長期分析坐骨神經傷害之大白鼠之脊髓體感覺神經誘發電位的變化

A Long-term Analysis of the Spinal Somatosensory Evoked Potential of Rats with Sciatic Constriction Injury

背景：本實驗藉由分析電生理改變，坐骨神經功能及疼痛行為表現來探討周邊神經病變性疼痛模式長時間的效應及坐骨神經的慢性緊縮性傷害。方法：12隻大白鼠依Bennett及Xie的方式，使坐骨神經產生慢性緊縮性傷害，之後監視其脊髓體感覺誘發電位，熱痛覺過敏反應及坐骨神經功能指數，上述這些資料會在慢性坐骨神經緊縮性傷害手術之前測得基礎值，而後在第5、12、19、26、33、47、61、75以及89天時，分別測量及紀錄。而體感覺誘發電位會在慢性坐骨神經緊縮性傷害手術之後三小時測得。而另一側肢體也同時測量。結果：所有慢性坐骨神經緊縮性傷害的大白鼠在第5天時會有熱痛覺過敏反應，這和神經受傷肢體在縮腳反應時距明顯下降及坐骨神經功能指數下降是相關的。慢性神經緊縮性傷害手術後3小時，誘發電位的振幅明顯下降且產生時間明顯延長，而這些電位改變會持續並且在統計上不會明顯惡化或恢復。實驗數據顯示在具有神經病變性疼痛表現的大白鼠神經緊縮性傷害後主要的電生理改變是在快速傳導神經束無法跨過受傷部位傳導，然而，在慢速傳導神經束卻保留傳導功能，而這樣的反應在神經緊縮性傷害手術後就會產生，並且持續至89天。結論：本實驗指出對慢性神經緊縮性傷害後的電生理評估而言，在急性期之評估上體感覺誘發電位是一項簡單操作且敏感度高的指標。但在長期之追蹤上則有其限制。

Background: This study was undertaken to evaluate the long-term effect of a peripheral neuropathic pain model, chronic constriction injury (CCI) of the sciatic nerve, through analyses of electrophysiologic change, sciatic nerve function, and pain behavior. Methods: CCI of the sciatic nerve was induced in twelve rats as described by Bennett and Xie. Three parameters were monitored: spinal somatosensory evoked potential (SSEP) elicited by supramaximal stimulation of the posterior tibial nerve and recorded from the thoracolumbar junctional space; thermal hyperalgesia assessed by measuring paw withdrawal latency (PWL); and sciatic function index (SFI). All the values of these parameters were obtained before the CCI procedure (day 1 as a preoperative baseline, and again on days 5, 12, 19, 26, 33, 47, 61, 75, and 89). SSEP was also measured 3 hr after the CCI operation. Data were also obtained from contralateral limbs. Results: All rats with CCI developed thermal hyperalgesia on day 5, as indicated by a significant reduction in PWL in the CCI limbs and a deterioration of the SFI compared with baseline values. These effects persisted to day 89. In the electrophysiologic study, 3 hrs after the CCI operation, the amplitude significantly decreased and latency significantly increased in all SSEP recordings. The changes persisted and showed no further statistically significant deterioration or recovery. The data demonstrated that the major electrophysiologic change after a constriction injury was the loss of conduction ability across the injury site in the fast-conducting fibers, but in the slow-conducting fibers the conduction ability was still preserved, which occurred immediately after the operation and persisted consistently for 89 days in the rats with behavior manifestations of neuropathic pain. Conclusions: Our findings suggest that SSEP is simple to obtain and sensitive in the acute phase of electrophysiological changes, but is limited for long-term evaluation after CCI.