A quantitative ultrastructural study of dorsal root regeneration.
Regeneration in rat lumbo-sacral dorsal roots was studied 5-71 days following crush lesions. Wallerian degeneration occurred up to 20 days. At 11 days degenerating myelin was found in both Schwann cells and macrophages. Myelination was first observed 4 mm central to the crush at 7 days, and myelin became compact when the mesaxon exhibited 3.5 turns about the axon (about 11 days post-operatively). At 71 days, 69% of all fibres were myelinated, compared with 36% in normal roots. An example of 2 axons myelinating within the same Schwann cell occurred at 20 days. In normal roots curvilinear relationships were found between axon diameter and fibre diameter, myelin thickness and axon diameter, and between g and fibre diameter. In contrast, linear relationships between these parameters occurred in post-operative roots up to 71 days. Curvilinearity returned at 71 days. Alterations in the relationship between axon diameter and myelin thickness during regeneration indicated that myelin growth lagged behind axon growth throughout, but was more noticeable in larger calibre fibres. By 71 days, larger fibres exhibited disproportionately thin myelin, whilst small fibres possessed abnormally thick myelin compared to normal fibres of similar calibre. Regeneration was limited by axons failing to make successful central synaptic connections and by the poor metabolic response of dorsal root ganglion cells to sectioning of their central processes.
D000818:Animals; D005727:Ganglia, Spinal / Q000648:ultrastructure*; D008854:Microscopy, Electron; D009185:Myelin Proteins / Q000096:biosynthesis; D009186:Myelin Sheath / Q000648:ultrastructure; D009412:Nerve Fibers / Q000648:ultrastructure; D009413:Nerve Fibers, Myelinated / Q000648:ultrastructure; D009416:Nerve Regeneration; D051381:Rats; D012583:Schwann Cells / Q000648:ultrastructure; D014855:Wallerian Degeneration
D009185:Myelin Proteins