Effects of early tooth loss on the hippocampus in senescence-accelerated mice

We evaluated whether long-term tooth loss induces functional and morphologic changes in the hippocampus in senescence-accelerated mice (SAMP8) maintained until old age after tooth extraction shortly after tooth eruption. First, to examine whether early tooth loss acts as a stressor, plasma concentration was measured as an index of stress. Plasma corticosterone concentration was significantly higher in old or mature mice with tooth extraction than in the age-matched controls. Plasma corticosterone concentration did not differ between the young tooth extraction and their age-matched control groups. Next, hippocampal function was assessed by evaluating spatial memory performance in the Morris water maze. In the Morris water maze learning and memory trials was significantly slower in the mature or old tooth extraction groups compared with the age-matched controls. There was no significant difference, however, between the young tooth extraction and control groups. Finally, hippocampal neuronal morphology was assessed by counting Nisslstained cells. The number of hippocampal neurons was significantly reduced in the CA3 region in the mature and old tooth extraction groups compared with their age-matched controls, but there was no significant difference in the CA1-region or dentate gyrus between the mature or old tooth extraction groups and their age-matched controls. In young mice, there was no significant difference in the number of neurons in CA1, CA3, or dentate gyrus region between the tooth extraction and control groups. The findings indicated that tooth extraction after tooth eruption enhances the effects of aging on the hippocampus in mice.