Neurobehavioral effects of subchronic exposure of weanling rats to toluene or hexane.

Using several behavioral and neurophysiologic tests, we examined the effects of subchronic inhalation exposure of rats to toluene and compared them with the effects of the known neurotoxicant hexane. The rats were exposed to toluene (900 and 1400 ppm) or hexane (2000 ppm) 14 hr/day, 7 days/week for 14 weeks. Both solvents inhibited weight gain. Hexane caused a neurotoxic syndrome characterized by reductions of grip strength (especially hindlimb), motor activity, and startle responses, and increased latencies of several evoked potential components. Initial acquisition of a conditioned avoidance response (CAR) was also impaired, but subsequent performance was intact. Toluene did not cause the peripheral motor symptoms associated with exposure to hexane. However, a component of the brainstem auditory-evoked response was depressed and CAR acquisition was impaired along with the acquisition of a tone-intensity discrimination task when tested within hours after the daily exposure ended.