Evidence of tolerance following repeated exposure to toluene in the rat.

Toluene shares pharmacological properties with other abused central nervous system depressants such as ethanol and the barbiturates. Although tolerance has been clearly demonstrated for these classic CNS depressants, evidence of tolerance following repeated toluene exposure is equivocal. The present work examined if tolerance would develop to the effects of repeated toluene exposure on learned behavior and examined the possibility that external discriminative stimuli could influence these effects. Two variants of a fixed-consecutive-number schedule of reinforcement were used as components in a multiple schedule. The components differed in whether or not behavior within them was under the control of external discriminative stimuli. Rats were exposed daily for two hours to toluene (1780 to 4500 ppm). Different patterns of effects emerged from repeated exposure; some rats displayed tolerance while the performance of others deteriorated. Behavior controlled by external discriminative stimuli was more resistant to disruption and showed tolerance more readily than did behavior not under such control.