Investigation of electrophysiological effects of intratympanic retinoic acid after acoustic trauma in rats

Objectives/Hypothesis: To electrophysiologically demonstrate the effects of intratympanic retinoic acid administered following an acoustic trauma with distortion product otoacoustic emissions (DPOAE) measurement. Material method: The trial was performed on 21 Sprague Downey rats. The rats underwent distortion product otoacoustic emissions (DPOAE) measurement before the acoustic trauma, and rats were exposed to noise for 12 hours at 4 kHz 110 dB SPL. Following acoustic trauma, the otoacoustic emission measurement was repeated. The rats were divided into three groups, the study group (n=7, retinoic acid) , the second group (n=7,alcohol) and the control group (n=7). The study rats were injected with reinoic acid via the intratympanic route throughout the study for two times, one hour and two days after trauma with 28 gauge dental syringe. In the alcohol group, the rats were injected with %96 1 to 10 percent dilueted alcohol solution at the same time with RA administiration (to reveal the effects of alcohol with 28 gauge dental syringe). The otoacoustic emission assessment performed for all the groups after acoustic trauma in one hour. In the study group RA was applied one hour after acoustic trauma. After 48 hours the second dose of RA was injected. After that all the groups otoacoustic emission assessment was performed. Results: The otoacoustic emission assessment performed before the acoustic trauma statistically similar DPOAE values between the three groups at the 1 kHz,1,4 kHz, 2 kHz, 2,8 kHz,4 kHz,6 kHz,8 kHz (p>0.05). After the acoustic trauma there was no significant difference between the three groups (p>0.05). After administration of RA first and second dose there was significiant difference at 1, 1.4, 2, 2.8, 4, 6 ve 8 kHz (p<0,001). In the study group between the first and second dose of retinoic acid administration there was significiant difference at 1.4, 2, 2.8, 6 ve 8 kHz (p<0,05). There was no significiant difference between the alcohol and control group (p>0,05). Conclusions: In this study retinoic acid injection administered following an acoustic trauma have an protective effect against acoustic trauma. On the other hand, this result should be supported with studies in humans. Key Words: Acoustic Trauma, intratympanic injection, retinoic acid, otoacoustic emissions