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Wang H, Sun R, Xu N, Wang X, Bao M, Li X, Li J, Lin A, Feng J. Untargeted metabolomics of the cochleae from two laryngeally echolocating bats. Front Mol Biosci 2023; 10:1171366. [PMID: 37152899 PMCID: PMC10154556 DOI: 10.3389/fmolb.2023.1171366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Accepted: 04/06/2023] [Indexed: 05/09/2023] Open
Abstract
High-frequency hearing is regarded as one of the most functionally important traits in laryngeally echolocating bats. Abundant candidate hearing-related genes have been identified to be the important genetic bases underlying high-frequency hearing for laryngeally echolocating bats, however, extensive metabolites presented in the cochleae have not been studied. In this study, we identified 4,717 annotated metabolites in the cochleae of two typical laryngeally echolocating bats using the liquid chromatography-mass spectroscopy technology, metabolites classified as amino acids, peptides, and fatty acid esters were identified as the most abundant in the cochleae of these two echolocating bat species, Rhinolophus sinicus and Vespertilio sinensis. Furthermore, 357 metabolites were identified as significant differentially accumulated (adjusted p-value <0.05) in the cochleae of these two bat species with distinct echolocating dominant frequencies. Downstream KEGG enrichment analyses indicated that multiple biological processes, including signaling pathways, nervous system, and metabolic process, were putatively different in the cochleae of R. sinicus and V. sinensis. For the first time, this study investigated the extensive metabolites and associated biological pathways in the cochleae of two laryngeal echolocating bats and expanded our knowledge of the metabolic molecular bases underlying high-frequency hearing in the cochleae of echolocating bats.
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Affiliation(s)
- Hui Wang
- College of Life Science, Jilin Agricultural University, Changchun, China
- *Correspondence: Hui Wang, ; Jiang Feng,
| | - Ruyi Sun
- College of Life Science, Jilin Agricultural University, Changchun, China
| | - Ningning Xu
- College of Life Science, Jilin Agricultural University, Changchun, China
| | - Xue Wang
- College of Life Science, Jilin Agricultural University, Changchun, China
| | - Mingyue Bao
- College of Life Science, Jilin Agricultural University, Changchun, China
| | - Xin Li
- College of Life Science, Jilin Agricultural University, Changchun, China
| | - Jiqian Li
- Jilin Provincial Key Laboratory of Animal Resource Conservation and Utilization, Northeast Normal University, Changchun, China
| | - Aiqing Lin
- Jilin Provincial Key Laboratory of Animal Resource Conservation and Utilization, Northeast Normal University, Changchun, China
| | - Jiang Feng
- College of Life Science, Jilin Agricultural University, Changchun, China
- Jilin Provincial Key Laboratory of Animal Resource Conservation and Utilization, Northeast Normal University, Changchun, China
- *Correspondence: Hui Wang, ; Jiang Feng,
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2
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Romero GE, Trussell LO. Central circuitry and function of the cochlear efferent systems. Hear Res 2022; 425:108516. [DOI: 10.1016/j.heares.2022.108516] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/14/2022] [Revised: 04/28/2022] [Accepted: 05/10/2022] [Indexed: 11/04/2022]
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3
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Chang HHV, Morley BJ, Cullen KE. Loss of α-9 Nicotinic Acetylcholine Receptor Subunit Predominantly Results in Impaired Postural Stability Rather Than Gaze Stability. Front Cell Neurosci 2022; 15:799752. [PMID: 35095424 PMCID: PMC8792779 DOI: 10.3389/fncel.2021.799752] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Accepted: 11/29/2021] [Indexed: 11/13/2022] Open
Abstract
The functional role of the mammalian efferent vestibular system (EVS) is not fully understood. One proposal is that the mammalian EVS plays a role in the long-term calibration of central vestibular pathways, for example during development. Here to test this possibility, we studied vestibular function in mice lacking a functional α9 subunit of the nicotinic acetylcholine receptor (nAChR) gene family, which mediates efferent activation of the vestibular periphery. We focused on an α9 (−/−) model with a deletion in exons 1 and 2. First, we quantified gaze stability by testing vestibulo-ocular reflex (VOR, 0.2–3 Hz) responses of both α9 (−/−) mouse models in dark and light conditions. VOR gains and phases were comparable for both α9 (−/−) mutants and wild-type controls. Second, we confirmed the lack of an effect from the α9 (−/−) mutation on central visuo-motor pathways/eye movement pathways via analyses of the optokinetic reflex (OKR) and quick phases of the VOR. We found no differences between α9 (−/−) mutants and wild-type controls. Third and finally, we investigated postural abilities during instrumented rotarod and balance beam tasks. Head movements were quantified using a 6D microelectromechanical systems (MEMS) module fixed to the mouse’s head. Compared to wild-type controls, we found head movements were strikingly altered in α9 (−/−) mice, most notably in the pitch axis. We confirmed these later results in another α9 (−/−) model, with a deletion in the exon 4 region. Overall, we conclude that the absence of the α9 subunit of nAChRs predominately results in an impairment of posture rather than gaze.
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Affiliation(s)
| | - Barbara J. Morley
- Center for Sensory Neuroscience, Boys Town National Research Hospital, Omaha, NE, United States
| | - Kathleen E. Cullen
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States
- Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, MD, United States
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, United States
- Kavli Neuroscience Discovery Institute, Johns Hopkins University, Baltimore, MD, United States
- *Correspondence: Kathleen E. Cullen,
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4
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Levic S. SK Current, Expressed During the Development and Regeneration of Chick Hair Cells, Contributes to the Patterning of Spontaneous Action Potentials. Front Cell Neurosci 2022; 15:766264. [PMID: 35069114 PMCID: PMC8770932 DOI: 10.3389/fncel.2021.766264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2021] [Accepted: 11/29/2021] [Indexed: 11/30/2022] Open
Abstract
Chick hair cells display calcium (Ca2+)-sensitive spontaneous action potentials during development and regeneration. The role of this activity is unclear but thought to be involved in establishing proper synaptic connections and tonotopic maps, both of which are instrumental to normal hearing. Using an electrophysiological approach, this work investigated the functional expression of Ca2+-sensitive potassium [IK(Ca)] currents and their role in spontaneous electrical activity in the developing and regenerating hair cells (HCs) in the chick basilar papilla. The main IK(Ca) in developing and regenerating chick HCs is an SK current, based on its sensitivity to apamin. Analysis of the functional expression of SK current showed that most dramatic changes occurred between E8 and E16. Specifically, there is a developmental downregulation of the SK current after E16. The SK current gating was very sensitive to the availability of intracellular Ca2+ but showed very little sensitivity to T-type voltage-gated Ca2+ channels, which are one of the hallmarks of developing and regenerating hair cells. Additionally, apamin reduced the frequency of spontaneous electrical activity in HCs, suggesting that SK current participates in patterning the spontaneous electrical activity of HCs.
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Affiliation(s)
- Snezana Levic
- Center for Neuroscience, University of California, Davis, Davis, CA, United States
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton, United Kingdom
- Brighton and Sussex Medical School, University of Sussex, Brighton, United Kingdom
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5
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Proulx É, Power SK, Oliver DK, Sargin D, McLaurin J, Lambe EK. Apamin Improves Prefrontal Nicotinic Impairment in Mouse Model of Alzheimer's Disease. Cereb Cortex 2021; 30:563-574. [PMID: 31188425 DOI: 10.1093/cercor/bhz107] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Revised: 04/29/2019] [Accepted: 05/01/2019] [Indexed: 12/11/2022] Open
Abstract
Disruption of attention is an early and disabling symptom of Alzheimer's disease (AD). The underlying cellular mechanisms are poorly understood and treatment options for patients are limited. These early attention deficits are evident in the TgCRND8 mouse, a well-established murine model of AD that recapitulates several features of the disease. Here, we report severe impairment of the nicotinic receptor-mediated excitation of prefrontal attentional circuitry in TgCRND8 mice relative to wild-type littermate controls. We demonstrate that this impairment can be remedied by apamin, a bee venom neurotoxin peptide that acts as a selective antagonist to the SK family of calcium-sensitive potassium channels. We probe this seeming upregulation of calcium-sensitive inhibition and find that the attenuated nicotinic firing rates in TgCRND8 attention circuits are mediated neither by greater cellular calcium signals nor by elevated SK channel expression. Instead, we find that TgCRND8 mice show enhanced functional coupling of nicotinic calcium signals to inhibition. This SK-mediated inhibition exerts a powerful negative feedback on nicotinic excitation, dampening attention-relevant signaling in the TgCRND8 brain. These mechanistic findings identify a new cellular target involved in the modulation of attention and a novel therapeutic target for early attention deficits in AD.
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Affiliation(s)
- É Proulx
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada, M5S 1A8
| | - S K Power
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada, M5S 1A8
| | - D K Oliver
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada, M5S 1A8
| | - D Sargin
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada, M5S 1A8
| | - J McLaurin
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8.,Biological Sciences and Hurvitz Brain Sciences Research Program, Sunnybrook Research Institute, Toronto, Ontario, Canada M4N 3M5
| | - E K Lambe
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada, M5S 1A8.,Department of Obstetrics and Gynaecology, University of Toronto, Toronto, Ontario, Canada M5G 1E2.,Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada M5T 1R8
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6
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Du H, Ye C, Wu D, Zang YY, Zhang L, Chen C, He XY, Yang JJ, Hu P, Xu Z, Wan G, Shi YS. The Cation Channel TMEM63B Is an Osmosensor Required for Hearing. Cell Rep 2021; 31:107596. [PMID: 32375046 DOI: 10.1016/j.celrep.2020.107596] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Revised: 02/21/2020] [Accepted: 04/10/2020] [Indexed: 01/08/2023] Open
Abstract
Hypotonic stress causes the activation of swelling-activated nonselective cation channels (NSCCs), which leads to Ca2+-dependent regulatory volume decrease (RVD) and adaptive maintenance of the cell volume; however, the molecular identities of the osmosensitive NSCCs remain unclear. Here, we identified TMEM63B as an osmosensitive NSCC activated by hypotonic stress. TMEM63B is enriched in the inner ear sensory hair cells. Genetic deletion of TMEM63B results in necroptosis of outer hair cells (OHCs) and progressive hearing loss. Mechanistically, the TMEM63B channel mediates hypo-osmolarity-induced Ca2+ influx, which activates Ca2+-dependent K+ channels required for the maintenance of OHC morphology. These findings demonstrate that TMEM63B is an osmosensor of the mammalian inner ear and the long-sought cation channel mediating Ca2+-dependent RVD.
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Affiliation(s)
- Han Du
- State Key Laboratory of Pharmaceutical Biotechnology, Department of Neurology, Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing University, Nanjing 210032, China; Ministry of Education Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210032, China
| | - Chang Ye
- State Key Laboratory of Pharmaceutical Biotechnology, Department of Neurology, Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing University, Nanjing 210032, China; Ministry of Education Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210032, China
| | - Dan Wu
- State Key Laboratory of Pharmaceutical Biotechnology, Department of Neurology, Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing University, Nanjing 210032, China; Ministry of Education Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210032, China
| | - Yan-Yu Zang
- State Key Laboratory of Pharmaceutical Biotechnology, Department of Neurology, Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing University, Nanjing 210032, China; Ministry of Education Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210032, China
| | - Linqing Zhang
- Ministry of Education Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210032, China
| | - Chen Chen
- Ministry of Education Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210032, China
| | - Xue-Yan He
- Ministry of Education Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210032, China
| | - Jian-Jun Yang
- Department of Anesthesiology and Perioperative Medicine, First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan Province 450052, China
| | - Ping Hu
- Department of Prenatal Diagnosis, Women's Hospital of Nanjing Medical University, Nanjing Maternity and Child Healthcare Hospital, Nanjing 210004, China
| | - Zhengfeng Xu
- Department of Prenatal Diagnosis, Women's Hospital of Nanjing Medical University, Nanjing Maternity and Child Healthcare Hospital, Nanjing 210004, China
| | - Guoqiang Wan
- Ministry of Education Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210032, China; Institute for Brain Sciences, Nanjing University, Nanjing 210032, China.
| | - Yun Stone Shi
- State Key Laboratory of Pharmaceutical Biotechnology, Department of Neurology, Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing University, Nanjing 210032, China; Ministry of Education Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210032, China; Institute for Brain Sciences, Nanjing University, Nanjing 210032, China; Chemistry and Biomedicine Innovation Center, Nanjing University, Nanjing 210032, China.
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7
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Olson A, Zhang F, Cao H, Baranova A, Slavin M. In silico Gene Set and Pathway Enrichment Analyses Highlight Involvement of Ion Transport in Cholinergic Pathways in Autism: Rationale for Nutritional Intervention. Front Neurosci 2021; 15:648410. [PMID: 33958984 PMCID: PMC8093449 DOI: 10.3389/fnins.2021.648410] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Accepted: 03/22/2021] [Indexed: 12/12/2022] Open
Abstract
Food is the primary human source of choline, an essential precursor to the neurotransmitter acetylcholine, which has a central role in signaling pathways that govern sensorimotor functions. Most Americans do not consume their recommended amount of dietary choline, and populations with neurodevelopmental conditions like autism spectrum disorder (ASD) may be particularly vulnerable to consequences of choline deficiency. This study aimed to identify a relationship between ASD and cholinergic signaling through gene set enrichment analysis and interrogation of existing database evidence to produce a systems biology model. In gene set enrichment analysis, two gene ontologies were identified as overlapping for autism-related and for cholinergic pathways-related functions, both involving ion transport regulation. Subsequent modeling of ion transport intensive cholinergic signaling pathways highlighted the importance of two genes with autism-associated variants: GABBR1, which codes for the gamma aminobutyric acid receptor (GABAB 1), and KCNN2, which codes for calcium-activated, potassium ion transporting SK2 channels responsible for membrane repolarization after cholinergic binding/signal transmission events. Cholinergic signal transmission pathways related to these proteins were examined in the Pathway Studio environment. The ion transport ontological associations indicated feasibility of a dietary choline support as a low-risk therapeutic intervention capable of modulating cholinergic sensory signaling in autism. Further research at the intersection of dietary status and sensory function in autism is warranted.
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Affiliation(s)
- Audrey Olson
- Department of Nutrition and Food Studies, College of Health and Human Services, George Mason University, Fairfax, VA, United States
- School of Systems Biology, College of Science, George Mason University, Manassas, VA, United States
| | - Fuquan Zhang
- Department of Psychiatry, Nanjing Medical University, Nanjing, China
| | - Hongbao Cao
- School of Systems Biology, College of Science, George Mason University, Manassas, VA, United States
- Department of Psychiatry, Shanxi Medical University, Taiyuan, China
| | - Ancha Baranova
- School of Systems Biology, College of Science, George Mason University, Manassas, VA, United States
- Research Centre for Medical Genetics, Moscow, Russia
| | - Margaret Slavin
- Department of Nutrition and Food Studies, College of Health and Human Services, George Mason University, Fairfax, VA, United States
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8
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Sex difference in the efferent inner hair cell synapses of the aging murine cochlea. Hear Res 2021; 404:108215. [PMID: 33677192 DOI: 10.1016/j.heares.2021.108215] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Revised: 02/12/2021] [Accepted: 02/14/2021] [Indexed: 11/20/2022]
Abstract
Efferent innervation of the inner hair cells changes over time. At an early age in mice, inner hair cells receive efferent feedback, which helps fine-tune tonotopic maps in the brainstem. In adulthood, inner hair cell efferent innervation wanes but increases again in older animals. It is not clear, however, whether age-related inner hair cell efferents increase along the entire range of the cochlear frequencies, or if this increase is restricted to a particular frequency-region, and whether this phenomenon occurs in both sexes. Age-related hearing loss, presbycusis, affects men and women differently. In mice, this difference is also strain specific. In aging black six mice, the auditory brainstem response thresholds increase in females earlier than in males. Here, we study age-related increase of the inner hair cell efferent innervation throughout the cochlea before hearing onset, in one month old and in ten months old and older male and female black six mice. We collected confocal images of immunostained inner hair cell efferents and quantified the labeled terminals in the entire cochlea using a machine learning algorithm. The overall number of the inner hair cell efferents in both sexes did not change significantly between age-groups. The distribution of the inner hair cell efferent innervation did not differ across frequencies in the cochlea. However, in females, inner hair cells received on average up to four times more efferent innervation than in males per each of the frequency regions tested. Sex differences were also found in the oldest age-group tested (≥ 10 months) where on average inner hair cells received six times more efferents in females than in males of matching age. Our findings emphasize the importance of including both sexes in sensorineural hearing loss research.
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9
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Age-related hearing loss pertaining to potassium ion channels in the cochlea and auditory pathway. Pflugers Arch 2020; 473:823-840. [PMID: 33336302 PMCID: PMC8076138 DOI: 10.1007/s00424-020-02496-w] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2020] [Revised: 10/27/2020] [Accepted: 11/10/2020] [Indexed: 12/12/2022]
Abstract
Age-related hearing loss (ARHL) is the most prevalent sensory deficit in the elderly and constitutes the third highest risk factor for dementia. Lifetime noise exposure, genetic predispositions for degeneration, and metabolic stress are assumed to be the major causes of ARHL. Both noise-induced and hereditary progressive hearing have been linked to decreased cell surface expression and impaired conductance of the potassium ion channel KV7.4 (KCNQ4) in outer hair cells, inspiring future therapies to maintain or prevent the decline of potassium ion channel surface expression to reduce ARHL. In concert with KV7.4 in outer hair cells, KV7.1 (KCNQ1) in the stria vascularis, calcium-activated potassium channels BK (KCNMA1) and SK2 (KCNN2) in hair cells and efferent fiber synapses, and KV3.1 (KCNC1) in the spiral ganglia and ascending auditory circuits share an upregulated expression or subcellular targeting during final differentiation at hearing onset. They also share a distinctive fragility for noise exposure and age-dependent shortfalls in energy supply required for sustained surface expression. Here, we review and discuss the possible contribution of select potassium ion channels in the cochlea and auditory pathway to ARHL. We postulate genes, proteins, or modulators that contribute to sustained ion currents or proper surface expressions of potassium channels under challenging conditions as key for future therapies of ARHL.
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10
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Ashmore J. Tonotopy of cochlear hair cell biophysics (excl. mechanotransduction). CURRENT OPINION IN PHYSIOLOGY 2020. [DOI: 10.1016/j.cophys.2020.06.010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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11
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Hair cell α9α10 nicotinic acetylcholine receptor functional expression regulated by ligand binding and deafness gene products. Proc Natl Acad Sci U S A 2020; 117:24534-24544. [PMID: 32929005 DOI: 10.1073/pnas.2013762117] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Auditory hair cells receive olivocochlear efferent innervation, which refines tonotopic mapping, improves sound discrimination, and mitigates acoustic trauma. The olivocochlear synapse involves α9α10 nicotinic acetylcholine receptors (nAChRs), which assemble in hair cells only coincident with cholinergic innervation and do not express in recombinant mammalian cell lines. Here, genome-wide screening determined that assembly and surface expression of α9α10 require ligand binding. Ion channel function additionally demands an auxiliary subunit, which can be transmembrane inner ear (TMIE) or TMEM132e. Both of these single-pass transmembrane proteins are enriched in hair cells and underlie nonsyndromic human deafness. Inner hair cells from TMIE mutant mice show altered postsynaptic α9α10 function and retain α9α10-mediated transmission beyond the second postnatal week associated with abnormally persistent cholinergic innervation. Collectively, this study provides a mechanism to link cholinergic input with α9α10 assembly, identifies unexpected functions for human deafness genes TMIE/TMEM132e, and enables drug discovery for this elusive nAChR implicated in prevalent auditory disorders.
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12
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Zhang Y, Glowatzki E, Roux I, Fuchs PA. Nicotine evoked efferent transmitter release onto immature cochlear inner hair cells. J Neurophysiol 2020; 124:1377-1387. [PMID: 32845208 DOI: 10.1152/jn.00097.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Olivocochlear neurons make temporary cholinergic synapses on inner hair cells of the rodent cochlea in the first 2 to 3 wk after birth. Repetitive stimulation of these efferent neurons causes facilitation of evoked release and increased spontaneous release that continues for seconds to minutes. Presynaptic nicotinic acetylcholine receptors (nAChRs) are known to modulate neurotransmitter release from brain neurons. The present study explores the hypothesis that presynaptic nAChRs help to increase spontaneous release from efferent terminals on cochlear hair cells. Direct application of nicotine (which does not activate the hair cells' α9α10-containing nAChRs) produces sustained efferent transmitter release, implicating presynaptic nAChRs in this response. The effect of nicotine was reduced by application of ryanodine that reduces release of calcium from intraterminal stores.NEW & NOTEWORTHY Sensory organs exhibit spontaneous activity before the onset of response to external stimuli. Such activity in the cochlea is subject to modulation by cholinergic efferent neurons that directly inhibit sensory hair cells (inner hair cells). Those efferent neurons are themselves subject to various modulatory mechanisms. One such mechanism is positive feedback by released acetylcholine onto presynaptic nicotinic acetylcholine receptors causing further release of acetylcholine.
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Affiliation(s)
- Y Zhang
- The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - E Glowatzki
- The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - I Roux
- The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland.,Otolaryngology Branch, National Institute on Deafness and Other Communication Disorders (NIDCD), National Institutes of Health, Porter Neuroscience Research Center, Bethesda, Maryland
| | - P A Fuchs
- The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland
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13
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Yu Z, McIntosh JM, Sadeghi SG, Glowatzki E. Efferent synaptic transmission at the vestibular type II hair cell synapse. J Neurophysiol 2020; 124:360-374. [PMID: 32609559 DOI: 10.1152/jn.00143.2020] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In the vestibular peripheral organs, type I and type II hair cells (HCs) transmit incoming signals via glutamatergic quantal transmission onto afferent nerve fibers. Additionally, type I HCs transmit via "non-quantal" transmission to calyx afferent fibers, by accumulation of glutamate and potassium in the synaptic cleft. Vestibular efferent inputs originating in the brainstem contact type II HCs and vestibular afferents. Here, synaptic inputs to type II HCs were characterized by using electrical and optogenetic stimulation of efferent fibers combined with in vitro whole cell patch-clamp recording from type II HCs in the rodent vestibular crista. Properties of efferent synaptic currents in type II HCs were similar to those found in cochlear HCs and mediated by activation of α9-containing nicotinic acetylcholine receptors (nAChRs) and small-conductance calcium-activated potassium (SK) channels. While efferents showed a low probability of release at low frequencies of stimulation, repetitive stimulation resulted in facilitation and increased probability of release. Notably, the membrane potential of type II HCs during optogenetic stimulation of efferents showed a strong hyperpolarization in response to single pulses and was further enhanced by repetitive stimulation. Such efferent-mediated inhibition of type II HCs can provide a mechanism to adjust the contribution of signals from type I and type II HCs to vestibular nerve fibers, with a shift of the response to be more like that of calyx-only afferents with faster non-quantal responses.NEW & NOTEWORTHY Type II vestibular hair cells (HCs) receive inputs from efferent neurons in the brain stem. We used in vitro optogenetic and electrical stimulation of vestibular efferent fibers to study their synaptic inputs to type II HCs. Stimulation of efferents inhibited type II HCs, similar to efferent effects on cochlear HCs. We propose that efferent inputs adjust the contribution of signals from type I and II HCs to vestibular nerve fibers.
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Affiliation(s)
- Zhou Yu
- Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland.,Department of Otolaryngology-Head and Neck Surgery, The Center for Hearing and Balance, and The Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland
| | | | - Soroush G Sadeghi
- Department of Communicative Disorders and Sciences, and Center for Hearing and Deafness, State University of New York at Buffalo, Buffalo, New York.,Neuroscience Program, State University of New York at Buffalo, Buffalo, New York
| | - Elisabeth Glowatzki
- Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland.,Department of Otolaryngology-Head and Neck Surgery, The Center for Hearing and Balance, and The Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland
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14
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Effects of Efferent Activity on Hair Bundle Mechanics. J Neurosci 2020; 40:2390-2402. [PMID: 32086256 DOI: 10.1523/jneurosci.1312-19.2020] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Revised: 01/31/2020] [Accepted: 02/09/2020] [Indexed: 11/21/2022] Open
Abstract
Hair cells in both the auditory and vestibular systems receive efferent innervation. A number of prior studies have indicated that efferent regulation serves to diminish the overall sensitivity of the auditory system. The efferent pathway is believed to affect the sensitivity and frequency selectivity of the hair cell by modulating its membrane potential. However, its effect on the mechanical response of the hair cell has not been established. We explored how stimulation of the efferent neurons affects the mechanical responsiveness of an individual hair bundle. We tested this effect on in vitro preparations of hair cells in the sacculi of American bullfrogs of both genders. Efferent stimulation routinely resulted in an immediate increase of the frequency of hair bundle spontaneous oscillations for the duration of the stimulus. Enlarging the stimulus amplitude and pulse length, or conversely, decreasing the interpulse interval led to oscillation suppression. Additionally, we tested the effects of efference on the hair bundle response to mechanical stimulation. The receptive field maps of hair cells undergoing efferent actuation demonstrated an overall desensitization with respect to those of unstimulated cells.SIGNIFICANCE STATEMENT The efferent system is an important aide for the performance of the auditory system. It has been seen to contribute to sound detection and localization, ototoxicity prevention, and speech comprehension. Although measurements have demonstrated that efference suppresses basilar membrane movement, there is still much unknown about how efferent activity affects hearing mechanics. Here, we explore the mechanical basis for the efferent system's capabilities at the level of the hair bundle. We present optical recordings, receptive field maps, and sensitivity curves that show a hair bundle is desensitized by efferent stimulation. This supports the hypothesis that efferent regulation may be a biological control parameter for tuning the hair bundle's mechanical sensitivity.
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15
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Poppi LA, Holt JC, Lim R, Brichta AM. A review of efferent cholinergic synaptic transmission in the vestibular periphery and its functional implications. J Neurophysiol 2019; 123:608-629. [PMID: 31800345 DOI: 10.1152/jn.00053.2019] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
It has been over 60 years since peripheral efferent vestibular terminals were first identified in mammals, and yet the function of the efferent vestibular system remains obscure. One reason for the lack of progress may be due to our deficient understanding of the peripheral efferent synapse. Although vestibular efferent terminals were identified as cholinergic less than a decade after their anatomical characterization, the cellular mechanisms that underlie the properties of these synapses have had to be inferred. In this review we examine how recent mammalian studies have begun to reveal both nicotinic and muscarinic effects at these terminals and therefore provide a context for fast and slow responses observed in classic electrophysiological studies of the mammalian efferent vestibular system, nearly 40 years ago. Although incomplete, these new results together with those of recent behavioral studies are helping to unravel the mysterious and perplexing action of the efferent vestibular system. Armed with this information, we may finally appreciate the behavioral framework in which the efferent vestibular system operates.
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Affiliation(s)
- L A Poppi
- School of Biomedical Sciences and Pharmacy, The University of Newcastle, Newcastle, NSW, Australia.,Hunter Medical Research Institute, New Lambton Heights, NSW, Australia.,Preclinical Neurobiology Research Group, The University of Newcastle, Newcastle, NSW, Australia
| | - J C Holt
- Department of Otolaryngology, University of Rochester Medical Center, Rochester, New York
| | - R Lim
- School of Biomedical Sciences and Pharmacy, The University of Newcastle, Newcastle, NSW, Australia.,Hunter Medical Research Institute, New Lambton Heights, NSW, Australia.,Preclinical Neurobiology Research Group, The University of Newcastle, Newcastle, NSW, Australia
| | - A M Brichta
- School of Biomedical Sciences and Pharmacy, The University of Newcastle, Newcastle, NSW, Australia.,Hunter Medical Research Institute, New Lambton Heights, NSW, Australia.,Preclinical Neurobiology Research Group, The University of Newcastle, Newcastle, NSW, Australia
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16
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Abstract
Cholinergic efferent neurons originating in the brainstem innervate the acoustico-lateralis organs (inner ear, lateral line) of vertebrates. These release acetylcholine (ACh) to inhibit hair cells through activation of calcium-dependent potassium channels. In the mammalian cochlea, ACh shunts and suppresses outer hair cell (OHC) electromotility, reducing the essential amplification of basilar membrane motion. Consequently, medial olivocochlear neurons that inhibit OHCs reduce the sensitivity and frequency selectivity of afferent neurons driven by cochlear vibration of inner hair cells (IHCs). The cholinergic synapse on hair cells involves an unusual ionotropic ACh receptor, and a near-membrane postsynaptic cistern. Lateral olivocochlear (LOC) neurons modulate type I afferents by still-to-be-defined synaptic mechanisms. Olivocochlear neurons can be activated by a reflex arc that includes the auditory nerve and projections from the cochlear nucleus. They are also subject to modulation by higher-order central auditory interneurons. Through its actions on cochlear hair cells, afferent neurons, and higher centers, the olivocochlear system protects against age-related and noise-induced hearing loss, improves signal coding in noise under certain conditions, modulates selective attention to sensory stimuli, and influences sound localization.
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Affiliation(s)
- Paul Albert Fuchs
- The Center for Hearing and Balance, Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2195
| | - Amanda M Lauer
- The Center for Hearing and Balance, Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2195
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17
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Compartmentalization of antagonistic Ca 2+ signals in developing cochlear hair cells. Proc Natl Acad Sci U S A 2018; 115:E2095-E2104. [PMID: 29439202 DOI: 10.1073/pnas.1719077115] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
During a critical developmental period, cochlear inner hair cells (IHCs) exhibit sensory-independent activity, featuring action potentials in which Ca2+ ions play a fundamental role in driving both spiking and glutamate release onto synapses with afferent auditory neurons. This spontaneous activity is controlled by a cholinergic input to the IHC, activating a specialized nicotinic receptor with high Ca2+ permeability, and coupled to the activation of hyperpolarizing SK channels. The mechanisms underlying distinct excitatory and inhibitory Ca2+ roles within a small, compact IHC are unknown. Making use of Ca2+ imaging, afferent auditory bouton recordings, and electron microscopy, the present work shows that unusually high intracellular Ca2+ buffering and "subsynaptic" cisterns provide efficient compartmentalization and tight control of cholinergic Ca2+ signals. Thus, synaptic efferent Ca2+ spillover and cross-talk are prevented, and the cholinergic input preserves its inhibitory signature to ensure normal development of the auditory system.
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18
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Wu JS, Vyas P, Glowatzki E, Fuchs PA. Opposing expression gradients of calcitonin-related polypeptide alpha (Calca/Cgrpα) and tyrosine hydroxylase (Th) in type II afferent neurons of the mouse cochlea. J Comp Neurol 2017; 526:425-438. [PMID: 29055051 DOI: 10.1002/cne.24341] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Revised: 10/04/2017] [Accepted: 10/10/2017] [Indexed: 12/20/2022]
Abstract
Type II spiral ganglion neurons (SGNs) are small caliber, unmyelinated afferents that extend dendritic arbors hundreds of microns along the cochlear spiral, contacting many outer hair cells (OHCs). Despite these many contacts, type II afferents are insensitive to sound and only weakly depolarized by glutamate release from OHCs. Recent studies suggest that type II afferents may be cochlear nociceptors, and can be excited by ATP released during tissue damage, by analogy to somatic pain-sensing C-fibers. The present work compares the expression patterns among cochlear type II afferents of two genes found in C-fibers: calcitonin-related polypeptide alpha (Calca/Cgrpα), specific to pain-sensing C-fibers, and tyrosine hydroxylase (Th), specific to low-threshold mechanoreceptive C-fibers, which was shown previously to be a selective biomarker of type II versus type I cochlear afferents (Vyas et al., ). Whole-mount cochlear preparations from 3-week- to 2-month-old CGRPα-EGFP (GENSAT) mice showed expression of Cgrpα in a subset of SGNs with type II-like peripheral dendrites extending beneath OHCs. Double labeling with other molecular markers confirmed that the labeled SGNs were neither type I SGNs nor olivocochlear efferents. Cgrpα starts to express in type II SGNs before hearing onset, but the expression level declines in the adult. The expression patterns of Cgrpα and Th formed opposing gradients, with Th being preferentially expressed in apical and Cgrpα in basal type II afferent neurons, indicating heterogeneity among type II afferent neurons. The expression of Th and Cgrpα was not mutually exclusive and co-expression could be observed, most abundantly in the middle cochlear turn.
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Affiliation(s)
- Jingjing Sherry Wu
- Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland.,The Center for Hearing and Balance and the Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - Pankhuri Vyas
- The Center for Hearing and Balance and the Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland.,Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - Elisabeth Glowatzki
- Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland.,The Center for Hearing and Balance and the Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland.,Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - Paul Albert Fuchs
- Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland.,The Center for Hearing and Balance and the Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland.,Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland
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19
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Fettiplace R. Hair Cell Transduction, Tuning, and Synaptic Transmission in the Mammalian Cochlea. Compr Physiol 2017; 7:1197-1227. [PMID: 28915323 DOI: 10.1002/cphy.c160049] [Citation(s) in RCA: 197] [Impact Index Per Article: 28.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Sound pressure fluctuations striking the ear are conveyed to the cochlea, where they vibrate the basilar membrane on which sit hair cells, the mechanoreceptors of the inner ear. Recordings of hair cell electrical responses have shown that they transduce sound via submicrometer deflections of their hair bundles, which are arrays of interconnected stereocilia containing the mechanoelectrical transducer (MET) channels. MET channels are activated by tension in extracellular tip links bridging adjacent stereocilia, and they can respond within microseconds to nanometer displacements of the bundle, facilitated by multiple processes of Ca2+-dependent adaptation. Studies of mouse mutants have produced much detail about the molecular organization of the stereocilia, the tip links and their attachment sites, and the MET channels localized to the lower end of each tip link. The mammalian cochlea contains two categories of hair cells. Inner hair cells relay acoustic information via multiple ribbon synapses that transmit rapidly without rundown. Outer hair cells are important for amplifying sound-evoked vibrations. The amplification mechanism primarily involves contractions of the outer hair cells, which are driven by changes in membrane potential and mediated by prestin, a motor protein in the outer hair cell lateral membrane. Different sound frequencies are separated along the cochlea, with each hair cell being tuned to a narrow frequency range; amplification sharpens the frequency resolution and augments sensitivity 100-fold around the cell's characteristic frequency. Genetic mutations and environmental factors such as acoustic overstimulation cause hearing loss through irreversible damage to the hair cells or degeneration of inner hair cell synapses. © 2017 American Physiological Society. Compr Physiol 7:1197-1227, 2017.
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Affiliation(s)
- Robert Fettiplace
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
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20
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Mohammadi SA, Christie MJ. Conotoxin Interactions with α9α10-nAChRs: Is the α9α10-Nicotinic Acetylcholine Receptor an Important Therapeutic Target for Pain Management? Toxins (Basel) 2015; 7:3916-32. [PMID: 26426047 PMCID: PMC4626711 DOI: 10.3390/toxins7103916] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Revised: 09/14/2015] [Accepted: 09/18/2015] [Indexed: 11/16/2022] Open
Abstract
The α9α10-nicotinic acetylcholine receptor (nAChR) has been implicated in pain and has been proposed to be a novel target for analgesics. However, the evidence to support the involvement of the α9α10-nAChR in pain is conflicted. This receptor was first implicated in pain with the characterisation of conotoxin Vc1.1, which is highly selective for α9α10-nAChRs and is an efficacious analgesic in chronic pain models with restorative capacities and no reported side effects. Numerous other analgesic conotoxin and non-conotoxin molecules have been subsequently characterised that also inhibit α9α10-nAChRs. However, there is evidence that α9α10-nAChR inhibition is neither necessary nor sufficient for analgesia. α9α10-nAChR-inhibiting analogues of Vc1.1 have no analgesic effects. Genetically-modified α9-nAChR knockout mice have a phenotype that is markedly different from the analgesic profile of Vc1.1 and similar conotoxins, suggesting that the conotoxin effects are largely independent of α9α10-nAChRs. Furthermore, an alternative mechanism of analgesia by Vc1.1 and other similar conotoxins involving non-canonical coupling of GABAB receptors to voltage-gated calcium channels is known. Additional incongruities regarding α9α10-nAChRs in analgesia are discussed. A more comprehensive characterisation of the role of α9α10-nAChRs in pain is crucial for understanding the analgesic action of conotoxins and for improved drug design.
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Affiliation(s)
- Sarasa A Mohammadi
- Discipline of Pharmacology, the University of Sydney, Sydney, NSW 2006, Australia.
| | - MacDonald J Christie
- Discipline of Pharmacology, the University of Sydney, Sydney, NSW 2006, Australia.
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21
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Activation of BK and SK channels by efferent synapses on outer hair cells in high-frequency regions of the rodent cochlea. J Neurosci 2015; 35:1821-30. [PMID: 25653344 DOI: 10.1523/jneurosci.2790-14.2015] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Cholinergic neurons of the brainstem olivary complex project to and inhibit outer hair cells (OHCs), refining acoustic sensitivity of the mammalian cochlea. In all vertebrate hair cells studied to date, cholinergic inhibition results from the combined action of ionotropic acetylcholine receptors and associated calcium-activated potassium channels. Although inhibition was thought to involve exclusively small conductance (SK potassium channels), recent findings have shown that BK channels also contribute to inhibition in basal, high-frequency OHCs after the onset of hearing. Here we show that the waveform of randomly timed IPSCs (evoked by high extracellular potassium) in high-frequency OHCs is altered by blockade of either SK or BK channels, with BK channels supporting faster synaptic waveforms and SK channels supporting slower synaptic waveforms. Consistent with these findings, IPSCs recorded from high-frequency OHCs that express BK channels are briefer than IPSCs recorded from low-frequency (apical) OHCs that do not express BK channels and from immature high-frequency OHCs before the developmental onset of BK channel expression. Likewise, OHCs of BKα(-/-) mice lacking the pore-forming α-subunit of BK channels have longer IPSCs than do the OHCs of BKα(+/+) littermates. Furthermore, serial reconstruction of electron micrographs showed that postsynaptic cisterns of BKα(-/-) OHCs were smaller than those of BKα(+/+) OHCs, and immunofluorescent quantification showed that efferent presynaptic terminals of BKα(-/-) OHCs were smaller than those of BKα(+/+) OHCs. Together, these findings indicate that BK channels contribute to postsynaptic function, and influence the structural maturation of efferent-OHC synapses.
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22
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Nouvian R, Eybalin M, Puel JL. Cochlear efferents in developing adult and pathological conditions. Cell Tissue Res 2015; 361:301-9. [DOI: 10.1007/s00441-015-2158-z] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Accepted: 02/19/2015] [Indexed: 10/23/2022]
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23
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Im GJ, Moskowitz HS, Lehar M, Hiel H, Fuchs PA. Synaptic calcium regulation in hair cells of the chicken basilar papilla. J Neurosci 2014; 34:16688-97. [PMID: 25505321 PMCID: PMC4261095 DOI: 10.1523/jneurosci.2615-14.2014] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2014] [Revised: 09/26/2014] [Accepted: 10/30/2014] [Indexed: 11/21/2022] Open
Abstract
Cholinergic inhibition of hair cells occurs by activation of calcium-dependent potassium channels. A near-membrane postsynaptic cistern has been proposed to serve as a store from which calcium is released to supplement influx through the ionotropic ACh receptor. However, the time and voltage dependence of acetylcholine (ACh)-evoked potassium currents reveal a more complex relationship between calcium entry and release from stores. The present work uses voltage steps to regulate calcium influx during the application of ACh to hair cells in the chicken basilar papilla. When calcium influx was terminated at positive membrane potential, the ACh-evoked potassium current decayed exponentially over ∼100 ms. However, at negative membrane potentials, this current exhibited a secondary rise in amplitude that could be eliminated by dihydropyridine block of the voltage-gated calcium channels of the hair cell. Calcium entering through voltage-gated channels may transit through the postsynaptic cistern, since ryanodine and sarcoendoplasmic reticulum calcium-ATPase blockers altered the time course and magnitude of this secondary, voltage-dependent contribution to ACh-evoked potassium current. Serial section electron microscopy showed that efferent and afferent synaptic structures are juxtaposed, supporting the possibility that voltage-gated influx at afferent ribbon synapses influences calcium homeostasis during long-lasting cholinergic inhibition. In contrast, spontaneous postsynaptic currents ("minis") resulting from stochastic efferent release of ACh were made briefer by ryanodine, supporting the hypothesis that the synaptic cistern serves primarily as a calcium barrier and sink during low-level synaptic activity. Hypolemmal cisterns such as that at the efferent synapse of the hair cell can play a dynamic role in segregating near-membrane calcium for short-term and long-term signaling.
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Affiliation(s)
- Gi Jung Im
- The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, and the Center for Sensory Biology, the Institute for Basic Biomedical Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Howard S Moskowitz
- The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, and the Center for Sensory Biology, the Institute for Basic Biomedical Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Mohammed Lehar
- The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, and the Center for Sensory Biology, the Institute for Basic Biomedical Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Hakim Hiel
- The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, and the Center for Sensory Biology, the Institute for Basic Biomedical Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Paul Albert Fuchs
- The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, and the Center for Sensory Biology, the Institute for Basic Biomedical Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
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24
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Rahnama’i MS, Hohnen R, Van Kerrebroeck PEV, van Koeveringe GA. Phosphodiesterase type 2 distribution in the guinea pig urinary bladder. World J Urol 2014; 33:1623-33. [DOI: 10.1007/s00345-014-1455-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Accepted: 11/24/2014] [Indexed: 12/20/2022] Open
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25
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Katz E, Elgoyhen AB. Short-term plasticity and modulation of synaptic transmission at mammalian inhibitory cholinergic olivocochlear synapses. Front Syst Neurosci 2014; 8:224. [PMID: 25520631 PMCID: PMC4251319 DOI: 10.3389/fnsys.2014.00224] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Accepted: 11/06/2014] [Indexed: 12/23/2022] Open
Abstract
The organ of Corti, the mammalian sensory epithelium of the inner ear, has two types of mechanoreceptor cells, inner hair cells (IHCs) and outer hair cells (OHCs). In this sensory epithelium, vibrations produced by sound waves are transformed into electrical signals. When depolarized by incoming sounds, IHCs release glutamate and activate auditory nerve fibers innervating them and OHCs, by virtue of their electromotile property, increase the amplification and fine tuning of sound signals. The medial olivocochlear (MOC) system, an efferent feedback system, inhibits OHC activity and thereby reduces the sensitivity and sharp tuning of cochlear afferent fibers. During neonatal development, IHCs fire Ca2+ action potentials which evoke glutamate release promoting activity in the immature auditory system in the absence of sensory stimuli. During this period, MOC fibers also innervate IHCs and are thought to modulate their firing rate. Both the MOC-OHC and the MOC-IHC synapses are cholinergic, fast and inhibitory and mediated by the α9α10 nicotinic cholinergic receptor (nAChR) coupled to the activation of calcium-activated potassium channels that hyperpolarize the hair cells. In this review we discuss the biophysical, functional and molecular data which demonstrate that at the synapses between MOC efferent fibers and cochlear hair cells, modulation of transmitter release as well as short term synaptic plasticity mechanisms, operating both at the presynaptic terminal and at the postsynaptic hair-cell, determine the efficacy of these synapses and shape the hair cell response pattern.
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Affiliation(s)
- Eleonora Katz
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) Buenos Aires, Argentina ; Departamento de Fisiología, Biología Molecular y Celular "Prof. Héctor Maldonado", Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires Buenos Aires, Argentina
| | - Ana Belén Elgoyhen
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) Buenos Aires, Argentina ; Tercera Cátedra de Farmacología, Facultad de Medicina, Universidad de Buenos Aires Buenos Aires, Argentina
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26
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Fuchs PA, Lehar M, Hiel H. Ultrastructure of cisternal synapses on outer hair cells of the mouse cochlea. J Comp Neurol 2014; 522:717-29. [PMID: 24122766 PMCID: PMC4474150 DOI: 10.1002/cne.23478] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2013] [Revised: 09/20/2013] [Accepted: 09/20/2013] [Indexed: 12/31/2022]
Abstract
C (cisternal) synapses with a near membrane postsynaptic cistern are found on motor neurons and other central neurons, where their functional role is unknown. Similarly structured cisternal synapses mediate cholinergic inhibition of cochlear hair cells via α9α10-containing ionotropic receptors and associated calcium-activated (SK2) potassium channels, providing the opportunity to examine the ultrastructure of genetically altered cisternal synapses. Serial section electron microscopy was used to examine efferent synapses of outer hair cells (OHCs) in mice with diminished or enhanced cholinergic inhibition. The contact area of efferent terminals, the appositional area of the postsynaptic cistern, the distance of the cistern from the plasma membrane, and the average width of the cisternal lumen were recorded. The synaptic cisterns of wild-type OHCs were closely aligned (14-nm separation) with the hair cell membrane and coextensive with the micrometers-long synaptic terminals. The cisternal lumen averaged 18 nm so that the cisternal volume was approximately 30% larger than that of the cytoplasmic space between the cistern and the plasma membrane. Synaptic ultrastructure of α9L9'T knockin OHCs (acetylcholine receptor gain of function) were like those of wild-type littermates except that cisternal volumes were significantly larger. OHCs of SK2 knockout mice had few small efferent terminals. Synaptic cisterns were present, but smaller than those of wild-type littermates. Taken together, these data suggest that the cistern serves as a sink or buffer to isolate synaptic calcium signals.
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Affiliation(s)
- Paul Albert Fuchs
- Center for Hearing and Balance, Otolaryngology-Head and
Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland
21205
- Center for Sensory Biology, Johns Hopkins University School
of Medicine, Baltimore, Maryland 21205
| | - Mohamed Lehar
- Center for Hearing and Balance, Otolaryngology-Head and
Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland
21205
| | - Hakim Hiel
- Center for Hearing and Balance, Otolaryngology-Head and
Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland
21205
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27
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Scholl ES, Pirone A, Cox DH, Duncan RK, Jacob MH. Alternative splice isoforms of small conductance calcium-activated SK2 channels differ in molecular interactions and surface levels. Channels (Austin) 2014; 8:62-75. [PMID: 24394769 PMCID: PMC4048344 DOI: 10.4161/chan.27470] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Small conductance Ca2+-sensitive potassium (SK2) channels are voltage-independent, Ca2+-activated ion channels that conduct potassium cations and thereby modulate the intrinsic excitability and synaptic transmission of neurons and sensory hair cells. In the cochlea, SK2 channels are functionally coupled to the highly Ca2+ permeant α9/10-nicotinic acetylcholine receptors (nAChRs) at olivocochlear postsynaptic sites. SK2 activation leads to outer hair cell hyperpolarization and frequency-selective suppression of afferent sound transmission. These inhibitory responses are essential for normal regulation of sound sensitivity, frequency selectivity, and suppression of background noise. However, little is known about the molecular interactions of these key functional channels. Here we show that SK2 channels co-precipitate with α9/10-nAChRs and with the actin-binding protein α-actinin-1. SK2 alternative splicing, resulting in a 3 amino acid insertion in the intracellular 3′ terminus, modulates these interactions. Further, relative abundance of the SK2 splice variants changes during developmental stages of synapse maturation in both the avian cochlea and the mammalian forebrain. Using heterologous cell expression to separately study the 2 distinct isoforms, we show that the variants differ in protein interactions and surface expression levels, and that Ca2+ and Ca2+-bound calmodulin differentially regulate their protein interactions. Our findings suggest that the SK2 isoforms may be distinctly modulated by activity-induced Ca2+ influx. Alternative splicing of SK2 may serve as a novel mechanism to differentially regulate the maturation and function of olivocochlear and neuronal synapses.
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Affiliation(s)
- Elizabeth Storer Scholl
- Department of Neuroscience; Tufts University Sackler School of Graduate Biomedical Sciences; Boston, MA USA
| | - Antonella Pirone
- Department of Neuroscience; Tufts University Sackler School of Graduate Biomedical Sciences; Boston, MA USA
| | - Daniel H Cox
- Department of Neuroscience; Tufts University Sackler School of Graduate Biomedical Sciences; Boston, MA USA
| | - R Keith Duncan
- Department of Otolaryngology; University of Michigan; Ann Arbor, MI USA
| | - Michele H Jacob
- Department of Neuroscience; Tufts University Sackler School of Graduate Biomedical Sciences; Boston, MA USA
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28
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Fuchs PA. It takes two to tango. Channels (Austin) 2014; 8:167. [PMID: 25469408 PMCID: PMC5210167 DOI: 10.4161/chan.28999] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2014] [Accepted: 02/11/2014] [Indexed: 11/19/2022] Open
Affiliation(s)
- Paul Albert Fuchs
- The Center for Hearing and Balance; Department of Otolaryngology-Head and Neck Surgery; Center for Sensory Biology in the Institute for Basic Biomedical Science; Johns Hopkins University School of Medicine; Baltimore, MD USA
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29
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Presynaptic maturation in auditory hair cells requires a critical period of sensory-independent spiking activity. Proc Natl Acad Sci U S A 2013; 110:8720-5. [PMID: 23650376 DOI: 10.1073/pnas.1219578110] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The development of neural circuits relies on spontaneous electrical activity that occurs during immature stages of development. In the developing mammalian auditory system, spontaneous calcium action potentials are generated by inner hair cells (IHCs), which form the primary sensory synapse. It remains unknown whether this electrical activity is required for the functional maturation of the auditory system. We found that sensory-independent electrical activity controls synaptic maturation in IHCs. We used a mouse model in which the potassium channel SK2 is normally overexpressed, but can be modulated in vivo using doxycycline. SK2 overexpression affected the frequency and duration of spontaneous action potentials, which prevented the development of the Ca(2+)-sensitivity of vesicle fusion at IHC ribbon synapses, without affecting their morphology or general cell development. By manipulating the in vivo expression of SK2 channels, we identified the "critical period" during which spiking activity influences IHC synaptic maturation. Here we provide direct evidence that IHC development depends upon a specific temporal pattern of calcium spikes before sound-driven neuronal activity.
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Lauer AM, Fuchs PA, Ryugo DK, Francis HW. Efferent synapses return to inner hair cells in the aging cochlea. Neurobiol Aging 2012; 33:2892-902. [PMID: 22405044 DOI: 10.1016/j.neurobiolaging.2012.02.007] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2011] [Revised: 02/09/2012] [Accepted: 02/10/2012] [Indexed: 01/04/2023]
Abstract
Efferent innervation of the cochlea undergoes extensive modification early in development, but it is unclear if efferent synapses are modified by age, hearing loss, or both. Structural alterations in the cochlea affecting information transfer from the auditory periphery to the brain may contribute to age-related hearing deficits. We investigated changes to efferent innervation in the vicinity of inner hair cells (IHCs) in young and old C57BL/6 mice using transmission electron microscopy to reveal increased efferent innervation of IHCs in older animals. Efferent contacts on IHCs contained focal presynaptic accumulations of small vesicles. Synaptic vesicle size and shape were heterogeneous. Postsynaptic cisterns were occasionally observed. Increased IHC efferent innervation was associated with a smaller number of afferent synapses per IHC, increased outer hair cell loss, and elevated auditory brainstem response thresholds. Efferent axons also formed synapses on afferent dendrites but with a reduced prevalence in older animals. Age-related reduction of afferent activity may engage signaling pathways that support the return to an immature state of efferent innervation of the cochlea.
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Affiliation(s)
- Amanda M Lauer
- The Center for Hearing and Balance, Department of Otolaryngology-HNS, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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Onset of cholinergic efferent synaptic function in sensory hair cells of the rat cochlea. J Neurosci 2011; 31:15092-101. [PMID: 22016543 DOI: 10.1523/jneurosci.2743-11.2011] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
In the developing mammalian cochlea, the sensory hair cells receive efferent innervation originating in the superior olivary complex. This input is mediated by α9/α10 nicotinic acetylcholine receptors (nAChRs) and is inhibitory due to the subsequent activation of calcium-dependent SK2 potassium channels. We examined the acquisition of this cholinergic efferent input using whole-cell voltage-clamp recordings from inner hair cells (IHCs) in acutely excised apical turns of the rat cochlea from embryonic day 21 to postnatal day 8 (P8). Responses to 1 mm acetylcholine (ACh) were detected from P0 on in almost every IHC. The ACh-activated current amplitude increased with age and demonstrated the same pharmacology as α9-containing nAChRs. Interestingly, at P0, the ACh response was not coupled to SK2 channels, so that the initial cholinergic response was excitatory and could trigger action potentials in IHCs. Coupling to SK current was detected earliest at P1 in a subset of IHCs and by P3 in every IHC studied. Clustered nAChRs and SK2 channels were found on IHCs from P1 on using Alexa Fluor 488 conjugated α-bungarotoxin and SK2 immunohistochemistry. The number of nAChRs clusters increased with age to 16 per IHC at P8. Cholinergic efferent synaptic currents first appeared in a subset of IHCs at P1 and by P3 in every IHC studied, contemporaneously with ACh-evoked SK currents, suggesting that SK2 channels may be necessary at onset of synaptic function. An analogous pattern of development was observed for the efferent synapses that form later (P6-P8) on outer hair cells in the basal cochlea.
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The efferent medial olivocochlear-hair cell synapse. ACTA ACUST UNITED AC 2011; 106:47-56. [PMID: 21762779 DOI: 10.1016/j.jphysparis.2011.06.001] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2011] [Accepted: 06/24/2011] [Indexed: 01/14/2023]
Abstract
Amplification of incoming sounds in the inner ear is modulated by an efferent pathway which travels back from the brain all the way to the cochlea. The medial olivocochlear system makes synaptic contacts with hair cells, where the neurotransmitter acetylcholine is released. Synaptic transmission is mediated by a unique nicotinic cholinergic receptor composed of α9 and α10 subunits, which is highly Ca2+ permeable and is coupled to a Ca2+-activated SK potassium channel. Thus, hyperpolarization of hair cells follows efferent fiber activation. In this work we review the literature that has enlightened our knowledge concerning the intimacies of this synapse.
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Lenz DR, Avraham KB. Hereditary hearing loss: from human mutation to mechanism. Hear Res 2011; 281:3-10. [PMID: 21664957 DOI: 10.1016/j.heares.2011.05.021] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2011] [Revised: 05/26/2011] [Accepted: 05/27/2011] [Indexed: 11/17/2022]
Abstract
The genetic heterogeneity of hereditary hearing loss is thus far represented by hundreds of genes encoding a large variety of proteins. Mutations in these genes have been discovered for patients with different modes of inheritance and types of hearing loss, ranging from syndromic to non-syndromic and mild to profound. In many cases, the mechanisms whereby the mutations lead to hearing loss have been partly elucidated using cell culture systems and mouse and other animal models. The discovery of the genes has completely changed the practice of genetic counseling in this area, providing potential diagnosis in many cases that can be coupled with clinical phenotypes and offer predictive information for families. In this review we provide three examples of gene discovery in families with hereditary hearing loss, all associated with elucidation of some of the mechanisms leading to hair cell degeneration and pathology of deafness.
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Affiliation(s)
- Danielle R Lenz
- Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
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Wersinger E, Fuchs PA. Modulation of hair cell efferents. Hear Res 2010; 279:1-12. [PMID: 21187136 DOI: 10.1016/j.heares.2010.12.018] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/07/2010] [Revised: 12/10/2010] [Accepted: 12/20/2010] [Indexed: 02/01/2023]
Abstract
Outer hair cells (OHCs) amplify the sound-evoked motion of the basilar membrane to enhance acoustic sensitivity and frequency selectivity. Medial olivocochlear (MOC) efferents inhibit OHCs to reduce the sound-evoked response of cochlear afferent neurons. OHC inhibition occurs through the activation of postsynaptic α9α10 nicotinic receptors tightly coupled to calcium-dependent SK2 channels that hyperpolarize the hair cell. MOC neurons are cholinergic but a number of other neurotransmitters and neuromodulators have been proposed to participate in efferent transmission, with emerging evidence for both pre- and postsynaptic effects. Cochlear inhibition in vivo is maximized by repetitive activation of the efferents, reflecting facilitation and summation of transmitter release onto outer hair cells. This review summarizes recent studies on cellular and molecular mechanisms of cholinergic inhibition and the regulation of those molecular components, in particular the involvement of intracellular calcium. Facilitation at the efferent synapse is compared in a variety of animals, as well as other possible mechanisms of modulation of ACh release. These results suggest that short-term plasticity contributes to effective cholinergic inhibition of hair cells.
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Affiliation(s)
- Eric Wersinger
- The Center for Hearing and Balance, Department of Otolaryngology Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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Wersinger E, McLean WJ, Fuchs PA, Pyott SJ. BK channels mediate cholinergic inhibition of high frequency cochlear hair cells. PLoS One 2010; 5:e13836. [PMID: 21079807 PMCID: PMC2973960 DOI: 10.1371/journal.pone.0013836] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2010] [Accepted: 10/07/2010] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Outer hair cells are the specialized sensory cells that empower the mammalian hearing organ, the cochlea, with its remarkable sensitivity and frequency selectivity. Sound-evoked receptor potentials in outer hair cells are shaped by both voltage-gated K(+) channels that control the membrane potential and also ligand-gated K(+) channels involved in the cholinergic efferent modulation of the membrane potential. The objectives of this study were to investigate the tonotopic contribution of BK channels to voltage- and ligand-gated currents in mature outer hair cells from the rat cochlea. METHODOLOGY/PRINCIPAL Findings In this work we used patch clamp electrophysiology and immunofluorescence in tonotopically defined segments of the rat cochlea to determine the contribution of BK channels to voltage- and ligand-gated currents in outer hair cells. Although voltage and ligand-gated currents have been investigated previously in hair cells from the rat cochlea, little is known about their tonotopic distribution or potential contribution to efferent inhibition. We found that apical (low frequency) outer hair cells had no BK channel immunoreactivity and little or no BK current. In marked contrast, basal (high frequency) outer hair cells had abundant BK channel immunoreactivity and BK currents contributed significantly to both voltage-gated and ACh-evoked K(+) currents. CONCLUSIONS/SIGNIFICANCE Our findings suggest that basal (high frequency) outer hair cells may employ an alternative mechanism of efferent inhibition mediated by BK channels instead of SK2 channels. Thus, efferent synapses may use different mechanisms of action both developmentally and tonotopically to support high frequency audition. High frequency audition has required various functional specializations of the mammalian cochlea, and as shown in our work, may include the utilization of BK channels at efferent synapses. This mechanism of efferent inhibition may be related to the unique acetylcholine receptors that have evolved in mammalian hair cells compared to those of other vertebrates.
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Affiliation(s)
- Eric Wersinger
- Department of Otolaryngology Head and Neck Surgery, Center for Hearing and Balance, and Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Will J. McLean
- Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, North Carolina, United States of America
| | - Paul A. Fuchs
- Department of Otolaryngology Head and Neck Surgery, Center for Hearing and Balance, and Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Sonja J. Pyott
- Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, North Carolina, United States of America
- * E-mail:
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Castellano-Muñoz M, Israel SH, Hudspeth AJ. Efferent control of the electrical and mechanical properties of hair cells in the bullfrog's sacculus. PLoS One 2010; 5:e13777. [PMID: 21048944 PMCID: PMC2966443 DOI: 10.1371/journal.pone.0013777] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2010] [Accepted: 08/25/2010] [Indexed: 11/22/2022] Open
Abstract
Background Hair cells in the auditory, vestibular, and lateral-line systems respond to mechanical stimulation and transmit information to afferent nerve fibers. The sensitivity of mechanoelectrical transduction is modulated by the efferent pathway, whose activity usually reduces the responsiveness of hair cells. The basis of this effect remains unknown. Methodology and Principal Findings We employed immunocytological, electrophysiological, and micromechanical approaches to characterize the anatomy of efferent innervation and the effect of efferent activity on the electrical and mechanical properties of hair cells in the bullfrog's sacculus. We found that efferent fibers form extensive synaptic terminals on all macular and extramacular hair cells. Macular hair cells expressing the Ca2+-buffering protein calretinin contain half as many synaptic ribbons and are innervated by twice as many efferent terminals as calretinin-negative hair cells. Efferent activity elicits inhibitory postsynaptic potentials in hair cells and thus inhibits their electrical resonance. In hair cells that exhibit spiking activity, efferent stimulation suppresses the generation of action potentials. Finally, efferent activity triggers a displacement of the hair bundle's resting position. Conclusions and Significance The hair cells of the bullfrog's sacculus receive a rich efferent innervation with the heaviest projection to calretinin-containing cells. Stimulation of efferent axons desensitizes the hair cells and suppresses their spiking activity. Although efferent activation influences mechanoelectrical transduction, the mechanical effects on hair bundles are inconsistent.
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Affiliation(s)
- Manuel Castellano-Muñoz
- Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, New York, New York, United States of America
| | - Samuel H. Israel
- Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, New York, New York, United States of America
| | - A. J. Hudspeth
- Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, New York, New York, United States of America
- * E-mail:
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Functional characterization of alpha9-containing cholinergic nicotinic receptors in the rat adrenal medulla: implication in stress-induced functional plasticity. J Neurosci 2010; 30:6732-42. [PMID: 20463235 DOI: 10.1523/jneurosci.4997-09.2010] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
An increase in circulating adrenal catecholamine levels constitutes one of the mechanisms whereby organisms cope with stress. Accordingly, stimulus-secretion coupling within the stressed adrenal medullary tissue undergoes persistent remodeling. In particular, cholinergic synaptic neurotransmission between splanchnic nerve terminals and chromaffin cells is upregulated in stressed rats. Since synaptic transmission is mainly supported by activation of postsynaptic neuronal acetylcholine nicotinic receptors (nAChRs), we focused our study on the role of alpha9-containing nAChRs, which have been recently described in chromaffin cells. Taking advantage of their specific blockade by the alpha-conotoxin RgIA (alpha-RgIA), we unveil novel functional roles for these receptors in the stimulus-secretion coupling of the medulla. First, we show that in rat acute adrenal slices, alpha9-containing nAChRs codistribute with synaptophysin and significantly contribute to EPSCs. Second, we show that these receptors are involved in the tonic inhibitory control exerted by cholinergic activity on gap junctional coupling between chromaffin cells, as evidenced by an increased Lucifer yellow diffusion within the medulla in alpha-RgIA-treated slices. Third, we unexpectedly found that alpha9-containing nAChRs dominantly (>70%) contribute to acetylcholine-induced current in cold-stressed rats, whereas alpha3 nAChRs are the main contributing channels in unstressed animals. Consistently, expression levels of alpha9 nAChR transcript and protein are overexpressed in cold-stressed rats. As a functional relevance, we propose that upregulation of alpha9-containing nAChR channels and ensuing dominant contribution in cholinergic signaling may be one of the mechanisms whereby adrenal medullary tissue appropriately adapts to increased splanchnic nerve electrical discharges occurring in stressful situations.
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Modulation of Cav1.3 Ca2+ channel gating by Rab3 interacting molecule. Mol Cell Neurosci 2010; 44:246-59. [PMID: 20363327 DOI: 10.1016/j.mcn.2010.03.011] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2010] [Revised: 03/19/2010] [Accepted: 03/25/2010] [Indexed: 01/10/2023] Open
Abstract
Neurotransmitter release and spontaneous action potentials during cochlear inner hair cell (IHC) development depend on the activity of Ca(v)1.3 voltage-gated L-type Ca(2+) channels. Their voltage- and Ca(2+)-dependent inactivation kinetics are slower than in other tissues but the underlying molecular mechanisms are not yet understood. We found that Rab3-interacting molecule-2alpha (RIM2alpha) mRNA is expressed in immature cochlear IHCs and the protein co-localizes with Ca(v)1.3 in the same presynaptic compartment of IHCs. Expression of RIM proteins in tsA-201 cells revealed binding to the beta-subunit of the channel complex and RIM-induced slowing of both Ca(2+)- and voltage-dependent inactivation of Ca(v)1.3 channels. By inhibiting inactivation, RIM induced a non-inactivating current component typical for IHC Ca(v)1.3 currents which should allow these channels to carry a substantial window current during prolonged depolarizations. These data suggest that RIM2 contributes to the stabilization of Ca(v)1.3 gating kinetics in immature IHCs.
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Current world literature. Curr Opin Otolaryngol Head Neck Surg 2009; 17:412-8. [PMID: 19755872 DOI: 10.1097/moo.0b013e3283318f24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Transcriptional and electrophysiological maturation of neocortical fast-spiking GABAergic interneurons. J Neurosci 2009; 29:7040-52. [PMID: 19474331 DOI: 10.1523/jneurosci.0105-09.2009] [Citation(s) in RCA: 215] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Fast-spiking (FS) interneurons are important elements of neocortical circuitry that constitute the primary source of synaptic inhibition in adult cortex and impart temporal organization on ongoing cortical activity. The highly specialized intrinsic membrane and firing properties that allow cortical FS interneurons to perform these functions are attributable to equally specialized gene expression, which is ultimately coordinated by cell-type-specific transcriptional regulation. Although embryonic transcriptional events govern the initial steps of cell-type specification in most cortical interneurons, including FS cells, the electrophysiological properties that distinguish adult cortical cell types emerge relatively late in postnatal development, and the transcriptional events that drive this maturational process are not known. To address this, we used mouse whole-genome microarrays and whole-cell patch clamp to characterize the transcriptional and electrophysiological maturation of cortical FS interneurons between postnatal day 7 (P7) and P40. We found that the intrinsic and synaptic physiology of FS cells undergoes profound regulation over the first 4 postnatal weeks and that these changes are correlated with primarily monotonic but bidirectional transcriptional regulation of thousands of genes belonging to multiple functional classes. Using our microarray screen as a guide, we discovered that upregulation of two-pore K(+) leak channels between P10 and P25 contributes to one of the major differences between the intrinsic membrane properties of immature and adult FS cells and found a number of other candidate genes that likely confer cell-type specificity on mature FS cells.
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Constitutive expression of the alpha10 nicotinic acetylcholine receptor subunit fails to maintain cholinergic responses in inner hair cells after the onset of hearing. J Assoc Res Otolaryngol 2009; 10:397-406. [PMID: 19452222 DOI: 10.1007/s10162-009-0173-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2009] [Accepted: 05/04/2009] [Indexed: 01/21/2023] Open
Abstract
Efferent inhibition of cochlear hair cells is mediated by alpha9alpha10 nicotinic cholinergic receptors (nAChRs) functionally coupled to calcium-activated, small conductance (SK2) potassium channels. Before the onset of hearing, efferent fibers transiently make functional cholinergic synapses with inner hair cells (IHCs). The retraction of these fibers after the onset of hearing correlates with the cessation of transcription of the Chrna10 (but not the Chrna9) gene in IHCs. To further analyze this developmental change, we generated a transgenic mice whose IHCs constitutively express alpha10 into adulthood by expressing the alpha10 cDNA under the control of the Pou4f3 gene promoter. In situ hybridization showed that the alpha10 mRNA is expressed in IHCs of 8-week-old transgenic mice, but not in wild-type mice. Moreover, this mRNA is translated into a functional protein, since IHCs from P8-P10 alpha10 transgenic mice backcrossed to a Chrna10(-/-) background (whose IHCs have no cholinergic function) displayed normal synaptic and acetylcholine (ACh)-evoked currents in patch-clamp recordings. Thus, the alpha10 transgene restored nAChR function. However, in the alpha10 transgenic mice, no synaptic or ACh-evoked currents were observed in P16-18 IHCs, indicating developmental down-regulation of functional nAChRs after the onset of hearing, as normally observed in wild-type mice. The lack of functional ACh currents correlated with the lack of SK2 currents. These results indicate that multiple features of the efferent postsynaptic complex to IHCs, in addition to the nAChR subunits, are down-regulated in synchrony after the onset of hearing, leading to lack of responses to ACh.
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Gómez-Casati ME, Wedemeyer C, Taranda J, Lipovsek M, Dalamon V, Elgoyhen AB, Katz E. Electrical properties and functional expression of ionic channels in cochlear inner hair cells of mice lacking the alpha10 nicotinic cholinergic receptor subunit. J Assoc Res Otolaryngol 2009; 10:221-32. [PMID: 19252947 DOI: 10.1007/s10162-009-0164-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2008] [Accepted: 02/11/2009] [Indexed: 01/12/2023] Open
Abstract
Cochlear inner hair cells (IHCs) release neurotransmitter onto afferent auditory nerve fibers in response to sound stimulation. During early development, synaptic transmission is triggered by spontaneous Ca2+ spikes which are modulated by an efferent cholinergic innervation to IHCs. This synapse is inhibitory and mediated by the alpha9alpha10 nicotinic cholinergic receptor (nAChR). After the onset of hearing, large-conductance Ca2+-activated K+ channels are acquired and both the spiking activity and the efferent innervation disappear from IHCs. In this work, we studied the developmental changes in the membrane properties of cochlear IHCs from alpha10 nAChR gene (Chrna10) "knockout" mice. Electrophysiological properties of IHCs were studied by whole-cell recordings in acutely excised apical turns of the organ of Corti from developing mice. Neither the spiking activity nor the developmental functional expression of voltage-gated and/or calcium-sensitive K+ channels is altered in the absence of the alpha10 nAChR subunit. The present results show that the alpha10 nAChR subunit is not essential for the correct establishment of the intrinsic electrical properties of IHCs during development.
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Affiliation(s)
- María Eugenia Gómez-Casati
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Consejo Nacional de Investigaciones Científicas y Técnicas, Vuelta de Obligado 2490, Buenos Aires 1428, Argentina
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