Synchronized Progression of Prestin Expression and Auditory Brainstem Response during Postnatal Development in Rats

Abstract

Prestin is the motor protein expressed in the cochlear outer hair cells (OHCs) of mammalian inner ear. The electromotility of OHCs driven by prestin is responsible for the cochlear amplification which is required for normal hearing in adult animals. Postnatal expression of prestin and activity of OHCs may contribute to the maturation of hearing in rodents. However, the temporal and spatial expression of prestin in cochlea during the development is not well characterized. In the present study, we examined the expression and function of prestin from the OHCs in apical, middle, and basal turns of the cochleae of postnatal rats. Prestin first appeared at postnatal day 6 (P6) for basal turn, P7 in middle turn, and P9 for apical turn of cochlea. The expression level increased progressively over the next few days and by P14 reached the mature level for all three segments. By comparison with the time course of the development of auditory brainstem response for different frequencies, our data reveal that prestin expression synchronized with the hearing development. The present study suggests that the onset time of hearing may require the expression of prestin and is determined by the mature function of OHCs.

Specific Influences of Early Acoustic Environments on Cochlear Hair Cells in Postnatal Mice

“…Therefore, the effects of low-frequency sounds were investigated. Consistent with our previous study [ 21 ], waves IV to VII were absent in the ABR waveforms recorded from pups in the present study. This observation may reflect the immature function of the central auditory system.…”

“…We propose that the over sound exposure in the present study is transmitted to the cochlea via the bone conduction and influence the sensorineural development before the hearing onset. This suggestion is supported by the results that high-intensity sound stimuli evoke ABR and behavior response before hearing onset [ 21 , 39 ]. In our study, low-frequency sound exerted stronger effects on the maturation of HCs than high-frequency sound.…”

“…In adult mice, ABR usually exhibits 5 to7 peaks generated by distinct nuclei along the ascending pathway of the auditory system. As reported in our previous study, only waves I to III of the ABR waveforms were observed in mice pups before P14 [ 21 ]. The absence of later ABR waveforms implies the weak activity of higher stages of auditory nuclei in the early postnatal epoch.…”

“…Driven by the receptor potential, intracellular chloride moves in and out of prestin and triggers prestin to switch between a long and short conformation, resulting in the elongation and shortening of OHCs [ 22 , 29 ]. The expression of prestin starts in the OHCs at the basal cochlea at approximately P5 and spreads to apical OHCs in the following days [ 21 , 31 ]. We found that low-frequency sound environment specifically increased the expression of prestin in apical OHCs, as evidenced by the Western blotting and qPCR data (Figures 4 and 5 ).…”

Functional Postnatal Maturation of the Medial Olivocochlear Efferent–Outer Hair Cell Synapse

“…The most conspicuous are those occurring in K 1 conductances (Marcotti and Kros, 1999), in the mechanotransduction apparatus, including changes in the stereocilia and associated proteins (Waguespack et al, 2007;Lelli et al, 2009), and in the size and shape of the cell (Marcotti and Kros, 1999;Oliver and Fakler, 1999). Moreover, prestin expression and electromotility, key factors in mature hearing, increase progressively after birth and are not fully functional until postnatal day 14 (P14) to P18 (Oliver and Fakler, 1999;Abe et al, 2007;Hang et al, 2016).…”