OBJECTIVES: To observe the effect of electroacupuncture (EA) on mast cell (MC) activity, substance P (SP) and glial fibrillary acidic protein (GFAP) expression in the lumbar spinal dorsal horns (SDHs) and related inflammatory factors in the anterior tibial muscle, lumbar spinal cord and serum of fibromyalgia syndrome (FMS) model rats, so as to explore its mechanisms underlying improvement of FMS. METHODS: Thirty-six male SD rats were randomly divided into blank control, model and EA groups, with 12 rats in each group. The FMS model was established by injecting 2-morphine phenol ethanol sulfate into the left anterior tibial muscle. After successful modeling, EA was applied to "Zusanli"(ST36) and "Yanglingquan"(GB34) on the left hind limb for 20 min, once every other day for a total of 7 times. von Frey test was used to detect the mechanical pain threshold (MPT) of both hind limbs. H.E. staining was used to observe morphological changes of the anterior tibial muscle. Immunofluorescence staining was used to determine the expressions of SP, MC, GFAP and 5-hydroxtryptamine (5-HT) in the lumbar SDHs. Suspension chip method was used to detect the contents of inflammatory factors in the lumbar spinal cord, left anterior tibial muscle and serum. RESULTS: Compared with the blank control group, the difference value of MPT between the bilateral hind-paws, immunofluorescence-positive number of SP and GFAP in the SDHs, contents of TNF-α, macrophage inflammatory protein-1α (MIP-1α), monocyte chemoattractant protein-1 (MCP-1) in the lumbar spinal cord, and the contents of MIP-α, MCP-1, interleukin (IL)-1α, granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte-colony stimulating factor (G-CSF) in the left anterior tibial muscle, as well as TNF-α, IL-1β, GM-CSF and 5-HT contents in the serum were significantly increased (<0.05), while the immunofluorescence-positive number of 5-HT and contents of 5-HT and IL-10 in the lumbar spinal cord, and IL-10 content in the left anterior tibial muscle and serum were strikingly decreased (<0.05) in the model group. In comparison with the model group, the increase of the difference value of MPT between the bilateral hind-paws, immunofluorescence-positive number of SP and GFAP, contents of TNF-α, MIP-α and MCP-1 in the lumbar spinal cord, and the contents of MIP-α, MCP-1, IL-1α, GM-CSF and G-CSF in the left anterior tibial muscle, as well as the contents of TNF-α, IL-1β, GM-CSF and 5-HT in the serum, and the decrease of the immunofluorescence-positive number of 5-HT and contents of 5-HT and IL-10 in the lumbar spinal cord, and IL-10 content in the left anterior tibial muscle and serum were reversed in the EA group (<0.05). Immunofluorescence staining displayed that no apparent changes in the number of MC in the lumbar SDHs after modeling and EA, and MCs presented degranulation in both the model group and EA group. H.E. staining showed disordered arrangement of muscle fibers, enlargement of the gaps between the muscle fibers, and obvious inflammatory infiltration of the anterior tibial muscle in the model group. Compared with the model group, the morphology of muscle fibers in the EA group was relatively complete, with orderly arrangement and reduction of the inflammatory infiltration. CONCLUSIONS: EA of ST36 and GB34 can relieve pain and reduce the central and peripheral inflammatory response in FMS rats, which may be related to its functions in suppressing the expressions of SP and GFAP, and astrocytes activation in the lumbar SDHs and up-regulating the expression of 5-HT in the lumbar spinal cord.