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PERSISTENT EFFECTS OF REPEATED INHALATION OF TOLUENE: 4 WEEKS VS. 13 WEEKS.
Citation:
SAMSAM, T. E., W. K. BOYES, L. DEGN, P. A. EVANSKY, AND P. J. BUSHNELL. PERSISTENT EFFECTS OF REPEATED INHALATION OF TOLUENE: 4 WEEKS VS. 13 WEEKS. Presented at Society of Toxicology, Seattle, WA, March 16 - 20, 2008.
Impact/Purpose:
To understand and predict the extent of neurotoxic damage from repeated exposure to volatile organic compounds
Description:
Understanding and predicting the extent of neurotoxic damage from repeated exposure to volatile organic compounds (VOCs) is a problem for many EPA programs. Eighty adult, male Long-Evans rats inhaled toluene (0, 10, 100, or 1000 ppm) 6 hr/day, 5 days/week for 4 weeks in a systematic replication of a previous 13 week exposure using the same conditions. Cohort 1 (N=40) was trained to perform a visual signal detection task to assess learning and sustained attention. Previously, 13 weeks of exposure delayed the acquisition of a lever-press response (autoshaping) in all toluene-exposed groups. In the current study, rats exposed for only 4 weeks showed no delay in acquiring a lever response task. 4-week exposed rats also did not show impairment in learning a subsequent visual discrimination task, whereas rats that were exposed to 1000 ppm toluene for 13 weeks were slow to learn the visual discrimination task. No further deficits were observed in either the 4-week or 13-week groups of rats in subsequent behavioral training or testing. Retinal function was assessed in Cohort 2 (N=40) approximately 2 weeks after termination of exposure by recording electroretinograms (ERGs) from dark-adapted, anesthetized rats. The amplitude of ERG B-waves was slightly reduced in rats exposed to 1000 ppm toluene, an effect similar in direction but of lesser magnitude than that observed after 13 weeks of exposure. These results suggest that neurotoxic effects of toluene appear and increase as exposure is increased from 4 and 13 weeks. Given the rapid tissue clearance of toluene, these results are consistent with a progressive impairment with ongoing repeated exposures.