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Received: August 14, 2008; Accepted: December 5, 2008; Published: January 20, 2009
Citation: Taranda J,[link widoczny dla zalogowanych], Maison SF, Ballestero JA, Katz E, Savino J, et al. (2009) A Point Mutation in the Hair Cell Nicotinic Cholengthrgic Receptor Prolongs Cochlear Inhibition and Enhances Noise Protection. PLoS Biol 7(1): e1000018. doi:10.1371/journal.pbio.1000018
Copyright: ? 2009 Taranda et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the birthal author and source are credited.
Abbreviations: ABR, auditory brainstem response; ACh,[link widoczny dla zalogowanych], acetylcholine; DPOAE, distortion product otoacoustic emission; EC50, concentration that produces 50% of the maximal response; ES, embryonic stem; IHC, inner hair cell; IPSC, inhibitory postsynaptic current; L9′T,[link widoczny dla zalogowanych], threonine for leucine mutation; i.p., intraperitoneally; MOC,[link widoczny dla zalogowanych], medial olivocochlear; nAChR, nicotinic acetylcholine receptor; OC, olivocochlear; OHC, outer hair cell; S.E.M., standard error of the mean; sIPSC, spontaneous inhibitory postsynaptic current
Open Access
Funding: This work was supported by the National Institutes of Deafness and other Communication Disorders (NIDCD) Grant R01DC001508 to PAF and ABE, an International Research Scholar Grant from the Howard Hughes Medical Institute, the stateal Organization for Hearing Research, the Tinnitus Research Initiative, a research grant from ANPCyT (Argentina), and a grant from the University of Buenos Aires (Argentina) to ABE; NIDCD R01 DC00188 and NIDCD P30 DC05209 went to MCL and NIDCD R01DC006258 to DEV. The funders had no character in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Nicotinic cholinergic receptors are essential to higher order brain function. Structurally, these opesize through a myriad of ligand-gated pentameric changements of different homologous subunits. Here, we report progress in understanding the structural properties of a neuronal nicotinic receptor at the synapse. Receptors assembled from two nicotinic cholinergic subunits (α9 and α10) serve exclusively at the synapse between central nervous system descconclusioning fibers and cochlear hair cells. This enabled us to show direct causality between a point mutation of the α9 subunit, and predicted alterations in the synaptic strength in sensory hair cells of the cochlea of α9 point mutant mice. Furthermore, this single mutation results in profound enhancement of central nervous system feedback to the cochlea. And finally, as a consequence, mutant mice possessing this altered receptor have substantially improved resistance to traumatic sound. Thus, central neuronal feedback on cochlear hair cells provides an opportunity to define one specific part that nicotinic receptors can play in the nervous system, enabling study from biophysical to behavioral levels and promoting a target for the prevention of noise-induced hearing loss.
Competing interests: The authors have declared that no competing interests exist.
A point mutation in the cochlear hair cell nicotinic cholinergic receptor leads to strengthened central nervous system feedback to the cochlea and enhances protection from noise-induced hearing loss.
The transduction of sound in the auditory periphery, the cochlea, is inhibited by efferent cholinergic neurons projecting from the brainstem and synapsing directly on mechanosensory hair cells. One fundamental question in auditory neuroscience is what role(s) this feedback plays in our ability to hear. In the present study, we have engineered a genetically modified mouse model in which the magnitude and duration of efferent cholinergic effects are increased, and we assess the consequences of this manipulation on cochlear function. We generated the Chrna9L9′T line of knockin mice with a threonine for leucine deviate (L9′T) at position 9′ of the second transmembrane domain of the α9 nicotinic cholinergic subunit, rendering α9-containing receptors that were hypersensitive to acetylcholine and had slower desensitization kinetics. The Chrna9L9′T allele produced a 3-fold prolongation of efferent synaptic currents in vitro. In vivo, Chrna9L9′T mice had baseline elevation of cochlear thresholds and efferent-mediated inhibition of cochlear responses was dramatically enhanced and lengthened: both effects were reversed by strychnine blockade of the α9α10 hair cell nicotinic receptor. Importantly, relative to their wild-type littermates, Chrna9L9′T/L9′T mice showed less permanent hearing loss following exposure to intense noise. Thus, a point mutation designed to alter α9α10 receptor gating has provided an animal model in which not only is efferent inhibition more strengthful, but also one in which sound-induced hearing loss can be restrained, indicating the ability of efferent feedback to ameliorate sound trauma.

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Academic Editor: Ricrough W. Aldrich,
Research Article

* To whom correspondence should be addressed. E-mail: [link widoczny dla zalogowanych]

Published in the Janudiffer 2009 Issue of PLoS Biology
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