Substance P and VIP in spinal nerve roots after epidural application of autologous nucleus pulposus

Recently, it was demonstrated experimentally that autologous nucleus pulposus, the main tissue component of a disc hernia, can induce significant changes in nerve root morphology and function if applied epidurally, in a pig model. Changes in the concentration of substance P and VIP have been demonstrated experimentally in various spinal pain models. An increase in substance P concentrations in the dorsal root ganglia and spinal nerve roots was recently described in a model for chronic nerve root compression in pigs. The aim of the present study was to assess changes in the concentrations of substance P and VIP in spinal nerve roots and dorsal root ganglia, after epidural application of autologous nucleus pulposus in a porcine model. After a partial laminectomy of the 1st and 2nd sacral vertebra, the S1-roots were exposed bilaterally and nucleus pulposus was placed around the left 1st sacral nerve root. After 1 or 4 weeks, tissue samples, for radioimmunoassays of substance P and VIP, were taken from the nerve roots at the application zone and from the dorsal root ganglia bilaterally. There were no statistically significant differences in substance P or VIP concentrations in the exposed nerve roots or dorsal root ganglia compared to control nerve roots and dorsal root ganglia, exposed to retroperitoneal fat, after 1 or 4 weeks. The study demonstrates that the functional and morphological changes seen after experimental nucleus pulposus application, using the same model, are not accompanied by changes in VIP and substance P concentrations.