Watery and dark axons in Wallerian degeneration of the opossum's optic nerve: different patterns of cytoskeletal breakdown?
In this paper we report a qualitative morphological analysis of Wallerian degeneration in a marsupial. Right optic nerves of opossums Didelphis marsupialis were crushed with a fine forceps and after 24, 48, 72, 96 and 168 hours the animals were anaesthetized and perfused with fixative. The optic nerves were immersed in fixative and processed for routine transmission electron microscopy. Among the early alterations typical of axonal degeneration, we observed nerve fibers with focal degeneration of the axoplasmic cytoskeleton, watery degeneration and dark degeneration, the latter being prevalent at 168 hours after crush. Our results point to a gradual disintegration of the axoplasmic cytoskeleton, opposed to the previous view of an "all-or-nothing" process (Griffin et al 1995). We also report that, due to an unknown mechanism, fibers show either a dark or watery pattern of axonal degeneration, as observed in axon profiles. We also observed fibers undergoing early myelin breakdown in the absence of axonal alterations.
Narciso
M S
MS
Departamento de Histologia e Embriologia, Instituto de Ciências Biomédicas, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, 21941-590 Brazil.
Hokoç
J N
JN
Martinez
A M
AM
D000818:Animals; D001369:Axons / Q000473:pathology / Q000648:ultrastructure; D008854:Microscopy, Electron; D009409:Nerve Crush; D009412:Nerve Fibers / Q000473:pathology / Q000648:ultrastructure*; D009893:Opossums; D009900:Optic Nerve / Q000473:pathology / Q000648:ultrastructure*; D020221:Optic Nerve Injuries / Q000473:pathology*; D013997:Time Factors; D014855:Wallerian Degeneration / Q000473:pathology*