A randomized clinical trial of MK-0777 for the treatment of cognitive impairments in people with schizophrenia

The excitatory-inhibitory balance as a target for the development of novel drugs to treat schizophrenia

The intricate balance between excitation and inhibition (E/I) in the brain plays a crucial role in normative information processing. Dysfunctions in the E/I balance have been implicated in various psychiatric disorders, including schizophrenia (SCZ). In particular, abnormalities in GABAergic signaling, specifically in parvalbumin (PV)-containing interneurons, have been consistently observed in SCZ pathophysiology. PV interneuron function is vital for maintaining an ideal E/I balance, and alterations in PV interneuron-mediated inhibition contribute to circuit deficits observed in SCZ, including hippocampus hyperactivity and midbrain dopamine system overdrive. While current antipsychotic medications primarily target D2 dopamine receptors and are effective primarily in treating positive symptoms, novel therapeutic strategies aiming to restore the E/I balance could potentially mitigate not only positive symptoms but also negative symptoms and cognitive deficits. This could involve, for instance, increasing the inhibitory drive onto excitatory neurons or decreasing the putative enhanced pyramidal neuron activity due to functional loss of PV interneurons. Compounds targeting the glycine site at glutamate NMDA receptors and muscarinic acetylcholine receptors on PV interneurons that can increase PV interneuron drive, as well as drugs that increase the postsynaptic action of GABA, such as positive allosteric modulators of α5-GABA-A receptors, and decrease glutamatergic output, such as mGluR2/3 agonists, represent promising approaches. Preventive strategies aiming at E/I balance also represent a path to reduce the risk of transitioning to SCZ in high-risk individuals. Therefore, compounds with novel mechanisms targeting E/I balance provide optimism for more effective and tailored interventions in the management of SCZ.

Dysfunctional Parvalbumin Neurons in Schizophrenia and the Pathway to the Clinical Application of Kv3 Channel Modulators

Based on the pathophysiological changes observed in schizophrenia, the gamma-aminobutyric acid (GABA) hypothesis may facilitate the development of targeted treatments for this disease. This hypothesis, mainly derived from postmortem brain results, postulates dysfunctions in a subset of GABAergic neurons, particularly parvalbumin-containing interneurons. In the cerebral cortex, the fast spike firing of parvalbumin-positive GABAergic interneurons is regulated by the Kv3.1 and Kv3.2 channels, which belong to a potassium channel subfamily. Decreased Kv3.1 levels have been observed in the prefrontal cortex of patients with schizophrenia, prompting the investigation of Kv3 channel modulators for the treatment of schizophrenia. However, biomarkers that capture the dysfunction of parvalbumin neurons are required for these modulators to be effective in the pharmacotherapy of schizophrenia. Electroencephalography and magnetoencephalography studies have demonstrated impairments in evoked gamma oscillations in patients with schizophrenia, which may reflect the dysfunction of cortical parvalbumin neurons. This review summarizes these topics and provides an overview of how the development of therapeutics that incorporate biomarkers could innovate the treatment of schizophrenia and potentially change the targets of pharmacotherapy.

Modulators of GABAA receptor-mediated inhibition in the treatment of neuropsychiatric disorders: past, present, and future

The predominant inhibitory neurotransmitter in the brain, γ-aminobutyric acid (GABA), acts at ionotropic GABAA receptors to counterbalance excitation and regulate neuronal firing. GABAA receptors are heteropentameric channels comprised from subunits derived from 19 different genes. GABAA receptors have one of the richest and well-developed pharmacologies of any therapeutic drug target, including agonists, antagonists, and positive and negative allosteric modulators (PAMs, NAMs). Currently used PAMs include benzodiazepine sedatives and anxiolytics, barbiturates, endogenous and synthetic neurosteroids, and general anesthetics. In this article, I will review evidence that these drugs act at several distinct binding sites and how they can be used to alter the balance between excitation and inhibition. I will also summarize existing literature regarding (1) evidence that changes in GABAergic inhibition play a causative role in major depression, anxiety, postpartum depression, premenstrual dysphoric disorder, and schizophrenia and (2) whether and how GABAergic drugs exert beneficial effects in these conditions, focusing on human studies where possible. Where these classical therapeutics have failed to exert benefits, I will describe recent advances in clinical and preclinical drug development. I will also highlight opportunities to advance a generation of GABAergic therapeutics, such as development of subunit-selective PAMs and NAMs, that are engendering hope for novel tools to treat these devastating conditions.

Targeting synapse function and loss for treatment of neurodegenerative diseases

Synapse dysfunction and loss are hallmarks of neurodegenerative diseases that correlate with cognitive decline. However, the mechanisms and therapeutic strategies to prevent or reverse synaptic damage remain elusive. In this Review, we discuss recent advances in understanding the molecular and cellular pathways that impair synapses in neurodegenerative diseases, including the effects of protein aggregation and neuroinflammation. We also highlight emerging therapeutic approaches that aim to restore synaptic function and integrity, such as enhancing synaptic plasticity, preventing synaptotoxicity, modulating neuronal network activity and targeting immune signalling. We discuss the preclinical and clinical evidence for each strategy, as well as the challenges and opportunities for developing effective synapse-targeting therapeutics for neurodegenerative diseases.

Axo-axonic cells in neuropsychiatric disorders: a systematic review

Imbalance between excitation and inhibition in the cerebral cortex is one of the main theories in neuropsychiatric disorder pathophysiology. Cortical inhibition is finely regulated by a variety of highly specialized GABAergic interneuron types, which are thought to organize neural network activities. Among interneurons, axo-axonic cells are unique in making synapses with the axon initial segment of pyramidal neurons. Alterations of axo-axonic cells have been proposed to be implicated in disorders including epilepsy, schizophrenia and autism spectrum disorder. However, evidence for the alteration of axo-axonic cells in disease has only been examined in narrative reviews. By performing a systematic review of studies investigating axo-axonic cells and axo-axonic communication in epilepsy, schizophrenia and autism spectrum disorder, we outline convergent findings and discrepancies in the literature. Overall, the implication of axo-axonic cells in neuropsychiatric disorders might have been overstated. Additional work is needed to assess initial, mostly indirect findings, and to unravel how defects in axo-axonic cells translates to cortical dysregulation and, in turn, to pathological states.

YY1 (Yin-Yang 1), a transcription factor regulating systemic inflammation, is involved in cognitive impairment of depression

AIM

Clinical and preclinical studies suggest that alterations in the peripheral and brain immune system are associated with the pathophysiology of depression, also leading to changes in local glucose metabolism in the brain. Here, the authors identified Yin-Yang 1 (YY1), a transcription factor closely associated with central and peripheral inflammation.

METHODS

Plasma levels of YY1, interleukin (IL) 6, and IL-1β in major depressive disorder (MDD) were collected before and after treatment with vortioxetine, and correlation with clinical and cognitive scores was studied. Chronic unpredictable mild stress was treated with vortioxetine. Micropositron emission tomography (microPET) was used to analyze glucose metabolism and mRNA, and the protein level of the YY1-nuclear factor κB (NF-κB)-IL-1β inflammatory pathway were measured in related brain regions.

RESULTS

Plasma levels of YY1 and IL-1β were significantly increased in MDD and decreased after treatment with vortioxetine. Meanwhile, the level of YY1 in plasma was negatively correlated with cognitive functions in patients with MDD and positively correlated with the level of IL-1β in plasma. Compared with the control group, in chronic unpredictable mild stress rats, (microPET) analysis showed that the decrease of glucose metabolism in the hippocampus, entorhinal cortex, amygdala, striatum, and medial prefrontal cortex was reversed after treatment. mRNA and protein level of related molecular in YY1-NF-κB-IL-1β inflammatory pathway decreased in the hippocampus and was reversed by vortioxetine.

CONCLUSION

The current study suggests that the YY1-NF-κB-IL-1β inflammatory pathway may play an essential role in both mood changes and cognitive impairment in depression, and may be associated with changes in glucose metabolism in emotion regulation and cognition. These findings provide new evidence for the inflammatory mechanisms of depression.

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.

Strategies for Treatment of Disease-Associated Dementia Beyond Alzheimer's Disease: An Update

Memory, cognition, dementia, and neurodegeneration are complexly interlinked processes with various mechanistic pathways, leading to a range of clinical outcomes. They are strongly associated with pathological conditions like Alzheimer's disease, Parkinson's disease, schizophrenia, and stroke and are a growing concern for their timely diagnosis and management. Several cognitionenhancing interventions for management include non-pharmacological interventions like diet, exercise, and physical activity, while pharmacological interventions include medicinal agents, herbal agents, and nutritional supplements. This review critically analyzed and discussed the currently available agents under different drug development phases designed to target the molecular targets, including cholinergic receptor, glutamatergic system, GABAergic targets, glycine site, serotonergic targets, histamine receptors, etc. Understanding memory formation and pathways involved therein aids in opening the new gateways to treating cognitive disorders. However, clinical studies suggest that there is still a dearth of knowledge about the pathological mechanism involved in neurological conditions, making the dropouts of agents from the initial phases of the clinical trial. Hence, a better understanding of the disease biology, mode of drug action, and interlinked mechanistic pathways at a molecular level is required.

Antipsychotics for schizophrenia spectrum disorders with catatonic symptoms

BACKGROUND

Whilst antipsychotics are the mainstay of treatment for schizophrenia spectrum disorders, there have been numerous attempts to identify biomarkers that can predict treatment response. One potential marker may be psychomotor abnormalities, including catatonic symptoms. Early studies suggested that catatonic symptoms predict poor treatment response, whilst anecdotal reports of rare adverse events have been invoked against antipsychotics. The efficacy and safety of antipsychotics in the treatment of this subtype of schizophrenia have rarely been studied in randomised controlled trials (RCTs).

OBJECTIVES

To compare the effects of any single antipsychotic medication with another antipsychotic or with other pharmacological agents, electroconvulsive therapy (ECT), other non-pharmacological neuromodulation therapies (e.g. transcranial magnetic stimulation), or placebo for treating positive, negative, and catatonic symptoms in people who have schizophrenia spectrum disorders with catatonic symptoms.

SEARCH METHODS

We searched the Cochrane Schizophrenia Group's Study-Based Register of Trials, which is based on CENTRAL, MEDLINE, Embase, CINAHL, PsycINFO, PubMed, ClinicalTrials.gov, the ISRCTN registry, and WHO ICTRP, on 19 September 2021. There were no language, date, document type, or publication status limitations for inclusion of records in the register. We also manually searched reference lists from the included studies, and contacted study authors when relevant.

SELECTION CRITERIA

All RCTs comparing any single antipsychotic medication with another antipsychotic or with other pharmacological agents, ECT, other non-pharmacological neuromodulation therapies, or placebo for people who have schizophrenia spectrum disorders with catatonic symptoms.

DATA COLLECTION AND ANALYSIS

two review authors independently inspected citations, selected studies, extracted data, and appraised study quality. For binary outcomes, we planned to calculate risk ratios and their 95% confidence intervals (CI) on an intention-to-treat basis. For continuous outcomes, we planned to calculate mean differences between groups and their 95% CI. We assessed risk of bias for the included studies, and created a summary of findings table; however, we did not assess the certainty of the evidence using the GRADE approach because there was no quantitative evidence in the included study.

MAIN RESULTS

Out of 53 identified reports, one RCT including 14 hospitalised adults with schizophrenia and catatonic symptoms met the inclusion criteria of the review. The study, which was conducted in India and lasted only three weeks, compared risperidone with ECT in people who did not respond to an initial lorazepam trial.   There were no usable data reported on the primary efficacy outcomes of clinically important changes in positive, negative, or catatonic symptoms. Whilst both study groups improved in catatonia scores on the Bush-Francis Catatonia Rating Scale (BFCRS), the ECT group showed significantly greater improvement at week 3 endpoint (mean +/- estimated standard deviation; 0.68 +/- 4.58; N = 8) than the risperidone group (6.04 +/- 4.58; N = 6; P = 0.035 of a two-way analysis of variance (ANOVA) for repeated measures originally conducted in the trial). Similarly, both groups improved on the Positive and Negative Syndrome Scale (PANSS) scores by week 3, but ECT showed significantly greater improvement in positive symptoms scores compared with risperidone (P = 0.04). However, data on BFCRS scores in the ECT group appeared to be skewed, and mean PANSS scores were not reported, thereby precluding further analyses of both BFCRS and PANSS data according to the protocol.  Although no cases of neuroleptic malignant syndrome were reported, extrapyramidal symptoms as a primary safety outcome were reported in three cases in the risperidone group. Conversely, headache (N = 6), memory loss (N = 4), and a prolonged seizure were reported in people receiving ECT. These adverse effects, which were assessed as specific for antipsychotics and ECT, respectively, were the only adverse effects reported in the study. However, the exact number of participants with adverse events was not clearly reported in both groups, precluding further analysis.  Our results were based only on a single study with a very small sample size, short duration of treatment, unclear or high risk of bias due to unclear randomisation methods, possible imbalance in baseline characteristics, skewed data, and selective reporting. Data on outcomes of general functioning, global state, quality of life, and service use, as well as data on specific phenomenology and duration of catatonic symptoms, were not reported.

AUTHORS' CONCLUSIONS

We found only one small, short-term trial suggesting that risperidone may improve catatonic and positive symptoms scale scores amongst people with schizophrenia spectrum disorders and catatonic symptoms, but that ECT may result in greater improvement in the first three weeks of treatment. Due to small sample size, methodological shortcomings and brief duration of the study, as well as risk of bias, the evidence from this review is of very low quality. We are uncertain if these are true effects, limiting any conclusions that can be drawn from the evidence. No cases of neuroleptic malignant syndrome were reported, but we cannot rule out the risk of this or other rare adverse events in larger population samples.  High-quality trials continue to be necessary to differentiate treatments for people with symptoms of catatonia in schizophrenia spectrum disorders. The lack of consensus on the psychopathology of catatonia remains a barrier to defining treatments for people with schizophrenia. Better understanding of the efficacy and safety of antipsychotics may clarify treatment for this unique subtype of schizophrenia.

Beyond antipsychotics: a twenty-first century update for preclinical development of schizophrenia therapeutics

Despite 50+ years of drug discovery, current antipsychotics have limited efficacy against negative and cognitive symptoms of schizophrenia, and are ineffective-with the exception of clozapine-against any symptom domain for patients who are treatment resistant. Novel therapeutics with diverse non-dopamine D2 receptor targets have been explored extensively in clinical trials, yet often fail due to a lack of efficacy despite showing promise in preclinical development. This lack of translation between preclinical and clinical efficacy suggests a systematic failure in current methods that determine efficacy in preclinical rodent models. In this review, we critically evaluate rodent models and behavioural tests used to determine preclinical efficacy, and look to clinical research to provide a roadmap for developing improved translational measures. We highlight the dependence of preclinical models and tests on dopamine-centric theories of dysfunction and how this has contributed towards a self-reinforcing loop away from clinically meaningful predictions of efficacy. We review recent clinical findings of distinct dopamine-mediated dysfunction of corticostriatal circuits in patients with treatment-resistant vs. non-treatment-resistant schizophrenia and suggest criteria for establishing rodent models to reflect such differences, with a focus on objective, translational measures. Finally, we review current schizophrenia drug discovery and propose a framework where preclinical models are validated against objective, clinically informed measures and preclinical tests of efficacy map onto those used clinically.

The Case for Clinical Trials with Novel GABAergic Drugs in Diabetes Mellitus and Obesity

Obesity and diabetes mellitus have become the surprising menaces of relative economic well-being worldwide. Gamma amino butyric acid (GABA) has a prominent role in the control of blood glucose, energy homeostasis as well as food intake at several levels of regulation. The effects of GABA in the body are exerted through ionotropic GABAA and metabotropic GABAB receptors. This treatise will focus on the pharmacologic targeting of GABAA receptors to reap beneficial therapeutic effects in diabetes mellitus and obesity. A new crop of drugs selectively targeting GABAA receptors has been under investigation for efficacy in stroke recovery and cognitive deficits associated with schizophrenia. Although these trials have produced mixed outcomes the compounds are safe to use in humans. Preclinical evidence is summarized here to support the rationale of testing some of these compounds in diabetic patients receiving insulin in order to achieve better control of blood glucose levels and to combat the decline of cognitive performance. Potential therapeutic benefits could be achieved (i) By resetting the hypoglycemic counter-regulatory response; (ii) Through trophic actions on pancreatic islets, (iii) By the mobilization of antioxidant defence mechanisms in the brain. Furthermore, preclinical proof-of-concept work, as well as clinical trials that apply the novel GABAA compounds in eating disorders, e.g., olanzapine-induced weight-gain, also appear warranted.

Application of evoked response audiometry for specifying aberrant gamma oscillations in schizophrenia

Gamma oscillations probed using auditory steady-state response (ASSR) are promising clinical biomarkers that may give rise to novel therapeutic interventions for schizophrenia. Optimizing clinical settings for these biomarker-driven interventions will require a quick and easy assessment system for gamma oscillations in psychiatry. ASSR has been used in clinical otolaryngology for evoked response audiometry (ERA) in order to judge hearing loss by focusing on the phase-locked response detectability via an automated analysis system. Herein, a standard ERA system with 40- and 46-Hz ASSRs was applied to evaluate the brain pathophysiology of patients with schizophrenia. Both ASSRs in the ERA system showed excellent detectability regarding the phase-locked response in healthy subjects and sharply captured the deficits of the phase-locked response caused by aberrant gamma oscillations in individuals with schizophrenia. These findings demonstrate the capability of the ERA system to specify patients who have aberrant gamma oscillations. The ERA system may have a potential to serve as a real-world clinical medium for upcoming biomarker-driven therapeutics in psychiatry.

Mechanisms underlying dorsolateral prefrontal cortex contributions to cognitive dysfunction in schizophrenia

Kraepelin, in his early descriptions of schizophrenia (SZ), characterized the illness as having "an orchestra without a conductor." Kraepelin further speculated that this "conductor" was situated in the frontal lobes. Findings from multiple studies over the following decades have clearly implicated pathology of the dorsolateral prefrontal cortex (DLPFC) as playing a central role in the pathophysiology of SZ, particularly with regard to key cognitive features such as deficits in working memory and cognitive control. Following an overview of the cognitive mechanisms associated with DLPFC function and how they are altered in SZ, we review evidence from an array of neuroscientific approaches addressing how these cognitive impairments may reflect the underlying pathophysiology of the illness. Specifically, we present evidence suggesting that alterations of the DLPFC in SZ are evident across a range of spatial and temporal resolutions: from its cellular and molecular architecture, to its gross structural and functional integrity, and from millisecond to longer timescales. We then present an integrative model based upon how microscale changes in neuronal signaling in the DLPFC can influence synchronized patterns of neural activity to produce macrocircuit-level alterations in DLPFC activation that ultimately influence cognition and behavior. We conclude with a discussion of initial efforts aimed at targeting DLPFC function in SZ, the clinical implications of those efforts, and potential avenues for future development.

Pharmacological Treatment for Social Cognition: Current Evidence

Cognitive impairment is currently considered a core feature of schizophrenia (SZ) and is gaining attention as a fundamental therapeutic target. Standard treatment for SZ involves the use of antipsychotics that are successfully used to control positive symptoms and disorganized behaviour. However, it is still unclear whether they are effective on social cognition (SC) impairment. Furthermore, different medications are currently being studied to improve SC in patients with SZ. A literature search on this topic was conducted using the PubMed database. All kinds of publications (i.e., reviews, original contributions and case reports) written in English and published in the last 15 years were included. The aim of our literature review is to draw a picture of the current state of the pharmacological treatment of SC impairment in SZ.

Cognitive dysfunction among inpatients and outpatients with schizophrenia: relationship to positive and negative symptoms

Background

Cognitive impairment is an established feature of schizophrenia and is a strong predictor of eventual social and functional outcome. Few studies have investigated cognitive impairment in hospital long-stay patients with schizophrenia. This study evaluates and compares cognitive function among a sample of patients with schizophrenia in both inpatient and outpatient departments in order to determine the relationship between cognitive impairment and clinical variables.

A cross-sectional comparative study based on a semi-structured interview investigating 100 inpatients with schizophrenia recruited from El-Abassia Mental Health Hospital departments compared to 100 patients with schizophrenia selected from the outpatients’ clinic matched with cases. The assessment tools included SCID-I, the Adult Wechsler Intelligence Scale, the computerized version of Wisconsin Card Sorting Test (WCST), Mini-Mental State Examination (MMSE), and Positive and Negative Syndrome Scale (PANSS).

Results

Patients with schizophrenia showed significant deficits on cognitive function with no statistically significant difference between the inpatient and outpatient groups. Executive function was significantly correlated with verbal, non-verbal, and total IQ. Executive function was negatively correlated with the positive and general symptoms of PANSS and not correlated with its negative symptoms. In addition, we did not find any statistically significant relationship between cognitive functions and the duration of illness.

Conclusion

The study provides evidence that institutionalization is not an influential factor on cognitive impairment patients with schizophrenia. However, the psychopathological aspects of the disorder are one of the crucial factors affecting the cognitive function in schizophrenia.

Linking peripheral IL-6, IL-1β and hypocretin-1 with cognitive impairment from major depression

BACKGROUND

Cognitive impairment has long challenged the patients with major depressive disorder (MDD), hypocretins and inflammation have recently been implicated in cognitive function. However, limited studies have compressively assessed their associations with cognitive impairment in MDD.

METHODS

A total of 100 MDD patients and 100 healthy controls (HC) were recruited for this study. They were tested with HAMD, HAMA, and MCCB scales. The plasma level of selected inflammatory factors (IL-1β, IL-6, and TNF-α) and hypocretin-1 were determined using enzyme-linked immunosorbent assay (ELISA). Correlation analysis was performed to explore the relationship between the plasma level of the factors and clinical performances.

RESULTS

Patients with MDD showed cognitive impairment in each MCCB subdomain except working memory compared with HC. The levels of IL-6, IL-1β and hypocretin-1 in MDD patients were higher than HC. Besides, IL-1β levels was negatively correlated with overall cognitive function in the combined group. Hypocretin-1 was positively correlated with socially cognitive impairment in MDD patients. A negative correlation between plasma hypocretin-1 levels and HAMA scales was also observed in MDD patients.

LIMITATION

The study was cross-sectional, thereby limiting causal inference, and had a relatively small sample size. There are no subcategories for MDD based on characteristics.

CONCLUSION

IL-1β, IL-6 and Hypocretin-1 were reported as potential factors involved in MDD pathology. Hypocretin-1 could contribute to the biological mechanisms of anxiety relief. Hypocretin-1, therefore, may be important in exploring the pathological mechanisms of social cognitive impairment in MDD patients. Conclusively, this study provides new insights for exploring cognitive impairment in depression.

erbb4 Deficits in Chandelier Cells of the Medial Prefrontal Cortex Confer Cognitive Dysfunctions: Implications for Schizophrenia

erbb4 is a known susceptibility gene for schizophrenia. Chandelier cells (ChCs, also known as axo-axonic cells) are a distinct GABAergic interneuron subtype that exclusively target the axonal initial segment, which is the site of pyramidal neuron action potential initiation. ChCs are a source of ErbB4 expression and alterations in ChC-pyramidal neuron connectivity occur in the medial prefrontal cortex (mPFC) of schizophrenic patients and animal models of schizophrenia. However, the contribution of ErbB4 in mPFC ChCs to the pathogenesis of schizophrenia remains unknown. By conditional deletion or knockdown of ErbB4 from mPFC ChCs, we demonstrated that ErbB4 deficits led to impaired ChC-pyramidal neuron connections and cognitive dysfunctions. Furthermore, the cognitive dysfunctions were normalized by L-838417, an agonist of GABAAα2 receptors enriched in the axonal initial segment. Given that cognitive dysfunctions are a core symptom of schizophrenia, our results may provide a new perspective for understanding the etiology of schizophrenia and suggest that GABAAα2 receptors may be potential pharmacological targets for its treatment.

Prefrontal cortical alterations of glutamate and GABA neurotransmission in schizophrenia: Insights for rational biomarker development

Certain cognitive deficits in schizophrenia, such as impaired working memory, are thought to reflect alterations in the neural circuitry of the dorsolateral prefrontal cortex (DLPFC). Gamma oscillations in the DLPFC appear to be a neural corollary of working memory function, and the power of these oscillations during working memory tasks is lower in individuals with schizophrenia. Thus, gamma oscillations represent a potentially useful biomarker to index dysfunction in the DLPFC circuitry responsible for working memory in schizophrenia. Postmortem studies, by identifying the cellular basis of DLPFC dysfunction, can help inform the utility of biomarker measures obtained in vivo. Given that gamma oscillations reflect network activity of excitatory pyramidal neurons and inhibitory GABA neurons, we review postmortem findings of alterations to both cell types in the DLPFC and discuss how these findings might inform future biomarker development and use.

Improving Cognition via Exercise (ICE): Study Protocol for a Multi-Site, Parallel-Group, Single-Blind, Randomized Clinical Trial Examining the Efficacy of Aerobic Exercise to Improve Neurocognition, Daily Functioning, and Biomarkers of Cognitive Change in Individuals with Schizophrenia

Individuals with schizophrenia (SZ) display cognitive deficits that have been identified as major determinants of poor functioning and disability, representing a serious public health concern and an important target for interventions. At present, available treatments offer only minimal to moderate benefits to ameliorate cognitive deficits. Thus, there remains an urgent need to identify novel interventions to improve cognition in people with SZ. Emerging evidence from animal and basic human research suggests aerobic exercise training (AE) has beneficial effects on cognition. Preliminary findings suggest that AE is efficacious in improving cognitive functioning in SZ, however the extant studies have been limited by small samples, a dearth of information on biologically-relevant covariates, and limited information on impact on daily functioning. Additionally, while AE-related cognitive benefits have been linked to Brain-Derived Neurotrophic Factor (BDNF) upregulation, this putative mechanism needs confirmation. The present report describes a study protocol designed to address these limitations-we review and summarize the current literature on treatment of cognitive deficits in SZ, state the rationale for employing AE to target these deficits, and describe the current protocol-a multi-site, single-blind, randomized clinical trial aiming to recruit 200 community-dwelling individuals with SZ. Participants are randomized to one of two 12-week interventions: AE using active-play video games (i.e., Xbox Kinect) and traditional cardiovascular exercise equipment or a stretching-and-toning (ST) control intervention. Participants undergo assessments of aerobic fitness, cognition, and daily functioning, as well as BDNF and other biomarkers of cognitive change, at baseline and after 6-and 12-weeks.

Discovery and Development of Non-Dopaminergic Agents for the Treatment of Schizophrenia: Overview of the Preclinical and Early Clinical Studies

Schizophrenia is a chronic psychiatric disorder that affects about 1 in 100 people around the world and results in persistent emotional and cognitive impairments. Untreated schizophrenia leads to deterioration in quality of life and premature death. Although the clinical efficacy of dopamine D2 receptor antagonists against positive symptoms of schizophrenia supports the dopamine hypothesis of the disease, the resistance of negative and cognitive symptoms to these drugs implicates other systems in its pathophysiology. Many studies suggest that abnormalities in glutamate homeostasis may contribute to all three groups of schizophrenia symptoms. Scientific considerations also include disorders of gamma-aminobutyric acid-ergic and serotonergic neurotransmissions as well as the role of the immune system. The purpose of this review is to update the most recent reports on the discovery and development of non-dopaminergic agents that may reduce positive, negative, and cognitive symptoms of schizophrenia, and may be alternative to currently used antipsychotics. This review collects the chemical structures of representative compounds targeting metabotropic glutamate receptor, gamma-aminobutyric acid type A receptor, alpha 7 nicotinic acetylcholine receptor, glycine transporter type 1 and glycogen synthase kinase 3 as well as results of in vitro and in vivo studies indicating their efficacy in schizophrenia. Results of clinical trials assessing the safety and efficacy of the tested compounds have also been presented. Finally, attention has been paid to multifunctional ligands with serotonin receptor affinity or phosphodiesterase inhibitory activity as novel strategies in the search for dedicated medicines for patients with schizophrenia.

The characteristics of cognitive neuroscience tests in a schizophrenia cognition clinical trial: Psychometric properties and correlations with standard measures

In comparison to batteries of standard neuropsychological tests, cognitive neuroscience tests may offer a more specific assessment of discrete neurobiological processes that may be aberrant in schizophrenia. However, more information regarding psychometric properties and correlations with standard neuropsychological tests and functional measures is warranted to establish their validity as treatment outcome measures. The N-back and AX-Continuous Performance Task (AX-CPT) are two promising cognitive neuroscience tests designed to measure specific components of working memory and contextual processing respectively. In the current study, we report the psychometric properties of multiple outcome measures from these two tests as well as their correlations with standard neuropsychological measures and functional capacity measures. The results suggest that while the AX-CPT and N-back display favorable psychometric properties, they do not exhibit greater sensitivity or specificity with functional measures than standard neurocognitive tests.

The Fragile Brain: Stress Vulnerability, Negative Affect and GABAergic Neurocircuits in Psychosis

Persons with schizophrenia exhibit sensitivity to stress and negative affect (NA), both strongly correlated with poor functional outcome. This theoretical review suggests that NA reflects a "fragile brain," ie, vulnerable to stress, including events not experienced as stressful by healthy individuals. Based on postmortem evidence of altered gamma-aminobutyric acid (GABA) function in parvalbumin positive interneurons (PVI), animal models of PVI abnormalities and neuroimaging data with GABAergic challenge, it is suggested that GABAergic disruptions weaken cortical regions, which leads to stress vulnerability and excessive NA. Neurocircuits that respond to stressful and salient environmental stimuli, such as the hypothalamic-pituitary-adrenal axis and the amygdala, are highly dysregulated in schizophrenia, exhibiting hypo- and hyper-activity. PVI abnormalities in lateral prefrontal cortex and hippocampus have been hypothesized to affect cognitive function and positive symptoms, respectively; in the medial frontal cortex (dorsal anterior cingulate cortex and dorsal medial prefrontal cortex), these abnormalities may lead to vulnerability to stress, NA and dysregulation of stress responsive systems. Given that postmortem PVI disruptions have been identified in other conditions, such as bipolar disorder and autism, stress vulnerability may reflect a transdiagnostic dimension of psychopathology.

Comprehensive review of the research employing the schizophrenia cognition rating scale (SCoRS)

This review of research utilizing the Schizophrenia Cognition Rating Scale (SCoRS) outlines the development, evaluation, validation, and implementation of the SCoRS to assess whether the scale meets the criteria as a functional co-primary as defined by the MATRICS-CT initiative. Interview-based co-primary assessments should be: 1) practical and easy to administer for a clinician or researcher; 2) validated in individuals with schizophrenia; 3) contain the relevant areas of cognition and functioning applicable to schizophrenia; 4) able to assess all phases and severity levels of schizophrenia; 5) capable of monitoring disease progression; 6) minimal burden to patients; and 7) sensitive to assess treatment effects. A review of the literature was conducted to present information on the development, psychometric properties and usage of the SCoRS. Review of the development of the SCoRS followed the parameters outlined for scale development on content expert validation and feedback. The SCoRS shows good psychometric properties in various studies, and demonstrates low burden on clinicians and patients. The items measure global concepts that do not require notable cultural modification, making international use feasible. While multiple performance-based tests in cognition and functional outcomes are available, there is a need for a multi-domain, interview-based assessment of cognitive progression and treatment response in clinical trials. The SCoRS appears to meet many of the criteria for an optimal co-primary measure for schizophrenia cognition clinical trials as defined in the MATRICS-CT initiative.

White matter neuron biology and neuropathology in schizophrenia

Schizophrenia is considered a neurodevelopmental disorder as it often manifests before full brain maturation and is also a cerebral cortical disorder where deficits in GABAergic interneurons are prominent. Whilst most neurons are located in cortical and subcortical grey matter regions, a smaller population of neurons reside in white matter tracts of the primate and to a lesser extent, the rodent brain, subjacent to the cortex. These interstitial white matter neurons (IWMNs) have been identified with general markers for neurons [e.g., neuronal nuclear antigen (NeuN)] and with specific markers for neuronal subtypes such as GABAergic neurons. Studies of IWMNs in schizophrenia have primarily focused on their density underneath cortical areas known to be affected in schizophrenia such as the dorsolateral prefrontal cortex. Most of these studies of postmortem brains have identified increased NeuN+ and GABAergic IWMN density in people with schizophrenia compared to healthy controls. Whether IWMNs are involved in the pathogenesis of schizophrenia or if they are increased because of the cortical pathology in schizophrenia is unknown. We also do not understand how increased IWMN might contribute to brain dysfunction in the disorder. Here we review the literature on IWMN pathology in schizophrenia. We provide insight into the postulated functional significance of these neurons including how they may contribute to the pathophysiology of schizophrenia.

Limited changes in activities of daily life performance ability among people with schizophrenia at clinical settings and the factors moderating the changes

Background

Impaired community functioning and functional ability are common among people with schizophrenia spectrum disorders (SSD). However, changes occurring in activities of daily life (ADL) ability through interventions provided at clinical settings have not been systematically examined in this population.

Methods

We retrospectively collated and analysed changes in ADL ability between admissions and discharges, measured utilising the Assessment of Motor and Process Skills (AMPS), among 72 people with SSD at a public inpatient treatment and rehabilitation facility in Western Australia. Clinical and demographic factors moderating the changes were also determined.

Results

The standardised AMPS motor (p = 0.0088) and process scores (p < 0.0001) improved significantly between admission and discharge. However, overall, the improvements were of small to moderate magnitude, and >60% of participants did not experience significant or meaningful changes. Furthermore, mild to moderate impairment in the AMPS standardised motor (-1.3 SD), and process (-1.6 SD) ability was present at discharge. A logistic regression analysis revealed that low admission AMPS scores and duration of illness of more than five years predicted improvement of the AMPS motor score by discharge, but only the former predicted changes in the process scores. Other demographic, clinical, and treatment-related variables did not affect the outcome of the AMPS scores.

Conclusions

Impairment of ADL ability is recalcitrant in schizophrenia. The improvement was modest and occurred only in a proportion of participants. However, promisingly, chronic illness, low baseline ADL ability, treatment with clozapine and presence of treatment-resistant schizophrenia did not have an adverse effect on the outcome.

The past and future of novel, non-dopamine-2 receptor therapeutics for schizophrenia: A critical and comprehensive review

Since the discovery of chlorpromazine in the 1950's, antipsychotic drugs have been the cornerstone of treatment of schizophrenia, and all attenuate dopamine transmission at the dopamine-2 receptor. Drug development for schizophrenia since that time has led to improvements in side effects and tolerability, and limited improvements in efficacy, with the exception of clozapine. However, the reasons for clozapine's greater efficacy remain unclear, despite the great efforts and resources invested therewith. We performed a comprehensive review of the literature to determine the fate of previously tested, non-dopamine-2 receptor experimental treatments. Overall we included 250 studies in the review from the period 1970 to 2017 including treatments with glutamatergic, serotonergic, cholinergic, neuropeptidergic, hormone-based, dopaminergic, metabolic, vitamin/naturopathic, histaminergic, infection/inflammation-based, and miscellaneous mechanisms. Despite there being several promising targets, such as allosteric modulation of the NMDA and α7 nicotinic receptors, we cannot confidently state that any of the mechanistically novel experimental treatments covered in this review are definitely effective for the treatment of schizophrenia and ready for clinical use. We discuss potential reasons for the relative lack of progress in developing non-dopamine-2 receptor treatments for schizophrenia and provide recommendations for future efforts pursuing novel drug development for schizophrenia.

Neurobiology and treatment of social cognition in schizophrenia: Bridging the bed-bench gap

Social cognition refers to the psychological processes involved in the perception, encoding, storage, retrieval, and regulation of information about others and ourselves. This process is essential for survival and reproduction in complex social environments. Recent evidence suggests that impairments in social cognition frequently occur in schizophrenia, mainly contributing to poor functional outcomes, including the inability to engage in meaningful work and maintain satisfying interpersonal relationships. With the ambiguous definition of social cognition, the neurobiology underlying impaired social cognition remains unknown, and the effectiveness of currently available intervention strategies in schizophrenia remain limited. Considering the advances and challenges of translational research for schizophrenia, social cognition has been considered a high-priority domain for treatment development. Here, we describe the current state of the framework, clinical concerns, and intervention approaches for social cognition in schizophrenia. Next, we introduce translatable rodent models associated with schizophrenia that allow the evaluation of different components of social behaviors, providing deeper insights into the neural substrates of social cognition in schizophrenia. Our review presents a valuable perspective that indicates the necessity of building bridges between basic and clinical science researchers for the development of novel therapeutic approaches in impaired social cognition in schizophrenia.

TPA-023 attenuates subchronic phencyclidine-induced declarative and reversal learning deficits via GABAA receptor agonist mechanism: possible therapeutic target for cognitive deficit in schizophrenia

GABAergic drugs are of interest for the treatment of anxiety, depression, bipolar disorder, pain, cognitive impairment associated with schizophrenia (CIAS), and other neuropsychiatric disorders. Some evidence suggests that TPA-023, (7-(1,1-dimethylethyl)-6-(2-ethyl-2H-1,2,4-triazol-3-ylmethoxy)-3-(2-fluorophenyl)-1,2,4-triazolo[4,3-b] pyridazine), a GABA_A α2,3 subtype-selective GABA_A partial agonist and α_1/5 antagonist, and the neurosteroid, pregnenolone sulfate, a GABA_A antagonist, may improve CIAS in pilot clinical trials. The goal of this study was to investigate the effect of TPA-023 in mice after acute or subchronic (sc) treatment with the N-methyl-D-aspartate receptor (NMDAR) antagonist, phencyclidine (PCP), on novel object recognition (NOR), reversal learning (RL), and locomotor activity (LMA) in rodents. Acute TPA-023 significantly reversed scPCP-induced NOR and RL deficits. Co-administration of sub-effective dose (SED) TPA-023 with SEDs of the atypical antipsychotic drug, lurasidone, significantly potentiated the effect of TPA-023 in reversing the scPCP-induced NOR deficit. Further, scTPA-023 co-administration significantly prevented scPCP-induced NOR deficit for 5 weeks. Also, administration of TPA-023 for 7 days following scPCP reversed the NOR deficit for 1 week. However, TPA-023 did not blunt acute PCP-induced hyperactivity, suggesting lack of efficacy as a treatment for psychosis. Systemic TPA-023 significantly blocked lurasidone-induced increases in cortical acetylcholine, dopamine, and glutamate without affecting increases in norepinephrine and with minimal effect on basal release of these neurotransmitters. TPA-023 significantly inhibited PCP-induced cortical and striatal dopamine, serotonin, norepinephrine, and glutamate efflux. These results suggest that TPA-023 and other GABA_A agonists may be of benefit to treat CIAS.

Efficacy of different types of cognitive enhancers for patients with schizophrenia: a meta-analysis

Cognitive impairment is a core feature of schizophrenia, which is predictive for functional outcomes and is, therefore, a treatment target in itself. Yet, literature on efficacy of different pharmaco-therapeutic options is inconsistent. This quantitative review provides an overview of studies that investigated potential cognitive enhancers in schizophrenia. We included pharmacological agents, which target different neurotransmitter systems and evaluated their efficacy on overall cognitive functioning and seven separate cognitive domains. In total, 93 studies with 5630 patients were included. Cognitive enhancers, when combined across all different neurotransmitter systems, which act on a large number of different mechanisms, showed a significant (yet small) positive effect size of 0.10 (k = 51, p = 0.023; 95% CI = 0.01 to 0.18) on overall cognition. Cognitive enhancers were not superior to placebo for separate cognitive domains. When analyzing each neurotransmitter system separately, agents acting predominantly on the glutamatergic system showed a small significant effect on overall cognition (k = 29, Hedges’ g = 0.19, p = 0.01), as well as on working memory (k = 20, Hedges’ g = 0.13, p = 0.04). A sub-analysis of cholinesterase inhibitors (ChEI) showed a small effect on working memory (k = 6, Hedges’ g = 0.26, p = 0.03). Other sub-analyses were positively nonsignificant, which may partly be due to the low number of studies we could include per neurotransmitter system. Overall, this meta-analysis showed few favorable effects of cognitive enhancers for patients with schizophrenia, partly due to lack of power. There is a lack of studies involving agents acting on other than glutamatergic and cholinergic systems, especially of those targeting the dopaminergic system.

Targeting hypothalamic-pituitary-adrenal axis hormones and sex steroids for improving cognition in major mood disorders and schizophrenia: a systematic review and narrative synthesis

Cognitive deficits are a core feature of serious mental illnesses such as schizophrenia, major depressive disorder (MDD) and bipolar disorder (BD) and are a common cause of functional disability. There is limited efficacy of pharmacological interventions for improving the cognitive deficits in these disorders. As pro-cognitive pharmacological treatments are lacking, hormones or drugs that target the endocrine system may become potential candidates for 'repurposing' trials aiming to improve cognition. We aimed to study whether treatment with drugs targeting the hypothalamic-pituitary-adrenal (HPA) axis and sex steroids can improve cognition in patients with schizophrenia, MDD or BD. A systematic search was performed using PubMed (Medline), PsychInfo and clinicaltrials.gov, and a narrative synthesis was included. The systematic review identified 12 studies dealing with HPA-related drugs (mifepristone [n = 3], cortisol synthesis inhibitors [ketoconazole, n = 2], dehydroepiandrosterone [n = 5], fludrocortisone [n = 2]) and 14 studies dealing with sex steroids (oestradiol [n = 2], selective oestrogen receptor modulators [raloxifene, n = 7], pregnenolone [n = 5]). Positive trials were found for BD (mifepristone), MDD (dehydroepiandrosterone and fludrocortisone) and schizophrenia (dehydroepiandrosterone, raloxifene and pregnenolone). A replication of positive findings by at least two clinical trials was found for mifepristone in BD and raloxifene and pregnenolone in schizophrenia. The use of drugs targeting hormones related to the HPA axis and sex steroids is a promising field of research that might help to improve the cognitive outcome of patients with schizophrenia, bipolar disorder and major depressive disorder in the near future.

PV Interneurons: Critical Regulators of E/I Balance for Prefrontal Cortex-Dependent Behavior and Psychiatric Disorders

Elucidating the prefrontal cortical microcircuit has been challenging, given its role in multiple complex behaviors, including working memory, cognitive flexibility, attention, social interaction and emotional regulation. Additionally, previous methodological limitations made it difficult to parse out the contribution of certain neuronal subpopulations in refining cortical representations. However, growing evidence supports a fundamental role of fast-spiking parvalbumin (PV) GABAergic interneurons in regulating pyramidal neuron activity to drive appropriate behavioral responses. Further, their function is heavily diminished in the prefrontal cortex (PFC) in numerous psychiatric diseases, including schizophrenia and autism. Previous research has demonstrated the importance of the optimal balance of excitation and inhibition (E/I) in cortical circuits in maintaining the efficiency of cortical information processing. Although we are still unraveling the mechanisms of information representation in the PFC, the E/I balance seems to be crucial, as pharmacological, chemogenetic and optogenetic approaches for disrupting E/I balance induce impairments in a range of PFC-dependent behaviors. In this review, we will explore two key hypotheses. First, PV interneurons are powerful regulators of E/I balance in the PFC, and help optimize the representation and processing of supramodal information in PFC. Second, diminishing the function of PV interneurons is sufficient to generate an elaborate symptom sequelae corresponding to those observed in a range of psychiatric diseases. Then, using this framework, we will speculate on whether this circuitry could represent a platform for the development of therapeutic interventions in disorders of PFC function.

GABAergic inhibitory neurons as therapeutic targets for cognitive impairment in schizophrenia

Schizophrenia is considered primarily as a cognitive disorder. However, functional outcomes in schizophrenia are limited by the lack of effective pharmacological and psychosocial interventions for cognitive impairment. GABA (gamma-aminobutyric acid) interneurons are the main inhibitory neurons in the central nervous system (CNS), and they play a critical role in a variety of pathophysiological processes including modulation of cortical and hippocampal neural circuitry and activity, cognitive function-related neural oscillations (eg, gamma oscillations) and information integration and processing. Dysfunctional GABA interneuron activity can disrupt the excitatory/inhibitory (E/I) balance in the cortex, which could represent a core pathophysiological mechanism underlying cognitive dysfunction in schizophrenia. Recent research suggests that selective modulation of the GABAergic system is a promising intervention for the treatment of schizophrenia-associated cognitive defects. In this review, we summarized evidence from postmortem and animal studies for abnormal GABAergic neurotransmission in schizophrenia, and how altered GABA interneurons could disrupt neuronal oscillations. Next, we systemically reviewed a variety of up-to-date subtype-selective agonists, antagonists, positive and negative allosteric modulators (including dual allosteric modulators) for α5/α3/α2 GABA_A and GABA_B receptors, and summarized their pro-cognitive effects in animal behavioral tests and clinical trials. Finally, we also discuss various representative histone deacetylases (HDAC) inhibitors that target GABA system through epigenetic modulations, GABA prodrug and presynaptic GABA transporter inhibitors. This review provides important information on current potential GABA-associated therapies and future insights for development of more effective treatments.

Altered brainstem responses to modafinil in schizophrenia: implications for adjunctive treatment of cognition

Candidate pro-cognitive drugs for schizophrenia targeting several neurochemical systems have consistently failed to demonstrate robust efficacy. It remains untested whether concurrent antipsychotic medications exert pharmacodynamic interactions that mitigate pro-cognitive action in patients. We used functional MRI (fMRI) in a randomized, double-blind, placebo-controlled within-subject crossover test of single-dose modafinil effects in 27 medicated schizophrenia patients, interrogating brainstem regions where catecholamine systems arise to innervate the cortex, to link cellular and systems-level models of cognitive control. Modafinil effects were evaluated both within this patient group and compared to a healthy subject group. Modafinil modulated activity in the locus coeruleus (LC) and ventral tegmental area (VTA) in the patient group. However, compared to the healthy comparison group, these effects were altered as a function of task demands: the control-independent drug effect on deactivation was relatively attenuated (shallower) in the LC and exaggerated (deeper) in the VTA; in contrast, again compared to the comparison group, the control-related drug effects on positive activation were attenuated in LC, VTA and the cortical cognitive control network. These altered effects in the LC and VTA were significantly and specifically associated with the degree of antagonism of alpha-2 adrenergic and dopamine-2 receptors, respectively, by concurrently prescribed antipsychotics. These sources of evidence suggest interacting effects on catecholamine neurons of chronic antipsychotic treatment, which respectively increase and decrease sustained neuronal activity in LC and VTA. This is the first direct evidence in a clinical population to suggest that antipsychotic medications alter catecholamine neuronal activity to mitigate pro-cognitive drug action on cortical circuits.

Cognitive Deficits in Schizophrenia: Understanding the Biological Correlates and Remediation Strategies

Cognitive deficits are one of the core symptoms of schizophrenia that evolve during the course of schizophrenia, after being originated even before the onset of illness. Existing pharmacological and biological treatment modalities fall short to meet the needs to improve the cognitive symptoms; hence, various cognitive remediation strategies have been adopted to address these deficits. Research evidences suggest that cognitive remediation measures improve the functioning, limit disability bettering the quality of life. The functional outcomes of cognitive remediation in schizophrenia are resultant of neurobiological changes in specific brain areas. Recent years witnessed significant innovations in cognitive remediation strategies in schizophrenia. This comprehensive review highlights the biological correlates of cognitive deficits in schizophrenia and the remedial measures with evidence base.

Psychometric characteristics of the MATRICS Consensus Cognitive Battery in a large pooled cohort of stable schizophrenia patients

The MATRICS Consensus Cognitive Battery (MCCB) was developed to assess cognitive treatment effects in schizophrenia clinical trials, and is considered the FDA gold standard outcome measure for that purpose. The aim of the present study was to establish pre-treatment psychometric characteristics of the MCCB in a large pooled sample. The dataset included 2616 stable schizophrenia patients enrolled in 15 different clinical trials between 2007 and 2016 within the United States (94%) and Canada (6%). The MCCB was administered twice prior to the initiation of treatment in 1908 patients. Test-retest reliability and practice effects of the cognitive composite score, the neurocognitive composite score, which excludes the domain Social Cognition, and the subtests/domains were examined using Intra-Class Correlations (ICC) and Cohen's d. Simulated regression models explored which domains explained the greatest portion of variance in composite scores. Test-retest reliability was high (ICC=0.88) for both composite scores. Practice effects were small for the cognitive (d=0.15) and neurocognitive (d=0.17) composites. Simulated bootstrap regression analyses revealed that 3 of the 7 domains explained 86% of the variance for both composite scores. The domains that entered most frequently in the top 3 positions of the regression models were Speed of Processing, Working Memory, and Visual Learning. Findings provide definitive psychometric characteristics and a benchmark comparison for clinical trials using the MCCB. The test-retest reliability of the MCCB composite scores is considered excellent and the learning effects are small, fulfilling two of the key criteria for outcome measures in cognition clinical trials.

Placebo Response and Practice Effects in Schizophrenia Cognition Trials

IMPORTANCE

Patients' previous experience with performance-based cognitive tests in clinical trials for cognitive impairment associated with schizophrenia can create practice-related improvements. Placebo-controlled trials for cognitive impairment associated with schizophrenia are at risk for these practice effects, which can be difficult to distinguish from placebo effects.

OBJECTIVES

To conduct a systematic evaluation of the magnitude of practice effects on the Measurement and Treatment Research to Improve Cognition in Schizophrenia Consensus Cognitive Battery (MCCB) in cognitive impairment associated with schizophrenia and to examine which demographic, clinical, and cognitive characteristics were associated with improvement in placebo conditions.

DESIGN, SETTING, AND PARTICIPANTS

A blinded review was conducted of data from 813 patients with schizophrenia who were treated with placebo in 12 randomized placebo-controlled clinical trials conducted mostly in outpatient clinics in North America, Europe, Asia, and Latin America from February 22, 2007, to March 1, 2014. A total of 779 patients provided data for the primary outcome measure at baseline and at least 1 follow-up. Seven trials had prebaseline assessments wherein the patients knew that they were not receiving treatment, allowing a comparison of practice and placebo effects in the same patients.

INTERVENTIONS

Placebo compared with various experimental drug treatments.

MAIN OUTCOMES AND MEASURES

Composite score on the MCCB.

RESULTS

Of the 813 patients in the study (260 women and 553 men; mean [SD] age, 41.2 [11.5] years), the mean MCCB composite score at baseline was 22.8 points below the normative mean, and the mean (SEM) total change in the MCCB during receipt of placebo was 1.8 (0.2) T-score points (95% CI, 1.40-2.18), equivalent to a change of 0.18 SD. Practice effects in the 7 studies in which there was a prebaseline assessment were essentially identical to the postbaseline placebo changes. Baseline factors associated with greater improvements in the MCCB during receipt of placebo included more depression/anxiety (F1,438 = 5.41; P = .02), more motivation (F1,272 = 4.63; P = .03), and less improvement from screening to baseline (F1,421 = 59.32; P < .001).

CONCLUSIONS AND RELEVANCE

Placebo effects were minimal and associated with the number of postbaseline assessments and several patient characteristics. Given that the patients performed 2.28 SDs below normative standards on average at baseline, a mean placebo-associated improvement of less than 0.2 SD provides evidence that ceiling effects do not occur in these trials. These minimal changes in the MCCB could not be responsible for effective active treatments failing to separate from placebo.

Dorsolateral Prefrontal Cortex GABA Concentration in Humans Predicts Working Memory Load Processing Capacity

The discovery of neural mechanisms of working memory (WM) would significantly enhance our understanding of complex human behaviors and guide treatment development for WM-related impairments found in neuropsychiatric conditions and aging. Although the dorsolateral prefrontal cortex (DLPFC) has long been considered critical for WM, we still know little about the neural elements and pathways within the DLPFC that support WM in humans. In this study, we tested whether an individual's DLPFC gamma-aminobutryic acid (GABA) content predicts individual differences in WM task performance using a novel behavioral approach. Twenty-three healthy adults completed a task that measured the unique contribution of major WM components (memory load, maintenance, and distraction resistance) to performance. This was done to address the possibility that components have differing GABA dependencies and the failure to parse WM into components would lead to missing true associations with GABA. The subjects then had their DLPFC GABA content measured by single-voxel proton magnetic spectroscopy. We found that individuals with lower DLPFC GABA showed greater performance degradation with higher load, accounting for 31% of variance, p_(corrected) = 0.015. This relationship was component, neurochemical, and brain region specific. DLPFC GABA content did not predict performance sensitivity to other components tested; DLPFC glutamate + glutamine and visual cortical GABA content did not predict load sensitivity. These results confirm the involvement of DLPFC GABA in WM load processing in humans and implicate factors controlling DLPFC GABA content in the neural mechanisms of WM and its impairments.

SIGNIFICANCE STATEMENT

This study demonstrated for the first time that the amount of gamma-aminobutryic acid (GABA), the major inhibitory neurotransmitter of the brain, in an individual's prefrontal cortex predicts working memory (WM) task performance. Given that WM is required for many of the most characteristic cognitive and behavioral capabilities in humans, this finding could have a significant impact on our understanding of the neural basis of complex human behavior. Furthermore, this finding suggests that efforts to preserve or increase brain GABA levels could be fruitful in remediating WM-related deficits associated with neuropsychiatric conditions.

Cognitive deficits caused by prefrontal cortical and hippocampal neural disinhibition

We review recent evidence concerning the significance of inhibitory GABA transmission and of neural disinhibition, that is, deficient GABA transmission, within the prefrontal cortex and the hippocampus, for clinically relevant cognitive functions. Both regions support important cognitive functions, including attention and memory, and their dysfunction has been implicated in cognitive deficits characterizing neuropsychiatric disorders. GABAergic inhibition shapes cortico-hippocampal neural activity, and, recently, prefrontal and hippocampal neural disinhibition has emerged as a pathophysiological feature of major neuropsychiatric disorders, especially schizophrenia and age-related cognitive decline. Regional neural disinhibition, disrupting spatio-temporal control of neural activity and causing aberrant drive of projections, may disrupt processing within the disinhibited region and efferent regions. Recent studies in rats showed that prefrontal and hippocampal neural disinhibition (by local GABA antagonist microinfusion) dysregulates burst firing, which has been associated with important aspects of neural information processing. Using translational tests of clinically relevant cognitive functions, these studies showed that prefrontal and hippocampal neural disinhibition disrupts regional cognitive functions (including prefrontal attention and hippocampal memory function). Moreover, hippocampal neural disinhibition disrupted attentional performance, which does not require the hippocampus but requires prefrontal-striatal circuits modulated by the hippocampus. However, some prefrontal and hippocampal functions (including inhibitory response control) are spared by regional disinhibition. We consider conceptual implications of these findings, regarding the distinct relationships of distinct cognitive functions to prefrontal and hippocampal GABA tone and neural activity. Moreover, the findings support the proposition that prefrontal and hippocampal neural disinhibition contributes to clinically relevant cognitive deficits, and we consider pharmacological strategies for ameliorating cognitive deficits by rebalancing disinhibition-induced aberrant neural activity. Linked Articles This article is part of a themed section on Pharmacology of Cognition: a Panacea for Neuropsychiatric Disease? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.19/issuetoc.

The impact of genetics on future drug discovery in schizophrenia

INTRODUCTION

Failures of investigational new drugs (INDs) for schizophrenia have left huge unmet medical needs for patients. Given the recent lackluster results, it is imperative that new drug discovery approaches (and resultant drug candidates) target pathophysiological alterations that are shared in specific, stratified patient populations that are selected based on pre-identified biological signatures. One path to implementing this paradigm is achievable by leveraging recent advances in genetic information and technologies. Genome-wide exome sequencing and meta-analysis of single nucleotide polymorphism (SNP)-based association studies have already revealed rare deleterious variants and SNPs in patient populations. Areas covered: Herein, the authors review the impact that genetics have on the future of schizophrenia drug discovery. The high polygenicity of schizophrenia strongly indicates that this disease is biologically heterogeneous so the identification of unique subgroups (by patient stratification) is becoming increasingly necessary for future investigational new drugs. Expert opinion: The authors propose a pathophysiology-based stratification of genetically-defined subgroups that share deficits in particular biological pathways. Existing tools, including lower-cost genomic sequencing and advanced gene-editing technology render this strategy ever more feasible. Genetically complex psychiatric disorders such as schizophrenia may also benefit from synergistic research with simpler monogenic disorders that share perturbations in similar biological pathways.

Disinhibition, an emerging pharmacology of learning and memory

Learning and memory are dependent on interactive excitatory and inhibitory mechanisms. In this review, we discuss a mechanism called disinhibition, which is the release of an inhibitory constraint that effectively results in an increased activity in the target neurons (for example, principal or projection neurons). We focus on discussing the role of disinhibition in learning and memory at a basic level and in disease models with cognitive deficits and highlight a strategy to reverse cognitive deficits caused by excess inhibition, through disinhibition of α5-containing GABA _A receptors mediating tonic inhibition in the hippocampus, based on subtype-selective negative allosteric modulators as a novel class of drugs.

Realising stratified psychiatry using multidimensional signatures and trajectories

Background

Stratified or personalised medicine targets treatments for groups of individuals with a disorder based on individual heterogeneity and shared factors that influence the likelihood of response. Psychiatry has traditionally defined diagnoses by constellations of co-occurring signs and symptoms that are assigned a categorical label (e.g. schizophrenia). Trial methodology in psychiatry has evaluated interventions targeted at these categorical entities, with diagnoses being equated to disorders. Recent insights into both the nosology and neurobiology of psychiatric disorder reveal that traditional categorical diagnoses cannot be equated with disorders. We argue that current quantitative methodology (1) inherits these categorical assumptions, (2) allows only for the discovery of average treatment response, (3) relies on composite outcome measures and (4) sacrifices valuable predictive information for stratified and personalised treatment in psychiatry.

Methods and findings

To achieve a truly ‘stratified psychiatry’ we propose and then operationalise two necessary steps: first, a formal multi-dimensional representation of disorder definition and clinical state, and second, the similar redefinition of outcomes as multidimensional constructs that can expose within- and between-patient differences in response. We use the categorical diagnosis of schizophrenia—conceptualised as a label for heterogeneous disorders—as a means of introducing operational definitions of stratified psychiatry using principles from multivariate analysis. We demonstrate this framework by application to the Clinical Antipsychotic Trials of Intervention Effectiveness dataset, showing heterogeneity in both patient clinical states and their trajectories after treatment that are lost in the traditional categorical approach with composite outcomes. We then systematically review a decade of registered clinical trials for cognitive deficits in schizophrenia highlighting existing assumptions of categorical diagnoses and aggregate outcomes while identifying a small number of trials that could be reanalysed using our proposal.

Conclusion

We describe quantitative methods for the development of a multi-dimensional model of clinical state, disorders and trajectories which practically realises stratified psychiatry. We highlight the potential for recovering existing trial data, the implications for stratified psychiatry in trial design and clinical treatment and finally, describe different kinds of probabilistic reasoning tools necessary to implement stratification.

Early postnatal GABAA receptor modulation reverses deficits in neuronal maturation in a conditional neurodevelopmental mouse model of DISC1

Exploring drug targets based on disease-associated molecular mechanisms during development is crucial for the generation of novel prevention and treatment strategies for neurodevelopmental psychiatric conditions. We report that prefrontal cortex (PFC)-specific postnatal knockdown of DISC1 via in utero electroporation combined with an inducible knockdown expression system drives deficits in synaptic GABAA function and dendritic development in pyramidal neurons, as well as abnormalities in sensorimotor gating, albeit without profound memory deficits. We show for the first time that DISC1 is specifically involved in regulating cell surface expression of α2 subunit-containing GABAA receptors in immature developing neurons, but not after full maturation. Notably, pharmacological intervention with α2/3 subtype-selective GABAA receptor positive allosteric modulators during the early postnatal period ameliorates dendritic deficits and behavioral abnormalities induced by knockdown of DISC1. These findings highlight a critical role of DISC1-mediated disruption of postnatal GABA signaling in aberrant PFC maturation and function.

Aerobic Exercise in People with Schizophrenia: Neural and Neurocognitive Benefits

Schizophrenia is characterized by extensive neurocognitive deficits, which are linked to greater disability, poorer functional outcome, and have been suggested to impact daily functioning more than clinical symptoms. Aerobic exercise (AE) has emerged as a potential intervention. This review examines the impact of AE on brain structure and function along with neurocognitive performance in individuals with schizophrenia. Preliminary evidence indicates that AE can increase hippocampal volume and cortical thickness, in addition to exerting a neuroprotective effect against hippocampal volume decrease and cortical thinning. There is also evidence that AE is able to significantly increase serum brain-derived neurotrophic factor (BDNF) levels, which are implicated in neurogenesis, neuroplasticity, and cognitive improvement. Finally, evidence suggests that AE plays a significant role in improving overall cognition, including improvements in processing speed, working memory, and visual learning. The authors discuss the implications of the findings and provide recommendations for future research and areas of inquiry.

Early interventions in risk groups for schizophrenia: what are we waiting for?

Intervention strategies in adolescents at ultra high-risk (UHR) for psychosis are promising for reducing conversion to overt illness, but have only limited impact on functional outcome. Recent studies suggest that cognition does not further decline during the UHR stage. As social and cognitive impairments typically develop before the first psychotic episode and even years before the UHR stage, prevention should also start much earlier in the groups at risk for schizophrenia and other psychiatric disorders. Early intervention strategies could aim to improve stress resilience, optimize brain maturation, and prevent or alleviate adverse environmental circumstances. These strategies should urgently be tested for efficacy: the prevalence of ~1% implies that yearly ~22 in every 100,000 people develop overt symptoms of this illness, despite the fact that for many of them—e.g., children with an affected first-degree family member or carriers of specific genetic variants—increased risk was already identifiable early in life. Our current ability to recognize several risk groups at an early age not only provides an opportunity, but also implies a clinical imperative to act. Time is pressing to investigate preventive interventions in high-risk children to mitigate or prevent the development of schizophrenia and related psychiatric disorders.

Phencyclidine-induced disruption of oscillatory activity in prefrontal cortex: Effects of antipsychotic drugs and receptor ligands

The non-competitive NMDA receptor (NMDA-R) antagonist phencyclidine (PCP) markedly disrupts thalamocortical activity, increasing excitatory neuron discharge and reducing low frequency oscillations (LFO, <4Hz) that temporarily group neuronal discharge. These actions are mainly driven by PCP interaction with NMDA-R in GABAergic neurons of the thalamic reticular nucleus and likely underlie PCP psychotomimetic activity. Here we report that classical (haloperidol, chlorpromazine, perphenazine) and atypical (clozapine, olanzapine, quetiapine, risperidone, ziprasidone, aripripazole) antipsychotic drugs--but not the antidepressant citalopram--countered PCP-evoked fall of LFO in the medial prefrontal cortex (mPFC) of anesthetized rats. PCP reduces LFO by breaking the physiological balance between excitatory and inhibitory transmission. Next, we examined the role of different neurotransmitter receptors to reverse PCP actions. D2-R and D1-R blockade may account for classical antipsychotic action since raclopride and SCH-23390 partially reversed PCP effects. Atypical antipsychotic reversal may additionally involve 5-HT1A-R activation (but not 5-HT2A-R blockade) since 8-OH-DPAT and BAYx3702 (but not M100907) fully countered PCP effects. Blockade of histamine H1-R (pyrilamine) and α1-adrenoceptors (prazosin) was without effect. However, the enhancement of GABAA-R-mediated neurotransmission (using muscimol, diazepam or valproate) and the reduction of excitatory neurotransmission (using the mGluR2/3 agonist LY379268 and the preferential kainite/AMPA antagonist CNQX--but not the preferential AMPA/kainate antagonist NBQX) partially or totally countered PCP effects. Overall, these results shed new light on the neurobiological mechanisms used by antipsychotic drugs to reverse NMDA-R antagonist actions and suggest that agents restoring the physiological excitatory/inhibitory balance altered by PCP may be new targets in antipsychotic drug development.

Report on ISCTM Consensus Meeting on Clinical Assessment of Response to Treatment of Cognitive Impairment in Schizophrenia

If treatments for cognitive impairment are to be utilized successfully, clinicians must be able to determine whether they are effective and which patients should receive them. In order to develop consensus on these issues, the International Society for CNS Clinical Trials and Methodology (ISCTM) held a meeting of experts on March 20, 2014, in Washington, DC. Consensus was reached on several important issues. Cognitive impairment and functional disability were viewed as equally important treatment targets. The group supported the notion that sufficient data are not available to exclude patients from available treatments on the basis of age, severity of cognitive impairment, severity of positive symptoms, or the potential to benefit functionally from treatment. The group reached consensus that cognitive remediation is likely to provide substantial benefits in combination with procognitive medications, although a substantial minority believed that medications can be administered without nonpharmacological therapy. There was little consensus on the best methods for assessing cognitive change in clinical practice. Some participants supported the view that performance-based measures are essential for measurement of cognitive change; others pointed to their cost and time requirements as evidence of impracticality. Interview-based measures of cognitive and functional change were viewed as more practical, but lacking validity without informant involvement or frequent contact from clinicians. The lack of consensus on assessment methods was viewed as attributable to differences in experience and education among key stakeholders and significant gaps in available empirical data. Research on the reliability, validity, sensitivity, and practicality of competing methods will facilitate consensus.

Efficacy of Zinc Sulfate as an Add-on Therapy to Risperidone Versus Risperidone Alone in Patients With Schizophrenia: A Double-Blind Randomized Placebo-Controlled Trial

BACKGROUND

Zinc can modulate fast-excitatory transmission, facilitate the release of amino butyric acid and potentiate nicotinic acetylcholine receptors. There are also emerging evidences discussing the implication of these neurotransmitters in pathophysiology of schizophrenia.

OBJECTIVES

The purpose of this study was to evaluate the efficacy of Zn sulfate as an add-on therapy in the treatment of schizophrenia in a 6-week, double-blind and placebo-controlled trial.

PATIENTS AND METHODS

Eligible participants were 30 inpatients with schizophrenia according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision criteria. Patients were randomly allocated into two equal groups; one group of patients received risperidone 6 mg/day plus capsules of Zn sulfate (each containing 50 mg elemental Zn) three times a day and another group received risperidone 6 mg/day plus placebo. The Positive and Negative Syndrome Scale (PANSS) was applied to assess the psychotic symptoms and aggression risk at baseline, week 2, 4, and 6 of the study.

RESULTS

The results of this study showed that both protocols significantly decreased the scores on all subscales of the PANSS and supplemental aggression risk subscale as well as PANSS total score over the study. However, this improvement was significantly higher in Zn sulfate receiving group compared to the placebo group. No major clinical side-effects were detected.

CONCLUSIONS

It may be concluded that Zn is an effective adjuvant agent in the management of patients with schizophrenia.