N~ω-硝基-L-精氨酸甲酯可抑制吗啡镇痛耐受大鼠的痛觉过敏以及脊髓和中脑c-Fos表达

目的:在福尔马林炎性疼痛模型观察非特异性一氧化氮合成酶(NOS)抑制剂/Nω-硝基-L-精氨酸甲酯(L-NAME)对吗啡镇痛耐受大鼠疼痛行为以及脊髓和中脑c-Fos表达的影响。方法:将24只健康成年SD大鼠随机平均分为4组:生理盐水(NS)组,即对照组,皮下注射(sc)NS1ml;L-NAME组、Mor组和L-NAME+Mor组,为处理组,分别scL-NAME20mg·kg-1、吗啡10mg·kg-1、L-NAME20mg.kg-1和吗啡10mg.kg-1。各组给药均为每天2次,连续7d。在d8上午最后1次给药后30min,于大鼠左后足掌侧sc5%福尔马林0.1ml,记录每5min内舔咬注射足时间(TTSLI),观察时间为50min。记录完毕后取脊髓和中脑做c-Fos免疫组化检查。结果:与NS组相比,L-NAME组的Ⅱ相TTSLI显著缩短,Mor组的Ⅰ相和Ⅱ相TTSLI显著延长,L-NAME+Mor组的Ⅰ相和Ⅱ相TTSLI均显著缩短。免疫组化检查结果显示,与NS组相比,L-NAME组、L-NAME+Mor组注射足同侧和对侧脊髓以及中脑导水管周围灰质(PAG)神经元的c-Fos样免疫反应阳性面积显著降低,但Mor组的F-LI阳性面积显著性增加。结论:吗啡镇痛耐受大鼠接受福尔马林刺激后表现为痛觉过敏,其脊髓和中脑PAG神经元的c-Fos表达增加,L-NAME可抑制吗啡镇痛耐受大鼠的痛觉过敏,并可抑制脊髓和中脑PAG神经元的c-Fos表达。本研究结果提示脊髓和中脑的一氧化氮系统与吗啡镇痛耐受时痛觉过敏的发生密切相关。

Nω-NITRO-L-ARGININE METHYL ESTER CAN INHIBIT HYPERALGESIA AND C-FOS EXPRESSIONS OF SPINAL CORD AND MIDBRAIN IN RATS WITH MORPHINE ANALGESIA TOLERANCE

Objective:To observe the effects of systemic administration of nonspecific nitric oxide synthase inhibitor,Nω-nitro-L-arginine methyl ester(L-NAME), on pain behavior and c-Fos expressions of spinal cord and midbrain induced by formalin in rats with morphine analgesia tolerance. Methods:Twenty four adult SD were randomly divided into 4 groups(n=6). Rats in group NS received 1 ml NS, while rats in group L-NAME, group Mor and group L-NAME + Mor were administered(sc)20 mg·kg-1 L-NAME, 10 mg·kg-1 Mor, and 20 mg·kg-1 L-NAME + 10 mg·kg-1 Mor, respectively. All rats were injected twice a day for 7 days. 30 min after the last treatment in the morning of the 8th day, 0.1 ml of 5% formalin was injected (sc) into the plantar surface of the left hindpaw. The total time spent in licking injected-paw(TTSLI) within every 5 min was recorded for 50 min thereafter. Subsequently, the rats were perfused with saline and fixed by 4% paraformaldehyde, and the spinal cord and midbrain were removed for the c-Fos immunohistochemical analysis. Results:As compared to group NS, TTSLI in phase Ⅱ decreased significantly in group L-NAME, and TTSLI in phases Ⅰ and Ⅱ increased significantly in group Mor and decreased significantly in group L-NAME+Mor. The immunohistochemical results showed that formalin-induced c-Fos-like immunoreactivity(F-LI)areas in the ipsilateral,controlateral spinal cord and midbrain PAG neurons decreased in groups L-NAME and L-NAME+Mor,but increased in group Mor as compared to group NS. Conclusion:Formalin stimulation might elicit hyperalgesia in rats with morphine analgesia tolerance, and result in significant increase in c-Fos expression of spinal cord and midbrain PAG. L-NAME could attenuate hyperalgesia and inhibit overexpression of c-Fos. Based on these results, it is concluded that nitric oxide system in spinal cord and midbrain is closely related to the development of hyperalgesia in morphine analgesia tolerance.