Ultrastructural localization of calcium in peripheral nerve fibres undergoing Wallerian degeneration: an oxalate-pyroantimonate and X-ray microanalysis study.

Calcium was demonstrated ultrastructurally as an electron dense precipitate with the oxalate-pyroantimonate technique in rat sural nerves undergoing early Wallerian degeneration after surgical crush (30 h after lesion). In normal nerves (controls) the distribution of calcium precipitates in the axoplasm appeared homogeneous in unmyelinated fibres and heterogeneous (with specific domains) in myelinated ones. Calcium precipitate was also found within the smooth reticulum and mitochondria of the fibers and Schwann cells, and in endoneurial space. In nerve fibres with early degenerative alterations, there was increased calcium precipitate within membranous profiles of smooth reticulum and mitochondria (in both nerve fibres and Schwann cells) and in areas where the cytoskeletal proteins were disintegrated. This last finding confirms the participation of calcium in the disruption of axonal microtubules and neurofilaments in early Wallerian degeneration process. Fibers with intense degenerative changes lost the usual distribution for calcium. The specificity of the reaction was demonstrated using EGTA chelation and X-ray microanalysis.