The Relationship Between the Number of Molar Teeth Lost and Higher Brain Function in Rats Using an Expression of TrkB mRNA

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  • TrkB mRNA発現からみたラット臼歯喪失歯数の多寡と高次脳機能の関連

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Purpose : The purpose of this study was to investigate changes in spatial learning and memory in rats after extraction of maxillary molar teeth by 8-arm radial maze test and measurements of numbers of TrkB mRNA positive cells in hippocampal pyramidal cells. Materials and Methods : Seventy-two male Wistar rats (7 weeks old) were divided into four groups for this study. In Group A, molar teeth were left intact. In Group B, maxillary first molar teeth were extracted. In Group C, maxillary first and second molar teeth were extracted. In Group D, maxillary first, second and third molar teeth were extracted. A series of spatial memory tasks were performed in an 8 -arm radial maze at 1, 4 and 7 weeks for all four groups. Following completion of this task period, levels of pyramidal cells and TrkB positive cells were observed. Results : At 7 weeks, the results showed that Groups B, C and D exhibited significant behavioral dysfunction compared to group A, yet behavioral dysfunction was more remarkable the greater the number of lost molar teeth. Group B, C and D also showed a significant decrease in the number of hippocampal pyramidal cells and TrkB positive cells in CA1, CA3 and CA4. Conclusions : In conclusion, since the effects of experimental tooth extractions in rats caused decreased amounts of TrkB mRNA positive cells in hippocampal pyramidal cells, spatial learning and memory were affected. As the number of teeth lost increased, higher brain function decreased.

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