|
中文摘要
中風是因腦部血流突發性受阻所造成，大部分是大腦動脈突然被阻斷造成缺氧性中風，其他的則是腦部血管破裂引起，又被稱作出血性中風。缺氧性的中風有超過80%的病患是由血栓塞造成，其中又有大約87%的阻塞是在大腦中動脈，這當中又有大約73%是單一性的阻塞。
腦-血管屏障主要的功能是避免大分子、微生物病原菌及循環中的血球細胞進入中樞神經系統，在生理功能上扮演一個重要的角色，如果遭受破壞，則會造成腦部受損及水腦等損傷。我們以一個經圓滑處理的尼龍線段單一阻塞大腦中動脈的方法，在小鼠建立一個模擬人類中風的動物模式。阻斷大腦中動脈後受損傷的區域與其主控的區域大小相似，約為40-50%左右。我們利用此動物模式，以一帶有β-galactosidase的E. coli突變株M4當追蹤物，以及利用免疫組織化學法偵測細胞激素與誘發性一氧化氮合成酶(inducible nitric oxide synthase, iNOS)，研究這些因子與局部大腦缺氧間的關係。結果顯示，TNF-α在大腦中動脈阻塞3小時之後就可以在血管、腦室及腦膜等區域發現其表現，而且是由星狀細胞與微血管所表現。在腦-血管屏障上的改變則必須等到6及15小時後才可以在腦實質中觀察到M4追蹤物，受損傷半腦M4的數量多於對側半腦，而且數量會隨著時間的增加而增加。由此結果中可以知道，受大腦中動脈阻塞的半腦其腦-血管屏障開啟的時間點早於對側的半腦。另外iNOS在15小時會表現在受損傷半腦的腦膜上。大腦在局部缺氧的情形下，自由基的產生會造成腦細胞的死亡，因此我們使用了一個自由基清除者、carboxyfullerene (C3)，來處理經大腦中動脈阻塞的小鼠。結果發現C3可以降低大腦損傷的區域，且有劑量依靠的關係，並且可以在受損傷半腦腦室及神經細胞中發現C3的蹤跡。如果C3延後6小時再給予，同樣也可看到部分治療的效果。除此之外，我們在C3處理的小鼠大腦上可以看到受損傷半腦表現內皮細胞型一氧化氮合成酶(endothelial nitric oxide synthase, eNOS)，其表現的區域鄰近C3存在的區域。所以C3在大腦局部缺氧中可能可以藉著抑制自由基的產生及增強eNOS的表現來避免細胞的死亡。
|
|
英文摘要
A stroke is a sudden interruption of the blood supply into the brain. Most strokes are caused by an abrupt blockage of arteries in brain (ischemic stroke). Other strokes are caused by bleeding in tissue after the burst of the blood vessel (hemorrhagic stroke). Up to 80% of ischemic stroke in human is caused by thromboembolism. Occlusion of the middle cerebral artery (MCA) was documented in 87% of patients with stroke and approximately 73% of MCA occlusions were induced by a single embolus. The blood-brain barrier (BBB) functions to eliminate the entry of macromolecules, microbial pathogens, and circulating leukocyte into the central nervous system (CNS). The integrity of the BBB may play an important role in the subsequent pathophysiology since BBB disruption relates closely to brain edema formation and cerebral infarction. We have set-up a murine model of middle cerebral artery occlusion (MCAO) with a single heat-blunted occluding suture of the tried gauge to mimic human stroke. Infarct volume was around 40-50%. This model was used to study the relationship between cerebral ischemia and BBB. Tracer M4 that constitutively expression b-galactosidase as a tracer can detect the alteration of vasopermeability of BBB. Cytokine and iNOS expression in focal cerebral ischemia were determined by immunohistochemical stain. We found that TNF-a was expressed in microvasocular, ventricle and meninge as early as 3 h post ischemia. Both astrocytes and microvessel expressed TNF-a. M4 tracer was found to deposit in parenchyma from 6 h to 15 h. The amounts of tracer in infract hemisphere were more than those in opposite hemisphere, and increased along time, indicating that BBB disruption in infract hemisphere was earlier and more severe than in opposite hemisphere. Furthermore, iNOS was expressed in meninges of infarct hemisphere at 15 h. Free radical will be released in focal cerebral ischemia and caused neuron cell death. Therefore carboxyfullerene (C3), a free radical scavenger, was used to treat middle cerebral artery occlusion mice. We found that C3 could decrease brain infarct size in a dose-dependent manner. C3 can be detected in neuron and ventricle of ipsilateral hemisphere. C3 has also partial therapeutic effect at 6 h post treatment. Furthermore, eNOS would be expressed in infarct area neighboring C3-positive neuron in C3 treated-MCAO mice. C3 might prevent neuron apoptosis in focal cerebral ischemia either inhibiting free radicals or enhancing eNOS expression.
|
