Axial hypersensitivity is associated with aberrant nerve sprouting in a novel model of disc degeneration in female Sprague Dawley rats

Chronic low back pain is a global socioeconomic crisis and treatments are lacking in part due to inadequate models. Etiological research suggests that the predominant pathology associated with chronic low back pain is intervertebral disc degeneration. Various research teams have created rat models of disc degeneration, but the clinical translatability of these models has been limited by an absence of robust chronic pain-like behavior. To address this deficit, disc degeneration was induced via an artificial annular tear in female Sprague Dawley rats. The subsequent degeneration, which was allowed to progress for 18-weeks, caused a drastic reduction in disc volume. Furthermore, from week 10 till study conclusion, injured animals exhibited significant axial hypersensitivity. At study end, intervertebral discs were assessed for important characteristics of human degenerated discs: extracellular matrix breakdown, hypocellularity, inflammation, and nerve sprouting. All these aspects were significantly increased in injured animals compared to sham controls. Also of note, 20 significant correlations were detected between selected outcomes including a moderate and highly significant correlation (R = 0.59, p < 0.0004) between axial hypersensitivity and disc nerve sprouting. These data support this model as a rigorous platform to explore the pathobiology of disc-associated low back pain and to screen treatments.