Relations between development and regeneration of tadpole spinal cord.

1. The developing spinal cords of bullfrogs and transected cords of stage IV tadpoles were subjected to two-dimensional gel electrophoresis and histological analysis. During development, the level of actin, alpha-tubulin or beta-tubulin in the 7-10th spinal segments increased with time and reached a maximum around stage XIII followed by a decrease, as shown from quantitative assay on protein spots of 2-dimensional gels of cord homogenates. In contrast, the level of 68 kD neurofilament subunit (NF68) was low in tadpoles but high in frog. 2. Following a complete transection made at the level of the 8th spinal segment, the cord tissue of the lesion zone degenerated; regeneration from each cut end then occurred, which lengthened for approximate 0.35 mm by 28 days after transection. The content of actin, alpha-tubulin and beta-tubulin in the cord within 1-2 mm of the transection site was elevated to 124-192% of control values 7-28 days post-transection, whereas NF68 declined to near non-detectable extent. 3. The regeneration of each cord stump included outgrowth of neuroepithelial cells and nerve fibers, reconstituting a newly regenerated cord segment. Ultrastructural examination revealed that features of the regrowth of fibers and guidance of neuroepithelial cells to the axonal growth resembled that seen in the developing cord. Thus the biochemical and morphological data support that the regeneration of the nervous system recaptulates its developmental events, providing evidence for molecular mechanism underlying central axonal regeneration.