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Contini D, Holstein GR, Art JJ. Simultaneous recordings from vestibular Type I hair cells and their calyceal afferents in mice. Front Neurol 2024; 15:1434026. [PMID: 39263277 PMCID: PMC11387672 DOI: 10.3389/fneur.2024.1434026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2024] [Accepted: 07/08/2024] [Indexed: 09/13/2024] Open
Abstract
The vestibular hair cell receptors of anamniotes, designated Type II, are presynaptic to bouton endings of vestibular nerve distal neurites. An additional flask-shaped hair cell receptor, Type I, is present in amniotes, and communicates with a chalice-shaped afferent neuritic ending that surrounds the entire hair cell except its apical neck. Since the full repertoire of afferent fiber dynamics and sensitivities observed throughout the vertebrate phyla can be accomplished through Type II hair cell-bouton synapses, the functional contribution(s) of Type I hair cells and their calyces to vestibular performance remains a topic of great interest. The goal of the present study was to investigate electrical coupling between the Type I hair cell and its enveloping calyx in the mouse semicircular canal crista ampullaris. Since there are no gap junctions between these two cells, evidence for electrical communication would necessarily involve other mechanisms. Simultaneous recordings from the two cells of the synaptic pair were used initially to verify the presence of orthodromic quantal synaptic transmission from the hair cell to the calyx, and then to demonstrate bi-directional communication due to the slow accumulation of potassium ions in the synaptic cleft. As a result of this potassium ion accretion, the equilibrium potentials of hair cell conductances facing the synaptic cleft become depolarized to an extent that is adequate for calcium influx into the hair cell, and the calyx inner face becomes depolarized to a level that is near the threshold for spike initiation. Following this, paired recordings were again employed to characterize fast bi-directional electrical coupling between the two cells. In this form of signaling, cleft-facing conductances in both the hair cell and calyx increase, which strengthens their coupling. Because this mechanism relies on the cleft resistance, we refer to it as resistive coupling. We conclude that the same three forms of hair cell-calyceal transmission previously demonstrated in the turtle are present in the mammalian periphery, providing a biophysical basis for the exceptional temporal fidelity of the vestibular system.
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Affiliation(s)
- Donatella Contini
- Anatomy and Cell Biology, College of Medicine, University of Illinois Chicago, Chicago, IL, United States
| | - Gay R Holstein
- Department of Neurology, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Jonathan J Art
- Anatomy and Cell Biology, College of Medicine, University of Illinois Chicago, Chicago, IL, United States
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2
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Baeza-Loya S, Raible DW. Vestibular physiology and function in zebrafish. Front Cell Dev Biol 2023; 11:1172933. [PMID: 37143895 PMCID: PMC10151581 DOI: 10.3389/fcell.2023.1172933] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Accepted: 04/06/2023] [Indexed: 05/06/2023] Open
Abstract
The vestibular system of the inner ear provides information about head motion and spatial orientation relative to gravity to ensure gaze stability, balance, and postural control. Zebrafish, like humans, have five sensory patches per ear that serve as peripheral vestibular organs, with the addition of the lagena and macula neglecta. The zebrafish inner ear can be easily studied due to its accessible location, the transparent tissue of larval fish, and the early development of vestibular behaviors. Thus, zebrafish are an excellent model for studying the development, physiology, and function of the vestibular system. Recent work has made great strides to elucidate vestibular neural circuitry in fish, tracing sensory transmission from receptors in the periphery to central computational circuits driving vestibular reflexes. Here we highlight recent work that illuminates the functional organization of vestibular sensory epithelia, innervating first-order afferent neurons, and second-order neuronal targets in the hindbrain. Using a combination of genetic, anatomical, electrophysiological, and optical techniques, these studies have probed the roles of vestibular sensory signals in fish gaze, postural, and swimming behaviors. We discuss remaining questions in vestibular development and organization that are tractable in the zebrafish model.
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Affiliation(s)
| | - David W. Raible
- Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology-HNS and Biological Structure, University of Washington, Seattle, WA, United States
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3
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Shi T, Beaulieu MO, Saunders LM, Fabian P, Trapnell C, Segil N, Crump JG, Raible DW. Single-cell transcriptomic profiling of the zebrafish inner ear reveals molecularly distinct hair cell and supporting cell subtypes. eLife 2023; 12:82978. [PMID: 36598134 PMCID: PMC9851615 DOI: 10.7554/elife.82978] [Citation(s) in RCA: 22] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Accepted: 01/04/2023] [Indexed: 01/05/2023] Open
Abstract
A major cause of human deafness and vestibular dysfunction is permanent loss of the mechanosensory hair cells of the inner ear. In non-mammalian vertebrates such as zebrafish, regeneration of missing hair cells can occur throughout life. While a comparative approach has the potential to reveal the basis of such differential regenerative ability, the degree to which the inner ears of fish and mammals share common hair cells and supporting cell types remains unresolved. Here, we perform single-cell RNA sequencing of the zebrafish inner ear at embryonic through adult stages to catalog the diversity of hair cells and non-sensory supporting cells. We identify a putative progenitor population for hair cells and supporting cells, as well as distinct hair and supporting cell types in the maculae versus cristae. The hair cell and supporting cell types differ from those described for the lateral line system, a distributed mechanosensory organ in zebrafish in which most studies of hair cell regeneration have been conducted. In the maculae, we identify two subtypes of hair cells that share gene expression with mammalian striolar or extrastriolar hair cells. In situ hybridization reveals that these hair cell subtypes occupy distinct spatial domains within the three macular organs, the utricle, saccule, and lagena, consistent with the reported distinct electrophysiological properties of hair cells within these domains. These findings suggest that primitive specialization of spatially distinct striolar and extrastriolar hair cells likely arose in the last common ancestor of fish and mammals. The similarities of inner ear cell type composition between fish and mammals validate zebrafish as a relevant model for understanding inner ear-specific hair cell function and regeneration.
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Affiliation(s)
- Tuo Shi
- Department of Stem Cell Biology and Regenerative Medicine, Keck School of Medicine, University of Southern CaliforniaLos AngelesUnited States
- Caruso Department of Otolaryngology-Head and Neck Surgery, Keck School of Medicine, University of Southern CaliforniaLos AngelesUnited States
| | - Marielle O Beaulieu
- Department of Otolaryngology-Head and Neck Surgery, University of WashingtonSeattleUnited States
| | - Lauren M Saunders
- Department of Genome Sciences, University of WashingtonSeattleUnited States
| | - Peter Fabian
- Department of Stem Cell Biology and Regenerative Medicine, Keck School of Medicine, University of Southern CaliforniaLos AngelesUnited States
| | - Cole Trapnell
- Department of Genome Sciences, University of WashingtonSeattleUnited States
| | - Neil Segil
- Department of Stem Cell Biology and Regenerative Medicine, Keck School of Medicine, University of Southern CaliforniaLos AngelesUnited States
- Caruso Department of Otolaryngology-Head and Neck Surgery, Keck School of Medicine, University of Southern CaliforniaLos AngelesUnited States
| | - J Gage Crump
- Department of Stem Cell Biology and Regenerative Medicine, Keck School of Medicine, University of Southern CaliforniaLos AngelesUnited States
| | - David W Raible
- Department of Otolaryngology-Head and Neck Surgery, University of WashingtonSeattleUnited States
- Department of Genome Sciences, University of WashingtonSeattleUnited States
- Department of Biological Structure, University of WashingtonSeattleUnited States
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4
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Disruption of tmc1/2a/2b Genes in Zebrafish Reveals Subunit Requirements in Subtypes of Inner Ear Hair Cells. J Neurosci 2020; 40:4457-4468. [PMID: 32371604 DOI: 10.1523/jneurosci.0163-20.2020] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Revised: 04/14/2020] [Accepted: 04/16/2020] [Indexed: 01/11/2023] Open
Abstract
Detection of sound and head movement requires mechanoelectrical transduction (MET) channels at tips of hair-cell stereocilia. In vertebrates, the transmembrane channel-like (TMC) proteins TMC1 and TMC2 fulfill critical roles in MET, and substantial evidence implicates these TMCs as subunits of the MET channel. To identify developmental and functional roles of this Tmc subfamily in the zebrafish inner ear, we tested the effects of truncating mutations in tmc1, tmc2a, and tmc2b on in vivo mechanosensation at the onset of hearing and balance, before gender differentiation. We find that tmc1/2a/2b triple-mutant larvae cannot detect sound or orient with respect to gravity. They lack acoustic-evoked behavioral responses, vestibular-induced eye movements, and hair-cell activity as assessed with FM dye labeling and microphonic potentials. Despite complete loss of hair-cell function, tmc triple-mutant larvae retain normal gross morphology of hair bundles and proper trafficking of known MET components Protocadherin 15a (Pcdh15a), Lipoma HMGIC fusion partner-like 5 (Lhfpl5), and Transmembrane inner ear protein (Tmie). Transgenic, hair cell-specific expression of Tmc2b-mEGFP rescues the behavioral and physiological deficits in tmc triple mutants. Results from tmc single and double mutants evince a principle role for Tmc2a and Tmc2b in hearing and balance, respectively, whereas Tmc1 has lower overall impact. Our experiments reveal that, in developing cristae, hair cells stratify into an upper, Tmc2a-dependent layer of teardrop-shaped cells and a lower, Tmc1/2b-dependent tier of gourd-shaped cells. Collectively, our genetic evidence indicates that auditory/vestibular end organs and subsets of hair cells therein rely on distinct combinations of Tmc1/2a/2b.SIGNIFICANCE STATEMENT We assessed the effects of tmc1/2a/2b truncation mutations on mechanoelectrical transduction (MET) in the inner-ear hair cells of larval zebrafish. tmc triple mutants lacked behavioral responses to sound and head movements, while further assays demonstrated no observable mechanosensitivity in the tmc1/2a/2b triple mutant inner ear. Examination of tmc double mutants revealed major contributions from Tmc2a and Tmc2b to macular function; however, Tmc1 had less overall impact. FM labeling of lateral cristae in tmc double mutants revealed the presence of two distinct cell types, an upper layer of teardrop-shaped cells that rely on Tmc2a, and a lower layer of gourd-shaped cells that rely on Tmc1/2b.
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Nam JH, Grant JW, Rowe MH, Peterson EH. Multiscale modeling of mechanotransduction in the utricle. J Neurophysiol 2019; 122:132-150. [PMID: 30995138 DOI: 10.1152/jn.00068.2019] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
We review recent progress in using numerical models to relate utricular hair bundle and otoconial membrane (OM) structure to the functional requirements imposed by natural behavior in turtles. The head movements section reviews the evolution of experimental attempts to understand vestibular system function with emphasis on turtles, including data showing that accelerations occurring during natural head movements achieve higher magnitudes and frequencies than previously assumed. The structure section reviews quantitative anatomical data documenting topographical variation in the structures underlying macromechanical and micromechanical responses of the turtle utricle to head movement: hair bundles, OM, and bundle-OM coupling. The macromechanics section reviews macromechanical models that incorporate realistic anatomical and mechanical parameters and reveal that the system is significantly underdamped, contrary to previous assumptions. The micromechanics: hair bundle motion and met currents section reviews work based on micromechanical models, which demonstrates that topographical variation in the structure of hair bundles and OM, and their mode of coupling, result in regional specializations for signaling of low frequency (or static) head position and high frequency head accelerations. We conclude that computational models based on empirical data are especially promising for investigating mechanotransduction in this challenging sensorimotor system.
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Affiliation(s)
- Jong-Hoon Nam
- Department of Mechanical Engineering, Department of Biomedical Engineering, University of Rochester , Rochester, New York
| | - J W Grant
- Department of Biomedical Engineering and Mechanics, Virginia Tech, Blacksburg, Virginia
| | - M H Rowe
- Department of Biology, Neuroscience Program, Quantitative Biology Institute, Ohio University , Athens, Ohio
| | - E H Peterson
- Department of Biology, Neuroscience Program, Quantitative Biology Institute, Ohio University , Athens, Ohio
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6
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Perelmuter JT, Forlano PM. Connectivity and ultrastructure of dopaminergic innervation of the inner ear and auditory efferent system of a vocal fish. J Comp Neurol 2017; 525:2090-2108. [PMID: 28118481 DOI: 10.1002/cne.24177] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Revised: 01/17/2017] [Accepted: 01/18/2017] [Indexed: 12/23/2022]
Abstract
Dopamine (DA) is a conserved modulator of vertebrate neural circuitry, yet our knowledge of its role in peripheral auditory processing is limited to mammals. The present study combines immunohistochemistry, neural tract tracing, and electron microscopy to investigate the origin and synaptic characteristics of DA fibers innervating the inner ear and the hindbrain auditory efferent nucleus in the plainfin midshipman, a vocal fish that relies upon the detection of mate calls for reproductive success. We identify a DA cell group in the diencephalon as a common source for innervation of both the hindbrain auditory efferent nucleus and saccule, the main hearing endorgan of the inner ear. We show that DA terminals in the saccule contain vesicles but transmitter release appears paracrine in nature, due to the apparent lack of synaptic contacts. In contrast, in the hindbrain, DA terminals form traditional synaptic contacts with auditory efferent neuronal cell bodies and dendrites, as well as unlabeled axon terminals, which, in turn, form inhibitory-like synapses on auditory efferent somata. Our results suggest a distinct functional role for brain-derived DA in the direct and indirect modulation of the peripheral auditory system of a vocal nonmammalian vertebrate.
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Affiliation(s)
- Jonathan T Perelmuter
- Program in Behavioral and Cognitive Neuroscience, The Graduate Center, City University of New York, New York, New York, 10016.,Department of Biology, Brooklyn College, City University of New York, Brooklyn, New York, 11210
| | - Paul M Forlano
- Program in Behavioral and Cognitive Neuroscience, The Graduate Center, City University of New York, New York, New York, 10016.,Program in Ecology, Evolutionary Biology and Behavior, The Graduate Center, City University of New York, New York, New York, 10016.,Program in Neuroscience, The Graduate Center, City University of New York, New York, New York, 10016.,Department of Biology, Brooklyn College, City University of New York, Brooklyn, New York, 11210.,Aquatic Research and Environmental Assessment Center, Brooklyn College, Brooklyn NY, New York, 11210
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7
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Chemical Ototoxicity of the Fish Inner Ear and Lateral Line. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 877:419-37. [PMID: 26515324 DOI: 10.1007/978-3-319-21059-9_18] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Hair cell-driven mechanosensory systems are crucial for successful execution of a number of behaviors in fishes, and have emerged as good models for exploring questions relevant to human hearing. This review focuses on ototoxic effects in the inner ear and lateral line system of fishes. We specifically examine studies where chemical ototoxins such as aminoglycoside antibiotics have been employed as tools to disable the lateral line. Lateral line ablation results in alterations to feeding behavior and orientation to water current in a variety of species. However, neither behavior is abolished in the presence of additional sensory cues, supporting the hypothesis that many fish behaviors are driven by multisensory integration. Within biomedical research, the larval zebrafish lateral line has become an important model system for understanding signaling mechanisms that contribute to hair cell death and for developing novel pharmacological therapies that protect hair cells from ototoxic damage. Furthermore, given that fishes robustly regenerate damaged hair cells, ototoxin studies in fishes have broadened our understanding of the molecular and genetic events in an innately regenerative system, offering potential targets for mammalian hair cell regeneration. Collectively, studies of fish mechanosensory systems have yielded insight into fish behavior and in mechanisms of hair cell death, protection, and regeneration.
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8
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Ernest S, Guadagnini S, Prévost MC, Soussi-Yanicostas N. Localization of anosmin-1a and anosmin-1b in the inner ear and neuromasts of zebrafish. Gene Expr Patterns 2007; 7:274-81. [PMID: 17064968 DOI: 10.1016/j.modgep.2006.09.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2006] [Revised: 09/05/2006] [Accepted: 09/06/2006] [Indexed: 11/28/2022]
Abstract
Anosmin-1, encoded by the KAL-1 gene, is the protein defective in the X-linked form of Kallmann syndrome. This human developmental disorder is characterized by defects in cell migration and axon target selection. Anosmin-1 is an extracellular matrix protein that plays a role, in vitro, in processes such as cell adhesion, neurite outgrowth, axon guidance, and axon branching. The zebrafish possesses two orthologues of the KAL-1 gene: kal1a and kal1b, which encode anosmin-1a and anosmin-1b, respectively. Previous in situ hybridization studies have shown that kal1a and kal1b mRNAs are expressed in undetermined cells of the inner ear but not in neuromast cells. Using specific antibodies against anosmin-1a and anosmin-1b, we report here that both proteins are expressed in sensory hair cells of the inner ear cristae ampullaris and the lateral line neuromasts. Accumulation of these proteins was observed mainly at the level of the hair bundle and also at the cell membrane. In neuromast hair cells, immunogold scanning electronmicroscopy demonstrated that anosmin-1a and anosmin-1b were present at the surface of the stereociliary bundle. In addition, anosmin-1a, but not anosmin-1b, was detected on the track of the ampullary nerve. This is the first report of anosmin-1 expression in sensory hair cells of the inner ear and lateral line, and along the ampullary nerve track.
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MESH Headings
- Animals
- Ear, Inner/anatomy & histology
- Ear, Inner/chemistry
- Ear, Inner/metabolism
- Extracellular Matrix Proteins/analysis
- Extracellular Matrix Proteins/genetics
- Fluorescent Antibody Technique
- Hair Cells, Auditory/chemistry
- Hair Cells, Auditory/metabolism
- Hair Cells, Auditory/ultrastructure
- Immunohistochemistry
- Lateral Line System/chemistry
- Lateral Line System/cytology
- Lateral Line System/metabolism
- Microscopy, Confocal
- Microscopy, Electron, Scanning
- Microscopy, Immunoelectron
- Nerve Tissue Proteins/analysis
- Nerve Tissue Proteins/genetics
- Sensory Receptor Cells/chemistry
- Sensory Receptor Cells/metabolism
- Zebrafish/anatomy & histology
- Zebrafish/genetics
- Zebrafish/metabolism
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9
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Ohnishi K, Ogawa Y, Takahashi A, Yamashita M, Ohnishi T. Comparative study of otolith organs between two species of upside-down swimming catfish Synodontis nigriventris showing converse swimming postures. ACTA ZOOL-STOCKHOLM 2005. [DOI: 10.1111/j.0001-7272.2004.00171.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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10
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Holstein GR, Martinelli GP, Boyle R, Rabbitt RD, Highstein SM. Ultrastructural observations of efferent terminals in the crista ampullaris of the toadfish, Opsanus tau. Exp Brain Res 2004; 157:128-36. [PMID: 15318400 DOI: 10.1007/s00221-004-1898-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The present study was conducted to visualize the ultrastructural features of vestibular efferent boutons in the oyster toadfish, Opsanus tau. The crista ampullaris of the horizontal semicircular canal was processed for and examined by routine transmission electron microscopy. The results demonstrate that such boutons vary in size and shape, and contain a heterogeneous population of lucent vesicles with scattered dense core vesicles. Efferent contacts with hair cells are characterized by local vesicle accumulations in the presynaptic terminal and a subsynaptic cistern in the postsynaptic region of the hair cell. Serial efferent to hair cell to afferent synaptic arrangements are common, particularly in the central portion of the crista. However, direct contacts between efferent terminals and afferent neurites were not observed in our specimens. The existence of serial synaptic contacts, often with a row of vesicles in the efferent boutons lining the efferent-afferent membrane apposition, suggests that the efferent influence on the crista may involve both synaptic and nonsynaptic, secretory mechanisms. Further, it is suggested that differences in more subtle aspects of synaptic architecture and/or transmitter and receptor localization and interaction may render the efferent innervation of the peripheral crista less effective in influencing sensory processing.
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Affiliation(s)
- G R Holstein
- Department of Neurology, Mount Sinai School of Medicine, New York, NY 10029, USA.
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11
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12
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Holstein GR, Martinelli GP, Boyle R, Rabbitt RD, Highstein SM. Ultrastructural observations of efferent terminals in the crista Ampullaris of the toadfish, opsanus tau. Exp Brain Res 2003; 155:265-73. [PMID: 14689144 DOI: 10.1007/s00221-003-1734-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2003] [Accepted: 09/25/2003] [Indexed: 10/26/2022]
Abstract
The present study was conducted to visualize the ultrastructural features of vestibular efferent boutons in the oyster toadfish, Opsanus tau. The crista ampullaris of the horizontal semicircular canal was processed for and examined by routine transmission electron microscopy. The results demonstrate that such boutons vary in size and shape, and contain a heterogeneous population of lucent vesicles with scattered dense core vesicles. Efferent contacts with hair cells are characterized by local vesicle accumulations in the presynaptic terminal and a subsynaptic cistern in the postsynaptic region of the hair cell. Serial efferent to hair cell to afferent synaptic arrangements are common, particularly in the central portion of the crista. However, direct contacts between efferent terminals and afferent neurites were not observed in our specimens. The existence of serial synaptic contacts, often with a row of vesicles in the efferent boutons lining the efferent-afferent membrane apposition, suggests that the efferent influence on the crista may involve both synaptic and nonsynaptic, secretory mechanisms. Further, it is suggested that differences in more subtle aspects of synaptic architecture and/or transmitter and receptor localization and interaction may render the efferent innervation of the peripheral crista less effective in influencing sensory processing.
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Affiliation(s)
- G R Holstein
- Department of Neurology, Mount Sinai School of Medicine, One Gustave L. Levy Place, Box 1140, New York, NY 10029, USA.
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13
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Abstract
Biotinylated dextran amine (BDA) was used to retrogradely label afferents innervating the utricular macula in adult pigeons. The pigeon utriclar macula consists of a large rectangular-shaped neuroepithelium with a dorsally curved anterior edge and an extended medioposterior tail. The macula could be demarcated into several regions based on cytoarchitectural differences. The striola occupied 30% of the macula and contained a large density of type I hair cells with fewer type II hair cells. Medial and lateral extrastriola zones were located outside the striola and contained only type II hair cells. A six- to eight-cell-wide band of type II hair cells existed near the center of the striola. The reversal line marked by the morphological polarization of hair cells coursed throughout the epithelium, near the peripheral margin, and through the center of the type II band. Calyx afferents innervated type I hair cells with calyceal terminals that contained between 2 and 15 receptor cells. Calyx afferents were located only in the striola region, exclusive of the type II band, had small total fiber innervation areas and low innervation densities. Dimorph afferents innervated both type I and type II hair cells with calyceal and bouton terminals and were primarily located in the striola region. Dimorph afferents had smaller calyceal terminals with few type I hair cells, extended fiber branches with bouton terminals and larger innervation areas. Bouton afferents innervated only type II hair cells in the extrastriola and type II band regions. Bouton afferents innervating the type II band had smaller terminal fields with fewer bouton terminals and smaller innervation areas than fibers located in the extrastriolar zones. Bouton afferents had the most bouton terminals on the longest fibers, the largest innervation areas with the highest innervation densities of all afferents. Among all afferents, smaller terminal innervation fields were observed in the striola and large fields were located in the extrastriola. The cellular organization and innervation patterns of the utricular maculae in birds appear to represent an organ in adaptive evolution, different from that observed for amphibians or mammals.
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Affiliation(s)
- Xiaohong Si
- Department of Psychiatry and Human Behavior, University of Mississippi Medical Center, Jackson, Mississippi 39211, USA
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14
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Abstract
The innervation patterns of vestibular saccular afferents were quantitatively investigated in pigeons using biotinylated dextran amine as a neural tracer and three-dimensional computer reconstruction. Type I hair cells were found throughout a large portion of the macula, with the highest density observed in the striola. Type II hair cells were located throughout the macula, with the highest density in the extrastriola. Three classes of afferent innervation patterns were observed, including calyx, dimorph, and bouton units, with 137 afferents being anatomically reconstructed and used for quantitative comparisons. Calyx afferents were located primarily in the striola, innervated a number of type I hair cells, and had small innervation areas. Most calyx afferent terminal fields were oriented parallel to the anterior-posterior axis and the morphological polarization reversal line. Dimorph afferents were located throughout the macula, contained fewer type I hair cells in a calyceal terminal than calyx afferents and had medium sized innervation areas. Bouton afferents were restricted to the extrastriola, with multi-branching fibers and large innervation areas. Most of the dimorph and bouton afferents had innervation fields that were oriented dorso-ventrally but were parallel to the neighboring reversal line. The organizational morphology of the saccule was found to be distinctly different from that of the avian utricle or lagena otolith organs and appears to represent a receptor organ undergoing evolutionary adaptation toward sensing linear motion in terrestrial and aerial species.
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Affiliation(s)
- M Zakir
- Research Department, Central Institute for the Deaf, Washington University, St. Louis, Missouri 63110, USA
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15
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Abstract
This paper considers aspects of the evolution of the vertebrate auditory system from an 'ichthyocentric' perspective. It is argued that all vertebrate auditory systems are required to do certain basic tasks including acoustic feature discrimination, sound source localization, frequency analysis, and auditory scene analysis, among others. These sorts of capabilities arose very early in the evolution of the vertebrates and have been modified by selection in different species. In some cases the same structures have been involved in detection and analysis throughout the vertebrates, while in other cases the mechanism by which the same type of analysis takes place may have changed.
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Affiliation(s)
- R R Fay
- Department of Psychology and Parmly Hearing Institute, Loyola University of Chicago, Chicago, IL 60626, USA
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16
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Popper AN. Hair cell heterogeneity and ultrasonic hearing: recent advances in understanding fish hearing. Philos Trans R Soc Lond B Biol Sci 2000; 355:1277-80. [PMID: 11079414 PMCID: PMC1692857 DOI: 10.1098/rstb.2000.0683] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The past decade has seen a wealth of new data on the auditory capabilities and mechanisms of fishes. We now have a significantly better appreciation of the structure and function of the auditory system in fishes with regard to their peripheral and central anatomy, physiology, behaviour, sound source localization and hearing capabilities. This paper deals with two of the newest of these findings, hair cell heterogeneity and the detection of ultrasound. As a result of this recent work, we now know that fishes have several different types of sensory hair cells in both the ear and lateral line and there is a growing body of evidence to suggest that these hair cell types arose very early in the evolution of the octavolateralis system. There is also some evidence to suggest that the differences in the hair cell types have functional implications for the way the ear and lateral line of fishes detect and process stimuli. Behavioural studies have shown that, whereas most fishes can only detect sound to 1-3 kHz, several species of the genus Alosa (Clupeiformes, i.e. herrings and their relatives) can detect sounds up to 180 kHz (or even higher). It is suggested that this capability evolved so that these fishes can detect one of their major predators, echolocating dolphins. The mechanism for ultrasound detection remains obscure, though it is hypothesized that the highly derived utricle of the inner ear in these species is involved.
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Affiliation(s)
- A N Popper
- Department of Biology, Univesity of Maryland, College Park, MD 20742, USA.
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18
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Sobkowicz HM, Slapnick SM, Nitecka LM, August BK. Compound synapses within the GABAergic innervation of the auditory inner hair cells in the adolescent mouse. J Comp Neurol 1997; 377:423-42. [PMID: 8989656 DOI: 10.1002/(sici)1096-9861(19970120)377:3<423::aid-cne9>3.0.co;2-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Ultrastructural investigation of the gamma-aminobutyric acid (GABA) component of the inner spiral bundle in adolescent mice revealed a pathway of glutamic acid decarboxylase (GAD)-positive and -negative fibers and vesiculated endings that contact inner hair cells and their afferents through a complex of axosomatic and axodendritic synapses. Ultrastructural details were investigated by using conventional electron microscopy. Several synaptic arrangements were observed: Main axosomatic synapses form between vesiculated endings and individual or adjoining inner hair cells (interreceptor synapses). Spinous synapses form on long, spinelike processes that protrude from inner hair cells to reach distant efferent endings. The efferent endings associate with inner hair cells and their synaptic afferents through compound synapses-serial, "converging," and triadic-otherwise characteristic of sensory relay nuclei. Serial synapses form by the sequential presynaptic alignment of the efferent-->receptor-->afferent components. Converging synapses result from the simultaneous apposition of a receptor ribbon synapse and a presynaptic efferent terminal on a recipient afferent dendrite. Triadic synapses comprise a vesiculated efferent ending in contact with an inner hair cell and with its synaptic afferent. Additionally, efferent endings may form simple axodendritic and axoaxonal synapses with GAD-negative vesiculated endings. The combination of different synaptic arrangements leads to short chains of compound synapses. It is assumed that these synaptic patterns seen in the adolescent mouse represent adult synaptology. The patterns of synaptic connectivity suggest an integrative role for the GABA/GAD lateral efferent system, and imply its involvement in the pre- and postsynaptic modulation of auditory signals.
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Affiliation(s)
- H M Sobkowicz
- Department of Neurology, University of Wisconsin, Madison 53706, USA.
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Affiliation(s)
- A Lysakowski
- Department of Anatomy and Cell Biology, University of Illinois College of Medicine, Chicago 60612, USA.
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