Abstract: AIMTo observe mRNA expression of muscarinic acetylcholine receptors in spinal cord and brainstem in morphine dependent or withdrawal rats. METHODSThe mRNA expression level of m₁, m₂, m₃, m₄ and m₅ were determined by RT-PCR, the β-actin mRNA expression was used as internal control. RESULTSThe mRNA level of m₁, m₂, m₃, m₄ and m₅ in spinal cord and m₁ and m₂ in brainstem were increased significantly during morphine dependence, and the levels of m₁, m₂, m₃ and m₄ in spinal cord and m₁ in brainstem were decreased 1 h after the injection of naloxone (4 mg·kg^-1, ip) in morphine dependent rats. Either scopolamine (0.5 mg·kg^-1) or pirenzepine (10 mg·kg^-1) was shown to significantly decrease the morphine withdrawal symptoms in rats. The levels of m₁, m₂, m₃ and m₅ in spinal cord were increased by pretreatment with pirenzepine and the levels of m₂, m₃ and m₄ in spinal cord were increased by pretreatment with scopolamine. CONCLUSIONThe adaptive expression of muscarinic receptors at spinal and supraspinal levels play important role in mediating morphine dependence and withdrawal in rats.