A New Hypothesis on the Frequency Discrimination of the Cochlea

Abstract

OBJECTIVE:Medial olivocochlear efferent (MOCE) neurons innervate outer hair cells (OHCs) of the cochlea, which in turn leads to basilar membrane motion. We hypothesized that MOCE-induced alterations in basilar membrane motion, independent of traveling waves, is responsible for the cochlear frequency discrimination of sound. MATERIALS and METHODS:Eleven guinea pigs underwent bilateral otoscopic and audiologic evaluations under general anesthesia. The study comprised two parts. Part I (n=11) included spontaneous otoacoustic emission (SOAE) recordings with or without contralateral pure-tone acoustic stimuli (1 and 8 kHz) at 60 dB sound pressure level (SPL). Part II involved pure-tone (1 or 8 kHz) acoustic trauma in the right ears of two randomly selected subgroups (G1: 1 kHz; n=4 and G8: 8 kHz; n=4). The remaining three animals served as controls. After frequency-specific deafness was confirmed by distortion product otoacoustic emission (DPOAE), SOAEs were recorded in the left ears in the presence of a contralateral pure-tone (1 and 8 kHz) stimulus of 60 dB SPL. Furthermore, the surface of the organ of Corti was examined by scanning electron microscopy (SEM). RESULTS:The contralateral pure tone led to frequency-specific activation in SOAEs in part I (without trauma) and part II (with trauma) measurements. SEM showed heterogeneous OHC damage along the cochlea in traumatized ears with pure tone. CONCLUSION:We suggest that MOCEs convey acoustic information from traumatized ears to intact ears. Traumatized ears can show frequency-specific activation in the presence of diffuse damage in OHCs that excludes the passive transmission of the pressure wave from the perilymph to the basilar membrane.

Does Oral Monosodium Glutamate Have a Cochleotoxic Effect? An Experimental Study

“…These animals were housed at 16-21°C under a 12-h light-dark cycle and fed ad libitum pellet. The reason why we chose to use guinea pigs as a model in our study is that they are widely used in otological studies [Albuquerque et al, 2009], and the experience of guinea pigs in terms of electrophysiological measurements and histopathological examinations was well gained in previous experimental inner ear studies of our clinic [Bulut et al, 2017]. The guinea pigs underwent electrophysiological measurements under general an-aesthesia, which was achieved by intramuscular administration of ketamine hydrochloride 40 mg/kg + xylazine hydrochloride 5 mg/kg.…”

Evaluation of the Olivocochlear Efferent System Activation After Exposure to Music in Young Individuals

“…In studies on the temporal bone performed in human subjects who were exposed to chronic occupational noise for 30 years, the loss of internal hairy cells in the basal rotation of the cochlea was limited, but a significant loss of external hairy cells (DTH) was observed (20). In experimental animal studies (21)(22)(23), the primary target cell group has been reported to be DTH at acute noise-induced hearing loss. Together with the increase in the duration and intensity of the noise, this causes the structural deterioration in the internal hairy cells and the entire Corti Organ (23).…”