Critical ischemia duration thresholds in the rat middle cerebral artery occlusion model: Implications for drug screening

The growing incidence of stroke and the absence of drugs to fight its devastating consequences highlight the urgent need to identify therapeutic agents. The middle cerebral artery occlusion model is commonly used to screen new putative anti-stroke agents in rodents. However, differences in ischemia and reperfusion times result in differences in neurological deficit and infarct volume, two of the most commonly used parameters in preclinical assays. These differences make it difficult to select the optimal screening conditions. Here, we report a parallel study comparing behavior, infarct volume, and transcriptomic outcomes after 15 days of reperfusion in a rat middle cerebral artery occlusion model with mild (45 minutes) and moderate (60 minutes) ischemia. The behavioral assays revealed that motor and sensory responses, but not the infarct volume, are sensitive to slight variations in the time of ischemia. The transcriptomic profiling demonstrated striking changes in the number of up- and downregulated genes between mild and moderate ischemia. Gene Ontology analysis supported noteworthy differences between mild and moderate ischemia, particularly in genes related to protein synthesis and processing. Complementary quantitative polymerase chain reaction and western blotting assays confirmed these differences. These results indicate a threshold between mild and moderate ischemia, where changes in behavior and molecular responses mirror a substantial alteration in brain cell biology that appears critical for molecular screening. These findings pinpoint the critical role of selecting the appropriate ischemia model in preclinical stroke studies to enhance the translational relevance of the results and therapeutic strategies.