The effects of active and passive intravenous heroin and heroin conditioned stimuli on consolidation of object memory

Abstract

Drugs of abuse and their associated conditioned stimuli (CS) modulate memory consolidation, but it is possible that these effects are influenced by the mode of administration (i.e., active vs passive). This study employed a self-administration/yoked design in male Sprague-Dawley rats (N = 36): one group (n = 18) intravenously self-administered infusions of 0.05 mg/kg heroin paired with the activation of a light CS, and a yoked group (n = 18) received an equal number of infusions and light CS presentations independent of their lever responses. Self-administration/yoked training was followed by extinction during which responses on the active lever had no consequences, and by a cue-induced reinstatement session during which active lever responses resulted in the reactivation of the light CS, but no heroin delivery. The post-training effects of self-administered/yoked heroin, extinction and reinstatement sessions on memory consolidation were tested using the object location memory task. It was found that post-sample heroin enhanced object location memory in yoked, but not self-administering rats. However, post-sample extinction and reinstatement sessions equally modulated memory in both groups. Taken together, these data in rats support the perspective that mode of administration impacts the cognitive consequences of exposure to drugs and environmental stimuli linked to their reinforcing effects.