Initial reperfusion level determines brain infarct size after transient focal ischemia in mice
The intraluminal middle cerebral artery (MCA) thread occlusion model in mice was modified to allow reperfusion at different levels after an epsiode of 1 h transient focal cerebral ischemia. This was achieved by keeping the ipsilateral common carotid artery (CCA) either patent or ligated after thread withdrawal. Our aim was to examine to what extent the degree of initial reperfusion influences brain infarct evolution and neurological outcome. C57Black/6 mice were subjected to 1 h MCA occlusion, followed by 0, 1,3, 6, 24, and 72 h reperfusion, with ligated or open CCA (n=4/group). Prior to termination of the experiment by in situ freezing with liquid nitrogen, cerebral protein synthesis (CPS) and blood flow (CBF) were measured simultaneously using H3-leucine and C14-iodoantipyrine, respectively. Multiparametric imaging of H3-CPS and C14-CBF was achieved by double tracer autoradiography, and regional ATP levels by bioluminescent imaging. ATP-depleted and CPS-suppressed areas were expressed as percentage of hemisphere. Relative CBF was calculated in the area of inhibited CPS and expressed as percent of the contralateral homotopic area. In addition, the neurological score of animals was monitored after reperfusion. At the end of ischemia, metabolic disturbances were the same in both experimental groups. After 1 h recirculation, ATP initially recovered despite lower relative CBF in the CCA-ligated (57±9%) as compared to the CCA open group (82 ± 12%; p<0.05). With increasing recirculation time, however, the areas of secondary ATP depletion and CPS suppression in the CCA-ligated (ATP:54±12%; CPS: 58±11%) were significantly larger than in the CCA-open group (ATP: 24±22%; CPS: 33±22; p<0.05) at comparable relative CBF values (80%). Metabolic improvement also correlated with significantly better neurologic scores at 24 h (1.3±0.5 vs. 2.4±0.6 points; p<0.05) and 72 h (1.8±0.5 vs. 2.6±0.6; p<0.05) after reperfusion. Our data suggest that improved initial reperfusion decreases infarct size and ameliorates functional recovery after transient ischemia probably by prevention of relative hypoxia in the presence of ongoing mitochondrial dysfunction.