Effects of acute stress and environmental enrichment on cocaine self‐administration in socially housed monkeys

Abstract

Previous research has shown that social rank can influence the reinforcing effects of cocaine in monkeys (Morgan et al. 2002; Czoty et al. 2005). It has been hypothesized that dominant and subordinate monkeys represent a continuum from environmental enrichment to socially‐derived stress. Whereas social rank reflects a chronic condition, the effects of additional enrichment or stress on cocaine self‐administration (SA) has not been examined. The goal of these studies was to determine if sensitivity to cocaine reinforcement could be altered by acute presentation of environmental enrichment or stressors. Adult male dominant and subordinate cynomolgus monkeys self‐administered cocaine (0.003–0.1 mg/kg) under a concurrent schedule with 1‐g food pellets as the alternative; dose‐response curves were determined in single sessions. When SA was stable, one of two manipulations was performed prior to SA sessions: either the monkey was placed into a larger enclosure for 2 days or he was exposed to a toy snake for 10 min. Acute enrichment shifted the cocaine dose‐response curves to the right for all monkeys, while the acute stressor shifted the cocaine curves to the left only in subordinate monkeys. These results indicate that the model is sensitive to acute manipulations and that environmental enrichment impacts all monkeys, while the effects of stress are more prominent in subordinate monkeys. DA10584.