Short‐ and long‐term effects of various milk‐delivery contingencies on sucking and nipple attachment in rat pups

Abstract

Varied milk delivery contingencies differentially affect sucking in rat pups as measured by jaw-muscle electromyographic activity. In Experiment 1 we found that 11-1 3-day-old pups sucked more frequently when receiving tiny intermittent pulses of milk than when receiving no milk, and continued to suck at a high rate for at least 30 min after cessation of milk delivery. In subsequent experiments we found that pups 13-18 days of age engaged in more frequent sucking if receiving milk continuously rather than intermittently, and that this increased rate of sucking persisted for at least 24 hr after cessation of milk delivery. Pups given experience with continuous milk delivery from 14 to 18 days of age also spent significantly more time attached to the nipple at 19 days of age than did pups in control groups. It was concluded that experience with different milk delivery schedules can affect subsequent sucking and nipple attachment behavior.Several investigators have demonstrated that 2-week-old rats traverse runways and mazes more efficiently when reinforcement consists of sucking a nipple which provides milk rather than sucking a nipple which does not (Letz, Burdette, Gregg, Kittrell, & Amsel, 1978;Kenny, Stolhoff, Bruno, & Blass, 1979). We are now finding that the pup's behavior while on the nipple is also affected by milk delivery. Eleven-to thrteenday-old pups engage in more frequent sucking while receiving milk than do pups which receive no milk (Brake, Sager, Sullivan, & Hofer, 1982). Rat pups are also capable of acquiring conditioned preferences for previously aversive olfactory stimuli when those stimuli are paired with milk delivery (Brake, 1981). These findings suggest that suckling rat pups might learn when and how to feed as a function of when and how they have been fed in the past.In this series of experiments we begin to test the hypothesis that specific milk delivery schedules have both immediate and long-term effects on sucking and nippleattachment behavior. In the 1st experiment we explore the short-term effects of milk R,eprint requests should be sent to Stephen C. Brake,

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

“…Although gastrointestinal preloads had no effect on sucking frequency durlng the "dry" test (as in Experiments 1 and 11), intraoral preloads seemed to stimulate sucking as much as milk delivered during the suckling test in Experiment I. Apparently, the stimulating effects of milk delivery are relatively long-lasting and do not necessarily depend on the pups receiving the milk while attached to the nipple (see Brake et al, 1982). However, with milk available during the test, not only did gastrointestinal preloads reduce sucking as in Experiments I and 11, but intraoral preloads also acted to reduce the stimulating effects of milk delivery.…”

“…In this experiment we tested the contribution of gastrointestinal factors to the increase in sucking which occurs following maternal separation (e.g. Brake & Hofer, 1980;Brake et al, 1979;Brake, et al, 1982). We reasoned that if gastrointestinal factors play a role in the elevation of sucking, then a 5% body-weight preload of milk administered before testing should attenuate this increase, just as 5% preloads depress milk consumption in suckling pups (Hall & Rosenblatt, 1978;Lorenz et al, 1982).…”

“…Brake, Department of Psychiatry, Montefiore Hospital and Medical Center, 111 East 210th Street, Bronx, New York 10467, U.S.A. & Hofer, 1980;Brake, Sullivan, Sager, & Hofer, 1982;Brake, Wolfson, & Hofer, 1979). At all ages, but particularly during the 1st 2 weeks, maternal deprivation increases the frequency of a mode of sucking which we call rhythmic sucking, while having little effect on more erratic, arrhythmic sucking.…”

Nursing interaction of Wistar rats is modified by prior experience of altered nursing bout length

“…Perhaps the most remarkable demonstration that learning and memorial processes can govern the pup's role in this system are the observed effects of altering milk delivery schedules and contingencies of reinforcement (Brake, Sullivan, Sager, & Hofer, 1982). Pups provided with milk through a tongue cannula while sucking on the teat of an anesthetized (nonmilk releasing) dam quickly acquired different sucking patterns according to the degree to which milk delivery was provided in relation to their sucking efforts.…”

“…'The behavior of the pups in the nursing situation has been shown to be influenced by prior learning experience and level of motivation (as induced by duration of deprivation) in regards to nipple attachment (Kenny & Blass, 1977) and to sucking patterns (Brake et al, 1988). Perhaps the most remarkable demonstration that learning and memorial processes can govern the pup's role in this system are the observed effects of altering milk delivery schedules and contingencies of reinforcement (Brake, Sullivan, Sager, & Hofer, 1982). Pups provided with milk through a tongue cannula while sucking on the teat of an anesthetized (nonmilk releasing) dam quickly acquired different sucking patterns according to the degree to which milk delivery was provided in relation to their sucking efforts.…”