Degeneration of long-term fetal neostriatal allografts in the rhesus monkey: an electron microscopic study

Primate fetal neostriatal neurons were implanted into the ibotenic acid-lesioned primate striatum and the animals were allowed to survive for 8 months. Light microscopic examination of the transplanted tissue demonstrated that the grafts were between 1.0 and 1.5 mm in diameter. The transplants were highly gliotic, but contained both normal appearing and degenerating neurons. At the electron microscopic level, the transplanted neurons displayed ultrastructural features identical to those of medium spiny, medium aspiny, and large aspiny striatal neurons. However, the majority of the grafted neurons showed evidence of degeneration. The grafts' neuropil demonstrated numerous glial processes, as well as mature axodendritic and axospinous synapses. Although this study was limited to only two graft recipients, the degenerative changes seen in the long-term primate allografts suggest that extension of these techniques into the clinical setting may be premature at the present time.