To test the hypothesis that presence of metalloproteases (MMPs), their inhibitors (TIMPs) and their substrate laminin-5 differs between the ischemic core and the surrounding tissue, we examined the impact of middle cerebral artery occlusion/reperfusion (MCA:O/R) on these molecules in different regions of the infarct. We also investigated the influence of hypothermia on the progression of the ischemic lesion and MMP activity. Brain sections from 64 Wistar rats subjected to MCA:O/R were examined by means of cytohistochemistry and zymography. The artery was occluded for 2 h followed by 3, 5, 8 and 12 h of reperfusion. Well characterized antibodies against laminin-5, MMPs and TIMP-2 were used. A total of 32 rats were treated with hypothermia. The presence of each antigen was related to the following regions of interest: ischemic core with BBB breakdown (I c), surrounding ischemic tissue without BBB breakdown (I r), and the contralateral non-ischemic region (N). Regions of interest were defined by MRI. The I c increased over time at the cost of the I r. BBB breakdown occurred early in the ischemic core and increased over time. Hypothermia reduced the BBB breakdown at all time points. A graded decreased presence of laminin-5 was observed with 16.5±3.7(N)>10±2.8(I r)>4±1.4(I c) immunopositive microvessels/mm 2 at 3 h of reperfusion. MMP-9 showed a reverse pattern with 0 (N)<4±0.8(I r)<10±1.5(I c) immunopositive microvessels/mm 2. Hypothermia decreased the MMP activity measured by zymography. Laminin-5 and MMP presence relate directly to the degree of postischemic injury. Hypothermia reduces the conversion from the I r to ischemic core and the degree of BBB as well as MMP abundance.