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

(1)老年大鼠在100,400和1,000 ppm的甲苯暴露组中，对DRL 12秒时间表的时间行为习得较慢（方差分析p<0.01）。(2) 1000ppm暴露组的DRL 12秒计划表学习成就水平低于其他组（方差分析p<0.01）： 1000ppm暴露组的学习能力下降。(3)幼龄成年大鼠在100ppm、400ppm和1000ppm三种浓度的甲苯暴露条件下，计时行为的习得速度显著加快，但四组间的计时行为习得水平无显著差异。(1)在老年大鼠中，即使暴露在100 ppm的甲苯中，也能清楚地检测到东莨菪碱刺激对海马胆碱能神经元行为（P<0.01）和自发运动活动（P<0.05）的慢性影响。另一方面，对于幼龄大鼠，三组间在任何甲苯水平下的任何指标均无显著差异。这些基于(1)神经行为测试电池和(2)脑微透析的发现表明，老年可能会增加对中枢神经系统有机溶剂慢性不良反应的脆弱性。在确定未来的职业接触限值时应考虑到这一点。

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.