Effects of stress during reactivation on rewarding memory

When a stabilized memory is recalled or reactivated, it becomes labile and sensitive to disruptors such as protein-synthesis inhibitors. Previous evidence demonstrates that stress modulates different aspects of memory. The role of stress during reactivation on rewarding or aversive memory is not known, however. This study examines the effects of stress on rewarding or aversive memory using the conditioned place preference or conditioned place aversion paradigm. Rats were trained to acquire a sucrose and cocaine-conditioned place preference or naloxone-conditioned place aversion. Subsequently, rats were reexposed to the previous sucrose-paired, cocaine-paired and naloxone-paired chamber for 10 min before experiencing the stressful Morris water maze. All rats were tested for conditioned place preference or conditioned place aversion after the stressful water-maze task. After 5-day repeated exposure to the previously reward-paired chamber and experiencing stress, cocaine-conditioned place preference disappeared and sucrose-conditioned place preference was reversed; however, after 5-day repeated exposure to the previously naloxone-paired chamber and experiencing stress, naloxone-conditioned place aversion was not significantly changed. Our results provide the first evidence that the rewarding memory may have been reduced by exposing rats to stress during reexposure to the reward-paired context, which suggests that manipulations of drug memory during reactivation can provide a potential treatment for drug addiction.