Properties of auditory nerve responses in absence of outer hair cells

1978 ◽  
Vol 41 (2) ◽  
pp. 365-383 ◽  
Author(s):  
P. Dallos ◽  
D. Harris
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Auditory Nerve ◽  
Outer Hair Cell ◽  
Nerve Fibers ◽  
Outer Hair Cells ◽  
Border Region ◽  
Histological Evaluation ◽  
High Threshold ◽  
Time Pattern

1. Recordings were made from chinchilla auditory nerve fibers after portions of the cochlear outer hair cell (OHC) population were destroyed with the antibiotic kanamycin. In most cases the inner hair cell (IHC) population was completely preserved as determined by phase-contrast microscopy. We presume that the remaining IHCs are functionally normal, and thus that recordings obtained from fibers originating from the lesioned cochlear segment reflect IHC behavior. 2. Behavioral thresholds were measured for all animals both before and after the production of the cochlear lesion. The audiograms and the histological evaluation of the ears were the basis for assessing whether a particular fiber originated in a normal, pathological (shifted threshold; IHC only), or border region. These criteria also identified the animals that sustained IHC damage together with the destruction of part of the OHC population. Only the data obtained from those fibers which probably originated from the OHC-free segment of the cochlea are considered in detail. 3. Fibers whose characteristic frequency (CF) identified them as belonging to the normal (audiometrically and histologically) region, were found to be normal in all respects. 4. Fibers from the border region (where the audiogram has a steep slope between normal and hearing-loss regions probably corresponding to the segment where OHC loss progresses from less than 10% to more than 90%) had very complex response patterns. Their frequency threshold curves (FTC) showed great variability. In general, the closer the fiber was to the fully developed lesion, the more abnormal its FTC became. 5. Those units that were concluded to have originated from the OHC-free part of the cochlea could be divided into three categories on the basis of the shape of their FTCs. A small fraction had very broad tuning (9%). The majority (53%) had approximately normal tail segment, normal bandwidth of the tip segment, and highly elevated threshold at CF. A group of fibers (38%) could not be assigned a CF. Probably the FTC of most of these latter fibers are similar to those of the previous group, but the sharply tuned short tip segment was either missed or was not reachable on account of its extremely high threshold level. 6. Such indexes of fiber response as latency, spontaneous rate, and time pattern (PST histograms) were not affected by the loss of OHCs. 7. On the basis of the data and of the assumptions made it was suggested that outer hair cells provide a frequency-dependent sensitizing influence to the inner hair cells. The frequency dependence could best be expressed as a flat-topped band pass characteristic.

Psychophysical Tuning Curves in Subjects with Tinnitus Suggest Outer Hair Cell Lesions

1995 ◽  
Vol 113 (3) ◽  
pp. 223-233 ◽  
Author(s):  
Curtin R. Mitchell ◽  
Thomas A. Creedon
Keyword(s):  
Hearing Loss ◽  
Hair Cell ◽  
Hair Cells ◽  
Outer Hair Cell ◽  
Tuning Curve ◽  
Control Design ◽  
Nerve Fibers ◽  
Outer Hair Cells ◽  
Tuning Curves ◽  
Hearing Thresholds

A study by Penner (J Speech Hear Res 1980;23:779–86) found evidence for Impaired lateral suppression in subjects with tinnitus and sensorineural hearing loss. If lateral suppression is related to tuning curve sharpness and lateral suppression is impaired, the shape of the tuning curve should be affected. The purpose of this study was to determine whether subjects with tinnitus have psychophysical tuning curves that are different from those of subjects without tinnitus. Psychophysical tuning curves and hearing thresholds were obtained from 18 subjects, 7 with tinnitus and 11 without tinnitus. Only subjects with normal audiograms (through 8 kHz) were selected for this study. In subjects with tinnitus psychophysical tuning curves were obtained in the region pitch-matched to their tinnitus. In nontinnitus subjects psychophysical tuning curves were determined at the same frequencies as for the tinnitus subjects in a yoked-control design. The slopes of the tails and tips and the Q10 and other measures were calculated for each tuning curve. The psychophysical tuning curves in subjects with tinnitus were significantly different (0.01 level) from those of control subjects and often had hypersensitive tails and some elevated tips. These shapes of tuning curves are consistent with cochlear lesions involving the loss of outer hair cells without damage to the Inner hair cells or nerve fibers.

scholarly journals Synaptic migration and reorganization after noise exposure suggests regeneration in a mature mammalian cochlea

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Tyler T. Hickman ◽  
Ken Hashimoto ◽  
Leslie D. Liberman ◽  
M. Charles Liberman
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Auditory Nerve ◽  
Guinea Pigs ◽  
Noise Exposure ◽  
Recovery Period ◽  
Nerve Fibers ◽  
Neural Regeneration ◽  
Adult Mice ◽  
Synaptic Markers

AbstractOverexposure to intense noise can destroy the synapses between auditory nerve fibers and their hair cell targets without destroying the hair cells themselves. In adult mice, this synaptopathy is immediate and largely irreversible, whereas, in guinea pigs, counts of immunostained synaptic puncta can recover with increasing post-exposure survival. Here, we asked whether this recovery simply reflects changes in synaptic immunostaining, or whether there is actual retraction and extension of neurites and/or synaptogenesis. Analysis of the numbers, sizes and spatial distribution of pre- and post-synaptic markers on cochlear inner hair cells, in guinea pigs surviving from 1 day to 6 months after a synaptopathic exposure, shows dramatic synaptic re-organization during the recovery period in which synapse counts recover from 16 to 91% of normal in the most affected regions. Synaptic puncta move all over the hair cell membrane during recovery, translocating far from their normal positions at the basolateral pole, and auditory-nerve terminals extend towards the hair cell’s apical end to re-establish contact with them. These observations provide stronger evidence for spontaneous neural regeneration in a mature mammalian cochlea than can be inferred from synaptic counts alone.

A study of active artificial hair cell models inspired by outer hair cell somatic motility

2016 ◽  
Vol 28 (6) ◽  
pp. 811-823 ◽  
Author(s):  
Bryan S Joyce ◽  
Pablo A Tarazaga
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Outer Hair Cell ◽  
Dynamic Range ◽  
Outer Hair Cells ◽  
Quality Factors ◽  
Control Laws ◽  
Sensor Performance ◽  
Nonlinear Amplification ◽  
Key Aspects

The cochlea displays an important, nonlinear amplification of sound-induced oscillations. In mammals, this amplification is largely powered by the somatic motility of the outer hair cells. The resulting cochlear amplifier has three important characteristics useful for hearing: an amplification of responses from low sound pressures, an improvement in frequency selectivity, and an ability to transduce a broad range of sound pressure levels. These useful features can be incorporated into designs for active artificial hair cells, bio-inspired sensors for use as microphones, accelerometers, or other dynamic sensors. The sensor consists of a cantilever beam with piezoelectric actuators. A feedback controller applies a voltage to the actuators to mimic the outer hair cells’ somatic motility. This article describes three control laws for an active artificial hair cell inspired by models of the outer hair cells’ somatic motility. The first control law is based on a phenomenological model of the cochlea while the second and third models incorporate physiological aspects of the biological cochlea to further improve sensor performance. Simulations show that these models qualitatively reproduce the key aspects of the mammalian cochlea, namely, amplification of oscillations from weak stimuli, higher quality factors, and a wider input dynamic range.

Two-tone suppression in the basilar membrane of the cochlea: mechanical basis of auditory-nerve rate suppression

1992 ◽  
Vol 68 (4) ◽  
pp. 1087-1099 ◽  
Author(s):  
M. A. Ruggero ◽  
L. Robles ◽  
N. C. Rich
Keyword(s):  
Auditory Nerve ◽  
Outer Hair Cell ◽  
Basilar Membrane ◽  
Frequency Tuning ◽  
Low Frequency ◽  
Nerve Fibers ◽  
Oval Window ◽  
Outer Hair Cells ◽  
Probe Intensity ◽  
Rate Suppression

1. The vibratory response to two-tone stimuli was measured in the basilar membrane of the chinchilla cochlea by means of the Mossbauer technique or laser velocimetry. Measurements were made at sites with characteristic frequency (CF, the frequency at which an auditory structure is most sensitive) of 7-10 kHz, located approximately 3.5 mm from the oval window. 2. Two-tone suppression (reduction in the response to one tone due to the presence of another) was demonstrated for CF probe tones and suppressor tones with frequencies both higher and lower than CF, at moderately low stimulus levels, including probe-suppressor combinations for which responses to the suppressor were lower than responses to the probe tone alone. 3. For a fixed suppressor tone, suppression magnitude decreased as a function of increasing probe intensity. 4. The magnitude of suppression increased monotonically with suppressor intensity. 5. The rate of growth of suppression magnitude with suppressor intensity was higher for suppressors in the region below CF than for those in the region above CF. 6. For low-frequency suppressor tones, suppression magnitude varied periodically, attaining one or two maxima within each period of the suppressor tone. 7. Suppression was frequency tuned: for either above-CF or below-CF suppressor tones, suppression magnitude reached a maximum for probe frequencies near CF. 8. Cochlear damage or death diminished or abolished suppression. There was a clear positive correlation between magnitude of suppression and basilar-membrane sensitivity for responses to CF tones. 9. Suppression tended to be accompanied by small phase lags in responses to CF probe tones. 10. Because all of the features of two-tone suppression at the basilar membrane match qualitatively (and, generally, also quantitatively) the features of two-tone rate suppression in auditory-nerve fibers, it is concluded that neural two-tone rate suppression originates in mechanical phenomena at the basilar membrane. 11. Because the lability of mechanical suppression parallels the loss of sensitivity and frequency tuning due to outer hair cell dysfunction, the present findings suggest that mechanical two-tone suppression arises from an interaction between the outer hair cells and the basilar membrane.

Passive compliance and active force generation in the guinea pig outer hair cell

1995 ◽  
Vol 74 (6) ◽  
pp. 2319-2328 ◽  
Author(s):  
R. Hallworth
Keyword(s):  
Hair Cell ◽  
Cell Motility ◽  
Hair Cells ◽  
Outer Hair Cell ◽  
Outer Hair Cells ◽  
Force Generation ◽  
Axial Stiffness ◽  
Sinusoidal Voltage ◽  
Apparent Stiffness ◽  
Outer Hair Cell Motility

1. Cochlear outer hair cells 20-80 microns in length were compressed axially in vitro using calibrated glass fibers mounted on a piezoelectric actuator. 2. When driven by rectangular pulses in the compression direction, the motion of the fiber tip consisted of a rapid initial compression that was complete in 10-20 ms followed by a smaller compression of slower time course. 3. The initial fiber deflections were found to be linear in amplitude for compressions up to 400 nm. The axial compliances of outer hair cells were calculated from the difference between the fiber tip motions when unattached and when in contact with a cell. Axial compliances were found to be in the range of 0.04-1.2 km/N for 149 cells. The axial compliance was an increasing function of cell length. 4. The peak forces generated by electrically stimulated outer hair cells were measured from the deflection of a glass fiber when the cells were stimulated by sinusoidal voltage commands. The slope gains of force generation (force generated per mV of command at the cell membrane) were estimated to range from 0.01 to 100 pN/mV. Most of the results fell in the range of 0.1-20 pN/mV. 5. When the apparent stiffness of the fiber was increased by moving the cell closer to the fiber base, the peak amplitude of the fiber deflection generated by the cell decreased and the peak force increased, for the same sinusoidal voltage command. 6. The results of the previous experiment were interpreted in the light of a model of outer hair cell motility in which an ideal extension generating element is in series with an internal stiffness element. This internal stiffness was then calculated for 13 cells. 7. The internal stiffnesses of cells calculated by the above procedure were found to be positively correlated with the axial stiffness measurements obtained for the same cells. 8. The implications of the above results for the effectiveness of outer hair cell motility in vivo are discussed.

scholarly journals Unmyelinated type II afferent neurons report cochlear damage

2015 ◽  
Vol 112 (47) ◽  
pp. 14723-14727 ◽  
Author(s):  
Chang Liu ◽  
Elisabeth Glowatzki ◽  
Paul Albert Fuchs
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Outer Hair Cell ◽  
Cell Damage ◽  
Large Diameter ◽  
Outer Hair Cells ◽  
Type I ◽  
Type Ii ◽  
Inner Hair Cell ◽  
Hair Cell Damage

In the mammalian cochlea, acoustic information is carried to the brain by the predominant (95%) large-diameter, myelinated type I afferents, each of which is postsynaptic to a single inner hair cell. The remaining thin, unmyelinated type II afferents extend hundreds of microns along the cochlear duct to contact many outer hair cells. Despite this extensive arbor, type II afferents are weakly activated by outer hair cell transmitter release and are insensitive to sound. Intriguingly, type II afferents remain intact in damaged regions of the cochlea. Here, we show that type II afferents are activated when outer hair cells are damaged. This response depends on both ionotropic (P2X) and metabotropic (P2Y) purinergic receptors, binding ATP released from nearby supporting cells in response to hair cell damage. Selective activation of P2Y receptors increased type II afferent excitability by the closure of KCNQ-type potassium channels, a potential mechanism for the painful hypersensitivity (that we term “noxacusis” to distinguish from hyperacusis without pain) that can accompany hearing loss. Exposure to the KCNQ channel activator retigabine suppressed the type II fiber’s response to hair cell damage. Type II afferents may be the cochlea’s nociceptors, prompting avoidance of further damage to the irreparable inner ear.

Biomechanics of Hearing Sensitivity

1991 ◽  
Vol 113 (1) ◽  
pp. 1-13 ◽  
Author(s):  
Sir James Lighthill
Keyword(s):  
Hair Cells ◽  
Auditory Nerve ◽  
Basilar Membrane ◽  
Nerve Fibers ◽  
Outer Hair Cells ◽  
Hearing Sensitivity ◽  
Sound Levels ◽  
Auditory Nerve Fibers ◽  
The Brain ◽  
Stiffness Distribution

This survey lecture on the biomechanics of hearing sensitivity is concerned, not with how the brain in man and other mammals analyzes the data coming to it along auditory nerve fibers, but with the initial capture of that data in the cochlea. The brain, needless to say, can produce all its miracles of interpretation only where it works on good initial data. For frequency selectivity these depend on some remarkable properties of the cochlea as a passive macromechanical system, comprising the basilar membrane with its steeply graded stiffness distribution vibrating within the cochlear fluids. But the biomechanics of hearing sensitivity to low levels of sound (at any particular frequency) calls also into play an active micromechanical system, which during the past few years has progressively been identified as located in the outer hair cells, and which, through a process of positive feedback, amplifies (in healthy ears) that basilar membrane vibration. This in turn offers the inner hair cells an enhanced signal at low sound levels, so that the threshold at which they can generate activity in auditory nerve fibers is, in consequence, very substantially lowered.

scholarly journals The Effects of Urethane on Rat Outer Hair Cells

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Mingyu Fu ◽  
Mengzi Chen ◽  
Xiao Yan ◽  
Xueying Yang ◽  
Jinfang Xiao ◽  
...  
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Outer Hair Cell ◽  
Electrical Response ◽  
Outward Current ◽  
Outer Hair Cells ◽  
Dependent Manner ◽  
Cochlear Microphonic ◽  
Patch Clamp Recording ◽  
Electrical Impulses

The cochlea converts sound vibration into electrical impulses and amplifies the low-level sound signal. Urethane, a widely used anesthetic in animal research, has been shown to reduce the neural responses to auditory stimuli. However, the effects of urethane on cochlea, especially on the function of outer hair cells, remain largely unknown. In the present study, we compared the cochlear microphonic responses between awake and urethane-anesthetized rats. The results revealed that the amplitude of the cochlear microphonic was decreased by urethane, resulting in an increase in the threshold at all of the sound frequencies examined. To deduce the possible mechanism underlying the urethane-induced decrease in cochlear sensitivity, we examined the electrical response properties of isolated outer hair cells using whole-cell patch-clamp recording. We found that urethane hyperpolarizes the outer hair cell membrane potential in a dose-dependent manner and elicits larger outward current. This urethane-induced outward current was blocked by strychnine, an antagonist of theα9 subunit of the nicotinic acetylcholine receptor. Meanwhile, the function of the outer hair cell motor protein, prestin, was not affected. These results suggest that urethane anesthesia is expected to decrease the responses of outer hair cells, whereas the frequency selectivity of cochlea remains unchanged.

scholarly journals Persistence of Cav1.3 Ca2+ Channels in Mature Outer Hair Cells Supports Outer Hair Cell Afferent Signaling

2007 ◽  
Vol 27 (24) ◽  
pp. 6442-6451 ◽  
Author(s):  
M. Knirsch ◽  
N. Brandt ◽  
C. Braig ◽  
S. Kuhn ◽  
B. Hirt ◽  
...  
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Outer Hair Cell ◽  
Outer Hair Cells ◽  
Afferent Signaling ◽  
Ca2 Channels

scholarly journals Response Growth With Sound Level in Auditory-Nerve Fibers After Noise-Induced Hearing Loss

2004 ◽  
Vol 91 (2) ◽  
pp. 784-795 ◽  
Author(s):  
Michael G. Heinz ◽  
Eric D. Young
Keyword(s):  
Hearing Loss ◽  
Hair Cell ◽  
Auditory Nerve ◽  
Outer Hair Cell ◽  
Dynamic Range ◽  
Nerve Fibers ◽  
Sound Level ◽  
Broadband Noise ◽  
Noise Induced Hearing Loss ◽  
Rate Level

People with sensorineural hearing loss are often constrained by a reduced acoustic dynamic range associated with loudness recruitment; however, the neural correlates of loudness and recruitment are still not well understood. The growth of auditory-nerve (AN) activity with sound level was compared in normal-hearing cats and in cats with a noise-induced hearing loss to test the hypothesis that AN-fiber rate-level functions are steeper in impaired ears. Stimuli included best-frequency and fixed-frequency tones, broadband noise, and a brief speech token. Three types of impaired responses were observed. 1) Fibers with rate-level functions that were similar across all stimuli typically had broad tuning, consistent with outer-hair-cell (OHC) damage. 2) Fibers with a wide dynamic range and shallow slope above threshold often retained sharp tuning, consistent with primarily inner-hair-cell (IHC) damage. 3) Fibers with very steep rate-level functions for all stimuli had thresholds above approximately 80 dB SPL and very broad tuning, consistent with severe IHC and OHC damage. Impaired rate-level slopes were on average shallower than normal for tones, and were steeper in only limited conditions. There was less variation in rate-level slopes across stimuli in impaired fibers, presumably attributable to the lack of suppression-induced reductions in slopes for complex stimuli relative to BF-tone slopes. Sloping saturation was observed less often in impaired fibers. These results illustrate that AN fibers do not provide a simple representation of the basilar-membrane I/O function and suggest that both OHC and IHC damage can affect AN response growth.

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