• Akira Onda, Michiko Hamba, Shoji Yabuki, and Shinichi Kikuchi.
• Department of Orthopaedic Surgery, Fukushima Medical University School of Medicine, Fukushima, Japan. aonda@fmu.ac.jp
• Spine. 2002 Aug 1;27(15):1618-24; discussion 1624.

Study DesignAn electrophysiologic study to examine effects of exogenous application of tumor necrosis factor-alpha (TNF-alpha ) activities and nociresponses of dorsal horn neurons in the spinal cord at L5.ObjectivesTo investigate the role of TNF-alpha in the induction and development of hyperalgesia in neural mechanisms responsible for a radicular pain.Summary Of Background DataTNF-alpha is found in the herniated disc and known to play a pivotal role in the development of inflammatory hyperalgesia; however, it is not known whether TNF-alpha causes abnormal discharge in the dorsal horn neurons and enhances nociresponse.MethodsSingle-unit activities of neurons in the L5 superficial dorsal horn were extracellularly recorded, using 28 urethane-anesthetized rats. The wide dynamic range and nociceptive-specific neurons activated by stimulation of the hind paw were selected. Effects of exogenous TNF-alpha were examined regarding 1) spontaneous discharges of wide dynamic range and nociceptive-specific neurons, 2) responses of wide dynamic range neurons to noxious stimulation, and 3) morphologic changes in the dorsal root ganglion.ResultsApplication of TNF-alpha to the nerve root induced 1) a significant increase in spikes/sec in spontaneous discharges of wide dynamic range and nociceptive-specific neurons, 2) enhanced responses of wide dynamic range neurons to noxious stimulation, and 3) inflammatory changes in the ganglion.ConclusionThese results suggest the possibility that TNF-alpha produced in the vicinity of nerve roots due to disc herniation might cause ectopic discharges in primary afferent fibers and thereby induce the prolonged excitation in pain-processing neurons responsible for radicular pain.

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