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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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Seicol BJ, Guo Z, Garrity K, Xie R. Potential uses of auditory nerve stimulation to modulate immune responses in the inner ear and auditory brainstem. Front Integr Neurosci 2023; 17:1294525. [PMID: 38162822 PMCID: PMC10755874 DOI: 10.3389/fnint.2023.1294525] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Accepted: 12/01/2023] [Indexed: 01/03/2024] Open
Abstract
Bioelectronic medicine uses electrical stimulation of the nervous system to improve health outcomes throughout the body primarily by regulating immune responses. This concept, however, has yet to be applied systematically to the auditory system. There is growing interest in how cochlear damage and associated neuroinflammation may contribute to hearing loss. In conjunction with recent findings, we propose here a new perspective, which could be applied alongside advancing technologies, to use auditory nerve (AN) stimulation to modulate immune responses in hearing health disorders and following surgeries for auditory implants. In this article we will: (1) review the mechanisms of inflammation in the auditory system in relation to various forms of hearing loss, (2) explore nerve stimulation to reduce inflammation throughout the body and how similar neural-immune circuits likely exist in the auditory system (3) summarize current methods for stimulating the auditory system, particularly the AN, and (4) propose future directions to use bioelectronic medicine to ameliorate harmful immune responses in the inner ear and auditory brainstem to treat refractory conditions. We will illustrate how current knowledge from bioelectronic medicine can be applied to AN stimulation to resolve inflammation associated with implantation and disease. Further, we suggest the necessary steps to get discoveries in this emerging field from bench to bedside. Our vision is a future for AN stimulation that includes additional protocols as well as advances in devices to target and engage neural-immune circuitry for therapeutic benefits.
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Affiliation(s)
- Benjamin J. Seicol
- Department of Otolaryngology, The Ohio State University, Columbus, OH, United States
- Department of Neuroscience, The Ohio State University, Columbus, OH, United States
| | - Zixu Guo
- Department of Otolaryngology, The Ohio State University, Columbus, OH, United States
- Department of Neuroscience, The Ohio State University, Columbus, OH, United States
| | - Katy Garrity
- Department of Neuroscience, The Ohio State University, Columbus, OH, United States
| | - Ruili Xie
- Department of Otolaryngology, The Ohio State University, Columbus, OH, United States
- Department of Neuroscience, The Ohio State University, Columbus, OH, United States
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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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Hu S, Sun Q, Xu F, Jiang N, Gao J. Age-related hearing loss and its potential drug candidates: a systematic review. Chin Med 2023; 18:121. [PMID: 37730634 PMCID: PMC10512576 DOI: 10.1186/s13020-023-00825-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2023] [Accepted: 08/25/2023] [Indexed: 09/22/2023] Open
Abstract
BACKGROUND Age-related hearing loss (ARHL) is one of the main illnesses afflicting the aged population and has a significant negative impact on society, economy, and health. However, there is presently no appropriate therapeutic treatment of ARHL due to the absence of comprehensive trials. OBJECTIVES The goal of this review is to systematically evaluate and analyze recent statistics on the pathologic classifications, risk factors, treatment strategies, and drug candidates of ARHL, including that from traditional Chinese medicine (TCM), to provide potential new approaches for preventing and treating ARHL. METHODS Literature related to ARHL was conducted in databases such as PubMed, WOS, China National Knowledge Infrastructure (CNKI), and Wanfang from the establishment of the database to Jan, 2023. The pathology, causal factor, pathophysiological mechanism, treatment strategy, and the drug candidate of ARHL were extracted and pooled for synthesis. RESULTS Many hypotheses about the etiology of ARHL are based on genetic and environmental elements. Most of the current research on the pathology of ARHL focuses on oxidative damage, mitochondrial dysfunction, inflammation, cochlear blood flow, ion homeostasis, etc. In TCM, herbs belonging to the kidney, lung, and liver meridians exhibit good hearing protection. Seven herbs belonging to the kidney meridian, 9 belonging to the lung meridian, and 4 belonging to the liver meridian were ultimately retrieved in this review, such as Polygonum multiflorum Thunb., Panax ginseng C.A. Mey, and Pueraria lobata (Willd.) Ohwi. Their active compounds, 2,3,4',5-Tetrahydroxystilbene-2-O-D-glucoside, ginsenoside Rb1, and puerarin, may act as the molecular substance for their anti-ARHL efficacy, and show anti-oxidative, neuroprotective, anti-inflammatory, anti-apoptotic, or mitochondrial protective effects. CONCLUSION Anti-oxidants, modulators of mitochondrial function, anti-inflammation agents, vasodilators, K+ channel openers, Ca2+ channel blockers, JNK inhibitors, and nerve growth factors/neurotrophic factors all contribute to hearing protection, and herbs are an important source of potential anti-ARHL drugs.
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Affiliation(s)
- Shiyu Hu
- School of Pharmaceutical Sciences, Zhejiang Chinese Medical University, Hangzhou, 310053, Zhejiang, People's Republic of China
| | - Qingru Sun
- School of Pharmaceutical Sciences, Zhejiang Chinese Medical University, Hangzhou, 310053, Zhejiang, People's Republic of China
| | - Fei Xu
- School of Medical Technology and Information Engineering, Zhejiang Chinese Medical University, Hangzhou, 310053, Zhejiang, People's Republic of China
| | - Ninghua Jiang
- Department of Pharmacy, The Second Affiliated Hospital of Jiaxing University, Jiaxing, 314000, Zhejiang, People's Republic of China
| | - Jianli Gao
- School of Pharmaceutical Sciences, Zhejiang Chinese Medical University, Hangzhou, 310053, Zhejiang, People's Republic of China.
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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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Yu X, Wang Y. Peripheral Fragile X messenger ribonucleoprotein is required for the timely closure of a critical period for neuronal susceptibility in the ventral cochlear nucleus. Front Cell Neurosci 2023; 17:1186630. [PMID: 37305436 PMCID: PMC10248243 DOI: 10.3389/fncel.2023.1186630] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2023] [Accepted: 05/08/2023] [Indexed: 06/13/2023] Open
Abstract
Alterations in neuronal plasticity and critical periods are common across neurodevelopmental diseases, including Fragile X syndrome (FXS), the leading single-gene cause of autism. Characterized with sensory dysfunction, FXS is the result of gene silencing of Fragile X messenger ribonucleoprotein 1 (FMR1) and loss of its product, Fragile X messenger ribonucleoprotein (FMRP). The mechanisms underlying altered critical period and sensory dysfunction in FXS are obscure. Here, we performed genetic and surgical deprivation of peripheral auditory inputs in wildtype and Fmr1 knockout (KO) mice across ages and investigated the effects of global FMRP loss on deafferentation-induced neuronal changes in the ventral cochlear nucleus (VCN) and auditory brainstem responses. The degree of neuronal cell loss during the critical period was unchanged in Fmr1 KO mice. However, the closure of the critical period was delayed. Importantly, this delay was temporally coincidental with reduced hearing sensitivity, implying an association with sensory inputs. Functional analyses further identified early-onset and long-lasting alterations in signal transmission from the spiral ganglion to the VCN, suggesting a peripheral site of FMRP action. Finally, we generated conditional Fmr1 KO (cKO) mice with selective deletion of FMRP in spiral ganglion but not VCN neurons. cKO mice recapitulated the delay in the VCN critical period closure in Fmr1 KO mice, confirming an involvement of cochlear FMRP in shaping the temporal features of neuronal critical periods in the brain. Together, these results identify a novel peripheral mechanism of neurodevelopmental pathogenesis.
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Affiliation(s)
| | - Yuan Wang
- Program in Neuroscience, Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL, United States
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Wang M, Zhang C, Lin S, Xie R. Dendritic Degeneration and Altered Synaptic Innervation of a Central Auditory Neuron During Age-related Hearing Loss. Neuroscience 2023; 514:25-37. [PMID: 36738912 PMCID: PMC9992229 DOI: 10.1016/j.neuroscience.2023.01.037] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2022] [Revised: 01/08/2023] [Accepted: 01/30/2023] [Indexed: 02/05/2023]
Abstract
Cellular morphology and synaptic configuration are key determinants of neuronal function and are often modified under pathological conditions. In the first nucleus of the central auditory system, the cochlear nucleus (CN), principal bushy neurons specialize in processing temporal information of sound critical for hearing. These neurons alter their physiological properties during aging that contribute to age-related hearing loss (ARHL). The structural basis of such changes remains unclear, especially age-related modifications in their dendritic morphology and the innervating auditory nerve (AN) synapses. Using young (2-5 months) and aged (28-33 months) CBA/CaJ mice of either sex, we filled individual bushy neurons with fluorescent dye in acute brain slices to characterize their dendritic morphology, followed by immunostaining against vesicular glutamate transporter 1 (VGluT1) and calretinin (CR) to identify innervating AN synapses. We found that dendritic morphology of aged bushy neurons had significantly reduced complexity, suggesting age-dependent dendritic degeneration, especially in neurons with predominantly non-CR-expressing synapses on the soma. These dendrites were innervated by AN bouton synapses, which were predominantly non-CR-expressing in young mice but had increased proportion of CR-expressing synapses in old mice. While somatic AN synapses degenerated substantially with age, as quantified by VGluT1-labeled puncta volume, no significant difference was observed in the total volume of dendritic synapses between young and old mice. Consequently, synaptic density on dendrites was significantly higher in old mice. The findings suggest that dendritic degeneration and altered synaptic innervation in bushy neurons during aging may underlie their changed physiological activity and contribute to the development of ARHL.
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Affiliation(s)
- Meijian Wang
- Department of Otolaryngology, The Ohio State University, Columbus, OH, USA
| | - Chuangeng Zhang
- Department of Otolaryngology, The Ohio State University, Columbus, OH, USA
| | - Shengyin Lin
- Department of Otolaryngology, The Ohio State University, Columbus, OH, USA
| | - Ruili Xie
- Department of Otolaryngology, The Ohio State University, Columbus, OH, USA; Department of Neuroscience, The Ohio State University, Columbus, OH, USA.
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Chequer Charan D, Hua Y, Wang H, Huang W, Wang F, Elgoyhen AB, Boergens KM, Di Guilmi MN. Volume electron microscopy reveals age-related circuit remodeling in the auditory brainstem. Front Cell Neurosci 2022; 16:1070438. [PMID: 36589288 PMCID: PMC9799098 DOI: 10.3389/fncel.2022.1070438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Accepted: 11/21/2022] [Indexed: 12/23/2022] Open
Abstract
The medial nucleus of the trapezoid body (MNTB) is an integral component of the auditory brainstem circuitry involved in sound localization. The giant presynaptic nerve terminal with multiple active zones, the calyx of Held (CH), is a hallmark of this nucleus, which mediates fast and synchronized glutamatergic synaptic transmission. To delineate how these synaptic structures adapt to reduced auditory afferents due to aging, we acquired and reconstructed circuitry-level volumes of mouse MNTB at different ages (3 weeks, 6, 18, and 24 months) using serial block-face electron microscopy. We used C57BL/6J, the most widely inbred mouse strain used for transgenic lines, which displays a type of age-related hearing loss. We found that MNTB neurons reduce in density with age. Surprisingly we observed an average of approximately 10% of poly-innervated MNTB neurons along the mouse lifespan, with prevalence in the low frequency region. Moreover, a tonotopy-dependent heterogeneity in CH morphology was observed in young but not in older mice. In conclusion, our data support the notion that age-related hearing impairments can be in part a direct consequence of several structural alterations and circuit remodeling in the brainstem.
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Affiliation(s)
- Daniela Chequer Charan
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Dr. Héctor N. Torres, INGEBI-CONICET, Buenos Aires, Argentina
| | - Yunfeng Hua
- Shanghai Institute of Precision Medicine, Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Haoyu Wang
- Shanghai Institute of Precision Medicine, Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Wenqing Huang
- Shanghai Institute of Precision Medicine, Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Fangfang Wang
- Shanghai Institute of Precision Medicine, Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Ana Belén Elgoyhen
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Dr. Héctor N. Torres, INGEBI-CONICET, Buenos Aires, Argentina
| | - Kevin M. Boergens
- Department of Physics, The University of Illinois at Chicago, Chicago, IL, United States,*Correspondence: Kevin M. Boergens Mariano N. Di Guilmi
| | - Mariano N. Di Guilmi
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Dr. Héctor N. Torres, INGEBI-CONICET, Buenos Aires, Argentina,*Correspondence: Kevin M. Boergens Mariano N. Di Guilmi
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Wong NF, Xu-Friedman MA. Induction of Activity-Dependent Plasticity at Auditory Nerve Synapses. J Neurosci 2022; 42:6211-6220. [PMID: 35790402 PMCID: PMC9374128 DOI: 10.1523/jneurosci.0666-22.2022] [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: 04/05/2022] [Revised: 05/26/2022] [Accepted: 06/25/2022] [Indexed: 11/21/2022] Open
Abstract
Exposure to nontraumatic noise in vivo drives long-lasting changes in auditory nerve synapses, which may influence hearing, but the induction mechanisms are not known. We mimicked activity in acute slices of the cochlear nucleus from mice of both sexes by treating them with high potassium, after which voltage-clamp recordings from bushy cells indicated that auditory nerve synapses had reduced EPSC amplitude, quantal size, and vesicle release probability (P r). The effects of high potassium were prevented by blockers of nitric oxide (NO) synthase and protein kinase A. Treatment with the NO donor, PAPA-NONOate, also decreased P r, suggesting NO plays a central role in inducing synaptic changes. To identify the source of NO, we activated auditory nerve fibers specifically using optogenetics. Strobing for 2 h led to decreased EPSC amplitude and P r, which was prevented by antagonists against ionotropic glutamate receptors and NO synthase. This suggests that the activation of AMPA and NMDA receptors in postsynaptic targets of auditory nerve fibers drives release of NO, which acts retrogradely to cause long-term changes in synaptic function in auditory nerve synapses. This may provide insight into preventing or treating disorders caused by noise exposure.SIGNIFICANCE STATEMENT Auditory nerve fibers undergo long-lasting changes in synaptic properties in response to noise exposure in vivo, which may contribute to changes in hearing. Here, we investigated the cellular mechanisms underlying induction of synaptic changes using high potassium and optogenetic stimulation in vitro and identified important signaling pathways using pharmacology. Our results suggest that auditory nerve activity drives postsynaptic depolarization through AMPA and NMDA receptors, leading to the release of nitric oxide, which acts retrogradely to regulate presynaptic neurotransmitter release. These experiments revealed that auditory nerve synapses are unexpectedly sensitive to activity and can show dramatic, long-lasting changes in a few hours that could affect hearing.
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Affiliation(s)
- Nicole F Wong
- Department of Biological Sciences, University at Buffalo, State University of New York, Buffalo, New York 14260
| | - Matthew A Xu-Friedman
- Department of Biological Sciences, University at Buffalo, State University of New York, Buffalo, New York 14260
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10
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Farahani ED, Wouters J, van Wieringen A. Age-related hearing loss is associated with alterations in temporal envelope processing in different neural generators along the auditory pathway. Front Neurol 2022; 13:905017. [PMID: 35989932 PMCID: PMC9389009 DOI: 10.3389/fneur.2022.905017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2022] [Accepted: 07/11/2022] [Indexed: 11/22/2022] Open
Abstract
People with age-related hearing loss suffer from speech understanding difficulties, even after correcting for differences in hearing audibility. These problems are not only attributed to deficits in audibility but are also associated with changes in central temporal processing. The goal of this study is to obtain an understanding of potential alterations in temporal envelope processing for middle-aged and older persons with and without hearing impairment. The time series of activity of subcortical and cortical neural generators was reconstructed using a minimum-norm imaging technique. This novel technique allows for reconstructing a wide range of neural generators with minimal prior assumptions regarding the number and location of the generators. The results indicated that the response strength and phase coherence of middle-aged participants with hearing impairment (HI) were larger than for normal-hearing (NH) ones. In contrast, for the older participants, a significantly smaller response strength and phase coherence were observed in the participants with HI than the NH ones for most modulation frequencies. Hemispheric asymmetry in the response strength was also altered in middle-aged and older participants with hearing impairment and showed asymmetry toward the right hemisphere. Our brain source analyses show that age-related hearing loss is accompanied by changes in the temporal envelope processing, although the nature of these changes varies with age.
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11
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Crozier RA, Wismer ZQ, Parra-Munevar J, Plummer MR, Davis RL. Amplification of input differences by dynamic heterogeneity in the spiral ganglion. J Neurophysiol 2022; 127:1317-1333. [PMID: 35389760 PMCID: PMC9054264 DOI: 10.1152/jn.00544.2021] [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: 12/20/2021] [Revised: 03/30/2022] [Accepted: 03/30/2022] [Indexed: 11/22/2022] Open
Abstract
A defining feature of type I primary auditory afferents that compose ∼95% of the spiral ganglion is their intrinsic electrophysiological heterogeneity. This diversity is evident both between and within unitary, rapid, and slow adaptation (UA, RA, and SA) classes indicative of specializations designed to shape sensory receptor input. But to what end? Our initial impulse is to expect the opposite: that auditory afferents fire uniformly to represent acoustic stimuli with accuracy and high fidelity. Yet this is clearly not the case. One explanation for this neural signaling strategy is to coordinate a system in which differences between input stimuli are amplified. If this is correct, then stimulus disparity enhancements within the primary afferents should be transmitted seamlessly into auditory processing pathways that utilize population coding for difference detection. Using sound localization as an example, one would expect to observe separately regulated differences in intensity level compared with timing or spectral cues within a graded tonotopic distribution. This possibility was evaluated by examining the neuromodulatory effects of cAMP on immature neurons with high excitability and slow membrane kinetics. We found that electrophysiological correlates of intensity and timing were indeed independently regulated and tonotopically distributed, depending on intracellular cAMP signaling level. These observations, therefore, are indicative of a system in which differences between signaling elements of individual stimulus attributes are systematically amplified according to auditory processing constraints. Thus, dynamic heterogeneity mediated by cAMP in the spiral ganglion has the potential to enhance the representations of stimulus input disparities transmitted into higher level difference detection circuitry.NEW & NOTEWORTHY Can changes in intracellular second messenger signaling within primary auditory afferents shift our perception of sound? Results presented herein lead to this conclusion. We found that intracellular cAMP signaling level systematically altered the kinetics and excitability of primary auditory afferents, exemplifying how dynamic heterogeneity can enhance differences between electrophysiological correlates of timing and intensity.
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Affiliation(s)
| | - Zachary Q Wismer
- AtlantiCare Regional Medical Center, Department of Family Medicine, Atlantic City, New Jersey
| | - Jeffrey Parra-Munevar
- Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, New Jersey
| | - Mark R Plummer
- Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, New Jersey
| | - Robin L Davis
- Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, New Jersey
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12
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Zhang C, Wang M, Lin S, Xie R. Calretinin-Expressing Synapses Show Improved Synaptic Efficacy with Reduced Asynchronous Release during High-Rate Activity. J Neurosci 2022; 42:2729-2742. [PMID: 35165172 PMCID: PMC8973423 DOI: 10.1523/jneurosci.1773-21.2022] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 01/27/2022] [Accepted: 02/07/2022] [Indexed: 11/21/2022] Open
Abstract
Calretinin (CR) is a major calcium binding protein widely expressed in the CNS. However, its synaptic function remains largely elusive. At the auditory synapse of the endbulb of Held, CR is selectively expressed in different subtypes. Combining electrophysiology with immunohistochemistry, we investigated the synaptic transmission at the endbulb of Held synapses with and without endogenous CR expression in mature CBA/CAJ mice of either sex. Two synapse subtypes showed similar basal synaptic transmission, except a larger quantal size in CR-expressing synapses. During high-rate stimulus trains, CR-expressing synapses showed improved synaptic efficacy with significantly less depression and lower asynchronous release, suggesting more efficient exocytosis than non-CR-expressing synapses. Conversely, CR-expressing synapses had a smaller readily releasable pool size, which was countered by higher release probability and faster synaptic recovery to support sustained release during high-rate activity. EGTA-AM treatment did not change the synaptic transmission of CR-expressing synapses, but reduced synaptic depression and decreased asynchronous release at non-CR-expressing synapses, suggesting that CR helps to minimize calcium accumulation during high-rate activity. Both synapses express parvalbumin, another calcium-binding protein with slower kinetics and higher affinity than CR, but not calbindin. Furthermore, CR-expressing synapses only express the fast isoform of vesicular glutamate transporter 1 (VGluT1), while most non-CR-expressing synapses express both VGluT1 and the slower VGluT2, which may underlie their lagged synaptic recovery. The findings suggest that, paired with associated synaptic machinery, differential CR expression regulates synaptic efficacy among different subtypes of auditory nerve synapses to accomplish distinctive physiological functions in transmitting auditory information at high rates.SIGNIFICANCE STATEMENT CR is a major calcium-binding protein in the brain. It remains unclear how endogenous CR impacts synaptic transmission. We investigated the question at the large endbulb of Held synapses with selective CR expression and found that CR-expressing and non-CR-expressing synapses had similar release properties under basal synaptic transmission. During high-rate activity, however, CR-expressing synapses showed improved synaptic efficacy with less depression, lower asynchronous release, and faster recovery. Furthermore, CR-expressing synapses use exclusive VGluT1 to refill synaptic vesicles, while non-CR-expressing synapses use both VGluT1 and the slower isoform of VGluT2. Our findings suggest that CR may play significant roles in promoting synaptic efficacy during high-rate activity, and selective CR expression can differentially impact signal processing among different synapses.
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Affiliation(s)
- Chuangeng Zhang
- Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, Ohio 43210
| | - Meijian Wang
- Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, Ohio 43210
| | - Shengyin Lin
- Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, Ohio 43210
| | - Ruili Xie
- Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, Ohio 43210
- Department of Neuroscience, The Ohio State University, Columbus, Ohio 43210
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13
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Seicol BJ, Lin S, Xie R. Age-Related Hearing Loss Is Accompanied by Chronic Inflammation in the Cochlea and the Cochlear Nucleus. Front Aging Neurosci 2022; 14:846804. [PMID: 35418849 PMCID: PMC8995794 DOI: 10.3389/fnagi.2022.846804] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Accepted: 03/07/2022] [Indexed: 12/24/2022] Open
Abstract
Age-related hearing loss (ARHL) is a major hearing impairment characterized by pathological changes in both the peripheral and central auditory systems. Low-grade inflammation was observed in the cochlea of deceased human subjects with ARHL and animal models of early onset ARHL, which suggests that inflammation contributes to the development of ARHL. However, it remains elusive how chronic inflammation progresses during normal aging in the cochlea, and especially the accompanying changes of neuroinflammation in the central auditory system. To address this, we investigated chronic inflammation in both the cochlea and the cochlear nucleus (CN) of CBA/CaJ mice, an inbred mouse strain that undergoes normal aging and develops human, like-late-onset ARHL. Using immunohistochemistry, confocal microscopy, and quantitative image processing, we measured the accumulation and activation of macrophages in the cochlea and microglia in the CN using their shared markers: ionized calcium binding adaptor molecule 1 (Iba1) and CD68—a marker of phagocytic activity. We found progressive increases in the area covered by Iba1-labeled macrophages and enhanced CD68 staining in the osseous spiral lamina of the cochlea that correlated with elevated ABR threshold across the lifespan. During the process, we further identified significant increases in microglial activation and C1q deposition in the CN, indicating increased neuroinflammation and complement activation in the central auditory system. Our study suggests that during normal aging, chronic inflammation occurs in both the peripheral and the central auditory system, which may contribute in coordination to the development of ARHL.
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Affiliation(s)
- Benjamin J. Seicol
- Department of Otolaryngology—Head and Neck Surgery, The Ohio State University, Columbus, OH, United States
- Department of Neuroscience, The Ohio State University, Columbus, OH, United States
| | - Shengyin Lin
- Department of Otolaryngology—Head and Neck Surgery, The Ohio State University, Columbus, OH, United States
| | - Ruili Xie
- Department of Otolaryngology—Head and Neck Surgery, The Ohio State University, Columbus, OH, United States
- Department of Neuroscience, The Ohio State University, Columbus, OH, United States
- *Correspondence: Ruili Xie
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14
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Elliott KL, Fritzsch B, Yamoah EN, Zine A. Age-Related Hearing Loss: Sensory and Neural Etiology and Their Interdependence. Front Aging Neurosci 2022; 14:814528. [PMID: 35250542 PMCID: PMC8891613 DOI: 10.3389/fnagi.2022.814528] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2021] [Accepted: 01/03/2022] [Indexed: 12/19/2022] Open
Abstract
Age-related hearing loss (ARHL) is a common, increasing problem for older adults, affecting about 1 billion people by 2050. We aim to correlate the different reductions of hearing from cochlear hair cells (HCs), spiral ganglion neurons (SGNs), cochlear nuclei (CN), and superior olivary complex (SOC) with the analysis of various reasons for each one on the sensory deficit profiles. Outer HCs show a progressive loss in a basal-to-apical gradient, and inner HCs show a loss in a apex-to-base progression that results in ARHL at high frequencies after 70 years of age. In early neonates, SGNs innervation of cochlear HCs is maintained. Loss of SGNs results in a considerable decrease (~50% or more) of cochlear nuclei in neonates, though the loss is milder in older mice and humans. The dorsal cochlear nuclei (fusiform neurons) project directly to the inferior colliculi while most anterior cochlear nuclei reach the SOC. Reducing the number of neurons in the medial nucleus of the trapezoid body (MNTB) affects the interactions with the lateral superior olive to fine-tune ipsi- and contralateral projections that may remain normal in mice, possibly humans. The inferior colliculi receive direct cochlear fibers and second-order fibers from the superior olivary complex. Loss of the second-order fibers leads to hearing loss in mice and humans. Although ARHL may arise from many complex causes, HC degeneration remains the more significant problem of hearing restoration that would replace the cochlear implant. The review presents recent findings of older humans and mice with hearing loss.
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Affiliation(s)
- Karen L. Elliott
- Department of Biology, University of Iowa, Iowa City, IA, United States
| | - Bernd Fritzsch
- Department of Biology, University of Iowa, Iowa City, IA, United States
- *Correspondence: Bernd Fritzsch
| | - Ebenezer N. Yamoah
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, NV, United States
| | - Azel Zine
- LBN, Laboratory of Bioengineering and Nanoscience, University of Montpellier, Montpellier, France
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15
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Liu W, Liu Q, Crozier RA, Davis RL. Analog Transmission of Action Potential Fine Structure in Spiral Ganglion Axons. J Neurophysiol 2021; 126:888-905. [PMID: 34346782 DOI: 10.1152/jn.00237.2021] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Action potential waveforms generated at the axon initial segment (AIS) are specialized between and within neuronal classes. But is the fine structure of each electrical event retained when transmitted along myelinated axons or is it rapidly and uniformly transmitted to be modified again at the axon terminal? To address this issue action potential axonal transmission was evaluated in a class of primary sensory afferents that possess numerous types of voltage-gated ion channels underlying a complex repertoire of endogenous firing patterns. In addition to their signature intrinsic electrophysiological heterogeneity, spiral ganglion neurons are uniquely designed. The bipolar, myelinated somata of type I neurons are located within the conduction pathway, requiring that action potentials generated at the first heminode must be conducted through their electrically excitable membrane. We utilized this unusual axonal-like morphology to serve as a window into action potential transmission to compare locally-evoked action potential profiles to those generated peripherally at their glutamatergic synaptic connections with hair cell receptors. These comparisons showed that the distinctively-shaped somatic action potentials were highly correlated with the nodally-generated, invading ones for each neuron. This result indicates that the fine structure of the action potential waveform is maintained axonally, thus supporting the concept that analog signaling is incorporated into each digitally-transmitted action potential in the specialized primary auditory afferents.
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Affiliation(s)
- Wenke Liu
- Department of Cell Biology and Neuroscience, Rutgers, The State University of New Jersey, Piscataway, NJ, United States.,Institute for System Genetics, New York University School of Medicine, New York, NY, United States
| | - Qing Liu
- Department of Cell Biology and Neuroscience, Rutgers, The State University of New Jersey, Piscataway, NJ, United States.,Inscopix, Inc., Palo Alto, California, United States
| | - Robert A Crozier
- Department of Cell Biology and Neuroscience, Rutgers, The State University of New Jersey, Piscataway, NJ, United States.,Synergy Pharmaceuticals Inc., New York, NY, United States
| | - Robin L Davis
- Department of Cell Biology and Neuroscience, Rutgers, The State University of New Jersey, Piscataway, NJ, United States
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16
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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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17
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Shityakov S, Hayashi K, Störk S, Scheper V, Lenarz T, Förster CY. The Conspicuous Link between Ear, Brain and Heart-Could Neurotrophin-Treatment of Age-Related Hearing Loss Help Prevent Alzheimer's Disease and Associated Amyloid Cardiomyopathy? Biomolecules 2021; 11:biom11060900. [PMID: 34204299 PMCID: PMC8235707 DOI: 10.3390/biom11060900] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2021] [Revised: 06/05/2021] [Accepted: 06/14/2021] [Indexed: 12/23/2022] Open
Abstract
Alzheimer's disease (AD), the most common cause of dementia in the elderly, is a neurodegenerative disorder associated with neurovascular dysfunction and cognitive decline. While the deposition of amyloid β peptide (Aβ) and the formation of neurofibrillary tangles (NFTs) are the pathological hallmarks of AD-affected brains, the majority of cases exhibits a combination of comorbidities that ultimately lead to multi-organ failure. Of particular interest, it can be demonstrated that Aβ pathology is present in the hearts of patients with AD, while the formation of NFT in the auditory system can be detected much earlier than the onset of symptoms. Progressive hearing impairment may beget social isolation and accelerate cognitive decline and increase the risk of developing dementia. The current review discusses the concept of a brain-ear-heart axis by which Aβ and NFT inhibition could be achieved through targeted supplementation of neurotrophic factors to the cochlea and the brain. Such amyloid inhibition might also indirectly affect amyloid accumulation in the heart, thus reducing the risk of developing AD-associated amyloid cardiomyopathy and cardiovascular disease.
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Affiliation(s)
- Sergey Shityakov
- Department of Anaesthesiology, Intensive Care, Emergency and Pain Medicine, University Hospital Würzburg, D-97080 Würzburg, Germany;
- Infochemistry Scientific Center, Laboratory of Chemoinformatics, ITMO University, 191002 Saint-Petersburg, Russia
| | - Kentaro Hayashi
- Advanced Stroke Center, Shimane University Hospital, 89-1 Enya, Shimane, Izumo 693-8501, Japan;
| | - Stefan Störk
- Comprehensive Heart Failure Q9 Center, University of Würzburg, D-97080 Würzburg, Germany;
| | - Verena Scheper
- Department of Otolaryngology, Hannover Medical School and Cluster of Excellence “Hearing4All”, 30625 Hannover, Germany;
| | - Thomas Lenarz
- Department of Otolaryngology, Hannover Medical School and Cluster of Excellence “Hearing4All”, 30625 Hannover, Germany;
- Correspondence: (T.L.); (C.Y.F.)
| | - Carola Y. Förster
- Department of Anaesthesiology, Intensive Care, Emergency and Pain Medicine, University Hospital Würzburg, D-97080 Würzburg, Germany;
- Correspondence: (T.L.); (C.Y.F.)
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18
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Encina-Llamas G, Dau T, Epp B. On the use of envelope following responses to estimate peripheral level compression in the auditory system. Sci Rep 2021; 11:6962. [PMID: 33772043 PMCID: PMC7997911 DOI: 10.1038/s41598-021-85850-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Accepted: 03/08/2021] [Indexed: 12/22/2022] Open
Abstract
Individual estimates of cochlear compression may provide complementary information to traditional audiometric hearing thresholds in disentangling different types of peripheral cochlear damage. Here we investigated the use of the slope of envelope following response (EFR) magnitude-level functions obtained from four simultaneously presented amplitude modulated tones with modulation frequencies of 80-100 Hz as a proxy of peripheral level compression. Compression estimates in individual normal hearing (NH) listeners were consistent with previously reported group-averaged compression estimates based on psychoacoustical and distortion-product oto-acoustic emission (DPOAE) measures in human listeners. They were also similar to basilar membrane (BM) compression values measured invasively in non-human mammals. EFR-based compression estimates in hearing-impaired listeners were less compressive than those for the NH listeners, consistent with a reduction of BM compression. Cochlear compression was also estimated using DPOAEs in the same NH listeners. DPOAE estimates were larger (less compressive) than EFRs estimates, showing no correlation. Despite the numerical concordance between EFR-based compression estimates and group-averaged estimates from other methods, simulations using an auditory nerve (AN) model revealed that compression estimates based on EFRs might be highly influenced by contributions from off-characteristic frequency (CF) neural populations. This compromises the possibility to estimate on-CF (i.e., frequency-specific or "local") peripheral level compression with EFRs.
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Affiliation(s)
- Gerard Encina-Llamas
- Hearing Systems Section, Department of Health Technology, Technical University of Denmark (DTU), 2800, Kongens Lyngby, Denmark.
| | - Torsten Dau
- Hearing Systems Section, Department of Health Technology, Technical University of Denmark (DTU), 2800, Kongens Lyngby, Denmark
| | - Bastian Epp
- Hearing Systems Section, Department of Health Technology, Technical University of Denmark (DTU), 2800, Kongens Lyngby, Denmark
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19
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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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20
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Lu Y. Biased synaptopathy as a central mechanism of age-related hearing loss. J Physiol 2021; 599:1723-1724. [PMID: 33517580 DOI: 10.1113/jp281348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Accepted: 01/29/2021] [Indexed: 11/08/2022] Open
Affiliation(s)
- Yong Lu
- Hearing Research Group, Department of Anatomy and Neurobiology, College of Medicine, Northeast Ohio Medical University, Rootstown, OH, USA
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