甘丙肽第2型受體在正中神經病變疼痛中所扮演的角色

Abstract

Galanin對於周邊神經疼痛訊息傳遞具有促進或抑制的效果，可能來自於周邊神經產生病變之後造成不同的神經傳遞物質以及受體的活化，因而改變了其在疼痛傳遞上所扮演的角色。而研究指出galanin藉由其第二型受體 (galanin receptor 2, GalR2 )調控而促進周邊神經病變疼痛的傳遞，但對於正中神經損傷後影響GalR2及所含神經傳遞物質數量上的變化仍欠缺直接證據，更遑論它對於正中神經損傷後引發的感覺疼痛異常的影響。 本研究發現在正常大白鼠的背根神經節 (dorsal root ganglia)中，GalR2免疫反應神經元主要表現在小型神經元，而當正中神經慢性纏繞傷害後一週，背根神經節中GalR2免疫反應神經元百分比會有顯著的上升，且在形態上觀察發現GalR2免疫反應神經元的分布相較之下開始出現於偏中大型神經元。當配合與matrix metalloproteinase-9 (MMP-9)、acid-sensing ion channel 3 (ASIC3)、protease-activated receptor 2 (PAR2)、P2X3、hyperpolarization-activated cyclic nucleotide-gated channel 1 (HCN1)等傳遞物質或通道蛋白進行雙重免疫螢光標誌，結果發現神經損傷後一週共同免疫螢光標誌神經元所佔百分比有顯著增加，證明周邊神經損傷損傷伴隨著許多發炎現象或離子通道蛋白的活化極可能為促進GalR2增加表現的原因之一，接著再觀察GalR2與NF200、galanin、neuropeptide Y (NPY)、neuronal nitric oxide synthase (nNOS)等神經傳遞因子有雙重免疫螢光標誌神經元的數量及其佔背根神經節的百分比，發現都有顯著的增加。結果顯示正中神經慢性纏繞傷害後，誘導GalR2免疫反應神經元增升部分為中大型神經元且同時具有NPY、galanin、nNOS的表現。接著我們研究發現給予GalR2增效劑AR-M1896及拮抗劑M871處理時，分析其行為反應及楔狀神經核內原致癌基因免疫反應神經元的數量變化，結果發現觸覺痛以及電刺激所引發楔狀神經核內c-Fos神經元的數量以AR-M1896和M871處理組別分別有顯著加劇並且數量增加或緩解並且數量下降的情形。綜合以上結果顯示，正中神經慢性纏繞傷害GalR2免疫反應數量的增加可能透過疼痛相關因子的活化，並且同時促進所含之神經傳遞物質向下游傳遞釋放，進而促使楔狀神經核內c-Fos免疫反應神經元的增加，而與外在痛覺訊息傳遞有所關聯。經由本實驗結果推論GalR2的活化或許對於腕隧道症候群所造成的神經病變疼痛可能誘發的機制是一個關鍵的因素，希望藉此研究能提供臨床上一個新的治療方向。

Galanin is a neuropeptide expressed in dorsal root ganglion (DRG) neurons and spinal dorsal horn neurons. It is involved in a variety of biological functions, including a important role in nociception. Previous studies have shown that galanin modulated neuropathic pain via galanin receptor 2 (GalR2) after peripheral nerve injury. However, the direct evidence of GalR2 involved in the median nerve induced neuropathic pain sensation is unavailable. Our experimental animal model is median nerve chronic constriction injury (CCI) for inducing neuropathic pain in. Then, we found that the percentage of GalR2-LI neurons in the C6 DRG peaked at 1 week after CCI treatment. We further investigate the relationship between GalR2 and proinflammatory factor matrix metalloproteinase-9 (MMP-9), protease-activated receptor 2 (PAR2) and pain-related channels or markers including acid-sensing ion channel 3 (ASIC3)、P2X3、hyperpolarization-activated cyclic nucleotide-gated channel 1 (HCN1)、galanin、neuropeptide Y (NPY) and neuronal nitric oxide synthase (nNOS) in the C6 DRGs of CCI and naïve rats by immunofluorescence (IF) double labeling. The result showed that the percentage of the above-mentioned double labeling neurons in the injured DRG were all have significantly increased. These result suggested that CCI treatment induced neuronal inflammation, proton, ATP and ectopic discharge may be reasonable to up-regulate GalR2 expression in the A-type and injury side of DRG neurons and cuneate nucleus. Furthermore, the percentage of GalR2-LI DRG containing galanin、NPY and nNOS was significantly increased. Then, we employed CCI treatment along with GalR2 agonist (AR-M1896) and GalR2 antagonist (M871) intraplantar application to examine their effect on median neuropathic pain and c-Fos expression in the stimulated side in cuneate nucleus. Our result revealed that the level of mechanical allodynia、thermal hyperalgesia and the number of c-Fos neuron were markedly increased in the GalR2 agonist treatment and attenuated in the GalR2 antagonist treatment group. According to our findings, CCI induced GalR2-LI neurons activation probably through galanin, NPY or NO triggers c-Fos expression in the CN and transmits neuropathic pain sensation to the thalamus. These evidence shows that GalR2 may be a potential clinical therapeutic target of neuropathic pain after median nerve injury.