Electroacupuncture alleviates the transition from acute to chronic pain through the p38 MAPK/TNF-α signalling pathway in the spinal dorsal horn

Hyperalgesic priming (HP) is a model of the transition from acute to chronic pain. Electroacupuncture (EA) could inhibit pain development through the peripheral dorsal root ganglia; however, it is unclear whether it can mitigate the transition from acute to chronic pain by attenuating protein expression in the p38 MAPK (mitogen-activated protein kinase)/tumour necrosis factor alpha (TNF-α) pathway in the spinal dorsal horn.We aimed to determine whether EA could prevent the transition from acute to chronic pain by affecting the p38 MAPK/TNF-α pathway in the spinal dorsal horn in a rat model established using HP.We first randomly subdivided 30 male Sprague-Dawley (SD) rats into 5 groups (n = 6 per group): control (N), sham HP (Sham-HP), HP, HP + SB203580p38 MAPK (HP+SB203580), and HP + Lenalidomide (CC-5013) (HP+Lenalidomide). We then randomly subdivided a further 30 male SD rats into 5 groups (n = 6 per group): Sham-HP, HP, sham EA (Sham EA), EA (EA), and EA + U-46619 p38 MAPK agonist (EA+U-46619). We assessed the effects of EA on the mechanical paw withdrawal threshold and p38 MAPK/TNF-α expression in the spinal dorsal horn of rats subjected to chronic inflammatory pain.Rats in the EA group had reduced p38 MAPK and TNF-α expression and had significantly reduced mechanical hyperalgesia compared with rats in the other groups.Our findings indicate that EA could increase the mechanical pain threshold in rats and inhibit the transition from acute pain to chronic pain. This mechanism could involve reduced p38 MAPK/TNF-α expression in the spinal dorsal horn.