Physiological Parameters in the Blood of a Murine Stress-Induced Depression Model before and after Repeated Passive Exercise

BACKGROUND Animal models are necessary to study the mechanism underlying the effects of exercise on depression but an effective procedure for exercise treatment and exercise effects on physiological parameters in a specific depression model need to be characterized. METHODS Physiological parameters including lactate, partial pressue of O₂ (pO₂) and CO₂ (pCO₂) saturated O₂ (sO₂), pH, HCO₃, total CO₂ (TCO₂), and base excess extracellular fluid (BEecf) levels in the blood were measured after treatment with passive exercise in normal mice and a stress-induced depression model. RESULTS Normal mice or mice that were subjected to daily 2-hour restraint for 14 days (2 hours × 14 days of restraint) were placed on a running wheel that was rotating at a speed of 9 m/min for 1 hour per day for 1 to 21 days. After repeated exercise in mice that were previously subjected to 2 hours × 14 days restraint, plasma lactate levels decreased, the levels of pO₂, sO₂, and pH tended to increase, and the levels of pCO₂ decreased in the absence of significant changes in HCO₃, TCO₂, and BEecf. However, none of these changes were additive to the stress effects or were much more severe than those induced after repeated passive exercise in normal mice. CONCLUSION These results suggest that passive exercise for 1 hour daily for 14 to 21 consecutive days on a running wheel rotating at a speed of 9 m/min may be used as an exercise protocol without inducing severe additive effects on physiological burdens.