Abstract
Purpose: Loss of molar teeth in rats has been reported to be associated with impairment of spatial memory, which may be related to hypo function of the hippocampus. However, the effects of tooth loss on the higher brain functions still remain unclear. In the present study, the glutamate levels in the hippocampus were measured as an index of the functions of the hippocampus, in order to elucidate the neurochemical changes in the brain in edentulous rats.
Methods: At the start of this study, 4-week-old male Sprague-Dawley rats were divided into 3 groups: EXT, in which all the maxillary molar teeth were extracted; ANE, in which anesthesia was administered, but no tooth extraction was performed; UNT, in which neither anesthesia was administered nor tooth extraction was performed. A guide cannula and recording electrode were then fixed in the right hippocampus of the rats at 7 weeks of age. A dialysis probe with a stimulation electrode was introduced into the guide cannula after allowing a 1-week recovery period, and the glutamate levels in the hippocampus were measured in the rats at 8 weeks of age. Tetanic stimulation (100 pulses of 0.2-ms duration at 100 Hz) was applied to the hippocampus through the stimulation electrode undermonitoring by extracellular recording via the recording electrode when the glutamate levels had stabilized. The fluctuations in the glutamate levels following the tetanic stimulation were compared among the three experimental groups using a brain microdialysis system.
Results: The extracellular glutamate concentrations within the hippocampus increased in all the 3 experimental groups following tetanic stimulation. However, the edentulous rats exhibited lower increases in the glutamate levels as compared with the sham and untreated groups.
Conclusion: Decreased afferent information from periodontal sensory receptors resulting from molar tooth loss in rats appears to cause hippocampal hypofunction. Tooth loss may thus cause impairment of memory and learning in humans.
