MIGRATION BEHAVIOR OF GRANULE CELL NEURONS IN CEREBELLAR CULTURES .1.A PKH26 LABELING STUDY IN MICROEXPLANT AND ORGANOTYPIC CULTURES

Granule cells were dissociated from early postnatal mouse cerebella an d labeled with a fluorescent dye probe PKH26. Small number of the labe led cells were mixed with cerebellar cortical microexplant cultures or transplanted into cerebellar cortical organotypic explants, and their time-dependent morphological changes during cultures were examined wi th fluorescence microscopy. Granule cell neurons first extended asymme trical short bipolar processes in both cultures, and migrated actively in microexplant cultures. After elongation of symmetrically bipolar l ong and thin neurites, they sprouted short thick processes from cell b odies and migrated perpendicular to neurite bundles that were devoid o f glia in microexplant cultures, or migrated vertically inward into th e internal granular layer in the organotypic explant. During such migr ations, they extended short thick processes in front and thin processe s behind the cell body. The latter processes were connected to thin lo ng neurites with T- or Y-shaped junctions in both cultures. Finally, t hey extended many short thick processes from cell bodies in both cultu res. Such behaviors of granule cell neurons in microexplant cultures w ere, thus, similar to those in organotypic explant cultures despite of the absence of Bergmann glial cells. These migration patterns may be closely related to migration of granule cells in histogenesis of the c erebellar cortex.