Characterization of thermal hyperalgesia, c-fos expression, and alterations in neuropeptides after mechanical irritation of the dorsal root ganglion

Study Design. This study analysed hypersansltiza- tion in sensory systems after mechanical irritation of the dorsal root ganglion. Objectives. To develop e reliable and reproducible animal model of hyperalgesia arising from tha dorsal ganglion and to understand lhs unique contribu-tions of the darsar root ganglion to clinical manifestations of sciatica, Summary of Background Data. The dorsal loot ganglion likely plays an important rale in disorders of eciet- icB. However, no previous study has analyzed sciatica after irritation of the dorsal root ganglion. Thermal hy-peralgesia indicates a decrease ir thermal nociceptive threshold end hypersensitte&tiiph In sensory systems. Methods, The left L4 and L& dorsal root ganglia in rats in = 22) were exposed circumfeientfally. Other rats (n = 2Z) also had the left L4 and L5 dorsal rocrt ganglia ligated loosely with two 4-0 chromic gut sutures. Changes In thermal withdrawal latency were examinee in the hindpaws across time. Substance P and vasoac-tive intestinal polypeptide contents were quanlifed in the dorsal toot ganglion and spiral cord. Substance P, calcitonin gene-related peptide, and c-fos expression also were examined in tha spinal cord by immunohistci- Lhcinistry. In addition, histologic changes in myelinated nerve content were examined in the dorsai root ganglion Results. Thermal hyperalgesia occurred in lb With exposure of the dorsal root ganglion and in rats with loose ligation of the dorsal root Ganglion, and was a;- companied by an increase in c-fos expression and spontaneous pain-related behaviors. Conclusions. This experimental mode) reliably pro-duced a disorder resembling an ecutu phase sciatica and should help further advance the understanding of pal ho mechanisms of spinal pain after irrilation of tha dorsal root ganglion Fn humans.