Abstract
The number of neurons in the brain increases over time, even in adults. This phenomenon, known as “neurogenesis”, is associated with neural stem cells present only in the dentate gyrus of the hippocampus. However, the frequency of neurogenesis is regulated by various factorsand mastication has been suggested as one such factor. In the present study, we examined the effects of varying the input of masticatory stimulation on neural stem cells using feed with different degrees of hardness. Male C57BL/5 mice were used in a comparative study. After weaning at 3weeks old, experimental mice were fed a soft or hard diet for 4 or 11weeks. To study the dynamic behavior of neural stem cells, the expression of two markers （nestin, a neural stem/progenitor cell marker; and doublecortin, a microtubule-associated protein） was quantitatively analyzed via immunostaining, whereas gene expression was analyzed by real-time polymerase chain reaction （RT-PCR）. Immunostaining-based quantification and gene expression analysis by RT-PCR revealed the decreased expression of markers in the hippocampus in the soft diet group compared to that in the hard diet group. Based on these results, the repression of neurogenesis by a soft diet was associated with changes in neural stem cells in the hippocampus and the frequency of neurogenesis.
