Regeneration of Rapid Escape Reflex Pathways in Earthworms

SYNOPSIS. The medial and lateral giant nerve fibers in the earthworm, Eisenia foetida, regenerate cell-specific connections and recover through-conduction capabilities in as little as 1–2 days after ventral nerve cord (VNC) transection Similar cell-specific reconnections between giant fibers occur approximately 4–10 days after grafting together two posterior pieces of worms or transplanting lengths of VNC from donor to recipient worms from which a comparable length of VNC has been removed In the latter case, touch-sensory and giant motor neurons within the transplanted VNC also regenerate, leading to restoration of escape reflex function in segments receiving the transplant Results from heterotopically transplanted VNC indicate that both central and peripheral regeneration is cell-specific, but specificity is sufficiently broad to include segmentally homologous target cells from body regions other than those of the transplant origin E. foetida and related species may be useful for studying the extent to which differentiated nervous systems, composed of serially homologous neuronal networks, can be remodelled by experimental manipulations such as grafts and transplants.