The brains of decapitated pigs can be partially revived several hours after the animal has died, researchers have revealed, with some of the functions of cells booted back up when an oxygen-rich fluid is circulated through the organ.
The scientists stress that the brains do not show any signs of consciousness — for example, there was no sign that different parts of the brain were sending signals to each other — and that it does not change the definition of death. “This is not a living brain. But it is a cellularly active brain,” said Prof Nenad Sestan from Yale University, who led the research.
A number of studies have suggested brain cells might not inevitably die after blood stops circulating. Writing in the journal Nature, researchers in the US reported how they sought to examine this further by taking brains from 32 pigs that had been killed in a slaughterhouse. Four hours after their deaths the arteries of the pig brains were hooked up to a sophisticated system dubbed BrainEx, which pumped an oxygenated synthetic blood through the organ. This fluid contained a host of nutrients as well as other substances to tackle processes that lead to cell death, and the circulation was continued for six hours.
Photo: REUTERS
照片：路透
At that point, the team found the circulating fluid successfully flowed through blood vessels in the brain, including tiny capillaries, and that the blood vessels were able to dilate in response to a drug, while the brain as a whole consumed oxygen and glucose from the fluid and released carbon dioxide back into it at similar rates to an intact brain.
What is more, the cells showed certain functions, including the release of various immune-response substances when triggered. After tissues were removed from the brains and flushed of the BrainEx fluid the researchers found individual neurons were still able to function.
The team said that while the BrainEx fluid was circulating, they monitored the brains to check for any signs of organized electrical activity that might suggest consciousness. “That monitoring didn’t show any kind of organized global electrical activity,” said Dr Stephen Latham, a bioethicist and co-author of the study.
But, he said, the team had been ready for signs of consciousness. “Had that appeared they would have lowered the temperature of the brain and used anesthesia to stop that kind of activity,” said Latham, adding that at present there are no ethics committees set up for such an eventuality, and it remained unclear in any case if the technique could ever restore consciousness.
The team said the approach could provide a new way to study the brain, and even help in the development and testing of new therapies for stroke and other conditions in which bloodflow to parts of the brain is blocked, causing cells to die.
(The Guardian)
研究人員近日指出，宰殺後的豬隻大腦在死亡數個小時之後，仍然可以被「部分復甦」──藉由一種富含氧氣的液體在器官中進行循環，死亡豬隻的腦細胞部分功能被重新啟動。
科學家強調，實驗中的大腦並未顯示任何具有意識的徵兆──舉例而言，大腦不同部位並沒有出現互相傳遞訊號的跡象──而這項實驗也並未改變死亡的定義。耶魯大學的內納德‧塞斯坦教授是這篇研究的主持人，他表示：「這並不代表它是一個活的大腦，但確實是一個就細胞層面而言仍在活動中的大腦。」
曾有多份研究指出，在血液停止循環後，大腦細胞可能不會必然死亡。在期刊《自然》這次刊出的報告中，美國的研究人員解釋他們如何藉由三十二頭豬在屠宰廠被宰殺後留下的大腦，試圖進一步檢驗這個現象。在豬隻死亡四個小時後，豬的大腦動脈被接上一個稱為「BrainEx」的複雜系統，它會把加入氧氣的人工合成血液灌注到器官中。液體內含有許多營養物和其他物質，能夠阻撓導致細胞死亡的過程，並在大腦中持續循環六個小時。
此時，研究團隊發現循環的液體順利流經大腦中的血管──包括極細的微血管──而血管也能夠對某種藥物產生擴張反應，大腦整體則會消耗液體中的氧氣和葡萄糖，並釋出二氧化碳回到液體中，速率近似於正常大腦。
此外，細胞更開始出現某些功能，例如在受到刺激時會釋放出多種免疫反應物質。研究人員移除部分腦組織、並且沖洗掉「BrainEx」液體後，發現單獨的神經元仍然能夠運作。
研究團隊表示，當「BrainEx」液體正在循環時，他們有偵測大腦，檢查是否有任何可能代表意識的組織性帶電活動跡象。生物倫理學家史蒂芬‧拉譚姆博士是這份研究的共同作者，他指出：「監測過程中並未顯示出任何組織性的整體帶電活動」。
不過，他也表示，研究團隊已做好準備，面對隨時出現意識的徵兆。拉譚姆博士說：「如果有類似跡象出現，研究人員就會降低腦部溫度，並且用麻醉藥物阻止這類活動。」但他也補充說，目前並沒有為這種可能性成立任何倫理委員會，而且無論如何，該技術是否能夠恢復意識仍然在未定之天。
研究團隊表示，這個方法可望提供新的大腦研究方式，甚至有助於開發和測試新療法，治療中風和其他因為大腦部分血流受阻而導致細胞死亡的相關疾病。
（台北時報章厚明編譯）
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