Cessation of cerebral blood flow (stroke) occurred in 3 of 4 rats treated with topical L-NAME (1 mmol/L) within 30 minutes after infusion of SS-RBCs. Rats were prepared with cranial windows and superfused with artificial cerebrospinal fluid containing 1 mmol/L L-NAME beginning at time −60 minutes as described in the Materials and Methods. Fluorescently labeled human SS-RBCs (2 to 3 mL) were infused into prepared rats (completed at time 0 minutes) and video images of fluorescent RBCs in 6 preselected areas within the cranial window were obtained. MAP (solid line) and etCO₂ (broken line) is plotted for each animal (A, B, C, and D) that experienced stroke (solid symbols) or maintained stable cerebral blood flow (open symbols). The open arrows depict the time that blood flow first stopped in a postcapillary venule measuring greater than 25 μm in diameter. The solid arrow depicts the time the blood flow of all vessels in all observed areas ceased. Rat B died at time 11 minutes. Because the endpoint for this investigation was stroke, the experiments were terminated in rats A and D before spontaneous death. In one experiment, an EEG over the frontal cortex was also obtained and is depicted at times −60, 0, 8, and 20 minutes (D; EEG).