Environmental enrichment decreases intravenous self-administration of amphetamine in female and male rats

Rationale: Previous work has shown that environmental enrichment alters amp hetamine-induced locomotor activity and conditioned place preference. Objec tive: The present study examined the effect of environmental enrichment on amphetamine self-administration. Methods: Female and male rats were raised from 21 days of age in one of three different conditions: an enriched condi tion (EC) containing novel objects and social partners, a social condition (SC) containing social partners only, or an isolated conditioned (IC) witho ut objects or social partners. Beginning at 51 days of age, rats were then tested for operant responding for a sucrose reinforcer using an incremental fixed ratio (FR) requirement across four sessions. Rats were then implante d with a chronic indwelling intravenous catheter and were allowed to self-a dminister amphetamine (0.03 or 0.1 mg/kg per infusion) for five FR1 session s, followed by a progressive ratio (PR) session. Results: EC rats initially showed an increase in sucrose-reinforced responding relative to IC rats an d this environment-induced difference was greater in females than in males. However, in both sexes, the environment-induced difference in sucrose-rein forced responding dissipated completely across repeated sessions. With amph etamine self-administration, both EC and SC rats earned fewer infusions tha n IC rats across repeated FR1 sessions using the low dose of amphetamine (0 .03 mg/kg per infusion), but not using the higher dose of amphetamine (0.1 mg/kg per infusion). EC rats also earned fewer self-infusions of the low am phetamine dose on the PR session relative to IC rats. The effects of enviro nmental enrichment on amphetamine self-administration were similar in both females and males. Conclusion: These results suggest that environmental enr ichment may serve as a protective factor for reducing amphetamine self-admi nistration.