Behavioral effects of toluene are modulated by stimulus control.

Behavior that is strongly controlled by environmental stimuli is less susceptible to disruption by certain chemicals than is such behavior not under strong external control. To determine whether toluene's effects can also be minimized by environmental stimuli, two varieties of a fixed consecutive number schedule were studied. With one, a lever press response was reinforced with milk only if preceded by a minimum of eight consecutive responses on a second lever, no cues indicating that the minimum number had been reached. With the other, a combination of lights and a tone served as a discriminative stimulus signaling the completion of the minimum response number. In an experiment studying these schedules separately, rats were exposed to toluene concentrations up to 3000 ppm for 4-hr periods immediately before their performance was tested. Toluene reduced the accuracy of both types of behavior in a concentration-related fashion. Clear differential effects occurred, with the signaled behavior, i.e., that under stronger stimulus control, showing less disruption by toluene. Similar results were produced after 2-hr exposures with a multiple schedule in which the signaled and unsignaled performances alternated within a single session. Response rate changes were observed at 560 ppm, but changes in rate were independent of effects on the accuracy of performance. The EC50 for significant behavior disruption was 1081 ppm for the unsignaled component of the multiple schedule; the EC10 was 480 ppm. No performance disruption was observed in the signaled component below 1780 ppm. The finding of differential sensitivity could be useful in guiding the development of more sensitive tests of performance impairment.