J Int Adv Otol 2017; 13(3): 308-12 • DOI: 10.5152/iao.2017.1674 Original Article INTRODUCTION It is well known that excessive noise exposure can cause hearing loss through diferent mechanisms [1] . Noise-triggered damage leads to impairment of the stereocilias of the hair cells, the loss of hair cells, and structural distortion at the spiral ligament and spiral ganglion [2, 3] . It was reported that hair cells become dysfunctional within 2 weeks after noise exposure, and an edema develops in the spiral ganglion neurons [4, 5] . Nevertheless, the molecular mechanisms of noise-induced hearing loss are still not fully under- stood. In the broadest sense, excessive noise causes direct mechanical trauma to cochlear structures and an increase in reactive nitrogen species and reactive oxygen species, which can then destroy the DNA and cell membranes [1] . The roles of the proinfammatory cytokines of the inner ear after the noise exposure have been enlightened in some studies [6-8] . The main reason for cochlear cell damage might be the local increase in proinfammatory cytokines because the amount of these molecules at the damaged cochlea increases within a day and induces a gathering of infammatory cells. Furthermore, proinfammatory cytokines are secreted from some blood-originated infammatory cells and neurons. A potential role in the second-line infammatory efects of these molecules has been previously proposed [9] . However, the secretion mechanism of cytokines at the damaged cochlea is not yet fully clear. Therefore, measuring proinfammatory cytokines in the cochlea exposed to noise may shed light on the relationship between hearing level and cytokines in noise-induced hearing loss (NIHL). This study aimed to seek a correlation between hearing thresholds and the level of proinfammatory cytokines. Changes in Proinfammatory Cytokines in the Cochlea in Relation to Hearing Thresholds in Noise-Exposed Rats OBJECTIVE: Our aim was to investigate time efects in proinfammatory cytokines and the auditory brainstem response (ABR) thresholds of rat cochlea exposed to noise. MATERIALS and METHODS: Twenty-one rats were divided into two groups: the control group and the noise group. As high as 115 dB sound pressure of white noise was administered to the noise group of 16 rats for 3 h a day for 10 days. This group was further split into four subgroups based on the timing of sacrifce: 3 rd hour group, 12 th hour group, 24 th hour group, and 28th day group. ABR thresholds were measured in all the rats, after the noise exposure and right before being sacrifced. Proinfammatory cytokine levels (IL-6, IL-1β, and TNF-α) at the cochlea were measured. RESULTS: We found a signifcant diference between the frst ABR thresholds (5 dB nHL) and the post-exposure ABR thresholds in each group (25 dBnHL, 35 dBnHL, 15 dBnHL, and 17.50 dBnHL for the 3 rd hour group, 12 th hour group, 24 th hour group, and 28 th day group, respectively). The IL-1β levels in the 3 rd hour group and 12 th hour group were signifcantly higher than those in the control group and other noise subgroups. The TNF-α level in the 3 rd hour group was signifcantly higher than that in the control group and other noise subgroups. CONCLUSION: It seems reasonable to point out a direct correlation between the cytokine levels and hearing threshold levels after the noise exposure. This correlation was the highest for IL-1β. This result suggested a signifcant role of proinfammatory cytokines in hearing deterio- ration after noise exposure. KEYWORDS: Noise-induced hearing loss, proinfammatory cytokines, noise Hasan Hüseyin Arslan, Bülent Satar, Muhittin Serdar, Emine Yılmaz Department of Otorhinolaryngology and Head and Neck Surgery, Centrium Hospital, İstanbul, Turkey (HHA) Department of Otorhinolaryngology and Head and Neck Surgery, Gülhane Medical School, Ankara, Turkey (BS, EY) Department of Biochemistry, Acıbadem University School of Medicine, İstanbul, Turkey (MS) Corresponding Address: Hasan Hüseyin Arslan E-mail: hharslan@ymail.com Submitted: 16.09.2015 Revision received: 14.06.2016 Accepted: 20.04.2016 ©Copyright 2017 by The European Academy of Otology and Neurotology and The Politzer Society - Available online at www.advancedotology.org Cite this article as: Arslan HH, Satar B, Serdar M, Yılmaz E. Changes in Proinfammatory Cytokines in the Cochlea in Relation to Hearing Thresholds in Noise-Exposed Rats. J Int Adv 2017; 13: 308-12. 308