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  

guillotine: n. 斷頭臺；裁切機

lock: n. 一縷頭發(fā)

melanocyte: n. 黑色素細胞

follicle: n. 卵泡,；濾泡,；小囊

cortisol: n.皮質醇

stress hormone: 應激激素

adrenal: adj. 腎上腺的

sympathetic nervous system: 交感神經系統(tǒng)

傳說瑪麗·安托瓦內特（MarieAntoinette，法國國王路易十六的王后）在上斷頭臺之前頭發(fā)一夜變白,，壓力真的能對頭發(fā)顏色產生如此戲劇性的效果嗎,？一項新的小鼠研究得出結論，壓力會讓神經過度活化,，從而導致動物毛發(fā)褪色,，這可能也包括我們的頭發(fā)。

哈佛干細胞研究所（HarvardStem Cell Institute）的研究人員對壓力和毛發(fā)顏色課題很感興趣,，所以他們決定細致觀察一下這些能夠生成黑色素細胞的干細胞,，黑色素細胞能將色素傳遞到每一個毛囊。干細胞成為了一個顯然的研究對象,。

該研究的資深作者Ya-ChiehHsu說：“因為干細胞數(shù)量的變化表現(xiàn)為毛發(fā)顏色的變化,，而毛發(fā)顏色的變化會非常明顯，很容易識別出來,?！?/span>

一開始，她和同事讓小鼠面臨一些嚙齒動物常見的壓力,，例如傾斜籠子,、弄濕鼠窩，或者一整晚亮著燈,。

“那我們發(fā)現(xiàn)了什么呢,？我們發(fā)現(xiàn)壓力確實讓小鼠‘早生華發(fā)’。但是,，我們花了挺長時間，才真正錨定了這一過程發(fā)生的原因,?！?/span>

首先，他們認為可能是免疫系統(tǒng)攻擊了生黑色素干細胞,。

“然而,，缺乏免疫細胞的小鼠仍然在壓力之下過早地長出白發(fā)?！?/span>

然后,，他們認為關鍵因素可能是皮質醇,，一種典型的應激激素。

“但當我們移除小鼠的腎上腺,，讓它們無法產生皮質醇樣激素時,，壓力仍會讓它們的毛發(fā)變成灰白色?！?/span>

接下來,，她們將注意力轉向了交感神經系統(tǒng)，這一系統(tǒng)協(xié)調全身對壓力的反應,，包括典型的戰(zhàn)斗或逃避反應,。這些神經一直延伸到我們的肌肉、器官,，對的,，甚至毛發(fā)。

“神經末梢就像絲帶一樣,，纏繞著每一個毛囊,。”

Ya-Chieh Hsu團隊切斷這些神經聯(lián)系后,，干細胞得以幸免,，這讓動物們即使面對輕微的病痛，毛發(fā)仍然保持烏黑靚麗,。該研究發(fā)現(xiàn)發(fā)表在《自然》（Nature）雜志上,。

目前還不清楚，隨年紀增長的頭發(fā)變白是否源于同樣的交感神經,。但研究結果帶來了一種可能性,，那就是某一天我們也許能夠努力留住自己的天然發(fā)色，避免每個月去美發(fā)沙龍和發(fā)型師纏斗一番,。

翻譯：阿金