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Behavioral and autonomic manifestations of acute isolation distress were studied in 2-week-old rats under novel and home-cage conditions. Levels of ultrasonic vocalization, heart rate, self-grooming, and rises were higher in novel surroundings, while locomotion and digging were more frequent in home cages. Next, we found that a group of 8 unanesthetized agemate pups was just as effective as an anesthetized dam in reducing (by 80-90%) all behaviors of isolated pups in novel surroundings. Finally, singletons reared without littermates during postnatal days 7-14 showed normal isolation responses, and these were as effectively alleviated by littermates as those of normally reared pups. Thus, isolation distress in rats this age is a complex response, modulated over time by aspects of the pups' environment and virtually prevented by the presence of cues common to both mother and littermates.
Hofer et al. (Wed,) studied this question.