Effects of toluene exposure on the rest-activity cycle of rats.

Rats were exposed to toluene at a concentration of 1000 ppm, 6 h/day, 6 times weekly, for 4 weeks. Functional disturbance of the circadian rhythm of spontaneous activity was found after repeated exposure to toluene, although single exposure under the same conditions did not influence the rhythm. The disturbance was characterized by a significant increase in distribution of activity in the "Light' (L) period, and a significant relationship was observed between the total number of days of exposure and the activity level in the L period. The toluene concentration in the blood immediately after the exposure was 6.8-7.2 microgram/ml after one and 18 days of exposure, respectively.