INVOLVEMENT OF NITRIC OXIDE IN MAINTAINING AND FACILITATING THE HYPERALGESIA ASSOCIATED WITH CHRONIC NOCICEPTION IN THE SITE OF THE FIRST SYNAPTIC RELAY OF THE PAIN PATHWAY

为了阐明一氧化氮在脊髓伤害性加工中的作用，我们分析了大鼠腰背角在佐剂或热诱导炎症后，热戒断潜伏期与一氧化氮合酶染色神经元的相关性。在后爪皮下注射完全弗氏佐剂后4小时至5天，观察到受热区域施加热刺激后明显的热痛觉过敏。对照大鼠腰椎背角第I至第V层可见nadph -diaphorase阳性神经元，在第II和第III层交界处密度较高，并对其进行大鼠小脑一氧化氮合酶免疫组织化学染色。在佐剂诱导炎症的第3天，炎症后爪同侧背角浅层nadph -二磷酸腺苷酶和一氧化氮合酶阳性神经元显著增加。在佐剂诱导炎症1小时、1天，或热诱导炎症1小时、1天、3天（47 C 30 min）时，nadph -diaphorase阳性神经元未见变化。静脉注射一氧化氮合酶拮抗剂N^< ω >- l -精氨酸甲酯（LNAME,50 mg/kg），在炎症第3天显著阻断佐剂诱导的热痛觉过敏，但在第1天没有，对非炎症大鼠没有影响。LNAME在炎症第3天的这种抗痛觉作用被前给药l -精氨酸（500mg /kg i.p）逆转，l -精氨酸是一种一氧化氮合酶的底物。这些数据表明，在疼痛通路的第一突触中继部位产生一氧化氮的神经元参与维持和促进与慢性痛觉相关的痛觉过敏。

In order to elucidate the involvement of nitric oxide in spinal nociceptive processing, a correlation of thermal withdrawal latency with nitric oxide synthase-stained neurons in the rat lumbar dorsal horn was analyzed after adjuvant- or heat-induced inflammation. From 4 hrs through 5 days after subcutaneous injection of complete Freund's adjuvant into the hind paw, a marked thermal hyperalgesia was observed following heat stimulus applied to the affected region. In control rats, NADPH-diaphorase-positive neurons were observed in laminae I through V with a higher density at the border between laminae II and III in the lumbar spinal dorsal horn, and they were also stained immunohistochemically for rat cerebellar nitric oxide synthase. NADPH-diaphorase- and nitric oxide synthase-positive neurons increased significantly in the superficial layrs of the dorsal horn ipsilateral to the inflamend hind paw at day 3 of adjuvant-induced inflammation. No change in NADPH-diaphorase-positive neurons was observed at 1 hr and 1 day of adjuvant-induced inflammation, or at 1 hr, 1 and 3 days of heat-induced inflammation (47ﾟC for 30 min). The intravenous administration of N^<omega>-L-arginine methyl ester (LNAME,50 mg/kg), an antagonist of nitric oxide synthase, significantly blocked the adjuvant-induced thermal hyperalgesia at day 3 of inflammation, but not at day 1, and had no effect in non-inflamed rats. This anti-hyperalgesic effect of LNAME at day 3 of inflammation was reversed by the priodministration of L-arginine (500 mg/kg i.p.), a substrate of nitric oxide synthase.These data suggest that nitric oxide producing neurons in the site of the first synaptic relay of the pain pathway are involved in maintaining and facilitating the hyperalgesia associated with chronic nociception.