右美托咪定对瑞芬太尼诱发切口痛大鼠痛觉过敏时脊髓背角神经元NMDA受体转运的影响

Effect of dexmedetomidine on trafficking of N-methyl-D-aspartate receptors in spinal dorsal hornneurons during remifentanil-induced hyperalgesia in rats with incisional pain

目的 探讨右美托咪定对瑞芬太尼诱发切口痛大鼠痛觉过敏时脊髓背角神经元NM-DA受体转运的影响.方法 雄性SD大鼠24只,体重240～ 260 g,2～3月龄,采用随机数字表法,将其分为3组（n=8）：对照组（C组）、瑞芬太尼＋切口痛组（R＋Ⅰ组）和右美托咪定＋瑞芬太尼＋切口痛组（D＋R＋Ⅰ组）.D＋R＋Ⅰ组制备切口痛模型前30 min皮下注射右美托咪定50 μg/kg,R＋Ⅰ组和D＋R＋Ⅰ组制备切口痛的同时开始静脉输注瑞芬太尼1.2 μg＆#183;kg-1＆#183;min-1,输注90 min.分别于给予右美托咪定前（T0）、瑞芬太尼停止输注后2、6、24、48 h（T1-4）时测定热缩足潜伏期（TWL）和机械缩足反应阈（MWT）.最后一次痛行为学测试后处死大鼠,取脊髓L4-6节段,采用Western blot法测定脊髓背角膜蛋白（m）及总蛋白（t）NMDA受体NR1、NR2A和NR2B亚基的表达,计算mNR1与tNR1表达的比值（mNR1/tNR1）、mNR2A与tNR2A表达的比值（mNR2A/tN R2A）和mNR2B与tNR2B表达的比值（mNR2B/tNR2B）.结果 与C组比较,R＋Ⅰ组和D＋R＋Ⅰ组TWL缩短,MWT降低,脊髓背角mNR1、tNR1、mNR2B及tNR2B表达上调,脊髓背角mNR1/tNR1及mNR2B/tNR2B升高（P＜0.05）;而脊髓背角mNR2A、tNR2A表达及mNR2A/tNR2A差异无统计学意义（P＞0.05）;与R＋Ⅰ组比较,D＋R＋Ⅰ组TWL延长,MWT升高,脊髓背角mNR1、tNR1、mNR2B及tNR2B表达下调,脊髓背角mNR1/tNR1及mNR2B/tNR2B降低（P＜0.05）;而脊髓背角mNR2A、tNR2A表达及mNR2A/tNR2A差异无统计学意义（P＞0.05）.结论 右美托咪定预防瑞芬太尼诱发切口痛大鼠痛觉过敏的机制与减少脊髓背角神经元含NR1和NR2B亚基的NMDA受体转运有关.

Objective To investigate the effect of dexmedetomidine on trafficking of N-methyl-D-aspartate （NMDA） receptors in spinal dorsal horn neurons during remifentanil-induced hyperalgesia in the rats with incisional pain.Methods Twenty-four male Sprague-Dawley rats,aged 2-3 months,weighing 240-260 g,were randomly divided into 3 groups （n =8 each） using a random number table：control group （group C）,remifentanil ＋ incisional pain group （group R＋Ⅰ）,and dexmedetomidine ＋ remifentanil ＋ incisional pain group （group D＋R＋Ⅰ）.A 1 cm longitudinal incision was made in the plantar surface of the left hindpaw to establish the model of incisional pain in anesthetized rats.In group D＋R＋Ⅰ,dexmedetomidine 50 μg/kg was injected subcutaneously at 30 min before establishment of the model.In R＋Ⅰ and D＋R＋Ⅰ groups,remifentanil was infused for 90 min at a rate of 1.2 μg ＆#183; kg-1 ＆#183; min-1 at the same time as the model was established.In group C,normal saline was infused for 90 min at a rate of 0.12 ml ＆#183; kg-1 ＆#183; min-1.The thermal paw withdrawal latency （TWL） and mechanical paw withdrawal threshold （MWT） were measured before administration of dexmedetomidine （T0）,and at 2,6,24 and 48 h after stopping infusion of remifentanil （T1-4）.The rats were sacrificed after the last behavioral testing,and the L4-6 segments of the spinal cord were removed for determination of the expression of NMDA receptor NR1,NR2A and NR2B subunits in membrane （m） and total （t） proteins in the spinal dorsal horn by Western blot analysis.The ratios of mNR1/tNR1,mNR2A/tNR2A and mNR2B/tNR2B were calculated.Results Compared with group C,the TWL was significantly shortened,the MWT was significantly decreased,the expression of mNR1,tNR1,mNR2B and tNR2B was significantly up-regulated,the ratios of mNR1/tNR1 and mNR2B/tNR2B were significantly increased （P〈0.05）,and no significant change was found in the expression of mNR2A and tNR2A and ratio of mNR2A/tNR2A in R＋Ⅰ and D＋R＋Ⅰ groups （P〉0.05）.Compared with group R＋Ⅰ,the TWL was significantly prolonged,the MWT was significantly increased,the expression of mNR1,tNR1,mNR2B and tNR2B was significantly down-regulated,the ratios of mNR1/tNR1 and mNR2B/tNR2B were significantly decreased （P〈0.05）,and no significant change was found in the expression of mNR2A and tNR2A and ratio of mNR2A/tNR2A in group D＋R＋Ⅰ （P〉0.05）.Conclusion The mechanism by which dexmedetomidine prevents remifentanil-induced hyperalgesia is related to reduction of trafficking of NR1 and NR2B subunits-containing NMDA receptors in spinal dorsal horn neurons of the rats with incisional pain.