PROJECT SUMMARY Chronic low back pain associated with disc degeneration is a leading cause of chronic pain and has a substantial economic impact in the United States. Treatments for discogenic low back pain exhibit poor long-term efficacy highlighting an important unmet medical need. However, efforts to improve pain management are hampered by limited knowledge of the mechanisms underlying low back pain. Improving our understanding of the mechanisms driving these chronic pain states is hampered by a lack of well characterized and validated preclinical models. The current unmet need is a model of chronic low back pain that robustly mimics human presentation and etiology. To develop a robust model of chronic discogenic low back pain, this proposal brings together experts in orthopedics and animal models (Wachs) with neuroscience and behavioral measures of chronic pain (King). The overarching goal of this proposal is to reproduce and validate a recently published rat model of disc degeneration induced low back pain developed in Dr. Wachs’ lab. For the R61 portion of this proposal, we will establish that this model can be reproduced in a second laboratory (King lab) to demonstrate external replication of this new model of discogenic low back pain. To ensure consistency, Dr. Wachs and her veterinary surgeon will both go to the King lab prior to the study start to train the King lab in the surgery and assays. Concurrent animal studies will then be performed in the Wachs and King labs using the single puncture method in both sexes of animals over an 18-week time course. Real-time disc degeneration will be monitored using either µCT or high- speed x-ray. Pain-like behavior will be assessed using grip strength (evoked) and open arena (non-evoked) testing. Post-processing will include histological analysis of disc degeneration, nerve growth, and inflammation. Quantitative measures will be used to compare results between the Wachs and King labs to ensure robust model reproducibility and provide tangible milestones for progression to the R33 phase. The R33 phase will consist of external validation to establish face, construct, and predictive validity. Concurrent studies will be performed in the Wachs and King labs over an 18-week time course. In this phase, we will increase resolution, frequency, and quantification of assays to more accurately compare to human disease. For example, MRI will be used to examine changes in disc degeneration and water content over time which, although more expensive, is more directly comparable to the gold standard in human disease assessment. In addition, we will perform behavioral analyses every three weeks to compare with the time course in humans. Histological analyses will be broadened to include more robust analysis that will determine specific localization of nerves, blood vessels, and inflammatory cells to allow comparison to previously published data of human biological features of discogenic pain. Finally, we will use conditioned place preferences (CPP) testing in conjunction with administration of anti- inflammatories to test predictive validity. The outcomes of this work have the potential to create a robust model of discogenic pain with high translational potential.

PROJECT NARRATIVE Chronic low back pain is a leading cause of chronic pain and has a substantial economic impact in the United States. Treatments for disc-associated low back pain exhibit poor long-term efficacy highlighting an important unmet medical need. Our work will develop a novel model of chronic low back pain that sufficiently mimics human patients, to more accurately screen therapeutics for treatment.