OBJECTIVE:To evaluate the protective effect of betahistine on noise-induced hearing loss (NIHL) using scanning electron microscopy (SEM) and distortion product otoacoustic emission (DPOAE). MATERIALS and METHODS:A total of 8 adult albino guinea pigs were used in this study (study group: n=4 and control group: n=4). DPOAE measurements of both groups were performed before the procedure. Two hours before noise exposure, 0.9% NaCl solution was injected perorally to the control group and betahistine was administered through a peroral catheter to the study group. Both groups were then exposed to 105-dB sound pressure level (SPL) 4-kHz frequency-based narrow-band noise for 2 h per day for 5 days. DPOAE measurements were performed again on the 6th day and cochleae were dissected and examined by SEM on the 7 th day. RESULTS:Regarding the results of DPOAE, NIHL was observed in both groups on the 6th day (p<0.05). Loss, flattening, and fusion, which are findings of permanent hearing loss, were determined in the stereocilia of the inner and outer hair cells by SEM. These findings were evaluated as signs of permanent increase in the threshold. When DPOAE measurements and SEM results were evaluated in the study group, no significant difference was observed in NIHL compared with the control group (p>0.05). CONCLUSION:In our study, it was observed that simultaneous administration of betahistine during noise had no protective effect on permanent increase in the threshold. However, further studies on noise and long-term use of betahistine can be performed. KEYWORDS:Betahistine, noise-induced hearing loss (NIHL), scanning electron microscopy (SEM), distortion product otoacoustic emission (DPOAE) INTRODUCTIONNoise is one of the most important occupational and environmental health hazards. Exposure to loud noise causes irreversible auditory damage, resulting in sensorineural hearing loss. In addition, it can result in temporary threshold shifts (TTSs) and/or permanent threshold shifts (PTSs). Moderate exposure over a short time period may initially cause TTSs, which may fully recover within 24-48 h. If the noise causing TTSs is continuous or frequent, PTSs may develop. Noise exposure leads to damage and loss of hair cells in the organ of Corti, which is contained in a spiral-shaped structure called the cochlea. These sensory hair cells and the surrounding structures are vibrated by incoming acoustic signals and then convert this mechanical vibration into electrical events in the form of firings of the 8th cranial nerve fibers. Chronic exposure to intense noise initially damages the outer hair cells that are responsible for high-frequency sounds [1,2] .Betahistine dihydrochloride (betahistine) has beneficial effects on inner ear disorders such as vertigo that affect cochlear blood flow (CoBF). It has been shown to increase CoBF in animal models and a number of hypotheses have been proposed for its mechanism and site of action. Betahistine is a strong histaminergic H3 receptor antagonist; this property may account for the increase in ...