Feelings of anxiety following a harrowing experience are normal; they help us survive in a world of real threats. But as time passes and a potential threat diminishes, stress, in turn, ought to die down. It doesn't for everyone. Sufferers of post-traumatic stress disorder (PTSD), as well as anxiety disorders and depression , are unable to switch off their feelings of extreme stress long after the trauma that induced it has ended.
Researchers at the Weizmann Institute of Science in Israel have identified the proteins that switch off the stress response. As reported in the Proceedings of the National Academy of Sciences, they are urocortin 1, 2 and 3, members of a family of proteins present in all mammals.
Alon Chen, the neurobiologist who led the research, and his team made this discovery by inflicting trauma on two groups of lab mice - a control group, and a group of mice that had been genetically engineered to lack the three urocortin proteins. Before the trauma, neither group of mice showed signs of stress. Immediately afterward, they both did.
A full 24 hours later, though, the control mice had overcome the stress and anxiety caused by the trauma, and were back to normal. The genetically engineered mice, on the other hand, were still suffering from the same level of stress they exhibited immediately after the trauma ended the day before.
Chen and his colleagues discovered that, in the control mice, urocotrin 1, 2 and 3 were activating a program of gene expression that returned the mice to a normal neurophysiological state when the time was right. That gene expression program wasn't happening in the mice that lacked the urocotrin proteins.
The findings opens up a line of inquiry: Perhaps the urocotrin proteins of those who suffer from such diseases as anxiety disorders, depression , anorexia and PTSD are under-performing. And if that's the case, researchers can look for ways to give them a boost.
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