Chronic Stress May Boost Anxiety
Short-Term Stress Doesn't Have the Same Effect, Tests on Mice Show
April 17, 2006 -- Being stressed out for a long period of time might
increase anxiety, a new study shows.
The study, published in Behavioral Neuroscience, lays some of the
blame on stress hormones. Those stress hormones -- such
as cortisol and corticotropin-releasing hormone -- can help respond to an
But if stress stays high instead of easing up, those hormones could boost
anxiety and lead to mood disorders. That's the theory explored in the new
The researchers included Paul Ardayfio, BSC, a graduate student in molecular
neurobiology at Harvard Medical School and its affiliate, Boston's McLean
Hospital. They studied female mice, not people, but the findings may hold clues
about how chronic stress affects mood disorders.
Brief or Constant Stress
Ardayfio and colleagues spiked the mice's drinking water with
corticosterone, a stress hormone. That way, they avoided stressing the mice out
Some mice got the spiked water for 17 or 18 days, mimicking long-term
exposure to the stress hormone. For comparison, the other mice only got the
spiked water for one day.
The mice got two tests, without any training to prepare for those tests. In
one test, mice in a dark part of a cage got the chance to explore a bright,
open part of a cage.
The mice who drank the spiked water day after day were more hesitant to
enter the exposed space. The researchers interpreted that hesitancy as
What's That Sound?
In the other test, the researchers exposed the mice to a high-frequency
You might expect that mice under constant corticosterone exposure would have
an exaggerated reaction to that sound. But that's not what happened.
The mice under long-term exposure to corticosterone had a dulled reaction to
that sound the first 10 times they heard it, the study shows.
Constant exposure to the stress hormone may have depressed those mice,
dimming immediate reactions, the researchers write. In other words, the study
suggests that long-term stress may have left those mice less prepared to handle
a stressful event instead of improving their stress reactions.