Influences of molar loss of rat on learning and memory

Purpose: The maxillary unilateral or bilateral molars of rats were extracted, and the influences of the partial loss of occlusal support were evaluated using an 8-arm radial maze and a step-through type passive-avoidance apparatus. Methods: Rats were randomly allocated to three groups not undergoing molar extraction or undergoing extraction of the maxillary unilateral or bilateral molars. Each group was further divided into two groups for maze or passive-avoidance experiments. Thus, a total of six groups were established. The maze experiment was conducted once daily for 10 days. The number of correct choices, number of errors, and the trial time were recorded. The passive-avoidance experiment consisted of an acquisition trial and retention trial. In the acquisition trial, rats were placed in a light room, and the response latency until their entry into a dark room was measured. After 24 h, a similar procedure was performed as a retention trial. Results: In the maze experiment, there was no significant difference by all the groups except on the day 1 in the number of correct choices. But bilateral molar loss group, the number of errors were significantly lower than no extraction group on days 1, 2, 3, 4, and 7. In the passive-avoidance experiment, though the response latency in the retention trial was longer than that in the acquisition trial in all three groups, according to the increase in the number of tooth extraction, it became significantly shorter between P1 and P3. Conclusion: These results suggested that molar loss may be a cause of learning/memory impairment. (C) 2009 Published by Elsevier Ireland on behalf of Japan Prosthodontic Society.