Influence of tooth loss on spatial learning ability in rats

Purpose: The purpose was to investigate the influence of tooth loss on ability of the spatial learning and memory in rats. Methods: 72 male Winster rats, seven weeks old, were randomly divided into four experimental groups; rats with all teeth (Group A, control), those lost their upper bilateral first molar teeth (Group B), those lost their upper bilateral first and second molar teeth (Group C), and those lost their upper bilateral first to third molar teeth (Group D). One investigator executed all the extractions for creating the experimental tooth loss in rats. Capability of the spatial learning and memory was measured by the behavioral performance test by means of the 8-arm radial maze. The test was repeated one, four and eight weeks after the tooth extraction. Following completion of the test, each rat was killed and donated to calculation of the TrkB positive cells in the areas from the trigeminal nerve to hippocampus, that is, the amygdala, CA1, CA3 and CA4 of the hippocampus, periofactory cortex, and ventromedial nucleus of the hypothalamus. ANOVA test was conducted to determine the statistical significant difference among the experimental groups, followed by the Fisher's PLSD. Results: Difference in the behavioral performance between the groups was not significant at one and four weeks after the extraction; however, it became significant seven weeks after the extractions (p?.01). As the number of tooth loss increased, the reduction of the performance became greater. The TrkB positive cells in all areas in Groups B to D were significantly less than those in Group A. Conclusions: The reduction of the TrkB positive cell indicates the deteriorated nerve response to BDNF, or a transmission between synapse and synapse. The result of this study suggests that ability of the spatial learning and memory is decreased by the tooth loss in rats.