Asymmetry of turning behavior in rats is modulated by early life stress.

Atypical leftward behavioral asymmetries have been associated with early life stress and psychopathologies in humans and animals. Maternal separation (MS) is a frequently used model to investigate early life stress and psychopathologies but has not yet been studied in terms of asymmetries. This study aims to investigate whether prolonged MS induces atypical leftward asymmetries in the turning behavior of rats. MS was performed from postnatal days 2-20 followed by a second stressor from postnatal days 21-40. Asymmetry of turning behavior was then examined in the elevated plus-maze test upon weaning (juveniles and dams) or adolescence. The number of left and right turns was calculated per animal using the deep learning software package DeepLabCut enabling markerless pose estimation. Then, a lateralization quotient (LQ) was determined for each animal allowing to investigate the strength as well as the preferred side of asymmetry. LQ analysis revealed a significant leftward asymmetry in the prolonged stress group. Moreover, analyzing the number of turns revealed significantly more left than right turns in total in this group. Control animals showed no asymmetries in turning behavior. These results indicate that prolonged stress during the early postnatal days led to atypical leftward turning behavior. The stress-induced atypical asymmetry might be a mediator of early life stress and the development of psychiatric disorders.