• Hiroyuki Anzai, Michiko Hamba, Akira Onda, Shinichi Konno, and Shinichi Kikuchi.
• Department of Orthopaedic Surgery, Fukushima Medical University, School of Medicine, Fukushima, Japan.
• Spine. 2002 Feb 1;27(3):E50-5.

Study DesignAn electrophysiologic study to examine responses of dorsal horn neurons in the rat L5 spinal cord to noxious stimuli after disc herniation or application of the nucleus pulposus to the L5 nerve root.ObjectivesTo investigate the pathogenic role of nucleus pulposus in the neural mechanism underlying sciatica and low back pain.Summary Of Background DataApplication of the nucleus pulposus to the lumbar nerve root induced morphologic, vascular, and functional changes in the nerve root, suggesting that some factors in the nucleus pulposus may be implicated in the pathogenesis of chronic changes. However, it has not been studied whether the epidural application of nucleus pulposus enhances nociresponses of pain-processing neurons in the superficial dorsal horn of the spinal cord.MethodsExtracellular recordings were made from the L5 dorsal horn neurons in 20 Wistar rats. The wide-dynamic-range (WDR) neurons activated by electric stimulation of the ipsilateral footpad of hindpaw were selected, and their responses to noxious and innocuous stimulation were examined after L5-L6 disc herniation onto the L5 nerve root (Group A) and application of the autologous nucleus pulposus (Group B) or fat tissues (Groups C and D).ResultsThe herniation of the nucleus pulposus (Group A) and application of the autologous nucleus pulposus (Group B) to the nerve root remarkably enhanced responses of WDR neurons to noxious stimuli for hours, whereas application of fat tissue scarcely enhanced nociresponses (Groups C and D).ConclusionsResults suggest that somewhat pathogenic factors in the nucleus pulposus may have a crucial role in the induction of hyperalgesia. This may help to elucidate the reason why a severe pain is sometimes induced without a visually identified protrusion.

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