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Barrallo-Gimeno A, Llorens J. Hair cell toxicology: With the help of a little fish. Front Cell Dev Biol 2022; 10:1085225. [PMID: 36582469 PMCID: PMC9793777 DOI: 10.3389/fcell.2022.1085225] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Accepted: 11/28/2022] [Indexed: 12/15/2022] Open
Abstract
Hearing or balance loss are disabling conditions that have a serious impact in those suffering them, especially when they appear in children. Their ultimate cause is frequently the loss of function of mechanosensory hair cells in the inner ear. Hair cells can be damaged by environmental insults, like noise or chemical agents, known as ototoxins. Two of the most common ototoxins are life-saving medications: cisplatin against solid tumors, and aminoglycoside antibiotics to treat infections. However, due to their localization inside the temporal bone, hair cells are difficult to study in mammals. As an alternative animal model, zebrafish larvae have hair cells similar to those in mammals, some of which are located in a fish specific organ on the surface of the skin, the lateral line. This makes them easy to observe in vivo and readily accessible for ototoxins or otoprotective substances. These features have made possible advances in the study of the mechanisms mediating ototoxicity or identifying new potential ototoxins. Most importantly, the small size of the zebrafish larvae has allowed screening thousands of molecules searching for otoprotective agents in a scale that would be highly impractical in rodent models. The positive hits found can then start the long road to reach clinical settings to prevent hearing or balance loss.
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Affiliation(s)
- Alejandro Barrallo-Gimeno
- Department de Ciències Fisiològiques, Facultat de Medicina i Ciències de la Salut, Campus de Bellvitge, Universitat de Barcelona, L’Hospitalet de Llobregat, Spain,Institut de Neurociències, Universitat de Barcelona, Barcelona, Spain,Institut D'Investigació Biomèdica de Bellvitge, IDIBELL, L’Hospitalet de Llobregat, Spain,*Correspondence: Alejandro Barrallo-Gimeno,
| | - Jordi Llorens
- Department de Ciències Fisiològiques, Facultat de Medicina i Ciències de la Salut, Campus de Bellvitge, Universitat de Barcelona, L’Hospitalet de Llobregat, Spain,Institut de Neurociències, Universitat de Barcelona, Barcelona, Spain,Institut D'Investigació Biomèdica de Bellvitge, IDIBELL, L’Hospitalet de Llobregat, Spain
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2
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Coffin AB, Dale E, Doppenberg E, Fearington F, Hayward T, Hill J, Molano O. Putative COVID-19 therapies imatinib, lopinavir, ritonavir, and ivermectin cause hair cell damage: A targeted screen in the zebrafish lateral line. Front Cell Neurosci 2022; 16:941031. [PMID: 36090793 PMCID: PMC9448854 DOI: 10.3389/fncel.2022.941031] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Accepted: 07/29/2022] [Indexed: 11/13/2022] Open
Abstract
The biomedical community is rapidly developing COVID-19 drugs to bring much-need therapies to market, with over 900 drugs and drug combinations currently in clinical trials. While this pace of drug development is necessary, the risk of producing therapies with significant side-effects is also increased. One likely side-effect of some COVID-19 drugs is hearing loss, yet hearing is not assessed during preclinical development or clinical trials. We used the zebrafish lateral line, an established model for drug-induced sensory hair cell damage, to assess the ototoxic potential of seven drugs in clinical trials for treatment of COVID-19. We found that ivermectin, lopinavir, imatinib, and ritonavir were significantly toxic to lateral line hair cells. By contrast, the approved COVID-19 therapies dexamethasone and remdesivir did not cause damage. We also did not observe damage from the antibiotic azithromycin. Neither lopinavir nor ritonavir altered the number of pre-synaptic ribbons per surviving hair cell, while there was an increase in ribbons following imatinib or ivermectin exposure. Damage from lopinavir, imatinib, and ivermectin was specific to hair cells, with no overall cytotoxicity noted following TUNEL labeling. Ritonavir may be generally cytotoxic, as determined by an increase in the number of TUNEL-positive non-hair cells following ritonavir exposure. Pharmacological inhibition of the mechanotransduction (MET) channel attenuated damage caused by lopinavir and ritonavir but did not alter imatinib or ivermectin toxicity. These results suggest that lopinavir and ritonavir may enter hair cells through the MET channel, similar to known ototoxins such as aminoglycoside antibiotics. Finally, we asked if ivermectin was ototoxic to rats in vivo. While ivermectin is not recommended by the FDA for treating COVID-19, many people have chosen to take ivermectin without a doctor’s guidance, often with serious side-effects. Rats received daily subcutaneous injections for 10 days with a clinically relevant ivermectin dose (0.2 mg/kg). In contrast to our zebrafish assays, ivermectin did not cause ototoxicity in rats. Our research suggests that some drugs in clinical trials for COVID-19 may be ototoxic. This work can help identify drugs with the fewest side-effects and determine which therapies warrant audiometric monitoring.
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Affiliation(s)
- Allison B. Coffin
- Department of Integrative Physiology and Neuroscience, Washington State University, Vancouver, WA, United States
- College of Arts and Sciences, Washington State University, Vancouver, WA, United States
- *Correspondence: Allison B. Coffin,
| | - Emily Dale
- College of Arts and Sciences, Washington State University, Vancouver, WA, United States
| | - Emilee Doppenberg
- College of Arts and Sciences, Washington State University, Vancouver, WA, United States
| | - Forrest Fearington
- College of Arts and Sciences, Washington State University, Vancouver, WA, United States
| | - Tamasen Hayward
- College of Arts and Sciences, Washington State University, Vancouver, WA, United States
| | - Jordan Hill
- College of Arts and Sciences, Washington State University, Vancouver, WA, United States
| | - Olivia Molano
- College of Arts and Sciences, Washington State University, Vancouver, WA, United States
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3
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Dietz GP, Bähr M. Editorial: Special issue on inner ear biology. Mol Cell Neurosci 2022; 121:103753. [DOI: 10.1016/j.mcn.2022.103753] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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4
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García-Añoveros J, Clancy JC, Foo CZ, García-Gómez I, Zhou Y, Homma K, Cheatham MA, Duggan A. Tbx2 is a master regulator of inner versus outer hair cell differentiation. Nature 2022; 605:298-303. [PMID: 35508658 PMCID: PMC9803360 DOI: 10.1038/s41586-022-04668-3] [Citation(s) in RCA: 32] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Accepted: 03/21/2022] [Indexed: 01/03/2023]
Abstract
The cochlea uses two types of mechanosensory cell to detect sounds. A single row of inner hair cells (IHCs) synapse onto neurons to transmit sensory information to the brain, and three rows of outer hair cells (OHCs) selectively amplify auditory inputs1. So far, two transcription factors have been implicated in the specific differentiation of OHCs, whereas, to our knowledge, none has been identified in the differentiation of IHCs2-4. One such transcription factor for OHCs, INSM1, acts during a crucial embryonic period to consolidate the OHC fate, preventing OHCs from transdifferentiating into IHCs2. In the absence of INSM1, embryonic OHCs misexpress a core set of IHC-specific genes, which we predict are involved in IHC differentiation. Here we find that one of these genes, Tbx2, is a master regulator of IHC versus OHC differentiation in mice. Ablation of Tbx2 in embryonic IHCs results in their development as OHCs, expressing early OHC markers such as Insm1 and eventually becoming completely mature OHCs in the position of IHCs. Furthermore, Tbx2 is epistatic to Insm1: in the absence of both genes, cochleae generate only OHCs, which suggests that TBX2 is necessary for the abnormal transdifferentiation of INSM1-deficient OHCs into IHCs, as well as for normal IHC differentiation. Ablation of Tbx2 in postnatal, largely differentiated IHCs makes them transdifferentiate directly into OHCs, replacing IHC features with those of mature and not embryonic OHCs. Finally, ectopic expression of Tbx2 in OHCs results in their transdifferentiation into IHCs. Hence, Tbx2 is both necessary and sufficient to make IHCs distinct from OHCs and maintain this difference throughout development.
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Affiliation(s)
- Jaime García-Añoveros
- Department of Anesthesiology, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA.,Department of Neurology, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA.,Department of Neuroscience, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA.,Hugh Knowles Center for Clinical and Basic Science in Hearing and its Disorders, Northwestern University, Chicago, IL, USA.,These authors jointly supervised this work: Jaime García-Añoveros, Anne Duggan.,Correspondence and requests for materials should be addressed to Jaime García-Añoveros or Anne Duggan. ;
| | - John C. Clancy
- Department of Anesthesiology, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA
| | - Chuan Zhi Foo
- Department of Anesthesiology, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA.,Driskill Graduate Program in Life Sciences, Northwestern University, Chicago, IL, USA
| | - Ignacio García-Gómez
- Department of Anesthesiology, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA
| | - Yingjie Zhou
- Department of Anesthesiology, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA.,Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL, USA
| | - Kazuaki Homma
- Hugh Knowles Center for Clinical and Basic Science in Hearing and its Disorders, Northwestern University, Chicago, IL, USA.,Department of Otolaryngology–Head and Neck Surgery, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA
| | - Mary Ann Cheatham
- Hugh Knowles Center for Clinical and Basic Science in Hearing and its Disorders, Northwestern University, Chicago, IL, USA.,Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL, USA
| | - Anne Duggan
- Department of Anesthesiology, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA.,These authors jointly supervised this work: Jaime García-Añoveros, Anne Duggan.,Correspondence and requests for materials should be addressed to Jaime García-Añoveros or Anne Duggan. ;
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5
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Plazas PV, Elgoyhen AB. The Cholinergic Lateral Line Efferent Synapse: Structural, Functional and Molecular Similarities With Those of the Cochlea. Front Cell Neurosci 2021; 15:765083. [PMID: 34712122 PMCID: PMC8545859 DOI: 10.3389/fncel.2021.765083] [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: 08/26/2021] [Accepted: 09/21/2021] [Indexed: 11/25/2022] Open
Abstract
Vertebrate hair cell (HC) systems are innervated by efferent fibers that modulate their response to external stimuli. In mammals, the best studied efferent-HC synapse, the cholinergic medial olivocochlear (MOC) efferent system, makes direct synaptic contacts with HCs. The net effect of MOC activity is to hyperpolarize HCs through the activation of α9α10 nicotinic cholinergic receptors (nAChRs) and the subsequent activation of Ca2+-dependent SK2 potassium channels. A serious obstacle in research on many mammalian sensory systems in their native context is that their constituent neurons are difficult to access even in newborn animals, hampering circuit observation, mapping, or controlled manipulation. By contrast, fishes and amphibians have a superficial and accessible mechanosensory system, the lateral line (LL), which circumvents many of these problems. LL responsiveness is modulated by efferent neurons which aid to distinguish between external and self-generated stimuli. One component of the LL efferent system is cholinergic and its activation inhibits LL afferent activity, similar to what has been described for MOC efferents. The zebrafish (Danio rerio) has emerged as a powerful model system for studying human hearing and balance disorders, since LL HC are structurally and functionally analogous to cochlear HCs, but are optically and pharmacologically accessible within an intact specimen. Complementing mammalian studies, zebrafish have been used to gain significant insights into many facets of HC biology, including mechanotransduction and synaptic physiology as well as mechanisms of both hereditary and acquired HC dysfunction. With the rise of the zebrafish LL as a model in which to study auditory system function and disease, there has been an increased interest in studying its efferent system and evaluate the similarity between mammalian and piscine efferent synapses. Advances derived from studies in zebrafish include understanding the effect of the LL efferent system on HC and afferent activity, and revealing that an α9-containing nAChR, functionally coupled to SK channels, operates at the LL efferent synapse. In this review, we discuss the tools and findings of these recent investigations into zebrafish efferent-HC synapse, their commonalities with the mammalian counterpart and discuss several emerging areas for future studies.
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Affiliation(s)
- Paola V Plazas
- Instituto de Farmacología, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Ana Belén Elgoyhen
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
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6
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Holmgren M, Ravicz ME, Hancock KE, Strelkova O, Kallogjeri D, Indzhykulian AA, Warchol ME, Sheets L. Mechanical overstimulation causes acute injury and synapse loss followed by fast recovery in lateral-line neuromasts of larval zebrafish. eLife 2021; 10:69264. [PMID: 34665127 PMCID: PMC8555980 DOI: 10.7554/elife.69264] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Accepted: 10/18/2021] [Indexed: 12/14/2022] Open
Abstract
Excess noise damages sensory hair cells, resulting in loss of synaptic connections with auditory nerves and, in some cases, hair-cell death. The cellular mechanisms underlying mechanically induced hair-cell damage and subsequent repair are not completely understood. Hair cells in neuromasts of larval zebrafish are structurally and functionally comparable to mammalian hair cells but undergo robust regeneration following ototoxic damage. We therefore developed a model for mechanically induced hair-cell damage in this highly tractable system. Free swimming larvae exposed to strong water wave stimulus for 2 hr displayed mechanical injury to neuromasts, including afferent neurite retraction, damaged hair bundles, and reduced mechanotransduction. Synapse loss was observed in apparently intact exposed neuromasts, and this loss was exacerbated by inhibiting glutamate uptake. Mechanical damage also elicited an inflammatory response and macrophage recruitment. Remarkably, neuromast hair-cell morphology and mechanotransduction recovered within hours following exposure, suggesting severely damaged neuromasts undergo repair. Our results indicate functional changes and synapse loss in mechanically damaged lateral-line neuromasts that share key features of damage observed in noise-exposed mammalian ear. Yet, unlike the mammalian ear, mechanical damage to neuromasts is rapidly reversible.
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Affiliation(s)
- Melanie Holmgren
- Department of Otolaryngology, Washington University School of Medicine, St Louis, United States
| | - Michael E Ravicz
- Eaton-Peabody Laboratory, Massachusetts Eye and Ear, Boston, United States.,Department of Otolaryngology-Head and Neck Surgery, Harvard Medical School, Boston, United States
| | - Kenneth E Hancock
- Eaton-Peabody Laboratory, Massachusetts Eye and Ear, Boston, United States.,Department of Otolaryngology-Head and Neck Surgery, Harvard Medical School, Boston, United States
| | - Olga Strelkova
- Eaton-Peabody Laboratory, Massachusetts Eye and Ear, Boston, United States.,Department of Otolaryngology-Head and Neck Surgery, Harvard Medical School, Boston, United States
| | - Dorina Kallogjeri
- Department of Otolaryngology, Washington University School of Medicine, St Louis, United States
| | - Artur A Indzhykulian
- Eaton-Peabody Laboratory, Massachusetts Eye and Ear, Boston, United States.,Department of Otolaryngology-Head and Neck Surgery, Harvard Medical School, Boston, United States
| | - Mark E Warchol
- Department of Otolaryngology, Washington University School of Medicine, St Louis, United States.,Department of Neuroscience, Washington University School of Medicine, St Louis, United States
| | - Lavinia Sheets
- Department of Otolaryngology, Washington University School of Medicine, St Louis, United States.,Department of Developmental Biology, Washington University School of Medicine, St. Louis, United States
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7
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Duarte CM, Chapuis L, Collin SP, Costa DP, Devassy RP, Eguiluz VM, Erbe C, Gordon TAC, Halpern BS, Harding HR, Havlik MN, Meekan M, Merchant ND, Miksis-Olds JL, Parsons M, Predragovic M, Radford AN, Radford CA, Simpson SD, Slabbekoorn H, Staaterman E, Van Opzeeland IC, Winderen J, Zhang X, Juanes F. The soundscape of the Anthropocene ocean. Science 2021; 371:371/6529/eaba4658. [DOI: 10.1126/science.aba4658] [Citation(s) in RCA: 161] [Impact Index Per Article: 53.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Carlos M. Duarte
- Red Sea Research Centre (RSRC) and Computational Bioscience Research Center (CBRC), King Abdullah University of Science and Technology, Thuwal 23955, Saudi Arabia
- Arctic Research Centre, Department of Biology, Aarhus University, C.F. Møllers Allé 8, DK-8000 Århus C, Denmark
| | - Lucille Chapuis
- Biosciences, University of Exeter, Prince of Wales Road, Exeter EX4 4PS, UK
| | - Shaun P. Collin
- School of Life Sciences, La Trobe University, Bundoora, VIC 3086, Australia
| | - Daniel P. Costa
- Institute of Marine Sciences, University of California, Santa Cruz, CA 95060, USA
| | - Reny P. Devassy
- Red Sea Research Centre (RSRC) and Computational Bioscience Research Center (CBRC), King Abdullah University of Science and Technology, Thuwal 23955, Saudi Arabia
| | - Victor M. Eguiluz
- Instituto de Física Interdisciplinar y Sistemas Complejos IFISC (CSIC-UIB), E07122 Palma de Mallorca, Spain
| | - Christine Erbe
- Centre for Marine Science & Technology, Curtin University, Perth, WA 6102, Australia
| | - Timothy A. C. Gordon
- Biosciences, University of Exeter, Prince of Wales Road, Exeter EX4 4PS, UK
- Australian Institute of Marine Science, Perth, WA 6009, Australia
| | - Benjamin S. Halpern
- National Center for Ecological Analysis and Synthesis, University of California, Santa Barbara, CA 93101, USA
- Bren School of Environmental Science and Management, University of California, Santa Barbara, CA 93106, USA
| | - Harry R. Harding
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Michelle N. Havlik
- Red Sea Research Centre (RSRC) and Computational Bioscience Research Center (CBRC), King Abdullah University of Science and Technology, Thuwal 23955, Saudi Arabia
| | - Mark Meekan
- Australian Institute of Marine Science, Perth, WA 6009, Australia
| | - Nathan D. Merchant
- Centre for Environment, Fisheries and Aquaculture Science, Lowestoft NR33 0HT, UK
| | - Jennifer L. Miksis-Olds
- Center for Acoustics Research and Education, University of New Hampshire, Durham, NH 03824, USA
| | - Miles Parsons
- Centre for Marine Science & Technology, Curtin University, Perth, WA 6102, Australia
- Australian Institute of Marine Science, Perth, WA 6009, Australia
| | - Milica Predragovic
- Red Sea Research Centre (RSRC) and Computational Bioscience Research Center (CBRC), King Abdullah University of Science and Technology, Thuwal 23955, Saudi Arabia
| | - Andrew N. Radford
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Craig A. Radford
- Institute of Marine Science, Leigh Marine Laboratory, University of Auckland, P.O. Box 349, Warkworth 0941, New Zealand
| | - Stephen D. Simpson
- Biosciences, University of Exeter, Prince of Wales Road, Exeter EX4 4PS, UK
| | - Hans Slabbekoorn
- Institute of Biology, Leiden University, P.O. Box 9505, 2300 RA Leiden, Netherlands
| | | | - Ilse C. Van Opzeeland
- Alfred-Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany
| | | | - Xiangliang Zhang
- Computer, Electrical and Mathematical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955, Saudi Arabia
| | - Francis Juanes
- Department of Biology, University of Victoria, Victoria, BC, Canada
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8
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Yao Q, Wang L, Mittal R, Yan D, Richmond MT, Denyer S, Requena T, Liu K, Varshney GK, Lu Z, Liu XZ. Transcriptomic Analyses of Inner Ear Sensory Epithelia in Zebrafish. Anat Rec (Hoboken) 2019; 303:527-543. [PMID: 31883312 DOI: 10.1002/ar.24331] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Revised: 08/01/2019] [Accepted: 11/18/2019] [Indexed: 12/25/2022]
Abstract
Analysis of gene expression has the potential to assist in the understanding of multiple cellular processes including proliferation, cell-fate specification, senesence, and activity in both healthy and disease states. Zebrafish model has been increasingly used to understand the process of hearing and the development of the vertebrate auditory system. Within the zebrafish inner ear, there are three otolith organs, each containing a sensory macula of hair cells. The saccular macula is primarily involved in hearing, the utricular macula is primarily involved in balance and the function of the lagenar macula is not completely understood. The goal of this study is to understand the transcriptional differences in the sensory macula associated with different otolith organs with the intention of understanding the genetic mechanisms responsible for the distinct role each organ plays in sensory perception. The sensory maculae of the saccule, utricle, and lagena were dissected out of adult Et(krt4:GFP)sqet4 zebrafish expressing green fluorescent protein in hair cells for transcriptional analysis. The total RNAs of the maculae were isolated and analyzed by RNA GeneChip microarray. Several of the differentially expressed genes are known to be involved in deafness, otolith development and balance. Gene expression among these otolith organs was very well conserved with less than 10% of genes showing differential expression. Data from this study will help to elucidate which genes are involved in hearing and balance. Furthermore, the findings of this study will assist in the development of the zebrafish model for human hearing and balance disorders. Anat Rec, 303:527-543, 2020. © 2019 American Association for Anatomy.
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Affiliation(s)
- Qi Yao
- Department of Otolaryngology, Miller School of Medicine, University of Miami, Miami, Florida.,Department of Biology, University of Miami, Miami, Florida
| | - Lingyu Wang
- Department of Biology, University of Miami, Miami, Florida
| | - Rahul Mittal
- Department of Otolaryngology, Miller School of Medicine, University of Miami, Miami, Florida
| | - Denise Yan
- Department of Otolaryngology, Miller School of Medicine, University of Miami, Miami, Florida
| | | | - Steven Denyer
- Department of Biology, University of Miami, Miami, Florida
| | - Teresa Requena
- Genes & Human Disease Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma
| | - Kaili Liu
- Genes & Human Disease Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma
| | - Gaurav K Varshney
- Genes & Human Disease Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma
| | - Zhongmin Lu
- Department of Biology, University of Miami, Miami, Florida
| | - Xue Zhong Liu
- Department of Otolaryngology, Miller School of Medicine, University of Miami, Miami, Florida.,Department of Otolaryngology, Xiangya Hospital, Central South University, Changsha, Hunan, China
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9
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Schulz-Mirbach T, Ladich F, Plath M, Heß M. Enigmatic ear stones: what we know about the functional role and evolution of fish otoliths. Biol Rev Camb Philos Soc 2018; 94:457-482. [DOI: 10.1111/brv.12463] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Revised: 08/16/2018] [Accepted: 08/20/2018] [Indexed: 12/11/2022]
Affiliation(s)
- Tanja Schulz-Mirbach
- Department Biology II, Zoology; Ludwig-Maximilians-University; Großhaderner Strasse 2, 82152 Planegg-Martinsried Germany
| | - Friedrich Ladich
- Department of Behavioural Biology; University of Vienna; Althanstrasse 14, 1090 Vienna Austria
| | - Martin Plath
- College of Animal Science & Technology; Northwest A&F University; 22 Xinong Road, Yangling Shaanxi China
| | - Martin Heß
- Department Biology II, Zoology; Ludwig-Maximilians-University; Großhaderner Strasse 2, 82152 Planegg-Martinsried Germany
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10
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Kindt KS, Sheets L. Transmission Disrupted: Modeling Auditory Synaptopathy in Zebrafish. Front Cell Dev Biol 2018; 6:114. [PMID: 30258843 PMCID: PMC6143809 DOI: 10.3389/fcell.2018.00114] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Accepted: 08/23/2018] [Indexed: 01/04/2023] Open
Abstract
Sensorineural hearing loss is the most common form of hearing loss in humans, and results from either dysfunction in hair cells, the sensory receptors of sound, or the neurons that innervate hair cells. A specific type of sensorineural hearing loss, referred to as auditory synaptopathy, occurs when hair cells are able to detect sound but fail to transmit sound stimuli at the hair-cell synapse. Auditory synaptopathy can originate from genetic alterations that specifically disrupt hair-cell synapse function. Additionally, environmental factors such as noise exposure can leave hair cells intact but result in loss of hair-cell synapses, and represent an acquired form of auditory synaptopathy. The zebrafish model has emerged as a valuable system for studies of hair-cell function, and specifically hair-cell synaptopathy. In this review, we describe the experimental tools that have been developed to study hair-cell synapses in zebrafish. We discuss how zebrafish genetics has helped identify and define the roles of hair-cell synaptic proteins crucial for hearing in humans, and highlight how studies in zebrafish have contributed to our understanding of hair-cell synapse formation and function. In addition, we also discuss work that has used noise exposure or pharmacological mimic of noise-induced excitotoxicity in zebrafish to define cellular mechanisms underlying noise-induced hair-cell damage and synapse loss. Lastly, we highlight how future studies in zebrafish could enhance our understanding of the pathological processes underlying synapse loss in both genetic and acquired auditory synaptopathy. This knowledge is critical in order to develop therapies that protect or repair auditory synaptic contacts.
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Affiliation(s)
- Katie S. Kindt
- Section on Sensory Cell Development and Function, NIDCD/National Institutes of Health, Bethesda, MD, United States
| | - Lavinia Sheets
- Department of Otolaryngology, Washington University School of Medicine, St. Louis, MO, United States
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11
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Abstract
Sensory hair cells are specialized secondary sensory cells that mediate our senses of hearing, balance, linear acceleration, and angular acceleration (head rotation). In addition, hair cells in fish and amphibians mediate sensitivity to water movement through the lateral line system, and closely related electroreceptive cells mediate sensitivity to low-voltage electric fields in the aquatic environment of many fish species and several species of amphibian. Sensory hair cells share many structural and functional features across all vertebrate groups, while at the same time they are specialized for employment in a wide variety of sensory tasks. The complexity of hair cell structure is large, and the diversity of hair cell applications in sensory systems exceeds that seen for most, if not all, sensory cell types. The intent of this review is to summarize the more significant structural features and some of the more interesting and important physiological mechanisms that have been elucidated thus far. Outside vertebrates, hair cells are only known to exist in the coronal organ of tunicates. Electrical resonance, electromotility, and their exquisite mechanical sensitivity all contribute to the attractiveness of hair cells as a research subject.
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12
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McPherson DR, Swalla BJ. High Time for Hair Cells: An Introduction to the Symposium on Sensory Hair Cells. Integr Comp Biol 2018; 58:276-281. [PMID: 30137315 DOI: 10.1093/icb/icy070] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Sensory hair cells are highly specialized cells that form the basis for our senses of hearing, orientation to gravity, and perception of linear acceleration (head translation in space) and angular acceleration (head rotation). In many species of fish and aquatic amphibians, hair cells mediate perception of water movement through the lateral line system, and electroreceptors derived from hair cell precursors mediate electric field detection. In tunicates, cells of the mechanosensory coronal organ on the incurrent siphon meet the structural, functional, and developmental criteria to be described as hair cells, and they function to deflect large particles from entering the animal. The past two decades have witnessed significant breakthroughs in our understanding of hair cell biology and how their specialized structures influence their functions. This symposium combines the approaches of developmental biology, evolutionary biology, and physiology to share the gains of recent research in understanding hair cell function in different model systems. We brought together researchers working on sensory hair cells in organisms spanning the chordates in order to examine the depth and breadth of hair cell evolution. It is clear that these specialized cells serve a range of functions in different animals, due to evolutionary tinkering with a basic specialized cell type. This collection of papers will serve to mark the progress that has been made in this field and also stimulate the next wave of progress in this exciting field.
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Affiliation(s)
| | - Billie J Swalla
- Friday Harbor Laboratories, Friday Harbor, 620 University Road, WA 98250, USA
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Neveux S, Smith NK, Roche A, Blough BE, Pathmasiri W, Coffin AB. Natural Compounds as Occult Ototoxins? Ginkgo biloba Flavonoids Moderately Damage Lateral Line Hair Cells. J Assoc Res Otolaryngol 2016; 18:275-289. [PMID: 27896487 DOI: 10.1007/s10162-016-0604-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2016] [Accepted: 11/10/2016] [Indexed: 01/14/2023] Open
Abstract
Several drugs, including aminoglycosides and platinum-based chemotherapy agents, are well known for their ototoxic properties. However, FDA-approved drugs are not routinely tested for ototoxicity, so their potential to affect hearing often goes unrecognized. This issue is further compounded for natural products, where there is a lack of FDA oversight and the manufacturer is solely responsible for ensuring the safety of their products. Natural products such as herbal supplements are easily accessible and commonly used in the practice of traditional eastern and alternative medicine. Using the zebrafish lateral line, we screened a natural products library to identify potential ototoxins. We found that the flavonoids quercetin and kaempferol, both from the Gingko biloba plant, demonstrated significant ototoxicity, killing up to 30 % of lateral line hair cells. We then examined a third Ginkgo flavonoid, isorhamnetin, and found similar levels of ototoxicity. After flavonoid treatment, surviving hair cells demonstrated reduced uptake of the vital dye FM 1-43FX, suggesting that the health of the remaining hair cells was compromised. We then asked if these flavonoids enter hair cells through the mechanotransduction channel, which is the site of entry for many known ototoxins. High extracellular calcium or the quinoline derivative E6 berbamine significantly protected hair cells from flavonoid damage, implicating the transduction channel as a site of flavonoid uptake. Since known ototoxins activate cellular stress responses, we asked if reactive oxygen species were necessary for flavonoid ototoxicity. Co-treatment with the antioxidant D-methionine significantly protected hair cells from each flavonoid, suggesting that antioxidant therapy could prevent hair cell loss. How these products affect mammalian hair cells is still an open question and will be the target of future experiments. However, this research demonstrates the potential for ototoxic damage caused by unregulated herbal supplements and suggests that further supplement characterization is warranted.
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Affiliation(s)
- Sarah Neveux
- College of Arts and Sciences, Washington State University, Vancouver, WA, 98686, USA
| | - Nicole K Smith
- College of Arts and Sciences, Washington State University, Vancouver, WA, 98686, USA.
| | - Anna Roche
- College of Arts and Sciences, Washington State University, Vancouver, WA, 98686, USA
- Camas High School, Camas, WA, 98607, USA
| | - Bruce E Blough
- RTI International, Research Triangle Park, NC, 27709, USA
| | | | - Allison B Coffin
- College of Arts and Sciences, Washington State University, Vancouver, WA, 98686, USA.
- Department of Integrative Physiology and Neuroscience, Washington State University, Vancouver, WA, 98686, USA.
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14
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Manley GA. Comparative Auditory Neuroscience: Understanding the Evolution and Function of Ears. J Assoc Res Otolaryngol 2016; 18:1-24. [PMID: 27539715 DOI: 10.1007/s10162-016-0579-3] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Accepted: 08/01/2016] [Indexed: 11/25/2022] Open
Abstract
Comparative auditory studies make it possible both to understand the origins of modern ears and the factors underlying the similarities and differences in their performance. After all lineages of land vertebrates had independently evolved tympanic middle ears in the early Mesozoic era, the subsequent tens of millions of years led to the hearing organ of lizards, birds, and mammals becoming larger and their upper frequency limits higher. In extant species, lizard papillae remained relatively small (<2 mm), but avian papillae attained a maximum length of 11 mm, with the highest frequencies in both groups near 12 kHz. Hearing-organ sizes in modern mammals vary more than tenfold, up to >70 mm (made possible by coiling), as do their upper frequency limits (from 12 to >200 kHz). The auditory organs of the three amniote groups differ characteristically in their cellular structure, but their hearing sensitivity and frequency selectivity within their respective hearing ranges hardly differ. In the immediate primate ancestors of humans, the cochlea became larger and lowered its upper frequency limit. Modern humans show an unusual trend in frequency selectivity as a function of frequency. It is conceivable that the frequency selectivity patterns in humans were influenced in their evolution by the development of speech.
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Affiliation(s)
- Geoffrey A Manley
- Cochlear and Auditory Brainstem Physiology, Department of Neuroscience, School of Medicine and Health Sciences, Cluster of Excellence "Hearing4all", Research Centre Neurosensory Science, Carl von Ossietzky University Oldenburg, Carl von Ossietzky Strasse 9-11, 26129, Oldenburg, Germany.
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15
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Tang PC, Smith KM, Watson GM. Repair of traumatized mammalian hair cells via sea anemone repair proteins. ACTA ACUST UNITED AC 2016; 219:2265-70. [PMID: 27489215 DOI: 10.1242/jeb.135459] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 05/18/2016] [Indexed: 12/25/2022]
Abstract
Mammalian hair cells possess only a limited ability to repair damage after trauma. In contrast, sea anemones show a marked capability to repair damaged hair bundles by means of secreted repair proteins (RPs). Previously, it was found that recovery of traumatized hair cells in blind cavefish was enhanced by anemone-derived RPs; therefore, the ability of anemone RPs to assist recovery of damaged hair cells in mammals was tested here. After a 1 h incubation in RP-enriched culture media, uptake of FM1-43 by experimentally traumatized murine cochlear hair cells was restored to levels comparable to those exhibited by healthy controls. In addition, RP-treated explants had significantly more normally structured hair bundles than time-matched traumatized control explants. Collectively, these results indicate that anemone-derived RPs assist in restoring normal function and structure of experimentally traumatized hair cells of the mouse cochlea.
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Affiliation(s)
- Pei-Ciao Tang
- Department of Biology, University of Louisiana at Lafayette, Lafayette, LA 70503, USA
| | - Karen Müller Smith
- Department of Biology, University of Louisiana at Lafayette, Lafayette, LA 70503, USA
| | - Glen M Watson
- Department of Biology, University of Louisiana at Lafayette, Lafayette, LA 70503, USA
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16
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Smith ME, Monroe JD. Causes and Consequences of Sensory Hair Cell Damage and Recovery in Fishes. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 877:393-417. [PMID: 26515323 DOI: 10.1007/978-3-319-21059-9_17] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
Sensory hair cells are the mechanotransductive receptors that detect gravity, sound, and vibration in all vertebrates. Damage to these sensitive receptors often results in deficits in vestibular function and hearing. There are currently two main reasons for studying the process of hair cell loss in fishes. First, fishes, like other non-mammalian vertebrates, have the ability to regenerate hair cells that have been damaged or lost via exposure to ototoxic chemicals or acoustic overstimulation. Thus, they are used as a biomedical model to understand the process of hair cell death and regeneration and find therapeutics that treat or prevent human hearing loss. Secondly, scientists and governmental natural resource managers are concerned about the potential effects of intense anthropogenic sounds on aquatic organisms, including fishes. Dr. Arthur N. Popper and his students, postdocs and research associates have performed pioneering experiments in both of these lines of fish hearing research. This review will discuss the current knowledge regarding the causes and consequences of both lateral line and inner ear hair cell damage in teleost fishes.
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Affiliation(s)
- Michael E Smith
- Department of Biology, Western Kentucky University, Bowling Green, KY, 42101, USA.
| | - J David Monroe
- Department of Biology, Western Kentucky University, Bowling Green, KY, 42101, USA.
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17
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Bhandiwad AA, Zeddies DG, Raible DW, Rubel EW, Sisneros JA. Auditory sensitivity of larval zebrafish (Danio rerio) measured using a behavioral prepulse inhibition assay. ACTA ACUST UNITED AC 2014; 216:3504-13. [PMID: 23966590 DOI: 10.1242/jeb.087635] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Zebrafish (Danio rerio) have become a valuable model for investigating the molecular genetics and development of the inner ear in vertebrates. In this study, we employed a prepulse inhibition (PPI) paradigm to assess hearing in larval wild-type (AB) zebrafish during early development at 5-6 days post-fertilization (d.p.f.). We measured the PPI of the acoustic startle response in zebrafish using a 1-dimensional shaker that simulated the particle motion component of sound along the fish's dorsoventral axis. The thresholds to startle-inducing stimuli were determined in 5-6 d.p.f. zebrafish, and their hearing sensitivity was then characterized using the thresholds of prepulse tone stimuli (90-1200 Hz) that inhibited the acoustic startle response to a reliable startle stimulus (820 Hz at 20 dB re. 1 m s(-2)). Hearing thresholds were defined as the minimum prepulse tone level required to significantly reduce the startle response probability compared with the baseline (no-prepulse) condition. Larval zebrafish showed greatest auditory sensitivity from 90 to 310 Hz with corresponding mean thresholds of -19 to -10 dB re. 1 m s(-2), respectively. Hearing thresholds of prepulse tones were considerably lower than previously predicted by startle response assays. The PPI assay was also used to investigate the relative contribution of the lateral line to the detection of acoustic stimuli. After aminoglycoside-induced neuromast hair-cell ablation, we found no difference in PPI thresholds between treated and control fish. We propose that this PPI assay can be used to screen for novel zebrafish hearing mutants and to investigate the ontogeny of hearing in zebrafish and other fishes.
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Affiliation(s)
- Ashwin A Bhandiwad
- Department of Psychology, University of Washington, Seattle, WA 98195, USA.
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18
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19
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Radford CA, Montgomery JC, Caiger P, Higgs DM. Pressure and particle motion detection thresholds in fish: a re-examination of salient auditory cues in teleosts. ACTA ACUST UNITED AC 2012; 215:3429-35. [PMID: 22693030 DOI: 10.1242/jeb.073320] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The auditory evoked potential technique has been used for the past 30 years to evaluate the hearing ability of fish. The resulting audiograms are typically presented in terms of sound pressure (dB re. 1 μPa) with the particle motion (dB re. 1 m s(-2)) component largely ignored until recently. When audiograms have been presented in terms of particle acceleration, one of two approaches has been used for stimulus characterisation: measuring the pressure gradient between two hydrophones or using accelerometers. With rare exceptions these values are presented from experiments using a speaker as the stimulus, thus making it impossible to truly separate the contribution of direct particle motion and pressure detection in the response. Here, we compared the particle acceleration and pressure auditory thresholds of three species of fish with differing hearing specialisations, goldfish (Carassius auratus, weberian ossicles), bigeye (Pempheris adspersus, ligamentous hearing specialisation) and a third species with no swim bladder, the common triplefin (Forstergyian lappillum), using three different methods of determining particle acceleration. In terms of particle acceleration, all three fish species have similar hearing thresholds, but when expressed as pressure thresholds goldfish are the most sensitive, followed by bigeye, with triplefin the least sensitive. It is suggested here that all fish have a similar ability to detect the particle motion component of the sound field and it is their ability to transduce the pressure component of the sound field to the inner ear via ancillary hearing structures that provides the differences in hearing ability. Therefore, care is needed in stimuli presentation and measurement when determining hearing ability of fish and when interpreting comparative hearing abilities between species.
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Affiliation(s)
- Craig A Radford
- Leigh Marine Laboratory, University of Auckland, Warkworth 0941, New Zealand.
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21
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Meyer M, Fay RR, Popper AN. Frequency tuning and intensity coding of sound in the auditory periphery of the lake sturgeon, Acipenser fulvescens. ACTA ACUST UNITED AC 2010; 213:1567-78. [PMID: 20400642 DOI: 10.1242/jeb.031757] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Acipenser fulvescens, the lake sturgeon, belongs to one of the few extant non-teleost ray-finned (bony) fishes. The sturgeons (family Acipenseridae) have a phylogenetic history that dates back about 250 million years. The study reported here is the first investigation of peripheral coding strategies for spectral analysis in the auditory system in a non-teleost bony fish. We used a shaker system to simulate the particle motion component of sound during electrophysiological recordings of isolated single units from the eighth nerve innervating the saccule and lagena. Background activity and response characteristics of saccular and lagenar afferents (such as thresholds, response-level functions and temporal firing) resembled the ones found in teleosts. The distribution of best frequencies also resembled data in teleosts (except for Carassius auratus, goldfish) tested with the same stimulation method. The saccule and lagena in A. fulvescens contain otoconia, in contrast to the solid otoliths found in teleosts, however, this difference in otolith structure did not appear to affect threshold, frequency tuning, intensity- or temporal responses of auditory afferents. In general, the physiological characteristics common to A. fulvescens, teleosts and land vertebrates reflect important functions of the auditory system that may have been conserved throughout the evolution of vertebrates.
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Affiliation(s)
- Michaela Meyer
- Department of Biology, University of Maryland, College Park, MD 20742, USA.
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22
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Coffin AB, Ou H, Owens KN, Santos F, Simon JA, Rubel EW, Raible DW. Chemical screening for hair cell loss and protection in the zebrafish lateral line. Zebrafish 2010; 7:3-11. [PMID: 20192852 DOI: 10.1089/zeb.2009.0639] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
In humans, most hearing loss results from death of hair cells, the mechanosensory receptors of the inner ear. Two goals of current hearing research are to protect hair cells from degeneration and to regenerate new hair cells, replacing those that are lost due to aging, disease, or environmental challenges. One limitation of research in the auditory field has been the relative inaccessibility of the mechanosensory systems in the inner ear. Zebrafish possess hair cells in both their inner ear and their lateral line system that are morphologically and functionally similar to human hair cells. The external location of the mechanosensory hair cells in the lateral line and the ease of in vivo labeling and imaging make the zebrafish lateral line a unique system for the study of hair cell toxicity, protection, and regeneration. This review focuses on the lateral line system as a model for understanding loss and protection of mechanosensory hair cells. We discuss chemical screens to identify compounds that induce hair cell loss and others that protect hair cells from known toxins and the potential application of these screens to human medicine.
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Affiliation(s)
- Allison B Coffin
- Virginia Merrill Bloedel Hearing Research Center, University of Washington, Seattle, Washington 98195-7923, USA.
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23
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Popper AN, Hastings MC. The effects of anthropogenic sources of sound on fishes. JOURNAL OF FISH BIOLOGY 2009; 75:455-89. [PMID: 20738551 DOI: 10.1111/j.1095-8649.2009.02319.x] [Citation(s) in RCA: 175] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
There is increasing concern about the effects of pile driving and other anthropogenic (human-generated) sound on fishes. Although there is a growing body of reports examining this issue, little of the work is found in the peer-reviewed literature. This review critically examines both the peer-reviewed and 'grey' literature, with the goal of determining what is known and not known about effects on fish. A companion piece provides an analysis of the available data and applies it to estimate noise exposure criteria for pile driving and other impulsive sounds. The critical literature review concludes that very little is known about effects of pile driving and other anthropogenic sounds on fishes, and that it is not yet possible to extrapolate from one experiment to other signal parameters of the same sound, to other types of sounds, to other effects, or to other species.
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Affiliation(s)
- A N Popper
- Department of Biology and Center for Comparative and Evolutionary Biology of Hearing, University of Maryland, College Park, MD 20742, USA.
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Manni L, Mackie GO, Caicci F, Zaniolo G, Burighel P. Coronal organ of ascidians and the evolutionary significance of secondary sensory cells in chordates. J Comp Neurol 2006; 495:363-73. [PMID: 16485286 DOI: 10.1002/cne.20867] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
A new mechanoreceptor organ, the coronal organ, in the oral siphon of some ascidians belonging to the order Pleurogona has recently been described. In contrast to the known mechanoreceptor organs of ascidian atrium that consist of sensory neurons sending their own axons to the cerebral ganglion, coronal sensory cells are secondary mechanoreceptors, i.e., axonless cells forming afferent and efferent synapses with neurites of neurons located in the ganglion. Moreover, coronal cells exhibit an apical apparatus composed of a cilium accompanied or flanked by rod-like microvilli (stereovilli). Because of the resemblance of these cells to vertebrate hair cells, their ectodermal origin and location in a linear array bordering the bases of the oral tentacles and velum, the coronal organ has been proposed as a homologue to the vertebrate acousticolateralis system. Here we describe the morphology of the coronal organs of six ascidians belonging to the suborders Phlebobranchia and Aplousobranchia (order Enterogona). The sensory cells are ciliated, lack typical stereovilli, and at their bases form synapses with neurites. In two species, the sensory cells are accompanied by large cells involved in synthesis and secretion of protein. We hypothesize that the coronal organ with its secondary sensory cells represents a plesiomorphic feature of ascidians. We compare the coronal organ with other chordate sensory organs formed of secondary sensory cells, i.e., the ventral lip receptors of appendicularians, the oral secondary sensory cells of cephalochordates, and the acousticolateralis system of vertebrates, and we discuss their homologies at different levels of organization.
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Affiliation(s)
- Lucia Manni
- Dipartimento di Biologia, Università di Padova, I-35121 Padova, Italy.
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