Effect of mechanical compression on the vascular permeability of the dorsal root ganglion.

The dorsal root ganglion contains primary sensory neurons and is closely related to low back pain and sciatia. The present study investigated whether endoneurial edema, which is involved in the onset of pain and nerve dysfunction, was increased in the dorsal root ganglion by compression. The influence of mechanical compression on the vascular permeability of the lumbar dorsal root ganglion was determined. The dorsal root ganglion is reported to have a higher vascular permeability compared with other nerve tissues as well as lacking a blood-nerve barrier. However, only a few studies have assessed the influence of mechanical compression on the dorsal root ganglion. especially its vascular permeability. In dogs, laminectomy was performed at L7 and the dorsal root ganglion of the seventh lumbar spinal nerve was compressed for 1 h using four kinds of clips with various strengths. After clip removal, Evans blue albumin (EBA) or horseradish peroxidase (HRP) was administered intravenously as a tracer. After sacrifice, the EBA-injected specimens were observed by fluorescence microscopy and the HRP-injected specimens were observed by light and transmission electron microscopy. After compression of the dorsal root ganglion at 15 gf or more, leakage of tracer into the endoneurial space was markedly increased compared with the sham-operated group and severe edema was noted. Extravascular leakage of tracer was obvious around venules and capillaries. Electron microscopy showed an increase of extravascular HRP in the gap junctions and fenestrae between endothelial cells due to increased vascular permeability. However, the dorsal root ganglion was covered with a thick perineurium and HRP that leaked from the blood vessels did not enter the epineurium even after compression at 60 gf. It was proven that the increased vascular permeability occurred as well as in leakage of dye within the dorsal root ganglion after a single hour of compression of the dorsal root ganglion.