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PubMed1983

Electron microscopic atlas of the simian cochlea.

An electron microscopic atlas of simian cochlear duct structures is presented with the hope that it may help to clarify certain questions of structural-functional relationships. Emphasis is placed on structures directly involved in sensory transduction and in synaptic transmission, at afferent and efferent nerve fiber terminals. A brief discussion is included as an introduction to the possibilities of interpretation of electron microscopic data. Orientation of electron micrographs is assisted by means of numerical coding on light microscopic photographs, and by means of a diagram which combines electron microscopic and light microscopic data.

Animals↗
PubMed1983

Responses of gerbil and guinea pig auditory nerve fibers to low-frequency sinusoids.

The characteristics of time-locked auditory nerve fiber responses to 50 Hz acoustic sinusoids were studied in gerbils and guinea pigs. Whereas the time-locked responses of all guinea pig fibers produced single-peaked period histograms, those of the gerbil produced distorted, multiple-peaked response histograms, especially fibers with characteristic frequencies (CFs) between 2 and 10 kHz. Although the shapes of the period histograms vary with stimulus intensity, the phases of the fundamental components are essentially invariant over the range of stimulus intensities used. In contrast to the phase of the cochlear microphonic produced by the 50 Hz stimulus, which was constant along the length of the cochlea in both species, the phase of the neural responses depends on the fiber CF in each of the two species. In guinea pigs, the phase of the neural responses relative to the acoustic stimulus decreases with the fiber CF from a phase lead of 90 degrees for fibers with CFs below 300 Hz to a phase lag of nearly 60 degrees for fibers with CFs greater than 3 kHz. In gerbils, the response phase also decreases with increasing CF below 2 kHz and above 10 kHz but undergoes an abrupt 160 degrees phase increase between those frequencies.

Acoustic Stimulation↗
PubMed1984

Dimensions of the cochlear stereocilia in man and the guinea pig.

The tuning properties of the basilar membrane and the presence of acoustic emissions from the cochlea suggest that an energy consuming, mechanically active cochlear amplifier exists. Some models of this amplifier demand a mechanical resonator within the cochlea. The lengths of the stereocilia of the inner and outer hair cells in man and the guinea pig have been measured from scanning electron micrographs using a stereometric technique. In both species there is a linear increase in the length of the longest inner hair cell stereocilia with distance along the cochlea. There are, however, marked differences between the dimensions of the outer hair cell stereocilia in the two species. In man, there is an increase in length which is is a hyperbolic function of distance along the cochlear duct. The picture is more complicated in the guinea pig. This could account for some of the differences in auditory physiology between the two groups. The mechanical resonance properties of the human OHC stereocilia have been assessed, and, with certain assumptions, these properties are such that resonance of the stereocilia of the OHCs could form part of the cochlea amplifier, at least in man.

Animals↗
PubMed1984

The reconnection of auditory posterior root fibers in the red-eared turtle, Chrysemys scripta elegans.

The auditory portion of the eighth nerve, the posterior root, was transected in Chrysemys scripta elegans. Two groups of animals were allowed to survive; one for 22 days and the second for 64 days. Each group was then reoperated to inject HRP into the cochlear duct and allowed to survive for an additional three days - for a total survival time of 25 days and 67 days. The 67 day survivors had HRP reaction product in the eighth nerve and the primary auditory nuclei, while the 25-day survivors did not. Degeneration byproduct was present in the same structures in the 25-day survivors while little was in the 67-day survivors. These results indicate as reconnection of the eighth nerve fibers to the acoustic tubercle.

Animals↗
PubMed1985

Effects of barium and ion substitutions in artificial blood on endocochlear potential.

Previously, a qualitative assessment was made (Marcus, D.C. (1984): Am. J. Physiol. 247, C240-C246) of the ion-selective properties of the cells bounding the cochlear duct by observing the effects of ion substitutions in the perilymph on the transepithelial potential difference (endocochlear potential; EP). Contributions by the marginal cells of the stria vascularis to the observed changes in the EP may have been masked, however, due to their 'isolation' from the perilymph by a continuous layer of basal cells. Since the ionic milieu of the basolateral membranes of the marginal cells is controlled more directly by the blood supply than by the perilymph, we report here on the effects of ion substitutions via vascular perfusion. Elevated K (substituted for Na or N-methyl-D-glucamine; NMDG) or Ba caused marked depression of the EP. Decreased Na or Cl (replaced by NMDG and gluconate, respectively) also depressed the EP. These changes in the EP were distinctly different from those observed previously by perilymphatic perfusion, and were interpreted in terms of a modified model of the strial marginal cells.

Barium↗
PubMed1986

Incorporation of inositol in the cochlear tissues as determined by autoradiography.

The sites of incorporation of [3H]inositol perfused perilymphatically in the guinea pig cochlea were localized autoradiographically. In the organ of Corti, active incorporation occurred in the synapses, nerve fibers, pillars and nuclei of various cells. Both hair cells and supporting cells moderately incorporated inositol. In the lateral wall of the cochlear duct marked incorporation was observed in the epithelia of the vascular stria and spiral prominence. The possible involvement of inositol phospholipids in auditory transduction at the organ of Corti and in ionic transport in the lateral wall of the cochlea is briefly discussed.

Animals↗
PubMed1987

Immunocytochemical and quantitative studies of Na+,K+-ATPase distribution in the developing chick cochlea.

Immunocytochemical methods were used to examine cryosections of the embryonic and neonatal chicken cochlea in order to study the histological distribution of the Na+,K+-ATPase molecule during maturation. In complementary studies the Na+,K+-ATPase capacity of microdissected freeze-dried substructures of the cochlea was determined fluorometrically. The dark cell of the tegmentum vasculosum exhibited intense immunochemical staining of the convoluted basolateral infoldings. The adjacent light cells demonstrated very little staining. The plasma membrane of the hair cell was also stained as were the first order auditory neurons, including the cell soma. The homogene cells and the supporting cells were unstained. The dark cell was only lightly stained with the antibody at stage 45 but became more intense and selective by the seventh postnatal day. The other cells of the cochlear duct exhibited specific immunofluorescent staining of their plasma membranes from stage 45 onwards and the fluorescent intensity did not change. The tegmentum vasculosum exhibited very high activities of the Na+,K+-ATPase enzyme relative to the other structures of the cochlea. Furthermore, a pronounced gradient of enzymatic activity was detected longitudinally. The proximal tip (or high-frequency end) had a sixteen-fold greater capacity for Na+- and K+-dependent ATP hydrolysis relative to the distal tip (or low-frequency end). The appearance of this enzyme in the tegmentum vasculosum during the development of the cochlea paralleled the known rate of improvement in hearing thresholds.

Animals↗
PubMedDate not supplied

Cobalt labelling of single primary auditory neurones: an alternative to HRP.

We have labelled single, primary auditory neurones in three reptile and one bird species. After functional characterization of the neurones, hexamminecobaltic chloride was iontophoretically injected through the recording micropipette. Precipitation of cobalt sulfide followed by silver intensification of the cochlear duct as a whole-mount preparation revealed stained neurones in over 90% of cases. This method has several advantages over labelling with HRP.

Animals↗
PubMed1989

Changes in cochlear microphonic and neural sensitivity produced by acoustic trauma.

The low-frequency (200 Hz) microphonic potentials at the round window and in the organ of Corti of the first turn of the guinea pig cochlea have been measured before and after acoustic overstimulation. Reductions in the amplitude of this microphonic after loud sound are highly correlated with neural threshold elevation in this region. The fall in the microphonic amplitude appears due to an inactivation of mechano-electrical transduction channels at the apex of the outer hair cells into a closed state. These results are consistent with the idea that the current through the outer hair cells controls the mechanical sensitivity of the organ of Corti, and that the temporary loss of mechanical and neural sensitivity following loud sound is due to a simple inactivation of the mechano-electrical transduction channels.

Action Potentials↗
PubMed1990

Quantitative assessment of the rat stria vascularis.

Stria vascularis tissues from standardized regions in the basal, middle and apical turns of the rat cochlear duct were assessed quantitatively. Strial width, number of marginal cells across the strial width, radial area, as well as the volume density of the different components of the stria vascularis were determined for each standardized region. Strial width, number of marginal cells across the strial width and the radial area were greatest in the basal region and least in the apical region of the cochlea. The volume density of intermediate cells and capillary space was statistically unchanged in the three examined regions of the stria vascularis. However, the volume density of marginal cells and that of basal cells were different between regions. The volume density of marginal cells was highest in the basal turn while the volume density of basal cells was greatest in the apical turn. An objective assessment of the response of the stria vascularis to environmental conditions can be made by kant of its cellular architecture, providing a means to compare the effects of various agents between animal models used to study human inner ear dysfunction.

Animals↗
PubMed1993

The innervation of the organ of Corti in the rat.

To date our knowledge of the baso-apical distribution of the afferent and efferent nerve fibers innervating the organ of Corti is only fragmentary. This study makes an effort to lay the basis for a comprehensive analysis of cochlear innervation. Using a quantitative electronmicroscopic method, the fiber density of all cochlear fibers along the entire length of the cochlear duct was investigated in adult rats, Rattus norvegicus. Myelinated and unmyelinated nerve fibers in the primary osseous spiral lamina and afferent and efferent nerve fibers to the outer hair cells (OHCs) in the tunnel of Corti were counted. The rat cochlea is innervated by 19000 nerve fibers which consist of 79% afferent and 21% efferent fibers. The inner hair cells (IHCs) are innervated by 14000 afferent and 2000 efferent fibers. The OHCs are innervated by 1000 afferent and 2000 efferent fibers. The maximum fiber density of IHC afferents, OHC afferents and IHC efferents was found in the middle of the cochlea. This corresponds to the region at the basilar membrane where the frequency range of maximum sensitivity is located [8 kHz-31 kHz; Kelly and Masterton, J. Comp. Physiol. Psychol. 91, 930-936 (1977)]. The efferent nerve fibers to the OHCs consists of two different morphological sub-types: large fibers containing mitochondria and neurotubules (type I) and small fibers containing neurofilaments (type II). The fiber density of type I OHC efferents decreases from base to apex corresponding to the frequency dispersion along the basilar membrane. The fiber density of type II OHC efferents has maxima at the base and at the apex and a minimum in the middle of the cochlea. This minimum corresponds to the region at the basilar membrane where the frequency range of maximum sensitivity is located.

Animals↗
PubMed1996

Localization of bone morphogenetic protein-4 messenger RNA in developing mouse cochlea.

Bone morphogenetic protein-4 (BMP-4) is a cytokine that belongs to the TGF-beta superfamily. It has been implicated that it plays an important role during embryogenesis including epithelial-mesenchymal interactions and mesenchymal cells condensation. To investigate whether BMP-4 is involved in the embryogenesis of the inner ear, we performed in situ hybridization at various stages of the developing inner ear of mice. BMP-4 mRNA was detected only in the developmental stage. Its initial expression was detected in part of the otic vesicle at 9 days post-coitum (PC). As development proceeded, the hair cells of the cochlear duct were morphologically distinguishable. and BMP-4 expressing cells were found in Claudius cell region at 16 days PC. At this stage, the signal was most intense during development and the structure notably changed under the expressing cells. Mesenchymal cells were assembled and condensed underneath the BMP-4-expressing cells. The basilar membrane, with a rich extracellular matrix and elasticity, would be produced in the area between the Claudius' cells and condensed mesenchymal cells. Previous reports support the notion that BMP-4 expressed in the epithelium causes mesenchymal cell condensation and induces a structure with elasticity. In the developing cochlea. BMP-4 may be involved in the condensation and differentiation of the mesenchymal cells as well as basilar membrane formation. BMP-4 might be an essential factor for the normal development of the basilar membrane.

Animals↗
PubMed1996

Localization of actin in basal cells of stria vascularis.

The distribution of actin in the lateral wall of the cochlear duct was investigated in the gerbil, rat, mouse and hamster. A monoclonal antibody specific for muscle alpha and gamma actins, and a polyclonal antiserum reactive with smooth muscle gamma and non-muscle beta actins yielded strong immunostaining of basal cells in the stria vascularis and of smooth muscle cells in lateral wall blood vessels. Both cell types stained in all four genera. Diffuse cytosolic staining was observed along the full-length of the basal cell layer including the blunt cell processes which they extend toward strial marginal cells. Immunoreactive basal cells appeared continuous with morphologically similar cells investing vessels penetrating the stria from the spiral ligament. The basal cells failed to bind antibodies to smooth muscle alpha actin and sarcomeric actin. By electron microscopic immunocytochemistry, gold labeling for actin was observed on dense, fine fibrils in the cytoplasm of the basal cells. In paraffin sections adjacent to those stained for actin, antibody to vimentin stained intermediate and basal cells in the stria vascularis whereas antibody to isoform 1 of the facilitated glucose transporter protein family (GLUT1) labeled only the non-overlapping apical and basal plasmalemma of basal cells. Content of vimentin, GLUT1 and muscle gamma actin supports the derivation of basal cells from mesoderm. The presence of stress fibers containing muscle gamma actin points to a possible contractile activity of basal cells which conceivably could be related to transport of K+ to and within the intrastrial compartment or regulation of blood flow in the stria vascularis.

Actins↗
PubMed1996

Postnatal changes in the reticular lamina of the guinea pig organ of Corti.

The dimensions of the apical surfaces of hair cells were measured in guinea pigs, aged from 3 weeks before term to 25 weeks after birth. In the basal two-thirds of the cochlea, the apical surfaces of the outer hair cells and their supporting cells changed with age, shrinking in a direction radial across the cochlear duct. There was an associated widening of the angle of the 'V' of the rows of stereocilia. Further apically, between 12 and 16 mm from the base of the cochlea, the outer hair cells and their supporting cells underwent the opposite change, becoming wider in a radial direction with age. The changes were seen before birth and continued for more than 3 weeks after birth. The results suggest that the guinea pig cochlea continues certain developmental processes for a considerable time after birth.

Aging↗
PubMed1990

Histological examination of the temporal bone in medicolegal cases of asphyxia.

Histological findings of the temporal bone in 23 autopsy cases of various asphyxial fatalities were studied. The temporal bones of 12 cases who died of tumors including mammary cancer, gastric cancer, myxoma of heart and craniopharyngioma, the bones of 3 cases of heart attack and the bones of 17 cases who died of various poisoning (barbiturate, amphetamine, paraquat and alcohol) were used as controls. In drowning, the primary finding was hemorrhage in the mastoid air cells of the bilateral temporal bones. In cases of strangulation by ligature, hemorrhage and edema of the cochlear duct in the inner ear as well as hemorrhage in the mastoid air cells were demonstrated bilaterally. In contrast, congestion and edema in the mastoid air cells and inner ear were found in cases of manual strangulation but there was no hemorrhage. From these results, the histological examination of the temporal bone is useful as an adjunct procedure for diagnosing the cause of asphyxia. Differentiation between drowning, strangulation by ligature and manual strangulation may be possible by observing hemorrhages or their absence in the mastoid air cells and inner ear.

Adolescent↗
PubMed1995

Embryo brain kinase: a novel gene of the eph/elk receptor tyrosine kinase family.

A new gene belonging to the Eph/Eck/Elk receptor tyrosine kinase family has been cloned from mouse brain. The gene maps to mouse chromosome 4. In the adult brain it is expressed exclusively and abundantly in the hippocampus. We propose to name it Ebk (embryo brain kinase), as in situ hybridisation shows expression in many parts of the developing mouse brain. The most abundant expression is in the subcommissural organ, and the earliest expression is in the forebrain neural folds, in rhombomeres 2-6, and in somites and heart. Other regions positive at various stages include the cochlear duct, trigeminal ganglion, lung, first branchial arch, and tooth primordia. Also positive are areas of mesenchyme underlying various epithelia during morphogenesis, especially in the mouth and nose, as well as in the eyelids and toes. We compare these patterns with the available data on the 12 other known members of this gene family. Most of them, like Ebk, are expressed in brain (especially adult hippocampus and embryonic rhombomeres) and in organs rich in epithelia (especially lung), although the spatial and temporal patterns differ. We suggest that combinatorial patterns of these receptors act as labels for the regional identity of neurons and epithelia, and could mediate fine control of neurite pathfinding and epithelial morphogenesis.

Aging↗
PubMed2006

Endocytosis of microperoxidase in the marginal cells of stria vascularis.

OBJECTIVE: Endocytosis has been thought to control entry into the cell and play a crucial role in the development, immune response, neurotransmission, intercellular communication, signal transduction, and cellular and organismal homeostasis. We investigated the basic properties of endocytosis in the marginal cells of stria vascularis (SV) to discuss whether marginal cells have a potential to maintain the endolymph homeostasis. METHODS: We perfused microperoxidase (MPO), an endocytosis tracer, into the cochlear duct. After 5-60 min of endolymphatic perfusion, the tissues were fixed and the distribution of MPO within the marginal cell was observed by transmission electron microscopy. RESULTS: Endocytosis started already at 5 min after MPO perfusion. Small MPO-loaded endosomes were observed up to 30 min after MPO perfusion. The small tubulovesicular endosomes and the plasma membrane invagination were not decorated by an electron dense bristle structure. After endocytosis, MPO labeled preendosomes were quickly transported to the large vacuolar endosomes that connected with tubular endosomes. At 60 min after MPO perfusion, MPO-loaded large vesicles that have small vesicles in the lumen were observed. CONCLUSION: The time-course of MPO-loaded endosomes was similar to that of CF-loaded endosomes in the marginal cells of SV. The strial marginal cells have vigorous endocytotic activity both in clathrin-independent and clathrin-dependent endocytosis. This high activity of endocytosis in SV seems to be needed to maintain the homeostasis of endolymph via membranous channels and/or receptors regulations.

Animals↗
PubMed2004

A new method for imaging and 3D reconstruction of mammalian cochlea by fluorescent confocal microscopy.

Traditional methods for anatomical and morphometric studies of cochlear tissues have relied upon either microdissection of the organ of Corti or the generation of serial sections of the cochlea. Such methods are time-consuming, disruptive to three-dimensional relationships and often restrict sampling to very limited numbers of cells. We have found that cells and tissue components of the cochlear duct may be labelled by fluorescent markers within intact cochleae, which are then embedded in epoxy resin for subsequent viewing by fluorescent microscopy methods. This approach allows imaging through thick optical volumes with preservation of three-dimensional relationships. Unlike sectioned tissue, alignment of the sample relative to the focal axis may be easily corrected by re-orientation of the optical volume with common image processing software. Fluorescently labelled cochleae embedded in epoxy can be viewed by most fluorescent microscopy methods including laser scanning confocal microscopy, multi-photon confocal microscopy and widefield epi-fluorescence microscopy with deconvolution. Furthermore, semi-thin sections made from these preparations are compatible with traditional histological stains, as well as allowing brightly labelled epi-fluorescent images.

Animals↗