Contrasting biomechanics and neuropathology of spinal cord injury in neonatal and adult rats following vertebral dislocation

Clinically, spinal cord injuries (SCI) in infants are different from SCIs in adults. SCI is rarer in infants, and the most common types of associated spinal column injury are different for adults and infants. Initially, infants tend to have higher injury severities and mortality; however, young survivors of SCI typically have greater and more rapid functional recovery. The objective of this study was to contrast the biomechanics and neuropathology of SCI in adult and neonatal rats to investigate these differences. Thoracolumbar vertebrae of anaesthetized rats were dislocated laterally (T12 held stationary and L1 displaced laterally, with T13 between these levels) by 10 mm at 250 mm/sec in adults and by 4 mm at 100 mm/sec in neonates (13-15 days), and rats were euthanized 6 h later. Spinal cord sections were stained to detect hemorrhage (with hematoxylin and eosin [H&E]), axonal injury (with beta-amyloid precursor protein [beta APP]), and neuronal nuclei (with NeuN). Maximum load was significantly higher in adults (25.7 +/- 2.4N) than neonates (11.0 +/- 2.4N; p < 0.001). Adult and neonatal hemorrhage volumes were not significantly different for either the raw or normalized data sets (p = 0.064 for normalized dataset). Un-normalized axonal injury densities were similar for adults and neonates, but normalized axonal injury density was significantly higher in neonates (p < 0.001). Reduction of NeuN immunoreactivity was significantly lower in neonates, for both un-normalized (p < 0.004) and normalized (p < 0.001) data sets. The findings of this study may explain the different common types of spinal column injury associated with SCI, and the greater initial severity of SCI in infants.