The role of intraoral and gastrointestinal cues in the control of sucking and milk consumption in rat pups.

Nutritive deprivation, suckling deprivation, gastronintestinal fill, and milk availability contribute to the control of sucking (as measured by jaw-muscle electromyograph) and ingestion of milk (provided via a tongue cannula) in 11-13-day-old rat pups. Depriving pups of the opportunity to suckle reliably increases subsequent sucking and milk intake. Intraoral delivery of milk also increases sucking, regardless of whether or not pups are suckling-deprived. Gastrointestinal preloads have no effect on sucking if pups are not receiving milk, but reliably block the increase in sucking which accompanies milk delivery. Finally, milk delivered to the pup's mouth prior to a suckling opportunity can either enhance or attenuate subsequent sucking depending on whether pups are allowed to consume milk while suckling. In all cases, a particular mode of sucking ("rhythmic" sucking) is most affected by experimental manipulation, and appears to be an important component of the pup's ingestive behavior.