Voltage gradients and ionic currents in injured and regenerating axons.

When an axon is damaged, a strong, persistent, injury current enters the damaged area, driven by the ionic pumps of the healthy portion of the cell. This current is associated with an electrical field, existing within the damaged axon and in the extracellular space around it. Such currents and fields are a common feature of neuronal damage and probably play a role in Ca2+-mediated degenerative events soon after transection, retrograde die-back, a structuring of the axonal terminus into zones, and perhaps organelle movement within damaged fibers. The long-term persistent currents may be a common feature of growing axons and might play a role in development and regeneration. Altogether, electrical effects of injury provide an alternative to conjecture concerning the physiological basis for immediate cellular responses to axonal injury. They also provide a possible basis for modulating the responses of neurons to injury by applied electric fields.