Contribution of GABAergic modulation in DRGs to electroacupuncture analgesia in incisional neck pain rats.

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 α2R and GABAB R1 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), GABAA α2R, glial fibrillary acidic protein (GFAP; a marker of satellite glial cells [SGCs]), and GABAB R1 and the expression of GABAA α2R and GABAB R1 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 GABAA α2 R expressed on SP+ neurons, and GABAB R1 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 GABAA α2R and GABAB R1 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.