Intraparenchymal grafting of cerebellar cell suspensions to the deep cerebellar nuclei of pcd mutant mice, with particular emphasis on re-establishment of a Purkinje cell cortico-nuclear projection

In transplanting embryonic cerebellar grafts to the cerebellar cortex of "Purkinje cell degeneration" (pcd) mutant mice to replace missing Purkinje cells (PC), donor PC leave the graft and migrate to the molecular layer of the host. However, PC axons do not always reach the deep cerebellar nuclei of the host, which would be a key element in restoring much of the necessary inhibitory cortico-nuclear projection associated with normal cerebellar function. Rather, grafted PC axons often innervate a region containing deep cerebellar nuclei neurons inside the transplant, while the perikaryon migrates to the host molecular layer. In the present study, aimed at re-establishing a PC innervation of the deep nuclei, we implanted E12 cerebellar cell suspensions intraparenchymally to the deep cerebellar mass of the hosts. The development of grafted PC was monitored with 28-kDa calcium-binding protein (CaBP) immunocytochemistry at various times after transplantation. At short survival times (5 days after grafting), grafts were confined to the site of the original injection. At longer survival times (7-32 days after grafting), grafted PC formed a migratory stream that reached the cerebellar cortex of the host. The most robust graft development was seen 1 month after grafting, the longest survival time allowed in this series of experiments. At that time, clusters of donor PC were found both in the deep nuclei parenchyma and aligned along cortical folia. The orientation of the dendritic trees of PC that had migrated to the cortex was toward the pia. A CaBP-immunoreactive fibre plexus innervated the host deep cerebellar nuclei. The stream of grafted PC extended from the deep cerebellar nuclei to the cerebellar cortex of the host, indicating that donor PC could establish their axonal contacts in the deep nuclei and then move to their final cortical locality, thus recapitulating a migratory path normally taken during cerebellar ontogeny. It appears therefore that both from the pathophysiological and ontogenetic standpoints, the deep cerebellar nuclei represent the appropriate site for PC implantation in cerebellocortical atrophy.