NEUROPEPTIDE CHANGES IN COMPRESSED SPINAL NERVE ROOTS

Study Design. Compression-induced changes in the concentration of subs tance P and VIP (vasoactive intestinal polypeptide), in spinal nerve r oots and dorsal root ganglia were studied in an experimental nerve roo t compression model in pigs. Objectives. To analyze by radioimmunoassa y the concentration of the neuropeptides substance P and VIP in a mode l for experimental chronic nerve root compression. Summary of Backgrou nd Data. Neuropeptides such as substance P and VIP seen to be involved in the transmission of pain and changes in the levels of these neurop eptides have been described in models where peripheral or spinal nerve injury was induced. Methods. An ameroid constrictor was applied on a spinal nerve root just cranial to the dorsal root ganglion. The inner diameter of this constrictor is gradually reduced. After 1 or 4 weeks, tissue samples were taken from the nerve root cranial to the constric tor and from the dorsal root ganglion for measurement of substance P a nd VIP concentrations. Results. There was a statistically significant increase in substance P concentrations in the compressed dorsal root g anglia when compared to the noncompressed dorsal root ganglia at both 1 and 4 weeks. Substance P concentration was also significantly increa sed in the nerve root after 1 but not after 4 weeks. The VIP levels we re not significantly changed in either tissue. Conclusions. The result s of the study indicates an increase in substance P levels in the dors al root ganglion (after 1 and 4 weeks) and in the nerve root (after 1 week) in a model for chronic nerve root compression in pigs. There wer e no significant differences in the VIP concentrations. The study thus indicates that changes in substance P are related to experimental chr onic nerve root compression.