Neuronal chain migration from SVZ explants.A, Explants from the SVZ of the olfactory bulb of P3 rats were cultured for 2 d on poly-d-lysine-coated tissue culture dishes in medium containing 10% serum.Arrowheads point to the chains of migrating cells, andarrows mark cells migrating in “sheets.” Scale bar, 300 μm. The explants were fixed, and the chains were processed for transmission electron microscopy. Longitudinal (B) and cross-sectional (C) views were examined. Two cells types were detected: cell type A (not labeled), the most abundant, with electron-dense nuclei that are presumably neuroblasts; cell type B, with electron-lucent nuclei that are presumably glia. Scale bar, 4 μm.