Mouse models for the central melanocortin system.

Obesity is characterized by an excess storage of body fat and promotes the risk for complex disease traits such as diabetes mellitus and cardiovascular diseases. The obesity prevalence in Europe is rising and meanwhile ranges from 10 to 20% in men and 15-25% in women. Body fat accumulation occurs in states of positive energy balance and is favored by interactions among environmental, psychosocial and genetic factors. Energy balance is regulated by a complex neuronal network of anorexigenic and orexigenic neurons which integrates peripheral and central hormonal and neuronal signals relaying information on the metabolic status of organs and tissues in the body. A key component of this network is the central melanocortin pathway in the hypothalamus that elicits metabolic and behavioral adaptations for the maintenance of energy homeostasis. Genetic defects in this system cause obesity in mice and humans. In this review we emphasize mouse models with spontaneous natural mutations as well as targeted mutations that contributed to our understanding of the central melanocortin system function in the control of energy balance.