The Ontogeny of Neurochemical Systems for Control of Feeding and Drinking

Abstract

It is common knowledge that suckling gives way to feeding and drinking in the ontogeny of young mammals. The transition from nursing like an infant to eating and drinking like a miniadult is a conventional milestone in their development. But few appreciate the completeness with which ingestive behavior is changed when neonates make this transition. When suckling, the neonate is extracting a single fluid from a maternal teat positioned deep in its pharynx, to which it is attached almost continuously, and on which it sucks rhythmically. When feeding and drinking the juvenile forages for food and water as separate commodities which are ingested with behaviors (licking, biting, chewing) that are more varied than sucking and distinctly different from it. Although both result in the ingestion of food and water the behaviors of suckling, on the one hand, and of feeding and drinking, on the other, are entirely different.

Research of the past decade on the newborn rat has yielded several insights into how this transition is made. First, the newborn rat is competent at birth to identify a maternal nipple by its odor (1, 2) and to contribute to the control of its milk intake by utilizing signals from the upper GI tract (3) while it remains attached to a nipple without interruption as long as the dam is with her litter (4). The mechanisms for these behaviors are well developed at birth. Second, as it matures, behaviors are added to the suckling's repertory that make it more competent for ingestion, both for suckling and for ingestion while away from the dam. At 8 or 10 days of age the animal's nutritive state gains control of its attachment behavior (5).