The effects of inhaled toluene, halothane, 1,1,1-trichloroethane, and ethanol on fixed-interval responding in mice

Adult male mice were trained to lever press under a fixed-interval (FI) 60-sec schedule for milk presentation during 15-min sessions. Concentration-effect curves were then determined at the termination of 30-min inhalation exposures to various volatile agents--halothane, toluene, 1,1,1-trichloroethane (1,1,1-TCE), and ethanol. The mice were also tested after ethanol administered orally. Each compound produced both response rate increases and decreases, initially or during the recovery phase. Recovery from the response rate decreasing effects generally occurred during the 15-min sessions. The highest concentration of toluene and the high dose of oral ethanol produced the longest duration of effects. Response rates in the first 3 min of the session were used to evaluate peak effects following inhalation. Linear regression analyses of these data indicated the potency order to be toluene greater than halothane greater than 1,1,1-TCE greater than ethanol. Patterning of responding characteristics of FI performance was affected after high concentrations of all but ethanol vapor. This study provided evidence that the effects of two industrial solvents, toluene and 1,1,1-TCE, were qualitatively similar to those of two volatile CNS depressants, halothane and ethanol, as well as to those reported for other centrally-acting drugs.