Making an Effort to Listen: Mechanical Amplification in the Ear

Hudspeth, A. J.

doi:10.1016/j.neuron.2008.07.012

Cited by 364 publications

(356 citation statements)

References 133 publications

(182 reference statements)

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“…Active amplification is characterized by nonlinear compression, which essentially entails that the gain is disproportionally higher at lower stimulus intensities (Hudspeth, 2008). Consequently, inhibition of active amplification would suppress the gain specifically at the lower range of test stimuli, as we observed in long-term adaptation (Fig.…”

Section: Long-term Adaptation Results From Suppression Of Active Amplsupporting

confidence: 53%

“…At the lower end of the intensity range, auditory thresholds are close to thermal noise levels (De Vries, 1948), reflecting the process of active mechanical amplification which increases mechanotransduction gain (Hudspeth, 2008). The amplification is termed active since it is a process that produces mechanical forces (Brass and Kemp, 1993) and it requires energy supply (Robertson and Manley, 1974).…”

Section: Introductionmentioning

confidence: 99%

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Dissection of Gain Control Mechanisms inDrosophilaMechanotransduction

Chadha

Cook

2012

J. Neurosci.

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Mechanoreceptor cells respond to a vast span of stimulus intensities, which they transduce into a limited response-range using a dynamic regulation of transduction gain. Weak stimuli are detected by enhancing the gain of responses through the process of active mechanical amplification. To preserve responsiveness, the gain of responses to prolonged activation is rapidly reduced through the process of adaptation. We investigated long-term processes of mechanotransduction gain control by studying responses from single mechanoreceptor neurons in Drosophila. We found that mechanical stimuli elicited a sustained reduction of gain that we termed long-term adaptation. Long-term adaptation and the adaptive decay of responses during stimuli had distinct kinetics and they were independently affected by manipulations of mechanotransduction. Therefore, long-term adaptation is not associated with the reduction of response gain during stimulation. Instead, the long-term adaptation suppressed canonical features of active amplification which were the high gain of weak stimuli and the spontaneous emission of noise. In addition, depressing amplification using energy deprivation recapitulated the effects of long-term adaptation. These data suggest that long-term adaptation is mediated by suppression of active amplification. Finally, the extent of long-term adaptation matched with cytoplasmic Ca 2ϩ levels and dTrpA1-induced Ca 2ϩ elevation elicited the effects of long-term adaptation. Our data suggest that mechanotransduction employs parallel adaptive mechanisms: while a rapid process exerts immediate gain reduction, long-term adjustments are achieved by attenuating active amplification. The slow adjustment of gain, manifest as diminished sensitivity, is associated with the accumulation of Ca 2ϩ .

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Section: Long-term Adaptation Results From Suppression Of Active Amplsupporting

confidence: 53%

Section: Introductionmentioning

confidence: 99%

Dissection of Gain Control Mechanisms inDrosophilaMechanotransduction

Chadha

Cook

2012

J. Neurosci.

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“…In some nonmammalian groups, such as chickens and to some extent monotreme mammals, both transporter and motor functions are evident, but the dramatic development of strong motor forces within a relevant range of cellular membrane potentials, as seen in therian mammals, did not evolve (Franchini and Elgoyhen 2006;Elgoyhen and Franchini 2011;Tan et al 2011). In the mammalian cochlea, the motor system involving prestin is more important at high frequencies (Hudspeth 2008), perhaps due to the unique cellular structure of the organ of Corti that permits the prestin motor system to amplify the movements of the entire organ of Corti.…”

Section: Prestin and Its Relevance To Mammalian Frequency Limitsmentioning

confidence: 99%

Evolutionary Paths to Mammalian Cochleae

Manley

2012

JARO

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Evolution of the cochlea and high-frequency hearing (920 kHz; ultrasonic to humans) in mammals has been a subject of research for many years. Recent advances in paleontological techniques, especially the use of micro-CT scans, now provide important new insights that are here reviewed. True mammals arose more than 200 million years (Ma) ago. Of these, three lineages survived into recent geological times. These animals uniquely developed three middle ear ossicles, but these ossicles were not initially freely suspended as in modern mammals. The earliest mammalian cochleae were only about 2 mm long and contained a lagena macula. In the multituberculate and monotreme mammalian lineages, the cochlea remained relatively short and did not coil, even in modern representatives. In the lineage leading to modern therians (placental and marsupial mammals), cochlear coiling did develop, but only after a period of at least 60 Ma. Even Late Jurassic mammals show only a 270°cochlear coil and a cochlear canal length of merely 3 mm. Comparisons of modern organisms, mammalian ancestors, and the state of the middle ear strongly suggest that high-frequency hearing (920 kHz) was not realized until the early Cretaceous (~125 Ma). At that time, therian mammals arose and possessed a fully coiled cochlea. The evolution of modern features of the middle ear and cochlea in the many later lineages of therians was, however, a mosaic and different features arose at different times. In parallel with cochlear structural evolution, prestins in therian mammals evolved into effective components of a new motor system. Ultrasonic hearing developed quite late-the earliest bat cochleae (~60 Ma) did not show features characteristic of those of modern bats that are sensitive to high ultrasonic frequencies.

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“…Chez l'homme, un dysfonctionnement des CCE, quelle qu'en soit origine (hérédité, traumatisme, médicaments ototoxiques, ou vieillissement, etc. ), entraîne une perte de la sensibilité et de la sélectivité en fréquence de l'organe auditif (pour revues, voir [2][3][4]). Les CCE réagissent mécaniquement à la dépolarisation-repolarisation électri-que induite par la stimulation sonore, par un cycle de contraction-élongation de leur paroi latérale entraînant un changement de leur taille (Figure 2A).…”

Section: Les Différents Compartiments De L'oreille Interne Et La Tranunclassified