Astrocyte-conditioned medium and Slit-conditioned medium exert opposite effects on migration from SVZ explants in Matrigel. A, Explants were cultured in Matrigel containing Slit-CM, HEK-CM, or ACM. Migration from SVZ explants was symmetric under all conditions. However, ACM increased and Slit-CM decreased the number of migrating SVZ cells compared with HEK-CM (p = 0.007 and p= 0.001, respectively). B, Slit decreases migration from SVZ explants in a dose-dependent manner. SVZ explants were cultured in Matrigel containing different amounts of Slit-CM for 11 hr. The number of cells migrating from SVZ explants was correspondingly reduced with increasing amounts of Slit-CM. Maximal levels of Slit resulted in a >20-fold decrease in the number of migrating cells compared with control explants. The error bars represent SEM.