Emotional consequences of wheel running in mice: which is the appropriate control?

An overview of the literature on the emotional impacts of wheel running reveals contradictory findings. Among the hypotheses underlying such a discrepancy, that related to the different housing conditions of the controls, i.e., standard housing without any object or housing with blocked running wheels, merits attention. We addressed this point in C57Bl/6N mice by examining the consequences of chronic wheel running on anxiety, context fear recall, and behavioral despair compared either to standard control housing or to housing with blocked wheels. Compared to standard housing, wheel running proved anxiolytic while facilitating fear memory. On the other hand, wheel running increased behavioral despair but influenced neither anxiety nor fear memory when compared to housing with blocked wheels. This study suggests that investigations aimed at measuring the emotional consequences of wheel running should take into consideration the housing conditions of the controls to which are compared the runners.