Passive basilar membrane vibrations in gerbil neonates: mechanical bases of cochlear maturation

Abstract

Using a laser velocimeter, basilar membrane (BM) responses to tones were measured in neonatal gerbils at a site near the round window of the cochlea. In adult gerbils, ‘active’ BM responses at this site are most sensitive at 34–37 kHz and exhibit a compressive non‐linearity. Postmortem, BM responses in adults become ‘passive’, i.e. linear and insensitive, and the best frequency (BF) shifts downwards by about 0.5 octaves. At 14 and 16 days after birth (DAB), BM responses in neonatal gerbils were passive but otherwise very different from postmortem responses in adult gerbils: BF was more than an octave lower, the steep slopes of the phase vs. frequency curves were shifted downwards in frequency by nearly 1 octave, and the maximum phase lags amounted to only 180 deg relative to stapes. BFs and phase lags increased systematically between 14 and 20 DAB, implying drastic alterations of the passive material properties of cochlear tissues and accounting for a large part of the shift in BF that characterizes maturation of auditory nerve responses during the same period.

Fast cochlear amplification with slow outer hair cells

“…According to Kolston (1999), when OHC motility is absent, motion across the entire width of the BM is significant; therefore, in the passive cochlea, the extent of the entire BM should be reflected in the 1D model rather than just the region near the Deiters' cells as in the active case (Nilsen and Russell, 2000). Not surprisingly, the solid blue curves fit experimental data for the passive case better and have phase plateaus near the post-mortem adult phase plateaus reported in Overstreet et al (2002) and Ren and Nuttall (2001). The peak shifts with respect to the active case in both the dotted black and the solid blue curves of Fig.…”

Early Postnatal Development of Spontaneous and Acoustically Evoked Discharge Activity of Principal Cells of the Medial Nucleus of the Trapezoid Body: AnIn VivoStudy in Mice

“…conduction to the inner ear or to mechanoelectrical signal transduction by hair cells in the inner ear (Finck et al, 1972;Huangfu and Saunders, 1983;Woolf and Ryan, 1988;He et al, 1994;Kaltenbach and Falzarano, 1994;Overstreet et al, 2002).…”

Developmental Changes of Mechanics Measured in the Gerbil Cochlea

“…No sound-evoked electrophysiologi-cal responses can be elicited from the gerbil cochlea until 12 days after birth (Harris and Dallos 1984;Woolf and Ryan 1984;Echteler et al 1989). The best frequencies measured electrophysiologically in basal turn regions shift upward by approximately 1.5 octaves between 12 and 18 days postnatal, and adult-like frequency responses are not evident in these regions until approximately 18 days after birth (Harris and Dallos 1984;Woolf and Ryan 1984;Yancey and Dallos 1985;Arjmand et al 1988;Echteler et al 1989;McGuirt et al 1995;Mills and Rubel 1996, 1997, 1998Overstreet et al 2002). Beyond 18 days, only subtle maturation of cochlear function can be detected (McGuirt et al 1995;Overstreet et al 2003).…”

“…The best frequencies measured electrophysiologically in basal turn regions shift upward by approximately 1.5 octaves between 12 and 18 days postnatal, and adult-like frequency responses are not evident in these regions until approximately 18 days after birth (Harris and Dallos 1984;Woolf and Ryan 1984;Yancey and Dallos 1985;Arjmand et al 1988;Echteler et al 1989;McGuirt et al 1995;Mills and Rubel 1996, 1997, 1998Overstreet et al 2002). Beyond 18 days, only subtle maturation of cochlear function can be detected (McGuirt et al 1995;Overstreet et al 2003). Middle turn regions, on the other hand, do not exhibit any such developmental shift of best frequency between the time of hearing onset and maturation (Arjmand et al 1988;Müller 1996;.…”