Repeated paired-testing impairs extinction of morphine-induced conditioned place preference dependent on the inter-test interval in rats

Abstract

Using exposure to morphine- and saline-paired sides alternatively as the extinction training procedure, we find that post-retrieval extinction training enhances or hinders the extinction of morphine-induced conditioned place preference (CPP) dependent on the retrieval-extinction training intervals. Here, we examine the influence of post-retrieval extinction training with repeated paired testing on extinction of morphine-induced CPP of rats. Our results demonstrate that paired-testing with a 10-min inter-test interval does not influence the extinction of CPP, while post-retrieval extinction training blocks the extinction of CPP with a 3-h retrieval-extinction interval. These results strongly indicate that the interval between exposure trials influences the outcome of exposure therapy in addiction treatment.