The vascular response to nerve crush: relationship to Wallerian degeneration and regeneration

The response of the endoneurial vasculature in rat sciatic nerve following crush injury was investigated by morphometric analysis of serial nerve transverse sections at the site of injury and in distal segments at 1, 2, 3, 6, and 9 weeks after injury. Quantitative analysis included determination of the number of vessels, vessel radius, vessel perimeter, and transfascicular area. The vascular response to crush injury consisted of two phases: an early phase, which peaked at 1 week after crush, consisted of an increase in vessel size but not vessel number. The second phase, which peaked at 6 weeks after crush, consisted of an increase in the number of vessels and in their density. This two-phase response was also evident as a dual peak in the total endoneurial vessel perimeter, a measure of vascular surface area, when this variable was plotted against time. The first phase of the vascular response was temporally related to the recruitment of macrophages and the clearance of degenerating axonal and myelin tissue during the early phase of Wallerian degeneration. The second phase involved an increase in the number of blood vessels and was associated with cellular proliferation, neurite elongation, and myelination during the subsequent period of nerve regeneration.