High-Frequency Repetitive Transcranial Magnetic Stimulation Improves Oxidative Stress, Iron Metabolism, and Synaptic Plasticity in the Visual Cortex of Amblyopic Rats: Association With the NRF2/GPX4 Pathway.

BACKGROUND: Amblyopia is a neurodevelopmental disorder with limited treatment efficacy after the developmental critical period. Repetitive transcranial magnetic stimulation (rTMS) improves visual perception in patients with amblyopia, although its specific mechanism remains unclear. In this study, we investigated whether rTMS improves abnormal ocular dominance (OD) distribution in monocular deprivation (MD) amblyopic rats by modulating oxidative stress, iron metabolism, and synaptic plasticity through the nuclear factor erythroid 2-related factor 2/glutathione peroxidase-4 (NRF2/GPX4) pathway.

METHODS: Sprague-Dawley (SD) rats were randomly assigned to four groups (n = 20 each): normal control+rTMS (NC+rTMS), NC+sham stimulation (NC+sham), MD+sham, and MD+rTMS. The rTMS groups received 20-Hz rTMS treatment for 28 consecutive days. Visual function was assessed using flash visual evoked potentials (F-VEP). The morphological structure of the visual cortex, synaptic function, oxidative stress levels, iron metabolism, and expression of NRF2/GPX4 were analyzed using histopathological staining, transmission electron microscopy (TEM), biochemical assay, and molecular biology experiments. Statistical analyses were performed using repeated-measures analysis of variance (ANOVA) and two-way ANOVA. Bonferroni post-hoc tests were used afterward.

RESULTS: Following rTMS treatment, the contralateral vs. ipsilateral value (C/I values) in the MD+rTMS group were higher than baseline (p < 0.0001). Compared with the MD+sham group, rTMS alleviated visual cortex synaptic ultrastructural damage and upregulated postsynaptic density protein 95 (PSD-95) and brain-derived neurotrophic factor (BDNF) levels in MD rats (p = 0.016, p = 0.041). The MD+rTMS group showed significantly decreased reactive oxygen species (ROS) and malondialdehyde (MDA) levels (p < 0.05, p < 0.0001) and increased glutathione (GSH) content (p < 0.0001) in comparison with the MD+sham group. Additionally, rTMS elevated NRF2, GPX4, and ferroportin-1 (FPN1) expression in the MD group (all p < 0.01) and reduced ferrous iron (Fe2+) accumulation (p < 0.01) relative to the MD+sham group.

CONCLUSIONS: High-frequency rTMS improves abnormal OD distribution in amblyopic rats, an effect associated with the upregulation of NRF2/GPX4 pathway protein expression, reduced oxidative stress, restored iron metabolism, and enhanced synaptic plasticity in the visual cortex. This finding offers novel insights into the mechanisms of rTMS and the pathology of amblyopia.