The researchers used 58 mice for their study. They put hormones in the
drinking water. They considered chronic doses to be 17 to 18 days of
exposure and acute doses were 24 hours of exposure.
Then they used a standard test to evaluate anxiety in animals. Mice
that received the stress hormone for more than two weeks took
significantly longer to emerge from a small dark compartment into a
brightly lit open field. They seemed more fearful and were less willing
to explore their new environment. Chronic exposure to corticosterone
also dulled their reactions to a startling stimulus. This was another
sign that their nervous system was overwhelmed.
This is likely the first experiment that compared the effects of chronic
corticosterone with the effects of acute corticosterone on anxiety-like
behavior. These new findings did not surprise researchers, especially
since more than half of the people with Cushing's disease, in which a
disordered adrenal system releases too much cortisol, have depression
and anxiety.
Researchers already knew that the "anxious-retarded" subtype of
depression is commonly associated with disruption of that same hormonal
system. They also were aware that people getting corticosteroid therapy
for inflammatory and other disorders have increased mood-related side
effects, including anxiety and depression. Another reason doctors have
suspected that stress causes depression is because higher glucocorticoid
levels for chronic periods have been linked to increased activity in
anxiety-related brain regions such as the amygdala in both rodents and
humans.
The authors wrote, "Our results suggest that chronically high levels of
cortisol, which occurs in Cushing's disease and some subtypes of
depression, can increase anxiety on the one hand and dull responses to
external stimuli on the other." The difference between the responses to
acute and chronic hormone exposure strengthen the view that
very-short-term or acute exposure, they add, "may be adaptive, whereas
chronic exposure has detrimental effects on brain and behavior."
It is hoped the research will help doctors design new psychiatric drugs
that treat the causes of depression rather than the peripheral
disease-related phenomena. Ardyflo and Kim speculate that drugs that
reverse or block the deleterious effects of chronically elevated stress
hormones may help guard against some types of anxiety symptoms in
depression, citing the preclinical evidence in rats. The
research appears in the April issue of Behavioral Neuroscience, which is
published by the American Psychological Association.
By Dan Wilson
Best Syndication
Books on the Mind
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