Reversal of auditory cortical hyperexcitability and restoration of synaptic plasticity balance by GluN1-mediated photobiomodulation in noise-induced tinnitus.

Abstract

Glutamate receptors regulate neuronal excitability and drive synaptic plasticity in the auditory cortex (AC), with aberrant activation or dysfunction contributing to tinnitus pathogenesis. Photobiomodulation (PBM) exerts sustained modulatory effects on neural activity and behavioral responses across species, including humans. However, its therapeutic potential and mechanisms in noise-induced tinnitus remain unexplored. Here, we developed a noninvasive low-irradiance PBM device to target the AC of animal models, investigating near-infrared light mechanisms for reversing cortical hyperexcitability and restoring synaptic plasticity. In noise-exposed tinnitus models without significant neuronal loss, we observed abnormally elevated GluN1 activation and increased synaptic structural complexity compared to non-tinnitus or sham-exposed controls. Tinnitus models were subjected to PBM interventions with varying parameters (irradiance power: 20/40/80 mW/cm²; exposure duration: 300/600 s). Therapeutic efficacy was validated through auditory brainstem response (ABR), gap-prepulse inhibition of acoustic startle (GPIAS), and prepulse inhibition (PPI) behavioral assays. Fluorescence microscopy of brain sections quantified c-Fos/GluN1 co-localization to image activated NMDARs, while Nissl staining assessed PBM safety across parameters. Phosphoproteomic profiling explored mechanistic pathways, with neuronal morphological changes visualized via Golgi staining and transmission electron microscopy. To confirm GluN1's pivotal role in auditory cognition, we engineered transgenic mice with GluN1 overexpression or knockdown. GluN1-overexpressing mice exhibited tinnitus-like behaviors at specific frequencies, whereas GluN1-deficient tinnitus models showed aberrant behaviors due to impaired auditory cognition. Our findings delineate noise-induced tinnitus mechanisms and PBM-mediated regulation of neuronal excitability and structural plasticity, establishing an irradiance-duration optimization framework for clinical translation.