Abstract
Chronic low back pain accompanied by intervertebral disk degeneration is a common musculoskeletal disorder. Physical exercise, which is clinically recommended by international guidelines, has proven to be effective for degenerative disc disease (DDD) patients. However, the mechanism underlying the analgesic effects of physical exercise on DDD remains largely unclear. The results of the present study showed that mechanical withdrawal thresholds of bilateral hindpaw were significantly decreased beginning on day three after intradiscal complete Freund’s adjuvant (CFA) injection and daily running exercise remarkably reduced allodynia in the CFA exercise group beginning at day 28 compared to the spontaneous recovery group (controls). The hindpaw withdrawal thresholds of the exercise group returned nearly to baseline at the end of experiment, but severe pain persisted in the control group. Histological examinations performed on day 70 revealed that running exercise restored the degenerative discs and increased the cell densities of the annulus fibrosus (AF) and nucleus pulposus (NP). Furthermore, immunofluorescence labeling revealed significantly higher numbers of 5-bromo-2-deoxyuridine (BrdU)-positive cells in the exercise group on days 28, 42, 56 and 70, which indicated more rapid proliferation compared to the control at the corresponding time points. Taken together, these results suggest that running exercise might alleviate the mechanical allodynia induced by intradiscal CFA injection via disc repair and cell proliferation, which provides new evidence for future clinical use.
Highlights
Chronic low back pain accompanied with intervertebral disc (IVD) degeneration is a prevalent and complicated musculoskeletal disorder [1,2]
Mechanical withdrawal thresholds were determined based on the bilateral hindpaw withdrawal responses to von Frey hair stimulation according to the up-down method described by Dixon [16]
These results suggested that the intradiscal complete Freund’s adjuvant (CFA) injection resulted in mechanical allodynia (p 0.01)
Summary
Chronic low back pain accompanied with intervertebral disc (IVD) degeneration is a prevalent and complicated musculoskeletal disorder [1,2]. Despite previous studies that have suggested that various factors, including age, hereditary and environmental factors, might contribute to the degeneration process, the underlying mechanisms of symptomatic degenerative disc disease (DDD). In 2009, Lee et al [8] proposed a rat model that involved the injection of complete Freund’s adjuvant (CFA) into the 5th/6th lumbar (L5-6) IVD; this model is characterized by degenerative disc changes, mechanical allodynia in the bilateral hindpaws and up-regulation of inflammatory factors. This model successfully mimics clinical situations of chronic low back pain and disc degeneration
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