Abbadie C, Taylor B K, Peterson M A, Basbaum A I
Department of Anatomy, University of California San Francisco 94143, USA.
Pain. 1997 Jan;69(1-2):101-10. doi: 10.1016/s0304-3959(96)03285-x.
Injection of formalin in the rat hindpaw produces two phases of nociceptive behavior. Although it is generally agreed that the first phase results from direct chemical activation of nociceptive primary afferent fibers, the factors that contribute to the second phase are not established. In the present study, we monitored the expression of the c-fos protein to evaluate whether the pattern of activity of dorsal horn neurons differs as a result of ongoing afferent activity during the two phases. To selectively block the first or second phase, we respectively used remifentanil, a potent and short acting opiate agonist, and QX-314, a quaternary derivative of lidocaine, which does not cross the blood brain barrier. We also evaluated the effect of eliminating nociceptive behavior in both phases using both remifentanil and lidocaine or a combination of local anesthetics, bupivicaine and quaternary lidocaine. In all groups, formalin (5%, 50 microliters) was injected subcutaneously into the plantar surface of the hindpaw. To assess the nociceptive behavior produced by formalin, we monitored the number of flinches. Injection of remifentanil during the first phase completely blocked the first phase formalin-evoked nociceptive behavior, and had no effect on the second phase. Injection of lidocaine during the interphase completely blocked second phase nociceptive behavior. As expected, when remifentanil was administered during the first phase and lidocaine during the second phase, all formalin-evoked nociceptive behavior was blocked. The same was true for rats that received injections of bupivicaine and lidocaine during phases 1 and 2, respectively. In laminae I-II of the L4-L5 segment, the magnitude of the decrease in Fos expression was comparable for remifentanil (26.5%) and lidocaine (27.3%); the decrease was greater when both remifentanil and lidocaine were administered (50.5%), and even greater when bupivicaine and lidocaine were used (74.2%). In laminae V-VI, remifentanil, by itself, decreased c-fos expression by 39.4%; for lidocaine alone, the decrease was 58.4%. We did not observe further significant decreases when both remifentanil and lidocaine, or bupivacaine and lidocaine were injected (69.7% and 74.6%, respectively). Our results not only provide strong evidence that activity during the second phase is necessary for maintaining the maximal expression of c-fos in the spinal cord, but also reveal significant regional differences in the central patterns of activity generated during the two phases. These results also confirm our previous reports that c-fos expression is not eliminated when the behavioral manifestation of the noxious stimulus is completely blocked.
在大鼠后爪注射福尔马林会产生两个阶段的伤害性反应行为。虽然人们普遍认为第一阶段是由伤害性初级传入纤维的直接化学激活引起的，但导致第二阶段的因素尚未明确。在本研究中，我们监测了c-fos蛋白的表达，以评估在这两个阶段中，由于持续的传入活动，背角神经元的活动模式是否有所不同。为了选择性地阻断第一阶段或第二阶段，我们分别使用了瑞芬太尼（一种强效短效阿片类激动剂）和QX-314（利多卡因的季铵衍生物，不能穿过血脑屏障）。我们还评估了使用瑞芬太尼和利多卡因或局部麻醉药布比卡因和季铵利多卡因的组合消除两个阶段伤害性反应行为的效果。在所有组中，将福尔马林（5%，50微升）皮下注射到后爪的足底表面。为了评估福尔马林产生的伤害性反应行为，我们监测了退缩的次数。在第一阶段注射瑞芬太尼完全阻断了第一阶段福尔马林诱发的伤害性反应行为，对第二阶段没有影响。在间期注射利多卡因完全阻断了第二阶段的伤害性反应行为。正如预期的那样，当在第一阶段给予瑞芬太尼而在第二阶段给予利多卡因时，所有福尔马林诱发的伤害性反应行为都被阻断。分别在第1阶段和第2阶段接受布比卡因和利多卡因注射的大鼠也是如此。在L4-L5节段的I-II层，瑞芬太尼（26.5%）和利多卡因（27.3%）导致的Fos表达降低幅度相当；当同时给予瑞芬太尼和利多卡因时，降低幅度更大（50.5%），当使用布比卡因和利多卡因时，降低幅度甚至更大（74.2%）。在V-VI层，瑞芬太尼单独使用时使c-fos表达降低39.4%；单独使用利多卡因时，降低幅度为58.4%。当同时注射瑞芬太尼和利多卡因或布比卡因和利多卡因时，我们没有观察到进一步的显著降低（分别为69.7%和74.6%）。我们的结果不仅提供了有力证据，表明第二阶段的活动对于维持脊髓中c-fos的最大表达是必要的，而且还揭示了两个阶段中产生的中枢活动模式存在显著的区域差异。这些结果也证实了我们之前的报道，即当有害刺激的行为表现被完全阻断时，c-fos表达并未消除。
