Littermates can affect on maternal-separation induced ultrasonic vocalization in rat pups

Abstract

Rat pups emit ultrasonic vocalizations (USVs) when they are isolated from their mothers. USVs are an anxiety-like behavior in rat pups that increases maternal-behavior. Previous studies reported that USVs are reduced by the presence of anesthetized mothers and anesthetized littermates and that USVs are affected by surrounding environment and body temperature. In this study, we examined the effect of unanesthetized littermates on pups' USVs, body temperature and physical strength. Before and after maternal-separation on postnatal day 5, male pups were assessed for the number of USVs, the rate of change in USVs and body temperature. Also, physical strength was measured by the righting reflex test and the negative geotaxis test. As the results, we found that maternal-separation reduced the number of USVs and that the presence of unanesthetized littermates during maternal-separation inhibited the decrease in the number of USVs. Furthermore, maternal-separation without any littermates shortened the latency in the righting reflex test. This study suggested that the decrease in rat pups' USVs induced by maternal-separation is not always related to body temperature and physical strength and it is attributed to other mechanism and factors, for example, littermates and anxiety.