Study on the branching pattern of the middle cerebral artery in rats -With special reference to reproducibility of focal cerebral infarction

As a focal ischemic model, occlusion of the middle cerebral artery (MCA) of rats is frequently employed, and many methods have been reported such as direct MCA occulusion or intravascular occlusion. One major problem in creating the infarction is the variability in size of the resultant ischemic lesion due to collateral circulation. To examine this variability, we observed the MCA in rats under an operative microscope and established a method for creating a reproducible infarcted region. Among 100 rats in which the MCA was investigated in this study, 35 were sacrificed between 24 and 48 hours after surgery and the sectioned brains were stained with TTC (2, 3, 5-triphenyltetrazolium chloride) and subjected to evaluation of the infarcted area. The MCA observed through the microscope within the operative field was divided into three sections by the olfactory tract and the inferior cerebral vein which runs just above the rhinal fissure. In a large number of cases (87 cases, 87%), a couple of branching arteries ran anterioly and posteriorly, and the MCA bifurcated into frontal and parietal branches. In addition to this standard type of branching pattern, 8 cases (8%) revealed an early bifurcation of the MCA, 4 cases (4%) showed a fenestrated MCA, and one case (1%) had no bifurcation within the operative fleld. To eliminate collateral blood circulation from the frontal branch through the anterior cerebral artery, we cauterized the MCA from its origin to the bifurcated region. Among the 35 cases evaluated by TTC staining, 33 (94%) demonstrated high-grade cortical infarction. We conclude that in order to create a reproducible cortical infarction in the rat by direct MCA occlusion, it is necessary to obliterate the MCA from its origin to just distal to the emerging frontal branch.