Ultrastructural study on avulsion effects of the cat cervical moto-axonal pathways in the spinal cord

After selective avulsion of the ventral root cervical 7 (C7) from the adult cat spinal cord, the intraspinal trajectories of the torn axons in the white matter were studied at different survival times. Two phases could be discerned: an early phase which showed changes that occurred up to 14 days after avulsion and a second phase from day 30 onwards. Two days postoperatively, considerably swollen, empty myelin sheaths occurred, which remained present up to 14 days after avulsion. A primary increase in the number of glial cells (microglia) was noted on days 2 and 4 after avulsion. Ultrastructurally, unmyelinated and myelinated terminal clubs were found 8 and 14 days after avulsion. These clubs were characterized as cones of growth, related to axonal regeneration. A second glial increase was present after 30 days. At that time, the entire moto-axonal pathway clearly showed a degeneration pattern. This finding was light microscopically confirmed by an increase of GFAP-positive astrocytes. During the first 30 days, a front of small calibre myelinated axons, starting at the transition zone of the grey and white matter traversed halfway through the moto-axonal pathway. However, on days 60 and 90 no further shift of the front had occurred.