Importance of schedule of exposure to hexane in causing neurotoxicity.

Male Fischer rats exposed continuously (24 hr per day) to 1,000 ppm hexane five days per week for 11 weeks developed clear and long-lasting neurotoxic signs, as reflected by a marked decrease in hind-limb grip strength and severe impairment of performance of a multisensory conditioned avoidance response (CAR); transient decreases in undifferentiated motor activity and fore-limb grip strength were also seen. Other rats were only slightly affected by repeated, brief (10 min) exposures to high concentrations (24,000 or 48,000 ppm) of hexane 6 or 12 times per day, five days per week for 18 weeks; when the frequency of exposure to 48,000 ppm hexane was increased to 24 times per day (10 min on and 5 min off), five days per week, for 4 additional weeks, more severe signs of neurobehavioral toxicity appeared.