Background: Clinical studies have shown that applying pulsed radiofrequency (PRF) to the neural stem could relieve
neuropathic pain (NP), albeit through an unclear
analgesic mechanism. And animal experiments have indicated that
calcitonin gene-related peptide (CGRP) expressed in the dorsal root ganglion (DRG) is involved in generating and maintaining NP. In this case, it is uncertain whether PRF plays an
analgesic role by affecting CGRP expression in DRG. Methods: Rats were randomly divided into four groups: Groups A, B, C, and D. In Groups C and D, the right sciatic nerve was ligated to establish the CCI model, while in Groups A and B, the sciatic nerve was isolated without
ligation. After 14 days, the right sciatic nerve in Groups B and D re-exposed and was treated with PRF on the
ligation site. Thermal withdrawal latency (TWL) and hindpaw withdrawal threshold (HWT) were measured before PRF treatment (Day 0) as well as after 2, 4, 8, and 14 days of treatment. At the same time points of the behavioral tests, the right L4-L6 DRG was sampled and analyzed for CGRP expression using RT-qPCR and an
enzyme-linked
immunosorbent assay (ELISA). Results: Fourteen days after sciatic nerve
ligation, rats in Groups C and D had a shortened TWL (P<0.001) and a reduced HWT (P<0.001) compared to those in Groups A and B. After PRF treatment, the TWL of the rats in Group D gradually extended with HWT increasing progressively. Prior to PRF treatment (Day 0), CGRP
mRNA expressions in the L4-L6 DRG of Groups C and D increased significantly (P<0.001) and were 2.7 and 2.6 times that of Group A respectively. ELISA results showed that the CGRP content of Groups C and D significantly increased in comparison with that of Groups A and B (P<0.01). After PRF treatment, the
mRNA expression in the DRG of Group D gradually decreased and the
mRNA expression was 1.7 times that of Group A on the 4th day(P> 0.05). On the 8th and 14th days, the
mRNA levels in Group D were restored to those of Groups A and B. Meanwhile, the CGRP content of Group D gradually dropped over time, from 76.4 pg/mg (Day 0) to 57.5 pg/mg (Day 14). Conclusions: In this study, we found that, after sciatic nerve
ligation, rats exhibited apparent
hyperalgesia and
allodynia, and CGRP
mRNA and CGRP contents in the L4-L6 DRG increased significantly. Through lowering CGRP expression in the DRG, PRF treatment might relieve the
pain behaviors of NP.