Maternal separation after postnatal day 10 induces increase in depression-like behavior with decrease in hippocampal dendritic spines, but no change in anxiety-like behavior in male rats

Neurodevelopment has a "sensitive period" during which the brain is highly sensitive to experience. In this study, we used maternal separation (MS) models of male Long-Evans rats to examine whether sensitivity to stress changes after postnatal day (PND) 10, when dendritic spine density begins to increase rapidly in the CA (Cornu Ammonis)1 region of the hippocampus. We assigned littermates to three groups: early maternal separation group (EMS: MS during PND 1-9), late maternal separation group (LMS: MS during PND 10-20), and control group. During adulthood (PND 56-75, which strictly corresponds to young adulthood), LMS showed increased depression-like behaviors and decreased dendritic spine density in the CA1 hippocampal region; however, EMS did not show any such changes. Accordingly, littermates at PND 10-20 have a greater vulnerability to MS than those at PND 1-9. These findings suggest that dendritic spine formation in the hippocampus is an important factor in determining sensitivity to MS.