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Marchetta P, Dapper K, Hess M, Calis D, Singer W, Wertz J, Fink S, Hage SR, Alam M, Schwabe K, Lukowski R, Bourien J, Puel JL, Jacob MH, Munk MHJ, Land R, Rüttiger L, Knipper M. Dysfunction of specific auditory fibers impacts cortical oscillations, driving an autism phenotype despite near-normal hearing. FASEB J 2024; 38:e23411. [PMID: 38243766 DOI: 10.1096/fj.202301995r] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2023] [Revised: 12/04/2023] [Accepted: 12/22/2023] [Indexed: 01/21/2024]
Abstract
Autism spectrum disorder is discussed in the context of altered neural oscillations and imbalanced cortical excitation-inhibition of cortical origin. We studied here whether developmental changes in peripheral auditory processing, while preserving basic hearing function, lead to altered cortical oscillations. Local field potentials (LFPs) were recorded from auditory, visual, and prefrontal cortices and the hippocampus of BdnfPax2 KO mice. These mice develop an autism-like behavioral phenotype through deletion of BDNF in Pax2+ interneuron precursors, affecting lower brainstem functions, but not frontal brain regions directly. Evoked LFP responses to behaviorally relevant auditory stimuli were weaker in the auditory cortex of BdnfPax2 KOs, connected to maturation deficits of high-spontaneous rate auditory nerve fibers. This was correlated with enhanced spontaneous and induced LFP power, excitation-inhibition imbalance, and dendritic spine immaturity, mirroring autistic phenotypes. Thus, impairments in peripheral high-spontaneous rate fibers alter spike synchrony and subsequently cortical processing relevant for normal communication and behavior.
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Affiliation(s)
- Philine Marchetta
- Molecular Physiology of Hearing, Department of Otolaryngology, Head and Neck Surgery, Tübingen Hearing Research Centre, University of Tübingen, Tübingen, Germany
| | - Konrad Dapper
- Molecular Physiology of Hearing, Department of Otolaryngology, Head and Neck Surgery, Tübingen Hearing Research Centre, University of Tübingen, Tübingen, Germany
| | - Morgan Hess
- Molecular Physiology of Hearing, Department of Otolaryngology, Head and Neck Surgery, Tübingen Hearing Research Centre, University of Tübingen, Tübingen, Germany
| | - Dila Calis
- Molecular Physiology of Hearing, Department of Otolaryngology, Head and Neck Surgery, Tübingen Hearing Research Centre, University of Tübingen, Tübingen, Germany
| | - Wibke Singer
- Molecular Physiology of Hearing, Department of Otolaryngology, Head and Neck Surgery, Tübingen Hearing Research Centre, University of Tübingen, Tübingen, Germany
| | - Jakob Wertz
- Molecular Physiology of Hearing, Department of Otolaryngology, Head and Neck Surgery, Tübingen Hearing Research Centre, University of Tübingen, Tübingen, Germany
| | - Stefan Fink
- Molecular Physiology of Hearing, Department of Otolaryngology, Head and Neck Surgery, Tübingen Hearing Research Centre, University of Tübingen, Tübingen, Germany
| | - Steffen R Hage
- Werner Reichardt Centre for Integrative Neuroscience, University of Tübingen, Tübingen, Germany
| | - Mesbah Alam
- Experimental Neurosurgery, Department of Neurosurgery, Hannover Medical School, Hannover, Germany
| | - Kerstin Schwabe
- Experimental Neurosurgery, Department of Neurosurgery, Hannover Medical School, Hannover, Germany
| | - Robert Lukowski
- Institute of Pharmacy, Pharmacology, Toxicology and Clinical Pharmacy, University of Tübingen, Tübingen, Germany
| | - Jerome Bourien
- Institute for Neurosciences Montpellier, Institut National de la Santé et de la Recherche Médical, University of Montpellier, Montpellier, France
| | - Jean-Luc Puel
- Institute for Neurosciences Montpellier, Institut National de la Santé et de la Recherche Médical, University of Montpellier, Montpellier, France
| | - Michele H Jacob
- Department of Neuroscience, Tufts University School of Medicine, Sackler School of Biomedical Sciences, Boston, Massachusetts, USA
| | - Matthias H J Munk
- Department of Psychiatry & Psychotherapy, University of Tübingen, Tübingen, Germany
- Department of Biology, Technical University Darmstadt, Darmstadt, Germany
| | - Rüdiger Land
- Department of Experimental Otology, Institute of Audioneurotechnology, Hannover Medical School, Hannover, Germany
| | - Lukas Rüttiger
- Molecular Physiology of Hearing, Department of Otolaryngology, Head and Neck Surgery, Tübingen Hearing Research Centre, University of Tübingen, Tübingen, Germany
| | - Marlies Knipper
- Molecular Physiology of Hearing, Department of Otolaryngology, Head and Neck Surgery, Tübingen Hearing Research Centre, University of Tübingen, Tübingen, Germany
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2
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Li L, Chen GD, Salvi R. Effect of antiepileptic drug levetiracetam on cochlear function. Hear Res 2021; 415:108396. [PMID: 34903423 DOI: 10.1016/j.heares.2021.108396] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 11/12/2021] [Accepted: 11/17/2021] [Indexed: 11/26/2022]
Abstract
BACKGROUND Levetiracetam (LEV, 5-100 mg/kg) has been shown to prevent audiogenic seizures in a dose-dependent manner. This chemical is known to bind to synaptic vesicle protein 2A and inhibit l-type calcium channels, affecting neurotransmitter release. We hypothesize that the drug prevents audiogenic seizures partially by affecting cochlear neural response. METHODS To test this hypothesis, rats were given 1000, 500, 50, or 0 mg/kg (saline control) LEV-injection. Distortion product otoacoustic emissions (DPOAE), reflecting outer hair cell (OHC) function, and cochlear compound action potentials (CAP), reflecting cochlear neural output, were recorded and compared pre- and post-LEV. RESULTS 1000 mg/kg LEV-injection did not significantly affect DPOAE. The high dose LEV-injection, however, significantly reduced CAP amplitude resulting threshold shift (TS), prolonged CAP latency, and enhanced CAP forward masking. CAP latency and forward masking were significantly affected at the 500 mg/kg dose, but CAP-TS remained unchanged after LEV-injection. Interestingly, CAP latency wassignificantly prolonged, at least at the low stimulation levels, although the amplitude of CAP remained constant after a clinical dose of LEV-injection (50 mg/kg). DISCUSSION Since the clinical dose of LEV-injection does not reduce CAP amplitude, the reduction of cochlear neural output is unlikely to be the underlying mechanism of LEV in the treatment of audiogenic seizure. The delayed cochlear neural response may be partially related to the prevention of audiogenic seizure. However, neuropharmacological changes in the central nervous system must play a major role in the treatment of audiogenic seizure, as it does in the treatment of focal epilepsy.
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Affiliation(s)
- Li Li
- Center for Hearing and Deafness, SUNY at Buffalo, Buffalo, NY 14214, USA
| | - Guang-Di Chen
- Center for Hearing and Deafness, SUNY at Buffalo, Buffalo, NY 14214, USA.
| | - Richard Salvi
- Center for Hearing and Deafness, SUNY at Buffalo, Buffalo, NY 14214, USA
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Gratias P, Nasr J, Affortit C, Ceccato JC, François F, Casas F, Pujol R, Pucheu S, Puel JL, Wang J. Impulse Noise Induced Hidden Hearing Loss, Hair Cell Ciliary Changes and Oxidative Stress in Mice. Antioxidants (Basel) 2021; 10:antiox10121880. [PMID: 34942983 PMCID: PMC8698479 DOI: 10.3390/antiox10121880] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 11/19/2021] [Accepted: 11/22/2021] [Indexed: 12/14/2022] Open
Abstract
Recent studies demonstrated that reversible continuous noise exposure may induce a temporary threshold shift (TTS) with a permanent degeneration of auditory nerve fibers, although hair cells remain intact. To probe the impact of TTS-inducing impulse noise exposure on hearing, CBA/J Mice were exposed to noise impulses with peak pressures of 145 dB SPL. We found that 30 min after exposure, the noise caused a mean elevation of ABR thresholds of ~30 dB and a reduction in DPOAE amplitude. Four weeks later, ABR thresholds and DPOAE amplitude were back to normal in the higher frequency region (8–32 kHz). At lower frequencies, a small degree of PTS remained. Morphological evaluations revealed a disturbance of the stereociliary bundle of outer hair cells, mainly located in the apical regions. On the other hand, the reduced suprathreshold ABR amplitudes remained until 4 weeks later. A loss of synapse numbers was observed 24 h after exposure, with full recovery two weeks later. Transmission electron microscopy revealed morphological changes at the ribbon synapses by two weeks post exposure. In addition, increased levels of oxidative stress were observed immediately after exposure, and maintained for a further 2 weeks. These results clarify the pathology underlying impulse noise-induced sensory dysfunction, and suggest possible links between impulse-noise injury, cochlear cell morphology, metabolic changes, and hidden hearing loss.
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Affiliation(s)
- Paul Gratias
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, 34091 Montpellier, France; (P.G.); (J.N.); (C.A.); (J.-C.C.); (F.F.); (R.P.); (J.-L.P.)
| | - Jamal Nasr
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, 34091 Montpellier, France; (P.G.); (J.N.); (C.A.); (J.-C.C.); (F.F.); (R.P.); (J.-L.P.)
| | - Corentin Affortit
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, 34091 Montpellier, France; (P.G.); (J.N.); (C.A.); (J.-C.C.); (F.F.); (R.P.); (J.-L.P.)
| | - Jean-Charles Ceccato
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, 34091 Montpellier, France; (P.G.); (J.N.); (C.A.); (J.-C.C.); (F.F.); (R.P.); (J.-L.P.)
| | - Florence François
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, 34091 Montpellier, France; (P.G.); (J.N.); (C.A.); (J.-C.C.); (F.F.); (R.P.); (J.-L.P.)
| | - François Casas
- Unité Dynamique Du Muscle et Métabolisme (DMEM), Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), University Montpellier, 34060 Montpellier, France;
| | - Rémy Pujol
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, 34091 Montpellier, France; (P.G.); (J.N.); (C.A.); (J.-C.C.); (F.F.); (R.P.); (J.-L.P.)
| | - Sylvie Pucheu
- Cilcare, 371 Rue du Professeur J. Blayac, 34080 Montpellier, France;
| | - Jean-Luc Puel
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, 34091 Montpellier, France; (P.G.); (J.N.); (C.A.); (J.-C.C.); (F.F.); (R.P.); (J.-L.P.)
| | - Jing Wang
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, 34091 Montpellier, France; (P.G.); (J.N.); (C.A.); (J.-C.C.); (F.F.); (R.P.); (J.-L.P.)
- ENT Department, Hospital and University of Montpellier, 34091 Montpellier, France
- Correspondence: ; Tel.: +33-499-636-048; Fax: +33-499-636-020
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Age-related decline in cochlear ribbon synapses and its relation to different metrics of auditory-nerve activity. Neurobiol Aging 2021; 108:133-145. [PMID: 34601244 DOI: 10.1016/j.neurobiolaging.2021.08.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Revised: 07/30/2021] [Accepted: 08/29/2021] [Indexed: 11/21/2022]
Abstract
Loss of inner hair cell-auditory nerve fiber synapses is considered to be an important early stage of neural presbyacusis. Mass potentials, recorded at the cochlear round window, can be used to derive the neural index (NI), a sensitive measure for pharmacologically-induced synapse loss. Here, we investigate the applicability of the NI for measuring age-related auditory synapse loss in young-adult, middle-aged, and old Mongolian gerbils. Synapse loss, which was progressively evident in the 2 aged groups, correlated weakly with NI when measured at a fixed sound level of 60 dB SPL. However, the NI was confounded by decreases in single-unit firing rates at 60 dB SPL. NI at 30 dB above threshold, when firing rates were similar between age groups, did not correlate with synapse loss. Our results show that synapse loss is poorly reflected in the NI of aged gerbils, particularly if further peripheral pathologies are present. The NI may therefore not be a reliable clinical tool to assess synapse loss in aged humans with peripheral hearing loss.
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5
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Occelli F, Hasselmann F, Bourien J, Puel JL, Desvignes N, Wiszniowski B, Edeline JM, Gourévitch B. Temporal Alterations to Central Auditory Processing without Synaptopathy after Lifetime Exposure to Environmental Noise. Cereb Cortex 2021; 32:1737-1754. [PMID: 34494109 DOI: 10.1093/cercor/bhab310] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2021] [Revised: 07/28/2021] [Accepted: 07/29/2021] [Indexed: 11/13/2022] Open
Abstract
People are increasingly exposed to environmental noise through the cumulation of occupational and recreational activities, which is considered harmless to the auditory system, if the sound intensity remains <80 dB. However, recent evidence of noise-induced peripheral synaptic damage and central reorganizations in the auditory cortex, despite normal audiometry results, has cast doubt on the innocuousness of lifetime exposure to environmental noise. We addressed this issue by exposing adult rats to realistic and nontraumatic environmental noise, within the daily permissible noise exposure limit for humans (80 dB sound pressure level, 8 h/day) for between 3 and 18 months. We found that temporary hearing loss could be detected after 6 months of daily exposure, without leading to permanent hearing loss or to missing synaptic ribbons in cochlear hair cells. The degraded temporal representation of sounds in the auditory cortex after 18 months of exposure was very different from the effects observed after only 3 months of exposure, suggesting that modifications to the neural code continue throughout a lifetime of exposure to noise.
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Affiliation(s)
- Florian Occelli
- NeuroScience Paris-Saclay Institute (NeuroPSI), CNRS, University of Paris-Saclay, Orsay F-91405, France
| | - Florian Hasselmann
- Institute for Neurosciences of Montpellier (INM), INSERM, University of Montpellier, Montpellier F-34091, France
| | - Jérôme Bourien
- Institute for Neurosciences of Montpellier (INM), INSERM, University of Montpellier, Montpellier F-34091, France
| | - Jean-Luc Puel
- Institute for Neurosciences of Montpellier (INM), INSERM, University of Montpellier, Montpellier F-34091, France
| | - Nathalie Desvignes
- NeuroScience Paris-Saclay Institute (NeuroPSI), CNRS, University of Paris-Saclay, Orsay F-91405, France
| | - Bernadette Wiszniowski
- NeuroScience Paris-Saclay Institute (NeuroPSI), CNRS, University of Paris-Saclay, Orsay F-91405, France
| | - Jean-Marc Edeline
- NeuroScience Paris-Saclay Institute (NeuroPSI), CNRS, University of Paris-Saclay, Orsay F-91405, France
| | - Boris Gourévitch
- NeuroScience Paris-Saclay Institute (NeuroPSI), CNRS, University of Paris-Saclay, Orsay F-91405, France.,Institut de l'Audition, Institut Pasteur, INSERM, Paris F-75012, France.,CNRS, France
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6
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Jeffers PWC, Bourien J, Diuba A, Puel JL, Kujawa SG. Noise-Induced Hearing Loss in Gerbil: Round Window Assays of Synapse Loss. Front Cell Neurosci 2021; 15:699978. [PMID: 34385909 PMCID: PMC8354318 DOI: 10.3389/fncel.2021.699978] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2021] [Accepted: 07/05/2021] [Indexed: 01/31/2023] Open
Abstract
Previous work in animals with recovered hearing thresholds but permanent inner hair cell synapse loss after noise have suggested initial vulnerability of low spontaneous rate (SR) auditory nerve fibers (ANF). As these fibers have properties of response that facilitate robust sound coding in continuous noise backgrounds, their targeted loss would have important implications for function. To address the issue of relative ANF vulnerabilities after noise, we assessed cochlear physiologic and histologic consequences of temporary threshold shift-producing sound over-exposure in the gerbil, a species with well-characterized distributions of auditory neurons by SR category. The noise exposure targeted a cochlear region with distributed innervation (low-, medium- and high-SR neurons). It produced moderate elevations in outer hair cell-based distortion-product otoacoustic emission and whole nerve compound action potential thresholds in this region, with accompanying reductions in suprathreshold response amplitudes, quantified at 24 h. These parameters of response recovered well with post-exposure time. Chronic synapse loss was maximum in the frequency region initially targeted by the noise. Cochlear round window recorded mass potentials (spontaneous neural noise and sound-driven peri-stimulus time responses, PSTR) reflected parameters of the loss not detected by the conventional assays. Spontaneous activity was acutely reduced. Steady-state (PSTR plateau) activity was correlated with synapse loss in frequency regions with high concentrations of low-SR neurons, whereas the PSTR onset peak and spontaneous round window noise, both dominated by high-SR fiber activity, were relatively unaltered across frequency in chronic ears. Together, results suggest that acute targets of noise were of mixed SR subtypes, but chronic targets were predominantly low-SR neurons. PSTRs captured key properties of the auditory nerve response and vulnerability to injury that should yield important diagnostic information in hearing loss etiologies producing cochlear synaptic and neural loss.
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Affiliation(s)
- Penelope W C Jeffers
- Program in Speech and Hearing Bioscience and Technology, Harvard University, Boston, MA, United States.,Eaton-Peabody Laboratories, Massachusetts Eye and Ear, Boston, MA, United States
| | - Jérôme Bourien
- Institute for Neurosciences of Montpellier, University of Montpellier, INSERM, Montpellier, France
| | - Artem Diuba
- Institute for Neurosciences of Montpellier, University of Montpellier, INSERM, Montpellier, France
| | - Jean-Luc Puel
- Institute for Neurosciences of Montpellier, University of Montpellier, INSERM, Montpellier, France
| | - Sharon G Kujawa
- Program in Speech and Hearing Bioscience and Technology, Harvard University, Boston, MA, United States.,Eaton-Peabody Laboratories, Massachusetts Eye and Ear, Boston, MA, United States.,Department of Otolaryngology-Head and Neck Surgery, Harvard Medical School, Boston, MA, United States
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7
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Hutson KA, Pulver SH, Ariel P, Naso C, Fitzpatrick DC. Light sheet microscopy of the gerbil cochlea. J Comp Neurol 2020; 529:757-785. [PMID: 32632959 DOI: 10.1002/cne.24977] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2020] [Revised: 05/13/2020] [Accepted: 06/21/2020] [Indexed: 01/19/2023]
Abstract
Light sheet fluorescence microscopy (LSFM) provides a rapid and complete three-dimensional image of the cochlea. The method retains anatomical relationships-on a micrometer scale-between internal structures such as hair cells, basilar membrane (BM), and modiolus with external surface structures such as the round and oval windows. Immunolabeled hair cells were used to visualize the spiraling BM in the intact cochlea without time intensive dissections or additional histological processing; yet material prepared for LSFM could be rehydrated, the BM dissected out and reimaged at higher resolution with the confocal microscope. In immersion-fixed material, details of the cochlear vasculature were seen throughout the cochlea. Hair cell counts (both inner and outer) as well as frequency maps of the BM were comparable to those obtained by other methods, but with the added dimension of depth. The material provided measures of angular, linear, and vector distance between characteristic frequency regions along the BM. Thus, LSFM provides a unique ability to rapidly image the entire cochlea in a manner applicable to model and interpret physiological results. Furthermore, the three-dimensional organization of the cochlea can be studied at the organ and cellular level with LSFM, and this same material can be taken to the confocal microscope for detailed analysis at the subcellular level.
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Affiliation(s)
- Kendall A Hutson
- Department of Otolaryngology/Head and Neck Surgery, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Stephen H Pulver
- Department of Otolaryngology/Head and Neck Surgery, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Pablo Ariel
- Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Caroline Naso
- Department of Otolaryngology/Head and Neck Surgery, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Douglas C Fitzpatrick
- Department of Otolaryngology/Head and Neck Surgery, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
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8
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Occelli F, Hasselmann F, Bourien J, Eybalin M, Puel J, Desvignes N, Wiszniowski B, Edeline JM, Gourévitch B. Age-related Changes in Auditory Cortex Without Detectable Peripheral Alterations: A Multi-level Study in Sprague–Dawley Rats. Neuroscience 2019; 404:184-204. [DOI: 10.1016/j.neuroscience.2019.02.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2018] [Revised: 01/21/2019] [Accepted: 02/01/2019] [Indexed: 01/31/2023]
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9
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Peterson AJ, Huet A, Bourien J, Puel JL, Heil P. Recovery of auditory-nerve-fiber spike amplitude under natural excitation conditions. Hear Res 2018; 370:248-263. [DOI: 10.1016/j.heares.2018.08.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/22/2018] [Revised: 08/20/2018] [Accepted: 08/22/2018] [Indexed: 12/23/2022]
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10
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Huet A, Batrel C, Wang J, Desmadryl G, Nouvian R, Puel JL, Bourien J. Sound Coding in the Auditory Nerve: From Single Fiber Activity to Cochlear Mass Potentials in Gerbils. Neuroscience 2018; 407:83-92. [PMID: 30342201 DOI: 10.1016/j.neuroscience.2018.10.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2018] [Revised: 10/01/2018] [Accepted: 10/08/2018] [Indexed: 12/21/2022]
Abstract
Auditory nerve fibers (ANFs) convey acoustic information from the sensory cells to the brainstem using an elaborated neural code based on both spike timing and rate. As the stimulus tone frequency increases, time coding fades and ceases, resulting in high-frequency tone encoding that relies mostly on the spike discharge rate. Here, we recapitulated our recent single-unit data from gerbil's auditory nerve to highlight the most relevant mode of coding (spike timing versus spike rate) in tone-in-noise. We report that high-spontaneous rate (SR) fibers driven by low-frequency tones in noise are able to phase lock ∼30 dB below the level that evoked a significant elevation of the discharge rate, whereas medium- and low-SR fibers switch their preferential mode of coding from rate coding in quiet, to time coding in noise. For high-frequency tone, the low-threshold/high-SR fibers reach their maximum discharge rate in noise and do not respond to tones, whereas medium- and low-SR fibers are still able to respond to tones making them more resistant to background noise. Based on these findings, we first discuss the ecological function of the ANF distribution according to their spontaneous discharge rate. Then, we point out the poor synchronization of the low-SR ANFs, accounting for the discrepancy between ANF number and the amplitude of the compound action potential of the of the auditory nerve. Finally, we proposed a new diagnostic tool to assess low-SR fibers, which does not rely on the onset response of the ANFs.
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Affiliation(s)
- A Huet
- INM, Inserm, Univ Montpellier, Montpellier, France
| | - C Batrel
- INM, Inserm, Univ Montpellier, Montpellier, France
| | - J Wang
- INM, Inserm, Univ Montpellier, Montpellier, France
| | - G Desmadryl
- INM, Inserm, Univ Montpellier, Montpellier, France
| | - R Nouvian
- INM, Inserm, Univ Montpellier, Montpellier, France
| | - J L Puel
- INM, Inserm, Univ Montpellier, Montpellier, France.
| | - J Bourien
- INM, Inserm, Univ Montpellier, Montpellier, France
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11
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Synaptopathy in the Aging Cochlea: Characterizing Early-Neural Deficits in Auditory Temporal Envelope Processing. J Neurosci 2018; 38:7108-7119. [PMID: 29976623 DOI: 10.1523/jneurosci.3240-17.2018] [Citation(s) in RCA: 112] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Revised: 06/27/2018] [Accepted: 06/28/2018] [Indexed: 12/12/2022] Open
Abstract
Aging listeners, even in the absence of overt hearing loss measured as changes in hearing thresholds, often experience impairments processing temporally complex sounds such as speech in noise. Recent evidence has shown that normal aging is accompanied by a progressive loss of synapses between inner hair cells and auditory nerve fibers. The role of this cochlear synaptopathy in degraded temporal processing with age is not yet understood. Here, we used population envelope following responses, along with other hair cell- and neural-based measures from an age-graded series of male and female CBA/CaJ mice to study changes in encoding stimulus envelopes. By comparing responses obtained before and after the application of the neurotoxin ouabain to the inner ear, we demonstrate that we can study changes in temporal processing on either side of the cochlear synapse. Results show that deficits in neural coding with age emerge at the earliest neural stages of auditory processing and are correlated with the degree of cochlear synaptopathy. These changes are seen before losses in neural thresholds and particularly affect the suprathreshold processing of sound. Responses obtained from more central sources show smaller differences with age, suggesting compensatory gain. These results show that progressive cochlear synaptopathy is accompanied by deficits in temporal coding at the earliest neural generators and contribute to the suprathreshold sound processing deficits observed with age.SIGNIFICANCE STATEMENT Aging listeners often experience difficulty hearing and understanding speech in noisy conditions. The results described here suggest that age-related loss of cochlear synapses may be a significant contributor to those performance declines. We observed aberrant neural coding of sounds in the early auditory pathway, which was accompanied by and correlated with an age-progressive loss of synapses between the inner hair cells and the auditory nerve. Deficits first appeared before changes in hearing thresholds and were largest at higher sound levels relevant to real world communication. The noninvasive tests described here may be adapted to detect cochlear synaptopathy in the clinical setting.
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