Pregnancy inhibits cell proliferation and neuroblast differentiation without neuronal damage in the hippocampal dentate gyrus in C57BL/6N mice

Neural changes occur in the dam during gestation, and brain size has been shown to decrease across pregnancy in humans as well as rodents. In this study, we monitored neuronal damage, cell proliferation and neuroblast differentiation in the hippocampal dentate gyrus (DG) at age-matched virgin control (17- to 18-week-old), gestation day (GD) 14.5, 16.5 and 18.5 (17- to 18-week-old dams), using NeuN for mature neurons, terminal deoxynucleotidyl dUTP nick-end labeling (TUNEL) and Fluoro-Jade B (F-J B) for neuronal death, Ki67 for cell proliferation and doublecortin (DCX) for neuroblast differentiation in C57BL/6 mice. There were no significant differences in NeuN-immunoreactive (+) neurons between the age-matched control and gestating groups. TUNEL or F-J B positive neurons were rarely detected in the DG in all the groups. Ki67+ cell proliferation was significantly decreased in the subgranular zone of the dentate gyrus (SZDG) at GD16.5. In addition, DCX+ neuroblasts with/without tertiary dendrites were decreased in the SZDG with gestation by GD16.5. However, in the GD18.5 group, the number of Ki67+ nuclei and DCX+ neuroblasts with/without tertiary dendrites was slightly increased compared to that observed at GD16.5. DCX protein levels were low at GD16.5, and thereafter slightly increased. These results suggest that cell proliferation and neuroblast differentiation in DG of the hippocampus is decreased during gestation.