Swimming exercise may not alleviate the depressive-like behaviors and circadian alterations of neuroendocrine induced by chronic unpredictable mild stress in rats

Abstract

Many clinical studies have shown that circadian rhythmic abnormalities are strongly associated with major depression. Meanwhile a large number of researches have indicated that physical exercise could effectively reduce the stress impairment and improve one’s mood, cognition and self-concept. We examined the effects of chronic unpredictable mild stress (CUMS) on rodent behaviors and the circadian rhythm of hormone and peptide levels in the plasma. We collected blood samples at 4-h intervals for 24h to examine circadian rhythmic expression of corticosterone, melatonin and vasoactive intestinal peptide (VIP). We found that CUMS led to depressive-like behaviors and inversed rhythm in corticosterone and blunted circadian rhythms in melatonin and VIP compared to control group. Levels of corticosterone showed no differences from control group. But levels of melatonin were decreased and VIP was increased compared to control group, respectively. Swimming exercise could not alleviate the depressive-like behaviors and the blunted circadian rhythmic expression of blood hormone and peptide, also could not rescue levels of melatonin and VIP. These findings indicate that swimming exercise as a physical exercise, unexpectedly, may not act as a protect factor rather than as an additional stress in the present study. It has no effect on the depressive-like behaviors and alterations of blood hormone and peptide whether in circadian rhythm or in blood levels induced by CUMS.