Dentate gyrus neurons that are born at the peak of development, but not before or after, die in adulthood

In the dentate gyrus of the rodent hippocampus, neurogenesis begins prenatally and continues to the end of life. Adult-born neurons often die in the first few weeks after mitosis, but then survive indefinitely. In contrast, neurons born at the peak of development are initially stable but can die later in adulthood. Physiological and pathological changes in hippocampal structure may therefore result from both the addition of new neurons and the loss of older neurons. However, it is unknown whether neurons born at other stages of development also undergo delayed cell death. Here, we used BrdU to label dentate granule cells that were born in rats on embryonic day 19 (E19; before the developmental peak), postnatal day 6 (P6; peak) and P21 (after the peak). We quantified BrdU+ neurons in separate groups of rats at 2 and 6 months post-BrdU injection. Consistent with previous work, there was a 15% loss of P6-born neurons between 2 and 6 months of age. In contrast, E19- or P21-born neurons were stable throughout young adulthood. Delayed death of P6-born neurons suggests they may play a unique role in hippocampal plasticity and pathology in adulthood.