Brief but enough: 45-min maternal separation elicits behavioral and physiological responses in neonatal mice and changes in dam maternal behavior.

Currently, two gaps exist in the study of early stress response caused by maternal separation (MS) in rodents. Firstly, the influence of brief maternal separation (less than 1 hour) on physiological and behavioral development of offspring is still largely unexplored despite its fundamental and applied value. Secondly, little information is available on the social context of pups' ultrasonic vocalizations (USVs), one marker of stress response to MS, with a virtual absence of studies 1) comparing pups' USV rates during MS (absence of social interaction) with that of home cage (presence of social interaction) and 2) analysing the relationship between pup call composition and maternal behavior. After maternal separation (45 min/day) on postnatal days (PND) 3-7 we showed greater corticosterone levels on PND 7 and USV rates on PNDs 3 and 6 compared to home cage levels. Returning the pups to the dams led to a decrease in these measures. Dams' licking and grooming and pup investigation behaviors during the post-reunion period were higher on PND 3 and nursing levels were lower on PND 6 compared to control and MS baseline conditions. The pups' call composition also differed between these three conditions. Each type of dam behavior was characterized by a unique pattern of pup calls. Our previous research has demonstrated the numerous short- and long-term effects of repeated 45-min MS on development of 129Sv mice. Results presented here suggest the hormonal and behavioral responses described above might be early-life predictors of such effects.