Evaluation of click and chirp stimulus factor by creating sodium salicylate induced Tinnitus model in rats

Tinnitus is defined as a phantom auditory perception experienced in the absence of any external acoustic stimulus, and its etiopathogenesis has not yet been fully elucidated. In this study, an experimental animal model was established by inducing tinnitus in rats through the administration of sodium salicylate, and auditory brainstem responses (ABRs) were recorded using both click and chirp stimuli. The aim was to evaluate the validity of the model through a dual approach that combines electrophysiological data with behavioral assessments. A total of 24 five-month-old male Sprague-Dawley rats with normal hearing confirmed via ABR were used. The rats were randomly divided into two groups: sham and tinnitus. Prior to the experiment, all rats underwent acoustic conditioning using the T-shaped water maze method developed by Guitton and Dudai, which involved pairing one arm of the maze with sound and the other with silence. Following conditioning, the tinnitus group received daily intraperitoneal injections of sodium salicylate at a dose of 300 mg/kg for six consecutive days. The sham group received the same volume of 0.9% sodium chloride via intraperitoneal injection over the same period. After the injection period, all rats were subjected to a swimming test in the T-maze to behaviorally assess the presence of tinnitus. The time spent in the sound-paired versus silent-paired arms of the maze was recorded. Following behavioral testing, ABRs were recorded under anesthesia using both click and chirp stimuli. Latencies and amplitudes of waves I, II, III, IV, and V at 80 dB nHL were analyzed. In addition, wave II responses at 20 dB nHL were evaluated to assess potential hearing loss. The results showed that rats in the tinnitus group spent significantly more time in the arm previously paired with sound, even in the absence of any acoustic stimulus, suggesting a behavioral representation of tinnitus perception. Following salicylate administration, statistically significant increases were observed in the amplitudes of waves II and III in the ABR recordings (p < 0.05). Click-evoked responses were found to be more markedly affected compared to chirp-evoked responses. Furthermore, click stimuli appeared to provide a more sensitive assessment of both peripheral and central auditory pathway alterations, offering enhanced neurophysiological characterization of tinnitus. In conclusion, this thesis demonstrates that an experimental tinnitus model induced by sodium salicylate in rats can be reliably evaluated using both electrophysiological and behavioral methods. Click stimuli were found to offer greater sensitivity compared to chirp stimuli. This study not only proposes a standardized methodology for developing experimental tinnitus models but also lays the groundwork for the development of potential treatment strategies based on experimental modeling.