Ultrastructural studies of spinal cord in rats subjected to hyperbaric oxygen exposure and experimental spinal cord trauma have resulted in frequent degeneration of axons. In both experimental situations central nervous system myelinated fibers containing complex cytoplasmic interdigitations of electron lucent, normal appearing cytoplasm, and dense cytoplasm, interpreted as degenerative, were observed. In some of the complex profiles the electron lucent cytoplasm could be traced back to the inner mesaxon, where its relation to the latter indicated a glial origin. Cytochemical evaluation of acid phosphatase activity in the complex cytoplasmic interdigitations revealed that both components contain significant lysosomal activity. The complex structures are interpreted as being sequestrations of degenerating axoplasm by distal adaxonal oligodendroglial processes, possibly representing an unusual form of heterophagocytosis.

Balentine, , , , , , , , (1977). Complex oligodendroglial invaginations within myelinated nerve fibers of the central nervous system during axonal degeneration. Journal of neuropathology and experimental neurology, 1977 Nov;36(6):897-906. https://www.ncbi.nlm.nih.gov/pubmed/925717