The mechanisms of reduced analgesic effect of morphine in neuropathic pain

点击翻译按钮获取中文摘要

Morphine produces powerful analgesic effects against acute pain, but it is not as effective against neuropathic pain. Intraperitoneal administration of morphine produced analgesic effects in normal and SNL rats, but the effects were greater in normal rats. Morphine increased 5-HT release, but not noradrenaline release, in the spinal dorsal horn via activation of serotonergic neurons in the rostral ventromedial medulla. Intrathecal pretreatment with ondansetron or 5,7-dihydroxytryptamine creatinine sulfate attenuated the analgesic effect of morphine in normal rats but increased the analgesic effect of morphine in SNL rats.Systemic administration of morphine increases 5-HT levels in the spinal cord, and the increase in 5-HT contributes to morphine-induced analgesia in the normal state, but attenuates that in neuropathic pain through spinal 5-HT3 receptors. The plasticity of the descending serotonergic system may contribute to the reduced efficacy of systemic morphine in neuropathic pain.