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Mechanical compression of the lumbar nerve root alters pain‐related behaviors induced by the nucleus pulposus in the rat
Author(s) -
Kawakami Mamoru,
Tamaki Tetsuya,
Hayashi Nobuhiro,
Hashizume Hiroshi,
Matsumoto Takuji,
Minamide Akihito,
Kihira Tameko
Publication year - 2000
Publication title -
journal of orthopaedic research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.041
H-Index - 155
eISSN - 1554-527X
pISSN - 0736-0266
DOI - 10.1002/jor.1100180214
Subject(s) - nerve root , nucleus , hyperalgesia , spinal nerve , lumbar , nerve injury , medicine , anatomy , lumbar nerve , chemistry , anesthesia , nociception , dorsum , receptor , psychiatry
The purpose of this study was to refine a method of nerve‐root injury in the rat to produce hyperalgesia, a pain‐related behavior, and to determine if there were any relationships between the histological extent of nerve‐root injury and the magnitude of hyperalgesia. Three methods were used to produce hyperalgesia: irritation of a nerve root by ectopic nucleus pulposus, silk loop alone, or both silk loop and ectopic nucleus pulposus. Autologous nucleus pulposus obtained from coccygeal intervertebral discs was relocated on the lumbar nerve roots after laminectomy. Two loops of 4‐0 silk were placed around the exposed nerve roots. Hyperalgesia was measured preoperatively and postoperatively. The distribution of myelinated axons in the dorsal nerve roots was evaluated histologically. Mechanical hyperalgesia was detected in rats in which autologous nucleus pulposus was applied to the nerve root but not in those in which silk loops were used. Silk loops around the nerve root resulted in thermal hyperalgesia only in rats in which autologous nucleus pulposus was applied to the nerve root. Fewer large myelinated fibers were seen in the rats in which silk loops were used. Although a silk loop around the nerve root was not sufficient to produce hyperalgesia, supplemental application of autologous nucleus pulposus to the nerve root produced thermal hyperalgesia. It is possible that mechanical constriction of the nerve root alters the pain‐related behavior elicited by chemical factors from the nucleus pulposus.