Chronobiological disturbances with hyperthermia and hypercortisolism induced by chronic mild stress in rats.

The chronic mild stress (CMS) model has been established as a realistic model of depressive disorder as it simulates anhedonia. In the present study, the consumption of sucrose solution was decreased in the rats exposed to CMS, which coincided with many published studies. Since depression is a multifaceted disorder, and a number of symptoms may be present, including circadian rhythm disturbances, we attempted to find the chronobiological abnormalities in CMS rats. After 4-week of the stress procedure, the rhythmic pattern of rectal temperature in the CMS group was extinguished. In particular, the temperature in the CMS group in the light phase was significantly higher than that in the control group. The plasma corticosterone levels in the CMS group were remarkably increased in the light phase compared to the control group, but not in the dark phase. It was concluded that the CMS procedure caused the disturbance of circadian rhythms with hyperthermia and hypercortisolism.