Differential effects of upper gastrointestinal fill on milk ingestion and nipple attachment in the suckling rat

Abstract

Milk intake and nipple attachment behaviors were studied in the natural suckling situation after gastrointestinal preloading. Rat pups, deprived of their dam for 9 hr at 1, 10, or 20 days of age, were preloaded by gavage with volumes ranging from 2 to 16% of their body weight and returned to suckle. Preloads of artificial bitch's milk decreased the intake of mother's milk in a volume-related manner at all ages. At 1 and 10 days 4% preloads decreased milk intake without affecting attachment behaviors; larger preloads of 8 and 16% decreased intake and reduced the incidence of attachment. At 20 days of age small and large preloads decreased both incidence of attachment and milk intake. Preloads up to 8% of body weight had no effect on latency to attach at any age. Complete subdiaphragmatic bilateral vagotomy increased milk intake of 7-9 day-old pups fed automatically through an anterior mouth cannula in a nonsuckling situation. Vagotomy combined with spinal cordotomy (T2-T3) resulted in a synergistic hyperphagia and massive distension of the upper GI tract. The results indicate that suckling rats can control their intake of mother's milk while remaining attached to a nipple as early as 1 day of age. The suppression of ingestion in response to GI filling appears to be mediated by visceral afferent activity. Conversely, attachment behaviors are less affected by GI fill. This suggests that ingestive behaviors and attachment behaviors have different controls during the 1st 10 days of postnatal development.

Filling the gut activates paradoxical sleep in suckling rats

“…The sleep data, when considered with the observations of attachment behaviors, indicate that the gut load at 4% was optimal for activating PS and reducing SWS without interfering with nipple attachment ( Table 1). Knowing that this volume of milk in the stomach is within the normal range for pups at this age (Lorenz et al, 1982) and that all pups remained attached to the dam, the data suggest postingestive satiety. The idea that there is an optimal gut volume for postingestive satiety in suckling rats is supported by the fact that, in a previous report (Lorenz et al, 1982), the milk load at 4% of body weight was the largest effective load for reducing milk intake from the unanesthetized mother, without interfering with nipple attachment behaviors.…”

“…coated with Teflon (Medwire Corp. 316SS3T). The pups were anesthetized using hypothermia (Lorenz, Ellis, & Epstein, 1982;Lorenz, 1986). A short incision was made in the scalp, then a small hole (1.0 mm) was drilled in the skull 2 mm lateral to the sagittal suture and midway between the lambda and bregma sutures on the left side.…”

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

“…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). We also compared the sucking of pups which were allowed to consume freely available milk during the 30-min test with the sucking of pups which were not allowed to consume milk while suckling, since preloads might differentially affect sucking in these 2 situations, as well as the amount of milk consumed by pups with access to it.…”

“…Further, the preloads appear to block only the increase in rhythmic sucking which can be attributed t o milk delivery. This effect might be mediated by the caloric value of the preload or to stomach distension cues ( e g Lorenz et al, 1982). In either case, the behavioral effects of the preloads were quite specific; they affected only rhythmic sucking and not the pup's frequency of limb movement (treadles), its initial latency to attach, or the amount of time it spent unattached to a nipple.…”

“…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 nipple to another are not affected by privational status (Cramer, Blass, & Hall, 1980;Hall & Rosenblatt, 1977; but see Dollinger, Holloway, & Denenberg, 1978). Nevertheless, pups younger than 15 days of age do control the amount of milk they consume according to whether they are maternally deprived or have received gastric preloads (Hall & Rosenblatt, 1978;Houpt & Epstein, 1973;Lorenz, Ellis, & Epstein, 1982), suggesting that it is the 2nd strategy that they employ.…”