Effects of acute and chronic toluene inhalation on behavior and (3H)-serotonin binding in rat

Influence of Environmental Exposure to Steel Waste on Endocrine Dysregulation and PER3 Gene Polymorphisms

OBJECTIVE

To evaluate the association between environmental exposure to the following chemical substances: cadmium (Cd), lead (Pb), nickel (Ni), manganese (Mn), benzene (BZN), and toluene (TLN), and Period Circadian Regulator 3 (PER3) gene variable number of tandem repeats (VNTR) polymorphisms, according to chronotype in a population living in a steel residue-contaminated area.

METHODS

This assessment comprises a study conducted from 2017 to 2019 with 159 participants who completed health, work, and Pittsburgh sleep scale questionnaires. Cd, Pb, Ni, Mn, BZN, and TLN concentrations in blood and urine were determined by Graphite Furnace Atomic Absorption Spectrometry (GFAAS) and Headspace Gas Chromatography (GC), and genotyping was carried out using Polymerase Chain Reaction (PCR).

RESULTS

A total of 47% of the participants were afternoon chronotype, 42% were indifferent, and 11% were morning chronotype. Insomnia and excessive sleepiness were associated with the indifferent chronotype, while higher urinary manganese levels were associated with the morning chronotype (Kruskal-Wallis chi-square = 9.16; p < 0.01). In turn, the evening chronotype was associated with poorer sleep quality, higher lead levels in blood, and BZN and TLN levels in urine (χ² = 11.20; p < 0.01) in non-occupationally exposed individuals (χ² = 6.98; p < 0.01) as well as the highest BZN (χ² = 9.66; p < 0.01) and TLN (χ² = 5.71; p < 0.01) levels detected in residents from the influence zone 2 (far from the slag).

CONCLUSION

Mn, Pb, benzene, and toluene contaminants may have influenced the different chronotypes found in the steel residue-exposed population.

Serotonin Content of the Lungs, Brains, and Blood of Mice Exposed to 0.45 ppm Nitrogen Dioxide

Young adult male Swiss Webster mice were exposed to 0.45 ppm of nitrogen dioxide (NO2) for 7 hours per day for 4 weeks. The lungs and brains were assayed for serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) content by high-performance liquid chromatography. Lung 5-HT content for the exposed animals was 13.1% less than that for the control group, but this difference was not statistically significant. Brain 5-HT and 5-HIAA were significantly elevated, +17.3% (P < 0.005) and +47.3% (P 0.001), respectively, and the ratios of 5-HIAA to 5-HT were also higher (P 0.005). The results suggest that further exploration of lung and brain serotonin alterations by air pollutants may offer useful discriminates for the evaluation of air quality.

Preclinical characterization of toluene as a non-classical hallucinogen drug in rats: participation of 5-HT, dopamine and glutamate systems

RATIONALE

Toluene is a misused inhalant with hallucinogenic properties and complex effects. Toluene blocks N-methyl-D-aspartate (NMDA) receptors, releases dopamine (DA), and modifies several neurotransmitter levels; nonetheless, the mechanism by which it produces hallucinations is not well characterized.

OBJECTIVES

This study aims (a) to study toluene's effects on the 5-HT2A-mediated head-twitch response (HTR), dopamine (DA), and serotonin (5-HT) tissue levels in discrete brain regions; (b) to compare the actions of toluene, ketamine, and 1-[2,5-dimethoxy-4-iodophenyl]-2-aminopropane (DOI) on HTR; and (c) to study the pharmacological blockade of toluene's and ketamine's effects by selective drugs.

METHODS

Independent groups of rats inhaled toluene (500-12,000 ppm) for 30 min during which the occurrence of serotonergic signs was analyzed. Brains were obtained after exposure to determine DA and 5-HT levels by HPLC.

RESULTS

Toluene concentration-dependently induced HTR. Other serotonin syndrome signs were evident at high concentrations. Toluene (4000 and 8000 ppm), and ketamine (3 and 10 mg/kg), significantly increased 5-HT levels in the frontal cortex (FC) striatum, hippocampus, and brain stem, as well as DA levels in the striatum and FC. Pretreatment with ketanserin (5HT2A/2C receptor antagonist), M100907 (selective 5-HT2A receptor antagonist), D-serine (co-agonist of the NMDA receptor glycine site), and haloperidol (D2 receptor antagonist) significantly decreased toluene's and ketamine's actions. The 5HT1A receptor antagonist WAY100635 had no effect.

CONCLUSION

Toluene stimulates 5HT2A and 5HT2C receptors, and increases 5-HT and DA levels. These actions are similar to those produced by ketamine and involve activation of a complex neurotransmitter network that includes NMDA receptor antagonism.

Slow heart-slow brain: consequence of short-term occupational exposure to toluene in a young woman: what is the real mechanism?

Herein we describe a case of acute occupational exposure to toluene in a 27-year-old female patient, presented to the emergency department of our institute. On admission she had electrocardiographic signs of profound sinus bradycardia with sinus arrhythmia and low amplitude slow wave activity recorded on her electroencephalogram (EEG). The mechanisms underlying the cerebral and cardiac effects of toluene are also discussed.

Cardiovascular effects of oral toluene exposure in the rat monitored by radiotelemetry

Toluene is a hazardous air pollutant that can be toxic to the nervous and cardiovascular systems. The cardiotoxicity data for toluene come from acute studies in anesthetized animals and from clinical observations made on toluene abusers and there is little known on the response of the cardiovascular and other autonomic processes to graded doses of toluene. This study assessed the effects of toluene (0.4, 0.8, and 1.2 g/kg; gavage) on heart rate (HR), blood pressure, core temperature (Tc), and motor activity (MA) in unrestrained, male Long-Evans rats monitored by telemetry. Toluene doses of 0.8 and 1.2 g/kg elicited significant elevations in HR, characterized by a transient 100 beats/min increase in HR lasting 1 h followed with a steady state tachycardia lasting >6 h. Overall, HR increased by 25 and 50 beats/min in the 0.8 and 1.2 g/kg groups, respectively. MA increased markedly in the 0.8 and 1.2 g/kg groups but the tachycardia persisted in spite of recovery of MA in the 0.8 g/kg group. There was a small (<0.5 degrees C) increase in Tc above controls in rats dosed with 0.8 g/kg toluene, whereas 1.2 g/kg toluene elicited a transient reduction in Tc followed by a small elevation lasting several hours. In a second study, rats were implanted with transmitters to monitor blood pressure (BP), and were administered with toluene as in the first study. HR, Tc, and MA were also monitored. The tachycardic effects of toluene at 0.8 and 1.2 g/kg were associated with a rise in blood pressure. Doses of 0.8 and 1.2 g/kg elicited a mean BP elevation of 6 and 16 mm Hg, respectively, for 7-hour post-dosing. The biphasic tachycardia to toluene suggests multiple sites for eliciting the cardiotoxic effects of this toxicant.

Gestational toluene exposure effects on spontaneous and amphetamine-induced locomotor behavior in rats

Gestational Toluene Exposure Effects on Spontaneous and Amphetamine-Induced Locomotor Behavior in Rats. Bowen, S.E., Mohammadi, M.H., Batis, J.C., and Hannigan, J.H. Neurotoxicology and Teratology, XX, 2006. The abuse of volatile organic solvents (inhalants) continues to be a major health concern throughout the world. Toluene, which is found in many products such as glues and household cleaners, is among the most commonly abused organic solvents. The neurobehavioral teratogenic sequelae of solvent abuse (i.e., repeated, brief inhalation exposures to very high concentrations of solvents) have not been examined thoroughly. In a preclinical model of inhalant abuse, timed-pregnant Sprague-Dawley rats were exposed to 0, 8000, or 12,000 parts per million (ppm) for 15 min twice daily from gestation day 8 (GD8) through GD20. In the first experiment, separate groups of offspring were observed individually in an open-field on postnatal day 22 (PN22), PN42 or PN63. In the second experiment, other offspring given identical prenatal toluene exposures were observed in an "open-field" following an acute i.p. injection of amphetamine (0, 0.56, 1.78 mg/kg) on PN28. Automated measurements of distance traveled and ambulatory time were recorded. Prenatal toluene exposure resulted in small alterations in spontaneous activity compared to non-exposed rats. Prenatal exposure to 12,000 ppm toluene resulted in significant hyposensitivity to the locomotor stimulatory effects of the amphetamine challenge in male but not female rats on PN28. The results demonstrate that prenatal exposure to abuse patterns of high concentrations of toluene through inhalation can alter spontaneous and amphetamine-induced locomotor behavior in rats. The expression of these effects also appears to depend upon the postnatal age of testing. These results imply that abuse of organic solvents during pregnancy in humans may also produce long-lasting effects on biobehavioral development.

Increases in amphetamine-like discriminative stimulus effects of the abused inhalant toluene in mice

RATIONALE

Toluene, an abused solvent, shares behavioral and pharmacological effects with abused depressant drugs. These effects include ethanol- and pentobarbital-like discriminative stimulus effects. There is also emerging evidence that this abused inhalant may share stimulus effects with abused central nervous system (CNS) stimulants.

OBJECTIVE

To further explore the discriminative stimulus effects of one abused inhalant, this experiment evaluated the amphetamine-like discriminative stimulus effects of toluene.

MATERIALS AND METHODS

Mice were trained to discriminate between d-amphetamine (1.0 mg/kg) and saline in a two-lever drug discrimination procedure in which responding was under the control of a fixed-ratio 15 schedule. Mice were tested after 10-min inhalation exposures to air or toluene (500-6,000 ppm) and stimulus generalization was examined at 0, 15, 30, 45, 60, and 75 min post-exposure.

RESULTS

Concentration-related increases in amphetamine-lever responding were observed for amphetamine doses >0.56 mg/kg with full substitution occurring immediately after testing for 1.0 and 1.78 mg/kg. Partial amphetamine-lever responding was observed for all concentrations of toluene across the 75-min post-exposure test trials. Response rates that had decreased immediately after all toluene exposures recovered within 15-min post exposure.

CONCLUSION

This partial substitution of toluene for amphetamine suggests that studies of the effects of abused solvents on brain dopaminergic systems need to be included in the study of possible CNS mechanisms.

Effect of Toluene and Nutritional Status on Serotonin, Lipid Peroxidation Levels and NA+/K+-ATPase in Adult Rat Brain

The aim was to evaluate the effect of toluene and nutritional status on levels of serotonin (5-HT), 5-hydroxytryptophan (5-HTP), Na+/K+-ATPase, total ATPase and lipid peroxidation (TBARS) in rat brain. Study was conducted with malnourished (MN), well-nourished (WN) and normal Wistar rats. Three groups were formed for each nutritional status: control group I received 0.9% NaCl; toluene (1 g/kg) was administered to group II, and 1.5 g/kg to group III. Levels of 5-HT decreased (P < 0.05) in WN toluene groups, and 5-HTP decreased (P < 0.05) in the WN 1 g toluene and MN 1.5 g toluene groups. TBARS decreased (P < 0.05) in WN toluene groups. A trend to increase in Na+/K+-ATPase was found in WN and MN toluene groups, while total ATPase increased (P < 0.05) in the WN 1.5 g toluene group. The results suggest that high concentrations of toluene in single doses induce significant changes in the serotonergic system and alter membrane fluidity more perceptibly in the brain of adult animals with regular diet than in malnourished animals.

Effects of toluene exposure on signal transduction: toluene reduced the signaling via stimulation of human muscarinic acetylcholine receptor m2 subtypes in CHO cells

The organic solvent toluene is used widely in industry and is toxic to the central nervous system (CNS). To clarify the mechanisms of CNS toxicity following toluene exposure, especially with respect to the G protein-coupling of receptors, we determined the effects of toluene on the activation of Gi by stimulating human muscarinic acetylcholine receptor m2 subtypes (hm2 receptors) expressed in Chinese hamster ovary (CHO) cells. We first examined whether toluene affects the inhibition of adenylyl cyclase by Gi. The attenuation of forskolin-stimulated cAMP formation by the stimulation of hm2 receptors was reduced in a medium containing toluene. Next, we determined the effects of toluene on carbamylcholine-stimulated [35S]GTPgammaS binding using membrane fractions of CHO cell expressing hm2 receptors. Carbamylcholine-stimulated [35S]GTPgammaS binding activity was markedly reduced when assayed using reaction buffers containing toluene. However, carbamylcholine-stimulated [35S]GTPgammaS binding activity was essentially unchanged following pretreatment of the cells with a toluene-saturated medium prior to membrane isolation. Toluene pretreatment and the toluene itself did not alter the characteristics of the binding of carbamylcholine and [3H]N-methylscopolamine to hm2 receptors. On the contrary of the effect of toluene for [35S]GTPgammaS binding, the effect of toluene for attenuation of forskolin-stimulated cAMP formation by the stimulation of hm2 receptors was irreversible. These observations indicate that toluene acts as an inhibitor of the signal transduction via hm2 receptor stimulation in CHO cells, and at least two mechanisms exist in the inhibition mechanisms by toluene.

Effects of short-term toluene exposure on ligand binding to muscarinic acetylcholine receptors in the rat frontal cortex and hippocampus

Changes in the binding affinity of the muscarinic acetylcholine receptor agonist carbamylcholine were determined in membranes isolated from the brains of rats exposed to toluene at concentrations of 500-2,000 ppm for 6 h. Membrane fractions of the frontal cortex and hippocampus were prepared and agonist-binding affinities were determined by measuring the displacement of [3H]N-methyl scopolamine-binding activity by carbamylcholine. In the frontal cortex, the affinity of high-affinity carbamylcholine binding was reduced following exposure to toluene at a concentration of 1000 ppm or higher. However, in the hippocampus, the affinity of high-affinity binding of carbamylcholine was increased following exposure to toluene. These observations suggest that toluene exposure affects binding affinity of carbamylcholine, and the effect differs by brain region.

Neonatal capsaicin administration: effects on behavioral development of the rat

The effect of a single dose of capsaicin administered neonatally on the development of six motor behavioral patterns (scratching, rearing, grooming, searching, remaining still, and sniffing) was examined in Wistar rats. Treated animals exhibited a significant increment in scratching, rearing, grooming, and searching. Capsaicin also provoked precocious eye opening of one to two days and a reduction in remaining still, sniffing, and body weight. These effects were accompanied by pelage dishevelment and presence of skin ulcers in the region of the head, neck, and shoulders. The distribution of skin ulcers suggests that the fifth cranial nerve and roots innervating C1-C3 spinal cord segments contain a high proportion of capsaicin-sensitive "C" and A delta fibers.

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.

Persistent effects of subchronic toluene exposure on spatial learning and memory, dopamine-mediated locomotor activity and dopamine D2 agonist binding in the rat

The effects of subchronic inhalation exposure to toluene (80 ppm, for 4 weeks, 5 days/week, 6 h/day) was studied on spatial learning (postexposure days 3-6) and memory (postexposure day 14) using a water maze, on spontaneous and apomorphine-induced (1 mg/kg, subcutaneously (s.c.)) locomotor activity (postexposure day 17) and on the binding parameters of the dopamine D2 agonist S(-)[N-propyl-3H(N)]propylnorapomorphine ([H]NPA) in membrane preparations of the neostriatum of the rat. Toluene treatment was found to cause a statistically significant impairment in acquisition and retention of the spatial learning task. Furthermore, toluene significantly increased (2-fold) apomorphine-induced locomotion and caused a trend for a 50-60% increase in motility without any significant effect on rearing. Spontaneous locomotion, motility and rearing were not affected by toluene. Toluene treatment produced a significant 30-40% increase in the Bmax values of [3H]NPA and a trend for a 20-30% increase in the KD values. These results indicate that subchronic exposure to toluene in low concentrations causes a slight but persistent deficit in spatial learning and memory, a persistent increase in dopamine-mediated locomotor activity and an increase in the number of dopamine D2 receptors in the rat.

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.

Behavioral effects of chronic toluene exposure in the developing rat

The effects of acute and chronic toluene exposure on the hypnotic effect, the righting reflex latencies and the blood and tissue toluene contents were studied in rats during development. The data showed a progressive significant prolongation of the hypnotic effect latencies until the third and fourth postnatal weeks, followed by a significant continuous declining trend until the eighth week postpartum. The measure of the righting reflex latencies followed an opposite temporal course compared to that of hypnotic effect measurements. The acute and chronic toluene exposure did not reveal significant differences in toluene concentrations of blood, brain and liver tissues. The data suggest that chronic toluene treatment may probably be inducing behavioral manifestations of a tolerance phenomenon combined with maturational influences in the developing rat.

Toluene and benzene inhalation influences on ventricular arrhythmias in the rat

We have previously found that toluene did not share the capacity of benzene for increasing the arrhythmogenic action of epinephrine in the rat, but appeared to elicit the opposite effect. The present experiments were carried out to verify this observation in rats subjected to more severe ventricular arrhythmias. In animals previously inhaling either air, toluene or benzene and anesthetized with pentobarbital, arrhythmias were produced by coronary ligation or aconitine. In both models, toluene decreased and benzene increased the number of ectopic ventricular beats in the 30 min following induction of arrhythmia. Gas chromatographic measurement of toluene levels in the heart during and after inhalation revealed essentially constant concentrations at the time of arrhythmia evaluation, equivalent to approximately one-third the peak levels observed at the end of inhalation. Although the mechanism of the effect of toluene on arrhythmia could not be ascertained, nonspecific membrane stabilization or central serotonergic stimulation were considered as possible explanations. Since both mechanisms could be operant also in the case of benzene, the opposite effects of the solvents on arrhythmia could not be readily accounted for.

Effect of toluene on rat synaptosomal phospholipid methylation and membrane fluidity

This study investigated the effects of toluene (1 g/kg, 1 hr, i.p.) on rat synaptosomal phospholipid methylation (PLM), phospholipid composition, and membrane fluidity. Toluene significantly decreased basal PLM (35%) in studies using [3H]methionine [( 3H]Met) as the methyl donor; this was reflected by similar decreases in phosphatidylmonomethylethanolamine (PME) (30%). No effects were observed in either PLM reactions that used [3H]adenosylmethionine [( 3H]AdoMet) as methyl donor, or AdoMet synthetase, suggesting that toluene preferentially affects PLM reactions that derive methyl groups from [3H]Met. Also, toluene decreased synaptosomal phosphatidylethanolamine (PE) (24%), the initial substrate for PLM, and the addition of PE back to PE-depleted synaptosomes restored methyltransferase activity. Agonist-stimulated PLM using norepinephrine (NE) demonstrated that agonist-receptor coupling returned PLM to control values in synaptosomes from toluene-treated rats. NE-stimulated PLM was also blocked by propranolol (PRO), suggesting a role for toluene in receptor-mediated events. Membrane fluidity studies demonstrated that in vivo administration of toluene increased the outer synaptosomal membrane fluidity, whereas in vitro administration of toluene had no effect. Our observations support a positive relationship between increased PLM activity and increased outer, not core, membrane fluidity. These data demonstrate that specific toluene-phospholipid interactions occur in synaptosomes, resulting in altered membrane composition, function and fluidity.

Actions of 1,1,1-trichloroethane on the cAMP metabolism in mouse brain

Inhalation or intraperitoneal administration of 1,1,1-trichloroethane (TCE) increased the cAMP content in the brain stem in a dose-related and time-dependent fashion. TCE had no effect on the cAMP level in the cerebellum and hippocampus, but slightly reduced that in the cerebral cortex. Following intraperitoneal administration of TCE the activity of norepinephrine- and F- -activated adenylate cyclase (AC) in a brain stem homogenate was enhanced, while the serotonin-stimulated AC activity was decreased. Neither the basal AC activity nor the guanine nucleotide- and forskolin-activated enzyme was affected by TCE. TCE had no effect on the soluble cAMP-dependent phosphodiesterase activity. It is suggested that the increased cAMP content in the brain stem induced by TCE may be mediated via adrenoreceptor interaction with the guanine nucleotide-binding regulatory component, resulting in activation of the catalytic unit of the adenylate cyclase and thereby an increase in the cAMP level.

Partial insomnia, hyperactivity and hyperdipsia induced by repeated administration of toluene in rats: their relation to brain monoamine metabolism

In an attempt to examine chronic effects of toluene on sleep, spontaneous locomotor activity and drinking behavior, rats were repeatedly administered toluene i.p. at doses of 100 and 200 mg/kg body weight for 14 consecutive days. The 200-mg/kg injections induced a decrease in total sleep on Day 1, an increase in locomotor activity on Days 1 through 4 and an increase in drinking activity on Days 0 through 6 after discontinuation of the daily injections. Both the reduced sleep and the increased locomotor activity appeared during the light period, whereas the drinking activity increased during the dark period. In order to find neurochemical correlates of the toluene-induced changes in behavior, regional concentrations of brain monoamines and their metabolites were determined. The toluene-induced partial insomnia and hyperactivity were associated with lowered concentrations of serotonin in frontal cortex, hippocampus and midbrain and 5-hydroxyindoleacetic acid in midbrain and hypothalamus. The increased drinking activity was associated with increased concentrations of striatal 3,4-dihydroxy-phenylacetic acid and homovanillic acid and hypothalamic noradrenaline and 3-methoxy-4-hydroxyphenylethyleneglycol. Central monoaminergic mechanisms were implicated in the toluene-induced partial insomnia, hyperactivity and hyperdipsia.

Effects of toluene inhalation on behavior and expired carbon dioxide in macaque monkeys

Cynomolgus macaque monkeys received head-only exposure to 0, 100, 200, 500, 1000, 2000, 3000, and 4500 ppm toluene for 50 min while simultaneously tested for delayed matching-to-sample behavior, a test of cognitive functions. Response time increased and accuracy of matching decreased at 2000 ppm or more of toluene, indicating an attentional deficit but not specific memory effects. Behavioral indices exhibited monotonic concentration-related changes. Expired carbon dioxide (CO2), the most sensitive index, displayed an inverted U-shaped concentration-effect curve, which increased at 100 ppm (the TLV) and decreased at 4500 ppm toluene. Changes in expired CO2 provide new evidence of physiological changes at very low levels of toluene. These changes may indicate combined behavioral, respiratory, sensory, and metabolic effects. No behavioral measure exhibited either cumulative effects or tolerance to 4500 ppm during two 3-day exposures. However, both response time and expired CO2 exhibited an acute, within-session tolerance. The results indicate that brief inhalation exposure to toluene impairs cognitive and motor abilities at concentrations below those causing overt signs, such as ataxia and intention tremoring.

Acute effects of toluene on circadian rhythms of sleep-wakefulness and brain monoamine metabolism in rats

Acute effects of a single i.p. injection of toluene on circadian rhythms of sleep-wakefulness were investigated in rats which were chronically implanted with EEG and EMG electrodes for polygraphic recordings. The toluene injection produced an initial increase in wakefulness (W) and a subsequent increase in slow-wave sleep (SWS) during the dark period. In an attempt to clarify mechanisms of these biphasic effects of toluene on sleep-wakefulness rhythms, brain monoamines and their metabolites were determined at the times of the initial increase in W and the increased SWS. The initial increase in W was associated with an increase in cortical NA, MHPG and 5-HT together with a decrease in cortical 5-hydroxyindoleacetic acid (5-HIAA), while the increased SWS during the dark period was associated with an increase in 5-HIAA and a concomitant decrease in 3-methoxy-4-hydroxyphenylglycol (MHPG). The toluene-induced changes in sleep-wakefulness seemed to be manifested at lower blood levels of toluene than the behavioral signs of central nervous system (CNS) depression. These biphasic effects of toluene on circadian sleep-wakefulness rhythms are discussed in terms of the reciprocal interactions between central 5-HT and NA neurons.

Effects of subacute treatment with toluene on central monoamine receptors in the rat. Reduced affinity in [3H]5-hydroxytryptamine binding sites and in [3H]spiperone binding sites linked to dopamine receptors

Subacute treatment with toluene leads to a dose-related reduction of affinity in the [3H]spiperone binding sites labeling striatal dopamine (DA) receptors of the D2 type and cortical [3H]5-hydroxytryptamine (5-HT)-binding sites. It is suggested that these results represent a down regulation of activity at striatal DA and cortical 5-HT synapses, since they now may operate at higher concentrations of transmitters. The reduced affinity may be caused by the physicochemical properties of toluene leading to changes in membrane fluidity and thus in the regulation of DA and 5-HT receptors in the local circuits of the striatum and the dorsal cerebral cortex.