2-NAP, a peripheral CCK-A receptor antagonist, modulates the development of a preference for the mother by the newborn lamb.

The aim of this study was to investigate the effect of devazepide (DEV), a cholecystokinin (CCK)-A receptor antagonist, which crosses the blood-brain barrier (BBB) and prevents the development of a preferential relationship with the dam, and compare it to that of 2-NAP, which acts peripherally. At birth, lambs received either an intraperitoneal injection of saline (CTL), DEV (0.1 mg/kg), or 2-NAP (0.01, 0.1, or 1 mg/kg). No major side effects were observed after the injection, however, there was a trend for lambs receiving CCK-A antagonists to be more vocal in the first 2 h and to loose more weight between birth and 3 h. When tested in a two-choice test situations at 24 h of age, the latency to reach a ewe and the total time spent next to them were not affected by the treatments. On the other hand, unlike CTLs, lambs receiving DEV or 0.1 mg of 2-NAP did not spend significantly more time near their dam than near the alien ewe. 2-NAP had no effect at 0.01 mg/kg, but at 1 mg/kg, it improved the preference score. There was no relationship between preference scores and the variations in weight recorded during the neonatal period. The effects of DEV, but not those of 2-NAP, persisted at 48 h of age. Thus, these results support the hypothesis that peripheral CCK receptors are involved in the development of a preference for the mother, but the effects differ according to the amount of 2-NAP that the lambs receive.

Colostrum mediates the development of mother preference by newborn lambs.

The first sucking bouts have strong rewarding properties in the establishment of a preference for the mother by newborn lambs. In this study we designed an artificial teat (Experiment 1) and a method of tube feeding (Experiment 2) to investigate the role of nonnutritive sucking and colostrum intake as reinforcers in the development of this relationship (Experiment 3). In this third experiment, lambs of the control group (n=10) had free access to the udder. In the other groups they were prevented from sucking between birth and 6 h by covering the ewe's udder while lambs received one of the following treatments: access to nonnutritive teats fitted onto the mother's udder (n=12), tube fed with colostrum (n=11), or fully deprived (n=10). When tested in a two-choice test at 24 h of age, controls and lambs receiving colostrum spent significantly more time near their mother than near the alien ewe. By contrast, deprived lambs did not. Half of the lambs having access to nonnutritive teats displayed a preference for their mother; the other half chose the alien ewe. However, most lambs that were affected by the treatments displayed a preference for their mother when a second test was performed at 48 h. In conclusion, these results demonstrate that a neonatal nasogastric infusion of colostrum has the same rewarding properties as a complete sucking bout. They also provide evidence for the first time that a relationship with the dam can be established via a nutritional signal originating from the gastrointestinal sphere.

Cholecystokinin receptors mediate the development of a preference for the mother by newly born lambs.

The aim of this study was to investigate the effect of selective cholecystokinin (CCK) antagonists on the development of a preference for the mother by newly born lambs. At birth lambs received an injection of the CCK-A antagonist devazepide (0.01 or 0.1 mg/kg), the CCK-B antagonist PD135158 (0.01 or 0.1 mg/kg), or saline for the controls (1 ml/kg). No major side effects were observed in the first 4 postnatal hours except that lambs receiving PD135158 displayed more exploratory behavior towards the maternal body than lambs from the other groups. When tested in a 2-choice test situation at 24 hr of age, lambs treated with PD135158 or saline spent significantly more time near their dams than near the alien ewes, whereas lambs treated with devazepide did not show any discrimination. The effect of devazepide persisted at 48 hr of age. The use of a CCK-A antagonist, but not a CCK-B antagonist, was concluded to prevent the formation of a preferential relationship between the lamb and its mother, most probably by impairing neonatal learning.