Abstract: Objective: To analyze the neural pathways and their underlying mechanisms of H-reflex in masseter muscles, the simultaneous recording techniques of electrical activities in bilateral trigeminal motor nucleus (Mo5) and masseter muscle during H-reflex were established in rats. Methods: Adult Wistar rats (n=5) were anesthetized and bilateral Mo5 were chosen to conduct extracellular recordings. Bilateral electromyography (EMG) of masseter muscle and other physiological functions were simultaneously monitored by a polygraph. The responses evoked by electrical stimulation of masseter nerve were preliminarily analyzed. Results: During the baseline recording for 30 minutes, a low-frequency discharge pattern was observed in bilateral Mo5 (Left: 1.25±0.09 Hz, Right: 1.20±0.39 Hz, P>0.05), but masseter EMG did not reveal any measurable activity. Not only ipsilateral masseter H-reflex but also contralateral masseter H-reflex were induced simultaneously by giving unilateral masseter nerve electrical stimulation. Moreover, responses of ipsilateral and contralateral Mo5 were evoked during the masseter H-reflex. The response amplitude of ipsilateral masseter EMG was higher than that of contralateral one (P<0.05), but no significant difference between ipsilateral and contralateral Mo5 was observed (P>0.05). Conclusion: It is feasible to analyze the electrical activities in bilateral Mo5 and masseter muscle during masseter H-reflex. This may serve as an appropriate approach to exploring the neural pathways and plasticity mechanisms of H-reflex in masseter muscles.

Key words: Trigeminal motor nucleus , H-reflex , Extracellular recording