A behavioral analysis of the effects of amphetamine on play and locomotor activity in the post-weaning rat

Amphetamine has been shown to canalize or direct the activity of a young rat towards ethologically relevant stimuli. In the five-day-old, amphetamine increases the speed of approach to the nipple of an anesthetized dam; in the 15-day-old, amphetamine increases motor activity and directs it toward an anesthetized adult, however, in the juvenile rat amphetamine reportedly disrupts species-specific behaviors such as huddling and play. The present experiments further assessed the effects of amphetamine in the post-weaning rat by measuring drug-induced behaviors in the presence of an alert and anesthetized companion. In Experiment 1, subjects were videotaped in the presence of an alert non-treated, same-age rat and components of play, a predominant behavior of the post-weaning rat, were recorded. Results confirmed previous reports that low doses of amphetamine (0.5 mg/kg) disrupt play behavior, however, in the present experiment higher doses of amphetamine (1.0 mg/kg) did not disrupt the percentage of time spent in play. Further analysis of drug-induced behavior revealed that the 1.0 mg/kg amphetamine-injected rat engaged in play with the companion, although the drug-treated animal did exhibit marked alterations in the flexibility of its motor patterns. The second experiment confirmed that amphetamine did not disrupt the amount of time a juvenile rat spent with an anesthetized age-mate. In fact, amphetamine-induced activity was directed towards the anesthesized same-age rat. Following amphetamine treatment, all subjects were active nearly 100% of the observation period whether they were tested alone or in the presence of an anesthetized same-age rat.(ABSTRACT TRUNCATED AT 250 WORDS)