Does aging enhance vulnerability of the CNS to chronic effects of repeated exposure to low levels of toluene? By (1) neurobehavioral test battery and by (2) in vivo brain microdialysis in rats

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I)By neurobehavioral test battery(1)In the case of elderly rats, slow acquisition of the timing behavior of the DRL 12 sec schedule in toluene exposed groups (100,400 and 1,000 ppm) was reveal ed (p<0.01 by ANOVA). (2)Level of the achievement of acquisition of DRL 12 sec schedule of the 1,000 ppm exposed group was lower than that of the other (p<0.01 by ANOVA) : dsecreased learning in the 1,000 ppm exposed group. (3) In the case of young adult rats, significantly rapid acquisition of timing behavior in the toluen exposed groups (100,400 and 1,000 ppm) was observed, although no significant difference was detected on the level of achievement among 4 groups.II)By brain microdialysis(1)In the case of elderly rats, even at 100 ppm toluene exposure, chronic effects on the behavior of cholinergic neuron in the hippocumpus (P<0.01) and spontaneous motor activity (P<0.05) following scopolamine challenge were clealy detected. On the other hand, in the case of young rats, no significant difference could be detected among 3 groups for any index at any level of toluene which were examined.These findings based on (1) the neurobehavioral test battery and (2) the brain microdialysis suggest that advanced age may enhance the vulnerability to the chronic adverse effects of organic solvents in the CNS.This should be taken into account in the setting of future occupational exposure limits.