NPY and Y receptors: lessons from transgenic and knockout models. 
Neuropeptide Y (NPY) in the central nervous system is a major regulator of food consumption and energy homeostasis.  It also regulates blood pressure, induces anxiolysis, enhances memory retention, affects circadian rhythms and modulates hormone release.  Five Y receptors (Y1, Y2, Y4, Y5 and Y6) are known to mediate the action of NPY and its two other family members, peptide YY (PYY) and pancreatic polypeptide (PP).  Increased NPY signaling due to elevated NPY expression in the hypothalamus leads to the development of obesity and its related phenotypes, Type II diabetes and cardiovascular disease.  Dysregulation in NPY signaling also causes alterations in bone formation, alcohol consumption and seizure susceptibility.  The large number of Y receptors has made it difficult to delineate their individual contributions to these physiological processes.  However, recent studies analysing NPY and Y receptor overexpressing and knockout models have started to unravel some of the different functions of these Y receptors.  Particularly, the use of conditional knockout models has made it possible to pinpoint a specific function to an individual Y receptor in a particular location.