Redox dysregulation, neurodevelopment, and schizophrenia

Cognitive impairment is related to oxidative stress and chemokine levels in first psychotic episodes

INTRODUCTION

This study measures the levels of various markers of oxidative stress and inflammation in blood samples from first-episode psychosis (FEP) patients, and examines the association between these peripheral biomarkers and cognitive performance at 6 months after treatment.

METHODS

Twenty-eight FEP patients and 28 healthy controls (matched by age, sex and educational level) had blood samples taken at admission for assessment of total antioxidant status, superoxide dismutase (SOD), total glutathione (GSH), catalase (CAT), glutathione peroxidase, lipid peroxidation, nitrites and the chemokine monocyte chemoattractant protein-1 (MCP-1). A battery of cognitive tests was also applied to the healthy controls and those FEP patients who were in remission at 6 months after the acute episode.

RESULTS

FEP patients had significantly lower levels of total antioxidant status, catalase and glutathione peroxidase, compared with the healthy controls. Regression analyses found that MCP-1 levels were negatively associated with learning and memory (verbal and working), nitrite levels were negatively associated with executive function, and glutathione levels were positively associated with executive function.

CONCLUSION

Our results suggest an association between certain peripheral markers of oxidative stress and inflammation and specific aspects of cognitive functioning in FEP patients. Further studies on the association between MCP-1 and cognition are warranted.

NADPH oxidase elevations in pyramidal neurons drive psychosocial stress-induced neuropathology

Oxidative stress is thought to be involved in the development of behavioral and histopathological alterations in animal models of psychosis. Here we investigate the causal contribution of reactive oxygen species generation by the phagocyte NADPH oxidase NOX2 to neuropathological alterations in a rat model of chronic psychosocial stress. In rats exposed to social isolation, the earliest neuropathological alterations were signs of oxidative stress and appearance of NOX2. Alterations in behavior, increase in glutamate levels and loss of parvalbumin were detectable after 4 weeks of social isolation. The expression of the NOX2 subunit p47(phox) was markedly increased in pyramidal neurons of isolated rats, but below detection threshold in GABAergic neurons, astrocytes and microglia. Rats with a loss of function mutation in the NOX2 subunit p47(phox) were protected from behavioral and neuropathological alterations induced by social isolation. To test reversibility, we applied the antioxidant/NOX inhibitor apocynin after initiation of social isolation for a time period of 3 weeks. Apocynin reversed behavioral alterations fully when applied after 4 weeks of social isolation, but only partially after 7 weeks. Our results demonstrate that social isolation induces rapid elevations of the NOX2 complex in the brain. Expression of the enzyme complex was strongest in pyramidal neurons and a loss of function mutation prevented neuropathology induced by social isolation. Finally, at least at early stages, pharmacological targeting of NOX2 activity might reverse behavioral alterations.

The use of cortical spreading depression for studying the brain actions of antioxidants

OBJECTIVES

We review the main adverse effects of reactive oxygen species (ROS) in the mammalian organism, introducing the reader on the worldwide problem of the ROS neurophysiological impact on the developing and the adult brain, and discussing the neuroprotective action of antioxidant molecules.

METHODS

We briefly present the electrophysiological phenomenon designated as 'cortical spreading depression' (CSD), as a parameter of normal brain functioning. We highlight recent electrophysiological advances obtained in experimental studies from our laboratory and from others, showing how to investigate the ROS effects on the brain by using the CSD phenomenon.

RESULTS

Under conditions such as aging, ROS production by photo-activation of dye molecules and ethanol consumption, we describe the effects, on CSD, of treating animals with (1) antioxidants and (2) with antioxidant-deficient diets.

DISCUSSION

The current understanding of how ROS affect brain electrophysiological activity and the possible interaction between these ROS effects and those effects of altered nutritional status of the organism are discussed.

Behavioral and neurochemical consequences of cortical oxidative stress on parvalbumin-interneuron maturation in rodent models of schizophrenia

Oxidative stress, in response to the activation of the superoxide-producing enzyme Nox2, has been implicated in the schizophrenia-like behavioral dysfunction that develops in animals that were subject to either neonatal NMDA receptor-antagonist treatment or social isolation. In both of these animal models of schizophrenia, an environmental insult occurring during the period of active maturation of the fast-spiking parvalbumin-positive (PV+) interneuronal circuit leads to a diminished expression of parvalbumin in GABA-inhibitory neurons when animals reach adulthood. The loss of PV+ interneurons in animal models had been tentatively attributed to the death of these neurons. However, present results show that for the perinatal NMDA-R antagonist model these interneurons are still alive when animals are 5-6 weeks of age even though they have lost their phenotype and no longer express parvalbumin. Alterations in parvalbumin expression and sensory-evoked gamma-oscillatory activity, regulated by PV+ interneurons, are consistently observed in schizophrenia. We propose that cortical networks consisting of faulty PV+ interneurons interacting with pyramidal neurons may be responsible for the aberrant oscillatory activity observed in schizophrenia. Thus, oxidative stress during the maturation window for PV+ interneurons by alteration of normal brain development, leads to the emergence of schizophrenia-like behavioral dysfunctions when subjects reach early adulthood.

Transcriptional regulation of neurodevelopmental and metabolic pathways by NPAS3

The basic helix-loop-helix PAS (Per, Arnt, Sim) domain transcription factor gene NPAS3 is a replicated genetic risk factor for psychiatric disorders. A knockout (KO) mouse model exhibits behavioral and adult neurogenesis deficits consistent with human illness. To define the location and mechanism of NPAS3 etiopathology, we combined immunofluorescent, transcriptomic and metabonomic approaches. Intense Npas3 immunoreactivity was observed in the hippocampal subgranular zone-the site of adult neurogenesis--but was restricted to maturing, rather than proliferating, neuronal precursor cells. Microarray analysis of a HEK293 cell line over-expressing NPAS3 showed that transcriptional targets varied according to circadian rhythm context and C-terminal deletion. The most highly up-regulated NPAS3 target gene, VGF, encodes secretory peptides with established roles in neurogenesis, depression and schizophrenia. VGF was just one of many NPAS3 target genes also regulated by the SOX family of transcription factors, suggesting an overlap in neurodevelopmental function. The parallel repression of multiple glycolysis genes by NPAS3 reveals a second role in the regulation of glucose metabolism. Comparison of wild-type and Npas3 KO metabolite composition using high-resolution mass spectrometry confirmed these transcriptional findings. KO brain tissue contained significantly altered levels of NAD(+), glycolysis metabolites (such as dihydroxyacetone phosphate and fructose-1,6-bisphosphate), pentose phosphate pathway components and Kreb's cycle intermediates (succinate and α-ketoglutarate). The dual neurodevelopmental and metabolic aspects of NPAS3 activity described here increase our understanding of mental illness etiology, and may provide a mechanism for innate and medication-induced susceptibility to diabetes commonly reported in psychiatric patients.

Plasma antioxidant capacity is reduced in Asperger syndrome

Recent evidence suggests that children with autism have impaired detoxification capacity and may suffer from chronic oxidative stress. To our knowledge, there has been no study focusing on oxidative metabolism specifically in Asperger syndrome (a milder form of autism) or comparing this metabolism with other psychiatric disorders. In this study, total antioxidant status (TAOS), non-enzymatic (glutathione and homocysteine) and enzymatic (catalase, superoxide dismutase, and glutathione peroxidase) antioxidants, and lipid peroxidation were measured in plasma or erythrocyte lysates in a group of adolescent patients with Asperger syndrome, a group of adolescents with a first episode of psychosis, and a group of healthy controls at baseline and at 8-12 weeks. TAOS was also analyzed at 1 year. TAOS was reduced in Asperger individuals compared with healthy controls and psychosis patients, after covarying by age and antipsychotic treatment. This reduced antioxidant capacity did not depend on any of the individual antioxidant variables measured. Psychosis patients had increased homocysteine levels in plasma and decreased copper and ceruloplasmin at baseline. In conclusion, Asperger patients seem to have chronic low detoxifying capacity. No impaired detoxifying capacity was found in the first-episode psychosis group in the first year of illness.

Glutathione precursor N-acetyl-cysteine modulates EEG synchronization in schizophrenia patients: a double-blind, randomized, placebo-controlled trial

Glutathione (GSH) dysregulation at the gene, protein, and functional levels has been observed in schizophrenia patients. Together with disease-like anomalies in GSH deficit experimental models, it suggests that such redox dysregulation can play a critical role in altering neural connectivity and synchronization, and thus possibly causing schizophrenia symptoms. To determine whether increased GSH levels would modulate EEG synchronization, N-acetyl-cysteine (NAC), a glutathione precursor, was administered to patients in a randomized, double-blind, crossover protocol for 60 days, followed by placebo for another 60 days (or vice versa). We analyzed whole-head topography of the multivariate phase synchronization (MPS) for 128-channel resting-state EEGs that were recorded at the onset, at the point of crossover, and at the end of the protocol. In this proof of concept study, the treatment with NAC significantly increased MPS compared to placebo over the left parieto-temporal, the right temporal, and the bilateral prefrontal regions. These changes were robust both at the group and at the individual level. Although MPS increase was observed in the absence of clinical improvement at a group level, it correlated with individual change estimated by Liddle's disorganization scale. Therefore, significant changes in EEG synchronization induced by NAC administration may precede clinically detectable improvement, highlighting its possible utility as a biomarker of treatment efficacy.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01506765.

Deletion of selenoprotein P results in impaired function of parvalbumin interneurons and alterations in fear learning and sensorimotor gating

One of the primary lines of defense against oxidative stress is the selenoprotein family, a class of proteins that contain selenium in the form of the 21st amino acid, selenocysteine. Within this class of proteins, selenoprotein P (Sepp1) is unique, as it contains multiple selenocysteine residues and is postulated to act in selenium transport. Recent findings have demonstrated that neuronal selenoprotein synthesis is required for the development of parvalbumin (PV)-interneurons, a class of GABAergic neurons involved in the synchronization of neural activity. To investigate the potential influence of Sepp1 on PV-interneurons, we first mapped the distribution of the Sepp1 receptor, ApoER2, and parvalbumin in the mouse brain. Our results indicate that ApoER2 is highly expressed on PV-interneurons in multiple brain regions. Next, to determine whether PV-interneuron populations are affected by Sepp1 deletion, we performed stereology on several brain regions in which we observed ApoER2 expression on PV-interneurons, comparing wild-type and Sepp1(-/-) mice. We observed reduced numbers of PV-interneurons in the inferior colliculus of Sepp1(-/-) mice, which corresponded with a regional increase in oxidative stress. Finally, as impaired PV-interneuron function has been implicated in several neuropsychiatric conditions, we performed multiple behavioral tests on Sepp1(-/-) mice. Our behavioral results indicate that Sepp1(-/-) mice have impairments in contextual fear extinction, latent inhibition, and sensorimotor gating. In sum, these findings demonstrate the important supporting role of Sepp1 on ApoER2-expressing PV-interneurons.

The PPARα Agonist Fenofibrate Reduces Prepulse Inhibition Disruption in a Neurodevelopmental Model of Schizophrenia

Oxidative stress has been implicated in neurodevelopmental theories of schizophrenia. Antioxidant Peroxysome Proliferator-Activated Receptors α (PPARα) agonist fenofibrate has neuroprotective properties and could reverse early preclinical infringements that could trigger the illness. We have evaluated the neuroprotective interest of fenofibrate in a neurodevelopmental rat model of schizophrenia. The oxidative lesion induced by Kainic Acid (KA) injection at postnatal day (PND) 7 has previously been reported to disrupt Prepulse Inhibition (PPI) at PND56 but not at PND35. In 4 groups of 15 male rats each, KN (KA-PND7 + normal postweaning food), KF (KA-PND7 + fenofibrate 0.2% food), ON (saline-PND7 + normal food), and OF (saline + fenofibrate food), PPI was recorded at PND35 and PND56. Three levels of prepulse were used: 73 dB, 76 dB, and 82 dB for a pulse at 120 dB. Four PPI scores were analyzed: PPI73, PPI76, PPI82, and mean PPI (PPIm). Two-way ANOVAs were used to evaluate the effects of both factors (KA + fenofibrate), and, in case of significant results, intergroup Student's t-tests were performed. We notably found a significant difference (P < 0.05) in PPIm between groups KN and KF at PND56, which supposes that fenofibrate could be worthy of interest for early neuroprotection in schizophrenia.

Differential developmental trajectories for CB1 cannabinoid receptor expression in limbic/associative and sensorimotor cortical areas

Cannabis use during adolescence is associated with an increased risk for schizophrenia and other disorders. The neuronal basis is unclear, but prefrontal cortical mechanisms have been implicated. Here, we investigated developmental changes in the endocannabinoid system by assessing expression and function of the CB1 cannabinoid receptor in prefrontal and other cortical areas in juvenile (postnatal day 25, P25), adolescent (P40), and adult (P70) rats. Overall, the expression of CB1 receptors in the cortex is highest in juveniles and drops thereafter toward adult levels. However, CB1 receptor expression follows distinct developmental trajectories in different cortical areas. The most pronounced and progressive decrease in CB1 expression was observed in medial prefrontal and other limbic/associative regions. In contrast, major changes in sensorimotor cortices occurred only after P40. We also assessed electrophysiological measures of CB1 receptor function and found that CB1-dependent inhibition of synaptic transmission in the prefrontal cortex follows the same developmental trajectory as observed for receptor expression. Together, these findings indicate that CB1 receptor-mediated signaling decreases during development but is differentially regulated in limbic/associative vs. sensorimotor systems. Therefore, cannabis use during adolescence likely differentially affects limbic/associative and sensorimotor cortical circuits.

Intracerebral adult stem cells transplantation increases brain-derived neurotrophic factor levels and protects against phencyclidine-induced social deficit in mice

Stem cell-based regenerative therapy is considered a promising cellular therapeutic approach for the patients with incurable brain diseases. Mesenchymal stem cells (MSCs) represent an attractive cell source for regenerative medicine strategies for the treatment of the diseased brain. Previous studies have shown that these cells improve behavioral deficits in animal models of neurological disorders such as Parkinson's and Huntington's diseases. In the current study, we examined the capability of intracerebral human MSCs transplantation (medial pre-frontal cortex) to prevent the social impairment displayed by mice after withdrawal from daily phencyclidine (PCP) administration (10 mg kg(-1) daily for 14 days). Our results show that MSCs transplantation significantly prevented the PCP-induced social deficit, as assessed by the social preference test. In contrast, the PCP-induced social impairment was not modified by daily clozapine treatment. Tissue analysis revealed that the human MSCs survived in the mouse brain throughout the course of the experiment (23 days). Significantly increased cortical brain-derived neurotrophic factor levels were observed in the MSCs-treated group as compared with sham-operated controls. Furthermore, western blot analysis revealed that the ratio of phosphorylated Akt to Akt was significantly elevated in the MSCs-treated mice compared with the sham controls. Our results demonstrate that intracerebral transplantation of MSCs is beneficial in attenuating the social deficits induced by sub-chronic PCP administration. We suggest a novel therapeutic approach for the treatment of schizophrenia-like negative symptoms in animal models of the disorder.

Impaired kynurenine pathway metabolism in the prefrontal cortex of individuals with schizophrenia

The levels of kynurenic acid (KYNA), an astrocyte-derived metabolite of the branched kynurenine pathway (KP) of tryptophan degradation and antagonist of α7 nicotinic acetylcholine and N-methyl-D-aspartate receptors, are elevated in the prefrontal cortex (PFC) of individuals with schizophrenia (SZ). Because endogenous KYNA modulates extracellular glutamate and acetylcholine levels in the PFC, these increases may be pathophysiologically significant. Using brain tissue from SZ patients and matched controls, we now measured the activity of several KP enzymes (kynurenine 3-monooxygenase [KMO], kynureninase, 3-hydroxyanthranilic acid dioxygenase [3-HAO], quinolinic acid phosphoribosyltransferase [QPRT], and kynurenine aminotransferase II [KAT II]) in the PFC, ie, Brodmann areas (BA) 9 and 10. Compared with controls, the activities of KMO (in BA 9 and 10) and 3-HAO (in BA 9) were significantly reduced in SZ, though there were no significant differences between patients and controls in kynureninase, QPRT, and KAT II. In the same samples, we also confirmed the increase in the tissue levels of KYNA in SZ. As examined in rats treated chronically with the antipsychotic drug risperidone, the observed biochemical changes were not secondary to medication. A persistent reduction in KMO activity may have a particular bearing on pathology because it may signify a shift of KP metabolism toward enhanced KYNA synthesis. The present results further support the hypothesis that the normalization of cortical KP metabolism may constitute an effective new treatment strategy in SZ.

Prenatal exposure to cigarette smoke causes persistent changes in the oxidative balance and in DNA structural integrity in rats submitted to the animal model of schizophrenia

Epidemiological studies have indicated that prenatal exposure to environmental insults can bring an increased risk of schizophrenia. The objective of our study was to determine biochemical parameters in rats exposed to cigarette smoke (CS) in the prenatal period, evaluated in adult offspring submitted to animal model of schizophrenia induced by acute subanaesthetic doses of ketamine (5 mg/kg, 15 mg/kg and 25 mg/kg). Pregnant female Wistar rats were exposed to 12 commercially filtered cigarettes per day, daily for a period of 28 days. We evaluated the oxidative damage in lipid and protein in the rat brain, and DNA damage in the peripheral blood of male adult offspring rats. To determine oxidative damage in the lipids, we measured the formation of thiobarbituric acid reactive species (TBARS) and the oxidative damage to the proteins was assessed by the determination of carbonyl groups content. We also evaluated DNA damage using single-cell gel electrophoresis (comet assay). Our results showed that rats exposed to CS in the prenatal period presented a significant increase of the lipid peroxidation, protein oxidation and DNA damage in adult age. We can observe that the animals submitted at acute doses of ketamine also presented an increase of the lipid peroxidation and protein oxidation at different doses and structures. Finally, we suggest that exposure to CS during the prenatal period affects two essential cerebral processes during development: redox regulation and DNA integrity, evaluated in adult offspring. These effects can leads to several neurochemical changes similar to the pathophysiology of schizophrenia.

Anti-inflammatory signaling in schizophrenia

A great deal of interest has been centered upon activated inflammatory processes in schizophrenia and their contribution to disease-relevant brain and behavioral impairment. In contrast, the role of anti-inflammatory signaling has attracted somewhat less attention in this context. The present article focuses on the emerging role of anti-inflammatory signaling in schizophrenia and discusses the potential influence of altered anti-inflammatory activity on progressive inflammatory processes, physical and metabolic functions, and treatment effects related to the use of conventional antipsychotic drugs and immunomodulatory agents in the pharmacotherapy of schizophrenia. By reviewing existing evidence, it appears that enhanced anti-inflammatory activity has many faces in schizophrenia: On the one hand, it may effectively limit potentially harmful inflammatory processes and may contribute to the improvement of psychopathological symptoms, especially when the anti-inflammatory system is boosted at early stages of the disease. On the other hand, enhanced anti-inflammatory activity may render affected individuals more susceptible to distinct physiological abnormalities such as cardiovascular disease, and may further impede the resistance to specific infectious agents. Therefore, an enhancement of anti-inflammatory signaling in schizophrenia might not simply be said to be either advantageous or disadvantageous, but rather should be interpreted and dealt with in a context-dependent manner. Increased awareness of the multiple roles of anti-inflammatory signaling may readily help to reduce additional health burdens in schizophrenia, and at the same time, may provide opportunities to further explore the benefits associated with anti-inflammatory strategies in the symptomatological and/or preventive treatment of this disorder.

Behavioral phenotyping of glutathione-deficient mice: relevance to schizophrenia and bipolar disorder

Redox-dysregulation represents a common pathogenic mechanism in schizophrenia (SZ) and bipolar disorder (BP). It may in part arise from a genetically compromised synthesis of glutathione (GSH), the major cellular antioxidant and redox-regulator. Allelic variants of the genes coding for the rate-limiting GSH synthesizing enzyme glutamate-cysteine-ligase modifier (GCLM) and/or catalytic (GCLC) subunit have been associated with SZ and BP. Using mice knockout (KO) for GCLM we have previously shown that impaired GSH synthesis is associated with morphological, functional and neurochemical anomalies similar to those in patients. Here we asked whether GSH deficit is also associated with SZ- and BP-relevant behavioral and cognitive anomalies. Accordingly, we subjected young adult GCLM-wildtype (WT), heterozygous and KO males to a battery of standard tests. Compared to WT, GCLM-KO mice displayed hyperlocomotion in the open field and forced swim test but normal activity in the home cage, suggesting that hyperlocomotion was selective to environmental novelty and mildly stressful situations. While spatial working memory and latent inhibition remained unaffected, KO mice showed a potentiated hyperlocomotor response to an acute amphetamine injection, impaired sensorymotor gating in the form of prepulse inhibition and altered social behavior compared to WT. These anomalies resemble important aspects of both SZ and the manic component of BP. As such our data support the notion that redox-dysregulation due to GSH deficit is implicated in both disorders. Moreover, our data propose the GCLM-KO mouse as a valuable model to study the behavioral and cognitive consequences of redox dysregulation in the context of psychiatric disease.

Genetic dysregulation of glutathione synthesis predicts alteration of plasma thiol redox status in schizophrenia

Genetic studies have shown an association between schizophrenia and a GAG trinucleotide repeat (TNR) polymorphism in the catalytic subunit (GCLC) of the glutamate cysteine ligase (GCL), the key enzyme for glutathione (GSH) synthesis. The present study was aimed at analyzing the influence of a GSH dysregulation of genetic origin on plasma thiols (total cysteine, homocysteine, and cysteine-glycine) and other free amino acid levels as well as fibroblast cultures GSH levels. Plasma thiols levels were also compared between patients and controls. As compared with patients with a low-risk GCLC GAG TNR genotype, patients with a high-risk genotype, having an impaired GSH synthesis, displayed a decrease of fibroblast GSH and plasma total cysteine levels, and an increase of the oxidized form of cysteine (cystine) content. Increased levels of plasma free serine, glutamine, citrulline, and arginine were also observed in the high-risk genotype. Taken together, the high-risk genotypes were associated with a subgroup of schizophrenia characterized by altered plasma thiols and free amino acid levels that reflect a dysregulation of redox control and an increased susceptibility to oxidative stress. This altered pattern potentially contributes to the development of a biomarker profile useful for early diagnosis and monitoring the effectiveness of novel drugs targeting redox dysregulation in schizophrenia.

Oxidative stress in schizophrenia: pathogenetic and therapeutic implications

Over a century, a wide-ranging variety of pathophysiological models and causal hypotheses have been conceptualized for schizophrenia. One among these is the role for free radical-mediated pathology in schizophrenia, indicating impaired antioxidant defense system (AODS) and presence of oxidative stress in patients with schizophrenia. For the past two decades, the whole investigative domain of AODS and oxidative stress has broadened to include the wider AODS components, direct central nervous system assays of AODS, chemical imaging studies, proteomics, genetics of AODS, and, of importance to sufferers of schizophrenia, antioxidant therapeutics. These are some of the perspectives that are reviewed by several articles in this Forum. Overall, there has been growing recognition of the importance of oxidative stress in the pathophysiology of schizophrenia and in treatment-related side effects. The totality of the evidence from biochemistry, metabolomics, proteomics, genetics, and in vivo brain imaging points to the presence of multifarious abnormalities in the AODS and redox signaling in schizophrenia.

Magnetic resonance spectroscopy study of the antioxidant defense system in schizophrenia

Accumulating evidence suggests that oxidative stress associated with impaired metabolism of the antioxidant glutathione (GSH) plays a key role in the pathophysiology of schizophrenia. Magnetic resonance spectroscopy (MRS) is one of the brain-imaging techniques that can quantitatively measure bioactive substances such as GSH in the intact human brain. Four different measurement sequences including double quantum coherence (DQC) filtering, MEscher-GArwood Point-RESolved Spectroscopy (MEGA-PRESS), Stimulated Echo Acquisition Mode (STEAM), and PRESS have been used to evaluate the (1)H-MRS measurement of GSH in the brains of patients with schizophrenia. Although the results of these studies were somewhat diverse, a negative correlation between brain GSH levels and the severity of negative symptoms in schizophrenia patients suggests that increasing the brain GSH levels might be beneficial for schizophrenia patients with negative symptoms. Moreover, a recent double-blind, placebo-controlled study demonstrated that add-on of N-acetyl-l-cysteine (NAC), a precursor of GSH, to antipsychotics improved the negative symptoms and reduced the side effects (akathisia) in patients with chronic schizophrenia. MRS study of the antioxidant defense system in schizophrenia still remains in the infantile stage; future studies are needed to examine the brain GSH level before and after NAC treatment, and thereby to provide direct evidence of the induced production of GSH in the living brain.

Genetic association studies of antioxidant pathway genes and schizophrenia

The endogenous production of highly reactive oxidation species is an inherent by-product of cellular energy metabolism. Cellular antioxidant defense systems (AODS) comprising various antioxidants counter these damaging effects. Several lines of evidence, including postmortem studies, suggest increased oxidative stress in patients with schizophrenia. Some genetic association studies and gene-expression studies suggest that patients also may have altered ability to mount antioxidative mechanisms. As the genetic associations may provide etiologic evidence in support of the oxidative-stress hypothesis of schizophrenia, a focused review has been conducted. We also suggest avenues for further research.

Antioxidants, redox signaling, and pathophysiology in schizophrenia: an integrative view

Schizophrenia (SZ) is a brain disorder that has been intensively studied for over a century; yet, its etiology and multifactorial pathophysiology remain a puzzle. However, significant advances have been made in identifying numerous abnormalities in key biochemical systems. One among these is the antioxidant defense system (AODS) and redox signaling. This review summarizes the findings to date in human studies. The evidence can be broadly clustered into three major themes: perturbations in AODS, relationships between AODS alterations and other systems (i.e., membrane structure, immune function, and neurotransmission), and clinical implications. These domains of AODS have been examined in samples from both the central nervous system and peripheral tissues. Findings in patients with SZ include decreased nonenzymatic antioxidants, increased lipid peroxides and nitric oxides, and homeostatic imbalance of purine catabolism. Reductions of plasma antioxidant capacity are seen in patients with chronic illness as well as early in the course of SZ. Notably, these data indicate that many AODS alterations are independent of treatment effects. Moreover, there is burgeoning evidence indicating a link among oxidative stress, membrane defects, immune dysfunction, and multineurotransmitter pathologies in SZ. Finally, the body of evidence reviewed herein provides a theoretical rationale for the development of novel treatment approaches.

Meta-analysis of the efficacy of adjunctive NMDA receptor modulators in chronic schizophrenia

BACKGROUND

Based on the glutamatergic NMDA receptor hypofunction theory of schizophrenia, NMDA receptor modulators (NMDARMs) may have therapeutic potential in the treatment of schizophrenia.

OBJECTIVE

This meta-analysis aimed to evaluate the potential of modulators of the NMDA receptor as adjunctive therapy for schizophrenia, using the results from published trials.

DATA SOURCES

A primary electronic search for controlled clinical trials using NMDARMs in schizophrenia was conducted on the PubMed, Cochrane Library, EMBASE, CINAHL® and PsycINFO databases. A secondary manual search of references from primary publications was also performed.

STUDY SELECTION

Inclusion criteria were the application of an established method of diagnosis, randomized case assignment, comparison of NMDARM add-on therapy with placebo, and double-blind assessment of symptoms in chronic schizophrenia using standardized rating scales. Results were based on a total sample size of 1253 cases from 29 trials that fulfilled the specified criteria.

DATA EXTRACTION

Scores on rating scales or on their relevant subscales were obtained for all selected studies from published results for the minimum dataset to compute the difference between post- and pre-trial scores and their pooled standard deviation for NMDARM add-on therapy and placebo groups for negative, positive and total symptoms.

RESULTS

A negative standardized mean difference (SMD) indicates therapeutic benefit in favour of NMDARM add-on therapy and all SMD results mentioned here are statistically significant. The overall effect size for NMDARMs as a group was small for negative (SMD -0.27) and medium for total (SMD -0.40) symptoms of chronic schizophrenia. Subgroup analysis revealed medium effect sizes for D-serine and N-acetyl-cysteine (NAC) for negative (SMD -0.53 and -0.45, respectively) and total (SMD -0.40 and -0.64, respectively) symptoms, and for glycine (SMD -0.66) and sarcosine (SMD -0.41) for total symptoms. As adjuvants to non-clozapine antipsychotics, additional therapeutic benefits were observed for NMDARM as a group (SMD -0.14) and glycine (SMD -0.54) for positive symptoms; D-serine (SMD -0.54), NAC (SMD -0.45) and sarcosine (SMD -0.39) for negative symptoms; and NMDARM as a group (SMD -0.38), D-serine (SMD -0.40), glycine (SMD -1.12), NAC (SMD -0.64) and sarcosine (SMD -0.53) for total symptoms. When added to clozapine, none of the drugs demonstrated therapeutic potential, while addition of glycine (SMD +0.56) worsened positive symptoms.

CONCLUSIONS

Taking into consideration the number of trials and sample size in subgroup analyses, D-serine, NAC and sarcosine as adjuncts to non-clozapine antipsychotics have therapeutic benefit in the treatment of negative and total symptoms of chronic schizophrenia. While glycine improves positive and total symptoms as an adjuvant to non-clozapine antipsychotics, it worsens them when added to clozapine.

Translating glutamate: from pathophysiology to treatment

The neurotransmitter glutamate is the primary excitatory neurotransmitter in mammalian brain and is responsible for most corticocortical and corticofugal neurotransmission. Disturbances in glutamatergic function have been implicated in the pathophysiology of several neuropsychiatric disorders-including schizophrenia, drug abuse and addiction, autism, and depression-that were until recently poorly understood. Nevertheless, improvements in basic information regarding these disorders have yet to translate into Food and Drug Administration-approved treatments. Barriers to translation include the need not only for improved compounds but also for improved biomarkers sensitive to both structural and functional target engagement and for improved translational models. Overcoming these barriers will require unique collaborative arrangements between pharma, government, and academia. Here, we review a recent Institute of Medicine-sponsored meeting, highlighting advances in glutamatergic theories of neuropsychiatric illness as well as remaining barriers to treatment development.

Proteomic and metabolomic profiling of a trait anxiety mouse model implicate affected pathways

Depression and anxiety disorders affect a great number of people worldwide. Whereas singular factors have been associated with the pathogenesis of psychiatric disorders, growing evidence emphasizes the significance of dysfunctional neural circuits and signaling pathways. Hence, a systems biology approach is required to get a better understanding of psychiatric phenotypes such as depression and anxiety. Furthermore, the availability of biomarkers for these disorders is critical for improved diagnosis and monitoring treatment response. In the present study, a mouse model presenting with robust high versus low anxiety phenotypes was subjected to thorough molecular biomarker and pathway discovery analyses. Reference animals were metabolically labeled with the stable (15)N isotope allowing an accurate comparison of protein expression levels between the high anxiety-related behavior versus low anxiety-related behavior mouse lines using quantitative mass spectrometry. Plasma metabolomic analyses identified a number of small molecule biomarkers characteristic for the anxiety phenotype with particular focus on myo-inositol and glutamate as well as the intermediates involved in the tricarboxylic acid cycle. In silico analyses suggested pathways and subnetworks as relevant for the anxiety phenotype. Our data demonstrate that the high anxiety-related behavior and low anxiety-related behavior mouse model is a valuable tool for anxiety disorder drug discovery efforts.

Progress in defining the biological causes of schizophrenia

Schizophrenia is a common mental illness resulting from a complex interplay of genetic and environmental risk factors. Establishing its primary molecular and cellular aetiopathologies has proved difficult. However, this is a vital step towards the rational development of useful disease biomarkers and new therapeutic strategies. The advent and large-scale application of genomic, transcriptomic, proteomic and metabolomic technologies are generating data sets required to achieve this goal. This discovery phase, typified by its objective and hypothesis-free approach, is described in the first part of the review. The accumulating biological information, when viewed as a whole, reveals a number of biological process and subcellular locations that contribute to schizophrenia causation. The data also show that each technique targets different aspects of central nervous system function in the disease state. In the second part of the review, key schizophrenia candidate genes are discussed more fully. Two higher-order processes - adult neurogenesis and inflammation - that appear to have pathological relevance are also described in detail. Finally, three areas where progress would have a large impact on schizophrenia biology are discussed: deducing the causes of schizophrenia in the individual, explaining the phenomenon of cross-disorder risk factors, and distinguishing causative disease factors from those that are reactive or compensatory.

Altered glycogen metabolism in cultured astrocytes from mice with chronic glutathione deficit; relevance for neuroenergetics in schizophrenia

Neurodegenerative and psychiatric disorders including Alzheimer's, Parkinson's or Huntington's diseases and schizophrenia have been associated with a deficit in glutathione (GSH). In particular, a polymorphism in the gene of glutamate cysteine ligase modulatory subunit (GCLM) is associated with schizophrenia. GSH is the most important intracellular antioxidant and is necessary for the removal of reactive by-products generated by the utilization of glucose for energy supply. Furthermore, glucose metabolism through the pentose phosphate pathway is a major source of NADPH, the cofactor necessary for the regeneration of reduced glutathione. This study aims at investigating glucose metabolism in cultured astrocytes from GCLM knockout mice, which show decreased GSH levels. No difference in the basal metabolism of glucose was observed between wild-type and knockout cells. In contrast, glycogen levels were lower and its turnover was higher in knockout astrocytes. These changes were accompanied by a decrease in the expression of the genes involved in its synthesis and degradation, including the protein targeting to glycogen. During an oxidative challenge induced by tert-Butylhydroperoxide, wild-type cells increased their glycogen mobilization and glucose uptake. However, knockout astrocytes were unable to mobilize glycogen following the same stress and they could increase their glucose utilization only following a major oxidative insult. Altogether, these results show that glucose metabolism and glycogen utilization are dysregulated in astrocytes showing a chronic deficit in GSH, suggesting that alterations of a fundamental aspect of brain energy metabolism is caused by GSH deficit and may therefore be relevant to metabolic dysfunctions observed in schizophrenia.

Bimodal distribution of polyunsaturated fatty acids in schizophrenia suggests two endophenotypes of the disorder

BACKGROUND

There is conflicting evidence of whether polyunsaturated fatty acids (PUFA) in red blood cells are bimodally distributed in schizophrenia. The purpose of this study was to examine the distribution of PUFA, as well as its links to plausible causal factors.

METHODS

A 16-week cohort study and a case-control study as part of a randomized controlled trial. Ninety-nine patients with DSM-IV schizophrenia, schizoaffective disorder, or schizophreniform disorder, aged 18 to 39, were consecutively included at admission to psychiatric departments of nine Norwegian hospitals. Fatty acids were measured in 97 of these patients and in 20 healthy control subjects. The primary outcome measure was the bimodality test statistic T, assessed by a χ(2) test of the likelihood of one or two normal distributions of PUFA.

RESULTS

At baseline, levels of polyunsaturated fatty acids were highly significantly bimodally distributed among patients. One third of patients constituted a group (low PUFA) who had PUFA levels at one fifth (p < .001) of those in high PUFA patients and healthy control subjects, which did not differ. Bimodality was mainly accounted for by docosahexaenoic acid and arachidonic acid. Bimodality was confirmed after 16 weeks. α-tocopherol was a robust predictor of PUFA at both occasions. Desaturase and elongase indexes differed between PUFA groups. Smoking, gender, antipsychotic medication, and dietary factors did not explain the bimodal distribution.

CONCLUSIONS

Red blood cell PUFA were bimodally distributed among acutely ill patients with schizophrenia and schizoaffective disorder. Endogenous deficiencies of redox regulation or synthesis of long-chain PUFA in the low PUFA group may explain our findings.

Aripiprazole inhibits superoxide generation from phorbol-myristate-acetate (PMA)-stimulated microglia in vitro: implication for antioxidative psychotropic actions via microglia

Altered antioxidant status has been implicated in schizophrenia. Microglia, major sources of free radicals such as superoxide (•O(2)(-)), play crucial roles in various brain pathologies. Recent postmortem and imaging studies have indicated microglial activation in the brain of schizophrenic patients. We previously demonstrated that atypical antipsychotics including aripiprazole significantly inhibited the release of nitric oxide and proinflammatory cytokines from interferon-γ-stimulated microglia in vitro. Antioxidative effects of antipsychotics via modulating microglial superoxide generation have never been reported. Therefore, we herein investigated the effects of antipsychotics on the •O(2)(-) generation from phorbol-myristate-acetate (PMA)-stimulated rodent microglia by the electron spin resonance (ESR) spectroscopy and also examined the intracellular mechanism by intracellular Ca(2+) imaging and immunostaining. Neuronal damage induced by microglial activation was also investigated by the co-culture experiment. Among various antipsychotics, only aripiprazole inhibited the •O(2)(-) generation from PMA-stimulated microglia. Aripiprazole proved to inhibit the •O(2)(-) generation through the cascade of protein kinase C (PKC) activation, intracellular Ca(2+) regulation and NADPH oxidase activation via cytosolic p47(phox) translocation to the plasma/phagosomal membranes. Formation of neuritic beading, induced by PMA-stimulated microglia, was attenuated by pretreatment of aripiprazole. D2R antagonism has long been considered as the primary therapeutic action for schizophrenia. Aripiprazole with D2R partial agonism is effective like other antipsychotics with fewer side effects, while aripiprazole's therapeutic mechanism itself remains unclear. Our results imply that aripiprazole may have psychotropic effects by reducing the microglial oxidative reactions and following neuronal reactions, which puts forward a novel therapeutic hypothesis in schizophrenia research.

Inflammatory processes in schizophrenia: a promising neuroimmunological target for the treatment of negative/cognitive symptoms and beyond

Emerging evidence indicates that schizophrenia is associated with activated peripheral and central inflammatory responses. Such inflammatory processes seem to be influenced by a number of environmental and genetic predisposition factors, and they may critically depend on and contribute to the progressive nature of schizophrenic disease. There is also appreciable evidence to suggest that activated inflammatory responses can undermine disease-relevant affective, emotional, social, and cognitive functions, so that inflammatory processes may be particularly relevant for the precipitation of negative and cognitive symptoms of schizophrenia. Recent clinical trials of anti-inflammatory pharmacotherapy in this disorder provide promising results by showing superior beneficial treatment effects when standard antipsychotic drugs are co-administered with anti-inflammatory compounds, as compared with treatment outcomes using antipsychotic drugs alone. Given the limited efficacy of currently available antipsychotic drugs to ameliorate negative and cognitive symptoms, the further exploration of inflammatory mechanisms and anti-inflammatory strategies may open fruitful new avenues for improved treatment of symptoms undermining affective, emotional, social and cognitive functions pertinent to schizophrenic disease.

Reduced plasma total antioxidant status in first-episode drug-naive patients with schizophrenia

Excessive free radical production leading to oxidative stress may be involved in the pathophysiology of schizophrenia. Determination of total antioxidant status (TAS) provides an index of the sum of activities of all antioxidants. However, there have been few systematic studies to examine the relationship between TAS levels and psychopathology in first-episode and drug-naive patients with schizophrenia. TAS levels were determined in the plasma of 60 never-medicated first-episode patients with schizophrenia and 68 healthy control subjects. The schizophrenia symptomatology and the depressive symptoms were assessed by the positive and negative syndrome scale (PANSS) and the Hamilton rating scale for depression (HAMD). The results showed that TAS levels were significantly lower in first-episode patients with schizophrenia than in healthy control subjects (159.8 ± 45.8 U/ml vs 211.4 ± 46.8 U/ml, F=39.5, df=1, 126, p < 0.001). A trend toward significant inverse correlation between TAS levels and PANSS negative subscore was observed (r = 0.25, df=60, p = 0.06). Our results suggest that oxidative stress occurs in an early course of schizophrenia and may have an important role in pathogenesis and perhaps, negative symptomatology of schizophrenia.

Glutathione is a physiologic reservoir of neuronal glutamate

Glutamate, the principal excitatory neurotransmitter of the brain, participates in a multitude of physiologic and pathologic processes, including learning and memory. Glutathione, a tripeptide composed of the amino acids glutamate, cysteine, and glycine, serves important cofactor roles in antioxidant defense and drug detoxification, but glutathione deficits occur in multiple neuropsychiatric disorders. Glutathione synthesis and metabolism are governed by a cycle of enzymes, the γ-glutamyl cycle, which can achieve intracellular glutathione concentrations of 1-10mM. Because of the considerable quantity of brain glutathione and its rapid turnover, we hypothesized that glutathione may serve as a reservoir of neural glutamate. We quantified glutamate in HT22 hippocampal neurons, PC12 cells and primary cortical neurons after treatment with molecular inhibitors targeting three different enzymes of the glutathione metabolic cycle. Inhibiting 5-oxoprolinase and γ-glutamyl transferase, enzymes that liberate glutamate from glutathione, leads to decreases in glutamate. In contrast, inhibition of γ-glutamyl cysteine ligase, which uses glutamate to synthesize glutathione, results in substantial glutamate accumulation. Increased glutamate levels following inhibition of glutathione synthesis temporally precede later effects upon oxidative stress.

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!

Interaction of GAG trinucleotide repeat and C-129T polymorphisms impairs expression of the glutamate-cysteine ligase catalytic subunit gene

Glutamate cysteine ligase (GCL) catalyzes the rate-limiting step in the de novo synthesis of glutathione (GSH). The catalytic subunit (GCLC) of GCL contains a GAG trinucleotide-repeat (TNR) polymorphism within the 5'-untranslated region (5'-UTR) that has been associated with various human disorders. Although several studies suggest that this variation influences GSH content, its implication for GCLC expression remains unknown. To better characterize its functional significance, we performed reporter gene assays with constructs containing the complete GCLC 5'-UTR upstream of a luciferase gene. Transfection of these vectors into various human cell lines did not reveal any significant differences between 7, 8, 9, or 10 GAG repeats, under either basal or oxidative stress conditions. To correlate these results with the previously described down-regulation induced by the C-129T GCLC promoter polymorphism, combinations of both variations were tested. Interestingly, the -129T allele down-regulates gene expression when combined with 7 GAG but not with 8, 9, or 10 GAG TNRs. This observation was confirmed in primary fibroblast cells, in which the combination of GAG TNR 7/7 and -129C/T genotypes decreased the GCLC protein level. These results provide evidence that interaction of the two variations can efficiently impair GCLC expression and thus suggest its involvement in the pathogenesis of diseases related to GSH metabolism.

A fluorescent dual labeling technique for the quantitative measurement of reduced and oxidized protein thiols in tissue samples

Oxidative stress can result in the reversible oxidation of protein thiols. Because the activity of numerous proteins is sensitive to thiol oxidation, this has the potential to affect many cellular functions. We describe a highly sensitive, quantitative labeling technique that measures global and specific protein thiol oxidative state in skeletal muscle tissue. The technique involves labeling the reduced and oxidized protein thiols with different fluorescent dyes. The resulting sample is assayed using a 96-well plate fluorimeter, or individual protein bands are separated using SDS-PAGE. We show that artifactual oxidation during sample preparation and analysis has the potential to confound results, and techniques to prevent this are described. We tested the technique by analyzing the muscles of mdx and c57 mice and found that the muscles of mdx mice were significantly (p<0.05) more oxidized (13.1±1.5% oxidized thiols) than those of c57 mice (8.9±0.7% oxidized thiols). This technique provides an effective means to measure the extent to which oxidative stress affects the oxidation of protein thiols in biological tissues.

GABAergic interneuron origin of schizophrenia pathophysiology

Hypofunction of N-methyl-d-aspartic acid-type glutamate receptors (NMDAR) induced by the systemic administration of NMDAR antagonists is well known to cause schizophrenia-like symptoms in otherwise healthy subjects. However, the brain areas or cell-types responsible for the emergence of these symptoms following NMDAR hypofunction remain largely unknown. One possibility, the so-called "GABAergic origin hypothesis," is that NMDAR hypofunction at GABAergic interneurons, in particular, is sufficient for schizophrenia-like effects. In one attempt to address this issue, transgenic mice were generated in which NMDARs were selectively deleted from cortical and hippocampal GABAergic interneurons, a majority of which were parvalbumin (PV)-positive. This manipulation triggered a constellation of phenotypes--from molecular and physiological to behavioral--resembling characteristics of human schizophrenia. Based on these results, and in conjunction with previous literature, we argue that during development, NMDAR hypofunction at cortical, PV-positive, fast-spiking interneurons produces schizophrenia-like effects. This review summarizes the data demonstrating that in schizophrenia, GABAergic (particularly PV-positive) interneurons are disrupted. PV-positive interneurons, many of which display a fast-spiking firing pattern, are critical not only for tight temporal control of cortical inhibition but also for the generation of synchronous membrane-potential gamma-band oscillations. We therefore suggest that in schizophrenia the specific ability of fast-spiking interneurons to control and synchronize disparate cortical circuits is disrupted and that this disruption may underlie many of the schizophrenia symptoms. We further argue that the high vulnerability of corticolimbic fast-spiking interneurons to genetic predispositions and to early environmental insults--including excitotoxicity and oxidative stress--might help to explain their significant contribution to the development of schizophrenia.

The environment and susceptibility to schizophrenia

In the present article the putative role of environmental factors in schizophrenia is reviewed and synthesized. Accumulating evidence from recent studies suggests that environmental exposures may play a more significant role in the etiopathogenesis of this disorder than previously thought. This expanding knowledge base is largely a consequence of refinements in the methodology of epidemiologic studies, including birth cohort investigations, and in preclinical research that has been inspired by the evolving literature on animal models of environmental exposures. This paper is divided into four sections. In the first, the descriptive epidemiology of schizophrenia is reviewed. This includes general studies on incidence, prevalence, and differences in these measures by urban-rural, neighborhood, migrant, and season of birth status, as well as time trends. In the second section, we discuss the contribution of environmental risk factors acting during fetal and perinatal life; these include infections [e.g. rubella, influenza, Toxoplasma gondii (T. gondii), herpes simplex virus type 2 (HSV-2)], nutritional deficiencies (e.g., famine, folic acid, iron, vitamin D), paternal age, fetal/neonatal hypoxic and other obstetric insults and complications, maternal stress and other exposures [e.g. lead, rhesus (Rh) incompatibility, maternal stress]. Other putative neurodevelopmental determinants, including cannabis, socioeconomic status, trauma, and infections during childhood and adolescence are also covered. In the third section, these findings are synthesized and their implications for prevention and uncovering biological mechanisms, including oxidative stress, apoptosis, and inflammation, are discussed. Animal models, including maternal immune activation, have yielded evidence suggesting that these exposures cause brain and behavioral phenotypes that are analogous to findings observed in patients with schizophrenia. In the final section, future studies including new, larger, and more rigorous epidemiologic investigations, and research on translational and clinical neuroscience, gene-environment interactions, epigenetics, developmental trajectories and windows of vulnerability, are elaborated upon. These studies are aimed at confirming observed risk factors, identifying new environmental exposures, elucidating developmental mechanisms, and shedding further light on genes and exposures that may not be identified in the absence of these integrated approaches. The study of environmental factors in schizophrenia may have important implications for the identification of causes and prevention of this disorder, and offers the potential to complement, and refine, existing efforts on explanatory neurodevelopmental models.

The maturation of cortical interneuron diversity: how multiple developmental journeys shape the emergence of proper network function

If the classical functional attribute of cortical GABAergic interneurons is to mediate synaptic inhibition in the adult cortex, it is becoming evident that their major task is instead to shape the spatio-temporal dynamics of the network oscillations that support most brain functions. This complex function involves a division of labour between morpho-physiologically diverse interneuron subtypes. Both the central network function and the bewildering heterogeneity of the interneuron population are especially emphasized during cortical development: at early postnatal stages, a single GABAergic neuron can efficiently pace the activity of hundreds of other cells, whereas some interneuron subtypes are still poorly developed. Given the role of coherent activity in brain development, this confers to GABAergic interneurons a major role in the proper maturation of cortical networks.

Oxidative stress in schizophrenia: an integrated approach

Oxidative stress has been suggested to contribute to the pathophysiology of schizophrenia. In particular, oxidative damage to lipids, proteins, and DNA as observed in schizophrenia is known to impair cell viability and function, which may subsequently account for the deteriorating course of the illness. Currently available evidence points towards an alteration in the activities of enzymatic and nonenzymatic antioxidant systems in schizophrenia. In fact, experimental models have demonstrated that oxidative stress induces behavioral and molecular anomalies strikingly similar to those observed in schizophrenia. These findings suggest that oxidative stress is intimately linked to a variety of pathophysiological processes, such as inflammation, oligodendrocyte abnormalities, mitochondrial dysfunction, hypoactive N-methyl-d-aspartate receptors and the impairment of fast-spiking gamma-aminobutyric acid interneurons. Such self-sustaining mechanisms may progressively worsen producing the functional and structural consequences associated with schizophrenia. Recent clinical studies have shown antioxidant treatment to be effective in ameliorating schizophrenic symptoms. Hence, identifying viable therapeutic strategies to tackle oxidative stress and the resulting physiological disturbances provide an exciting opportunity for the treatment and ultimately prevention of schizophrenia.

Effects of N-acetyl-cysteine treatment on glutathione depletion and a short-term spatial memory deficit in 2-cyclohexene-1-one-treated rats

Glutathione (GSH) is the primary antioxidant in the body and is present in high levels in the brain. Levels of GSH and other antioxidants are significantly altered in major psychiatric illnesses, such as schizophrenia. Recent clinical trials have demonstrated that chronic treatment with N-acetyl-l-cysteine (NAC), a GSH precursor, improved symptoms in individuals with this illness. We previously showed in rats and mice that depletion of GSH by treatment with 2-cyclohexene-1-one (CHX) induced short-term spatial memory deficits in the Y-maze test. The aim of present study was to characterise the effect of NAC in this CHX-induced glutathione depletion model. Consistent with our previous studies, CHX treatment induced approximately 50% reduction of GSH levels in striatum, hippocampus and frontal cortex tissue. GSH depletion was significantly rescued by either 1.2 g/kg or 1.6 g/kg of NAC administration, with a full recovery observed in the frontal cortex after the high dose of NAC. CHX treatment also induced a disruption in short-term spatial recognition memory in Y-maze test, as measured by the duration of time spent in the novel arm. This disruption was reversed by treatment with 1.6 g/kg of NAC. In conclusion, this study suggests that rescue of depleted levels of GSH in the brain restores cognitive deficits, as measured by the Y-maze. These effects appear to be dose-dependent and region-specific. These results may be relevant to the understanding and management of the cognitive symptoms of schizophrenia and bipolar disorder.

Dicarboxylate carrier-mediated glutathione transport is essential for reactive oxygen species homeostasis and normal respiration in rat brain mitochondria

Glutathione transport into mitochondria is mediated by oxoglutarate (OGC) and dicarboxylate carrier (DIC) in the kidney and liver. However, transport mechanisms in brain mitochondria are unknown. We found that both carriers were expressed in the brain. Using cortical mitochondria incubated with physiological levels of glutathione, we found that butylmalonate, a DIC inhibitor, reduced mitochondrial glutathione to levels similar to those seen in mitochondria incubated without extramitochondrial glutathione (59% of control). In contrast, phenylsuccinate, an OGC inhibitor, had no effect (97% of control). Additional experiments with DIC and OGC short hairpin RNA in neuronal-like PC12 cells resulted in similar findings. Significantly, DIC inhibition resulted in increased reactive oxygen species (ROS) content in and H(2)O(2) release from mitochondria. It also led to decreased membrane potential, increased basal respiration rates, and decreased phosphorus-to-oxygen (P/O) ratios, especially when electron transport was initiated from complex I. Accordingly, we found that DIC inhibition impaired complex I activity, but not those for complexes II and III. This impairment was not associated with dislodgment of complex subunits. These results suggest that DIC is the main glutathione transporter in cortical mitochondria and that DIC-mediated glutathione transport is essential for these mitochondria to maintain ROS homeostasis and normal respiratory functions.

Redox dysregulation affects the ventral but not dorsal hippocampus: impairment of parvalbumin neurons, gamma oscillations, and related behaviors

Elevated oxidative stress and alteration in antioxidant systems, including glutathione (GSH) decrease, are observed in schizophrenia. Genetic and functional data indicate that impaired GSH synthesis represents a susceptibility factor for the disorder. Here, we show that a genetically compromised GSH synthesis affects the morphological and functional integrity of hippocampal parvalbumin-immunoreactive (PV-IR) interneurons, known to be affected in schizophrenia. A GSH deficit causes a selective decrease of PV-IR interneurons in CA3 and dendate gyrus (DG) of the ventral but not dorsal hippocampus and a concomitant reduction of beta/gamma oscillations. Impairment of PV-IR interneurons emerges at the end of adolescence/early adulthood as oxidative stress increases or cumulates selectively in CA3 and DG of the ventral hippocampus. Such redox dysregulation alters stress and emotion-related behaviors but leaves spatial abilities intact, indicating functional disruption of the ventral but not dorsal hippocampus. Thus, a GSH deficit affects PV-IR interneuron's integrity and neuronal synchrony in a region- and time-specific manner, leading to behavioral phenotypes related to psychiatric disorders.

Abnormal neural oscillations and synchrony in schizophrenia

Converging evidence from electrophysiological, physiological and anatomical studies suggests that abnormalities in the synchronized oscillatory activity of neurons may have a central role in the pathophysiology of schizophrenia. Neural oscillations are a fundamental mechanism for the establishment of precise temporal relationships between neuronal responses that are in turn relevant for memory, perception and consciousness. In patients with schizophrenia, the synchronization of beta- and gamma-band activity is abnormal, suggesting a crucial role for dysfunctional oscillations in the generation of the cognitive deficits and other symptoms of the disorder. Dysfunctional oscillations may arise owing to anomalies in the brain's rhythm-generating networks of GABA (gamma-aminobutyric acid) interneurons and in cortico-cortical connections.

Does schizophrenia arise from oxidative dysregulation of parvalbumin-interneurons in the developing cortex?

An imbalance in the redox-state of the brain may be part of the underlying pathophysiology in schizophrenia. Inflammatory mediators, such as IL-6, which can tip the redox balance into a pro-oxidant state, have been consistently found to be altered in schizophrenia patients. However, the relationship of altered redox-state to altered brain functions observed in the disease has been unclear. Recent data from a pharmacological model of schizophrenia suggest that redox and inflammatory imbalances may be directly linked to the pathophysiology of the disease by alterations in fast-spiking interneurons. Repetitive adult exposure to the NMDA-R antagonist ketamine increases the levels of the proinflammatory cytokine interleukin-6 in brain which, through activation of the superoxide-producing enzyme NADPH oxidase (Nox2), leads to the loss of the GABAergic phenotype of PV-interneurons and to decreased inhibitory activity in prefrontal cortex. This effect is not observed after a single exposure to ketamine, suggesting that the first exposure to the NMDA-R antagonist primes the brain such that deleterious effects on PV-interneurons appear upon repetitive exposures. The effects of activation of the IL-6/Nox2 pathway on the PV-interneuronal system are reversible in the adult brain, but permanent in the developing cortex. The slow development of PV-interneurons, although essential for shaping of neuronal circuits during postnatal brain development, increases their vulnerability to deleterious insults that can permanently affect their maturational process. Thus, in individuals with genetic predisposition, the persistent activation of the IL-6/Nox2 pathway may be an environmental factor that tips the redox balance leading to schizophrenia symptoms in late adolescence and early adulthood.

A classification of sociomedical health indicators: perspectives for health administrators and health planners

The conceptualization and operationalization of measures of health status are considered. Health indicators are conceived as a subset of social indicators, and therefore, as any social indicator, they are viewed as derivative from social issues. The interrelationships of different frames of reference for defining and measuring health that have accompained three distinct health problem patterns in the United States are viewed from a developmental perspective. Mortality and morbidity rates, the traditional health indicators, by themselves no longer serve to assess health status in developed nations. Their deficiencies as indicators serve as background for a classification schema for sociomedical health status indicators that relates health definition frames of reference, measures of health status, and health problems. The role of a group of health indicators-sociomedical heath indicators-in the current formulation of health status measures is assessed.