MMP-9 cleaves 31 kDa in vitro. (a) Gelatinase activity was measured in tissue lysates prepared in phosphate-buffered saline without protease inhibitors using a fluorimetric assay; bars represent mean, and error bars represent standard deviation. *P < 0.05 versus C57BL/6 and Balc/c; **P < 0.05 versus C57BL/6 (n = 5). (b) Recombinant mouse matrix metalloprotease (MMP)-2 and MMP-9 were incubated with brain lysate and analysed by Western blotting (n = 3). Numbers represent mass (kDa), as determined using a molecular weight marker.