The Neurobiological Mechanisms Of Morphine Dependence Mediated By Muscarinic Acetylcholine Receptors In Rat Spinal Cord

Objective:The present study is to characterize the muscarinic receptor subtypes mRNA expression in rat spinal cord during morphine dependence, and to elucidate the role of muscarinic receptor subtypes m_1-5 in mediating the morphine dependence by intrathecal or intracerebroventricDlar administering with antisense oligodeoxynucleotides targeting on m_1-5. The present study is not only to investigate the effects of muscarinic receptor on the NO-cGMP pathway, cAMP-PKA pathway and glutamate-NMDA receptor system in rat spinal cord during morphine withdrawal, but also to examine the effects of m_1-5 antisense oligodeoxynucleotides on expression of nNOS, m_1-5, NR_1A and α₂ in spinal cord during morphine withdrawal.Methods:The rats were made dependent by consecutive injecting morphine (sc,bid) for 6 days at doses increasing from 10 mg.kg^-1 to 50 mg.kg^-1. After 3h from last injection of morphine, naloxone was given to precipitate withdrawal syndrome. Ratings of opiate withdrawal signs were made every 15 min for lh and body weight loss were assessed by subtracting the weight after precipitated opioid withdrawal from the pre-naloxone injection weight over lh. The NO^-2/NO^-3(the end product of NO) was analyzed by fluorometry , the NOS activity was analyzed based on the conversion of arginine to citrDlline and production of NADPH. The soluble guanylate cyclase activity was measured by the production of GTP to cGMP, the cGMP contents were assayed by radioimmunoassay. Glutamate concentrations in microdialysate from PAG were assayed by capillary zone electrophoresis with laser-induced fluorescence detection. Norepinephrine contents in spinal cord was analyzed by using high-performance liquid chromatography with electrochemical detection. AC activity in the supernatant was...