Energy homeostasis and locomotor activity: the role of leptin and of the melanocortin system

Twin studies indicate that genetic factors are important determinants of the variance of physical activity. Several genes or loci which may affect physical activity are also involved in body weight homeostasis. Polymorphisms of the melanocortin-4 and leptin receptors have repeatedly been associated with the level of physical activity. Clearly, the regulation of locomotor behavior is closely inter-connected with the pathways involved in energy homeostasis. In rodents, the reduction in leptin levels that physiologically occur in the event of acute food deprivation or shrinkage of the fat mass consequent to prolonged caloric restrictions is associated with a decrease in total activity and an increase in food anticipatory activity; these actions are likely aimed at minimizing energy wasting, while stimulating at the same time the locomotor behavior necessary to the acquisition of nutrient resources for survival.