Co-transplantation of embryonic neural tissue and autologous peripheral nerve segments to severe spinal cord injury of the adult rat. Guided axogenesis from transplanted neurons.

The present study is the first of a series of experiments designed to investigate the possibilities of reconstructing the severely injured spinal cord by means of transplantation techniques. Special attention has been given here to the capability of transplanted embryonic neurons to extend axons into autologous peripheral nerve grafts (PNGs). A cavity, made unilaterally in the cervical enlargement of the spinal cord of adult rats, was filled with solid pieces of different embryonic tissues: spinal cord (SC), cortex (CT) or dorsal root ganglia (DRG). In more than half of the transplanted animals, one end of a PNG was inserted into the center of the transplants, while the other, extraspinal end, was crushed and tied to peripheral tissues. After a postgrafting period ranging from 1 to 6 months, we found that the 3 types of transplants in general had survived and become integrated with the host spinal cord, although their overall organization remained atypical. Surviving graft neurons had developed processes, some of which had become myelinated. The ability of the grafted neurons to extend axons into the PNG differed strikingly from one type of graft to another, being apparently non-existent for cortical grafts, moderate for spinal cord grafts and quite extensive for dorsal root ganglia transplants. Interestingly, these differences reflected what was observed for the corresponding, fully differentiated qeurons in adult animals, when their cut axons were put in contact with non-neuronal components of peripheral nerves.