Sympathectomy reduces mechanical allodynia, tumor necrosis factor-alpha expression, and dorsal root ganglion apoptosis following nerve root crush injury

Study Design. An analysis of pain behavior and neuronal apoptosis in the dorsal root ganglion ( DRG) following crush injury to the L5 nerve root, with or without surgical sympathectomy. Objectives. To determine whether sympathectomy prevents pain behavior and to compare pain behavior with expression of tumor necrosis factor ( TNF)- alpha and apoptosis in the DRG. Summary of Background Data. Sympathetic block is used to relieve symptoms in radiculopathy patients. One effect of the block is improvement of blood flow to the nerve. However, this beneficial effect continues longer than the expected duration of local anesthesia, suggesting an unknown neuroprotective effect involving interference with sympathetic activity. Methods. Sprague- Dawley rats ( n = 102) were used and divided into 4 experimental groups. In the crush group, animals received a crush injury to the L5 nerve root. In the sympathectomy group, animals received sympathectomy ( Syx) on the left side. In the Syx + crush group, both sympathectomy and crush injury were performed. In the sham group, the surgical procedure was the same, but neither sympathectomy nor crush injury took place. Mechanical allodynia was determined in 4 groups. Expression of TNF- alpha was compared in rats with crush injury, with and without sympathectomy. Using immunostaining for caspase 3, NeuN, and GFAP, localization of apoptotic cells was observed. In addition, we compared the percentage of neurons undergoing apoptosis in the DRG. Results. Sympathectomy prevented mechanical allodynia throughout the 14- day experimental period. TNF- alpha expression was increased in the DRG following crush-only injury, whereas it was decreased in animals undergoing sympathectomy after the crush injury. DRG apoptosis in the crush group was significantly higher than in the sympathectomy group at day 7 ( P < 0.05). Conclusion. Surgical sympathectomy reduced mechanical allodynia for 14 days after nerve root crush injury, and that DRG apoptosis was decreased in injured animals that underwent sympathectomy. Sympathetic block may not only cause an increase in nerve blood flow, but may also prevent the development of significant TNF- alpha elevation, DRG apoptosis, and neuropathic pain.