Is the loss of the tooth a risk factor of the Alzheimer's disease? Examination by microdialysis methods

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Purpose : To clarify the effects of molar tooth loss on learning and memory, hippocampal glutamate release during a passive-avoidance task was measured with a telemetric glutamate biosensor.Methods: Male Sprague-Dawley rats were used. Under general anesthesia, all the maxillary molars were extracted from the EXT group rats (n=8); those in the CON group (control, n=8) were anesthetized without tooth extraction. At age 7 weeks, the rats were subjected to a passive-avoidance task consisting of acquisition and retention trials. Simultaneously, hippocampal glutamate release was measured. First, during the acquisition trial, the rats were placed in a light compartment, and the duration before they entered a dark compartment was measured (reaction latency). Immediately after the rat entered the dark compartment, an electric shock was applied through a grid floor. After 24h, the retention trial was performed, and the reaction latency was measured in the same manner. Further, a biosensor was used to measure the release of hippocampal glutamate before and after the start of each trial.Results: Regarding the reaction latency during the passive-avoidance task, no significant differences were seen between the groups in the acquisition trial. Reaction latency increased in both groups in the retention trial, but was significantly shorter in the EXT group. Furthermore, hippocampal glutamate release in the acquisition trial was significantly shorter in the EXT group, but in the retention trial, no significant difference in glutamate release was seen between the groups.Conclusion: Molar tooth loss may impede learning and memory.