Effect of tPA deficiency on ischemic cell death. (A-D) Immunohistochemical analysis of neuronal pAkt in the area of interest-2 (AOI-2) 1 (A,B) and 24 (C,D) hours after middle cerebral artery occlusion (MCAO) in wild-type (A,C) and tPA^−/− (B,D) mice. Blue indicates 4′,6-diamidino-2-phenylindole and red indicates pAkt in panels A and B and NeuN in panels C and D. Green indicates GFAP in panels A and B and pAkt in panels C and D. Original magnification, A-D, 40×. Images were visualized using a Leica DMRBE microscope (Leica, Houston, TX) equipped with a 100×/1.30 numeric aperture (NA) and a LeicaDC500 camera. Images were processed using software provided by the camera manufacturer. (E) Representative Western blot analysis of PARP-1 cleavage in brain extracts from wild-type (WT) and tPA^−/− mice 6 and 24 hours after MCAO. C denotes a control WT animal. The arrow indicates an approximately 89-kDa PARP-1 cleavage product. Each observation was repeated 4 times. (F) Mean percentage of TUNEL-positive cells in the area of ischemic penumbra in WT and tPA^−/− mice 24 hours after MCAO; n = 7. *P < .005 compared with WT mice.