Striatal metabolic alterations in non-psychotic adolescent offspring at risk for schizophrenia: a (1)H spectroscopy study

Reduction of N-acetyl aspartate (NAA) in association with relapse in early-stage psychosis: a 7-Tesla MRS study

Understanding the biological underpinning of relapse could improve the outcomes of patients with psychosis. Relapse is elicited by multiple reasons/triggers, but the consequence frequently accompanies deteriorations of brain function, leading to poor prognosis. Structural brain imaging studies have recently been pioneered to address this question, but a lack of molecular investigations is a knowledge gap. Following a criterion used for recent publications by others, we defined the experiences of relapse by hospitalization(s) due to psychotic exacerbation. We hypothesized that relapse-associated molecules might be underscored from the neurometabolites whose levels have been different between overall patients with early-stage psychosis and healthy subjects in our previous report. In the present study, we observed a significant decrease in the levels of N-acetyl aspartate in the anterior cingulate cortex and thalamus in patients who experienced relapse compared to patients who did not. Altogether, decreased N-acetyl aspartate levels may indicate relapse-associated deterioration of neuronal networks in patients.

Treatment resistance NMDA receptor pathway polygenic score is associated with brain glutamate in schizophrenia

Dysfunction of glutamate neurotransmission has been implicated in the pathophysiology of schizophrenia and may be particularly relevant in severe, treatment-resistant symptoms. The underlying mechanism may involve hypofunction of the NMDA receptor. We investigated whether schizophrenia-related pathway polygenic scores, composed of genetic variants within NMDA receptor encoding genes, are associated with cortical glutamate in schizophrenia. Anterior cingulate cortex (ACC) glutamate was measured in 70 participants across 4 research sites using Proton Magnetic Resonance Spectroscopy (1H-MRS). Two NMDA receptor gene sets were sourced from the Molecular Signatories Database and NMDA receptor pathway polygenic scores were constructed using PRSet. The NMDA receptor pathway polygenic scores were weighted by single nucleotide polymorphism (SNP) associations with treatment-resistant schizophrenia, and associations with ACC glutamate were tested. We then tested whether NMDA receptor pathway polygenic scores with SNPs weighted by associations with non-treatment-resistant schizophrenia were associated with ACC glutamate. A higher NMDA receptor complex pathway polygenic score was significantly associated with lower ACC glutamate (β = -0.25, 95 % CI = -0.49, -0.02, competitive p = 0.03). When SNPs were weighted by associations with non-treatment-resistant schizophrenia, there was no association between the NMDA receptor complex pathway polygenic score and ACC glutamate (β = 0.05, 95 % CI = -0.18, 0.27, competitive p = 0.79). These results provide initial evidence of an association between common genetic variation implicated in NMDA receptor function and ACC glutamate levels in schizophrenia. This association was specific to when the NMDA receptor complex pathway polygenic score was weighted by SNP associations with treatment-resistant schizophrenia.

Associations between N-Acetylaspartate and white matter integrity in individuals with schizophrenia and unaffected relatives

Compromised white matter has been reported in schizophrenia; however, few studies have investigated neurochemical abnormalities underlying microstructural differences. N-acetylaspartate (NAA) is used to synthesize myelin and is often reduced in persons with schizophrenia (PSZ) and their unaffected first-degree relatives (REL). Low levels of NAA could affect white matter by preventing the synthesis or repair of myelin. We used magnetic resonance spectroscopy and diffusion tensor imaging to investigate the relationship between NAA and white matter integrity in PSZ. REL were included to examine whether putative relationships are associated with symptom expression or illness liability. 52 controls, 23 REL and 25 PSZ underwent 7T proton magnetic resonance spectroscopy and/or 3T diffusion tensor imaging. NAA in the visual cortex and basal ganglia were measured and compared across groups. Diffusivity measures were compared across groups using tract-based spatial statistics and related to NAA concentrations. Visual cortex NAA was significantly reduced in PSZ compared to controls. White matter integrity did not differ between groups. Reduced cortical and subcortical NAA were associated with diffusivity measures of poor white matter microstructure. These data suggest that levels of neural NAA may be related to white matter integrity similarly across individuals with schizophrenia, those at genetic risk, and controls.

Dopamine and glutamate in individuals at high risk for psychosis: a meta-analysis of in vivo imaging findings and their variability compared to controls

Dopaminergic and glutamatergic dysfunction is believed to play a central role in the pathophysiology of schizophrenia. However, it is unclear if abnormalities predate the onset of schizophrenia in individuals at high clinical or genetic risk for the disorder. We systematically reviewed and meta-analyzed studies that have used neuroimaging to investigate dopamine and glutamate function in individuals at increased clinical or genetic risk for psychosis. EMBASE, PsycINFO and Medline were searched form January 1, 1960 to November 26, 2020. Inclusion criteria were molecular imaging measures of striatal presynaptic dopaminergic function, striatal dopamine receptor availability, or glutamate function. Separate meta-analyses were conducted for genetic high-risk and clinical high-risk individuals. We calculated standardized mean differences between high-risk individuals and controls, and investigated whether the variability of these measures differed between the two groups. Forty-eight eligible studies were identified, including 1,288 high-risk individuals and 1,187 controls. Genetic high-risk individuals showed evidence of increased thalamic glutamate + glutamine (Glx) concentrations (Hedges' g=0.36, 95% CI: 0.12-0.61, p=0.003). There were no significant differences between high-risk individuals and controls in striatal presynaptic dopaminergic function, striatal D2/D3 receptor availability, prefrontal cortex glutamate or Glx, hippocampal glutamate or Glx, or basal ganglia Glx. In the meta-analysis of variability, genetic high-risk individuals showed reduced variability of striatal D2/D3 receptor availability compared to controls (log coefficient of variation ratio, CVR=-0.24, 95% CI: -0.46 to -0.02, p=0.03). Meta-regressions of publication year against effect size demonstrated that the magnitude of differences between clinical high-risk individuals and controls in presynaptic dopaminergic function has decreased over time (estimate=-0.06, 95% CI: -0.11 to -0.007, p=0.025). Thus, other than thalamic glutamate concentrations, no neurochemical measures were significantly different between individuals at risk for psychosis and controls. There was also no evidence of increased variability of dopamine or glutamate measures in high-risk individuals compared to controls. Significant heterogeneity, however, exists between studies, which does not allow to rule out the existence of clinically meaningful differences.

A meta-analysis of ultra-high field glutamate, glutamine, GABA and glutathione 1HMRS in psychosis: Implications for studies of psychosis risk

Ultra-high field proton magnetic resonance spectroscopy (1HMRS) offers a unique opportunity to measure the concentration of neurometabolites implicated in psychosis (PSY). The extant 7 T 1HMRS literature measuring glutamate-associated neurometabolites in the brain in PSY in vivo is small, but a comprehensive, quantitative summary of these data can offer insight and guidance to this emerging field. This meta-analysis examines proton spectroscopy (1HMRS) measures of glutamate (Glu), glutamine (Gln), glutamate+glutamine (Glx), gamma aminobutyric acid (GABA), and glutathione (GSH) across 255 individuals with PSY (121 first episode) and 293 healthy comparison participants (HC). While all five neurometabolites were lower in PSY as compared to HC, only Glu (Cohen's d = -0.18) and GSH (Cohen's d = -0.21) concentrations were significantly lower in PSY, whereas concentrations of Gln, Glx, and GABA did not significantly differ between groups. Notably, 1HMRS methodological choices and sample demographic characteristics did not impact study-specific effect sizes for PSY-related Glu or GSH differences. This review thus provides further evidence of neurometabolite dysfunction in first episode and chronic PSY, and thereby suggests that Glu and GSH abnormalities may additionally play a role in more incipient stages of the disorder: in clinical high risk stages. Additional 7 T neurochemical imaging studies in larger, longitudinal, and unmedicated samples and in youth at risk for developing psychosis are needed. Such studies will be critical for elucidating the neurodevelopmental and clinical time course of PSY-related neurometabolite alterations, and for assessing the potential for implicated metabolites to serve as druggable targets for decreasing PSY risk.

Metabolite abnormalities in psychosis risk: A meta-analysis of proton magnetic resonance spectroscopy studies

Accumulating evidence implicates that individuals at high-risk of psychosis have already exhibited pathophysiological changes in brain metabolites including glutamate, gamma-Aminobutyric Acid (GABA), N-Acetylaspartate (NAA), creatine (Cr), myo-inositol (MI) and choline (Cho). These changes may contribute to the development of schizophrenia and associate with psychotic genes. However, specific metabolic changes of brain sub-regions in individuals at risk have still been controversial. Thus, the current study aimed to investigate the brain metabolic changes including glutamate, Glx, GABA, GABA/Glx, NAA, Cr, MI and Cho levels in individuals at risk by conducting a case-control meta-analysis and meta-regression of proton magnetic resonance spectroscopy studies. Primary outcomes revealed that individuals at risk exhibited increased Cr levels at the rostral medial prefrontal cortex (rmPFC), decreased NAA and Cr levels at the thalamus, and increased MI levels at the dorsolateral prefrontal cortex. Sub-group analyses further indicated that individuals with clinical high-risk (CHR) exhibited increased Cr levels at the medial prefrontal cortex (mPFC) and decreased Glx levels at the thalamus, while individuals with genetic risk (siblings of psychiatric patients) exhibited significant increased Glx and MI levels at the mPFC. However, GABA, GABA/Glx and Cho levels showed no significant result. These findings suggest that the dysfunctional metabolites at the mPFC and the thalamus may be an essential neurobiological basis at the early stage of psychosis.

Magnetic resonance spectroscopy studies in subjects with high risk for psychosis: A meta-analysis and review

INTRODUCTION

Even though anomalies on brain metabolites have been found in schizophrenia, researches about subjects with high risk (HR) show heterogeneous results. Thus, this meta-analysis aims to characterize the metabolic profile of HR subjects, first, compared to controls (HC) and then compared to people with schizophrenia.

METHODS

After a systematic database search, means and standard deviations were extracted to calculate standardized mean differences (SMD). Cerebral metabolites levels were compared between HR subjects and HC or patients with schizophrenia in all regions of interest investigated in included studies. Meta-regressions were performed to explore the influence of demographic and clinical variables on metabolites level's SMDs.

RESULTS

Thirty-nine studies were included in this meta-analysis. A higher level of glutamine + glutamate (Glx) was found in the medial prefrontal cortex (mPFC) (p < 0.01) and potentially in the basal ganglia (p = 0,05) as well as a higher level of myo-inositol (mI) in the dorsolateral prefrontal cortex (DLPFC) (p = 0.04) in HR subjects compared to HC. A higher level of choline (Cho) was found in people with schizophrenia compared to HR subjects in the DLPFC (p < 0.001) and the medial temporal lobe (p = 0.02). Meta-regression analyses showed negative associations between SMD for Cho concentration, the percentage of females or the age (p = 0.01).

CONCLUSIONS

The present meta-analysis provides evidence that some brain metabolites concentrations are disrupted before the transition to psychosis and could be considered like a vulnerability.

Cerebral glutamate and GABA levels in high-risk of psychosis states: A focused review and meta-analysis of 1H-MRS studies

Disturbances in the brain glutamate and GABA (γ-aminobutyric acid) homeostasis may be markers of transition to psychosis in individuals at high-risk (HR). Knowledge of GABA and glutamate levels in HR stages could give an insight into changes in the neurochemistry underlying psychosis. Studies on glutamate in HR have provided conflicting data, and GABA studies have only recently been initialized. In this meta-analysis, we compared cerebral levels of glutamate and GABA in HR individuals with healthy controls (HC). We searched Medline and Embase for articles published on ¹H-MRS studies on glutamate and GABA in HR states until April 9th, 2019. We identified a total of 28 eligible studies, of which eight reported GABA (243 HR, 356 HC) and 26 reported glutamate (299 HR, 279 HC) or Glx (glutamate + glutamine) (584 HR, 632 HC) levels. Sample sizes varied from 6 to 75 for HR and 10 to 184 for HC. Our meta-analysis of ¹H-MRS studies on glutamate and GABA in HR states displayed significantly lower (P = 0.0003) levels of thalamic glutamate in HR individuals than in HC and significantly higher (P = 0.001) Glx in the frontal lobe of genetic HR individuals (1st-degree relatives) than in HC. No other significant differences in glutamate and GABA levels were found. Subject numbers in the studies on glutamate as well as GABA levels were generally small and the data conflicting. Our meta-analytical findings highlight the need for larger and more homogeneous studies of glutamate and GABA in high-risk states.

Glutamatergic function in a genetic high-risk group for psychosis: A proton magnetic resonance spectroscopy study in individuals with 22q11.2 deletion

Glutamatergic dysregulation is one of the leading theories regarding the pathoaetiolopy of schizophrenia. Meta-analysis of magnetic resonance spectroscopy studies in schizophrenia shows increased levels of glutamate and glutamine (Glx) in the medial frontal cortex and basal ganglia in clinical high-risk groups for psychosis and increased glutamine levels in the thalamus, but it is unclear if this is also the case in people at genetic high risk for psychosis. The aim of this study was to investigate glutamatergic function in the anterior cingulate cortex, striatum and thalamus in carriers of a genetic variant (22q11.2 deletion) associated with a high risk for psychosis. 53 volunteers (23 22q11.2 deletion carriers and 30 controls) underwent proton magnetic resonance spectroscopy imaging and neuropsychological assessments for prodromal psychotic symptoms, schizotypy, anxiety, depression and FSIQ. We did not find any difference between groups in Glx in the anterior cingulate cortex, striatum or thalamus (Glx: t(50)=-1.26, p = 0.21; U = 251, z = -0.7, p = 0.49; U = 316, z= -0.26, p = 0.79, respectively). No correlation was detected between Glx levels in any region and symptomatology or FSIQ. Our findings indicate that glutamatergic function is not altered in people at genetic high risk of psychosis due to the 22q11.2 deletion, which could suggest that this is not the mechanism underlying psychosis risk in 22q11.2 deletion carriers.

The impact of endurance training and table soccer on brain metabolites in schizophrenia

Higher glutamate and glutamine (together: Glx) and lower N-acetyl-aspartate (NAA) levels were reported in schizophrenia. Endurance training normalizes NAA in the hippocampus, but its effects on other metabolites in the brain and the relationship of metabolites to clinical symptoms remain unknown. For 12 weeks, 20 schizophrenia inpatients (14 men, 6 women) and 23 healthy controls (16 men, 7 women) performed endurance training and a control group of 21 schizophrenia inpatients (15 men, 6 women) played table soccer. A computer-assisted cognitive performance training program was introduced after 6 weeks. We assessed cognitive performance, psychopathological symptoms, and everyday functioning at baseline and after 6 and 12 weeks and performed single voxel magnetic resonance spectroscopy of the hippocampus, left dorsolateral prefrontal cortex (DLPFC), and thalamus. We quantified NAA, Glx, total creatine (tCr), calculated NAA/tCr and Glx/tCr and correlated these ratios with physical fitness, clinical and neurocognitive scores, and everyday functioning. At baseline, in both schizophrenia groups NAA/tCr was lower in the left DLPFC and left hippocampus and Glx/tCr was lower in the hippocampus than in the healthy controls. After 6 weeks, NAA/tCr increased in the left DLPFC in both schizophrenia groups. Brain metabolites did not change significantly in the hippocampus or thalamus, but the correlation between NAA/tCr and Glx/tCr normalized in the left DLPFC. Global Assessment of Functioning improvements correlated with NAA/tCr changes in the left DLPFC. In our study, endurance training and table soccer induced normalization of brain metabolite ratios in the brain circuitry associated with neuronal and synaptic elements, including metabolites of the glutamatergic system.

Neurochemical effects of oxytocin in people at clinical high risk for psychosis

Alterations in neurochemical metabolites are thought to play a role in the pathophysiology of psychosis onset. Oxytocin, a neuropeptide with prosocial and anxiolytic properties, modulates glutamate neurotransmission in preclinical models but its neurochemical effects in people at high risk for psychosis are unknown. We used proton magnetic resonance spectroscopy (¹H-MRS) to examine the effects of intranasal oxytocin on glutamate and other metabolites in people at Clinical High Risk for Psychosis (CHR-P) in a double-blind, placebo-controlled, crossover design. 30 CHR-P males were studied on two occasions, once after 40IU intranasal oxytocin and once after placebo. The effects of oxytocin on the concentration of glutamate, glutamate+glutamine and other metabolites (choline, N-acetylaspartate, myo-inositol) scaled to creatine were examined in the left thalamus, anterior cingulate cortex (ACC) and left hippocampus, starting approximately 75, 84 and 93 min post-dosing, respectively. Relative to placebo, administration of oxytocin was associated with an increase in choline levels in the ACC (p=.008, Cohen's d = 0.54). There were no other significant effects on metabolite concentrations (all p>.05). Our findings suggest that, at ∼75-99 min post-dosing, a single dose of intranasal oxytocin does not alter levels of neurochemical metabolites in the thalamus, ACC, or hippocampus in those at CHR-P, aside from potential effects on choline in the ACC.

Metabolomics in patients with psychosis: A systematic review

The purpose of this article is to provide a comprehensive review of metabolomics studies for psychosis, as a means of biomarker discovery. Manuscripts were selected for review if they involved discovery of metabolites using high-throughput analysis in human subjects and were published in the last decade. The metabolites identified were searched in Human Metabolome Data Base (HMDB) for a link to psychosis. Metabolites associated with psychosis based on evidence in HMBD were then searched using PubMed to explore the availability of further evidence. Almost all of the studies which underwent full review involved patients with schizophrenia. Ten biomarkers were identified. Six of them were reported in two or more independent metabolomics studies: N-acetyl aspartate, lactate, tryptophan, kynurenine, glutamate, and creatine. Four additional metabolites were encountered in a single metabolomics study but had significant evidence (two supporting articles or more) for a link to psychosis based on PubMed: linoleic acid, D-serine, glutathione, and 3-hydroxybutyrate. The pathways affected are discussed as they may be relevant to the pathophysiology of psychosis, and specifically of schizophrenia, as well as, constitute new drug targets for treatment of related conditions. Based on the biomarkers identified, early diagnosis of schizophrenia and/or monitoring may be possible.

Magnetic Resonance Spectroscopy in Schizophrenia: Evidence for Glutamatergic Dysfunction and Impaired Energy Metabolism

In the past couple of decades, major efforts were made to increase reliability of metabolic assessments by magnetic resonance methods. Magnetic resonance spectroscopy (MRS) has been valuable for providing in vivo evidence and investigating biomarkers in neuropsychiatric disorders, namely schizophrenia. Alterations of glutamate and glutamine levels in brains of schizophrenia patients relative to healthy subjects are generally interpreted as markers of glutamatergic dysfunction. However, only a small fraction of MRS-detectable glutamate is involved in neurotransmission. Here we review and discuss brain metabolic processes that involve glutamate and that are likely to be implicated in neuropsychiatric disorders.

Glutamatergic metabolites among adolescents at risk for psychosis

Proton-Magnetic Resonance Spectroscopy (¹H-MRS) may serve as an important tool for identifying biomarkers that aid the understanding of early psychosis, as development of this condition may be associated with metabolite concentration changes that reflect an alteration in glutamatergic mechanisms. The current study explored ¹H-MRS metabolite concentrations in the striatum and anterior cingulate cortex (ACC) as potential biomarkers of psychosis-risk symptom severity. In a sample of 12 adolescents at clinical high-risk for psychosis, the subclinical symptom of grandiosity significantly correlated with glutamate in the ACC. Striatal glutathione, a marker of oxidative stress linked to the glutamatergic system, significantly correlated with grandiosity. Anterior cingulate glutathione significantly correlated with grandiosity and disorganized communication. These findings suggest that within a small sample of young people at clinical high-risk, glutamatergic metabolites are correlated with symptomatology generally predictive of conversion to psychosis. These mechanisms may serve as relevant biomarkers for facilitating prediction of symptom severity and providing insight into the etiology of early psychosis.

Brain bioenergetics and redox state measured by 31P magnetic resonance spectroscopy in unaffected siblings of patients with psychotic disorders

BACKGROUND

Brain bioenergetic anomalies and redox dysregulation have been implicated in the pathophysiology of psychotic disorders. The present study examined brain energy-related metabolites and the balance between nicotinamide adenine dinucleotide metabolites (oxidized NAD+ and reduced NADH) using ³¹P-magnetic resonance spectroscopy (³¹P-MRS) in unaffected siblings, compared to first episode psychosis (FEP) patients and healthy controls.

METHODS

21 unaffected siblings, 32 FEP patients (including schizophrenia spectrum and affective psychoses), and 21 controls underwent ³¹P-MRS in the frontal lobe (6×6×4cm³) on a 4T MR scanner, using custom-designed dual-tuned surface coil with outer volume suppression. Brain parenchymal pH and steady-state metabolite ratios of high energy phosphate compounds were measured. NAD+ and NADH levels were determined using a ³¹P-MRS fitting algorithm. 13 unaffected sibling-patient pairs were related; other patients and siblings were unrelated. ANCOVA analyses were used to examine ³¹P-MRS measures, with age and gender as covariates.

RESULTS

The phosphocreatine/adenosine triphosphate ratio was significantly reduced in both unaffected siblings and FEP patients, compared to controls. NAD+/NADH ratio was significantly reduced in patients compared to siblings and controls, with siblings showing a reduction in NAD+/NADH compared to controls that was not statistically significant. Compared to patients and controls, siblings showed significantly reduced levels of NAD+. Siblings did not differ from patients or controls on brain pH.

DISCUSSION

Our results indicate that unaffected siblings show some, but not all the same abnormalities in brain energy metabolites and redox state as FEP patients. Thus, ³¹P-MRS studies may identify factors related both to risk and expression of psychosis.

Glutamate imaging (GluCEST) reveals lower brain GluCEST contrast in patients on the psychosis spectrum

Psychosis commonly develops in adolescence or early adulthood. Youths at clinical high risk (CHR) for psychosis exhibit similar, subtle symptoms to those with schizophrenia (SZ). Malfunctioning neurotransmitter systems, such as glutamate, are implicated in the disease progression of psychosis. Yet, in vivo imaging techniques for measuring glutamate across the cortex are limited. Here, we use a novel 7 Tesla MRI glutamate imaging technique (GluCEST) to estimate changes in glutamate levels across cortical and subcortical regions in young healthy individuals and ones on the psychosis spectrum. Individuals on the psychosis spectrum (PS; n=19) and healthy young individuals (HC; n=17) underwent MRI imaging at 3 and 7 T. At 7 T, a single slice GluCEST technique was used to estimate in vivo glutamate. GluCEST contrast was compared within and across the subcortex, frontal, parietal and occipital lobes. Subcortical (χ2 (1)=4.65, P=0.031) and lobular (χ2 (1)=5.17, P=0.023) GluCEST contrast levels were lower in PS compared with HC. Abnormal GluCEST contrast levels were evident in both CHR (n=14) and SZ (n=5) subjects, and correlated differentially, across regions, with clinical symptoms. Our findings describe a pattern of abnormal brain neurochemistry early in the course of psychosis. Specifically, CHR and young SZ exhibit diffuse abnormalities in GluCEST contrast attributable to a major contribution from glutamate. We suggest that neurochemical profiles of GluCEST contrast across cortex and subcortex may be considered markers of early psychosis. GluCEST methodology thus shows promise to further elucidate the progression of the psychosis disease state.

Social isolation stress and chronic glutathione deficiency have a common effect on the glutamine-to-glutamate ratio and myo-inositol concentration in the mouse frontal cortex

Environmental stress can interact with genetic predisposition to increase the risk of developing psychopathology. In this work, we tested the hypothesis that social isolation stress interacts with impaired glutathione synthesis and have cumulative effects on the neurochemical profile of the frontal cortex. A mouse model with chronic glutathione deficit induced by knockout (-/-) of the glutamate-cysteine ligase modulatory subunit (Gclm) was exposed to social isolation stress from weaning to post-natal day 65. Using magnetic resonance methods at high-field (14.1 T), we analysed the neurochemical profile in the frontal cortex, brain size and ventricular volume of adult animals. Glutathione deficit was accompanied by elevated concentrations of N-acetylaspartate, alanine, and glutamine, as well as the ratio of glutamine-to-glutamate (Gln/Glu), and by a reduction in levels of myo-inositol and choline-containing compounds in the frontal cortex of -/- animals with respect to wild-type littermates. Although there was no significant interaction between social isolation stress and glutathione deficiency, mice reared in isolation displayed lower myo-inositol concentration (-8.4%, p < 0.05) and larger Gln/Glu (+7.6%, p < 0.05), relative to those in group housing. Furthermore, glutathione deficiency caused a reduction in whole brain volume and enlargement of ventricles, but social isolation had no effect on these parameters. We conclude that social isolation caused neurochemical alterations that may add to those associated to impaired glutathione synthesis.

Are there glutamate abnormalities in subjects at high risk mental state for psychosis? A review of the evidence

New approaches to underlying alterations in psychosis suggest increasing evidence of glutamatergic abnormalities in schizophrenia and an association between these abnormalities and certain core psychopathological alterations such as cognitive impairment and negative symptoms. Proton magnetic resonance spectroscopy ((1)H MRS) is an MR-based technique that enables investigators to study glutamate function by measuring in vivo glutamatergic indices in the brain. In this article we review the published studies of (1)H MRS in subjects with an at-risk mental state (ARMS) for psychosis. The primary aim was to investigate whether alterations in glutamate function are present before the illness develops in order to expand our understanding of glutamatergic abnormalities in prodromal phases. Three databases were consulted for this review. Titles and abstracts were examined to determine if they fulfilled the inclusion criteria. The reference lists of the included studies were also examined to identify additional trials. Eleven final studies were included in this review. Significant alterations in glutamate metabolites across different cerebral areas (frontal lobe, thalamus, and the associative striatum) in subjects with an ARMS for psychosis are reported in six of the trials. A longitudinal analysis in two of these trials confirmed an association between these abnormalities and worsening of symptoms and final transition to psychosis. Considering that five other studies found no significant differences across these same areas, we can conclude that more research is needed to confirm glutamatergic abnormalities in subjects with an ARMS for psychosis. However, future research must overcome the methodological limitations of existing studies to obtain reliable results.

The cuprizone-induced changes in (1)H-MRS metabolites and oxidative parameters in C57BL/6 mouse brain: Effects of quetiapine

Cuprizone is a copper-chelating agent and able to induce oligodendrocyte loss and demyelination in C57BL/6 mouse brain. Recent studies have used the cuprizone-fed mouse as an animal model of schizophrenia to examine putative roles of altered oligodendrocytes in this mental disorder. The present study reported the effects of cuprizone on the brain metabolites and oxidative parameters with the aim of providing neurochemical evidence for the application of the cuprizone mouse as an animal model of schizophrenia. In addition, we examined effects of quetiapine on the cuprizone-induced changes in brain metabolites and oxidative parameters; this atypical antipsychotic was shown to ameliorate the cuprizone-induced demyelination and behavioral changes in previous studies. C57BL/6 mice were fed a standard rodent chow without or with cuprizone (0.2% w/w) for four weeks during which period they were given sterilized saline or quetiapine in saline. The results of the proton magnetic resonance spectroscopy (1H-MRS) showed that cuprizone-feeding decreased (1)H-MRS signals of N-acetyl-l-aspartate (NAA), total NAA (NAA + NAAG), and choline-containing compounds (phosphorylcholine and glycerophosphorylcholine), suggestive of mitochondrial dysfunction in brain neurons. Biochemical analyses showed lower activities of catalase and glutathione peroxidase, but higher levels of malondialdehyde and H2O2 in the brain tissue of cuprizone-fed mice, indicative of an oxidative stress. These cuprizone-induced changes were effectively relieved in the mice co-administered with cuprizone and quetiapine, although the antipsychotic alone showed no effect. These findings suggest the toxic effects of cuprizone on mitochondria and an antioxidant capacity of quetiapine, by which this antipsychotic relieves the cuprizone-induced mitochondrial dysfunction in brain cells.

Apoptotic markers in cultured fibroblasts correlate with brain metabolites and regional brain volume in antipsychotic-naive first-episode schizophrenia and healthy controls

Cultured fibroblasts from first-episode schizophrenia patients (FES) have shown increased susceptibility to apoptosis, which may be related to glutamate dysfunction and progressive neuroanatomical changes. Here we determine whether apoptotic markers obtained from cultured fibroblasts in FES and controls correlate with changes in brain glutamate and N-acetylaspartate (NAA) and regional brain volumes. Eleven antipsychotic-naive FES and seven age- and gender-matched controls underwent 3-Tesla magnetic resonance imaging scanning. Glutamate plus glutamine (Glx) and NAA levels were measured in the anterior cingulate (AC) and the left thalamus (LT). Hallmarks of apoptotic susceptibility (caspase-3-baseline activity, phosphatidylserine externalization and chromatin condensation) were measured in fibroblast cultures obtained from skin biopsies after inducing apoptosis with staurosporine (STS) at doses of 0.25 and 0.5 μM. Apoptotic biomarkers were correlated to brain metabolites and regional brain volume. FES and controls showed a negative correlation in the AC between Glx levels and percentages of cells with condensed chromatin (CC) after both apoptosis inductions (STS 0.5 μM: r = -0.90; P = 0.001; STS 0.25 μM: r = -0.73; P = 0.003), and between NAA and cells with CC (STS 0.5 μM induction r = -0.76; P = 0.002; STS 0.25 μM r = -0.62; P = 0.01). In addition, we found a negative correlation between percentages of cells with CC and regional brain volume in the right supratemporal cortex and post-central region (STS 0.25 and 0.5 μM; P < 0.05 family-wise error corrected (FWEc)). We reveal for the first time that peripheral markers of apoptotic susceptibility may correlate with brain metabolites, Glx and NAA, and regional brain volume in FES and controls, which is consistent with the neuroprogressive theories around the onset of the schizophrenia illness.

Glutamate and dopamine in schizophrenia: an update for the 21st century

The glutamate and dopamine hypotheses are leading theories of the pathoaetiology of schizophrenia. Both were initially based on indirect evidence from pharmacological studies supported by post-mortem findings, but have since been substantially advanced by new lines of evidence from in vivo imaging studies. This review provides an update on the latest findings on dopamine and glutamate abnormalities in schizophrenia, focusing on in vivo neuroimaging studies in patients and clinical high-risk groups, and considers their implications for understanding the biology and treatment of schizophrenia. These findings have refined both the dopamine and glutamate hypotheses, enabling greater anatomical and functional specificity, and have been complemented by preclinical evidence showing how the risk factors for schizophrenia impact on the dopamine and glutamate systems. The implications of this new evidence for understanding the development and treatment of schizophrenia are considered, and the gaps in current knowledge highlighted. Finally, the evidence for an integrated model of the interactions between the glutamate and dopamine systems is reviewed, and future directions discussed.

The neurobiology and treatment of first-episode schizophrenia

It is evident that once psychosis is present in patients with schizophrenia, the underlying biological process of the illness has already been ongoing for many years. At the time of diagnosis, patients with schizophrenia show decreased mean intracranial volume (ICV) as compared with healthy subjects. Since ICV is driven by brain growth, which reaches its maximum size at approximately 13 years of age, this finding suggests that brain development in patients with schizophrenia is stunted before that age. The smaller brain volume is expressed as decrements in both grey and white matter. After diagnosis, it is mainly the grey matter loss that progresses over time whereas white matter deficits are stable or may even improve over the course of the illness. To understand the possible causes of the brain changes in the first phase of schizophrenia, evidence from treatment studies, postmortem and neuroimaging investigations together with animal experiments needs to be incorporated. These data suggest that the pathophysiology of schizophrenia is multifactorial. Increased striatal dopamine synthesis is already evident before the time of diagnosis, starting during the at-risk mental state, and increases during the onset of frank psychosis. Cognitive impairment and negative symptoms may, in turn, result from other abnormalities, such as NMDA receptor hypofunction and low-grade inflammation of the brain. The latter two dysfunctions probably antedate increased dopamine synthesis by many years, reflecting the much earlier presence of cognitive and social dysfunction. Although correction of the hyperdopaminergic state with antipsychotic agents is generally effective in patients with a first-episode psychosis, the effects of treatments to correct NMDA receptor hypofunction or low-grade inflammation are (so far) rather modest at best. Improved efficacy of these interventions can be expected when they are applied at the onset of cognitive and social dysfunction, rather than at the onset of psychosis.

Brain metabolite changes in subcortical regions after exposure to cuprizone for 6 weeks: potential implications for schizophrenia

Cuprizone is a copper chelating agent able to selectively damage the white matter in the mouse brain. Recent studies have reported behavioral abnormalities relevant to some of schizophrenia symptoms. While associating white matter damage to the behavioral abnormalities, these previous studies did not rule out the possible impairment in neuronal functions in cuprizone-exposed mice. The aim of this study was to examine brain metabolites of the cuprizone-exposed mice by proton magnetic resonance spectroscopy ((1)H-MRS). The examined brain regions were the caudoputamen, midbrain, and thalamus; these subcortical regions showed different susceptibilities to cuprizone in terms of demyelination and oligodendrocyte loss in previous studies. Young C57BL/6 mice were fed a standard rodent chow without or with cuprizone (0.2 %) for 6 weeks. At the end, open-field and Y-maze tests were performed to measure the emotional and cognitive behaviors of the animals, followed by (1)H-MRS procedure to evaluate the brain metabolites. Cuprizone-exposure increased anxiety levels and impaired spatial working memory. The same treatment increased T2 signal intensity in the cerebral cortex, hippocampus, and caudoputamen, but not in the thalamus. Cuprizone-exposure decreased the concentrations of NAA and NAA+NAAG in caudoputamen, but not in thalamus and midbrain. It decreased levels of Cr+PCr, GPC+PCh and myo-inositol in all the three brain regions. These results provided neurochemical evidence for the impairment in neuronal functions by cuprizone treatment.

Imaging-based neurochemistry in schizophrenia: a systematic review and implications for dysfunctional long-term potentiation

Cognitive deficits are commonly observed in patients with schizophrenia. Converging lines of evidence suggest that these deficits are associated with impaired long-term potentiation (LTP). In our systematic review, this hypothesis is evaluated using neuroimaging literature focused on proton magnetic resonance spectroscopy, positron emission tomography, and single-photon emission computed tomography. The review provides evidence for abnormal dopaminergic, GABAergic, and glutamatergic neurotransmission in antipsychotic-naive/free patients with schizophrenia compared with healthy controls. The review concludes with a model illustrating how these abnormalities could lead to impaired LTP in patients with schizophrenia and consequently cognitive deficits.

Concurrent changes in ¹H MRS metabolites and antioxidant enzymes in the brain of C57BL/6 mouse short-termly exposed to cuprizone: possible implications for schizophrenia

Cuprizone (CPZ) is a copper chelating agent able to selectively insult mature oligodendrocytes (OLs) in brains of rodents. The CPZ-exposed mice show behavioral changes and have been employed to examine a putative role of altered OLs in the pathophysiology of schizophrenia. The aims of this study were to examine the brain metabolites in the CPZ-exposed mice during the early stage and to measure some antioxidant enzymes, lipid peroxidation and hydrogen peroxide (H2O2) in brain tissue. C57BL/6 mice were fed normal or CPZ-containing diet for 7 days. On days 7 and 8, mice were subjected to behavioral tests. On days 9 and 10, mice were subjected to (1)H MRS procedure. On day 10 mice were sacrificed and their brain tissue was processed for biochemical analyses. CPZ-exposure for 7 days caused an anxiety-like behavior, but had no effect on the social interaction and spatial working memory in C57BL/6 mice. The treatment significantly decreased levels of GPC+PCh, ml, NAA, NAA+NAAG, and PCr in the thalamus and hippocampus. It impaired the activities of some antioxidant enzymes, but did not increase levels of MDA and H2O2. This first (1)H MRS study with CPZ-exposed mice provided neurochemical evidence for mitochondrial dysfunction in brain cells of living mice during the early stage of CPZ-exposure. The results are of relevance to the pathophysiology of schizophrenia in which mitochondrial dysfunction of neural cells and altered OLs are two important players.

Glutamatergic abnormalities in schizophrenia: a review of proton MRS findings

The last fifteen years have seen a great increase in our understanding of the role of glutamate in schizophrenia (SCZ). The glutamate hypothesis focuses on disturbances in brain glutamatergic pathways and impairment in signaling at glutamate receptors. Proton Magnetic Resonance Spectroscopy ((1)H-MRS) is an MR-based technique that affords investigators the ability to study glutamate function by measuring in vivo glutamatergic indices in the brains of individuals with SCZ. (1)H-MRS studies have been performed comparing glutamatergic levels of individuals with SCZ and healthy control subjects or studying the effect of antipsychotic medications on glutamatergic levels. In this article we summarize the results of these studies by brain region. We will review the contribution of (1)H-MRS studies to our knowledge about glutamatergic abnormalities in the brains of individuals with SCZ and discuss the implications for future research and clinical care.

Imaging glutamate in schizophrenia: review of findings and implications for drug discovery

Currently, all treatments for schizophrenia (SCZ) function primarily by blocking D(2)-type dopamine receptors. Given the limitations of these medications, substantial efforts have been made to identify alternative neurochemical targets for treatment development in SCZ. One such target is brain glutamate. The objective of this article is to review and synthesize the proton magnetic resonance spectroscopy ((1)H MRS) and positron emission tomography (PET)/single-photon emission computed tomography (SPECT) investigations that have examined glutamatergic indices in SCZ, including those of modulatory compounds such as glutathione (GSH) and glycine, as well as data from ketamine challenge studies. The reviewed (1)H MRS and PET/SPECT studies support the theory of hypofunction of the N-methyl-D-aspartate receptor (NMDAR) in SCZ, as well as the convergence between the dopamine and glutamate models of SCZ. We also review several advances in MRS and PET technologies that have opened the door for new opportunities to investigate the glutamate system in SCZ and discuss some ways in which these imaging tools can be used to facilitate a greater understanding of the glutamate system in SCZ and the successful and efficient development of new glutamate-based treatments for SCZ.

A review of neuroimaging studies of young relatives of individuals with schizophrenia: a developmental perspective from schizotaxia to schizophrenia

In an effort to identify the developing abnormalities preceding psychosis, Dr. Ming T. Tsuang and colleagues at Harvard expanded Meehl's concept of "schizotaxia," and examined brain structure and function in families affected by schizophrenia (SZ). Here, we systematically review genetic (familial) high-risk (HR) studies of SZ using magnetic resonance imaging (MRI), examine how findings inform models of SZ etiology, and suggest directions for future research. Neuroimaging studies of youth at HR for SZ through the age of 30 were identified through a MEDLINE (PubMed) search. There is substantial evidence of gray matter volume abnormalities in youth at HR compared to controls, with an accelerated volume reduction over time in association with symptoms and cognitive deficits. In structural neuroimaging studies, prefrontal cortex (PFC) alterations were the most consistently reported finding in HR. There was also consistent evidence of smaller hippocampal volume. In functional studies, hyperactivity of the right PFC during performance of diverse tasks with common executive demands was consistently reported. The only longitudinal fMRI study to date revealed increasing left middle temporal activity in association with the emergence of psychotic symptoms. There was preliminary evidence of cerebellar and default mode network alterations in association with symptoms. Brain abnormalities in structure, function and neurochemistry are observed in the premorbid period in youth at HR for SZ. Future research should focus on the genetic and environmental contributions to these alterations, determine how early they emerge, and determine whether they can be partially or fully remediated by innovative treatments.

Glutamate levels in the associative striatum before and after 4 weeks of antipsychotic treatment in first-episode psychosis: a longitudinal proton magnetic resonance spectroscopy study

IMPORTANCE

Increased glutamate levels in the right associative striatum have been described in patients during a first episode of psychosis. Whether this increase would persist after effective antipsychotic treatment is unknown.

OBJECTIVES

To compare the glutamate levels in antipsychotic-naive patients with first-episode psychosis in the right associative striatum and right cerebellar cortex using proton magnetic resonance spectroscopy before and 4 weeks after antipsychotic treatment and to compare these results with normative data from sex-matched healthy control subjects.

DESIGN, SETTING, AND PARTICIPANTS

Before-after trial in an inpatient psychiatric research unit among 24 antipsychotic-naive patients with first-episode psychosis and 18 healthy controls matched for age, sex, handedness, and cigarette smoking.

INTERVENTIONS

Participants underwent 2 proton magnetic resonance spectroscopy studies: patients were imaged at baseline and after 4 weeks of antipsychotic treatment, while controls were imaged at baseline and at 4 weeks after the baseline measurement. Patients were treated with oral risperidone (open label) for 4 weeks with dosages that were titrated on the basis of clinical judgment.

MAIN OUTCOMES AND MEASURES

Glutamate levels were estimated using LCModel (version 6.2-1T) and were corrected for the cerebrospinal fluid proportion within the voxel.

RESULTS

Patients with first-episode psychosis had higher levels of glutamate in the associative striatum and the cerebellum during the antipsychotic-naive condition compared with controls. After clinically effective antipsychotic treatment, glutamate levels significantly decreased in the associative striatum, with no significant change in the cerebellum. No differences in glutamate levels were observed between groups at 4 weeks.

CONCLUSIONS AND RELEVANCE

Increased glutamate levels observed at baseline in patients with first-episode psychosis normalized after 4 weeks of clinically effective antipsychotic treatment. These results provide support for the hypothesis that improvement in clinical symptoms might be related to a decrease in glutamate levels.

T2 relaxation effects on apparent N-acetylaspartate concentration in proton magnetic resonance studies of schizophrenia

Over the past two decades, many magnetic resonance spectroscopy (MRS) studies reported lower N-acetylaspartate (NAA) in key brain regions of patients with schizophrenia (SZ) compared to healthy subjects. A smaller number of studies report no difference in NAA. Many sources of variance may contribute to these discordant results including heterogeneity of the SZ subject populations and methodological differences such as MRS acquisition parameters, and post-acquisition analytic methods. The current study reviewed proton MRS literature reporting measurements of NAA in SZ with a focus on methodology. Studies which reported lower NAA were significantly more likely to have used longer echo times (TEs), while studies with shorter TEs reported no concentration difference. This suggests that NAA quantitation using MRS was affected by the choice of TE, and that published MRS literature reporting NAA in SZ using a long TE is confounded by apparent differential T2 relaxation effects between SZ and healthy control groups. Future MRS studies should measure T2 relaxation times. This would allow for spectral concentration measurements to be appropriately corrected for these relaxation effects. In addition, as metabolite concentration and T2 relaxation times are completely independent variables, this could offer distinct information about the metabolite of interest.

Brain metabolite alterations in young adults at familial high risk for schizophrenia using proton magnetic resonance spectroscopy

BACKGROUND

Proton magnetic resonance spectroscopy ((1)H MRS) enables in-vivo measurement of several relevant brain metabolites and has provided evidence of a range of neurochemical abnormalities in schizophrenia, especially in glutamate and N-acetyl-aspartate (NAA). While individuals at high familial risk for schizophrenia (HR) exhibit some neurobiological findings observed in the disorder, (1)H MRS findings and their clinical correlates are not well characterized in this population.

METHODS

We compared 23 adolescent and young adult offspring of schizophrenia patients with 24 age- and sex-matched healthy controls using (1)H MRS. We acquired multi-voxel, short TE (1)H MRS measurements at 1.5T and obtained metabolite concentrations of N-acetyl-aspartate (NAA), combined glutamate and glutamine (Glu+Gln) and choline-containing compounds (GPC+PC) for the left and right thalamus, anterior cingulate gyrus, and caudate. We also assessed the relationship between regional metabolite levels, clinical measures and brain volume in a subset of 16 high-risk and 15 control subjects.

RESULTS

Compared to healthy controls, high-risk subjects showed reductions in NAA levels in all three regions (thalamus, caudate, and anterior cingulate cortex), increases in Glu+Gln in the thalamus and caudate, and increases in GPC+PC in the anterior cingulate. In HR, thalamic Glu+Gln concentration was positively correlated and thalamic NAA inversely correlated with measures of schizotypy. Anterior cingulate GPC+PC and caudate Glu+Gln were significantly correlated with attenuated psychotic symptom severity. Anterior cingulate NAA was correlated with executive function.

CONCLUSIONS

Our data suggest the occurrence of metabolic alterations in young relatives of schizophrenia patients similar to those seen in patients with established illness. The observed correlations with cognitive deficits and psychosis-related psychopathology suggest that these metabolic measures may have value as biomarkers of risk for schizophrenia.

Glutamate in schizophrenia: a focused review and meta-analysis of ¹H-MRS studies

Schizophrenia is a severe chronic psychiatric illness, characterized by hallucinations and delusions. Decreased brain volumes have been observed in the disease, although the origin of these changes is unknown. Changes in the n-methyl-d-aspartate (NMDA)-receptor mediated glutamatergic neurotransmission are implicated, since it is hypothesized that NMDA-receptor dysfunction in schizophrenia leads to increased glutamate release, which can have excitotoxic effects. However, the magnitude and extent of changes in glutamatergic metabolites in schizophrenia are not clear. With (1)H magnetic resonance spectroscopy ((1)H-MRS), in vivo information about glutamate and glutamine concentrations can be obtained in the brain. A systematic search through the MEDLINE database was conducted to identify relevant (1)H-MRS studies that examined differences in glutamate and glutamine concentrations between patients with schizophrenia and healthy control subjects. Twenty-eight studies were identified and included a total of 647 patients with schizophrenia and 608 healthy-control subjects. For each study, Cohen's d was calculated and main effects for group analyses were performed using the random-effects model. Medial frontal region glutamate was decreased and glutamine was increased in patients with schizophrenia as compared with healthy individuals. Group-by-age associations revealed that in patients with schizophrenia, glutamate and glutamine concentrations decreased at a faster rate with age as compared with healthy controls. This could reflect aberrant processes in schizophrenia, such as altered synaptic activity, changed glutamate receptor functioning, abnormal glutamine-glutamate cycling, or dysfunctional glutamate transport.

Altered development of the dorsolateral prefrontal cortex in chromosome 22q11.2 deletion syndrome: an in vivo proton spectroscopy study

BACKGROUND

Chromosome 22q11.2 deletion syndrome (22q11DS), the most common microdeletion in humans, is associated with multiple medical features, almost universal cognitive deficits, and a high risk of schizophrenia. The metabolic basis of the psychological/psychiatric features is not well understood. Volumetric brain imaging studies have shown that gray matter abnormalities in the dorsolateral prefrontal cortex (DLPFC), an area that is believed to be integral for higher neurocognition, as well as being involved in schizophrenia, are associated with the psychological manifestations. However, studies have not characterized any possible metabolite alterations within the DLPFC of children with 22q11DS and their correlations with the psychological findings.

METHODS

We conducted a short echo time, single-voxel, in vivo proton spectroscopy study involving children with 22q11DS (n = 26) and matched control subjects (n = 23).

RESULTS

Absolute N-acetylaspartate (NAA) levels from the DLPFC were significantly elevated in children with 22q11DS compared with control subjects and the elevations were associated with poor global functioning and higher rates of comorbid attention-deficit/hyperactivity disorder. Children with 22q11DS had a lack of an age-associated decrease in NAA levels, a trend seen in the control subjects. However, the results did not remain statistically significant after corrections for multiple comparisons were made.

CONCLUSIONS

These findings represent the first report of proton spectroscopy in children with 22q11DS. The elevated DLPFC NAA levels and the lack of decreasing trends in NAA with age in the 22q11DS group relative to control subjects suggest an alteration in cortical development. Also, such neuronal dysmaturation is associated with psychopathology in children with 22q11DS.

N-acetylcysteine normalizes neurochemical changes in the glutathione-deficient schizophrenia mouse model during development

BACKGROUND

Glutathione (GSH) is the major cellular redox-regulator and antioxidant. Redox-imbalance due to genetically impaired GSH synthesis is among the risk factors for schizophrenia. Here we used a mouse model with chronic GSH deficit induced by knockout (KO) of the key GSH-synthesizing enzyme, glutamate-cysteine ligase modulatory subunit (GCLM).

METHODS

With high-resolution magnetic resonance spectroscopy at 14.1 T, we determined the neurochemical profile of GCLM-KO, heterozygous, and wild-type mice in anterior cortex throughout development in a longitudinal study design.

RESULTS

Chronic GSH deficit was accompanied by an elevation of glutamine (Gln), glutamate (Glu), Gln/Glu, N-acetylaspartate, myo-Inositol, lactate, and alanine. Changes were predominantly present at prepubertal ages (postnatal days 20 and 30). Treatment with N-acetylcysteine from gestation on normalized most neurochemical alterations to wild-type level.

CONCLUSIONS

Changes observed in GCLM-KO anterior cortex, notably the increase in Gln, Glu, and Gln/Glu, were similar to those reported in early schizophrenia, emphasizing the link between redox imbalance and the disease and validating the model. The data also highlight the prepubertal period as a sensitive time for redox-related neurochemical changes and demonstrate beneficial effects of early N-acetylcysteine treatment. Moreover, the data demonstrate the translational value of magnetic resonance spectroscopy to study brain disease in preclinical models.

Creatine metabolism and psychiatric disorders: Does creatine supplementation have therapeutic value?

Athletes, body builders, and military personnel use dietary creatine as an ergogenic aid to boost physical performance in sports involving short bursts of high-intensity muscle activity. Lesser known is the essential role creatine, a natural regulator of energy homeostasis, plays in brain function and development. Creatine supplementation has shown promise as a safe, effective, and tolerable adjunct to medication for the treatment of brain-related disorders linked with dysfunctional energy metabolism, such as Huntington's Disease and Parkinson's Disease. Impairments in creatine metabolism have also been implicated in the pathogenesis of psychiatric disorders, leaving clinicians, researchers and patients alike wondering if dietary creatine has therapeutic value for treating mental illness. The present review summarizes the neurobiology of the creatine-phosphocreatine circuit and its relation to psychological stress, schizophrenia, mood and anxiety disorders. While present knowledge of the role of creatine in cognitive and emotional processing is in its infancy, further research on this endogenous metabolite has the potential to advance our understanding of the biological bases of psychopathology and improve current therapeutic strategies.

Auditory steady state response in the schizophrenia, first-degree relatives, and schizotypal personality disorder

The power and phase synchronization of the auditory steady state response (ASSR) at 40 Hz stimulation is usually reduced in schizophrenia (SZ). The sensitivity of the 40 Hz ASSR to schizophrenia spectrum phenotypes, such as schizotypal personality disorder (SPD), or to familial risk has been less well characterized. We compared the ASSR of patients with SZ, persons with schizotypal personality disorder, first degree relatives of patients with SZ, and healthy control participants. ASSRs were obtained to 20, 30, 40 and 50 Hz click trains, and assessed using measures of power (mean trial power or MTP) and phase consistency (phase locking factor or PLF). The MTP to 40 Hz stimulation was reduced in relatives, and there was a trend for MTP reduction in SZ. The 40 Hz ASSR was not reduced in SPD participants. PLF did not differ among groups. These data suggest the 40 Hz ASSR is sensitive to familial risk factors associated with schizophrenia.

The neural correlates of performance in adolescents at risk for schizophrenia: inefficiently increased cortico-striatal responses measured with fMRI

BACKGROUND

fMRI studies indicate that schizophrenia patients and their adult relatives require greater prefrontal activation to maintain performance at levels equal to controls, but studies have not established if this pattern of inefficiency is observed in child and adolescent offspring of schizophrenia patients (SCZ-Off).

METHODS

Using a task with visual working memory demands, we investigated activation in cortico-striatal networks and dorsal prefrontal modulation of regions underlying visual working memory in a group of SCZ-Off (n = 19) and controls with no family history of psychosis (n = 25 subjects) using an event-related design. Trials were divided based on memory performance (correct vs. incorrect) to specifically identify the neural correlates of correct working memory performance.

RESULTS

Whereas groups did not differ in terms of behavioral accuracy, SCZ-Off demonstrated significantly increased fMRI-measured activation in dorsal prefrontal cortex and the caudate nucleus during correct, relative to incorrect memory performance. Whereas activation in SCZ-Off was high and independent of performance in each region, in controls the fMRI response was related to behavioral proficiency in the caudate. Further, exploratory analyses indicated that this inefficiency in the dorsal prefrontal cortex response increased with age in SCZ-Off (but in no other regions or group). Finally, these differences were not based in differences in dorsal prefrontal modulation of other regions during successful performance.

DISCUSSION

These results are consistent with observed patterns in adult patients and first-degree relatives. Inefficient fronto-striatal responses during working memory may characterize the schizophrenia diathesis and may reflect the effects of the illness and vulnerability for the illness.

1 H-MR spectroscopy in ultra-high risk and first episode stages of schizophrenia

Using proton magnetic resonance spectroscopy biochemical characteristics in early stages of schizophrenia were examined. N-acetylaspartate, choline and creatine were measured in hippocampus, anterior cingulate gyrus (ACC) and medial prefrontal cortex (mPFC) of 24 first episode and 30 ultra-high risk patients. Careful LCModel analyses revealed no differences between the patient groups and 31 healthy controls, casting doubt upon the idea of metabolic changes in early stages of psychosis.

Magnetic resonance spectroscopy of limbic structures displays metabolite differences in young unaffected relatives of schizophrenia probands

Imaging studies of schizophrenia patients showed fronto-temporal brain volume deficits, while magnetic resonance spectroscopy (MRS) studies of patients and unaffected biological relatives have found a decrement of the neuronal marker N-acetyl-aspartate (NAA) in the hippocampus and frontal lobes, and increased choline-containing phospholipids. Using a 3T MR scanner, we determined the metabolite profile within limbic regions (anterior cingulate cortex (ACC) and left hippocampus) of 36 unaffected, adolescent/young adult relatives of schizophrenia probands (first-degree=16, second-degree=20) and 25 healthy controls with no family history of schizophrenia. Significant main effects of group were found on NAA/Cho ratios for both the left hippocampus (F = 6.11, p ≤ 0.02) and ACC (F = 4.89, p ≤ 0.03) as well as for the left hippocampus Cho/Cr ratio (F = 5.55, p ≤ 0.02). Compared to age and sex matched healthy controls without a family history of schizophrenia, first-degree relatives of probands had greater MRS metabolite deviations than second-degree relatives. Greater familial proximity to the schizophrenia proband (or higher schizophrenia susceptibility) among biological relatives was associated with stepwise lowering of NAA/Cho and elevations in Cho/Cr ratios. The observed limbic metabolite changes among young, nonpsychotic biological relatives are likely related to shared genetic vulnerability factors, and may assist in the early identification of schizophrenia for primary and secondary prevention.

Inefficiently increased anterior cingulate modulation of cortical systems during working memory in young offspring of schizophrenia patients

BACKGROUND

Children and adolescent offspring of schizophrenia patients are at increased risk for schizophrenia and are also characterized by impairments in brain structure and function. To date, few studies have investigated whether functional interactions between brain regions are intact or altered. Using an established verbal working memory paradigm with variable levels of memory load, we investigated the modulatory effect of activity in cognitive control regions of the brain (specifically the dorsal anterior cingulate cortex) on activity in core working memory regions, in particular the dorsal prefrontal cortex and the parietal lobe.

METHODS

Forty four subjects participated. An n-back task with two levels of working memory load (1- and 2-back) was employed during fMRI (4 T Bruker MedSpec system). Data were processed with SPM5 and the modulatory effects of the anterior cingulate were investigated using psycho-physiological interaction (PPI).

RESULTS

In spite of only subtle activation differences, and no significant differences in performance accuracy, a significant group x memory load interaction in the parietal lobe, indicated aberrantly increased modulatory inputs to this region under conditions of high working memory load in schizophrenia offspring.

DISCUSSION

Increased modulatory inputs from a central control region like the anterior cingulate presumably reflect relative inefficiency in intra-cortical interactions in the vulnerable brain. This inefficiency may reflect a developmentally mediated impairment in functional brain interactions in this important vulnerable population. It is highly plausible that the resultant effect of these altered interactions is an increased vulnerability to impaired brain development, and therefore to psychiatric disorders including schizophrenia.

Higher levels of glutamate in the associative-striatum of subjects with prodromal symptoms of schizophrenia and patients with first-episode psychosis

The glutamatergic and dopaminergic systems are thought to be involved in the pathophysiology of schizophrenia. Their interaction has been widely documented and may have a role in the neurobiological basis of the disease. The aim of this study was to compare, using proton magnetic resonance spectroscopy ((1)H-MRS), glutamate levels in the precommissural dorsal-caudate (a dopamine-rich region) and the cerebellar cortex (negligible for dopamine) in the following: (1) 18 antipsychotic-naïve subjects with prodromal symptoms and considered to be at ultra high-risk for schizophrenia (UHR), (2) 18 antipsychotic-naïve first- episode psychosis patients (FEP), and (3) 40 age- and sex- matched healthy controls. All subjects underwent a (1)H-MRS study using a 3Tesla scanner. Glutamate levels were quantified and corrected for the proportion of cerebrospinal fluid and percentage of gray matter in the voxel. The UHR and FEP groups showed higher levels of glutamate than controls, without differences between UHR and FEP. In the cerebellum, no differences were seen between the three groups. The higher glutamate level in the precommissural dorsal-caudate and not in the cerebellum of UHR and FEP suggests that a high glutamate level (a) precedes the onset of schizophrenia, and (b) is present in a dopamine-rich region previously implicated in the pathophysiology of schizophrenia.

Hypo-activation in the executive core of the sustained attention network in adolescent offspring of schizophrenia patients mediated by premorbid functional deficits

Adolescent offspring of schizophrenia patients (SCZ-Off) are vulnerable to psychiatric disorders. Assessing relationships between clinical and biological measures (such as functional magnetic resonance imaging, fMRI) may elucidate pathways of vulnerability in this group. Here we assessed the relationship between clinically assessed premorbid function, and cortico-striatal activity during sustained attention in controls (HC: with no family history of psychosis) and SCZ-Off. Subjects (n=39) were assessed using the Structured Interview for Prodromal Syndromes and the Scale of Prodromal Symptoms. Based on the Global Assessment of Functioning (GAF) score, SCZ-Off were cleaved into "high" or "low" clinically functioning sub-groups (SCZ-Off(HF), SCZ-Off(LF) respectively). During fMRI, subjects participated in a modified continuous performance task (CPT-IP). fMRI was conducted on a Bruker MedSpec 4T system (345 EPI scans; TR=2s; 24 slices; 3.8×3.8×4mm). Results show SCZ-Off(LF) evinced less activation than both HC and SCZ-Off(HF) in the executive core of the brain's attentional system (anterior cingulate, dorsal prefrontal cortex and caudate), but not visuo-spatial regions such as primary visual or superior parietal cortex. Differences were independent of behavioral performance, and reduction in activity was related to GAF score in a dose-dependent manner. Assessing the relationship between clinical measures and brain activity in domains such as attention provides a window into mechanisms of vulnerability in the developing adolescent brain.

Magnetic resonance imaging and spectroscopy: how useful is it for prediction and prognosis?

MRI/MRS can produce information on over 40 physico-chemical parameters regarded as biomarkers of structural, functional or metabolic significance. Though of undisputed worth in the detection of macroscopic lesions or of metabolic derangements, MRI's use in prognosis and prediction has not been so extensively studied. Serial studies can be performed to show early pre-clinical changes in biomarkers caused by disease progression or therapy, such as the adverse effect on heart function of certain cancer therapies. It can utilise various haemodynamic measures to predict the evolution of stroke and so help justify certain interventions. Changes in cerebral metabolite concentrations or the volumes of brain sub-structures can be used as objective measures of drug response in psychiatric conditions. However care must be exercised as MR can sometimes be considered 'too sensitive' as it often detects real abnormalities even in asymptomatic volunteers, the actual predictive significance of which have yet to be fully assessed.

Schizophrenia, "Just the Facts" 6. Moving ahead with the schizophrenia concept: from the elephant to the mouse

The current construct of schizophrenia as a unitary disease is far from satisfactory, and is in need of reconceptualization. The first five papers in our "facts" series reviewed what is known about schizophrenia to date, and a limited number of key facts appear to stand out. Schizophrenia is characterized by persistent cognitive deficits, positive and negative symptoms typically beginning in youth, substantive heritability, and brain structural, functional and neurochemical alterations including dopaminergic dysregulation. Several pathophysiological models have been proposed with differing interpretations of the illness, like the fabled six blind Indian men groping different parts of an elephant coming up with different conclusions. However, accumulating knowledge is integrating the several extant models of schizophrenia etiopathogenesis into unifying constructs; we discuss an example, involving a neurodevelopmental imbalance in excitatory/inhibitory neural systems leading to impaired neural plasticity. This imbalance, which may be proximal to clinical manifestations, could result from a variety of genetic, epigenetic and environmental causes, as well as pathophysiological processes such as inflammation and oxidative stress. Such efforts to "connect the dots" (and visualizing the elephant) are still limited by the substantial clinical, pathological, and etiological heterogeneity of schizophrenia and its blurred boundaries with several other psychiatric disorders leading to a "fuzzy cluster" of overlapping syndromes, thereby reducing the content, discriminant and predictive validity of a unitary construct of this illness. The way ahead involves several key directions: a) choosing valid phenotype definitions increasingly derived from translational neuroscience; b) addressing clinical heterogeneity by a cross-diagnostic dimensional and a staging approach to psychopathology; c) addressing pathophysiological heterogeneity by elucidating independent families of "extended" intermediate phenotypes and pathophysiological processes (e.g. altered excitatory/inhibitory, salience or executive circuitries, oxidative stress systems) that traverse structural, functional, neurochemical and molecular domains; d) resolving etiologic heterogeneity by mapping genomic and environmental factors and their interactions to syndromal and specific pathophysiological signatures; e) separating causal factors from consequences and compensatory phenomena; and f) formulating or reformulating hypotheses that can be refuted/tested, perhaps in the mouse or other experimental models. These steps will likely lead to the current entity of schizophrenia being usefully deconstructed and reconfigured into phenotypically overlapping, but etiopathologically unique and empirically testable component entities (similar to mental retardation, epilepsy or cancer syndromes). The mouse may be the way to rescue the trapped elephant!

Early and broadly defined psychosis risk mental states

Current definitions of the prodromal (or at-risk mental state) phase of schizophrenia include attenuated and/or transient psychotic symptoms as well as a combination of different risk indicators and a recent significant deterioration in global functioning. Data accumulated to date suggest rates of conversion to frank psychosis within two years in 25 to 40% of cases supporting the validity of these criteria. However, at this late phase of illness, functional deterioration is often already pronounced, highlighting the need for earlier identification. Moreover, negative symptoms and social impairments, cognitive deficits, other non-psychotic psychopathology and/or functional decline and non-specific biological indicators, often can be detected well before the at-risk mental state as currently defined; indicating that a broad characterization of an earlier stage may be possible. Identifying specific criteria to define this group of individuals, starting from the framework of familial high-risk, can help define a broader group of people, including earlier at-risk mental states, for future research. The hope is that this research will help facilitate intervention at earlier stages that may in turn minimize functional deterioration, and delay, attenuate or even prevent transition to psychosis. The disadvantages as well as the potential benefits of this approach are discussed.