Glutathione-induced inhibition of Na+-independent and -dependent bindings of L-[3H]glutamate in rat brain

Cardiovascular responses to l-glutamate microinjection into the NTS are abrogated by reduced glutathione

Redox imbalance in regions of the CNS controlling blood pressure is increasingly recognized as a leading factor for hypertension. Nucleus tractus solitarius (NTS) of the dorsomedial medulla is the main region receiving excitatory visceral sensory inputs that modulate autonomic efferent drive to the cardiovascular system. This study sought to determine the capacity of reduced glutathione, a major bioactive antioxidant, to modulate NTS-mediated control of cardiovascular function in unanaesthetized rats. Male Fischer 344 rats were used for microinjection experiments. Cardiovascular responses to l-glutamate were first used to verify accurate placement of injections into the dorsomedial region comprising the NTS. Next, responses to GSH or vehicle were recorded followed by responses to l-glutamate again at the same site. GSH microinjection increased mean arterial pressure (MAP) compared to vehicle and abrogated responses to subsequent injection of l-glutamate. These data indicate that GSH microinjection into the NTS affects blood pressure regulation by dorsomedial neuronal circuits and blunts l-glutamate driven excitation in this region. These findings raise the possibility that increased antioxidant actions of GSH in NTS could contribute to autonomic control dysfunctions of the cardiovascular system.

Glutathione induces GABA release through P2X7R activation on Müller glia

The retinal tissue of warm-blooded vertebrates performs surprisingly complex and accurate transduction of visual information. To achieve precision, a multilayered neuroglia structure is established throughout the embryonic development, and the presence of radial Müller (glial) cells ensure differentiation, growth and survival for the neuronal elements within retinal environment. It is assumed that Müller cells serve as a dynamic reservoir of progenitors, capable of expressing transcription factors, differentiating and proliferating as either neuronal or glial cells depending on extrinsic cues. In the postnatal period, Müller glia may re-enter cell cycle and produce new retinal neurons in response to acute damage. In this context, glutathione (GSH), a virtually ubiquitous tripeptide antioxidant, which is found at milimolar concentrations in central glial cells, plays a vital role as a reducing agent, buffering radical oxygen species (ROS) and preventing cell death in severely injured retinal tissues. Despite its antioxidant role, data also point to GSH as a signaling agent, suggesting that GABA release and P2X₇R-mediated calcium inwards occur in Müller cells in a GSH-enriched environment. These phenomena indicate a novel mechanistic response to damage in the vertebrate retinal tissue, particularly in neuron-glia networks.

New Pharmacological Agents to Aid Smoking Cessation and Tobacco Harm Reduction: What Has Been Investigated, and What Is in the Pipeline?

A wide range of support is available to help smokers to quit and to aid attempts at harm reduction, including three first-line smoking cessation medications: nicotine replacement therapy, varenicline and bupropion. Despite the efficacy of these, there is a continual need to diversify the range of medications so that the needs of tobacco users are met. This paper compares the first-line smoking cessation medications with (1) two variants of these existing products: new galenic formulations of varenicline and novel nicotine delivery devices; and (2) 24 alternative products: cytisine (novel outside Central and Eastern Europe), nortriptyline, other tricyclic antidepressants, electronic cigarettes, clonidine (an anxiolytic), other anxiolytics (e.g. buspirone), selective serotonin reuptake inhibitors, supplements (e.g. St John's wort), silver acetate, Nicobrevin, modafinil, venlafaxine, monoamine oxidase inhibitors (MAOIs), opioid antagonists, nicotinic acetylcholine receptor (nAChR) antagonists, glucose tablets, selective cannabinoid type 1 receptor antagonists, nicotine vaccines, drugs that affect gamma-aminobutyric acid (GABA) transmission, drugs that affect N-methyl-D-aspartate (NMDA) receptors, dopamine agonists (e.g. levodopa), pioglitazone (Actos; OMS405), noradrenaline reuptake inhibitors and the weight management drug lorcaserin. Six 'ESCUSE' criteria-relative efficacy, relative safety, relative cost, relative use (overall impact of effective medication use), relative scope (ability to serve new groups of patients) and relative ease of use-are used. Many of these products are in the early stages of clinical trials; however, cytisine looks most promising in having established efficacy and safety with low cost. Electronic cigarettes have become very popular, appear to be efficacious and are safer than smoking, but issues of continued dependence and possible harms need to be considered.

The effects of n-acetylcysteine and/or deferoxamine on manic-like behavior and brain oxidative damage in mice submitted to the paradoxal sleep deprivation model of mania

Bipolar disorder (BD) is a severe psychiatric disorder associated with social and functional impairment. Some studies have strongly suggested the involvement of oxidative stress in the pathophysiology of BD. Paradoxal sleep deprivation (PSD) in mice has been considered a good animal model of mania because it induces similar manic-like behavior, as well as producing the neurochemical alterations which have been observed in bipolar patients. Thus, the objective of the present study was to evaluate the effects of the antioxidant agent's n-acetylcysteine (Nac) and/or deferoxamine (DFX) on behavior and the oxidative stress parameters in the brains of mice submitted to the animal model of mania induced by PSD. The mice were treated for a period of seven days with saline solution (SAL), Nac, DFX or Nac plus DFX. The animals were subject to the PSD protocol for 36 h. Locomotor activity was then evaluated using the open-field test, and the oxidative stress parameters were subsequently evaluated in the hippocampus and frontal cortex of mice. The results showed PSD induced hyperactivity in mice, which is considered a manic-like behavior. In addition to this, PSD increased lipid peroxidation and oxidative damage to proteins, as well as causing alterations to antioxidant enzymes in the frontal cortex and hippocampus of mice. The Nac plus DFX adjunctive treatment prevented both the manic-like behavior and oxidative damage induced by PSD. Improving our understanding relating to oxidative damage in biomolecules, and the antioxidant mechanisms presented in the animal models of mania are important in helping to improve our knowledge concerning the pathophysiology and development of new therapeutical treatments for BD.

Oxidative stress in early stage Bipolar Disorder and the association with response to lithium

BACKGROUND

Several studies have described increased oxidative stress (OxS) parameters and imbalance of antioxidant enzymes in Bipolar Disorder (BD) but few is know about the impact of treatment at these targets. However, no study has evaluated OxS parameters in unmedicated early stage BD and their association with lithium treatment in bipolar depression.

METHODS

Patients with BD I or II (n = 29) in a depressive episode were treated for 6 weeks with lithium. Plasma samples were collected at baseline and endpoint, and were also compared to age-matched controls (n = 28). The thiobarbituric acid reactive substances (TBARS), and the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities were measured.

RESULTS

Subjects with BD depression at baseline presented a significant increase in CAT (p = 0.005) and GPx (p < 0.001) levels, with lower SOD/CAT ratio (p = 0.001) and no changes on SOD or TBARS compared to healthy controls. Regarding therapeutics, lithium only induced a decrease in TBARS (p = 0.023) and SOD (p = 0.029) levels, especially in BDII. Finally, TBARS levels were significantly lower at endpoint in lithium responders compared to non-responders (p = 0.018) with no difference in any biomarker regarding remission.

CONCLUSION

The present findings suggest a reactive increase in antioxidant enzymes levels during depressive episodes in early stage BD with minimal prior treatment. Also, decreased lipid peroxidation (TBARS) levels were observed, associated with lithium's clinical efficacy. Overall, these results reinforce the role for altered oxidative stress in the pathophysiology of BD and the presence of antioxidant effects of lithium in the prevention of illness progression and clinical efficacy.

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.

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.

Intracerebroventricular injection of glutathione and its derivative induces sedative and hypnotic effects under an acute stress in neonatal chicks

Glutathione-related enzymes glyoxalase 1 and glutathione reductase 1 regulates anxiety in mice. To clarify the central function of glutathione as a neurotransmitter in the stress reaction, the effect of intracerebroventricular (i.c.v.) injection of reduced (GSH) (0.5, 1, 2 micromol) and oxidized (GSSG) glutathione (0.25, 0.5, 1 micromol) were investigated under an isolation-induced stress in the neonatal chick. Both GSH and GSSG dose-dependently decreased distress vocalizations and induced sleep-like behavior in chicks under acute stressful conditions. However, which glutathione is actually responsible for inducing sleep was unclear since glutathione cycles between GSH and GSSG in which two tripeptides are linked by a disulfide bond. Therefore, the behavior of chicks was monitored following the i.c.v. injection of S-methylglutathione (SMG) (0.0625, 0.25, 1 micromol). SMG does not form a disulfide bond due to the methylation of the SH group of the cysteine moiety. SMG had similar effects as observed in GSH and GSSG. In conclusion, glutathione and its derivative have sedative and hypnotic effects, and might be effective in improving psychic stress such as anxiety.

Modulation of [3H]dopamine release by glutathione in mouse striatal slices

Glutathione (gamma-glutamylcysteinylglycine, GSH and oxidized glutathione, GSSG), may function as a neuromodulator at the glutamate receptors and as a neurotransmitter at its own receptors. We studied now the effects of GSH, GSSG, glutathione derivatives and thiol redox agents on the spontaneous, K(+)- and glutamate-agonist-evoked releases of [(3)H]dopamine from mouse striatal slices. The release evoked by 25 mM K(+) was inhibited by GSH, S-ethyl-, -propyl-, -butyl- and pentylglutathione and glutathione sulfonate. 5,5'-Dithio-bis-2-nitrobenzoate (DTNB) and L-cystine were also inhibitory, while dithiothreitol (DTT) and L-cysteine enhanced the K(+)-evoked release. Ten min preperfusion with 50 microM ZnCl(2) enhanced the basal unstimulated release but prevented the activation of K(+)-evoked release by DTT. Kainate and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) evoked dopamine release but the other glutamate receptor agonists N-methyl-D-aspartate (NMDA), glycine (1 mM) and trans-1-aminocyclopentane-1,3-dicarboxylate (t-ACPD, 0.5 mM), and the modulators GSH, GSSG, glutathione sulfonate, S-alkyl-derivatives of glutathione, DTNB, cystine, cysteine and DTT (all 1 mM) were without effect. The release evoked by 1 mM glutamate was enhanced by 1 mM GSH, while GSSG, glutathionesulfonate and S-alkyl derivatives of glutathione were generally without effect or inhibitory. NMDA (1 mM) evoked release only in the presence of 1 mM GSH but not with GSSG, other peptides or thiol modulators. L-Cysteine (1 mM) enhanced the glutamate-evoked release similarly to GSH. The activation by 1 mM kainate was inhibited by S-ethyl-, -propyl-, and -butylglutathione and the activation by 0.5 mM AMPA was inhibited by S-ethylglutathione but enhanced by GSSG. Glutathione alone does not directly evoke dopamine release but may inhibit the depolarization-evoked release by preventing the toxic effects of high glutamate, and by modulating the cysteine-cystine redox state in Ca(2+ )channels. GSH also seems to enhance the glutamate-agonist-evoked release via both non-NMDA and NMDA receptors. In this action, the gamma-glutamyl and cysteinyl moieties of glutathione are involved.

Brain oxidation is an initial process in sleep induction

CNS activity is generally coupled to the vigilance state, being primarily active during wakefulness and primarily inactive during deep sleep. During periods of high neuronal activity, a significant volume of oxygen is used to maintain neuronal membrane potentials, which subsequently produces cytotoxic reactive oxygen species (ROS). Glutathione, a major endogenous antioxidant, is an important factor protecting against ROS-mediated neuronal degeneration. Glutathione has also been proposed to be a sleep-promoting substance, yet the relationship between sleep and cerebral oxidation remains unclear. Here we report that i.c.v. infusion of the organic peroxide t-butyl-hydroperoxide at a concentration below that triggering neurodegeneration (0.1 micromol/100 microl/10 h) promotes sleep in rats. Also, microinjection (2 nmol, 2 microl) or microdialysis (100 microM, 20 min) of t-butyl-hydroperoxide into the preoptic/anterior hypothalamus (POAH) induces the release of the sleep-inducing neuromodulators, nitric oxide and adenosine, without causing neurodegeneration. Nitric oxide and adenosine release was inhibited by co-dialysis of the N-methyl-D-aspartate receptor antagonist, d(-)-2-amino-5-phosphonopentanoic acid (D-AP5; 1 mM), suggesting that glutamate-induced neuronal excitation mediates the peroxide-induced release of nitric oxide and adenosine. Indeed, Ca2+ release from mitochondria and delayed-onset Ca2+ influx via N-methyl-D-aspartate receptors was visualized during peroxide exposure using Ca2+ indicator proteins (YC-2.1 and mitochondrial-targeted Pericam) expressed in organotypic cultures of the POAH. In the in vitro models, t-butyl-hydroperoxide (50 microM) causes dendritic swelling followed by the intracellular Ca2+ mobilization, and D-AP5 (100 microM) or glutathione (500 microM) inhibited t-butyl-hydroperoxide-induced intracellular Ca2+ mobilization and protected POAH neurons from oxidative stress. These data suggest that low-level subcortical oxidation under the control of an antioxidant system may trigger sleep via the Ca(2+)-dependent release of sleep-inducing neuromodulators in the POAH, and thus we propose that a moderate increase of ROS during wakefulness in the neuronal circuits regulating sleep may be an initial trigger in sleep induction.

In vitro and in vivo antagonistic activities of SM-31900 for the NMDA receptor glycine-binding site

The purpose of this study was to clarify the in vitro pharmacological profile and the in vivo activity of (3S)-7-chloro-3-[2-((1R)-1-carboxyethoxy)-4-aminomethylphenyl]aminocarbonylmethyl-1,3,4,5-tetrahydrobenz[c,d]indole-2-carboxylic acid hydrochloride (SM-31900). SM-31900 inhibited the binding of [3H]glycine and [3H]5,7-dichlorokynurenic acid, radioligands for the N-methyl-D-aspartate (NMDA) receptor glycine-binding site, to rat brain membranes in a competitive manner, with K(i) values of 11+/-2 and 1.0+/-0.1 nM, respectively, and completely prevented the binding of [3H]dizocilpine (MK-801), a radioligand for the NMDA receptor channel site. In cultures of rat cortical neurons, SM-31900 markedly prevented the neuronal cell death induced by transient exposure to glutamate, in a concentration-dependent manner. Its neuroprotective potency was much stronger than those of other glycine-binding site antagonists (4-trans-2-carboxy-5,7-dichloro-4-phenylaminocarbonylamino-1,2,3,4-tetrahydroquinoline (L-689,560), 5,7-dichlorokynurenic acid, and 7-chlorokynurenic acid). Furthermore, SM-31900 showed anticonvulsant activity when administered systemically, unlike other antagonists. These data indicate that SM-31900 is a systemically active antagonist with high affinity for the NMDA receptor glycine-binding site.

Consolidation of transient ionotropic glutamate signals through nuclear transcription factors in the brain

Long-lasting alterations of neuronal functions could involve mechanisms associated with consolidation of transient extracellular signals through modulation of de novo synthesis of particular functional proteins in the brain. In eukaryotes, protein de novo synthesis is mainly under the control at the level of gene transcription by transcription factors in the cell nucleus. Transcription factors are nuclear proteins with an ability to recognize particular core nucleotides at the upstream and/or downstream of target genes, and thereby to modulate the activity of RNA polymerase II that is responsible for the formation of mRNA from double stranded DNA. Gel retardation electrophoresis is widely employed for conventional detection of DNA binding activities of a variety of transcription factors with different protein motifs. Extracellular ionotropic glutamate (Glu) signals lead to rapid and selective potentiation of DNA binding of the nuclear transcription factor activator protein-1 (AP1) that is a homo- and heterodimeric complex between Jun and Fos family members, in addition to inducing expression of the corresponding proteins, in a manner unique to each Glu signal in murine hippocampus. Therefore, extracellular Glu signals may be differentially transduced into the nucleus to express AP1 with different assemblies between Jun and Fos family members, and thereby to modulate de novo synthesis of the individual target proteins at the level of gene transcription in the hippocampus. Such mechanisms may be operative on synaptic plasticity as well as delayed neuronal death through consolidation of alterations of a variety of cellular functions induced by transient extracellular signals in the brain.

Quinolinic acid induces oxidative stress in rat brain synaptosomes

The oxidative action of quinolinic acid (QUIN), and the protective effects of glutathione (GSH), and 2-amino-5-phosphonovaleric acid (APV), were tested in rat brain synaptosomes, Reactive oxygen species (ROS) formation was quantified after the exposure of synaptosomes to increasing concentrations of QUIN (25-500 microM). The potency of QUIN to induce lipid peroxidation (LP) was tested as a regional index of thiobarbituric acid-reactive substances (TBARS) production, and the antioxidant actions of both GSH (50 microM) and APV (250 microM) on QUIN-induced LP were evaluated in synaptosomes prepared from different brain regions. QUIN induced concentration-dependent increases in ROS formation and TBARS in all regions analyzed, but increased production of fluorescent peroxidized lipids only in the striatum and the hippocampus, whereas both GSH and APV decreased this index. These results suggest that the excitotoxic action of QUIN involves regional selectivity in the oxidative status of brain synaptosomes, and may be prevented by substances exhibiting antagonism at the NMDA receptor.

Cerebral antioxidant status and free radical generation following glutathione depletion and subsequent recovery

This study was aimed to evaluate the oxidative damage, production of reactive oxygen species and the status of antioxidative defenses following cerebral GSH depletion induced by two classical depletors, diethylmaleate (DEM, 3 mmol/kg, i.p.) and phorone (PHO, 4 mmol/kg, i.p.). The treatment decreased (40-43%) brain glutathione levels at 2 h, followed by a partial recovery at 24 h. Cerebral glutathione depletion by these agents increased the levels of superoxide anion and hydroxyl radical at both the time intervals; however, hydrogen peroxide was high at 24 h only. It also produced a dramatic increase in the protein carbonyls at 2 h but not at 24h, without any significant effect on lipid peroxidation and conjugated diene levels. These rats showed a significantly lowered superoxide dismutase activity both at 2 h and 24 h of exposure, as compared to controls. Glutathione depletion enhanced catalase activity markedly at 2 h, followed by some recovery at 24 h. While Se-independent glutathione peroxidase (GPx) and glutathione S-transferase activities were increased at both 2 and 24 h time intervals, Se-dependent GPx and glucose-6-phosphate dehydrogenase were induced at 2 h only. Glutathione depletion decreased ceruloplasmin and vitamin E levels significantly at 2 h. However, ascorbic acid remained unaffected. It may be concluded that an acute cerebral glutathione depletion generates higher levels of reactive oxygen species, which may be responsible for oxidative modification of proteins. Some of these changes appear to recover soon after an activation of a variety of cellular antioxidant defense mechanisms and glutathione restoration. It appears that central nervous system is highly vulnerable to oxidative damage following a moderate glutathione depletion that may result from certain diseases or xenobiotic exposures.

Glutathione and signal transduction in the mammalian CNS

The tripeptide glutathione (GSH) has been thoroughly investigated in relation to its role as antioxidant and free radical scavenger. In recent years, novel actions of GSH in the nervous system have also been described, suggesting that GSH may serve additionally both as a neuromodulator and as a neurotransmitter. In the present article, we describe our studies to explore further a potential role of GSH as neuromodulator/neurotransmitter. These studies have used a combination of methods, including radioligand binding, synaptic release and uptake assays, and electrophysiological recording. We report here the characteristics of GSH binding sites, the interrelationship of GSH with the NMDA receptor, and the effects of GSH on neural activity. Our results demonstrate that GSH binds via its gamma-glutamyl moiety to ionotropic glutamate receptors. At micromolar concentrations GSH displaces excitatory agonists, acting to halt their physiological actions on target neurons. At millimolar concentrations, GSH, acting through its free cysteinyl thiol group, modulates the redox site of NMDA receptors. As such modulation has been shown to increase NMDA receptor channel currents, this action may play a significant role in normal and abnormal synaptic activity. In addition, GSH in the nanomolar to micromolar range binds to at least two populations of binding sites that appear to be distinct from all known excitatory amino acid receptor subtypes. GSH bound to these sites is not displaceable by glutamatergic agonists or antagonists. These binding sites, which we believe to be distinct receptor populations, appear to recognize the cysteinyl moiety of the GSH molecule. Like NMDA receptors, the GSH binding sites possess a coagonist site(s) for allosteric modulation. Furthermore, they appear to be linked to sodium ionophores, an interpretation supported by field potential recordings in rat cerebral cortex that reveal a dose-dependent depolarization to applied GSH that is blocked by the absence of sodium but not by lowering calcium or by NMDA or (S)-2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate antagonists. The present data support a reevaluation of the role of GSH in the nervous system in which GSH may be involved both directly and indirectly in synaptic transmission. A full accounting of the actions of GSH may lead to more comprehensive understanding of synaptic function in normal and disease states.

Increased glutathione levels in neurochemically identified fibre systems in the aged rat lumbar motor nuclei

The spinal cord motor nuclei have been the focus of a number of investigations exploring neurodegenerative mechanisms, e.g. excitotoxicity mediated by glutamate and oxidative stress. Here, high-resolution quantitative post-embedding immunocytochemistry with antibodies to oxidized and reduced glutathione (GSH), an ubiquitously expressed scavenger of free radicals, was used to examine if GSH synthesis is upregulated pre- and/or postsynaptically in the lumbar motor nuclei of aged (30 month old) rats. The purpose was, moreover, to resolve the extent of correlation between GSH expression, transmitter identity and degenerative changes. Tissue from young adult rats was co-processed for comparison. The quantitative immunogold analysis revealed an increase in GSH-immunoreactivity in both pre- and postsynaptic compartments in the lumbar motor nuclei of aged rats. Presynaptically, the enrichment of GSH-immunoreactivity was seen in axonal boutons of normal appearance, and was furthermore restricted to the extra-mitochondrial compartment. Postsynaptically, the aged rats disclosed, in comparison with young adults, higher values for GSH-immunoreactivity both over mitochondria (+49%) and cytoplasmic matrix (+130%). When analysing the transmitter identity of the bouton profiles, it turned out that close to 50% of all glutamate-immunoreactive boutons in the aged rats contained very high levels (> 40 gold particles/microm2) of GSH-immunoreactivity. Strong GSH-immunoreactivity was also a typical feature of a subset of axon terminal- and axon fibre-like profiles in the aged rat that showed signs of axon dystrophy and degeneration. When comparing with normally appearing axon fibre profiles located in close vicinity, the population of aberrant axons had higher average levels of glutamate-immunoreactivity (+93%), and lower average levels of glycine-immunoreactivity (-88%). No difference was seen regarding the levels of GABA. The results of this study lend support to the idea that aging in the spinal cord motor nuclei is associated with an increased oxidative stress and indicate that different transmitter systems are differentially affected by the degenerative process.

Sensitization by prolonged glutathione depletion of kainic acid to potentiate DNA binding of the nuclear transcription factor activator protein-1 in murine hippocampus

In four of four mice intracerebroventricularly injected with the inhibitor of glutathione synthesis L-buthionine-[S,R]-sulfoximine (BSO) 2 days before, an intraperitoneal injection of kainic acid (KA) invariably led to marked potentiation of DNA binding activity of the nuclear transcription factor activator protein-I (AP1) in the hippocampus at a dose which was ineffective in animals previously injected with vehicle alone. However, KA failed to potentiate binding in animals injected with BSO 1 day before. The intracerebroventricular injection of BSO induced marked and prolonged depletion of a total glutathione content in murine hippocampus for 1-2 days after administration. These results suggest that prolonged depletion of endogenous glutathione for a period longer than 1 day may lead to sensitization of KA signals to potentiate AP1 DNA binding in cell nuclei and thereby modulate de novo synthesis of particular proteins at the level of gene transcription in murine hippocampus.

Glutathione depletion causes an uncoupling effect on retinal horizontal cells through oxidative stress

To investigate a physiological role of glutathione in the horizontal cells of carp retina, the gap junctional intercellular communication between horizontal cells was studied using the techniques of intracellular recording of light-induced responses and coupling of the fluorescence dye Lucifer Yellow. Intravitreal injection of 2.5 micromol L-buthionine sulfoximine, an inhibitor of glutathione synthesis, induced a dramatic reduction (20% of control) of retinal glutathione level two days after treatment. The low level of glutathione continued for a further four to five days, and thereafter gradually recovered to about 40% (20 days after injection) and 70% (50 days after injection) of the control level. The spatial properties of the photopic L-type horizontal cell response were examined by enlarging the diameter of the central spot and peripheral annulus over the recording point. In normal retinas, the response amplitude of horizontal cells was monotonically enhanced as the diameter of the spot increased (0.5-4.0 mm) and correspondingly the dye diffusion area was wide, as the injected Lucifer Yellow normally diffused to several neighboring cells. Treatment with L-buthionine sulfoximine significantly altered the spatial properties of horizontal cells by increasing the response amplitude to central spots and slightly decreasing that to peripheral annuli, which were observed by four days after injection. It also restricted intracellular Lucifer Yellow to one or two cells. Accompanying the recovery of the cellular level of glutathione, the spatial properties and dye coupling of horizontal cells were restored to normal. A time lag (two days) of initiation in retinal glutathione depletion and alteration of spatial or dye coupling properties of horizontal cells is discussed, together with reactive oxygen species accumulation.

Preventive effects of exogenous phospholipases on inhibition by ferrous ions of [3H]MK-801 binding in rat brain synaptic membranes

Prior treatment with ferrous chloride led to marked inhibition of [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne (MK-801) binding to an open ion channel associated with the N-methyl-D-aspartate (NMDA) receptor in a concentration-dependent manner at concentrations of higher than 1 microM in rat brain synaptic membranes. Both phospholipases A2 and C significantly prevented the inhibition when treated before the treatment with ferrous chloride, while neither superoxide dismutase nor alpha-tocopherol affected the inhibition even when treated simultaneously with ferrous chloride. Of various saturated and unsaturated free fatty acids, moreover, both oleic and arachidonic acids exclusively decreased the potency of ferrous chloride to inhibit binding when membranes were first treated with fatty acids, followed by the second treatment with ferrous chloride. These results suggest that membrane phospholipids may be at least in part responsible for interference by ferrous ions with opening processes of the native NMDA channel through molecular mechanisms associated with the liberation of unsaturated free fatty acids in rat brain.

Differential inhibition by ferrous ions of [3H]MK-801 binding to native N-methyl-D-aspartate channel in neonatal and adult rat brains

In vitro addition or pretreatment with >/=1 microM ferrous chloride markedly inhibited in a concentration-dependent manner [3H]dizocilpine (MK-801) binding to an open ion channel associated with the N-methyl-D-aspartate (NMDA) receptor in rat brain synaptic membranes. The addition of NMDA agonists invariably attenuated the inhibition of [3H]MK-801 binding in hippocampal synaptic membranes previously treated with ferrous chloride, without significantly affecting that in cerebellar synaptic membranes. In the absence of spermidine, ferrous chloride was more potent in inhibiting binding in the cerebral cortex and hippocampus in adult rats than in those in rats at 3 days after birth, while in the striatum [3H]MK-801 binding was 10 times more sensitive to inhibition by added ferrous chloride in neonatal rats than in adult rats. Addition of spermidine significantly attenuated the potency of ferrous chloride to inhibit binding in the cerebral cortex of adult rats, with facilitation of the inhibition in newborn rats. Moreover, spermidine significantly reduced the inhibitory potency of ferrous chloride in neonatal rat striatum, without markedly affecting that in adult rat striatum. These results suggest that ferrous ions may interfere with opening processes of the native NMDA channel through molecular mechanisms peculiar to neuronal development in a manner associated with the polyamine recognition domain.

Glutathione is an endogenous ligand of rat brain N-methyl-D-aspartate (NMDA) and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors

A study was made of the effects of reduced (GSH) and oxidized (GSSG) glutathione on the Na(+)-independent and N-methyl-D-aspartate (NMDA) displaceable bindings of glutamate, on the binding of kainate, 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), and ligand of the brain NMDA receptor-ionophore complex: glycine, dizocilpine (MK-801) and (+/-)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonate (CPP). GSH and GSSG strongly inhibited the binding of glutamate, CPP and AMPA, kainate and glycine binding being less affected. Both peptides enhanced the binding of dizocilpine in a time- and concentration-dependent manner. This activatory effect was not additive to that of saturating concentrations of glutamate or glutamate plus glycine. The activation of dizocilpine binding by GSH and GSSG was prevented by the competitive NMDA and glycine antagonists DL-2-amino-5-phosphonovalerate and 7-chlorokynurenate. GSH and GSSG may be endogenous ligands of AMPA and NMDA receptors, binding preferably to the glutamate recognition site via their gamma-glutamyl moieties. In addition to this, at millimolar concentrations they may regulate the redox state of the NMDA receptor-ionophore complex.

Modulation by both diphenyliodonium and diphenyleneiodonium of [3H]MK-801 binding to rat brain synaptic membranes

Binding of [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne (MK-801) was significantly inhibited by the addition of several different compounds related to generation of nitric oxide (NO) at 100 microM in rat brain synaptic membranes. These included sodium nitroprusside, diphenyliodonium (DI), diphenyleneiodonium (DPI) and methylene blue. However, neither S-nitroso-N-acetylpenicillamine nor S-nitroso-L-glutathione inhibited binding at 100 microM. Both DI and DPI inhibited binding in a concentration-dependent manner at a concentration range of over 1 microM, while further addition of spermidine (SPD) significantly attenuated the potency of DPI to inhibit binding without affecting that of DI. In contrast, SPD induced significant potentiation of the ability of unlabelled MK-801 to displace [3H]MK-801 binding in a fashion sensitive to antagonism by the novel polyamine antagonist bis-(3-aminopropyl)nonanediamine. This novel polyamine antagonist also prevented the reversing effect of SPD on inhibition by DPI of [3H]MK-801 binding. Moreover, DPI competitively exacerbated the ability of SPD to potentiate [3H]MK-801 binding in the presence of both L-glutamic acid and glycine at maximally effective concentrations. On the other hand, SPD was effective in reversing the inhibition by DPI in cerebellar, but not hippocampal, synaptic membranes. These results suggest that both DI and DPI may modulate synaptic responses mediated by the N-methyl-D-aspartate receptor through inhibition of opening processes of the ion channel in a manner irrespective of generation of NO radicals in particular situations. Possible involvement of the polyamine domain in the inhibition by DPI is also suggested.

Modulation of sensory and excitatory amino acid responses by nitric oxide donors and glutathione in the ventrobasal thalamus of the rat

Nitric oxide has been identified as having a role in synaptic transmission in the central nervous system. In the ventrobasal complex of the thalamus (VB), the precursor of nitric oxide synthesis, L-arginine, causes enhancement of excitatory amino acid responses and somatosensory transmission. In this study, the nitric oxide donors sodium nitroprusside, 3-morpholinosydnonimine and S-nitrosoglutathione were applied to VB relay neurons by iontophoresis and responses of single neurons were recorded extracellularly. Sodium nitroprusside caused selective inhibition of responses to NMDA, probably mediated by a by-product, ferrocyanide, as described in previous studies. 3-Morpholinosydnonimine and S-nitrosoglutathione, however, caused potentiation of responses to sensory stimuli and to excitatory amino acids. In contrast, glutathione in both its reduced and oxidized forms reduced such responses, and this suggests that the potentiating effect of S-nitrosoglutathione could be due to nitric oxide production. These results are consistent with the hypothesis that nitric oxide may have a local modulatory role in the thalamus. Data are presented which suggest that glutathione may have a negative modulatory influence on neurotransmission and excitatory amino acid responses in the ventrobasal thalamus.

Sulfhydryl modification inhibits K+ (M) current with kinetics close to acetylcholine in rodent NG108-15 cells

The effects of sulfhydryl reagents on M-type voltage-dependent potassium currents (IK(M)) were examined in NG108-15 cells transformed to express ml muscarinic acetylcholine receptors (mAChRs), a NGPM1-27 clone. Focal application of glutathione at millimolar concentrations dissolved in acidic solutions caused a transient inward current in NGPM1-27 cells at holding potentials of -30mV, associated with an inhibition of IK(M). The glutathione-induced response was mimicked by cysteine. These effects were also reproduced by superfusion with micromolar concentrations of HgCl2, AgNO3, N-methylmaleimide and p-chloromercuribenzoic acid (pCMB), agents which target protein thiols. Glutathione, HgCl2, AgNO3 and pCMB inhibited the peak conductance of IK(M) without shifting the half activating voltage (V1/2), which was comparable to the acetylcholine (ACh)-induced response. The voltage dependence of time constants for IK(M) deactivation in sulfhydryl reagent-, ACh- and non-treated cells resembled, but differed from that in Ba(2+)-treated cells. These results reveal that there is an accessible cysteine moiety, but not a disulfide bond, either on the M channel protein itself or on a protein directly involved in agonist-M channel coupling.

State-dependent changes of extracellular glutamate in the medial preoptic area in freely behaving rats

Microdialysis technique was applied to the medial preoptic area (mPOA) of the hypothalamus, a crucial site for the regulation of sleep, in order to analyze the interrelationship between the extracellular level of glutamate (Glu) and the vigilance states. Dialysates from the mPOA were sampled at 5-min intervals for 2-h diurnal period with a perfusion rate of 2.0 microliters/min in freely moving rats, whose sleep-waking behaviors were polysomnographically monitored. Extracellular Glu increased during wakefulness, exhibiting a peak at the transition period from wakefulness to non-rapid-eye-movement sleep (NREMS) (18.0% above the average), whereas it decreased during NREMS (9.2% below the average). It is likely that Glu in the mPOA is dynamically involved in the alterations of the vigilance states.

Simultaneous determination of binding of a variety of radioligands related to ionotropic excitatory amino acid receptors in fetal and neonatal rat brains

Expression of ionotropic excitatory amino acid receptors was assessed by membrane binding assays using a variety of radioligands in fetal and neonatal rat brains. In fetal rat brain, receptors sensitive to N-methyl-D-aspartate (NMDA) exhibited delayed onset of expression during the last 7 days before birth as compared with those insensitive to NMDA. In addition, developmental increases in agonist-preferring sites preceded those in antagonist-preferring sites within the first 7 postnatal days in particular brain structures with respect to each domain on the NMDA receptor complex. Growth of animals led to drastic increments of [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine (MK-801) binding to the NMDA channel in telencephalic regions until 21 to 28 days after birth, with concomitant desensitization to inhibition by protons of [3H]MK-801 binding in cortical membranes. By contrast, three different agonists were invariably effective in more potently potentiating [3H]MK-801 binding in cortical membranes of 14- and 28-day-old rats than in those of 5-day-old rats. These results suggest that the NMDA-sensitive subclass may play more critical roles in mechanisms underlying postnatal development of rat telencephalon than do the NMDA-insensitive subclasses.

Sleep as neuronal detoxification and restitution

The classical 'hypnotoxin theory' was followed by extensive search for an endogenous sleep substance. Brain tissues and body fluids of sleeping and sleep-deprived animals contained active sleep-inducing factors like the sleep-promoting substance (SPS). Uridine and oxidized glutathione (GSSG), two components of SPS, seem to regulate physiological sleep differentially. Uridine may facilitate the inhibitory neurotransmission at the synaptic level of the GABAA-uridine receptor complex. In contrast, GSSG may inhibit the excitatory neurotransmission at the synaptic level of the glutamate receptor. Thus, the two SPS components promote sleep by exerting a complementary action on the two major neurotransmitter systems in the brain that have mutually reciprocal functions. Further, among multidimensional functions of sleep, uridine may contribute to recover the activity of neurons, while glutathione may counteract excitotoxic events. Hence sleep at the behavioral level is a process of neuronal restitution and detoxification at the cellular level. Such a concept can be regarded as a modern version of the Ishimori-Piéron's hypnotoxin theory proposed early in this century.

Search for novel ligands selective at a polyamine recognition domain on the N-methyl-D-aspartate receptor complex using membrane binding techniques

Among over 60 polyamine derivatives tested, only N-(3-aminopropyl)octanediamine and bis-(3-aminopropyl)nonanediamine (TE393) markedly inhibited [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne (MK-801) binding at equilibrium in the presence of added spermidine (SPD) in "non-washed" rat brain synaptic membranes, without affecting that in the absence of added SPD. Although TE393 significantly potentiated [3H]MK-801 binding before equilibrium in the presence of L-glutamic acid (Glu) alone or both Glu and glycine (Gly) added in "Triton-treated" membranes, the putative polyamine antagonists 1,10-decanediamine (DA10) and arcaine invariably inhibited binding irrespective of the addition of agonists. In the absence of added SPD, in addition, TE393 markedly enhanced abilities of both Glu and Gly to potentiate [3H]MK-801 binding before equilibrium. However, TE393 induced a rightward shift of the concentration-response curve of SPD for [3H]MK-801 binding before equilibrium. Moreover, TE393 was effective in potentiating binding of an antagonist but not an agonist radioligand to the NMDA domain and in inhibiting binding of an antagonist but not an agonist radioligand to the Gly domain. The potentiation of NMDA antagonist binding by TE393 occurred in a manner sensitive to prevention by arcaine but not by DA10. These results suggest that TE393 may be a novel ligand at the polyamine domain with an ability to interact with both the NMDA and Gly recognition domains in antagonist-preferring forms.

Non-steroidal anti-inflammatory drugs and spinal nociceptive processing

Non-steroidal anti-inflammatory drugs have a direct action on spinal nociceptive processing in vivo with a relative order of potency which correlates with their capacity as inhibitors of cyclooxygenase activity. However, recent clinical surveys and new in vivo evidence strongly suggest that for some of these agents, centrally mediated analgesia may also be achieved by additional mechanisms, which are independent of prostaglandin synthesis inhibition. In this review we explore the likelihood for such mechanisms following an extensive survey of existing data. The implications of these mechanisms are discussed in the light of our current understanding of spinal nociceptive processing.

Possible dysfunction of ionotropic glutamate receptors in cerebellum of epileptic E1 mouse brain

Binding of [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten- 5,10-imine (MK-801) to an ion channel domain on the N-methyl-D-aspartate (NMDA)-sensitive subclass of brain glutamate (Glu) receptors was highest in the hippocampus of the hereditary epileptogenic mutant El as well as its parent ddY strain mice, when determined before and at equilibrium in the presence of 3 different agonists at the respective domains on the NMDA receptor complex, including Glu, glycine (Gly) and spermidine (SPD). Cerebellar [3H]MK-801 binding before equilibrium was significantly lower in El mice than in ddY mice, while the binding was not significantly different from each other in other brain structures of both strains of mice. Kinetic analysis revealed that the association rate was significantly lower with [3H]MK-801 binding in the cerebellum of El mice than of ddY mice. In contrast to ddY mice, furthermore, Gly failed to potentiate cerebellar [3H]MK-801 binding before equilibrium in El mice, with SPD being active in significantly inhibiting the binding. However, saturation analysis revealed that the affinity and density of cerebellar [3H]MK-801 binding at equilibrium in El mice were not significantly different from those in ddY mice. In addition, epileptogenic El mice had significantly higher levels of [3H]SPD binding in all brain structures examined than ddY mice, whereas [3H]DL-alpha-amino-3-hydroxy-5- methylisoxazole-4-propionate binding was significantly lower in the cerebellum of El mice than of ddY mice. These results suggest that dysfunction of cerebellar Glu receptors may be at least in part responsible for a variety of abnormal symptoms observed in epileptic El mice.

Partial purification of [3H]glutamate-associating-proteins with sensitivity to displacement by N-methyl-D-aspartate from rat brain

An attempt was made to solubilize and isolate [3H]L-glutamic acid (Glu) binding sensitive to displacement by N-methyl-D-aspartic acid (NMDA) from rat brain. Brain synaptic membranes were solubilized by deoxycholic acid, followed by gel filtration with Sephadex G-25. In these turbid supernatants, significant but fragile binding was detected with a variety of radioligands related to ionotropic subclasses of receptors for excitatory amino acids. These included [3H]5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cyclohepten-5,10-imine (MK-801), [3H]glycine, [3H]spermidine, [3H]Glu, [3H]DL-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic and [3H]kainic acids. Re-solubilization of turbid supernatants by Triton X-100 resulted in detection of [3H]Glu binding which was only stable for 24 h, with [3H]MK-801 binding being entirely lost. In these clear preparations after re-solubilization, Glu was exclusively effective in completely displacing [3H]Glu binding with other ligands being partially active. Furthermore, [3H]Glu binding displaceable by NMDA was eluted with 0.5 M KCl together with [3H]Glu binding insensitive to NMDA on DEAE-Toyopearl column chromatography, while fractions eluted with 0.2 M KCl had NMDA-insensitive [3H]Glu binding only. Chromatography on chelate (Zn)-Toyopearl resin resulted in elution of both NMDA-sensitive and NMDA-insensitive [3H]Glu binding with 10 mM EDTA. High performance liquid chromatography revealed that NMDA-sensitive [3H]Glu binding was detected at retention times of 10-20 min when eluted from an Asahipak ES-502N column with NaCl at linearly graded concentrations up to 0.5 M. In order to detect NMDA-sensitive [3H]Glu binding, however, the whole procedures needed to be completed within 24 h after re-solubilization. Accordingly, the identity of the NMDA-sensitive [3H]Glu binding partially purified here is still unclear at present. The NMDA recognition domain could be more stable than the NMDA channel domain on the NMDA receptor ionophore complex under aqueous conditions.

Release of [3H]GABA evoked by glutamate agonists from hippocampal slices: effects of dithiothreitol and glutathione

The effects of dithiothreitol (DTT) and, reduced (GSH) and oxidized (GSSG), glutathione on the release of [3H]GABA evoked by glutamate and its agonists were studied in rat hippocampal slices. DTT had no effect on the basal release of [3H]GABA but it enhanced and prolonged the glutamate agonist-evoked release. This effect was abolished by (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohept-5,10-imine hydrogen maleate (MK-801), a noncompetitive NMDA antagonist, and blocked by Mg2+ ions. It was only slightly attenuated by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA receptor antagonist, and not affected by L-(+)-2-amino-3-phosphonopropionate (L-AP3), a selective antagonist of the metabotropic glutamate receptor. The effect of DTT on the NMDA-evoked release of GABA was only slightly affected by extracellular Ca2+ but completely blocked by verapamil even in the absence of Ca2+. GSH and GSSG attenuated or abolished the effects of DTT on the agonist-induced release of [3H]GABA. The results imply that the enhanced and prolonged release of GABA evoked by the coexistence of DTT and excitatory amino acids and attenuated by endogenous GSH and GSSG is a consequence of sustained activation of the NMDA receptor-governed ionophores, which contain functional thiol groups. DTT, GSH and GSSG may regulate the redox state and accessibility of these groups. In addition to the influx of extracellular Ca2+, DTT mobilizes Ca2+ from intracellular pools distinct from those regulated by metabotropic glutamate receptors.

Antisera to glutathione: characterization and immunocytochemical application to the rat cerebellum

Rabbits were immunized with reduced glutathione (gamma-glutamyl-cysteinyl-glycine) coupled to bovine serum albumin by glutaraldehyde or a mixture of glutaraldehyde and formaldehyde. The antisera that were formed were tested qualitatively, by screening them against more than 50 amino acids and peptide conjugates that had been immobilized on cellulose discs (spot test), and quantitatively, by immunogold analysis of test conjugates that had been embedded in an epoxy resin. It was shown that the antisera selectively recognized the reduced and oxidized forms of glutathione and that they did not exhibit any significant crossreactivity with glutamate, cysteine, glycine, gamma-glutamyl-cysteine or cysteinyl-glycine. Immunocytochemistry of Vibratome sections of rat cerebellum suggested that glutathione occurs in glial cells as well as in neurons. This was confirmed by electron microscopic, immunogold cytochemistry of tissue from rat cerebellum that had been freeze-substituted and embedded in Lowicryl under low temperature. Gold particles were concentrated over Golgi epithelial cells and perivascular glial processes, but also occurred over several types of neuronal profile including Purkinje and granule cell bodies, and mossy fibre terminals. At the subcellular level, glutathione-like immunoreactivity was found in the cytoplasmic matrix, mitochondria and nuclei. The immunolabelling intensity was strongly reduced in animals that had been pretreated with buthionine sulphoximine, which is known to depress the level of glutathione by inhibiting gamma-glutamyl-cysteine synthetase. The availability of antisera to glutathione is likely to further our understanding of the physiological and pathophysiological roles of this tripeptide.

Supporting evidence for negative modulation by protons of an ion channel associated with the N-methyl-D-aspartate receptor complex in rat brain using ligand binding techniques

The addition of L-glutamic acid (Glu) alone, both Glu and glycine (Gly) or Glu/Gly/spermidine (SPD) was effective in potentiating [3H]5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10- imine (MK-801) binding before equilibrium to an ion channel associated with the N-methyl-D-aspartate (NMDA) receptor complex in brain synaptic membranes extensively washed and treated with Triton X-100. The binding dependent on Glu almost linearly increased in proportion to decreasing proton concentrations at a pH range of 6.0 to 9.0 in external incubation medium, while a Gly-dependent portion of the binding increased with decreasing proton concentrations up to a pH of 7.5 with a plateau thereafter. In contrast, the SPD-dependent binding increased in proportion to decreasing proton concentrations up to a pH of 7.0 with a gradual decline thereafter. Similar profiles were also obtained with [3H]MK-801 binding at equilibrium, with an exception that significant binding of [3H]MK-801 was detected in the absence of any added agonists. The potency of SPD to potentiate [3H]MK-801 binding before equilibrium increased in proportion to decreasing proton concentrations, with those of both Glu and Gly being unchanged. In contrast, the ability of (+)MK-801 to displace [3H]MK-801 binding at equilibrium was not significantly affected by a decrement of external proton concentrations from pH 7.5 to pH 8.5 in the presence of Glu/Gly and Glu/Gly/SPD added. However, similar changes in external proton concentrations did not similarly affect binding of several radioligands for the NMDA and Gly domains on the receptor complex. Decreasing proton concentrations were effective in exponentially potentiating binding of [3H]SPD at a pH range of 6.0 to 9.0 without virtually altering [3H]D,L-alpha-amino-3- hydroxy-5-methyl-isoxazole-4-propionic acid binding. In addition, [3H]kainic acid binding markedly decreased with decreasing proton concentrations only in the presence of Ca2+ ions. These results suggest that protons negatively modulate neuronal responses mediated by the NMDA receptor ionophore complex through interference with opening mechanisms of the channel domain without disturbing association processes of the endogenous agonists with the respective recognition domains in rat brain. Moreover, possible modulation by protons of responses mediated by the kainate receptor in the presence of Ca2+ ions at concentrations that occur in vivo is also suggested.

Oxidized glutathione regulates physiological sleep in unrestrained rats

Oxidized glutathione (GSSG) is an active component of sleep-promoting substance (SPS) which was originally extracted from the brainstems of 24-h sleep-deprived rats. We analyzed somnogenic and thermoregulatory activities of five doses of GSSG in unrestrained rats. A nocturnal 10-h intracerebroventricular infusion of GSSG significantly enhanced slow wave sleep (SWS) at the dosage range from 20 to 50 nmol and paradoxical sleep (PS) at 25 nmol at the expense of wakefulness during the 12-h dark period. The dose-response relations exhibited a bell shape for both SWS and PS. The administration of 25 nmol/10 h GSSG induced the maximal increase in the total time of nocturnal sleep (35% above the baseline for SWS and 86% for PS). The enhancement of sleep was mainly due to an increase in the duration of SWS episodes and in the number of PS episodes. GSSG at 25 nmol/10 h elicited significant fluctuations in brain temperature (Tbrain), biphasic hypothermal and hyperthermal reactions during the infusion period, followed by a hyperthermal state during the subsequent light period of the recovery day and then a hypothermal state during the dark period. On the basis of recent literature on the inhibitory action of GSSG on the excitatory synaptic membrane of rat brain, we speculate that the sleep-enhancing activity of GSSG was caused by its physiological modulation on the glutamatergic neurotransmission in the brain.

Differential profiles of binding of a radiolabeled agonist and antagonist at a glycine recognition domain on the N-methyl-D-aspartate receptor ionophore complex in rat brain

Addition of several polyamines, including spermidine and spermine, was effective in inhibiting binding of the antagonist ligand [3H]5,7-dichlorokynurenic acid ([3H]-DCKA) a Gly recognition domain on the N-methyl-D-aspartic acid (NMDA) receptor ionophore complex in rat brain synaptic membranes. In contrast, [3H]DCKA binding was significantly potentiated by addition of proposed polyamine antagonists, such as ifenprodil and (+/-)-alpha-(4-chlorophenyl)-4-[(4-fluorophenyl) methyl]-1-piperidine ethanol, with [3H]Gly binding being unchanged. The inhibition by spermidine was significantly prevented by inclusion of ifenprodil. In addition, spermidine significantly attenuated the abilities of four different antagonists at the Gly domain to displace [3H]DCKA binding virtually without affecting those of four different agonists. Phospholipases A2 and C and p-chloromercuribenzosulfonic acid were invariably effective in significantly inhibiting [3H]DCKA binding with [3H]Gly binding being unaltered. Moreover, the densities of [3H]DCKA binding were not significantly different from those of [3H]-Gly binding in the hippocampus and cerebral cortex, whereas the cerebellum had more than a fourfold higher density of [3H]Gly binding than of [3H]DCKA binding. These results suggest that the Gly domain may have at least two different forms based on the preference to agonists and antagonists in the rodent brain.

Vitamin E, ascorbate, glutathione, glutathione disulfide, and enzymes of glutathione metabolism in cultures of chick astrocytes and neurons: evidence that astrocytes play an important role in antioxidative processes in the brain

GSH, GSSG, vitamin E, and ascorbate were measured in 14-day cultures of chick astrocytes and neurons and compared with levels in the forebrains of chick embryos of comparable age. Activities of enzymes involved in GSH metabolism were also measured. These included gamma-glutamylcysteine synthetase, GSH synthetase, gamma-glutamyl cyclotransferase, gamma-glutamyltranspeptidase, glutathione transferase (GST), GSH peroxidase, and GSSG reductase. The concentration of lipid-soluble vitamin E in the cultured neurons was found to be comparable with that in the forebrain. On the other hand, the concentration of vitamin E in the astrocytes was significantly greater in the cultured astrocytes than in the neurons, suggesting that the astrocytes are able to accumulate exogenous vitamin E more extensively than neurons. The concentrations of major fatty acids were higher in the cell membranes of cultured neurons than those in the astrocytes. Ascorbate was not detected in cultured cells although the chick forebrains contained appreciable levels of this antioxidant. GSH, total glutathione (i.e., GSH and GSSG), and GST activity were much higher in cultured astrocytes than in neurons. gamma-Glutamylcysteine synthetase activity was higher in the cultured astrocytes than in the cultured neurons. GSH reductase and GSH peroxidase activities were roughly comparable in cultured astrocytes and neurons. The high levels of GSH and GST in cultured astrocytes appears to reflect the situation in vivo. The data suggest that astrocytes are resistant to reactive oxygen species (and potentially toxic xenobiotics) and may play a protective role in the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutathione modulates the N-methyl-D-aspartate receptor-activated calcium influx into cultured rat cerebellar granule cells

The effects of reduced (GSH) and oxidized (GSSG) glutathione and dithiothreitol (DTT) and L-cysteine on the influx of 45Ca2+ were studied with cultured cerebellar granule cells. DTT slightly enhanced the basal influx but strongly activated the influx stimulated by glutamate or N-methyl-D-aspartate (NMDA). The effects on the kainate- or quisqualate-induced influx were less pronounced. Extracellular GSH had no effect on the basal influx of Ca2+. A concentration of 0.5 mM GSH slightly activated the glutamate- and NMDA-induced influx while GSSG was inhibitory. The enhancement by DTT and cysteine of the responses to excitatory amino acids was attenuated by GSH and GSSG. We propose that both the accessibility and redox state of the functional sulfhydryl groups in NMDA receptor-ionophores may be regulated by endogenous glutathione. These effects are attributed to the gamma-glutamyl moiety and sulfhydryl group in the tripeptide molecule.

Excitatory amino acid receptor binding in hippocampus of gerbils with transient global brain ischemia

Binding of a variety of ligands for brain excitatory amino acid receptors was examined in membrane preparations extensively washed and treated with Triton X-100 that were obtained from the hippocampus and cerebral cortex of gerbils that survived for different periods after transient global brain ischemia. Bilateral occlusion of the carotid arteries for 5 min did not affect the binding of [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne (MK-801) to an open ion channel associated with the N-methyl-D-aspartate (NMDA)-sensitive subclass in both central structures of gerbils that survived for 1 to 4 weeks after the injury when determined at equilibrium in the presence of 3 different endogenous agonists including L-glutamic acid (Glu), glycine (Gly) and spermidine at maximally effective concentrations. In contrast, the ischemic occlusion significantly diminished [3H]MK-801 binding when determined before equilibrium in the presence of the 3 stimulants in hippocampal membranes without altering that in cortical membrane 2 weeks after the insult, so that the initial association rates were invariably reduced by more than 60%. Moreover, the occlusion not only reduced the binding of both [3H]Glu and [3H]D,L-(E)-2-amino-4-propyl-5-phosphono-3-pentenoic acid to the NMDA domain on the NMDA receptor ionophore complex, but also decreased the binding of both [3H]Gly and [3H]5,7-dichlorokynurenic acid to the Gly domain. However, the insult did not induce any detectable changes under the experimental conditions employed in either the binding of [3H]DL-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) to the AMPA-sensitive subclass or the binding of kainic acid (KA) to the KA-sensitive subclass in both central regions of animals that survived for 2 weeks. These results suggest that transient global brain ischemia may predominantly impair neuronal and/or glial cells enriched of the NMDA receptor ionophore complex in gerbil hippocampus.

Effects of in vitro ethanol and fetal ethanol exposure on glutathione stimulation of N-methyl-D-aspartate receptor function

The present studies investigated the effects of glutathione (GSH; gamma-glutamylcysteinylglycine) and its oxidized form (GSSG) on neuronal N-methyl-D-aspartate (NMDA) receptor activation in both acute and chronic preparations of ethanol exposure. It was demonstrated using fura-2-loaded dissociated brain cells from newborn rat pups that both GSH and GSSG (0-4 mM) produced concentration-dependent increases in intracellular calcium similar to those produced by NMDA and other agonists of the NMDA receptor. GSH-stimulated calcium entry was not inhibited by low intoxicating concentrations of ethanol, which contrasts with ethanol's typical inhibitory effect on NMDA-stimulated receptor activation. Behavioral studies in adult rats demonstrated that ethanol-induced sleep times were significantly decreased when 10 microliters of GSSG (20 mM) were administered intracerebroventricularly approximately 5 min before an intraperitoneal injection of 20% (w/v) ethanol (3 g/kg). These findings suggest that the less potent effect of ethanol on GSH-stimulated calcium entry as well as the reduction in ethanol-induced sleep times may be related to the presence of glycine in the peptide. The glycine found in GSH may activate the glycine site and block or reduce ethanol's action on this site. It appears that although GSH may play an important role in the activation of the NMDA receptor, this action does not involve a process that is sensitive to acute ethanol exposure. In contrast, when rat pups were chronically exposed to ethanol via prenatal exposure before the fura-2 preparation, increases in NMDA- and GSH-stimulated calcium entry were significantly decreased relative to those in pair-fed and ad libitum-fed controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative studies on binding of 3 different ligands to the N-methyl-D-aspartate recognition domain in brain synaptic membranes treated with Triton X-100

Treatment with a low concentration of Triton X-100 almost tripled the binding of [3H]D,L-(E)-2-amino-4-propyl-5-phosphono-3-pentenoic acid (CGP 39653), a novel competitive antagonist at an N-methyl-D-aspartate (NMDA)-sensitive subclass of brain excitatory amino acid receptors, in synaptic membranes of the rat brain. The binding linearly increased with increasing protein concentrations of up to 0.4 mg/ml and also increased in proportion to incubation time with a plateau within 60 min after the initiation of incubation at 2 degrees C in Triton-treated membranes. Elevation of incubation temperature from 2 degrees C to 30 degrees C resulted in a marked decrease in the binding at equilibrium by 80%, and a maximal level was obtained within 1 min after the initiation of incubation at 30 degrees C with a gradual decline of up to 10 min. Bound [3H]CGP 39653 was rapidly dissociated by the addition of excess unlabeled L-glutamic acid (Glu), and the time required to attain complete dissociation was 60 min at 2 degrees C and 1 min at 30 degrees C, respectively. Among several agonists and antagonists tested, Glu was the most potent displacer of [3H]CGP 39653 binding with progressively less potent displacement by D-2-amino-5-phosphonovaleric, (+-)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic (CPP), D-2-amino-7-phosphonoheptanoic, N-methyl-D-aspartic and N-methyl-L-aspartic acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential potentiation by spermidine of abilities of a variety of displacers for [3H]MK-801 binding in hippocampal synaptic membranes

Binding of [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne (MK-801) to an ion channel associated with the N-methyl-D-aspartate (NMDA)-sensitive subtype of brain excitatory amino acid receptors was studied in Triton-treated preparations of synaptic membranes of rat brain. The initial association rate of the binding measured at 30 min after onset of incubation was markedly potentiated by the addition of either L-glutamic acid (Glu) alone or both Glu and glycine (Gly) in a concentration-dependent manner at 10 nM to 0.1 mM. Potentiation occurred to a significantly greater extent in the hippocampus and cerebral cortex than in the cerebellum. In the presence of both Glu and Gly, the endogenous polyamine spermidine (SPD) further potentiated binding in hippocampal and cortical membranes at concentrations above 10 microM without significantly affecting that in cerebellar membranes. The binding of [3H]MK-801 was slowly equilibrated in 16 h. When examined in hippocampal synaptic membranes, the binding at equilibrium was markedly displaced by numerous noncompetitive antagonists for the NMDA receptor. The addition of SPD markedly enhanced potencies of those displacers having a high affinity to [3H]MK-801 binding sites, without affecting other displacers having a low affinity. These results suggest that SPD promotes transition of sites responsible for mediating NMDA responses within the channel to a state with higher affinity for noncompetitive blockers.

Support for radiolabeling of a glycine recognition domain on the N-methyl-D-aspartate receptor ionophore complex by 5,7-[3H]dichlorokynurenate in rat brain

Pretreatment with Triton X-100 more than doubled the binding of radiolabeled 5,7-dichlorokynurenic acid (DCKA), a proposed antagonist at a glycine (Gly) recognition domain on the N-methyl-D-aspartate (NMDA) receptor ionophore complex, in rat brain synaptic membranes. The binding exhibited an inverse temperature dependency, reversibility, and saturability, the binding sites consisting of a single component with a high affinity (27.5 nM) and a relatively low density (2.87 pmol/mg of protein). The binding of both [3H]DCKA and [3H]Gly was similarly displaced by numerous putative agonists and antagonists at the Gly domain in a concentration-dependent manner at a concentration range of 100 nM to 0.1 mM. Among the 24 putative ligands tested, DCKA was the second most potent displacer of the binding of both radioligands with no intrinsic affinity for the binding of [3H]kainic acid and alpha-amino-3-hydroxy-5- [3H]methylisoxazole-4-propionic acid (AMPA) to the non-NMDA receptors. In contrast, the other proposed potent Gly antagonist, 5,7-dinitroquinoxaline-2,3-dione, was active in displacing the binding of [3H]glutamic ([3H]Glu) and D,L-(E)-2-amino-4-[3H]propyl-5-phosphono-3-pentenoic acids to the NMDA recognition domain with a relatively high affinity for the non-NMDA receptors. In addition, the proposed antagonist at the AMPA-sensitive receptor, 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline, not only displaced weakly the binding of both [3H]-Gly and [3H]DCKA, but also inhibited the binding of (+)-5-[3H]methyl-10,11- dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine ([3H]MK-801) to an ion channel associated with the NMDA-sensitive receptor in the presence of added Glu alone in a manner sensitive to antagonism by further added Gly. Clear correlations were seen between potencies of the displacers to displace [3H]DCKA binding and [3H]Gly binding, in addition to between the potencies to displace [3H]-DCKA or [3H]Gly binding and to potentiate or inhibit [3H]MK-801 binding. All quinoxalines tested were invariably more potent displacers of [3H]DCKA binding than [3H]Gly binding, whereas kynurenines were similarly effective in displacing the binding of both [3H]Gly and [3H]DCKA. These results undoubtedly give support to the proposal that [3H]DCKA is one useful radioligand available in terms of its high selectivity and affinity for the Gly domain in the brain. Possible multiplicity of the Gly domain is suggested by the differential pharmacological profiles between the binding of [3H]Gly and [3H]DCKA.

Characterization and localization of glutathione binding sites on cultured astrocytes

Glutathione (GSH) binding sites found in brain white matter in a previous study using biotinylated GSH (Third IBRO World Congress Neurosci. Abstr., 1991, P59.17) suggested that there might GSH receptors on glial cells. In the present study, radioligand receptor assays were performed on cultured astrocytes using [35S]GSH. Scatchard analyses of saturation binding of [35S]GSH revealed two binding sites: Kd1 = 2.0 +/- 0.1 nM, Bmax1 = 89.5 +/- 1.5 fmole/2.2 x 10(5) cells and Kd2 = 12.8 +/- 0.4 nM, Bmax2 = 187.7 +/- 2.4 fmol/2.2 x 10(5) cells. The saturable and displacible high affinity [35S]GSH binding we have observed suggests that this binding is not due to GSH sequestration by uptake sites or to the association of GSH with GSH S-transferases or GSH peroxidases which have Kds in the microM range. Colloidal gold and immunofluorescence double labelling were used to visualize the binding sites at the cellular level. Positive colloidal gold decoration further suggests that these labelled binding sites are membrane receptors on astrocytes.

Inhibition by calmodulin antagonists of [3H]MK-801 binding in brain synaptic membranes

In brain synaptic membranes not extensively washed, (+)-5-[3H]methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5, 10-imine ([3H]MK-801) binding was markedly inhibited in a concentration-dependent manner (at concentrations above 1 microM) by several compounds having antagonistic activity at the Ca(2+)-binding protein calmodulin. Scatchard analysis revealed that N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) inhibited the binding through a significant decrease in the density of binding sites without affecting the affinity at 10 microM. In membranes extensively washed and treated with a low concentration of Triton X-100, L-glutamic acid (Glu) drastically accelerated the initial association rate of [3H]MK-801 binding with glycine (Gly), almost doubling the initial association rate found in the presence of Glu alone. The addition of W-7 invariably reduced the initial association rate observed in the presence of either Glu alone or both Glu and Gly, without significantly altering the dissociation rate of bound [3H]-MK-801, irrespective of the presence of the two stimulatory amino acids. The maximal potencies of Glu, Gly, and spermidine in potentiating the binding were all attenuated by W-7. These results suggest that calmodulin antagonists may interfere with opening processes of an ion channel associated with an N-methyl-D-aspartate-sensitive subclass of excitatory amino acid receptors in rat brain.

Modulatory role of glutathione on mu-opioid, substance P/neurokinin-1, and kainic acid receptor binding sites

Reduced glutathione (L-gamma-glutamyl-L-cysteinylglycine; GSH) is an endogenous tripeptide involved in the formation and maintenance of protein thiol groups as well as in various detoxification reactions. Because multiple receptor types contain thiol groups or disulfide bridges, effects of GSH treatments on mu-opioid, neurokinin-1/substance P, and kainic acid receptor binding sites were investigated and compared with those produced by dithiothreitol (DTT), a potent synthetic reducing agent. GSH inhibited binding more potently than did DTT at all three receptor types in porcine striatal membrane homogenates as well as in CHAPS-solubilized preparations of the mu and neurokinin-1 sites. GSH-induced inhibitory effects were associated with decreases in maximal binding capacity (Bmax) without significant alteration in apparent affinity (KD). Cysteine, the functional moiety of GSH, mimicked GSH effects albeit with lower potencies, whereas oxidized glutathione had no effects at similar concentrations. In CHAPS-solubilized preparations, the combination of low concentrations of GSH and guanylylimidodiphosphate markedly decreased the Bmax values of the binding of [3H][D-Ala2,Gly-ol5]enkephalin and [3H]substance P. This GSH-mediated mechanism may be important to prevent cell overstimulation by accelerating receptor uncoupling, desensitization, and/or internalization. This is in keeping with purported roles of GSH related to the maintenance of cellular integrity.

Differential modulation by divalent cations of [3H]MK-801 binding in brain synaptic membranes

Endogenous divalent cations, such as Mg2+, Ca2+, and Zn2+, differentially affected the binding of (+)-[3H]5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne maleate ([3H]MK-801) to an ion channel associated with an N-methyl-D-aspartate-sensitive subclass of excitatory amino acid receptors in different preparations of brain synaptic membranes. Both Mg2+ and Ca2+ were weak inhibitors of the binding in membranes which had not been extensively washed (nonwashed membranes), over a concentration range effective in markedly potentiating the binding in the absence of any added stimulants in membranes which had been extensively washed, but not treated with a detergent (untreated membranes). In membranes extensively washed and treated with Triton X-100 (Triton-treated membranes), both cations significantly potentiated the binding in the presence of added glutamate alone. In contrast, Zn2+ was invariably active as a potent inhibitor of the binding irrespective of the membrane preparations used. In untreated membranes, Ca2+ markedly accelerated the initial association rate of [3H]MK-801 binding without affecting the binding at equilibrium in a manner similar to that found with glycine, as well as with glutamate; Mg2+, however, facilitated the initial association rate with a concomitant reduction of the binding at equilibrium. Zn2+ was effective in accelerating the initial rapid phase of association, with the initial slow phase being delayed, and in markedly reducing the binding at equilibrium. Both Mg2+ and Ca2+ also facilitated dissociation of the bound [3H]MK-801 and Zn2+ slowed the dissociation in untreated membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Screening of thiol compounds: depolarization-induced release of glutathione and cysteine from rat brain slices

Superfusates from rat brain slices were screened for thiol compounds after derivatization with monobromobimane by reversed-phase HPLC. Only glutathione and cysteine were detected. The Ca(2+)-dependent release of these compounds from slices of different regions of rat brain was investigated, applying a highly sensitive and reproducible quantification method, based on reduction of superfusates with dithiothreitol, reaction of thiols with iodoacetic acid, precolumn derivatization with o-phthalaldehyde reagent solution, and analysis with reversed-phase HPLC. This methodology allowed determination of reduced and total thiols in aliquots of the same superfusates. Mostly reduced glutathione and cysteine were released upon K+ depolarization and the Ca2+ dependency suggests that they originate from a neuronal compartment. The GSH release was most prominent in the mesodiencephalon, cortex, hippocampus, and striatum and lowest in the pons-medulla and cerebellum. This underscores a physiologically significant role for glutathione in CNS neurotransmission.

Effects of ifenprodil on the N-methyl-d-aspartate receptor ionophore complex in rat brain

The effects of a cerebral anti-ischemic drug ifenprodil on the receptor ionophore complex of an N-methyl-D-aspartate (NMDA)-sensitive subclass of central excitatory amino acid receptors were examined using [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10- imine (MK-801) binding in rat brain synaptic membrane preparations as a biochemical measure. The binding in membrane preparations not extensively washed was markedly inhibited not only by competitive NMDA antagonists such as (+/-)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic, D-2-amino-5-phosphonovaleric and D-2-amino-7-phosphonoheptanoic acids, but also by competitive antagonists at the strychnine-insensitive glycine (Gly) site including 7-chlorokynurenic acid and 6,7-dichloroquinoxaline-2,3-dione. Among several proposed ligands for alpha-adrenergic receptors tested, ifenprodil most potently inhibited the binding in these membrane preparations due to a decrease in the density of the binding sites without significantly affecting the affinity. Ifenprodil also inhibited the binding of [3H]N-[1-(2-thienyl)cyclohexyl]piperidine as well as of [3H]MK-801 to open NMDA channels in a concentration-dependent manner at concentrations above 10 nM in membrane preparations extensively washed but not treated by a detergent, with a Hill coefficient of less than unity. Further treatment of extensively washed membrane preparations with a low concentration of Triton X-100 resulted in an almost complete abolition of [3H]MK-801 binding, and the binding was restored to the level found in membrane preparations not extensively washed following the addition of both L-glutamic acid (Glu) and Gly. Ifenprodil was effective in inhibiting [3H]MK-801 binding via reducing both initial association and dissociation rates in Triton-treated membrane preparations, irrespective of the presence of Glu and Gly added. The binding in Triton-treated membrane preparations was additionally potentiated by the polyamine spermidine in a concentration-dependent manner at concentrations above 10 microM in the presence of both Glu and Gly at maximally effective concentrations. Ifenprodil invariably diminished the abilities of these three stimulants to potentiate [3H]MK-801 binding at concentrations over 1 microM in a manner that the maximal responses each were reduced. These results suggest that ifenprodil does not interfere with the NMDA receptor complex as a specific isosteric antagonist at the polyamine domain in contrast to the prevailing view.

Effects of exogenous factors on the cerebral glutathione in rodents

Since glutathione is thought to be involved in cerebral functions, changes in the glutathione level imply modulations of the neurotransmission in addition to all the known effects of GSH. It was investigated whether alterations of the cerebral glutathione can be induced by consumption of GSH, by inhibition or stimulation of the synthesis of GSH, or by an inhibition of the re-reduction of the oxidized glutathione. Aminophenazone, propyphenazone, acetaminophen, phenytoin, morphine and nitrofurantoin, known to deplete hepatic GSH, had no effects on cerebral GSH. Diethyl maleate (0.6 ml/kg) decreased the cerebral content of GSH and GSSG in adult rats as well as in fetuses. The depletion of the cerebral GSH caused by diethyl maleate treatment for 4 days was followed by an increase up to 125% and a subsequent return to the normal level after 1 week. In rats starved up to 71 h deficiency of exogenous amino acids caused only a minimal or no decrease in cerebral GSH. The specific inhibitor of the gamma-glutamylcysteine synthetase BSO only depleted GSH in the brain of young mice following the repeated s.c. administration of a high dose (890 mg/kg). After cobaltous chloride (20 mg/kg; twice a day for 2 or 4 days) the GSH level in the brain was unchanged. In vivo inhibition of the cerebral glutathione reductase was caused by ammonium metavanadate (12.5 mg/kg; three times a week for 6 weeks). Nitrofurantoin (150 mg/kg) had no effect. After lomustine (10 mg/kg) a minimal increase in glutathione reductase was found, but simultaneously also an increase in GSSG and of the ratio GSSG/total glutathione.