Nipple attachment in rats during the first 24 hours of life.

Abstract

The purpose of these experiments was to investigate nipple attachment in laboratory rat pups during the first 24 hr of life and to identify determinants that influence its expression. In Experiment 1, nipple attachment was shown to be age dependent: 1-hr-old pups exhibited a low percentage of attachment, and 12-and 24-hr-old pups exhibited high percentages when tested against an anesthetized lactator. Experiments 2-6 .investigated several factors that might influence the nipple-attachment time course. These experiments clearly established the time course as age related. Experiments 7-10 explored the behavioral mechanism responsible for the increase in attachment from Hour 1 to Hour 12. They showed that nipple experience, independent of milk acquisition, was the responsible factor for the increase. The findings suggest that learning is employed as a behavioral strategy by the newborn, and they reemphasize the value of using species-relevant measures in the assessment of behavioral development.

Classical conditioning in the rat fetus: Involvement of mu and kappa opioid systems in the conditioned response

“…This ®rst exposure to the nipple, and the resulting kappa opioid activity, produces behavioral activation and a temporary reduction in responsiveness to the nipple (Browne, Robinson, & Smotherman, 1994). After this ®rst suckling experience, the pup again locates, grasps, and attaches to the nipple (Dollinger, Holloway, & Denenberg, 1978;Drewett, Statham, & Wakerly, 1974). This second suckling experience, analogous to the CS reexposure of the current experiments, results in a conditioned activation of the mu and kappa opioid systems.…”

Oral grasping of a surrogate nipple by the newborn rat

“…Only a small percentage of 1-hr-old pups show ened to become aligned with the body trunk prior to the oral grasp. To verify an oral grasp response, attachment to the nipple of an anesthetized female, whereas a high percentage of pups tested 12 the experimenter exerted gentle force in an attempt to withdraw the nipple from the mouth of or 24 hr after birth show attachment (Dollinger, Holloway, & Denenberg, 1978). These results sugthe subject (Figure 1).…”

“…ever, that experiences at the nipple during the first 24 hr after birth can lead to changes in the responsiveness of pups in the suckling context Results Holloway et al, 1978). UnThe one-factor ANOVAs that compared oral beder normal conditions, during the first day after havior during presentation of the artificial nipple delivery, the rat pup spends nearly all of its time indicated the significant effect of treatment condiat the nipple.…”

“…At all times, rats used in these Denenberg and colleagues have shown that there experiments were maintained and treated in accoris an improvement in nipple attachment behavior dance with guidelines for animal care established during the first 12 hr after birth (Dollinger, Hollo-by the National Institutes of Health (1986). way, & Denenberg, 1978Holloway, Dollinger, & Denenberg, 1978). One-hour-old pups exhibit a low percentage of attachments to the nipple of an…”

“…The pregnant rat was placed in a holding device havior can occur in the absence of experience with and direct access to the uterine horns was provided milk (Holloway et al, 1978). Clearly, early experiby a midline laparotomy.…”