Introduction: Preventing acute lumbar radiculopathy (LR) from progressing to chronic pain is essential, as existing treatments are largely ineffective for chronic LR. Understanding the neurobiological mechanisms of pain chronicity is the first step toward developing new preventive therapies.
Methods: We established a mice LR model by applying an aneurysm clip to the right L4 spinal nerve distal to the dorsal root ganglia (DRG). Male and female C57BL/6 mice were divided into sham (N=8), 0-minute (N=8), and 30-minute (N=9) clipping groups. To assess pain behavior, muscle pressure pain threshold (MPPT) of the tibialis anterior and gastrocnemius muscles in the affected hindlimb was measured pre- and post-surgery at set intervals for 3 months using a handheld pressure application device. Additionally, the L4 DRG tissue sample (n=3 per group) was collected 24 hours post-surgery for immunohistochemical staining with Hypoxyprobe.
Results: One week post-surgery, all animals had decreased MPPT at tibialis anterior and gastrocnemius muscles. By 6 weeks, MPPT in the Sham and 0-minute groups returned to baseline, but the 30-minute group remained reduced for over 12 weeks, indicating chronic pain. Two-way ANOVA showed a significant effect of clipping duration on MPPT at both muscles: gastrocnemius, F (2, 176) = 132.2, p < 0.0001 and tibialis anterior, F (2, 176) = 38.6, p < 0.0001. Tukey’s test confirmed a lower MPPT in the 30-minute group compared to Sham and 0-minute groups (p < 0.0001), with no difference between Sham and 0-minute groups. Immunohistochemistry revealed that mean hypoxic neuron percentages in the DRG were significantly higher in the 30-minute group (34.67%) compared to the Sham (0.72%) and 0-minute (6.97%) groups (p < 0.0012).
Conclusion : Prolonged clipping duration causes chronic pain and increased hypoxia in DRG neurons. This hypoxic stress may be the key factor in the pain chronicity of LR.
.jpg)