ABR findings, electrocochleograms and caloric tests in vertebrobasilar ischemic rats.

In rats with ischemia induced by occlusion of the anterior inferior cerebellar artery (AICA) or vertebral artery (VA), we investigated the auditory brainstem response (ABR), electrocochleogram and caloric test result. Upon occlusion of the VA, there was no change of the ABR, whereas in the caloric test the duration of nystagmus upon stimulation of both ears shortened. Upon occlusion of the AICA, the cochlear blood flow (CoBF) showed one of three patterns of change no change: n = 5; decrease: n = 10; and transient decrease with recovery: n = 5. The cochlear potentials were dependent on the residual CoBF. In the caloric test, when the left AICA was occluded, the duration of nystagmus induced by stimulation of the left (ipsilateral) ear was shorter than that induced by the right (contralateral) ear. Based on the functional test results, we conclude that in this model of ischemia the function of the vestibular structures including the semicircular canals is more severely affected than is the hearing function.