Changes in the Numbers of Ribbon Synapses and Expression of RIBEYE in Salicylate-Induced Tinnitus

Abstract

Background: This study was performed to explore the mechanism underlying tinnitus by investigating the changes in the synaptic ribbons and RIBEYE expression in cochlear inner hair cells in salicylate-induced tinnitus. Methods: C57BL/6J mice were injected with salicylate (350 mg/kg) for 10 days and grouped. Behavioral procedures were performed to assess whether the animals experienced tinnitus. The specific presynaptic RIBEYE protein and non-specific postsynaptic glutamate receptor 2&3 protein in basilar membrane samples were examined by immunofluorescent labeling. RT-PCR and Western blot assays were used to examine RIBEYE expression. Serial sections were used to build three-dimensional models using 3ds MAX software to evaluate the changes in the synaptic ribbons. Results: The administration of salicylate increased false positives in the behavioral procedure from 3 d to 10 d. The membrane profiles of inner hair cells in all mice were intact. The number of synaptic ribbons in the salicylate group increased on the 7^th d and decreased on the 9^th and 10^th d. mRNA and protein expression of RIBEYE were initially up-regulated and later down-regulated by injecting salicylate for 10 consecutive days. Conclusion: This change in the ribbon synapses of cochlear inner hair cells in salicylate-induced mice might serve as a compensatory mechanism in the early stages of ototoxicity and contribute to tinnitus later. The alteration of RIBEYE expression could be responsible for the changes in the morphology of ribbon synapses and for salicylate-induced tinnitus.