Ontogeny of suckling in rats: Transitions toward adult ingestion.

Abstract

Suckling behavior of neonatal rats on their own anesthetized mother was studied from the day of birth until after weaning (35 days). Even newborn rats were capable of nipple attachment without maternal assistance. Before 11-13 days of age, pups deprived of suckling for 22 h and nondeprived pups quickly attached to their mother''s nipples, sucked, and remained attached to the nipple though no milk delivery occurred. Then behavior underwent at least 3 changes: after 11-13 days of age latency to attach became considerably elevated in nondeprived pups; a 2nd change in latency occurred at 23-25 days of age, when nondeprived pups no longer even attached to the nipples of anesthetized mothers; and about 14 days of age, deprived pups began to shift from one nipple to the next after initial attachment. These developmental changes were seen in other test situations in which pups were placed directly on a nipple and not required to search and when various periods of deprivation were utilized. These transitions were not critically dependent on the onset of visual function or on the pup''s experience with food other than mother''s milk. Suckling is not an unmodified reflex but is an appetitive behavior that undergoes a series of changes during development. These transitions constitute major developmental events in the ontogeny of rat ingestive behavior.