Abstract: Aim To investigate the effect of cholinergic receptors in central nervous system on morphine dependent rats.Methods Male Sprague-Dawley rats w eighing 200～250 g were rendered dependent on morphine by subcutaneous injection of mo rphine in increasing doses for 5 days.Prior to testing, rats received infusion of either asolution of drug (scopolamine, pirenzepine, methoctramine)or vehicle (normal saline)in lateral cerebral vent ricle.Withdrawal behavior was monitored for 60 min after int raperitoneal administ ration of naloxone.Results The animal pretreatment with scopolamine (25, 50 μg)or muscarinic subtype antagonists (20 μg pi renzepine, 25 μg methoct ramine) could significantly at tenuate naloxone precipitated morphine abstinence syndrome.Cent ral administ ration of scopolamine could reduce reaction of morphine withdrawal in a dose-dependent manner.Conclusion The central cholinergic receptors may be play an impo rtant role in the process of morphine withdraw al. Both M1 and M2 receptors may cont ribute to the development of morphine dependence and tolerance.

Key words: scopolamine, pirenzepine, methoctramine, morphine withdrawal, muscarinic receptor