|Abstract: ||周邊神經常因壓迫、牽拉、缺氧或外傷性撕裂而受傷，並造成肢體產生過度性疼痛。而腦內啡（endo-morphin）已為眾人所知為一內生性止痛物質並由下視丘-腦下垂體-腎上腺所調控。它可以對於疼痛的病患產生顯著止痛效果。而前-腦啡-黑細胞促素-皮促素（pro-opiomelanocortin, POMC）基因是可以產生腦內啡、促腎上腺皮質激素、促黑色素細胞激素等荷爾蒙。 本研究是將大鼠的坐骨神經綁紮後，造成實驗性的周邊神經受損去產生劇烈疼痛並以POMC基因治療，用電生理檢查及兩種行為測試來評估其治療或減緩疼痛效果。我們將大鼠分成三組: 第一組為控制組(n = 8)； 第二組採用對大鼠左側坐骨神經綁紮(n = 8)造成神經損傷後，注射腺病毒攜帶綠螢光蛋白(Ad-GFP)；第三組仍採用對大鼠左側坐骨神經進行綁紮(n = 8)，造成神經損傷後以腺病毒攜帶POMC基因治療(Ad-POMC)。並在神經綁紮後第三天對大鼠左後肢脛前肌、腓腸肌注射腺病毒攜帶綠螢光蛋白及POMC基因。電生理評估與兩種行為測試的時點為術前三天、術後第三、七及十四天，電生理部分包括坐骨神經(至脛前肌、腓腸肌)的運動神經傳導速度與複合神經電位振幅大小、H反射、F波、潛時(latency)、肌電圖訊號(脛前肌、腓腸肌)，兩種行為測試包括溫度與機械性刺激大鼠左後肢去評估其對疼痛刺激之反應時間。 研究結果顯示電刺激神經損傷模式中均可見到電位振幅大小明顯下降。至於神經損傷老鼠潛時並未在神經損傷模式中明顯延長，而在神經傳導速度部份只有神經損傷後以腺病毒攜帶綠螢光蛋白(Ad-GFP)組別之脛神經在損傷後第十四天有變慢現象，其它神經傳導速度部份則否。電刺激評估中呈現神經損傷老鼠之H反射與F波潛時延長或消失。此外，肌電圖可明顯偵測到神經損傷老鼠的去神經自發性電位。整體而言，電生理評估部份對於以POMC基因治療在神經損傷老鼠的治療前後並無明顯差異。至於兩種行為測試包括溫度與機械性刺激大鼠左後肢部份，則在術後第十四天及二十一天，具有顯著之治療效果。綜言之，POMC基因治療有其止痛效果，但對於是否可以阻斷神經受損過程或具神經修補效果，則需累積更多數據與進一步深入探討。|
Peripheral nerves are most commonly affected by pressure, traction, friction, anoxia or cutting and these injuries can easily cause allodynia of the limbs. Beta-endorphin is an endogenous pain inhibitor. It can produce profound and long-lasting analgesia for patients with intractable pain. Prominent endogenous opioid peptides are modulated by the hypothalamic-pituitary-adrenal axis. The expression of pro-opiomelanocortin (POMC) produces opioid peptides, including the beta-endorphins, other shorter endorphins, adrenocorticotropic hormones (ACTH), and melanocyte-stimulating hormones (MSH). The aim of this study is to evaluate the efficacy of POMC gene therapy for neuropathic pain that is caused by chronic constriction injury (CCI) in a rat model. Experimental painful peripheral neuropathy is induced by CCI of the sciatic nerve which results in allodynia of the hind limb. We used the method of conventional electrical stimulation to quantitatively analyze the efficacy of gene therapy. In addition, two nociceptive tests, including thermal-withdrawal latency and mechanical withdrawal threshold, were also conducted to evaluate the effect of treatment. Adult male Sprague Dawley rats (250-300 g, n = 24) were divided into three groups: (1) the control group (n = 8); (2) the sciatic nerve ligation group that received an injection of adenoviral vectors with green fluorescent protein (Ad-GFP) (n = 8); and (3) the sciatic nerve ligation group that received an injection of adenoviral vectors with POMC gene (Ad-POMC) (n = 8). The electrophysiological studies and nociceptive tests were carried out on day 3 before ligation and days 3, 7 and 14 after ligation. The POMC injection was performed on day 3 after ligation. We measured the amplitude and onset latency of maximal compound muscle action potential (CMAP) in braches of the sciatic nerve (nerves to the gastrocnemius, tibialis anterior), motor nerve conduction velocity, H-reflex and F-wave by electrical stimulation and denervation sign by electromyography (gastrocnemius, tibialis anterior). In addition, the latency of the thermal-withdrawal and threshold of mechanical withdrawal were also recorded. The results showed that prominent thermal-withdrawal latencies and mechanical withdrawal thresholds were elevated in the sciatic nerve ligation group with POMC gene therapy on days 14 and 21 after ligation. It also demonstrated that administrations of POMC gene therapy which produced the beta-endorphins to elevate the pain threshold and reduced the allodynia of the injured limbs. In conventional electrophysiological studies, no significant differences were noted between the Ad-GFP and Ad-POMC groups. The reduction of CMAP amplitude was recorded in rats of the sciatic nerve ligation groups. There was no significant difference in the mean onset latency of CMAP and nerve conduction velocity (NCV) within these three groups, except for the fact that the NCV of the tibial nerve was slowing in the Ad-GFP group on day 14. Electrophysiological analysis was revealed prolonged or absent H-reflex and F-wave in animals of the neuropathy groups by electrical stimulation. Electromyography showed prominent denervation potentials over the sampling muscles in the sciatic nerve ligation groups. In conclusion, POMC gene therapy for neuropathic pain is very efficacious. However, the influence of POMC gene therapy for nerve protection or minimizing the progress of nerve injury will require further investigations.