Embryonic central nervous system transplants mediate adult dorsal root regeneration into host spinal cord

OBJECTIVE: The aim of this study was to determine whether embryonic central nervous system transplants assisted cut dorsal root axons of adult rats to regenerate into the spinal cord. METHODS: Rats received transplants of emb ryonic spinal cord, hippocampus, or neocortex into dorsal quadrant cavities aspirated in the lumbar enlargement. The transected L5 dorsal root stump w as secured between the transplant and the spinal cord. Regenerated dorsal r oots were subsequently labeled by using immunohistochemical methods to dete ct calcitonin gene-related peptide. RESULTS: Calcitonin gene-related peptid e-immunoreactive axons extended into all host spinal cords examined, but th e patterns of regrowth differed in rats that had received embryonic spinal cord and brain transplants. In rats with embryonic spinal cord transplants, regenerated axons traversed the dorsal root/spinal cord interface, entered the spinal cord, and frequently formed plexuses with arborizations in moto neuron pools; some of these axons established synapses on spinal cord neuro ns. In rats with embryonic brain transplants, regenerated axons were diffus ely distributed in the spinal cord but did not form plexuses. Few axons reg enerated into the spinal cords of lesion-only animals. The results of quant itative analyses confirmed these findings. CONCLUSION: These findings sugge st that transplants of embryonic spinal cord and brain supply cues that ena ble cut dorsal roots to regenerate into the host spinal cord and that the c ues provided by spinal cord transplants favor more extensive growth than do those provided by brain transplants. These cues ave likely to depend in pa rt on neurotrophic effects of embryonic central nervous system tissues. The refore, embryonic central nervous system transplants, especially spinal cor d grafts, may contribute to techniques for restoring interrupted spinal ref lex arcs.