Hypothesis underlying the sensitivity of mammalian auditory system
overturned

Date:
August 14, 2020
Source:
University of Colorado Anschutz Medical Campus
Summary:
A new study challenges a decades-old hypothesis on adaptation,
a key feature in how sensory cells of the inner ear (hair cells)
detect sound.



FULL STORY ==========================================================================
A new study from the University of Colorado Anschutz Medical Campus
challenges a decades-old hypothesis on adaptation, a key feature in how
sensory cells of the inner ear (hair cells) detect sound.


==========================================================================
The paper, out today in Science Advances, examines how hair cells
transform mechanical forces arising from sound waves into a neural
electrical signal, a process called mechano-electric transduction
(MET). Hair cells possess an intrinsic ability to fine-tune the
sensitivity of the MET process (termed adaptation), which underlies our capacity to detect a wide range of sound intensities and frequencies
with extremely high precision. Up until now, 30+ years of research
had convinced auditory scientists that the molecules and proteins
responsible for adaptation have been figured out. First published in
1987, the prevailing model for how adaptation works asserted that the
sound- sensitive "antenna" of the hair cell (called the hair bundle)
undergoes a mechanical change during adaptation, such that a decrease
in stiffness of the hair bundle caused a decrease in MET sensitivity.

Ancillary experiments conducted over the ensuing decades have suggested
that a motor protein, myosin 1c, is required for MET adaptation. Through multiple experiments and a variety of controls, Anschutz researchers
determined that this existing hypothesis needs to be reexamined; that
although adaptation does require myosin motors, it does not involve a mechanical change in the hair bundle.

Anschutz researchers performed a series of sophisticated experiments to
examine the relationship between the mechanical properties of the hair
bundle and the electrical response of the hair cell. Using a custom-built high-speed imaging technique, Giusy Caprara, PhD, post-doctoral fellow
at the University of Colorado School of Medicine and lead author of
the study, performed simultaneous electrical recording and imaging
of hair cells in a variety of mammalian species at 10,000 frames per
second to examine the mechanical changes to the hair bundle during
adaptation, an extreme departure from the experiments of 1987 which used photodiodes. "The reason this wasn't uncovered earlier is because there
are very few experiments that tested the mechanical properties of the
hair bundle," says Anthony Peng, PhD, supervising author and assistant professor of physiology and biophysics at the University of Colorado
School of Medicine. "Technology drove and made this discovery possible." Understanding the mechanism of adaptation is important for determining
how the sensory cells of the inner ear work. While the research is
not directly translational, it is an important first step in fixing
and replacing cochlear function, potentially leading to technological improvements for better sound processing and treatment of hearing
dysfunction down the line.

"The discovery that the original model of adaptation was incorrect is
important in a couple of ways," says Peng. "In basic science, this has
opened avenues for more research, including proposing a new model of how adaptation works. More importantly, hearing sensitivity and the range of hearing we are able to achieve relies on this process, so understanding
this will help us better understand different types of hearing loss
people experience."

========================================================================== Story Source: Materials provided by University_of_Colorado_Anschutz_Medical_Campus. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Giusy A. Caprara, Andrew A. Mecca and Anthony W. Peng. Decades-old
model
of slow adaptation in sensory hair cells is not supported in
mammals.

Science Advances, 2020 DOI: 10.1126/sciadv.abb4922 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200814142948.htm

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