Serotonin Circuit Linked to Tinnitus Symptoms in New Study

New research has identified a specific brain circuit involving serotonin that appears to induce tinnitus-like effects in mice. The findings, published in the Proceedings of the National Academy of Sciences, could explain why some individuals report a worsening of tinnitus symptoms when taking certain antidepressants.

Key Findings

• A study from Oregon Health & Science University and Anhui University found elevated serotonin levels in the brain were associated with increased behavioral symptoms of tinnitus in mice.
• Using optogenetics, researchers stimulated serotonin-producing neurons and observed increased activity in the auditory region of the brain.
• Mice exhibited behaviors consistent with tinnitus perception during this stimulation.
• When the serotonin circuit was deactivated, tinnitus symptoms were significantly reduced.

"Now, using mice, we've found a specific brain circuit involving serotonin that goes straight to the auditory system, and found that it can induce tinnitus-like effects," said co-author Zheng-Quan Tang.

Background and Context

Tinnitus involves the perception of ringing or buzzing sounds without an external source, affecting up to an estimated 14% of people globally. Selective serotonin reuptake inhibitors (SSRIs), which increase serotonin levels, are commonly prescribed for depression and anxiety. While a 2017 study hinted at serotonin's involvement in tinnitus, the precise mechanism remained unclear until now.

This new research suggests serotonin's role involves a direct neural circuit connecting to the auditory system. The findings align with anecdotal reports from individuals who experience a worsening of their tinnitus when taking serotonin-elevating medications.

"People with tinnitus should work with their prescribing physician to find a drug regimen that gives them a balance between relief of psychiatric symptoms like depression and anxiety, while minimizing the experience of tinnitus," advised co-senior author Laurence Trussell.

Research Implications

The study opens the door to future investigations, including the possibility of developing more targeted drugs that could elevate serotonin in specific brain regions without affecting the auditory circuit. The research was supported by a National Institutes of Health award, and all animal research was reviewed and approved by the relevant institutional committee.