Repetitive transcranial magnetic stimulation suppresses glia-associated neuroinflammation and promotes peripheral nerve recovery in neuropathic pain

Background: Neuropathic pain (NP) is a chronic condition caused by peripheral nerve damage and is characterized by persistent neuroinflammation and limited treatment options. Repetitive transcranial magnetic stimulation (rTMS) has been reported to modulate neuroinflammation in the brain. However, it remains unclear whether rTMS also influences inflammatory responses in the spinal cord and peripheral nerve structures. Methods: A rat NP model was established by unilateral sciatic nerve ligation, and the effects of rTMS were evaluated through behavioral testing and molecular, histological, and ultrastructural analyses of the spinal cord and sciatic nerve. Results: NP induced thermal hyperalgesia and mechanical allodynia, whereas rTMS significantly alleviated these pain-related behaviors (p < 0.05). In the spinal cord, NP increased the expression of pro-inflammatory markers including CD40, CD86, ionized calcium-binding adapter molecule-1 (Iba-1), and transient receptor potential cation channel subfamily V member 1 (TRPV1) (p < 0.05 for TRPV1; p < 0.01 for the others). rTMS significantly attenuated the increases in CD86, Iba-1, and TRPV1 (p < 0.01 for Iba-1; p < 0.05 for the others), while CD40 showed a decreasing trend without statistical significance. In the sciatic nerve, NP also elevated glial and inflammatory markers (Iba-1, TRPV1, S100, and glial fibrillary acidic protein (GFAP), which were significantly reduced following rTMS treatment (p < 0.01 for S100; p < 0.05 for the others). Immunostaining confirmed a reduction in both the number and activation state of Iba-1(+) and GFAP(+) cells in the rTMS-treated group. Ultrastructural analysis demonstrated improved myelin integrity in the sciatic nerve after rTMS, including increased myelin thickness, higher myelinated axon density, and a reduced G-ratio. rTMS also mitigated NP-induced gastrocnemius muscle atrophy, as indicated by increased muscle mass and cross-sectional area (p < 0.01). rTMS was associated with changes in ERK and Akt signaling pathways that were reduced under NP conditions. Conclusion: rTMS alleviates NP by suppressing glia-associated neuroinflammation in both the spinal cord and sciatic nerve and by promoting structural recovery of peripheral nerves. These findings support rTMS as a promising non-invasive therapeutic strategy for NP.