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PubMed2005

[Methods for evaluation of perimodiolar ci electrode arrays in human temporal bones].

BACKGROUND: Cochlear implants (CI) are the established treatment for cochlear deafness. Recently, indications for cochlear implantation have been expanded to include severely hearing-impaired patients. The use of bilateral implants seems to provide additional benefit. Moreover, new electrode designs, i. e. perimodiolar electrode arrays, aim at improving benefit for patients. However, in addition to providing functional improvements, modern electrode array development must also address safety aspects, because damage to the cochlear morphology (especially the osseous spiral lamina) may lead to degeneration of residual neuronal structures and bony obliteration or scarring within the cochlear ducts. METHODS: Therefore, insertion trauma of the newly developed electrode arrays in human temporal bones must be evaluated before applied to patients. Several methods for testing electrode location and intracochlear trauma are described. RESULTS: Combining cross-sectional imaging, histological analysis and elements of risk-assessment valid information about trauma and possible consequences for use in patients can be determined, based on our experience in 57 temporal bones. CONCLUSIONS: Following our results, safety studies with prototype electrode arrays should, in addition to radiological examination, always include careful histomorphological evaluation.

Adult↗
PubMed1976

Experimental pathogenesis of hydrops.

1. The best method for inducing hydrops in guinea pigs is obliteration of the endolymphatic duct. 2. The location of hydrops produced in the guinea pig is comparable to that of Menière's disease. 3. The major histopathological finding in the guinea pig is atrophy of sensorineural elements in the apical turns of the cochlea. 4. The vestibular sensory cell population is rarely decreased, though ultrastructural changes are noted. 5. Attempts to prevent or minimize development of hydrops by surgical fistulization of the vestibular endolymphatic walls or by administration of a diuretic drug, ethacrynic acid, failed in the guinea pig. Treatment of Menière's disease by these means is questionable. 6. Electron microscopy of the organ of Corti in cochleas taken from a patient with bilateral Menière's disease revealed that only a small percentage of te sensorineural elements was abnormal at the apical turns. Thus, it is questionable whether these small ultrastructural changes in the organ of Corti are a major cause of severe hearing loss. 7. In Menière's disease biochemical changes in cochlear fluid and/or changes in motion mechanics of the cochlear duct are probably important factors producing the hearing loss. 8. The present ultrastructural study did not resolve the question of the etiology of Menière's disease.

Animals↗
PubMed1992

Characteristics of stria vascularis melanocytes of viable dominant spotting (Wv/Wv) mouse mutants.

The Wv mutation lies in the kinase domain of the proto-oncogene c-kit which is expressed in a variety of cells including neural crest derived melanoblasts. The mutation results in the abnormal migration, proliferation, survival and/or differentiation of melanoblasts. Viable Dominant Spotting (Wv/Wv) mouse mutants have a white coat due to the absence of melanocytes. The majority of these animals have no melanocytes within the stria vascularis and no endocochlear potential (EP). A proportion of homozygous mutants partially escape the effects of the mutation: 47.2% of pinnae and 21% of vestibular regions were pigmented and 10.8% of ears had an EP. All ears with an EP that were available for histology had some pigmentation of the stria. There was no obvious correlation between external and internal spotting in Wv/Wv mice, and asymmetrical pigmentation of the ears was common. Both light and dark intermediate cells (which are derived from melanocytes) were present in the middle and/or basal turns of these cochlear ducts and they appeared to function normally in enabling the stria to produce an EP (although the EP was usually lower than normal). This suggests that the c-kit gene product is needed only during development of the stria, and not for mature melanocyte function because the melanocytes present in the mutant strias were carrying the mutant version of the c-kit gene. Melanocytes were similar in appearance in controls and mutants, except that fewer melanin granules were observed in the strias of Wv/Wv mice. The observations that strial melanocytes with very few melanin granules in Wv/Wv mutants are able to support EP production, together with previous observations that albino animals with strial melanocytes but no melanin have a normal EP, suggest that melanocytes but not melanin are essential for normal strial function.

Animals↗
PubMed1979

[Physiological basis for a cochlear prosthesis (author's transl)].

For the attempt to develop a cochlear prosthesis, which allows some understanding of speech, it seems--at least for the first attempts--to be appropriate to mimic natural conditions as far as possible. The auditory nerve contains about 30,000 afferent fibres. Qualitatively, their behavior is similar but quantitative measures show considerably differences (2.3). Nothing certain can be said at present however about the spiral fibres originating from the outer hair cells. The quantitative differences between single afferents concern tuning, frequency selectivity, thresholds, intensity functions and--of particular interest for electrical stimulation--differences in timing of the activity pattern, brought about by differences in travelling time along the cochlear duct (2.3). The time differences seen in the activity pattern of different fibres are in the order of several ms (2.3.6;2.3.7). Actionpotentials elicited by natural acoustic stimuli show probabilistic behavior, that is they are not strictly determined. It is obvious that with artificial electrical stimulation not every surviving single fibre can be selectively stimulated. An electrode will always stimulate a group of fibres simultaneously. With any conceivable electrical stimulation all fibres in the suprathreshold region of the electrode will be synchronously activated (3.2); a fundamental difference to the natural situation. To estimate the number of channels, necessary to stimulate the auditory nerve with sufficient accuracy to allow speech perception we consider some psychoacoustic data. These have shown that the auditory system possesses the ability to differentiate a great number of different pitches, but on the other hand it is capable of integrating different frequency areas to a so called critical bandwidth. Sound energy falling into one critical bandwidth is integrated to a uniform auditory sensation. If one is to integrate various fibres of the auditory nerve to one channel of stimulation it seems to be adequate to use the critical bandwidth as a measure (3.1). According to this criterion 15 channels would have to be introduced into the speech region of the cochlea. This would allow 1.2 mm of cochlear length for each channel. Perfect electrical separation of the channels is required. Considering the severe distortions in neuronal activity pattern, introduced by electrical stimulation in comparison to the natural conditions it is not clear even whether the number given would be sufficient. On the other hand, current spreading would appear to prohibit any higher electrode density. As far as coding of sound parameters within one channel is concerned it is proposed that full use should be made of frequency analysis according to the place principle. In respect to coding of periodicity and loudness it is proposed to approach natural conditions as far as possible (3.3). Here delay times between the individual channels and a probabilistic character of the stimuli should be introduced to avoid dominance of periodicity pitch...

Action Potentials↗
PubMed2001

A quantitative analysis of the nerve fibers in the VIIIth nerve of Belgian Waterslager canaries with a hereditary sensorineural hearing loss.

The number of auditory nerve fibers was determined for non-Belgian Waterslager canaries (non-BWS) and Belgian Waterslager canaries (BWS) that are affected by a sensorineural high frequency hearing loss and a 30% reduction in the number of auditory hair cells. Counts were obtained from semithin cross sections of the Durcupan-embedded auditory nerve at the level of the internal auditory meatus. In addition, the number of lagenar fibers was determined from cross sections near the apical end of the cochlear duct in order to separate them from the total number of auditory nerve fibers. The mean number of auditory nerve fibers was 6076 in non-BWS and 5363 in BWS canaries, representing a 12% reduction in BWS. This small reduction in the number of auditory nerve fibers, as compared to the larger reduction in hair cell number, might be explained by a predominant loss of abneural hair cells in BWS, since it has been shown for other species that a large proportion of abneural hair cells are devoid of afferent innervation. In addition, we observed that despite the prominent hair cell pathologies documented for BWS canaries, the mean diameter of auditory nerve fibers from non-BWS canaries (2.22+/-0.81 microm) did not differ from those of BWS canaries (2.21+/-0.96 microm).

Animals↗
PubMed2001

Efferent axons in the avian auditory nerve.

The sensory hair cells of the inner ear receive both afferent and efferent innervation. The efferent supply to the auditory organ has evolved in birds and mammals into a separate complex system, with several types of neurons of largely unknown function. In this study, the efferent axons in four different species of birds (chicken, starling, barn owl and emu) were examined anatomically. Total numbers of efferents supplying the cochlear duct (auditory basilar papilla and the vestibular lagenar macula) were determined; separate estimates of the efferents to the lagenar macula only were also derived and subtracted. The numbers for auditory efferents thus varied between 120 (chicken) and 1068 (barn owl). Considering the much larger numbers of hair cells in the basilar papilla, each efferent is predicted to branch extensively. However, pronounced species-specific differences as well as regional differences along the tonotopic gradient of the basilar papilla were documented. Myelinated and unmyelinated axons were found, with mean diameters of about 1 microm and about 0.5 microm, respectively. This suggests two basic populations of efferents, however, they did not appear to be distinguished sharply. Evidence is presented that some efferents lose their myelination at the transition from central oligodendrocyte to peripheral Schwann cell myelin. Finally, a comparison of the four bird species evaluated suggests that the efferent population with smaller, unmyelinated axons is the phylogenetically more primitive one. A new population probably arose in parallel with the evolution and differentiation of the specialized hair-cell type it innervates, the short hair cell.

Acetylcholinesterase↗
PubMed1975

Pathologic features of the inner ear in congenital deafness.

We present the morphologic findings of the temporal bones and brain of a patient with congenital deafness. We discuss these findings in relation to pathologic observations in other reported cases of congenital deafness. Morphologic abnormalities in the patient were mainly in the pars inferior of the membranous labyrinths. The osseous labyrinths were well developed. There was severe dilation of the cochlear duct with herniation of the Reissner membrane, extensive atrophy of the stria vascularis that was associated with calcified thrombi to the strial vessels, encasement of the tectorial membrane in a syncytium, and dyspiastic or regressive degeneration of the organ of Corti. Absence of spiral ganglion cells and their fibers was a prominent feature. The extensive and varied pathologic changes that were present in our patient simultaneously suggest a congenital abnormality in endolymph production and raise the possibility of anomalous development of the labyrinthine vasculature.

Aged↗
PubMed1977

Histopathologic changes in the temporal bone resulting from measles infection.

We report the pathologic changes in the temporal bones of four children who died of bronchoppenumonia secondary to acute measles infection. All suffered from severe necrotizing otitis media characterized by round cell infiltration. In one case, multilobulated giant cells (Warthin-Finkelday) were found in the middle ear. These cells appear to be similar to those found elsewhere within the body during acute measles infection. Inner ear changes were seen in two cases. Severe loss of nerve fibers and ganglion cells with atrophy of the striae vascularis was present in one case. Adhesions were seen between the Reissner membrane and the tectorial membrane in one case and the Reissner membrane and the inner spiral limbus in a second case. Such findings are characteristic of those seen in the cochlear duct of persons suffering from prenatal rubella.

Child, Preschool↗
PubMed1980

Temporal bone histopathologic features in Fanconi's anemia syndrome.

A histopathologic study of the temporal bones from a 7-year-old girl with Fanconi's anemia syndrome demonstrated (1) hemorrhage in the submucosal layer and the cavity of the middle ear and mastoid, massive in the right ear; (2) hypocellularity of the bone marrow; (3) minor but multiple anomalies of the middle ear; and (4) hypodevelopment of the hook portion of the cochlea and reduced overall length of the cochlear duct. The histopathologic features of these temporal bones appears to suggest that congenital anomalies of the inner ear, as well as those of the external and middle ears, would be possible causes of the deafness that accompanies Fanconi's anemia syndrome.

Anemia, Aplastic↗
PubMed1981

Sudden hearing loss associated with cochlear membrane rupture. Two human temporal bone reports.

Cochlear membrane ruptures occurred in the left temporal bones of two patients--one was a result of barotrauma caused by flying and was associated with sudden deafness, tinnitus, and some vertigo and the second occurred in a patient with profound deafness in a previously normal-hearing ear. Both occurred as ruptures of Reissner's membrane at the junction of the ductus reuniens with the cecum vestibulare portion of the cochlear duct. With healing, a balloon-like structure formed from the rupture site into the adjacent vestibule, resulting in a secondarily ruptured saccule duct in one case and in collapse of the saccule in the second case. Left-sided preponderance of such ruptures and the vulnerability of the ductus reuniens junction with the cochlea are described.

Aged↗
PubMed1984

Influence of catecholamines on perilymph Po2.

In a previous study, a special rheological model of intra-arterial perfusion was used to examine the existence and effectiveness of vasomotor control of the cochlear vessels in guinea pigs. Catecholamines were injected intra-arterially into this animal model and the changes induced in the cochlear action potentials were examined. In this investigation, we used the same animal model and technique to measure the perilymph Po2 after perfusion of the cochlea with catecholamines. In addition, the effect of drainage of the CSF before infusion was examined. The results indicated that opening the labyrinth allows the escape of CSF through the patent cochlear duct. This may modify the concentration of the substance under study in the perilymph and cause inaccuracies in the data obtained.

Animals↗
PubMed1987

A histological study of the temporal bones and the nose in Wolf-Hirschhorn syndrome.

We report the histopathological findings of the temporal bones and the nasal and paranasal specimen of a 7-month-old girl diagnosed as having Wolf-Hirschhorn or 4p- syndrome (deletion of the short arm of chromosome 4). This syndrome is characterized by growth retardation, mental retardation, and multiple congenital abnormalities, including craniofacial anomalies and hearing disturbance. These temporal bones displayed malformation of the ossicles, absence of the oval windows, abnormal course of the facial nerve with incomplete bony canal, and depression of the cochlear duct and the saccule. In addition, cholesteatoma, which might be of congenital origin, was present behind the eardrum. The nasal and paranasal specimen showed bilateral complete cleft palate with normal development of paranasal sinuses, nasal septum, and conchae.

Abnormalities, Multiple↗
PubMed1996

Morphology of the monotreme organ of Corti and macula lagena.

The organ of Corti and macula lagena were studied by scanning and transmission electron microscopy in two species of monotreme, the platypus and echidna. In both species, the organ of Corti had a fundamentally mammalian conformation, with distinct outer and inner hair cells, separated by a tunnel of Corti. However, unlike eutherian mammals, the monotremes had three or four rows of pillar cells, and four to five rows of inner hair cells. The organ of Corti was much shorter than in eutherian mammals, at 4.4 mm (platypus), and 7.6 mm (echidna). While the total number of outer hair cells (3,350 platypus, 5,050 echidna) was many fewer than in most eutherian mammals, the total number of inner hair cells (1,600 platypus, 2,700 echidna) was comparable with that in eutherian mammals. The stereocilia on both inner and outer hair cells underwent a systematic change in orientation across the cochlear duct, with those nearest the tunnel of Corti having their axis of symmetry oriented transversely across the duct, and those on the outer edge of the organ having the axis oriented nearly longitudinally along the duct. The macula lagena had signs of a vestibular epithelium, with tall bundles of stereocilia, a division into areas with bundles of opposing orientation and type I and type II hair cells.

Animals↗
PubMed1996

Developmental expression of murine Beta-trace in embryos and adult animals suggests a function in maturation and maintenance of blood-tissue barriers.

The complete cDNA for murine Beta-trace protein was isolated by RT-PCR using degenerate primers designed according to amino acid sequences derived from tryptic peptides. It encodes a protein of 165 amino acids (calculated molecular weight 18,472 Da) with a predicted 24-amino-acid leader peptide. In situ analyses during mouse embryonic development and in adult animals revealed a specific temporal expression pattern of Beta-trace. Beta-Trace mRNA was initially detected at 14.5 days postconception in mesenchymal cells destined to become leptomeninges and in the developing testis. Later in development, a lower level of expression was additionally observed in choroid plexus epithelium, in strictly confined regions of the eye (pigment and ciliary epithelium), in the ear (cochlear duct), and within single cells in the brain. Expression was also found in epithelia of the epididymis and the testis Leydig cells of postpubertal animals. The highly specific expression at blood-tissue barriers such as the blood-cerebrospinal fluid, blood-retina blood-aqueous humor, and blood-testis barriers indicates a potential role for this lipocalin in transport and/or in maturation and maintenance of these barriers.

Amino Acid Sequence↗
PubMed1997

Micro-magnetic resonance imaging of the inner ear in the guinea pig.

We applied a magnetic resonance microscopy at 7.05 T with a gradient coil unit to image the fine structure of the guinea pig cochlea. First, a three-dimensional MR image of the surface of the cochlea was obtained to select the location of cross-sectional images. Then, cross-sectional images of the basal turn, the second turn and the apical turn of the cochlea were obtained. Based upon the different protein concentrations of the endolymph vs the perilymph, the scala vestibuli, scala tympani and the cochlear duct could be clearly distinguished. This allowed a determination of the location of both the basilar membrane and Reissner's membrane. We raise the possibility that MRM may become useful in the diagnosis of endolymphatic hydrops (Meniere's disease).

Animals↗
PubMed1982

DNA content, mitotic activity, and incorporation of tritiated thymidine in the developing inner ear of the rat.

The rat inner ear is ectodermally derived from a region adjacent to the developing hindbrain. Beginning on day 8 of a 22-day gestational period, This zone of ectoderm first forms the otic placode, then the otocyst, and ultimately the definitive membranous labyrinth. This report provides an estimation of total DNA content of the developing inner ear, and hence an estimation of the total number of cells that comprise the inner ear at each developmental stage. The incorporation of 3H-thymidine indicates that most cells of the inner ear undergo DNA synthetic activity during gestational days 13 to 15. Radioautographic observations indicate a zone of DNA synthetic activity at the base of the outpocketing cochlear duct during early development. At the later stages of development, DNA synthesis is restricted to the cristae ampullares of the semicircular canals and the maculae of the utricle and the saccule. In contradistinction to the findings of other investigators, the statoacoustic ganglion complex undergoes terminal mitosis during gestational days 17 and 18. The gestational period between days 13 and 15 may prove to be a critical stage in normal otic development. The normal values of total DNA content and the number of cells that comprise the inner ear during development, established by these methods, can be compared with pathologic inner ears to provide quantitative means of assessing the damage in malformed inner ears. These values also form the baseline for future experimental studies of inner ear development.

Animals↗
PubMed1994

Ultrastructure of melanocytes in the dark cell area of human vestibular organs: functional implications of gap junctions, isolated cilia, and annulate lamellae.

BACKGROUND: It is known that melanocytes exist in almost all parts of the inner ear, such as the cochlear duct, stria vascularis, Reissner's membrane, modiolus, vestibular organs in the region surrounding the cristae and maculae, semicircular canals, and pars rugosa of the endolymphatic sac. But there have been few studies using human materials, because of the difficulty of obtaining materials. We attempted to investigate the detailed ultrastructure of melanocytes in the vestibular organs of human inner ear. METHODS: Eight surgical specimens obtained from patients with vestibular schwannoma were studied by light microscopy and electron microscopy. RESULTS: Melanocytes were found in the subepithelial layer of the dark cell area. Melanocytes had round or spindle-shaped nuclei and clear cytoplasm with brown pigment granules. Besides melanocytes, there were melanophages, fibroblasts, and small blood vessels. Through electron microscopy we found melanocytes with round-shaped melanosomes in various stages of pigmentation, well-developed Golgi apparatus and endoplasmic reticulum in the cytoplasm, and many cytoplasmic processes. Gap junctions were occasionally found between the cytoplasmic processes. And there were pinocytotic vesicles just under the limiting membrane of melanocytes, and intermediate filaments were abundant in the cytoplasm. Isolated cilia of melanocytes, annulate lamellae, and fusiform banded structures in the connective tissue area around melanocytes were found. CONCLUSIONS: Melanocytes in human vestibular organs actively synthesize melanosomes. Frequent findings of isolated cilia and fusiform banded structures and the incidental existence of annulate lamellae may be an indicator of this metabolically activated state of melanocytes. Moreover, monitoring environmental changes by isolated cilia, melanocytes in the human inner ear could act not only as one cell but also as a group to achieve their physiological functions by means of information transmission through gap junctions.

Adult↗
PubMed1980

The cochlear nuclei of snakes.

The cochlear nuclei of three burrowing snakes (Xenopeltis unicolor, Cylindrophis rufus, and Eryx johni) and three non-burrowing snakes (Epicrates cenchris, Natrix sipedon, and Pituophis catenifer) were studied. The posterior branch of the statoacoustic nerve and its posterior ganglion were destroyed and the degenerated nerve fibers and terminals traced to primary cochlear nuclei in 13 specimens of Pituophis catenifer. All these snake species possess three primary and one secondary cochlear nuclei. The primary cochlear nuclei consist of a small nucleus angularis located at the cerebello-medullary junction and a fairly large nucleus magnocellularis forming a dorsal cap over the cephalic end of the alar eminence. Nucleus magnocellularis may be subdivided into a medially placed group of rounder cells, nucleus magnocellularis medialis, and a laterally placed group of more ovate and paler-staining cells, nucleus magnocellularis lateralis. A small but well-defined secondary nucleus which showed no degenerated nerve terminals after nerve root section, nucleus laminaris, underlies the cephalic part of both nucleus magnocellularis medialis and nucleus magnocellularis lateralis. Larger and better-developed cochlear nuclei were found in burrowing species than in non-burrowing species of snakes. Of the three burrowing species studied, Xenopeltis showed the greatest development of cochlear nuclei; Eryx cochlear nuclei were not quite as large but were better differentiated than in Xenopeltis; and Cylindrophis cochlear nuclei were fairly large but not as well developed nor as well differentiated as in either Xenopeltis or Eryx. The cochlear nuclei of the three non-burrowing snakes, Epicrates, Natrix, and Pituophis, were not as large nor as well developed as those of the burrowing snakes. There is some, but not complete, correlation between cochlear development and papilla basilaris length and number of hair cells. Thus, Xenopeltis and Eryx, with well-developed cochlear nuclei, have relatively long papillae basilares; but the boid, Epicrates, with less well-developed cochlear nuclei, has a fairly well-developed papilla basilaris. Cylindrophis, a burrowing species, shows only a moderate degree of cochear nuclei and papilla basilaris development. The non-burrowers, Natrix and Pituophis, have both small cochlear nuclei and relatively short papillae basilares.

Animals↗