Hippocampal cell proliferation and spatial memory performance after social instability stress in adolescence in female rats.

We investigated the immediate and lasting effect of social instability stress in adolescence [SS: daily 1h isolation and change of cage partner postnatal days (P) 30-45] on cell proliferation in the hippocampus and on spatial memory using an object spatial location (SL) test. Female rats were treated with bromodeoxyuridine (BrdU) P43-45, and on P49, SS had reduced cell hippocampal cell proliferation/survival compared to controls as indicated by BrdU immunoreactive cell counts (p=0.009), and did not differ in Ki67 immunoreactive cell counts (p=0.15) from CTL. A separate group of SS and CTL rats were tested at P47 and P48, and again at P72 and P73 on the SL test using 1 and 8h retention intervals. SS and CTL females did not differ in adolescence, but CTL had better memory than SS as adults (p=0.03). The better memory performance of CTL rats is not due to differential investigation of objects during the familiarization pre-tests or by differential locomotor activity. The lasting memory reduction and reduced cell proliferation/survival in SS rats is consistent with the hypothesis that ongoing development of the hippocampus renders the adolescent particularly vulnerable to chronic social stress.