Cutaneous Mast Cells Contribute to the Analgesic Effect of Manual Therapy on CCD Rats

Lumbar disc herniation (LDH) commonly induces low back and leg pain. Manual therapy (MT) is effective in relieving such pain clinically, but its mechanism remains unclear. Given that acupoint regions are enriched with mast cells that respond to mechanical stimulation, this study explored whether MT alleviates CCD-evoked neuropathic pain and its association with the modulation of cutaneous mast cells.

Sprague-Dawley (SD) rats were randomized into sham, chronic compression of dorsal root ganglion (CCD), MT, and mast cell inhibition (MCI) groups. After CCD modeling, MT was administered at BL57 starting on day 4 for 14 days, while MCI received acupoint cromolyn sodium injection. Paw withdrawal threshold (PWT) was measured. Mast cell activation was assessed using immunofluorescence and toluidine blue staining. Calcitonin gene-related peptide (CGRP), substance P (SP), Piezo1, and Piezo2 were determined via immunofluorescence; inflammatory cytokines and neurotransmitters by ELISA; expression of MAPK, Piezo1, and Piezo2 by qRT-PCR. MAPK expressions were also detected by Western blot.

CCD reduced PWT from day 3, whereas MT significantly restored PWT from day 11. In skin, CCD increased mast cell activation, CGRP, SP, tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-1β, 5-hydroxytryptamine (5-HT), and histamine (HA), all of which were attenuated by both interventions. In DRG, CCD elevated p-ERK, p-JNK, and p-p38 MAPK without altering total MAPK expression, and both interventions suppressed MAPK phosphorylation. Piezo2 was upregulated in CCD and reduced by MT and MCI in both tissues. In skin, Piezo1 remained unchanged, while in DRG, CCD downregulated Piezo1 significantly.

MT can relieve CCD-induced mechanical allodynia, an effect associated with inhibited cutaneous mast cell activation, attenuated peripheral neuroinflammation, and reduced MAPK hyperphosphorylation in the DRG.