Assessment of a Discogenic Pain Animal Model Induced by Applying Continuous Shear Force to Intervertebral Discs

Area of Science:

• Biomedical Engineering
• Pain Research
• Animal Models

Background:

• Chronic discogenic pain arises from degeneration-driven changes in the intervertebral disc's mechanical and biochemical microenvironment.
• These changes can lead to abnormal nociceptor ingrowth, but animal models reflecting this pathology are not well-assessed.
• The natural history of disc degeneration and associated pain pathways requires further investigation.

Purpose of the Study:

• To investigate the biochemical evidence of chronic discogenic pain using an animal model.
• To induce discogenic pain via shear force in a rat model.
• To assess the biochemical and neurological changes associated with induced discogenic pain.

Main Methods:

• An in vivo rat model utilizing a shear force device was employed.
• Fifteen rats were divided into three groups: a control group and two experimental groups subjected to shear force for 1 or 2 weeks.
• Pain was assessed using von Frey hairs, and growth factor and cytokine levels were analyzed in dorsal root ganglia (DRG) and plasma.

Main Results:

• Shear force application significantly increased specific variables in DRG tissues after 2 weeks, but not after 1 week.
• Increased levels of interleukin-6 (IL-6), neurotrophic factor (NGF), transforming growth factor-alpha (TGF-alpha), platelet-derived growth factor-beta (PDGF-beta), and vascular endothelial growth factor (VEGF) were observed in DRG.
• Plasma analysis revealed increased levels of tumor necrosis factor-alpha, IL-1beta, IL-5, IL-6, IL-12, and NGF after 1 week, and TGF-alpha, PDGF-beta, and VEGF after 2 weeks.

Conclusions:

• The developed animal model effectively generated biochemical responses to shear loading, indicating neurological changes without direct macrodamage to the outer annulus fibrosus.
• This model demonstrates that internal biochemical changes associated with chronic discogenic pain can be induced by external mechanical forces.
• The findings contribute to understanding the pathogenesis of chronic discogenic pain and validating animal models for its study.