胞外信号调节激酶信号通路在大鼠慢性吗啡耐受形成中的作用

目的 探讨胞外信号调节激酶(ERK)信号通路在慢性吗啡耐受形成中的作用.方法 鞘内置管成功的雄性SD大鼠30只,体重300～350 g,随机分为3组(n=10).置管后7 d开始给药,对照组(C组)鞘内注射0.4%二甲基亚砜10μl,慢性吗啡耐受组(M组)给予吗啡10μg,ERK上游激酶抑制剂+吗啡组(P组)于给予吗啡前30 min给予丝裂原激活蛋白激酶激酶抑制剂PD98059 10μg,2次/d,连续7 d.每天第1次给药后30 min及最后一次给药后1 d时测定甩尾潜伏期,并计算最大镇痛效应百分比.最后一次测定甩尾潜伏期后取脊髓L3-5节段,采用Western blot法和免疫荧光法测定脊髓背角μ受体和磷酸化ERK1/2(p-ERK/1/2)的表达水平.结果 M组和P组随着给药时间的延长,形成了吗啡耐受,而P组吗啡耐受程度轻于M组(P＜0.05).与C组比较,M组脊髓背角μ受体表达下调,p-ERK1/2表达上调(P＜0.01).与M组比较,P组脊髓背角μ受体表达上调,p-ERK1/2表达下调(P＜0.01).结论 ERK信号通路参与了大鼠慢性吗啡耐受的形成.

The role of extracellular signal-regulated kinase signal pathway in the development of chronic morphine tolerance in rats

Objective To investigate the role of extracellular signal-regulated kinase(ERK)signal pathway in the spinal cord in the development of chronic morphine tolerance.Methods Thirty healthy male SD rats weighing 300-350 g in which intrathecal(IT)catheters were successfully implanted without complication were randomly divided into 3 groups(n = 10 each): group Ⅰ control(group C);group Ⅱ morphine tolerance(group M)and group Ⅲ morphine tolerance + PD98059(ERK upstream kinase MEK inhibitor)(group P).Morphine tolerance was induced with IT morphine 10 μg twice a day for 7 consecutive days.In group P PD98059 10 μg was injected IT at 30 min before each morphine administration.Tail flick latency(TFL)(the time between the onset of heat stimulus and voluntary tail withdrawal)was measured once a day at 30 min after first IT morphine administration and at 1 day after last IT morphine.Maximum analgesic effect(MPE)was calculated.MPE =(TFL after IT morphine - baseline TFL)/(12 - baseline TFL)× 100%.The animals were sacrificed after last TFL measurement.The L3-5 segment of the spinal cord was isolated for determination of the expression of μ-receptor and phosphorylated ERK 1/2(p-ERK1/2)by Western blot analysis and fluoroimmunoassay.Results Morphine tolerance was induced in group M and M + P.MPE was higher in group P than in group M.The expression of μ-receptor in spinal dorsal horn was significantly lower while the p-ERK1/2 expression was higher in group M than in group C.IT PD98059 significantly up-regulated μ-receptor expression and down-regulated p-ERK expression in group P as compared with group M.Conclusion ERK signal pathway is involved in the development of chronic morphine tolerance in rats.