A new experimental model of brain stem ischemia in the rat which allows for recirculation

Recently, both permanent and transient experimental ischemic models have been reported using various laboratory animals. But, as far as the posterior fossa is concerned, there have been only a few ischemic models. This report describes a surgical approach in producing a new experimental aschemic model of the brain stem in the rat in which recirculation can be introduced in the ischemic area. 1) At first, we made a cast phenolic resin modek of the vascular structure of the rat's brain. Using this model, we made an embolus by coating a 6-0 monofilament nylon thread with silicon rubber latex. 2) Adult male Wister rats (300-350g) were anesthetized with pentobarbital sodium (40mg/kg). Through the median neck incision, cervical vertebra (C1-C2 portion) was exposed. The transverse process of the second vertebra was carefully removed and the vertebral artery exposed for 3-4mm at the C1-C2 level. Then, the basilar artery was occluded with prepared embolic thread which was 15 or 18mm long inserted into the vertebral artery. Next, the following studies were done. (a) In one group, carbon black perfusion was performed after 2 hours of ischemia. (b) In the other group, circulation in the brain stem was restored by taking out the embolic thread and removing clip after 6 hours of ischemia. And Evans blue dye was then injected. Moreover, 2hr after the recirculation, perfusion fixation was achieved. In all animals, gross brain was examined. In most of the basilar artery occluded animals, there was pallor (indicating failure to perfuse) of the brain stem in the carbon black perfusion. In the recirculation group, there was blue (indicating damage of blood brain barrier) which was stained by Evans blue. These lesions revealed almost same extension in both groups and restricted to the brain stem which, in the rat, is normally supplied by the basilar artery. These results appear to indicate that this model may be useful in the evaluation of pathophysiological and histpathological states of brain stem ischemia and recirculation.