But the sympathetic nervous system's response to stress is generally one of last resort, activated only in a dire emergency when other systems are too slow or have failed.
Marie Antoinette's hair suddenly turned white before the ill-fated French queen was taken to the guillotine to have her head chopped off, according to some historical accounts. In more recent history, John McCain experienced severe injuries as a prisoner of war during the Vietnam War - and lost color in his hair.
After much trial and error, scientists were able to link the graying of hair to the sympathetic nerve system, which controls our responses to stressful situations.
Hsu found that even during normal stress (not the fight-or-flight kind), the sympathetic nervous system is active, and produces the chemical norepinephrine, which leads to increased muscle contraction, including in the heart.
The researchers initially suspected that an stress-induced immune attack might be targeting the melanocyte stem cells, but that hypothesis did not pan out. But once more, it was a dead end.
Now, Harvard scientists have discovered how stress can suddenly sap hair of its color.
"Stress continuously elevates stages of the hormone cortisol within the physique, so we idea that cortisol could well play a process", Hsu acknowledged. It comprises a network of nerves that go everywhere including the skin, in which they are like ribbons wrapping around each hair follicle and are very close to the melanocyte stem cells.
Within the hair follicle, sure stem cells act as a reservoir of pigment-producing cells.
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The connection between stress and the nervous system and pigment-producing cells may be an evolutionarily conserved association among different species-cephalopods, including squid and octopi, also change color when under stress.
Researchers chanced on that the norepinephrine from sympathetic nerves causes the stem cells to activate excessively.
"After we began to jog trying this, I anticipated that stress changed into once wicked for the physique - however the detrimental influence of stress that we stumbled on changed into once beyond what I imagined", Hsu acknowledged.
The answer wasn't so easy to pin down, says Ya-Chieh Hsu, a stem cell biologistat Harvard University.
The damage to the pigment-regenerating cells, she added, is "permanent".
"Acute stress, particularly the fight-or-flight response, has been traditionally viewed to be beneficial for an animal's survival. Nonetheless in this case, acute stress causes eternal depletion of stem cells", acknowledged postdoctoral fellow Bing Zhang, the lead creator of the look.
The collaborators included Isaac Chiu, assistant professor of immunology at Harvard Scientific College who studies the interplay between anxious and immune systems.
"We know that peripheral neurons powerfully regulate organ function, blood vessels, and immunity, but less is known about how they regulate stem cells", Chiu said. "An interesting hypothesis could be that stress is an accelerated aging process".
The findings can help illuminate the broader effects of stress on various organs and tissues. Most of those systems come back online when the threat diminishes, but the new study shows some are damaged permanently if the stress is great enough.