Pre-pulse inhibition deficits in individuals at clinical high-risk for psychosis: A systematic review and meta-analysis

Whose Signals Are Being Amplified? Toward a More Equitable Clinical Psychophysiology

Research using psychophysiological methods holds great promise for refining clinical assessment, identifying risk factors, and informing treatment. Unfortunately, unique methodological features of existing approaches limit inclusive research participation and, consequently, generalizability. This brief overview and commentary provides a snapshot of the current state of representation in clinical psychophysiology, with a focus on the forms and consequences of ongoing exclusion of Black participants. We illustrate issues of inequity and exclusion that are unique to clinical psychophysiology, considering intersections among social constructions of Blackness and biased design of current technology used to measure electroencephalography, skin conductance, and other signals. We then highlight work by groups dedicated to quantifying and addressing these limitations. We discuss the need for reflection and input from a wider variety of stakeholders to develop and refine new technologies, given the risk of further widening disparities. Finally, we provide broad recommendations for clinical psychophysiology research.

The schizophrenia syndrome, circa 2024: What we know and how that informs its nature

With new data about different aspects of schizophrenia being continually generated, it becomes necessary to periodically revisit exactly what we know. Along with a need to review what we currently know about schizophrenia, there is an equal imperative to evaluate the construct itself. With these objectives, we undertook an iterative, multi-phase process involving fifty international experts in the field, with each step building on learnings from the prior one. This review assembles currently established findings about schizophrenia (construct, etiology, pathophysiology, clinical expression, treatment) and posits what they reveal about its nature. Schizophrenia is a heritable, complex, multi-dimensional syndrome with varying degrees of psychotic, negative, cognitive, mood, and motor manifestations. The illness exhibits a remitting and relapsing course, with varying degrees of recovery among affected individuals with most experiencing significant social and functional impairment. Genetic risk factors likely include thousands of common genetic variants that each have a small impact on an individual's risk and a plethora of rare gene variants that have a larger individual impact on risk. Their biological effects are concentrated in the brain and many of the same variants also increase the risk of other psychiatric disorders such as bipolar disorder, autism, and other neurodevelopmental conditions. Environmental risk factors include but are not limited to urban residence in childhood, migration, older paternal age at birth, cannabis use, childhood trauma, antenatal maternal infection, and perinatal hypoxia. Structural, functional, and neurochemical brain alterations implicate multiple regions and functional circuits. Dopamine D-2 receptor antagonists and partial agonists improve psychotic symptoms and reduce risk of relapse. Certain psychological and psychosocial interventions are beneficial. Early intervention can reduce treatment delay and improve outcomes. Schizophrenia is increasingly considered to be a heterogeneous syndrome and not a singular disease entity. There is no necessary or sufficient etiology, pathology, set of clinical features, or treatment that fully circumscribes this syndrome. A single, common pathophysiological pathway appears unlikely. The boundaries of schizophrenia remain fuzzy, suggesting the absence of a categorical fit and need to reconceptualize it as a broader, multi-dimensional and/or spectrum construct.

A novel locomotion-based prepulse inhibition assay in zebrafish larvae

Sensory gating, measured using prepulse inhibition (PPI), is an endophenotype of neuropsychiatric disorders that can be assessed in larval zebrafish models. However, current PPI assays require high-speed cameras to capture rapid c-bend startle behaviours of the larvae. In this study, we designed and employed a PPI paradigm that uses locomotion as a read-out of zebrafish larval startle responses. PPI percentage was measured at a maximum of 87% and strongly reduced upon administration of the NMDA receptor antagonist, MK-801. This work provides the foundation for simpler and more accessible PPI assays using larval zebrafish to model key endophenotypes of neurodevelopmental disorders.

Cannabidiol versus placebo as adjunctive treatment in early psychosis: study protocol for randomized controlled trial

BACKGROUND

Psychotic disorders are a leading cause of disability in young adults. Antipsychotics have been the primary intervention for psychosis for over 60 years, and yet, we have made little progress in treating negative symptoms, neurocognition, and functional disability. There is growing evidence that cannabidiol (CBD) is effective in treating positive psychotic symptoms, possibly also negative and neurocognitive symptoms, and moreover is well tolerated compared to other psychotropic medications. Anecdotally, patients participating in the Cognitive Assessment and Risk Evaluation (CARE) Early Psychosis Treatment Program at the University of California, San Diego, are self-administering CBD and report subjective improvement in stress, anxiety, and ability to cope with symptoms. The overarching aim of the trial is to explore the effectiveness of CBD augmentation on symptoms and neurocognition in early psychosis while also exploring the mechanism of action of CBD and predictors of response to treatment. The mechanism by which cannabidiol has a therapeutic effect on psychosis is poorly understood. Recent evidence has suggested that CBD may reduce stress and pro-inflammatory biomarker levels. Endocannabinoids also have powerful roles in eating behavior, reward, and mood, indicating these neurotransmitters may play a role in reducing hyperphagia and metabolic abnormalities that are present early in the course of psychotic illness and exacerbated by antipsychotic medication. The neurophysiological effects of CBD have been studied in animal models of psychosis that show improvements in information processing in response to CBD, but there are no studies in individuals with early psychosis.

METHOD

A total of 120 individuals in the early stages of psychosis will be randomized to 1000 mg of CBD versus placebo as an adjunct to existing treatment in a 8-week, double-blind superiority randomized control trial. The primary outcome measures are symptoms and neurocognition.

DISCUSSION

We hypothesized that CBD will improve symptoms and neurocognition as well as secondary outcome measures of neurohormones, inflammation, eating behaviors, and information processing. Importantly, predictors, moderators, and mediators of the CBD effects will be examined. A better understanding of which individuals are likely to respond to CBD can inform treatment planning and personalize treatment.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04411225. Registered on June 2, 2020.

P2X7 purinergic receptor modulates dentate gyrus excitatory neurotransmission and alleviates schizophrenia-like symptoms in mouse

ATP-gated P2X7 receptors (P2X7Rs) play a crucial role in brain disorders. However, how they affect normal and pathological synaptic transmission is still largely unclear. Here, by using whole-cell patch-clamp technique to record AMPA- and NMDA receptor-mediated excitatory postsynaptic currents (s/mEPSCs) in dentate gyrus granule cells (DG GCs), we revealed a modulation by P2X7Rs of presynaptic sites, especially originated from entorhinal cortex (EC)-GC path but not the mossy cell (MC)-GC path. The involvement of P2X7Rs was confirmed using a pharmacological approach. Additionally, the acute activation of P2X7Rs directly elevated calcium influx from EC-GC terminals. In postnatal phencyclidine (PCP)-induced mouse model of schizophrenia, we observed that P2X7R deficiency restored the EC-GC synapse alteration and alleviated PCP-induced symptoms. To summarize, P2X7Rs participate in the modulation of GC excitatory neurotransmission in the DG via EC-GC pathway, contributing to pathological alterations of neuronal functions leading to neurodevelopmental disorders.

Selective breeding of rats for high (HAB) and low (LAB) anxiety-related behaviour: A unique model for comorbid depression and social dysfunctions

Animal models of selective breeding for extremes in emotionality are a strong experimental approach to model psychopathologies. They became indispensable in order to increase our understanding of neurobiological, genetic, epigenetic, hormonal, and environmental mechanisms contributing to anxiety disorders and their association with depressive symptoms or social deficits. In the present review, we extensively discuss Wistar rats selectively bred for high (HAB) and low (LAB) anxiety-related behaviour on the elevated plus-maze. After 30 years of breeding, we can confirm the prominent differences between HAB and LAB rats in trait anxiety, which are accompanied by consistent differences in depressive-like, social and cognitive behaviours. We can further confirm a single nucleotide polymorphism in the vasopressin promotor of HAB rats causative for neuropeptide overexpression, and show that low (or high) anxiety and fear levels are unlikely due to visual dysfunctions. Thus, HAB and LAB rats continue to exist as a reliable tool to study the multiple facets underlying the pathology of high trait anxiety and its comorbidity with depression-like behaviour and social dysfunctions.

Neurophysiology in psychosis: The quest for disease biomarkers

Psychotic disorders affect 3% of the population at some stage in life, are a leading cause of disability, and impose a great economic burden on society. Major breakthroughs in the genetics of psychosis have not yet been matched by an understanding of its neurobiology. Biomarkers of perception and cognition obtained through non-invasive neurophysiological tools, especially EEG, offer a unique opportunity to gain mechanistic insights. Techniques for measuring neurophysiological markers are inexpensive and ubiquitous, thus having the potential as an accessible tool for patient stratification towards early treatments leading to better outcomes. In this paper, we review the literature on neurophysiological markers for psychosis and their relevant disease mechanisms, mainly covering event-related potentials including P50/N100 sensory gating, mismatch negativity, and the N100 and P300 waveforms. While several neurophysiological deficits are well established in patients with psychosis, more research is needed to study neurophysiological markers in their unaffected relatives and individuals at clinical high risk. We need to harness EEG to investigate markers of disease risk as key steps to elucidate the aetiology of psychosis and facilitate earlier detection and treatment.