• Yasuaki Murata, Ulf Nannmark, Björn Rydevik, Kazuhisa Takahashi, and Kjell Olmarker.
• Department of Orthopaedic Surgery, School of Medicine, Chiba University, Chiba City, Chiba, Japan. yasuakimurata@aol.com
• Spine. 2006 Feb 15;31(4):382-90.

Study DesignThe mechanisms behind the formation of a characteristic tissue reaction at the surface of the dorsal root ganglion (DRG) exposed to nucleus pulposus was studied with special reference to apoptosis using electron microscopy and immunohistochemistry in rats.ObjectivesTo study the mechanism of the characteristic tissue reaction at the surface of the DRG exposed to nucleus pulposus.Summary Of Background DataRecently, it was observed that local application of nucleus pulposus may induce a characteristic tissue reaction at the surface of the DRG. This change occurred as early as 1 day after the application of nucleus pulposus. METHODS.: Herniation of nucleus pulposus was created in the L4-L5 disc in rats. The L4 DRG were resected 3 and 24 hours after surgery. The sections of the specimens were observed using light and electron microscopy. The sections were processed for immunohistochemistry using antibodies to single-stranded DNA (ssDNA), caspase 3, and tumor necrosis factor alpha (TNF).ResultsThere were typical changes of the cell nuclei observed by light and electron microscopy, especially those of the small-sized cells, in the DRG 24 hours after application of nucleus pulposus, indicating the presence of apoptosis. The presence of ssDNA, caspase 3, and TNF further enhanced the impression that there was apoptosis in the DRG. Nucleus pulposus induced apoptosis in the DRG at the site of application within as little as 24 hours.ConclusionsNucleus pulposus herniated from the disc induced apoptosis in at the surface of the DRG exposed to nucleus pulpous as early as 24 hours after exposure.

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