作者：孝文 来源：新浪科技 发布时间：2013-3-4
# u1 u$ |0 ]4 H0 [9 ]1 r科学家将蝌蚪眼睛植入尾部治疗失明
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北京时间3月4日消息，据国外媒体报道，从古到今，在孩子看来，妈妈的后脑勺上长着眼睛，因为他们无论背着妈妈做什么，妈妈似乎都知道。但如今，“后脑勺长眼睛”的事儿有望变成现实。科学家有史以来第一次证明，将眼睛植入到蝌蚪的尾部，眼睛仍然可以看东西。
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* e' {6 S; {. B1 x. K这些研究人员把这一研究结果用“令人震惊”来形容。塔夫斯大学艺术与科学学院的生物学家指出，这一重大发现有众多深远影响，尤其对再生医学领域具有重要意义。
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这项新研究的负责人迈克尔-莱文说：“异位眼和脊髓连接而不是直接连接到大脑时，接受蝌蚪依然能看得见事物，这种能力真是令人震惊。医学的首要目标是有朝一日用生物或人造更换部件恢复受损或缺少的感官结构。这项研究有许多深远意义，但从医学角度来看，它的主要意义是治疗失明等感觉障碍时无需和大脑建立特殊连接。”9 ~% A; k. ]/ ?8 L' m7 ~5 n' a4 N; {
3 e; @+ [" Y; A0 n. u9 V3 d生物学家在实验中通过外科手术取出捐赠蝌蚪的眼睛，然后把它们植入接受蝌蚪的尾部，诱发这些异位眼的生长。研究人员移除接受蝌蚪的天生眼，只留下和脊髓连接的异位眼。这些科学家用常见实验室动物非洲爪蟾的134个蝌蚪进行实验。8 `+ N5 A# X, @
# M/ \6 A# A0 [) O& q他们把这些两栖动物研究对象放在一个有水的碟中，用红光照射它的一半，用蓝光照射另一半，在有规律的时间间隔中调换这两种光。实验期间，不管蝌蚪何时闯入被红光照射的一半碟子，就会受到一个小小的电击警告。这个科研组获得令人兴奋的发现：19%以上视神经和脊柱连接的蝌蚪对光作出反应。蓝光刺激自然运动时，它们就游离红光。1 D7 [; T. J4 W
& O6 Q) w/ B- i, [ r8 M' t研究人员用拥有完整天生眼的蝌蚪对照组进行实验，结果发现它们对光作出同样反应。但这种反应并没有在失明或没有受到任何电击的蝌蚪身上得到验证。莱文说：“我们的发现前所未有。没人会想到蝌蚪侧腹上的眼睛能看得见，尤其是在只把眼睛和脊髓而不是大脑连接时。”& P( m& c T2 F" p
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Scientists Put A Working Eyeball On A Tadpole's Tail
$ A$ ?" t/ H- GIt turns out we seriously underestimated the central nervous system.
t' K+ \ a& W; e# ?By Emily ElertPosted 03.01.2013 at 12:44 pm( M6 S) `& [2 Y# D: h" n8 C
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 Tadpole With Grafted Eye Douglas J. Blackiston
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, w6 U9 ?) w7 z" O[p=18, null, left]It's hard to say what's crazier: the fact that Tufts University researchers spent a year cutting out the tiny eyeballs of tadpole embryos and sticking them back on to the tadpoles' tails, or: the fact that, when they hatched, a few of the tadpoles COULD ACTUALLY SEE OUT OF THE EYES ON THEIR TAILS.[p=18, null, left]As you know, this is not the way vision is supposed to work--your eyeballs are supposed to be connected to a big fat nerve that carries incoming signals back to your brain, which combines the information from both your eyes into a 3D picture of the world in front of you. Without that direct link to the brain, your eyeballs are useless.[p=18, null, left]At least, that's the way scientists have thought about it for the last several centuries. But over the past few decades, experiments in animals and humans have repeatedly shown that the central nervous system--including the brain and spinal cord--is a lot more flexible and adaptable than people used to think it was. If one part of the brain gets damaged, for instance, the information that used to flow to the damaged sector is often re-routed, and another part of the brain takes on the job of processing it.[p=18, null, left]So these newer findings got the Tufts University researchers wondering: could the optic nerve really be the only route for incoming visual signals? And could a different part of the nervous system, like the nerves further down the spinal cord, process those signals on their own, without help from the brain?[p=18, null, left]Tadpoles, they realized, would be a good way to test this question: they would perform surgery at a time when the tadpoles were still developing, so that the transplanted eyes would have time to put down nerve roots that could potentially hook up to the rest of the tadpoles' nervous systems.[p=18, null, left]The surgeries were painstaking, but the researchers were able to successfully graft eyeballs onto the tails of over 200 tadpole embryos:' o8 F0 f* l# k( x) \! O
 Tadpole Eye Transplant, Before and After: Image F, on the left, shows a tadpole embryo with both its native eyes and a donor eye embedded in its tail (white arrows); Image G, on right, shows a blinded tadpole with a donor eye in its tail. Douglas J. Blackiston
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[p=18, null, left]When the altered tadpoles hatched, the researchers went to work testing their subjects' vision. Here's the Journal of Experimental Biology's description of the experiment:They placed their amphibious subjects in a well where half of the dish was illuminated with red light and the other half with blue light, which they inverted at regular intervals. During training sessions, whenever the tadpoles ventured into areas bathed in red light they received a little warning zap of electricity. After a break the tadpoles were tested to see whether they had learnt to associate the red light with electrical punishment and whether they would stick to the blue side of the dish.
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% }( x* o6 t* J( i* l8 e[p=18, null, left]While the blind tadpoles never developed a preference for one side of the dish or the other, seven of the tadpoles with transplanted eyes learned to stay in the blue light, demonstrating that they could see through their grafted eyes.[p=18, null, left]The question was, why only seven?[p=18, null, left]The answer turned out to have something to do with how the donor eyes sprouted nerves after the transplants. Since they'd labeled the donor eyes with red fluorescent protein, the researchers were able to image the tadpoles and compare the growth of their nerves. In half the subjects, the nerves hadn't grown at all, and in about a quarter of the others, the nerves had grown, but they'd ended up in the tadpoles' stomachs:- \5 ^- ~* w1 A. L1 }
 Nerves Ending In Stomach: White arrows show the location of the transplanted eye, and the nerves show up in red, tracing the path to the stomach. Douglas J. Blackiston
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7 u, P( h7 N3 S+ S$ U6 p[p=18, null, left]But in the other quarter of the subjects--31 tadpoles in total--the nerves extended all the way to the animals' spinal cords; six of the seven seeing tadpoles belonged to this group:
. Y. E% Z3 R& w! t Nerves Ending In Spinal Cord: White arrows show location of eye. In the image on left, you can see that the eye's nerves end after reaching the spinal cord (in other words, they don't make it all the way to the brain). Douglas J. Blackiston
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[p=18, null, left]The researchers' findings seem to indicate that the neurons in the spinal cord are capable of doing at least some of the tasks as the brain. If that's true, scientists could someday exploit the spinal cord's smarts for a number of medical treatments, like restoring movement to paralyzed limbs.http://www.popsci.com/science/article/2013-02/tadpoles-get-their-eyeballs-moved-their-tailsand-can-still-see
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发表于 2013-3-4 15:44
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