Abstract
Acute and chronic stress have been reported to have differing effects on physical activity in rodents, but no study has examined a chronic stress protocol that incorporates stressors often experienced by rodents throughout a day. To examine this, the effects of the Unpredictable Chronic Mild Stress (UCMS) protocol on voluntary running wheel activity at multiple time points, and/or in response to acute removal of chronic stress was determined. Twenty male Balb/c mice were given access and accustomed to running wheels for 4 weeks, after which they were randomized into 2 groups; exercise (EX, n = 10) and exercise with chronic stress using a modified UCMS protocol for 7 hours/day (8:00 a.m.-3:00p.m.), 5 days/week for 8 weeks (EXS, n = 10). All mice were given access to running wheels from approximately 3:30 p.m. to 7:30 a.m. during the weekday, however during weekends mice had full-time access to running wheels (a time period of no stress for the EXS group). Daily wheel running distance and time were recorded. The average running distance, running time, and work each weekday was significantly lower in EXS compared to EX mice, however, the largest effect was seen during week one. Voluntary wheel running deceased in all mice with increasing age; the pattern of decline appeared to be similar between groups. During the weekend (when no stress was applied), EXS maintained higher distance compared to EX, as well as higher daily distance, time, and work compared to their weekday values. These results indicate that mild chronic stress reduces total spontaneous wheel running in mice during the first week of the daily stress induction and maintains this reduced level for up to 8 consecutive weeks. However, following five days of UCMS, voluntary running wheel activity rebounds within 2–3 days.
Highlights
Acute stress may exert both positive and negative physiological responses, but chronic stress is known to result in many pathological conditions, including depression and other altered behaviors [1,2,3]
Stress effects on running wheel activity interaction (p
The primary findings are that daily stress reduced voluntary wheel running behavior, and that this effect was most pronounced during the first week, after which the difference between stressed (EXS) and non-stressed (EX) mice remained similar for the duration of the study
Summary
Acute stress may exert both positive and negative physiological responses, but chronic stress is known to result in many pathological conditions, including depression and other altered behaviors [1,2,3]. Stress effects on running wheel activity that mice bred for high voluntary wheel running have been reported to have an enhanced HPA activation as indicated by elevated glucocorticoid levels [6] The investigators attributed these latter responses to the chronically high glucocorticoid levels, which could be an evolutionary response to the greater need for energy with high aerobic capacity. It was reported in these mice that acute stress (i.e. running wheel deprivation) resulted in an increased depressive-like behavior defined as reduced swimming activity when compared with control animals [7]. This becomes especially important if mice are continuously exposed to these types of stressors in their normal environment
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