Acute reactive and regenerative changes in mature cortical axons following injury.

Live-imaging brain slice techniques were utilized to study the acute changes in transected adult mammalian neocortical neuronal processes. Transected distal axons, but not axon segments directly emerging from the cell body or dendrites, undergo rapid morphological changes leading to attempted sprouting within hours after injury. The stereotypical response involved an initial retraction of the severed axon segments, followed by rapid stabilization. Subsequently, the cut-end underwent extensive swelling, forming large singular or multiple bulb-like structures. Two to three hours after transection, sprout-like protuberances emanated from the swollen bulbs. These axonal sprouts were highly dynamic, with many showing increased length over time and a capacity to change direction. These results indicate that damaged mature axons have an intrinsic capacity to react adaptively and attempt regeneration.