In situ hybridization of tPA mRNA expression in the mouse brain. (A-D) Dark-field photomicrographs show significant up-regulation of tPA mRNA in the border of the ischemic core (IC) at 6 and 12 hours after MCAO in heparin (HEP)–treated WT mice (arrows in B, D) compared with untreated (UNT) WT mice (A, C). Cor indicates cerebral cortex. Bright-field photomicrographs show that increased tPA mRNA levels were expressed in microglial cells (F, arrowheads) but not neurons (F, arrows). Insets are 2.5-fold magnified cells from the area denoted by the asterisk. Scale bars equal 500 μm (A-D) and 50 μm (E-F).