(单词翻译:单击)
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This is Scientific American's 60-second Science. I'm Karen Hopkin.
Parasites live on or even inside another organism. And some can even change the behavior of their host to boost the odds of their transmission. Take the single-celled Toxoplasma gondii. Mice infected with this bug appear to become attracted to the smell of cat pee, an odor that uninfected mice smartly avoid. The infection thus raises the chances that a mouse will wind up in a cat's mouth. Obviously, bad news for the mouse—but good news for the parasite, which needs a kitty to complete its life cycle and spread to additional hosts.
Devious, indeed. But it turns out this cunning scheme may be less precisely targeted than it initially appears—because a new study finds that Toxoplasma doesn't specifically eliminate a mouse's natural aversion to cats. Rather the infection makes them generally less anxious and more adventurous—which makes them them curious about cats and pretty much everything else. Their work appears in the journal Cell Reports.
"The story about Toxoplasma gondii manipulating the behavior of its host is simply fascinating."
Biologist Ivan Rodriguez of the University of Geneva, one of the study's senior authors.
"It was particularly intriguing for us to understand how the parasite achieves a specific alteration of the neural circuits involved in the response toward feline predators—something that has never been elucidated."
So Rodriguez and his colleagues set out to determine the molecular mechanisms that underlie this legendary feline fatal attraction. For their first step:
"We decided to perform a quite broad panel of behavioral assays with infected mice in order to get an overview of how the parasite affects its host. We quickly observed that infected mice were less anxious, were more explorative and reacted quite differently than control mice when confronted with potential threats."
For example, mice infected with Toxoplasma were quicker to check out the far reaches of an elevated maze than their uninfected comrades. They interacted with the human investigators' hands and were unperturbed when an anesthetized rat was plonked into the middle of their cage—an event that caused uninfected mice to freeze in their tracks.
And the infected mice in this study did indeed show an attraction to the urine of bobcats. But they were even more interested in the scents of foxes and guinea pigs. Of course, whether or not infected mice are drawn specifically to the smell of cats, the parasite still gets what it wants, says Rodriguez.
"The end result is to favor the transmission of the infected rodent to the cat."
As to the mechanism, it appears that the parasite triggers a general inflammation of the brain.
"One interesting finding is that we observe a correlation between the level of inflammation and the severity of behavioral alterations."
Madlaina Boillat, a graduate student in the Rodriguez lab.
She and Rodriguez will continue to explore how neuroinflammation sends mice to their almost certain doom. Does it render these mice blind to danger—or endow them with the kind of curiosity that is usually associated with their feline foes?
Thanks for listening for Scientific American's 60-second Science. I'm Karen Hopkin.
参考译文
这里是科学美国人——60秒科学。我是凯伦·霍普金。
寄生虫生活在另一个生物体身上甚至体内。有些寄生虫甚至可以改变宿主的行为，以提高传播几率。以单细胞弓形虫为例。感染这种虫的老鼠似乎会被猫尿的气味吸引，而未感染的老鼠则会巧妙地避开。因此，感染会增加老鼠落入猫口的几率。显然，对老鼠来说这是个坏消息，但对寄生虫来说却是个好消息，因为寄生虫需要猫咪来完成其生命周期，并传播至其他宿主身上。
这的确很狡猾。但事实证明，这种狡猾的计谋可能没有最初看起来那么目标精准，因为一项新研究发现弓形虫并不能明确消除老鼠对猫的自然厌恶。相反，感染普遍令老鼠的焦虑减少，变得更喜欢冒险，这使它们对猫和几乎一切都感到好奇。他们的研究成果发表在《细胞报告》期刊上。
“弓形虫操纵宿主行为的故事简直令人着迷。”
日内瓦大学的生物学家伊万·罗德里格斯是这项研究的高级作者之一。
“我们特别感兴趣的是，这种寄生虫为何会明确改变神经回路，而且神经回路还包括对猫科捕食者的反应——这以前是从未阐明过的。”
因此，罗德里格斯及其同事开始研究，确定猫咪这种传奇的致命吸引力的分子机制。第一步：
“我们决定对受感染的老鼠进行大量行为分析，以了解寄生虫影响宿主的方式。我们很快观察到，与控制组老鼠相比，受感染老鼠在面对潜在威胁时，焦虑更低、探索欲更高、反应也大不相同。”
例如，相比未感染老鼠，感染弓形虫的老鼠会更快地检查遥远高处的迷宫。它们会与人类研究者的手互动，当被麻醉老鼠被扔进笼子中间时，它们并不会受到干扰，而未受感染老鼠则会当场呆住。
在这项研究中，受感染老鼠确实对山猫的尿液显示出兴趣。但它们对狐狸和豚鼠的气味更感兴趣。罗德里格斯表示，当然，无论受感染老鼠是否被猫的气味特别吸引，寄生虫都能得偿所愿。
“最终结果都是有利于寄生虫从受感染老鼠传播到猫身上。”
至于传播机制，似乎寄生虫会引发大脑的一般性炎症。
“一个有趣的发现是，我们观察到了炎症水平与行为改变严重程度之间的相关性。”
马德莱纳· 博拉特是罗德里格斯实验室的研究生。
她和罗德里格斯将继续探索神经炎症如何让老鼠走向几乎必然的厄运。神经炎症是会让这些老鼠对危险视而不见，还是让它们产生了通常与猫科敌人有关的好奇心？
谢谢大家收听科学美国人——60秒科学。我是凯伦·霍普金。
译文为可可英语翻译，未经授权请勿转载！
重点讲解
重点讲解：
1. wind up 最终沦落到；最终落得；(以…)告终；
He could wind up in gaol.
他可能最后会进监狱。
2. turn out 原来是；结果发现；
Cosgrave's forecast turned out to be quite wrong.
科斯格雷夫的预测最后证明是大错特错。
3. set out to do sth. 开始；着手；
We set out to find the truth behind the mystery.
我们开始着手揭开谜团背后的真相。
4. endown sb./sth. with sth. 赋予；使天生拥有；
Nature has endowed her with great musical ability.
上天赋予她极大的音乐才能。
