Neurogenesis in the rat hippocampus by dysfunctional mastication

Objectives: It is widely accepted that the rodent brain continues to produce neurons throughout adult life. Recently, the hippocampal neurogenesis has been shown to be changed in various environment conditions, e.g. exposure to enriched environments or stress. However, little is known about an interaction between oral environment changes and this hippocampal neural mechanism.

Methods: In this study, we examined in Wistar rats whether neurogenesis in the dentate gyrus of hippocampus varies by either chewing behavior with differential food texture or loss of the molar teeth. The experiments were done in the three groups: 1) molarless group whose molar teeth were extractedA2) soft-diet group which had fed with a powder diet, and 3) control group without any treatments. Immunohistochemistry for BrdU (5-bromo-2'deoxuridine) and immunofluorescent labeling for BrdU and NeuN were carried out as described previously. All the stainings were performed on free-floating 40µm coronal sections. The antibodies used rat anti-BrdU and mouse anti-NeuN. Anti Ig(H+L) rat FITC and RHODAMINE were used as secondary antibodies for double immunofluorescent staining. The differences among groups was statistically evaluated using one-way analysis of variance (ANOVA) and post hoc Fisher's PLSD test.

Results: When BrdU positive cells and neurons were counted in the hippocampal formation, significant decreases in the number of BrdU positive cells and neurons in the dentate gyrus was seen in the molarless(p<0.01) and soft diet groups(0.01).

Conclusions: The data suggest the link between abnormalities in mastication and hippocampal neurogenesis. Mastication is important for the survival of newly generated cells and may contributed to hippocampal functions.