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Substance P-Saporin Down-Regulates Substance P Receptor Immunoreactive Sensory Dorsal Root Ganglion Neurons Innervating the Lumbar Intervertebral Discs in Rats

Ohtori, Seiji, MD, PhD; Inoue, Gen, MD; Koshi, Takana, MD; Ito, Toshinori, MD; Doya, Hideo, MD, PhD; Moriya, Hideshige, MD, PhD; Takahashi, Kazuhisa, MD, PhD

doi: 10.1097/01.brs.0000250306.12996.fa
Basic Science
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Study Design. To examine changes in substance P receptors on dorsal root ganglion cells innervating the rat lumbar intervertebral discs using immunohistochemistry and a retrograde neurotracing method.

Objective. We evaluated the effects of intradiscal administration of substance P-saporin, a toxin selective for cells expressing substance P receptors.

Summary of Background Data. The rat L5/6 intervertebral disc is multi-segmentally innervated from the L1–L6 dorsal root ganglions. Substance P and the neurokinin-1 receptor contribute to inflammatory pain transmission. Substance P immunoreactive-sensory nerve fibers in human intervertebral discs and immunoreactive-dorsal root ganglion neurons innervating rat intervertebral discs have been reported to be important in the transmission of discogenic low back pain. In the current study, we evaluated the effects of intradiscal administration of substance P-saporin, a toxin selective for cells expressing substance P receptor.

Methods. Sixteen rats were used (control group, n = 8; substance P-saporin group, n = 8). To detect dorsal root ganglion neurons innervating the L5/6 intervertebral disc, neurotracer (fluoro-gold crystals) was placed into the intervertebral disc. Seven days after fluoro-gold application, the L5/6 intervertebral disc was exposed and injected with 175 ng of sterile substance P-saporin (substance P-saporin group, n = 8). Fourteen days after the first operation, each dorsal root ganglion was harvested, sectioned, and processed for neurokinin-1 immunohistochemistry using rabbit antibody to neurokinin-1. The numbers of fluoro-gold labeled neurons, and fluoro-gold labeled and neurokinin-1 immunoreactive neurons were counted in both groups.

Results. Neurons innervating the L5/6 intervertebral discs, retrogradely labeled with fluoro-gold, were distributed throughout dorsal root ganglions from L1 to L6 in both groups. Of fluoro-gold labeled neurons, the proportion of neurokinin-1 immunoreactive neurons was 35% in the control group. However, the proportion of neurokinin-1 immunoreactive neurons was 8% after administration of substance P-saporin into the intervertebral discs (substance P-saporin group). Substance P-saporin significantly decreased the ratio of neurokinin-1 immunoreactive neurons.

Conclusion. Substance P-saporin decreased the ratio of neurokinin-1 immunoreactive neurons innervating the disc related to discogenic low back pain. Substance P-saporin may be a useful tool to investigate the mechanism of discogenic low back pain.

We evaluated the effects of intradiscal administration of substance P-saporin, a toxin selective for cells expressing the substance P receptor. Substance P-saporin significantly decreased the ratio of substance P receptor immunoreactive neurons innervating the disc. This finding demonstrated that substance P-saporin may be a useful tool for investigating the mechanism of discogenic low back pain.

From the Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.

Acknowledgment date: December 8, 2005. First revision date: February 14, 2006. Acceptance date: February 20, 2006.

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Seiji Ohtori, MD, PhD, Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan; E-mail: sohtori@faculty.chiba-u.jp

© 2006 Lippincott Williams & Wilkins, Inc.