Blood-spinal cord barrier response to transection.

The integrity of the blood-spinal cord barrier (BSB) distal to a surgical transection was evaluated at the light and electron microscopic levels, using the tracers Evans blue albumin (EBA) and horseradish peroxidase (HRP). At the light microscopic level, the orange fluorescence of the EBA was detected as far as 0.45 mm distal to the transection. The tracer was not only diffusely distributed in the neuropil but also was apparently taken up by ventral horn neurons and glial cells. A feathery halo of EBA extending beyond their walls indicated that there had occurred some leakage of EBA from intrinsic vessels into the surrounding cord tissue. The microvasculature was evaluated at the ultrastructural level for evidence of changes in permeability to HRP. Pinocytosis and vesicular transport of the protein were apparent in some endothelial cells. In addition, there was limited evidence for leakage across tight junctions. After 1 day the barrier selectivity appeared to be restored and vesicular transport of HRP was not found. Endothelial pinocytosis, however, appeared enhanced for as long as 7 days following injury.