• Nina Gran Egeland, Aurora Moen, Linda Margareth Pedersen, Helena Brisby, and Johannes Gjerstad.
• National Institute of Occupational Health, Oslo, Norway Department of Molecular Biosciences, University of Oslo, Oslo, Norway Department of Physical Medicine and Rehabilitation, Oslo University Hospital, Oslo, Norway University of Gothenburg, Gothenburg, Sweden.
• Pain. 2013 Sep 1; 154 (9): 1743-1748.

AbstractSciatica after disc herniation may be associated with compression of spinal nerves, but also inflammatory substances released from the nucleus pulposus (NP) leaking into the spinal canal. Here, in an animal model mimicking clinical intervertebral disc herniation, we investigate the effect of NP on neuronal activity. In anaesthetized Lewis rats, extracellular single-unit recordings of spinal dorsal horn neurons were performed, and the C-fibre responses were examined. Moreover, quantitative polymerase chain reaction was used to explore the gene expression of proinflammatory cytokines in the NP tissue exposed to the spinal dorsal nerve roots L3-L5. In accordance with earlier studies, we showed a significant increase in the C-fibre response and an upregulation of the gene expression of interleukin 1β and tumour necrosis factor 180 minutes after application of NP onto the nerve roots. Moreover, based on a polymerase chain reaction array of 84 common inflammatory cytokines at the same time point, we demonstrated a highly significant upregulation of colony-stimulating factor 1 also termed macrophage colony-stimulating factor and Fas ligand. The pronounced upregulation of Csf1 and Fas ligand 180 minutes after application of NP onto the nerve roots suggests that macrophage activation and apoptosis may be involved in pain hypersensitivity and other sensory abnormalities after disc herniation.Copyright © 2013 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.

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