Background: Recently it has become well accepted that
neurogenesis occurs in the dentate gyrus of the hippocampus, a region
important to memory and learning function in rodents and humans.
Reports show that neurogenesis in the hippocampus is regulated by
certain factors, such as exposure to an enriched environment, physical
activity, aging and stress. The relationship between the change in the
task of chewing as one oral environmental factor, and the mechanisms of
hippocampal neuron generation are unclear. Objective: We
examined whether cell proliferation varies by chewing tasks with
different food textures in the dentate gyrus of the rat hippocampus. Methods:
Wistar rats were divided into two groups, one was fed a solid diet,
known as the hard-diet feeding group, and the soft-diet feeding group,
which was fed a powder diet containing the same components as the solid
one for 3, 7, 16 and 24 weeks. Thymidine analog 5-bromo-2'-deoxyuridine
(BrdU) was used as a marker of cell proliferation within the dentate
gyrus of the hippocampus and olfactory bulb. Results: The
results of this study indicated that the total number of BrdU-positive
cells in the hippocampal dentate gyrus significantly decreased with
aging and were significantly fewer in the soft-diet feeding group than
in hard-diet feeding group in 7-, 16- and 24-week-old rats after the
BrdU injection. The change of BrdU-positive cell expression between
soft and hard diets in 3- and 24-week-old rats was not observed in the
olfactory bulb. Conclusion: It has been suggested that cell
proliferation in the dentate gyrus of the rat hippocampus is
characteristically suppressed by soft diet feeding. | 
