Deafferentation versus cortical ischemia in a rabbit model of middle cerebral artery occlusion

A two-site middle cerebral artery occlusion model in rabbits was developed. Platinum electrodes served for simultaneous recordings of regional cerebral blood flow, auditory evoked potentials, and electroencephalogram in the left and right auditory cortex and in the left medial geniculate body. Auditory evoked potentials and regional cerebral blood flow were also recorded in the subcortical white matter, and regional cerebral blood flow was recorded in the internal capsule. Distal segment occlusion of the middle cerebral artery caused severe cortical ischemia in four of 11 rabbits (Group I), accompanied by abolition of the auditory evoked potential in the left auditory cortex and white matter and severe reduction of the left electrocorticogram. Deep subcortical regions were affected either little or not at all. In the remaining seven rabbits (Group II) with only mild disturbance of cortical perfusion after distal middle cerebral artery occlusion, additional clamping of the proximal middle cerebral artery stem reduced thalamocortical tract blood flow and abolished cortical auditory evoked potentials. Spontaneous electrocorticogram was less affected in Group II than in Group I; thalamic regional cerebral blood flow and auditory evoked potentials were not altered. Histologically, ischemic lesions predominated in the cortex of Group I and in the subcortical structures of Group II rabbits. While correlated reductions in regional cerebral blood flow and auditory evoked potentials indicate effective cortical ischemia, the impairment of auditory evoked potentials in Group II rabbits must be due to cortical deafferentation by ischemia in the afferent tract. This model permits the investigation of the effects of predominantly cortical or subcortical ischemia in one functional system.