BEHAVIORAL-CHANGES FOLLOWING 4-WEEK INHALATION EXPOSURE TO PSEUDOCUMENE (1,2,4-TRIMETHYLBENZENE) IN THE RAT

Pseudocumene (1,2,4-trimethylbenzene, TMB) is a component of several s olvent mixtures. During recent studies on rats we investigated the eff ect of a 4-week (6 h/day, 5 days/week) inhalation exposure to TMB at c oncentrations of 0, 25, 100, or 250 ppm on radial maze performance, op en field activity, passive avoidance, active two-way avoidance, and sh ock-induced changes in the pain sensitivity reflecting the magnitude o f the shock-induced fear response (hot plate test). The tests were per formed between days 14 and 54 after the last exposure. The radial maze performance was not disturbed in any dose group. During testing in th e open field grooming was significantly increased in rats exposed to 1 00 ppm TMB. In rats exposed to 100 and 250 ppm TNB, a foot shock appli ed after stepping off an elevated platform (a safe area) resulted in a significantly smaller increase in the step-down latency (i.e., passiv e avoidance, on days 3 and 7 after the foot shock) than in sham-expose d animals. Learning of a two-way active avoidance was slightly retarde d in rats exposed to 250 ppm of TMB, Results of the hot plate test rev ealed no differences between groups in the paw sensitivity to heat (54 .5 degrees C) before a 2-min intermittent foot shock, but in rats expo sed to 100 and 250 ppm of TMB the foot shock-induced fear response per sisted apparently longer. These results suggest that inhalation exposu re to TMB may lead to long-lasting disturbances in CNS functions. (C) 1997 Elsevier Science Inc.