Fatemeh Rahmati Dehkordi - Department of Physiology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran
Saeed Semnanian - Department of Physiology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran
Hossein Azizi - Department of Physiology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran

Background and Aim : In mammals, there is an underlying mechanism that dictates the organism’s biological functions and daily activity schedule, known as circadian rhythms, which play a major role in maintaining steady metabolism, homeostasis and immunity. Investigations have shown that the light-dark cycle can affect the mechanisms associated with reward and addiction so in this study the negative motivational effect of morphine withdrawal syndrome was evaluated during day and night.Methods : Male Wistar rats (250-300 g) were administered 10 mg/kg morphine every 12h, for 10 days (n=20). Control rats received saline with the same protocol (n=20). Thereafter, when they were made dependent on morphine, tested for opioid withdrawal-induced conditioned place aversion and physical symptoms of naloxone-induced withdrawal syndrome during day (8:00-12:00) and night (20:00-24:00).Results : The negative motivational aspect of morphine withdrawal syndrome was more severe during day compare to night.Conclusion : It seems that the effects of withdrawal syndrome are more severe during day and this may consider for detoxification of opiate addicts.

Light-dark cycle; morphine; withdrawal syndrome; conditioned place aversion; rat