Histochemical demonstration of nitric oxide in herniated lumbar discs - A clinical and animal model study

Study Design. This study was designed to localize the cells that produce nitric oxide in a lumbar disc herniation by histochemical method, including in situ hybridization. Objective. To clarify which cells in herniated lumbar discs produce nitric oxide. Summary of Background Data. It was reported that herniated lumbar intervertebral disc specimens in culture are capable of producing nitric oxide. Methods. Surgical specimens from lumbar disc herniation were examined to determine nitric oxide synthase histologically using nicotinamide adenine dinucleotide phosphate diaphorase histochemistry. Allografts of intervertebral disc materials were placed on the epidural space at L-6 level in the rat. Nitric oxide synthase was examined in the applied tissues using nicotinamide adenine dinucleotide phosphate diaphorase histochemistry and in situ hybridization histochemistry. Results. Nicotinamide adenine dinucleotide phosphate diaphorase (nitric oxide synthase) positive cells were observed in 2 (40%) of 5 herniated disc materials in patients. The positive cells were mainly in granulation tissue around intervertebral disc materials. In animal models, nitric oxide synthase-positive cells were observed in all specimens at 1 and 2 weeks postoperatively. Newly formed vessels and small round cells in granulation tissue around the grafted intervertebral disc showed positive reaction. In situ hybridization demonstrated the expression of inducible isoform of nitric oxide synthase messenger RNA (mRNA) identical to small round cells around the applied intervertebral disc. Conclusion. Nitric oxide in a lumbar disc herniation is mainly produced by cells in granulation tissue around the herniated intervertebral disc.