A single moment of severe stress could kill off new nerve cells in the brain and lead to depression, according to a study taken up by the Rosalind Franklin University of Medicine and Science in North Chicago.
The team led by Daniel Peterson put a young rat in a cage with two older rats for 20 minutes. The older rats quickly cornered, pinned down and often bit the younger one, the researchers report.
The younger rats became fearful and acted depressed in the presence of bigger animals. Their stress hormone levels were six times higher than in other young rats that did not undergo the encounter with the bullies.
The team had thought that that elevated stress hormone levels would prevent the development of young nerve cells in the victim rats or kill them off immediately.
Instead, when the rats' brains were examined under a microscope, the researchers found new cells had developed but that only about a third of them survived a week later.
That means in that one week it could be possible to medically intervene and save the nerve cells.
Dr. Peterson plans to examine what role antidepressants might play in rescuing the cells.
However other experts believe there is evidence to suggest that mild stress could be protective. The rule of thumb seems to be - a little stress is good for you but severe or unpredictable stress is bad, they contend.