Quantitative analysis of the effects of astrocytes and Slit-expressing cells on neuronal migration from SVZ explants. SVZ explants were cultured in the proximity of aggregates (1 × 106 cells) of HEK cells, x-Slit-expressing HEK cells, or astrocytes for 11 hr in Matrigel. The samples were then fixed, and the number of migrating cells was counted. Coculturing SVZ explants with aggregates of astrocytes increased the total number of migrating SVZ cells, with similar increases from the distal and proximal sides. Conversely, dramatically fewer cells migrated from SVZ explants cocultured with aggregates of x-Slit-expressing cells compared with control HEK cells. The effects of Slit on the proximal side were three times larger than in the distal part (p = 0.0001).
