Click Sound-induced Vestibular Masseter Muscle Reflex In Guinea Pig

PartⅠClick sound-induced reflex potentials on the masseter muscle of anesthesia guinea pig and its originObjective The aim of this study was to establish an animal model of the acoustically evoked vestibular masseter reflex. The potential origin was determined through unilateral inferior vestibular neurotomy and destruction of the cochlear nerve. Method Twenty guinea pigs were randomly divided into three groups,ten normal control guinea pig,five of the 20 guinea pig received unilateral inferior vestibular neurotomy and unilateral cochlear nerve were damaged in five guinea pig.Click sound-induced masseter muscle reflex potentials and auditory brainstem response (ABR) were recorded in three groups respectively. A metal clip was used to maintain masseter muscle tension by a clamping between the jaw and skull when masseter muscle reflex potentials were recorded under general anesthesia. Result The response rates of the negative peak(NP) using 100,90,80 and 70dBnHL monaural acoustic stimulation with unilateral recording were 100%,70%,40%and 0,respectively.The mean latencies of the NP for the potentials were 6.57±0.26ms, 6.64±0.23ms,6.69±0.19ms when elicited by 100,90 and 80 dBnHL acoustic stimulation respectively.There was no significant relationship between the stimulus intensity and the mean latency of the NP (P>0.05).NP was present when masseter muscle have tension,however NP was disappear when masseter muscle have no tension.The mean thresholds of ABR were31±7.88 dBnHL. Negative peak of click sound-induced masseter muscle reflex potentials was not observed in the unilateral inferior vestibular neurotomy group while ABR was preserved on operative ear.The mean thresholds of ABR were in the normal range. After unilateral damaging the cochlear nerve, ABR was abolished while the NP was preserved on operative ear. The mean thresholds and latencies of the NP were no significant relationship between the normal control group and the cochlear nerve damaged group (P>0.05).Conclusion Negative peak of click sound-induced myogenic reflex potentials on masseter muscle could be of vestibular origin. We have established an ideal animal model of the acoustically evoked vestibulo-masseter reflex by using a metal clip to maintain masseter muscle tension between the jaw and skull. PartⅡThe effect of part of the afferent neurotomy of trigeminal nerve mandibular branch on click sound-induced masseter muscle reflex potentialsObjective The aim of this study was to evaluate the effect of part of the afferent neurotomy of trigeminal nerve mandibular branch on click sound-induced masseter muscle reflex potentials. Method Fifteen guinea pigs were randomly divided into three groups,five normal control guinea pig, five of the 15 guinea pig received unilateral inferior alveolar nerve were damaged in five guinea pig, and auriculotemporal nerve were destructed in five guinea pig. Click sound-induced masseter muscle reflex potentials were recorded in three groups respectively. Result The thresholds of masseter muscle reflex in normal control group were 90±8.16dBnHL.The response rates for the potentials on the masseter muscle of guinea pig using 100,90,80and 70dBnHL monaural acoustic stimulation with unilateral recording were 100%,70%,40%and O,respectively.The mean latencies of the negative peaks for the potentials were 6.55±0.25ms,6.61±0.16ms,6.70±0.13ms when elicited by 100,90and80dBnHL acoustic stimulation respectively.There was no significant relationship between the stimulus intensity and the mean latency of negative peak (P>0.05). After damaging the inferior alveolar nerve and auriculotemporal nerve, negative peak was preserved. The mean thresholds and latencies of masseter muscle reflex were no significant relationship between the normal control group and the inferior alveolar nerve and auriculotemporal nerve destructed group (P>0.05).Conclusion Afferent of inferior alveolar nerve and auriculotemporal nerve of trigeminal nerve mandibular branch could not influence vestibular evoked masseter muscle reflex.