Injury of primary afferent neurons may contribute to osteoarthritis induced pain: an experimental study using the collagenase model in rats

Objective: Pain exacerbated by movement and loading on the joint is the major symptom of osteoarthritis (OA), but the mechanisms of chronic pain in this pathology are still poorly understood. Using the intra-articular (i.a.) injection of collagenase in the knee of rats as a model of OA, we aimed at evaluating whether injury of sensory neurons may contribute to the development of OA-associated nociception. Design: OA was induced by i.a. injection of collagenase into the left knee joint of adult male Wistar rats. Histopathological changes and movement and loading-induced nociception were assessed for 6 weeks. A time-course analysis of the expression of the neuronal injury markers activating transcription factor-3 (ATF-3) and neuropeptide Y (NPY) and of the neuropeptide SP in the dorsal root ganglion (DRG) was performed. Gabapentin's effect on nociception was evaluated, as well as the expression of the alpha 2 delta-1 voltage-gated calcium channel subunit. Results: Collagenase induced the development of OA-like histopathological changes and of movement-induced nociception. Altered expression of ATF-3, NPY and SP was observed in the DRG, correlating with the degree of articular degeneration after 6 weeks of disease progression. Repeated administration of gabapentin reversed the nociceptive responses 6 weeks after the induction of OA. alpha 2 delta-1 was upregulated in the DRG. Conclusion: By inducing nociceptive behaviours associated with relevant joint structural changes, the i.a. injection of collagenase presents itself as a pertinent model for the study of OA pain. The findings in this study support the hypothesis that injury of sensory neurons innervating OA joints may be a significant element in the mechanisms of OA-associated pain. (C) 2015 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.