Multiple cell populations in the early postnatal subventricular zone take distinct migratory pathways: A dynamic study of glial and neuronal progenitor migration

Neural progenitors in the subventricular zone (SVZ) of the postnatal rat forebrain give rise to either olfactory interneurons or glia. To investigate the overall patterns of progenitor movement, we labeled neonatal rat SVZ cells by stereotactic injection of a GFP-encoding retrovirus into the SVZ at various coronal levels. We then studied the movements of labeled cells by time-lapse videomicroscopy in living brain slices cut in different orientations. We observed two migration patterns: (1) progenitors migrated radially into the overlying white matter and cortex, but only at the level of viral injection; these were previously shown to give rise to astrocytes and oligodendrocytes, (2) progenitors migrated in a bidirectional, rostrocaudal pattern along the entire extent of the SVZ; many of these cells eventually migrated into the olfactory bulb and developed into interneurons, but they did not turn to migrate radially out of the SVZ until they reached the olfactory bulb. Video imaging showed apparent boundaries to migration between the SVZ and adjacent structures. These observations indicate that there are at least two distinct migratory pathways within the SVZ used differentially by immature neurons and glia.