Ganglioside GM1 prevents and reverses toluene-induced increases in membrane fluidity and calcium levels in rat brain synaptosomes

Volatile substance misuse : clinical considerations, neuropsychopharmacology and potential role of pharmacotherapy in management

Volatile substance misuse is among the most prevalent and toxic forms of psychoactive drug use, and often results in highly deleterious social, psychological and medical consequences. The prevalence of this pernicious form of substance misuse owes in part to the fact that volatile substances of misuse are ubiquitous in the natural environment. Commonly misused commercial products include glue, shoe polish, nail polish remover, butane lighter fluid, gasoline and computer duster spray. National samples of volatile substance misusers tend to exhibit high rates of psychiatric problems and antisocial behaviour. In addition, cognitive impairments and affective dysregulation are often observed among these individuals. Volatile substances exert their complex neuropharmacological effects on dopaminergic, glutamatergic, GABAergic and serotoninergic receptor systems, as well as on cell membranes and ion channels. Concomitantly, pharmacotherapies for volatile substance abuse might profitably target a number of mechanisms, including reward circuitry in the brain, symptoms of craving and withdrawal, neuropsychiatric and emotional impairments that promote volatile substance abuse, and cognitive enhancement to rectify deficits in executive function. This review details the modes of use, subjective effects, epidemiology, adverse consequences, neuropsychopharmacology and drug treatment of volatile substance misuse, and discusses the potential role of novel forms of pharmacological intervention for this oft-overlooked public health threat of epidemic proportions.

The Oxidative and Morphological Effects of High Concentration Chronic Toluene Exposure on Rat Sciatic Nerves

This study was designed to investigate the effects of chronic toluene inhalation in high concentration on lipid peroxidation, antioxidant enzyme activities and ultrastructural changes in the sciatic nerves of rats. Male Wistar albino rats (150-250 g) were divided in two experimental groups: the control and the toluene treated group (n = 10 for each). Toluene treatment was performed by inhalation of 3000 ppm toluene, in a 8 h/day and 6 day/week order for 16 weeks. Blood and tissue samples were obtained for biochemical and histopathological investigation. The blood and sciatic nerves were assayed for toluene by gas chromatography. Toluene significantly increased blood and tissue malondialdehyde (MDA), and decreased tissue superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), but not tissue catalase (CAT) levels when compared with controls. Electron micrographs of sciatic nerve in the toluene group shows myelin destructions with onion-bulb and bubble form protrusion on the myelin sheath and axolemma border of myelinated axons. The area of injury on the myelin sheath were measured by Image-Pro Plus. Mean of the injury area were estimated 34% each myelin. These findings indicate that chronic toluene inhalation might be involved with free radical processes.

Metabolite alterations in basal ganglia associated with psychiatric symptoms of abstinent toluene users: a proton MRS study

Long-term toluene abuse causes a variety of psychiatric symptoms. However, little is known about abnormalities at the neurochemical level in the living human brain after long-term exposure to toluene. To detect neurochemical changes in the basal ganglia of subjects with a history of long-term toluene use, proton magnetic resonance spectroscopy (1H MRS) was performed in 12 abstinent toluene users and 13 healthy comparisons with no history of drug abuse. N-acetylaspartate (NAA), creatine plus phosphocreatine (Cr + PCr), choline-containing compounds (Cho), and myo-inositol (MI) levels were measured in the left and right basal ganglia. The Cho/Cr + PCr ratio, a marker of membrane metabolism, was significantly increased in the basal ganglia of toluene users in comparison to that of the control subjects. Furthermore, the increase in the Cho/Cr + PCr ratio was significantly correlated with the severity of residual psychiatric symptoms. These findings suggest that long-term toluene use causes membrane disturbance in the basal ganglia, which is associated with residual psychiatric symptoms that persist even after long-term abstinence from toluene use.

Sensitization as a mechanism for multiple chemical sensitivity: relationship to evolutionary theory

Multiple chemical sensitivity (MCS) is a disorder in humans attributed to prior chemical exposure. Sensitization is an amplification of neuronal responsiveness that elicits increased behavioral responding to stimuli, and occurs in a recently developed rat model of MCS. Rats were exposed to repeated formaldehyde (Form) and their response in three behavioral tests, including locomotor activity after a cocaine challenge, conditioned fear, and behavioral avoidance of Form, was assessed. In all three tests, rats demonstrated sensitized behaviors, implicating amplified responding within specific limbic brain regions. Evolutionary theory in the context of MCS specifies how the behavioral strategies of those with MCS are consistent with the notion that their self-perceived sense of survival and reproductive fitness may be threatened by chemical exposures. This behavior may be mediated by the same limbic brain regions that become sensitized after repeated chemical exposure in animals.

Microvillar cell surface as a natural defense system against xenobiotics: a new interpretation of multidrug resistance

The phenomenon of multidrug resistance (MDR) is reinterpreted on the basis of the recently proposed concept of microvillar signaling. According to this notion, substrate and ion fluxes across the surface of differentiated cells occur via transporters and ion channels that reside in membrane domains at the tips of microvilli (MV). The flux rates are regulated by the actin-based cytoskeletal core structure of MV, acting as a diffusion barrier between the microvillar tip compartment and the cytoplasm. The expression of this diffusion barrier system is a novel aspect of cell differentiation and represents a functional component of the natural defense system of epithelial cells against environmental hazardous ions and lipophilic compounds. Because of the specific organization of epithelial Ca(2+) signaling and the secretion, lipophilic compounds associated with the plasma membrane are transferred from the basal to the apical cell surface by a lipid flow mechanism. Drug release from the apical pole occurs by either direct secretion from the cell surface or metabolization by the microvillar cytochrome P-450 system and efflux of the metabolites and conjugation products through the large multifunctional anion channels localized in apical MV. The natural microvillar defense system also provides a mechanistic basis of acquired MDR in tumor cells. The microvillar surface organization is lost in rapidly growing cells such as tumor or embryonic cells but is restored during exposure of tumor cells to cytotoxins by induction of a prolonged G(0)/G(1) resting phase.

The effect of aliphatic, naphthenic, and aromatic hydrocarbons on production of reactive oxygen species and reactive nitrogen species in rat brain synaptosome fraction: the involvement of calcium, nitric oxide synthase, mitochondria, and phospholipase A11Abbreviations: BIM, bisindolylmaleimide; [Ca2+]i, concentration of intracellular calcium; ChAT, cholin acetyltransferase; CSA, cyclosporin A; DCF, 2′,7′-dichlorofluorescein; H2DCF-DA, 2′,7′-dichlorodihydrofluorescin diacetate; DEDA, dimethyleicosadienoic acid; ERK, extracellular signal-regulated kinases; Fura-2 AM, 5-oxazolecarboxylic acid, 2-(6-(bis(2-((acetyloxy)methoxy)-2-oxoethyl)amino)-5-(2-(bis(2-((acetyloxy)methoxy)-2oxoethyl)amino)-5-methylphenoxy)ethoxy)-2-benzofuranyl)-, (acetyloxy) methyl ester; GABA-T, gamma-aminobutyric acid transaminase; HBSS, Hanks’ balanced salt solution; La3+, lanthanum; MAPK, mitogen-activated protein kinase; MeHg, methyl mercury; MEK, extracellular signal-regulated protein kinase; MeOH, methanol; MTP, mitochondrial permeability transition pore; L-NAME, Nω-nitro-l-arginine methyl ester; NO·, nitrogen oxide; NOS, NO· synthase; O2·−, superoxide; PLA2, phospholipase A2; PKC, protein kinase C; RNS, reactive nitrogen species; ROS, reactive oxygen species; SOD, superoxide dismutase; TMB, 1,2,4-trimethylbenzene; TMCH, 1,2,4-trimethylcyclohexane; and U73122, 1-(6-[17beta-3-methoxyestra- 1,3,5(10)-trien- 17-yl]-aminohexyl)- 1H-pyrrole-2,5-dione

This study investigated the effects of C7 and C9 aliphatic (n-heptane, n-nonane), naphthenic (methylcyclohexane, 1,2,4-trimethylcyclohexane (TMCH)) and aromatic (toluene, 1,2,4-trimethylbenzene (TMB)) hydrocarbons on the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in rat brain synaptosome fraction. Methyl mercury (MeHg) was included as a positive control. Exposure of the synaptosomes to the hydrocarbons produced a concentration-dependent linear increase in the formation of the fluorescence of 2',7'-dichlorofluorescein (DCF) as a measure of the production of ROS and RNS. Formation of RNS was demonstrated by preincubation of the synaptosome fraction with the neuronal nitric oxide synthase (nNOS) inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME), which reduced the MeHg and TMCH-stimulated fluorescence by 51% and 65%, respectively. The naphthenic hydrocarbon TMCH showed the strongest potential for ROS and RNS formation in rat brain synaptosomes, followed by TMB, toluene, n-nonane, n-heptane, and methylcyclohexane, respectively. TMCH was selected for mechanistic studies of the formation of ROS. Both MeHg and TMCH induced an increase in intracellular calcium concentration [Ca(2+)]i as measured with Fura-2. Blockade of voltage-dependent Ca(2+) channels with lanthanum prior to stimulation with MeHg and TMCH led to a reduction in the ROS/RNS formation of 72% and 70%, respectively. Furthermore, addition of cyclosporin A (CSA), a blocker of the mitochondrial permeability transition pore (MTP), lowered both the MeHg and TMCH-elevated DCF fluorescence by 72% and 59%. Preincubation of the synaptosome fraction with the protein tyrosine kinase inhibitor genistein lowered the MeHg and TMCH-stimulated fluorescence by 85% and 91%, respectively. Addition of the extracellular signal-regulated protein kinase (MEK)-1 and -2 inhibitor U0126 reduced the fluorescence stimulated by MeHg and TMCH by 62% and 63%. Furthermore, the protein kinase C inhibitor bisindolylmaleimide reduced the fluorescence stimulated by MeHg and TMCH by 52% and 56%. The compound 1-(6-[17beta-3-methoxyestra- 1,3,5(10)-trien- 17-yl]-aminohexyl)-1H-pyrrole-2,5-dione (U73122), which inhibits phospholipase C, was shown to decrease the ROS and RNS formation induced by MeHg and TMCH by 49% and 64%, respectively. The phospholipase A2 (PLA2) inhibitor 7,7-dimethyl eicosadienoic acid (DEDA) reduced fluorescence in response to MeHg and TMCH by 49% and 54%. Simultaneous addition of L-NAME, CSA, and DEDA to the synaptosome fraction totally abolished the DCF fluorescence. In conclusion, C7 and C9 aliphatic, naphthenic, and aromatic hydrocarbons stimulated formation of ROS and RNS in rat brain synaptosomes. The naphthenic hydrocarbon TMCH stimulated formation of ROS and RNS in the synaptosomes through Ca(2+)-dependent activation of PLA2 and nNOS, and through increased transition permeability of the MTP. Exposure of humans to the naphthenic hydrocarbon TMCH may stimulate formation of free radicals in the brain, which may be a key factor leading to neurotoxicity.

Repeated formaldehyde effects in an animal model for multiple chemical sensitivity

Chemical intolerance is a phenomenon observed in multiple chemical sensitivity (MCS) syndrome, an ill-defined disorder in humans attributed to exposure to volatile organic compounds. Amplification of symptoms in individuals with MCS resembles the phenomenon of psychostimulant- and stress-induced sensitization in rodents. We have recently tested in rats the hypothesis that repeated chemical exposure produces sensitization of central nervous system (CNS) circuitry. A rat model of MCS in our laboratory has employed several endpoints of CNS function after repeated formaldehyde (Form) exposure (1 h/day x 5 days/week x 4 weeks). Repeated Form exposure produced behavioral sensitization to later cocaine injection, suggesting altered dopaminergic sensitivity in mesolimbic pathways. Rats given repeated Form also demonstrated increased fear conditioning to odor paired with footshock, implicating amplification of neural circuitry guiding fear responding to a conditioned odor cue. Recent studies examining the effects of repeated Form on locomotor activity during each daily exposure showed a decrease in rearing activity after 12-15 days of Form exposure compared to air-exposed controls. EEG recordings taken 1 week after withdrawal from daily Form revealed altered sleep architecture. Some of the differences in sleep disappeared after subsequent brief (15 min) challenge with Form the next day. Overall, the findings indicate that repeated low-level chemical exposure produces behavioral changes that may be akin to those observed in individuals with MCS, such as greater sensitivity to chemicals manifest as increased anxiety upon chemical exposure and altered sleep and/or fatigue. Study of the underlying CNS changes will provide a basis for mechanistically based animal models for MCS.

Subchronic toluene exposure in low concentrations produces signs of reduced dysfunction in the 6-hydroxydopamine lesioned nigrostriatal dopaminergic system of the rat

The effect of a subchronic (4-week) exposure to low concentrations of toluene (40 or 80 parts per million, ppm) on the brain dopaminergic system has been examined in a rat model of Parkinson's disease. A unilateral lesion of the substantia nigra (SN) dopamine (DA) nerve cells was performed by injection of a low dose of 6-hydroxydopamine (6-OH DA). The peak activity of contralateral rotational behavior induced by apomorphine was significantly decreased after exposure to 80 ppm toluene. Analysis of the neostriatum and SN ipsilateral to the lesion revealed that toluene (80 ppm, but not 40 ppm) counteracted the 6-OH DA-induced reductions of DA tissue levels both within the SN and the neostriatum. Also the lesion-induced reduction of immunoreactivity for tyrosine hydroxylase (TH IR) in the neostriatum was partly counteracted by the toluene exposure (80 ppm). In conclusion, a subchronic exposure to low doses of toluene (80 ppm) leads to signs of reduced dysfunction of the nigrostriatal dopaminergic system after the neurotoxic treatment.

The effect of in vitro exposure to white spirit on [Ca2+i] in synaptosomes from rats exposed prenatally to white spirit

Female rats were exposed to white spirit (400 and 800 ppm for 6 hr/day) at day 7-20 during pregnancy. Thirty-five days after birth all female offspring were sacrificed, the brains removed, and the synaptosomal fractions prepared for in vitro studies. The cytosolic calcium concentration was measured using the FURA-2 technique. The results show that cytosolic calcium was increased in synaptosomes from rats exposed to white spirit prenatally compared to synaptosomes from unexposed rats. When synaptosomes were exposed to white spirit in vitro, the cytosolic calcium concentration changes were identical in all groups of rats. The membrane leakage measured as FURA-2 leakage from the synaptosomes identical in all three groups of animals. The results suggest that prenatal exposure to white spirit induces long-lasting and possibly irreversible changes in calcium homeostasis in the rat nervous system.

Behavioral sensitization after repeated formaldehyde exposure in rats

Multiple chemical sensitivity (MCS) is a phenomenon whereby individuals report increased sensitivity to chemicals in the environment, and attribute their sensitivities to prior exposure to the same or often structurally unrelated chemicals. A leading hypothesis suggests that MCS is akin to behavioral sensitization observed in rodents after repeated exposure to drugs of abuse or environmental stressors. Sensitization occurring within limbic circuitry of the central nervous system (CNS) may explain the multisymptom complaints in individuals with MCS. The present studies represent the continuing development of an animal model for MCS, the basis of which is the CNS sensitization hypothesis. Three behaviors were assessed in rats repeatedly exposed to formaldehyde (Form) inhalation. In the first series of experiments, rats were given high-dose Form exposure (11 parts per million [ppm]; 1 h/day x 7 days) or low-dose Form exposure (1 ppm; either 1 h/day x 7 days or 1 h/day x 5 days/week x 4 weeks). Within a few days after discontinuing daily Form, cocaine-induced locomotor activity was elevated after high-dose Form or 20 days of low-dose Form inhalation. Approximately 1 month later, cocaine-induced locomotor activity remained significantly elevated in the 20-day Form-exposed rats. The second experiment assessed whether prior exposure to Form (20 days, as above) would alter the ability to condition to an odor (orange oil) paired with footshock. The results suggested a tendency to increase the conditioned fear response to the odor but not the context of the footshock box, and a decreased tendency to extinguish the conditioned fear response to odor. The third experiment examined whether CNS sensitization to daily cocaine or stress would alter subsequent avoidance responding to odor (Form). Daily cocaine significantly elevated approach responses to Form, while daily stress pretreatment produced a trend in the opposite direction, producing greater avoidance of Form. Preliminary studies indicated that repeated daily Form inhalation (20 days, as above) produced a greater avoidance to subsequent Form presentation, suggesting that daily Form inhalation may serve as a stressor. The results support the hypothesis that repeated chemical exposure in rats may produce CNS plasticity manifest as greater sensitivity to dopaminergic drugs, enhanced fear conditioning to odor paired with an aversive event, and greater avoidance of odors. Some of these behavioral changes observed in rats may provide a link with symptoms in a subset of individuals with MCS.

Subacute toluene exposure increases DA dysfunction in the 6-OH dopamine lesioned nigrostriatal dopaminergic system of the rat

The potential neurotoxicity of the solvent toluene to the nigrostriatal dopaminergic system was assessed in a rat model of Parkinson's disease. Rats, 1 day after a unilateral injection of 6-hydroxydopamine (6-OH DA) into the substantia nigra, inhaled air or different concentrations of toluene (80, 300 or 1000 ppm), 6 h/day for 3 days. The animals were sacrificed 2 days after the last exposure and biochemical measurements of catecholamines and 3,4-dihydroxyphenylacetic acid (DOPAC) were performed in the neostriatum and substantia nigra. Toluene at 80 and 1000 ppm significantly enhanced the depletion of striatal DOPAC levels induced by the lesion and produced at 80 and 300 ppm a trend for intensifying the 6-OH DA-induced depletion of striatal DA stores. The alterations induced after the combined challenge to the dopaminergic nigrostriatal system may reflect endangering actions of toluene.

The effect of ageing and in vitro exposure to xylene and KCl on [Ca2+]i in synaptosomes from rats exposed prenatally to xylene

Female rats (Mol: WIST) were exposed prenatally to 500 p.p.m. of technical xylene on days 7-20. At the age of fourteen months the rats were sacrificed and the synaptosomal fraction prepared for in vitro studies. The cytosolic calcium concentration was measured using the FURA-2 technique. The cytosolic calcium was increased in synaptosomes from old rats compared to those from rats at the age of three months, but no effect of prenatal exposure was seen. When synaptosomes were incubated with xylene, potassium or both, the cytosolic calcium concentration was changed identically in all groups of rats. When synaptosomes were incubated simultaneously to xylene and potassium a dramatical leakage of FURA-2 was observed. The mechanisms behind the membrane leakage are discussed.

In vitro influences of alcohols on mouse synaptosomes, and structure-activity relationships

Little information is available on the structure-central nervous system membrane toxicity relationship of alcohols. The purpose of the present study was to study in vitro influence of alcohols (n = 20) on the activity of the toxic indicator Na+/K(+)-adenosine triphosphatase (Na+/K(+)-ATPase) and acetylcholinesterase (AchE), and membrane fluidity in mouse brain synaptosomes, in terms of the structure-activity relationship. The potency of inhibition for the enzymes (IC50) and the potency of increasing membrane fluidity (IC12.5) were determined experimentally, and n-octanol/water partition coefficient (P) and the steric constant Taft Es are cited from the literature. Regression analysis revealed that log 1/IC50 for Na+/K(+)-ATPase is a function of log P and Taft Es. The situation was true for AchE activity. The results indicate that the hydrophobicity expressed as log P and the steric effect of the alcohols play an important role in inhibiting both enzyme activities. A linear relationship between log 1/IC12.5 for membrane fluidity and log P is shown, indicating a significant effect of the alcohols on membrane fluidity. Based on these results, it is suggested that the alcohols inhibit the Na+/K(+)-ATPase and AchE activity through a direct action on the enzymes and/or through changing the membrane fluidity.

Gangliosides raise the intracellular Ca2+ level in different cell types

Total gangliosides from bovine brain at micromolar concentration induce intracellular Ca2+ increments in a temperature, time and dose dependent manner when assayed with suspensions of rat macrophages, rat and chicken neurons, human erythrocytes and liposomes, loaded with the fluorescent Ca2+ indicator FURA 2. The effect was independent on the endogenous ganglioside composition of the cells and in the case of neurons it was also independent on the differentiation state. Gangliosides do not induce the release of Ca2+ from inner stores. These findings indicate that the reported inhibition of arachidonic acid release (Bressler, J., et al., (1994) Life Sci., 54, 49-60) and anti-inflammatory properties of gangliosides (Correa, S.G. et al., (1991) Eur. J. Pharmacol. 199, 93-98) are not due to impairments of Ca2+ flux. The results also suggest the possibility that the well-known neurotrophic effect produced by gangliosides on undifferentiated neurons in culture may be due to subtoxic cytosolic Ca2+ increments.

Auditory and vestibular functions after single or combined exposure to toluene: a review

Toluene is a widely used organic solvent, heavily employed in many manufacturing industries. Recently, evidence has begun to accumulate on the deleterious effect of toluene exposure has on the auditory and vestibular systems. Although little published information exists regarding these effects, the reported findings indicate a need for further investigation. The results of such investigations may dramatically affect occupational hearing conservation practices and legislation. Both human and animal studies will be summarized in discussing the effects of toluene alone or in combination with noise or other chemicals. Gaps in scientific knowledge are highlighted to assist future research.

Physical-chemical-activity relationship of organic solvents: effects on Na(+)-K(+)-ATPase activity and membrane fluidity in mouse synaptosomes

Physical-chemical-activity relationship of aromatic hydrocarbons (n = 10) and alkyl acetates (n = 16) with respect to their in vitro effects on synaptosomal membranes was studied. Na(+)-K(+)-adenosine triphosphatase (Na(+)-K(+)-ATPase) activity and membrane fluidity, which was determined using the fluorescence probe 1,6-diphenyl-1,3,5-hexatriene, were used as potential indicators of neuronal cell toxicity. The potency of inhibition for the enzyme (IC50), the potency of increasing membrane fluidity (IC12.5), and n-octanol/water partition coefficient (P) were all determined experimentally for 26 solvents. Correlation analyses were made on aromatic hydrocarbons and on alkyl acetates. There were linear relationships between log P and pIC50 (log1/IC50) values, and between log P and pIC12.5 (log1/IC12.5) values, indicating that the hydrophobicity of the solvents determines their toxic ability to affect membrane environment; the more hydrophobic the solvents are, the more toxic they are. A direct linear relationship between Na(+)-K(+)-ATPase activity pIC50 and membrane fluidity pIC12.5 values was also shown. This predictive correlation suggests a similar mechanism of membrane surface interaction govering both processes that are common to the test solvents. The present results confirm the importance of the lipid environment of neuronal membranes in maintaining the normal function of membrane-bound protein.

Structure-toxicity relationship of monoketones: in vitro effects on beta-adrenergic receptor binding and Na(+)-K(+)-ATPase activity in mouse synaptosomes

The structure-toxicity relationship of monoketones, a class of organic solvents widely used in industry, was investigated with respect to their in vitro effects on synaptosomal membrane proteins. The toxic parameters used were Na(+)-K(+)-adenosine triphosphatase (Na(+)-K(+)-ATPase), a well-known marker enzyme often used as a membrane toxicity model, and 3H-dihydroalprenolol (3H-DHA)-labeled beta-adrenergic receptor binding that has been shown to be vulnerable to solvent-induced changes in membrane fluidity. In vitro treatments with 12 kinds of monoketones (carbon chain length from 3-10) dose-dependently inhibited both 3H-DHA binding to mouse synaptosomes and Na(+)-K(+)-ATPase activity. The potency of inhibition (IC50) for both the two parameters was linearly related to n-octanol/water partition coefficient and synaptosome/buffer partition coefficient of the test compounds. Additions of monoketones did not significantly alter the number of 3H-DHA binding sites but markedly decreased their affinity. In each monoketone, the IC50 values for 3H-DHA binding and Na(+)-K(+)-ATPase activity were generally within the same range. The anisotropy of fluorescence probe 1,6-diphenyl-1,3,5-hexatriene-labeled synaptosomal membranes was dose-dependently decreased by the monoketones, implying increased membrane fluidity. These results indicate that increasing lipophilicity of monoketones results in increased solvent penetration of synaptic membrane preparations, leading to conformational changes in membrane structure and increased ability to inhibit both neuroreceptor binding and enzyme activity. The present data confirm the importance of the lipid micro-environment of membranes in maintaining the normal functions of membrane-bound proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Free radical induction in the brain and liver by products of toluene catabolism

Toluene and its metabolites have been studied with respect to their reactive oxygen species-enhancing potential in isolated systems and in vivo. The induction of reactive oxygen species (ROS) production was assayed using the probe 2',7'-dichlorodihydrofluorescin diacetate (DCFH-DA). Intraperitoneal injection of toluene, benzyl alcohol or benzaldehyde caused a significant elevation in the rate of ROS formation within hepatic mitochondrial fractions (P2). In the brain, only toluene induced ROS formation, while benzyl alcohol and benzaldehyde did not have any effect. Glutathione (GSH) levels were depressed in liver and brain regions from toluene-treated rats. However, no such depression was evident in brains treated with toluene metabolites. P2 fractions from phenobarbital-pretreated rats exhibited a heightened ROS response when challenged with toluene, in vitro. Pretreatment of rats in vivo with 4-methylpyrazole, an alcohol dehydrogenase inhibitor, or sodium cyanamide, an aldehyde dehydrogenase inhibitor, prior to exposure to toluene, caused a significant decrease and increase, respectively, in toluene-stimulated rates of ROS generation in the CNS and liver. Electron spin resonance spectroscopy, employing the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO), was conducted. Incubation of the spin trap with P2 fractions and toluene or benzaldehyde elicited a spectrum corresponding to the hydroxyl radical. Incubation of benzaldehyde with aldehyde dehydrogenase produced a strong signal that was blocked completely by superoxide dismutase and inhibited partially by catalase, suggesting the presence of superoxide radicals and the involvement of the iron-catalyzed Haber-Weiss reaction leading to the production of hydroxyl radicals. Thus, ROS generation during toluene catabolism may occur at two steps: cytochrome P450 oxidation and aldehyde dehydrogenase oxidation. In addition, GSH may play an important role in protection against the induction of ROS generation in the CNS and liver following exposure to toluene.

Toluene-induced oxidative stress in several brain regions and other organs

The in vivo dose-response relationship between toluene and reactive oxygen species (ROS) formation in rat brain, liver, kidney, and lung, and the time-course of these effects has been characterized. The rate of oxygen radical formation was measured using the probe 2',7'-dichlorofluorescin diacetate. In vivo exposure to various doses of toluene (0.5, 1.0, and 1.5 g/kg ip) elicited a dose-dependent elevation of ROS generation within crude mitochondrial fractions obtained from rat lung and kidney, and within crude synaptosomal fractions from cerebellum. ROS formation in crude mitochondrial fractions from liver, and crude synaptosomal fractions from striatum and hippocampus, reached a maximum value at relatively low doses of toluene. Of the brain regions, the hippocampus had the highest induced levels of ROS. In vivo exposure to a single dose of toluene (1.5 g/kg ip), revealed that toluene-induced ROS reached a peak within 2 h, which correlated directly with measured toluene blood levels. This elevated oxidative activity was maintained throughout the next 24 h, even though blood values of toluene decreased to negligible amounts. These results demonstrate that exposure to toluene results in broad systemic elevation in the normal rate of oxygen radical generation, with such effects persisting in the tissues despite a rapid decline in toluene blood levels. Acute exposure to toluene may lead to extended ROS-related changes, and this may account for some of the clinical observations made in chronic toluene abusers.

Effects of toluene and n-hexane on rat synaptosomal membrane fluidity and integral enzyme activities

The effects of toluene and n-hexane on rat synaptosomal membrane fluidity and the integral enzymes acetylcholinesterase (AChE) and ATPase were studied in vitro. The synaptosome membranes were isolated in Percoll and sucrose gradients. After adding toluene and n-hexane to the incubation mixture (37 degrees) in 2,4,6 and 8 mM concentrations, the fluidity changes were measured by the lateral pyrene diffusion method from Percoll-isolated membranes, and the ATPase and acetylcholinesterase activities were determined from both synaptosome isolations. Addition of toluene caused a linearly correlated increase of the synaptosomal membrane fluidity and a linear decrease of the AChE activity. The ATPase activity did not decrease linearly but dose-dependently. In contrast to the effects of toluene in vitro, addition of n-hexane in the same concentration range had no comparable influence on membrane fluidity nor on the activities of both integral enzymes despite its even higher lipid/water partition coefficient. Toluene increases synaptosomal membrane fluidity and at the same time inhibits the integral enzymes, probably by disturbing the lipid/protein interaction.

Ganglioside GM1 counteracts the enhancing effects of subacute toluene exposure on apomorphine-induced locomotor activity

Previous studies indicate that subacute toluene exposure enhances the effects of postsynaptic doses of apomorphine on locomotor activity in the rat. We have now studied the effects of the ganglioside GM1 on toluene-affected apomorphine-induced (1 mg/kg, s.c.) locomotion, motility, and rearing. Treatment with GM1 (10 mg/kg, i.p., 1 h before exposure) was found to counteract or even reverse the enhancing effect of toluene on apomorphine-induced locomotion and rearing, but had similarly to toluene no significant effects on apomorphine-induced motility or on spontaneous locomotor activity. The antagonistic effects of GM1 may be due to its ability to block toluene-induced changes in D2 receptor binding.

Gangliosides prevent the dimethyl sulphoxide-induced increases in [3H]-noradrenaline release from rat isolated atria

1. In the rat isolated atria labelled with [3H]-noradrenaline ([3H]-NA), the exposure to 1-4% v/v dimethyl sulphoxide (DMSO) during 15 min caused a concentration-dependent increase in the spontaneous outflow of tritiated products, which reached up to 50% with 2% DMSO and up to 100% with 4% DMSO. These effects were entirely prevented by a 2 h in vitro pretreatment with 50 microM bovine brain gangliosides mixture (BBG). 2. The pattern of the spontaneous release of tritiated products was 17.5 +/- 1.9% of [3H]-NA; 38.7 +/- 2.1% of [3H]-3,4-dihydroxyphenylglycol ([3H]-DOPEG); 36.1 +/- 2.4% of [3H]-O-methylated deaminated metabolites ([3H]-OMDA); 4.7 +/- 0.9% of [3H]-3,4-dihydroxymandelic acid ([3H]-DOMA) and 2.9 +/- 0.2% of [3H]-NMN. After 10 min exposure to 2% DMSO, the increase in basal outflow by this agent consisted of 7.4 +/- 2.5% [3H]-NA and 89.0 +/- 3.6% [3H]-DOPEG. The 2 h preincubation with 50 microM BBG protected from the increase of total radioactivity and also from the metabolic alterations caused by DMSO. The BBG per se did not modify either the basal efflux or the metabolic fate of the [3H]-transmitter. 3. In addition to enhancing the spontaneous outflow of radioactivity, the exposure to 2% v/v DMSO increased by 400% the overflow of the [3H]-transmitter elicited by nerve stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of exogenous GM1 ganglioside on LTP in rat hippocampal slices perfused with different concentrations of calcium

Combined actions of GM1 ganglioside molecules and Ca2+ ions on long-term potentiation (LTP) of the hippocampal CA1 synapses were examined in slice preparations. Application of exogenous GM1 ganglioside significantly enhanced LTP. Antigenic blocking of endogenous GM1 ganglioside by applying anti-GM1 antiserum appeared to attenuate LTP. Exogenous GM1 treatment not only antagonized LTP suppression caused by low Ca2+ (1.0 microM) in the perfusion medium, but also amplified LTP at high Ca2+ (5.0 microM) condition. Thus, GM1 may stabilize intracellular calcium levels to enhance synaptic potentiation.

Advances in the use of the fluorescent probe fura-2 for the estimation of intrasynaptosomal calcium

Fura-2 has been used to measure intracellular Ca2+ with great success in a variety of cell and subcellular preparations, including synaptosomes. There is, however, a great deal of variability in the reported estimates of resting intrasynaptosomal Ca2+ ([Ca2+]i). Fura-2 AM is highly lipophilic and passes readily across the plasma membrane into the cytoplasm, where it is de-esterified and trapped. The lipophilicity of fura-2, however, promotes the formation of micelles in aqueous media, which may impede the passage of the probe across cell membranes. Our results suggest that some of the variability in the reported [Ca2+]i estimates may be related to fura-2 de-esterification and loading efficiencies. The use of the nonionic detergent pluronic F-127 is recommended to prevent the formation of fura-2 micelles. The use of a detergent is not always an acceptable practice, however, especially in studies in which detergent-lipid interactions may influence membrane parameters. We found that fatty acid free bovine serum albumin (BSA) (0.25%) greatly increases the intrasynaptosomal concentration of the probe, resulting in a significant increase in the signal-to-noise (S/N) ratio. The mechanism appears to be independent of effects of BSA on synaptosomal integrity and directly related to the prevention of fura-2 micelle formation, as evidenced by light spectroscopic scattering measurements. Thus, BSA appears to keep the probe in a form that crosses the synaptic plasma membrane more readily. The effectiveness of BSA in improving the loading of fura-2 into synaptosomes was comparable to the detergent pluronic F-127, making it possible to measure [Ca2+]i without compromising membrane integrity.

Siagoside selectively attenuates morphological and functional striatal impairments induced by transient forebrain ischemia in rats

BACKGROUND AND PURPOSE

Transient forebrain ischemia induced in rats by the four-vessel occlusion method is known to produce severe neural damage in the hippocampus and striatum and a behavioral syndrome the major symptom of which is a working memory deficit. Recent evidence suggests that monosialogangliosides can ameliorate postischemic symptoms. Our purpose was to study the effect of siagoside, the inner ester of GM1 ganglioside, on some behavioral and morphological impairments induced by four-vessel occlusion in rats.

METHODS

Rats were injected daily with 5 mg/kg i.p. siagoside starting 4 hours after the cerebral ischemia. After 14 days the rats were tested for working memory in a water T maze or scored for apomorphine-induced stereotypy. The rats were killed 21 days after the cerebral ischemia. Histological and computer-assisted morphometric analyses were performed on cresyl violet-stained brain sections, which were graded according to a neuropathologic score, and on sections stained with a monoclonal antiserum against dopamine and cyclic adenosine-3',5'-monophosphate-regulated phosphoprotein, a marker for striatal dopaminoceptive neurons.

RESULTS

Siagoside treatment reduced the stereotypy score induced by low doses of apomorphine and the extent of striatal lesions but did not affect the working memory deficit or the extent of hippocampal lesions.

CONCLUSION

Daily siagoside treatment after acute cerebral ischemia attenuates some morphological and functional deficits related to striatal damage. These effects can be interpreted as a selective protective action on striatal neural populations or as a modulatory action on neural systems involved in striatal control. These data are consistent with preliminary clinical reports showing that monosialogangliosides enhance motor recovery after acute ischemic stroke.

Disruption of the potential across the synaptosomal plasma membrane and mitochondria by neurotoxic agents

The effect of a neurotoxic organo-metal, methyl mercuric iodide, and an aromatic solvent, toluene, upon the transmembrane potential (psi), across both the limiting membrane of isolated nerve terminals and their mitochondria, has been studied. Exposure of nerve endings to either of these toxicants in vitro resulted in a dose-dependent diminution of psi that was especially pronounced in the case of mitochondria. This was not prevented by a concurrent exposure to an antioxidant (alpha-tocopherol), or an iron chelator (deferoxamine), or ganglioside GM1. No significant changes were detected in synaptosomal potentials derived from cortices of rats exposed to methyl mercury or toluene at levels known to increase the rate of formation of reactive oxygen species within this region. The special vulnerability of mitochondrial psi to these agents may be due to the disruption of oxidative phosphorylation and may be related to the increase in intrasynaptosomal free ionic calcium that both of these chemicals can induce.

Ganglioside (GM1)-treated T cells shed CD4

In previous studies (Morrison et al., 1990), we showed that ganglioside (GM1) modulation of CD4 was associated with activation of phospholipase C and increased production of inositol triphosphate, but not with activation of protein kinase C. These results demonstrated a unique signal transduction pathway related to GM1 modulation of CD4 on T cells and raised the question as to whether intracellular Ca2+ levels and related protein kinases would be affected by GM1-induced signalling. We now show that GM1 modulation of CD4 from human T cells corresponds to decreased cellular Ca2+ without significant changes in cellular protein phosphorylation. In the course of this study we discovered that T cells challenged with GM1 exhibited new proteins in their surrounding media. Fractionation of cellular and supernatant proteins show that cells treated with GM1 released proteins with an approximate molecular weight (Mr) of 49,000. This was exclusive of GM1 protein association and GM1-induced protein phosphorylation. Immunoblots demonstrated the presence of CD4 in GM1-treated cell supernatants. Western immunoblots using anti-CD4 antibodies detected a lower Mr form (49,000) of CD4 in the supernatants of GM1-treated cells. These studies further define the unique nature of GM1 signalling relating to modulation of CD4 and demonstrate that the fate of GM1 modulated CD4, in part, involves protein shedding.

Effects of toluene on platelet membrane glycoprotein Ib and actin-binding protein

Effects of the organic solvent toluene on the platelet membrane receptor glycoprotein Ib (GP Ib) and the cytoskeletal protein, actin-binding protein (ABP), were studied and related to the effects of the local anesthetic dibucaine. The glycocalicin-region of GP Ib contains the binding site for von Willebrand factor; intracellularly GP Ib is linked to the cytoskeleton via ABP. Both GP Ib and ABP are substrates for a calcium-dependent protease, calpain. Washed platelets were incubated with toluene or dibucaine. The toluene concentration in the platelet suspension was analysed by gas chromatography. Using 1.5-2.8 mmol/L toluene, calpain was activated, leading to degradation of ABP and release of glycocalicin from GP Ib. The latter phenomenon was paralleled by a reduced von Willebrand factor-induced platelet agglutination. At lower toluene concentrations (0.3-1.4 mmol/L), degradation of ABP was not detected but an initial increased agglutination that declined to the control level with time was observed. These effects of toluene on the GP Ib-ABP complex are similar to those observed with 1 mmol/L dibucaine. The lowest toluene concentrations used correspond to those that have been found in blood from toluene abusers ("sniffers").

Effects of toluene and its metabolites on cerebral reactive oxygen species generation

The effects of toluene on lipid peroxidation and rates of reactive oxygen species (ROS) formation have been studied in isolated systems and in vivo. The induction of reactive oxygen species was assayed using the probe 2',7'-dichlorofluorescin diacetate (DCFH-DA). Toluene exposure (1 g/kg, 1 hr, i.p.) did not stimulate cortical lipid peroxidation as evaluated by measurement of conjugated dienes. Exposure to toluene, however, both in vivo and in vitro, caused a significant elevation of ROS formation within cortical crude synaptosomal fractions (P2) and microsomal fractions (P3). The ROS-inducing properties of toluene were blocked in vivo in the presence of a mixed-function oxidase inhibitor, metyrapone. This suggested that a metabolite of toluene may catalyze reactive oxygen formation. Both benzyl alcohol and benzoic acid, in vitro, were found to have free radical quenching properties, while benzaldehyde exhibited significant induction of ROS generation. It appears that benzaldehyde is the metabolite responsible for the effect of toluene in accelerating reactive oxygen production within the nervous system. Benzaldehyde may also contribute to the overall neurotoxicity of toluene.

Subacute exposure to low concentrations of toluene affects dopamine-mediated locomotor activity in the rat

The effects of low concentrations of toluene (40-80 ppm, 3 days, 6 h/day) were investigated on spontaneous and on apomorphine-induced locomotor activity in the rat, and were correlated to effects on S(-)[N-propyl-3H(N)]-propylnorapomorphine ([3H]NPA) binding in rat neostriatal membranes, on membrane fluidity, membrane leakage, and calcium levels in synaptosomes from the frontoparietal cortex, the neostriatum and the subcortical limbic area, and on serum hormone levels. Toluene exposure (80 ppm, post-exposure delay 18 h) alone did not affect locomotor activity, but attenuated apomorphine-induced (0.05 mg/kg, s.c.) suppression of rearing, and potentiated apomorphine-induced (1 mg/kg, s.c.) increases in locomotion and rearing. Toluene exposure increased the KD value of [3H]NPA binding without affecting the Bmax. All these effects were absent at 40 ppm of toluene or at a post-exposure delay of 42 h. Toluene exposure (80 ppm, post-exposure delay of 18 h) did not affect the serum levels of prolactin, TSH, corticosterone, or aldosterone, or synaptosomal membrane fluidity and calcium levels, whereas membrane leakage was increased in the neostriatum. The present study indicates that the reduction of D-2 receptor affinity by short-term, low-dose toluene exposure is accompanied by a reduced D-2 autoreceptor function and an enhanced postsynaptic D-2 receptor function.

Persistent effects of chronic exposure to styrene on the affinity of neostriatal dopamine D-2 receptors

We have investigated whether chronic exposure to styrene could inflict persistent effects on the binding characteristics of dopamine D-2 agonist binding sites in rat neostriatal membranes. Styrene exposure (1000 ppm, 6 months, 16 h/d overnight, and left without exposure for another 5 months) caused a marked increase (+160%) in the IC50 value of dopamine without significantly affecting the total amount of specifically bound [3H]raclopride. The specific [3H]raclopride binding in membranes from subcortical limbic areas was too low to yield acceptable displacement curves. These data indicate that chronic exposure to styrene can induce a persistent decrease in affinity of the neostriatal dopamine D-2 agonist binding sites, possibly mediated by membrane perturbations.

Prevention of chemically induced changes in synaptosomal membrane order by ganglioside GM1 and alpha-tocopherol

Synaptosomal membrane order has been studied by analysis of light depolarization by fluorescent dyes intercalated within membranes following exposure to various environmental toxicants. Two probes were explored: 1,6-diphenyl-1,3,5-hexatriene (DPH), signaling predominantly from the lipid-rich membrane core, and 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH), reporting from the more hydrophilic membrane surface. Chlordecone, a neurotoxic insecticide, decreased the anisotropy of either dye and this change could be prevented by prior treatment of synaptosomes with ganglioside GM1 but not alpha-tocopherol. Exposure to an iron-ascorbic acid oxidizing mixture enhanced synaptosomal membrane order and this effect was blocked by preincubation with alpha-tocopherol but not ganglioside GM1. While these interactions may have partially reflected additive anisotropy changes, the protective agents were also effective at concentrations where they did not in themselves modulate membrane order. Methyl mercuric chloride at concentrations up to 100 microM had no discernable effect upon membrane order. It is suggested that these changes in membrane order may underlie some of the previously reported variations in the content of ionic calcium and in the leakiness of synaptosomes.