Neither rt-PA nor FTY720 induce significant changes in MMP-9 activity in brain homogenates 24 h after MCAO. A) Non-ischemic (NI) and ischemic (I) hemispheres were homogenized separately in ice-cold cell lysis buffer containing protease inhibitors and subjected to acrylamide gel electrophoresis on a gel containing 0.1% gelatin. Photographs of the Coomassie blue-stained gels were inverted and the MMP-9 band at 84 kDa densitometrically evaluated. We excluded all mice who showed greater MMP-9 activity in the NI as compared to the I hemisphere. B) We compared MMP-9 expression on the protein level (Western Blot, upper panel) with MMP-9 gelatinase activity (zymography, middle panel) from identical samples of brain tissue. Total protein staining with the azo dye Ponceau S served as a loading control.