Abstract
In order to elucidate the influence of tooth loss and concomitant masticatory alterations on learning memory in rats, male Wistar rats (25 weeks old) were divided into three groups: a control group (fed with a solid diet); a soft diet group (fed with a powder diet containing the same components as the solid one) and a molar crown-less group (all molars were removed at 25 weeks and then the rats were fed with a powder diet). At 40-weeks, the passive avoidance test using a one-way step through type of apparatus divided into light and dark chambers, the determination of dopamine (DA) concentration of the cerebral cortex, and the measurement of the number of DA-positive neurons in the nucleus of the ventral tegmental area (VTA) were performed. The results obtained were as follows.
1) At day 4 and 7 after the acquisition trials, the response latency of the molar crown-less group was significantly shorter than that in the control group (p<0.05).
2) The DA levels of the molar crown-less group and soft diet group in the cerebral cortex was significantly lower than those of the control group (p<0.05).
3) The number of DA-positive neurons in the nucleus of the VTA of the molar crown-less group was significantly smaller than those of the control group (p<0.05).
These results suggest that a decrease of oral sensory information or concomitant masticatory alterations caused a reduction in the number of DA-positive neurons in the nucleus of the VTA, which in turn caused a transient decline of DA concentrations in the cerebral cortex, resulting in a learning memory disorder in rats.
