In a drug discrimination procedure isolation-reared rats generalize to lower doses of cocaine and amphetamine than rats reared in an enriched environment.

Rats with different behavioral histories, defined by rearing and housing in either an enriched condition (EC) or an isolation condition (IC), were trained in a two-lever operant procedure to discriminate 5.0 mg/kg cocaine from saline. In cocaine dose-generalization tests, the IC rats exhibited an ED50 (1.01 mg/kg) significantly lower than the EC rats (ED50: 1.55 mg/kg). The cocaine-appropriate responding was emitted when the rats were treated with d-amphetamine, and for the d-amphetamine test doses the ED50 (0.19 mg/kg) was again significantly lower for the IC rats compared to the ECs (ED50: 0.33 mg/kg). These data suggest that IC rats are more sensitive to the stimulus properties of indirect dopaminergic agonists than EC rats and highlight the importance of environmental variables in governing an organism's response to the stimulus properties of abused drugs.