Directional running in mice: effects of cocaine and chlorpromazine.

Mice ran in a circular runway. Some received milk at every third circuit in a designated direction, clockwise or counterclockwise, in daily 1000-s sessions. Under control conditions, about 10 times as many circuits were made in the reinforced direction as in the non-reinforced direction. Cocaine (10, 30, 100 microM/kg) had little effect on the total number of circuits, but progressively increased the number in the non-reinforced direction. Chlorpromazine (1, 3, 10, 30 microM/kg) caused a monotonic decrease in total number of circuits and in number in non-reinforced direction. At the highest doses the proportion in the non-reinforced direction was increased. Mice, untrained in the runway and with no reinforcement of circuits in either direction, made many fewer total circuits than when running was reinforced and about equal numbers were in clockwise and in counterclockwise directions. Cocaine greatly increased the total number of circuits. As in the subjects whose running was reinforced, cocaine led to a much higher tendency for mice to run in a single direction. The similarities between the tendency to run in one direction after cocaine and the rotational behavior of rodents seen after cocaine and amphetamine suggest a common mechanism.