Purpose: Acupuncture therapy is effective for relieving postoperative pain. Our previous study showed that electroacupuncture (EA) at Futu (LI18) and Hegu (LI4)–Neiguan (PC6) could alleviate incisional neck pain, which was related with its effect in upregulating γ-aminobutyric acid (GABA) expression in cervical (C3–6) dorsal root ganglions (DRGs); but whether its receptor subsets GABAA_A2R and GABA_BR1 in C3–6 DRGs are involved in EA analgesia or not, it remains unknown.
Materials and methods: Seventy-five male Sprague Dawley rats were randomized to normal control, model, LI18, LI4–PC6, and Zusanli (ST36)–Yanglingquan (GB34) groups. The incisional neck pain model was established by making a longitudinal incision along the midline of the rats’ neck, followed by repeated mechanical stimulation. EA was applied to bilateral LI18, LI4–PC6, or ST36–GB34 for 30 minutes at 4, 24, and 48 hours after operation. The thermal pain threshold of the neck was detected by a tail-flick unit, and the C3–6 DRGs were removed for assaying the immunoactivity of substance P (SP), GABA_Aα2R, glial fibrillary acidic protein (GFAP; a marker of satellite glial cells [SGCs]), and GABA_BR1 and the expression of GABA_Aα2R and GABA_BR1 mRNA and proteins using immunofluorescence, real-time PCR, and Western blotting, respectively.
Results: The cervical thermal pain threshold was significantly lower in the model group than the normal group (P <0.001), indicating hyperalgesia after neck incision, and was considerably increased in both EA-LI18 and LI4–PC6 groups (P <0.001), but not in ST36–GB34 group compared with model group (P >0.05). Immunofluorescence staining showed that GABA_Aα2R R expressed on SP⁺ neurons, and GABA^BR1 on SGCs. EA of LI18 and LI4–PC6 markedly suppressed the modeling-induced upregulation of the immunoactivity of SP (P <0.001 and P <0.01, respectively) and GFAP (P <0.01 and P <0.001, respectively) and significantly reversed neck incision–induced downregulation of the expression of GABA_Aα2R and GABA_BR1 mRNAs and proteins (P <0.05).
Conclusion: EA of LI18 and LI4–PC6 has an analgesic effect in incisional neck pain rats, which is related to its effects in upregulating GABAergic inhibitory modulation on nociceptive peptidergic neurons and SGCs in cervical DRGs.
Keywords: electroacupuncture, incisional neck pain, substance P, satellite glial cells, GABA_Aα2R, GABA_BR1