It has been revealed through a study by neuroscientists at Harvard Medical School and its affiliate Mclean Hospital that long-term exposure to stress hormone in mice directly results in the anxiety that often comes with depression.
April issue of Behavioral Neuroscience, which is published by the American Psychological Association, has this article.
This would be helpful in treating depression in humans. It appears likely that long-term exposure to cortisol actually contributes to the symptoms of depression.
Paul Ardayfio, PhD candidate, and Kwang-Soo Kim, PhD, were the lead researchers and got these results by exposing mice to both short-term and long-term durations of stress hormone, which in rodents is corticosterone. In humans, usually ongoing, chronic stress, such as caring for a spouse with dementia, rather than acute stress, has been associated with depression.
Using 58 mice, the researchers gave the hormone in drinking water so as not to confound the results with the stress of injection. Chronic doses were 17 to 18 days of exposure; acute doses were 24 hours of exposure.
Compared with mice given stress hormone for a day, mice given stress hormone for more than two weeks took significantly longer to emerge from a small dark compartment into a brightly lit open field, a common behavioral test of anxiety in animals.
Stress hormone can cause anxiety, which appears with depression. The authors say, 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 may be adaptive, whereas chronic exposure has detrimental effects on brain and behavior.