To explore the mechanism of hyperalgesia priming (HP) and evaluate the intervention effect of electroacupuncture (EA) on pain transition.

Fifty-nine male C57 mice were used for 4 separate experiments. In the first experiment, the mice were divided into a control group, a sham sensitization group, and a sensitization group, with 5 mice per group. In the second experiment, the mice were divided into a sham sensitization group, a sensitization group, and a sensitization + EA group, with 5 mice per group. The third experiment consisted of a sensitization group and a sensitization + minocycline group, with 7 mice per group. In the fourth experiment, the mice were divided into a sensitization group, a sensitization + EA + PBS group, and a sensitization + EA + colony-stimulating factor (CSF) group, with 5 mice per group. A HP mouse model was established via consecutive intraplantar injections of carrageenan and prostaglandin E2. EA was applied to bilateral “Zusanli” (ST36) and “Kunlun” (BL60) for 30 min, once daily for 8 d. Mechanical paw withdrawal thresholds (PWTs) were measured at different time points to assess pain transition and the effect of EA. Immunofluorescence was used to detect the activation of microglia marker (Iba1) and astrocyte marker (GFAP) in the spinal cord dorsal horn. Intrathecal injection of minocycline was also administered, and its impacts on Iba1 activation and PWTs were tested. After the experiment, skeleton and Sholl analyses were performed to analyze the morphology of microglia. To further examine the role of CSF-1, the factor was administered intrathecally to assess its influence on the effects of EA.

In the pain transition mouse model, the PWTs at various time points decreased significantly (P<0.01). After modeling, the microglia was activated (P<0.01), but the astrocyte was not. EA increased the PWTs in pain transition mice (P<0.01) and suppressed microglia activation (P<0.01). Intrathecal minocycline administration inhibited microglia activation, reduced Iba1 expression in the spinal cord dorsal horn (P<0.01), and effectively reversed the PWTs reduction (P<0.01). Subsequent intrathecal CSF-1 injection promoted microglia activation and blocked the analgesic effect of EA in the model mice (P<0.01).

Microglia activation is critical in pain transition. EA can alleviate hyperalgesia in HP mice by inhibiting microglia activation.

To explore the peripheral neural mechanism underlying representation along the distribution of stomach meridian induced by intestinal inflammatory reaction using diarrhea predominant-irritable bowel syndrome (IBS-D) mice.

Among 62 healthy male C57BL/6 mice of clean grade, 12 mice were randomly selected and divided into a control group and a model group, 6 mice in each group, additionally, 12 mice were randomly selected and divided into a Tianshu group, a Liangqiu group and a Zusanli group, 4 mice in each group. In the model group, citrobacter was administered orally to establish IBS-D model. In the control group and the model group, the visceral pain threshold was observed using fecal colorectal distension (fCRD) induced electromyography of external oblique muscle, the positive cell number of neutrophil in the colonic muscularis was detected by myeloperoxidase (MPO) staining, the number, location and distribution rule of Evans blue (EB) extravasation points were observed by injection of EB staining solution into the tail vein. In the Tianshu group, the Liangqiu group and the Zusanli group, fluorescent dye Dil was injected at bilateral "Tianshu" (ST25), "Liangqiu" (ST34) and "Zusanli" (ST36) respectively, to observe the dye-positive cell number in different dorsal root ganglion (DRG) segments. In the control group and the model group, the activation of satellite glial cells (SGCs) in different DRG segments was observed by immunofluorescence.

Compared with the control group, in the model group, the area under curve of electromyography of external oblique muscle was increased at fCRD of 25, 50 and 75 μL distilled water (P＜0.001, P＜0.01); the MPO-positive cell number of neutrophil in the colonic muscularis was increased (P＜0.01). Few EB extravasation points could be found in the control group, while there were much more EB extravasation points observed in the model group, which was specially distribution in the area of stomach meridian, from "Huaroumen" (ST24) to "Zusanli" (ST36), as well as the surface area dominated by L₂-L₅ segment of the spinal cord. The Dil-positive cells were mainly exhibited in the DRG of T₁₁, L₅ and L₄ segments in the Tianshu group, the Liangqiu group and the Zusanli group, respectively. Compared with the control group, the ratio of glial fibrillary acidic protein (GFAP)/glutamine synthetase (GS) co-expression was increased in the DRG of T₁₁, L₄ and L₅ segments in the model group (P＜0.05, P＜0.01).

The activation of SGCs within DRG of T₁₁, L₄ and L₅ segments may relate closely to the occurrence of the representation along the stomach meridian distribution in IBS-D mice.