Formation of heterotopic granule cell in mouse cerebellum after neonatal administration of cytosine arabinoside.

The mice, ICR-JCL strain, were injected s.c. with 30 mg/kg body weight of cytosine arabinoside at the age of 2, 3, and 4 days. The external granular layer of these mice was destructed selectively, and subsequently these mice developed abnormal cytoarchitecture in the cerebellum, such as disarrangement of Purkinje cells and heterotopic granule cells in the molecular layer. This study was undertaken to elucidate the mechanism in the formation of heterotopic granule cells. In the cerebellum of the treated mouse, some mossy fibers and glomerular collaterals of climbing fibers extended abnormally even into the molecular layer by the age of 10 days, since no granule cells migrated to the inner granular layer until about 10 days when granule cell production started again in the regenerated external granular layer. Subsequently, these fibers, i.e. axons which extended into the molecular layer, established synapses in the molecular layer with the dendrites of migrating granule cells. These granule cells had no need to migrate to the inner granular layer, and so they remained in the molecular layer as heterotopic granule cells.