Effects of early rearing experience on feeding behavior in B6D2F2 mice

This work investigated putative factors contributing to the hyperphagia previously observed in mice which had been overfed during the preweaning period by rearing in small litters. In the first study, B6D2F2 mice, reared in small (Sm = 4), medium (Md = 8) and large (Lg = 12) litters, were subjected to a series of diets adulterated with varying concentrations of sucrose octa-acetate (1, 2, 4, and 8%). All animals reduced their food intake in response to the dietary adulteration, with evidence of a dose-response effect, but this response did not differ as a function of litter size. The second study addressed the involvement of the opioid system in the feeding response through the administration of a series of doses of naloxone (0.1, 0.25, 0.5, 1.0, 2.5, and 5.0 mg/kg, or 5, 7.5 and 10.0 mg/kg). Although naloxone treatment did reduce food intake, there was not a clear dose-response relationship. Again, there was no interaction with litter size. These results do not support effects of early rearing on the feeding response to dietary adulteration or to the effects of naloxone administration.