Consistent with an important role of NPY in the regulation of energy homeostasis, intracerebroventricular or hypothalamus-specific administration of NPY to normal rodents leads to defects characteristic of obesity, including hyperphagia, accelerated body weight gain, hyperleptinemia, hypercorticosteronemia, hyperinsulinemia and increased adiposity [18], [19], [20], [21]. This evidence concerns the gene NPY and obesity due to melanocortin 4 receptor deficiency.