“Sometimes scientists can’t discern if something went wrong in an animal model until clinical results show inconsistency. That is why we always exercise caution [about interpreting results with animal models] before we see the confirmation from clinical findings involving people,” Zhang said. Zhang is also a member of the ATA Board of Directors and former chair of the ATA’s Scientific Advisory Committee.

Shared by the American Tinnitus Association

“The research is significant because it suggests that noise-induced hearing loss causes neuroinflammation that is linked to increased levels of molecules called pro-inflammatory cytokines and the activation of non-neuronal cells called microglia in the primary cortex. With these findings, it is hoped that a treatment can be developed for tinnitus resulting from noise-induced hearing loss. Noise-induced hearing loss affects approximately 500 million people worldwide and plays a role in tinnitus. “

Abstract

Hearing loss is a major risk factor for tinnitus, hyperacusis, and central auditory processing disorder. Although recent studies indicate that hearing loss causes neuroinflammation in the auditory pathway, the mechanisms underlying hearing loss–related pathologies are still poorly understood. We examined neuroinflammation in the auditory cortex following noise-induced hearing loss (NIHL) and its role in tinnitus in rodent models. Our results indicate that NIHL is associated with elevated expression of proinflammatory cytokines and microglial activation—two defining features of neuroinflammatory responses—in the primary auditory cortex (AI). Genetic knockout of tumor necrosis factor alpha (TNF-α) or pharmacologically blocking TNF-α expression prevented neuroinflammation and ameliorated the behavioral phenotype associated with tinnitus in mice with NIHL. Conversely, infusion of TNF-α into AI resulted in behavioral signs of tinnitus in both wild-type and TNF-α knockout mice with normal hearing. Pharmacological depletion of microglia also prevented tinnitus in mice with NIHL. At the synaptic level, the frequency of miniature excitatory synaptic currents (mEPSCs) increased and that of miniature inhibitory synaptic currents (mIPSCs) decreased in AI pyramidal neurons in animals with NIHL. This excitatory-to-inhibitory synaptic imbalance was completely prevented by pharmacological blockade of TNF-α expression. These results implicate neuroinflammation as a therapeutic target for treating tinnitus and other hearing loss–related disorders.

Full paper link: https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3000307