Capturing the angel in "angel dust": twenty years of translational neuroscience studies of NMDA receptor antagonists in animals and humans

Copy number deletion of PLA2G4A affects the susceptibility and clinical phenotypes of schizophrenia

Phospholipase A2(PLA2) superfamily is recognized as being involved in the pathogenesis of schizophrenia by affecting lipid homeostasis in cell membranes. We hypothesized that PLA2 gene copy number variation (CNV) may affect PLA2 enzyme expression and be associated with schizophrenia risk. This study indicated that in the discovery stage, an increased copy number of PLA2G6 and the deletion of PLA2G3, PLA2G4A, PLA2G4F and PLA2G12F was associated with increased risk of schizophrenia. CNV segments involving six PLA2 genes were detected in publicly available datasets, including two deletion segments specific to the PLA2G4A gene. The relationship between the deletion of PLA2G4A and susceptibility to schizophrenia was then reaffirmed in the validation group of 806 individuals. There was a significant correlation between PLA2G4A deletion and the symptoms of poverty of thought in male patients and erotomanic delusion in females. Furthermore, ELISA results demonstrate a significant decrease in peripheral blood cytosolic PLA2(cPLA2) levels in patients with the PLA2G4A deletion genotype compared to those with normal and copy number duplicate genotypes. These data suggest that the functional copy number deletion in the PLA2G4A gene is associated with the risk of schizophrenia and clinical phenotypes by reducing the expression of cPLA2, which may be an indicator of susceptibility to schizophrenia.

New drug treatments for schizophrenia: a review of approaches to target circuit dysfunction

Schizophrenia is a leading cause of global disease burden. Current drug treatments are associated with significant side-effects and have limited efficacy for many patients; highlighting the need to develop new approaches that target other aspects of the neurobiology of schizophrenia. Preclinical, in vivo imaging, post-mortem, genetic and pharmacological studies have highlighted the key role of cortical GABA-glutamatergic microcircuits and their projections to subcortical dopaminergic circuits in the pathoetiology of negative, cognitive and psychotic symptoms. Antipsychotics primarily act downstream of the dopaminergic component of this circuit. However, multiple drugs are currently in development that could target other elements of this circuit to treat schizophrenia. These include drugs for GABA or glutamatergic targets, including glycine transporters, d-amino acid oxidase, sodium channels or potassium channels. Other drugs in development are likely to primarily act on pathways that regulate the dopaminergic system such as muscarinic or trace amine receptors or serotonin 2A receptors, whilst phosphodiesterase 10 A inhibitors are being developed to modulate the downstream consequences of dopaminergic dysfunction. Our review considers where new drugs may act on this circuit and their latest clinical trial evidence in terms of indication, efficacy and side-effects. Limitations of the circuit model, including whether there are neurobiologically distinct subgroups of patients, and future directions are also considered. Several drugs based on the mechanisms reviewed have promising clinical data, with the muscarinic agonist KarXT most advanced. If they are approved for clinical use, they have the potential to revolutionise understanding of the pathophysiology and treatment of schizophrenia.

Exploring causal mechanisms of psychosis risk

Robust epidemiological evidence of risk and protective factors for psychosis is essential to inform preventive interventions. Previous evidence syntheses have classified these risk and protective factors according to their strength of association with psychosis. In this critical review we appraise the distinct and overlapping mechanisms of 25 key environmental risk factors for psychosis, and link these to mechanistic pathways that may contribute to neurochemical alterations hypothesised to underlie psychotic symptoms. We then discuss the implications of our findings for future research, specifically considering interactions between factors, exploring universal and subgroup-specific factors, improving understanding of temporality and risk dynamics, standardising operationalisation and measurement of risk and protective factors, and developing preventive interventions targeting risk and protective factors.

Parvalbumin interneuron deficits in schizophrenia

Parvalbumin-expressing (PV+) interneurons represent one of the most abundant subclasses of cortical interneurons. Owing to their specific electrophysiological and synaptic properties, PV+ interneurons are essential for gating and pacing the activity of excitatory neurons. In particular, PV+ interneurons are critically involved in generating and maintaining cortical rhythms in the gamma frequency, which are essential for complex cognitive functions. Deficits in PV+ interneurons have been frequently reported in postmortem studies of schizophrenia patients, and alterations in gamma oscillations are a prominent electrophysiological feature of the disease. Here, I summarise the main features of PV+ interneurons and review clinical and preclinical studies linking the developmental dysfunction of cortical PV+ interneurons with the pathophysiology of schizophrenia.

P300 in schizophrenia: Then and now

The 1965 discovery of the P300 component of the electroencephalography (EEG)-based event-related potential (ERP), along with the subsequent identification of its alteration in people with schizophrenia, initiated over 50 years of P300 research in schizophrenia. Here, we review what we now know about P300 in schizophrenia after nearly six decades of research. We describe recent efforts to expand our understanding of P300 beyond its sensitivity to schizophrenia itself to its potential role as a biomarker of risk for psychosis or a heritable endophenotype that bridges genetic risk and psychosis phenomenology. We also highlight efforts to move beyond a syndrome-based approach to understand P300 within the context of the clinical, cognitive, and presumed pathophysiological heterogeneity among people diagnosed with schizophrenia. Finally, we describe several recent approaches that extend beyond measuring the traditional P300 ERP component in people with schizophrenia, including time-frequency analyses and pharmacological challenge studies, that may help to clarify specific cognitive mechanisms that are disrupted in schizophrenia. Moreover, we discuss several promising areas for future research, including studies of animal models that can be used for treatment development.

Mismatch Negativity and Theta Oscillations Evoked by Auditory Deviance in Early Schizophrenia

BACKGROUND

Amplitude reduction of mismatch negativity (MMN), an event-related potential component indexing NMDA receptor-dependent auditory echoic memory and predictive coding, is widely replicated in schizophrenia. Time-frequency analyses of single-trial electroencephalography epochs suggest that theta oscillation abnormalities underlie MMN deficits in schizophrenia. However, this has received less attention in early schizophrenia (ESZ).

METHODS

Patients with ESZ (n = 89), within 5 years of illness onset, and healthy control subjects (n = 105) completed an electroencephalography MMN paradigm (duration-deviant, pitch-deviant, duration + pitch double-deviant). Repeated measures analyses of variance assessed group differences in MMN, theta intertrial phase coherence (ITC), and theta total power from frontocentral electrodes, after normal age adjustment. Group differences were retested after covarying MMN and theta measures.

RESULTS

Relative to healthy control subjects, patients with ESZ showed auditory deviance deficits. Patients with ESZ had MMN deficits for duration-deviants (p = .041), pitch-deviants (ps = .007), and double-deviants (ps < .047). Patients with ESZ had reduced theta ITC for standards (ps < .040) and duration-deviants (ps < .030). Furthermore, patients with ESZ had reduced theta power across deviants at central electrodes (p = .013). MMN group deficits were not fully accounted for by theta ITC and power, and neither were theta ITC group deficits fully accounted for by MMN. Group differences in theta total power were no longer significant after covarying for MMN.

CONCLUSIONS

Patients with ESZ showed reduced MMN and theta total power for all deviant types. Theta ITC showed a relatively specific reduction for duration-deviants. Although MMN and theta ITC were correlated in ESZ, covarying for one did not fully account for deficits in the other, raising the possibility of their sensitivity to dissociable pathophysiological processes.

Development of the novel GlyT1 inhibitor, iclepertin (BI 425809), for the treatment of cognitive impairment associated with schizophrenia

Schizophrenia is a psychiatric disorder characterised by symptoms in three domains: positive (e.g. delusions, hallucinations), negative (e.g. social withdrawal, lack of motivation) and cognitive (e.g. working memory and executive function impairment). Cognitive impairment associated with schizophrenia (CIAS) is a major burden for patients and negatively impacts many aspects of a patient's life. Antipsychotics are the standard-of-care treatment for schizophrenia but only address positive symptoms. So far there are no approved pharmacotherapies for the treatment of CIAS. Iclepertin (BI 425809) is a novel, potent and selective glycine transporter 1 (GlyT1) inhibitor, under development by Boehringer Ingelheim for the treatment of CIAS. Phase I studies have shown it to be safe and well tolerated in healthy volunteers, and central target engagement (inhibition of GlyT1) was achieved in a dose-dependent manner from 5 to 50 mg in healthy volunteers. A Phase II study has demonstrated that iclepertin is safe and well tolerated in patients with schizophrenia and improves cognition at doses of 10 mg and 25 mg. Phase III studies are ongoing to confirm these initial positive safety and efficacy findings with the 10 mg dose, and if successful, iclepertin could become the first approved pharmacotherapy used to treat CIAS.

Association between increased anterior cingulate glutamate and psychotic-like experiences, but not autistic traits in healthy volunteers

Despite many differences, autism spectrum disorder and schizophrenia spectrum disorder share environmental risk factors, genetic predispositions as well as neuronal abnormalities, and show similar cognitive deficits in working memory, perspective taking, or response inhibition. These shared abnormalities are already present in subclinical traits of these disorders. The literature proposes that changes in the inhibitory GABAergic and the excitatory glutamatergic system could explain underlying neuronal commonalities and differences. Using magnetic resonance spectroscopy (1H-MRS), we investigated the associations between glutamate concentrations in the anterior cingulate cortex (ACC), the left/right putamen, and left/right dorsolateral prefrontal cortex and psychotic-like experiences (Schizotypal Personality Questionnaire) and autistic traits (Autism Spectrum Quotient) in 53 healthy individuals (26 women). To investigate the contributions of glutamate concentrations in different cortical regions to symptom expression and their interactions, we used linear regression analyses. We found that only glutamate concentration in the ACC predicted psychotic-like experiences, but not autistic traits. Supporting this finding, a binomial logistic regression predicting median-split high and low risk groups for psychotic-like experiences revealed ACC glutamate levels as a significant predictor for group membership. Taken together, this study provides evidence that glutamate levels in the ACC are specifically linked to the expression of psychotic-like experiences, and may be a potential candidate in identifying early risk individuals prone to developing psychotic-like experiences.

Age, Dose, and Locomotion: Decoding Vulnerability to Ketamine in C57BL/6J and BALB/c Mice

Ketamine has been abused as a psychedelic agent and causes diverse neurobehavioral changes. Adolescence is a critical developmental stage but vulnerable to substances and environmental stimuli. Growing evidence shows that ketamine affects glutamatergic neurotransmission, which is important for memory storage, addiction, and psychosis. To explore diverse biological responses, this study was designed to assess ketamine sensitivity in mice of different ages and strains. Male C57BL/6J and BALB/c mice were studied in adolescence and adulthood separately. An open field test assessed motor behavioral changes. After a 30-min baseline habituation, mice were injected with ketamine (0, 25, and 50 mg/kg), and their locomotion was measured for 60 min. Following ketamine injection, the travelled distance and speed significantly increased in C57BL/6J mice between both age groups (p < 0.01), but not in BALB/c mice. The pattern of hyperlocomotion showed that mice were delayed at the higher dose (50 mg/kg) compared to the lower dose (25 mg/kg) of ketamine treatment. Ketamine accentuated locomotor activation in adolescent C57BL/6J mice compared to adults, but not in the BALB/c strain. Here, we show that ketamine-induced locomotor behavior is modulated by dose and age. The discrepancy of neurobehaviors in the two strains of mice indicates that sensitivity to ketamine is biologically determined. This study suggests that individual vulnerability to ketamine's pharmacological responses varies biologically.

Links of platelet glutamate and glutathione metabolism with attenuated positive and negative symptoms in depressed patients at clinical high risk for psychosis

Aim of the study is to reveal clinical and biological correlations in patients with adolescent depression and attenuated psychotic symptoms. Activity of platelet enzymes involved in glutamate-, glutathione- and energy metabolism was evaluated in control group and in the patients, because these systems are suspected as related to pathogenesis of psychosis. Adolescents (78 men, 16-25 years old) hospitalized with the first acute depressive state composed two groups: with prevalence of attenuated psychotic positive or negative symptoms (Gr1 and Gr2, 48 and 30 patients, respectively). Control group comprised 20 mentally healthy men of 19-25 years old. Gr1 differed significantly from Gr2 in scores by the Scale of Prodromal Symptoms (SOPS) for positive symptoms, p < 0.001, for disorganization symptoms, p < 0.003, and for total SOPS score, p < 0.001, before the treatment started. When patients from either Gr1 or Gr2 were compared with the control group, significantly decreased baseline activities of platelet glutamate dehydrogenase (GDH), glutathione reductase (GR) and glutathione S-transferase (GST) were found (p < 0.0001). Different correlations were found between baseline enzymatic activities in Gr1 and Gr2: GDH activity correlated with GR activity in Gr1 (R = 0.37), and with GST activity in Gr2 (R = 0.70). Significant correlations were found only in Gr2 between the delta of scores by SOPS negative symptoms (SOPS-N) under treatment and baseline GDH, GST, and GR activities (R = - 0.36, R = - 0.60, and R = 0.38, respectively). The found correlations of the baseline enzymatic activity levels with the value of the decrease (delta) in SOPS-N scores under the treatment represent interest for the prediction of the pharmacotherapy efficiency.

Cognitive Impairment Associated with Schizophrenia: From Pathophysiology to Treatment

Cognitive impairment is a core feature of schizophrenia and a major contributor to poor functional outcomes. Methods for assessment of cognitive dysfunction in schizophrenia are now well established. In addition, there has been increasing appreciation in recent years of the additional role of social cognitive impairment in driving functional outcomes and of the contributions of sensory-level dysfunction to higher-order impairments. At the neurochemical level, acute administration of N-methyl-d-aspartate receptor (NMDAR) antagonists reproduces the pattern of neurocognitive dysfunction associated with schizophrenia, encouraging the development of treatments targeted at both NMDAR and its interactome. At the local-circuit level, an auditory neurophysiological measure, mismatch negativity, has emerged both as a veridical index of NMDAR dysfunction and excitatory/inhibitory imbalance in schizophrenia and as a critical biomarker for early-stage translational drug development. Although no compounds have yet been approved for treatment of cognitive impairment associated with schizophrenia, several candidates are showing promise in early-phase testing.

Mismatch Negativity in Response to Auditory Deviance and Risk for Future Psychosis in Youth at Clinical High Risk for Psychosis

Importance

Although clinical criteria for identifying youth at risk for psychosis have been validated, they are not sufficiently accurate for predicting outcomes to inform major treatment decisions. The identification of biomarkers may improve outcome prediction among individuals at clinical high risk for psychosis (CHR-P).

Objective

To examine whether mismatch negativity (MMN) event-related potential amplitude, which is deficient in schizophrenia, is reduced in young people with the CHR-P syndrome and associated with outcomes, accounting for effects of antipsychotic medication use.

Design, Setting, and Participants

MMN data were collected as part of the multisite case-control North American Prodrome Longitudinal Study (NAPLS-2) from 8 university-based outpatient research programs. Baseline MMN data were collected from June 2009 through April 2013. Clinical outcomes were assessed throughout 24 months. Participants were individuals with the CHR-P syndrome and healthy controls with MMN data. Participants with the CHR-P syndrome who developed psychosis (ie, converters) were compared with those who did not develop psychosis (ie, nonconverters) who were followed up for 24 months. Analysis took place between December 2019 and December 2021.

Main Outcomes and Measures

Electroencephalography was recorded during a passive auditory oddball paradigm. MMN elicited by duration-, pitch-, and duration + pitch double-deviant tones was measured.

Results

The CHR-P group (n = 580; mean [SD] age, 19.24 [4.39] years) included 247 female individuals (42.6%) and the healthy control group (n = 241; mean age, 20.33 [4.74] years) included 114 female individuals (47.3%). In the CHR-P group, 450 (77.6%) were not taking antipsychotic medication at baseline. Baseline MMN amplitudes, irrespective of deviant type, were deficient in future CHR-P converters to psychosis (n = 77, unmedicated n = 54) compared with nonconverters (n = 238, unmedicated n = 190) in both the full sample (d = 0.27) and the unmedicated subsample (d = 0.33). In the full sample, baseline medication status interacted with group and deviant type indicating that double-deviant MMN, compared with single deviants, was reduced in unmedicated converters compared with nonconverters (d = 0.43). Further, within the unmedicated subsample, deficits in double-deviant MMN were most strongly associated with earlier conversion to psychosis (hazard ratio, 1.40 [95% CI, 1.03-1.90]; P = .03], which persisted over and above positive symptom severity.

Conclusions and Relevance

This study found that MMN amplitude deficits were sensitive to future psychosis conversion among individuals at risk of CHR-P, particularly those not taking antipsychotic medication at baseline, although associations were modest. While MMN shows limited promise as a biomarker of psychosis onset on its own, it may contribute novel risk information to multivariate prediction algorithms and serve as a translational neurophysiological target for novel treatment development in a subgroup of at-risk individuals.

Targeted effects of ketamine on perceptual expectation during mediated learning in rats

RATIONALE

While neural correlates of hallucinations are known, the mechanisms have remained elusive. Mechanistic insight is more practicable in animal models, in which causal relationships can be established. Recent work developing animal models of hallucination susceptibility has focused on the genesis of perceptual expectations and perceptual decision-making. Both processes are encompassed within mediated learning, which involves inducing a strong perceptual expectation via associative learning, retrieving that memory representation, and deciding whether this internally generated percept is predictive of an external outcome. Mediated learning in rodents is sensitive to many psychotomimetic manipulations. However, we do not know if these manipulations selectively alter learning of perceptual expectations versus their retrieval because of their presence throughout all task phases.

OBJECTIVES

Here, we used mediated learning to study the targeted effect of a psychotomimetic agent on the retrieval of perceptual expectation.

METHODS

We administered (R,S)-ketamine to rats selectively during the devaluation phase of a mediated learning task, when the representation of the expected cue is retrieved, to test the hypothesis that internally generated perceptual experiences underlie this altered mediated learning.

RESULTS

We found that ketamine increased only mediated learning at a moderate dose in rats, but impaired direct learning at the high dose.

CONCLUSIONS

These results suggest that ketamine can augment retrieval of perceptual expectations and thus this may be how it induces hallucination-like experiences in humans. More broadly, mediated learning may unite the conditioning, perceptual decision-making, and even reality monitoring accounts of psychosis in a manner that translates across species.

Impaired verbal memory function is related to anterior cingulate glutamate levels in schizophrenia: findings from the STRATA study

Impaired cognition is associated with lower quality of life and poor outcomes in schizophrenia. Brain glutamate may contribute to both clinical outcomes and cognition, but these relationships are not well-understood. We studied a multicentre cohort of 85 participants with non-affective psychosis using proton magnetic resonance spectroscopy. Glutamate neurometabolites were measured in the anterior cingulate cortex (ACC). Cognition was assessed using the Brief Assessment for Cognition in Schizophrenia (BACS). Patients were categorised as antipsychotic responders or non-responders based on treatment history and current symptom severity. Inverted U-shaped associations between glutamate or Glx (glutamate + glutamine) with BACS subscale and total scores were examined with regression analyses. We then tested for an interaction effect of the antipsychotic response group on the relationship between glutamate and cognition. ACC glutamate and Glx had a positive linear association with verbal memory after adjusting for age, sex and chlorpromazine equivalent dose (glutamate, β = 3.73, 95% CI = 1.26-6.20, P = 0.004; Glx, β = 3.38, 95% CI = 0.84-5.91, P = 0.01). This association did not differ between good and poor antipsychotic response groups. ACC glutamate was also positively associated with total BACS score (β = 3.12, 95% CI = 0.01-6.23, P = 0.046), but this was not significant after controlling for antipsychotic dose. Lower glutamatergic metabolites in the ACC were associated with worse verbal memory, and this relationship was independent of antipsychotic response. Further research on relationships between glutamate and cognition in antipsychotic responsive and non-responsive illness could aid the stratification of patient groups for targeted treatment interventions.

Medial Septum Modulates Consciousness and Psychosis-Related Behaviors Through Hippocampal Gamma Activity

Abnormally high-amplitude hippocampal gamma activity (30–100 Hz) in behaving animals is seen after a hippocampal seizure, following injection of phencyclidine (PCP) or ketamine, and transiently in a delirium stage during induction of general anesthesia. High-amplitude hippocampal gamma activity in behaving rats is associated with hyperactive behavior and impairment in sensorimotor gating and sensory gating. The medial septum is necessary for the high-amplitude gamma activity and abnormal behaviors observed following a hippocampal seizure or injection of PCP/ketamine. Glutamatergic projection of the hippocampus to the nucleus accumbens (NAC) and dopaminergic transmission in NAC is necessary for abnormal behaviors. Large hippocampal gamma waves are suggested to contribute to seizure-induced automatism following temporal lobe seizures, and the schizophrenia-like symptoms induced by PCP/ketamine. Low-amplitude gamma activity is found during general anesthesia, associated with loss of consciousness in humans and loss of righting reflex in animals. Local inactivation or lesion of the medial septum, NAC, and brain areas connected to the septohippocampal-NAC system attenuates the increase in hippocampal gamma and associated behavioral disruptions induced by hippocampal seizure or PCP/ketamine. Inactivation or lesion of the septohippocampal-NAC system decreases the dose of anesthetic necessary for gamma decrease and loss of consciousness in animals. Thus, it is proposed that the septohippocampal-NAC system serves to control consciousness and the behavioral hyperactivity and neural dysfunctions during psychosis.

Effects of the glycine transporter-1 inhibitor iclepertin (BI 425809) on sensory processing, neural network function, and cognition in animal models related to schizophrenia

N-methyl-D-aspartate (NMDA) receptor hypofunction leading to neural network dysfunction is thought to play an important role in the pathophysiology of cognitive impairment associated with schizophrenia (CIAS). Increasing extracellular concentrations of the NMDA receptor co-agonist glycine through inhibition of glycine transporter-1 (GlyT1) has the potential to treat CIAS by improving cortical network function through enhanced glutamatergic signaling. Indeed, the novel GlyT1 inhibitor iclepertin (BI 425809) improved cognition in a recent clinical study in patients with schizophrenia. The present study tested the ability of iclepertin to reverse MK-801-induced deficits in auditory sensory processing and cortical network function using electroencephalography (EEG) to measure auditory event-related potentials (AERP) and 40 Hz auditory steady-state response (ASSR). In addition, improvements in memory performance with iclepertin were evaluated using the T-maze spontaneous alternation test in MK-801-treated mice and the social recognition test in naïve rats. Iclepertin reversed MK-801-induced deficits in the AERP readouts N1 amplitude and N1 gating, as well as 40 Hz ASSR power and inter-trial coherence. Additionally, iclepertin significantly attenuated an MK-801-induced increase in basal gamma power. Furthermore, iclepertin reversed MK-801-induced working memory deficits in mice and improved social recognition memory performance in rats. Overall, this study demonstrates that inhibition of GlyT1 is sufficient to attenuate MK-801-induced deficits in translatable EEG parameters relevant to schizophrenia. Moreover, iclepertin showed memory-enhancing effects in rodent cognition tasks, further demonstrating the potential for GlyT1 inhibition to treat CIAS. Significance Statement Despite the significant patient burden caused by cognitive impairment associated with schizophrenia, there are currently no approved pharmacotherapies. In this preclinical study, the novel glycine transporter inhibitor iclepertin (BI 425809) reversed sensory processing deficits and neural network dysfunction evoked by inhibition of N-methyl-D-aspartate (NMDA) receptors, and enhanced working memory performance and social recognition in rodents. These findings support previous clinical evidence for the pro-cognitive effects of iclepertin.

Electrocorticographic effects of acute ketamine on non-human primate brains

OBJECTIVE

Acute blockade of glutamate N-methyl-D-aspartate (NMDA) receptors by ketamine induces symptoms and electrophysiological changes similar to schizophrenia. Previous studies have shown that ketamine elicits aberrant gamma oscillations in several cortical areas and impairs coupling strength between the low-frequency phase and fast frequency amplitude (PAC), which plays an important role in integrating functional information.

APPROACH

This study utilized a customized wireless electrocorticography (ECoG) recording device to collect subdural signals from the somatosensory and primary auditory cortices in two monkeys. Ketamine was administered at a dose of 3 mg/kg (intramuscular) or 0.56 mg/kg (intravenous) to elicit brain oscillation reactions. We analyzed the raw data using methods such as power spectral density, time-frequency spectra, and PAC.

MAIN RESULTS

Acute ketamine triggered broadband gamma and high gamma oscillation power and decreased lower frequencies. The effect was stronger in the primary auditory cortex than in the somatosensory area. The coupling strength between the low phase of theta and the faster amplitude of gamma/high gamma bands was increased by a lower dose (0.56 mg/kg iv) and decreased with a higher dose (3 mg/kg im) ketamine.

SIGNIFICANCE

Our results showed that lower and higher doses of ketamine elicited differential effects on theta-gamma PAC. These findings support the utility of ECoG models as a translational platform for pharmacodynamic research in future research.

Anti-NMDA Receptor Encephalitis Associated With an Ovarian Teratoma Presenting as First-episode Psychosis: A Case Report

We report an unusual case of a 27-year-old previously healthy female who presented with a 15-day history of psychotic, cognitive, and unspecified somatic symptoms. She was admitted to the psychiatric ward of an early intervention in psychosis team and medicated with aripiprazole. The young age of onset, the rapid onset, the absent history of psychiatric disease, and the persistence of a marked memory deficit after the psychotic symptoms remitted strongly suggested a nonpsychiatric etiology and led us to hypothesize autoimmune encephalitis as the most probable diagnosis. An investigation was carried out for anti-N-methyl-D-aspartate (anti-NMDA) receptor antibodies in the patient's serum and cerebrospinal fluid, and both tests were positive. The patient was transferred to the neurology ward, where an endovaginal ultrasound showed an ovarian teratoma in her right ovary. She underwent laparoscopic surgery without complications. She was initially treated with intravenous immunoglobulin and methylprednisolone for 5 days, which resulted in marked improvement of her memory and attention performance. Anti-NMDA receptor encephalitis, first described in 2007 by Dalmau and colleagues, is a form of auto-immune encephalitis with prominent neuropsychiatric manifestations, particularly psychotic symptoms. At symptom onset, distinguishing the disease from a primary psychiatric disorder is challenging. This case report highlights the importance of early psychosis treatment teams considering the diagnosis of anti-NMDA receptor encephalitis when evaluating new referrals with a potential diagnosis of first-episode psychosis, particularly when young patients with no relevant personal or familial psychiatric history present with neuropsychiatric symptoms and a distinctive pattern of symptom fluctuation over time.

Pathway-specific contribution of parvalbumin interneuron NMDARs to synaptic currents and thalamocortical feedforward inhibition

Prefrontal cortex (PFC) is a site of information convergence important for behaviors relevant to psychiatric disorders. Despite the importance of inhibitory GABAergic parvalbumin-expressing (PV+) interneurons to PFC circuit function and decades of interest in N-methyl-D-aspartate receptors (NMDARs) in these neurons, examples of defined circuit functions that depend on PV+ interneuron NMDARs have been elusive. Indeed, it remains controversial whether all PV+ interneurons contain functional NMDARs in adult PFC, which has major consequences for hypotheses of the pathogenesis of psychiatric disorders. Using a combination of fluorescent in situ hybridization, pathway-specific optogenetics, cell-type-specific gene ablation, and electrophysiological recordings from PV+ interneurons, here we resolve this controversy. We found that nearly 100% of PV+ interneurons in adult medial PFC (mPFC) express transcripts encoding GluN1 and GluN2B, and they have functional NMDARs. By optogenetically stimulating corticocortical and thalamocortical inputs to mPFC, we show that synaptic NMDAR contribution to PV+ interneuron EPSCs is pathway-specific, which likely explains earlier reports of PV+ interneurons without synaptic NMDAR currents. Lastly, we report a major contribution of NMDARs in PV+ interneurons to thalamus-mediated feedforward inhibition in adult mPFC circuits, suggesting molecular and circuit-based mechanisms for cognitive impairment under conditions of reduced NMDAR function. These findings represent an important conceptual advance that has major implications for hypotheses of the pathogenesis of psychiatric disorders.

Therapeutic Potential of TAAR1 Agonists in Schizophrenia: Evidence from Preclinical Models and Clinical Studies

Trace amine-associated receptor 1 (TAAR1) has emerged as a promising therapeutic target for neuropsychiatric disorders due to its ability to modulate monoaminergic and glutamatergic neurotransmission. In particular, agonist compounds have generated interest as potential treatments for schizophrenia and other psychoses due to TAAR1-mediated regulation of dopaminergic tone. Here, we review unmet needs in schizophrenia, the current state of knowledge in TAAR1 circuit biology and neuropharmacology, including preclinical behavioral, imaging, and cellular evidence in glutamatergic, dopaminergic and genetic models linked to the pathophysiology of psychotic, negative and cognitive symptoms. Clinical trial data for TAAR1 drug candidates are reviewed and contrasted with antipsychotics. The identification of endogenous TAAR1 ligands and subsequent development of small-molecule agonists has revealed antipsychotic-, anxiolytic-, and antidepressant-like properties, as well as pro-cognitive and REM-sleep suppressing effects of TAAR1 activation in rodents and non-human primates. Ulotaront, the first TAAR1 agonist to progress to randomized controlled clinical trials, has demonstrated efficacy in the treatment of schizophrenia, while another, ralmitaront, is currently being evaluated in clinical trials in schizophrenia. Coupled with the preclinical findings, this provides a rationale for further investigation and development of this new pharmacological class for the treatment of schizophrenia and other psychiatric disorders.

Current findings and perspectives on aberrant neural oscillations in schizophrenia

There is now consistent evidence that neural oscillation at low- and high-frequencies constitute an important aspect of the pathophysiology of schizophrenia. Specifically, impaired rhythmic activity may underlie the deficit to generate coherent cognition and behavior, leading to the characteristic symptoms of psychosis and cognitive deficits. Importantly, the generating mechanisms of neural oscillations are relatively well-understood and thus enable the targeted search for the underlying circuit impairments and novel treatment targets. In the following review, we will summarize and assess the evidence for aberrant rhythmic activity in schizophrenia through evaluating studies that have utilized Electro/Magnetoencephalography to examine neural oscillations during sensory and cognitive tasks as well as during resting-state measurements. These data will be linked to current evidence from post-mortem, neuroimaging, genetics, and animal models that have implicated deficits in GABAergic interneurons and glutamatergic neurotransmission in oscillatory deficits in schizophrenia. Finally, we will highlight methodological and analytical challenges as well as provide recommendations for future research.

Brain Versus Blood: A Systematic Review on the Concordance Between Peripheral and Central Kynurenine Pathway Measures in Psychiatric Disorders

Objective

Disturbances in the kynurenine pathway have been implicated in the pathophysiology of psychotic and mood disorders, as well as several other psychiatric illnesses. It remains uncertain however to what extent metabolite levels detectable in plasma or serum reflect brain kynurenine metabolism and other disease-specific pathophysiological changes. The primary objective of this systematic review was to investigate the concordance between peripheral and central (CSF or brain tissue) kynurenine metabolites. As secondary aims we describe their correlation with illness course, treatment response, and neuroanatomical abnormalities in psychiatric diseases.

Methods

We performed a systematic literature search until February 2021 in PubMed. We included 27 original research articles describing a correlation between peripheral and central kynurenine metabolite measures in preclinical studies and human samples from patients suffering from neuropsychiatric disorders and other conditions. We also included 32 articles reporting associations between peripheral KP markers and symptom severity, CNS pathology or treatment response in schizophrenia, bipolar disorder or major depressive disorder.

Results

For kynurenine and 3-hydroxykynurenine, moderate to strong concordance was found between peripheral and central concentrations not only in psychiatric disorders, but also in other (patho)physiological conditions. Despite discordant findings for other metabolites (mainly tryptophan and kynurenic acid), blood metabolite levels were associated with clinical symptoms and treatment response in psychiatric patients, as well as with observed neuroanatomical abnormalities and glial activity.

Conclusion

Only kynurenine and 3-hydroxykynurenine demonstrated a consistent and reliable concordance between peripheral and central measures. Evidence from psychiatric studies on kynurenine pathway concordance is scarce, and more research is needed to determine the validity of peripheral kynurenine metabolite assessment as proxy markers for CNS processes. Peripheral kynurenine and 3-hydroxykynurenine may nonetheless represent valuable predictive and prognostic biomarker candidates for psychiatric disorders.

N-methyl-D-aspartate receptor availability in first-episode psychosis: a PET-MR brain imaging study

N-methyl-D-aspartate receptor (NMDAR) hypofunction is hypothesised to underlie psychosis but this has not been tested early in illness. To address this, we studied 40 volunteers (21 patients with first-episode psychosis and 19 matched healthy controls) using PET imaging with an NMDAR selective ligand, [18F]GE-179, that binds to the ketamine binding site to index its distribution volume ratio (DVR) and volume of distribution (VT). Hippocampal DVR, but not VT, was significantly lower in patients relative to controls (p = 0.02, Cohen's d = 0.81; p = 0.15, Cohen's d = 0.49), and negatively associated with total (rho = -0.47, p = 0.04), depressive (rho = -0.67, p = 0.002), and general symptom severity (rho = -0.74, p < 0.001). Exploratory analyses found no significant differences in other brain regions (anterior cingulate cortex, thalamus, striatum and temporal cortex). These findings are consistent with the NMDAR hypofunction hypothesis and identify the hippocampus as a key locus for relative NMDAR hypofunction, although further studies should test specificity and causality.

NMDARs Containing NR2B Subunit Do Not Contribute to the LTP Form of Hippocampal Plasticity: In Vivo Pharmacological Evidence in Rats

Synaptic plasticity is the key to synaptic health, and aberrant synaptic plasticity, which in turn impairs the functioning of large-scale brain networks, has been associated with neurodegenerative and psychiatric disorders. The best known and most studied form of activity-dependent synaptic plasticity remains long-term potentiation (LTP), which is controlled by glutamatergic N-methyl-d-aspartate) receptors (NMDAR) and considered to be a mechanism crucial for cellular learning and memory. Over the past two decades, discrepancies have arisen in the literature regarding the contribution of NMDAR subunit assemblies in the direction of NMDAR-dependent synaptic plasticity. Here, the nonspecific NMDAR antagonist ketamine (5 and 10 mg/kg), and the selective NR2B antagonists CP-101606 and Ro 25-6981 (6 and 10 mg/kg), were administered intraperitoneally in Sprague Dawley rats to disentangle the contribution of NR2B subunit in the LTP induced at the Schaffer Collateral-CA1 synapse using the theta burst stimulation protocol (TBS). Ketamine reduced, while CP-101606 and Ro 25-6981 did not alter the LTP response. The administration of CP-101606 before TBS did not influence the effects of ketamine when administered half an hour after tetanization, suggesting a limited contribution of the NR2B subunit in the action of ketamine. This work confirms the role of NMDAR in the LTP form of synaptic plasticity, whereas specific blockade of the NR2B subunit was not sufficient to modify hippocampal LTP. Pharmacokinetics at the doses used may have contributed to the lack of effects with specific antagonists. The findings refute the role of the NR2B subunit in the plasticity mechanism of ketamine in the model.

Oxidative Stress and the Pathophysiology and Symptom Profile of Schizophrenia Spectrum Disorders

Schizophrenia is associated with increased levels of oxidative stress, as reflected by an increase in the concentrations of damaging reactive species and a reduction in anti-oxidant defences to combat them. Evidence has suggested that whilst not the likely primary cause of schizophrenia, increased oxidative stress may contribute to declining course and poor outcomes associated with schizophrenia. Here we discuss how oxidative stress may be implicated in the aetiology of schizophrenia and examine how current understanding relates associations with symptoms, potentially via lipid peroxidation induced neuronal damage. We argue that oxidative stress may be a good target for future pharmacotherapy in schizophrenia and suggest a multi-step model of illness progression with oxidative stress involved at each stage.

GRIN2A and GRIN2B and Their Related Phenotypes

Glutamate is the most relevant excitatory neurotransmitter of the central nervous system; it binds with several receptors, including N-methyl-D-aspartate receptors (NMDARs), a subtype of ionotropic glutamate receptor that displays voltage-dependent block by Mg2+ and a high permeability to Ca2+. GRIN2A and GRIN2B genes encode the GluN2A and GluN2B subunits of the NMDARs, which play important roles in synaptogenesis, synaptic transmission, and synaptic plasticity, as well as contributing to neuronal loss and dysfunction in several neurological disorders. Recently, individuals with a range of childhood-onset drug-resistant epilepsies, such as Landau–Kleffner or Lennox–Gastaut syndrome, intellectual disability (ID), and other neurodevelopmental abnormalities have been found to carry mutations in GRIN2A and GRIN2B, with high variable expressivity in phenotype. The first one is found mainly in epilepsy-aphasia syndromes, while the second one mainly in autism, schizophrenia, and ID, such as autism spectrum disorders. Brain magnetic resonance imaging alterations are found in some patients, even if without a clear clinical correlation. At the same time, increasing data on genotype–phenotype correlation have been found, but this is still not fully demonstrated. There are no specific therapies for the treatment of correlated NMDARs epilepsy, although some evidence with memantine, an antagonist of glutamate receptor, is reported in the literature in selected cases with mutation determining a gain of function.

Glutamate and microglia activation as a driver of dendritic apoptosis: a core pathophysiological mechanism to understand schizophrenia

Schizophrenia disorder remains an unsolved puzzle. However, the integration of recent findings from genetics, molecular biology, neuroimaging, animal models and translational clinical research offers evidence that the synaptic overpruning hypothesis of schizophrenia needs to be reassessed. During a critical period of neurodevelopment and owing to an imbalance of excitatory glutamatergic pyramidal neurons and inhibitory GABAergic interneurons, a regionally-located glutamate storm might occur, triggering excessive dendritic pruning with the activation of local dendritic apoptosis machinery. The apoptotic loss of dendritic spines would be aggravated by microglia activation through a recently described signaling system from complement abnormalities and proteins of the MHC, thus implicating the immune system in schizophrenia. Overpruning of dendritic spines coupled with aberrant synaptic plasticity, an essential function for learning and memory, would lead to brain misconnections and synaptic inefficiency underlying the primary negative symptoms and cognitive deficits of schizophrenia. This driving hypothesis has relevant therapeutic implications, including the importance of pharmacological interventions during the prodromal phase or the transition to psychosis, targeting apoptosis, microglia cells or the glutamate storm. Future research on apoptosis and brain integrity should combine brain imaging, CSF biomarkers, animal models and cell biology.

Delayed-matching-to-position working memory in mice relies on NMDA-receptors in prefrontal pyramidal cells

A hypofunction of N-methyl-D-aspartate glutamate receptors (NMDARs) has been implicated in the pathogenesis of schizophrenia by clinical and rodent studies. However, to what extent NMDAR-hypofunction in distinct cell-types across the brain causes different symptoms of this disease is largely unknown. One pharmaco-resistant core symptom of schizophrenia is impaired working memory (WM). NMDARs have been suggested to mediate sustained firing in excitatory neurons of the prefrontal cortex (PFC) that might underlie WM storage. However, if NMDAR-hypofunction in prefrontal excitatory neurons may indeed entail WM impairments is unknown. We here investigated this question in mice, in which NMDARs were genetically-ablated in PFC excitatory cells. This cell type-selective NMDAR-hypofunction caused a specific deficit in a delayed-matching-to-position (DMTP) 5-choice-based operant WM task. In contrast, T-maze rewarded alternation and several psychological functions including attention, spatial short-term habituation, novelty-processing, motivation, sociability, impulsivity, and hedonic valuation remained unimpaired at the level of GluN1-hypofunction caused by our manipulation. Our data suggest that a hypofunction of NMDARs in prefrontal excitatory neurons may indeed cause WM impairments, but are possibly not accounting for most other deficits in schizophrenia.

Antipsychotic potential of the type 1 cannabinoid receptor positive allosteric modulator GAT211: preclinical in vitro and in vivo studies

RATIONALE

Antipsychotics help alleviate the positive symptoms associated with schizophrenia; however, their debilitating side effects have spurred the search for better treatment options. Novel compounds can be screened for antipsychotic potential in neuronal cell cultures and following acute N-methyl-D-aspartate (NMDA) receptor blockade with non-competitive antagonists such as MK-801 in rodent behavioral models. Given the known interactions between NMDA receptors and type 1 cannabinoid receptors (CB1R), compounds that modulate CB1Rs may have therapeutic potential for schizophrenia.

OBJECTIVES

This study assessed whether the CB1R positive allosteric modulator GAT211, when compared to ∆⁹-tetrahydrocannabinol (THC), has potential to reduce psychiatric behavioral phenotypes following acute MK-801 treatment in rats, and block hyperdopaminergic signalling associated with those behaviors.

METHODS

The effects of GAT211 and THC on cellular signaling were compared in Neuro2a cells, and behavioral effects of GAT211 and THC on altered locomotor activity and prepulse inhibition of the acoustic startle response caused by acute MK-801 treatment were assessed in male, Long Evans rats.

RESULTS

GAT211 limited dopamine D2 receptor-mediated extracellular regulated kinase (ERK) phosphorylation in Neuro2a cells, whereas THC did not. As expected, acute MK-801 (0.15 mg/kg) produced a significant increase in locomotor activity and impaired PPI. GAT211 treatment alone (0.3-3.0 mg/kg) dose-dependently reduced locomotor activity and the acoustic startle response. GAT211 (3.0 mg/kg) also prevented hyperlocomotion caused by MK-801 but did not significantly affect PPI impairments.

CONCLUSION

Taken together, these findings support continued preclinical research regarding the usefulness of CB1R positive allosteric modulators as antipsychotics.

Visual cortical plasticity and the risk for psychosis: An interim analysis of the North American Prodrome Longitudinal Study

BACKGROUND

Adolescence/early adulthood coincides with accelerated pruning of cortical synapses and the onset of schizophrenia. Cortical gray matter reduction and dysconnectivity in schizophrenia are hypothesized to result from impaired synaptic plasticity mechanisms, including long-term potentiation (LTP), since deficient LTP may result in too many weak synapses that are then subject to over-pruning. Deficient plasticity has already been observed in schizophrenia. Here, we assessed whether such deficits are present in the psychosis risk syndrome (PRS), particularly those who subsequently convert to full psychosis.

METHODS

An interim analysis was performed on a sub-sample from the NAPLS-3 study, including 46 healthy controls (HC) and 246 PRS participants. All participants performed an LTP-like visual cortical plasticity paradigm involving assessment of visual evoked potentials (VEPs) elicited by vertical and horizontal line gratings before and after high frequency ("tetanizing") visual stimulation with one of the gratings to induce "input-specific" neuroplasticity (i.e., VEP changes specific to the tetanized stimulus). Non-parametric, cluster-based permutation testing was used to identify electrodes and timepoints that demonstrated input-specific plasticity effects.

RESULTS

Input-specific pre-post VEP changes (i.e., increased negative voltage) were found in a single spatio-temporal cluster covering multiple occipital electrodes in a 126-223 ms time window. This plasticity effect was deficient in PRS individuals who subsequently converted to psychosis, relative to PRS non-converters and HC.

CONCLUSIONS

Input-specific LTP-like visual plasticity can be measured from VEPs in adolescents and young adults. Interim analyses suggest that deficient visual cortical plasticity is evident in those PRS individuals at greatest risk for transition to psychosis.

Determinants of Schizophrenia Endophenotypes Based on Neuroimaging and Biochemical Parameters

Despite extensive research, there is no convincing evidence of a reliable diagnostic biomarker for schizophrenia beyond clinical observation. Disorders of glutamatergic neurotransmission associated with N-methyl-D-aspartate (NMDA) receptor insufficiency, neuroinflammation, and redox dysregulation are the principal common mechanism linking changes in the periphery with the brain, ultimately contributing to the emergence of negative symptoms of schizophrenia that underlie differential diagnosis. The aim of the study was to evaluate the influence of these systems via peripheral and cerebral biochemical indices in relation to the patient's clinical condition. Using neuroimaging diagnostics, we were able to define endophenotypes of schizophrenia based on objective laboratory data that form the basis of a personalized approach to diagnosis and treatment. The two distinguished endophenotypes differed in terms of the quality of life, specific schizophrenia symptoms, and glutamatergic neurotransmission metabolites in the anterior cingulate gyrus. Our results, as well as further studies of the excitatory or inhibitory balance of microcircuits, relating the redox systems on the periphery with the distant regions of the brain might allow for predicting potential biomarkers of neuropsychiatric diseases, including schizophrenia. To the best of our knowledge, our study is the first to identify an objective molecular biomarker of schizophrenia outcome.

Positive modulation of NMDA receptors by AGN-241751 exerts rapid antidepressant-like effects via excitatory neurons

Dysregulation of the glutamatergic system and its receptors in medial prefrontal cortex (mPFC) has been implicated in major depressive disorder. Recent preclinical studies have shown that enhancing NMDA receptor (NMDAR) activity can exert rapid antidepressant-like effects. AGN-241751, an NMDAR positive allosteric modulator (PAM), is currently being tested as an antidepressant in clinical trials, but the mechanism and NMDAR subunit(s) mediating its antidepressant-like effects are unknown. We therefore used molecular, biochemical, and electrophysiological approaches to examine the cell-type-specific role of GluN2B-containing NMDAR in mediating antidepressant-like behavioral effects of AGN-241751. We demonstrate that AGN-241751 exerts antidepressant-like effects and reverses behavioral deficits induced by chronic unpredictable stress in mice. AGN-241751 treatment enhances NMDAR activity of excitatory and parvalbumin-inhibitory neurons in mPFC, activates Akt/mTOR signaling, and increases levels of synaptic proteins crucial for synaptic plasticity in the prefrontal cortex. Furthermore, cell-type-specific knockdown of GluN2B-containing NMDARs in mPFC demonstrates that GluN2B subunits on excitatory, but not inhibitory, neurons are necessary for antidepressant-like effects of AGN-241751. Together, these results demonstrate antidepressant-like actions of the NMDAR PAM AGN-241751 and identify GluN2B on excitatory neurons of mPFC as initial cellular trigger underlying these behavioral effects.

Akkouh I, Hughes T, Frei E, A. Andreassen O, Djurovic S. Using iPSC Models to Understand the Role of Estrogen in Neuron-Glia Interactions in Schizophrenia and Bipolar Disorder

Schizophrenia (SCZ) and bipolar disorder (BIP) are severe mental disorders with a considerable disease burden worldwide due to early age of onset, chronicity, and lack of efficient treatments or prevention strategies. Whilst our current knowledge is that SCZ and BIP are highly heritable and share common pathophysiological mechanisms associated with cellular signaling, neurotransmission, energy metabolism, and neuroinflammation, the development of novel therapies has been hampered by the unavailability of appropriate models to identify novel targetable pathomechanisms. Recent data suggest that neuron-glia interactions are disturbed in SCZ and BIP, and are modulated by estrogen (E2). However, most of the knowledge we have so far on the neuromodulatory effects of E2 came from studies on animal models and human cell lines, and may not accurately reflect many processes occurring exclusively in the human brain. Thus, here we highlight the advantages of using induced pluripotent stem cell (iPSC) models to revisit studies of mechanisms underlying beneficial effects of E2 in human brain cells. A better understanding of these mechanisms opens the opportunity to identify putative targets of novel therapeutic agents for SCZ and BIP. In this review, we first summarize the literature on the molecular mechanisms involved in SCZ and BIP pathology and the beneficial effects of E2 on neuron-glia interactions. Then, we briefly present the most recent developments in the iPSC field, emphasizing the potential of using patient-derived iPSCs as more relevant models to study the effects of E2 on neuron-glia interactions.

Involvement of Kynurenine Metabolism in Bipolar Disorder: An Updated Review

Bipolar disorder (BD) is a severe affective disorder, mainly characterized by alternative depressive and manic or hypomanic episodes, yet the pathogenesis of BD has not been fully elucidated. Recent researches have implicated the altered kynurenine (KYN) metabolism involved in the neurobiology of BD. Excessive activation of the immune system also occurs in patients with BD, which further accelerates the KYN pathway for tryptophan metabolism. Changes of the KYN metabolites have effects on neuronal receptors and are involved in neuroendocrine transmissions. Interactions between KYN metabolism and the immune system may contribute to the neuropathogenesis of BD. Various studies have shown that alterations of the KYN metabolites were associated with mood, psychotic symptoms, and cognitive functions in patients with BD. In this review, we briefly introduce the KYN pathway and describe the immune dysregulation in BD as well as their interactions. We then focus on the research advances on the KYN metabolism in BD, which hold promise for identifying novel treatment targets in patients stricken with this disorder.

Features of Psychotic Symptoms in Methamphetamine Use Disorder Patients and Ketamine Use Disorder Patients: A Cross-Sectional Study

BACKGROUND

Methamphetamine and ketamine are commonly used club drugs. Both of them have been reported to mimic psychotic symptoms of schizophrenia. However, the prevalence and detailed features of psychotic symptoms among methamphetamine use disorder (MUD) and ketamine use disorder (KUD) patients are largely unknown. This study aimed to measure psychotic symptoms among patients with MUD and KUD.

METHODS

A total sample of 842 patients from voluntary drug rehabilitation centers, including 462 MUD patients and 380 KUD patients, were invited to this study. The Positive and Negative Syndrome Scale (PANSS) was applied to assess psychotic symptoms in these two groups of patients.

RESULTS

The prevalence of psychotic symptoms was significantly higher among MUD patients than KUD patients (75.1 vs. 50.5%, 95% CI: 3.532 - 11.858, p < 0.001). Compared with KUD patients, MUD patients were more likely to experience positive symptoms (PANSS positive scores: 11.5 ± 6.07 vs. 15.1 ± 8.22, P < 0.001) and negative symptoms (PANSS negative scores: 12.4 ± 6.60 vs. 14.5 ± 8.63, P < 0.001), but not general symptoms (PANSS general scores: 31.2 ± 13.90 vs. 32.2 ± 15.13, P < 0.001).

CONCLUSIONS

The current study found that more than half of MUD and KUD patients experienced psychotic symptoms, and that patients with MUD are more likely to experience positive and negative symptoms than patients with KUD. The findings provide a new perspective for exploring the neuropathological mechanism of psychotic symptoms of schizophrenia.

Hippocampal Hyperactivity as a Druggable Circuit-Level Origin of Aberrant Salience in Schizophrenia

The development of current neuroleptics was largely aiming to decrease excessive dopaminergic signaling in the striatum. However, the notion that abnormal dopamine creates psychotic symptoms by causing an aberrant assignment of salience that drives maladaptive learning chronically during disease development suggests a therapeutic value of early interventions that correct salience-related neural processing. The mesolimbic dopaminergic output is modulated by several interconnected brain-wide circuits centrally involving the hippocampus and key relays like the ventral and associative striatum, ventral pallidum, amygdala, bed nucleus of the stria terminalis, nucleus reuniens, lateral and medial septum, prefrontal and cingulate cortex, among others. Unraveling the causal relationships between these circuits using modern neuroscience techniques holds promise for identifying novel cellular—and ultimately molecular—treatment targets for reducing transition to psychosis and symptoms of schizophrenia. Imaging studies in humans have implicated a hyperactivity of the hippocampus as a robust and early endophenotype in schizophrenia. Experiments in rodents, in turn, suggested that the activity of its output region—the ventral subiculum—may modulate dopamine release from ventral tegmental area (VTA) neurons in the ventral striatum. Even though these observations suggested a novel circuit-level target for anti-psychotic action, no therapy has yet been developed along this rationale. Recently evaluated treatment strategies—at least in part—target excess glutamatergic activity, e.g. N-acetyl-cysteine (NAC), levetiracetam, and mGluR2/3 modulators. We here review the evidence for the central implication of the hippocampus-VTA axis in schizophrenia-related pathology, discuss its symptom-related implications with a particular focus on aberrant assignment of salience, and evaluate some of its short-comings and prospects for drug discovery.

Effects of Doxycycline in Swiss Mice Predictive Models of Schizophrenia

Schizophrenia patients show very complex symptoms in several psychopathological domains. Some of these symptoms remain poorly treated. Therefore, continued effort is needed to find novel pharmacological strategies for improving schizophrenia symptoms. Recently, minocycline, a second-generation tetracycline, has been suggested as an adjunctive treatment for schizophrenia. The antipsychotic-like effect of doxycycline, a minocycline analog, was investigated here. We found that both minocycline and doxycycline prevented amphetamine-induced prepulse inhibition (PPI) disruption. However, neither of them blocked MK801-induced effects, albeit doxycycline had a modest impact against ketamine-induced effects. Neither c-Fos nor nNOS expression, which was evaluated in limbic regions, were modified after acute or sub-chronic treatment with doxycycline. Therefore, apomorphine inducing either PPI disruption and climbing behavior was not prevented by doxycycline. This result discards a direct blockade of D2-like receptors, also suggested by the lack of doxycycline cataleptic-induced effect. Contrasting, doxycycline prevented SKF 38393-induced effects, suggesting a preferential doxycycline action at D1-like rather than D2-like receptors. However, doxycycline did not bind to the orthosteric sites of D1, D2, D3, D4, 5-HT2A, 5-HT1A, and A2A receptors suggesting no direct modulation of these receptors. Our data corroborate the antipsychotic-like effect of doxycycline. However, these effects are probably not mediated by doxycycline direct interaction with classical receptors enrolled in the antipsychotic effect.

Targeting Serotonin 5-HT2A Receptors to Better Treat Schizophrenia: Rationale and Current Approaches

Schizophrenia is a major mental illness associated with profound disability. Current treatments for schizophrenia (antipsychotics) all have a similar mechanism of action and are primarily dopamine type 2 receptor (D₂R) antagonists. Antipsychotics are not fully effective for the majority of schizophrenia patients, suggesting the need for alternative approaches. The primary focus of this review is to assess the evidence for the role of the serotonin type 2A receptor (5-HT_2AR) in schizophrenia. Topics include an overview of 5-HT_2AR physiology and pathophysiology in schizophrenia, 5-HT_2AR interaction with other neurotransmitter systems, including the glutamatergic system, a review of the 5-HT_2AR/d-lysergic acid diethylamide (LSD) model of schizophrenia, a contrast of the 5-HT_2AR and glutamatergic models of schizophrenia, and finally, a review of Food and Drug Administration (FDA)-approved and investigational 5-HT_2AR-modulating compounds. Recent studies with lumeteperone, pimavanserin, and roluperidone are highlighted.

Glutamate in schizophrenia: Neurodevelopmental perspectives and drug development

Research into the neurobiological processes that may lead to the onset of schizophrenia places growing emphasis on the glutamatergic system and brain development. Preclinical studies have shown that neurodevelopmental, genetic, and environmental factors contribute to glutamatergic dysfunction and schizophrenia-related phenotypes. Clinical research has suggested that altered brain glutamate levels may be present before the onset of psychosis and relate to outcome in those at clinical high risk. After psychosis onset, glutamate dysfunction may also relate to the degree of antipsychotic response and clinical outcome. These findings support ongoing efforts to develop pharmacological interventions that target the glutamate system and could suggest that glutamatergic compounds may be more effective in specific patient subgroups or illness stages. In this review, we consider the updated glutamate hypothesis of schizophrenia, from a neurodevelopmental perspective, by reviewing recent preclinical and clinical evidence, and discuss the potential implications for novel therapeutics.

Fetal growth restriction mice are more likely to exhibit depression-like behaviors due to stress-induced loss of dopaminergic neurons in the VTA

Fetal growth restriction (FGR) is a severe perinatal complication that can increase risk for mental illness. To investigate the mechanism by which FGR mice develop mental illness in adulthood, we established the FGR mouse model and the FGR mice did not display obvious depression-like behaviors, but after environmental stress exposure, FGR mice were more likely to exhibit depression-like behaviors than control mice. Moreover, FGR mice had significantly fewer dopaminergic neurons in the ventral tegmental area but no difference in serotoninergic neurons in the dorsal raphe. RNA-seq analysis showed that the downregulated genes in the midbrain of FGR mice were associated with many mental diseases and were especially involved in the regulation of NMDA-selective glutamate receptor (NMDAR) activity. Furthermore, the NMDAR antagonist memantine can relieve the stress-induced depression-like behaviors of FGR mice. In summary, our findings provide a theoretical basis for future research and treatment of FGR-related depression.

Aberrant Auditory Steady-State Response of Awake Mice After Single Application of the NMDA Receptor Antagonist MK-801 Into the Medial Geniculate Body

BACKGROUND

Systemic administration of noncompetitive N-methyl-D-aspartate receptor (NMDAR) antagonists such as MK-801 is widely used to model psychosis of schizophrenia (SZ). Acute systemic MK-801 in rodents caused an increase of the auditory steady-state responses (ASSRs), the oscillatory neural responses to periodic auditory stimulation, while most studies in patients with SZ reported a decrease of ASSRs. This inconsistency may be attributable to the comprehensive effects of systemic administration of MK-801. Here, we examined how the ASSR is affected by selectively blocking NMDAR in the thalamus.

METHODS

We implanted multiple electrodes in the auditory cortex (AC) and prefrontal cortex to simultaneously record the local field potential and spike activity (SA) of multiple sites from awake mice. Click-trains at a 40-Hz repetition rate were used to evoke the ASSR. We compared the mean trial power and phase-locking factor and the firing rate of SA before and after microinjection of MK-801 (1.5 µg) into the medial geniculate body (MGB).

RESULTS

We found that both the AC and prefrontal cortex showed a transient local field potential response at the onset of click-train stimulus, which was less affected by the application of MK-801 in the MGB. Following the onset response, the AC also showed a response continuing throughout the stimulus period, corresponding to the ASSR, which was suppressed by the application of MK-801.

CONCLUSION

Our data suggest that the MGB is one of the generators of ASSR, and NMDAR hypofunction in the thalamocortical projection may account for the ASSR deficits in SZ.

Gamma-Band Auditory Steady-State Response as a Neurophysiological Marker for Excitation and Inhibition Balance: A Review for Understanding Schizophrenia and Other Neuropsychiatric Disorders

Altered gamma oscillations have attracted considerable attention as an index of the excitation/inhibition (E/I) imbalance in schizophrenia and other neuropsychiatric disorders. The auditory steady-state response (ASSR) has been the most robust probe of abnormal gamma oscillatory dynamics in schizophrenia. Here, we review recent ASSR studies in patients with schizophrenia and other neuropsychiatric disorders. Preclinical ASSR research, which has contributed to the elucidation of the underlying pathophysiology of these diseases, is also discussed. The developmental trajectory of the ASSR has been explored and may show signs of the maturation and disruption of E/I balance in adolescence. Animal model studies have shown that synaptic interactions between parvalbumin-positive GABAergic interneurons and pyramidal neurons contribute to the regulation of E/I balance, which is related to the generation of gamma oscillation. Therefore, ASSR alteration may be a significant electrophysiological finding related to the E/I imbalance in neuropsychiatric disorders, which is a cross-disease feature and may reflect clinical staging. Future studies regarding ASSR generation, especially in nonhuman primate models, will advance our understanding of the brain circuit and the molecular mechanisms underlying neuropsychiatric disorders.

mGluR5 mediates ketamine antidepressant response in susceptible rats exposed to prenatal stress

BACKGROUND

New insights have recently been gained into ketamine's potential anti-depressive effects. However, the mechanisms that underlie ketamine's rapid antidepressant activity still remain a mystery.

METHODS

We used a rat prenatal stress (PS) model of depression to explore the functional role of mGluR5 in ketamine's rapidly induced antidepressant activity. Effects of the antidepressants imipramine, escitalopram, ketamine, and fluoxetine were compared. AAV-mGluR5 and AAV-shRNA-mGluR5 were constructed to overexpress and knockdown hippocampal mGluR5 respectively.

RESULTS

This study shows that mGluR5, which is associated with depression-like behaviors, is increased in susceptible rats exposed to prenatal stress, and that ketamine could significantly alleviate these stress-induced effects. RU-38486 down-regulated expression of mGluR5 and up-regulated NR1. MPEP and CHPG also altered expression of both mGluR5 and NR1. Notably, hippocampal overexpression of mGluR5 in wild type rats changed NR1 and PSD-95 expression and induced depression-like behavior that could be blocked by ketamine activity. Further, knockdown of hippocampal mGluR5 in PS-S rats restored normal levels of mGluR5, NR1, and PSD-95, and alleviated depression-like behavior.

LIMITATIONS

The entire rat hippocampus was used for this study, but the role of mGluR5 may vary by sub-region.

CONCLUSION

These results suggest that hippocampal mGluR5 may play a key role in mediating the rapid antidepressant effects of ketamine in a prenatal stress model of depression. This provides a novel therapeutic target in clinical treatment of depression.

The protective effects of Mogroside V and its metabolite 11-oxo-mogrol of intestinal microbiota against MK801-induced neuronal damages

RATIONALE

Animal models, notably with non-competitive NMDA receptor antagonist MK801, are commonly used to investigate the mechanisms of schizophrenia and to pursue its mechanism-related drug discoveries.

OBJECTIVES

In the current study, we have extensively examined the protective effects of MogrosideV (MogV), a plant-derived three terpene glucoside known to exhibit anti-oxidative and anti-inflammatory activities.

METHODS AND RESULTS

Here, we investigated its protective effects against neuronal damages elicited by MK-801 treatment. Our behavioral experimental results showed that MK-801-induced PPI deficits and social withdrawal were prevented by MogV treatment. Moreover, the cellular and neurochemical responses of MK-801 in medial prefrontal cortical cortex (mPFC) were also ameliorated by MogV treatment. Also, profiling metabolites assay through artificial intestinal microbiota was performed to identify bioactive components of MogV. An in vitro study of primary neuronal culture demonstrated that MogV and its metabolite 11-oxo-mogrol treatment prevented the MK-801-induced neuronal damages through the mechanisms of promoting neurite outgrowth, inhibiting cell apoptosis, and [Ca²⁺]_i release. Additionally, 11-oxo-mogrol reversed inactivation of phosphorylation levels of AKT and mTOR induced by MK801.

CONCLUSIONS

These results suggest therapeutic potential of MogV for schizophrenia.

Cerebral Glutamate and Gamma-Aminobutyric Acid Levels in Individuals at Ultra-high Risk for Psychosis and the Association With Clinical Symptoms and Cognition

BACKGROUND

Studies examining glutamate or gamma-aminobutyric acid (GABA) in ultra-high risk for psychosis (UHR) and the association with pathophysiology and cognition have shown conflicting results. We aimed to determine whether perturbed glutamate and GABA levels in the anterior cingulate cortex and glutamate levels in the left thalamus were present in UHR individuals and to investigate associations between metabolite levels and clinical symptoms and cognition.

METHODS

We included 122 UHR individuals and 60 healthy control subjects. Participants underwent proton magnetic resonance spectroscopy to estimate glutamate and GABA levels and undertook clinical and cognitive assessments.

RESULTS

We found no differences in metabolite levels between UHR individuals and healthy control subjects. In UHR individuals, we found negative correlations in the anterior cingulate cortex between the composite of glutamate and glutamine (Glx) and the Comprehensive Assessment of At-Risk Mental States composite score (p = .04) and between GABA and alogia (p = .01); positive associations in the anterior cingulate cortex between glutamate (p = .01) and Glx (p = .01) and spatial working memory and between glutamate (p = .04), Glx (p = .04), and GABA (p = .02) and set-shifting; and a positive association in the thalamus between glutamate and attention (p = .04). No associations between metabolites and clinical or cognitive scores were found in the healthy control subjects.

CONCLUSIONS

An association between glutamate and GABA levels and clinical symptoms and cognition found only in UHR individuals suggests a loss of the normal relationship between metabolite levels and cognitive function. Longitudinal studies with investigation of clinical and cognitive outcome and the association with baseline levels of glutamate and GABA could illuminate whether glutamatergic and GABAergic dysfunction predicts clinical outcome.

Immune and Neuroendocrine Trait and State Markers in Psychotic Illness: Decreased Kynurenines Marking Psychotic Exacerbations

Objective: Different patterns of immune system upregulation are present in the acute vs. post-treatment states of psychotic illness. We explored the existence of state and trait markers in the peripheral immune system and two immune-associated neuroendocrine pathways (IDO and GTP-CH1 pathway) in a longitudinal sample of psychosis patients. We also evaluated the association of these markers with neuropsychiatric symptomatology. Method: Plasma concentrations of peripheral blood markers were measured in a transdiagnostic group of 49 inpatients with acute psychosis and 52 matched healthy control subjects. Samples were obtained in patients within 48 h after hospital admission for an acute psychotic episode (before initiation of antipsychotics), after 1-2 weeks and again after 8 weeks of treatment. Kynurenine, kynurenic acid (KA), 3-hydroxykynurenine (3-HK), quinolinic acid (QA), phenylalanine, tyrosine, nitrite, and neopterin were measured using HPLC and LC-MS/MS analysis. Concentrations of CRP, CCL2 (MCP1) and cytokines were determined with multiplex immunoassay. PANSS interviews and cognitive tests were performed at baseline and follow-up. Mixed model analyses were used to identify trait and state markers. Results: Patients had significantly higher plasma concentrations of CRP, CCL2, IL1RA, and lower concentrations of KA and KA/Kyn at all time points (F7.5-17.5, all p < 0.001). Increased concentrations of IL6, IL8, IL1RA, TNFα, and CCL2 and decreased QA and 3-HK (F8.7-21.0, all p < 0.005) were found in the acute psychotic state and normalized after treatment. Low nitrite concentrations at admission rose sharply after initiation of antipsychotic medication (F42.4, p < 0.001). PANSS positive scale scores during the acute episode correlated with pro-inflammatory immune markers (r ≥ |0.5|), while negative scale scores correlated inversely with IDO pathway markers (r ≥ |0.4|). Normalization of KA and 3-HK levels between admission and follow-up corresponded to a larger improvement of negative symptoms (r = 0.5, p < 0.030) A reverse association was found between relative improvement of SDST scores and decreasing KA levels (r = 0.5, p < 0.010). Conclusion: The acute psychotic state is marked by state-specific increases of immune markers and decreases in peripheral IDO pathway markers. Increased CRP, CCL2, and IL1RA, and decreased KA and KA/Kyn are trait markers of psychotic illness.

Glutathione and glutamate in schizophrenia: a 7T MRS study

In schizophrenia, abnormal neural metabolite concentrations may arise from cortical damage following neuroinflammatory processes implicated in acute episodes. Inflammation is associated with increased glutamate, whereas the antioxidant glutathione may protect against inflammation-induced oxidative stress. We hypothesized that patients with stable schizophrenia would exhibit a reduction in glutathione, glutamate, and/or glutamine in the cerebral cortex, consistent with a post-inflammatory response, and that this reduction would be most marked in patients with "residual schizophrenia", in whom an early stage with positive psychotic symptoms has progressed to a late stage characterized by long-term negative symptoms and impairments. We recruited 28 patients with stable schizophrenia and 45 healthy participants matched for age, gender, and parental socio-economic status. We measured glutathione, glutamate and glutamine concentrations in the anterior cingulate cortex (ACC), left insula, and visual cortex using 7T proton magnetic resonance spectroscopy (MRS). Glutathione and glutamate were significantly correlated in all three voxels. Glutamine concentrations across the three voxels were significantly correlated with each other. Principal components analysis (PCA) produced three clear components: an ACC glutathione-glutamate component; an insula-visual glutathione-glutamate component; and a glutamine component. Patients with stable schizophrenia had significantly lower scores on the ACC glutathione-glutamate component, an effect almost entirely leveraged by the sub-group of patients with residual schizophrenia. All three metabolite concentration values in the ACC were significantly reduced in this group. These findings are consistent with the hypothesis that excitotoxicity during the acute phase of illness leads to reduced glutathione and glutamate in the residual phase of the illness.