Glutamatergic metabolite correlations with neuropsychological tests in first episode schizophrenia

Connecting Neurobiological Features with Interregional Dysconnectivity in Social-Cognitive Impairments of Schizophrenia

Schizophrenia (SZ) is a devastating psychiatric disorder affecting about 1% of the world's population. Social-cognitive impairments in SZ prevent positive social interactions and lead to progressive social withdrawal. The neurobiological underpinnings of social-cognitive symptoms remain poorly understood, which hinders the development of novel treatments. At the whole-brain level, an abnormal activation of social brain regions and interregional dysconnectivity within social-cognitive brain networks have been identified as major contributors to these symptoms. At the cellular and subcellular levels, an interplay between oxidative stress, neuroinflammation and N-methyl-D-aspartate receptor hypofunction is thought to underly SZ pathology. However, it is not clear how these molecular processes are linked with interregional dysconnectivity in the genesis of social-cognitive symptoms. Here, we aim to bridge the gap between macroscale (connectivity analyses) and microscale (molecular and cellular mechanistic) knowledge by proposing impaired myelination and the disinhibition of local microcircuits as possible causative biological pathways leading to dysconnectivity and abnormal activity of the social brain. Furthermore, we recommend electroencephalography as a promising translational technique that can foster pre-clinical drug development and discuss attractive drug targets for the treatment of social-cognitive symptoms in SZ.

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

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

Gamma aminobutyric acid signaling disturbances and altered astrocytic morphology associated with Bisphenol A induced cognitive impairments in rat offspring

BACKGROUND

Bisphenol A (BPA) is a well-recognized endocrine disruptor and is globally used in the manufacture of many plastic items. Multiple studies suggest links between prenatal BPA exposure and alterations in neurodevelopment and behaviors in children, even at lower levels. This study was conducted to reveal the role of astrocyte morphology and Gamma aminobutyric acid (GABA) signaling in BPA induced cognitive defects in the offspring of Wistar albino rats when exposed during the prenatal and postnatal periods.

METHODS

Dams of Wistar albino rats were exposed to a dose of 5 mg/kg body weight of BPA throughout the pregnancy and lactation period until the third postnatal day (PND). After delivery of pups, cognitive tests were carried out on the 21st, 24th, and 28th PNDs. Blood samples were collected for measurement of serum GABA levels. On the same day as the blood collections, pups were sacrificed and their right frontal cortices were dissected out. Immunohistochemical analysis for glial fibrillar acidic protein + astrocytes was conducted.

RESULTS

Pre and postnatal BPA exposure led to anxiety like behavior in pups. This exposure also resulted in reduced serum GABA concentrations. Immunohistochemical analysis revealed reduced astrocyte numbers as well as decreased numbers of dendritic spines in the BPA exposed pups.

CONCLUSION

BPA exposure during critical periods of development leads to cognitive impairments that correlate with the defects in the GABA signaling pathways and deteriorated morphology of the astrocytes in the offspring of the Wistar rats.

Associations Between Cognitive Function and Levels of Glutamatergic Metabolites and Gamma-Aminobutyric Acid in Antipsychotic-Naïve Patients With Schizophrenia or Psychosis

BACKGROUND

Abnormal glutamate and GABA (gamma-aminobutyric acid) levels have been found in the early phase of schizophrenia and may underlie cognitive deficits. However, the association between cognitive function and levels of glutamatergic metabolites and GABA has not been investigated in a large group of antipsychotic-naïve patients.

METHODS

In total, 56 antipsychotic-naïve patients with schizophrenia or psychotic disorder and 51 healthy control subjects underwent magnetic resonance spectroscopy to measure glutamate, glutamate+glutamine (Glx), and GABA levels in dorsal anterior cingulate cortex (ACC) and glutamate and Glx levels in left thalamus. The cognitive domains of attention, working memory, and IQ were assessed.

RESULTS

The whole group of antipsychotic-naïve patients had lower levels of GABA in dorsal ACC (p = .03), and the subgroup of patients with a schizophrenia diagnosis had higher glutamate levels in thalamus (p = .01), but Glx levels in dorsal ACC and thalamus did not differ between groups. Glx levels in dorsal ACC were positively associated with working memory (logarithmically transformed: b = -.016 [higher score indicates worse performance], p = .005) and attention (b = .056, p = .035) in both patients and healthy control subjects, although the association with attention did not survive adjustment for multiple comparisons.

CONCLUSIONS

The findings suggest a positive association between glutamatergic metabolites and cognitive function that do not differ between patients and healthy control subjects. Moreover, our data indicate that decreased GABAergic levels in dorsal ACC are involved in schizophrenia and psychotic disorder, whereas increased glutamate levels in thalamus seem to be implicated in schizophrenia pathophysiology. The findings imply that first-episode patients with cognitive deficits may gain from glutamate-modulating compounds.

Treatment effects on neurometabolite levels in schizophrenia: A systematic review and meta-analysis of proton magnetic resonance spectroscopy studies

BACKGROUND

Although there is growing evidence of alterations in the neurometabolite status associated with the pathophysiology of schizophrenia, how treatments influence these metabolite levels in patients with schizophrenia remains poorly studied.

METHODS

We conducted a literature search using Embase, Medline, and PsycINFO to identify proton magnetic resonance spectroscopy studies that compared neurometabolite levels before and after treatment in patients with schizophrenia. Six neurometabolites (glutamate, glutamine, glutamate + glutamine, gamma-aminobutyric acid, N-acetylaspartate, myo-inositol) and six regions of interest (frontal cortex, temporal cortex, parieto-occipital cortex, thalamus, basal ganglia, hippocampus) were investigated.

RESULTS

Thirty-two studies (n = 773 at follow-up) were included in our meta-analysis. Our results demonstrated that the frontal glutamate + glutamine level was significantly decreased (14 groups; n = 292 at follow-up; effect size = -0.35, P = 0.0003; I² = 22%) and the thalamic N-acetylaspartate level was significantly increased (7 groups; n = 184 at follow-up; effect size = 0.47, P < 0.00001; I² = 0%) after treatment in schizophrenia patients. No significant associations were found between neurometabolite changes and age, gender, duration of illness, duration of treatment, or baseline symptom severity.

CONCLUSIONS

The current results suggest that glutamatergic neurometabolite levels in the frontal cortex and neuronal integrity in the thalamus in schizophrenia might be modified following treatment.

Early treatment response in first episode psychosis: a 7-T magnetic resonance spectroscopic study of glutathione and glutamate

Early response to antipsychotic medications is one of the most important determinants of later symptomatic and functional outcomes in psychosis. Glutathione and glutamate have emerged as promising therapeutic targets for patients demonstrating inadequate response to dopamine-blocking antipsychotics. Nevertheless, the role of these neurochemicals in the mechanism of early antipsychotic response remains poorly understood. Using a longitudinal design and ultrahigh field 7-T magnetic resonance spectroscopy (MRS) protocol in 53 subjects, we report the association between dorsal anterior cingulate cortex glutamate and glutathione, with time to treatment response in drug naive (34.6% of the sample) or minimally medicated first episode patients with schizophreniform disorder, schizophrenia, and schizoaffective disorder. Time to response was defined as the number of weeks required to reach a 50% reduction in the PANSS-8 scores. Higher glutathione was associated with shorter time to response (F = 4.86, P = 0.017), while higher glutamate was associated with more severe functional impairment (F = 5.33, P = 0.008). There were no significant differences between patients and controls on measures of glutamate or glutathione. For the first time, we have demonstrated an association between higher glutathione and favorable prognosis in FEP. We propose that interventions that increase brain glutathione levels may improve outcomes of early intervention in psychosis.

Astrocytic Regulation of Glutamate Transmission in Schizophrenia

According to the glutamate hypothesis of schizophrenia, the abnormality of glutamate transmission induced by hypofunction of NMDA receptors (NMDARs) is causally associated with the positive and negative symptoms of schizophrenia. However, the underlying mechanisms responsible for the changes in glutamate transmission in schizophrenia are not fully understood. Astrocytes, the major regulatory glia in the brain, modulate not only glutamate metabolism but also glutamate transmission. Here we review the recent progress in understanding the role of astrocytes in schizophrenia. We focus on the astrocytic mechanisms of (i) glutamate synthesis via the glutamate-glutamine cycle, (ii) glutamate clearance by excitatory amino acid transporters (EAATs), (iii) D-serine release to activate NMDARs, and (iv) glutamatergic target engagement biomarkers. Abnormality in these processes is highly correlated with schizophrenia phenotypes. These findings will shed light upon further investigation of pathogenesis as well as improvement of biomarkers and therapies for schizophrenia.

Functional dysconnectivity of the limbic loop of frontostriatal circuits in first-episode, treatment-naive schizophrenia

Frontostriatal circuits dysfunction has been implicated in the etiology and psychopathology of patients with schizophrenia (SZ). However, few studies have investigated SZ-related functional connectivity (FC) alterations in discrete frontostriatal circuits and their relationship with pathopsychology in first-episode schizophrenia (FESZ). The goal of this study was to identify dysfunctions in discrete frontostriatal circuits that are associated with key features of FESZ. To this end, a case-control, cross-sectional study was conducted, wherein resting-state (RS) functional magnetic resonance (fMRI) data were collected from 37 treatment-naïve FESZ patients and 29 healthy control (HC) subjects. Seed-based FC analyses were performed by placing six bilateral pairs of seeds within a priori defined subdivisions of the striatum. We observed significantly decreased FC for the FESZ group relative to the HC group [p < .05, family-wise error (FWE)-corrected] in the limbic loop, but not in the sensorimotor or associative loops, of frontostriatal circuitry. Moreover, bilaterally decreased inferior ventral striatum/nucleus accumbens (VSi)-dorsal anterior cingulate cortex (dACC) FC within the limbic loop correlated inversely with overall FESZ symptom severity and the disorganization factor score of PANSS. These findings provide new insight into the role of frontostriatal limbic loop hypoconnectivity in early-stage schizophrenia pathology and suggest potential novel therapeutic targets.

Increased glutamate/GABA+ ratio in a shared autistic and schizotypal trait phenotype termed Social Disorganisation

Autism and schizophrenia are multi-dimensional spectrum disorders that have substantial phenotypic overlap. This overlap is readily identified in the non-clinical population, and has been conceptualised as Social Disorganisation (SD). This study investigates the balance of excitatory glutamate and inhibitory γ-aminobutyric acid (GABA) concentrations in a non-clinical sample with high and low trait SD, as glutamate and GABA abnormalities are reported across the autism and schizophrenia spectrum disorders. Participants were 18 low (10 females) and 19 high (9 females) SD scorers aged 18 to 40 years who underwent 1H-MRS for glutamate and GABA+macromolecule (GABA+) concentrations in right and left hemisphere superior temporal (ST) voxels. Reduced GABA+ concentration (p = 0.03) and increased glutamate/GABA+ ratio (p = 0.003) in the right ST voxel for the high SD group was found, and there was increased GABA+ concentration in the left compared to right ST voxel (p = 0.047). Bilateral glutamate concentration was increased for the high SD group (p = 0.006); there was no hemisphere by group interaction (p = 0.772). Results suggest that a higher expression of the SD phenotype may be associated with increased glutamate/GABA+ ratio in the right ST region, which may affect speech prosody processing, and lead behavioural characteristics that are shared within the autistic and schizotypal spectra.

Cognitive performance is associated with gray matter decline in first-episode psychosis

Progressive loss of gray matter has been demonstrated over the early course of schizophrenia. Identification of an association between cognition and gray matter may lead to development of early interventions directed at preserving gray matter volume and cognitive ability. The present study evaluated the association between gray matter using voxel-based morphometry (VBM) and cognitive testing in a sample of 16 patients with first-episode psychosis. A simple regression was applied to investigate the association between gray matter at baseline and 80 months and cognitive tests at baseline. Performance on the Wisconsin Card Sorting Task (WCST) at baseline was positively associated with gray matter volume in several brain regions. There was an association between decreased gray matter at baseline in the nucleus accumbens and Trails B errors. Performing worse on Trails B and making more WCST perseverative errors at baseline was associated with gray matter decline over 80 months in the right globus pallidus, left inferior parietal lobe, Brodmann's area (BA) 40, and left superior parietal lobule and BA 7 respectively. All significant findings were cluster corrected. The results support a relationship between aspects of cognitive impairment and gray matter abnormalities in first-episode psychosis.

Relationships between dorsolateral prefrontal cortex metabolic change and cognitive impairment in first-episode neuroleptic-naive schizophrenia patients

The present study aimed to explore the possible associations between the dorsolateral prefrontal cortex (DLPFC) metabolites and the cognitive function in first-episode schizophrenia (FES).This study included 58 patients with FES (29 males and 29 females; mean age, 22.66 ± 7.64 years) recruited from the First Affiliated Hospital, College of Medicine, Zhejiang University, and 43 locally recruited healthy controls (16 males and 27 females; mean age, 23.07 ± 7.49 years). The single-voxel proton magnetic resonance spectroscopy was used to measure the levels of N-acetylaspartate (NAA); complex of glutamate, glutamine, and γ-aminobutyric acid (Glx); choline-containing compounds; and myo-inositol in the DLPFC. The ratios of metabolites to creatine (Cr) were calculated. The cognitive function was assessed by Measurement and Treatment Research to Improve Cognition in Schizophrenia Consensus Cognitive Battery (MCCB). Correlation analysis was used to assess the relationships between the DLPFC metabolites and the cognitive function.Compared with the healthy controls, the patients with FES showed significantly reduced scores in each part of the MCCB, significantly reduced NAA/Cr, and significantly increased Glx/Cr in the left DLPFC. Poor performance in verbal learning and visual learning was correlated to the reduced NAA/Cr ratio in the left DLPFC.These findings suggest that a lower NAA/Cr ratio in the left DLPFC is associated with the cognitive deficits in patients with FES, and may be an early biochemical marker for the cognitive impairment in schizophrenia.

Searching for Cross-Diagnostic Convergence: Neural Mechanisms Governing Excitation and Inhibition Balance in Schizophrenia and Autism Spectrum Disorders

Recent theoretical accounts have proposed excitation and inhibition (E/I) imbalance as a possible mechanistic, network-level hypothesis underlying neural and behavioral dysfunction across neurodevelopmental disorders, particularly autism spectrum disorder (ASD) and schizophrenia (SCZ). These two disorders share some overlap in their clinical presentation as well as convergence in their underlying genes and neurobiology. However, there are also clear points of dissociation in terms of phenotypes and putatively affected neural circuitry. We highlight emerging work from the clinical neuroscience literature examining neural correlates of E/I imbalance across children and adults with ASD and adults with both chronic and early-course SCZ. We discuss findings from diverse neuroimaging studies across distinct modalities, conducted with electroencephalography, magnetoencephalography, proton magnetic resonance spectroscopy, and functional magnetic resonance imaging, including effects observed both during task and at rest. Throughout this review, we discuss points of convergence and divergence in the ASD and SCZ literature, with a focus on disruptions in neural E/I balance. We also consider these findings in relation to predictions generated by theoretical neuroscience, particularly computational models predicting E/I imbalance across disorders. Finally, we discuss how human noninvasive neuroimaging can benefit from pharmacological challenge studies to reveal mechanisms in ASD and SCZ. Collectively, we attempt to shed light on shared and divergent neuroimaging effects across disorders with the goal of informing future research examining the mechanisms underlying the E/I imbalance hypothesis across neurodevelopmental disorders. We posit that such translational efforts are vital to facilitate development of neurobiologically informed treatment strategies across neuropsychiatric conditions.

Executive Dysfunction in Obsessive-Compulsive Disorder and Anterior Cingulate-Based Resting State Functional Connectivity

OBJECTIVE

Executive dysfunction might be an important determinant for response to pharmacotherapy in obsessive-compulsive disorder (OCD), and could be sustained independently of symptom relief. The anterior cingulate cortex (ACC) has been indicated as a potential neural correlate of executive functioning in OCD. The present study examined the brain-executive function relationships in OCD from the ACC-based resting state functional connectivity networks (rs-FCNs), which reflect information processing mechanisms during task performance.

METHODS

For a total of 58 subjects [OCD, n=24; healthy controls (HCs), n=34], four subdomains of executive functioning were measured using the Rey-Osterrieth Complex Figure Test (RCFT), the Stroop Color-Word Test (SCWT), the Wisconsin Card Sorting Test (WCST), and the Trail Making Test part B (TMT-B). To probe for differential patterns of the brain-cognition relationship in OCD compared to HC, the ACC-centered rs-FCN were calculated using five seed regions systemically placed throughout the ACC.

RESULTS

Significant differences between the OCD group and the HCs with respect to the WCST perseverative errors, SCWT interference scores, and TMT-B reaction times (p<0.05) were observed. Moreover, significant interactions between diagnosis×dorsal ACC [S3]-based rs-FCN strength in the right dorsolateral prefrontal cortex for RCFT organization summary scores as well as between diagnosis×perigenual ACC [S7]-based rs-FCN strength in the left frontal eye field for SCWT color-word interference scores were unveiled.

CONCLUSION

These network-based neural foundations for executive dysfunction in OCD could become a potential target of future treatment, which could improve global domains of functioning broader than symptomatic relief.

A review of altered biochemistry in the anterior cingulate cortex of first-episode psychosis

Relevant biochemicals of the brain can be quantified in vivo, non-invasively, using proton Magnetic Resonance Spectroscopy (¹H MRS). This includes metabolites associated with neural general functioning, energetics, membrane phospholipid metabolism and neurotransmission. Moreover, there is substantial evidence of implication of the frontal and prefrontal areas in the pathogenesis of psychotic disorders such as schizophrenia. In particular, the anterior cingulate cortex (ACC) plays an important role in cognitive control of emotional and non-emotional processes. Thus the study of its extent of biochemistry dysfunction in the early stages of psychosis is of particular interest in gaining a greater understanding of its aetiology. In this review, we selected ¹H MRS studies focused on the ACC of first-episode psychosis (FEP). Four studies reported increased glutamatergic levels in FEP, while other four showed preserved concentrations. Moreover, findings on FEP do not fully mirror those in chronic patients. Due to conflicting findings, larger longitudinal ¹H MRS studies are expected to further explore glutamatergic neurotransmission in ACC of FEP in order to have a better understanding of the glutamatergic mechanisms underlying psychosis, possibly using ultra high field MR scanners.

How Schizophrenia Develops: Cognitive and Brain Mechanisms Underlying Onset of Psychosis

Identifying cognitive and neural mechanisms involved in the development of schizophrenia requires longitudinal observation of individuals prior to onset. Here recent studies of prodromal individuals who progress to full psychosis are briefly reviewed in relation to models of schizophrenia pathophysiology. Together, this body of work suggests that disruption in brain connectivity, driven primarily by a progressive reduction in dendritic spines on cortical pyramidal neurons, may represent a key triggering mechanism. The earliest disruptions appear to be in circuits involved in referencing experiences according to time, place, and agency, which may result in a failure to recognize particular cognitions as self-generated or to constrain interpretations of the meaning of events based on prior experiences, providing the scaffolding for faulty reality testing.