Cell proliferation in the dentate gyrus of rat hippocampus is inhibited by soft diet feeding

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.