Insulin replacement prevents the acquisition but not the expression of morphine-induced conditioned place preference in streptozotocin-induced diabetic rats

Abstract Insulin receptors have distributed in all brain regions, including the nucleus Accumbens (NAc), and where is implicated in the reward properties of drugs. It is well known that insulin signaling can regulate dopamine release. Therefore, in the present study, we tried to examine the effect of insulin replacement on the acquisition and expression of morphine-induced conditioned place preference (CPP) in diabetic rats. Forty-eight male Wistar rats were divided into two non-diabetic (Naïve) and diabetic groups rendered by a single injection of streptozotocin (STZ). These groups separately received insulin (10U/kg) or saline (1 ml/kg) one hour prior to morphine administration (5mg/kg;s.c.) during conditioning days (acquisition phase) or post-conditioning day (expression phase) in the CPP paradigm. In this paradigm, conditioning score (CS) and locomotion activity were recorded by Ethovision. The STZ-induced diabetic rats displayed higher CS compared to naïve rats (P