mRNA EXPRESSION OF MUSCARINIC RECEPTORS IN SPINAL CORD AND BRAINSTEM IN MORPHINE DEPENDENT RATS

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.