Neurochemical and behavioural effects of long-term intermittent inhalation of xylene vapour and simultaneous ethanol intake

Effect of xylene inhalation on fixed-ratio responding in rats

The effect of xylene inhalation was studied on operant behavior under a fixed-ratio (FR24) schedule in rats. Experiments were performed while rats were being exposed to xylene vapor in an inhalational (flow-through) behavioral chamber. Rats were exposed successively to three graded concentrations (113, 216 and 430 ppm) of xylene vapor each for 2 hr in range-finding studies during 6 1/4-hr sessions. The reinforcement rate which is correlated with FR responding was shown to be decreased at hr 1, hr 3 and hr 5. However at hr 2, hr 4 and hr 6 the reinforcement rate in rats increased approaching the control levels, thereby indicating development of tolerance. When rats were exposed to one of the three graded concentrations of xylene for 2 hr on separate days, they also showed a decrease in the reinforcement rate at hr 1; development of acute tolerance was also noted in this schedule. Exposure to the lowest (98.5 ppm) level of xylene used during 5-hr sessions caused no significant decrease in the reinforcement rate. This study thus attempts to identify a minimum effective concentration of xylene and indicates the development of acute tolerance to behavioral effect of xylene.

Effects of xylene isomers on operant responding and motor performance in mice

Xylene, a widely used industrial solvent, is a mixture of the ortho-, meta-, and paraisomers. In this study we examined the effects of each individual isomer, as well as a commercial-grade mixture of xylenes, on two behavioral measures: (1) operant performance of 15 mice trained to lever-press under a DRL (differential reinforcement of low rates) 10-sec schedule, and (2) motor performance of mice on an inverted screen test. The 15-min operant sessions immediately followed 30-min exposures to solvent vapors (500 to 7000 ppm), or air, in static inhalation chambers. All mice were exposed to each isomer in a counterbalanced order, and the mixture was given last in all cases. Ortho-, meta-, para-, and mixed xylenes produced similar biphasic effects on response rates, and concentration-dependent decreases in reinforcement rates. The lowest significantly effective concentration for each isomer on any variable was 1400 ppm, where increases in response rates occurred. Half-maximal response rate decreases were produced by 5179 ppm (ortho-xylene) to 6176 ppm (meta-xylene). The temporal distribution of responses was only moderately disrupted, even at high concentrations. In other groups of mice, motor coordination was also disrupted by the xylenes in a concentration-dependent manner. Half-maximal effective concentrations were 2676 ppm (para-xylene) to 3790 ppm (meta-xylene). Minimally effective concentrations were 2000 to 3000 ppm, higher than those seen in the operant studies. Xylene produced pronounced behavioral actions following acute exposure and no substantial differences in overall effects, and only slight potency differences, were obtained between the individual isomers or the commercial mixture.

Burden and biochemical effects of extended tetrahydrofuran vapour inhalation of three concentration levels

Adult male rats exposed to tetrahydrofuran vapour at 8.2 (200 p.p.m.), 41 (1,000 p.p.m.) or 82 mumol/l (2,000 p.p.m.) for 2 to 18 weeks, five days a week, 6 hrs daily, showed dose-dependent brain and perirenal fat solvent burden linearly correlated to each other. After two weeks of exposure, the body burden of tetrahydrofuran seems to decrease. This might have been caused by increased oxidative metabolism as enhanced 7-ethoxycoumarin O-deethylase activity was detected in liver and kidneys in the 2nd week and onwards. The exposure also caused inhibition of alcohol and formaldehyde dehydrogenase activities in liver at the highest dose. Biochemical effects in the cerebellum were not detected while gluteal muscle specimens showed increased succinate dehydrogenase activity in a dose-related manner. This points to effects on the energy metabolism. Muscle acetylcholine esterase activity was also increased showing possible effects on the myoneural junctions.

Dose-related effects of m-xylene inhalation on the xenobiotic metabolism of the rat

1. Male Wistar rats were exposed for two weeks (6 h/d, 5 d/week) to 0, 50, 400 or 750 p.p.m. of m-xylene vapour in the air. 2. Microsomal enzyme activities were significantly increased in the liver as follows: NADPH-cytochrome c reductase (less than or equal to 1.2-fold), O-deethylation reactions (less than or equal to 1.8-fold) and UDP-glucuronosyltransferase activity (less than or equal to 2.9-fold). Cytochrome P-450 concentrations also increased with dose. 3. Microsomal affinity to m-xylene increased with dose of m-xylene in vivo, similar to the increased affinity seen in type I spectra390-420nm formation with cytochrome P-450 in vitro. 4. Reduced glutathione concn. in liver declined significantly, while in the kidneys the glutathione remained unchanged. 5. In the kidneys, the concn. of cytochrome P-450 (less than or equal to 1.3-fold), O-deethylation activity (less than or equal to 5.3-fold) and the rate of glucuronidation (less than or equal to 1.8-fold) increased with the dose of xylene. 6. Microsomal protein contents in liver and kidneys increased with the two highest doses of xylene. 7. The hepatic and renal effects were dose-dependent and closely related to the accumulation of m-xylene in perirenal fat. 8. Despite stimulation of xenobiotic metabolism by m-xylene, inhalation did not alter the serum transaminase activity or cause morphological changes in the liver.

Neurotoxicity of industrial chemicals and contaminants: aspects of biochemical mechanisms and effects

Nervous system toxicity by industrial chemicals and contaminants cannot be explained by a single mechanism because of the complex functional capacity of the brain and spinal cord. The nervous system is dependent on the adequate supply of oxygen, and therefore, its lack in the ambient air causes rapid dysfunction. Similar effects to hypoxia are caused by agents which reduce oxygen availability at the cellular level by histotoxic mechanisms, e.g., through the inhibition of mitochondrial respiration. Hypoxic effects are rapidly produced, and in cases where a significant number of cells are fatally damaged permanent disability may remain. Acutely harmful effects are also brought about by organic solvents. The typical mode of exposure is that of vapour inhalation. The lipid-soluble molecules pass the blood-brain barrier rapidly and depress the nerve cell membrane functions. This hinders the formation of action potentials. Neuronal cells acquire tolerance towards the membrane-depressant effects in repeated or prolonged exposure so that similar doses do not produce equivalent effects. The development of the tolerance can be regarded as one of the long-term effects of lipophilic chemicals. They may also produce metabolic adaptation so that their biotransformation is enhanced. This may increase the risk of producing more toxic intermediates. The toxic effects thus created can be cumulative since neurons do not multiply by cell division in the postnatal life. The neurotoxicity of metals is more clearly associated with the accumulation of the dose. Adult brain possesses a blood-brain barrier to many water-soluble compounds such that a threshold concentration must be overcome before appreciable toxic effects are seen. Children are in this respect more vulnerable because of their immature barrier function.

Dose-related effects of dichloromethane on rat brain in short-term inhalation exposure

Male Wistar rats were exposed to 500, 1000 or 100 ppm as time-weighted average (t.w.a.) concentrations of dichloromethane vapour. The 1000 (t.w.a.) ppm exposure consisted of two 1-h peak concentrations (2800 ppm) on a basal exposure of 100 ppm. All exposures lasted for 6 h, 5 days weekly and for 2 weeks. The solvent burdens were analyzed in the perirenal fat samples which showed a relation to the dose with the highest values in the 1000 (t.w.a.) ppm exposures. The solvent concentrations increased in the perirenal fat between the two weeks of exposure. Blood carbon monoxide concentrations did not accurately reflect the body solvent burdens. Neurochemical effects also displayed a dose relationship, and included decreased succinate dehydrogenase activity in the cerebellum at the two higher doses and increased acid proteinase activity at 1000 ppm in the cerebrum. Withdrawal of the animals for 7 days from the 2-week exposure showed that the biochemical changes were largely abolished with the exception of decreased succinate dehydrogenase activity at 1000 ppm (t.w.a.).

Dose-dependent neurochemical changes during short-term inhalation exposure to m-xylene

Male Wistar were exposed to m-xylene vapor at concentrations of 2.0, 16.1, and 30.3 mumol/1 for 2 weeks (5 days a week, 6 h daily). Xylene concentrations in brain and perirenal fat increased between weeks 1 and 2 of exposure, in proportion to the exposure concentrations. Increase in brain NADPH-diaphorase and azoreductase activities was seen after week 2 at the two higher exposure levels, while superoxide dismutase activity decreased in a dose-related manner at the same time. Biochemical analyses on rats withdrawn from exposure for 2 weeks indicated that the biochemical effects were largely abolished within that time, although cerebral RNA was above the control value at the two higher exposure levels.

Behavioural and glial cell effects of inhalation exposure to styrene vapour with special reference to interactions of simultaneous peroral ethanol intake

Male Wistar rats were exposed to 300 p.p.m. of styrene vapour with simultaneous ethanol ingestion for 4 to 17 weeks. The effects on behaviour were analyzed after 4, 9 and 13 weeks of the experiment. The most manifest behavioural effects were found in rats exposed to the combination, and the changes included increased preening time at the 4th week and increased ambulation and rearing at the end of the exposure. The ethanol ingestion affected also the accumulation of the solvent burden by delaying the peak solvent concentration in the perirenal fat to the 8th week of exposure. The fat solvent concentration did not differ from each other in the two groups at the end of the experiment, and they were similar as compared the concentration found in phenobarbital-pretreated rats exposed for reference. The styrene exposure had almost no effects on cerebral glial cells whereas ethanol induced unexpectedly increased protein destruction in them throughout the experiment. Co-exposure to ethanol and styrene decreased the magnitude of protein destruction in the glial cells. Withdrawal of the rats after an 8-week exposure showed that the styrene effects were largely abolished in two weeks of exposure-free period as analyzed by the determination of brain RNA and acid proteinase activity. Brain RNA was lower than control after two weeks of ethanol deprivation. The present data indicate that marked metabolic interactions between ethanol and styrene take place in agreement with experience on other similar solvent combinations.

Neurochemical and behavioural effects of extended exposure to isopropanol vapour with simultaneous ethanol intake

Exposure of male Wistar rats to 12.3 mumol/l (300 ppm) isopropanol vapour for 5-21 weeks, 5 days a week for 6 h daily with a simultaneous ethanol administration in drinking water (5% v/v) caused a significant increase in isopropanol removal as assessed by blood isopropanol and acetone determinations. Ethanol treatment caused a marked synergistic effect during early exposure. Neurochemical studies revealed decreased superoxide dismutase and azoreductase activities at the end of the exposure whereas increased protein degradation was found in glial cells isolated from ethanol-fed rats throughout the experiment. Analyses of spinal cord axon lipid composition showed increases in cholesterol content in relation to lipid phosphorus in animals exposed to isopropanol or to the isopropanol and ethanol combination. Behavioural tests indicated minor effects on emotional reactivity from the 10th week onwards with isopropanol exposure whereas caffeine-stimulated activity was augmented only in rats ingesting ethanol. Co-exposure to isopropanol vapour abolished the increased excitability. The data indicate that marked metabolic and functional adaptation towards the small-molecular-weight alcohols takes place at moderate dose levels.