The Distribution of Tissue Damage in the Spinal Cord Is Influenced by the Contusion Velocity

Abstract

A rat model of thoracic spinal cord contusion was used to examine the effect of velocity on the primary injury. The overall objective of this study was to determine the effect of the contusion velocity (slow vs. fast) on damage to the spinal cord immediately following mechanical injury. Secondary objectives were to demarcate between damage in the gray and white matters and to observe damage to the mechanical elements of the neurons (i.e., neurofilaments). Although studies have explored the effect of impact velocity on spinal cord damage and functional deficits, no study has addressed regional tissue damage of the primary injury (e.g., between the gray and white matter) as a function of velocity. A modified Spinal Cord Injury Research System generated 1 mm contusions in 24 male, Sprague-Dawley rats (210-320 g) at T10, using slow (3 mm/s) and fast (300 mm/s) velocities. The primary lesion (<2 minutes postinjury) was assessed using hematoxylin and eosin staining for hemorrhage volume and immunostaining for nonphosphorylated heavy neurofilament damage. The volume of hemorrhage in the white matter was significantly increased following fast impact (fast = 0.61 mm3, slow = 0.24 mm3, P = 0.013) whereas the total hemorrhage volume (fast = 1.51 mm, slow = 1.21 mm, P = 0.22) showed no effect. Complete axonal disruption was evident in the fast injury group around the injury epicenter. A significant increase in nonphosphorylated neurofilament staining (P = 0.013) was observed for fast impacts. Hemorrhage in the gray matter was similar between the slow and fast groups, but an increase in neurofilament dephosphorylation was observed in the gray matter following fast contusion (P = 0.03). We conclude that contusion velocity has an effect on the magnitude of injury within the white matter during spinal cord injury and the amount of neuronal damage in the gray matter. The results of this study demonstrate the importance of including high impact velocity as a variable in models of spinal cord injury.