Cerebral blood flow in the four-vessel occlusion rat model.

are most likely a result of MCA occlusion. For most old rats, the thicker skull requires more drilling, and connective tissue about the vessel presents more resistance to dissection of the MCA making hemorrhage more likely than in younger rats. While the smaller lesions in older rats (734-852) are larger (p < 0.05) than for the younger rats (752-842), the size difference may be due to more surgical trauma in exposing the vessel or some age factor. Since neither the Robinson nor the Tamura group differentiated the size of the lesion due to surgery from the one due to the occlusion, a good comparison of data is not yet possible. Very large infarcts (mean size > 60 mm 2 ) invariably occur after MCA occlusion above the rhinal fissure in young spontaneously hyper tensive Stroke-prone rats (SHRSP) but not normotensive controls and are reported in a forthcoming paper. 6 Factors that may be involved are discussed more fully and include rat strain, age, blood pressure, loca tion of the occlusion, altered cerebral metabolism, reduced blood flow due to inadequate or insufficient regulation of collaterals, and so forth. Therefore, a single factor or a multifactorial combination involving method of occlusion, metabolic, vascular structural or hemodynamic alterations with age may be responsible for infarcts after rapid MCA occlusion. Peter Coyle, M.D. 4643 Medical Science II Department of Anatomy and Cell Biology The University of Michigan Ann Arbor, Michigan 48109