Effects of age on immunohistochemical changes in the mouse hippocampus

We investigated the age-related changes in neuronal cell death and synaptophysin of the hippocampal CA1 sector in mice using immunohistochemistry. Microtubule-associated protein 2a, b (MAP2) and synaptophysin immunoreactivity was measured in 2-, 8-, 18-, 42- and 59-week-old mice. MAP2 immunoreactivity was unchanged in the hippocampal CA1 sector up to 42 weeks after birth. In 59-week-old mice, however, a significant decrease in MAP2 immunoreactivity was observed in the hippocampal CA1 sector. Total number of synaptophysin-positive boutons was also unchanged in the hippocampal CA1 sector up to 42 weeks of birth. In 59-week-old mice, however, a significant increase in synaptophysin-positive boutons was observed in the hippocampal CA1 sector. These results demonstrate that dendrites and axons in the hippocampal CA1 neurons are particularly susceptible to ageing processes. In contrast, a marked increase in synaptophysin-positive boutons was found in the hippocampal CA1 sector of aged mice. These findings suggest that increase in synaptophysin-positive boutons may play a role in the maintenance of the structural components in the hippocampal CA1 sector of aged mice although most postsynaptic CA1 pyramidal neurons are generated. Thus, our findings provide further valuable information on age-related neurodegeneration and deficits in hippocampus-dependent memory and synaptic plasticity.