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PubMed1975

[Ultrahistochemical demonstration of glucose-6-phosphatase in hair cells of the guinea pig organ of corti (author's transl)].

This study is concerned with the ultrahistochemical demonstration of glucose-6-phosphatase activity and its localization in inner and outer hair cells of the guinea pig organ of Corti. The enzyme activity has been demonstrated by a method according to Hugon et al. (1970). In hair cells of the organ of Corti a characteristic distribution pattern of reaction products has been registered. Subsurface cisterns and the Hensen's bodies of outer hair cells were heavily loaded with reaction products. In addition, the endoplasmic reticulum and the nuclear membrane as well as postsynaptic cisterns were rich in precipitates. With regard to their morphologic pecularities the inner hair cells show a more homogeneous distribution of enzyme activity. The findings corroborate the former assumption of a genetic relationship of either subsurface cisterns and Hensen's body to the endoplasmic reticulum of outer hair cells. Furthermore, the high glucose-6-phosphatase activity of both subsurface cisterns and Hensen's bodies are considered indicative of their participitation in the energy metabolism of outer hair cells. Referring to biochemical studies of Thalmann and associates (1973), the narrow spatial relationship of glucose-6-phosphatase positive ER membranes to mitochondria presumably represents a morphologic correlation of aerobic and anaerobic metabolic pathways in the guinea pig organ of Corti.

Animals↗

PubMed1997

Does the organ of Corti attempt to differentiate new hair cells after antibiotic intoxication in rat pups?

In the adult mammalian cochlea, post-injury hair cell losses are considered to be irreversible. Recent studies in cochlear explants of embryonic rodents show that the organ of Corti can replace lost hair cells after injury. We have investigated this topic in vivo during the period of cochlear development. Rat pups were treated with a daily subcutaneous injection of 500 mg/kg amikacin for eight consecutive days between postnatal day 9 (PND 9) and PND 16. During this period the organ of Corti is not fully mature, but hair cells are hyper-sensitive to aminoglycoside antibiotics. Scanning and transmission electron microscopy was used to evaluate morphological changes in the organs of Corti during the treatment and at different post-treatment periods, up until PND 90. A massive loss in outer and inner hair cells was observed at least as early as PND 14. A prominent feature in the apical part of cochleas at PND 21 and 35 was the transient presence of small atypical cells in the region of pre-existing outer hair cells. These atypical cells had tufts of microvilli reminiscent of nascent stereociliary bundles. A second striking observation was the replacement of degenerating inner hair cells by pear-shaped supporting cells throughout the cochlea. These cells were covered with long microvilli, and their basal pole was contacted by both afferent and efferent fibers, as in the early stages of inner hair cell maturation. At PND 55 and 90, these features were not clearly observed due to further cytological changes in the organ of Corti. It is possible that an attempt at hair cell neodifferentiation could occur in vivo after an amikacin treatment in the rat during the period of cochlear hyper-sensitivity to antibiotic.

Amikacin↗

PubMed1996

Computer-aided three-dimensional reconstruction in human cochlear maps: measurement of the lengths of organ of Corti, outer wall, inner wall, and Rosenthal's canal.

This paper describes the application of computer-aided three-dimensional reconstruction to measurements of the length of the organ of Corti (mean +/- SD, 35.58 +/- 1.41 mm), scala tympani outer wall (40.81 +/- 1.97 mm), scala tympani inner wall (18.29 +/- 1.47 mm), and Rosenthal's canal center (15.98 +/- 1.33 mm) in eight adult male cochleas. The Rosenthal's canal center ranged between 1 3/4 and 2 turns, did not appear to be linearly related to the organ of Corti, and lay near the basal end of the latter. The length of the organ of Corti measured with three-dimensional reconstruction differed by 7.6% +/- 3.2% ("cutting angle difference") from that derived from traditional two-dimensional reconstruction on the plane perpendicular to the plane of section, and by 2.6% +/- 1.7% ("geometric difference") from that derived from two-dimensional reconstruction on the axial plane at right angles to the modiolar axis.

Aged↗

PubMed1998

OCP2 exists as a dimer in the organ of Corti.

OCP2 is one of the most abundant proteins in the organ of Corti (OC), comprising approximately 5% of the total protein in the supporting cell population. Although the very close homolog, Skp1p, has been implicated in regulating cell-cycle progression, the function of OCP2 in the terminally differentiated cochlea is presently unknown. We have purified recombinant OCP2 from Escherichia coli and examined the protein by analytical ultracentrifugation. Interestingly, sedimentation equilibrium data collected at 20 degrees C unequivocally indicate that, at the concentrations present in the OC, free OCP2 would exist as a dimeric species. The apparent sedimentation coefficient is independent of concentration at loading concentrations between 10 and 100 microM, indicating the absence of a significant monomer-dimer equilibrium in this concentration range. The functional significance of this finding is discussed.

Animals↗

PubMed1977

Ultrahistochemical demonstration of cations in the guinea pig organ of Corti.

The distribution of cations in the guinea pig organ of CORTI was studied by means of the ultrahistochemical pyroantimonate method. In the outer hair cells precipitates were localized at the cell membrane, at stereocilia, in the subplasmalemmal cisterns, in the the nucleus, in mitochondria and within the ground plasm. Coarse precipitates at the cell membrane may consist mainly of cations other than calcium ions. The subplasmalemmal cisterns are suggested to sequester cations in the outer hair cells. The mechanism of the trapping reaction and factors injuring this histochemical method are discussed.

Animals↗

PubMed1998

Outer Hair Cells Provide Active Tuning in the Organ of Corti.

The detection of sound by the mammalian hearing organ, the organ of Corti, is far from a passive process with the sensory cells acting as mere receptors. The high sensitivity and sharp tuning of the auditory apparatus are very much dependant on the active mechanical behavior of the outer hair cells, acting as effector cells.

Journal Article↗

PubMed1986

Neurotransmitter-related immunocytochemistry of the organ of Corti.

The principles of immunocytochemistry were outlined in 1942 by Coons et al. and in the 1970's immunocytochemistry emerged as a powerful method for identifying structures and tracing pathways in the nervous system. It now plays a fundamental role in the neuroanatomical and histochemical analysis of the central nervous system. The first immunocytochemical studies of the mammalian cochlea were reported in 1980, from three different laboratories. Since then many studies on cochlear immunocytochemistry have been carried out, concerned with questions about neurotransmitter candidates or about structural proteins. This review describes immunoreactivity of enkephalin, choline acetyltransferase (ChAT), glutamate decarboxylase (GAD), gamma-aminobutyric acid (GABA), aspartate aminotransferase (AATase) and glutaminase (GLNase) in the organ of Corti. ChAT is the enzyme that catalyzes the synthesis of acetylcholine (ACh). GAD is the terminal enzyme in the biosynthesis of the inhibitory neurotransmitter GABA. AATase and GLNase are two enzymes involved in the metabolism of the excitatory neurotransmitter candidates aspartate and glutamate. We have much relied on surface preparations of the organ of Corti. We have also used cryostat sectioning of the cochlea, particularly when there was a need to apply a number of different antisera to comparable preparations from one and the same cochlea. We have used immunofluorescence and immunoperoxidase procedures. Immunoperoxidase procedures have given us better signal noise ratio for specific immunoreactivity (in surface preparations) than has immunofluorescence. Occasionally, to achieve maximal resolution of surface preparations in light microscopy studies, we have used enhanced contrast video display. We have found immunoreactivity in efferent fibers in the organ of Corti following the application of antisera to enkephalin, ChAT, GAD, GABA, AATase and GLNase. Most of these different antisera give different distributions of immunoreactivity and other antisera have evoked no immunoreactivity in the organ of Corti. To the best of our knowledge, the cells of origin of efferent axons and terminals in the organ of Corti are located in the brainstem. Originally described as crossed and uncrossed olivocochlear neurons, these efferents have recently been classified into a medial and a lateral system predominantly innervating, respectively, the outer hair cell region and the inner hair cell region. However, our findings on the distribution of GAD- and GABA-like immunoreactivity indicate that there may be more than two different systems of efferents in the organ of Corti, as previously suggested by Schwartz and Ryan (1983).

Animals↗

PubMed1984

Several distinct receptor binding enkephalins in olivocochlear fibers and terminals in the organ of Corti.

Biochemical studies centering on the use of reverse-phase high-performance liquid chromatography (HPLC) and radioimmunoassays (RIA) demonstrate the presence in the guinea pig organ of Corti of at least 3 enkephalin-related peptides, two of which are identified as Met- and Leu-enkephalin, respectively. Enkephalins were identified and quantitated by HPLC-RIA in the isolated second turn of the organ of Corti, but were not found in stria vascularis or auditory nerve dissected from the cochlea. Three enkephalin-immunoreactive HPLC fractions inhibited the binding of labeled naloxone to rat brain membranes. All enkephalins identified by the combined HPLC-RIA procedure had an apparent molecular weight similar to that of Met- and leu-enkephalin peptide standards. Immunocytochemistry, performed with the best-characterized Met-enkephalin antiserum used in the RIAs, localized the enkephalin-like immunoreactivity to lateral efferent fibers and terminals under inner hair cells of the organ of Corti. Other antisera raised against Met-enkephalin, not used for RIA, visualized enkephalin-like immunoreactivity in medial efferent fibers under outer hair cells as well. This enkephalin-like immunoreactivity may reflect the presence in the medial efferent system of other structurally similar peptides in addition to those detected biochemically. Efferent fiber lesion, by evulsion of the vestibular nerve close to the vestibulocochlear anastomosis in which the olivocochlear fibers run, eliminated enkephalin-like immunoreactivity and the enkephalin-related peptides identified by HPLC-RIA.

Animals↗

PubMed1983

Differential labeling of sensory cell and neural populations in the organ of Corti following amino acid incubations.

Label localization was compared by light and electron microscopic autoradiography in the organ of Corti of the gerbil, following in vivo incubation with one of eight 3H-labeled amino acids. Following incubation with GABA, efferent endings underneath the outer hair cells were heavily labeled, as were all tunnel crossing fibers, many small fibers in the inner spiral bundle and some efferents beneath the inner hair cells. This pattern was absent following incubations with the GABA analog muscimol. Following L- and especially D-aspartic acid incubations, efferent endings under the inner hair cells and small fibers of the inner spiral bundle were preferentially labeled. It is concluded that these differential labeling patterns after GABA and aspartic acid incubations reflect two populations of efferent fibers in the organ of Corti: one terminating primarily upon the outer hair cells and one underneath the inner hair cells. Cochlear hair cells showed the highest level of labeling following incubation with alanine. Inner hair cells were more heavily labeled than outer hair cells following incubations with alanine and glycine. Hair cell labeling was comparable to that of supporting cells for most amino acids. However, for alanine and glycine the labeling of inner hair cells, and for L-aspartic and glutamic acid the labeling of all hair cells, was higher than that of structural cells. Labeling of hair cells was substantially lower than that of structural cells following taurine incubations.

Amino Acids↗

PubMed1992

Electron-microscopic localization of type II, IX, and V collagen in the organ of Corti of the gerbil.

The presence of types II, IX and V collagen was probed in the organ of Corti of the adult gerbil cochlea by use of immunocytochemistry at the light- and electron-microscopic levels. Type II collagen is found in the connective tissues of the osseous spiral lamina and spiral limbus. In the region of the sensory hair cells it is present in the tectorial membrane and antibodies bind to the thick unbranched radial fibers. Type IX collagen co-localizes with type II collagen in the tectorial membrane, where antibodies bind to the thick unbranched radial fibers. Type V collagen is present in the connective tissue of the spiral limbus, the osseous spiral lamina, the eighth nerve, and the tectorial membrane. In the tectorial membrane, the staining with antibodies to type V collagen is more diffuse than that seen for types II and IX collagen and antibodies to type V bind to the thin, highly branched fibers in which the thick fibers are embedded. The results indicate that collagens characteristic of cartilage are localized in the organ of Corti. Within the tectorial membrane, types II and IX collagen form heterotypic thick fibers embedded in a reticular network of type V collagen fibers. These collagens form a highly structured matrix which contributes to the rigidity of the tectorial membrane and allow it to withstand the physical stresses associated with transmission of the stimuli necessary for sensory transduction.

Animals↗

PubMed1986

Dye coupling in the organ of Corti.

Dye-coupling in an in vitro preparation of the supporting cells of the guinea-pig organ of Corti was evaluated by use of the fluorescent dyes, Lucifer Yellow, fluorescein and 6 carboxyfluorescein. Despite the presence of good electrical coupling in Hensen cells (coupling ratios greater than 0.6) the spread of Lucifer yellow was inconsistent. Hensen cells are very susceptible to photoinactivation, i.e., cell injury upon illumination of intracellular dye; and this in conjunction with Lucifer Yellow's charge and K+-induced precipitability may account for its variability of spread. Fluorescein and 6 carboxyfluorescein, on the other hand, spread more readily and to a greater extent than Lucifer Yellow, often spreading to cell types other than those of Hensen. Dye spread is rapid, occurring within a few minutes. These results suggest that molecules of metabolic importance also may be shared by the supporting cells of the organ of Corti.

Animals↗

PubMed1996

Morphological indications of hair cell neodifferentiation in the organ of Corti of amikacin treated rat pups.

Postnatal rats were treated with amikacin during the period of cochlear supra-normal sensitivity to ototoxic antibiotics, i.e. from day 9 to day 16 when the organ of Corti is achieving its maturation. Scanning and transmission electron microscopies were used to evaluate morphological changes in the organs of Corti at different post-treatment periods, up until postnatal day 90. A massive loss in outer (OHCs) and inner (IHCs) hair cells was observed from as early as day 17. A prominent feature in the apical part of cochleas at days 21 and 35 was the transient presence of small atypical cells in the region of pre-existing OHCs. These atypical cells did not have the appearance of degenerating OHCs, but had tuffs of microvilli reminiscent of nascent stereociliary bundles. A second striking observation was the presence of pear-shaped cells in the place normally occupied by IHCs. These cells had neither cuticular plate nor stereocilia, but their basal pole was contacted by both afferent and efferent fibers, as in the early stages of IHC maturation. Such efferent contacts are very rare in the adult cochlea. These findings, not previously reported in antibiotic poisoned cochleas of adult animals, suggest that an attempt at sensory cell neodifferentiation occurs in vivo in the developing organ of Corti intoxicated with aminoglycoside antibiotics.

Amikacin↗

PubMed1992

P2 purinoceptors stimulate inositol phosphate release in the organ of Corti.

We examined the effects of purinoceptor agonists on inositol phosphate (IP) release in the guinea-pig organ of Corti. The P2y receptor agonist ATP-gamma-S (200 microM) increased IPs 4-fold; identical concentrations of alpha, beta-methylene ATP, a P2x agonist, and adenosine, a P1 agonist, did not significantly affect IP release. In calcium-free incubations, simulated IP release decreased by 35% indicating partial dependence of ATP-mediated phosphoinositide hydrolysis on calcium influx. ATP-stimulated IP release was not enhanced by the cholinergic agonist carbachol known to increase IPs via muscarinic receptors in the organ of Corti. This is consistent with the notion that ATP and carbachol have a common target, most likely outer hair cells. P2 purinoceptors coupled to the phosphoinositide cascade suggest ATP as an afferent neuromodulator or efferent neurotransmitter in the cochlea.

Animals↗

PubMed1983

Maturational and degenerative processes in the organ of Corti after neonatal hypothyroidism.

In order to study the long-term effects of neonatal hypothyroidism on the organ of Corti, rats were given propylthiouracil (PTU) during the first 30 days after birth. Cochlear changes occurring after the cessation of antithyroid treatment were studied by both physiological (brainstem auditory evoked responses: BAERs, electrocochleography) and morphological techniques (transmission and scanning electron microscopy). The first appearance of BAERs was noted between days 37 and 45. Maturation of auditory potentials was achieved within 10-15 days but was incomplete since the animals definitely demonstrated elevated thresholds around 60-70 dB SPL. Morphological results indicated that some structures, like the inner sulcus epithelium, were able to restart maturational processes that had been interrupted during the period of hypothyroidism. However, these maturational changes were considerably limited and rapidLy accompanied by severe degenerative changes involving almost all cochlear structures. Degenerative changes included the deposition of an amorphous substance within the organ of Corti, severe alterations in pillar cells (absence of formation of the tunnel of Corti, distortion of microtubules), severe outer hair cell losses with abnormalities in their innervation (absence of development of efferents and loss of afferent dendrites).

Aging↗

PubMed2002

Transforming growth factor-alpha-induced cellular changes in organotypic cultures of juvenile, amikacin-treated rat organ of corti.

Hair cell losses in the mammalian cochlea following an ototoxic insult are irreversible. However, past studies have shown that amikacin treatment in rat cochleae resulted in the transient presence of atypical Deiters' cells (ACs) in the damaged organ of Corti. These ACs arise through a transformation of Deiters' cells, which produce, at their apical pole, densely packed microvilli reminiscent of early-differentiating stereociliary bundles. The ACs do not, however, express typical hair cell markers such as parvalbumin or calbindin. The present study was designed to determine whether specific growth factors could influence the survival and differentiation of these ACs and stimulate hair cell regeneration processes in vitro. Apical-medial segments of organ of Corti of juvenile amikacin-treated rats were established as organotypic cultures, and the effects of epidermal growth factor (EGF), insulin-like growth factor 1 (IGF-1), transforming growth factor-alpha (TGFalpha), and retinoic acid were studied using morphological and molecular approaches. Our results indicate that TGFalpha supports the survival of the damaged organ of Corti and influences ACs differentiation in vitro, possibly acting through reorganization of the actin cytoskeleton. These effects could be directly mediated through activation of the EGF receptor, which is expressed by supporting cells in the mature organ of Corti. TGFalpha does not, however, allow the ACs to progress towards a hair cell phenotype.

Actins↗

PubMed1994

SEM observation and GABA immunoreactivity of human embryonic organ of Corti tissue culture.

Scanning electronic microscopy (SEM) observation and GABA immunoreactivity of the tissue culture of 6 human embryonic organs of Corti are reported. The normal structural appearance of the hair cells and the facts that there were no bulging of cuticular plates, and cytoplasmic protrusion proved that the hair cells were healthy. After GABA immunostaining, radial bundles, innerspiral bundles, and the ending of inner and outer hair cell regions displayed typical GABA-positive reactivity. The results indicate that the human embryonic organ of Corti is well developed differentiated, and mature at 19 gestational weeks and can continue to grow and differentiate in vitro. The study offers an ideal and important biological model for further research into the human ear.

Culture Techniques↗

PubMed1979

An evaluation of the use of scanning and transmission electronmicroscopy in a study of the gentamicin-damaged guinea-pig organ of Corti.

Scanning electronmicroscopy and transmission electronmicroscopy were used to study the normal and gentamicin-damaged guinea-pig organ of Corti. Scanning electronmicroscopy was principally used to locate the lesion and quantify the cell loss but also permitted and detailed study to be made of the degenerative surface changes. However, since consistent surface changes are not seen until intracellular degeneration has progressed to a great extent, scanning electronmicroscopy is not a suitable technique for identifying early degenerative changes in the sensory cells of the organ of Corti. Consequently, before conclusions may be drawn about the absence of pathological changes in the neuro-epithelium it also should be examined using transmission electron-miscroscopy.

Animals↗

PubMed1984

Some electrical circuit properties of the organ of Corti. II. Analysis including reactive elements.

The simplified network model of the organ of Corti-hair cell complex that was studied in previous publications (Dallos, P. (1983): In: Hearing - Physiological Bases and Biophysics, pp. 32-37, editors: R. Klinke and R. Hartmann; Dallos, P. (1983): Hearing Res. 12, 89-119) is extended to include the capacitive reactances of hair cell 12, 89-119) is extended to include the capacitive reactances of hair cell membranes. With the assumption that the circuit is parametrically excited by resistance changes of the apical hair cell membrane, intracellular responses for outer (eO) and inner (eI) hair cells and the organ of Corti potential (eOC) are computed for the linear case. In order that frequency-dependent effects be primarily determined by the network properties of the system, the eO/eOC and eI/eOC ratios are considered. The amplitude and phase dependence of these computed functions is compared to corresponding experimental results from the third turn of the guinea pig's cochlea. The eO/eOC function is predicted to be a simple low-pass filter whose cutoff frequency (1250 Hz) is determined by the parallel resistance-capacitance circuit of the cell's baso-lateral membrane. This circuit prediction is in excellent agreement with the data. The eI/eOC function is again derived as a low-pass filter. The cutoff frequency is obtained as 472 Hz, which corresponds to an RC membrane time constant of 0.34 ms. Experimental data are widely divergent from this predicted pattern. In order to bring the theoretical and experimental results in agreement, two steps are necessary. First, a differentiation (i.e., multiplication by j omega) needs to be included in the input to inner hair cells to account for their velocity dependence [4,10]. Second, an underdamped complex pole, located above the cell's best frequency must be introduced. The velocity dependence and the resonance represented by the underdamped pole-pair indicate that the electrical response pattern of inner hair cells is more complex than that of outer hair cells.

Cell Membrane↗