Adipose tissues and obesity.

In rats and mice the adipose organ consists of different depots, the most important are: the dermic, subcutaneous and visceral depots. Some areas of these depots are brown in colour and correspond to brown adipose tissue, while most are white and correspond to white adipose tissue. Varying amounts of brown adipocytes are found in white areas. Brown adipocyte precursors are different from those of white adipocytes, but among the brown adipocytes found in white depots precursors with an intermediate morphology can also be found. Together with a rich vascular supply, brown areas receive abundant noradrenergic and sensory innervation. The gross anatomy and histology of the organ vary considerably in different physiological (cold acclimation, warm acclimation, fasting, lactation) and pathological (obesity) conditions, and also many important genes such as leptin and uncoupling protein 1 are expressed differently in the two cell types. These basic mechanisms should be taken into account when addressing the physiopathology of obesity and its treatment.