Maculae and Dynamic Equilibrium

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Maculae and Dynamic Equilibrium Along with hearing, the inner ear is responsible for encoding information about equilibrium (the sense of balance), which it does in the vestibular apparatus. Similar to the cochlea, the vestibular structures use hair cells with stereocilia to detect movement of fluid, in this case, in response to changes in head position or acceleration. Detection of head position when the body is stationary is termed static equilibrium. The information for static equilibrium comes from the utricle and saccule. Dynamic equilibrium is the perception of acceleration. Information for dynamic equilibrium can come from the utricle and saccule, which detect linear acceleration, and/or the semicircular canals, which detect angular acceleration. The neural signals generated from the vestibule are transmitted to the brainstem and cerebellum from sensory neurons in the vestibular ganglion. The saccule and utricle each contain a sense organ, called the macula, where stereocilia and their supporting cells are found. These maculae (plural) are oriented 90 degrees to one another so that they respond to positions in different planes. The organs can respond to changes in position and acceleration because the tips of their stereocilia project into a dense otolithic membrane made up of a mixture containing granules of calcium and protein, called otoliths, which gives rise to their common name, the otolithic organs. When the maculae (otolithic organs) move, gravity causes the dense otolithic membrane to move relative to the less dense cell layer beneath the stereocilia. This causes the stereocilia to bend, initiating action potentials in the vestibular nerve fibers that innervate them. Bundles of stereocilia are arranged in various directions, so that any direction of inclination will depolarize a subset of the hair cells and hyperpolarize a corresponding subset of sensory neurons. How the body senses head position and the linear (horizontal or vertical) direction of acceleration is determined by the specific pattern of hair-cell activity across the maculae. .

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Stereocilia Rootlets: Actin-Based Structures That Are Essential for Structural Stability of the Hair Bundle

International Journal of Molecular Sciences Review Stereocilia Rootlets: Actin-Based Structures That Are Essential for Structural Stability of the Hair Bundle Itallia Pacentine, Paroma Chatterjee and Peter G. Barr-Gillespie * Oregon Hearing Research Center & Vollum Institute, Oregon Health & Science University, Portland, OR 97239, USA; [email protected] (I.P.); [email protected] (P.C.) * Correspondence: [email protected]; Tel.: +1-503-494-2936 Received: 12 December 2019; Accepted: 1 January 2020; Published: 3 January 2020 Abstract: Sensory hair cells of the inner ear rely on the hair bundle, a cluster of actin-filled stereocilia, to transduce auditory and vestibular stimuli into electrical impulses. Because they are long and thin projections, stereocilia are most prone to damage at the point where they insert into the hair cell’s soma. Moreover, this is the site of stereocilia pivoting, the mechanical movement that induces transduction, which additionally weakens this area mechanically. To bolster this fragile area, hair cells construct a dense core called the rootlet at the base of each stereocilium, which extends down into the actin meshwork of the cuticular plate and firmly anchors the stereocilium. Rootlets are constructed with tightly packed actin filaments that extend from stereocilia actin filaments which are wrapped with TRIOBP; in addition, many other proteins contribute to the rootlet and its associated structures. Rootlets allow stereocilia to sustain innumerable deflections over their lifetimes and exemplify the unique manner in which sensory hair cells exploit actin and its associated proteins to carry out the function of mechanotransduction. Keywords: rootlet; actin; stereocilia; hair cell 1. Introduction Eukaryotic cells use actin as a basic building block of the cytoskeleton.
Nomina Histologica Veterinaria, First Edition

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Ultrastructural Analysis and ABR Alterations in the Cochlear Hair-Cells Following Aminoglycosides Administration in Guinea Pig

Global Journal of Otolaryngology ISSN 2474-7556 Research Article Glob J Otolaryngol Volume 15 Issue 4 - May 2018 Copyright © All rights are reserved by Mohammed A Akeel DOI: 10.19080/GJO.2018.15.555916 Ultrastructural Analysis and ABR Alterations in the Cochlear Hair-cells Following Aminoglycosides Administration in Guinea Pig Mohammed A Akeel* Department of Anatomy, Faculty of Medicine, Jazan University, Jazan, Kingdom of Saudi Arabia Submission: April 18, 2018; Published: May 08, 2018 *Corresponding author: Mohammed A Akeel, Faculty of Medicine, Jazan University, P.O.Box 114, Jazan, Kingdom of Saudi Arabia. Tel: ; Email: Abstract Aims: since their introduction in the 1940. The aim of the present work was to characterize ultrastructural alterations of the sensory hair-cell following different aminoglycosides Aminoglycosides administration, (AG) antibiotics intratympanic were the first VS ototoxic intraperitoneal agents to and highlight to correlate the problem them with of drug-induced auditory brainstem hearing responses and vestibular (ABR). loss, Methods: streptomycin, gentamycin, or netilmicin; respectively, via the peritoneal route. The next four groups received similar treatment via trans- tympanic route. A Thetotal treatment of 48 adult was guinea administered pigs were dividedfor seven into consecutive 8 groups; sixdays. animals On day in 10,each ABR group. was The utilized first fourfor hearing groups receivedevaluation saline and (control),scanning electron microscopy (SEM) examination of the sensory organs was used for morphological study. Results: Streptomycin produced the most severe morphological changes and a higher elevation of ABR thresholds, followed, in order, by gentamycin and netilmicin. Netilmicin ototoxicity observed in both systemic and transtympanic routes was low because of lesser penetration into the inner ear or/ and lower intrinsic toxicity.
Physiology of the Inner Ear Balance

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Stiffness and Tension Gradients of the Hair Cell's Tip-Link Complex In

RESEARCH ARTICLE Stiffness and tension gradients of the hair cell’s tip-link complex in the mammalian cochlea Me´ lanie Tobin1,2, Atitheb Chaiyasitdhi1,2†, Vincent Michel2,3,4†, Nicolas Michalski2,3,4, Pascal Martin1,2* 1Laboratoire Physico-Chimie Curie, Institut Curie, PSL Research University, CNRS UMR168, Paris, France; 2Sorbonne Universite´, Paris, France; 3Laboratoire de Ge´ne´tique et Physiologie de l’Audition, Institut Pasteur, Paris, France; 4UMRS 1120, Institut National de la Sante´ et de la Recherche Me´dicale (INSERM), Paris, France Abstract Sound analysis by the cochlea relies on frequency tuning of mechanosensory hair cells along a tonotopic axis. To clarify the underlying biophysical mechanism, we have investigated the micromechanical properties of the hair cell’s mechanoreceptive hair bundle within the apical half of the rat cochlea. We studied both inner and outer hair cells, which send nervous signals to the brain and amplify cochlear vibrations, respectively. We find that tonotopy is associated with gradients of stiffness and resting mechanical tension, with steeper gradients for outer hair cells, emphasizing the division of labor between the two hair-cell types. We demonstrate that tension in the tip links that convey force to the mechano-electrical transduction channels increases at reduced Ca2+. Finally, we reveal gradients in stiffness and tension at the level of a single tip link. We conclude that mechanical gradients of the tip-link complex may help specify the characteristic frequency of the hair cell. DOI: https://doi.org/10.7554/eLife.43473.001 *For correspondence: [email protected] †These authors contributed equally to this work Introduction The cochlea—the auditory organ of the inner ear—is endowed with a few thousands of mechanosen- Competing interests: The sory hair cells that are each tuned to detect a characteristic sound frequency (Fettiplace and Kim, authors declare that no 2014).
Calcium Entry Into Stereocilia Drives Adaptation of the Mechanoelectrical Transducer Current of Mammalian Cochlear Hair Cells

Calcium entry into stereocilia drives adaptation of the mechanoelectrical transducer current of mammalian cochlear hair cells Laura F. Cornsa,1, Stuart L. Johnsona,1, Corné J. Krosb,c, and Walter Marcottia,2 aDepartment of Biomedical Science, University of Sheffield, Sheffield S10 2TN, United Kingdom; bSussex Neuroscience, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom; and cDepartment of Otorhinolaryngology, Head and Neck Surgery, University Medical Center Groningen, University of Groningen, 9700 RB, Groningen, The Netherlands Edited by A. J. Hudspeth, Howard Hughes Medical Institute, The Rockefeller University, New York, NY, and approved August 22, 2014 (received for review May 28, 2014) Mechanotransduction in the auditory and vestibular systems deflecting their hair bundles using a piezo-driven fluid jet, which is depends on mechanosensitive ion channels in the stereociliary believed to produce a more uniform deflection of the hair bundles bundles that project from the apical surface of the sensory hair (20–23) compared with the piezo-driven glass rod (19, 24). cells. In lower vertebrates, when the mechanoelectrical transducer (MET) channels are opened by movement of the bundle in the Results + excitatory direction, Ca2 entry through the open MET channels MET Currents Recorded in Mouse Outer and Inner Hair Cells. MET causes adaptation, rapidly reducing their open probability and re- currents were elicited by displacing the hair bundles of both outer setting their operating range. It remains uncertain whether such hair cells (OHCs) and inner hair cells (IHCs) with a piezoelectric + Ca2 -dependent adaptation is also present in mammalian hair fluid jet stimulator (20–22). The fluid jet was preferred to a rigid cells.
Fate of Mammalian Cochlear Hair Cells and Stereocilia After Loss of the Stereocilia

The Journal of Neuroscience, December 2, 2009 • 29(48):15277–15285 • 15277 Development/Plasticity/Repair Fate of Mammalian Cochlear Hair Cells and Stereocilia after Loss of the Stereocilia Shuping Jia,1 Shiming Yang (㧷Ⅴ㢝),2 Weiwei Guo (捼冃冃),2 and David Z. Z. He1 1Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, Nebraska 68178, and 2Department of Otolaryngology, Head and Neck Surgery, Institute of Otolaryngology, 301 Hospital, Beijing 100853, People’s Republic of China Cochlear hair cells transduce mechanical stimuli into electrical activity. The site of hair cell transduction is the hair bundle, an array of stereocilia with different height arranged in a staircase. Tip links connect the apex of each stereocilium to the side of its taller neighbor. The hair bundle and tip links of hair cells are susceptible to acoustic trauma and ototoxic drugs. It has been shown that hair cells in lower vertebrates and in the mammalian vestibular system may survive bundle loss and undergo self-repair of the stereocilia. Our goals were to determine whether cochlear hair cells could survive the trauma and whether the tip link and/or the hair bundle could be regenerated. We simulated the acoustic trauma-induced tip link damage or stereociliary loss by disrupting tip links or ablating the hair bundles in the culturedorganofCortifromneonatalgerbils.Hair-cellfateandstereociliarymorphologyandfunctionwereexaminedusingconfocaland scanning electron microscopies and electrophysiology. Most bundleless hair cells survived and developed for ϳ2 weeks. However, no spontaneous hair-bundle regeneration was observed. When tip links were ruptured, repair of tip links and restoration of mechanotrans- duction were observed in Ͻ24 h.
Evidence Concerning the Morphogenesis of Saccular Receptors in the Bullfrog (Rana Catesbeiana)

Evidence Concerning the Morphogenesis of Saccular Receptors in the Bullfrog (Rana catesbeiana) E. R. LEWIS AND c. w. LI Department of Electrical Engineering and Computer Sciences and the Electronics Research Laboratory, University of California, Berkeley, California 94720 ABSTRACT A dichotomy of hair-cell types has been found in the bullfrog sacculus, and considerable evidence supports the view that one type (“periph- eral”) is transformed during macular growth to the other type (“central”). Between the periphery and the center of the macula, one finds a gradation of form from “peripheral” to “central” type. Occasionally in adults and more often in stage-26 tadpoles one finds the presumably younger peripheral type of hair cell occurring well beyond the limits of the macula proper. The appar- ent morphogenic sequence for saccular hair cells is (1) development of a kinocillum on an endolymphatic epithelial cell, (2) gradual transformation of microvilli into stereocilia, (3) growth of the stereocilia and development of kinociliary bulb, (4) achievement of final size and form. The scanning electron microscope has in scanning micrographs by Hillman and been employed quite successfully in stud- Lewis (‘71). ies of the surfaces of ciliated cells in gen- eral (Barber and Boyde, ’68) and of audi- MATERIALS AND METHODS tory and vestibular receptors in particular (Bredberg, Lindeman, Ades, West and Eng- Twenty adult bullfrogs (Rana catesbei- strom, ’70; Hillman and Lewis, ’71; Lim ana) and ten stage-26 tadpoles (Gosner ’60) and Lane, ’69; Marovitz, Arenberg and were used in this study. The animals were Thalman, ’70). In a recently published killed by decapitation and then pithed to scanning microscopy paper, Lewis and prevent movement during dissection and Nemanic (‘72) reported two distinct types the early stages of fixation.
Mechanoreception

Mechanoreception Introduction Hair cells : the basic mechanosensory unit Hair cell structure Inner ear and accessory organ structures Vestibule Otolith organs Weberian ossicles Lateral line Lateral line structure Receptor organs Acoustic communication: sound production and reception Sound production mechanisms Locomotion and posture Introduction A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion. In fishes mechanoreception concerns the inner ear and the lateral line system. Hair cells are the UNIVERSAL MECHANOSENSORY TRANSDUCERS in both the lateral line and hearing systems. The INNER EAR is responsible for fish EQUILIBRIUM, BALANCE and HEARING LATERAL LINE SYSTEM detects DISTURBANCES in the water. Hair cell structure EACH HAIR CELL CONSISTS OF TWO TYPES OF "HAIRS" OR RECEPTOR PROCESSES: Many microvillar processes called STEREOCILIA. One true cilium called the KINOCILLIUM. COLLECTIVELY, the cluster is called a CILIARY BUNDLE. The NUMBER OF STEREOCILIA PER BUNDLE IS VARIABLE, and ranges from a 10s of stereocilia to more than a 100. The STEREOCILIA PROJECT into a GELATINOUS CUPULA ON THE APICAL (exposed) SURFACE of the cell. The cilium and villi are ARRANGED IN A STEPWISE GRADATION - the longest hair is the kinocillium, and next to it, the stereocilia are arranged in order of decreasing length. These cells SYNAPSE WITH GANGLION CELLS. They have DIRECTIONAL PROPERTIES - response to a stimulus depends on the direction in which the hairs are bent. So, if the displacement causes the stereocilia to bend towards the kinocilium, the cell becomes DEPOLARIZED = EXCITATION. If the stereocilia bend in the opposite direction, the cell becomes HYPERPOLARIZED = INHIBITION of the cell. If the hair bundles are bent at a 90o angle to the axis of the kinocilium and stereocilia there will be no response.
Solitary Hair Cells Are Distributed Throughout the Extramacular Epithelium in the Bullfrog’S Saccule

JARO 01: 172±182 (2000) DOI: 10.1007/s101620010037 Solitary Hair Cells Are Distributed Throughout the Extramacular Epithelium in the Bullfrog's Saccule JONATHAN E. GALE,JASON R. MEYERS, AND JEFFREY T. CORWIN Department of Otolaryngology±HNS and Department of Neuroscience, University of Virginia School of Medicine, Charlottesville, VA 22908, USA Received: 27 March 2000; Accepted: 5 June 2000; Online publication: 29 August 2000 ABSTRACT lium that has not been considered capable of giving rise to hair cells. The frog inner ear contains eight sensory organs that Keywords: hair cell, vestibular, balance, bullfrog, amphib- provide sensitivities to auditory, vestibular, and ian, sacculus, vital dye ground-borne vibrational stimuli. The saccule in bull- frogs is responsible for detecting ground- and air- borne vibrations and is used for studies of hair cell physiology, development, and regeneration. Based on INTRODUCTION hair bundle morphology, a number of hair cell types have been defined in this organ. Using immunocyto- The saccule of the bullfrog, Rana catesbieana, is sensi- chemistry, vital labeling, and electron microscopy, we tive to substrate and air-borne vibrations (Lewis et al. have characterized a new hair cell type in the bullfrog 1985). The saccular macula has been used for the study saccule. A monoclonal antibody that is specific to hair of hair cell anatomy and development (Hillman and cells revealed that a population of solitary hair cells Lewis 1971; Lewis and Li 1973, 1975; Kelley et al. 1992), exists outside the sensory macula in what was pre- hair cell physiology (Hudspeth and Corey 1977; Corey viously thought to be nonsensory epithelium.
Sensory Cell Damage in Two-Phase Endolymphatic Hydrops; a Morphologic Evaluation of a New Experimental Model by Low-Voltage Scanning Techniques

Chapter 6 Sensory cell damage in two-phase endolymphatic hydrops; a morphologic evaluation of a new experimental model by low-voltage scanning techniques Dunnebier EA, Segenhout JM, Dijk F, Albers FWJ. Sensory cell damage in two-phase endolymphatic hydrops; a morphologic evaluation of a new experimental model by low-voltage scanning techniques. Hearing Research 1998, in press. Introduction Since Hallpike and Cairns and also Yamakawa in 1938 discovered hydrops of the endo- lymphatic system in the temporal bones of patients with Menière’s disease, endolym- phatic hydrops has been generally accepted as the basic histopathological substrate of Menière’s disease1,2. The surgical destruction of the endolymphatic sac in guinea pigs and obstruction of the vestibular aqueduct with bone wax is a well-established model for inducing endo- lymphatic hydrops as observed in temporal bones of patients with Menière’s disease3. This is, however, a non-physiological profound model for Menière’s disease in humans. In our department we developed a new two-phase experimental model for endolymphatic hydrops to investigate the pathogenesis of Menière’s disease4. In this model the absorp- tion of endolymph has been chronically disturbed by surgical dissection of the distal portion of the endolymphatic sac without damaging the intermediate part. Periodic increase of endolymph production is induced by administration of aldosterone, to stimu- late the Na/K ATP-ase activity in the stria vascularis and the dark cells of the inner ear. The acute endolymph production will disturb the endolymph homeostasis which is not capable to restore immediately due to the borderline capacity of the endolymphatic sac resulting in the development or increase of hydrops.
Control of Hearing Sensitivity by Tectorial Membrane Calcium

Control of hearing sensitivity by tectorial membrane calcium Clark Elliott Strimbua,1,2, Sonal Prasada,1, Pierre Hakizimanaa, and Anders Fridbergera,3 aDepartment of Clinical and Experimental Medicine, Division of Neurobiology, Linköping University, SE-581 83 Linköping, Sweden Edited by Christine Petit, Institut Pasteur, College de France, INSERM, Université Pierre-et-Marie-Curie, Paris 15, France, and approved February 7, 2019 (received for review March 26, 2018) When sound stimulates the stereocilia on the sensory cells in the tation processes provide the hair cell with a high-pass filter and hearing organ, Ca2+ ions flow through mechanically gated ion the dynamic range of the transduction apparatus is extended. + channels. This Ca2 influx is thought to be important for ensuring Additionally, in both processes, as the MET channels close, they that the mechanically gated channels operate within their most exert a pulling force on the tip links that leads to a measurable sensitive response region, setting the fraction of channels open change in the position of the entire bundle of stereocilia (15, 16). at rest, and possibly for the continued maintenance of stereocilia. This mechanical correlate of adaptation results in active hair + Since the extracellular Ca2 concentration will affect the amount bundle motility that may contribute to the amplification of faint + of Ca2 entering during stimulation, it is important to determine sounds, a function that is critical for hearing (17). Much of the the level of the ion close to the sensory cells. Using fluorescence understanding of the two adaptation processes came from experi- imaging and fluorescence correlation spectroscopy, we measured ments performed on low-frequency hair cells from nonmammalian 2+ the Ca concentration near guinea pig stereocilia in situ.