Oxidative neuronal death caused by glutamate uptake inhibition in cultured hippocampal neurons

The protective effect of N-acetylcysteine against MK-801-induced neurodegeneration in mice

BACKGROUND

Neurological disorders result in not only a decline in the quality of life of patients but also a global economic burden. Therefore, protective medicine becomes more important for society. MK-801 is a chemical agent used to understand the etiology of behavioral disorders and brain degeneration in animal models. This study aims to determine whether N-acetylcysteine (NAC) is useful to treat brain degeneration caused by MK-801, an N-methyl-D-aspartate glutamate receptor antagonist.

METHODS AND RESULTS

Four groups were formed by dividing 24 male BALB/c mice into groups of six. The control group was given a saline solution (10 ml/kg-i.p.). MK-801 (1 mg/kg-i.p.) was given alone to one group, and it was given with NAC (100 mg/kg-i.p.) to another group, while the last group was given only NAC (100 mg/kg-i.p.). The administration of drugs lasted for fourteen days. After the behavioral tests (open field and elevated plus-maze), all animals were euthanised, and brain tissues were collected for real-time PCR, TAS-TOS analysis, hematoxylin-eosin, Kluver-Barrera, and TUNEL staining. In the MK-801 group, besides nuclear shrinkage in neurons, glial cell infiltration, vacuolization in cortical neurons, white matter damage, and apoptosis were observed.

CONCLUSION

In the mice given NAC as a protective agent, it was observed that behavioral problems improved, antioxidant levels increased, and nuclear shrinkage, glial cell infiltration, vacuolization in neurons, and white matter degeneration were prevented. Moreover, MBP expression increased, and the number of TUNEL-positive cells significantly decreased. As a result, it was observed that NAC may have a protective effect against brain degeneration.

Comparative efficacy, acceptability, and tolerability of adjunctive anti-inflammatory agents on bipolar disorder: A systemic review and network meta-analysis

OBJECTIVES

We performed a network meta-analysis (NMA) with up-to-date evidence to compare different anti-inflammatory agents to improve the treatment of bipolar disorder (BD) patients.

METHODS

Four databases (i.e., the Cochrane Library, Web of Science, PubMed, and Embase) were searched for randomized controlled trials (RCTs) published between 1995 and 2022 on the use of anti-inflammatory agents in the treatment of BD. A systematic review and NMA were conducted.

RESULTS

Adjunctive N-acetylcysteine (NAC) was superior to placebo for the treatment of BD according to the endpoint scale score (SMD -0.65, 95% confidence interval (CI): - 0.99 to - 0.31), response rate (odds ratio (OR) 3.42, 95% CI: 1.23-9.52), remission rate (OR 4.94, 95% CI: 1.03-41.38) and surface under the cumulative ranking curve (SUCRA) value of the endpoint scale score (0.84). Adjunctive nonsteroidal anti-inflammatory drugs (NSAIDs) were more favorable than placebo based on the remission rate (OR 3.93, 95% CI: 1.15-13.43) and were significantly more acceptable than other treatments (OR 0.60, 95% CI: 0.36-0.99). Adjunctive coenzyme Q10 (CoQ10) was superior to other agents in terms of the response rate (OR 18.85, 95% CI: 2.63-135.00), with a SUCRA value for the response rate of 0.90 and that for the remission rate of 0.71.

CONCLUSION

Adjunctive NAC is recommended for the treatment of BD. Adjunctive NSAIDs and CoQ10 are still seen as effective, but more high-quality clinical studies are needed to verify their efficacy. Other anti-inflammatory agents may not be recommended for clinical use at present. All anti-inflammatory agents demonstrated a good safety profile. We call for further research on the combined treatment of BD with different anti-inflammatory agents to be included in future trials.

Ceftriaxone as a Novel Therapeutic Agent for Hyperglutamatergic States: Bridging the Gap Between Preclinical Results and Clinical Translation

Dysregulation of glutamate homeostasis is a well-established core feature of neuropsychiatric disorders. Extracellular glutamate concentration is regulated by glutamate transporter 1 (GLT-1). The discovery of a beta-lactam antibiotic, ceftriaxone (CEF), as a safe compound with unique ability to upregulate GLT-1 sparked the interest in testing its efficacy as a novel therapeutic agent in animal models of neuropsychiatric disorders with hyperglutamatergic states. Indeed, more than 100 preclinical studies have shown the efficacy of CEF in attenuating the behavioral manifestations of various hyperglutamatergic brain disorders such as ischemic stroke, amyotrophic lateral sclerosis (ALS), seizure, Huntington’s disease, and various aspects of drug use disorders. However, despite rich and promising preclinical data, only one large-scale clinical trial testing the efficacy of CEF in patients with ALS is reported. Unfortunately, in that study, there was no significant difference in survival between placebo- and CEF-treated patients. In this review, we discussed the translational potential of preclinical efficacy of CEF based on four different parameters: (1) initiation of CEF treatment in relation to induction of the hyperglutamatergic state, (2) onset of response in preclinical models in relation to onset of GLT-1 upregulation, (3) mechanisms of action of CEF on GLT-1 expression and function, and (4) non-GLT-1-mediated mechanisms for CEF. Our detailed review of the literature brings new insights into underlying molecular mechanisms correlating the preclinical efficacy of CEF. We concluded here that CEF may be clinically effective in selected cases in acute and transient hyperglutamatergic states such as early drug withdrawal conditions.

Clinical translational neuroimaging of the antioxidant effect of N-acetylcysteine on neural microstructure

PURPOSE

Oxidative stress and downstream effectors have emerged as important pathological processes that drive psychiatric illness, suggesting that antioxidants may have a therapeutic role in psychiatric disease. However, no imaging biomarkers are currently available to track therapeutic response. The purpose of this study was to examine whether advanced DWI techniques are able to sensitively detect the potential therapeutic effects of the antioxidant N-acetylcysteine (NAC) in a Disc1 svΔ2 preclinical rat model of psychiatric illness.

METHODS

Male and female Disc1 svΔ2 rats and age-matched, sex-matched Sprague-Dawley wild-type controls were treated with a saline vehicle or NAC before ex vivo MRI acquisition at P50. Imaging data were fit to DTI and neurite orientation dispersion and density imaging models and analyzed for region-specific changes in quantitative diffusion metrics. Brains were further processed for cellular quantification of microglial density and morphology. All experiments were repeated for Disc1 svΔ2 rats exposed to chronic early-life stress to test how gene-environment interactions might alter effectiveness of NAC therapy.

RESULTS

The DTI and neurite orientation dispersion and density imaging analyses demonstrated amelioration of early-life, sex-specific neural microstructural deficits with concomitant differences in microglial morphology across multiple brain regions relevant to neuropsychiatric illness with NAC treatment, but only in male Disc1 svΔ2 rats. Addition of chronic early-life stress reduced the ability of NAC to restore microstructural deficits.

CONCLUSION

These findings provide evidence for a treatment pathway targeting endogenous antioxidant capacity, and the clinical translational utility of neurite orientation dispersion and density imaging microstructural imaging to sensitively detect microstructural alterations resulting from antioxidant treatment.

The efficacy of adjunctive N-acetylcysteine in acute bipolar depression: A randomized placebo-controlled study

OBJECTIVE

To investigate the efficacy of adjunctive N-acetylcysteine (NAC) for the treatment of acute bipolar depression.

METHOD

A randomized, double-blind, multicentre, placebo-controlled trial including adult subjects diagnosed with bipolar disorder, currently experiencing a depressive episode. Participants were treated with 3 g/day NAC or placebo as an adjunctive to standard treatment for 20 weeks, followed by a 4-week washout where the blinding was maintained. The primary outcome was the mean change in the Montgomery Asberg Depression Rating Scale (MADRS) score over the 20-week treatment phase. Linear Mixed Effects Repeated Measures (LMERM) was used for analysing the primary outcome.

RESULTS

A total of 80 subjects were included. The mean MADRS score at baseline was 30.1 and 28.8 in participants randomized to NAC and placebo, respectively. Regarding the primary outcome measure, the between-group difference (NAC vs. placebo) was 0.5, which was statistically non-significant (95% CI: -7.0-5.9;p = 0.88). All findings regarding secondary outcomes were statistically or clinically insignificant.

LIMITATIONS

The study had a placebo response rate of 55.6% - high placebo response rates are associated with failure to separate from placebo.

CONCLUSIONS

Based on our primary outcome measure, we could not confirm previous studies showing a therapeutic effect of adjunctive NAC treatment on acute bipolar depression. Further studies with larger samples are needed to elucidate if specific subgroups could benefit from adjunctive NAC treatment.

Neuroprotective effects of the ethanol stem bark extracts of Terminalia ivorensis in ketamine-induced schizophrenia-like behaviors and oxidative damage in mice

CONTEXT

Schizophrenia is a heterogenous neurological disorder, which has been hypothetically linked to oxidative imbalance and associated behavioral perturbations. Preliminary evidence from animal models predictive of human psychosis suggests that Terminalia ivorensis A. Chev. (Combretaceae) has antipsychotic-like activity in mice.

OBJECTIVE

This study investigates the neuroprotective property of the ethanol stem bark extracts of T. ivorensis (EETI) in reversal treatment of ketamine-induced schizophrenia-like behaviors and oxidative alteration in adult male Swiss albino mice.

MATERIALS AND METHODS

Animals were divided into six treatment groups (n = 5). Animals received distilled water or ketamine (20 mg/kg) once daily intraperitoneally (i.p.) for 14 days, and from the 8th to the 14th day, they were treated with EETI (125, 250 or 500 mg/kg), risperidone (RIS) or vehicle orally once daily. Behaviors related to positive (locomotor activity) and cognitive (Y maze) symptoms of schizophrenia were assessed. Glutathione (GSH) levels, superoxide dismutase (SOD) and catalase (CAT) activities, including malondialdehyde (MDA) concentration were measured in mice whole brains.

RESULT

The LD₅₀ of EETI was 2236.06 mg/kg, p.o. body weight. EETI (125, 250 or 500 mg/kg, p.o.) demonstrated significant (p < 0.05) inhibition of ketamine-induced hyperlocomotion and cognitive dysfunction. The extract decreased MDA concentration (39.0, 62.6 and 67.5%) in a dose-dependent manner. Moreover, EETI significantly (p < 0.05) reversed the depletion of GSH, and increased activities of SOD and CAT in brain tissues.

DISCUSSION AND CONCLUSION

These findings suggest that EETI probably exert its antipsychotic-like activity, via a neuroprotective compensatory mechanism of action, and as such, could be relevant in the management of schizophrenia.

Astroglial NMDA receptors inhibit expression of Kir4.1 channels in glutamate-overexposed astrocytes in vitro and in the brain of rats with acute liver failure

Astroglial inward rectifying Kir4.1 potassium channels are fundamental for the maintenance of ion and water homeostasis in the central nervous system (CNS). Down-regulation of Kir4.1 expression is observed in CNS disorders associated with excessive extracellular glutamate (Glu) accumulation, including hepatic encephalopathy related to acute liver failure (ALF). Here we demonstrate that prolonged (3 days) treatment of cultured rat cortical astrocytes with 2 mM Glu or 100 µM NMDA decreases the expression of Kir4.1 mRNA and protein. Inhibition by Glu of Kir4.1 mRNA expression was reversed by NMDA receptor antagonists MK-801 and AP-5 (each at 50 µM), and by a non-transportable inhibitor of Glu uptake TBOA (100 µM). MK-801 reversed the inhibitory effect of Glu on Kir4.1 protein expression. In contrast, transcription of Kir4.1 channels was not affected by: (i) a transportable Glu uptake inhibitor PDC (100 µM); (ii) by group I mGluR antagonist MTEP (100 µM); (iii) by antagonists of oxidative-nitrosative stress (ONS) in astrocytes, including the neuroprotective amino acid taurine (Tau; 10 mM), the NADPH oxidase inhibitor apocyanine (APO; 300 µM), the nitric oxide synthase inhibitor, L-NNA (100 µM), and a membrane permeable glutathione precursor, glutathione-diethyl ester (GEE; 3 mM). Down-regulation of Kir4.1 transcription in rats with ALF was attenuated by intraperitoneal administration of a competitive NMDA receptor antagonist memantine, but not by histidine, which reverses ONS associated with ALF. Collectively, the results indicate that over-activation of astroglial NMDA receptors, aided by as yet undefined effects of Glu entry to astrocytes, is a primary cause of the reduction of Kir4.1 expression in CNS disorders associated with increased exposure to Glu.

Efficacy of lovastatin on learning and memory deficits caused by chronic intermittent hypoxia-hypercapnia: through regulation of NR2B-containing NMDA receptor-ERK pathway

BACKGROUND

Chronic intermittent hypoxia-hypercapnia (CIHH) exposure leads to learnning and memory deficits in rats. Overactivation of N-methyl-D-aspartate receptors(NMDARs) can lead to the death of neurons through a process termed excitotoxicity, which is involved in CIHH-induced cognitive deficits. Excessively activated NR2B (GluN2B)-containing NMDARs was reported as the main cause of excitotoxicity. The ERK1/2 (extracellular signal-regulated kinase 1/2) signaling cascade acts as a key component in NMDARs-dependent neuronal plasticity and survival. Ca2+/calmodulin-dependent protein kinase II (CaMKII), synapse-associated protein 102 (SAP102) and Ras GTPase-activating protein (SynGAP) have been shown to be involved in the regulation of NMDAR-ERK signalling cascade. Recent studies revealed statins (the HMG-CoA reductase inhibitor) have effect on the expression of NMDARs. The present study intends to explore the potential effect of lovastatin on CIHH-induced cognitive deficits and the NR2B-ERK signaling pathway.

METHODS AND FINDINGS

Eighty male Sprague Dawley rats were randomly divided into five groups. Except for those in the control group, the rats were exposed to chronic intermittent hypoxia-hypercapnia (CIHH) (9 ∼ 11%O2, 5.5 ∼ 6.5%CO2) for 4 weeks. After lovastatin administration, the rats performed better in the Morris water maze test. Electron microscopy showed alleviated hippocampal neuronal synaptic damage. Further observation suggested that either lovastatin or ifenprodil (a selective NR2B antagonist) administration similarly downregulated NR2B subunit expression leading to a suppression of CaMKII/SAP102/SynGAP signaling cascade, which in turn enhanced the phosphorylation of ERK1/2. The phosphorylated ERK1/2 induced signaling cascade involving cAMP-response element-binding protein (CREB) phosphorylation and brain-derived neurotrophic factor (BDNF) activation, which is responsible for neuroprotection.

CONCLUSIONS

These findings suggest that the ameliorative cognitive deficits caused by lovastatin are due to the downregulation of excessive NR2B expression accompanied by increased expression of ERK signaling cascade. The effect of NR2B in upregulating pERK1/2 maybe due, at least in part, to inactivation of CaMKII/SAP102/SynGAP signaling cascade.

High glutamate attenuates S100B and LDH outputs from rat cortical slices enhanced by either oxygen-glucose deprivation or menadione

One hour incubation of rat cortical slices in a medium without oxygen and glucose (oxygen-glucose deprivation, OGD) increased S100B release to 6.53 ± 0.3 ng/ml/mg protein from its control value of 3.61 ± 0.2 ng/ml/mg protein. When these slices were then transferred to a medium containing oxygen and glucose (reoxygenation, REO), S100B release rose to 344 % of its control value. REO also caused 192 % increase in lactate dehydrogenase (LDH) leakage. Glutamate added at millimolar concentration into the medium decreased OGD or REO-induced S100B release and REO-induced LDH leakage. Alpha-ketoglutarate, a metabolic product of glutamate, was found to be as effective as glutamate in decreasing the S100B and LDH outputs. Similarly lactate, 2-ketobutyrate and ethyl pyruvate, a lipophilic derivative of pyruvate, also exerted a glutamate-like effect on S100B and LDH outputs. Preincubation with menadione, which produces H2O2 intracellularly, significantly increased S100B and LDH levels in normoxic medium. All drugs tested in the present study, with the exception of pyruvate, showed a complete protection against menadione preincubation. Additionally, each OGD-REO, menadione or H2O2-induced mitochondrial energy impairments determined by 2,3,5-triphenyltetrazolium chloride (TTC) staining and OGD-REO or menadione-induced increases in reactive oxygen substances (ROS) determined by 2,7-dichlorofluorescin diacetate (DCFH-DA) were also recovered by glutamate. Interestingly, H2O2-induced increase in fluorescence intensity derived from DCFH-DA in a slice-free physiological medium was attenuated significantly by glutamate and alpha-keto acids. All these drug actions support the conclusion that high glutamate, such as alpha-ketoglutarate and other keto acids, protects the slices against OGD- and REO-induced S100B and LDH outputs probably by scavenging ROS in addition to its energy substrate metabolite property.

Kallikrein 6 signals through PAR1 and PAR2 to promote neuron injury and exacerbate glutamate neurotoxicity

CNS trauma generates a proteolytic imbalance contributing to secondary injury, including axonopathy and neuron degeneration. Kallikrein 6 (Klk6) is a serine protease implicated in neurodegeneration, and here we investigate the role of protease-activated receptors 1 (PAR1) and PAR2 in mediating these effects. First, we demonstrate Klk6 and the prototypical activator of PAR1, thrombin, as well as PAR1 and PAR2, are each elevated in murine experimental traumatic spinal cord injury (SCI) at acute or subacute time points. Recombinant Klk6 triggered extracellular signal-regulated kinase (ERK1/2) signaling in cerebellar granule neurons and in the NSC34 spinal cord motoneuron cell line, in a phosphoinositide 3-kinae and MEK-dependent fashion. Importantly, lipopeptide inhibitors of PAR1 or PAR2, and PAR1 genetic deletion, each reduced Klk6-ERK1/2 activation. In addition, Klk6 and thrombin promoted degeneration of cerebellar neurons and exacerbated glutamate neurotoxicity. Moreover, genetic deletion of PAR1 blocked thrombin-mediated cerebellar neurotoxicity and reduced the neurotoxic effects of Klk6. Klk6 also increased glutamate-mediated Bim signaling, poly-ADP-ribose polymerase cleavage and lactate dehydrogenase release in NSC34 motoneurons and these effects were blocked by PAR1 and PAR2 lipopeptide inhibitors. Taken together, these data point to a novel Klk6-signaling axis in CNS neurons that is mediated by PAR1 and PAR2 and is positioned to contribute to neurodegeneration.

Protective and therapeutic potency of N-acetyl-cysteine on propionic acid-induced biochemical autistic features in rats

BACKGROUND

The investigation of the environmental contribution for developmental neurotoxicity is very critical. Many environmental chemical exposures are now thought to contribute to the development of neurological disorders, especially in children. Results from animal studies may guide investigations of human populations towards identifying either environmental toxicants that cause or drugs that protect from neurotoxicity and may help in treatment of neurodevelopmental disorders.

OBJECTIVE

To study both the protective and therapeutic effects of N-acetyl cysteine on brain intoxication induced by propionic acid (PPA) in rats.

METHODS

Twenty-eight young male Western Albino rats were enrolled in the present study. They were grouped into four equal groups, each of 7 animals. Group 1: control group, orally received only phosphate buffered saline; Group 2: PPA-treated group, received a neurotoxic dose of of PPA of 250 mg/kg body weight/day for 3 days; Group 3: protective group, received a dose of 50 mg/kg body weight/day N-acetyl-cysteine for one week followed by a similar dose of PPA for 3 days; and Group 4: therapeutic group, treated with the same dose of N-acetyl cysteine after being treated with the toxic dose of PPA. Serotonin, interferon gamma (IFN-γ), and glutathione-s-transferase activity, together with Comet DNA were assayed in the brain tissue of rats in all different groups.

RESULTS

The obtained data showed that PPA caused multiple signs of brain toxicity as measured by depletion of serotonin (5HT), increase in IFN-γ and inhibition of glutathione-s-transferase activity as three biomarkers of brain dysfunction. Additionally Comet DNA assay showed remarkably higher tail length, tail DNA % damage and tail moment. N-acetyl-cysteine was effective in counteracting the neurotoxic effects of PPA.

CONCLUSIONS

The low dose and the short duration of N-acetyl-cysteine treatment tested in the present study showed much more protective rather than therapeutic effects on PPA-induced neurotoxicity in rats, as there was a remarkable amelioration in the impaired biochemical parameters representing neurochemical, inflammatory, detoxification and DNA damage processes.

Glutamatergic modulation of auditory information processing in the human brain

BACKGROUND

Auditory mismatch negativity (MMN) and P300 event-related potentials (ERPs) are reduced in schizophrenia patients and healthy volunteers administered the N-methyl-D-aspartate glutamate receptor antagonist, ketamine. In rodents, N-acetylcysteine (NAC), a stimulator of the cystine-glutamate exchanger, attenuates the cognitive and behavioral effects of N-methyl-D-aspartate receptor antagonists. On the basis of these findings, we tested whether NAC would reduce ketamine effects on behavior, MMN, and P300 in healthy humans.

METHODS

This randomized, double-blind, placebo-controlled study consisted of 2 test days during which subjects (n = 16) were administered oral NAC (3000 mg in divided doses) or matching placebo 165 min before the infusion of saline and then ketamine (as a bolus of .23 mg/kg over 1 min followed by .58 mg/kg for 30 min, and then .29 mg/kg for 40 min) in a fixed order. Behavioral and ERP data including auditory MMN and P300 were collected during each test day.

RESULTS

Ketamine produced psychotic-like positive symptoms, reductions in working memory and sustained attention performance, and amplitude reductions for the frequency- and intensity-deviant MMNs and P300. NAC pretreatment did not reduce the behavioral or ERP effects of ketamine. In addition, NAC reduced frequency-deviant MMN amplitude and increased target and novelty P3 amplitudes. The decrements in frequency-deviant MMN amplitude produced by ketamine and NAC were not additive.

CONCLUSIONS

NAC did not attenuate the effects of ketamine in humans, in contrast to previous studies in animals. NAC merits further investigation as a cognitive enhancing agent due to its ability to increase the P300 amplitude.

N-acetylcysteine in psychiatry: current therapeutic evidence and potential mechanisms of action

There is an expanding field of research investigating the benefits of alternatives to current pharmacological therapies in psychiatry. N-acetylcysteine (NAC) is emerging as a useful agent in the treatment of psychiatric disorders. Like many therapies, the clinical origins of NAC are far removed from its current use in psychiatry. Whereas the mechanisms of NAC are only beginning to be understood, it is likely that NAC is exerting benefits beyond being a precursor to the antioxidant, glutathione, modulating glutamatergic, neurotropic and inflammatory pathways. This review outlines the current literature regarding the use of NAC in disorders including addiction, compulsive and grooming disorders, schizophrenia and bipolar disorder. N-acetylcysteine has shown promising results in populations with these disorders, including those in whom treatment efficacy has previously been limited. The therapeutic potential of this acetylated amino acid is beginning to emerge in the field of psychiatric research.

Prolonged activation of ERK triggers glutamate-induced apoptosis of astrocytes: neuroprotective effect of FK506

Although, astrocytes are more resistant than neurons to ischemic injury, astrocyte death has been demonstrated in animal models of brain ischemia. Astrocytes death after ischemia/reperfusion may strongly affect neuronal survival because of the absence of their trophic and metabolic support to neurons, and astrocytic glutamate uptake. Early signals involved in astrocytes death are poorly understood. We demonstrated enhanced and mostly cytoplasmic activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) during glutamate-induced apoptosis of cultured astrocytes. Treatment with UO126, inhibitor of MEK1, threo-beta-benzyloxyaspartic acid, glutamate transporter inhibitor, and FK506, a cytoprotective drug prevented ERK activation and glutamate-induced apoptosis. Over-expression of ERK dual specificity phosphatases 5 and 6 reduced apoptosis in transfected astrocytes. Prolonged ERK1/2 activation was observed in ischemic brain: in the nucleus and cytoplasm of astrocytes in the cerebral cortex, and exclusively in the cytoplasm of astrocytes in the striatum. Global gene expression profiling in the cortex revealed that FK506 blocks middle cerebral artery occlusion-induced expression of numerous genes associated with ERK signaling pathway and apoptosis. The results demonstrate a pro-apoptotic role of sustained activation of ERK1/2 signaling in glutamate-induced death of astrocytes and the ability of FK506 to block both ERK activation and astrocytic cell death in vitro and in ischemic brains.

The acute effects of NMDA antagonism: from the rodent to the human brain

In the past decade, the N-methyl-d-aspartate receptor (NMDAR) hypofunction hypothesis of schizophrenia has received support from several lines of clinical evidence, including genetic, postmortem and human psychosis modeling. Recently, superiority of a mGluR2/3 receptor agonist over placebo was demonstrated in a randomized double-blind clinical trial in patients with schizophrenia. Considering the fact that currently available antipsychotics are all dopamine blockers to varying degrees without direct effects on glutamate transmission, this clinical trial highlights the potential utility of glutamatergic agents. In healthy volunteers, the NMDA channel antagonist ketamine induces transient cognitive dysfunction, perceptual aberrations and changes reminiscent of the negative symptoms of schizophrenia. However, how ketamine produces these effects is unclear. Preclinical data on NMDAR hypofunction offer further insights into the pathogenesis of the disorder as it relates to disorganized behavior, stereotypic movements and cognitive dysfunction in the rodent. This review evaluates the existing clinical and preclinical literature in an effort to shed light on the mechanism of action of ketamine as a probe to model NMDAR hypofunction in healthy volunteers. Included in this perspective are direct and indirect effects of ketamine at the neuronal level and in the intact brain. In addition to ketamine's effects on presynaptic and postsynaptic function, effects on glia and other neurotransmitter systems are discussed. While increased extracellular glutamate levels following NMDA antagonist administration stand out as a well replicated finding, evidence suggests that ketamine's effects are not restricted to pyramidal cells, but extend to GABAergic interneurons and the glia. In the glia, ketamine has significant downstream effects on the glutathione metabolism. Further studies are needed to identify the mechanistic connections between ketamine's effects at the cellular and behavioral levels.

NR1 and GluR2 expression mediates excitotoxicity in chronic hypobaric hypoxia

Hypobaric hypoxia has been reported to cause memory dysfunction. The possible molecular mechanism involved, however, remains to be explored. The role that glutamate and its receptors play in causing excitotoxicity in ischemia and neurodegenerative diseases indicates the possible occurrence of a similar phenomenon in hypobaric hypoxia. The present study aimed to elucidate the molecular events occurring at glutamatergic synapses in hypobaric hypoxia using Sprague-Dawley rats as a model system. The animals were exposed to an altitude of 7,600 m for different durations. Hypobaric hypoxia was found to cause oxidative stress, chromatin condensation, and neurodegeneration. A temporal change in the expression of the ionotropic receptors of glutamate was also observed. Expression of the N-methyl-D-aspartate (NMDA) receptor increased, and expression of glutamate receptor subunit 2 of the alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate receptor decreased. We also observed increased activity of glutamate dehydrogenase, indicating greater synthesis and release of glutamate after 3 and 7 days of exposure. Administration of a selective NMDA antagonist during exposure was found to ameliorate neuronal degeneration, providing evidence for the occurrence of excitotoxicity in hypobaric hypoxia. Our study indicates that excitotoxicity occurs in hypobaric hypoxia. This study also indicates the appropriate period for drug administration during exposure to hypobaric hypoxia and establishes ionotropic receptors of glutamate as potential therapeutic targets for ameliorating high-altitude-induced cognitive dysfunction.

NAC for noise: from the bench top to the clinic

Noise-induced hearing loss (NIHL) is an important etiology of deafness worldwide. Hearing conservation programs are in place and have reduced the prevalence of NIHL, but this disorder is still far too common. Occupational and recreational pursuits expose people to loud noise and ten million persons in the US have some degree of noise-induced hearing impairment. It is estimated that 50 million in the US and 600 million people worldwide are exposed to noise hazards occupationally. Noise deafness is still an important and frequent cause of battlefield injury in the US military. A mainstay of hearing conservation programs is personal mechanical hearing protection devices which are helpful but have inherent limitations. Research has shown that oxidative stress plays an important role in noise-induced cochlear injury resulting in the discovery that a number of antioxidant and cell death inhibiting compounds can ameliorate deafness associated with acoustic trauma. This article reviews one such compound, N-acetylcysteine (NAC), in terms of its efficacy in reducing hearing loss in a variety of animal models of acute acoustic trauma and hypothesizes what its therapeutic mechanisms of action might be based on the known actions of NAC. Early clinical trials with NAC are mentioned.

Mobile phone emissions and human brain excitability

OBJECTIVE

To test-via Transcranial Magnetic Stimulation (TMS)-the excitability of each brain hemisphere after 'real' or 'sham' exposure to the electromagnetic field (EMF) generated by a mobile phone operating in the Global System for Mobile Communication (GSM).

METHODS

Fifteen male volunteers attended two experimental sessions, one week apart, in a cross-over, double-blind paradigm. In one session the signal was turned ON (EMF-on, real exposure), in the other it was turned OFF (EMF-off, sham exposure), for 45 minutes. Motor Evoked Potentials (MEPs) were recorded using a paired-pulse paradigm (testing intracortical excitability with 1 to 17 ms interstimulus intervals), both before and at different times after exposure to the EMF. Short Intracortical Inhibition (SICI) and Facilitation (ICF) curves were evaluated both on the exposed and non-exposed hemispheres. Tympanic temperature was collected during each session.

RESULTS

The intracortical excitability curve becomes significantly modified during real exposure, with SICI being reduced and ICF enhanced in the acutely exposed brain hemisphere as compared to the contralateral, non-exposed hemisphere or to sham exposure. Tympanic temperature showed no significant main effect or interactions.

INTERPRETATION

These results demonstrate that GSM-EMFs modify brain excitability. Possible implications and applications are discussed.

A sublethal dose of TNFalpha potentiates kainate-induced excitotoxicity in optic nerve oligodendrocytes

Glutamate receptor-induced cell death, known as excitotoxicity in both neurons and oligodendrocytes, has been implicated as a common pathway of cell death in numerous central nervous system (CNS) diseases and trauma. Research in both neuronal and oligodendrocyte excitotoxicity has examined glutamate's receptor-mediated effects on CNS cells, and explored strategies to protect cells exposed to the elevated glutamate levels that occur in CNS trauma and disease. Proinflammatory cytokines are also elevated in the injured CNS, and have also been implicated in CNS cell death. Recently, several laboratories have examined cytokines' effects on neuronal and glial excitotoxicity. Here, we review literature concerning the dynamic susceptibility of both neurons and oligodendrocytes to excitotoxicity, and present new data from our laboratory showing that the susceptibility of oligodendrocytes to excitotoxicity is acutely potentiated by the proinflammatory cytokine TNFalpha.

Antioxidant and antiinflammatory activities of xanthorrhizol in hippocampal neurons and primary cultured microglia

Xanthorrhizol, a natural sesquiterpenoid isolated from the rhizome of Curcuma xanthorrhiza Roxb (Zingiberaceae), has antibacterial activities and protective effects against cisplatin-induced hepatotoxicity. In this study, we investigated the activities of xanthorrhizol as an antioxidant or antiinflammatory agent using neuronal and microglial cells. Xanthorrhizol had potent neuroprotective effects on glutamate-induced neurotoxicity and reactive oxygen species (ROS) generation in the murine hippocampal HT22 cell line. Also, xanthorrhizol inhibited H(2)O(2)-induced lipid peroxidation in rat brain homogenates. The properties of xanthorrhizol as an antiinflammatory agent were investigated in microglial activation by lipopolysaccharide. It reduced the expression of cyclooxygenase-2 and the inducible nitric oxide synthase, which consequently resulted in the reduction of nitric oxide. The production of proinflammatory cytokines, such as interleukin-6 and tumor necrosis factor-alpha in activated microglial cells, was reduced by xanthorrhizol. These results suggest that xanthorrhizol could be an effective candidate for the treatment of Alzheimer's disease- and other neurological disease-related ROS and inflammation.

Neuronal glutathione deficiency and age-dependent neurodegeneration in the EAAC1 deficient mouse

Uptake of the neurotransmitter glutamate is effected primarily by transporters expressed on astrocytes, and downregulation of these transporters leads to seizures and neuronal death. Neurons also express a glutamate transporter, termed excitatory amino acid carrier-1 (EAAC1), but the physiological function of this transporter remains uncertain. Here we report that genetically EAAC1-null (Slc1a1(-/-)) mice have reduced neuronal glutathione levels and, with aging, develop brain atrophy and behavioral changes. EAAC1 can also rapidly transport cysteine, an obligate precursor for neuronal glutathione synthesis. Neurons in the hippocampal slices of EAAC1(-/-) mice were found to have reduced glutathione content, increased oxidant levels and increased susceptibility to oxidant injury. These changes were reversed by treating the EAAC1(-/-) mice with N-acetylcysteine, a membrane-permeable cysteine precursor. These findings suggest that EAAC1 is the primary route for neuronal cysteine uptake and that EAAC1 deficiency thereby leads to impaired neuronal glutathione metabolism, oxidative stress and age-dependent neurodegeneration.

Differential effects of the substrate inhibitor l-trans-pyrrolidine-2,4-dicarboxylate (PDC) and the non-substrate inhibitor DL-threo-beta-benzyloxyaspartate (DL-TBOA) of glutamate transporters on neuronal damage and extracellular amino acid levels in rat brain in vivo

The extracellular concentration of glutamate is highly regulated by transporter proteins, due to its neurotoxic properties. Dysfunction or reverse activation of these transporters is related to the extracellular accumulation of excitatory amino acids and neuronal damage associated with ischemia and hypoglycemia. We have investigated by microdialysis the effects of the substrate and the non-substrate inhibitors of glutamate transporters, l-trans-2,4-pyrrolidine dicarboxylate (PDC) and DL-threo-beta-benzyloxyaspartate (DL-TBOA), respectively, on the extracellular levels of amino acids in the rat hippocampus in vivo. In addition, we have studied the effect of both inhibitors on neuronal damage after direct administration into the hippocampus and striatum. Electroencephalographic activity was recorded after the intrahippocampal infusion of DL-TBOA or PDC. Microdialysis administration of 500 microM DL-TBOA into the hippocampus increased 3.4- and nine-fold the extracellular levels of aspartate and glutamate, respectively. Upon stereotaxic administration it induced neuronal damage dose-dependently in CA1 and dentate gyrus, and convulsive behavior. Electroencephalographic recording showed the appearance of limbic seizures in the hippocampus after DL-TBOA infusion. In the striatum it also induced dose-dependent neuronal damage. These effects were prevented by the i.p. administration of the glutamate receptor antagonists (+)-5-methyl-10,11-dihydroxy-5H-dibenzo(a,d)cyclohepten-5,10-iminemaleate and 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)-quinoxaline. In contrast to dl-TBOA, PDC (500 microM) induced a more discrete elevation of excitatory amino acids levels (2.6- and three-fold in aspartate and glutamate, respectively), no neuronal damage or behavioral changes, and no alterations in electroencephalographic activity. The differential results obtained with DL-TBOA and PDC might be attributed to their distinct effects on the extracellular concentration of amino acids. Results are relevant to the understanding of the role of glutamate transporters in amino acid removal or release and the induction of excitotoxic cell death.

Modification of epileptiform discharges in neocortical neurons following glutamate uptake inhibition

Sodium-dependent high-affinity glutamate transporters regulate synaptic glutamate levels to maintain low ambient levels of glutamate and prevent excitotoxicity. Most studies using pharmacological inhibition of glutamate transport to examine the involvement of glutamate transporters in regulating synaptic activity have examined small synaptic currents. Using in vitro brain slices, we investigated the effects of uptake inhibition on two types of epileptiform activity, bicuculline-induced paroxysmal activity, and epileptiform responses in the freeze-lesion epilepsy model. In layer II/III pyramidal cells of the prefrontal cortex, inhibiting uptake with low concentrations of DL-threo-ss-benzyloxyaspartic acid (TBOA) (20 or 30 microM) prolonged bicuculline-induced epileptiform activity. At higher concentrations, TBOA (150 or 300 microM) caused a transient enhancement of epileptiform discharges that was followed by a decrease. In the freeze-lesion model, inhibiting uptake also increased the amplitude and response area of evoked activity. The prolongation of epileptiform activity exhibited by the inhibition of glutamate uptake (TBOA 20 or 30 microM) is attributed to an increase in the level of glutamate extracellularly during uptake blockade, resulting in sustained activation of glutamate receptors. The decrease in epileptiform activity at higher TBOA concentration could be due to glutamate receptor desensitization or loss of excitability due to a depolarization block. The present results suggest that decreases in glutamate uptake can be proconvulsant in the two models of epilepsy examined.

Anti-oxidant and anti-inflammatory activities of macelignan in murine hippocampal cell line and primary culture of rat microglial cells

Epidemiological studies suggest that the treatments of anti-inflammatory agents and anti-oxidants slow the progress of neurological diseases. Lignans are anti-oxidants and phytoestrogens found in a variety of plants. In this study, we investigated the neuroprotective effect of macelignan on glutamate-induced neurotoxicity and reactive oxygen species (ROS) in murine hippocampal HT22 cell line. Macelignan significantly attenuated the ROS production and neurotoxicity induced by glutamate in HT22 cell. Also, the properties of macelignan as an anti-inflammatory agent were investigated in microglials activation by lipopolysaccharide (LPS). It potently suppressed the expression of cyclooxygenase-2 and inducible nitric oxide synthase, that consequently resulted in the reduction of nitric oxide in LPS-treated microglial cells. It also significantly suppressed the production of pro-inflammatory cytokine tumor necrosis factor-alpha and interleukin-6. These results suggest that macelignan possesses therapeutic potentials against neurodegenerative diseases with oxidative stress and neuroinflammation.

Gliotoxicity in hippocampal cultures is induced by transportable, but not by nontransportable, glutamate uptake inhibitors

Extracellular glutamate is kept below a toxic level by glial and neuronal glutamate transporters. Here we show that the transportable glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylate (t-PDC) induced cell death in mature, but not in immature, hippocampal neuron-enriched cultures. The cell death produced by a 24-hr treatment with t-PDC was dose-dependent and reached 85% of the cell population at a 250 microM concentration at 23 days in vitro (DIV). Immunocytochemistry experiments showed that, under these experimental conditions, t-PDC killed not only neurons as expected but also glial cells. The N-methyl-D-aspartate (NMDA) antagonist D-2-aminophosphonovalerate (D-APV; 250 microM) only partially reversed this toxicity, completely protecting the neuronal cell population but not the glial population. The antioxidant compounds alpha-tocopherol or Trolox, used at concentrations that reverse the oxidative stress-induced toxicity, did not block the gliotoxicity specifically produced by t-PDC in the presence of D-APV. The nontransportable glutamate uptake inhibitor DL-threo-beta-benzyloxyaspartate (TBOA) elicited cell death only in mature, but not in immature, hippocampal cultures. The TBOA toxic effect was dose dependent and reached a plateau at 100 microM in 23-DIV cultures. About 50% of the cell population died. TBOA affected essentially the neuronal population. D-APV (250 microM) completely reversed this toxicity. It is concluded that nontransportable glutamate uptake inhibitors are neurotoxic via overactivation of NMDA receptors, whereas transportable glutamate uptake inhibitors induce both an NMDA-dependent neurotoxicity and an NMDA- and oxidative stress-independent gliotoxicity, but only in mature hippocampal cultures.

Antioxidants are required during the early critical period, but not later, for neuronal survival

Methods for growing primary neuronal cultures rely on the inclusion of antioxidants in the culture medium, but no studies have determined precisely if or when antioxidants are required for neuronal survival, despite the significance this information would have for understanding neurodevelopment and studying oxidative stress. We show that cortical neurons grown in Neurobasal media with B27 supplement required antioxidants for only the first 24 hr post-explantation, after which the antioxidants could be removed permanently without noticeable loss of neuronal survival over the normal lifespan. Cortical cultures never exposed to antioxidants did not survive. These findings represent a novel method for substantially antioxidant-free neuronal culture, whereby antioxidants can be removed permanently from the cultures after only 1 day. This method may prove critical for studies of oxidative stress, because B27 antioxidants significantly diminished pro-oxidative effects of the excitatory neurotransmitter glutamate and hydrogen peroxide on cortical cultures, even if antioxidants were removed before the oxidizing treatment. Together, these findings suggest a brief window of high vulnerability to reactive oxygen species, and have important implications for studies of oxidative stress and developmental neuroscience.

Glutamate uptake inhibitor L-trans-pyrrolidine 2,4-dicarboxylate becomes neurotoxic in the presence of subthreshold concentrations of mitochondrial toxin 3-nitropropionate: involvement of mitochondrial reducing activity and ATP production

An increased concentration of extracellular glutamate is associated with neuronal damage induced by cerebral ischemia. We have demonstrated previously that exposure of cultured cerebellar granule neurons to L-trans-pyrrolidine-2,4-dicarboxylate (PDC), a glutamate uptake inhibitor, increases extracellular glutamate levels but does not induce neuronal damage. Coincubation of PDC, however, with a subthreshold concentration of the mitochondrial toxin, 3-nitropropionic acid (3-NP), results in severe damage to these neurons. We have investigated the time course of changes in mitochondrial reducing capacity and ATP levels in cerebellar granule cells after simultaneous exposure to 3-NP and PDC, and its relation to cell viability and nuclear condensation. Although individually, 3-NP and PDC treatments are not harmful to neurons, the simultaneous exposure to both compounds results in a progressive decline in mitochondrial reducing capacity during the first 4 hr, and a rapid decrease in ATP levels. At 4 hr, cells lose plasma membrane integrity and show condensed nuclei. In the presence of the energy substrates pyruvate and acetoacetate, the N-methyl-D-apartate (NMDA) receptor antagonist, MK-801, and the spin trapper alpha-phenyl-N-tert-butylnitrone (PBN), the decline in mitochondrial activity and ATP levels is prevented, the number of condensed nuclei is reduced, and plasma membrane integrity is preserved. In contrast, the broad-spectrum caspase inhibitor Z-Asp-DCB (Z-Asp-CH2-DCB) prevents nuclear condensation but has no effect on mitochondrial reducing capacity or cell survival. Our results show that glutamate uptake impairment rapidly induces neuronal death during inhibition of succinate dehydrogenase by a mechanism involving mitochondrial dysfunction that, if not prevented, leads to cell death.