酸刺激肌肉所誘導長期痛覺過敏時其脊髓內基因表現量之差異

酸是眾多可活化痛覺受器的刺激物之ㄧ，組織酸化現象常常伴隨著疼痛的發生，因此生理上主要負責偵測組織中酸濃度為神經細胞上的酸敏感離子孔道(Acid-sensing ion channels, ASICs)，其中又以ASIC3亞型對酸最為敏感。最近研究報導指出重複地在單側腓腸肌內注射酸性生理食鹽水可引起兩側腳掌長期痛覺過敏的現象。又因為長期、慢性的痛覺通常與中樞敏感化有關，此時脊髓內部的基因表現量改變，以類似建立LTP的機制造成中樞神經細胞的活性增加、動作電位閾值降低。因此本篇論文的目的在尋找一系列與中樞敏感化及動作電位相關的基因當中，何者基因表現量改變，並與長期痛覺過敏有關聯。由定量PCR的結果指出在腰椎部位的脊髓內，膜電位依賴性鈣離子孔道Cav3.2在第一次注射酸後五天，基因表現量增加了22倍，並持續增加到第二次注射酸後七天時，基因表現量增為24倍；此外膜電位依賴性鉀離子孔道Kv1.4在第二次注射酸後24小時，至第二次注射酸後七天，期間基因表現量一直維持21倍的增加。然而一般源自皮膚刺激而引起的中樞敏感化相關基因，包括NK1、Pdyn及一些麩胺酸(glutamate)受體等等，在本論文中則皆未觀察到表現量有任何變化。以上結果指出T型鈣離子孔道(T-type Calcium channels) Cav3.2的基因表現量與A型鉀離子孔道(A-type Potassium channels) Kv1.4的基因表現量增加的時間點與行為實驗中的長期痛覺過敏時間點相吻合，因此認為這兩個離子孔道在肌肉內施予酸刺激造成的長期痛覺過敏的機制中扮演很重要的角色，並且這種機制是不同於以往源自皮膚刺激的實驗模式。另外在皮下組織進行福馬林測試(formalin test)，並利用乳酸與低溫兩種變因來促進在皮膚層面ASIC3的作用，結果發現乳酸存在時並不影響福馬林引起的發炎痛覺；低溫條件下也只能延遲痛覺的反應時間而已。這個結果指出皮膚層面的ASIC3被活化後，對於調控發炎反應痛覺的作用不大。

關鍵字

肌肉內；酸注射；長期痛覺過敏

並列摘要

Acid is one of the chemical mediators that cause pain. Sensory neurons detect the pH drop of surrounding tissue when tissue acidosis occurs. The main ion channels responsible for detecting protons are acid-sensing ion channels called ASICs. Within this ASIC family, ASIC3 is the most sensitive to protons. A recent article showed that repeated acid-injection into muscle can induce bilateral long-lasting hyperalgesia. This experimental model is helpful for us to investigate chronic muscle-originated pain. Chronic or long-term nociception is always related to central sensitization, which is involved in a transcription-dependent mechanism for developing long-term potential effect. Therefore I used QPCR technique to exam gene expression level before and after acid-injection to see if any genes involved in central sensitization. Based on my QPCR data, a T-type Calcium channel, Cav3.2 was up-regulated 22 folds in 5th day after 1st acid-injection and 24 folds in 7th day after 2nd acid-injection and an A-type potassium channel, Kv1.4 was up-regulated 21 fold from 24hrs after 2nd acid-injection to 7th day after 2nd acid-injection. Comparing with behavioral tests, up-regulation of both genes is associated with the development of chronic hyperalgesia. It suggests that increasing expression levels of Cav3.2 and Kv1.4 in lumbar spinal cord may contribute hyperalgesia formation. However, the expression levels of NK1、Pdyn and some gultamate receptors, which are up-regulated after central sensitization induced by cutaneous stimulation, were constant in my experiment model. My data suggest that the mechanism of muscle-originated chronic hyperalgesia is different from skin-originated chronic hyperalgesia.. Another part of the thesis studied the effect of lactate and cold temperature in cutaneous formalin test. The result showed that both lactate and cold temperature did not affect the cutaneous inflammatory nociception but the formalin-induced late phase nociception was delayed.

並列關鍵字

muscle ； acid ； chronic hyperalgesia

參考文獻

Alvarez de la Rosa, D., Zhang, P., Shao, D., White, F. & Canessa, C.M. Functional implications of the localization and activity of acid-sensitive channels in rat peripheral nervous system. Proc. Natl. Acad. Sci. USA 99(4), 2326-2331 (2002).

Alvarez de la Rosa, D., Krueger, S.R., Kolar, A., Shao, D., Fitzsimonds, R.M. & Canessa, C.M. Distribution, subcellular localization and ontogeny of ASIC1 in the mammalian central nervous system. J. Physiol. 546(1), 77-87 (2003).

Armstrong, C.M.& Hille, B. Voltage-gated ion channels and electrical excitability. Neuron 20, 371-380 (1998).

Askwith, C.C., Benson C.J., Welsh, M.J & Snyder, P.M. DEG/ENaC ion channels involved in sensory transduction are modulated by cold temperature. Proc. Natl. Acad. Sci. USA 98(11), 6459-6463. (2001).

Benson, C.J., Eckert, S.P. & McCleskey E.W. Acid-evoked currents in cardiac sensory neurons : a possible mediator of myocardial ischemic sensation. Circ. Res. 84, 921-928 (1999).

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酸刺激肌肉所誘導長期痛覺過敏時其脊髓內基因表現量之差異

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