Previously we found apoE isoform-dependent effects of (137)Cs irradiation on cognitive function of female mice 3 months following irradiation. Alterations in the number of immature neurons and in the levels of the dendritic marker microtubule-associated protein 2 (MAP-2) might contribute to the cognitive changes following irradiation. Therefore, in the present study we determined if, following (137)Cs irradiation, there are apoE isoform-dependent effects on loss of doublecortin-positive neuroprogenitor cells or MAP-2 immumonoreactivity. In the dentate gyrus, CA1 and CA3 regions of the hippocampus, enthorhinal and sensorimotor cortex, and central and basolateral nuclei of the amygdala of apoE3 female mice, MAP-2 immunoreactivity increased 3 months following (137)Cs irradiation. In addition, at 8 h following irradiation, the number of doublecortin-positive cells was higher in apoE3 than apoE2 or apoE4 mice. Together, these data indicate that brains of apoE3 mice respond differently to (137)Cs irradiation than those of apoE2 or apoE4 mice.