Objective To investigate the effect of dexmedetomidine on the pain threshold of hit and the expression of neuronal nitric oxide synthase (nNOS)in the gray matter around the central canal in the spinal cord in a rat model of chronic neuropathic pain. Methods Thirty-six male SD rats were randomly assigned into 3 groups: sham operation group (group Sham), chronic constrictive injury operation group (group CCI), CCI+dexmedetomidine group (group DEX). Chronic neuropathic pain was induced by chronic constrictive injury. The behavioral studies of rats were scored and thethermal withdrawal latency (TWL) was measured. The expression of nNOS in the gray matter around the central canal in the spinal cord was observed by immunohistochemistry. Results Compared with group Sham, TWL was significantly decreased and the expression of nNOS was up-regulated after operation in group CCI and group DEX(P<0.05). Compared with group CCI, TWL was significantly increased and the expression of nNOS was significantly down-regulated on day 7 and 14 after operation in group DEX(P<0.05). Conclusion Down-regulated nNOS in the gray matter around the central canal in the spinal cord is involved in the attenuation of neuropathic pain by DEX.%目的：观察连续腹腔注射右美托咪定（dexmedetomidine，DEX）对神经病理性痛大鼠热痛阈改变和脊髓中央管周围灰质神经元型一氧化氮合酶（neuronal nitric oxide synthase，nNOS）表达的影响。方法健康成年雄性SD大鼠36只，随机分为3组，分别为假手术组（Sham组）、坐骨神经慢性缩窄性损伤组（chronic constrictive injury，CCI组）和CCI+右美托咪定组（DEX组）。采用坐骨神经慢性缩窄性损伤的方法制备慢性神经病理性痛模型；热缩足反射潜伏期（thermal withdrawal latency，TWL）测定大鼠热痛阈的变化作为行为学观察指标；采用免疫组化的方法观察大鼠脊髓中央管周围灰质nNOS表达的变化。结果与Sham组相比，CCI组和DEX组大鼠术后各时间点热痛阈值均降低（P＜0.05），脊髓中央管周围灰质nNOS阳性神经元数目显著增加（P＜0.05）；与CCI组相比，连续腹腔注射DEX 7、14 d大鼠热痛阈值升高（P＜0.05），脊髓中央管周围灰质nNOS阳性神经元数目显著减少（P＜0.05）。结论脊髓中央管周围灰质nNOS的表达下调参与了DEX对神经病理性痛的治疗作用。
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