Identification of miRNAs that regulate tinnitus development

To investigate which miRNAs regulate the development of tinnitus, we have performed microarray for miRNAs as a discovery platform. The changes in dorsal cochlear nucleus after noise exposure have been suggested to play an important role in the development of tinnitus. This study was performed using 12 week-old-male Sprague-Dawley rats. Based on our previous experiment about the development of tinnitus, we set a time point for harvesting dorsal cochlear nuclei: 3 weeks after the exposure of 6-8 kHz narrow-band noise (110 dB SPL for 2 h) at right side. Eight animals were divided into two experimental groups: tinnitus group showing evidence of tinnitus (n = 5); and non-tinnitus group showing no evidence of tinnitus (n = 3) in the gap pre-pulse inhibition of acoustic startle reflex (GPIAS) recordings. Three animals of each group were anesthetized deeply and euthanized at 3 weeks post noise exposure. Dorsal cochlear nucleus at right side was harvested. Microarray for miRNAs was performed using the Affymetrix miRNA 4.0 microarray. Considering the fold change of normalized signal intensities between tinnitus and non-tinnitus groups, miR-375-3p was selected as the candidate miRNA. This result was validated by quantitative reverse transcription-PCR. MiRNAs expression induced by the exposure of noise in dorsal cochlear nucleus of Sprague-Dawley rat was measured at 3 weeks post noise exposure. Comparing these results between tinnitus and non-tinnitus groups, the candidate miRNAs that might regulate tinnitus development were selected.