The effects of 24-hr maternal separation and of litter-size reduction on the isolation-distress response of 12-day-old rat pups.

Abstract

We asked whether the mother-infant interaction acted over time to regulate the ultrasonic vocalization (USV) and activity responses of 12-day-old rat pups to isolation in a novel test area. In a series of four experiments, we found that 24 hr of maternal deprivation did not alter USV isolation responses, but that reduction of litter size to 4 pups from 8 markedly attenuated the USV response and increased weight gain, without effects on activity level. Ambient temperatures during 24-hr maternal separation were varied from 23 degrees to 35 degrees C without effect on subsequent USV responses, but activity levels were markedly reduced in pups separated at the low heat level. Possible mechanisms for maternal regulation of USV responses involving nutrient effects, altered processing of thermal stimuli, and the inhibition of thermogenesis by nutrient deprivation are discussed.