Nature and nurture effects of voluntary activity and nutrition on energy balance and nutrition : a study in mice

Besides differences in the level of planned physical activity (which is sometimes necessary to deal with environmental challenges), animals and human beings can also greatly differ in the display of voluntary activity. The latter is regarded as a complex trait linked to several subordinate traits, which determine individual variation in sustainable emotional and physical/metabolic health. The present thesis focused on these relationships in selected mouse lines for high voluntary wheel running behavior and in a randomly bred control line. Even without running wheels, activity selected mice show higher spontaneous cage activity than non-selected mice. In our studies, we observed that activity selected mice have higher levels of anxiety, yet show more extravert and routine-like behaviors than control mice. Secondly, activity selected mice turn over energy at a higher rate, and are more obesity-resistant when fed a high-fat diet than controls. These characteristics may be adaptive in animals covering relatively large natural habitats. During reproduction and particularly lactation, however, selected mothers and their offspring are more efficiently gaining weight than controls. Cross-fostering of pups between activity selected and control mothers revealed that prenatal maternal/genetic factors are more important than postnatal environmental factors in determining physical and behavioral characteristics of these animals later in life. These studies highlight (i) the powerful role of voluntary physical activity in the prevention of metabolic and potentially mental diseases; and (ii) the use of selective breeding as a tool to study complex traits and their contributions to complex diseases such as obesity, depression and related abnormalities. (Summary)