Ionic shifts in myelinated nerve fibers during early stages of Wallerian degeneration.

The distribution and relative mass fraction of the diffusible ions Na, K, Cl and Ca were determined by X-ray microanalysis in the axons of rat sciatic nerve 18 h and 36 h after crush and in control nerves. The investigations were performed in freeze-dried ultrathin cryosections after shock freezing of the nerves in liquified propane. 18 h after crush, no definite alteration of the ions were found compared to the control nerves. In electron micrographs of routinely processed nerves, no ultrastructural changes were seen. 36 h after crush, two types of ionic imbalance were found, the first characterized by decreased K and slightly increased Na in the axon, the second by concurrently increasing axonal Na and Cl, accompanied, in some fibers, by accumulating Ca. These types of ionic imbalance presumably represent two stages of axolemmal permeability alteration corresponding to early structural changes of axoplasm in electron micrographs of routinely processed nerves at that time.