| Objective To explore the effect of transcutaneous electrical nerve stimulation (TENS) on interleukin-33 (IL-33)/growth stimulation expressed gene 2 (ST2) signaling pathway in the dorsal root ganglia (DRGs) of rats modeling hyperalgesia (HP). Methods This study consisted of two experiments. In the first, 30 Sprague-Dawley (SD) rats were randomly divided into a blank group, a Sham-HP group, an HP group, an antibody group and an inhibitor group, each of 6. HP was induced in all except the rats of the blank and Sham-HP groups by injecting carrageenan (Car) and prostaglandin E2 subcutaneously at the bottom of the left hind feet. The antibody and inhibitor groups were then given intrathecal injections of anti-ST2 antibody and a tumor necrosis factor α (TNF-α)-specific inhibitor, respectively. In the second experiment, 42 SD rats were randomly divided into a Sham-HP group, an HP group, a TENSⅠgroup, a TENS II group, a TENS I inhibitor group, a TENS II inhibitor group, and a Sham-TENS group, each of 6. All of the groups had HP induced as in experiment one. All of the rats except those in the Sham-HP, HP and Sham-TENS groups were then given TENS, and the TENS I and II inhibitor groups were offered intrathecal injection of TNF-α-specific inhibitors. Mechanical pain thresholds (MPTs) were documented 4h, 24h, 48h, 72h, 6d, 7d 4h, 7d 1h, and 7d after the Car injections. Western blotting was used to measure the protein expressions of IL-33, ST2 and TNF-α 6d after the Car injection in both experiments. Results In experiment one, the average MPTs of the HP, antibody and inhibitor groups had decreased significantly 4 hours after the Car injection compared with the blank and Sham-HP groups. However, 7d 1h after the Car injection the value had increased significantly in the Sham-HP, antibody and inhibitor groups compared with the HP group, while the expressions of IL-33, ST2 and TNF-α had decreased significantly. In experiment two, by 4 hours after the Car injection, the average MPT of all the other groups had decreased significantly compared with the Sham-HP group. Moreover, by 7d 1h after the Car injection, the average MPTs of the groups receiving TENS had increased significantly, with significantly lower MPT in the TENS Ⅱ group than in group Ⅰ, on average. There was also significantly higher expression of IL-33, ST2 and TNF-α in group II. Compared with the TENS Ⅰ and Ⅱ groups, the average MPT was significantly higher in the TENS I and Ⅱ inhibitor groups, but IL-33, ST2 and TNF-α expression was lower. Conclusions TENS can inhibit TNF-α expression, which influences the signals of the DRG IL-33/ST2 signaling pathway to reverse hyperalgesia. TENS combined with anti-TNF-α treatment is superior to TENS alone in treating hyperalgesia. |
