Phenotypic inflammation switch in rats shown by calcitonin gene-related peptide immunoreactive dorsal root ganglion neurons innervating the lumbar facet joints. (School of Medicine, Chiba University, Chiba, Japan) Spine. 2001;26:1009-1013.

Abstract

This study's objective was to determine by inflammatory stimulation the changes in calcitonin gene-related peptide-immunoreactive dorsal root ganglion neurons innervating the L5-L6 facet. Retrograde transport of fluorogold was used in 20 rats: 10 in the control group and 10 in the inflammatory group. Using the dorsal approach, fluorogold crystals were injected into the left L5-L6 facet joint. Then 5 days after application, complete Freund's adjuvant (50 injected μg Mycobacterium butyricum in oil saline emulsion) was injected into the same L5-L6 facet joint (inflammatory group). Of the total fluorogold-labeled dorsal root ganglion neurons from T13-L6, the number and cross-sectional area of the cell profiles of fluorogold-labeled, calcitonin gene-related peptide-immunoreactive neurons in the bilateral dorsal root ganglia of both groups were evaluated. Fluorogold-labeled neurons were distributed throughout the ipsilateral dorsal root ganglia from L1-L5 in both groups. Of the fluorogold-labeled neurons, the ratios of the calcitonin gene-related peptide-immunoreactive L1, L2, L3, L4, and L5 dorsal root ganglion neurons, respectively, were 17%, 24%, 44%, 56%, and 50% in the control group and 50%, 39%, 51%, 61%, and 56% in the inflammatory group. The ratios of the calcitonin gene-related peptide-immunoreactive L1 and L2 dorsal root ganglion neurons labeled by fluorogold were significantly higher in the inflammatory group than in the control group (P < 0.05). The mean cross-sectional area of fluorogold-labeled, calcitonin gene-related peptide-immunoreactive cells from the L1-L5 dorsal root ganglia increased from 621 ± 64 μm2 to 893 ± 63 μm2 in the inflammatory group (P < 0.01). Comment by Octavio Calvillo, M.D., Ph.D. This is a bench research study that demonstrated sympathetic activation of dorsal root ganglia distal to the pain response. The authors sought to establish the degree of innervation of the L5-6 facet joint of the rat from sympathetic fibers of L1 and 2 and to adjacent L3-5 segmental fibers. From histological analysis, they found that inflammation increased the production of CGRP-Ir in the dorsal root ganglion of L1 and L2. Additionally, the nerve fibers were noted to increase in size with the inflammation. These findings lend support for upper lumbar dorsal root blockade for non-segmental levels of inflammation.