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PubMed1994

Postnatal development of the hamster cochlea. I. Growth of hair cells and the organ of Corti.

A morphometric analysis of the developing organ of Corti and its component hair cells was carried out in an age-graded series of Syrian golden hamsters with the aid of scanning electron microscopy. The purpose was to establish a quantitative framework that would provide insight into the rules and principles by which the mammalian cochlea attains its adult proportions. This study examined postnatal development at two day intervals from birth to 22 days after birth. Our analysis included measures of cochlear length and hair cell numbers as well as measures of hair cell sizes in each of five sectors along the cochlear spiral. Our results demonstrate several principles of cochlear development: 1) The full two and one-fourths turns seen in the adult cochlea are already present at birth, but the cochlea continues to elongate for the next 10-12 days. 2) Development of hair cells in the apex generally lags behind that in the base. Whereas the stereocilia and apical margins of hair cells are clearly defined in the basal turn, they become well defined in the apex only postnatally. 3) Growth in cochlear length occurs mainly by increases in cell size rather than in cell numbers; although hair cells do increase in numbers during the first 4 days of cochlear growth, this increase involves addition of hair cells only to preexisting regions of the cochlear apex. Moreover, the full complement of hair cells is established 6 days before the full size of the cochlea is attained; in contrast, hair cell growth occurs at all positions along the cochlear spiral and spans the entire period of cochlear elongation. 4) The period of hair cell growth exceeds the period of organ of Corti growth and appears to be possible by decreases in intercellular spacing, primarily in the apical region of the cochlea; inner and outer hair cell growth was complete between 16 and 18 days after birth. 5) Inner and outer hair cell neighbors remain virtually constant at different ages indicating that the spatial relationships between the two hair cell populations is preserved as the cochlea grows. 6) Comparison with previous developmental studies of auditory function in the hamster reveals that the age of 16 days after birth, when hair cells attain their mature sizes, coincides with the onset of brainstem auditory evoked responses. Growth of hair cell somas alone, however, cannot explain either the subsequent maturation of evoked potential thresholds or changes in frequency representation in the developing cochlea.

Animals↗
PubMed2000

Tubulin expression in the developing and adult gerbil organ of Corti.

In the late stages of inner ear development, the relatively undifferentiated cells of Kollicker's organ are transformed into the elaborately specialized cell types of the organ of Corti. Microtubules are prominent features of adult cells in the organ of Corti, particularly supporting cells. To test the possible role of microtubules in organ of Corti development, the microtubule organization in the organ of Corti has been examined using indirect immunofluorescence to beta-tubulin in the developing gerbil cochlea. Tubulin first appears at post-natal day 0 (P0) as filamentous asters in inner hair cells and by P2, asters are also seen in outer hair cells. Tubulin appears at P3 in inner pillar cells in a tooth crown-like figure. By P6, tubulin expression is also evident in outer pillar cells and by P9, it is seen in Deiters cells. Elaboration of microtubules in pillar cells was observed to proceed from the reticular lamina towards the basilar membrane. The pattern of tubulin expression in the apical organ of Corti lags the base by about 3 days until P6, but by P9, apical and basal organ of Corti appear substantially the same.

Animals↗
PubMed1998

Terminal dendritic sprouting and reactive synaptogenesis in the postnatal organ of Corti in culture.

Synaptogenesis in the organ of Corti between the primary receptors, the inner hair cells, and the peripheral processes of their afferent spiral ganglion neurons in the mouse lasts for 5 days postnatally (Sobkowicz et al. [1986] J. Neurocytol. 15:693-714). The transplantation of the organ into culture at the fifth postnatal day induces a reactive sprouting of dendritic terminals and an extensive formation of new ribbon synapses within 24 hours. This reactive synaptogenesis differs strikingly from the primary synaptogenesis and has been seen thus far only in the inner hair cells. The synaptically engaged neuronal endings sprout a multitude of filopodia that intussuscept the inner hair cells. The filopodial tips contain a heavy electron-dense matter that appears to attract the synaptic ribbons, which form new synaptic contacts with the growing processes. The intensity of the filopodial growth and synaptogenesis subsides in about 3 days; the filopodia undergo resorption, leaving behind fibrous cytoplasmic plaques mostly stored in the supranuclear part of the hair cells. However, occasional filopodial growth and formation of new synaptic connections continued. The data demonstrate that any disruption or disturbance of the initial synaptic contacts between the inner hair cells and their afferent neurons caused by transplantation results in prompt synaptic reacquisition. Furthermore, we suggest that the transitory phase of terminal sprouting and multiribbon synapse formation manifests a trophic dependence that develops postnatally between the synaptic cells.

Animals↗
PubMed1986

Functional structure of the organ of Corti: a review.

The mammalian auditory organs have a dual sensory system (inner vs. outer hair cells) with distinctly different cellular organizations and innervation patterns. However, the inner (IHCs) and outer (OHCs) hair cells are mechanoreceptors sharing similar general characteristics such as organization of stereocilia (including linkage system) and a gradation of stereociliary height along the length of the cochlea. This gradation of stereociliary height may be the single most important anatomic feature in the tuning capability of the sensory cell. Several lines of evidence suggest that the stereociliary stiffness may be modulated by the sensory cells themselves, most likely via the cuticular plate-rootlet complex. The stereociliary bundles of both types of hair cell are organized in a 'W' formation with a steplike arrangement. In the OHCs, the 'W' formation is sharply angulated and slanted toward the apex, coinciding with the slanted fiber arrangement of the overlying tectorial membrane, which is firmly coupled to the tips of the tallest row of the stereociliary bundles. However, in the IHCs, the 'W' formation is wide and its long axis is linear and arranged at a right angle to the radial axis of the organ of Corti; also, the ciliary bundles are freestanding (with a few exceptions in the basal turn). This arrangement in the IHCs would be best suited for deflection by the radial flow of the endolymph. Present evidence suggests that the subtectorial fluid space exists, is filled with endolymph, and freely communicates with endolymph. Because of the discovery of the phenomenon of 'cochlear emission', the possible motility of the sensory cells, particularly of the OHCs, has drawn intense interest in recent years. Recent investigations with dissociated sensory cells (OHCs) indicate some motile capability under various experimental conditions, although it has not been established that this motility is present in vivo. For this reason, the specialized cellular organization for motility and localization of contractile and cytoskeletal proteins have been investigated. These results support the possibility that the OHCs may have cellular facilities for this function.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Early stages of innervation and sensory cell differentiation in the human fetal organ of Corti.

Early development of the human organ of Corti was investigated at the light and electron microscopic level. In 9-week fetal material the cochlea was completely coiled and nerve fibers penetrated into an undifferentiated Corti's primordium. By week 10 a single cell in radial sections, presumed to be the inner hair cell (IHC), could be found with many nerve fibers surrounding and contacting its base. It is possible to identify outer hair cells by the end of the 11th week while IHC development continues. During the 12th week stereocilia appear on IHCs and synaptic specializations could be found at the junctions between both types of hair cell and afferent dendrites. The first appearance of the efferent fibers beneath IHCs were also observed during week twelve.

Cell Differentiation↗
PubMed1985

The effects of cytoplasmic acidification upon electrical coupling in the organ of Corti.

The supporting cells of the organ of Corti are joined to one another by gap junctions, and electrical coupling among them is known to be good. It is demonstrated here, using an in vitro preparation, that electrical communication between Hensen's cells can be modified by treatments which are known to cause cytoplasmic acidification. Treatment of the preparation with 100% CO2-saturated medium causes a drop in membrane potential, increase in input resistance, and decrease in steady-state coupling ratio. These measures return to pretreatment levels upon washout of the CO2 medium. Also, direct injection of H+ into a Hensen's cell uncouples that cell from the supporting cell network. An increase in coupling ratio is sometimes observed immediately before and after uncoupling due to CO2 treatment. In fact, in some cases it is possible to solely increase coupling ratios with limited CO2 treatments, although prolonged treatment with CO2 invariably produces uncoupling. This phenomenon may be due to an increase in cell resistance without a change in junctional conductance. A few possible roles for gap junctions in the inner ear are suggested, and the significance of the present results discussed.

Acid-Base Equilibrium↗
PubMed1992

Ultrastructure of the horseshoe bat's organ of Corti. I. Scanning electron microscopy.

The organ of Corti of the echolocating horseshoe bat (Rhinolophus rouxi) was investigated with scanning electron microscopy in order to provide a comparison with non-echolocating mammals. Throughout the cochlea of horseshoe bats, each outer hair cell (OHC) possesses three rows of stereocilia and there are no morphological distinctions among the different rows of OHCs. However, there are morphological differences between different regions along the cochlea. In the lower and upper basal turn, the receptor surfaces of OHCs are characterized by extremely wide W-shaped stereocilia bundles and wingshaped cuticular plates. The cuticular plates of OHCs of the middle and outermost rows are arranged parallel to each other. Stereocilia length is only 0.8 microns and there is an exaggerated angle of inclination of the shortest row of stereocilia towards the next taller one. Stereocilia arrangements in the apex of the horseshoe bat's cochlea closely resembles those observed in the midbasal region of the rat cochlea. Inner hair cells (IHC) in the lower basal turn appear specialized. They possess only two rows of stereocilia and only 7-8 stereocilia per row. Their cuticular plates are small and oval and widely separated from one another in the longitudinal direction. IHCs at all other locations possess three and up to four rows of stereocilia and 17-20 stereocilia per row. Their cuticular plates are elongated and closely spaced. The transition from specialized to typical mammalian morphology occurs abruptly (over a distance of about 100-150 microns) at the border between the lower and the upper basal turn. This transition is not accompanied by a change in OHC morphology. In the subsurface of the tectorial membrane, throughout the cochlea, there are distinct imprints of the tallest row of stereocilia of all three rows of OHCs and of the IHCs. Data are discussed in relation to specialized aspects of the cochlear frequency map in horseshoe bats and as possible micromechanical adaptations to ultra-high frequency hearing.

Animals↗
PubMed1983

Intercellular communication in the supporting cells of the organ of Corti.

We have directly tested the concept that the supporting cells of the organ of Corti are functionally coupled through gap junctions. In vitro and in vivo preparations were evaluated. Electrical measurements clearly show that the cells are coupled ionically. Voltage drops measured in neighboring cells in response to intracellular current injections indicate that current spread decays rapidly. Despite the existence of electrical coupling, fluorescent dye injection studies revealed no dye spread into adjacent cells, other than a few instances which were clearly artifactual. However, it is possible that dye spread is very slow and that dye in adjacent cells is diluted below visual detectability. In any case, dye coupling is remarkably poor compared to other electrically coupled tissues. The role of coupling in the supporting cells may be nutritive, considering the avascular nature of Corti's organ.

Animals↗
PubMed1988

Met-enkephalin and Met-enkephalin-Arg6-Gly7-Leu8 immunofluorescence in the developing guinea-pig organ of Corti.

The immunofluorescence technique has been applied to the organ of Corti from developing guinea pigs to detect the immunoreactions to antibodies directed against Met-enkephalin and Met-enkephalin-Arg6-Gly7-Leu8. Four stages of gestation were studied (30, 41, 50 and 62 days). On days 30 and 41 of gestation, no specific fluorescence to both antibodies was seen in the organ of Corti. On day 50, the inner spiral bundle and the tunnel spiral bundle, two areas displaying anti-enkephalin immunoreactivity in the adult, showed a specific immunofluorescence to either the anti-Met-enkephalin and the anti-Met-enkephalin-Arg6-Gly7-Leu8 antibodies. On day 62, these two structures showed an immunofluorescence whose intensity was slightly increased compared with that seen on day 50. In no case, was an immunoreaction in the outer hair cell area seen. These results suggest that the enkephalins, which have been proposed as putative neurotransmitters or neuromodulators of neurons belonging to the lateral olivocochlear system, are present in the organ of Corti at about the time of onset of cochlear function. Thus, the enkephalin-containing lateral efferents may play a role in the early control of cochlear potentials.

Animals↗
PubMed1990

[The cytokeratin skeleton of the human organ of Corti and its functional significance].

In the adult human organ of Corti cytokeratin (CK) is expressed by all supporting cells enclosing it like a shell. The pattern of immunoreactivity clearly demonstrates a quantitative gradient in the expression of CK, with more CK at the apex than at the base of the cochlea. Predominantly in the apical cochlear turns, the CK-shell separates the compartment of the inner hair cells from that of the outer hair cells. Ultrastructurally, the supporting cells contain a loose fibrillary network which apically is oriented toward the desmosome chain and which can be clearly distinguished from the well-known tubular filaments (microtubuli). Some supporting cells show centrioles. Both the expression of CK and the presence of centrioles indicate a possible potential for cell regeneration. Ultrastructurally, outer hair cells and Deiters' cells show features of a specialized contact zone which might be of functional significance regarding the contractile abilities of the outer hair cells. In the human organ of Corti, vimentin is expressed only by the inner and outer pillar cells. These cells thus express CK together with vimentin. The distinct shell configuration of the CK network in the organ of Corti gives it a tonotopically related difference in rigidity which not only must be of importance for cochlear perception of sound but also could explain the reduced vulnerability of the ear to low frequencies.

Cytoskeleton↗
PubMed1985

[Immunolocalization of choline acetyltransferase in 2 types of efferent synapses of the organ of Corti].

The efferent (olivo-cochlear) innervation of the organ of Corti was studied using a monoclonal antibody against choline acetyltransferase (ChAT). In the inner spiral bundle (ISB), below the inner hair cells (IHCs), the anti-ChAT immunoreactivity was observed within unvesiculated fibers and vesiculated varicosities. Unreactive varicosities, at least as numerous as the immunoreactive ones, were also detected. Both types of vesiculated varicosities synapsed with the dendrites of the primary auditory neurons (afferent fibers) connected to the IHCs. At the outer hair cell (OHC) level, nearly all the vesiculated terminals making axo-somatic synapses with the OHCs were anti-ChAT immunoreactive. Only few terminals synapsing with the OHCs were unreactive. These findings allowed the differentiation of at least three types of efferent synapses in the organ of Corti. In the ISB, a first population of axo-dendritic synapses seems to be cholinergic whereas a second population might use another neurotransmitter. At the OHC level, our results support the hypothesis that acetylcholine is the neurotransmitter of nearly all the large axo-somatic synapses. The rare unreactive axo-somatic synapses could constitute a fourth and minor type of efferent synapse. Thus, it would be helpful to subclassify the efferent innervations of the organ of Corti according to their neurochemical nature. A re-evaluation of the whole body of available electrophysiological data would be also necessary, as until now, acetylcholine was considered as being the only efferent cochlear neurotransmitter.

Animals↗
PubMed2003

Immunodetection of surfactant proteins in human organ of Corti, Eustachian tube and kidney.

The presence of surfactant proteins was investigated in the human organ of Corti, Eustachian tube and kidney tissues. It has previously been shown that lamellar bodies are present in hairy cells of organ of Corti, in the cytoplasm of secretory and lumen of tubal glands of Eustachian tube and kidney renal basement membrane. No evidence for the presence of surfactant proteins in the organ of Corti and kidney has been presented until now. The aim of this study was to find out if surfactant proteins were expressed in other epithelia such as organ of Corti, Eustachian tube and kidney. Surfactant proteins were identified using one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting. On one-dimensional Western blots, bands for surfactant protein A in human Eustachian tube (SP-A, 34 kDa) and in kidney extracts, and for surfactant protein D (SP-D, 43 kDa) in Eustachian tube and in kidney extracts (SP-D, 86 kDa), and for surfactant protein B (SP-B, 8 kDa) in human Eustachian tube and organ of Corti extracts were detected. Bands corresponded to monomeric forms of lung surfactant proteins. These results indicate the presence of SP-A and SP-D in kidney epithelium, SP-A, SP-B and SP-D in Eustachian tube and SP-B in the organ of Corti.

Blotting, Western↗
PubMed2002

Notch/Notch ligands and Math1 expression patterns in the organ of Corti of wild-type and Hes1 and Hes5 mutant mice.

The sensory epithelium of the mammalian cochlea (the organ of Corti) represents an excellent developmental system. The organ of Corti contains two main cell types: the sensory hair cells and the supporting cells which are organized in a defined mosaic pattern. Previous results have demonstrated the participation of Notch signaling in the regulation of the pattern of hair cell differentiation within this sensory mosaic. It has also been shown that the basic helix-loop-helix (bHLH) transcription factor Math1 is a positive regulator of hair cell differentiation. We demonstrated that Hes1 and Hes5, two members of the inhibitory bHLH transcription factors, act as negative regulators of hair cell differentiation. Loss-of-function studies implicating the neurogenic genes Notch1, Jag2, Hes1 and Hes5 generated a significant increase in the number of hair cells. However, their functional interplay within the organ of Corti has not been determined. To clarify the mechanisms that regulate hair cell differentiation, we examined the expression of Notch/Notch ligand system and Math1 in the developing organ of Corti of Hes1- and Hes5-deficient mice. Our study suggests complex specific relationships between Notch signaling, Math1 and Hes1/Hes5 in the control of hair cell differentiation in the developing organ of Corti.

Animals↗
PubMedDate not supplied

Effects of hypothyroidism on the structural development of the organ of Corti in the rat.

The structural development of the organ of Corti was studied in 30 rat pups rendered hypothyroid by daily administration of propylthiouracil during the first 35 days after birth. Cochlear changes were observed by light microscopy and electronmicroscopy. Hypothyroid rat pups were found to have severe abnormalities in the organ of Corti. There was an abnormally prolonged persistence of Kölliker's organ and striking distortion of the tectorial membrane. The sensory epithelium exhibited marked signs of immaturity: the tunnel of Corti has not opened yet in animals 35 days old, sensory and supporting cells presented immature characteristics with abnormal persistence of the kinocilium. It is suggested that hypothyroidism results in an overall retardation of the maturation of cochlear structures and ultrastructural changes that appear to be significant enough to account for the hearing loss.

Animals↗
PubMedDate not supplied

Scanning electron microscopic study of the organ of Corti in normal and sound-damaged guinea pigs.

A method was evolved by which the organ of Corti could be examined in its entirety with the scanning electron microscope, the organ meanwhile retaining its spiral form. This made it possible to assess traumatic effects on the cochlea and qualify lesions in terms of extent, localization and pattern. It was also found possible eventually to cut the same specimen into sections for cellular and subcellular studies. The number of guinea pigs examined totalled 91, divided into three groups. The first group was used to study the anatomy of the organ of Corti with special reference to normal variations and artifacts. Unmistakable indications were found that the longest stereocilia of the inner hair cells are linked to the tectorial membrane. The animals of the second group were exposed to pure tones of high intensity, whereupon, lesions of the organ of Corti were described according to intensity, time, and frequency. Three different types of otologic drills were used to perform mastoidectomies on temporal bones and on the cadaver. The noise produced was analyzed as to intensity and frequency range. It was found that the drill with the lowest rpm (and highest torque) produced the highest noise intensities, at levels which can be traumatic to the human organ of hearing. The animals of the third group were exposed to the amplified noise produced by otologic drills of three different types. The resulting lesions in the organ of Corti were examined by the method described for scanning electron microscopy and compared. In spite of the wide variation in individual lesions, patterns of degeneration of three different types could be distinguished. The high-speed and the very-high-speed drill inflicted less damage on the organ of Corti than the low-speed drill. It is therefore advised to refrain from using the latter drill in prolonged operations.

Animals↗
PubMed1975

Organotypic development of the organ of Corti in culture.

The preservation and development of the innervation pattern in the organ of Corti have been studied in culture up to 27 days in vitro. The explants were obtained from the newborn mouse. Segments of the cochlear duct dissected together with the appropriate sectors of the spiral ganglion may retain their structural organization for about two weeks. Maturation of some nonneuronal elements which occurs during that time is followed by a subsequent regression of the organ. Only a fraction of the explanted neurons survive. However, the surviving neurons, if connected with the hair cell region, maintain a complex peripheral innervation pattern that contains all the major fibre components which characterize the normal pattern in a young mouse. The peripheral innervation pattern in culture seems largely composed of preserved fibres, that is, of fibres which at the time of explantation have already ramified within the organ of Corti. Nonetheless, there is evidence for growth or maturation, in culture, of at least some peripheral processes of the spiral neurons. Thus, only in older cultures is the innervation of the apical tip established. Likewise, it is only in older explants that the inner spiral bundle becomes prominent. Spiral neurons survive in culture in several modes. Most frequently, the central process is altogether absent and the neuron is effectively a unipolar cell which maintains only the peripheral process. A distinct minority of neurons is bipolar possessing both the peripheral process and a central axon which grows freely, though no central target is present. A neuron may survive also as a unipolar or, rarely, as a bipolar cell with no processes entering the organ of Corti. The observations imply that (1) most or all major fibre systems in the organ of Corti carry components of spiral neuron origin; (2) a small population of spiral neurons innervating a short segment of the organ contributes importantly not only to the radial but also to the spiral innervation of the segment.

Animals↗
PubMed1977

Scanning electron microscopy of the nerves within the organ of Corti.

A method of studying the innervation inside the organ of Corti is presented. Rabbits, guinea pigs and chinchillas were fixed with perfusion of the perilymphatic spaces. The cochleas were dissected according to the surface specimen technique and the specimens critical point dried, coated with gold and studied in the SEM. The final dissection into the planes of the fluid spaces of the organ of Corti was done in the dry state using especially sharpened watch makers forceps and razor blade knives. The course of the afferent and efferent innervation is described and differences between the species illustrated. Small high nerve endings on the outer hair cell degenerate after cutting the efferent nerve supply by dividing the vestibular nerve indicating their efferent nature.

Animals↗