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| 〖删除〗〖版主编辑〗〖转移帖子〗〖顶〗〖精〗[回复][短消息][编辑] | | [原创]恐惧消失——无所畏惧的老鼠 | 
——现在，老鼠不会从这种危险的气味面前逃走，尽管在后半生它将记住这个危险的气味。
——一小部分关键的嗅觉细胞被移除，使得老鼠无所畏惧。
这个实验说明了一个让人震惊的事实，对某些气味的恐惧是与生具来的。气味对于脑的刺激来自两个回路：先天的恐惧感和后天得到的无害感。一旦这种带有先天恐惧刺激的细胞被移除，从祖先那里获得的对某些有害气味的恐惧便荡然无存。
人类也许是同样的机制。
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发表的学术文献：
Kobayakawa, K. et al. Nature doi:10.1038/nature06281 (2007).
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国内媒体报道（参考）
但该报道并不客观,所谓"爱上"是没可能的，只是不惧怕。
在自然界，猫和老鼠之间从来没有“友谊”可言，就像卡通片中“汤姆”和“杰瑞”一样，你追我躲的游戏一刻不停。不过，日本科学家却通过基因改造逆转了老鼠的天性，让它不仅敢与猫“大眼瞪小眼”，还能玩得亲密无间，上演了一出现实版的《老鼠爱上猫》。
先天恐惧来自气味
日本东京大学的研究者给实验鼠移植了一种名为“白喉毒素”的基因，这样就能定向移除老鼠大脑中的嗅球神经细胞，而这种细胞的功能是接收从鼻腔的嗅觉感知细胞传来的神经刺激，并做出反应。
实验产生了非常奇异的效果，老鼠在失去这种神经细胞后出现了“大脑短路”，它面对自己的天敌猫非但毫无惧色，还表现得一脸好奇，甚至胆大妄为地爬到猫身上磨蹭翻滚。东京大学的板野说：“它们依然能闻到猫的气味或狐狸和雪豹的尿味，但没有任何恐惧表现。它们和猫相处得很愉快，还和猫嬉戏打闹。”
为了进一步验证气味感知与恐惧之间的关系，研究者又选取了另一组老鼠，它们的嗅球神经细胞完好无损，但鼻腔嗅觉感知细胞严重受损。板野表示：“它们感知、分辨气味的能力很弱。但一旦有气味信息传递到大脑，就能立刻激活危险信号，倒地装死。”
后天恐惧可以学习当然，恐惧感也不全是来自天生的。研究者还对经过基因改造的“勇敢老鼠”进行了训练，试图让它们在嗅到的气味和恐惧反应之间建立神经联系。结果发现，它们对猫等猎食者和腐烂食物产生了危险意识。
这次的实验是第一次发现动物如何把气味信息转化为恐惧反应。“我们在哺乳动物中发现两套系统，一种是天生的，一种是后天习得的。”人类对气味也有反应？
板野的研究在神经科学方面具有重要意义，表明哺乳动物对气味引发的先天恐惧、排斥感可以通过基因改造的方式来克服，人也不例外。
维也纳大学的教授卡尔．格莱默表示：“我们认为人在焦虑状态下释放出异常的身体气味，而别人也能够识别出来。虽然不像老鼠那样因气味引起恐惧，但他们知道这种气味有些异样并产生警觉。”□康娟（中国日报特稿）
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全文，from Nature网站：
The surprising result suggests that smells pass through distinct circuits along the path from nose to brain: one for innate fear, another for the learned kind. A single smell could activate both paths at the same time.
When a scent — noxious or pleasant — hits the nose of a mouse or any mammal, it activates a combination of olfactory neurons. Mice boast about a thousand types of these neurons, which reach from the nose to the brain. The combination of cells activated, like the notes in a piano chord, determines the scent experienced by the animal.
The olfactory neurons are located in a special structure in the nasal cavity called the olfactory epithelium, which has two major regions: dorsal and ventral. The olfactory neurons in each region differ at the molecular level, but until now, no one had much idea how the regions differed in their wiring.
From the olfactory epithelium, the neurons connect to a brain structure called the olfactory bulb. The organization of neurons in the epithelium is mimicked in the brain — the neurons are mapped out in the same way.
Eau de fox
To determine the difference between the dorsal and ventral neurons, Hitoshi Sakano, a neuroscientist at the University of Tokyo, and his team engineered a strain of mice that had no olfactory neurons in their dorsal epithelium. They then tested the mice for their response to a handful smells, good and bad.
Normal mice were drawn to smells of peanut butter and mouse urine; but couldn’t flee fast enough from the scents of rotting food, fox glands, and the urine of snow leopards.
But mice without these neurons showed less interest in the sweet smells and little aversion to spine-tingling ones, the team reports in Nature 1. The mice could still detect these smells, the researchers found, and could learn to hate the odours if researchers made the mice sick while delivering the 'nasty' smells.
The team concludes that the dorsal olfactory neurons transmit innate fear responses to the brain, whereas the ventral neurons convey learned aversion.
The team could also see a difference in the brain. In normal mice, a scent secreted by fox anal glands called trimethyl-thiazoline stimulates the brain to make adrenocorticotropic hormone, a sign of stress. The fearless mutants showed no such stimulation in response to the scent.
The work is a big step forward in explaining how odours are translated into actions, says Catherine Dulac, a neuroscientist at Harvard University in Cambridge, Massachusetts.
Humans probably have a similar system for discerning smells, says Sakano. But learned behaviours can sometimes over-rule innate ones, he notes. Natto — fermented soya beans — is a popular snack in Tokyo, despite its rancid smell. "I think an innate smell will tell us it's dangerous and don't eat it," says Sakano. "But based on the associative learning, some people in the Tokyo area learn to like it."
帖子在11/9/2007 4:17:27 AM被编辑过了 | 最初发表时间：2007-11-9 |  | 永远不要嫌弃你的父母行动迟缓，因为你永远想象不出你小的时候他们是如何耐心地教你走路；
永远不要嫌弃你的父母学不会电脑，因为你永远不会知道在你小的时候他们是如何不厌其烦地教你认字； |
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