Effects of environmental enrichment on extinction and reinstatement of amphetamine self-administration and sucrose-maintained responding

The current experiments aimed to determine whether differential rearing alters extinction and/or reinstatement of amphetamine self-administration or sucrose-maintained responding. Male Sprague-Dawley rats were raised in either an enriched condition or an isolated condition. Rats were then trained to lever press on a continuous reinforcement schedule across either 15 daily amphetamine self-administration sessions or 15 sucrose-reinforced sessions, followed by 10 sessions of extinction. After the extinction sessions, priming doses of amphetamine (0, 0.25 or 1.0 mg/kg) were administered 15 min before the session, or sucrose (one or 10 pellets) was delivered non-contingently at the beginning of the session. Enriched condition rats showed greater extinction for amphetamine and sucrose-maintained responding than isolated condition rats. When primed with amphetamine, isolated condition rats reinstated responding following 0.25 mg/kg of amphetamine, whereas enriched condition rats only reinstated responding after 1.0 mg/kg of amphetamine. Isolated condition rats failed to reinstate responding following sucrose delivery, while enriched condition rats reinstated responding following the delivery of 10 sucrose pellets. These results indicate that environmental enrichment enhanced the extinction of both amphetamine and sucrose-maintained responding. Environmental enrichment also raised the reinstatement threshold specific to the amphetamine prime, suggesting a reduction in the incentive motivational effect of amphetamine.