Effects of exercise on behavior and serum cortisol in depression due to chronic mild stress

Objective To investigate the effects of exercise on behavior and serum cortisol levels in depression caused by chronic,unpredictable,mild stress(CUMS).Methods Forty-eight male Sprague-Dawley rats were randomly divided into 3 groups:A,B and C.Each group was then divided into 3 subgroups:a blank control subgroup,a model subgroup,and an intervention subgroup.CUMS such as unpredictable forced swimming in cold water,electric stimulation of the animals'feet and shaking of the cage was used to establish a model of depression.Swimming exercise was administered as a therapeutic intervention.In group A it was administered while the animals were under stress,while in groups B and C,exercise was administered before and after the depression model had been established.Open-field test and fluid consumption data were recorded during the whole procedure.At the end of the experiment,radioimmunity assays were used to measure the levels of serum cortisol.Results Rats exposed to CUMS showed reduced water consumption;a preference for sucrose solutions;and decreased squares crossed,less rearing and increased bowel movement in open-field test.All of these changes were mitigated by the exercise performed while the animals were under stress,but not by exercise before or after the depression model had been established.Rats exposed to CUMS showed significant increases in serum cortisol,which was mitigated by exercise prior to and during stress.Conclusion Different exercise routines have different effects on behavior and serum cortisol levels in depressive rats under chronic unpredictable mild stress.Exercise has cumulative effects in decreasing the serum level of cortisol,but has only immediate effects on the behavior of depressive rats. Key words: Exercise training; Depression;  Rats;  Behavior;  Serum cortisol