Aim To investigate the effect of blocking interleukin-18 in the spinal cord on the development of morphine tolerance in rats and its possible underlying mechanisms. Methods Forty male Sprague Dawley ( SD ) rats were randomly divided into 5 groups ( n = 8 ): saline control group ( group Ⅰ ), morphine tolerance group ( group Ⅱ ), IgG control group ( group Ⅲ ), anti-rat IL-18 antibody treatment group ( group Ⅳ : 0. 4 μg and group V : 4 μg ). Firstly all rats were implanted with intrathecal ( i. t. ) catheters. Then they were tested to ensure the position of catheters five days after surgery ( recorded as the first day ). Tolerance to morphine antinociceptive effect was induced and drugs were injected from day 3 to day 9. On day 2 and 10, paw withdrawal thermal latency ( PWTL ) of the basic and 30 min after morphine injection via tail vein were evaluated in all rats and the percentage of maximal possible antinociceptive effect ( % MPE ) of 30 min was calculated. Lastly the spinal cord lumbar enlargement was obtained immediately after the behavioral tests on day 10 to determine the expression of ERK and p-ERK by western bolt and the immunoreactivity of GFAP by immunofluorescence. Results ① On day 2 there was no significant difference of the % MPE among five groups ( P > 0. 05 ). On day 10, compared with group Ⅰ, the % MPE was declined significantly in group Ⅱ -Ⅴ. Compared with group Ⅱ , the % MPE was increased significantly in group Ⅴ ( P 0. 05 ). ① Compared with group Ⅰ, the expression of p-ERK was increased significantly in group Ⅱ - Ⅴ - Compared with group Ⅱ , the expression of p-ERK was decreased significantly in group Ⅴ while no marked difference in group Ⅲ and Ⅳ. ③ Compared with group Ⅰ , the im-munoreactivity of GFAP was markedly increased in group Ⅱ ,Ⅲ andⅣ. Compared with group Ⅱ , the immunoreactivity was decreased significantly in group Ⅴ. Conclusion Anti-rat IL-18 antibody can attenuate the development of morphine tolerance in naive rats through inhibiting the phosphorylation of ERK and activation of astrocytes in the spinal cord.%目的 探讨阻断脊髓IL-18对大鼠吗啡耐受形成的影响及可能机制.方法 ♂ SD大鼠40只,随机均分为5组(n=8).Ⅰ组为生理盐水对照组,Ⅱ组为吗啡耐受组,Ⅲ组为IgG对照组,Ⅳ组、Ⅴ组为IL-18中和抗体(0.4 μg、4 μg)处理组.所有大鼠均行鞘内置管,手术5 d后确定导管位置(记为第1天).第3~9天,各组建立吗啡耐受模型并进行相应处理.第2、10天,测定各组大鼠热刺激缩足反应潜伏期(paw withdrawal thermal latency,PWTL)及尾静脉注射吗啡后30 min的PWTL,计算30 min时最大可能镇痛效应比值(%MPE).第10天行为学测试后,取大鼠脊髓腰膨大,采用免疫印迹法(Western blot)检测ERK与p-ERK蛋白表达水平,免疫荧光法分析星形胶质细胞标记物GFAP表达水平.结果 ①第2天:各组大鼠给予吗啡后30 min %MPE差异无统计学意义(P>0.05).第10天:给予吗啡30 min后,与Ⅰ组相比,其余4组%MPE均明显降低(P0.05),Ⅴ组%MPE明显升高(P0.05),V组明显降低(P<0.05).③ 免疫组织荧光染色结果显示,与Ⅰ组相比,Ⅱ、Ⅲ、Ⅳ组大鼠腰段脊髓背角GFAP阳性荧光明显增加.而与Ⅱ组相比,Ⅴ组大鼠腰段脊髓背角GFAP免疫荧光强度明显降低.结论 IL-18中和抗体可以缓解吗啡耐受的形成,该效应可能与其抑制脊髓ERK的磷酸化,缓解背角星形胶质细胞的活化有关.
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