Evidence that apomorphine and (+)-amphetamine produce different types of circling in rats.

Apomorphine and (+)-amphetamine are known to produce circling in naive rats. Frame by frame analysis of videotape recordings of the behaviour of Wistar rats treated with a subcutaneous injection of apomorphine (1.1 mg/kg; n = 8) or (+)-amphetamine (0.5 and 1.0 mg/kg; n = 8 and n = 8) was used to study this behaviour in more detail. In line with previously reported studies, apomorphine was found to change the functioning of hindlimb stepping. In contrast, (+)-amphetamine was found to change the functioning of forelimb stepping. These data imply that apomorphine and (+)-amphetamine produce their drug-specific circling via different substrates within the brain.