NEW ORLEANS --- It is well accepted that regular exercise reduces stress and improves mood, but just how this occurs is unknown.
Neuroscientists at Northwestern University believe that by studying the effects of exercise on circadian rhythms in mice, they may better understand how exercise attenuates the effects of stress and depression.
The initial findings of their study will be presented at the Society for Neuroscience's annual meeting in New Orleans Oct. 25-30. Collaborating on this ongoing works are researchers from the Northwestern University Center for Circadian Biology and Medicine and the Asher Center for the Study and Treatment of Depressive Disorders.
They found that chronic stress influenced daily activity rhythms during the time the mice were exposed to stress and that it induced depressive-like behaviorl changes which persisted for weeks after stressful conditions had been removed. Most dramatically, both changes in rhythms and behavior were more pronounced in animals without access to running wheels, suggesting that exercise may have protective properties against the effects of stress.
Depressed patients have disturbed patterns of sleep, variations in the patterns of hormonal rhythms and changes in the rhythm of body temperature. All of these changes suggest that the body's biological clock, which is responsible for generating these circadian rhythms, is malfunctioning. But the exact nature of the relationship between depression and circadian rhythm disturbances is unclear.
Both animal and human studies have shown that the acute effects of exercise include increased levels of the hormones cortisol, norepinephrine, serotonin and beta-endorphins. These substances play a major role in the body's response to stress, both psychologically and physically, and therefore may be involved in mood regulation after exercise. However, in humans, it is difficult to separate the psychological from the physiological factors that are involved in mood improvement after exercise.
The Northwestern group chose the mouse for this study because a great deal of genetic information is known about it, including the existence of the Clock gene, which controls circadian rhythms. The particular strain of mice they used has very strong circadian rhythms and was the mouse in which they originally isolated the Clock gene.
The Northwestern researchers believe further studies using the mouse model, as well as the additional genetic data that will be gained from these experiements, will increase understanding of the mechanisms involved in the effects of exercise on stress.
The study was conducted by Fred W. Turek, professor and chair of neurobiology and physiology and director of the Northwestern University Center for Circadian Biology and Medicine; Leah Solberg; Teresa H. Horton, research assistant professor neurobiology and physiology; Aisha Satar; Frank W. Farkas; and Janice H. Urban.
(Editor's note: Dr. Turek may be reached from Oct. 25-30 through the message center at the Ernest Morial Convention Center in New Orleans at 504-670-5000.