The loop system between neuropeptide Y and leptin in normal and obese rodents

Over the years, the work of research laboratories in Baton Rouge (USA), Seattle (USA) and Geneva (Switzerland) have reached analogous conclusions regarding the main etiology of obesity as studied in animals: it largely lies within the brain, notably within the hypothalamus. The hypothalamus is indeed known to modulate food intake and energy partitioning, while the periphery has also been proposed to feed-back on the central nervous system (CNS) to provide information on the state of body energy stores, the two together constituting a loop system connecting the brain to the periphery (1,2,3). This etiologic viewpoint of a pivotal role of the hypothalamus in obesity syndromes has been strengthened by the discovery of one hypothalamic neuropeptide and one peripheral (adipose tissue) hormone, respectively neuropeptide Y (4), and quite particularly, leptin (5). As neuropeptide Y produces hyperphagia (6, 7) and as leptin produces hypophagia in normal animals (8,9,10), the loop system just mentioned was thought to comprise functional relationships, at least between these two factors. Other evidence also suggested that such a loop system was altered in obese animals.