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Kreeger LJ, Honnuraiah S, Maeker S, Shea S, Fishell G, Goodrich LV. An Anatomical and Physiological Basis for Coincidence Detection Across Time Scales in the Auditory System. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.29.582808. [PMID: 38464181 PMCID: PMC10925315 DOI: 10.1101/2024.02.29.582808] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/12/2024]
Abstract
Coincidence detection is a common neural computation that identifies co-occurring stimuli by integration of inputs. In the auditory system, octopus cells act as coincidence detectors for complex sounds that include both synchronous and sequenced combinations of frequencies. Octopus cells must detect coincidence on both the millisecond and submillisecond time scale, unlike the average neuron, which integrates inputs over time on the order of tens of milliseconds. Here, we show that octopus cell computations in the cell body are shaped by inhibition in the dendrites, which adjusts the strength and timing of incoming signals to achieve submillisecond acuity. This mechanism is crucial for the fundamental process of integrating the synchronized frequencies of natural auditory signals over time.
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Affiliation(s)
- Lauren J Kreeger
- Harvard Medical School, Department of Neurobiology, Boston, MA 02115, USA
| | - Suraj Honnuraiah
- Harvard Medical School, Department of Neurobiology, Boston, MA 02115, USA
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA
| | - Sydney Maeker
- Harvard Medical School, Department of Neurobiology, Boston, MA 02115, USA
| | - Siobhan Shea
- Harvard Medical School, Department of Neurobiology, Boston, MA 02115, USA
| | - Gord Fishell
- Harvard Medical School, Department of Neurobiology, Boston, MA 02115, USA
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA
| | - Lisa V Goodrich
- Harvard Medical School, Department of Neurobiology, Boston, MA 02115, USA
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2
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Xie R, Wang M, Zhang C. Mechanisms of age-related hearing loss at the auditory nerve central synapses and postsynaptic neurons in the cochlear nucleus. Hear Res 2024; 442:108935. [PMID: 38113793 PMCID: PMC10842789 DOI: 10.1016/j.heares.2023.108935] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/11/2023] [Revised: 12/04/2023] [Accepted: 12/08/2023] [Indexed: 12/21/2023]
Abstract
Sound information is transduced from mechanical vibration to electrical signals in the cochlea, conveyed to and further processed in the brain to form auditory perception. During the process, spiral ganglion neurons (SGNs) are the key cells that connect the peripheral and central auditory systems by receiving information from hair cells in the cochlea and transmitting it to neurons of the cochlear nucleus (CN). Decades of research in the cochlea greatly improved our understanding of SGN function under normal and pathological conditions, especially about the roles of different subtypes of SGNs and their peripheral synapses. However, it remains less clear how SGN central terminals or auditory nerve (AN) synapses connect to CN neurons, and ultimately how peripheral pathology links to structural alterations and functional deficits in the central auditory nervous system. This review discusses recent progress about the morphological and physiological properties of different subtypes of AN synapses and associated postsynaptic CN neurons, their changes during aging, and the potential mechanisms underlying age-related hearing loss.
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Affiliation(s)
- Ruili Xie
- Department of Otolaryngology, The Ohio State University, 420 W 12th Ave, Columbus OH 43210, USA; Department of Neuroscience, The Ohio State University, 420W 12th Ave, Columbus, OH 43210, USA.
| | - Meijian Wang
- Department of Otolaryngology, The Ohio State University, 420 W 12th Ave, Columbus OH 43210, USA
| | - Chuangeng Zhang
- Department of Otolaryngology, The Ohio State University, 420 W 12th Ave, Columbus OH 43210, USA
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3
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Moverman DJ, Liberman LD, Kraemer S, Corfas G, Liberman MC. Ultrastructure of noise-induced cochlear synaptopathy. Sci Rep 2023; 13:19456. [PMID: 37945811 PMCID: PMC10636047 DOI: 10.1038/s41598-023-46859-6] [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: 08/25/2023] [Accepted: 11/06/2023] [Indexed: 11/12/2023] Open
Abstract
Acoustic overexposure can eliminate synapses between inner hair cells (IHCs) and auditory nerve fibers (ANFs), even if hair-cell function recovers. This synaptopathy has been extensively studied by confocal microscopy, however, understanding the nature and sequence of damage requires ultrastructural analysis. Here, we used focused ion-beam scanning electron microscopy to mill, image, segment and reconstruct ANF terminals in mice, 1 day and 1 week after synaptopathic exposure (8-16 kHz, 98 dB SPL). At both survivals, ANF terminals were normal in number, but 62% and 53%, respectively, lacked normal synaptic specializations. Most non-synapsing fibers (57% and 48% at 1 day and 1 week) remained in contact with an IHC and contained healthy-looking organelles. ANFs showed a transient increase in mitochondrial content (51%) and efferent innervation (34%) at 1 day. Fibers maintaining synaptic connections showed hypertrophy of pre-synaptic ribbons at both 1 day and 1 week. Non-synaptic fibers were lower in mitochondrial content and typically on the modiolar side of the IHC, where ANFs with high-thresholds and low spontaneous rates are normally found. Even 1 week post-exposure, many ANF terminals remained in IHC contact despite loss of synaptic specializations, thus, regeneration efforts at early post-exposure times should concentrate on synaptogenesis rather than neurite extension.
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Affiliation(s)
- Daniel J Moverman
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear, 243 Charles St., Boston, MA, 02114-3096, USA
| | - Leslie D Liberman
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear, 243 Charles St., Boston, MA, 02114-3096, USA
| | - Stephan Kraemer
- Center for Nanoscale Systems, Harvard College, Cambridge, MA, 02138, USA
| | - Gabriel Corfas
- Department of Otolaryngology-Head and Neck Surgery, Kresge Hearing Research Institute, University of Michigan, Ann Arbor, MI, USA
| | - M Charles Liberman
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear, 243 Charles St., Boston, MA, 02114-3096, USA.
- Department of Otolaryngology-Head and Neck Surgery, Harvard Medical School, Boston, MA, 02115, USA.
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4
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Wang M, Lin S, Xie R. Apical-basal distribution of different subtypes of spiral ganglion neurons in the cochlea and the changes during aging. PLoS One 2023; 18:e0292676. [PMID: 37883357 PMCID: PMC10602254 DOI: 10.1371/journal.pone.0292676] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Accepted: 09/26/2023] [Indexed: 10/28/2023] Open
Abstract
Sound information is transmitted from the cochlea to the brain mainly by type I spiral ganglion neurons (SGNs), which consist of different subtypes with distinct physiological properties and selective expression of molecular markers. It remains unclear how these SGN subtypes distribute along the tonotopic axis, and whether the distribution pattern changes during aging that might underlie age-related hearing loss (ARHL). We investigated these questions using immunohistochemistry in three age groups of CBA/CaJ mice of either sex, including 2-5 months (young), 17-19 months (middle-age), and 28-32 months (old). Mouse cochleae were cryo-sectioned and triple-stained using antibodies against Tuj1, calretinin (CR) and calbindin (CB), which are reportedly expressed in all type I, subtype Ia, and subtype Ib SGNs, respectively. Labeled SGNs were classified into four groups based on the expression pattern of stained markers, including CR+ (subtype Ia), CB+ (subtype Ib), CR+CB+ (dual-labeled Ia/Ib), and CR-CB- (subtype Ic) neurons. The distribution of these SGN groups was analyzed in the apex, middle, and base regions of the cochleae. It showed that the prevalence of subtype Ia, Ib and dual-labeled Ia/Ib SGNs are high in the apex and low in the base. In contrast, the distribution pattern is reversed in Ic SGNs. Such frequency-dependent distribution is largely maintained during aging except for a preferential reduction of Ic SGNs, especially in the base. These findings corroborate the prior study based on RNAscope that SGN subtypes show differential vulnerability during aging. It suggests that sound processing of different frequencies involves distinct combinations of SGN subtypes, and the age-dependent loss of Ic SGNs in the base may especially impact high-frequency hearing during ARHL.
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Affiliation(s)
- Meijian Wang
- Department of Otolaryngology, The Ohio State University, Columbus, OH, United States of Ameirca
| | - Shengyin Lin
- Department of Otolaryngology, The Ohio State University, Columbus, OH, United States of Ameirca
| | - Ruili Xie
- Department of Otolaryngology, The Ohio State University, Columbus, OH, United States of Ameirca
- Department of Neuroscience, The Ohio State University, Columbus, OH, United States of Ameirca
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Boothalingam S, Peterson A, Powell L, Easwar V. Auditory brainstem mechanisms likely compensate for self-imposed peripheral inhibition. Sci Rep 2023; 13:12693. [PMID: 37542191 PMCID: PMC10403563 DOI: 10.1038/s41598-023-39850-8] [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: 01/11/2023] [Accepted: 08/01/2023] [Indexed: 08/06/2023] Open
Abstract
Feedback networks in the brain regulate downstream auditory function as peripheral as the cochlea. However, the upstream neural consequences of this peripheral regulation are less understood. For instance, the medial olivocochlear reflex (MOCR) in the brainstem causes putative attenuation of responses generated in the cochlea and cortex, but those generated in the brainstem are perplexingly unaffected. Based on known neural circuitry, we hypothesized that the inhibition of peripheral input is compensated for by positive feedback in the brainstem over time. We predicted that the inhibition could be captured at the brainstem with shorter (1.5 s) than previously employed long duration (240 s) stimuli where this inhibition is likely compensated for. Results from 16 normal-hearing human listeners support our hypothesis in that when the MOCR is activated, there is a robust reduction of responses generated at the periphery, brainstem, and cortex for short-duration stimuli. Such inhibition at the brainstem, however, diminishes for long-duration stimuli suggesting some compensatory mechanisms at play. Our findings provide a novel non-invasive window into potential gain compensation mechanisms in the brainstem that may have implications for auditory disorders such as tinnitus. Our methodology will be useful in the evaluation of efferent function in individuals with hearing loss.
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Affiliation(s)
- Sriram Boothalingam
- Waisman Center and Department of Communication Sciences and Disorders, University of Wisconsin-Madison, Madison, WI, 53705, USA.
- Macquarie University, Sydney, NSW, 2109, Australia.
- National Acoustic Laboratories, Sydney, NSW, 2109, Australia.
| | - Abigayle Peterson
- Waisman Center and Department of Communication Sciences and Disorders, University of Wisconsin-Madison, Madison, WI, 53705, USA
- Macquarie University, Sydney, NSW, 2109, Australia
| | - Lindsey Powell
- Waisman Center and Department of Communication Sciences and Disorders, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Vijayalakshmi Easwar
- Waisman Center and Department of Communication Sciences and Disorders, University of Wisconsin-Madison, Madison, WI, 53705, USA
- Macquarie University, Sydney, NSW, 2109, Australia
- National Acoustic Laboratories, Sydney, NSW, 2109, Australia
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6
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Spirou GA, Kersting M, Carr S, Razzaq B, Yamamoto Alves Pinto C, Dawson M, Ellisman MH, Manis PB. High-resolution volumetric imaging constrains compartmental models to explore synaptic integration and temporal processing by cochlear nucleus globular bushy cells. eLife 2023; 12:e83393. [PMID: 37288824 PMCID: PMC10435236 DOI: 10.7554/elife.83393] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Accepted: 06/07/2023] [Indexed: 06/09/2023] Open
Abstract
Globular bushy cells (GBCs) of the cochlear nucleus play central roles in the temporal processing of sound. Despite investigation over many decades, fundamental questions remain about their dendrite structure, afferent innervation, and integration of synaptic inputs. Here, we use volume electron microscopy (EM) of the mouse cochlear nucleus to construct synaptic maps that precisely specify convergence ratios and synaptic weights for auditory nerve innervation and accurate surface areas of all postsynaptic compartments. Detailed biophysically based compartmental models can help develop hypotheses regarding how GBCs integrate inputs to yield their recorded responses to sound. We established a pipeline to export a precise reconstruction of auditory nerve axons and their endbulb terminals together with high-resolution dendrite, soma, and axon reconstructions into biophysically detailed compartmental models that could be activated by a standard cochlear transduction model. With these constraints, the models predict auditory nerve input profiles whereby all endbulbs onto a GBC are subthreshold (coincidence detection mode), or one or two inputs are suprathreshold (mixed mode). The models also predict the relative importance of dendrite geometry, soma size, and axon initial segment length in setting action potential threshold and generating heterogeneity in sound-evoked responses, and thereby propose mechanisms by which GBCs may homeostatically adjust their excitability. Volume EM also reveals new dendritic structures and dendrites that lack innervation. This framework defines a pathway from subcellular morphology to synaptic connectivity, and facilitates investigation into the roles of specific cellular features in sound encoding. We also clarify the need for new experimental measurements to provide missing cellular parameters, and predict responses to sound for further in vivo studies, thereby serving as a template for investigation of other neuron classes.
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Affiliation(s)
- George A Spirou
- Department of Medical Engineering, University of South FloridaTampaUnited States
| | - Matthew Kersting
- Department of Medical Engineering, University of South FloridaTampaUnited States
| | - Sean Carr
- Department of Medical Engineering, University of South FloridaTampaUnited States
| | - Bayan Razzaq
- Department of Otolaryngology, Head and Neck Surgery, West Virginia UniversityMorgantownUnited States
| | | | - Mariah Dawson
- Department of Otolaryngology, Head and Neck Surgery, West Virginia UniversityMorgantownUnited States
| | - Mark H Ellisman
- Department of Neurosciences, University of California, San DiegoSan DiegoUnited States
- National Center for Microscopy and Imaging Research,University of California, San DiegoSan DiegoUnited States
| | - Paul B Manis
- Department of Otolaryngology/Head and Neck Surgery, University of North Carolina at Chapel HillChapel HillUnited States
- Department of Cell Biology and Physiology, University of North CarolinaChapel HillUnited States
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Ma Y, Shu WC, Lin L, Cao XJ, Oertel D, Smith PH, Jackson MB. Imaging Voltage Globally and in Isofrequency Lamina in Slices of Mouse Ventral Cochlear Nucleus. eNeuro 2023; 10:ENEURO.0465-22.2023. [PMID: 36792362 PMCID: PMC9997695 DOI: 10.1523/eneuro.0465-22.2023] [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: 11/15/2022] [Revised: 02/02/2023] [Accepted: 02/06/2023] [Indexed: 02/17/2023] Open
Abstract
The cochlear nuclei (CNs) receive sensory information from the ear and perform fundamental computations before relaying this information to higher processing centers. These computations are performed by distinct types of neurons interconnected in circuits dedicated to the specialized roles of the auditory system. In the present study, we explored the use of voltage imaging to investigate CN circuitry. We tested two approaches based on fundamentally different voltage sensing technologies. Using a voltage-sensitive dye we recorded glutamate receptor-independent signals arising predominantly from axons. The mean conduction velocity of these fibers of 0.27 m/s was rapid but in range with other unmyelinated axons. We then used a genetically-encoded hybrid voltage sensor (hVOS) to image voltage from a specific population of neurons. Probe expression was controlled using Cre recombinase linked to c-fos activation. This activity-induced gene enabled targeting of neurons that are activated when a mouse hears a pure 15-kHz tone. In CN slices from these animals auditory nerve fiber stimulation elicited a glutamate receptor-dependent depolarization in hVOS probe-labeled neurons. These cells resided within a band corresponding to an isofrequency lamina, and responded with a high degree of synchrony. In contrast to the axonal origin of voltage-sensitive dye signals, hVOS signals represent predominantly postsynaptic responses. The introduction of voltage imaging to the CN creates the opportunity to investigate auditory processing circuitry in populations of neurons targeted on the basis of their genetic identity and their roles in sensory processing.
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Affiliation(s)
- Yihe Ma
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Wen-Chi Shu
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Lin Lin
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Xiao-Jie Cao
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Donata Oertel
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Philip H Smith
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Meyer B Jackson
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
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Mittring A, Moser T, Huet AT. Graded optogenetic activation of the auditory pathway for hearing restoration. Brain Stimul 2023; 16:466-483. [PMID: 36702442 PMCID: PMC10159867 DOI: 10.1016/j.brs.2023.01.1671] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 01/18/2023] [Accepted: 01/19/2023] [Indexed: 01/24/2023] Open
Abstract
Optogenetic control of neural activity enables innovative approaches to improve functional restoration of diseased sensory and motor systems. For clinical translation to succeed, optogenetic stimulation needs to closely match the coding properties of the targeted neuronal population and employ optimally operating emitters. This requires the customization of channelrhodopsins, emitters and coding strategies. Here, we provide a framework to parametrize optogenetic neural control and apply it to the auditory pathway that requires high temporal fidelity of stimulation. We used a viral gene transfer of ultrafast targeting-optimized Chronos into spiral ganglion neurons (SGNs) of the cochlea of mice. We characterized the light-evoked response by in vivo recordings from individual SGNs and neurons of the anteroventral cochlear nucleus (AVCN) that detect coincident SGN inputs. Our recordings from single SGNs demonstrated that their spike probability can be graded by adjusting the duration of light pulses at constant intensity, which optimally serves efficient laser diode operation. We identified an effective pulse width of 1.6 ms to maximize encoding in SGNs at the maximal light intensity employed here (∼35 mW). Alternatively, SGNs were activated at lower energy thresholds using short light pulses (<1 ms). An upper boundary of optical stimulation rates was identified at 316 Hz, inducing a robust spike rate adaptation that required a few tens of milliseconds to recover. We developed a semi-stochastic stimulation paradigm to rapidly (within minutes) estimate the input/output function from light to SGN firing and approximate the time constant of neuronal integration in the AVCN. By that, our data pave the way to design the sound coding strategies of future optical cochlear implants.
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Affiliation(s)
- Artur Mittring
- Auditory Circuit Lab, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany; Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany; Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany
| | - Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany; Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany; Auditory Neuroscience and Optogenetics Laboratory, German Primate Center, Göttingen, Germany; Auditory Neuroscience and Synaptic Nanophysiology Group, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.
| | - Antoine Tarquin Huet
- Auditory Circuit Lab, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany; Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany; Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany; Auditory Neuroscience and Optogenetics Laboratory, German Primate Center, Göttingen, Germany.
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9
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Cantu-Guerra HL, Papazian MR, Gorsky AL, Alekos NS, Caccavano A, Karagulyan N, Neef J, Vicini S, Moser T, Coate TM. Cochlear hair cell innervation is dependent on a modulatory function of Semaphorin-3A. Dev Dyn 2023; 252:124-144. [PMID: 36284453 PMCID: PMC9812910 DOI: 10.1002/dvdy.548] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Revised: 09/20/2022] [Accepted: 10/06/2022] [Indexed: 01/09/2023] Open
Abstract
BACKGROUND Proper connectivity between type I spiral ganglion neurons (SGNs) and inner hair cells (IHCs) in the cochlea is necessary for conveying sound information to the brain in mammals. Previous studies have shown that type I SGNs are heterogeneous in form, function and synaptic location on IHCs, but factors controlling their patterns of connectivity are not well understood. RESULTS During development, cochlear supporting cells and SGNs express Semaphorin-3A (SEMA3A), a known axon guidance factor. Mice homozygous for a point mutation that attenuates normal SEMA3A repulsive activity (Sema3aK108N ) show cochleae with grossly normal patterns of IHC innervation. However, genetic sparse labeling and three-dimensional reconstructions of individual SGNs show that cochleae from Sema3aK108N mice lacked the normal synaptic distribution of type I SGNs. Additionally, Sema3aK108N cochleae show a disrupted distribution of GLUA2 postsynaptic patches around the IHCs. The addition of SEMA3A-Fc to postnatal cochleae led to increases in SGN branching, similar to the effects of inhibiting glutamate receptors. Ca2+ imaging studies show that SEMA3A-Fc decreases SGN activity. CONCLUSIONS Contrary to the canonical view of SEMA3A as a guidance ligand, our results suggest SEMA3A may regulate SGN excitability in the cochlea, which may influence the morphology and synaptic arrangement of type I SGNs.
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Affiliation(s)
- Homero L. Cantu-Guerra
- Department of Biology, Georgetown University, Washington,
District of Columbia, USA
- Interdisciplinary Program in Neuroscience, Georgetown
University, Washington, District of Columbia, USA
| | - Michael R. Papazian
- Department of Biology, Georgetown University, Washington,
District of Columbia, USA
| | - Anna L. Gorsky
- Department of Biology, Georgetown University, Washington,
District of Columbia, USA
| | - Nathalie S. Alekos
- Department of Biology, Georgetown University, Washington,
District of Columbia, USA
| | - Adam Caccavano
- Interdisciplinary Program in Neuroscience, Georgetown
University, Washington, District of Columbia, USA
- Department of Pharmacology, Georgetown University School of
Medicine, Washington, District of Columbia, USA
| | - Nare Karagulyan
- Institute for Auditory Neuroscience and InnerEarLab,
University Medical Center, and Auditory Neuroscience & Synaptic Nanophysiology
Group, Max Planck Institute for Multidisciplinary Sciences, and Cluster of
Excellence “Multiscale Bioimaging: from Molecular Machines to Networks of
Excitable Cells” (MBExC), Göttingen, Germany
| | - Jakob Neef
- Institute for Auditory Neuroscience and InnerEarLab,
University Medical Center, and Auditory Neuroscience & Synaptic Nanophysiology
Group, Max Planck Institute for Multidisciplinary Sciences, and Cluster of
Excellence “Multiscale Bioimaging: from Molecular Machines to Networks of
Excitable Cells” (MBExC), Göttingen, Germany
| | - Stefano Vicini
- Interdisciplinary Program in Neuroscience, Georgetown
University, Washington, District of Columbia, USA
- Department of Pharmacology, Georgetown University School of
Medicine, Washington, District of Columbia, USA
| | - Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab,
University Medical Center, and Auditory Neuroscience & Synaptic Nanophysiology
Group, Max Planck Institute for Multidisciplinary Sciences, and Cluster of
Excellence “Multiscale Bioimaging: from Molecular Machines to Networks of
Excitable Cells” (MBExC), Göttingen, Germany
| | - Thomas M. Coate
- Department of Biology, Georgetown University, Washington,
District of Columbia, USA
- Interdisciplinary Program in Neuroscience, Georgetown
University, Washington, District of Columbia, USA
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10
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Ripley S, Xia L, Zhang Z, Aiken SJ, Wang J. Animal-to-Human Translation Difficulties and Problems With Proposed Coding-in-Noise Deficits in Noise-Induced Synaptopathy and Hidden Hearing Loss. Front Neurosci 2022; 16:893542. [PMID: 35720689 PMCID: PMC9199355 DOI: 10.3389/fnins.2022.893542] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2022] [Accepted: 04/22/2022] [Indexed: 12/26/2022] Open
Abstract
Noise induced synaptopathy (NIS) and hidden hearing loss (NIHHL) have been hot topic in hearing research since a massive synaptic loss was identified in CBA mice after a brief noise exposure that did not cause permanent threshold shift (PTS) in 2009. Based upon the amount of synaptic loss and the bias of it to synapses with a group of auditory nerve fibers (ANFs) with low spontaneous rate (LSR), coding-in-noise deficit (CIND) has been speculated as the major difficult of hearing in subjects with NIS and NIHHL. This speculation is based upon the idea that the coding of sound at high level against background noise relies mainly on the LSR ANFs. However, the translation from animal data to humans for NIS remains to be justified due to the difference in noise exposure between laboratory animals and human subjects in real life, the lack of morphological data and reliable functional methods to quantify or estimate the loss of the afferent synapses by noise. Moreover, there is no clear, robust data revealing the CIND even in animals with the synaptic loss but no PTS. In humans, both positive and negative reports are available. The difficulty in verifying CINDs has led a re-examination of the hypothesis that CIND is the major deficit associated with NIS and NIHHL, and the theoretical basis of this idea on the role of LSR ANFs. This review summarized the current status of research in NIS and NIHHL, with focus on the translational difficulty from animal data to human clinicals, the technical difficulties in quantifying NIS in humans, and the problems with the SR theory on signal coding. Temporal fluctuation profile model was discussed as a potential alternative for signal coding at high sound level against background noise, in association with the mechanisms of efferent control on the cochlea gain.
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Affiliation(s)
- Sara Ripley
- School of Communication Sciences and Disorders, Dalhousie University, Halifax, NS, Canada
| | - Li Xia
- Department of Otolaryngology-Head and Neck Surgery, Mianyang Central Hospital, School of Medicine, University of Electronic Science and Technology of China, Mianyang, China
| | - Zhen Zhang
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, China
- Otolaryngology Institute of Shanghai Jiao Tong University, Shanghai, China
| | - Steve J. Aiken
- School of Communication Sciences and Disorders, Dalhousie University, Halifax, NS, Canada
| | - Jian Wang
- School of Communication Sciences and Disorders, Dalhousie University, Halifax, NS, Canada
- Department of Otolaryngology-Head and Neck Surgery, Mianyang Central Hospital, School of Medicine, University of Electronic Science and Technology of China, Mianyang, China
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11
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Budak M, Roberts MT, Grosh K, Corfas G, Booth V, Zochowski M. Binaural Processing Deficits Due to Synaptopathy and Myelin Defects. Front Neural Circuits 2022; 16:856926. [PMID: 35498371 PMCID: PMC9050145 DOI: 10.3389/fncir.2022.856926] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Accepted: 03/23/2022] [Indexed: 11/13/2022] Open
Abstract
Hidden hearing loss (HHL) is a deficit in auditory perception and speech intelligibility that occurs despite normal audiometric thresholds and results from noise exposure, aging, or myelin defects. While mechanisms causing perceptual deficits in HHL patients are still unknown, results from animal models indicate a role for peripheral auditory neuropathies in HHL. In humans, sound localization is particularly important for comprehending speech, especially in noisy environments, and its disruption may contribute to HHL. In this study, we hypothesized that neuropathies of cochlear spiral ganglion neurons (SGNs) that are observed in animal models of HHL disrupt the activity of neurons in the medial superior olive (MSO), a nucleus in the brainstem responsible for locating low-frequency sound in the horizontal plane using binaural temporal cues, leading to sound localization deficits. To test our hypothesis, we constructed a network model of the auditory processing system that simulates peripheral responses to sound stimuli and propagation of responses via SGNs to cochlear nuclei and MSO populations. To simulate peripheral auditory neuropathies, we used a previously developed biophysical SGN model with myelin defects at SGN heminodes (myelinopathy) and with loss of inner hair cell-SGN synapses (synaptopathy). Model results indicate that myelinopathy and synaptopathy in SGNs give rise to decreased interaural time difference (ITD) sensitivity of MSO cells, suggesting a possible mechanism for perceptual deficits in HHL patients. This model may be useful to understand downstream impacts of SGN-mediated disruptions on auditory processing and to eventually discover possible treatments for various mechanisms of HHL.
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Affiliation(s)
- Maral Budak
- Biophysics Program, University of Michigan, Ann Arbor, MI, United States
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI, United States
| | - Michael T. Roberts
- Department of Otolaryngology Head and Neck Surgery, University of Michigan, Ann Arbor, MI, United States
- Kresge Hearing Research Institute, University of Michigan, Ann Arbor, MI, United States
| | - Karl Grosh
- Kresge Hearing Research Institute, University of Michigan, Ann Arbor, MI, United States
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, United States
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States
| | - Gabriel Corfas
- Department of Otolaryngology Head and Neck Surgery, University of Michigan, Ann Arbor, MI, United States
- Kresge Hearing Research Institute, University of Michigan, Ann Arbor, MI, United States
| | - Victoria Booth
- Department of Mathematics and Anesthesiology, University of Michigan, Ann Arbor, MI, United States
| | - Michal Zochowski
- Biophysics Program, University of Michigan, Ann Arbor, MI, United States
- Department of Physics, University of Michigan, Ann Arbor, MI, United States
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12
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Brughera A, Ballestero JA, McAlpine D. Sensitivity to Envelope Interaural Time Differences: Modeling Auditory Modulation Filtering. J Assoc Res Otolaryngol 2022; 23:35-57. [PMID: 34741225 PMCID: PMC8782955 DOI: 10.1007/s10162-021-00816-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Accepted: 08/30/2021] [Indexed: 02/03/2023] Open
Abstract
For amplitude-modulated sound, the envelope interaural time difference (ITDENV) is a potential cue for sound-source location. ITDENV is encoded in the lateral superior olive (LSO) of the auditory brainstem, by excitatory-inhibitory (EI) neurons receiving ipsilateral excitation and contralateral inhibition. Between human listeners, sensitivity to ITDENV varies considerably, but ultimately decreases with increasing stimulus carrier frequency, and decreases more strongly with increasing modulation rate. Mechanisms underlying the variation in behavioral sensitivity remain unclear. Here, with increasing carrier frequency (4-10 kHz), as we phenomenologically model the associated decrease in ITDENV sensitivity using arbitrarily fewer neurons consistent across populations, we computationally model the variable sensitivity across human listeners and modulation rates (32-800 Hz) as the decreasing range of membrane frequency responses in LSO neurons. Transposed tones stimulate a bilateral auditory-periphery model, driving model EI neurons where electrical membrane impedance filters the frequency content of inputs driven by amplitude-modulated sound, evoking modulation filtering. Calculated from Fisher information in spike-rate functions of ITDENV, for model EI neuronal populations distinctly reflecting the LSO range in membrane frequency responses, just-noticeable differences in ITDENV collectively reproduce the largest variation in ITDENV sensitivity across human listeners. These slow to fast model populations each generally match the best human ITDENV sensitivity at a progressively higher modulation rate, by membrane-filtering and spike-generation properties producing realistically less than Poisson variance. Non-resonant model EI neurons are also sensitive to interaural intensity differences. With peripheral filters centered between carrier frequency and modulation sideband, fast resonant model EI neurons extend ITDENV sensitivity above 500-Hz modulation.
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Affiliation(s)
- Andrew Brughera
- grid.1004.50000 0001 2158 5405Department of Linguistics, and the Australian Hearing Hub, Macquarie University, Macquarie Park, New South Wales Australia ,grid.189504.10000 0004 1936 7558Department of Biomedical Engineering, Boston University, Boston, MA USA
| | - Jimena A. Ballestero
- Instituto de Fisiología y Biofísica (IFIBIO) Bernardo Houssay, Grupo de Neurociencia de Sistemas, Universidad de Buenos Aires, CONICET, Buenos Aires, Argentina
| | - David McAlpine
- grid.1004.50000 0001 2158 5405Department of Linguistics, and the Australian Hearing Hub, Macquarie University, Macquarie Park, New South Wales Australia
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13
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Hockley A, Wu C, Shore SE. Olivocochlear projections contribute to superior intensity coding in cochlear nucleus small cells. J Physiol 2022; 600:61-73. [PMID: 34761815 PMCID: PMC9067393 DOI: 10.1113/jp282262] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Accepted: 11/05/2021] [Indexed: 11/08/2022] Open
Abstract
Understanding communication signals, especially in noisy environments, is crucial to social interactions. Yet, as we age, acoustic signals can be disrupted by cochlear damage and the subsequent auditory nerve fibre degeneration. The most vulnerable medium- and high-threshold-auditory nerve fibres innervate various cell types in the cochlear nucleus, among which the small cells are unique in receiving this input exclusively. Furthermore, small cells project to medial olivocochlear (MOC) neurons, which in turn send branched collaterals back into the small cell cap. Here, we use single-unit recordings to characterise small cell firing characteristics and demonstrate superior intensity coding in this cell class. We show converse effects when activating/blocking the MOC system, demonstrating that small-cell unique coding properties are facilitated by direct cholinergic input from the MOC system. Small cells also maintain tone-level coding in the presence of background noise. Finally, small cells precisely code low-frequency modulation more accurately than other ventral cochlear nucleus cell types, demonstrating accurate envelope coding that may be important for vocalisation processing. These results highlight the small cell olivocochlear circuit as a key player in signal processing in noisy environments, which may be selectively degraded in ageing or after noise insult. KEY POINTS: Cochlear nucleus small cells receive input from low/medium spontaneous rate auditory nerve fibres and medial olivocochlear neurons. Electrical stimulation of medial olivocochlear neurons in the ventral nucleus of the trapezoid body and blocking cholinergic input to small cells using atropine demonstrates an excitatory cholinergic input to small cells, which increases responses to suprathreshold sound. Unique inputs to small cells produce superior sound intensity coding. This coding of intensity is preserved in the presence of background noise, an effect exclusive to this cell type in the cochlear nucleus. These results suggest that small cells serve an essential function in the ascending auditory system, which may be relevant to disorders such as hidden hearing loss.
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Affiliation(s)
- Adam Hockley
- Department of Otolaryngology, Kresge Hearing Research Institute, Ann Arbor, MI, USA
| | - Calvin Wu
- Department of Otolaryngology, Kresge Hearing Research Institute, Ann Arbor, MI, USA
| | - Susan E Shore
- Department of Otolaryngology, Kresge Hearing Research Institute, Ann Arbor, MI, USA
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
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14
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Saddler MR, Gonzalez R, McDermott JH. Deep neural network models reveal interplay of peripheral coding and stimulus statistics in pitch perception. Nat Commun 2021; 12:7278. [PMID: 34907158 PMCID: PMC8671597 DOI: 10.1038/s41467-021-27366-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Accepted: 11/12/2021] [Indexed: 11/15/2022] Open
Abstract
Perception is thought to be shaped by the environments for which organisms are optimized. These influences are difficult to test in biological organisms but may be revealed by machine perceptual systems optimized under different conditions. We investigated environmental and physiological influences on pitch perception, whose properties are commonly linked to peripheral neural coding limits. We first trained artificial neural networks to estimate fundamental frequency from biologically faithful cochlear representations of natural sounds. The best-performing networks replicated many characteristics of human pitch judgments. To probe the origins of these characteristics, we then optimized networks given altered cochleae or sound statistics. Human-like behavior emerged only when cochleae had high temporal fidelity and when models were optimized for naturalistic sounds. The results suggest pitch perception is critically shaped by the constraints of natural environments in addition to those of the cochlea, illustrating the use of artificial neural networks to reveal underpinnings of behavior.
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Affiliation(s)
- Mark R Saddler
- Department of Brain and Cognitive Sciences, MIT, Cambridge, MA, USA.
- McGovern Institute for Brain Research, MIT, Cambridge, MA, USA.
- Center for Brains, Minds and Machines, MIT, Cambridge, MA, USA.
| | - Ray Gonzalez
- Department of Brain and Cognitive Sciences, MIT, Cambridge, MA, USA
- McGovern Institute for Brain Research, MIT, Cambridge, MA, USA
- Center for Brains, Minds and Machines, MIT, Cambridge, MA, USA
| | - Josh H McDermott
- Department of Brain and Cognitive Sciences, MIT, Cambridge, MA, USA.
- McGovern Institute for Brain Research, MIT, Cambridge, MA, USA.
- Center for Brains, Minds and Machines, MIT, Cambridge, MA, USA.
- Program in Speech and Hearing Biosciences and Technology, Harvard University, Cambridge, MA, USA.
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15
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Pagella S, Deussing JM, Kopp-Scheinpflug C. Expression Patterns of the Neuropeptide Urocortin 3 and Its Receptor CRFR2 in the Mouse Central Auditory System. Front Neural Circuits 2021; 15:747472. [PMID: 34867212 PMCID: PMC8633543 DOI: 10.3389/fncir.2021.747472] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Accepted: 10/18/2021] [Indexed: 11/16/2022] Open
Abstract
Sensory systems have to be malleable to context-dependent modulations occurring over different time scales, in order to serve their evolutionary function of informing about the external world while also eliciting survival-promoting behaviors. Stress is a major context-dependent signal that can have fast and delayed effects on sensory systems, especially on the auditory system. Urocortin 3 (UCN3) is a member of the corticotropin-releasing factor family. As a neuropeptide, UCN3 regulates synaptic activity much faster than the classic steroid hormones of the hypothalamic-pituitary-adrenal axis. Moreover, due to the lack of synaptic re-uptake mechanisms, UCN3 can have more long-lasting and far-reaching effects. To date, a modest number of studies have reported the presence of UCN3 or its receptor CRFR2 in the auditory system, particularly in the cochlea and the superior olivary complex, and have highlighted the importance of this stress neuropeptide for protecting auditory function. However, a comprehensive map of all neurons synthesizing UCN3 or CRFR2 within the auditory pathway is lacking. Here, we utilize two reporter mouse lines to elucidate the expression patterns of UCN3 and CRFR2 in the auditory system. Additional immunolabelling enables further characterization of the neurons that synthesize UCN3 or CRFR2. Surprisingly, our results indicate that within the auditory system, UCN3 is expressed predominantly in principal cells, whereas CRFR2 expression is strongest in non-principal, presumably multisensory, cell types. Based on the presence or absence of overlap between UCN3 and CRFR2 labeling, our data suggest unusual modes of neuromodulation by UCN3, involving volume transmission and autocrine signaling.
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Affiliation(s)
- Sara Pagella
- Division of Neurobiology, Faculty of Biology, Ludwig-Maximilians-University Munich, Munich, Germany
| | - Jan M Deussing
- Research Group Molecular Neurogenetics, Max Planck Institute of Psychiatry, Munich, Germany
| | - Conny Kopp-Scheinpflug
- Division of Neurobiology, Faculty of Biology, Ludwig-Maximilians-University Munich, Munich, Germany
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16
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Suthakar K, Liberman MC. Auditory-nerve responses in mice with noise-induced cochlear synaptopathy. J Neurophysiol 2021; 126:2027-2038. [PMID: 34788179 DOI: 10.1152/jn.00342.2021] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Cochlear synaptopathy is the noise-induced or age-related loss of ribbon synapses between inner hair cells (IHCs) and auditory-nerve fibers (ANFs), first reported in CBA/CaJ mice. Recordings from single ANFs in anesthetized, noise-exposed guinea pigs suggested that neurons with low spontaneous rates (SRs) and high thresholds are more vulnerable than low-threshold, high-SR fibers. However, there is extensive postexposure regeneration of ANFs in guinea pigs but not in mice. Here, we exposed CBA/CaJ mice to octave-band noise and recorded sound-evoked and spontaneous activity from single ANFs at least 2 wk later. Confocal analysis of cochleae immunostained for pre- and postsynaptic markers confirmed the expected loss of 40%-50% of ANF synapses in the basal half of the cochlea; however, our data were not consistent with a selective loss of low-SR fibers. Rather they suggested a loss of both SR groups in synaptopathic regions. Single-fiber thresholds and frequency tuning recovered to pre-exposure levels; however, response to tone bursts showed increased peak and steady-state firing rates, as well as decreased jitter in first-spike latencies. This apparent gain-of-function increased the robustness of tone-burst responses in the presence of continuous masking noise. This study suggests that the nature of noise-induced synaptic damage varies between different species and that, in mouse, the noise-induced hyperexcitability seen in central auditory circuits is also observed at the level of the auditory nerve.NEW & NOTEWORTHY Noise-induced damage to synapses between inner hair cells and auditory-nerve fibers (ANFs) can occur without permanent hair cell damage, resulting in pathophysiology that "hides" behind normal thresholds. Prior single-fiber neurophysiology in guinea pig suggested that noise selectively targets high-threshold ANFs. Here, we show that the lingering pathophysiology differs in mouse, with both ANF groups affected and a paradoxical gain-of-function in surviving low-threshold fibers, including increased onset rate, decreased onset jitter, and reduced maskability.
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Affiliation(s)
- Kirupa Suthakar
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear, Boston, Massachusetts.,Department of Otolaryngology Head and Neck Surgery, Harvard Medical School, Boston, Massachusetts
| | - M Charles Liberman
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear, Boston, Massachusetts.,Department of Otolaryngology Head and Neck Surgery, Harvard Medical School, Boston, Massachusetts
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17
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Ashida G, Tollin DJ, Kretzberg J. Robustness of neuronal tuning to binaural sound localization cues against age-related loss of inhibitory synaptic inputs. PLoS Comput Biol 2021; 17:e1009130. [PMID: 34242210 PMCID: PMC8270189 DOI: 10.1371/journal.pcbi.1009130] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Accepted: 05/30/2021] [Indexed: 11/19/2022] Open
Abstract
Sound localization relies on minute differences in the timing and intensity of sound arriving at both ears. Neurons of the lateral superior olive (LSO) in the brainstem process these interaural disparities by precisely detecting excitatory and inhibitory synaptic inputs. Aging generally induces selective loss of inhibitory synaptic transmission along the entire auditory pathways, including the reduction of inhibitory afferents to LSO. Electrophysiological recordings in animals, however, reported only minor functional changes in aged LSO. The perplexing discrepancy between anatomical and physiological observations suggests a role for activity-dependent plasticity that would help neurons retain their binaural tuning function despite loss of inhibitory inputs. To explore this hypothesis, we use a computational model of LSO to investigate mechanisms underlying the observed functional robustness against age-related loss of inhibitory inputs. The LSO model is an integrate-and-fire type enhanced with a small amount of low-voltage activated potassium conductance and driven with (in)homogeneous Poissonian inputs. Without synaptic input loss, model spike rates varied smoothly with interaural time and level differences, replicating empirical tuning properties of LSO. By reducing the number of inhibitory afferents to mimic age-related loss of inhibition, overall spike rates increased, which negatively impacted binaural tuning performance, measured as modulation depth and neuronal discriminability. To simulate a recovery process compensating for the loss of inhibitory fibers, the strength of remaining inhibitory inputs was increased. By this modification, effects of inhibition loss on binaural tuning were considerably weakened, leading to an improvement of functional performance. These neuron-level observations were further confirmed by population modeling, in which binaural tuning properties of multiple LSO neurons were varied according to empirical measurements. These results demonstrate the plausibility that homeostatic plasticity could effectively counteract known age-dependent loss of inhibitory fibers in LSO and suggest that behavioral degradation of sound localization might originate from changes occurring more centrally.
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Affiliation(s)
- Go Ashida
- Cluster of Excellence "Hearing4all", Department of Neuroscience, University of Oldenburg, Oldenburg, Germany
- * E-mail:
| | - Daniel J. Tollin
- Department of Physiology and Biophysics, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Jutta Kretzberg
- Cluster of Excellence "Hearing4all", Department of Neuroscience, University of Oldenburg, Oldenburg, Germany
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18
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Niwa M, Young ED, Glowatzki E, Ricci AJ. Functional subgroups of cochlear inner hair cell ribbon synapses differently modulate their EPSC properties in response to stimulation. J Neurophysiol 2021; 125:2461-2479. [PMID: 33949873 PMCID: PMC8285665 DOI: 10.1152/jn.00452.2020] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Spiral ganglion neurons (SGNs) form single synapses on inner hair cells (IHCs), transforming sound-induced IHC receptor potentials into trains of action potentials. SGN neurons are classified by spontaneous firing rates as well as their threshold response to sound intensity levels. We investigated the hypothesis that synaptic specializations underlie mouse SGN response properties and vary with pillar versus modiloar synapse location around the hair cell. Depolarizing hair cells with 40 mM K+ increased the rate of postsynaptic responses. Pillar synapses matured later than modiolar synapses. Excitatory postsynaptic current (EPSC) amplitude, area, and number of underlying events per EPSC were similar between synapse locations at steady state. However, modiolar synapses produced larger monophasic EPSCs when EPSC rates were low and EPSCs became more multiphasic and smaller in amplitude when rates were higher, while pillar synapses produced more monophasic and larger EPSCs when the release rates were higher. We propose that pillar and modiolar synapses have different operating points. Our data provide insight into underlying mechanisms regulating EPSC generation. NEW & NOTEWORTHY Data presented here provide the first direct functional evidence of late synaptic maturation of the hair cell- spiral ganglion neuron synapse, where pillar synapses mature after postnatal day 20. Data identify a presynaptic difference in release during stimulation. This difference may in part drive afferent firing properties.
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Affiliation(s)
- Mamiko Niwa
- Department of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, Stanford, California.,Center for Hearing and Balance, Johns Hopkins School of Medicine, Baltimore, Maryland.,Department of Otolaryngology-Head, and Neck Surgery, Johns Hopkins School of Medicine, Baltimore, Maryland
| | - Eric D Young
- Center for Hearing and Balance, Johns Hopkins School of Medicine, Baltimore, Maryland.,Department of Biomedical Engineering, Johns Hopkins School of Medicine, Baltimore, Maryland.,Department of Neuroscience, Johns Hopkins School of Medicine, Baltimore, Maryland
| | - Elisabeth Glowatzki
- Center for Hearing and Balance, Johns Hopkins School of Medicine, Baltimore, Maryland.,Department of Otolaryngology-Head, and Neck Surgery, Johns Hopkins School of Medicine, Baltimore, Maryland.,Department of Neuroscience, Johns Hopkins School of Medicine, Baltimore, Maryland
| | - Anthony J Ricci
- Department of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, Stanford, California.,Department of Molecular and Cellular Physiology, Stanford University, Stanford, California
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19
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Rutherford MA, von Gersdorff H, Goutman JD. Encoding sound in the cochlea: from receptor potential to afferent discharge. J Physiol 2021; 599:2527-2557. [PMID: 33644871 PMCID: PMC8127127 DOI: 10.1113/jp279189] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Accepted: 02/22/2021] [Indexed: 12/17/2022] Open
Abstract
Ribbon-class synapses in the ear achieve analog to digital transformation of a continuously graded membrane potential to all-or-none spikes. In mammals, several auditory nerve fibres (ANFs) carry information from each inner hair cell (IHC) to the brain in parallel. Heterogeneity of transmission among synapses contributes to the diversity of ANF sound-response properties. In addition to the place code for sound frequency and the rate code for sound level, there is also a temporal code. In series with cochlear amplification and frequency tuning, neural representation of temporal cues over a broad range of sound levels enables auditory comprehension in noisy multi-speaker settings. The IHC membrane time constant introduces a low-pass filter that attenuates fluctuations of the receptor potential above 1-2 kHz. The ANF spike generator adds a high-pass filter via its depolarization-rate threshold that rejects slow changes in the postsynaptic potential and its phasic response property that ensures one spike per depolarization. Synaptic transmission involves several stochastic subcellular processes between IHC depolarization and ANF spike generation, introducing delay and jitter that limits the speed and precision of spike timing. ANFs spike at a preferred phase of periodic sounds in a process called phase-locking that is limited to frequencies below a few kilohertz by both the IHC receptor potential and the jitter in synaptic transmission. During phase-locking to periodic sounds of increasing intensity, faster and facilitated activation of synaptic transmission and spike generation may be offset by presynaptic depletion of synaptic vesicles, resulting in relatively small changes in response phase. Here we review encoding of spike-timing at cochlear ribbon synapses.
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Affiliation(s)
- Mark A. Rutherford
- Department of Otolaryngology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Henrique von Gersdorff
- Vollum Institute, Oregon Hearing Research Center, Oregon Health and Sciences University, Portland, Oregon 97239
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20
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Ernst R, Linxweiler M, Rink KA, Rothe H, Lecomte G, Bozzato A, Hecker D. [Neurophysiological parameters for speech recognition in patients with cochlear implants]. Laryngorhinootologie 2021; 101:216-227. [PMID: 33836549 DOI: 10.1055/a-1399-9540] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
OBJECTIVES Cochlea Implants (CI) are the preferred treatment for deaf and highly hearing imparied people. While deaf people already profit enormously from any regained hearing perception, it is not as easy to predict a profitable outcome for people with a remaining sense of hearing. To provide patients the best possible outcome in speech understanding, a lot of parameters have to be identified and adjusted. The aim of this study is to show the influence of objective parameters on classified speech understanding using collected data. MATERIAL AND METHODS A total of 52 patients and 65 ears aged between 18 and 80 years were included in this study. ECAP-thresholds from intraoperative measurements and impedance were used as objective parameters. T- and C/M-levels were defined as subjective parameters. To classify the performance the value of speech understanding was used. RESULTS Differences between both groups (age, time after implantation) were not significant. The gained word scores at 500 Hz correlated significantly with the results of the speech perception threshold on two-digit numbers. The electrode impedances correlated on average with speech understanding with constant variability. The distributions of objective and subjective parameters showed partially significant differences. Many distributions showed significant differences to the normal distribution. Accordingly, the overlapping areas of the significance levels are very narrow. CONCLUSION Higher impedances and incorrectly adjusted T-levels resulted in a worse speech understanding. Relation of C/M-levels to ECAP thresholds seem to be crucial for good speech understanding.
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Affiliation(s)
- Robert Ernst
- Hals-, Nasen- und Ohrenklinik, Universitätsklinikum des Saarlandes, Homburg, Germany
| | - Maximilian Linxweiler
- Hals-, Nasen- und Ohrenklinik, Universitätsklinikum des Saarlandes, Homburg, Germany
| | - Katharina Anna Rink
- Hals-, Nasen- und Ohrenklinik, Universitätsklinikum des Saarlandes, Homburg, Germany
| | - Heike Rothe
- Hals-, Nasen- und Ohrenklinik, Universitätsklinikum des Saarlandes, Homburg, Germany
| | - Gregory Lecomte
- Hals-, Nasen- und Ohrenklinik, Universitätsklinikum des Saarlandes, Homburg, Germany
| | - Alessandro Bozzato
- Hals-, Nasen- und Ohrenklinik, Universitätsklinikum des Saarlandes, Homburg, Germany
| | - Dietmar Hecker
- Klinik für Hals-, Nasen- und Ohrenheilkunde, Universitätsklinikum des Saarlandes und Medizinische Fakultät der Universität des Saarlandes, Homburg, Germany
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21
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Hintze A, Gültas M, Semmelhack EA, Wichmann C. Ultrastructural maturation of the endbulb of Held active zones comparing wild-type and otoferlin-deficient mice. iScience 2021; 24:102282. [PMID: 33851098 PMCID: PMC8022229 DOI: 10.1016/j.isci.2021.102282] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Revised: 01/18/2021] [Accepted: 03/03/2021] [Indexed: 11/13/2022] Open
Abstract
Endbulbs of Held are located in the anteroventral cochlear nucleus and present the first central synapses of the auditory pathway. During development, endbulbs mature functionally to enable rapid and powerful synaptic transmission with high temporal precision. This process is accompanied by morphological changes of endbulb terminals. Loss of the hair cell-specific protein otoferlin (Otof) abolishes neurotransmission in the cochlea and results in the smaller endbulb of Held terminals. Thus, peripheral hearing impairment likely also leads to alterations in the morphological synaptic vesicle (SV) pool size at individual endbulb of Held active zones (AZs). Here, we investigated endbulb AZs in pre-hearing, young, and adult wild-type and Otof−/− mice. During maturation, SV numbers at endbulb AZs increased in wild-type mice but were found to be reduced in Otof−/− mice. The SV population at a distance of 0–15 nm was most strongly affected. Finally, overall SV diameters decreased in Otof−/− animals during maturation. Maturation of wt endbulb of Held active zones leads to more synaptic vesicles At endbulbs of otoferlin knockout mice, synaptic vesicles decline with age Mainly two distinct synaptic vesicle populations are affected Synaptic vesicles sizes are reduced in six-month-old otoferlin knockout animals
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Affiliation(s)
- Anika Hintze
- Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience, InnerEarLab and Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, 37075 Göttingen, Germany.,Collaborative Research Center 1286, University of Göttingen, Göttingen, Germany.,Göttingen Graduate School for Neurosciences, Biophysics and Molecular Biosciences, University of Göttingen, Göttingen, Germany
| | - Mehmet Gültas
- Breeding Informatics Group, Department of Animal Sciences, Georg-August-University Göttingen, Göttingen, Germany
| | - Esther A Semmelhack
- Developmental, Neural, and Behavioral Biology MSc/PhD Program, University of Göttingen, Göttingen, Germany
| | - Carolin Wichmann
- Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience, InnerEarLab and Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, 37075 Göttingen, Germany.,Collaborative Research Center 1286, University of Göttingen, Göttingen, Germany
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22
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Wang M, Zhang C, Lin S, Wang Y, Seicol BJ, Ariss RW, Xie R. Biased auditory nerve central synaptopathy is associated with age-related hearing loss. J Physiol 2021; 599:1833-1854. [PMID: 33450070 DOI: 10.1113/jp281014] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2020] [Accepted: 01/03/2021] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Sound information is transmitted by different subtypes of spiral ganglion neurons (SGN) from the ear to the brain. Selective damage of SGN peripheral synapses (cochlear synaptopathy) is widely recognized as one of the primary mechanisms of hearing loss, whereas the mechanisms at the SGN central synapses remain unclear. We report that different subtypes of SGN central synapses converge at different ratios onto individual target cochlear nucleus neurons with distinct physiological properties, and show biased morphological and physiological changes during age-related hearing loss (ARHL). The results reveal a new dimension in cochlear nucleus neural circuitry that systematically reassembles and processes auditory information from different SGN subtypes, which is altered during ageing and probably contributes to the development of ARHL. In addition to known cochlear synaptopathy, the present study shows that SGN central synapses are also pathologically changed during ageing, which collectively helps us better understand the structure and function of SGNs during ARHL. ABSTRACT Sound information is transmitted from the cochlea to the brain by different subtypes of spiral ganglion neurons (SGN), which show varying degrees of vulnerability under pathological conditions. Selective cochlear synaptopathy, the preferential damage of certain subtypes of SGN peripheral synapses, has been recognized as one of the main mechanisms of hearing loss. The organization and function of the auditory nerve (AN) central synapses from different subtypes of SGNs remain unclear, including how different AN synapses reassemble onto individual neurons in the cochlear nucleus, as well as how they differentially change during hearing loss. Combining immunohistochemistry with electrophysiology, we investigated the convergence pattern and subtype-specific synaptopathy of AN synapses at the endbulb of Held, as well as the response properties of their postsynaptic bushy neurons in CBA/CaJ mice of either sex under normal hearing and age-related hearing loss (ARHL). We found that calretinin-expressing (type Ia ) and non-calretinin-expressing (type Ib /Ic ) endbulbs converged along a continuum of different ratios onto individual bushy neurons with varying physiological properties. Endbulbs degenerated during ageing in parallel with ARHL. Furthermore, the degeneration was more severe in non-calretinin-expressing synapses, which correlated with a gradual decrease in bushy neuron subpopulation predominantly innervated by these inputs. These synaptic and cellular changes were profound in middle-aged mice when their hearing thresholds were still relatively normal and prior to severe ARHL. Our findings suggest that biased AN central synaptopathy and the correlated shift in cochlear nucleus neuronal composition play significant roles in weakened auditory input and altered central auditory processing during ARHL.
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Affiliation(s)
- Meijian Wang
- Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, OH, USA
| | - Chuangeng Zhang
- Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, OH, USA
| | - Shengyin Lin
- Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, OH, USA
| | - Yong Wang
- Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, OH, USA
| | - Benjamin J Seicol
- Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, OH, USA.,Department of Neuroscience, The Ohio State University, Columbus, OH, USA
| | - Robert W Ariss
- College of Medicine and Life Sciences, University of Toledo, Toledo, OH, USA
| | - Ruili Xie
- Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, OH, USA.,Department of Neuroscience, The Ohio State University, Columbus, OH, USA
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23
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Neuronal population model of globular bushy cells covering unit-to-unit variability. PLoS Comput Biol 2019; 15:e1007563. [PMID: 31881018 PMCID: PMC6934273 DOI: 10.1371/journal.pcbi.1007563] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2019] [Accepted: 11/25/2019] [Indexed: 01/02/2023] Open
Abstract
Computations of acoustic information along the central auditory pathways start in the cochlear nucleus. Bushy cells in the anteroventral cochlear nucleus, which innervate monaural and binaural stations in the superior olivary complex, process and transfer temporal cues relevant for sound localization. These cells are categorized into two groups: spherical and globular bushy cells (SBCs/GBCs). Spontaneous rates of GBCs innervated by multiple auditory nerve (AN) fibers are generally lower than those of SBCs that receive a small number of large AN synapses. In response to low-frequency tonal stimulation, both types of bushy cells show improved phase-locking and entrainment compared to AN fibers. When driven by high-frequency tones, GBCs show primary-like-with-notch or onset-L peristimulus time histograms and relatively irregular spiking. However, previous in vivo physiological studies of bushy cells also found considerable unit-to-unit variability in these response patterns. Here we present a population of models that can simulate the observed variation in GBCs. We used a simple coincidence detection model with an adaptive threshold and systematically varied its six parameters. Out of 567000 parameter combinations tested, 7520 primary-like-with-notch models and 4094 onset-L models were selected that satisfied a set of physiological criteria for a GBC unit. Analyses of the model parameters and output measures revealed that the parameters of the accepted model population are weakly correlated with each other to retain major GBC properties, and that the output spiking patterns of the model are affected by a combination of multiple parameters. Simulations of frequency-dependent temporal properties of the model GBCs showed a reasonable fit to empirical data, supporting the validity of our population modeling. The computational simplicity and efficiency of the model structure makes our approach suitable for future large-scale simulations of binaural information processing that may involve thousands of GBC units. In the auditory system, specialized neuronal circuits process various types of acoustic information. A group of neurons, called globular bushy cells (GBCs), faithfully transfer timing information of acoustic signals to their downstream neurons responsible for the perception of sound location. Previous physiological studies found representative activity patterns of GBCs, but with substantial individual variations among them. In this study, we present a population of models, instead of creating one best model, to account for the observed variations of GBCs. We varied all six parameters of a simple auditory neuron model and selected the combinations of parameters that led to acceptable activity patterns of GBCs. In total, we tested more than half a million combinations and accepted ~11600 GBC models. Temporal spiking patterns of real GBCs depend on the sound frequency, and our model population was able to replicate this trend. The model used here is computationally efficient and can thus serve as a building block for future large-scale simulations of auditory information processing.
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24
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Kuenzel T. Modulatory influences on time-coding neurons in the ventral cochlear nucleus. Hear Res 2019; 384:107824. [DOI: 10.1016/j.heares.2019.107824] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Revised: 09/10/2019] [Accepted: 10/14/2019] [Indexed: 02/07/2023]
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25
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Yin TC, Smith PH, Joris PX. Neural Mechanisms of Binaural Processing in the Auditory Brainstem. Compr Physiol 2019; 9:1503-1575. [DOI: 10.1002/cphy.c180036] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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26
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Encina-Llamas G, Harte JM, Dau T, Shinn-Cunningham B, Epp B. Investigating the Effect of Cochlear Synaptopathy on Envelope Following Responses Using a Model of the Auditory Nerve. J Assoc Res Otolaryngol 2019; 20:363-382. [PMID: 31102010 PMCID: PMC6646444 DOI: 10.1007/s10162-019-00721-7] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Accepted: 04/08/2019] [Indexed: 12/16/2022] Open
Abstract
The healthy auditory system enables communication in challenging situations with high levels of background noise. Yet, despite normal sensitivity to pure tones, many listeners complain about having difficulties in such situations. Recent animal studies demonstrated that noise overexposure that produces temporary threshold shifts can cause the loss of auditory nerve (AN) fiber synapses (i.e., cochlear synaptopathy, CS), which appears to predominantly affect medium- and low-spontaneous rate (SR) fibers. In the present study, envelope following response (EFR) magnitude-level functions were recorded in normal hearing (NH) threshold and mildly hearing-impaired (HI) listeners with thresholds elevated above 2 kHz. EFRs were elicited by sinusoidally amplitude modulated (SAM) tones presented in quiet with a carrier frequency of 2 kHz, modulated at 93 Hz, and modulation depths of 0.85 (deep) and 0.25 (shallow). While EFR magnitude-level functions for deeply modulated tones were similar for all listeners, EFR magnitudes for shallowly modulated tones were reduced at medium stimulation levels in some NH threshold listeners and saturated in all HI listeners for the whole level range. A phenomenological model of the AN was used to investigate the extent to which hair-cell dysfunction and/or CS could explain the trends observed in the EFR data. Hair-cell dysfunction alone, including postulated elevated hearing thresholds at extended high frequencies (EHF) beyond 8 kHz, could not account for the recorded EFR data. Postulated CS led to simulations generally consistent with the recorded data, but a loss of all types of AN fibers was required within the model framework. The effects of off-frequency contributions (i.e., away from the characteristic place of the stimulus) and the differential loss of different AN fiber types on EFR magnitude-level functions were analyzed. When using SAM tones in quiet as the stimulus, model simulations suggested that (1) EFRs are dominated by the activity of high-SR fibers at all stimulus intensities, and (2) EFRs at medium-to-high stimulus levels are dominated by off-frequency contributions.
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Affiliation(s)
- Gerard Encina-Llamas
- Hearing Systems section, Department of Health Technology, Technical University of Denmark (DTU), Kongens Lyngby, Denmark.
| | - James M Harte
- Interacoustics Research Unit, Kongens Lyngby, Denmark
| | - Torsten Dau
- Hearing Systems section, Department of Health Technology, Technical University of Denmark (DTU), Kongens Lyngby, Denmark
| | - Barbara Shinn-Cunningham
- Carnegie Mellon Neuroscience Institute, Pittsburgh, PA, USA.,Department of Biomedical Engineering, Boston University, Boston, MA, USA
| | - Bastian Epp
- Hearing Systems section, Department of Health Technology, Technical University of Denmark (DTU), Kongens Lyngby, Denmark
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27
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Galazyuk A, Longenecker R, Voytenko S, Kristaponyte I, Nelson G. Residual inhibition: From the putative mechanisms to potential tinnitus treatment. Hear Res 2019; 375:1-13. [DOI: 10.1016/j.heares.2019.01.022] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/30/2018] [Revised: 01/23/2019] [Accepted: 01/30/2019] [Indexed: 01/04/2023]
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28
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Müller MK, Jovanovic S, Keine C, Radulovic T, Rübsamen R, Milenkovic I. Functional Development of Principal Neurons in the Anteroventral Cochlear Nucleus Extends Beyond Hearing Onset. Front Cell Neurosci 2019; 13:119. [PMID: 30983974 PMCID: PMC6447607 DOI: 10.3389/fncel.2019.00119] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 03/11/2019] [Indexed: 01/23/2023] Open
Abstract
Sound information is transduced into graded receptor potential by cochlear hair cells and encoded as discrete action potentials of auditory nerve fibers. In the cochlear nucleus, auditory nerve fibers convey this information through morphologically distinct synaptic terminals onto bushy cells (BCs) and stellate cells (SCs) for processing of different sound features. With expanding use of transgenic mouse models, it is increasingly important to understand the in vivo functional development of these neurons in mice. We characterized the maturation of spontaneous and acoustically evoked activity in BCs and SCs by acquiring single-unit juxtacellular recordings between hearing onset (P12) and young adulthood (P30) of anesthetized CBA/J mice. In both cell types, hearing sensitivity and characteristic frequency (CF) range are mostly adult-like by P14, consistent with rapid maturation of the auditory periphery. In BCs, however, some physiological features like maximal firing rate, dynamic range, temporal response properties, recovery from post-stimulus depression, first spike latency (FSL) and encoding of sinusoid amplitude modulation undergo further maturation up to P18. In SCs, the development of excitatory responses is even more prolonged, indicated by a gradual increase in spontaneous and maximum firing rates up to P30. In the same cell type, broadly tuned acoustically evoked inhibition is immediately effective at hearing onset, covering the low- and high-frequency flanks of the excitatory response area. Together, these data suggest that maturation of auditory processing in the parallel ascending BC and SC streams engages distinct mechanisms at the first central synapses that may differently depend on the early auditory experience.
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Affiliation(s)
- Maria Katharina Müller
- Carl Ludwig Institute for Physiology, Faculty of Medicine, University of Leipzig, Leipzig, Germany
| | - Sasa Jovanovic
- Carl Ludwig Institute for Physiology, Faculty of Medicine, University of Leipzig, Leipzig, Germany
| | - Christian Keine
- Carver College of Medicine, Department of Anatomy and Cell Biology, University of Iowa, Iowa City, IA, United States.,Institute of Biology, Faculty of Life Sciences, University of Leipzig, Leipzig, Germany
| | - Tamara Radulovic
- Carl Ludwig Institute for Physiology, Faculty of Medicine, University of Leipzig, Leipzig, Germany.,Carver College of Medicine, Department of Anatomy and Cell Biology, University of Iowa, Iowa City, IA, United States
| | - Rudolf Rübsamen
- Institute of Biology, Faculty of Life Sciences, University of Leipzig, Leipzig, Germany
| | - Ivan Milenkovic
- Carl Ludwig Institute for Physiology, Faculty of Medicine, University of Leipzig, Leipzig, Germany.,School of Medicine and Health Sciences, Carl von Ossietzky University Oldenburg, Oldenburg, Germany
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29
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Shaheen LA, Liberman MC. Cochlear Synaptopathy Changes Sound-Evoked Activity Without Changing Spontaneous Discharge in the Mouse Inferior Colliculus. Front Syst Neurosci 2018; 12:59. [PMID: 30559652 PMCID: PMC6286982 DOI: 10.3389/fnsys.2018.00059] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Accepted: 10/26/2018] [Indexed: 12/12/2022] Open
Abstract
Tinnitus and hyperacusis are life-disrupting perceptual abnormalities that are often preceded by acoustic overexposure. Animal models of overexposure have suggested a link between these phenomena and neural hyperactivity, i.e., elevated spontaneous rates (SRs) and sound-evoked responses. Prior work has focused on changes in central auditory responses, with less attention paid to the exact nature of the associated cochlear damage. The demonstration that acoustic overexposure can cause cochlear neuropathy without permanent threshold elevation suggests cochlear neuropathy per se may be a key elicitor of neural hyperactivity. We addressed this hypothesis by recording responses in the mouse inferior colliculus (IC) following a bilateral, neuropathic noise exposure. One to three weeks post-exposure, mean SRs were unchanged in mice recorded while awake, or under anesthesia. SRs were also unaffected by more intense, or unilateral exposures. These results suggest that neither neuropathy nor hair cell loss are sufficient to raise SRs in the IC, at least in 7-week-old mice, 1-3 weeks post exposure. However, it is not clear whether our mice had tinnitus. Tone-evoked rate-level functions at the CF were steeper following exposure, specifically in the region of maximal neuropathy. Furthermore, suppression driven by off-CF tones and by ipsilateral noise were reduced. Both changes were especially pronounced in neurons of awake mice. This neural hypersensitivity may manifest as behavioral hypersensitivity to sound - prior work reports that this same exposure causes elevated acoustic startle. Together, these results indicate that neuropathy may initiate a compensatory response in the central auditory system leading to the genesis of hyperacusis.
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Affiliation(s)
- Luke A. Shaheen
- Oregon Hearing Research Center, Oregon Health and Science University, Portland, OR, United States
| | - M. Charles Liberman
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, Boston, MA, United States
- Department of Otolaryngology, Harvard Medical School, Boston, MA, United States
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30
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Petitpré C, Wu H, Sharma A, Tokarska A, Fontanet P, Wang Y, Helmbacher F, Yackle K, Silberberg G, Hadjab S, Lallemend F. Neuronal heterogeneity and stereotyped connectivity in the auditory afferent system. Nat Commun 2018; 9:3691. [PMID: 30209249 PMCID: PMC6135759 DOI: 10.1038/s41467-018-06033-3] [Citation(s) in RCA: 142] [Impact Index Per Article: 23.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Accepted: 07/31/2018] [Indexed: 01/07/2023] Open
Abstract
Spiral ganglion (SG) neurons of the cochlea convey all auditory inputs to the brain, yet the cellular and molecular complexity necessary to decode the various acoustic features in the SG has remained unresolved. Using single-cell RNA sequencing, we identify four types of SG neurons, including three novel subclasses of type I neurons and the type II neurons, and provide a comprehensive genetic framework that define their potential synaptic communication patterns. The connectivity patterns of the three subclasses of type I neurons with inner hair cells and their electrophysiological profiles suggest that they represent the intensity-coding properties of auditory afferents. Moreover, neuron type specification is already established at birth, indicating a neuronal diversification process independent of neuronal activity. Thus, this work provides a transcriptional catalog of neuron types in the cochlea, which serves as a valuable resource for dissecting cell-type-specific functions of dedicated afferents in auditory perception and in hearing disorders.
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Affiliation(s)
- Charles Petitpré
- Department of Neuroscience, Karolinska Institutet, Biomedicum, Stockholm, 171 77, Sweden
| | - Haohao Wu
- Department of Neuroscience, Karolinska Institutet, Biomedicum, Stockholm, 171 77, Sweden
| | - Anil Sharma
- Department of Neuroscience, Karolinska Institutet, Biomedicum, Stockholm, 171 77, Sweden
| | - Anna Tokarska
- Department of Neuroscience, Karolinska Institutet, Biomedicum, Stockholm, 171 77, Sweden
| | - Paula Fontanet
- Department of Neuroscience, Karolinska Institutet, Biomedicum, Stockholm, 171 77, Sweden
| | - Yiqiao Wang
- Department of Neuroscience, Karolinska Institutet, Biomedicum, Stockholm, 171 77, Sweden
| | - Françoise Helmbacher
- Aix-Marseille Université, CNRS UMR7288, Institut de Biologie du Développement de Marseille (IBDM), 13009, Marseille, France
| | - Kevin Yackle
- Department of Physiology, University of California-San Francisco, San Francisco, CA, 94158, USA
| | - Gilad Silberberg
- Department of Neuroscience, Karolinska Institutet, Biomedicum, Stockholm, 171 77, Sweden
| | - Saida Hadjab
- Department of Neuroscience, Karolinska Institutet, Biomedicum, Stockholm, 171 77, Sweden
| | - François Lallemend
- Department of Neuroscience, Karolinska Institutet, Biomedicum, Stockholm, 171 77, Sweden.
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31
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Shrestha BR, Chia C, Wu L, Kujawa SG, Liberman MC, Goodrich LV. Sensory Neuron Diversity in the Inner Ear Is Shaped by Activity. Cell 2018; 174:1229-1246.e17. [PMID: 30078709 PMCID: PMC6150604 DOI: 10.1016/j.cell.2018.07.007] [Citation(s) in RCA: 237] [Impact Index Per Article: 39.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Revised: 04/23/2018] [Accepted: 07/02/2018] [Indexed: 01/02/2023]
Abstract
In the auditory system, type I spiral ganglion neurons (SGNs) convey complex acoustic information from inner hair cells (IHCs) to the brainstem. Although SGNs exhibit variation in physiological and anatomical properties, it is unclear which features are endogenous and which reflect input from synaptic partners. Using single-cell RNA sequencing, we derived a molecular classification of mouse type I SGNs comprising three subtypes that express unique combinations of Ca2+ binding proteins, ion channel regulators, guidance molecules, and transcription factors. Based on connectivity and susceptibility to age-related loss, these subtypes correspond to those defined physiologically. Additional intrinsic differences among subtypes and across the tonotopic axis highlight an unexpectedly active role for SGNs in auditory processing. SGN identities emerge postnatally and are disrupted in a mouse model of deafness that lacks IHC-driven activity. These results elucidate the range, nature, and origins of SGN diversity, with implications for treatment of congenital deafness.
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Affiliation(s)
- Brikha R Shrestha
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Chester Chia
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Lorna Wu
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Sharon G Kujawa
- Department of Otolaryngology, Harvard Medical School, Boston, MA 02115, USA; Eaton-Peabody Laboratories, Massachusetts Eye & Ear Infirmary, Boston, MA 02114, USA
| | - M Charles Liberman
- Department of Otolaryngology, Harvard Medical School, Boston, MA 02115, USA; Eaton-Peabody Laboratories, Massachusetts Eye & Ear Infirmary, Boston, MA 02114, USA
| | - Lisa V Goodrich
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
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32
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Carney LH. Supra-Threshold Hearing and Fluctuation Profiles: Implications for Sensorineural and Hidden Hearing Loss. J Assoc Res Otolaryngol 2018; 19:331-352. [PMID: 29744729 PMCID: PMC6081887 DOI: 10.1007/s10162-018-0669-5] [Citation(s) in RCA: 93] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Accepted: 04/19/2018] [Indexed: 12/22/2022] Open
Abstract
An important topic in contemporary auditory science is supra-threshold hearing. Difficulty hearing at conversational speech levels in background noise has long been recognized as a problem of sensorineural hearing loss, including that associated with aging (presbyacusis). Such difficulty in listeners with normal thresholds has received more attention recently, especially associated with descriptions of synaptopathy, the loss of auditory nerve (AN) fibers as a result of noise exposure or aging. Synaptopathy has been reported to cause a disproportionate loss of low- and medium-spontaneous rate (L/MSR) AN fibers. Several studies of synaptopathy have assumed that the wide dynamic ranges of L/MSR AN fiber rates are critical for coding supra-threshold sounds. First, this review will present data from the literature that argues against a direct role for average discharge rates of L/MSR AN fibers in coding sounds at moderate to high sound levels. Second, the encoding of sounds at supra-threshold levels is examined. A key assumption in many studies is that saturation of AN fiber discharge rates limits neural encoding, even though the majority of AN fibers, high-spontaneous rate (HSR) fibers, have saturated average rates at conversational sound levels. It is argued here that the cross-frequency profile of low-frequency neural fluctuation amplitudes, not average rates, encodes complex sounds. As described below, this fluctuation-profile coding mechanism benefits from both saturation of inner hair cell (IHC) transduction and average rate saturation associated with the IHC-AN synapse. Third, the role of the auditory efferent system, which receives inputs from L/MSR fibers, is revisited in the context of fluctuation-profile coding. The auditory efferent system is hypothesized to maintain and enhance neural fluctuation profiles. Lastly, central mechanisms sensitive to neural fluctuations are reviewed. Low-frequency fluctuations in AN responses are accentuated by cochlear nucleus neurons which, either directly or via other brainstem nuclei, relay fluctuation profiles to the inferior colliculus (IC). IC neurons are sensitive to the frequency and amplitude of low-frequency fluctuations and convert fluctuation profiles from the periphery into a phase-locked rate profile that is robust across a wide range of sound levels and in background noise. The descending projection from the midbrain (IC) to the efferent system completes a functional loop that, combined with inputs from the L/MSR pathway, is hypothesized to maintain "sharp" supra-threshold hearing, reminiscent of visual mechanisms that regulate optical accommodation. Examples from speech coding and detection in noise are reviewed. Implications for the effects of synaptopathy on control mechanisms hypothesized to influence supra-threshold hearing are discussed. This framework for understanding neural coding and control mechanisms for supra-threshold hearing suggests strategies for the design of novel hearing aid signal-processing and electrical stimulation patterns for cochlear implants.
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Affiliation(s)
- Laurel H Carney
- Departments of Biomedical Engineering, Neuroscience, and Electrical & Computer Engineering, Del Monte Institute for Neuroscience, University of Rochester, 601 Elmwood Ave., Box 603, Rochester, NY, 14642, USA.
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33
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Baizer JS, Wong KM, Salvi RJ, Manohar S, Sherwood CC, Hof PR, Baker JF, Witelson SF. Species Differences in the Organization of the Ventral Cochlear Nucleus. Anat Rec (Hoboken) 2018; 301:862-886. [PMID: 29236365 PMCID: PMC5902649 DOI: 10.1002/ar.23751] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Revised: 08/18/2017] [Accepted: 09/17/2017] [Indexed: 01/18/2023]
Abstract
The mammalian cochlear nuclei (CN) consist of two major subdivisions, the dorsal (DCN) and ventral (VCN) nuclei. We previously reported differences in the structural and neurochemical organization of the human DCN from that in several other species. Here we extend this analysis to the VCN, considering both the organization of subdivisions and the types and distributions of neurons. Classically, the VCN in mammals is composed of two subdivisions, the anteroventral (VCA) and posteroventral cochlear nuclei (VCP). Anatomical and electrophysiological data in several species have defined distinct neuronal types with different distributions in the VCA and VCP. We asked if VCN subdivisions and anatomically defined neuronal types might be distinguished by patterns of protein expression in humans. We also asked if the neurochemical characteristics of the VCN are the same in humans as in other mammalian species, analyzing data from chimpanzees, macaque monkeys, cats, rats and chinchillas. We examined Nissl- and immunostained sections, using antibodies that had labeled neurons in other brainstem nuclei in humans. Nissl-stained sections supported the presence of both VCP and VCA in humans and chimpanzees. However, patterns of protein expression did not differentiate classes of neurons in humans; neurons of different soma shapes and dendritic configurations all expressed the same proteins. The patterns of immunostaining in macaque monkey, cat, rat, and chinchilla were different from those in humans and chimpanzees and from each other. The results may correlate with species differences in auditory function and plasticity. Anat Rec, 301:862-886, 2018. © 2017 Wiley Periodicals, Inc.
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Affiliation(s)
- Joan S Baizer
- Department of Physiology and Biophysics, University at Buffalo, Buffalo, New York
| | - Keit Men Wong
- Department of Physiology and Biophysics, University at Buffalo, Buffalo, New York
| | - Richard J Salvi
- Department of Communicative Disorders and Sciences, Center for Hearing and Deafness, University at Buffalo, Buffalo, New York
| | - Senthilvelan Manohar
- Department of Communicative Disorders and Sciences, Center for Hearing and Deafness, University at Buffalo, Buffalo, New York
| | - Chet C Sherwood
- Department of Anthropology, The George Washington University, Washington, DC
| | - Patrick R Hof
- Fishberg Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, New York
| | - James F Baker
- Department of Physiology, Northwestern University Medical School, Chicago, Illinois
| | - Sandra F Witelson
- Department of Psychiatry and Behavioural Neurosciences, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, L8S 4K1, Canada
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34
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Abstract
The classic view of sensorineural hearing loss has been that the primary damage targets are hair cells and that auditory nerve loss is typically secondary to hair cell degeneration. Recent work has challenged that view. In noise-induced hearing loss, exposures causing only reversible threshold shifts (and no hair cell loss) nevertheless cause permanent loss of >50% of the synaptic connections between hair cells and the auditory nerve. Similarly, in age-related hearing loss, degeneration of cochlear synapses precedes both hair cell loss and threshold elevation. This primary neural degeneration has remained a "hidden hearing loss" for two reasons: 1) the neuronal cell bodies survive for years despite loss of synaptic connection with hair cells, and 2) the degeneration is selective for auditory nerve fibers with high thresholds. Although not required for threshold detection when quiet, these high-threshold fibers are critical for hearing in noisy environments. Research suggests that primary neural degeneration is an important contributor to the perceptual handicap in sensorineural hearing loss, and it may be key to the generation of tinnitus and other associated perceptual anomalies. In cases where the hair cells survive, neurotrophin therapies can elicit neurite outgrowth from surviving auditory neurons and re-establishment of their peripheral synapses; thus, treatments may be on the horizon.
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Affiliation(s)
- M Charles Liberman
- Department of Otolaryngology, Harvard Medical School, Eaton Peabody Laboratories, Massachusetts Eye and Ear, 243 Charles St., Boston, MA, 02114, USA
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35
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Rudnicki M, Hemmert W. High Entrainment Constrains Synaptic Depression Levels of an In vivo Globular Bushy Cell Model. Front Comput Neurosci 2017; 11:16. [PMID: 28373839 PMCID: PMC5357671 DOI: 10.3389/fncom.2017.00016] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2016] [Accepted: 03/02/2017] [Indexed: 12/15/2022] Open
Abstract
Globular bushy cells (GBCs) located in the ventral cochlear nucleus are an essential part of the sound localization pathway in the mammalian auditory system. They receive inputs directly from the auditory nerve and are particularly sensitive to temporal cues due to their synaptic and membrane specializations. GBCs act as coincidence detectors for incoming spikes through large synapses-endbulbs of Held-which connect to their soma. Since endbulbs of Held are an integral part of the auditory information conveying and processing pathway, they were extensively studied. Virtually all in vitro studies showed large synaptic depression, but on the other hand a few in vivo studies showed relatively small depression. It is also still not well understood how synaptic properties functionally influence firing properties of GBCs. Here we show how different levels of synaptic depression shape firing properties of GBCs in in vivo-like conditions using computer simulations. We analyzed how an interplay of synaptic depression (0-70%) and the number of auditory nerve fiber inputs (10-70) contributes to the variability of the experimental data from previous studies. We predict that the majority of synapses of GBCs with high characteristic frequencies (CF > 500 Hz) have a rate dependent depression of less than 20%. GBCs with lower CF (<500 Hz) work also with strong depressing synapses (up to 50% or more). We also showed that synapses explicitly fitted to in vitro experiments with paired-pulse stimuli did not operate properly in in vivo-like conditions and required further extension to capture the differences between in vitro and in vivo experimental conditions. Overall, this study helps to understand how synaptic properties shape temporal processing in the auditory system. It also integrates, compares, and reconciles results of various experimental studies.
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Affiliation(s)
- Marek Rudnicki
- Bio-Inspired Information Processing, Technische Universität München München, Germany
| | - Werner Hemmert
- Bio-Inspired Information Processing, Technische Universität München München, Germany
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Bender DA, Ni R, Barbour DL. Spontaneous activity is correlated with coding density in primary auditory cortex. J Neurophysiol 2016; 116:2789-2798. [PMID: 27707812 DOI: 10.1152/jn.00474.2016] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Accepted: 09/30/2016] [Indexed: 11/22/2022] Open
Abstract
Sensory neurons across sensory modalities and specific processing areas have diverse levels of spontaneous firing rates (SFRs) in the absence of sensory stimuli. However, the functional significance of this spontaneous activity is not well-understood. Previous studies in the auditory system have demonstrated that different levels of spontaneous activity are correlated with a variety of physiological and anatomic properties, suggesting that neurons with differing SFRs make unique contributions to the encoding of auditory stimuli. Additionally, altered SFRs are a correlate of tinnitus, arising in several auditory areas after exposure to ototoxic substances and noise trauma. In this study, we recorded single-unit activity from primary auditory cortex of awake marmoset monkeys while delivering wide-band random-spectrum stimuli and white Gaussian noise (WGN) to examine any divergences in stimulus encoding properties across SFR classes. We found that higher levels of spontaneous activity were associated with both higher levels of activation relative to suppression across a variety of wide-band stimuli and higher driven rates in response to WGN. Moreover, response latencies to WGN were negatively correlated with the level of activation in response to both stimulus types. These findings are consistent with a novel view of the role spontaneous spiking may play during normal stimulus processing in primary auditory cortex and how it may malfunction in cases of tinnitus.
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Affiliation(s)
- David A Bender
- Laboratory of Sensory Neuroscience and Neuroengineering, Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri; and.,Department of Biology, Washington University in St. Louis, St. Louis, Missouri
| | - Ruiye Ni
- Laboratory of Sensory Neuroscience and Neuroengineering, Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri; and
| | - Dennis L Barbour
- Laboratory of Sensory Neuroscience and Neuroengineering, Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri; and
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Liberman LD, Liberman MC. Postnatal maturation of auditory-nerve heterogeneity, as seen in spatial gradients of synapse morphology in the inner hair cell area. Hear Res 2016; 339:12-22. [PMID: 27288592 DOI: 10.1016/j.heares.2016.06.002] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Revised: 05/09/2016] [Accepted: 06/06/2016] [Indexed: 02/06/2023]
Abstract
Auditory nerve fibers in the adult ear are divided into functional subgroups according to spontaneous rate (SR) and threshold sensitivity. The high-threshold, low-SR fibers are morphologically and spatially distinct from the low-threshold high-SR fibers at their synaptic contacts with inner hair cells. This distinction between SR groups in the adult ear is visible in confocal microscopy as complementary size gradients of presynaptic ribbons and post-synaptic glutamate receptor patches across the modiolar-pillar and habenular-cuticular axes in the inner hair cell area. The aim of the present study was to track the post-natal development of this morphological gradient, in mouse, to determine the earliest age at which this important aspect of cochlear organization is fully mature. Here we show, using morphometric analysis of the organ of Corti immunostained for pre- and post-synaptic markers of efferent and afferent innervation, that this SR-based morphological gradient is not fully established until postnatal day 28, well after other features, such as synaptic counts and efferent innervation density in both the inner and outer hair cell areas, appear fully mature.
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Affiliation(s)
- Leslie D Liberman
- Eaton-Peabody Laboratories, Massachusetts Eye & Ear Infirmary, Boston, MA, USA
| | - M Charles Liberman
- Department of Otology and Laryngology, Harvard Medical School, Boston, MA, USA; Eaton-Peabody Laboratories, Massachusetts Eye & Ear Infirmary, Boston, MA, USA.
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Valero MD, Hancock KE, Liberman MC. The middle ear muscle reflex in the diagnosis of cochlear neuropathy. Hear Res 2016; 332:29-38. [PMID: 26657094 PMCID: PMC5244259 DOI: 10.1016/j.heares.2015.11.005] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/06/2015] [Revised: 11/14/2015] [Accepted: 11/17/2015] [Indexed: 02/04/2023]
Abstract
Cochlear neuropathy, i.e. the loss of auditory nerve fibers (ANFs) without loss of hair cells, may cause hearing deficits without affecting threshold sensitivity, particularly if the subset of ANFs with high thresholds and low spontaneous rates (SRs) is preferentially lost, as appears to be the case in both aging and noise-damaged cochleas. Because low-SR fibers may also be important drivers of the medial olivocochlear reflex (MOCR) and middle-ear muscle reflex (MEMR), these reflexes might be sensitive metrics of cochlear neuropathy. To test this hypothesis, we measured reflex strength and reflex threshold in mice with noise-induced neuropathy, as documented by confocal analysis of immunostained cochlear whole-mounts. To assay the MOCR, we measured contra-noise modulation of ipsilateral distortion-product otoacoustic emissions (DPOAEs) before and after the administration of curare to block the MEMR or curare + strychnine to also block the MOCR. The modulation of DPOAEs was 1) dominated by the MEMR in anesthetized mice, with a smaller contribution from the MOCR, and 2) significantly attenuated in neuropathic mice, but only when the MEMR was intact. We then measured MEMR growth functions by monitoring contra-noise induced changes in the wideband reflectance of chirps presented to the ipsilateral ear. We found 1) that the changes in wideband reflectance were mediated by the MEMR alone, and 2) that MEMR threshold was elevated and its maximum amplitude was attenuated in neuropathic mice. These data suggest that the MEMR may be valuable in the early detection of cochlear neuropathy.
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Affiliation(s)
- Michelle D Valero
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA; Department of Otology and Laryngology, Harvard Medical School, Boston, MA 02115, USA.
| | - Kenneth E Hancock
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA; Department of Otology and Laryngology, Harvard Medical School, Boston, MA 02115, USA
| | - M Charles Liberman
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA; Department of Otology and Laryngology, Harvard Medical School, Boston, MA 02115, USA
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Pannese A, Grandjean D, Frühholz S. Subcortical processing in auditory communication. Hear Res 2015; 328:67-77. [DOI: 10.1016/j.heares.2015.07.003] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Revised: 06/23/2015] [Accepted: 07/01/2015] [Indexed: 12/21/2022]
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Eggermont JJ. Animal models of spontaneous activity in the healthy and impaired auditory system. Front Neural Circuits 2015; 9:19. [PMID: 25983679 PMCID: PMC4415415 DOI: 10.3389/fncir.2015.00019] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Accepted: 04/10/2015] [Indexed: 11/30/2022] Open
Abstract
Spontaneous neural activity in the auditory nerve fibers and in auditory cortex in healthy animals is discussed with respect to the question: Is spontaneous activity noise or information carrier? The studies reviewed suggest strongly that spontaneous activity is a carrier of information. Subsequently, I review the numerous findings in the impaired auditory system, particularly with reference to noise trauma and tinnitus. Here the common assumption is that tinnitus reflects increased noise in the auditory system that among others affects temporal processing and interferes with the gap-startle reflex, which is frequently used as a behavioral assay for tinnitus. It is, however, more likely that the increased spontaneous activity in tinnitus, firing rate as well as neural synchrony, carries information that shapes the activity of downstream structures, including non-auditory ones, and leading to the tinnitus percept. The main drivers of that process are bursting and synchronous firing, which facilitates transfer of activity across synapses, and allows formation of auditory objects, such as tinnitus.
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Affiliation(s)
- Jos J Eggermont
- Department of Physiology and Pharmacology, Department of Psychology, University of Calgary Calgary, AB, Canada
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Wan G, Corfas G. No longer falling on deaf ears: mechanisms of degeneration and regeneration of cochlear ribbon synapses. Hear Res 2015; 329:1-10. [PMID: 25937135 DOI: 10.1016/j.heares.2015.04.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/02/2015] [Revised: 04/01/2015] [Accepted: 04/20/2015] [Indexed: 01/02/2023]
Abstract
Cochlear ribbon synapses are required for the rapid and precise neural transmission of acoustic signals from inner hair cells to the spiral ganglion neurons. Emerging evidence suggests that damage to these synapses represents an important form of cochlear neuropathy that might be highly prevalent in sensorineural hearing loss. In this review, we discuss our current knowledge on how ribbon synapses are damaged by noise and during aging, as well as potential strategies to promote ribbon synapse regeneration for hearing restoration.
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Affiliation(s)
- Guoqiang Wan
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, Ann Arbor, MI 48109, USA
| | - Gabriel Corfas
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, Ann Arbor, MI 48109, USA.
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The Effects of Spontaneous Random Activity on Information Transmission in an Auditory Brain Stem Neuron Model. ENTROPY 2014. [DOI: 10.3390/e16126654] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Liu W, Davis RL. Calretinin and calbindin distribution patterns specify subpopulations of type I and type II spiral ganglion neurons in postnatal murine cochlea. J Comp Neurol 2014; 522:2299-318. [PMID: 24414968 DOI: 10.1002/cne.23535] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2013] [Revised: 12/27/2013] [Accepted: 01/04/2014] [Indexed: 01/02/2023]
Abstract
As the first neural element in the auditory pathway, neurons in the spiral ganglion shape the initial coding of sound stimuli for subsequent processing. Within the ganglion, type I and type II neurons form divergent and convergent innervation patterns, respectively, with their hair cell sensory receptors, indicating that very different information is gathered and conveyed. Layered onto these basic innervation patterns are structural and electrophysiological features that provide additional levels of processing multifaceted sound stimuli. To understand the nature of this additional complexity of signal coding, we characterized the distribution of calretinin and calbindin, two regulators of intracellular calcium that serve as markers for neuronal subpopulations. We showed in acute preparations and in vitro that calretinin and calbindin staining levels were heterogeneous. Immunocytochemical analysis of colocalization further showed that high levels of staining for the two molecules rarely overlapped. Although varied amounts of calbindin and calretinin were found within each tonotopic location and neuronal type, some distinct subdistributions were noted. For example, calretinin levels were highest in neurons innervating the midcochlea region, whereas calbindin levels were similar across the entire ganglion. Furthermore, we noted that apical type II neurons, identified by antiperipherin labeling, had significantly lower levels of calretinin and higher levels of calbindin. We also established that the endogenous firing feature of onset tau of the subthreshold response showed a pattern related to quantified calretinin and calbindin staining levels. Taken together, our results suggest an additional dimension of complexity within the spiral ganglion beyond that currently categorized.
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Affiliation(s)
- Wenke Liu
- Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, New Jersey, 08854
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Abstract
In the auditory system, large somatic synapses convey strong excitation that supports temporally precise information transfer. The information transfer of such synapses has predominantly been investigated in the endbulbs of Held in the anterior ventral cochlear nucleus and the calyx of Held in the medial nucleus of the trapezoid body. These large synapses either work as relays or integrate over a small number of inputs to excite the postsynaptic neuron beyond action potential (AP) threshold. In the monaural system, another large somatic synapse targets neurons in the ventral nucleus of the lateral lemniscus (VNLL). Here, we comparatively analyze the mechanisms of synaptic information transfer in endbulbs in the VNLL and the calyx of Held in juvenile Mongolian gerbils. We find that endbulbs in the VNLL are functionally surface-scaled versions of the calyx of Held with respect to vesicle availability, release efficacy, and synaptic peak currents. This functional scaling is achieved by different calcium current kinetics that compensate for the smaller AP in VNLL endbulbs. However, the average postsynaptic current in the VNLL fails to elicit APs in its target neurons, even though equal current suffices to generate APs in neurons postsynaptic to the calyx of Held. In the VNLL, a postsynaptic A-type outward current reduces excitability and prevents AP generation upon a single presynaptic input. Instead, coincidence detection of inputs from two converging endbulbs is ideal to reliably trigger APs. Thus, even large endbulbs do not guarantee one-to-one AP transfer. Instead, information flow appears regulated by circuit requirements.
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Bharadwaj HM, Verhulst S, Shaheen L, Liberman MC, Shinn-Cunningham BG. Cochlear neuropathy and the coding of supra-threshold sound. Front Syst Neurosci 2014; 8:26. [PMID: 24600357 PMCID: PMC3930880 DOI: 10.3389/fnsys.2014.00026] [Citation(s) in RCA: 185] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Accepted: 02/05/2014] [Indexed: 11/13/2022] Open
Abstract
Many listeners with hearing thresholds within the clinically normal range nonetheless complain of difficulty hearing in everyday settings and understanding speech in noise. Converging evidence from human and animal studies points to one potential source of such difficulties: differences in the fidelity with which supra-threshold sound is encoded in the early portions of the auditory pathway. Measures of auditory subcortical steady-state responses (SSSRs) in humans and animals support the idea that the temporal precision of the early auditory representation can be poor even when hearing thresholds are normal. In humans with normal hearing thresholds (NHTs), paradigms that require listeners to make use of the detailed spectro-temporal structure of supra-threshold sound, such as selective attention and discrimination of frequency modulation (FM), reveal individual differences that correlate with subcortical temporal coding precision. Animal studies show that noise exposure and aging can cause a loss of a large percentage of auditory nerve fibers (ANFs) without any significant change in measured audiograms. Here, we argue that cochlear neuropathy may reduce encoding precision of supra-threshold sound, and that this manifests both behaviorally and in SSSRs in humans. Furthermore, recent studies suggest that noise-induced neuropathy may be selective for higher-threshold, lower-spontaneous-rate nerve fibers. Based on our hypothesis, we suggest some approaches that may yield particularly sensitive, objective measures of supra-threshold coding deficits that arise due to neuropathy. Finally, we comment on the potential clinical significance of these ideas and identify areas for future investigation.
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Affiliation(s)
- Hari M Bharadwaj
- Center for Computational Neuroscience and Neural Technology, Boston University Boston, MA, USA ; Department of Biomedical Engineering, Boston University Boston, MA, USA
| | - Sarah Verhulst
- Center for Computational Neuroscience and Neural Technology, Boston University Boston, MA, USA ; Department of Otology and Laryngology, Harvard Medical School Boston, MA, USA
| | - Luke Shaheen
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary Boston, MA, USA ; Harvard-MIT Division of Health Sciences and Technology, Speech and Hearing Bioscience and Technology Program Cambridge, MA, USA
| | - M Charles Liberman
- Department of Otology and Laryngology, Harvard Medical School Boston, MA, USA ; Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary Boston, MA, USA ; Harvard-MIT Division of Health Sciences and Technology, Speech and Hearing Bioscience and Technology Program Cambridge, MA, USA
| | - Barbara G Shinn-Cunningham
- Center for Computational Neuroscience and Neural Technology, Boston University Boston, MA, USA ; Department of Biomedical Engineering, Boston University Boston, MA, USA
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Abstract
Release of neurotransmitter is an inherently random process, which could degrade the reliability of postsynaptic spiking, even at relatively large synapses. This is particularly important at auditory synapses, where the rate and precise timing of spikes carry information about sounds. However, the functional consequences of the stochastic properties of release are unknown. We addressed this issue at the mouse endbulb of Held synapse, which is formed by auditory nerve fibers onto bushy cells (BCs) in the anteroventral cochlear nucleus. We used voltage clamp to characterize synaptic variability. Dynamic clamp was used to compare BC spiking with stochastic or deterministic synaptic input. The stochastic component increased the responsiveness of the BC to conductances that were on average subthreshold, thereby increasing the dynamic range of the synapse. This had the benefit that BCs relayed auditory nerve activity even when synapses showed significant depression during rapid activity. However, the precision of spike timing decreased with stochastic conductances, suggesting a trade-off between encoding information in spike timing versus probability. These effects were confirmed in fiber stimulation experiments, indicating that they are physiologically relevant, and that synaptic randomness, dynamic range, and jitter are causally related.
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Kumsa P, Mino H. Effects of the rates of pseudo-spontaneous spikes generated by electric stimuli on information transmission in an auditory nerve fiber model. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2013; 2013:5246-9. [PMID: 24110919 DOI: 10.1109/embc.2013.6610732] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In this study, the effects of the rate of pseudo-spontaneous spikes on information transmission of the spike trains in response to the electric pulsatile stimulus currents in an auditory nerve fiber (ANF) model is investigated through computer simulation. The pseudo-spontaneous spikes can be generated by high rate pulsatile electric stimuli, making it possible to efficiently encode sound stimuli into the spike trains of the ANF in cochlear prostheses. In this investigation, the information rate of the spike trains in response to sinusoidally modulated pulsatile electric stimuli was estimated as the amplitude of the pulsatile electric stimuli (the rate of pseudo-spontaneous spikes) was varied. The results show that the information rates increased, reached a maximum, and then decreased, in several different values of modulation depth, as the rate of pseudo-spontaneous spikes increased. This may imply a resonance phenomenon dependent on the rate of pseudo-spontaneous spikes generated by electric stimuli in the ANF model. These findings may play a key role in the design of better cochlear prostheses.
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Brown MC, Drottar M, Benson TE, Darrow K. Commissural axons of the mouse cochlear nucleus. J Comp Neurol 2013; 521:1683-96. [PMID: 23124982 DOI: 10.1002/cne.23257] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Revised: 08/07/2012] [Accepted: 10/26/2012] [Indexed: 11/10/2022]
Abstract
The axons of commissural neurons that project from one cochlear nucleus to the other were studied after labeling with anterograde tracer. Injections were made into the dorsal subdivision of the cochlear nucleus in order to restrict labeling only to the group of commissural neurons that gave off collaterals to, or were located in, this subdivision. The number of labeled commissural axons in each injection was correlated with the number of labeled radiate multipolar neurons, suggesting radiate neurons as the predominant origin of the axons. The radiate commissural axons are thick and myelinated, and they exit the dorsal acoustic stria of the injected cochlear nucleus to cross the brainstem in the dorsal half, near the crossing position of the olivocochlear bundle. They enter the opposite cochlear nucleus via the dorsal and ventral acoustic stria and at its medial border. Reconstructions of single axons demonstrate that terminations are mostly in the core and typically within a single subdivision of the cochlear nucleus. Extents of termination range from narrow to broad along both the dorsoventral (i.e., tonotopic) and the rostrocaudal dimensions. In the electron microscope, labeled swellings form synapses that are symmetric (in that there is little postsynaptic density), a characteristic of inhibitory synapses. Our labeled axons do not appear to include excitatory commissural axons that end in edge regions of the nucleus. Radiate commissural axons could mediate the broadband inhibition observed in responses to contralateral sound, and they may balance input from the two ears with a quick time course.
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Affiliation(s)
- M Christian Brown
- Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114, USA.
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Furman AC, Kujawa SG, Liberman MC. Noise-induced cochlear neuropathy is selective for fibers with low spontaneous rates. J Neurophysiol 2013; 110:577-86. [PMID: 23596328 DOI: 10.1152/jn.00164.2013] [Citation(s) in RCA: 526] [Impact Index Per Article: 47.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Acoustic overexposure can cause a permanent loss of auditory nerve fibers without destroying cochlear sensory cells, despite complete recovery of cochlear thresholds (Kujawa and Liberman 2009), as measured by gross neural potentials such as the auditory brainstem response (ABR). To address this nominal paradox, we recorded responses from single auditory nerve fibers in guinea pigs exposed to this type of neuropathic noise (4- to 8-kHz octave band at 106 dB SPL for 2 h). Two weeks postexposure, ABR thresholds had recovered to normal, while suprathreshold ABR amplitudes were reduced. Both thresholds and amplitudes of distortion-product otoacoustic emissions fully recovered, suggesting recovery of hair cell function. Loss of up to 30% of auditory-nerve synapses on inner hair cells was confirmed by confocal analysis of the cochlear sensory epithelium immunostained for pre- and postsynaptic markers. In single fiber recordings, at 2 wk postexposure, frequency tuning, dynamic range, postonset adaptation, first-spike latency and its variance, and other basic properties of auditory nerve response were all completely normal in the remaining fibers. The only physiological abnormality was a change in population statistics suggesting a selective loss of fibers with low- and medium-spontaneous rates. Selective loss of these high-threshold fibers would explain how ABR thresholds can recover despite such significant noise-induced neuropathy. A selective loss of high-threshold fibers may contribute to the problems of hearing in noisy environments that characterize the aging auditory system.
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Affiliation(s)
- Adam C Furman
- Department of Otology and Laryngology, Harvard Medical School, Boston, MA, USA
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