortex and posterior cingulate cortex of the subjects by using the echo time-averaged proton MRS technique at 4T (i.e., modified point resolved spectroscopy sequence: 24 echo time steps with 20-ms increments). Metabolite levels were quantified using LCModel with simulated basis sets.

RESULTS

Significantly higher Glu and Gly levels were found in both the anterior cingulate cortex and posterior cingulate cortex of patients with first-episode psychosis as compared with healthy control subjects. Glu and Gly levels were positively correlated in patients. Patients with a schizophrenia spectrum disorder and bipolar disorder showed similar abnormalities.

CONCLUSIONS

Our findings demonstrate abnormally elevated brain Glu and Gly levels in patients with first-episode psychosis by means of echo time-averaged proton MRS at 4T. The findings implicate dysfunction of N-methyl-D-aspartate receptor and glutamatergic neurotransmission in the pathophysiology of the acute early phase of psychotic illnesses.

The effects of ketamine on dopaminergic function: meta-analysis and review of the implications for neuropsychiatric disorders

Ketamine is a non-competitive antagonist at the N-methyl-d-aspartate receptor. It has recently been found to have antidepressant effects and is a drug of abuse, suggesting it may have dopaminergic effects. To examine the effect of ketamine on the dopamine systems, we carried out a systematic review and meta-analysis of dopamine measures in the rodent, human and primate brain following acute and chronic ketamine administration relative to a drug-free baseline or control condition. Systematic search of PubMed and PsychInfo electronic databases yielded 40 original peer-reviewed studies. There were sufficient rodent studies of the acute effects of ketamine at sub-anaesthetic doses for meta-analysis. Acute ketamine administration in rodents is associated with significantly increased dopamine levels in the cortex (Hedge's g= 1.33, P<0.01), striatum (Hedge's g=0.57, P<0.05) and the nucleus accumbens (Hedge's g=1.30, P<0.05) compared to control conditions, and 62-180% increases in dopamine neuron population activity. Sub-analysis indicated elevations were more marked in in vivo (g=1.93) than ex vivo (g=0.50) studies. There were not enough studies for meta-analysis in other brain regions studied (hippocampus, ventral pallidum and cerebellum), or of the effects of chronic ketamine administration, although consistent increases in cortical dopamine levels (from 88 to 180%) were reported in the latter studies. In contrast, no study showed an effect of anaesthetic doses (>100 mg kg^-1) of ketamine on dopamine levels ex vivo, although this remains to be tested in vivo. Findings in non-human primates and in human studies using positron emission tomography were not consistent. The studies reviewed here provide evidence that acute ketamine administration leads to dopamine release in the rodent brain. We discuss the inter-species variation in the ketamine induced dopamine release as well as the implications for understanding psychiatric disorders, in particular substance abuse, schizophrenia, and the potential antidepressant properties of ketamine, and comparisons with stimulants and other NMDA antagonists. Finally we identify future research needs.

Glutamate homeostasis in the adult rat prefrontal cortex is altered by cortical docosahexaenoic acid accrual during adolescence: An in vivo1H MRS study

Major psychiatric disorders are associated with dysregulated glutamate homeostasis and deficits in the omega-3 fatty acid docosahexaenoic acid (DHA). This study determined the effects of dietary-induced alterations in brain DHA accrual on cortical glutamate homeostasis in the adult rat brain. Adolescent rats were fed a control diet (n = 20), a n-3 fatty acid-deficient diet (DEF, n = 20), or a fish oil-fortified diet containing preformed DHA (FO, n = 20). In adulthood ¹H MRS scans were performed with voxels in the prefrontal cortex (PFC) and thalamus. Compared with controls, erythrocyte, PFC, and thalamus DHA levels were significantly lower in DEF rats and significantly higher in FO rats. In the PFC, but not the thalamus, glutamate was significantly elevated in DEF rats compared with controls and FO rats. Glutamine did not differ between groups and the glutamine/glutamate ratio was lower in DEF rats. No differences were observed for markers of excitotoxicity (NAA, GFAP), or astrocyte glutamate transporter (GLAST, GLT-1) or glutamine synthetase expression. Across diet groups, PFC DHA levels were inversely correlated with PFC glutamate levels and positively correlated with GLAST expression. Together these findings demonstrate that rat cortical DHA accrual during adolescence impacts glutamate homeostasis in the adult PFC.

Applications of high-resolution magic angle spinning MRS in biomedical studies I-cell line and animal models

High-resolution magic angle spinning (HRMAS) MRS allows for direct measurements of non-liquid tissue and cell specimens to present valuable insights into the cellular metabolisms of physiological and pathological processes. HRMAS produces high-resolution spectra comparable to those obtained from solutions of specimen extracts but without complex metabolite extraction processes, and preserves the tissue cellular structure in a form suitable for pathological examinations following spectroscopic analysis. The technique has been applied in a wide variety of biomedical and biochemical studies and become one of the major platforms of metabolomic studies. By quantifying single metabolites, metabolite ratios, or metabolic profiles in their entirety, HRMAS presents promising possibilities for diagnosis and prediction of clinical outcomes for various diseases, as well as deciphering of metabolic changes resulting from drug therapies or xenobiotic interactions. In this review, we evaluate HRMAS MRS results on animal models and cell lines reported in the literature, and present the diverse applications of the method for the understanding of pathological processes and the effectiveness of therapies, development of disease animal models, and new progress in HRMAS methodology.

Suppression of Methamphetamine Self-Administration by Ketamine Pre-treatment Is Absent in the Methylazoxymethanol (MAM) Rat Model of Schizophrenia

Ketamine may prove to be a potential candidate in treating the widespread drug addiction/substance abuse epidemic among patients with schizophrenia. Clinical studies have shown ketamine to reduce cocaine and heroin cravings. However, the use of ketamine remains controversial as it may exacerbate the symptoms of schizophrenia. Therefore, the aim of this study is to characterize the effects of ketamine on drug addiction in schizophrenia using the methylazoxymethanol (MAM) acetate rat model on operant IV methamphetamine (METH) self-administration. MAM was administered intraperitoneally (22 mg/kg) on gestational day 17. Locomotor activity test and later IV self-administration (IVSA) were then performed in the male offspring followed by a period of forced abstinence and relapse of METH taking. After reaching stable intakes in the relapse phase, ketamine (5 mg/kg) was administered intraperitoneally 30 min prior to the self-administration session. As documented previously, the MAM rats showed a lack of habituation in the locomotor activity test but developed stable maintenance of METH self-administration with no difference in operant behaviour to control animals. Results show that ketamine treatment significantly reduced the METH intake in the control animals but not in MAM animals. Ketamine effect on METH self-administration may be explained by increased glutamatergic signalling in the prefrontal cortex caused by the N-methyl-D-aspartate antagonism and disinhibition of GABA interneurons which was shown to be impaired in the MAM rats. This mechanism may at least partly explain the clinically proven anti-craving potential of ketamine and allow development of more specific anti-craving medications with fewer risks.

Superior effects of quetiapine compared with aripiprazole and iloperidone on MK-801-induced olfactory memory impairment in female mice

Cognitive dysfunction is commonly observed in schizophrenic patients and the administration of antipsychotic treatments results in different outcomes. Although the typical antipsychotic treatments, such as haloperidol, appear to be unable to improve cognition dysfunction, the atypical antipsychotic drugs (quetiapine, aripiprazole and iloperidone) exert a beneficial effect. The purpose of the current study was to investigate the effects of atypical antipsychotics on olfactory memory in mice, utilizing the social transmission of food preference (STFP) tests to evaluate the effects of drugs on MK-801-induced cognitive dysfunction. Female BALB/c mice were treated with quetiapine (5 and 10 mg/kg), aripiprazole (3 and 6 mg/kg), iloperidone (0.5 and 1 mg/kg) or MK-801 (0.1 mg/kg) alone or concurrently prior to retention sessions of STFP tests. In the STFP tests, quetiapine (10 mg/kg; P<0.05), aripiprazole (3 and 6 mg/kg; P<0.01 and P<0.001, respectively), iloperidone (0.5 and 1 mg/kg; P<0.01 and P<0.001, respectively) and MK-801 (P<0.001) significantly decreased cued/total food eaten (%). Quetiapine (5 mg/kg; P<0.05) significantly increased MK-801-induced decreases in cued/total food eaten (%), while aripiprazole and iloperidone demonstrated no significant effects. The results revealed that all of the drugs disturbed olfactory memory in the naive mice; however, only quetiapine reversed MK-801-induced memory impairment in the STFP test.

Subanesthetic ketamine decreases the incentive-motivational value of reward-related cues

The attribution of incentive-motivational value to reward-related cues contributes to cue-induced craving and relapse in addicted patients. Recently, it was demonstrated that subanesthetic ketamine increases motivation to quit and decreases cue-induced craving in cocaine-dependent individuals. Although the underlying mechanism of this effect is currently unknown, one possibility is that subanesthetic ketamine decreases the incentive-motivational value of reward-related cues. In the present study, we used a Pavlovian conditioned approach procedure to identify sign-trackers, rats that attribute incentive-motivational value to reward-related cues, and goal-trackers, rats that assign only predictive value to reward-related cues. This model is of interest because sign-trackers are more vulnerable to cue-induced reinstatement of drug-seeking behavior and will persist in this drug-seeking behavior despite adverse consequences. We tested the effect of subanesthetic ketamine on the expression of Pavlovian conditioned approach behavior and the conditioned reinforcing properties of a reward-related cue in sign- and goal-trackers. We found that subanesthetic ketamine decreased sign-tracking and increased goal-tracking behavior in sign-trackers, though it had no effect on conditioned reinforcement. These results suggest that subanesthetic ketamine may be a promising pharmacotherapy for addiction that acts by decreasing the incentive-motivational value of reward-related cues.

Effects of repeated dizocilpine treatment on glutamatergic activity in the prefrontal cortex in an animal model of schizophrenia: An in vivo proton magnetic resonance spectroscopy study at 9.4T

Repeated exposure to dizocilpine (MK-801) can be used as a model of schizophrenia that incorporates disease progression. Proton magnetic resonance spectroscopy (¹H MRS) has been widely used to investigate schizophrenia-related alterations in glutamate (Glu). The purpose of this study was to investigate metabolic alterations in the prefrontal cortex (PFC) in an animal model of schizophrenia by using in vivo ¹H MRS. Because of the spectral overlap of Glu and glutamine (Gln), high-field ¹H MRS with short echo time (TE) was used. A point-resolved spectroscopy sequence was used to measure the levels of Glu and Gln, and the brain metabolites in a volume of interest (22.5μL) located in the PFC region of rats (n=13) before and after 6days of MK-801 (0.5mg/kg) treatment. Analysis of the spectra showed that the cross-contamination of Glu and Gln can be considered to comparably low. No metabolic parameters were altered (p>0.05). However, differences in Glu and N-acetylaspartate (NAA) levels between two times were significantly correlated (p<0.01). The results showed both decreased (in 6 of the 13 rats) and increased (7 of the 13 rats) levels of Glu and NAA, which suggested that these opposite metabolic alterations reflect two stage of disease progression. The results suggest that high-field and short TE in vivo ¹H MRS can quantify Glu and Gln with reliably low level of cross-contamination and that repeated exposure to MK-801 induces the progressive development of schizophrenia.

Different dosing regimens of repeated ketamine administration have opposite effects on novelty processing in rats

Repeated exposure to sub-anesthetic doses of ketamine in rats has been shown to induce cognitive deficits, as well as behavioral changes akin to the negative symptoms of schizophrenia, giving much face validity to the use of ketamine administration as a pharmacological model of schizophrenia. This study sought to further characterize the behavioral effects of two different ketamine pre-treatment regimens, focusing primarily on the effects of repeated ketamine administration on novelty processing, a capacity that is disrupted in schizophrenia. Rats received 5 or 14 intra-peritoneal injections of 30mg/kg ketamine or saline across 5 or 7days, respectively. They were then tested in an associative mismatch detection task to examine their ability to detect novel configurations of familiar audio-visual sequences. Furthermore, rats underwent a sequential novel object and novel object location exploration task. Subsequently, rats were also tested on the delayed matching to place T-maze task, sucrose preference task and locomotor tests involving administering a challenge dose of amphetamine (AMPH). The high-dose ketamine pre-treatment regimen elicited impairments in mismatch detection and working memory. In contrast, the low-dose ketamine pre-treatment regimen improved performance of novelty detection. In addition, low-dose ketamine pre-treated rats showed locomotor sensitization following an AMPH challenge, while the high-dose ketamine pre-treated rats showed an attenuated locomotor response to AMPH, compared to control rats. These findings demonstrate that different regimens of repeated ketamine administration induce alterations in novelty processing in opposite directions, and that differential neural adaptations occurring in the mesolimbic dopamine system may underlie these effects.

Role of the NMDA receptor GluN2D subunit in the expression of ketamine-induced behavioral sensitization and region-specific activation of neuronal nitric oxide synthase

The present study aimed to investigate the involvement of the NMDA receptor (NMDAR) and/or nitric oxide (NO) pathway in ketamine-induced behavioral sensitization. Mice received repeated subcutaneous administration of ketamine (25mg/kg), once daily or once weekly for a total of five doses. Even three administrations of ketamine, daily or weekly, induced a rapid increase in locomotor activity in wild-type (WT), but not in GluN2D knockout (GluN2D-KO) mice. Furthermore, for WT mice receiving daily ketamine, elevated locomotor activity was maintained after a 1-month withdrawal period; however, this was not the case when ketamine was administered weekly. The effect of acute ketamine on nNOS activities was estimated with nicotinamide adenine dinucleotide hydrogen phosphate-diaphorase (NADPH-d) histochemistry. Ketamine rapidly increased the number of NADPH-d activated cells and strongly stained dendrites in the dorsal striatum and prefrontal cortex of WT mice, but not GluN2D-KO mice. These results suggest that ketamine-induced locomotor sensitization and nNOS activation in the frontal cortex-striatum neuronal circuit are positively correlated and that the NMDAR GluN2D subunit plays an important role in the acquisition and maintenance of ketamine-induced behavioral sensitization.

Ketamine Dysregulates the Amplitude and Connectivity of High-Frequency Oscillations in Cortical-Subcortical Networks in Humans: Evidence From Resting-State Magnetoencephalography-Recordings

Hypofunctioning of the N-methyl-D-aspartate receptor (NMDA-R) has been prominently implicated in the pathophysiology of schizophrenia (ScZ). The current study tested the effects of ketamine, a dissociative anesthetic and NMDA-R antagonist, on resting-state activity recorded with magnetoencephalography (MEG) in healthy volunteers. In a single-blind cross-over design, each participant (n = 12) received, on 2 different sessions, a subanesthetic dose of S-ketamine (0.006 mg/Kg) and saline injection. MEG-data were analyzed at sensor- and source-level in the beta (13-30 Hz) and gamma (30-90 Hz) frequency ranges. In addition, connectivity analysis at source-level was performed using transfer entropy (TE). Ketamine increased gamma-power while beta-band activity was decreased. Specifically, elevated 30-90 Hz activity was pronounced in subcortical (thalamus and hippocampus) and cortical (frontal and temporal cortex) regions, whilst reductions in beta-band power were localized to the precuneus, cerebellum, anterior cingulate, temporal and visual cortex. TE analysis demonstrated increased information transfer in a thalamo-cortical network after ketamine administration. The findings are consistent with the pronounced dysregulation of high-frequency oscillations following the inhibition of NMDA-R in animal models of ScZ as well as with evidence from electroencephalogram-data in ScZ-patients and increased functional connectivity during early illness stages. Moreover, our data highlight the potential contribution of thalamo-cortical connectivity patterns towards ketamine-induced neuronal dysregulation, which may be relevant for the understanding of ScZ as a disorder of disinhibition of neural circuits.

Chronic social isolation decreases glutamate and glutamine levels and induces oxidative stress in the rat hippocampus

Social isolation (SI) rearing of rodents is a developmental manipulation, which is commonly compared with the psychological stressors in humans as it produces several behavioral outcomes similar to those observed in humans with early life stress. To explain the SI-induced behavioral outcomes, animal studies have been performed to examine the dopaminergic and glutamatergic systems in the brain. In this study, we measured possible changes in levels of glutamate and glutamine of SI-rats using proton magnetic resonance spectroscopy. We also assessed the oxidative stress parameters in certain brain regions to see if glutamate and/or glutamine changes, if any, are associated with oxidative stress. SI rearing for 8 weeks decreased the activities of antioxidant enzymes catalase, glutathione peroxidase, superoxide dismutase, and the total antioxidant capacity, but increased levels of hydrogen peroxide, in certain brain regions, of which prefrontal cortex and hippocampus were most vulnerable. It also decreased levels of glutamate, glutamine, N-acetyl-l-aspartate (NAA), and phosphocreatine in the dorsal hippocampus, but not in the cerebral cortex. Decreased phosphocreatine and NAA indicate energy metabolism deficit in brain cells; the latter also suggests the neuronal viability was inhibited. Decreased glutamate and glutamine may suggest the neuron-glial integrity was implicated by chronic SI. These neurochemical and biochemical changes may contribute to the SI-induced behavioral abnormalities including a high level of anxiety, social interaction deficit, and impaired spatial working memory shown in this study.

Glutamate and dopamine in schizophrenia: an update for the 21st century

The glutamate and dopamine hypotheses are leading theories of the pathoaetiology of schizophrenia. Both were initially based on indirect evidence from pharmacological studies supported by post-mortem findings, but have since been substantially advanced by new lines of evidence from in vivo imaging studies. This review provides an update on the latest findings on dopamine and glutamate abnormalities in schizophrenia, focusing on in vivo neuroimaging studies in patients and clinical high-risk groups, and considers their implications for understanding the biology and treatment of schizophrenia. These findings have refined both the dopamine and glutamate hypotheses, enabling greater anatomical and functional specificity, and have been complemented by preclinical evidence showing how the risk factors for schizophrenia impact on the dopamine and glutamate systems. The implications of this new evidence for understanding the development and treatment of schizophrenia are considered, and the gaps in current knowledge highlighted. Finally, the evidence for an integrated model of the interactions between the glutamate and dopamine systems is reviewed, and future directions discussed.

Application of cross-species PET imaging to assess neurotransmitter release in brain

RATIONALE

This review attempts to summarize the current status in relation to the use of positron emission tomography (PET) imaging in the assessment of synaptic concentrations of endogenous mediators in the living brain.

OBJECTIVES

Although PET radioligands are now available for more than 40 CNS targets, at the initiation of the Innovative Medicines Initiative (IMI) "Novel Methods leading to New Medications in Depression and Schizophrenia" (NEWMEDS) in 2009, PET radioligands sensitive to an endogenous neurotransmitter were only validated for dopamine. NEWMEDS work-package 5, "Cross-species and neurochemical imaging (PET) methods for drug discovery", commenced with a focus on developing methods enabling assessment of changes in extracellular concentrations of serotonin and noradrenaline in the brain.

RESULTS

Sharing the workload across institutions, we utilized in vitro techniques with cells and tissues, in vivo receptor binding and microdialysis techniques in rodents, and in vivo PET imaging in non-human primates and humans. Here, we discuss these efforts and review other recently published reports on the use of radioligands to assess changes in endogenous levels of dopamine, serotonin, noradrenaline, γ-aminobutyric acid, glutamate, acetylcholine, and opioid peptides. The emphasis is on assessment of the availability of appropriate translational tools (PET radioligands, pharmacological challenge agents) and on studies in non-human primates and human subjects, as well as current challenges and future directions.

CONCLUSIONS

PET imaging directed at investigating changes in endogenous neurochemicals, including the work done in NEWMEDS, have highlighted an opportunity to further extend the capability and application of this technology in drug development.

Neurochemical changes observed by in vivo proton magnetic resonance spectroscopy in the mouse brain postadministration of scopolamine

RATIONALE AND OBJECTIVES

This study is aimed at investigating neurochemical changes in scopolamine (SCP)-induced memory impairment using spatially localized in vivo magnetic resonance spectroscopy (MRS) of the hippocampus.

MATERIALS AND METHODS

Four groups of mice (eight mice per group) were scanned after the injection of different SCP doses: 0, 1, 3, and 5 mg/kg (intraperitoneally). All the animals received (1)H MRS of their hippocampus at two time intervals: 30 minutes and 72 hours after SCP injection.

RESULTS

This work demonstrated that the doses of 3 mg/kg SCP or higher reduce the concentration of total choline-containing compounds, and these levels returned to baseline after 72 hours. These results are consistent with observations made by others using more invasive brain dialysis approaches. The levels of glutamate and glutamic compounds (glutamate + glutamine) were slightly changed at 3 and 5 mg/kg SCP dose, but the differences were not statistically significant (P > .05). These findings suggest that SCP produces transient, in vivo measurable alterations in the cholinergic system in the hippocampus.

CONCLUSIONS

On this basis, we conclude that in vivo MRS is a feasible noninvasive method to probe aspects of the alterations induced by SCP in the cholinergic neurotransmission pathways in both animal models and human studies of memory impairment.

In vivo neurometabolic profiling to characterize the effects of social isolation and ketamine-induced NMDA antagonism: a rodent study at 7.0 T

Continued efforts are undertaken to develop animal models of schizophrenia with translational value in the quest for much needed novel drugs. Existing models mimic specific neurobiological aspects of schizophrenia, but not its full complexity. Here, we used proton magnetic resonance spectroscopy ((1)H-MRS) to assess the metabolic profile in the prefrontal cortex (PFC) of two established models, rearing in social isolation and acute N-methyl-D-aspartate receptor (NMDA-R) antagonism and their combination. Rats reared in social isolation or group housed underwent (1)H-MRS at baseline and dynamically after ketamine challenge (25mg/kg, intraperitoneal) under isoflurane anesthesia. A 7 T animal scanner was used to perform spectra acquisition from the anterior cingulate/medial PFC. LCModel was used for metabolite quantification and effects of rearing and ketamine injection were analyzed. Social isolation did not lead to significant differences in the metabolic profile of the PFC at baseline. Ketamine induced a significant increase in glutamine in both groups with significance specifically reached by the group-housed animals alone. Only rats reared in social isolation showed a significant 11% γ-aminobutyric acid (GABA) decrease. This study provides preliminary evidence that social interactions in early life predict the glutamatergic and GABAergic response to acute NMDA-R blockade. The similarity between the prefrontal GABA reduction in patients with schizophrenia and in rats reared as social isolates after challenge with ketamine suggests good potential translational value of this combined animal model for drug development.

Glutamate, N-acetyl aspartate and psychotic symptoms in chronic ketamine users

RATIONALE

Ketamine, a non-competitive NMDA receptor antagonist, induces acute effects resembling the positive, negative and cognitive symptoms of schizophrenia. Chronic use has been suggested to lead to persistent schizophrenia-like neurobiological changes.

OBJECTIVES

This study aims to test the hypothesis that chronic ketamine users have changes in brain neurochemistry and increased subthreshold psychotic symptoms compared to matched poly-drug users.

METHODS

Fifteen ketamine users and 13 poly-drug users were included in the study. Psychopathology was assessed using the Comprehensive Assessment of At-Risk Mental State. Creatine-scaled glutamate (Glu/Cr), glutamate + glutamine (Glu + Gln/Cr) and N-acetyl aspartate (NAA/Cr) were measured in three brain regions-anterior cingulate, left thalamus and left medial temporal cortex using proton magnetic resonance spectroscopy.

RESULTS

Chronic ketamine users had higher levels of subthreshold psychotic symptoms (p < 0.005, Cohen's d = 1.48) and lower thalamic NAA/Cr (p < 0.01, d = 1.17) compared to non-users. There were no differences in medial temporal cortex or anterior cingulate NAA/Cr or in Glu/Cr or Glu + Gln/Cr in any brain region between the two groups. In chronic ketamine users, CAARMS severity of abnormal perceptions was directly correlated with anterior cingulate Glu/Cr (p < 0.05, r = 0.61-uncorrected), but NAA/Cr was not related to any measures of psychopathology.

CONCLUSIONS

The finding of lower thalamic NAA/Cr in chronic ketamine users may be secondary to the effects of ketamine use compared to other drugs of abuse and resembles previous reports in individuals at genetic or clinical risk of schizophrenia.

Reviewing the ketamine model for schizophrenia

The observation that antagonists of the N-methyl-D-aspartate receptor (NMDAR), such as phencyclidine (PCP) and ketamine, transiently induce symptoms of acute schizophrenia had led to a paradigm shift from dopaminergic to glutamatergic dysfunction in pharmacological models of schizophrenia. The glutamate hypothesis can explain negative and cognitive symptoms of schizophrenia better than the dopamine hypothesis, and has the potential to explain dopamine dysfunction itself. The pharmacological and psychomimetic effects of ketamine, which is safer for human subjects than phencyclidine, are herein reviewed. Ketamine binds to a variety of receptors, but principally acts at the NMDAR, and convergent genetic and molecular evidence point to NMDAR hypofunction in schizophrenia. Furthermore, NMDAR hypofunction can explain connectional and oscillatory abnormalities in schizophrenia in terms of both weakened excitation of inhibitory γ-aminobutyric acidergic (GABAergic) interneurons that synchronize cortical networks and disinhibition of principal cells. Individuals with prenatal NMDAR aberrations might experience the onset of schizophrenia towards the completion of synaptic pruning in adolescence, when network connectivity drops below a critical value. We conclude that ketamine challenge is useful for studying the positive, negative, and cognitive symptoms, dopaminergic and GABAergic dysfunction, age of onset, functional dysconnectivity, and abnormal cortical oscillations observed in acute schizophrenia.

Relationship between Glutamate Dysfunction and Symptoms and Cognitive Function in Psychosis

The glutamate hypothesis of schizophrenia, proposed over two decades ago, originated following the observation that administration of drugs that block NMDA glutamate receptors, such as ketamine, could induce schizophrenia-like symptoms. Since then, this hypothesis has been extended to describe how glutamate abnormalities may disturb brain function and underpin psychotic symptoms and cognitive impairments. The glutamatergic system is now a major focus for the development of new compounds in schizophrenia. Relationships between regional brain glutamate function and symptom severity can be investigated using proton magnetic resonance spectroscopy (1H-MRS) to estimate levels of glutamatergic metabolites in vivo. Here we briefly review the 1H-MRS studies that have explored relationships between glutamatergic metabolites, symptoms, and cognitive function in clinical samples. While some of these studies suggest that more severe symptoms may be associated with elevated glutamatergic function in the anterior cingulate, studies in larger patient samples selected on the basis of symptom severity are required.

Proton magnetic resonance spectroscopy measures related to short-term symptomatic outcome in chronic schizophrenia

INTRODUCTION

Proton magnetic resonance spectroscopy (¹H MRS) enables the evaluation of in vivo brain function. The purpose of the study was to compare ¹H MRS measurements in schizophrenic patients, who were clinical responders after short-term antipsychotic treatment, with non-responders and healthy controls.

METHODS

We investigated a group of 47 patients diagnosed with schizophrenia. Patients were examined twice--once after a period of at least 7 days without neuroleptics and the second time at least 4 weeks after therapy with stable doses of medication. The follow-up was available in 42 patients. Baseline MRS measurements of clinical responders were compared with non-responders and the group of healthy controls (N=26). We assessed the following metabolite ratios: NAA (N-acetylaspartate), Glx (complex of GABA, glutamine and glutamate), Cho (choline) and mI (myo-inositol) to creatinine (Cr) in the left frontal and temporal lobes and the thalamus.

RESULTS

Responders showed a significantly lower baseline frontal Glx/Cr level than non-responders. Both groups had a significantly lower NAA/Cr ratio in the frontal lobe than the controls, but only non-responders had a significantly lower NAA/Cr ratio in the thalamus.

CONCLUSIONS

Our results confirm the relationship between the glutamatergic system and pathophysiology of schizophrenia and suggest a significant value of ¹H MRS examination in the assessment of the future treatment effect.

Ketamine as a fast acting antidepressant: current knowledge and open questions

Several recent studies have shown that a single intravenous subanesthetic dose of ketamine, a NMDA receptor antagonist, exerts rapid antidepressant effects in patients with treatment refractory mood disorders and reduces suicidal ideation. Those insights have fueled tremendous excitement in the efforts to elucidate the mechanism underlying ketamine's antidepressant properties in animal models of depression, as well as in humans through the use of brain imaging as well as peripheral blood measurements. For example, there is emerging evidence that ketamine's antidepressant properties rely on increasing AMPA signaling and rapidly inducing synaptogenesis. While pilot clinical studies are promising, a number of critical questions still remain unanswered. They relate to the safe and effective use of ketamine in patients with mood disorders regarding the optimal dose range, modality and method of administration for acute and long-term maintenance of effect, and the biomarkers associated with response/nonresponse. In this review article, we first summarize the clinical evidence about the use of ketamine in mood disorders, as well as preclinical and humans studies which investigated the mechanisms of action of ketamine, and predictors of antidepressant response in clinical populations. We then provide a critical overview of the knowledge gaps about the use of ketamine in depression and suggest some future research directions for the investigation of ketamine as a promising tool to develop novel more effective and fast acting antidepressants.

Quantitative assessment of neurochemical changes in a rat model of long-term alcohol consumption as detected by in vivo and ex vivo proton nuclear magnetic resonance spectroscopy

The aim of present study was to quantitatively investigate the neurochemical profile of the frontal cortex region in a rat model of long-term alcohol consumption, by using in vivo proton magnetic resonance spectroscopy ((1)H-MRS) at 4.7 T and ex vivo(1)H high-resolution magic angle spinning (HR-MAS) technique at 11.7 T. Twenty male rats were divided into two groups and fed a liquid diet for 10 weeks. After 10 weeks, in vivo(1)H MRS spectra were acquired from the frontal cortex brain region. After in vivo(1)H MRS experiments, all animals were sacrificed and 20 frontal cortex tissue samples were harvested. All tissue examinations were performed with the 11.7 T HR-MAS spectrometer and high-resolution spectra were acquired. The in vivo and ex vivo spectra were quantified as absolute metabolite concentrations and normalized ratios of total signal-intensity (i.e., metabolitesNorm), respectively. The absolute quantifications of in vivo spectra showed significantly higher glycerophosphocholine plus phosphocholine (GPC+PCh) and lower myo-inositol (mIns) concentrations in ethanol-treated rats compared to controls. The quantifications of ex vivo spectra showed significantly higher PChNorm, ChoNorm and tChoNorm, and lower GPCNorm and mInsNorm ratio levels in ethanol-treated rats compared to controls. Our findings suggest that reduced mIns concentrations caused by the long-term alcohol consumption may lead to hypo-osmolarity syndrome and astrocyte hyponatremia. In addition, increased choline-containing compound concentrations may reflect an increased cell turnover rate of phosphatidylcholine and other phospholipids, indicating an adaptive mechanism. Therefore, these results might be utilized as key markers in chronic alcohol intoxication metabolism.

Associative blocking to reward-predicting cues is attenuated in ketamine users but can be modulated by images associated with drug use

RATIONALE

Blocking is an associative learning process that is attenuated in schizophrenia, can be modulated by cue salience and is accompanied by changes in selective attention. Repeated exposure to ketamine can model aspects of schizophrenia, and frequent users selectively attend to images of the drug.

OBJECTIVES

This study aimed to establish whether (1) ketamine users show attenuated blocking to reward-predicting cues and (2) drug cues can modulate blocking and cause overshadowing of neutral cues that are equally predictive of reward in these individuals.

METHODS

Ketamine users (n = 18) and polydrug controls (n = 16) were assessed on the Drug Cue Reward Prediction Error Task, which indexes blocking and overshadowing to neutral and drug-related cues following Pavlovian reward conditioning. Schizotypy, depression, drug history and ketamine dependence were also assessed.

RESULTS

Compared to controls, ketamine users showed elevated delusional, schizotypal and depressive symptoms, and a reduction in blocking as evidenced by higher accuracy to blocked cues. Drug-related cues were resistant to blocking and seen as more important for earning money by ketamine users compared to controls. Both groups showed overshadowing of neutral cues by drug cues, and ketamine users gave both of these cues higher importance ratings than controls.

CONCLUSIONS

These findings provide the first evidence that (1) glutamatergic perturbation is linked to a reduction in blocking and (2) blocking can be modulated by the presence of drug-related cues. The ability of drug cues to bias selective learning about 'alternative rewards' has implications for contingency management based addiction treatments.

Preclinical (1)H-MRS neurochemical profiling in neurological and psychiatric disorders

The ongoing development of animal models of neurological and psychiatric disorders in combination with the development of advanced nuclear magnetic resonance (NMR) techniques and instrumentation has led to increased use of in vivo proton NMR spectroscopy ((1)H-MRS) for neurochemical analyses. (1)H-MRS is one of only a few analytical methods that can assay in vivo and longitudinal neurochemical changes associated with neurological and psychiatric diseases, with the added advantage of being a technique that can be utilized in both preclinical and clinical studies. In this review, recent progress in the use of (1)H-MRS to investigate animal models of neurological and psychiatric disorders is summarized with examples from the literature and our own work.

Altered neurochemical profile in the McGill-R-Thy1-APP rat model of Alzheimer's disease: a longitudinal in vivo 1 H MRS study

We investigated metabolite levels during the progression of pathology in McGill-R-Thy1-APP rats, a transgenic animal model of Alzheimer's disease, and in healthy age-matched controls. Rats were subjected to in vivo (1) H magnetic resonance spectroscopy (MRS) of the dorsal hippocampus at age 3, 9 and 12 months and of frontal cortex at 9 and 12 months. At 3 months, a stage in which only Aβ oligomers are present, lower glutamate, myo-inositol and total choline content were apparent in McGill-R-Thy1-APP rats. At age 9 months, lower levels of glutamate, GABA, N-acetylaspartate and total choline and elevated myo-inositol and taurine were found in dorsal hippocampus, whereas lower levels of glutamate, GABA, glutamine and N-acetylaspartate were found in frontal cortex. At age 12 months, only the taurine level was significantly different in dorsal hippocampus, whereas taurine, myo-inositol, N-acetylaspartate and total creatine levels were significantly higher in frontal cortex. McGill-R-Thy1-APP rats did not show the same changes in metabolite levels with age as displayed in the controls, and overall, prominent and complex metabolite differences were evident in this transgenic rat model of Alzheimer's disease. The findings also demonstrate that in vivo (1) H MRS is a powerful tool to investigate disease-related metabolite changes in the brain.

Glutamate carboxypeptidase II and folate deficiencies result in reciprocal protection against cognitive and social deficits in mice: implications for neurodevelopmental disorders

Interactions between genetic and environmental risk factors underlie a number of neuropsychiatric disorders, including schizophrenia (SZ) and autism (AD). Due to the complexity and multitude of the genetic and environmental factors attributed to these disorders, recent research strategies focus on elucidating the common molecular pathways through which these multiple risk factors may function. In this study, we examine the combined effects of a haplo-insufficiency of glutamate carboxypeptidase II (GCPII) and dietary folic acid deficiency. In addition to serving as a neuropeptidase, GCPII catalyzes the absorption of folate. GCPII and folate depletion interact within the one-carbon metabolic pathway and/or of modulate the glutamatergic system. Four groups of mice were tested: wild-type, GCPII hypomorphs, and wild-types and GCPII hypomorphs both fed a folate deficient diet. Due to sex differences in the prevalence of SZ and AD, both male and female mice were assessed on a number of behavioral tasks including locomotor activity, rotorod, social interaction, prepulse inhibition, and spatial memory. Wild-type mice of both sexes fed a folic acid deficient diet showed motor coordination impairments and cognitive deficits, while social interactions were decreased only in males. GCPII mutant mice of both sexes also exhibited reduced social propensities. In contrast, all folate-depleted GCPII hypomorphs performed similarly to untreated wild-type mice, suggesting that reduced GCPII expression and folate deficiency are mutually protective. Analyses of folate and neurometabolite levels associated with glutamatergic function suggest several potential mechanisms through which GCPII and folate may be interacting to create this protective effect.

Ketamine decreases resting state functional network connectivity in healthy subjects: implications for antidepressant drug action

Increasing preclinical and clinical evidence underscores the strong and rapid antidepressant properties of the glutamate-modulating NMDA receptor antagonist ketamine. Targeting the glutamatergic system might thus provide a novel molecular strategy for antidepressant treatment. Since glutamate is the most abundant and major excitatory neurotransmitter in the brain, pathophysiological changes in glutamatergic signaling are likely to affect neurobehavioral plasticity, information processing and large-scale changes in functional brain connectivity underlying certain symptoms of major depressive disorder. Using resting state functional magnetic resonance imaging (rsfMRI), the „dorsal nexus “(DN) was recently identified as a bilateral dorsal medial prefrontal cortex region showing dramatically increased depression-associated functional connectivity with large portions of a cognitive control network (CCN), the default mode network (DMN), and a rostral affective network (AN). Hence, Sheline and colleagues (2010) proposed that reducing increased connectivity of the DN might play a critical role in reducing depression symptomatology and thus represent a potential therapy target for affective disorders. Here, using a randomized, placebo-controlled, double-blind, crossover rsfMRI challenge in healthy subjects we demonstrate that ketamine decreases functional connectivity of the DMN to the DN and to the pregenual anterior cingulate (PACC) and medioprefrontal cortex (MPFC) via its representative hub, the posterior cingulate cortex (PCC). These findings in healthy subjects may serve as a model to elucidate potential biomechanisms that are addressed by successful treatment of major depression. This notion is further supported by the temporal overlap of our observation of subacute functional network modulation after 24 hours with the peak of efficacy following an intravenous ketamine administration in treatment-resistant depression.