Tinnitus Generation and Behavioral Changes Caused by Chronic Stress: A Behavioral and Brain Study in a Rat Model.

Objectives: This study explores the connection between chronic stress and tinnitus, a phantom auditory perception, using an animal model.

Methods: Rats were subjected to 2 h of daily restraint stress for 10 days. Tinnitus was assessed on the last day of stress exposure using the gap response of pre-pulse inhibition acoustic reflex, measured at 60 dB background sound level at 8, 16, and 20 kHz. Chronic stress-exposed rats were categorized into two groups: tinnitus (RTG) and non-tinnitus (RNTG). Various tests, including hearing assessments (distortion product otoacoustic emissions and auditory brainstem response), behavioral evaluations (elevated plus maze test and forced swimming test), and immunohistochemical studies in the auditory and limbic brain regions, were conducted to understand the relationship between chronic stress, tinnitus, and behavioral changes.

Results: Following chronic restraint stress, 64.3% of the rats exhibited tinnitus with no audiometric changes. EPM and FST indicated an increase of anxiety- and depression-related behavior in RTG. Immunohistochemical analyses identified specific alterations in the expression of neurotransmitter receptors within brain regions implicated in tinnitus. Specifically, we observed a decrease in γ-aminobutyric acid A receptor α1 expression and an increase in glutamate receptor (N-methyl-D-aspartate receptor subunit 1 and receptor subunit 2B) expression in specific brain region. These changes suggest a reorganization of neural circuits associated with the tinnitus generation and behavioral changes of the rats after chronic stress exposure.

Conclusion: Chronic stress alone can be a causal factor for the generation of tinnitus and behavioral changes through altered neural activities in tinnitus-related brain networks.

Level of evidence: NA Laryngoscope, 2024.