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PubMed1975

[Intercellular junctions in the guinea pig stria vascularis as shown by freeze-etching (author's transl)].

Freeze-fracture replicas of the guinea pig inner ear were analyzed to study the occurrence and structure of zonulae and fasciae occludentes (tight junctions) and nexuses (gap junctions) in the stria vascularis. Zonulae occludents of the marginal cells, which form a barrier towards the potassium-rich endolymph of the cochlear duct, were demonstrated to be of the "intermediate to tight" type (Claude and Goodenough, 1973). Abundant, extensive cell contacts of the basal cells were identified as fasciae occludentes forming a barrier towards the spiral ligament. Nexuses were found connecting marginal, intermediate and basal cells of the stria vascularis as well as between the basal cells and fibrocytes of the spiral ligament. Frequently, nexuses were seen within the areas of the basal cell fasciae occludentes. It is supposed that nexuses mediate the electrotonic coupling between neighbouring stria vascularis cells and that probably they are an essential factor for the development of the endocochlear potential. It is pointed out that the intercellular spaces of the stria vascularis represent a compartment with high oxygen supply and an important metabolic system. A high intramembrane particle density was observed on some nonjunctional areas of the cell membranes, especially on the A-fracture faces of the marginal cell extensions. It appears that these membranes exhibit a high metabolic activity. Finally, the findings are discussed with respect to the production and maintenance of the endocochlear potential.

Animals↗
PubMed1976

Endolymphatic hydrops: mechanical causes of hearing loss.

An explanation for the mechanical origin of the hearing loss in endolymphatic hydrops is presented that is based on studies in mechanical cochlear models. An elastic bias of the basilar membrane and/or a mass loading of the cochlear duct account for the low-frequency hearing loss, diplacusis, and even-harmonic distortion. In addition, the static shearing displacement between the tectorial membrane and the organ of Corti, caused by the displacement of the basilar membrane, may partially decouple the hair cells from the tectorial membrane, an event that would explain the tinnitus, recruitment, and perhaps even the disportional loss of speech intelligibility associated with endolymphatic hydrops.

Basilar Membrane↗
PubMed1985

Dissociation of the cochlear microphonics and endocochlear potential after injection of ethacrynic acid.

The cochlear microphonics (CM), endocochlear potential (EP) and summating potential (SP) were simultaneously recorded for 60 min after injection of 30 mg/kg body weight of ethacrynic acid. The EP decreased parallel with the CM for about 20 min after injection, but they differed in the recovery stage. Even when the EP was still negative, the output of CM for 500 Hz acoustic stimulus recovered to its original level and was supernormal. A large SP observed in the recovery stage of CM and EP seemed to suggest that some functional change in the hair cells might be connected with the supernormal CM. Four minutes of anoxia during the supernormal CM decreased CM to only 68% of its level prior to anoxia. A cathodal polarization of the scala media, to change the polarity of the dc potential gradient, reversed the polarity of CM in the anoxic guinea-pig cochlea but not in the guinea-pig cochlea administered ethacrynic acid. These results suggest that supernormal CM observed in this experiment may not be dependent on the dc potential gradient, but due to some functional change in the hair cells after the injection of ethacrynic acid, although CM is essentially dependent on the dc potential gradient between the scala media and the inside of the hair cells.

Acoustic Stimulation↗
PubMed1987

DC potentials of the lateral wall of the scala media.

We recorded DC potential and resistance changes of the cochlear lateral wall in guinea pigs, using (3M KCl) electrolyte glass microelectrodes. The patterns found for slow penetration showed different potential and resistance characteristics at different segments of the lateral wall. In addition, our findings demonstrate that the monitoring of microelectrode tip resistance is a useful procedure for DC cochlear recordings.

Animals↗
PubMed1987

Light and electron microscopic studies of a case with simultaneous Mondini and Michel deformities of the inner ears.

We performed light and electron microscopic studies on the temporal bones of a patient with genetic aplastic deafness, in which the right ear had a Mondini-type defect and the left ear a Michel-type anomaly. The round window of each ear was absent. The stapedial foot plate of the right ear was depressed at its central part and was covered by thin membrane. The course of the internal auditory meatus of the left ear was deviated ventrally. There was total aplasia of the cochlea in the left ear, while that of the right ear showed only three-quarters of a turn. In this ear, three sites of spherical bulging were found and were believed to represent outer hair cells. Other structures of the normal cochlear duct were not present. The modiolus of the left ear was round and dome-shaped, contained sparse nerve fibers and a primitive spiral ganglion. The saccule, utricle and semicircular canals of each ear were missing, so that a common cavity of the vestibular system was present. Several otoliths could be seen under the surface of the membrane covering the common cavity. No sensory cells or their related tissues could be found in either ear.

Aged↗
PubMed1977

Growth in culture of the peripheral axons of the spiral neurons in response to displacement of the receptors.

Observations were made on the growth of the peripheral axons of the spiral neurons in injured explants of the cochlea of the mouse. Opening of the cochlear duct during explantation usually results in a displacement of the hair cells into the outgrowth zone if the basilar membrane of the excised organ of Corti faces the substrate. Spiral neurons respond with vigorous growth to the stress created by the displacement of their receptors. Two different growth reactions occur in succession: 1) growth by elongation of the synaptically engaged fibre 2) free growth. The response of the neuron to an incipient displacement of the hair cells is an elongation of the fibre while its contacts with the receptors are, at least partly, preserved. Most or all fibres that are connected with the displaced cells elongate. The growth is well organized, limited to the region of the displaced hair cells, and restricted in length by the position of the receptors. It is inferred that tension on the synaptically engaged fibre may be a stimulus for its growth and that the growth ceases when the tension is relieved. Continuous stress eventually leads to a rupture of the fibre. The break usually occurs near or at the terminals, leaving the terminals attached to the hair cells. The proximal end of the fibre--now free--starts to grow. The growth is independent of the receptors, unrestricted in length, uncontrolled in amount, and continues for at least three weeks after explantation. The path of the fibre is tortuous, and collaterals are often emitted. Free growth proceeds at a markedly faster rate than growth by elongation. Maintenance of the synapse and growth of the fibre seem to be mutually dependent events. A peripheral axon of the spiral neuron can sustain in culture a normal innervation pattern, without any obvious signs of abnormal growth, if its connections with the hair cells are undisturbed; it elongates in an organized manner, if these connections come under stress; it responds with an uninhibited growth if the connections are broken.

Animals↗
PubMed1975

Organotypic development of the organ of Corti in culture.

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

Animals↗
PubMed2003

[Computed tomography and magnetic resonance tomography of the normal temporal bone].

The normal anatomy of the temporal bone and the inner ear will be described in detail on high resolution computed tomography (HRCT) and magnetic resonance images. The imaging technique of computer tomography--either single detector or multi detector CT--is normally obtained in an axial plane without the intravenous application of contrast material. The images are reconstructed in a high resolution bone window level setting. The coronal images are reconstructed either if used single detector or multi detector CT. Only in some cases a scan in the coronal plane is directly obtained using a single detector CT. MR imaging of temporal bone is usually performed in a head coil. Axial high resolution 3D-T2-weighted sequences either in fast spin echo technique or gradient echo technique--for example CISS-sequence--are obtained, then an axial high resolution T1-weighted sequence before and after the application of gadopentate dimiglumine is performed. HRCT excellently demonstrates the osseous structures of the temporal bone as well as of the inner ear, while MRI excellently depicts soft tissue structures especially those of the inner ear. Due to the susceptibility artifacts MRI is not very suitable for imaging the external auditory canal or the middle ear or the pneumatic system. In conclusion HRCT is so far excellent to delineate the osseous structures of the temporal bone and inner ear while MRI excellently depicts the soft tissue structures of the inner ear, the internal auditory canal and the cerebellopontine angle. Reissner's membrane, the cochlear duct, and the organ of Corti cannot be visualized even using high-resolution MRI. HRCT and MRI are therefore used as complementary methods for imaging the temporal bone.

Anatomy, Cross-Sectional↗
PubMed2003

Expression of aquaporin 1 and 5 in the developing mouse inner ear and audiovestibular assessment of an Aqp5 null mutant.

To examine the potential roles of aquaporins 1 and 5 (AQP1 and AQP5, respectively) in inner ear development and function, we defined their spatial and temporal expression patterns in the developing mouse inner ear and examined the morphologic and physiologic effects of loss of Aqp5 function. Standard in situ hybridization (ISH) and immunohistochemical (IHC) assays were used for expression studies with routine morphologic, behavioral, and physiologic assessments of hearing and balance in Aqp5 null mutant mice. AQP1 was first detected at embryonic day 10.5 (E10.5) in the otocyst but eventually localized to specific nonsensory portions of the inner ear and connective tissue cells surrounding the membranous labyrinth. AQP5 displayed specific cochlear expression, first detectable at E15.5 in the nonsensory epithelium and later restricted to the lateral wall of the cochlear duct near the spiral prominence. AQP5 expression continued through postnatal periods with a change of expression domain to the stria vascularis between postnatal day 7 (P7) and P14. By in situ hybridization and immunohistochemical techniques, subtle differences between transcript and protein expression patterns were noted for both AQP1 and 5. Although AQP5 is dynamically expressed in the developing mouse inner ear, adult Aqp5 knockout mice show normal hearing when tested and normal inner ear structural development. These results suggest redundant or alternative mechanisms that likely regulate water homeostasis in the developing and mature inner ear.

Aging↗
PubMed1996

Development of the auditory receptors of the rat: a SEM study.

Fetal and postnatal ontogenesis of the rat cochlea, from the 16th gestational day (16DG) until 3 months post partum, were studied using scanning electron microscopy with emphasis on the stereocilia during the earliest stages of development. The epithelium of the cochlear duct in 16DG rat consisted of plygonal cells topped with numerous microvilli and one central kinocilium, which form the so-called Kölliker's organ. Inner hair cells (IHCs) appeared at 18DG in the basal cochlea. They were characterized by tufts of cilia of the same height and with a kinocilium. The first outer hair cells (OHCs) can be seen at 20DG. The earliest stages of ciliary differentiation, at 18DG for IHCs and 20DG for OHCs, were similar on both types of cells and were characterized by the presence of round bundles of cilia arising from the surrounding microvilli. A three-dimensional V-shaped organization for OHCs and the linear arrangement for IHCs appeared by the end of the first postnatal week, accompanied by the disappearance of transient cilia on the modiolar side of the hair cell and the kinocilium on the external side. The apical pole of OHCs reached adult-like morphology before that of IHCs. Various links between stereocilia were detected already at birth. Morphometric analysis showed that auditory cells from the base of the cochlea reached adult size by the end of the first postnatal week while those from the apex increased their size later. A review of the literature including comparative observations across species on the ontogenesis of the stereocilia shows that hair cells of the stato-acoustic system may present the same early ontogenesis.

Animals↗
PubMed1994

Developmental study of the long QT with deafness syndrome in the chick embryo: cochlear pathology.

Developmental abnormalities of the peripheral auditory structures in an experimental animal model of the cardio-auditory (long QT with deafness) syndrome are described. Prolonged QT intervals in the electrocardiogram and deafness were induced in chick embryos by removal of tissue in the region of the right nodose and otic placodes on the first day of incubation. Electrocardiographic recordings, cochlear potential and brainstem auditory evoked responses were recorded in late embryonic life (E17), and used to identify embryos with long QTs and deafness. External and middle ears were evaluated under a dissecting microscope. Inner ears were evaluated in histological sections. Anomalies of the external and middle ears, such as the external auditory meatus, tympanic membrane and stapes, were attributed to disturbance of neural crest development. Anomalies of the inner ear, such as a complete absence of the cochlear duct and auditory nerve, or decreased length of the basilar papilla, were attributed to disturbance of otic placode development. The fact that a small lesion in the region of the nodose and otic placodes during early development in the chick animal model can produce a long QT interval in the electrocardiogram and deafness suggests that abnormal development in this region early in development might be the underlying cause of the human syndrome.

Animals↗
PubMed1981

The origin of centrifugal fibers to the inner ear in Caiman crocodilus. A horseradish peroxidase study.

The origin of acoustic and vestibular efferent fibers was investigated in Caiman crocodilus. After injection of horseradish peroxidase (HRP) into the cochlear duct or into the ampullae of the horizontal and anterior semi-circular canals, cells in the medulla oblongata exhibited retrogradely transported HRP reaction product. Efferent vestibular fibers were found in the medial reticular nucleus, at the level of the oliva superior. There were more labeled neurons ipsilateral to the injection site. Efferent acoustic neurons were found close to or inside the rostroventral division of the oliva superior. They spread out into the medial reticular nucleus bilaterally, More labeled efferent acoustic neurons occurred contralateral to the injection site.

Alligators and Crocodiles↗
PubMed1978

The effects of ethacrynic acid upon the potassium concentration in guinea pig cochlear fluids.

After i.v. injection of 50 mg/kg ethacrynic acid (EA), potassium concentration in the endolymph (Ke+) measured with K+-specific microelectrodes decreases by 10 mM at the most and endocochlear potential falls to negative values. Potassium concentration in the perilymph (Kp+) generally does not change, but sometimes a transient decrease in Kp+ level of about 0.5 mM was observed, presumably due to the electrogenic effect of the time-related decrease of the endocochlear potential. When anoxia is induced approximately 120 min after EA administration Ke+ slowly decreases. The decrease in Ke+ 50 min after the arrest of ventilation is smaller when compared with the Ke+ anoxic decrease without preceding EA administration. The endocochlear potential, which falls to negative values during anoxia after EA administration, does not return to the zero level as in the case when only anoxia is applied. Similarly, during anoxia, which follows EA administration, the perilymphatic Ke+ concentration increases more slowly than in the case when only anoxia is introduced. It is assumed from the results that EA abolishes activity of the positive electrogenic K+ pump and reduces the passive permeability of the walls of the cochlear duct to the potassium ions.

Animals↗
PubMed1980

Voltage-dependent elements are involved in the generation of the cochlear microphonic and the sound-induced resistance changes measured in scala media of the guinea pig.

The injection of d.c. current into scale media alters both the cochlear microphonic (CM) and the acoustically synchronized changing resistance (CR) measured in scala media. Positive current increases the CM and decreases the CR. The effect on the CM is greatest at high sound pressure level (SPL), whereas the effect on CR is greatest at low SPL. Negative current has a similar but opposite effect on both the CM and the CR. The results suggest that a voltage-dependent nonlinear element exists in cochlear hair cells.

Acoustic Stimulation↗
PubMed1980

Stimulation of efferents alters the cochlear microphonic and the sound-induced resistance changes measured in scale media of the guinea pig.

Electrical stimulation of the crossed olivo-cochlear bundle (COCB) increases both the cochlear microphonic and the acoustically synchronized changing resistance (CR) and it causes a decrease in the electrical impedance of scala media of the guinea pig. The similarity between the change in CR due to COCB stimulation and the change in CR due to negative d.c. polarization (Mountain, D.C., Hubbard, A.E. and Geisler, C.D. (1980): Hearing Res. 3, 215-229) suggests that the CR is dependent on the hair cell membrane potential measured with respect to scale tympani.

Acoustic Stimulation↗
PubMed1982

Cochlear microphonic evidence for mechanical propagation of distortion products (f2 - f1) and (2f1 - f2).

The present cochlear microphonic (CM) study was undertaken to help resolve a conflict in the literature regarding cochlear nonlinear properties. The CM studies of Dallos and his coworkers have concluded that "(up to 70-80 dB SPL [re 20 mu Pa]), all orders of distortion components...do not seem to be accompanied by traveling waves of their own" (Dallos, P. (1973): The Auditory Periphery: Biophysics and Physiology. Academic Press, New York). However, studies of spatial distributions of cochlear nerve fiber responses, acoustic distortion products in the ear canal, and related modeling studies of Kim et al. (Kim, D.O. and Molnar, C.E. (1975): in: The Nervous System, Vol. 3: Human Communication and Its Disorders. Editor: D.B. Tower. Raven Press, New York; Kim, D.O., Molnar, C.E. and Matthews, J.W. (1980): J. Acoust. Soc. Am. 67, 1704-1721) have led to conclusions to the contrary. In the present study, CM data were obtained from the second and third turns of the chinchilla cochlea using fluid-filled glass micropipettes in scala media and nichrome wire electrodes in scala vestibuli and scala tympani. We sought responses containing predominant distortion products (f2 - f1) and (2f1 - f2) by fixing a distortion frequency (fD) near the characteristic frequency (CF) of the recording site and varying the stimulus frequencies f1 and f2 and SPLs (with L1 = L2). By subsequently varying the distortion frequency around the CF, e.g., fixing f1 well above the CF and varying f2, we measured the tuning characteristics of the distortion products (f2 - f1) and (2f1 - f2). Tuning characteristics of single-tone responses were measured by applying single-tone stimuli of various frequencies with a constant SPL at the eardrum. We have observed, with SPLs as low as 25 dB, that these distortion products in CM display tuning similar to the single-tone response which is consistent with above neural results. From these tuning similarities, we conclude that our CM data reflect the presence of mechanically propagated distortion products at low SPLs, in agreement with the above studies by Kim et al. Validity of our results is supported by the sensitivity and sharp tuning of our CM data and, in the case of the scala media recordings, by the presence of a normal d.c. endolymphatic potential. Plausible explanations for the opposing conclusions of previous studies of Dallos et al. and the present study are discussed.

Acoustic Stimulation↗
PubMed1982

Comparison of the non-adrenergic action of phentolamine with that of vanadate on cochlear function.

Two drugs, which upon superficial examination appeared to be acting on common processes, have been found upon closer investigation to act by quite different means. Both act primarily at the organ of Corti, causing a pronounced increase of the endocochlear potential and a depression of the cochlear microphonic (CM). These effects are accompanied by the elimination of a negative component of the EP; however, it was found that these three effects are produced by phentolamine in scala media (or, more slowly, in scala tympani) but by vanadate only in scala tympani. This difference in locus of action isd manifested further by different changes of the summating potential (SP): phentolamine has little effect on the magnitude of SP-, while vanadate leads to an elevated SP-. In spite of this difference in the 'zeroth order harmonic', the second harmonic of the CM is depressed by both agents. It is argued that phentolamine may act either by blocking the acoustically-modulated ion channels in the luminal membranes of the hair cells or by inducing a large, non-selective, paracellular conductance in the organ of Corti. The present results, in conjunction with our previous results (Marcus, D.C., DeMott, J.E., Kobayashi, T., Ge, X.-X. and Thalmann, R. (1981): Hearing Res. 5, 231-243), are further interpreted as suggesting that vanadate may initially act by depolarizing the hair cells.

Adrenergic alpha-Antagonists↗
PubMed1982

Two-tone interactions in the cochlear microphonic.

Two-tone interactions are explored for the cochlear microphonic (CM) in the guinea pig. Recordings are made from turns one and three using differential electrodes in the perilymphatic space or pipettes placed in scala media through a fenestra over the stria vascularis. We focus on magnitude changes associated with the introduction of appropriate interference tones and on various types of phase shift concomitant with these magnitude variations that have not received documentation in the literature. Based on extensive parametric data, it is suggested that some features of the gross interference phenomenon may be a consequence of the vectorial summation of outputs from contributing hair cell generators. These spatial effects appear to determine phase behavior and the influence of probe frequency on the frequency of maximal interference. In addition, the apparent interval between out defined best frequency (CF) and the frequency of maximal interference is most likely due to an underestimation of CF resulting from phase cancellation between CM-producing hair cell populations. However, after compensating for these spatial effects, several aspects of the CM interference phenomenon seem to be analogous to two-tone suppression in auditory nerve fibers. A direct one-to-one relationship is not implied since the latter reflect the outputs of inner hair cells while CM interference most likely reflects outer hair cell behavior. As a result, the association between suppression and interference must be sought in the process by which outer hair cell influence inner hair cell transduction.

Acoustic Stimulation↗