Long-term survival of anucleate axons and its implications for nerve regeneration.

Severed distal segments of nerve axons (anucleate axons) have now been reported to survive for weeks to years in representative organisms from most phyla, including the vertebrates. Among invertebrates (especially crustaceans), such long-term survival might involve transfer of proteins from adjacent intact cells to anucleate axons. In lower vertebrates and mammals, long-term survival of anucleate axons is more likely attributed to a slow turnover of axonal proteins and/or a lack of phagocytosis by macrophages or other cell types. Invertebrate anucleate axons that exhibit long-term survival are often reactivated by neurites that have grown from proximal nucleate segments. In mammals, induction of long-term survival in anucleate axons might allow more time to use artificial mechanisms to repair nerve axons by fusing the two severed halves with polyethylene glycol, a technique recently developed to fuse severed halves of myelinated axons in earthworms.