1998 Volume 18 Issue 2 Pages 159-164
Jaw reflexes are evoked bilaterally even when stimulated unilaterally. This bilateral cooperation is one of the characteristics of jaw reflexes. The periodontal masseteric reflex also has this bilateral cooperation. The mechanism underlying bilateral cooperation in the periodontal masseteric reflex, however, still remains unclear. The present study was designed to clarify this mechanism. Experiments were performed on male Wistar albino rats weighing 250-320 g. Electrical stimulation was applied to either the left masseteric nerve or the left maxillary molar periodontal ligament. Recordings were made from the trigeminal mesencephalic nucleus and its vicinity. When the periodontal ligament was stimulated, evoked potentials were obtained from the caudal part of the trigeminal mesencephalic nucleus and the reticular formation in the recording region ipsilateral to the site of the stimulation. The latency of evoked potential was in the range of 1.05-1.73 ms, indicating the conduction velocity of Group II and III afferent fibers. In the recording region contralateral to the site of electrical stimulation, evoked potentials were recorded from the rostral and the caudal parts of the trigeminal mesencephalic nucleus and the reticular formation. These evoked potentials were abolished by both local anesthesia around the stimulating electrodes and repetitive stimulation at a high frequency (300 Hz). The latency was in the range of 1.16-1.85 ms which was longer than that of the evoked potential ipsilateral to the site of stimulation. These results suggest that synaptic transmission in the brainstem is involved in the bilateral cooperation of the periodontal masseteric reflex.
