The Experience of Auditory Brainstem Response Audiometry in Wistar Rats

Abstract The rat auditory sensitivity to ultrasound necessitates objective audiometry in a frequency range corresponding to the evolutionary adaptation of the acoustic analyzer in these animals. The aim of this study was to develop a method for investigating auditory thresholds in rats that would physiologically match their species-specific auditory sensitivity. We used a Neuro-Audio device (Neurosoft Ltd., Ivanovo, Russia) equipped with the Neuro-Audio.NET software, updated for the purpose of hearing assessment within the ultrasonic range. The study was carried out on six SPF male Wistar rats. Auditory Brainstem Responses (ABRs) were studied during monaural ipsilateral stimulation with 8, 16, 20, and 30 kHz tones in a free sound field. Hearing threshold, amplitude, and peak II latency were assessed in the ABR complexes. For comparison, we used ABR data obtained with a conventional method of delivering an 8 kHz tone stimulus via an insert earphone. In adult rats, analysis of ABRs to 16–30 kHz tone stimulation in a free sound field environment showed hearing thresholds of 30–40 dB. A morphological feature of the ABR complex at an ultrasonic stimulus intensity of 85 dB is the presence of sharply distinct peaks II and V with an amplitude of 2.3–2.7 µV and a latency of approximately 4.1–4.2 ms. An amplitude–time feature associated with pitching in a free sound field is the elongation of the peak II latency and the appearance of a pronounced peak V. An affordable method for performing objective audiometry in rats using ABRs in the species-specific (ultrasonic) range of auditory sensitivity and the Russian-made clinical diagnostic device Neuro Audio is presented. The morphology of the ABRs complexes obtained in response to 16–30 kHz tone feeds and the features associated with their production when studied in a free sound field are shown.