Electroacupuncture alleviates inflammatory pain via the activation of GABAergic inhibitory interneurons in mouse spinal dorsal horn

Electroacupuncture (EA), a modern adaptation of traditional acupuncture, has shown promising analgesic effects across various pain models. However, the underlying central mechanisms remain insufficiently characterized. The dorsal horn of the spinal cord serves as a critical hub for the transmission and modulation of nociceptive signals. Increasing evidence suggests that spinal disinhibition, primarily resulting from impaired excitability of inhibitory interneurons and diminished synthesis or release γ-aminobutyric acid (GABA) and glycine, accounts for the development and maintenance of pain. In this study, we investigated whether EA alleviates inflammatory pain by modulating the activity of GABAergic inhibitory interneurons in the superficial dorsal horn of the spinal cord. A murine model of inflammatory pain was established by subcutaneous injection of complete Freund's adjuvant (CFA) into the hind paw. EA was applied at the Huantiao (GB30) and Yanglingquan (GB34) acupoints on alternate days following CFA injection. Mechanical hypersensitivity was assessed by paw withdrawal threshold. Neuronal activity was evaluated using immunofluorescence staining for c-fos, Lmx1b, Pax2, and GABA. Furthermore, whole-cell patch-clamp recordings were conducted on spinal slices from GAD67-GFP transgenic mice to assess the electrophysiological properties of GABAergic interneurons. EA significantly attenuated mechanical hypersensitivity in CFA-treated mice without affecting locomotor function. Immunofluorescence staining revealed that EA enhanced c-fos expression in the dorsal horn during early stages of treatment, reduced the proportion of c-fos-positive excitatory (Lmx1b-positive) neurons, and markedly increased the activation of inhibitory (Pax2-positive and GABA-positive) interneurons. In addition, electrophysiological recordings demonstrated that EA significantly depolarized the resting membrane potential and increased the firing frequency of GAD67-GFP-positive inhibitory interneurons in the CFA + EA group compared to the CFA group. Collectively, our results suggest EA at Huantiao and Yanglingquan acupoints could relieve inflammatory pain, potentially through enhancing of the excitability and activity of GABAergic inhibitory interneurons in the spinal dorsal horn. This study provides novel mechanistic insight into spinal modulation of nociceptive processing by EA and supports its therapeutic promise for inflammatory pain management.