Grafted granule and Purkinje cells can migrate into the mature cerebellum of normal adult rats.

Cerebellar primordia of different ages (embryonic days of 14 to 20) were transplanted into cerebella of normal syngeneic adult rats (Fischer 344). After 1-12 months (mostly 5-6 months), the host brains were examined by light and electron microscopy. In about 80% of our successful experiments, grafted Purkinje and/or granule cells migrated into the host molecular layer. Some granule cells migrated down along host Bergmann glia, reminiscent of their normal developmental migration route. Other granule cells migrated along astroglial processes that ensheathed capillary walls. Some grafted Purkinje cells were also located ectopically in the host molecular layer. They were identified as graft origins autoradiographically. This migration seemed to be encouraged under conditions where the subjacent host Purkinje cells had been lost. Where the grafted Purkinje cells were located on top of the host molecular layer, their primary dendrites faced vertically downwards into the host molecular layer. However, the position of the apical poles of migrated Purkinje cell bodies in the deeper aspect of the molecular layer varied considerably, suggesting that the orientation of the Purkinje cell dendrites is probably determined by the availability of afferent fibers. Thus, the present study has demonstrated that Purkinje and granule cells can migrate from embryonic cerebellar grafts into the molecular layer of the normal, adult host rat cerebellum.