Valproic acid sodium inhibits the morphine-induced conditioned place preference in the central nervous system of rats

The present study was performed to investigate the effects of valproic acid sodium (VPA), a widely utilized antiepileptic drug, on the establishment of chronic morphine-induced conditioned place preference (CPP). The rat model of morphine-induced CPP was conditioned with alternating intracerebroventricular (i.c.v.) injections of morphine (60 μg/6 μl) and saline for 5 days. To investigate the influence of VPA on morphine-induced CPP, rats received chronic pretreatment of i.c.v. VPA (500 μg/rat) 10 min previous to the daily morphine injection. The results demonstrated that the morphine-induced CPP was significantly attenuated by VPA pretreatment, while the VPA itself could not induce any CPP or conditioned place aversion (CPA) effects. The results of the present study not only confirmed the reliability of establishing morphine-induced CPP model by i.c.v. injection, but also suggest that the antiepileptic drug VPA may be utilized as potential therapeutic medications for drug abuse in the future.