Maze learning in rats exposed to xylene intoxication

ATSDR evaluation of health effects of chemicals. V. Xylenes: health effects, toxicokinetics, human exposure, and environmental fate

Xylenes, or dimethylbenzenes, are among the highest-volume chemicals in production. Common uses are for gasoline blending, as a solvent or component in a wide variety of products from paints to printing ink, and in the production of phthalates and polyester. They are often encountered as a mixture of the three dimethyl isomers, together with ethylbenzene. As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that are of greatest concern for public health purposes. These profiles comprehensively summarize toxicological and environmental information. This article constitutes the release of the bulk of this profile (ATSDR, 1995) into the mainstream scientific literature. An extensive listing of known human and animal health effects, organized by route, duration, and end point, is presented. Toxicological information on toxicokinetics, biomarkers, interactions, sensitive subpopulations, reducing toxicity after exposure, and relevance to public health is also included. Environmental information encompasses physical properties, production and use, environmental fate, levels seen in the environment, analytical methods, and a listing of regulations. ATSDR, as mandated by CERCLA (or Superfund), prepares these profiles to inform and assist the public.

Health effects of the alkylbenzenes. II. Xylenes

The alkylbenzenes are a class of six-membered ring aromatic compounds that have a variety of alkyl groups attached. These chemicals are liquids with relatively low boiling points used primarily as solvents or as starting materials in the synthesis of other chemicals and drugs. They are integral components of gasoline, distillate fuels and other petroleum products and are economically important in the chemical, petroleum, pharmaceutical, polymer, paint and dye industries. Alkylbenzenes such as toluene, the xylenes, ethylbenzene, styrene and cumene are produced and utilized in large quantities and therefore, present the possibility of exposure to humans and to wildlife. Fortunately, the toxicity of alkylbenzenes has been found to be rather low and therefore, the human and environmental risks are probably low. In modern industrial activities, exposures to the alkylbenzenes are minimized by workplace controls or personal protective equipment which meet guidelines for maximum allowable exposure concentrations that have been established for the workplace. Nevertheless, considerable quantities of alkylbenzenes are released to the environment each year through solvent and fuel evaporation, accidental spills and misuse, and considerable toxicological information for these materials has appeared in the recent literature. This present paper, the second in a series reviewing the potential health effects of alkylbenzenes, covers the toxicology and disposition of the dimethyl-substituted benzenes (the xylenes) in animals and man.

Behavioral effects of acute p-xylene inhalation in rats: autoshaping, motor activity, and reversal learning

p-Xylene is a ubiquitous solvent and chemical precursor used in industry, gasoline, and household products. While the population at risk for exposure is thus quite large, little is known about its neurobehavioral effects. To evaluate the possibility that p-xylene affects cognitive behavior, male Long-Evans hooded rats inhaled p-xylene at concentrations of 0 or 1600 ppm, 4 hr per day for 1 to 5 days, and were evaluated after exposure on two learning tasks and a test of motor activity. Autoshaping was carried out across 5 successive days with p-xylene exposure in the morning followed by testing in the afternoon. For this test, the retraction of a single response lever on a variable-time 35-sec schedule was followed by delivery of a food pellet. When the force required to depress the lever was low (0.10 N), response acquisition was faster in animals having inhaled 1600 ppm p-xylene than in air-exposed controls. When the force was increased to 0.20 N, however, p-xylene-exposed rats acquired the response no faster than controls. In contrast, inhaled p-xylene at 1600 ppm suppressed response rates in an automaintained reversal learning paradigm without affecting reversal rate. Studies of motor activity showed that while vertically-directed activity was unaffected by p-xylene, horizontally-directed activity was increased by about 30% for the first 15 min of each daily 25-min test.(ABSTRACT TRUNCATED AT 250 WORDS)

Conditioned flavor aversion induced by inhaled p-xylene in rats

Xylenes have the potential for widespread public exposure, yet their neurotoxic properties are poorly understood. The conditioned flavor aversion (CFA) paradigm provides a sensitive behavioral assay for the aversiveness of many drugs and toxic chemicals. Male Long-Evans rats were placed on a restricted water schedule (30 min/day) 1 week after arrival in the laboratory at 40 days of age. Ten days later, all rats received 0.1% saccharin in place of water, and then were exposed immediately either to filtered air or to 50, 100, 200, 400, 800 or 1,600 ppm p-xylene for 4 hr, or to air or 400 ppm p-xylene for 0.5, 1, 2, 4 or 8 hr. The restricted water schedule remained in effect for the next 72 hr, at which time the rats were given a choice between saccharin and water. Inhalation of all concentrations of p-xylene reduced relative saccharin intake, with maximal aversion at 800 and 1,600 ppm. The aversion produced by 400 ppm p-xylene was maximal at exposures of 2 or more hr, with shorter exposures producing intermediate effects. Total fluid intake was unaffected by p-xylene exposure with the exception of a slight (nonsignificant) decrease in consumption following 1,600 ppm. Exposure to saccharin 24 hr prior to p-xylene produce no aversion, indicating that the reduction in saccharin intake required close temporal pairing of saccharin and p-xylene. Thus inhaled p-xylene at a concentration of 1/2 its TLV (= 100 ppm) caused a significant, learned change in rats' normal consumption of saccharin-flavored water, without disrupting total fluid consumption.

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.

Postnatal evaluation of prenatal exposure to p-xylene in the rat

Pregnant Sprague-Dawley rats were exposed to either 3500 or 7000 mg/m3 p-xylene from days 7-16 of gestation. Dams were allowed to give birth, and litters were counted, weighed, and observed for external malformations on postnatal days (PD) 1 and 3. Litters were normalized to 8 pups (4 males and 4 females +/- 1) on PD4. On PD21 animals were weaned and littermates housed by sex. Body weights were recorded weekly until weaning and once every 2 weeks thereafter. Central nervous system (CNS) development was evaluated by acoustic startle response on PD13, 17, 21, and 63 as well as figure-8 maze activity on PD22 and 65. Maternal weight gain during the treatment period was significantly less in the high-dose group. No effects were seen on litter size or weight at birth or on PD3. There were no effects of xylene exposure on growth rate. There were no treatment-related effects on acoustic startle response or figure-8 maze activity. Thus, p-xylene as administered in this study does not appear to be a selective developmental toxicant in the rat.

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.

Toxicology updates. Xylene

Like most organic solvents, xylene has irritating effects on the skin, mucous membranes and respiratory tract. It has a narcotic effect on the nervous system, variable effects on the liver and kidneys, and questionable effects on the cardiovascular system and female reproductive system. Xylene was thought to be deleterious to the hemopoietic system, but more recent studies concluded that such effects were due to benzene contamination or inflammation response to xylene injection. The latest evidence indicates that xylenes are not co-carcinogenic, carcinogenic or teratogenic. If maternal toxicity is avoided, xylenes do not have embryotoxic effects.