Suckling

Suckling is the only behavior that is common among mammals. In newborn albino rats it is originally elicited by amniotic fluid deposited by the mother during parturition. Subsequent suckling is stimulated by saliva deposited on the nipples by the infant rats. Internal controls over the volume of milk suckled do not appear until infant rats are about 2 weeks of age at which time gastric distension, milk, systemic dehydration, and intestinal hormone cholecystokinin suppress milk intake derived through suckling. The development of controls over suckling appetite appears to parallel that of consummatory control. Until about 2 weeks of age infant rats choose to suckle a nonlactating nipple with the same frequency as a lactating nipple. Thereafter, the lactating nipple is unanimously chosen. These studies suggest differences and commonalities in the suckling behavior of laboratory rats and other mammals.

The ontogeny of nipple-shifting behavior in albino rats: mechanisms of control and possible significance

Nipple-shifting behavior was studied in rats 3--30 days old in 4 experimental paradigms. The incidence of nipple-shifting of rats tested in groups of 3 on their nonlactating, anesthetized mother was age-related. Rats 12 days of age and younger did not leave the nipple first suckled during the 2-hr test period. Starting by Day 15, however, nipple-shifting increased and reached its maximum in 24-day-old rats. This behavior's incidence was directly related to maternal (and, therefore, nutrient and water) deprivation (Experiment I). Milk letdown reduced the incidence of nipple-shifting behavior at all ages studied and synchronized its occurrence, as almost all shifts occurred immediately aftet letdown and almost none during the 15-min interval between successive milk letdowns (Experiment II). Testing rats individually on the nonlactating, anesthetized mother produced age-related effects. Shifting was virtually eliminated in 15-day-old rats, markedly reduced in 21-day-old rats, and not affected in 27-day-old rats tested individually (Experiment III). Rats 27 and 30 days of age, upon leaving a nipple, ate and did not return to suckle. Rats 15 days old never ate and always returned to suckle (Experiment IV). Twenty-one-day-old rats suckled, and many ate in the mother's presence. The significance of these findings relates to maximizing milk intake and facilitating the process of weaning.

Developmental changes in the suckling behavior of hamster pups: a comparison with rat pups

The suckling behavior of hamster pups was observed to undergo several transitions during the preweaning period. Pups 10 days of age and younger attached to the nipples of their anesthetized mothers and suckled. After 10 days of age, however, only animals which had been deprived of suckling (and food and water) reliably attached to their mothers' nipples. By 25 days of age, deprived pups no longer suckled. The pattern of response after nipple attachment also changed during development: pups younger than 5 days of age remained on 1 nipple after initial attachment, whereas older pups shifted from 1 nipple to another. The development of suckling in hamster pups resembles that in rat pups, although certain changes or transitions occur at different ages in the 2 species. These changes may provide important markers for neural and behavioral development in each species and for comparisons between the two.

L-[3H]Carnosine binding in the olfactory bulb. II. Biochemical and biological studies

During the first 10 days after peripheral deafferentation of the mouse olfactory bulb stereoselective binding of L-[3H]carnosine declines markedly. The initial phase of this decline is due to a decrease in binding site stereoselectivity, which is then followed by a loss of assayable binding sites. The specificity of inhibition of L-[3H]carnosine binding by various peptides is also altered after denervation. Competitive inhibitors of carnosine binding become less potent after denervation, while analogues which are not competitive inhibitors remain equipotent before and after denervation. Several carnosine analogues that are normally poor inhibitors become more potent after denervation. Treatment of bulb membranes with trypsin, RNase and hyaluronidase, but not DNase or collagenase, resulted in significant alterations in carnosine binding. L-, but not D-carnosine, protected the binding site from trypsin digestion, and induced additional binding in bulb membranes in a dose-and temperature-dependent fashion. Preincubation of membranes with L-carnosine also led to the induction of additional carnosine binding in membranes from cerebral cortex, cerebellum and deafferentated bulbs but not from muscle. Bulbs from newborn mice contain about one-half of the adult levels of binding and no significant sex differences in carnosine binding were detected in bulbs from adult rats. L-[3H]carnosine binding was two-fold higher in the anterior compared to the posterior portion of the bulb, but there were no significant differences in binding of opiate, GABA, alpha-adrenergic, muscarinic cholinergic, benzodiazepine of glutamic acid receptor ligands.

First suckling response of the newborn albino rat: the roles of olfaction and amniotic fluid

Washing the nipples of anesthetized parturient rats virtually eliminated nipple attachment by their young. Normal attachment was induced only by painting the washed nipples with a distillate of the nipple wash, parturient-mother saliva, or her amniotic fluids. Reinstatement was not achieved by coating the washed nipples with the saliva of virgin females eating the same diet, the parturient mother's urine, isotonic saline, amyl acetate, or vanilla extract. These experiments also provide behavioral evidence for olfactory function in the newborn albino rat.