Effects of occlusal disharmony on the hippocampal dentate gyrus in aged senescence-accelerated mouse prone 8 (SAMP8).

BACKGROUND AND OBJECTIVE: Malocclusion induced by raising the bite causes chronic stress. Chronic stress leads to increased plasma corticosterone levels and impaired hippocampal function due to impaired neurogenesis or increased apoptosis in the hippocampus. The present study aimed to clarify the mechanisms underlying the impaired hippocampal function induced by the bite-raised condition in aged senescence-accelerated mouse prone 8 (SAMP8). DESIGN: Nine-month-old aged SAMP8 mice were randomly divided into control and bite-raised groups. The vertical dimension of the bite was raised by applying resin to the molars. We evaluated newborn cell proliferation, survival, differentiation, and apoptosis in the hippocampal dentate gyrus (DG). Hippocampal brain-derived neurotrophic factor (BDNF) levels were also measured. RESULTS: The bite-raised mice exhibited a significant decrease in proliferation, survival, and differentiation of newborn cells into neurons in the hippocampal DG compared with controls. The number of apoptotic cells in the hippocampal DG was increased at 7 and 14 days after the bite-raising procedure. Expression of BDNF protein and mRNA in the hippocampus was also decreased in the bite-raised mice. CONCLUSION: Bite-raised aged SAMP8 mice exhibited decreased neurogenesis, increased apoptosis in the hippocampal DG, and decreased hippocampal BDNF expression, in association with hippocampus-dependent learning and memory deficits.