英语听力文摘 English Digest 515、失去知觉之后

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　　失去知觉之后

 

　　If you’ve ever had major surgery, you probably remember lying down and waking up–but nothing in between. Thanks to the anesthesiologist, during the actual surgery you were out of it: immobilized and insensitive to pain. But until recently scientists had little understanding of how anesthetics actually work on the cellular² level.

 

　　That’s changed thanks to recent experiments performed by researchers at the University of Zurich, in Switzerland. They knew that anesthetics caused pain receptors in the brain to turn off by acting³ like most drugs do: anesthetizing drugs attach to particular sites on nerve cells and turn them off. The question was, where on nerve cells do these drugs attach?

 

　　Nerve cell membranes⁴ have receptors for different kinds of chemicals produced by the brain. Gamma-amino butyric acid, or GABA, for example, is a chemical that shuts down nerve cells. The hypothesis was that general anesthesia works by binding⁵ to GABA receptors on a nerve cell, thereby⁶ activating⁷ the receptor and instructing the cell to shut down. So it made sense for the Zurich researchers to focus on GABA receptors.

 

　　To do this they worked with mice that had been genetically⁸ engineered to have nerve cells with GABA receptors that wouldn’t respond to anesthetics. And sure enough, when such mice were given anesthetic¹ drugs they weren’t nearly as immune to pain as regular mice that had also been given pain-blocking drugs. Clearly, GABA receptor sites on nerve cells are part of what allows anesthetics to do their job.

 

　　While the Zurich experiment fills in only one piece of the puzzle, it is an important step towards learning how these amazing drugs work, and how to make them even better.

 

　　如果你曾经做过重大手术，那么你肯定只记得躺下去和醒来这么2个动作，而其间过程是浑然不知的。多亏了麻醉师，你才能在手术中无知觉地度过：不能动弹，也感觉不到疼痛。但是直到最近科学家们才多少了解到麻醉药是如何在细胞层面上工作的。

 

　　还得感谢瑞士苏黎世大学的研究员们最近做的实验，这一困惑才得以解开。他们弄清楚了麻药是通 过关闭大脑中的疼痛接收器才使人感觉不到疼痛，原理跟大多数药物一样：麻药附着在神经细胞上某个特殊位置，然后将感知功能关闭。问题是，麻药到底附着在什么位置呢？

 

　　神经细胞膜有多个接收器来识别大脑产生的不同类别的化学物质。例如γ-氨基丁酸，或者简写为GABA，就是可以关闭神经细胞感知功能的化学物质。假设全身麻醉是将麻药和在神经细胞上的GABA接收器绑定在一起，从而激活接收器，然后再传达闭接收功能的指令关的。这样的假设就使苏黎世大学的研究员们明白，集中精力研究GABA接收器是关键所在。

 

　　为了证明这点，他们用基因改造过的老鼠做实验，这种老鼠身上的 GABA接收器对麻药免疫。毫无疑问，这样的老鼠在使用了麻药后，比起正常的用了麻药的老鼠，疼痛感几乎没有降低。显然位于神经细胞上的GABA接收器是让麻药起作用的原因之一。

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