Redox mechanisms at the glutamate synapse and their significance: a review

[Hypoxic-ischemic brain damage in premature newborns]

One of the main causes of cerebral dysfunction in premature newborns is hypoxia. High mortality and lifelong morbidity in these children is a frequent result of neonatal hypoxic brain damage. The article presents some data on the prevalence of neurological diseases that have arisen in the perinatal period, and highlights the key etiological factors leading to hypoxia in both the intranatal and early postnatal periods. The pathogenesis of hypoxic-ischemic brain lesions in premature infants is described in detail. At the same time, more careful consideration is given to the glutathione system, which protects against lipid peroxidation, the glutamate-calcium cascade, and the excitotoxicity mediated by it, as well as the processes of necrosis and apoptosis of nerve cells. The advantages and disadvantages of modern methods for diagnosing cerebral lesions are noted, and the principles of treatment of these disorders are analyzed.

Hydrogen peroxide inhibits neurons in the paraventricular nucleus of the hypothalamus via potassium channel activation

The paraventricular nucleus (PVN) of the hypothalamus is an important homeostatic and reflex center for neuroendocrine, respiratory, and autonomic regulation, including during hypoxic stressor challenges. Such challenges increase reactive oxygen species (ROS) to modulate synaptic, neuronal, and ion channel activity. Previously, in the nucleus tractus solitarius, another cardiorespiratory nucleus, we showed that the ROS H₂O₂ induced membrane hyperpolarization and reduced action potential discharge via increased K⁺ conductance at the resting potential. Here, we sought to determine the homogeneity of influence and mechanism of action of H₂O₂ on PVN neurons. We recorded PVN neurons in isolation and in an acute slice preparation, which leaves neurons in their semi-intact network. Regardless of preparation, H₂O₂ hyperpolarized PVN neurons and decreased action potential discharge. In the slice preparation, H₂O₂ also decreased spontaneous excitatory postsynaptic current frequency, but not amplitude. To examine potential mechanisms, we investigated the influence of the K⁺ channel blockers Ba²⁺, Cs⁺, and glibenclamide on membrane potential, as well as the ionic currents active at resting potential and outward K⁺ currents (I_K) upon depolarization. The H₂O₂ hyperpolarization was blocked by K⁺ channel blockers. H₂O₂ did not alter currents between -50 and -110 mV. However, H₂O₂ induced an outward I_K at -50 mV yet, at potentials more positive to 0 mV H₂O₂, decreased I_K. Elevated intracellular antioxidant catalase eliminated H₂O₂ effects. These data indicate that H₂O₂ alters synaptic and neuronal properties of PVN neurons likely via membrane hyperpolarization and alteration of I_K, which may ultimately alter cardiorespiratory reflexes.

Reactive Oxygen Species: Physiological and Physiopathological Effects on Synaptic Plasticity

In the mammalian central nervous system, reactive oxygen species (ROS) generation is counterbalanced by antioxidant defenses. When large amounts of ROS accumulate, antioxidant mechanisms become overwhelmed and oxidative cellular stress may occur. Therefore, ROS are typically characterized as toxic molecules, oxidizing membrane lipids, changing the conformation of proteins, damaging nucleic acids, and causing deficits in synaptic plasticity. High ROS concentrations are associated with a decline in cognitive functions, as observed in some neurodegenerative disorders and age-dependent decay of neuroplasticity. Nevertheless, controlled ROS production provides the optimal redox state for the activation of transductional pathways involved in synaptic changes. Since ROS may regulate neuronal activity and elicit negative effects at the same time, the distinction between beneficial and deleterious consequences is unclear. In this regard, this review assesses current research and describes the main sources of ROS in neurons, specifying their involvement in synaptic plasticity and distinguishing between physiological and pathological processes implicated.

A new method for identifying causal genes of schizophrenia and anti-tuberculosis drug-induced hepatotoxicity

Schizophrenia (SCZ) may cause tuberculosis, the treatments for which can induce anti-tuberculosis drug-induced hepatotoxicity (ATDH) and SCZ-like disorders. To date, the causal genes of both SCZ and ATDH are unknown. To identify them, we proposed a new network-based method by integrating network random walk with restart algorithm, gene set enrichment analysis, and hypergeometric test; using this method, we identified 500 common causal genes. For gene validation, we created a regularly updated online database ATDH-SCZgenes and conducted a systematic meta-analysis of the association of each gene with either disease. Till now, only GSTM1 and GSTT1 have been well studied with respect to both diseases; and a total of 23 high-quality association studies were collected for the current meta-analysis validation. Finally, the GSTM1 present genotype was confirmed to be significantly associated with both ATDH [Odds Ratio (OR): 0.71, 95% confidence interval (CI): 0.56–0.90, P = 0.005] and SCZ (OR: 0.78, 95% CI: 0.66–0.92, P = 0.004) according to the random-effect model. Furthermore, these significant results were supported by “moderate” evidence according to the Venice criteria. Our findings indicate that GSTM1 may be a causal gene of both ATDH and SCZ, although further validation pertaining to other genes, such as CYP2E1 or DRD2, is necessary.

Effects of glutamate positive modulators on cognitive deficits in schizophrenia: a systematic review and meta-analysis of double-blind randomized controlled trials

Hypofunction of N-methyl-d-aspartate (NMDA) receptors has been proposed to have an important role in the cognitive impairments observed in schizophrenia. Although glutamate modulators may be effective in reversing such difficult-to-treat conditions, the results of individual studies thus far have been inconsistent. We conducted a systematic review and meta-analysis to examine whether glutamate positive modulators have beneficial effects on cognitive functions in patients with schizophrenia. A literature search was conducted to identify double-blind randomized placebo-controlled trials in schizophrenia or related disorders, using Embase, Medline, and PsycINFO (last search: February 2015). The effects of glutamate positive modulators on cognitive deficits were evaluated for overall cognitive function and eight cognitive domains by calculating standardized mean differences (SMDs) between active drugs and placebo added to antipsychotics. Seventeen studies (N=1391) were included. Glutamate positive modulators were not superior to placebo in terms of overall cognitive function (SMD=0.08, 95% confidence interval=-0.06 to 0.23) (11 studies, n=858) nor each of eight cognitive domains (SMDs=-0.03 to 0.11) (n=367-940) in this population. Subgroup analyses by diagnosis (schizophrenia only studies), concomitant antipsychotics, or pathway of drugs to enhance the glutamatergic neurotransmission (glycine allosteric site of NMDA receptors or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors) suggested no procognitive effect of glutamate positive modulators. Further, no effect was found in individual compounds on cognition. In conclusion, glutamate positive modulators may not be effective in reversing overall cognitive impairments in patients with schizophrenia as adjunctive therapies.

Meta-Analysis-Based Preliminary Exploration of the Connection between ATDILI and Schizophrenia by GSTM1/T1 Gene Polymorphisms

Anti-tuberculosis drugs have some adverse effects such as anti-tuberculosis drug-induced liver injury (ATDILI) and mental disorders. The involvement of glutathione S-transferase (GST) genes in pathogenesis of ATDILI or schizophrenia (SCZ) has been reported. Therefore, GST genes may exemplify molecular connectors between ATDILI and SCZ. However, association studies of GSTM1/T1 polymorphisms with these two diseases have yielded conflicting results. After searching case-control association studies in PubMed, ISI Web of Science, EMBASE, Chinese National Knowledge Infrastructure (CNKI), and Chinese BioMedical Literature Database, we performed meta-analyses across a total of 20 published association studies on 3146 subjects for the association of GSTM1 and ATDILI, 2587 for the GSTT1-ATDILI association, 2283 for GSTM1-SCZ and 1116 for GSTT1-SCZ to test the associations of GSTM1/T1 polymorphisms with ATDILI and SCZ. The GSTM1 present genotype was significantly associated with decreased risks of ATDILI (risk ratio(RR): 0.81, 95% confidence interval (CI): 0.75-0.88, P < 0.0001) and SCZ (RR: 0.88, 95%CI: 0.80-0.96, P = 0.004) according to the fixed-effect model, while the GSTT1 present genotype was significantly associated only with a high risk of SCZ (RR: 1.17, 95%CI: 1.04-1.32, P = 0.01) according to both the random- and fixed-effect models, but not with ATDILI (P = 0.82) according to the fixed-effect model. Moreover, these significant results were supported with moderate evidence according to the Venice criteria. These results indicate that GSTM1 represents a genetic connection between ATDILI and SCZ, and suggest that ATDILI and SCZ may be co-occurring for the subjects with GSTM1 null genotype.

Why are neurotransmitters neurotoxic? An evolutionary perspective

In the CNS, minor changes in the concentration of neurotransmitters such as glutamate or dopamine can lead to neurodegenerative diseases. We present an evolutionary perspective on the function of neurotransmitter toxicity in the CNS. We hypothesize that neurotransmitters are selected because of their toxicity, which serves as a test of neuron quality and facilitates the selection of neuronal pathways. This perspective may offer additional explanations for the reduction of neurotransmitter concentration in the CNS with age, and suggest an additional role for the blood-brain barrier. It may also suggest a connection between the specific toxicity of the neurotransmitters released in a specific region of the CNS, and elucidate their role as chemicals that are optimal for testing the quality of cells in that region.

N-Acetyl cysteine reverses social isolation rearing induced changes in cortico-striatal monoamines in rats

Schizophrenia is causally associated with early-life environmental stress, implicating oxidative stress in its pathophysiology. N-acetyl cysteine (NAC), a glutathione precursor and antioxidant, is emerging as a useful agent in the adjunctive treatment of schizophrenia and other psychiatric illnesses. However, its actions on brain monoamine metabolism are unknown. Social isolation rearing (SIR) in rats presents with face, predictive and construct validity for schizophrenia. This study evaluated the dose-dependent effects of NAC (50, 150 and 250 mg/kg/day × 14 days) on SIR- vs. socially reared induced changes in cortico-striatal levels of dopamine (DA), serotonin (5-HT) noradrenaline (NA) and their associated metabolites. SIR induced significant deficits in frontal cortical DA and its metabolites, 3,4-dihydroxyphenylacetic acid (Dopac) and homovanillic acid (HVA), reduced 5-HT and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA), and reduced levels of the NA metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG). In addition, significant elevations in frontal cortical NA and striatal DA, Dopac, HVA, 5-HT, 5-HIAA, NA and MHPG were also observed in SIR rats. NAC at 150 and 250 mg/kg reversed all cortico-striatal DA, Dopac, HVA, 5-HT, 5-HIAA and striatal NA alterations in SIR animals, with 250 mg/kg of NAC also reversing alterations in cortico-striatal MHPG. In conclusion, SIR profoundly alters cortico-striatal DA, 5-HT and NA pathways that parallel observations in schizophrenia, while these changes are dose-dependently reversed or abrogated by sub-chronic NAC treatment. A modulatory action on cortico-striatal monoamines may explain NACs' therapeutic use in schizophrenia and possibly other psychiatric disorders, where redox dysfunction or oxidative stress is a causal factor.

A preliminary, randomized, double-blind, placebo-controlled trial of L-carnosine to improve cognition in schizophrenia

BACKGROUND

Targeting glutamatergic dysfunction provides an exciting opportunity to improve cognitive impairment in schizophrenia. One treatment approach has targeted inadequate antioxidant defenses at glutamatergic synapses. Animal and human data suggest NMDA antagonists worsen executive cognitive controls--e.g. increase perseverative responses and impair set-shifting. We conducted a preliminary study to test the hypothesis that L-carnosine, an antioxidant and anti-glycation agent which is co-localized and released with glutamate would improve executive dysfunction, a cognitive domain associated with glutamate.

METHODS

Seventy-five symptomatically stable adults with chronic schizophrenia were randomly assigned to L-carnosine as adjunctive treatment (2 g/day) or a matched placebo in a double-blind manner for 3 months. Cognitive domains (executive dysfunction, memory, attention and motor speed) were assessed using a computerized battery at baseline, 4 and 12 weeks, along with psychopathology ratings and safety parameters.

RESULTS

The L-carnosine group performed significantly faster on non-reversal condition trials of the set-shifting test compared with placebo but reversal reaction times and errors were not significantly different between treatments. On the strategic target detection test, the L-carnosine group displayed significantly improved strategic efficiency and made fewer perseverative errors compared with placebo. Other cognitive tests showed no significant differences between treatments. Psychopathology scores remained stable. The carnosine group reported more adverse events (30%) compared with the placebo group (14%). Laboratory indices remained within acceptable ranges.

CONCLUSIONS

These preliminary findings suggest that L-carnosine merits further consideration as adjunctive treatment to improve executive dysfunction in persons with schizophrenia.

Schizophrenia: redox regulation and volume neurotransmission

Here, we show that volume neurotransmission and the redox property of dopamine, as well as redox-regulated processes at glutamate receptors, can contribute significantly to our understanding of schizophrenia. Namely, volume neurotransmission may play a key role in the development of dysconnectivity between brain regions in schizophrenic patients, which can cause abnormal modulation of NMDA-dependent synaptic plasticity and produce local paroxysms in deafferented neural areas. During synaptic transmission, neuroredox regulations have fundamental functions, which involve the excellent antioxidant properties and nonsynaptic neurotransmission of dopamine. It is possible that the effect of redox-linked volume neurotransmission (diffusion) of dopamine is not as exact as communication by the classical synaptic mechanism, so approaching the study of complex schizophrenic mechanisms from this perspective may be beneficial. However, knowledge of redox signal processes, including the sources and molecular targets of reactive species, is essential for understanding the physiological and pathophysiological signal pathways in cells and the brain, as well as for pharmacological design of various types of new drugs.

Analysis of glutathione S-transferase genes polymorphisms and the risk of schizophrenia in a sample of Iranian population

Glutathione S-transferases (GSTs) are major intracellular antioxidants, which, impaired in their function, are involved in the progress of schizophrenia (SCZ). The aim of this case-control study was to investigate the association between the polymorphism of glutathione S-transferases M1 (GSTM1), T1 (GSTT1), the glutathione S-transferase P1 gene (GSTP1) and SCZ. We isolated genomic DNA from peripheral blood of 93 individuals with SCZ and 99 healthy control subjects' genotypes analyzing them for GSTM1, GSTT1 and GSTP1 using polymerase chain reaction. The analysis of the gene-gene interaction between GSTs indicated that the magnitude of the association was greater for the combined AG/GSTT1 & GSTM1 genotypes (OR = 2.51; 95% CI: 1.13-5.63, P = 0.02). The AG and combined AG + GG genotypes of GSTP1 increased the risk of SCZ (OR = 1.83; 95% CI: 0.94-3.75 and OR = 1.71; 95% CI: 0.92-3.19, respectively). The genotypes of GSTT/NULL, NULL/GSTM and NULL/NULL increased the risk of SCZ (OR = 2.05; 95% CI: 0.9-4.74; OR = 2.0; 95% CI: 1.68-2.31; and OR = 1.8; 95% CI: 0.57-2.46, respectively). The present study supports previous data that suggest that impairment in the function of GSTs genes may increase the risk of SCZ.

Isolation rearing-induced deficits in sensorimotor gating and social interaction in rats are related to cortico-striatal oxidative stress, and reversed by sub-chronic clozapine administration

Social isolation rearing (SIR) in rats induces behavioral and glutamatergic changes akin to schizophrenia. We studied the effects of 8 weeks SIR on cortico-striatal redox and social and cognitive behaviors in rats. SIR increased superoxide dismutase activity, decreased oxidized:reduced glutathione ratio and increased lipid peroxidation in both brain regions, and induced deficits in prepulse inhibition and social and self-directed interactive behaviors. Both behavioral and cortico-striatal redox disturbances were corrected by clozapine (5 mg/kg/day×11days). Behavioral changes evoked by SIR are associated with cortico-striatal oxidative stress that is reversed by clozapine treatment, providing novel insight into the neurobiology and treatment of schizophrenia.

Effects of atypical (risperidone) and typical (haloperidol) antipsychotic agents on astroglial functions

Although classical and atypical antipsychotics may have different neurotoxic effects, their underlying mechanisms remain to be elucidated, especially regarding neuroglial function. In the present study, we compared the atypical antipsychotic risperidone (0.01-10 μM) with the typical antipsychotic haloperidol (0.01-10 μM) regarding different aspects such as glutamate uptake, glutamine synthetase (GS) activity, glutathione (GSH) content, and intracellular reactive oxygen species (ROS) production in C6 astroglial cells. Risperidone significantly increased glutamate uptake (up to 27%), GS activity (14%), and GSH content (up to 17%). In contrast, haloperidol was not able to change any of these glial functions. However, at concentration of 10 μM, haloperidol increased (12%) ROS production. Our data contribute to the clarification of different hypothesis concerning the putative neural responses after stimulus with different antipsychotics, and may establish important insights about how brain rewiring could be enhanced.

Is our brain hardwired to produce God, or is our brain hardwired to perceive God? A systematic review on the role of the brain in mediating religious experience

To figure out whether the main empirical question "Is our brain hardwired to believe in and produce God, or is our brain hardwired to perceive and experience God?" is answered, this paper presents systematic critical review of the positions, arguments and controversies of each side of the neuroscientific-theological debate and puts forward an integral view where the human is seen as a psycho-somatic entity consisting of the multiple levels and dimensions of human existence (physical, biological, psychological, and spiritual reality), allowing consciousness/mind/spirit and brain/body/matter to be seen as different sides of the same phenomenon, neither reducible to each other. The emergence of a form of causation distinctive from physics where mental/conscious agency (a) is neither identical with nor reducible to brain processes and (b) does exert "downward" causal influence on brain plasticity and the various levels of brain functioning is discussed. This manuscript also discusses the role of cognitive processes in religious experience and outlines what can neuroscience offer for study of religious experience and what is the significance of this study for neuroscience, clinicians, theology and philosophy. A methodological shift from "explanation" to "description" of religious experience is suggested. This paper contributes to the ongoing discussion between theologians, cognitive psychologists and neuroscientists.

High-sensitive glutamate biosensor based on NADH at Lauth's violet/multiwalled carbon nanotubes composite film on gold substrates

A highly sensitive amperometric L-glutamate biosensor based on the electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide has been developed on Lauth's Violet (known as thionine)/multiwalled carbon nanotubes (Th-MWCNTs) composite film, which is used as a mediator and an enzyme immobilization matrix. The glutamate biosensor, which is fabricated by immobilizing glutamate dehydrogenase (GLDH) on the surface of Th-MWCNTs, displayed a precipitous response (ca. 3 s), a low detection limit (15.9 nM), a wide linear dynamic range (0.1 to 500 microM), and high sensitivity of 281.6 microAmM(-1) cm(-2), higher biological affinity, as well as good stability and repeatability. Interferences from other biological compounds were also studied for the fabricated sensor. The Th-MWCNTs system exemplifies a simple and efficient approach to the assimilation of GLDH and electrodes, which can provide analytical access to a large group of enzymes for wide range of bioelectrochemical applications in health care fields.

Antipsychotic drugs: comparison in animal models of efficacy, neurotransmitter regulation, and neuroprotection

Various lines of evidence indicate the presence of progressive pathophysiological processes occurring within the brains of patients with schizophrenia. By modulating chemical neurotransmission, antipsychotic drugs may influence a variety of functions regulating neuronal resilience and viability and have the potential for neuroprotection. This article reviews the current literature describing preclinical and clinical studies that evaluate the efficacy of antipsychotic drugs, their mechanism of action and the potential of first- and second-generation antipsychotic drugs to exert effects on cellular processes that may be neuroprotective in schizophrenia. The evidence to date suggests that although all antipsychotic drugs have the ability to reduce psychotic symptoms via D(2) receptor antagonism, some antipsychotics may differ in other pharmacological properties and their capacities to mitigate and possibly reverse cellular processes that may underlie the pathophysiology of schizophrenia.

Low potential detection of glutamate based on the electrocatalytic oxidation of NADH at thionine/single-walled carbon nanotubes composite modified electrode

A glutamate biosensor based on the electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH), which was generated by the enzymatic reaction, was developed via employing a single-walled carbon nanotubes/thionine (Th-SWNTs) nanocomposite as a mediator and an enzyme immobilization matrix. The biosensor, which was fabricated by immobilizing glutamate dehydrogenase (GlDH) on the surface of Th-SWNTs, exhibited a rapid response (ca. 5s), a low detection limit (0.1 microM), a wide and useful linear range (0.5-400 microM), high sensitivity (137.3+/-15.7) microA mM(-1)cm(-2), higher biological affinity, as well as good stability and repeatability. In addition, the common interfering species, such as ascorbic acid, uric acid, and 4-acetamidophenol, did not cause any interference due to the use of a low operating potential (190 mV vs. NHE). The biosensor can be used to quantify the concentration of glutamate in the physiological level. The Th-SWNTs system represents a simple and effective approach to the integration of dehydrogenase and electrodes, which can provide analytical access to a large group of enzymes for wide range of bioelectrochemical applications including biosensors and biofuel cells.

Involvement of striatal lipid peroxidation and inhibition of calcium influx into brain slices in neurobehavioral alterations in a rat model of short-term oral exposure to manganese

Manganese is an essential element for biological systems, nevertheless occupational exposure to high levels of Mn can lead to neurodegenerative disorder, characterized by excessive Mn accumulation, especially in astrocytes of basal ganglia and symptoms closely resembling idiopathic Parkinson's disease (PD). The purpose of this study was to evaluate behavioral and biochemical alterations in adult rats exposed for 30 days to 10 and 25mg/mL of MnCl(2) in their drinking water. MnCl(2) intoxicated rats showed impaired locomotor activity in comparison to control animals. Furthermore, lipid peroxidation were increased, delta-aminolevulinate dehydratase (delta-ALA-D, an enzyme sensitive to pro-oxidant situations) activity was inhibited and (45)Ca(2+) influx into striatal slices was decreased in rats exposed to 25mg/mL of Mn, indicating that this brain region was markedly affected by short-term Mn exposure. In contrast, Mn exposure was not associated with characteristic extrapyramidal effects and did not modify protein oxidation, suggesting that the striatal damage represents early stages of Mn-induced damage. In addition, treatment with Mn was associated with reduced body weight gain, but there were no discernible alterations in liver and kidney function. In conclusion, Mn caused increased oxidative stress and decreased (45)Ca(2+) influx into the striatum, which are likely linked to impaired locomotor activity, but not with the occurrence of orofacial dyskinesia.

Genetic polymorphism of glutathione S-transferase T1: a candidate genetic modifier of individual susceptibility to schizophrenia

Schizophrenia is highly heritable, but the specific genes involved remain to be determined. A genome wide scan approach has indicated that human chromosome 22q11.2 potentially influences schizophrenia susceptibility. The gene encoding glutathione S-transferase T1 (GSTT1), which pertains to phase II biotransformation enzymes, was also mapped to the above-mentioned band. The present case-control study was performed on 292 (206 males, 86 females) in-patients with schizophrenia, and a total of 292 healthy blood donors matched to the patients according to age (+/-5 years) and gender as a control group. The patients were chronic cases. The patients were diagnosed as chronic schizophrenia according to structured clinical interview using the Structured Clinical Interview for DSM-IV (clinician version) to confirm and document DSM-IV diagnosis. The GSTT1 genotypes were determined using a PCR-based method. The GSTT1 null genotype was 17.8% and 33.9% in the patients and control groups, respectively. The GSTT1 null genotype was associated with a significantly reduced risk of developing schizophrenia. On the other word, the positive GSTT1 genotype significantly increased the risk of schizophrenia. The present finding indicated that GSTT1 is a candidate gene for susceptibility to schizophrenia.

Antioxidant activity of timolol on endothelial cells and its relevance for glaucoma course

PURPOSE

A growing evidence in the scientific literature suggests that oxidative damage plays a pathogenic role in primary open-angle glaucoma. Therefore, it is of interest to test whether drugs effective against glaucoma display antioxidant activity. We test the hypothesis that the classic beta-blocker therapy for glaucoma with timolol involves the activation of antioxidant protective mechanisms towards endothelial cells.

METHODS

Oxidative stress was induced in cultured human endothelial cells by iron/ascorbate with or without timolol pretreatment. Analysed parameters included cell viability (neutral red uptake and tetrazolium salt tests), lipid peroxidation (thiobarbituric reactive substances), and occurrence of molecular oxidative damage to DNA (8-hydroxy-2'-deoxyguanosine).

RESULTS

Oxidative stress decreased 1.8-fold cell viability, increased 3.0-fold lipid peroxidation and 64-fold oxidative damage to DNA. In the presence of timolol, oxidative stress did not modify cell viability, whereas lipid peroxidation was increased 1.3-fold, and DNA oxidative damage 3.6-fold only.

CONCLUSIONS

The obtained results indicate that timolol exerts a direct antioxidant activity protecting human endothelial cells from oxidative stress. These cells employ mechanisms similar to those observed in the vascular endothelium. It is hypothesized that this antioxidant activity is involved in the therapeutic effect of this drug against glaucoma.

Neurobiology of pain

The neurobiology of pain had a notable interest in research focused on the study of neuronal plasticity development, nociceptors, molecular identity, signaling mechanism, ionic channels involved in the generation, modulation and propagation of action potential in all type of excitable cells. All the findings open the possibility for developing new therapeutic treatment. Nociceptive/inflammatory pain and neuropathic pain represent two different kinds of persistent chronic pain. We have reviewed the different mechanism suggested for the maintenance of pain, like descending nociceptive mechanism and their changes after tissue damage, including suppression and facilitation of defence behavior during pain. The role of these changes in inducing NMDA and AMPA receptors gene expression, after prolonged inflammation is emphasized by several authors. Furthermore, a relation between a persistent pain and amygdale has been shown. Molecular biology is the new frontier in the study of neurobiology of pain. Since the entire genome has been studied, we will able to find new genes involved in specific condition such as pain, because an altered gene expression can regulate neuronal activity after inflammation or tissue damage.

Possible Mechanisms of Neurodegeneration in Schizophrenia

Brain morphological alterations in schizophrenic patients have led to the neurodevelopmental hypothesis of schizophrenia. On the other hand, a progressive neurodegenerative process has also been suggested and some follow-up studies have shown progressive morphological changes in schizophrenic patients. Several neurotransmitter systems have been suggested to be involved in this disorder and some of them could lead to neuronal death under certain conditions. This review discusses some of the biochemical pathways that could lead to neurodegeneration in schizophrenia showing that neuronal death may have a role in the etiology or natural course of this disorder.

Mitochondrial uncoupling proteins in the CNS: in support of function and survival

Mitochondrial uncoupling mediated by uncoupling protein 1 (UCP1) is classically associated with non-shivering thermogenesis by brown fat. Recent evidence indicates that UCP family proteins are also present in selected neurons. Unlike UCP1, these proteins (UCP2, UCP4 and BMCP1/UCP5) are not constitutive uncouplers and are not crucial for non-shivering thermogenesis. However, they can be activated by free radicals and free fatty acids, and their activity has a profound influence on neuronal function. By regulating mitochondrial biogenesis, calcium flux, free radical production and local temperature, neuronal UCPs can directly influence neurotransmission, synaptic plasticity and neurodegenerative processes. Insights into the regulation and function of these proteins offer unsuspected avenues for a better understanding of synaptic transmission and neurodegeneration.

Trigeminal pain transmission requires reactive oxygen species production

Three experiments were conducted in order to investigate the possible involvement of the reactive oxygen species in the nociception within the subnucleus caudalis of the spinal trigeminal nucleus (Vc). In the first experiment the extracellular level of hydrogen peroxide was evaluated by microdialysis in the Vc of two groups of six rats before and after a formalin (group 1) or saline solution (group 2) injection into the upper lip. In the second experiment the formalin test was conducted in three groups of 6 rats after a microinjection of 2-methoxyestradiol (2-ME, a superoxide-dismutase inhibitor; group 1) or N-acetylcysteine (NAC, an oxygen intermediate scavenger; group 2) or saline solution (group 3) into the Vc. In the third experiment an histochemical assay for superoxide dismutase activity was performed on two groups of 4 rats each 2 h after a formalin (group 1) or saline solution (group 2) injection into the upper lip. The results showed that (1) the level of hydrogen peroxide increases into the Vc during facial pain (134% of baseline); (2) the inhibition of superoxide dismutase or the removal of oxygen intermediate within the Vc decreases the sensibility to facial pain stimuli; and (3) persistent facial pain stimuli decrease the superoxide activity into the Vc (90% of counter-lateral). These data indicate that reactive oxygen species are produced in the Vc during persistent facial pain and are necessary for the transmission of pain.

Modulation of Aspartate Release by Ascorbic Acid and Endobain E, an Endogenous Na+, K+-ATPase Inhibitor

The isolation of a soluble brain fraction which behaves as an endogenous ouabain-like substance, termed endobain E, has been described. Endobain E contains two Na+, K+ -ATPase inhibitors, one of them identical to ascorbic acid. Neurotransmitter release in the presence of endobain E and ascorbic acid was studied in non-depolarizing (0 mM KCl) and depolarizing (40 mM KCl) conditions. Synaptosomes were isolated from cerebral cortex of male Wistar rats by differential centrifugation and Percoll gradient. Synaptosomes were preincubated in HEPES-saline buffer with 1 mM D-[3H]aspartate (15 min at 37 degrees C), centrifuged, washed, incubated in the presence of additions (60 s at 37 degrees C) and spun down; radioactivity in the supernatants was quantified. In the presence of 0.5-5.0 mM ascorbic acid, D-[3H]aspartate release was roughly 135-215% or 110-150%, with or without 40 mM KCI, respectively. The endogenous Na+, K+ -ATPase inhibitor endobain E dose-dependently increased neurotransmitter release, with values even higher in the presence of KCl, reaching 11-times control values. In the absence of KCl, addition of 0.5-10.0 mM commercial ouabain enhanced roughly 100% D-[3H]aspartate release; with 40 mM KCl a trend to increase was recorded with the lowest ouabain concentrations to achieve statistically significant difference vs. KCl above 4 mM ouabain. Experiments were performed in the presence of glutamate receptor antagonists. It was observed that MPEP (selective for mGluR5 subtype), failed to decrease endobain E response but reduced 50-60% ouabain effect; LY-367385 (selective for mGluR1 subtype) and dizocilpine (for ionotropic NMDA glutamate receptor) did not reduce endobain E or ouabain effects. These findings lead to suggest that endobain E effect on release is independent of metabotropic or ionotropic glutamate receptors, whereas that of ouabain involves mGluR5 but not mGluR1 receptor subtype. Assays performed at different temperatures indicated that in endobain E effect both exocytosis and transporter reversion are involved. It is concluded that endobain E and ascorbic acid, one of its components, due to their ability to inhibit Na+, K+ -ATPase, may well modulate neurotransmitter release at synapses.

Glutathione S-transferase M1 polymorphism may contribute to schizophrenia in the Korean population

The association between Glutathione S-Transferase M1 gene (GSTM1) polymorphism and schizophrenia was examined. One hundred and eleven in-patients with schizophrenia and 130 healthy controls were enrolled in this study. Genotyping was performed using a polymerase chain reaction-based method. The GSTM1 null genotype was significantly more frequent in the schizophrenia patients than in the controls (P=0.014, odds ratio=1.93, 95% confidence interval=1.115-3.351). On the other hand, the GSTM1 genotype variants were not associated with tardive dyskinesia or total abnormal involuntary movement scale scores. This study suggests that, at least in the Korean population, the GSTM1 polymorphism may confer susceptibility to the development of schizophrenia but not to tardive dyskinesia.

Cyclooxygenase Inhibitors Attenuate Augmented Glutamate Release in Organum Vasculosum Laminae Terminalis and Fever Induced by Staphylococcal Enterotoxin A

Both the hyperthermia and augmented glutamate release in the organum vasculosum laminae terminalis (OVLT) after an intravenous dose (30 ng/kg) of staphylococcal enterotoxin A (SEA) were significantly reduced by pretreatment with intravenous administration of cyclooxygenase inhibitors such as aspirin (1 - 10 mg/kg), sodium salicylate (1 - 10 mg/kg), or diclofenac (10 mg/kg). Intra-OVLT administration of 50 - 200 microg in 1.0 microl of either aspirin or sodium salicylate 60 min before or 120 min after an intra-OVLT dose (50 microg in 1.0 microl) of glutamate also significantly suppressed the glutamate-induced hyperthermia. These findings suggest that inhibition of cyclooxygenase receptor mechanisms suppresses SEA fever by inhibition of glutamate release in the OVLT of rabbit brain.

Mitochondrial potassium channels and uncoupling proteins in synaptic plasticity and neuronal cell death

The function of the nervous system relies upon synaptic transmission, a process in which a neurotransmitter released from pre-synaptic terminals of one neuron (in response to membrane depolarization and calcium influx) activates post-synaptic receptors on dendrites of another neuron. Synapses are subjected to repeated bouts of oxidative and metabolic stress as the result of changing ion gradients and ATP usage. Mitochondria play central roles in meeting the demands of synapses for ATP and in regulating calcium homeostasis, and mitochondrial dysfunction can cause dysfunction and degeneration of synapses, and can trigger cell death. We have identified two types of mitochondrial proteins that serve the function of protecting synapses and neurons against dysfunction and death. Mitochondrial ATP-sensitive potassium (MitoKATP) channels modulate inner membrane potential and oxyradical production; mitochondrial potassium fluxes can affect cytochrome c release and caspase activation and may determine whether neurons live or die in experimental models of stroke and Alzheimer's disease. Uncoupling proteins (UCPs) are a family of mitochondrial membrane proteins that uncouple electron transport from ATP production by transporting protons across the inner membrane. Neurons express at least three UCPs including the widely expressed UCP-2 and the neuron-specific UCP-4 and UCP-5 (BMCP-1). We have found that UCP-4 protects neurons against apoptosis by a mechanism involving suppression of oxyradical production and stabilization of cellular calcium homeostasis. The expression of UCP-4 is itself regulated by changes in energy metabolism. In addition to their roles in neuronal cell survival and death, MitoKATP channels and UCPs may play roles in regulating neuronal differentiation during development and synaptic plasticity in the adult.

Association study between glutathione S-transferase P1 polymorphism and schizophrenia in the Korean population

This study is aimed to test the association between the coding sequence functional polymorphism (Ile105Val) of glutathione S-transferase P gene (GSTP1) and schizophrenia in the Korean population. Two hundred fourteen patients with schizophrenia according to the Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) criteria and 110 healthy controls were enrolled in this study. Patients and controls were biologically unrelated age and sex-matched native Koreans. Genotyping for GSTP1 polymorphism was performed by polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP). Genotype and allele distributions of GSTP1 polymorphism in patients with schizophrenia were not significantly different from those of the controls. Comparisons of clinical variables including Positive and Negative Syndrome Scale (PANSS), change of Brief Psychiatric Rating Scale (BPRS), number of admission, and onset age also were not different according to genotype distribution. The present study suggests that GSTP1 polymorphism may not confer susceptibility to development of schizophrenia in the Korean population.

Mitochondrial dysfunction in schizophrenia: a possible linkage to dopamine

Mitochondria are not only the principal source of high energy intermediates, but play an important role in intracellular calcium buffering, are main producers of reactive oxygen species, and are the source of pro- and antiapoptotic key factors. Moreover, the mitochondria are of a ubiquitous nature and the respiratory chain has a dual genetic basis, i.e. the mitochondrial and the nuclear DNAs. Thus mitochondrial impairment could provide an explanation for the tremendous heterogeneity of clinical and pathological manifestations in schizophrenia. This article reviews several independent lines of evidence that suggest an involvement of mitochondrial dysfunction in schizophrenia. Among them are altered cerebral energy metabolism, mitochondrial hypoplasia, dysfunction of the oxidative phosphorylation system and altered mitochondrial related gene expression. In addition, the interaction between dopamine, a predominant etiological factor in schizophrenia, and mitochondrial respiration is considered as a possible mechanism underlying the hyper- and hypo-activity cycling in schizophrenia. Understanding the role of mitochondria in schizophrenia may encourage novel treatment approaches, the identification of candidate genes and new insights into the pathophysiology and etiology of the disorder.

Protective action of nipradilol against ischemia-induced retinal damage in rats

The purpose of this study was to investigate whether nipradilol, a beta-blocker having both vasodilating and alpha(1)-blocking activities, can protect retinal cells from the injury induced by ischemia and reperfusion. Rats were anesthetized and, after an intravitreal injection of nipradilol, the intraocular pressure was raised for 45 min to induce retinal ischemia and reperfusion. Before, and 3 and 7 days after the ischemia, electroretinograms were recorded. After the ischemia, the mean amplitude of the b-waves in rats receiving 5 microl of 1.0 x 10(-6) M nipradilol was significantly larger than of controls (injected with phosphate-buffered saline). Histologically, the reduction in the number of retinal ganglion cells (1.0 x 10(-6) M), and the thickness of the inner and outer plexiform layers and the inner nuclear layer (1.0 x 10(-6), 10(-7) and 10(-8) M) was suppressed by nipradilol. These results indicate that nipradilol protected the retina against retinal ischemia and reperfusion and should be considered for therapeutic use in cases of transient retinal ischemia.

Par-4 is a synaptic protein that regulates neurite outgrowth by altering calcium homeostasis and transcription factor AP-1 activation

Although Par-4 (prostate apoptosis response-4) is involved in initiation of neurodegenerative cascades associated with certain neurodegenerative disorders, normal physiological roles of Par-4 in neurons have remained elusive. It was recently reported that Par-4 protein levels could be regulated at translational level in synaptic terminals following apoptotic insults, suggesting that Par-4 might play a role in synaptic function. We report that Par-4 is a synaptic protein preferably localized in postsynaptic density (PSD). The expression of Par-4 in synaptosome preparations and PSDs are developmentally and regionally regulated. Synaptic Par-4 is enriched in the cerebral cortex and the hippocampus, but not in the cerebellum. In vitro as well as in vivo experiments demonstrate that the levels of synaptic Par-4 increase as the neurons mature. Overexpression of Par-4 in transfected PC12 cells inhibits nerve growth factor (NGF)-induced cellular differentiation and neurite outgrowth by a mechanism involving aberrant elevation of intracellular calcium levels and suppression of activation of the transcription factor AP-1. The actions of Par-4 were consistently blocked by co-expression of the dominant negative regulator of Par-4 activity (the leucine zipper domain of Par-4). Since the leucine zipper domain of Par-4 (Leu.zip) may mediate protein--protein interactions, the results indicate that the actions of Par-4 require its interaction with other protein(s) or dimerization with itself. These results suggest that Par-4 may play an important role in postsynaptic signal transduction and regulation of cellular pathways associated with cellular differentiation and neurite outgrowth. Identification of Par-4 as a novel synaptic protein may have significant implications in understanding the mechanisms of synaptic functions in physiological and pathological settings.

Reactive oxygen species regulate signaling pathways induced by M1 muscarinic receptors in PC12M1 cells

Activation of the m1 muscarinic receptor subtype in rat pheochromocytoma (PC12) cells stably expressing cloned m1 muscarinic acetylcholine receptors was previously shown to induce morphological changes and growth arrest. However, the signaling pathways which lead to these effects were not identified. In an attempt to characterize the intracellular signaling that might be involved in the muscarinic-induced effects, we investigated the role of reactive oxygen species in the regulation of these processes. Stimulation of the muscarinic receptor in these cells increased the intracellular concentrations of reactive oxygen species. Muscarinic activation induced intracellular signaling pathways that involve activation of Ras, extracellular signal-regulated kinase (ERK), and p38. These pathways were partially blocked when reactive oxygen species (ROS) production was prevented by the antioxidant N-acetylcysteine. Other muscarinic-induced signals, such as activation of c-Jun NH(2)-terminal kinase (JNK) or an increase in the binding activity of the transcription factors nuclear factor-kappa B and activator protein-1, were inhibited by the antioxidant dicoumarol. N-Acetylcysteine also blocked the growth arrest and changes in cell shape induced by stimulation of the muscarinic receptor in PC12M1 cells. These findings suggest that ROS act as second messengers in muscarinic-induced cellular signaling. Moreover, generation of ROS appears to be an early and critical intermediary event, which occurs immediately after stimulation of the muscarinic receptor and affects in a variety of mechanisms the muscarinic-mediated cellular signaling.

Reducing conditions significantly attenuate the neuroprotective efficacy of competitive, but not other NMDA receptor antagonists in vitro

Inappropriate activation of NMDA receptors during a period of cerebral ischaemia is a crucial event in the pathway leading to neuronal degeneration. However, significant research has failed to deliver a clinically active NMDA receptor antagonist, and competitive NMDA antagonists are ineffective in many experimental models of ischaemia. The NMDA receptor itself has a number of modulatory sites which may affect receptor function under ischaemic conditions. Using rat organotypic hippocampal slice cultures we have investigated whether the redox modulatory site affects the neuroprotective efficacy of NMDA receptor antagonists against excitotoxicity and experimental ischaemia (OGD). NMDA toxicity was significantly enhanced in cultures pretreated with a reducing agent. The noncompetitive antagonist MK-801 and a glycine-site blocker were equally neuroprotective in both normal and reduced conditions, but there was a significant rightward shift in the dose-response curves of the competitive antagonists APV and CPP and the uncompetitive antagonist memantine. OGD produced neuronal damage predominantly in the CA1 region, which was prevented by MK-801 and memantine, but not by APV or CPP. Inclusion of an oxidizing agent during the period of OGD had no effect alone, but significantly enhanced the neuroprotective potency of the competitive antagonists. These data clearly demonstrate that chemical reduction of the redox modulatory site of the NMDA receptor decreases the ability of competitive antagonists to block NMDA receptor-mediated neuronal damage, and that the reducing conditions which occur during simulated ischaemia are sufficient to produce a similar effect. This may have important implications for the design of future neuroprotective agents.

Ultrastructural localization of nitrotyrosine within the caudate-putamen nucleus and the globus pallidus of normal rat brain

Nitration of protein tyrosine residues by nitric oxide (NO)-derived reactive species results in the production of stable nitrotyrosine (NT) moieties that are immunochemically detectable in many regions of normal brain and enriched in those areas containing constitutive nitric oxide synthase (cNOS). These include the caudate-putamen nucleus (CPN) and the globus pallidus, which receives major inhibitory input from the CPN. To determine the functional sites for NT production in these critical motor nuclei, we examined the electron microscopic immunocytochemical localization of NT and cNOS in rat brain. In the CPN, NT was localized to the somata and dendrites of cNOS-containing interneurons and spiny neurons, some of which received input from cNOS-labeled terminals. The NT immunoreactivity was most prevalent on outer mitochondrial membranes and nearby segments of the plasma membranes in dendrites and within asymmetric synapses on dendritic spines. In the CPN and globus pallidus, there was also a prominent labeling of NT in astrocytic processes, small axons, and tubulovesicles and/or synaptic vesicles in axon terminals. These terminals formed mainly asymmetric synapses in the CPN and inhibitory-type synapses in the globus pallidus where they often apposed cNOS-containing terminals that also formed asymmetric, excitatory-type synapses. Our results suggest that NT is generated by mechanisms requiring the dual actions of excitatory transmitters and NO derived either from interneurons in the CPN or from excitatory afferents in the globus pallidus. The findings also implicate NT in the physiological actions of NO within the striatal circuitry and, particularly, in striatopallidal neurons severely affected in Huntington's disease.

Roles of NMDA receptor activity and nitric oxide production in brain development

The concept that neural activity is important for brain maturation has focused much research interest on the developmental role of the NMDA receptor, a key mediator of experience-dependent synaptic plasticity. However, a mechanism able to link spatial and temporal parameters of synaptic activity during development emerged as a necessary condition to explain how axons segregate into a common brain region and make specific synapses on neuronal sub-populations. To comply with this developmental constraint, it was proposed that nitric oxide (NO), or other substances having similar chemical and biological characteristics, could act as short-lived, activity-dependent spatial signals, able to stabilize active synapses by diffusing through a local volume of tissue. The present article addresses this issue, by reviewing the experimental evidence for a correlated role of the activity of the NMDA receptor and the production of NO in key steps of neural development. Evidence for such a functional coupling emerges not only concerning synaptogenesis and formation of neural maps, for which it was originally proposed, but also for some earlier phases of neurogenesis, such as neural cell proliferation and migration. Regarding synaptogenesis and neural map formation in some cases, there is so far no conclusive experimental evidence for a coupled functional role of NMDA receptor activation and NO production. Some technical problems related to the use of inhibitors of NO formation and of gene knockout animals are discussed. It is also suggested that other substances, known to act as spatial signals in adult synaptic plasticity, could have a role in developmental plasticity. Concerning the crucial developmental phase of neuronal survival or elimination through programmed cell death, the well-documented survival role related to NMDA receptor activation also starts to find evidence for a concomitant requirement of downstream NO production. On the basis of the reviewed literature, some of the major controversial issues are addressed and, in some cases, suggestions for possible future experiments are proposed.

Redox aspects of signaling by catecholamines and their metabolites

This review covers certain novel aspects of catecholamine signaling in neurons that involve redox systems and synaptic plasticity. The redox hypothesis suggests that one important factor in neurocomputation is the formation of new synapses and the removal of old ones (synaptic plasticity), which is modulated in part by the redox balance at the synapse between reactive oxygen species (ROS) (such as hydrogen peroxide and the nitric oxide radical) and neuroprotective antioxidants (such as ascorbate, glutathione, and catecholamines). Catecholamines, in particular dopamine, which signals positive reinforcement, may play a key role in this activity. Dopamine has powerful antioxidant properties by several separate mechanisms-direct ROS scavenging, activation of the synthesis of antioxidant proteins, and possibly via dismuting complexes with iron inside endosomes or in catecholaminergic synaptic vesicles. This may contribute to synaptic growth and reinforcement-directed learning. On the other hand, catecholamines are easily oxidized to toxic quinones on the neuromelanin pathway. This might contribute under certain circumstances to synaptic deletion. Evidence is presented that abnormalities in this system may contribute to the pathogenesis of Parkinson's disease and schizophrenia.