Fight-or-FlightNerves Make Mice Go Gray
一项新的小鼠研究表明，压力会导致白发生长，毛发的颜色变化源于过度活跃的神经。
[听力全文]（点击展开/收起）
They say that Marie Antoinette’s hair turned white the nightbefore she lost her head to the guillotine. But can stress really have such adramatic effect on hair color? A new study in mice concludes that it can andcredits overactive nerves with stripping the color from the animals’ locks—andpossibly ours.
Researchers at Harvard’s Stem Cell Institute were interestedin the stress and hair color issue. So they decided to take a closer look atthose stem cells that give rise to melanocytes—thecells that pump pigments into each hair follicle.The stem cells were an obvious target ...
“Because changes in the stem cell population translate tochanges in hair color, which are very visible and easy to identify.”
Ya-Chieh Hsu, the study’s senior author.
To start, she and her colleagues subjected mice to somerodent-sized stressors—like having their cage tilted, their bedding dampened ortheir lights left on all night.
“So what did we find? We found that stress indeed leads topremature hair graying in mice. But it took a long time for us to actuallynarrow down how it occurs.”
First, they thought it could be the immune system attackingthe melanocyte stem cell population.
“However, mice lacking immune cells still show prematurehair graying under stress.”
Then they thought the key factor could be cortisol, the quintessential stress hormone.
“But when we removed the adrenalglands from the mice so they cannot produce cortisol-like hormones,their hair still turned gray under stress.”
That’s when they turned their attention to the sympathetic nervous system, which orchestrates thebody’s overall reaction to stress, including the classic fight-or-flightresponse. Those nerves reach out to our muscles, organs and, yes, even ourhair.
“The nerve terminals wrap around each hair follicle like aribbon.”
And when Hsu and her team cut those connections, the stemcells were spared, and the animals kept their shiny black coat even in the faceof minor discomfort. The findings appear in the journal Nature. [Bing Zhang etal., Hyperactivation of sympathetic nerves drives depletion of melanocyte stemcells]
It’s unclear whether the same sympathetic nerves make usgray as we age. But the results provide hope that we may someday be able tofight to hold onto our natural hair color—and avoid that monthly flight to thehairdresser.
—Karen Hopkin
[重难点词汇、短语]（点击展开/收起）
guillotine: n. 断头台；裁切机
lock: n. 一缕头发
melanocyte: n. 黑色素细胞
follicle: n. 卵泡；滤泡；小囊
cortisol: n.皮质醇
stress hormone: 应激激素
adrenal: adj. 肾上腺的
sympathetic nervous system: 交感神经系统
[参考译文]（点击展开/收起）
传说玛丽·安托瓦内特（MarieAntoinette，法国国王路易十六的王后）在上断头台之前头发一夜变白，压力真的能对头发颜色产生如此戏剧性的效果吗？一项新的小鼠研究得出结论，压力会让神经过度活化，从而导致动物毛发褪色，这可能也包括我们的头发。
哈佛干细胞研究所（HarvardStem Cell Institute）的研究人员对压力和毛发颜色课题很感兴趣，所以他们决定细致观察一下这些能够生成黑色素细胞的干细胞，黑色素细胞能将色素传递到每一个毛囊。干细胞成为了一个显然的研究对象。
该研究的资深作者Ya-ChiehHsu说：“因为干细胞数量的变化表现为毛发颜色的变化，而毛发颜色的变化会非常明显，很容易识别出来。”
一开始，她和同事让小鼠面临一些啮齿动物常见的压力，例如倾斜笼子、弄湿鼠窝，或者一整晚亮着灯。
“那我们发现了什么呢？我们发现压力确实让小鼠‘早生华发’。但是，我们花了挺长时间，才真正锚定了这一过程发生的原因。”
首先，他们认为可能是免疫系统攻击了生黑色素干细胞。
“然而，缺乏免疫细胞的小鼠仍然在压力之下过早地长出白发。”
然后，他们认为关键因素可能是皮质醇，一种典型的应激激素。
“但当我们移除小鼠的肾上腺，让它们无法产生皮质醇样激素时，压力仍会让它们的毛发变成灰白色。”
接下来，她们将注意力转向了交感神经系统，这一系统协调全身对压力的反应，包括典型的战斗或逃避反应。这些神经一直延伸到我们的肌肉、器官，对的，甚至毛发。
“神经末梢就像丝带一样，缠绕着每一个毛囊。”
Ya-Chieh Hsu团队切断这些神经联系后，干细胞得以幸免，这让动物们即使面对轻微的病痛，毛发仍然保持乌黑靓丽。该研究发现发表在《自然》（Nature）杂志上。
目前还不清楚，随年纪增长的头发变白是否源于同样的交感神经。但研究结果带来了一种可能性，那就是某一天我们也许能够努力留住自己的天然发色，避免每个月去美发沙龙和发型师缠斗一番。
翻译：阿金
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