Morphological observation of Schwann cell autophagy during regenerative course of sciatic nerve

objective: To investigate the autophagic effects of Schwann cell during regenerative course of rat sciatic nerve. Methods: Nerve injury and regeneration model was made by transecting rat sciatic nerve. Nerve samples from the proximal end of injuring nerves were obtained 0, 0.5, 1, 1.5, 2, 3, 4, 5, 7, 10, 15 days after transection respectively and ultrathin sections were prepared for examination under electron microscope. Results: Axons started to separate from myelin sheath at the first day after transection and degenerated quickly with vacuole appearance. And then, myelin sheath creased, strangled and fell off into fragments, and large amounts of myelin debris of different sizes and shapes appeared in Schwann cells and fused with lysosomes to form AcPase reaction-positive autophagic vacuoles. Juvenile cells were seen firstly around the newly-born blood capillary at the 7th day after transection and many of them appeared later. Conclusions: The degenerating myelin debris is cleared mainly by autophagy of Schwann cells during regeneration of rat sciatic nerve and lysosomes play a remarkable role in the process. Schwann cells dedifferentiated into young cells named precursor Schwann cell, then proliferate and differentiate to take part in the regeneration of nerves.