Rationale and objectives: Accumulating clinical and preclinical studies have shown that the memories of the rewarding effects of drugs and their paired cues may contribute to relapse and persistent cocaine use. Glutaminergic actions in the ventral tegmental area (VTA) have been shown to regulate the rewarding effect of drugs and conditioned responses to drug-associated cues, but the role of the VTA in the acquisition, retrieval, and reconsolidation of cocaine cues is not yet known.
Methods: In the present study, we used 7-chlorothiokynurenic acid (7-CTKA), an N-methyl-D-aspartate (NMDA) receptor glycine modulatory site antagonist with no rewarding effects, to examine the role of the NMDA receptor glycine modulatory site in the acquisition, retrieval, and reconsolidation of cocaine-related reward memory using the conditioned place preference (CPP) paradigm.
Results: Separate groups of Sprague-Dawley rats were trained to acquire cocaine-induced CPP. Vehicle or 7-CTKA was microinjected into the VTA or substantia nigra (SN) (5 μg/μl) at different time points: 10 min before each CPP training session (acquisition), 10 min before the reactivation of CPP (retrieval), and immediately after the reactivation of CPP (reconsolidation). Cocaine-induced CPP was retested 24 h and 1 and 2 weeks after 7-CTKA administration. 7-CTKA microinjected into the VTA, but not SN, significantly impaired the acquisition, retrieval, and reconsolidation of cocaine-induced CPP without affecting cocaine-induced locomotion.
Conclusions: Our findings suggest that the NMDA receptor glycine modulatory site in the VTA plays a major role in cocaine reward memory, and NMDA receptor glycine site antagonists may be potential pharmacotherapies for the management of relapse.