Brain EC migration into neurospheres. Mouse brain EC were prepared, labelled with cell tracker, and then plated onto mouse neurospheres, as described in Methods. 5 days later, the distribution of fluorescent-labelled EC within neurospheres was examined by fluorescent microscopy of frozen sections of EC-neurosphere co-cultures, using Hoechst (blue) to identify all cell nuclei (A and C) and the FITC channel (green) to identify the cell tracker-labelled EC (B and D). Scale bar = 100 μm. Panel E shows a histogram of the distribution of EC number within neurospheres in a representative experiment (n = 3). Note that EC were detected in the majority of neurospheres.