Detailed Differentiation of Calbindin D-28k-Immunoreactive Cells in the Dentate Gyrus in C57BL/6 Mice at Early Postnatal Stages

The hippocampus makes new memories and is involved in mental cognition, and the hippocampal dentate gyrus (DG) is critical because neurogenesis, which occurs throughout life, occurs in the DG. We observed the differentiation of neuroblasts into mature neurons (granule cells) in the DG of C57BL/6 mice at various early postnatal (P) ages: P1, P7, P14, and P21 using doublecortin (DCX) immunohistochemistry (IHC) for neuroblasts and calbindin D-28k (CB) IHC for granule cells. DCX-positive cells decreased in the DG with age; however, CB(+) cells increased over time. At P1, DCX and CB double-labeled (DCX(+)CB(+)) cells were scattered throughout the DG. At P7, DCX(+)CB(+) cells (about 92% of CB(+) cells) were seen only in the granule cell layer (GCL) of the dorsal blade. At P14, DCX(+)CB(+) cells (about 66% of CB(+) cells) were found in the lower half of the GCL of both blades. In contrast, at P21, about 18% of CB(+) cells were DCX(+)CB(+) cells, and they were mainly located only in the subgranular zone of the DG. These results suggest that the developmental pattern of DCX(+)CB(+) cells changes with time in the early postnatal stages.