Roles of ERK-CREB signaling pathway in spinal cord in naloxone-induced withdrawal response in morphine-dependent rats / 中华麻醉学杂志

ABSTRACT

Objective To evaluate the role of extracelluar signal-regulated kinase (ERK)-cyclic AMP response element binding protein (CREB) signaling pathway in the spinal cord in naloxone-induced withdrawal response in morphine-dependent rats.Methods Fifty male adult SD rats,aged 2 months,weighing 200-250 g,in which intrathecal catheters were successfully implanted without complications,were randomly divided into 5 groups (n =10 each)group control (group C); group morphine dependence (group MD); group morphine withdrawal (group MW); group U0126 (ERK signaling pathway blocker); group dimethyl sulfoxide (DMSO,solvent for U0126).Morphine dependence was induced by increasing doses of subcutaneous morphine for 6 days.The initial dose of morphine was 10 mg/kg twice a day and was increased by 10 mg/kg twice every other day until 50 mg/kg on 6th day in groups MD,MW,U0126 and DMSO.Morphine withdrawal response was induced by intraperitoneal naloxone 4 mg/kg at 4 h after last morphine administration in groups MW,U0126 and DMSO.U0126 150μg (in DMSO 10 μl) and DMSO 10 μl were administered intrathecally at 30 min before naloxone administration in groups U0126 and DMSO respectively.Morphine withdrawal response (0=no withdrawal response,3 =severe response)and touch evoked agitation (0 =no agitation,2 =severe agitation) were observed and scored during 1 h after naloxone administration.The animals were then sacrificed and the spinal cord was removed for determination of the expression of phosphorylated ERK (p-ERK) and phosphorylated CREB (p-CREB) by immuno-histochemistry and Western blot.Results Morphine withdrawal significantly up-regulated the p-ERK and p-CREB expression in group MW compared with group C ( P ＜ 0.05).Withdrawal response score and touch evoked agitation score were significantly increased in groups MW,U0126 and DMSO as compared with group MD ( P ＜ 0.05).U0126 pretreatment significantly attenuated naloxone-induced increase in withdrawal response score and touch evoked agitation score and down-regulated p-ERK and p-CREB expression in group U0126 as compared with group MW ( P ＜ 0.05).Conclusion ERK-CREB signaling pathway in the spinal cord is involved in morphine withdrawal response in morphine-dependent rats.