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TNF-alpha and phosphorylation of ERK in DRG and spinal cord: insights into mechanisms of sciatica.

Takahashi N, Kikuchi S, Shubayev VI, Campana WM, Myers RR

Department of Anesthesiology, University of California, School of Medicine, San Diego, CA, USA.

STUDY DESIGN: Characterize extracellular signal-regulated kinase (ERK) and its phosphorylation (pERK) in neural tissues after topical application of tumor necrosis factor-alpha (TNF-alpha) to L5 nerve root. OBJECTIVE: Identify time-course, localization, and expression of pERK. SUMMARY OF BACKGROUND DATA: TNF-alpha has a key role in disc herniation and sciatica as an inflammatory component of the nucleus pulposus. ERK is associated with neuronal signal transduction and nociception. METHODS: We studied tissue from naive rats, vehicle-treated rats, and rats receiving rat recombinant TNF-alpha using Western blots of total and phosphorylated ERK (pERK). We used immunohistochemistry of pERK with neuronal nuclear (NeuN) antibody to identify its cellular distribution. RESULTS: Topical application of TNF-alpha to rat nerve root increased pERK in ipsilateral dorsal root ganglion (DRG) neurons and glia within 5 hours. pERK was not expressed in DRG during the first hour after TNF-alpha application, nor was it seen at anytime in spinal cord dorsal horn. DRG satellite cells had increased pERK 5 hours after TNF-alpha or vehicle treatment. TNF-alpha treatment increased pERK in small- and medium-sized DRG neurons and to a lesser degree in large neurons. CONCLUSIONS: These findings suggest that ERK signaling plays a role in the activation of DRG cells following inflammatory injuries to nerve roots and further documents the importance of inflammation in the pathogenesis of painful spine disorders.

Published 1 March 2006 in Spine, 31(5): 523-9.
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