Click-evoked myogenic potentials recorded on alert guinea pigs.

The aim of this study was to establish an animal model of acoustically evoked vestibulo-collic reflex using guinea pigs. A special clamp was applied to restrain the head and body of the guinea pigs, but leaving its four legs free. Each animal underwent vestibular evoked myogenic potential (VEMP) and caloric tests using clip electrode method without general anesthesia or decerebrate surgery. The response rates for the myogenic potentials on the neck of guinea pigs using 100, 90, 80 and 70 dB monaural acoustic stimulation with unilateral recording were 100%, 62%, 50% and 0%, respectively. The mean latencies of the positive and negative peaks for the myogenic potentials were 7.24+/-0.49 and 9.15+/-0.47 ms, 7.09+/-0.43 and 9.28+/-0.42 ms, as well as 7.03+/-0.59 and 9.14+/-0.56 ms, when elicited by 100, 90 and 80 dB acoustic stimulation, respectively. The median (minimum-maximum) peak-to-peak amplitudes were 11.93 (6.14-16.86), 10.99 (5.28-19.40), and 11.17 (5.02-20.72) microV, when elicited by 100, 90 and 80 dB acoustic stimulation, respectively. We found no significant relationship between the stimulus intensity and the mean latencies or peak-to-peak amplitude of the myogenic potentials in guinea pigs. For those treated with gentamicin unilaterally, all guinea pigs showed absent caloric responses on the lesion side, and absent myogenic potentials on the neck when using ipsi-lesional acoustic stimulation, while the hearing was preserved. Hence, the use of gentamicin-treated animals, along with normal controls and auditory brainstem responses, results in convincing results that the recorded myogenic potentials are in fact of vestibular origin.