Animals were euthanized and perfused with sterile saline and thereafter with 4% paraformaldehyde. Brains were removed, suspended in 30% sucrose for three days, and then snap frozen in isopentane chilled with dry ice. Coronal sections (12 mm) were prepared on a cryostat. For immunofluorescence analysis, sections were stained with human-specific anti-nestin antibodies (Millipore) for human glioblastoma cells, mouse-anti-NeuN (Millipore) antibodies for neurons, rat specific mouse-anti-nestin antibodies (Millipore) for astrocytes and progenitor cells. Primary antibodies (dilution 1:200) were incubated overnight at 4uC. Biotinylated goat-anti-mouse and goat-anti-rabbit (Vector Laboratories, Burlinghame, CA) were used as secondary antibodies (dilution 1:100) for 2 h at room temperature. Sections were incubated with Extravidin-Cy3 (Sigma, St. Louis, MO) as fluorochrome (dilution 1:200) for 1 h at room temperature. The sections were examined under a fluorescence microscope (Nikon) and analyzed by confocal scanning laser microscopy (Zeiss, Jena, Germany).