Locomotor and rewarding effects of amphetamine in enriched, social, and isolate reared rats

This study examined the influence of environmental enrichment on the behavioral response to amphetamine. Beginning at 21 days of age, rats were raised in one of three different environmental conditions: a) an enriched condition (EC), in which animals were caged in groups and provided with novel objects daily; b) a social condition (SC), in which animals were caged in groups without any novel objects; and c) an isolated condition (IC), in which animals were caged individually without any novel objects. At 53 days of age, animals from each environmental condition were assessed for amphetamine-induced changes in locomotor activity and reward using the conditioned place preference (CPP) paradigm. Results from saline-injected control animals indicated that EC animals exhibited less vertical activity than IC animals when exposed to the CPP apparatus. When challenged with amphetamine (0.5 or 2.0 mg/kg), there were no significant differences between SC and IC animals in either locomotor behavior or CPP. However, EC animals exhibited more horizontal and vertical activity following amphetamine than both the SC and IC animals. Similarly, EC animals exhibited a greater magnitude of amphetamine-induced CPP than both the SC and IC animals.