Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB254

Poster Communications

Re-Organisation Of Frequency Discrimination In The Cochlear Tonotopy.


1. Audiology, Trakya University, Edirne, Turkey. 2. Biophysics, Trakya University, Edirne, Turkey. 3. Histology and Embriology, Marmara University, Istanbul, Turkey. 4. Audiology, Istanbul University, Istanbul, Turkey. 5. Physiology, Trakya University, Edirne, Turkey.

Frequency selectivity is a functional feature of the inner ear and this feature has not been fully resolved since the beginning of hearing studies (Manley and van Dijk 2016). Frequency selectivity is defined as a combination of passive cochlear mechanics due to travelling wave motion proposed by von Bekesy (Bekesy, 1960) and active processes evaluated by outer hair cells proposed by Dallos (Dallos, 1996). Psychoacoustic frequency selectivity is that resolution is sharper than mechanically travelling wave motion along the cochlea (Evans, 1975). In our study, reorganization of the frequency distribution in cochlear tonotopic which an important product/output of frequency selectivity was evaluated at electrophysiological, ultrastructural and molecular level. Following electrophysiological tests, 30 guinea pigs (60 ears) with auropalpebral reflexes were randomly assigned to three groups, one control group and two study groups. All measurements were performed with the guinea pigs under general anesthesia achieved by an intramuscular injection of ketamine (50 mg/kg) and xylazine (10 mg/kg). At 1 and 8 kHz frequencies, an acoustic trauma was generated by giving a sound stimulus of 110 dB HL for 10 minutes. Frequency specific hearing loss was assessed by Distortion Product Otoacoustic Emission (DPOAE) and Auditory Brainstem Response (ABR) tests. For ultrastructural evaluation, temporal bones (Figure 1) were dissected and stereocilia morphology of outer hair cells (DTH) was evaluated. In the dissected temporal bones, the cochlea was homogenized and the gene expression of Glu2 /3 receptors was examined as a segment. As a result of electrophysiological tests pure tone acoustic trauma was performed at frequencies of 1 and 8 kHz. In ultrastructural evaluations and molecular analyzes, a heterogeneous distribution was observed in which OHC degeneration in certain segmental regions was not observed after acoustic trauma Glu2/3 receptors did not increase, and DTH degeneration and Glu2/3 receptors increased in different segmental regions due to wave propagation along the tonotopic axis of the cochlea. In our study, we suggest that basilar membrane movements play secondary role whereas outer hair cell electromotility provides primary mechanism in the cochlear analysis of sound. Thus, tonotopic map of cochlea should be reorganized in the light of these new findings.

Where applicable, experiments conform with Society ethical requirements