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

Abstract

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. lntraoral 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 whilc 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.There are at least 2 ways that a suckling infant might control the amount of milk it consumes from the nipple. It might vary the amount of time it spends attached to the nipple or it might vary the frequency and intensity of its suckling while on a nipple. Infant rats do not appear to employ the 1st strategy until they are about 15 days old. Before this age, a pup's latency to attach to a nipple, the time it spends attached to a nipple, and the number of times it will shift from 1

Mercaptoacetate decreases latency to initiate independent ingestion, but not suckling, in preweanling rats

“…For example, one study found that latency to attach to a nipple in 11-to 13-day-old pups that had been deprived for 22 hr was similar to latency to attach in nondeprived pups with latencies in both groups less than 150 s (Hall, Cramer, & Blass, 1977). In addition, manipulations which are known to alter the intake of young pups in the suckling context (e.g., gastric fill, deprivation) do not appear to do so by altering appetitive behaviors such as latency to attach, but instead alter the vigor of suckling behavior once attached (e.g., Brake, Sager, Sullivan, & Hofer, 1982;Brake, Wolfson, & Hofer, 1979;Drewett, Statham, & Wakerley, 1974). However, by 14 to 16 days of age, the latency of attachment of nondeprived pups has been reported to increase, and prolonged deprivation has been demonstrated to decrease latency to attach when control pups are demonstrating these longer latencies (Hall et al, 1977).…”

Hidden Regulators Within the Mother–Infant Interaction

“…By studying a number of additional systems, such as those controlling sleep-wake states (Hofer, 1976), activity level (Hofer, 1975), sucking pattern (Brake, Sager, Sullivan, & Hofer, 1982), and blood pressure, we found different components of the mother-infant interaction, such as olfaction, taste, touch, warmth, and texture, that either up-regulated or downregulated each of these functions. Thus we concluded that, in maternal separation, all these regulatory components of the mother-infant interaction are withdrawn at once.…”

Learning as adaptation of the infant

“…Not only is the survival or maintenance of suckling dependent on experience, but the "microstructure" of suckling behavior can be shaped by experience. Brake et al (19) made electromyographic (EMG) recordings of digastric (jaw) muscles and described different types of suckling patterns. They used an intraoral cannula to deliver milk according to different schedules to the mouths of pups that were attached to the nipples of an anesthetized dam.…”