Effects of Running Exercise on Disk Degeneration and Low Back Pain in Mice

Abstract

Introduction

Chronic low back pain (LBP) affects over 10% of the adult population and seriously decreases quality of life. The aging intervertebral disk (IVD) is prone to degeneration, which is associated with an increased risk of LBP. (Luoma et al., 2000) Physical activity influences IVD physiology. Animal studies show that cyclic loading increases proteoglycan synthesis in the disk suggesting a role for running exercise in disk repair. (Brisby et al., 2010) Additionally, an active lifestyle has been shown to either contribute to the onset of chronic pain onset or to be protective against chronic pain depending on the circumstances.

Our laboratory has validated a rodent model of LBP, the aging SPARC-null mouse. These mice demonstrate accelerated lumbar disk degeneration as they age, similar to the degeneration observed in human subjects with LBP. SPARC-null mice also display axial and radiating pain that mirrors LBP in humans and is pharmacologically reversible. (Millecamps, Tajerian, Sage, & Stone, 2011)

Hypothesis Habitual running exercise will delay disk degeneration and decrease pain behavior in aging SPARC-null mice.

Materials and Methods

Total 2- to 3-month-old male SPARC-null and C57B wild type mice were used in this study. After recording baseline behavioral measurements, animals had free access to either a circular treadmill (exercise group) or a fixed nonrotating treadmill (control group) in their home cages. Axial LBP was assessed using the tail suspension test and radiating LBP was assessed using the acetone test for cold hypersensitivity in the hindpaw. SPARC-null mice exhibit signs of both axial and radiating LBP in these assays that is sensitive to pharmacological manipulation. Additional assays included tests for mechanical sensory thresholds and motor capacity. Tests were performed at 2 weeks and monthly thereafter.

Results

After 2 months with access to running wheels, SPARC-null mice show significantly reduced cold sensitivity in the hindpaw compared to baseline (p < 0.05) and control group (p < 0.01) with no accompanying change in mechanical sensitivity, indicating a reduction of radiating pain. No effect on axial pain was detected in the tail suspension test, suggesting an effect specific to radiating pain.

Conclusion

Total 2 months of voluntary running exercise partially reversed the development of radiating LBP in SPARC-null mice. Reversal of axial pain may require longer exposure.

Future studies These mice will be followed for 6 months postwheel exposure. Following sacrifice, disk degeneration will be assessed using radiographic and histological methods. Disk innervation will be determined by immunohistochemistry, and the relationships between anatomical and behavioral measures will be determined.

I confirm having declared any potential conflict of interest for all authors listed on this abstract

No

Disclosure of Interest

None declared

Brisby, H., Wei, A. Q., Molloy, T., Chung, S. A., Murrell, G. A., Diwan, A. D. The effect of running exercise on intervertebral disk extracellular matrix production in a rat model Spine 2010;35(15):1429–1436

Luoma, K., Riihimäki, H., Luukkonen, R., Raininko, R., Viikari-Juntura, E., Lamminen, A. Low back pain in relation to lumbar disk degeneration Spine 2000;25(4):487–492

Millecamps, M., Tajerian, M., Sage, E. H., Stone, L. S. Behavioral signs of chronic back pain in the SPARC-null mouse Spine 2011;36(2):95–102