Nodal and paranodal structure during Wallerian degeneration in frog spinal nerve.

The nodal and paranodal regions of myelinated peripheral nerve fibers in frogs were examined at sequential times (1-24 days) during Wallerian degeneration. In the region up to 3 mm distal to the transection, paranodal demyelination and axoplasmic degeneration became apparent on day 4 and progressed to involve most of the nodes by day 8. The E-fracture face of the axolemma showed a patchy distribution of nodal particles and some paranodal demyelination on days 4 and 6. On day 8, nodal particles were evenly distributed at low concentration and the adjacent demyelinated paranodal regions showed a corresponding increase in particle density, suggesting redistribution of the nodal particles. The sequence of changes seen in comparable to that in Wallerian degeneration of central nervous system (CNS) fibers but progressed more rapidly in the peripheral nervous system (PNS). In addition a higher proportion of PNS fibers shows pathological changes at corresponding time periods.