Assessment of long-term effects of exposure to toluene based on the analysis of selected behavioral responses with particular reference to the ability to trigger behavioral hypersensitivity in rats.

Toluene is a major component of numerous commercial organic solvent formulations. It is often listed among the chemicals capable of producing the organic solvent syndrome and a neurobehavioral hypersensitivity condition. The hypersensitivity condition (continued long-term intensification of some behavioral reactions in response to pharmacological or environmental stressors) is usually associated with the increased tonus of the functional dopaminergic system. The aim of our current research was to determine whether, under conditions of inhalation exposure, toluene can produce long-term behavioral changes or modify the intensity of the behavioral response to apomorphine, a dopaminergic receptor agonist. In our experiment, male rats were exposed to 25, 100 and 250 ppm toluene for 4 weeks (5 days/week, 6h/day). The following behaviors were tested: finding water in a radial maze; open field motor activity, acquiring the conditional response of passive avoidance; sensitivity to a thermal pain stimulus (hot plate test) and changes in this sensitivity caused by stress; and acquiring the conditional response of two-directional active avoidance. The behavioral response to apomorphine, i.e. the increased spontaneous locomotor activity, was assessed on day 10 after the termination of the exposure in the rotary drum test. In the behavioral experiment, significant differences between groups were recorded only for the hot plate test; in the 100 and 250 ppm rats, electric-shock-related anxiety response was stronger than in the control group. In the experiment using pharmacological provocation, the behavioral response to apomorphine in the rats exposed to 100 ppm or 250 ppm toluene was significantly lower. Our results indicate that low concentrations of toluene may produce long-term behavioral changes in rats. However, these changes seem to be linked with reduced rather than increased functional tonus of the dopaminergic system.