Abstract:

Objective To investigate the mechanisms of pain hypersensitivity to lowdose capsaicin in a mouse model of chronic compression of dorsal root ganglion (CCD). Methods Chronic compression of L4 DRG was performed in mice by inserting an L-shaped stainless steel rod into the L4 intervertebral foramina. Different doses of capsaicin（0.01, 0.1, 1 g/L）1 μl were injected into the skin on the calf area and behavior responses were videotaped on pre-CCD 1 days and post-CCD 1, 3, 5, 7 days. The optimal concentration that led to a significant difference after CCD was determined and was used in the following in-vivoDRG imaging studies. Immunofluorescent staining was conducted to evaluate the expression of transient receptor potential vanilloid 1 (TRPV1) in DRG from na?ve and CCD mice. Results Behavioral tests showed that 0.1 g/L capsaicin elicits a significant difference in pain-like behaviors after CCD（n=8; post-CCD 1 day, P<0.01; post-CCD 5, 7 days P<0.01; post-CCD 3 days, P> 0.05. In vivocalcium imaging showed an enhanced number of activated DRG neurons to the injection of capsaicin in CCD mice, which was 75 in total of 398(n=4) for control mice and 169 in total of 382(n=6) (P<0.01). According to immunofluorescent staining results, there were 148 TRPV1+ neurons in total 653 counted neurons (n=10) for control mice and 237 TRPV1+ neurons in total of 611 neurons (n=6) for CCD mice (P<0.01). Conclusion Chronically compressed DRG neurons show upregulated TRPV1 receptor and enhanced responses to low-dose capsaicin, that produce pain hypersensitivity in the CCD mice.

Key words: Chronic pain, Capsaicin, Transient receptor potential vanilloid 1, Chronic compression of dorsal root ganglia, Laser scanning confocal imaging in viro, Mouse