BRAIN-STEM AUDITORY-EVOKED POTENTIALS DURING BRAIN-STEM ISCHEMIA AND REPERFUSION IN GERBILS

To evaluate the reversibility of neural function in the brainstem foll owing ischemia, we investigated the effect of transient brainstem isch emia on the brainstem auditory evoked potential in gerbils. Brainstem ischemia was produced by bilateral extracranial occlusion of vertebral arteries. Local cerebral blood flow was measured by quantitative auto radiography after 5 min of ischemia and was reduced to less than 3 ml/ 100 g per min in the pens and lower midbrain, indicating severe and re producible brainstem ischemia. During brainstem ischemia, brainstem au ditory evoked potential waveforms disappeared completely. After a brie f ischemic insult (5 min), all four brainstem auditory evoked potentia l components recovered to normal. After longer ischemic insults (10-30 min), brainstem auditory evoked potential components never recovered to normal. Microtubule-associated protein 2 immunoreactivity revealed differential vulnerability of the acoustic relay nuclei in the brainst em. Neurons in the lateral lemniscus were most vulnerable, followed in order by neurons in the trapezoid body, the superior olive and the co chlear nucleus. We also demonstrated a close relationship between the reversibility of ischemia-induced changes on brainstem auditory evoked potential and ischemic lesions of these relay nuclei. These data may be useful for evaluating the therapeutic window of thrombolytic therap y during acute vertebrobasilar occlusion. (C) 1997 IBRO. Published by Elsevier Science Ltd.