Postnatal development in most mammals is accompanied by the acquisition of controls of ingestion. In rodents, the initial and default controller appears to be gastric stretch. In the second week of life, rat pups acquire the ability to sense the presence of nutrients within the gut and appropriately modulate ingestion. In the third week of life, rat pups start to become weaned from the dam's milk and begin independent ingestion. There have been strong indications that neuropeptide Y is a stimulator of ingestion in adults, although there was very little information in pups. Dr. Gerard Smith initiated a series of studies that provide strong evidence to indicate that hypothalamic neuropeptide Y (NPY) neurons are strong candidates for providing the ability of preweaning rat pups to modulate ingestion according to caloric intake. Moreover, the studies also suggest that the overactivity of hypothalamic NPY neurons presage the onset of hyperphagia in syndromes associated with defects in leptin signaling.