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PubMed1995

Calcium-binding proteins in organ of Corti and basilar papilla: CBP-15, an unidentified calcium-binding protein of the inner ear.

In a previous paper (Thalmann et al., 1993) we reported that the amino acid sequence of OCP2, a low molecular weight acidic protein present in extremely high concentrations in the organ of Corti and absent in the basilar papilla, exhibits a rudimentary EF-hand--a potential calcium-binding domain. The present study was undertaken to determine whether OCP2 binds 45-calcium under non-denaturing conditions following separation by isoelectric focusing and transblotting. The same criterion was used to determine whether the EF-hands of several other calcium-binding proteins (CBP) are functional in organ of Corti and basilar papilla. OCP2 exhibited no 45-calcium binding. Calmodulin, present in the organ of Corti in extremely high concentrations and lower in basilar papilla, showed strong 45-calcium binding in both structures. While calbindin represents a major protein in basilar papilla and binds 45-calcium, this protein is a minor component in the organ of Corti; whether it binds 45-calcium remains to be decided. By extending the pI range in the acidic region of isoelectric focusing, a 15 kDa, highly acidic (pI approximately 3.1) protein was revealed that constitutes a major protein in the organ of Corti; the protein was not detectable in the basilar papilla, spiral ligament/stria vascularis complex and numerous other organs tested. It remains to be resolved whether this protein represents an isoform of parvalbumin or a novel CBP. The differential make-up of CBPs between the mammalian organ of Corti and the avian basilar papilla is discussed.

Animals↗
PubMed1997

Development of the organ of Corti in horseshoe bats: scanning and transmission electron microscopy.

The late prenatal and early postnatal development of the organ of Corti were studied in the horseshoe bat (Rhinolophus rouxi) by using scanning and transmission electron microscopy. Arrangements and dimensions of stereocilia bundles, together with their contacts with the tectorial membrane, were found to be adult-like shortly before birth, and thus before the biological onset of hearing (3-5 days after birth). During the first postnatal week, there were baso-apical gradients in disappearing kinocilia on inner hair cells (IHC), microvillis of supporting cells, and marginal pillars. The lower basal cochlear turn was mature with respect to these regressing structures at 3 days after birth, the apical turn at 10 days after birth. At birth, cytodifferentiation was found to be completed, and the tunnel of Corti and innermost spaces of Nuel had opened. The ultrastructure of IHCs was not markedly different from that at later ages. In outer hair cells (OHC), the adult-like regular arrangement of a single layer of subsurface cisternae and pillars was seen as soon as protrusions of supporting cells had withdrawn from the lateral wall of OHCs (basal turn at birth and throughout the cochlea 2 days after birth). Numerous efferent endings contacted the somata of IHCs up to the second postnatal week. Since the medial olivocochlear system is absent in horseshoe bats, the adult-like innervation pattern of OHCs was established at the biological onset of hearing. During the first 2 postnatal weeks, the cytoskeleton of pillar and Deiters cells, and the specialized Deiters cups developed. The organ of Corti appeared adult-like at 14 days, apart from the persistence of a reduced tympanic cover layer attached to the basilar membrane. Morphological data support physiological findings that the first broadly tuned auditory responses arise from the basal turn. The distinct low to high frequency gradient in development of sensitivity during the first 2 postnatal weeks of the horseshoe bat was not, however, matched by morphological gradients, and it would appear that the development of the cytoskeleton of supporting cells contributed to the establishment of tuning in the auditory fovea. Adult-like morphology of the organ of Corti coincided with the emergence of sharply tuned responses from the auditory fovea, but there was no clear-cut correlate for the shift in tuned foveal frequency representation that occurred during the following 3 weeks.

Animals↗
PubMedDate not supplied

Time sequence of degeneration pattern of the organ of Corti after acoustic overstimulation. A light microscopical and electrophysiological investigation in the guinea pig.

In order to obtain information about the sequence of events leading to degenerative changes in the cochlea after acoustic trauma, a systematic LM study was performed in the guinea pig organ of Corti. The results were correlated with measurements of CAP N1 thresholds from the same animals. Twenty pigmented guinea pigs were used in the study. Ten of these animals were exposed to a 3.85 kHz pure tone with an intensity varying between 108 and 120 dB SPL for 22.5 to 360 min and were sacrificed after 4 weeks. Eight animals were exposed to 120 dB SPL for 22.5 min and sacrificed at regular intervals after exposure, viz. 5 min, 4, 24 h and 5 days. Prior to sound exposure the animals in the 4-week group were implanted with a permanent round window electrode for measurements of CAP N1 thresholds. The study indicates that the degeneration and reparative processes are not entirely completed after 4 weeks. The development of holes in the reticular lamina may result in further degeneration of cells bilateral to the initial maximum damage. Darkly stained cells seem to be activated in the reparative process in the organ of Corti. Local appearance of dendritic macrophages in the organ of Corti indicate the existence of a local mechanism for disposal of degeneration products from the organ of Corti. The retrograde degeneration of radial nerve fibres seems to be closely associated with that of the pillar cells. A close correlation between structural hair cell damage and CAP N1 threshold shift was found in the region of the organ of Corti corresponding to the exposure frequency. The TS 5 min, 4 h and 24 h after exposure showed a close correlation with swellings in the afferent nerve endings below the IHC in the area of maximum damage and basalwards.

Acoustic Stimulation↗
PubMed1991

The organ of Corti in the bat Hipposideros bicolor.

The bat Hipposideros bicolor (Hipposideridae, Microchiroptera) is the mammalian species with the highest upper limit of hearing in which the structure of the organ of Corti has been studied. H. bicolor emits pure tone echo-locating signals of 153 kHz, compensates for Doppler shifts in the echo and hears ultrasonic frequencies up to 200 kHz (Neuweiler et al., 1984). The organ of Corti was investigated qualitatively and quantitatively using the technique of semi-thin sectioning. Some complementary ultra-thin sections were also examined. Length, width and cross-sectional area of the basilar membrane, the tectorial membrane, the hair cells with their stereocilia and the organ of Corti were measured at equi-distant positions on the basilar membrane. The organ of Corti of H. bicolor is composed of elements similar to those found in the cochleae of other eutherian mammals studied. However, in H. bicolor some of these elements show species-specific differences when compared to auditorily unspecialized mammals. The most basal region of the cochlea is characterized by miniaturization and re-inforcement of macro- and micro-mechanically important elements. This is interpreted as an adaptation for hearing extremely high frequencies. Specialized structures as well as local maxima of 'normal' elements in the basal and middle cochlear region are associated with evaluation of the echos of emitted pure tones. Besides the basal specializations. Hipposideros also shows specializations in the apical, low frequency, region which can be correlated with passive acoustic orientation.

Animals↗
PubMed1992

Ionic coupling among cells in the organ of Corti.

Gap junctions have been demonstrated morphologically among the supporting cells of the mammalian organ of Corti but, in contradistinction to reptiles, evidence for their existence between the supporting cells and hair cells is equivocal. The literature is ambiguous with respect to electrical coupling and dye coupling among the supporting cells, and no coupling of either kind has been demonstrated for the hair cells. We found strong coupling of both kinds among the supporting cells in the cochleas of live Mongolian gerbils and a less stable coupling between the supporting cells and the outer hair cells. The electrical coupling was established by recording alternating receptor potentials in the hair cells and following their decrement in the population of Hensen's cells; the dye coupling, by injecting Lucifer yellow electrophoretically into the hair cells or the supporting cells and investigating its spread to the neighboring cells. The electrical recordings were made by means of microelectrodes filled with either 1.5 or 3 M KCl or 1 M LiCl with 6% Lucifer yellow, the latter used for dye injection. The electrode resistances ranged from about 20 to 60 M omega in the first instance, and from about 50 to 110 M omega, in the second. The electrodes were inserted into the organ of Corti through scala media according to the method of Dallos, Santos-Sacchi and Flock (1982) modified by us. The alternating potential in Hensen's cells was usually larger than in the outer tunnel of Corti and remained practically constant up to the outer margin of the Hensen's-cell population. Its phase was the same as in the outer hair cells. When the dye was injected into a Hensen's cell, it always spread to neighboring Hensen's cells and often to Deiter's cells. Dye injected into outer hair cells (identified according to anatomical and physiological criteria) also spread to Deiter's and Hensen's cells and, usually, to other outer hair cells. Stained cells were identified in surface preparations and, on two occasions, in serial sections from plastic embedded cochleas.

Animals↗
PubMed1997

Oncomodulin is abundant in the organ of Corti.

A small, acidic Ca(2+)-binding protein (CBP-15) was recently detected in extracts of the mammalian auditory receptor organ, the organ of Corti [Senarita et al. (1995) Hear. Res. 90, 169-175]. N-terminal sequence data for CBP-15 [Thalmann et al. (1995) Biochem. Biophys. Res. Commun. 215, 142-147] implied membership in the parvalbumin family and possible identity with the mammalian beta-parvalbumin oncomodulin. As shown herein, the latter conclusion is supported by strong cross-reactivity between CBP-15 and isoform-specific antibodies to oncomodulin. Moreover, we have succeeded in amplifying the guinea pig CBP-15 coding sequence from organ of Corti cDNA using degenerate oligonucleotide primers based on the rat oncomodulin sequence. The deduced amino acid sequence of guinea pig CBP-15 displays 90%, 92%, and 98% identity with mouse, rat, and human oncomodulin isoforms. Demonstration of the presence of oncomodulin in the organ of Corti is the first documentation of this substance in a postnatal mammalian tissue.

Amino Acid Sequence↗
PubMed2006

p27(Kip1) deficiency causes organ of Corti pathology and hearing loss.

p27(Kip1) (p27) has been shown to inhibit several cyclin-dependent kinase molecules and to play a central role in regulating entry into the cell cycle. Once hair cells in the cochlea are formed, p27 is expressed in non-sensory cells of the organ of Corti and prevents their re-entry into the cell cycle. In one line of p27 deficient mice (p27(-/-)), cell division in the organ of Corti continues past its normal embryonic time, leading to continual production of cells in the organ of Corti. Here we report on the structure and function of the inner ear in another line of p27 deficient mice originating from the Memorial Sloan-Kettering Cancer Center. The deficiency in p27 expression of these mice is incomplete, as they retain expression of amino acids 52-197. We determined that mice homozygote for this mutation had severe hearing loss and their organ of Corti exhibited an increase in the number of inner and outer hair cells. There also was a marked increase in the number of supporting cells, with severe pathologies in pillar cells. These data show similarities between this p27(Kip1) mutation and another, previously reported null allele of this gene, and suggest that reducing the inhibition on the cell cycle in the organ of Corti leads to pathology and dysfunction. Manipulations to regulate the time and place of p27 inhibition will be necessary for inducing functionally useful hair cell regeneration.

Animals↗
PubMed1985

Glutaminase-like immunoreactivity in the organ of Corti of guinea pig.

The distribution of glutaminase (GLNase)-like immunoreactivity (IR) in the normal and surgically de-efferented organ of Corti of guinea pig was studied. Primary antisera were against phosphate-dependent GLNase from rat kidney. Indirect immunocytochemical techniques were used; IR was visualized in cryostat sections through immunofluorescence, and through immunofluorescence or with horseradish peroxidase reaction product in surface preparations. Standard microscopy and video-enhanced light microscopy with asymmetric illumination contrast were used. GLNase-like IR was found at inner hair cells (IHCs) in the normal and in the de-efferented organ of Corti, in the tunnel spiral bundle, in tunnel-crossing fibers, in endings high up on outer hair cells (OHCs), in outer spiral bundles, in puncta close to OHCs, and in large, efferent endings at OHC bases. There was no GLNase-like IR at OHCs in the de-efferented organ of Corti. It is concluded that GLNase-like IR is present in auditory nerve dendrites at IHCs and in olivocochlear efferents of the medial system, and that future studies are needed to determine whether also the lateral system of olivocochlear efferents contains GLNase-like IR. A diagram is included depicting the relation between OHCs and efferent nerve endings along the cochlear spiral, showing that in the apicalmost 3/4 turn of the spiral OHCs have no efferent endings.

Animals↗
PubMed1991

Protein phosphorylation in the organ of Corti: differential regulation by second messengers between base and apex.

Major aspects of cellular physiology are regulated by the phosphorylation state of proteins through the action of protein kinases and protein phosphatases. Phosphorylation of proteins by endogenous protein kinase activity was assayed in homogenates from guinea pig inner ear tissues with [gamma-32P] ATP. Phosphoproteins showed distinct distributions in organ of Corti, lateral wall and spiral ganglion. In the organ of Corti, several protein kinase activities were distinguished by their activation by appropriate agonists: protein kinase C, calmodulin-dependent protein kinases and cyclic nucleotide-dependent protein kinases. Twelve putative substrates for these kinases were identified in organ of Corti on the basis of increased 32P-incorporation with addition of lipids, calmodulin, and cyclic nucleotides, respectively. In addition, differences in phosphorylation were observed between the base and apex of the organ of Corti. 32P-incorporation into proteins of molecular weights between 45 and 100 kDa was significantly higher in apical tissue than in tissue from the base. In contrast, phosphate incorporation into proteins of around 29 kDa was much lower in apical tissues than in basal tissues. Furthermore, labeling of both the high and low molecular weight proteins from the apex but not the base markedly increased in response to calcium. These data indicate the presence of differential modes of regulation that may underlie structural and functional gradients along the sensory epithelium.

Animals↗
PubMed1984

A re-evaluation of cell coupling in the organ of Corti.

Intercellular electrical coupling was assessed in an in vitro organ of Corti preparation using separate electrodes to inject current and record voltage drops in Hensen's cells. The results demonstrate much better coupling among these supporting cells than previously thought. Coupling ratios between adjacent Hensen's cells are greater than 0.6.

Animals↗
PubMed1982

Ultrastructural changes in the cochlear sensory epithelium following damage to the organ of Corti.

The repair pattern of the reticular lamina of the organ of Corti was studied after idiophatic hair-cell loss and ototoxic damage. The present report examines the repairing capacities of the inner and outer pillars of Corti and Deiters' cells in guinea pigs that received aminoglycosides for 21 days. By means of scanning electron microscopy, the defects of the reticular lamina, the hypertrophic processes of the supporting cells, and numerical increase of microvilli were observed.

Aminoglycosides↗
PubMed1986

Tannic acid staining of the cell coat of the organ of Corti.

Tannic acid staining of the cell coat of the organ of Corti shows a deep asymmetry between the endo- and the perilymphatic surfaces, the former being 6 times thicker. This fact may be related to a barrier mechanism against potassium-induced cell damage. Horizontal cross-links between stereocilia were heavily stained, but vertical ones were not preserved, thus suggesting they are not glycoconjugates.

Animals↗
PubMed1995

Replacement of hair cells after laser microbeam irradiation in cultured organs of corti from embryonic and neonatal mice.

This study examined the potential for hair cell regeneration in embryonic and neonatal mouse organs of Corti maintained in vitro. Small numbers of hair cells were killed by laser microbeam irradiation and the subsequent recovery processes were monitored by differential interference contrast (DIC) microscopy combined with continuous time-lapse video recordings. Replacement hair cells were observed to develop in lesion sites in embryonic cochleae and on rare occasions in neonatal cochleae. In embryonic cochleae, replacement hair cells did not arise through renewed proliferation, but instead developed from preexisting cells that changed from their normal developmental fates in response to the loss of adjacent hair cells. In cochleae established from neonates, lost hair cells usually were not replaced, but 11 apparently regenerated hair cells and a single hair cell labeled by 3H-thymidine were observed as rare responses to the creation of hair cell lesions in these organs. The results indicate that the organ of Corti can replace lost hair cells during embryonic and on rare occasions during early neonatal development. The ability of preexisting cells to change their developmental fates in response to hair cell death is consistent with the hypothesis that during embryonic development hair cells may inhibit neighboring cells from specializing as hair cells. In neonatal cultures, the rare occurrence of apparently regenerated hair cells indicates that some cells in the postembryonic organ of Corti retain response mechanisms that can lead to self-repair.

Aging↗
PubMed2003

Cell type-specific reduction of beta tubulin isotypes synthesized in the developing gerbil organ of Corti.

There are seven isotypic forms of the microtubule protein beta tubulin in mammals, but not all isotypes are synthesized in every cell type. In the adult organ of Corti, each of the five major cell types synthesizes a different subset of isotypes. Inner hair cells synthesize only betaI and betaII tubulin, while outer hair cells make betaI and betaIV tubulin. Only betaII and betaIV tubulin are found in inner and outer pillar cells, while betaI, betaII, and betaIV tubulin are present in Deiters cells, and betaI, betaII and betaIII tubulin are found in organ of Corti dendrites. During post-natal organ of Corti development in the gerbil, microtubules are elaborated in an orderly temporal sequence beginning with hair cells, followed by pillar cells and Deiters cells. Using beta tubulin isotype-specific antibodies, we show that, in the gerbil cochlea, the same three isotypes are present in each cell type at birth, and that a cell type-specific reduction in the isotypes synthesized occurs in hair cells and pillar cells at an unusually late stage in development. No beta tubulin isotypes were detected in mature afferent dendrites, but we show that this is because few microtubules are present in mature dendrites. In addition, we show that primary cilia in inner hair cells, a feature of early development, persist much later than previously reported. The findings represent the first description of developmental cell type-specific reductions in tubulin isotypes in any system.

Aging↗
PubMed1992

Construction of a cDNA library from microdissected guinea pig organ of Corti.

Poly (A) RNA was isolated from microdissected guinea pig organ of Corti and converted into cDNA with RNase H- murine leukemia virus reverse transcriptase. After size fractionation, the cDNA was directionally ligated into the vector pSPORT 1 and the plasmids were transformed into DH10B E. coli via electroporation. The library was found to have 3.35 x 10(6) independent colonies with ten percent of the colonies lacking an insert. After checking 33 randomly selected colonies for inserts, the average insert size was 1218 base pairs, ranging from 3300 base pairs to 400 base pairs. The library was screened with a beta-actin oligonucleotide probe and 1.4% of the colonies contained an insert hybridizing to the probe.

Actins↗
PubMed1990

The effect of hypothyroidism on the development of the glycogen content of organ of Corti's hair cells.

The density of glycogen particles in organ of Corti's sensory cells was measured to determine the effect of congenital hypothyroidism upon the normal development of this energy source. This density in both normal and hypothyroid inner hair cells remains in low values from birth to adulthood. On the other hand, that of normal outer hair cells undergoes a great increase between the 10th and the 20th postnatal days, coinciding with the maturation of both the efferent innervation of these cells and the tuning properties of the auditory receptor. The glycogen stores of the hypothyroid outer hair cells do not show any significant increase from birth to adulthood. This latter fact suggests that the congenital hypothyroidism restrains the development of an important energy source of outer hair cells, most surely disturbing the physiological processes relying on glycogen metabolism.

Animals↗
PubMedDate not supplied

The innervation of the organ of Corti. A scanning electron microscopic study.

The innervation within the organ of Corti of guinea pigs, chinchillas and rabbits was studied in the scanning electron microscope. Specimens were fixed, dissected, critical point dried and coated with gold. Final dissection of the specimens was done in the dry state in the planes of the former fluid spaces. The courses of the efferent and afferent nerve fibres are described. The efferent fibres reach the outer hair cells by crossing the tunnel space, run between the outer pillars and divide several times in the space of Nuel. The afferent fibres cross the floor of the tunnel and turn basalwards in the outer spiral bundles where they run for at least 0.5-0.8 mm before connecting with the outer hair cells. Small nerve endings on every fifth to tenth outer hair cell disappear after cutting the efferent nerves, thus indicating their efferent nature.

Animals↗
PubMed1981

Scanning and transmission electron microscope studies on the organ of Corti and stria vascularis in human fetal cochlear ducts.

The organ of Corti in human fetuses aged 5 and 7 months, respectively, was observed with the scanning and transmission electron microscope (SEM and TEM). By SEM observation, bulbous cytoplasmic structures protruding from the apical surface of the outer and inner hair cells were observed as was the case in SEM reports by others. By TEM observation, it was revealed that these structures are cytoplasmic projections from the so-called cuticular notch which, in adults, houses the basal body and is a site for synthesis of auditory stereocilia and a single kinocilium. The stria vascularis was examined only in the 5 month specimen. The cytoplasm of the differentiating marginal cells is characterized by the presence of thick walled tubular membranes. The observation suggests that this tubular system may represent "a particular site" for secretion of some ions into the endolymph in the fetal condition.

Cochlea↗