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At least 19 recordsLinked to original sources
PubMed1979

Stereocilia mediate transduction in vertebrate hair cells (auditory system/cilium/vestibular system).

The vertebrate hair cell is a sensory receptor that responds to mechanical stimulation of its hair bundle, which usually consists of numerous large microvilli (stereocilia) and a single true cilium (the kinocilium). We have examined the roles of these two components of the hair bundle by recording intracellularly from bullfrog saccular hair cells. Detachment of the kinocilium from the hair bundle and deflection of this cilium produces no receptor potentials. Mechanical stimulation of stereocilia, however, elicits responses of normal amplitude and sensitivity. Scanning electron microscopy confirms the assessments of ciliary position made during physiological recording. Stereocilia mediate the transduction process of the vertebrate hair cell, while the kinocilium may serve primarily as a linkage conveying mechanical displacements to the stereocilia.

Animals↗
PubMed1992

Ion channels for the mechano-electrical transduction and efferent synapse of the hair cell.

Auditory and vestibular information is applied to the hair cell hair bundle as mechanical energy, and is transduced into electrical energy by gating ion channels. The m-e.t. channel has a unitary conductance of 50 pS and a broad selectivity to monovalent cations and to divalent cations. Ca ions are the most permeable through the channel. The angular displacement of the hair bundle is the primary gating factor. Circumstantial evidence indicates the possibility of the direct gating of channels by the membrane deformation itself. The transduction potential activates voltage gated Ca channel and leads to the release of neurotransmitters which activate afferent neurones. Cholinergic muscarinic receptors likely mediate the inhibitory efferent innervation to the hair cell.

Animals↗
PubMed1979

Hair cell degeneration in guinea pigs intoxicated with kanamycin during intrauterine life; a structural and ultrastructural study.

The structural ototoxic effect of kanamycin during intrauterine life has been shown in guinea pigs. The extent of the loss mostly affected the outer hair cells of the basal part of the cochlea. Ultrastructural studies demonstrated a hair cell degeneration pattern similar to that previously described in adult animals following antibiotic intoxication.

Animals↗
PubMed1979

Morphological changes in afferent vestibular hair cell synapses during the postnatal development of the cat.

In the course of postnatal development in the cat, there is a decrease of about 93% in the total number of synaptic bodies (synaptic balls and synaptic bars) in type I hair cells. In type II hair cells, there is no change in the number of synaptic balls. Simultaneously, the length of specialized neuroepithelial contact increases by approximately 300% during type I hair cell maturation. Only the synaptic bars displaying a polylamellar ultrastructure persist in the type I hair cells of the adult animal. It is suggested that the afferent vestibular synapses of the type I hair cell are transformed during ontogeny.

Animals↗
PubMed1979

Significance of presynaptic formations in early stages of cochlear synaptogenesis.

Very early stages of cochlear synaptogenesis are described in inner (IHCs) and outer hair cells (OHCs) of cat foetuses. Ten days before birth (DBB) well-formed synaptic contacts were found between afferent dendrites and both IHCs and OHCs. At the IHC level a preliminary stage before functioning has been proposed. But at the OHC level where the adult cell membrane becomes mainly postsynaptic, we could only formulate hypotheses based on phylogenetic considerations (afferents precede efferents), or on embryology (presynaptic specializations play a role in the arrival and growth of fibers around the hair cell).

Animals↗
PubMed1992

Height changes in the organ of Corti after noise exposure.

To determine whether or not exposure to noise causes an alteration in the height of the organ of Corti (OC), 16 cochleas which had been exposed for one or two hours to an octave band of noise with a center frequency of 4 kHz and a sound pressure level of 108 dB were examined microscopically as whole mounts. These specimens were divided into four groups: early ears (N = 3) recovered less than 0.6 hours following the exposure; intermediate ears (N = 5) recovered 0.6-4.0 hours; 1-day ears (N = 3) recovered 24 hours; and late ears (N = 5) recovered 2-21 days. Height was measured at three positions across the OC and at multiple percentage locations from apex to base. The OC-height data from the noise-exposed cochleas were compared statistically to those from ten control cochleas. A significant reduction (P < or = 0.01) in OC height at the third outer hair cell (OHC) was first evident in the early ears in the region 65-95% distance from the apex. The height was reduced even further in the intermediate ears and included a region from 15-25% distance from the apex as well as the 65-95% region. In the late ears, heights had returned to control values, except within focal OC lesions. Height at the first row of OHCs was less affected than at the third row, and height at the inner hair cell (IHC) was least affected. These height changes were accompanied by distortion of the shape and position of OHCs, the shape of Deiters' cells and buckling of inner and outer pillar bodies. Sometimes IHCs had distorted shapes and were displaced from their usual positions. Although no functional measures were obtained from these ears, data from the literature indicate that the exposure described above would have produced a sizable threshold shift. Transient reduction in OC height likely accounts for some portion of noise-induced threshold shifts.

Acoustic Stimulation↗
PubMed1992

Two-tone suppression by a saturating feedback model of the cochlear partition.

A model of a small strip of cochlear partition was computer simulated. The model is composed of two elements, approximations to the transfer functions of an inner hair cell (IHC) and an outer hair cell (OHC), respectively. The IHC element was insensitive to DC stimulation. Input was one or two sinusoids. One sinusoid, at the characteristic frequency (CF), was multiplied by the gain of the 'cochlear amplifier'. A second sinusoid, representing a tone with much lower frequency, was not affected by the amplifier gain. This gain was determined by the OHC transfer function. In one form of the model ('fixed-gain'), this gain was set at a fixed number determined from the furthest point reached on the OHC transfer function. This form of the model produced very realistic single-tone responses as well as showing 'two-tone suppression': that is, the IHC DC response produced by CF stimulation was reduced when the lower-frequency sinusoid, at suitable intensities, was added to the stimulus. When a DC component was added to the two-tone stimulus, the magnitude of this two-tone suppression was enhanced. In the second form of the model ('variable-gain'), the cochlear-amplifier gain varied throughout the stimulus cycle. Its value was re-calculated at each instant, determined by the point on the OHC transfer function current at that particular instant. This form of the model showed two-tone suppression only when a DC component was added to the two-tone stimulus.

Acoustic Stimulation↗
PubMed1992

Acoustic lesions in the mammalian cochlea: implications for the spatial distribution of the 'active process'.

The spatial contribution of mechanically active hair cells to tuning and sensitivity at a single point in the mammalian cochlea has been investigated in the basal turn of the guinea pig cochlea. Following the destruction of outer hair cells with acoustic overstimulation it was possible to record apparently normal tuning and sensitivity from spiral ganglion neurones innervating inner hair cells located on the apical edges of substantial lesions. The distance between the recording site, where neurones showed normal sensitivity, and areas of the cochlea showing 60-100% of the outer hair cells either damaged or missing varied between 0.2 and 1.3 mm which incorporates approximately 70 to 450 outer hair cells. In one animal neurones that demonstrated normal sensitivity were recorded within 0.2 mm of a lesion where 67% of the outer hair cells were either missing or showed severe damage to their stereocilia and within 0.5 mm of areas of the organ of Corti showing damage to 97% of the outer hair cells. This distance includes approximately 50 inner hair cells or 180 outer hair cells. The location of these neurones, whose sharp tuning presumably mirrors basilar membrane mechanics, suggests that a substantial proportion of point tuning in the cochlea may be derived over a distance of less than 0.5 mm and involve fewer than 200 active outer hair cells.

Acoustic Stimulation↗
PubMed1992

Hair cell damage after continuous and interrupted pure tone overstimulation: a scanning electron microscopic study in the guinea pig.

In our earlier investigations [Fredelius et al., Hear. Res. 30, 157-167 (1987)] acoustic trauma was studied after continuous 3.85-kHz pure tone exposures of different intensities and durations. In the present investigation, the importance of the introduction of a break during longer 3.85-kHz pure tone exposures was studied. Female pigmented guinea pigs were exposed to 108, 114, or 120 dB SPL for 6 h with or without a 1-h break after the first 3 h. Four weeks after exposure the cochleas were prepared for scanning electron microscopy and the resulting hair cell damage was evaluated according to a 4-grade damage scale. Significant differences could be demonstrated in the hair cell damage in the animals exposed to continuous acoustic overstimulation and those exposed to intermittent overstimulation. The importance of rest periods to decrease hair cell damage during long periods of acoustic overstimulation was clearly demonstrated.

Acoustic Stimulation↗
PubMed1977

Actin filaments in sensory hairs of inner ear receptor cells.

Receptor cells in the ear are excited through the bending of sensory hairs which project in a bundle from their surface. The individual stereocilia of a bundle contain filaments about 5 nm in diameter. The identity of these filaments has been investigated in the crista ampullaris of the frog and guinea pig by a technique of decoration with subfragment-1 of myosin (S-1). After demembranation with Triton X-100 and incubation with S-1, "arrowhead" formation was observed along the filaments of the stereocilia and their rootlets and also along filaments in the cuticular plate inside the receptor cell. The distance between attached S-1 was 35 nm and arrowheads pointed in towards the cell soma. It is concluded that the filaments of stereocilia are composed of actin.

Actin Cytoskeleton↗
PubMed1992

Nonlinear mechanical responses of mouse cochlear hair bundles.

The stiffness of sensory hair bundles of both inner (IHC) and outer (OHC) hair cells was measured with calibrated silica fibres in mouse cochlear cultures to test the hypothesis that the mechanical properties of the hair bundle reflect processes underlying mechanotransduction. For OHCs, the displacement of the hair bundle relaxed with time constants of 6 ms for displacements which open transducer channels and 4 ms for displacements which close the channels. The corresponding values of the time constants for IHCs were 10 ms and 8 ms, respectively. A displacement-dependent change in the stiffness of the hair bundle was not observed when the bundle was displaced orthogonally to the direction of excitation. The stiffness of the hair bundle as a function of nanometre displacements from the resting position was remarkably nonlinear. The stiffness declined to a minimum from the resting stiffness by about 12% for OHCs and 20% for IHCs when the hair bundle was displaced by about 20 nm in the excitatory direction, and it increased by a similar amount when the bundle was displaced by 20 nm in the inhibitory direction. The displacement at which the stiffness reached a minimum was within the most sensitive region of the hair-cell transducer function (receptor potential as a function of hair-bundle displacement), and the displacement at which the stiffness reached a maximum was at the point of saturation of the transducer function in the inhibitory direction. The nonlinear displacement-dependent compliance change is reversibly abolished, and the time constant of relaxation of the bundle for excitatory displacements is reversibly reduced, when mechanotransduction is blocked by the addition of either neomycin sulphate or cobalt chloride to the solution bathing the hair cells. The displacement-dependent compliance change was not apparently reduced when the receptor potential was attenuated through the substitution of sodium in the bathing solution with a less permeant cation, tetraethylammonium. These findings suggest that the nonlinear mechanical properties of the hair bundle are associated with aspects of the hair-cell mechanotransducer process. The mechanical properties of the hair bundle are discussed in relation to the 'gating-spring' hypothesis of hair-cell transduction.

Animals↗
PubMedDate not supplied

Organ of Corti in the human fetus: scanning and transmission electronmicroscope studies.

The organ of Corti in the five-month human fetus was studied by transmission and scanning electronmicroscopy. Differentiation of the surface organization of the organ of Corti into a single row of inner and three to four rows of outer hair cells was complete at this stage except at the apical end. The morphological aspects of the hair bundles changed with maturation of the sensory cells; the inner hair cells preceded the outer hair cells in cytodifferentiation at a given location.

Cell Differentiation↗
PubMed1992

[Techniques for isolating hair cells from guinea pig cochlea].

Isolated live hair cells are important models for studying the electrophysiology, pathology and pharmacology of the hair cell. Using mechanical isolation method after papain treatment 70 +/- 27 hair cells, including 0 to 4 inner hair cells, could be obtained from each cochlea of 4 guinea pigs. The criteria for a good viability of isolated cochlear hair cells were: 1. a smooth hair cell membrane; 2. hair cells not swollen; 3. the nucleus in the normal position; 4. the cytoplasm in a state of semitransparency with a halo at the periphery (birefringence) and 5. no Brownian movement of the organelles within the cytoplasm. With short-term culturing at room temperature, approximately 90% of the isolated hair cells retained a good viability at the end of two hours. Subsequently the hair cells gradually degenerated but still, at the end of five hours, about 40% of them appeared intact. The degeneration patterns have been carefully observed and described.

Animals↗
PubMed1992

The phase and magnitude of hair cell receptor potentials and frequency tuning in the guinea pig cochlea.

Voltage responses to tones were recorded intracellularly from inner (IHC) and outer (OHC) hair cells in the basal turn of the guinea pig cochlea. Tone-evoked voltage responses were also recorded extracellularly from fluid-filled spaces adjacent to the hair cells and from supporting cells. The AC component of the OHC voltage responses to tones at frequencies between 8 and 24 kHz and those recorded extracellularly were remarkably similar with respect to phase as a function of sound level, but the magnitude of the AC response was 2-10 times larger when recorded intracellularly from an OHC. At frequencies more than half an octave below the characteristic frequency (CF), the phase of OHC AC response was independent of level, and the slope of the magnitude/level functions was 1 dB/db. At levels exceeding about 70 dB SPL, the slopes became less steep and depolarizing IHC and OHC DC responses appeared. At frequencies one-half an octave below CF and at frequencies between one-third and one-half an octave above CF, notches were present in the AC/level function between 70-100 dB SPL that were accompanied by a sudden phase lag of -180 degrees. These frequency- and level-dependent characteristics were also present in relatively insensitive preparations and were attributed to a change in the phase of OHC excitation due to level-dependent changes in the relative stiffness of the mechanical components of the cochlear partition. At CF the detection thresholds of the OHC AC response and IHC DC response and slopes of the response/level functions were similar. At sound levels around 60 dB SPL, the AC signal began to phase lead, amounting to approximately 90 degrees at 70 dB SPL. Within the same range of levels, the OHC DC potentials first appeared and the IHC DC response began to saturate. At frequencies just above the CF, the phase of the AC component increased with level to a lead of about 180 degrees. OHC and IHC tuning curves are comparable in the tip region, but they differ in that the low- and high-frequency shoulders of the OHC AC tuning curves are more sensitive by 10-30 dB SPL. On the basis of the frequency- and level-dependent characteristics of the IHC and OHC responses, it is proposed that OHC AC potentials provide a measure of the phase and magnitude of the proposed electromechanical feedback of the cochlear partition that enhance frequency tuning in the cochlea.

Acoustic Stimulation↗
PubMed1992

A comparison of changes in the stereocilia between temporary and permanent hearing losses in acoustic trauma.

A comparison of stereociliary changes at different post-exposure intervals in ears with temporary and permanent hearing losses has been made. Twenty guinea pigs were exposed to either 110 dB SPL broadband white noise for 30 min (N = 10) or 120 dB SPL white noise for 150 min (N = 10). The recovery patterns for threshold shifts for both groups were systematically assessed at regular post-exposure intervals for 80 days, using the auditory cortex evoked response to tone bursts between 0.5 and 8kHz. Thirty-two animals that had been exposed to the same noise at either 110 dB for 30 min (N = 16) or 120 dB for 150 min (N = 16) were decapitated for scanning electron microscopic examination at the same post-exposure intervals. The threshold shifts induced by 110 dB noise were reversible while those induced by 120 dB were generally irreversible, although extreme variabilities existed among the animals. In the acute TTS ears, damage was confined to the third row of OHCs, where only the tips of the stereocilia were affected. Neither discontinuity of cuticular plate nor expelled cytoplasm was found in these cells. In the lesions of PTS, either all the three rows of OHCs or the IHCs and the first row of OHCs were involved. The entire length of the stereocilia, more severe in the lower part was always damaged. Expelled cytoplasm and fusion between stereocilia were frequently seen. In the chronic TTS ears, no abnormalities of stereocilia were found while in the PTS ears, a complete absence of the organ of Corti was noticed. The results of the present study clearly suggest that the status of the lower part of the stereocilia and the continuity of the cuticular plate play an important role in determining the reversibility of threshold shifts.

Animals↗