Long lasting alteration in REM sleep of female rats submitted to long maternal separation.

Early adverse experiences represent risk factors for the development of anxiety and mood disorders. Maternal separation can induce biobehavioral alterations in male rodents similar to those seen in depressed humans, such as hyperresponsiveness to stress and sleep disturbances. Nonetheless, no study has yet explored the effects of early life events on the relationship between stress and sleep in female rats. Whole litters of Wistar rats were submitted to brief- or long maternal separations (15 [BMS] or 180 min/day [LMS], from postnatal days 2-14) or kept undisturbed with their mothers (CTL). When adults, female rats were sleep-recorded for 22 h before (baseline) and after a 1 h exposure to cold stress (post-stress). Additional subsets of animals were sacrificed before, 1 or 3 h after the stressor for plasma corticosterone determination. No differences in baseline sleep were observed among the groups. Female rats submitted to LMS exhibited a significant increase of REM sleep on the night following a 1 h exposure to cold stress, whereas the sleep of BMS rats was barely altered by stress. All groups exhibited similar basal and stress-induced corticosterone levels. The present results are compared to a previous study performed in male rats, and corroborate that manipulations applied during infancy modify the expression of stress-induced sleep rebound.