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At least 19 recordsLinked to original sources
PubMed1983

Actin filaments, stereocilia, and hair cells of the bird cochlea. I. Length, number, width, and distribution of stereocilia of each hair cell are related to the position of the hair cell on the cochlea.

Located on the sensory epithelium of the sickle-shaped cochlea of a 7- to 10-d-old chick are approximately 5,000 hair cells. When the apical surface of these cell is examined by scanning microscopy, we find that the length, number, width, and distribution of the stereocilia on each hair cell are predetermined. Thus, a hair cell located at the distal end of the cochlea has 50 stereocilia, the longest of which are 5.5 microns in length and 0.12 microns in width, while those at the proximal end number 300 and are maximally 1.5 microns in length and 0.2 micron in width. In fact, if we travel along the cochlea from its distal to proximal end, we see that the stereocilia on successive hair cells gradually increase in number and width, yet decrease in length. Also, if we look transversely across the cochlea where adjacent hair cells have the same length and number of stereocilia (they are the same distance from the distal end of the cochlea), we find that the stereocilia of successive hair cells become thinner and that the apical surface area of the hair cell proper, not including the stereocilia, decreases from a maximum of 80 microns2 to 15 microns2. Thus, if we are told the length of the longest stereocilium on a hair cell and the width of that stereocilium, we can pinpoint the position of that hair cell on the cochlea in two axes. Likewise, if we are told the number of stereocilia and the apical surface of a hair cell, we can pinpoint the location of that cell in two axes. The distribution of the stereocilia on the apical surface of the cell is also precisely determined. More specifically, the stereocilia are hexagonally packed and this hexagonal lattice is precisely positioned relative to the kinocilium. Because of the precision with which individual hair cells regulate the length, width, number, and distribution of their cell extensions, we have a magnificent object with which to ask questions about how actin filaments that are present within the cell are regulated. Equally interesting is that the gradient in stereociliary length, number, width, and distribution may play an important role in frequency discrimination in the cochlea. This conclusion is amplified by the information presented in the accompanying paper (Tilney, L.G., E.H. Egelman, D.J. DeRosier, and J.C. Saunders, 1983, J. Cell Biol., 96:822-834) on the packing of actin filaments in this stereocilia.

Animals↗
PubMed1986

The responses of inner and outer hair cells in the basal turn of the guinea-pig cochlea and in the mouse cochlea grown in vitro.

Until recently the responses of the mechanosensitive hair cells of the cochlea have been inferred from their morphology, morphological relationships with other structures in the cochlea, and by indirect electrophysiological measurements. With the advent of techniques for making intracellular recordings from hair cells in the cochleas of anaesthetised mammals it has been possible to measure the responses of hair cells to acoustic stimulation and to assess their roles in sensory transduction in the cochlea. Intracellular recordings of the responses of inner and outer hair cells in the basal turn of the guinea-pig cochlea show that they differ considerably from each other. The receptor potentials of inner hair cells are larger, predominantly depolarizing to low frequency tones and at their best frequencies (16-20 kHz) they generate depolarizing dc receptor potentials. Outer hair cells generate predominantly hyperpolarizing potentials to low frequency tones. They do not produce significant voltage responses at high frequencies except at high intensities when they generate slowly rising depolarizing potentials which are associated with loss of cochlear sensitivity. At low frequencies the receptor potentials of the inner hair cells phase lead those of the outer hair cell. Measurements of their frequency selectivity show that inner and outer hair cells are both sharply tuned. It is proposed that the responses of inner and outer hair cells are consistent with sensory and motor roles respectively in mechanoelectric transduction and that the outer hair cells are the site of an active mechanical process responsible for the frequency selectivity and sensitivity of the cochlea. Intracellular recordings from hair cells in the mouse cochlea maintained in vivo have provided a direct measure of the mechanosensitivity of cochlear hair cells (approximately 30 mV per degree of displacement of their stereociliary bundles) and indirect evidence that the transfer characteristics of the outer hair cells in vivo may be due to their mechanoelectrical interaction with the tectorial membrane. This is because the transfer characteristics of the inner and outer hair cells are similar in vitro in the absence of a tectorial membrane. Considerable importance is attributed to the shape of the transfer characteristics of the inner and outer hair cells. Changes in these characteristics during anoxia and following exposure to intense tones are associated with depolarization of the outer hair cells and loss of cochlear sensitivity and frequency selectivity. Current-voltage studies of hair cells in vivo show the inner and outer hair cells to be electrically nonlinear.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2002

OCP2 immunoreactivity in the human fetal cochlea at weeks 11, 17, 20, and 28, and the human adult cochlea.

The two most abundant proteins of the organ of Corti, OCP1 and OCP2, are acidic, cytosolic, low molecular weight proteins diffusely distributed within the cytoplasm of supporting cells. A recent study by Henzl et al. (2001) found first, that these two proteins co-localize with connexin 26 along the epithelial gap junction system and second, that OCP2 could participate with OCP1 in an organ of Corti-specific SCF complex (Skp1, cul1in, and Fbp), a ubiquitin ligase complex. Previous study has also implicated OCP2 in the recycling and regulation of intracellular K(+) efflux as well as pH homeostatic mechanisms. In the present study, we document the emergence and distribution features of OCP2 through various stages (weeks 11-28) of gestation in human fetal cochleae. Four fetal cochleae, the cochleae of a normal hearing human adult and a mature rat for positive control were fixed in 4% formalin within 2 h post mortem. Immunohistochemical studies were performed using a rabbit polyclonal antibody raised against a synthetic peptide corresponding to amino acids 3-16. Specimens were mounted in paraffin sections. Results show that OCP2 immunoreactivity is evident at a prenatal age of 11 weeks, peaks in expression at the onset of cochlear function at 20 weeks and achieves adult-like patterns of distribution just prior to histological maturation at 28 weeks. Though this protein could be associated with the development, maturation, and electrochemical maintenance of the cochlear gap junction system, the nature of this protein's function in the developing and mature human cochlea remains unclear.

Adult↗
PubMed1984

Determination of the regional cochlear blood flow in the rat cochlea using non-radioactive microspheres and serially sectioned cochleas.

The regional blood flow to the rat cochlea has been studied using a method which combines the microsphere method with observation of serially-sectioned, plastic-embedded cochleas. Direct quantitation of the microspheres in a reference blood sample and in the different vascular areas of the cochlea allows the analysis of blood flow patterns with respect to the different capillary beds.

Animals↗
PubMed1991

Radial communication between the perilymphatic scalae of the cochlea. II: Estimation by bolus injection of tracer into the sealed cochlea.

Radial communication between ST and SV was measured in the sealed cochlea by monitoring the dispersal of an ionic tracer, trimethylphenylammonium (TMPA) injected in the form of a minute bolus. Tracer movements were recorded by a pair of ion-selective electrodes sealed into the injected and non-injected scalae close to the injection site. Measurements were made in the basal or third turn of the guinea pig cochlea. In the third turn, radial communication occurred rapidly with a ST half time from ST to SV of 25 min and from SV to ST of 26 min. In the basal turn the communication was markedly slower, with a ST half time from ST to SV of 170 min and from SV to ST of 240 min. However, the difference between the basal and third turns can be shown to arise almost totally from differences in cross-sectional area of the perilymphatic scalae. When normalized with respect to scala cross-section, the process of tracer movement across the spiral ligament is similar in the basal and third turns. These results demonstrate that radial communication between scala tympani and scala vestibuli is an important route which must be considered in studies involving perilymph.

Animals↗
PubMed2001

[The early postnatal development of the hamster cochlea].

The Early Postnatal Development of the Hamster Cochlea. Inborn deafness can be diagnosed very early. Deafness in early childhood can be caused by: genetic defects (30 % - 40 %), embryopathies, embryonic noxae (60 %) and pre-, peri- and postnatal noxae. Which structures of the cochlea are disturbed, is unknown in most cases. Systematic studies are necessary with directed experimental impairments of the cochlea in the early development to elucidate these mechanisms. An animal model has to be established in which directed impairments can be carried out in single individuals. The cochlea of the hamster is at birth in a very early state of development. In the apical turn the epithelial layer of the cochlear duct is undifferentiated, whereas in the basal turn the papilla basilaris (Kölliker's organ), the lateral wall and Reissner's membrane are visible. Between the base of the cochlea (1st coil lateral) and the apical part (3rd coil lateral) the difference in the development of the hamster cochlea is exactly four days. This is evident for the 1st and the 5th day after birth. The cochlea development of the hamster is very rapid. The development during one day represents one week of development in the human cochlea. The difference in development in one hamster cochlea from the apex to the base at a certain day representing four days of development is comparable with the development time of four weeks in human. The different developmental stages which are present in the hamster cochlea of a certain day represent the development of the human cochlea of a whole month. The hamster cochlea at the 1st day after birth covers the 2nd embryonic month of the human (4th to 8th week) and at the 5th day the 3rd embryonic month (8th to 12th week). The hamster cochlea at the 1st and the 5th day after birth is especially suitable to study experimental disturbances in the early stages of the development of the cochlear duct when the tectorial membrane, the spiral limbus, the stria vascularis, Reissners membrane and the external spiral Sulcus with the root cells are differentiating. The biggest advantage is that the noxae (hypoxia, teratogenic substances, ototoxic antibiotics and intense noise) can be applied to single individuals which offers better control than the treatment of the mother.

Animals↗
PubMed1987

The distribution of hair cell bundle lengths and orientations suggests an unexpected pattern of hair cell stimulation in the chick cochlea.

A detailed analysis of the morphological polarity of the hair cell bundles on the chick cochlea was carried out. Although the pattern is identical from cochlea to cochlea, the morphological polarity of the bundles varies at different positions on the cochlea. More specifically, the hair cell bundles located immediately adjacent to the inferior and superior edges are oriented with their morphological polarity perpendicular to the margins. As we move across the cochlea (transect it), there is a gradual rotation in the polarity of the bundles so that in the center of the cochlea the hair cells are oriented at an angle to those at the edges. As we continue to the superior edge the polarity gradually rotates back again. The amount of rotation depends on the position of the transect such that at the extreme proximal end there is little rotation, while at the distal end the rotation is up to 90 degrees. The rotation is always in the same direction with the tallest rows of stereocilia nearest the distal end of the cochlea. Measurements of the length of the longest stereocilia in the hair cell bundles revealed that not only are the bundles systematically longer from the proximal to distal end of the cochlea, but also the hair cells on the superior edge are significantly longer than those on the inferior edge at the same distance from one end of the cochlea. If we draw on micrographs of the cochlea contour lines through hair cells whose stereocilia are the same height, these lines coincide with the morphological polarity of the hair cells included in these contours. Furthermore analysis of damage to the cochlea induced by pure tones of high intensity also roughly follows the same contour lines. We conclude that unlike what has been thought, the stimulation of hair cells by pure tones may not occur in a strictly transverse pattern, but instead may follow the oblique contours demonstrated here.

Acoustic Stimulation↗
PubMed2002

The shortened cochlea: its classification and histopathologic features.

INTRODUCTION: The term 'Mondini dysplasia' has been used to describe virtually any congenital abnormality of the osseous labyrinth resulting in confusion and seemingly contradictory observations and conclusions about this type of deformity. The purpose of this study is to histopathologically classify and describe temporal bones whose cochleas have less than 2.5 turns. METHODS: Of the 1800 temporal bones in our collection, 21 from 12 cases were found to have cochleas with less than 2.5 cochlear turns. Ages ranged from stillborn to 50 years. Temporal bones were harvested at autopsy, processed and embedded in celloidin. Sections were cut at a thickness of 20 microm and every 10th section stained with hematoxylin-eosin and examined using light microscopy. The number of turns, length of cochlea, integrity of cochlear base, length of modiolus, abnormalities of the semicircular canals and vestibule, enlargement of the vestibular aqueduct and middle ears were documented. Twenty-one temporal bones from age-matched patients without cochlear deformities were used as controls for modiolar length measurements. RESULTS: Malformation of the shortened cochlea was histopathologically classified into three groups as follows: (1) Common cavity, cochlear dysplasia (one ear)--severe dysplasia of the cochlea without a complete basal turn; (2) Mondini dysplasia (11 ears)--1.5 cochlear turns, a complete basal turn, an incomplete or absent interscalar septum and a complete bone at the base of the modiolus; and (3) Mondini-like dysplasia type A (five ears)--2 turns to the cochlea including a complete basal turn and complete bone at the base of the modiolus; and type B (four ears)--1.5-2 turns to the cochlea, hypoplasia of or a missing bone at the base of the modiolus (either with or without a communication between the internal auditory canal and the cochlea) and a complete basal turn. CONCLUSION: The range of congenital malformations in short cochlea is highly variable. Fundamental to the accurate evaluation of a labyrinthine anomaly, malformations of the inner ear should be classified according to the findings in the labyrinth. We suggest the use of common cavity cochlear dysplasia, Mondini dysplasia and Mondini-like dysplasia to describe these variable anomalies.

Adolescent↗
PubMed1997

Green fluorescent protein as a reporter for gene transfer studies in the cochlea.

This study examined the 'humanized, red-shifted' version of the jellyfish Aequorea victoria green fluorescent protein (hrGFP) as a novel reporter for in vivo gene transfer studies in the cochlea using adeno-associated virus (AAV) vectors. Approximately 10(5) AAV vectors containing the hrGFP reporter gene were infused over 2 days or 1 week into the cochlea of the guinea pig via an osmotic minipump. Saline infused, non-infused, as well as AAV-beta-galactosidase infused guinea pigs served as the negative controls. The hrGFP transgene expression was detected as moderate intensity fluorescence easily distinguished from the background. Increased fluorescence was seen in the spiral ganglion, spiral ligament, spiral limbus, organ of Corti, and Reissner's membrane of the AAV-hrGFP infused animals. Control animals showed minimal fluorescence throughout the cochlea. Comparison of the 2 day and 1 week AAV-hrGFP infused animals showed qualitatively increased fluorescence in the 2 day animals. Background autofluorescence in the stria vascularis was noted in both the experimental and the control animals. In addition, fluorescence was detected in the contralateral cochlea of the AAV-hrGFP infused animals. Subsequent PCR analysis confirmed the presence of viral particles in the AAV-hrGFP infused cochlea as well as in the brain and the contralateral cochlea. This finding has important implications for the eventual implementation of cochlear gene therapy. The results not only reinforce the need to assess the introduction and expression of foreign genes in the target cochlea but also consider issues of viral spread, safety, and modes of gene delivery. This study establishes hrGFP as an effective reporter of gene transfer and transgene expression in the cochlea. GFP's small gene size, stability, ease of detection, and potential for diverse biological applications will be invaluable for a variety of future gene transfer and expression studies in the cochlea.

Animals↗
PubMed1987

Hair cell distributions in the normal human cochlea.

This supplement presents the results of a collaborative project between workers from several European nations. The study was started in order to provide data describing the distribution of the sensory hair cells in the normal human cochlea and to allow the evaluation of age-related changes in the hair cell density. Fifty-three cochleas (including nine from fetuses) were preserved by perilymphatic perfusion with fixative shortly after death. In the non-fetal material the hearing was clinically normal prior to death. Some subjects had audiograms available and these also had to be normal for their age for inclusion of the cochlea in the study. Dissection of cochleas permitted surface preparation techniques to be used to count the hair cells and allow the hair cell density to be described as inner or outer hair cells per mm. The total length in mm of each cochlea was also measured (Length). The location of each hair cell density count was defined as distance in mm from the base (Distance), distance in mm from the apex (Length minus Distance), or as a proportion of the total length of the cochlea when the location of that count was measured as distance from the base (Distance/Length). The material was allocated to one of six age bands. For each age band and at each point in the cochlea for which data existed the average hair cell density and its standard deviation were calculated. This allowed average cytocochleograms to be drawn for both inner and outer hair cells. The proportional method of representation of location within the cochlea gave the best fit of the available data and the proportional cytocochleograms are presented, although the data for all three methods are included in tabular form. The average cytocochleograms indicate a progressive age-related loss of outer hair cells. This loss was exacerbated at both the apical and basal ends of the cochlea. The overall loss was less marked for the inner hair cell population but was accentuated at the base, like that of the inner hair cells, although not at the apex. With the proportional datasets, and taking fetal age as zero, a model of hair cell loss was developed. A simple linear equation in the form: Hair cell density(i) = (Age in years X Age Coefficient(i)) + Constant(i) gave the best fit at each proportional location (i) for both inner and outer hair. The age coefficients and constants are given in tables for inner and outer hair cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell Count↗
PubMed1996

Scanning electron microscopic study of the postnatal development of the rabbit cochlea, with an emphasis on innervation.

The development of nerve fiber arrangements of the organ of Corti was studied in rabbits 1, 3, 5, 7 and 12-days-old using thick sections from celloidin-embedded cochleas which were examined under a scanning electron microscope. The arrangements of nerve fibers varied with developmental age. The tunnel spiral bundle was thick and loosely collected in the immature cochlea. The outer spiral fibers were recognized even in the narrow space of Nuel in the one-day-old cochlea. As Nuel's space is extending, the fibers course along the medial side of Deiters' cells. The arrangement of the outer spiral fibers was irregular and sparse in the five-day-old cochlea, in contrast to the regular parallel pattern of the adult cochlea. Adult-like parallel arrangement of the outer spiral fibers was seen in the twelve-day-old cochlea. In the three-day-old cochlea, irregularly running nerve fibers were seen along the outer spiral fibers. They may be efferent axons which develop afterwards. Club-like immature nerve endings were recognized at the base of the outer hair cells in the seven-day-old cochlea. Some fibers climbed high up along the medial wall of the outer hair cells. A nearly mature pattern was seen in the twelve-day-old cochlea. This study confirms previous reports on the development of cochlear innervation.

Animals↗
PubMed1989

Descending projections from auditory brainstem nuclei to the cochlea and cochlear nucleus of the guinea pig.

Projections from auditory brainstem nuclei to the cochlea and cochlear nuclei in the guinea pig were studied by injection of two retrograde fluorescent neuronal tracers. For seven experiments fast blue was injected into the scala tympani of one cochlea and diamidino yellow was injected into dorsal or anteroventral cochlear nucleus of the same side. The results show that the efferent projections to the cochlea and cochlear nucleus generally form two separate neuronal systems even though they share many common nuclei of origin. The largest projections to the cochlear nucleus come bilaterally from the lateral and ventral nuclei of the trapezoid body. Other nuclei, the lateral superior olive, the ventral nucleus of the lateral lemniscus, the dorsomedial periolivary nuclei, and the medial nucleus of the trapezoid body showed an ipsilateral bias in their projections to the cochlear nucleus. An upper limit of 3.5% of the medial system olivocochlear efferent neurones projecting to the cochlea were labelled with both diamidino yellow and fast blue, suggesting that few efferent neurones projecting to the cochlea send collaterals to the cochlear nucleus in this species. However, the site of medial system olivocochlear efferent collateral terminations is the granule cell area for the cat, mouse, and gerbil. When diamidino yellow was injected in the superficial layers of the cochlear nucleus, including the superficial granule cell layer of the ventral cochlear nucleus, approximately 3.6% of medial system olivocochlear efferents projecting to the cochlea sent collaterals to the cochlear nucleus. In three animals fast blue was injected into the cochlear nucleus and diamidino yellow into the cochlea. These experiments revealed a greater proportion of the medial system olivocochlear efferents projecting to the cochlea sending collaterals to the cochlear nucleus, but this proportion was still less than 10%. These results were confirmed by the extracellular injection of horseradish peroxidase into the intraganglionic spiral bundle. Only three medial system olivocochlear efferents were observed to send collaterals to the cochlear nucleus. This number was less than 10% of all labelled medial system fibres. Although these experiments suggest that in the guinea pig the number of olivocochlear efferents sending collaterals to the cochlear nucleus is considerably smaller than is found for the cat, mouse, and gerbil, it is not possible with the current experimental procedures to conclude whether the results are due to species or methodological differences.

Animals↗
PubMed1993

Effect of unilateral partial cochlear lesions in adult cats on the representation of lesioned and unlesioned cochleas in primary auditory cortex.

We examined the effect of unilateral restricted cochlear lesions in adult cats on the topographic representations ("maps") of the lesioned and unlesioned cochleas in the primary auditory cortex (AI) contralateral to the lesioned cochlea. Frequency (tonotopic) maps were derived by conventional multineuron mapping procedures in anesthetized animals. In confirmation of a study in adult guinea pigs (Robertson and Irvine [1989] J. Comp. Neurol. 282:456-471), we found that 2-11 months after the unilateral cochlear lesion the map of the lesioned cochlea in the contralateral AI was altered so that the AI region in which frequencies with lesion-induced elevations in cochlear neural sensitivity would have been represented was occupied by an enlarged representation of lesion-edge frequencies (i.e., frequencies adjacent to those with elevated cochlear neural sensitivity). Along the tonotopic axis of AI the total representation of lesion-edge frequencies could extend up to approximately 2.6 mm rostal to the area of normal representation of these frequencies. There was no topographic order within this enlarged representation. Examination of threshold sensitivity at the characteristic frequency (CF, frequency to which the neurons were most sensitive) in the reorganized regions of the map of the lesioned cochlea established that the changes in the map reflected a plastic reorganization rather than simply reflecting the residue of prelesion input. In contrast to the change in the map of the lesioned contralateral cochlea, the map of the unlesioned ipsilateral cochlea did not differ from those in normal animals. Thus, in contrast to the normal very good congruency between ipsilateral and contralateral AI maps, in the lesioned animals ipsilateral and contralateral maps differed in the region of AI in which there had been a reorganization of the map of the lesioned cochlea. Outside the region of contralateral map reorganization, ipsilateral and contralateral AI maps remained congruent within normal limits. The difference between the two maps in the region of contralateral map reorganization suggested, in light of the physiology of binaural interactions in the auditory pathway, that the cortical reorganization reflected subcortical changes. Finally, response properties of neuronal clusters within the reorganized map of the lesioned cochlea were compared to normative data with respect to threshold sensitivity at CF, the size of frequency "response areas," and response latencies. In the majority of cases, CF thresholds were similar to normative data. The frequency "response areas" were slightly less sharply tuned than normal, but not significantly. Response latencies were significantly shorter than normal in three animals and significantly longer in one animal.

Animals↗
PubMed1994

Rapid increase in mitochondrial volume in nucleus magnocellularis neurons following cochlea removal.

Second-order auditory neurons in nucleus magnocellularis (NM) of the chick brainstem undergo a series of rapid metabolic changes following unilateral cochlea removal, culminating in the death of 25% of NM neurons. Within hours of cochlea removal, ipsilateral NM neurons show marked increases in histochemical staining for the mitochondrial enzymes succinate dehydrogenase and cytochrome oxidase. We investigated corresponding ultrastructural changes in NM neurons by preparing animals undergoing unilateral cochlea removal for transmission electron microscopy. We quantified changes in NM mitochondrial volume by stereological methods and qualitatively compared mitochondrial morphology between NM neurons destined to survive and those destined to die after cochlea removal. Within hours of cochlea removal, ipsilateral NM neurons show striking increases in mitochondrial volume (84% at 6 hours and 236% at 12 hours after cochlea removal compared to unoperated, control animals). At 2 week survival times, ipsilateral NM neurons contain fewer mitochondria than contralateral neurons. Surprisingly, anesthesia alone causes short-term increases in NM mitochondrial volume. Animals anesthetized with pentobarbital and ketamine and sacrificed 6 or 12 hours later showed a 45% increase in mitochondrial volume compared to previously unanesthetized animals. NM neurons destined to die within days of cochlea removal can be identified within several hours after deafferentation by the appearance of their ribosomes. We observed qualitative differences in mitochondrial morphology in dying neurons. Mitochondria in neurons destined to die consistently showed mitochondrial swelling and vacuolization indicative of metabolic dysfunction. Similar mitochondrial changes have been reported when mitochondria take up excess calcium. Ultrastructural changes in NM after cochlea removal display features of both programmed and pathological cell death, in which increased intracellular calcium is thought to play a role.

Anesthesia↗