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PubMedDate not supplied

A quantitative analysis of the afferent innervation of the organ of corti in guinea pig.

A quantitative analysis of the afferent innervation of the organ of Corti was made on normal and vestibular nerve-sectioned guinea pigs. Section of the vestibular nerve at the internal auditory meatus provided an efficient means of eliminating the efferent innervation to the cochlea without significant loss of afferent fibres. Nerve counts on normal and de-efferented animals revealed that about 10-15 % of the cochlear afferent innervation supplies the outer hair cells. The remaining 85-90% of afferent fibres innervate the inner hair cells. As in cats, all tunnel spiral bundle fibres and upper tunnel crossing fibres were efferent to outer hair cells. Since unmyelinated fibres in the osseous spiral bundle were not counted, quantitative analysis of the efferent innervation to inner hair cells could not be made. However, a significant loss of myelinated fibres in the osseous spiral lamina after vestibular nerve section confirms that many myelinated efferent fibres are present in this region.

Animals↗
PubMed1980

Denervation study of synapses of organ of Corti of old world monkeys.

Fine structural characteristics of synapses in the spiral organ of Corti were examined, with reference to differences between inner and outer hair-cell systems, and to location of neurons of origin of efferent axons. Surgical interruption of crossed olivocochlear bundle, of vestibular nerve, of facial nerve, and excision of superior cervical ganglia were used to determine the pathways of different axons. Interruption of the vestibular nerve near the brainstem results in degeneration of all efferent terminals on outer hair cells. Mid-line lesions at, and caudal to, the facial colliculus result in degeneration of about half of these efferent terminals. Efferent synaptic bulbs to the inner hair-cell system are small, of the order of one micron, and form type 2 junctions with afferent dendrites. They tend to have more large dense-core vesicles (about 80 nm) than the large efferent terminals of the outer hair-cell system, and appear to be the terminals of axons in the habenula perforata, which exhibit varicosities laden with large dense core vesicles. The varicosities are unaffected by excision of the superior cervical ganglia. So far as our material can reveal, it appears that the varicosities in the habenula perforata do not survive vestibular root interruption, nor do the efferent processes in the internal spiral bundle or at the base of inner hair cells. Most interestingly, the afferent processes of the inner hair-cell system, as identified for example by their relation to pre-synaptic bodies in the inner hair cells, are subject to a trans-synaptic reaction after severance of the vestibular root. They undergo a dramatic cytological transformation, characterized by increase of volume, engorgement with microtubules, microfilaments, microvesicles of various sizes, and clusters of lysosomes. Thus, both the efferent and afferent terminals of the inner hair-cell system show marked cytological differences from the corresponding terminals of the outer hair cell system.

Afferent Pathways↗
PubMed1996

The early postnatal development of F-actin patterns in the organ of Corti of the gerbil (Meriones unguiculatus) and the horseshoe bat (Rhinolophus rouxi).

The arrangements of F-actin in hair cells and non-sensory cells were studied in paraformaldehyde-fixed cochleae of horseshoe bats and gerbils in several postnatal stages and in the adult. Phallotoxin-labeled midmodiolar cryostat sections of the organ of Corti were analyzed with confocal fluorescence microscopy. In both species, the arrangement of F-actin in the adult organ of Corti was essentially similar to that described in other mammals; however, both species showed their own species-typical specializations in staining of the Deiters cells. In the gerbil, a distinct baso-apical gradient in morphology and staining properties was found in the upper compartment of the Deiters cells. In the bat, F-actin label within the Deiters cups was most pronounced in the basal cochlear turn and less abundant in the apical turns. During the first postnatal week, the sensory epithelium of the gerbil lacked the tunnel of Corti and the spaces of Nuel. Only the reticular lamina and the surface of the greater epithelial ridge were intensely labeled for F-actin. At 9 days after birth (DAB), when the tunnel of Corti and the inner spiral sulcus were formed, the footplates of Deiters and pillar cells and the apices of pillar cells began to show intense F-actin label. At 12 DAB, corresponding to onset of hearing, F-actin staining was found throughout the supporting cell bodies, but was less intense than in the adult. The specialized upper compartment of the Deiters cells differentiated around 15-20 DAB. In the neonate bat, gross-morphology of the organ of Corti was almost adult-like, but only the reticular lamina and the head- and footplates of pillar cells showed intense F-actin staining. The F-actin cytoskeleton of the Deiters cells bodies was poorly developed. At the onset of hearing (between 3rd and 5th DAB), supporting cells showed only a slight increase of F-actin mainly at mechanically important cell regions, namely the Deiters cups, the contact zone of pillar headplates and the footplates of supporting cells. The most intense increase of F-actin occurred between onset of hearing and 16 DAB. At 16 DAB, the F-actin distribution within the supporting cells was similar to the adult. In both species, there were no clear baso-apical gradients in development of F-actin patterns. It is proposed that F-actin insertion in supporting cells after the onset of hearing contributes to maturation of cochlear function.

Actins↗
PubMed1995

The site of action of neuronal acidic fibroblast growth factor is the organ of Corti of the rat cochlea.

Here we show that the mature cochlear neurons are a rich source of acidic fibroblast growth factor (aFGF), which is expressed in the neuronal circuitry consisting of afferent and efferent innervation. The site of action of neuronal aFGF is likely to reside in the organ of Corti, where one of the four known FGF receptor (FGFR) tyrosine kinases--namely, FGFR-3 mRNA--is expressed. Following acoustic overstimulation, known to cause damage to the organ of Corti, a rapid up-regulation of FGFR-3 is evident in this sensory epithelium, at both mRNA and protein levels. The present results provide in vivo evidence for aFGF being a sensory neuron-derived, anterogradely transported factor that may exert trophic effects on a peripheral target tissue. In this sensory system, aFGF, rather than being a neurotrophic factor, seems to promote maintenance of the integrity of the organ of Corti. In addition, aFGF, released from the traumatized nerve endings, may be one of the first signals initiating protective recovery and repair processes following damaging auditory stimuli.

Animals↗
PubMed2001

Supernumerary outer hair cells arise external to the last row of sensory cells in the organ of corti.

During the development of the mammalian inner ear, the number of hair cells produced is highly regulated and remains constant throughout life. The mechanism underlying this regulation is beginning to be understood although many aspects still remain obscure. When late embryonic or early postnatal rat organs of Corti were cultured, the production of supernumerary hair cells was observed. This overproduction of sensory cells could be modulated by the addition of several growth factors. In this study, we examined explants of rat organs of Corti that produced supernumerary hair cells. In the supernumerary hair cell region, up to two rows of inner hair cells and five rows of outer hair cells were observed. Morphological evaluation of these specimens revealed that less mature hair cells were located in the most external rows of these sensory cells. When a supernumerary hair cell was produced, a supporting cell (i.e. Deiters' cell) was also produced, strongly suggesting that the conversion of a Deiters' cell into a hair cell was not the mechanism that produced these extra hair cells. Based on these results, we propose that prosensory cells located at the external edge of the organ of Corti retain a capacity to form hair cells and that it is these prosensory cells that differentiate into supernumerary hair cells and Deiters' cells.

Animals↗
PubMed1990

Immunocytochemical detection of glutamate decarboxylase in the postnatal developing rat organ of Corti.

Using a fluorescent avidin-biotin technique, we have immunolocalized the GABA synthesizing enzyme, glutamate decarboxylase, in postnatal developing and adult rat organs of Corti. At birth, the glutamate decarboxylase-like immunoreactivity is already present in the basal turn below the inner hair cells, i.e. within lateral olivocochlear efferent fibers of the inner spiral bundle. In the apical turn, the inner spiral bundle displays an immunoreactivity as early as postnatal day 3. Only the outer hair cells of the upper second turn and apex receive fibers immunostained for glutamate decarboxylase that most probably belong to the medial olivocochlear efferent innervation. They first appear at this level at postnatal day 15. Within these two regions of the organ of Corti, the glutamate decarboxylase-like immunoreactivity reaches an adult-like pattern at postnatal days 17-18. These results strengthen the hypothesis that GABA is a putative neurotransmitter that could be used by subpopulations of the two olivocochlear innervations. They also suggest that GABA either plays a neurotrophic function or participates in the regulation of the first cochlear potentials at the level of lateral efferent synapses.

Aging↗
PubMed2004

Vibration pattern of the organ of Corti up to 50 kHz: evidence for resonant electromechanical force.

Electromechanical force derived from the soma of the outer hair cell has long been postulated as the basis of the exquisite sensitivity of the cochlea. The problem with this postulate is that the electrical source and mechanical load for the electromechanical outer hair cell might be severely attenuated and phase-shifted by the electrical impedance of the cell and the mechanical impedance of the organ of Corti, respectively. Until now, it has not been possible to experimentally derive the high-frequency electrically induced force at the reticular lamina when the cells are embedded within the organ of Corti. In the study reported here, we succeeded in determining the frequency spectrum of the force up to 50 kHz. This was achieved by measuring both the electrically induced velocity and the mechanical impedance at different radial positions on the reticular lamina without tectorial membrane and with clamped basilar membrane. Velocity was measured with a laser interferometer and impedance, with a magnetically driven atomic force cantilever. The electromechanical force, normalized to the electric current density, exhibited a broad amplitude maximum at 7-20 kHz with a quality factor, Q(3dB), of 0.6 - 0.8. The displacement response was independent of frequency up to 10-20 kHz. The force response compensates for the viscoelastic impedance of the organ of Corti, extending the amplitude response of the organ to high frequencies. It is proposed that the electrical phase response of the cell is compensated with Zwislocki's original mechanism of a parallel resonance in the tectorial membrane-stereocilia complex.

Animals↗
PubMed1980

Embryonic development of the human organ of Corti: electron microscopic study.

A morphological approach by the electron microscope was used to obtain findings suggestive of the onset of auditory function in the fetal human cochlea. The organs of Corti at three different embryonic ages: 20 weeks 3 days, 22 weeks, and 24 weeks, were studied from the following standpoints: auditory hairs; hair cell bodies; the interrelationship between sensory cells and supporting cells; fluid spaces in the organ of Corti; and nerve endings to the sensory cells. Assessment of these findings implies that the peripheral auditory organ is ready for sending afferent impulses at around 24 weeks of embryonic age.

Cochlea↗
PubMed1979

Fluid motion in the mammalian organ of Corti. A possible source of the second filter.

A mechanical analysis of the functioning of the mammalian organ of Corti as deduced from experimental observations and electronmicroscopic studies of the organ has been conducted. It was found that the arch of Corti is responsible for initiating a fluid motion in the spiral sulcus and reticular lamina which could stimulate the inner hair cells. A three-dimensional linear mathematical model with no arbitrary parameters is proposed to describe the force acting on the inner hair cell cilia as a function of arch displacement. Analysis of the model results show that the model (a) correctly predicts the form of the neural response for a low frequency square wave of arch motion, (b) demonstrates a physiologically reasonable time constant of 245 musec, (c) shows a sharpening of neural stimulation of physiological importance, (d) can explain the qualitative difference of neural responses to arch motions of opposite polarity, (e) demonstrates a phase difference between outer and inner hair cell stimulation, and (f) appears to be chemically and metabolically vulnerable.

Animals↗
PubMed1995

[Scanning electron microscopic study of the sensory hairs of the organ of Corti using transtympanic infusion of fluids with different osmotic pressure].

Morphological examination of the sensory hairs of the lower half of the 2nd turn of the organ of Corti of the guinea pig after transtympanic infusion of the aseptic fluids with different osmotic pressure was performed using a scanning electron microscope. Group A fluids (0-315 mosmol/l) did not have any injurious effect on the sensory hairs of the OHCs (outer hair cells) or IHCs (inner hair cells). In contrast, Group B fluids (720, 743 mosmol/l) appeared to cause disarrangement of the stereocilia of the OHCs. Alterations were found to be more extensive and severe in the 3rd row of OHCs. Group C fluids (1224, 1248 mosmol/l) induced total loss of sensory hairs in the 3rd and 2nd row of OHC. The remaining stereocilia in the 1st and 2nd rows showed coalescence of adjacent stereocilia. Based on these findings, the authors concluded that there is a close relationship between osmotic induction/deduction by transtympanic infusion of fluids and high osmotic pressure on the hairs of the organ of Corti.

Animals↗
PubMed1997

[Accumulation sites of kanamycin in the organ of Corti by microautoradiography].

The accumulation sites of the 3H-labelled kanamycin in the organ of Corti were observed with electron microscope. The results showed that the accumulation of kanamycin was mainly in the mitochondria, cell membrane and stereocilia of the hair cells. The possible mechanism of the kanamycin accumulation in the mitochondria is their similarity with bacteria in the protein synthesis, i.e. the way that kanamycin might inhibit the protein synthesis in the mitochondria is similar to that of bacteria. The kanamycin accumulation in the cell membrane may indicate the entrance of kanamycin into the hair cells. The kanamycin deposition in the stereocilia was most likely related to its high chemical affinity with glycocalyx.

Animals↗
PubMed1986

Intracellular structure of the outer hair cell of the organ of Corti.

The intracellular structure of the outer hair cells of the normal guinea pig organ of Corti was investigated three dimensionally by scanning electron microscope. Freeze fracturing technique followed by maceration with a 0.1% OsO4 solution (osmic maceration method) was used. Among the cell organelles, the endoplasmic reticulum (ER) showed the most interesting features, such as subsurface cisternae and lamellar bodies. The subsurface cisterna which formed a stratiform network covered the inner surface of the cell membrane and the stratiform structure disappeared at the infranuclear region. Variously shaped mitochondria (spherical, cylindrical and branched) were found on the innermost layer of the subsurface cisterna. The lamellar body which was located beneath the cuticular plate consisted of dilated cisternae and tubular ER and was surrounded by mitochondria. The tubular ER of the lamellar body were continuous with the subsurface cisterna.

Animals↗
PubMed1996

Organization of AMPA receptor subunits at a glutamate synapse: a quantitative immunogold analysis of hair cell synapses in the rat organ of Corti.

Sensitive and high-resolution immunocytochemical procedures were used to investigate the spatial organization of AMPA receptor subunits (GluR1-4) at the synapse between the inner hair cells and the afferent dendrites in the rat organ of Corti. This is a synapse with special functional properties and with a presynaptic dense body that defines the center of the synapse and facilitates its morphometric analysis. A quantitative postembedding immunocytochemical analysis was performed on specimens that had been embedded in a metachrylate resin at low temperature after freeze substitution. Single- and double-labeling procedures indicated that GluR2/3 and GluR4 subunits were colocalized throughout the postsynaptic density, with a maximum distance of 300 nm from the presynaptic body and with higher concentrations peripherally than centrally. No receptor immunolabeling was found at extrasynaptic membranes, but some GluR4 subunits appeared to be expressed presynaptically. The synapses between outer hair cells and afferent dendrites were devoid of labeling. The present data indicate that AMPA receptor subunits are inserted into the postsynaptic membrane in a very precise manner and that their density increases on moving away from the center of the synapse.

Animals↗
PubMed1984

A freeze-fracture study of afferent and efferent synapses of hair cells in the sensory epithelium of the organ of Corti in the guinea pig.

Afferent and efferent synapses of hair cells in the organ of Corti of the guinea pig have been examined in freeze-fracture replicas. Afferent synapse. In the inner hair cells, intramembranous particles 10 nm in diameter are aggregated on the ridge on the P-face of the presynaptic membrane directly beneath the synaptic rod. In the outer hair cells, in which the synaptic rod is located in the presynaptic cytoplasm underneath the presynaptic membrane, small aggregations of intramembranous particles 10 nm in diameter can be found on the P-face of the presynaptic membrane corresponding to the site of the presynaptic dense projection. Intramembranous particles 10 nm in diameter are also densely aggregated on the P-face of the postsynaptic membrane of the outer hair cells. Efferent synapse of the outer hair cells. Large intramembranous particles 13 nm in diameter are distributed in clusters composed of four to ten particles on the P-face of the presynaptic membrane. In the P-face of the postsynaptic membrane, disc-like aggregations of intramembranous particles 9 nm in diameter are found. The subsynaptic cistern covers the cytoplasmic surface of the postsynaptic membrane of the efferent synapse; it may cover more than one postsynaptic membrane when several efferent synapses are in close proximity to one another.

Afferent Pathways↗
PubMedDate not supplied

Time sequence of degeneration pattern of the organ of Corti after acoustic overstimulation. A transmission electron microscopy study.

Female pigmented guinea pigs were exposed to a 3.85 kHz pure tone of 120 dB SPL for 22.5 min. The exposed animals were sacrificed after varying post-exposure intervals (5 min, 4 and 24 h, 5 and 28 days). Transmission electron microscopical examination was performed after serial-sectioning in areas of maximum damage and both basal to and apical to this region. By serial-sectioning, the degradation pattern of the individual cell structures in the organ of Corti could be studied in relation to post-exposure time and proximity to the well-demarcated area of maximum damage in the organ of Corti. The results provide further information on the non-reversible changes leading to degeneration and loss of sensory and supportive structures in the organ of Corti.

Animals↗
PubMed1977

Regional specialization of the hair cell plasmalemma in the organ of corti.

Nonjunctional and nonsynaptic membranes of hair cells in the chinchilla organ of Corti were examined using the freeze-fracture technique. Cytoplasmic leaflets of the apical membranes of hair cells have particles, 6-12 nm in diameter, but many more particles are found on apical membranes of outer hair cells than on inner hair cells. Cytoplasmic leaflets of the lateral membranes of outer hair cells are covered with large particles, but the corresponding regions of the inner hair cell membrane have fewer particles and these are small or medium-sized. Two types of particle aggregate also distinguish this region of the inner hair cell. The first consists of patches of particles closely spaced in rectilinear arrays. The second consists of parallel strands of widely spaced large particles similar in size, but not in distribution, to the large particles on the lateral membranes of the outer hair cells. The basal membrane of outer hair cells is distinguished from that of inner hair cells by plaques consisting of cross-hatched incisures in the external membrane leaflet. While the significance of these anatomical features is not yet apparent, they give the hair cell plasmalemma a richness or regional specialization found in few other cells and suggest that there are important functional differences between inner and outer hair cells.

Animals↗
PubMed1994

Expression of actin isoforms in the guinea pig organ of Corti: muscle isoforms are not detected.

The specificity of antibodies to actin was assayed by use of immunoblots and histological sections of control tissues enriched for each of six different isoforms. On immunoblots, all antibodies stained at most one band of protein in most of the control materials, with a molecular weight of approximately 43 kDa. Their pattern of staining of muscle and nonmuscle tissues indicated their isoform specificity. On tissue sections, immunocytochemical staining demonstrated cellular and subcellular localization of the different isoforms. Once characterized with regard to specificity, these antibodies were used to probe actin in the guinea pig organ of Corti. None of the four muscle isoforms of actin were found in either immunoblots or tissue sections of the organ of Corti. Both beta- and gamma-cytoplasmic isoforms of actin were present in hair cells and supporting cells. This leaves open to investigation the role which cytoplasmic actins play in these cells of the organ of Corti.

Actins↗