Autophagy of neuron axon during regeneration of rat sciatic nerves.

OBJECTIVE: To investigate the autophagic clearance of degenerated neuron axon during regeneration of rat sciatic nerves. METHODS: Wallerian degeneration model was established in rats by sciatic nerve transection. Samples from the distal stump were collected at different time points after the transaction and ultrathin sections prepared for electron microscopic examination and acid phosphatase (AcPase) activity detection. RESULTS: Neuron axon degeneration occurred after transection of rat sciatic nerve, presenting predominantly swelling of the axoplasm and separation of the axon from the myelin sheath seen 5 h to 2 d after the transection. On day 4, axoplasm condensation took place and the axons were completely separated from the myelin sheath to form dissociative axon body. Vacuoles of various sizes were identified in the axon in the early stage after operation and later when the axons were completely dissociated from the nerve sheath, larger dissociative axon bodies occurred. The axolemma surrounding the axon body was derived from the neuronal cytomembrane, and the condensed axoplasm contained numerous autophagic vacuoles at all levels along with large number of neurofilaments, microtubules and microfilaments arranged in a crisscross pattern. The autophagic vacuoles exhibited acid phosphatase (AcPase) activities. Since the day 7, the axon bodies were absorbed after degradation and macrophages could be spotted occasionally. CONCLUSION: The degenerated axons were cleared mainly through autophagy during regeneration of rat sciatic nerve and macrophages only assist in this process.