Background and Purpose-To analyze the effects of substrain and gender differences in spontaneously hypertensive rats (SHR) and distal middle cerebral artery (MCA) branching patterns on infarct size, we compared infarct volumes produced by photothrombotic distal MCA occlusion using SHR/Kyushu and SHR/Izumo (Izm). Methods-Twenty-four male and 8 female SHR/Kyushu, 15 male and 5 female SHR/Izm, and 6 male Wistar-Kyoto rats (WKY)/Izm (5 to 7 months old) were subjected to photothrombotic distal MCA occlusion, and infarct volumes were determined. Results-Although blood pressure levels were essentially the same between the two substrains of hypertensive rats, infarct volumes were significantly larger in the SHR/Kyushu substrain than in SHR/Izm of either sex (PϽ0.001); infarct volumes in male and female SHR/Kyushu were 83.8Ϯ11.7 and 58.5Ϯ9.2 mm 3 , and those in male and female SHR/Izm were 61.5Ϯ10.7 and 34.8Ϯ7.9 mm 3 , respectively (values are meanϮSD). Male SHR/Kyushu that had simple Y-shaped MCA showed smaller infarcts (75.8Ϯ14.6 mm 3 , nϭ11) than those with more branching (regular) MCA (93.2Ϯ19.1, nϭ13), the difference being significant (Pϭ0.022). Male SHR/Izm with simple distal MCA also produced smaller infarctions than those with regular MCA (51.0Ϯ3.7 versus 68.9Ϯ8.7 mm 3 , Pϭ0.0004). Conclusions-Photothrombotic occlusion of distal MCA in hypertensive rats provides a simple and reproducible model of focal ischemia. Most importantly, this study emphasizes the substantial variabilities in infarct sizes caused by the differences in substrains of SHR, gender, and distal MCA patterns. (Stroke. 1998;29:1982-1987 Key Words: stroke, experimental Ⅲ cerebral ischemia, focal Ⅲ photochemistry Ⅲ models, animal R eproducible animal models of stroke or focal ischemic infarction are crucial to the study of the pathophysiology of ischemic brain injury. Focal ischemia models are relevant to the human clinical setting, because ischemic stroke is the predominant type of cerebrovascular disease. The subtemporal approach technique of Tamura et al, 1,2 occluding the proximal part of the middle cerebral artery (MCA), has been established as a standard focal cerebral ischemia model in the rat. Occlusion of the proximal MCA in the rat is technically feasible, but this model is surgically demanding. Chen et al 3 used a method of more distal occlusion of MCA above the rhinal fissure combined with permanent ipsilateral and temporary contralateral common carotid artery (CCA) occlusions. Brint et al 4 also used a distal MCA occlusion with permanent occlusion of the ipsilateral CCA and found great variability in cortical infarct volumes in normotensive rat strains. However, the infarcts were large and fairly consistent in spontaneously hypertensive rat(s) (SHR).
See Editorial Comment, page 1986The results of Duverger and MacKenzie 5 revealed considerable differences in lesion size and location, depending on such factors as strain, arterial blood pressure, and blood glucose concentration. Proximal MCA occlusion causes a small and variable infarctio...