Role of glutathione deficit in the disconnectivity syndrome in schizophrenia: from pathogenetic mechanisms to therapeutic interventions

In the cerebrospinal fluid of 26 drug-naive schizophrenics (DSM-III- R), we observed that the level of glutathione ([GSH]) and of its metabolite γ-Glu-Gln was decreased by 27% and 16% respectively. Using a new in-vivo method based on magnetic resonance spec- troscopy, [GSH] was measured in the medial prefrontal cortex of 18 schizophrenics and found to be 52 % lower than in controls (n = 20). This is consistent with the recently observed decreased mRNA levels in fibroblasts of patients (n=32) of the two GSH synthesizing en- zymes (glutathione synthetase (GSS), and glutamate-cysteine ligase M (GCLM) the modulatory subunit of glutamate-cysteine ligase). Moreover, the level of GCLM expression in fibroblasts correlates neg- atively with the psychopathology (positive, general and some nega- tive symptoms). Thus, the observed difference in gene expression is not only the cause of low brain [GSH], but is also related to the sever- ity of symptoms, suggesting that fibroblasts are adequate surrogate for brain tissue. A hypothesis was proposed, based on a central role of GSH in the pathophysiology of schizophrenia. GSH is an important endogenous redox regulator and neuroactive substance. GSH is pro- tecting cells from damage by reactive oxygen species generated, among others, by the metabolism of dopamine. A GSH deficit-in- duced oxidative stress would lead to lipid peroxidation and micro-le- sions in the surrounding of catecholamine terminals, affecting the synaptic contacts on dendritic spines of cortical neurones, where ex- citatory glutamatergic terminals converge with dopaminergic ones. This would lead to spines degeneration and abnormal nervous con- nections or structural disconnectivity, possibly responsible for posi- tive, perceptive and cognitive symptoms of schizophrenia. In addi- tion, a GSH deficit could also lead to a functional disconnectivity by depressing NMDA neurotransmission, in analogy to phencyclidine effects. Present experimental biochemical, cell biological and behav- ioral data are consistent with the proposed mechanism: decreasing pharmacologically [GSH] in experimental models, with or without blocking DA uptake (GBR12909), induces morphological and behav- ioral changes similar to those observed in patients. Dendritic spines: (a) In neuronal cultures, low [GSH] and DA induce decreased density of neural processes; (b) In developing rats (p5-p16), [GSH] deficit and GBR induce a decrease in normal spines in prefrontal pyramids and in GABA-parvalbumine but not of -calretinine immunoreactivity in anterior cingulate. NMDA-dependant synaptic plasticity: GSH deple- I/13 tion in hippocampal slices impairs long-term potentiation. Develop- ing rats with low [GSH] and GBR have deficit in olfactory integration and in object recognition which appears earlier in males than fe- males, in analogy to the delay of the psychosis onset between man and woman. In summary, a deficit of GSH and/or GSH-related enzymes during early development could constitute a major vulnerability fac- tor in schizophrenia.

Early glutathione deficit impairs parvalbumin expression in gaba interneurons and kainate-induced gamma oscillations

An increased oxidative stress and alteration of the antioxidant systems have been observed in schizophrenia. Glutathione (GSH), a major redox regulator, is decreased in patients' cerebrospinal fluid, prefrontal cortex in vivo and striatum post-mortem tissue. Most importantly, there is genetic and functional evidence for the implication of the gene of the glutamate cysteine ligase (GCL) catalytic subunit, the key GSH-synthesizing enzyme. We have developed animal models for a GSH deficit to study the consequences of such deficit on the brain development. A GSH deficit combined with elevated dopamine (DA) during development leads to reduced parvalbumin (PV) expression in a subclass of GABA interneurons in rat anterior cingulate cortex (ACC). Similar changes are observed in postmortem brain tissue of schizophrenic patients. GSH dysregulation increases vulnerability to oxidative stress, that in turn could lead to cortical circuit anomalies in the schizophrenic brain. In the present study, we use a GCL modulatory subunit (GCLM) knock-out (KO) mouse model that presents up to 80% decreased brain GSH levels. During postnatal development, a subgroup of animals from each genotype is exposed to elevated oxidative stress induced by treatment with the DA reuptake inhibitor GBR12909. Results reveal a significant genotype-specific delay International Congress on Schizophrenia Research 136 10. 10. Neuroanatomy, Animal Downloaded from http://schizophreniabulletin.oxfordjournals.org at Bibliotheque Cantonale et Universitaire on June 18, 2010 in cortical PV expression at postnatal day P10 in GCLM-KO mice, as compared to wild-type. This effect seems to be further exaggerated in animals treated with GBR12909 from P5 to P10. At P20, PV expression is no longer significantly reduced in GCLM-KO ACC without GBR but is reduced if GBR is applied from P10 to P20. However, our result show that GCLM-KO mice exhibit increased oxidative stress, cortical altered myelin development as shown by MBP marker, and more specifically impairment of the peri-neuronal net known to modulate PV connectivity. In addition, we also observe a reduced PV expression in the ventro-temporal hippocampus of adult GCLM-KO mice, suggesting that anomalies of the PV interneurons prevail at least in some brain regions throughout the adulthood. Interestingly, the power of kainate-induced gamma oscillations, known to be dependent on proper activation of PV interneuron's, is also lower in hippocampal slices of adult GCLM KO mice. These results suggest that the PV positive GABA interneurons is particularly vulnerable to increased oxidative stress

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.

Metabolic alterations in the cortex of a mouse model with glutathione deficit - relevance to schizophrenia

Background: Glutathione (GSH) is a major redox regulator and antioxidant and is decreased in cerebrospinal fluid and prefrontal cortex of schizophrenia patients [Do et al. (2000) Eur J Neurosci 12:3721]. The genes of the key GSH-synthesizing enzyme, glutamate- cysteine ligase catalytic (GCLC) and modifier (GCLM) subunits, are associated with schizophrenia, suggesting that the deficit in GSH synthesis is of genetic origin [Gysin et al. (2007) PNAS 104:16621]. GCLM knock-out (KO) mice, which display an 80% decrease in brain GSH levels, have abnormal brain morphology and function [Do et al. (2009) Curr Opin Neurobiol 19:220]. Developmental redox deregulation by impaired GSH synthesis and environmental risk factors generating oxidative stress may have a central role in schizophrenia. Here, we used GCLM KO mice to investigate the impact of a genetically dysregulated redox system on the neurochemical profile of the developing brain. Methods: The neurochemical profile of the anterior and posterior cortical areas of male and female GCLM KO and wild-type mice was determined by in vivo 1H NMR spectroscopy on postnatal days 10, 20, 30, 60 and 90, under 1 to 1.5% isoflurane anaesthesia. Localised 1H NMR spectroscopy was performed on a 14.1 T, 26 cm VNMRS spectrometer (Varian, Magnex) using a home-built 8 mm diameter quadrature surface coil (used both for RF excitation and signal reception). Spectra were acquired using SPECIAL with TE of 2.8 ms and TR of 4 s from VOIs placed in anterior or posterior regions of the cortex [Mlynárik et al. (2006) MRM 56:965]. LCModel analysis allowed in vivo quantification of a neurochemical profile composed of 18 metabolites. Results: GCLM KO mice displayed nearly undetectable GSH levels as compared to WT mice, demonstrating their drastic redox deregulation. Depletion of GSH triggered alteration of metabolites related to its synthesis, namely increase of glycine and glutamate levels during development (P20 and P30). Concentrations of glutamine and aspartate that are produced from glutamate were also increased in GCLM KO animals relative to WT. In addition, GCLM KO mice also showed higher levels of N-acetylaspartate that originates from the acetylation of aspartate. These metabolites are particularly implicated in neurotransmission processes and in mitochondrial oxidative metabolism. Their increase may indicate impaired mitochondrial metabolism with concomitant accumulation of lactate in the adult mice (P60 and P90). In addition, the GSH depletion triggers reduction of GABA concentration in anterior cortex of the P60 mice, which is in accordance with known impairment of GABAergic interneurons in that area. Changes were generally more pronounced in males than in females at P60, which is consistent with earlier disease onset in male patients. Discussion: In conclusion, the observed metabolic alterations in the cortex of a mouse model of redox deregulation suggest impaired mitochondrial metabolism and altered neurotransmission. The results also highlight the age between P20 and P30 as a sensitive period during the development for these alterations.

Mechanistic insights into cytosolic molecular chaperones in protein unfolding and disaggregation

Under optimal non-physiological conditions of low concentrations and low temperatures, proteins may spontaneously fold to the native state, as all the information for folding lies in the amino acid sequence of the polypeptide. However, under conditions of stress or high protein crowding as inside cells, a polypeptide may misfold and enter an aggregation pathway resulting in the formation of misfolded conformers and fibrils, which can be toxic and lead to neurodegenerative illnesses, such as Alzheimer's, Parkinson's or Huntington's diseases and aging in general. To avert and revert protein misfolding and aggregation, cells have evolved a set of proteins called molecular chaperones. Here, I focussed on the human cytosolic chaperones Hsp70 (DnaK) and HspllO, and co-chaperone Hsp40 (DnaJ), and the chaperonin CCT (GroEL). The cytosolic molecular chaperones Hsp70s/Hspll0s and the chaperonins are highly upregulated in bacterial and human cells under different stresses and are involved both in the prevention and the reversion of protein misfolding and aggregation. Hsp70 works in collaboration with Hsp40 to reactivate misfolded or aggregated proteins in a strict ATP dependent manner. Chaperonins (CCT and GroEL) also unfold and reactivate stably misfolded proteins but we found that it needed to use the energy of ATP hydrolysis in order to evict over- sticky misfolded intermediates that inhibited the unfoldase catalytic sites. Ill In this study, we initially characterized a particular type of inactive misfolded monomeric luciferase and rhodanese species that were obtained by repeated cycles of freeze-thawing (FT). These stable misfolded monomeric conformers (FT-luciferase and FT-rhodanese) had exposed hydrophobic residues and were enriched with wrong ß-sheet structures (Chapter 2). Using FT-luciferase as substrate, we found that the Hsp70 orthologs, called HspllO (Sse in yeast), acted similarly to Hsp70 as were bona fide ATP- fuelled polypeptide unfoldases and was much more than a mere nucleotide exchange factor, as generally thought. Moreover, we found that HspllO collaborated with Hsp70 in the disaggregation of stable protein aggregates in which Hsp70 and HspllO acted as equal partners that synergistically combined their individual ATP-consuming polypeptide unfoldase activities to reactivate the misfolded/aggregated proteins (Chapter 3). Using FT-rhodanese as substrate, we found that chaperonins (GroEL and CCT) could catalytically reactivate misfolded rhodanese monomers in the absence of ATP. Also, our results suggested that encaging of an unfolding polypeptide inside the GroEL cavity under a GroES cap was not an obligatory step as generally thought (Chapter 4). Further, we investigated the role of Hsp40, a J-protein co-chaperone of Hsp70, in targeting misfolded polypeptides substrates onto Hsp70 for unfolding. We found that even a large excess of monomeric unfolded a-synuclein did not inhibit DnaJ, whereas, in contrast, stable misfolded a-synuclein oligomers strongly inhibited the DnaK-mediated chaperone reaction by way of sequestering the DnaJ co-chaperone. This work revealed that DnaJ could specifically distinguish, and bind potentially toxic stably aggregated species, such as soluble a-synuclein oligomers involved in Parkinson's disease, and with the help of DnaK and ATP convert them into from harmless natively unfolded a-synuclein monomers (chapter 5). Finally, our meta-analysis of microarray data of plant and animal tissues treated with various chemicals and abiotic stresses, revealed possible co-expressions between core chaperone machineries and their co-chaperone regulators. It clearly showed that protein misfolding in the cytosol elicits a different response, consisting of upregulating the synthesis mainly of cytosolic chaperones, from protein misfolding in the endoplasmic reticulum (ER) that elicited a typical unfolded protein response (UPR), consisting of upregulating the synthesis mainly of ER chaperones. We proposed that drugs that best mimicked heat or UPR stress at increasing the chaperone load in the cytoplasm or ER respectively, may prove effective at combating protein misfolding diseases and aging (Chapter 6).  - Dans les conditions optimales de basse concentration et de basse température, les protéines vont spontanément adopter un repliement natif car toutes les informations nécessaires se trouvent dans la séquence des acides aminés du polypeptide. En revanche, dans des conditions de stress ou de forte concentration des protéines comme à l'intérieur d'une cellule, un polypeptide peu mal se replier et entrer dans un processus d'agrégation conduisant à la formation de conformères et de fibrilles qui peuvent être toxiques et causer des maladies neurodégénératives comme la maladie d'Alzheimer, la maladie de Parkinson ou la chorée de Huntington. Afin d'empêcher ou de rectifier le mauvais repliement des protéines, les cellules ont développé des protéines appelées chaperonnes. Dans ce travail, je me suis intéressé aux chaperonnes cytosoliques Hsp70 (DnaK) et HspllO, la co-chaperones Hsp40 (DnaJ), le complexe CCT/TRiC et GroEL. Chez les bactéries et les humains, les chaperonnes cytosoliques Hsp70s/Hspl 10s et les « chaperonines» sont fortement activées par différentes conditions de stress et sont toutes impliquées dans la prévention et la correction du mauvais repliement des protéines et de leur agrégation. Hsp70 collabore avec Hsp40 pour réactiver les protéines agrégées ou mal repliées et leur action nécessite de 1ATP. Les chaperonines (GroEL) déplient et réactivent aussi les protéines mal repliées de façon stable mais nous avons trouvé qu'elles utilisent l'ATP pour libérer les intermédiaires collant et mal repliés du site catalytique de dépliage. Nous avons initialement caractérisé un type particulier de formes stables de luciférase et de rhodanese monomériques mal repliées obtenues après plusieurs cycles de congélation / décongélation répétés (FT). Ces monomères exposaient des résidus hydrophobiques et étaient plus riches en feuillets ß anormaux. Ils pouvaient cependant être réactivés par les chaperonnes Hsp70+Hsp40 (DnaK+DnaJ) et de l'ATP, ou par Hsp60 (GroEL) sans ATP (Chapitre 2). En utilisant la FT-Luciferase comme substrat nous avons trouvé que HspllO (un orthologue de Hsp70) était une authentique dépliase, dépendante strictement de l'ATP. De plus, nous avons trouvé que HspllO collaborait avec Hsp70 dans la désagrégation d'agrégats stables de protéines en combinant leurs activités dépliase consommatrice d'ATP (Chapitre 3). En utilisant la FT-rhodanese, nous avons trouvé que les chaperonines (GroEL et CCT) pouvaient réactiver catalytiquement des monomères mal repliés en absence d'ATP. Nos résultats suggérèrent également que la capture d'un polypeptide en cours de dépliement dans la cavité de GroEL et sous un couvercle du complexe GroES ne serait pas une étape obligatoire du mécanisme, comme il est communément accepté dans la littérature (Chapitre 4). De plus, nous avons étudié le rôle de Hsp40, une co-chaperones de Hsp70, dans l'adressage de substrats polypeptidiques mal repliés vers Hsp70. Ce travail a révélé que DnaJ pouvait différencier et lier des polypeptide mal repliés (toxiques), comme des oligomères d'a-synucléine dans la maladie de Parkinson, et clairement les différencier des monomères inoffensifs d'a-synucléine (Chapitre 5). Finalement une méta-analyse de données de microarrays de tissus végétaux et animaux traités avec différents stress chimiques et abiotiques a révélé une possible co-expression de la machinerie des chaperonnes et des régulateurs de co- chaperonne. Cette meta-analyse montre aussi clairement que le mauvais repliement des protéines dans le cytosol entraîne la synthèse de chaperonnes principalement cytosoliques alors que le mauvais repliement de protéines dans le réticulum endoplasmique (ER) entraine une réponse typique de dépliement (UPR) qui consiste principalement en la synthèse de chaperonnes localisées dans l'ER. Nous émettons l'hypothèse que les drogues qui reproduisent le mieux les stress de chaleur ou les stress UPR pourraient se montrer efficaces dans la lutte contre le mauvais repliement des protéines et le vieillissement (Chapitre 6).

Schizophrenia: glutathione deficit as a new vulnerability factor for disconnectivity syndrome

(from the journal abstract) Schizophrenia, a major psychiatric disease, affects individuals in the centre of their personality. Its aetiology is not clearly established. In this review, we will present evidence that patients suffering of schizophrenia present a brain deficit in glutathione, a major endogenous redox regulator and antioxidant. We will also show that, in experimental models, a decrease in glutathione, particularly during development, induces morphological, electrophysiological and behavioural anomalies consistent with those observed in the disease. In the cerebrospinal fluid of drug-naive schizophrenics, glutathione level was decreased by 27% and its direct metabolite of glutathione by 16%. Glutathione level in prefrontal cortex of patients, measured by magnetic resonance spectroscopy, was 52% lower than in controls. Patients' fibroblasts reveal a decrease in mRNA levels of the two glutathione synthesising enzymes, glutamatecysteine ligase modulatory subunit (GCLM) and glutathione synthetase. GCLM expression level in fibroblasts correlates negatively with symptoms severity. Glutathione is an important endogenous redox regulator and neuroactive substance. It is protecting cells from damage by reactive oxygen species generated, among others, by dopamine metabolism. A glutathione deficit-induced oxidative stress would lead to lipid peroxidation and micro-lesions at the level of dendritic spines, a synaptic damage responsible for abnormal nervous connections or structural disconnectivity. On the other hand, a glutathione deficit could also lead to a functional disconnectivity by depressing NMDA neurotransmission, in analogy to phencyclidine effects. Present experimental data are consistent with the proposed hypothesis: decreasing pharmacologically glutathione level in experimental models, with or without blocking dopamine (DA) uptake (GBR12909), induces morphological, electrophysiological and behavioural changes similar to those observed in patients. In summary, a deficit of glutathione and/or glutathione-related enzymes during early development would lead to both a functional and a structural disconnectivity, which could be at the basis of some perceptive, cognitive and behavioural troubles of the disease. It could constitute a major vulnerability factor for schizophrenia. Attempts to restore physiological glutathione functions could open new therapeutic avenues. This translational research, made possible by a close interaction between clinicians and neuroscientists, should also pave the way to the identification of biological markers for schizophrenia. In turn, they should allow early diagnostic and hopefully preventive intervention to this devastating disease. (PsycINFO Database Record (c) 2005 APA, all rights reserved)

Glutathione deficit in schizophrenia: strategies to increase glutathione levels in " in vitro " and clinical studies

Summary: Decrease in glutathione (GSH) levels was observed in cerebrospinal fluid, prefrontal cortex and post-mortem striatum of schizophrenia patients. Evidences suggest a defect in GSH synthesis at the levels of the rate-limiting synthesizing enzyme, glutamate cysteine ligase (GCL). Indeed, polymorphisms in the gene of the modifier subunit of GCL (GCLM) was shown to be associated with the disease in three different populations, GCLM gene expression is decreaséd in fibroblasts from patients and the increase in GCL activity induced by an oxidative stress is lower in patients' fibroblasts compared to controls. GSH being a major antioxydant and redox regulator, its presence is of high importance for protecting cells against oxidative stress. The aim of the present work was to use various substances to increase GSH levels by diverse strategies. Since the synthesizing enzyme GCL is defective, bypassing this enzyme was the first strategy we used. GSH ethyl ester (GSHEE), a membrane permeable analog of GSH, succeeded in replenishing GSH levels in cultured neurons and astrocytes previously depleted in GSH by L-buthionine-(S,R)-sulfoximine (BSO), an inhibitor of GCL. GSHEE also abolished dopamine-induced decrease of NMDA-mediated calcium response observed in BSO-treated neurons. y-Glutamylcysteine ethyl ester (GCSE), a membrane permeable analog of the product of GCL, increased GSH levels only in astrocytes. The second strategy was to boost the defective enzyme GCL. While quercetin (flavonoid) could increase GSH levels only in astrocytes, curcumin (polyphenol) and tertbutylhydroquinone (quinone) were successful in both neurons and astrocytes, via an increase in the gene expression of the two subunits of GCL and, consequently, an increase in the activity of the enzyme. However, FK506, an immunosupressant, was unefficient. Treating astrocytes from GCLM KO mice showed that the modulatory subunit is necessary for the action of the substances. Finally, since cysteine is the limiting precursor in the synthesis of GSH, we hypothesized that we could increase GSH levels by providing more of this precursor. N-acetyl-cysteine (NAC), a cysteine donor, was administered to schizophrenia patients, using adouble-blind and cross-over protocol. NAC significantly improved the mismatch negativity (MMN), a component of the auditory evoked potentials, thought to reflect selective current flowing through open, unblocked NMDA channels. Considering that NMDA function is reduced when GSH levels are low, increasing these levels with NAC could improve NMDA function as reflected by the improvement in the generation of the MMN. Résumé: Les taux de glutathion (GSH) dans le liquide céphalo-rachidien, le cortex préfrontal ainsi que le striatum post-mortem de patients schizophrènes, sont diminués. L'enzyme limitante dans la synthèse du GSH, la glutamyl-cysteine ligase (GCL), est défectueuse. En effet, des polymorphismes dans le gène de la sous-unité modulatrice de GCL (GCLM) sont associés à la maladie, l'expression du gène GCLM est diminuée dans les fibroblastes de patients et, lors d'un stress oxidative, l'augmentation de l'activité de GCL est plus faible chez les patients que chez les contrôles. Le GSH étant un important antioxydant et régulateur du status redox, sa présence est primordiale afin de protéger les cellules contre les stress oxydatifs. Au cours du présent travail, une variété de substances ont été utilisées dans le but d'augmenter les taux de GSH. Passer outre l'enzyme de synthèse GCL qui est défectueuse fut la première stratégie utilisée. L'éthylester de GSH (GSHEE), un analogue du GSH qui pénètre la membrane cellulaire, a augmenté les taux de GSH dans des neurones et des astrocytes déficitaires en GSH dû au L-buthionine-(S,R)-sulfoximine (BSO), un inhibiteur du GCL. Dans ces neurones, le GSHEE a aussi aboli la diminution de la réponse NMDA, induite parla dopamine. L'éthyl-ester de y-glutamylcysteine (GCEE), un analogue du produit de la GCL qui pénètre la membrane cellulaire, a augmenté les taux de GSH seulement dans les astrocytes. La seconde stratégie était d'augmenter l'activité de l'enzyme GCL. Tandis que la quercétine (flavonoïde) n'a pu augmenter les taux de GSH que dans les astrocytes, la curcumin (polyphénol) et le tert-butylhydroquinone (quinone) furent efficaces dans les deux types de cellules, via une augmentation de l'expression des gènes des deux sous-unités de GCL et de l'activité de l'enzyme. Le FK506 (immunosupresseur) n' a démontré aucune efficacité. Traiter des astrocytes provenant de souris GCLM KO a permis d'observer que la sous-unité modulatoire est nécessaire à l'action des substances. Enfin, puisque la cysteine est le substrat limitant dans la synthèse du GSH, fournir plus de ce présurseur pourrait augmenter les taux de GSH. Nacétyl-cystéine (NAC), un donneur de cystéine, a été administrée à des schizophrènes, lors d'une étude en double-aveugle et cross-over. NAC a amélioré le mismatch negativity (MMN), un composant des potentials évoqués auditifs, qui reflète le courant circulant via les canaux NMDA. Puisque la fonctionnalité des R-NMDA est diminuée lorsque les taux de GSH sont bas, augmenter ces taux avec NAC pourrait améliorer la fonction des R-NMDA, réflété par une augmentation de l'amplitude du MMN.