A neuroanatomical analysis of spinal cord injury in the rhesus monkey ( Macaca mulatta)

Abstract

Thirteen rhesus monkeys were subjected to impacts of either 200, 300, 400, or 500 g-cm, on the dorsal surface of the spinal cord (Allen 1911). Six monkeys served as controls to determine the results of transection of the cord as well as the optimal survival time, and 2 additional subjects underwent the operative procedures only. Most of the animals were sacrificed 1 week postoperatively and the brains and spinal cords were processed by the Fink and Heimer (1967) technique for degenerating axons. Two controls and 1 experimental subject, sacrificed at 1 week, were prepared for electron-microscopic analysis. The results indicate that, with the possible exception of the dorsal spinocerebellar tracts, all pathways are affected either primarily or secondarily by contusion of the cord. The dorsal columns appear to be particularly susceptible to trauma not only at the impact site, but also on either side of it due to the spread of hemorrhagic necrosis. From our material, it appears that with damage at high thoracic-low cervical levels, the central grey is not as susceptible as is the case with damage at lower thoracic levels. The region of greatest susceptibility at both levels was just above the central canal. The causal factors underlying these findings are not known, but the structural properties of the cord which determine the resolution of a force applied outside the cord, as well as the resolution of those forces built up within the cord itself, and the overall pattern of the blood supply, seem to be significant factors. Generally, the amount of degeneration in the cord following calibrated trauma was correlated with the force of the impact, but this was not always the case. The degree of involvement of any system was mainly a function of its distance from the center of the cord. Thus, a tendency for sparing of peripherally located fibers was noted. Such sparing was greatest in cases subjected to minimal impact and in some was even present directly beneath the point of impact. The presence of a paralysis was also generally correlated with the impact force, but damage to the descending motor systems did not necessarily result in a paralysis.