Two-photon microscopy of small cortical vessels. In vivo imaging of SHRSP and Wistar control rats revealed the excellent detectability of arterioles and the capillary bed (A, SHRSP, 30 w). Non pathological vessels (B, Wistar, 31 w) and arteriolar Dextran leakage indicative for vessel wall damage with suspected perivascular bleeds (C, SHRSP, 31 w) were detected. D (SHRSP, 31 w) shows a capillary with suspected erythrocyte thrombi indicated by not moving dark spots (local gaps of Dextran contrast agent, white arrows), E (SHRSP, 30 w) displays the accumulation of Dextran in an arteriole (white arrow). The arrowhead in F (Wistar, 36 w) marks a rather plane lack of contrast agent in the vessel wall possibly indicative of endothelial injuries. w – age in weeks, scale bars = 50 μm.