Evidence for an Active Process and a Cochlear Amplifier in Nonmammals

2001 ◽  
Vol 86 (2) ◽  
pp. 541-549 ◽  
Author(s):  
Geoffrey A. Manley
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Organ Of Corti ◽  
Outer Hair Cells ◽  
Lateral Line System ◽  
Cochlear Amplifier ◽  
Fluid Viscosity ◽  
Active Process ◽  
Line System ◽  
Active Processes

The last two decades have produced a great deal of evidence that in the mammalian organ of Corti outer hair cells undergo active shape changes that are part of a “cochlear amplifier” mechanism that increases sensitivity and frequency selectivity of the hearing epithelium. However, many signs of active processes have also been found in nonmammals, raising the question as to the ancestry and commonality of these mechanisms. Active movements would be advantageous in all kinds of sensory hair cells because they help signal detection at levels near those of thermal noise and also help to overcome fluid viscosity. Such active mechanisms therefore presumably arose in the earliest kinds of hair cells that were part of the lateral line system of fish. These cells were embedded in a firm epithelium and responded to relative motion between the hair bundle and the hair cell, making it highly likely that the first active motor mechanism was localized in the hair-cell bundle. In terrestrial nonmammals, there are many auditory phenomena that are best explained by the presence of a cochlear amplifier, indicating that in this respect the mammalian ear is not unique. The latest evidence supports siting the active process in nonmammals in the hair-cell bundle and in intimate association with the transduction process.

scholarly journals Single-unit labeling of medial olivocochlear neurons: the cochlear frequency map for efferent axons

2014 ◽  
Vol 111 (11) ◽  
pp. 2177-2186 ◽  
Author(s):  
M. Christian Brown
Keyword(s):  
Hair Cells ◽  
Single Unit ◽  
Dynamic Range ◽  
Organ Of Corti ◽  
Nerve Fibers ◽  
Outer Hair Cells ◽  
Cochlear Amplifier ◽  
Noise Masking ◽  
Efferent Neurons ◽  
Medial Olivocochlear

Medial olivocochlear (MOC) neurons are efferent neurons that project axons from the brain to the cochlea. Their action on outer hair cells reduces the gain of the “cochlear amplifier,” which shifts the dynamic range of hearing and reduces the effects of noise masking. The MOC effects in one ear can be elicited by sound in that ipsilateral ear or by sound in the contralateral ear. To study how MOC neurons project onto the cochlea to mediate these effects, single-unit labeling in guinea pigs was used to study the mapping of MOC neurons for neurons responsive to ipsilateral sound vs. those responsive to contralateral sound. MOC neurons were sharply tuned to sound frequency with a well-defined characteristic frequency (CF). However, their labeled termination spans in the organ of Corti ranged from narrow to broad, innervating between 14 and 69 outer hair cells per axon in a “patchy” pattern. For units responsive to ipsilateral sound, the midpoint of innervation was mapped according to CF in a relationship generally similar to, but with more variability than, that of auditory-nerve fibers. Thus, based on CF mappings, most of the MOC terminations miss outer hair cells involved in the cochlear amplifier for their CF, which are located more basally. Compared with ipsilaterally responsive neurons, contralaterally responsive neurons had an apical offset in termination and a larger span of innervation (an average of 10.41% cochlear distance), suggesting that when contralateral sound activates the MOC reflex, the actions are different than those for ipsilateral sound.

scholarly journals Insights into Electroreceptor Development and Evolution from Molecular Comparisons with Hair Cells

2018 ◽  
Vol 58 (2) ◽  
pp. 329-340 ◽  
Author(s):  
Clare V H Baker ◽  
Melinda S Modrell
Keyword(s):  
Gene Expression ◽  
Hair Cell ◽  
Electric Fields ◽  
Lateral Line ◽  
Hair Cells ◽  
Water Movement ◽  
Low Frequency ◽  
Lateral Line System ◽  
Line System ◽  
Ribbon Synapses

Abstract The vertebrate lateral line system comprises a mechanosensory division, with neuromasts containing hair cells that detect local water movement (“distant touch”); and an electrosensory division, with electrosensory organs that detect the weak, low-frequency electric fields surrounding other animals in water (primarily used for hunting). The entire lateral line system was lost in the amniote lineage with the transition to fully terrestrial life; the electrosensory division was lost independently in several lineages, including the ancestors of frogs and of teleost fishes. (Electroreception with different characteristics subsequently evolved independently within two teleost lineages.) Recent gene expression studies in a non-teleost actinopterygian fish suggest that electroreceptor ribbon synapses employ the same transmission mechanisms as hair cell ribbon synapses, and show that developing electrosensory organs express transcription factors essential for hair cell development, including Atoh1 and Pou4f3. Previous hypotheses for electroreceptor evolution suggest either that electroreceptors and hair cells evolved independently in the vertebrate ancestor from a common ciliated secondary cell, or that electroreceptors evolved from hair cells. The close developmental and putative physiological similarities implied by the gene expression data support the latter hypothesis, i.e., that electroreceptors evolved in the vertebrate ancestor as a “sister cell-type” to lateral line hair cells.

Morphology of Synapses at the Base of Hair Cells in the Organ of Corti of the Chimpanzee

1990 ◽  
Vol 99 (3) ◽  
pp. 215-220 ◽  
Author(s):  
Joseph B. Nadol ◽  
Barbara J. Burgess
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Single Neuron ◽  
Outer Hair Cell ◽  
Mammalian Species ◽  
Organ Of Corti ◽  
Outer Hair Cells ◽  
Nerve Terminals ◽  
Section Electron ◽  
Serial Section Electron Microscopy

The synaptic morphology of inner and outer hair cells of the organ of Corti of the chimpanzee was evaluated by serial section electron microscopy. The morphology of nerve terminals and synapses at both sites was very similar to that of human and other mammalian species. Two types of nerve terminals, nonvesiculated and vesiculated, with distinct synaptic morphology were found. In addition, between some nonvesiculated endings and outer hair cells, a reciprocal synaptic relationship was seen. In such terminals there was morphologic evidence for transmission from hair cell to neuron and from neuron to hair cell between a single neuron and an outer hair cell.

scholarly journals β-Catenin is required for radial cell patterning and identity in the developing mouse cochlea

2019 ◽  
Vol 116 (42) ◽  
pp. 21054-21060 ◽  
Author(s):  
Lina Jansson ◽  
Michael Ebeid ◽  
Jessica W. Shen ◽  
Tara E. Mokhtari ◽  
Lee A. Quiruz ◽  
...  
Keyword(s):  
Cell Adhesion ◽  
Hair Cell ◽  
Hair Cells ◽  
Organ Of Corti ◽  
Outer Hair Cells ◽  
Supporting Cells ◽  
Aberrant Expression ◽  
Cell Identity ◽  
Pillar Cell ◽  
Radial Patterning

Development of multicellular organs requires the coordination of cell differentiation and patterning. Critical for sound detection, the mammalian organ of Corti contains functional units arranged tonotopically along the cochlear turns. Each unit consists of sensory hair cells intercalated by nonsensory supporting cells, both specified and radially patterned with exquisite precision during embryonic development. However, how cell identity and radial patterning are jointly controlled is poorly understood. Here we show that β-catenin is required for specification of hair cell and supporting cell subtypes and radial patterning of the cochlea in vivo. In 2 mouse models of conditional β-catenin deletion, early specification of Myosin7-expressing hair cells and Prox1-positive supporting cells was preserved. While β-catenin-deficient cochleae expressed FGF8 and FGFR3, both of which are essential for pillar cell specification, the radial patterning of organ of Corti was disrupted, revealed by aberrant expression of cadherins and the pillar cell markers P75 and Lgr6. Moreover, β-catenin ablation caused duplication of FGF8-positive inner hair cells and reduction of outer hair cells without affecting the overall hair cell density. In contrast, in another transgenic model with suppressed transcriptional activity of β-catenin but preserved cell adhesion function, both specification and radial patterning of the organ of Corti were intact. Our study reveals specific functions of β-catenin in governing cell identity and patterning mediated through cell adhesion in the developing cochlea.

Reciprocal Synapses at the Base of Outer Hair Cells in the Organ of Corti of Man

1981 ◽  
Vol 90 (1) ◽  
pp. 12-17 ◽  
Author(s):  
Joseph B. Nadol
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Outer Hair Cell ◽  
Organ Of Corti ◽  
Postsynaptic Membrane ◽  
Opposite Polarity ◽  
Outer Hair Cells ◽  
Human Organ ◽  
Single Nerve ◽  
Small Collection

Reciprocal synapses have been found between nerve terminals and the outer hair cells in the human organ of Corti. A single nerve ending of the nonvesiculated type may possess two types of synaptic specialization of opposite polarity. The first is typical of the “afferent” synapse with a presynaptic body in the hair cell and pre- and postsynaptic membrane thickening. The second consists of a small collection of presynaptic vesicles in the neural cytoplasm near the plasma membrane facing the hair cell and a subsynaptic cisterna within the hair cell cytoplasm. The second type of specialization is similar to the synapses seen in “efferent” endings. This suggests that both an afferent (hair cell to neuron) and efferent (neuron to hair cell) synaptic relationship may exist between an outer hair cell and a single nerve terminal.

Active Hair Bundle Movements and the Cochlear Amplifier

2003 ◽  
Vol 14 (06) ◽  
pp. 325-338 ◽  
Author(s):  
Anthony Ricci
Keyword(s):  
Hearing Loss ◽  
Hair Cell ◽  
Sensorineural Hearing Loss ◽  
Outer Hair Cell ◽  
Sensorineural Hearing ◽  
Hair Bundle ◽  
Cochlear Amplifier ◽  
Active Process ◽  
Slow Adaptation ◽  
Active Processes

The “active process” is a term used to describe amplification and filtering processes that are essential for obtaining the exquisite sensitivity of hearing organs. Understanding the components of the active process is important both for our understanding of the normal physiology of hearing and because perturbations of the cochlear amplifier may lead to such maladies as threshold shifts (both temporary and permanent), tinnitus, sensorineural hearing loss and presbicusis. To date the cochlear amplifier has largely been attributed to outer hair cell electro motility; however, recent evidence suggests, that active properties of the hair bundle may also be important. Most likely both somatic motility and active hair bundle movements contribute to establishing the cochlear active process. This paper reviews recent evidence regarding known active processes in the hair bundle gating compliance, and fast and slow adaptation.

scholarly journals CNGA3 is expressed in inner ear hair cells and binds to an intracellular C-terminus domain of EMILIN1

2012 ◽  
Vol 443 (2) ◽  
pp. 463-476 ◽  
Author(s):  
Dakshnamurthy Selvakumar ◽  
Marian J. Drescher ◽  
Jayme R. Dowdall ◽  
Khalid M. Khan ◽  
James S. Hatfield ◽  
...  
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Transmembrane Domain ◽  
Cell Model ◽  
Organ Of Corti ◽  
Outer Hair Cells ◽  
Sensory Transduction ◽  
Molecular Characteristics ◽  
Cone Photoreceptors ◽  
C Terminus

The molecular characteristics of CNG (cyclic nucleotide-gated) channels in auditory/vestibular hair cells are largely unknown, unlike those of CNG mediating sensory transduction in vision and olfaction. In the present study we report the full-length sequence for three CNGA3 variants in a hair cell preparation from the trout saccule with high identity to CNGA3 in olfactory receptor neurons/cone photoreceptors. A custom antibody targeting the N-terminal sequence immunolocalized CNGA3 to the stereocilia and subcuticular plate region of saccular hair cells. The cytoplasmic C-terminus of CNGA3 was found by yeast two-hybrid analysis to bind the C-terminus of EMILIN1 (elastin microfibril interface-located protein 1) in both the vestibular hair cell model and rat organ of Corti. Specific binding between CNGA3 and EMILIN1 was confirmed with surface plasmon resonance analysis, predicting dependence on Ca2+ with Kd=1.6×10−6 M for trout hair cell proteins and Kd=2.7×10−7 M for organ of Corti proteins at 68 μM Ca2+. Pull-down assays indicated that the binding to organ of Corti CNGA3 was attributable to the EMILIN1 intracellular sequence that follows a predicted transmembrane domain in the C-terminus. Saccular hair cells also express the transcript for PDE6C (phosphodiesterase 6C), which in cone photoreceptors regulates the degradation of cGMP used to gate CNGA3 in phototransduction. Taken together, the evidence supports the existence in saccular hair cells of a molecular pathway linking CNGA3, its binding partner EMILIN1 (and β1 integrin) and cGMP-specific PDE6C, which is potentially replicated in cochlear outer hair cells, given stereociliary immunolocalizations of CNGA3, EMILIN1 and PDE6C.

scholarly journals A role for tectorial membrane mechanics in activating the cochlear amplifier

2020 ◽  
Author(s):  
A. Nankali ◽  
Y. Wang ◽  
C. E. Strimbu ◽  
E. S. Olson ◽  
K. Grosh
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Phase Shift ◽  
Hair Cells ◽  
Basilar Membrane ◽  
Outer Hair Cells ◽  
Tectorial Membrane ◽  
Cochlear Amplifier ◽  
Active Process ◽  
Electrical Responses

ABSTRACTThe mechanical and electrical responses of the mammalian cochlea to acoustic stimuli are nonlinear and highly tuned in frequency. This is due to the electromechanical properties of cochlear outer hair cells (OHCs). At each location along the cochlear spiral, the OHCs mediate an active process in which the sensory tissue motion is enhanced at frequencies close to the most sensitive frequency (called the characteristic frequency CF). Previous experimental results showing an approximate 0.3 cycle phase shift in the OHC-generated extracellular voltage relative the basilar membrane displacement that is initiated at a frequency approximately one-half octave lower than the CF are repeated in the present paper with similar findings. This shift is significant because it brings the phase of the OHC-derived electromotile force near to that of the basilar membrane velocity at frequencies above the shift, thereby enabling the transfer of electrical to mechanical power at the basilar membrane. In order to seek a candidate physical mechanism for this phenomenon, we used a comprehensive electromechanical mathematical model of the cochlear response to sound. The model predicts the phase shift in the extracellular voltage referenced to the basilar membrane at a frequency approximately one-half octave below CF, in accordance with the experimental data. In the model, this feature arises from a minimum in the radial impedance of the tectorial membrane and its limbal attachment. These experimental and theoretical results are consistent with the hypothesis that a tectorial membrane resonance introduces the correct phasing between mechanical and electrical responses for power generation, effectively turning on the cochlear amplifier.SIGNIFICANCEThe mechanical and electrical responses of the mammalian cochlea are nonlinear exhibiting up to a thousand-fold difference in gain depending on the frequency and level of sound stimulus. Cochlear outer hair cells (OHC) are broadband electro-mechanical energy converters that mediate this nonlinear active process. However, the mechanism by which the OHC electromotile force acquires the appropriate phase to power this nonlinearity remains unknown. By analyzing new and existing experimental data and using a mathematical model, we address this open issue. We present evidence which suggests that a relatively simple feature, the frequency dependence of the radial impedance of the tectorial membrane, provides requisite mechanics to turn on the frequency-specific nonlinear process essential for healthy hearing.

Design of a Microfluidic Device to Induce Noise Damage in Hair Cells of the Zebrafish Lateral Line

2012 ◽  
Author(s):  
Hyuck-Jin Kwon ◽  
Yuhao Xu ◽  
Stephen A. Solovitz ◽  
Wei Xue ◽  
Alexander G. Dimitrov ◽  
...  
Keyword(s):  
Hair Cell ◽  
Flow Pattern ◽  
Boundary Layers ◽  
Microfluidic Device ◽  
Lateral Line ◽  
Hair Cells ◽  
Cfd Simulation ◽  
Lateral Line System ◽  
Line System ◽  
Noise Damage

Hearing loss affects millions of people worldwide and often results from death of the sensory hair cells in the inner ear. Noise-induced damage is one of the leading causes of hair cell loss. Recently, the zebrafish lateral line system has emerged as a powerful in vivo model for real-time studies of hair cell damage and protection. In this research, we designed a microfluidic device to induce noise damage in hair cells of the zebrafish lateral line. As the first step, a 3-D computational fluid dynamics (CFD) simulation was utilized to predict the flow pattern inside the device. An ideal flow pattern for our application should feature higher velocity at the side and lower velocity in the middle of a channel. Flow induced from ordinary channel geometry with single inlet/outlet pair would not work for us because the boundary layers from the two side walls will grow and merge with each other and induce the maximum flow speed in the middle of the channel. In order to achieve the desired flow pattern, side-wall inlet/outlet pairs were used to suppress the growth of boundary layers. CFD simulation was used to design important parameters such as dimensions of the microfluidic channel and the angle of inlets and outlets. It was found that flow velocity at the side of the channel could be 6.7 times faster than the velocity in the middle when we array the inlets and outlets alternatively and set the angle of the inlet to 45° with 2.0 mm main channel width. This 3-D CFD model will serve as a convenient model to design a microfluidic device to induce noise damage in hair cells of a zebrafish lateral line by manipulating the flow pattern inside the device.

scholarly journals Active outer hair cell motility can suppress vibrations in the organ of Corti

2020 ◽  
Author(s):  
T. Jabeen ◽  
J. C. Holt ◽  
J. R. Becker ◽  
J.-H. Nam
Keyword(s):  
Electrical Stimulation ◽  
Hair Cell ◽  
Hair Cells ◽  
Acoustic Pressure ◽  
Outer Hair Cell ◽  
Organ Of Corti ◽  
Sensory Epithelium ◽  
Outer Hair Cells ◽  
Cochlear Tuning ◽  
Cell Force

AbstractHigh sensitivity and selectivity of hearing require active cochlea. The cochlear sensory epithelium, the organ of Corti, vibrates due to external and internal excitations. The external stimulation is acoustic pressures mediated by the scala fluids, while the internal excitation is generated by a type of sensory receptor cells (the outer hair cells) in response to the acoustical vibrations. The outer hair cells are cellular actuators that are responsible for cochlear amplification. The organ of Corti is highly structured for transmitting vibrations originating from acoustic pressure and active outer hair cell force to the inner hair cells that synapse on afferent nerves. Understanding how the organ of Corti vibrates due to acoustic pressure and outer hair cell force is critical for explaining cochlear function. In this study, excised cochlear turns were freshly isolated from young gerbils. The organ of Corti in the excised cochlea was subjected to mechanical and electrical stimulation that are analogous to acoustical and cellular stimulation in the natural cochlea. Organ of Corti vibrations including those of individual outer hair cells were measured using optical coherence tomography. Respective vibration patterns due to mechanical and electrical stimulation were characterized. Interactions between the two vibration patterns were investigated by applying the two forms of stimulation simultaneously. Our results show that the interactions could be either constructive or destructive, which implies that the outer hair cells can either amplify or suppress vibrations in the organ of Corti. We discuss a potential consequence of the two interaction modes for cochlear frequency tuning.Statement of SignificanceThe function of the mammalian cochlea is characterized by sharp tuning and high-level of amplification. Both tuning and amplification are achieved mechanically through the action of cellular actuators in the sensory epithelium. According to widely accepted theory, cochlear tuning is achieved by ‘selectively amplifying’ acoustic vibrations. This study presents a set of data suggesting that the cochlear actuators can both amplify and suppress vibrations to enhance cochlear tuning. Presented results will explain why the actuator cells in the cochlea spend energy in the locations where there is no need for amplification.

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