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Glutamatergic dysfunction is implicated in schizophrenia pathoaetiology, but this may vary in extent between patients. It is unclear whether inter-individual variability in glutamate is greater in schizophrenia than the general population. We conducted meta-analyses to assess (1) variability of glutamate measures in patients relative to controls (log coefficient of variation ratio: CVR); (2) standardised mean differences (SMD) using Hedges g; (3) modal distribution of individual-level glutamate data (Hartigan’s unimodality dip test). MEDLINE and EMBASE databases were searched from inception to September 2022 for proton magnetic resonance spectroscopy (1H-MRS) studies reporting glutamate, glutamine or Glx in schizophrenia. 123 studies reporting on 8256 patients and 7532 controls were included. Compared with controls, patients demonstrated greater variability in glutamatergic metabolites in the medial frontal cortex (MFC, glutamate: CVR = 0.15,p p = 0.003; Glx: CVR = 0.11,p = 0.002), dorsolateral prefrontal cortex (glutamine: CVR = 0.14,p = 0.05; Glx: CVR = 0.25,p p = 0.008; Glx: CVR = 0.19,p = 0.008). Studies in younger, more symptomatic patients were associated with greater variability in the basal ganglia (BG glutamate with age:z = −0.03,p = 0.003, symptoms:z = 0.007,p = 0.02) and temporal lobe (glutamate with age:z = −0.03,p = 0.02), while studies with older, more symptomatic patients associated with greater variability in MFC (glutamate with age:z = 0.01,p = 0.02, glutamine with symptoms:z = 0.01,p = 0.02). For individual patient data, most studies showed a unimodal distribution of glutamatergic metabolites. Meta-analysis of mean differences found lower MFC glutamate (g = −0.15,p = 0.03), higher thalamic glutamine (g = 0.53,p g = 0.28,p z = −0.02,p z = −0.03,p = 0.02) in patients relative to controls. Patient PANSS total score was positively associated with glutamate SMD in BG (z = 0.01,p = 0.01) and temporal lobe (z = 0.05,p = 0.008). Further research into the mechanisms underlying greater glutamatergic metabolite variability in schizophrenia and their clinical consequences may inform the identification of patient subgroups for future treatment strategies.

Background: Given the likelihood of progressive illness in bipolar disorder (BD), it is important to understand the benefits and risks of interventions administered early in illness course. We conducted a systematic review of the effectiveness of interventions in the early course of BD I or II. Methods We completed a systematic search on MEDLINE, PsycINFO, EMBASE, the Cochrane Central Register of Controlled Trials, CINAHL and Google Scholar from 1/1/1979 till 14/9/2022. We included controlled trials examining intervention effects on symptomatic, course, functional and tolerability outcomes of patients in the ‘early course’ of BD I or II. We classified patients to be in early course if they (a) were seeking help for the first time for a manic episode, (b) had a lifetime history of up to 3 manic episodes, or (c) had up to 6 lifetime mood episodes. Evidence quality was assessed using the GRADE approach. Results From 4135 unique publications we included 25 reports representing 2212 participants in 16 randomized studies, and 17,714 participants from nine non-randomized studies. Available evidence suggested that in early illness course, lithium use was associated with lower recurrence risk compared with other mood stabilizers. Mood stabilizers were also associated with better global functioning, compared with the use of antipsychotics in the medium term. While summative findings regarding psychological therapies were limited by heterogeneity, family-focused and cognitive-behavioral interventions were associated with reduced recurrence risk or improved symptomatic outcomes. There was some evidence that the same pharmacological interventions were more efficacious in preventing recurrences when utilized in earlier rather than later illness course. Conclusions and recommendations While there are promising initial findings, there is a need for more adequately powered trials to examine the efficacy and tolerability of interventions in youth and adults in early illness course. Specifically, there is a compelling need to compare the relative benefits of lithium with other pharmacological agents in preventing recurrences. In addition to symptomatic outcomes, there should be a greater focus on functional impact and tolerability. Effective pharmacological and psychological interventions should be offered to those in early course of BD, balancing potential risks using shared decision-making approaches.

Psychotic illnesses show variable responses to treatment. Determining the neurobiology underlying this is important for precision medicine and the development of better treatments. It has been proposed that dopaminergic differences underlie variation in response, with striatal dopamine synthesis capacity (DSC) elevated in responders and unaltered in non-responders. We therefore aimed to test this in a prospective cohort, with a nested case-control comparison. 40 volunteers (26 patients with first-episode psychosis and 14 controls) received an 18F-DOPA Positron Emission Tomography scan to measure DSC (Kicer) prior to antipsychotic treatment. Clinical assessments (Positive and Negative Syndrome Scale, PANSS, and Global Assessment of Functioning, GAF) occurred at baseline and following antipsychotic treatment for a minimum of 4 weeks. Response was defined using improvement in PANSS Total score of >50%. Patients were followed up for at least 6 months, and remission criteria applied. There was a significant effect of group on Kicer in associative striatum (F(2, 37) = 7.9, p = 0.001). Kicer was significantly higher in responders compared with non-responders (Cohen’s d = 1.55, p = 0.01) and controls (Cohen’s d = 1.31, p = 0.02). Kicer showed significant positive correlations with improvements in PANSS-positive (r = 0.64, p

BACKGROUND: The pathophysiology of psychosis is incompletely understood. Disruption in cortical glutamatergic signalling causing aberrant striatal dopamine synthesis capacity is a proposed model for psychosis, but has not been tested in vivo. We therefore aimed to test the relationship between cortical glutamate concentrations and striatal dopamine synthesis capacity, and psychotic symptoms.METHODS: In this cross-sectional multimodal imaging study, 28 individuals with first-episode psychosis and 28 healthy controls underwent 18F-DOPA PET (measuring striatal dopamine synthesis capacity), and proton magnetic resonance spectroscopy (measuring anterior cingulate cortex glutamate concentrations). Participants were recruited from first-episode psychosis services in London, UK and were required to be in the first episode of a psychotic illness, with no previous illness or treatment episodes. Exclusion criteria for all participants were: history of substantial head trauma, dependence on illicit substances, medical comorbidity (other than minor illnesses), and contraindications to scanning (such as pregnancy). Symptoms were measured using the Positive and Negative Syndrome Scale. The primary endpoint was the relationship between anterior cingulate cortex glutamate concentrations and striatal dopamine synthesis capacity in individuals with their first episode of psychosis as shown by imaging, examined by linear regression. Linear regression was used to examine relationships between measures.FINDINGS: Glutamate concentrations showed a significant inverse relationship with striatal dopamine synthesis capacity in patients with psychosis (R2=0·16, p=0·03, β -1·71 × 10-4, SE 0·76 × 10-4). This relationship remained significant after the addition of age, gender, ethnicity, and medication status to the model (p=0·015). In healthy controls, there was no significant relationship between dopamine and glutamate measures (R2=0·04, p=0·39). Positive and Negative Syndrome Scale positive psychotic symptoms were positively associated with striatal dopamine synthesis capacity (R2=0·14, p=0·046, β 2546, SE 1217) and showed an inverse relationship with anterior cingulate glutamate concentrations (R2=0·16, p=0·03, β -1·71 × 10-4, SE 7·63 × 10-5). No relationships were seen with negative symptoms (positive symptoms, mean [SD] -18·4 (6·6) negative symptoms, mean [SD] -15·4 [6·1]).INTERPRETATION: These observations are consistent with the hypothesis that cortical glutamate dysfunction is related to subcortical dopamine synthesis capacity and psychosis. Although the precise mechanistic relationship between cortical glutamate and dopamine in vivo remains unclear, our findings support further studies to test the effect of modulating cortical glutamate in the treatment of psychosis.FUNDING: Medical Research Council, Wellcome Trust, Biomedical Research Council, South London and Maudsley NHS Foundation Trust, JMAS Sim Fellowship, Royal College of Physicians (Edinburgh) (SJ).

Background A wide range of neuropsychiatric disorders, from schizophrenia to drug addiction, involve abnormalities in both the mesolimbic dopamine system and the cortical salience network. Both systems play a key role in the detection of behaviorally relevant environmental stimuli. Although anatomical overlap exists, the functional relationship between these systems remains unknown. Preclinical research has suggested that the firing of mesolimbic dopamine neurons may activate nodes of the salience network, but in vivo human research is required given the species-specific nature of this network. Methods We employed positron emission tomography to measure both dopamine release capacity (using the D2/3 receptor ligand 11C-PHNO, n = 23) and dopamine synthesis capacity (using 18F-DOPA, n = 21) within the ventral striatum. Resting-state functional magnetic resonance imaging was also undertaken in the same individuals to investigate salience network functional connectivity. A graph theoretical approach was used to characterize the relationship between dopamine measures and network connectivity. Results Dopamine synthesis capacity was associated with greater salience network connectivity, and this relationship was particularly apparent for brain regions that act as information-processing hubs. In contrast, dopamine release capacity was associated with weaker salience network connectivity. There was no relationship between dopamine measures and visual and sensorimotor networks, indicating specificity of the findings. Conclusions Our findings demonstrate a close relationship between the salience network and mesolimbic dopamine system, and they are relevant to neuropsychiatric illnesses in which aberrant functioning of both systems has been observed.

Bipolar affective disorder is a common neuropsychiatric disorder. Whilst its neurobiological underpinnings are incompletely understood, the dopamine hypothesis has been a key theory of the pathophysiology of both manic and depressive phases of the illness for over four decades. The increased use of antidopaminergics in the treatment of this disorder and new in vivo neuroimaging and post-mortem studies makes it timely to review this theory. To do this, we conducted a systematic search for post-mortem, pharmacological and imaging studies of dopamine function in bipolar disorder. Converging findings from pharmacological and imaging studies support the hypothesis that a state of hyperdopaminergia, specifically elevations in D2/3 receptor availability and a hyperactive reward processing network, underlies mania. In bipolar depression imaging studies show increased dopamine transporter levels, but changes in other aspects of dopaminergic function are inconsistent. Puzzlingly, pharmacological evidence shows that both dopamine agonists and antidopaminergics can improve bipolar depressive symptoms and perhaps actions at other receptors may reconcile these findings. Tentatively, this evidence suggests a model where an elevation in striatal D2/3 receptor availability would lead to increased dopaminergic neurotransmission and mania, whilst increased striatal dopamine transporter (DAT) levels would lead to reduced dopaminergic function and depression. Thus, it can be speculated that a failure of dopamine receptor and transporter homeostasis might underlie the pathophysiology of this disorder. The limitations of this model include its reliance on pharmacological evidence, as these studies could potentially affect other monoamines, and the scarcity of imaging evidence on dopaminergic function. This model, if confirmed, has implications for developing new treatment strategies such as reducing the dopamine synthesis and/or release in mania and DAT blockade in bipolar depression.

Importance: The dopamine hypothesis suggests that dopamine abnormalities underlie psychosis, irrespective of diagnosis, implicating dopamine dysregulation in bipolar affective disorder and schizophrenia, in line with the research domain criteria approach. However, this hypothesis has not been directly examined in individuals diagnosed with bipolar disorder with psychosis.Objectives: To test whether dopamine synthesis capacity is elevated in bipolar disorder with psychosis and how this compares with schizophrenia and matched controls and to examine whether dopamine synthesis capacity is associated with psychotic symptom severity, irrespective of diagnostic class.Design, Setting, and Participants: This cross-sectional case-control positron emission tomographic study was performed in the setting of first-episode psychosis services in an inner-city area (London, England). Sixty individuals participated in the study (22 with bipolar psychosis [18 antipsychotic naive or free], 16 with schizophrenia [14 antipsychotic naive or free], and 22 matched controls) and underwent fluorodihydroxyphenyl-l-alanine ([18F]-DOPA) positron emission tomography to examine dopamine synthesis capacity. Standardized clinical measures, including the Positive and Negative Syndrome Scale, Young Mania Rating Scale, and Global Assessment of Functioning, were administered. The study dates were March 2013 to November 2016.Main Outcomes and Measures: Dopamine synthesis capacity (Kicer) and clinical measures (Positive and Negative Syndrome Scale, Young Mania Rating Scale, and Global Assessment of Functioning).Results: The mean (SD) ages of participants were 23.6 (3.6) years in 22 individuals with bipolar psychosis (13 male), 26.3 (4.4) years in 16 individuals with schizophrenia (14 male), and 24.5 (4.5) years in controls (14 male). There was a significant group difference in striatal dopamine synthesis capacity (Kicer) (F2,57 = 6.80, P = .002). Kicer was significantly elevated in both the bipolar group (mean [SD], 13.18 [1.08] × 10-3 min-1; P = .002) and the schizophrenia group (mean [SD], 12.94 [0.79] × 10-3 min-1; P = .04) compared with controls (mean [SD], 12.16 [0.92] × 10-3 min-1). There was no significant difference in striatal Kicer between the bipolar and schizophrenia groups. Kicer was significantly positively correlated with positive psychotic symptom severity in the combined bipolar and schizophrenia sample experiencing a current psychotic episode, explaining 27% of the variance in symptom severity (n = 32, r = 0.52, P = .003). There was a significant positive association between Kicer and positive psychotic symptom severity in individuals with bipolar disorder experiencing a current psychotic episode (n = 16, r = 0.60, P = .01), which remained significant after adjusting for manic symptom severity.Conclusions and Relevance: These findings are consistent with a transdiagnostic role for dopamine dysfunction in the pathoetiology of psychosis and suggest dopamine synthesis capacity as a potential novel drug target for bipolar disorder and schizophrenia.