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Dewey JB, Shera CA. Bandpass Shape of Distortion-Product Otoacoustic Emission Ratio Functions Reflects Cochlear Frequency Tuning in Normal-Hearing Mice. J Assoc Res Otolaryngol 2023:10.1007/s10162-023-00892-4. [PMID: 37072566 DOI: 10.1007/s10162-023-00892-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2022] [Accepted: 02/02/2023] [Indexed: 04/20/2023] Open
Abstract
The frequency selectivity of the mammalian auditory system is critical for discriminating complex sounds like speech. This selectivity derives from the sharp tuning of the cochlea's mechanical response to sound, which is largely attributed to the amplification of cochlear vibrations by outer hair cells (OHCs). Due to its nonlinearity, the amplification process also leads to the generation of distortion products (DPs), some of which propagate out to the ear canal as DP otoacoustic emissions (DPOAEs). However, the insight that these signals provide about the tuned micro- and macro-mechanics underlying their generation remains unclear. Using optical coherence tomography to measure cochlear vibrations in mice, we show that the cochlea's frequency tuning is reflected in the bandpass shape that is observed in DPOAE amplitudes when the ratio of the two evoking stimulus frequencies is varied (here termed DPOAE "ratio functions"). The tuning sharpness of DPOAE ratio functions and cochlear vibrations co-varied with stimulus level, with a similar quantitative agreement in tuning sharpness observed for both apical and mid-cochlear locations. Measurement of intracochlear DPs revealed that the tuning of the DPOAE ratio functions was not caused by mechanisms that shape DPs locally near where they are generated. Instead, simple model simulations indicate that the bandpass shape is due to a more global wave interference phenomenon. It appears that the filtering of DPOAEs by wave interactions over an extended spatial region allows them to provide a window onto the frequency tuning of single cochlear locations.
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Affiliation(s)
- James B Dewey
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, 90033, CA, USA.
| | - Christopher A Shera
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, 90033, CA, USA
- Department of Physics and Astronomy, University of Southern California, Los Angeles, CA, 90089, USA
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Flaherty SM, Russell IJ, Lukashkin AN. Drug distribution along the cochlea is strongly enhanced by low-frequency round window micro vibrations. Drug Deliv 2021; 28:1312-1320. [PMID: 34176371 PMCID: PMC8238068 DOI: 10.1080/10717544.2021.1943059] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The cochlea’s inaccessibility and complex nature provide significant challenges to delivering drugs and other agents uniformly, safely and efficiently, along the entire cochlear spiral. Large drug concentration gradients are formed along the cochlea when drugs are administered to the middle ear. This undermines the major goal of attaining therapeutic drug concentration windows along the whole cochlea. Here, utilizing a well-known physiological effect of salicylate, we demonstrate a proof of concept in which drug distribution along the entire cochlea is enhanced by applying round window membrane low-frequency micro vibrations with a probe that only partially covers the round window. We provide evidence of enhanced drug influx into the cochlea and cochlear apical drug distribution without breaching cochlear boundaries. It is further suggested that ossicular functionality is not required for the effective drug distribution we report. The novel method presented here of local drug delivery to the cochlea could be implemented when ossicular functionality is absent or impeded and can be incorporated in clinically approved auditory protheses for patients who suffer with conductive, sensorineural or mixed hearing loss.
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Affiliation(s)
- Samuel M Flaherty
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton, UK.,Centre for Regenerative Medicine and Devices, University of Brighton, Brighton, UK
| | - Ian J Russell
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton, UK
| | - Andrei N Lukashkin
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton, UK.,Centre for Regenerative Medicine and Devices, University of Brighton, Brighton, UK
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Russell IJ, Lukashkina VA, Levic S, Cho YW, Lukashkin AN, Ng L, Forrest D. Emilin 2 promotes the mechanical gradient of the cochlear basilar membrane and resolution of frequencies in sound. SCIENCE ADVANCES 2020; 6:eaba2634. [PMID: 32577518 PMCID: PMC7286672 DOI: 10.1126/sciadv.aba2634] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/19/2019] [Accepted: 04/02/2020] [Indexed: 06/11/2023]
Abstract
The detection of different frequencies in sound is accomplished with remarkable precision by the basilar membrane (BM), an elastic, ribbon-like structure with graded stiffness along the cochlear spiral. Sound stimulates a wave of displacement along the BM with maximal magnitude at precise, frequency-specific locations to excite neural signals that carry frequency information to the brain. Perceptual frequency discrimination requires fine resolution of this frequency map, but little is known of the intrinsic molecular features that demarcate the place of response on the BM. To investigate the role of BM microarchitecture in frequency discrimination, we deleted extracellular matrix protein emilin 2, which disturbed the filamentous organization in the BM. Emilin2 -/- mice displayed broadened mechanical and neural frequency tuning with multiple response peaks that are shifted to lower frequencies than normal. Thus, emilin 2 confers a stiffness gradient on the BM that is critical for accurate frequency resolution.
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Affiliation(s)
- Ian J. Russell
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Huxley Building, Brighton BN2 4GJ, UK
| | - Victoria A. Lukashkina
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Huxley Building, Brighton BN2 4GJ, UK
| | - Snezana Levic
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Huxley Building, Brighton BN2 4GJ, UK
- Brighton and Sussex Medical School, University of Sussex, Brighton BN1 9PX, UK
| | - Young-Wook Cho
- Laboratory of Endocrinology and Receptor Biology, NIDDK, National Institutes of Health, 10 Center Drive, Bethesda, MD 20892, USA
| | - Andrei N. Lukashkin
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Huxley Building, Brighton BN2 4GJ, UK
| | - Lily Ng
- Laboratory of Endocrinology and Receptor Biology, NIDDK, National Institutes of Health, 10 Center Drive, Bethesda, MD 20892, USA
| | - Douglas Forrest
- Laboratory of Endocrinology and Receptor Biology, NIDDK, National Institutes of Health, 10 Center Drive, Bethesda, MD 20892, USA
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