Regular voluntary exercise reduces anxiety-related behaviour and impulsiveness in mice

We embarked on a study to delineate the behavioural changes in mice after 4 weeks of voluntary exercise. As an initial behavioural characterization, we exposed the control and exercising mice to a modified hole board and an open field test. As compared to control mice, exercising animals showed clear signs of increased behavioural inhibition (e.g. a longer latency to enter unprotected areas), suggesting increased anxiety in these animals. In addition, the exercising mice were reluctant to spend time in the open field's centre during the beginning of the 30-min open field test, but compensated for this at later times. Paradoxically, the exercising animals showed more rearings on the board of the modified hole board, indicating decreased anxiety. Thus, the behavioural inhibition seen in exercising mice is likely to represent decreased stress responsiveness at the behavioural level which can also be interpreted as reduced impulsiveness. To clarify whether voluntary exercise evolves in more or less anxiety-related behaviour, we exposed animals to the elevated plus-maze and the dark-light box, two selective tests for unconditioned anxiety. Clearly, compared to the control animals, exercising mice spent significantly more time on the open arm of the plus-maze and spent double the amount of time in the light compartment of the dark-light box. Taken together, we conclude that long-term voluntary exercise appears to result in decreased anxiety-related behaviour and impulsiveness. Thus, our observations fit into the concept that regular exercise strengthens endogenous stress coping mechanisms, thereby protecting the organism against the deleterious effects of stress. (C) 2004 Elsevier B.V. All rights reserved.