Slow learning in rats due to long-term inhalation of toluene.

Rats were exposed to toluene at the concentrations of 1,000, 4,000 and 7,000 ppm for 1 hr a day, 6 days a week for 6 months and a half; 154 days' exposure. Behavioral tests on a test battery were carried out after the termination of 154 days' exposure. The performance level of FR 1, extinction of the FR 30 schedule, wheel running activity, scores of open field test and body weight were not influenced. Slow acquisition of the timing behavior of the DRL 12 sec schedule in toluene-exposed rats was revealed: higher responses from the 1st session onwards, lower percent reinforced responses from the 1st session onwards and higher relative frequency of shorter interresponse-time (IRT) from the 9th to 12th sessions, respectively than those of the control rats. At the 33rd session onwards, the highest relative frequency of IRT of the DRL 12 sec schedule was at around 12 sec in all groups except one exposed group (7,000 ppm).