Effects of Acoustic Environment on Tinnitus Behavior in Sound-Exposed Rats

Abstract

Laboratory studies often rely on a damaging sound exposure to induce tinnitus in animal models. Because the time course and ultimate success of the induction process is not known in advance, it is not unusual to maintain sound-exposed animals for months while they are periodically assessed for behavioral indications of the disorder. To demonstrate the importance of acoustic environment during this period of behavioral screening, sound-exposed rats were tested for tinnitus while housed under quiet or constant noise conditions. More than half of the quiet-housed rats developed behavioral indications of the disorder. None of the noise-housed rats exhibited tinnitus behavior during 2 months of behavioral screening. It is widely assumed that the “phantom sound” of tinnitus reflects abnormal levels of spontaneous activity in the central auditory pathways that are triggered by cochlear injury. Our results suggest that sustained patterns of noise-driven activity may prevent the injury-induced changes in central auditory processing that lead to this hyperactive state. From the perspective of laboratory studies of tinnitus, housing sound-exposed animals in uncontrolled noise levels may significantly reduce the success of induction procedures. From a broader clinical perspective, an early intervention with sound therapy may reduce the risk of tinnitus in individuals who have experienced an acute cochlear injury.

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Assessment of the Importance of Tympanic Membrane Mechanoreceptors on Eustachian Tube Function Based on Pressure Chamber Measurements

Introduction: Previously, it was demonstrated how the Eustachian tube (ET) opening function can be influenced by middle ear pressure and movement of the tympanic membrane via neural control. Mechanoreceptors on the tympanic membrane may be part of the afferent arc and could influence the middle ear pressure by activating the musculus veli palatini as part of a reflex. Methods: In a hypo and hyperbaric pressure chamber, 17 participants (34 ears) were twice exposed to a standardized pressure profile of pressure decrease and increase. The ET function reflecting parameters—ET opening pressure (ETOP), ET opening duration (ETOD), and ET opening frequency (ETOF)—were determined before and after local anesthesia of the right tympanic membrane. Results: After pressure exposure by pressure increase (active induced equalization) and pressure decrease (passive equalization) there was no significant difference between the mean value of ETOP, ETOD, and ETOF before and after local anesthesia of the right tympanic membrane on the right (anesthetized) or left side (not anesthetized). Conclusion: These results may lead to the hypothesis that tympanic membrane mechanoreceptors may play a minor role in regulating the ET function in humans. Address correspondence and reprint requests to Moritz F. Meyer, M.D., Department of Otorhinolaryngology, Head and Neck Surgery, Faculty of Medicine, University of Cologne, Kerpener Straße 62, 50937 Cologne, Germany; E-mail: moritz.meyer@uk-koeln.de All authors of the manuscript “Assessment of the importance of tympanic membrane mechanoreceptors on Eustachian tube function based on pressure chamber measurements” disclose any financial and personal relationships with other people or organisations that could inappropriately influence (bias) their work. The authors disclose no conflicts of interest. Copyright © 2017 by Otology & Neurotology, Inc. Image copyright © 2010 Wolters Kluwer Health/Anatomical Chart Company

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