Environmental Enrichment Attenuates Morphine-Induced Conditioned Place Preference and Locomotor Sensitization in Maternally Separated Rat Pups

Introduction: This study investigated the effect of the environmental enrichment during adolescence on morphine-induced Conditioned Place Preference (CPP) and locomotor sensitization in maternally separated male and female rat pups. Methods: Male Wistar rats were allowed to mate with female virgin Wistar rats. Pups were separated from them 3 hours per day during 2-14 days postnatal. All pups were weaned at 21 Postnatal Day (PND) and reared in standard environment or enriched environment from 21 to 50 PND with litter-mates of the same sex. The CPP and behavioral sensitization to morphine were assessed by an unbiased place conditioning paradigm and open filed method. Results: The results showed that the maternal separation enhanced morphine-induced CPP in both sexes, locomotor sensitization in male pups and tolerance to morphine-induced motor activity in female pups during adolescence. While, male and female pups reared in an EE exhibited a decrease in morphine-induced CPP, locomotor sensitization and tolerance induced by maternal separation compared to their control pups. Conclusion: Access to enriched environment during adolescence may have a protective effect against morphine-induced reward, locomotor sensitization and tolerance in adolescent male and female rats following maternal separation.