NES and Stroke: In addition to activation of pre-existing brain astrocytes, new GFAP positive radial glial cells are also generated in the neurogenic niche of the subventricular zone after stroke, which by three days can be seen migrating towards the intensifying glial scar [44,79]; between 7 and 14 days, large, densely arborized nestin positive astrocytes can be observed around the infarct border [38,44,79], which by 28 days poses a major physical and chemical barrier to the stroke affected brain [38,55,65,79].