Everolimus Attenuates Salicylate-Induced Tinnitus-Like Behavior and Auditory Cortical Hyperexcitability

Tinnitus is an auditory perception without external stimuli, driven by maladaptive neuroplasticity. This study investigated whether targeting the mTOR pathway with everolimus (EVE) could ameliorate pathological synaptic marker alterations, neurochemical imbalance, and neural hypersynchrony in the primary auditory cortex (A1) using a sodium salicylate (SS)-induced acute tinnitus rat model.

Adult rats were divided into Control, Tinnitus, and Tinnitus+EVE groups. Behavioral phenotypes were assessed using gap prepulse inhibition of the acoustic startle (GPIAS) test. In vivo multi-channel electrophysiology was used to measure spontaneous firing rates (SFR) and local field potentials (LFPs), focusing on gamma-band power and theta-gamma phase-amplitude coupling (PAC) in A1. Molecular changes were quantified via Western blotting, immunofluorescence, immunohistochemistry, and targeted LC-MS/MS neurotransmitter profiling.

Salicylate-induced tinnitus-like gap-detection deficits were mitigated by systemic EVE administration. Rats with tinnitus-like behavior displayed A1 hyperexcitability, reflected by elevated spontaneous firing rates and heightened c-Fos expression. Their network activity was disrupted, showing increased gamma-band power and significantly strengthened theta-gamma phase-amplitude coupling. At the molecular level, the mTOR pathway was activated, and the synaptic proteins BDNF and PSD95 were upregulated. Neurochemically, the excitatory neurotransmitter glutamate accumulated significantly. Everolimus administration suppressed these abnormalities, attenuating the aberrant firing rates, pathological theta-gamma coupling, and the excessive synaptic protein and glutamate levels.

Targeted mTOR inhibition attenuates salicylate-induced tinnitus-like behavior by modulating maladaptive synaptic plasticity markers and mitigating pathological network hypersynchrony in A1. These findings suggest the mTOR cascade as a potential target for regulating cortical oscillatory and synaptic homeostasis in auditory phantom perception models.