Neuropeptide changes in compressed spinal nerve roots. 
Compression-induced changes in the concentration of substance P and VIP (vasoactive intestinal polypeptide), in spinal nerve roots and dorsal root ganglia were studied in an experimental nerve root compression model in pigs.  To analyze by radioimmunoassay the concentration of the neuropeptides substance P and VIP in a model for experimental chronic nerve root compression.  Neuropeptides such as substance P and VIP seem to be involved in the transmission of pain and changes in the levels of these neuropeptides have been described in models where peripheral or spinal nerve injury was induced.  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 constrictor and from the dorsal root ganglion for measurement of substance P and VIP concentrations.  There was a statistically significant increase in substance P concentrations in the compressed dorsal root ganglia when compared to the noncompressed dorsal root ganglia at both 1 and 4 weeks.  Substance P concentration was also significantly increased in the nerve root after 1 but not after 4 weeks.  The VIP levels were not significantly changed in either tissue.  The results of the study indicates an increase in substance P levels in the dorsal 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 were no significant differences in the VIP concentrations.  The study thus indicates that changes in substance P are related to experimental chronic nerve root compression.