FIGURE 4.

Stained sections of living (a–l) rats and a sacrificed rat (m–x) 90 min post injection. Representative sections were stained with antibodies against collagen IV (a,g,m,s), laminin (d,j,p,v), DAPI (c,I,o,u), tracer (b,h,n,t), magnification 20× (a–e,g–k, m–q,s–w). The corresponding scanned horizontal section at magnification 0.2× provides the exact location of the taken pictures (f,l,r,w). In living animals the tracer is clearly transported along the vascular wall not diffusing through the outer lamina. These vessels can be identified as arterioles by their size and the orientation of the two layers of nuclei. In sacrificed animals some of the tracer spreads along the vascular wall, but also provides a background staining of the neuropil (m–q). The tracer accumulates in the parenchyma surrounding vessels/the perivascular space. (s–w). Subfigure (y) shows normalized tracer intensity inside and outside of vessels. There is a highly significant difference for L90 (***p ≤ 0.001) and significant difference for S90 (**p = 0.003). The tracer amount outside of vessels in living animals is highly significant lower compared to sacrificed ones.