Persistence of rubrospinal projections following spinal cord injury in the rat

Recent neurophysiological and magnetic resonance imaging studies of clinically "complete" human spinal cord injuries indicate that some patients have considerable subclinical function and substantial morphological integrity of descending spinal tracts. In contrast, extensive histopathological changes, including cell death, have been described in central nervous system nuclei projecting to the cord following experimental transection or hemisection of the spinal cord in animal models. We have used a rodent model of severe compression cord injury that more closely resembles the clinical pathophysiology to investigate the extent of the persistence of the rubrospinal projection. Counts of red nucleus neurons retrogradely labelled with Fluorogold demonstrate that in contrast to the results obtained with transection models, compression injuries of the spinal cord do not result in massive loss of rubrospinal projections, at least up to 8 weeks postinjury. The results also suggest that many of the axons persist distal to the lesion site and that they are functionally intact with respect to retrograde transport capabilities.