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PubMed1992

Rapid growth of astrocytic processes in N. magnocellularis following cochlea removal.

Removal of the cochlea or pharmacological blockade of eighth nerve activity in young postnatal chickens results in rapid transneuronal cell death and atrophy in neurons of n. magnocellularis. The present experiments were designed to examine the influence of afferent input on astrocyte structure in n. magnocellularis. Young chickens were subjected to unilateral cochlea removal. At times ranging from 5 minutes to 72 hours later, the brainstems were histologically processed with a polyclonal antibody against glial fibrillary acidic protein (GFAP). A second group of chick brainstems was impregnated by a Golgi method 6 hours after unilateral cochlea removal and impregnated three-dimensional reconstructions were made of glial cells in n. magnocellularis (NM). Analyses of GFAP positive processes in NM revealed an observable increase in the number of astrocytic processes at the borders of the nucleus within 30 minutes of cochlea removal and a twofold increase in GFAP + glial processes by 6 hours. A secondary increase in the number and density of GFAP + processes occurred between 24 and 72 hours following cochlea removal, during the period of axonal degeneration, and transneuronal cell atrophy and death. Analyses of astrocytes impregnated by the Golgi method revealed that individual glial cells had increased their total process length and the number of processes by approximately twofold by 6 hours after cochlea removal. These results suggest that the structure of astrocytes is rapidly and dramatically influenced by the level of excitatory activity in a neuronal system. Furthermore, the similarity of results obtained with GFAP immunohistochemistry and three-dimensional reconstruction of astrocytes provides evidence that the short-term changes observed following cochlea removal represent the actual growth of glial processes. We speculate that modulations in glial processes as a function of afferent activity may act to influence synaptic efficacy.

Afferent Pathways↗

PubMed1994

Postnatal development of the hamster cochlea. I. Growth of hair cells and the organ of Corti.

A morphometric analysis of the developing organ of Corti and its component hair cells was carried out in an age-graded series of Syrian golden hamsters with the aid of scanning electron microscopy. The purpose was to establish a quantitative framework that would provide insight into the rules and principles by which the mammalian cochlea attains its adult proportions. This study examined postnatal development at two day intervals from birth to 22 days after birth. Our analysis included measures of cochlear length and hair cell numbers as well as measures of hair cell sizes in each of five sectors along the cochlear spiral. Our results demonstrate several principles of cochlear development: 1) The full two and one-fourths turns seen in the adult cochlea are already present at birth, but the cochlea continues to elongate for the next 10-12 days. 2) Development of hair cells in the apex generally lags behind that in the base. Whereas the stereocilia and apical margins of hair cells are clearly defined in the basal turn, they become well defined in the apex only postnatally. 3) Growth in cochlear length occurs mainly by increases in cell size rather than in cell numbers; although hair cells do increase in numbers during the first 4 days of cochlear growth, this increase involves addition of hair cells only to preexisting regions of the cochlear apex. Moreover, the full complement of hair cells is established 6 days before the full size of the cochlea is attained; in contrast, hair cell growth occurs at all positions along the cochlear spiral and spans the entire period of cochlear elongation. 4) The period of hair cell growth exceeds the period of organ of Corti growth and appears to be possible by decreases in intercellular spacing, primarily in the apical region of the cochlea; inner and outer hair cell growth was complete between 16 and 18 days after birth. 5) Inner and outer hair cell neighbors remain virtually constant at different ages indicating that the spatial relationships between the two hair cell populations is preserved as the cochlea grows. 6) Comparison with previous developmental studies of auditory function in the hamster reveals that the age of 16 days after birth, when hair cells attain their mature sizes, coincides with the onset of brainstem auditory evoked responses. Growth of hair cell somas alone, however, cannot explain either the subsequent maturation of evoked potential thresholds or changes in frequency representation in the developing cochlea.

Animals↗

PubMed2003

Topographic relationship between the cochlea and the middle fossa floor: the anatomical basis for an alternative approach to the cochlear turns.

The cochlea has attained extreme surgical interest since cochlear implantation has been recognized as an established method for the management of certain types of bilateral profound hearing loss. Traditionally access to the cochlear turns is achieved through the middle ear. Extremely limited references exist in the literature regarding alternative surgical approaches to the cochlea. In the present study we tried to highlight the anatomic relationships of the superior aspect of the bony cochlea to the adjacent superficial structures of the petrous bone, as there have been suggestions that the cochlea is surgically accessible through the floor of the middle cranial fossa (MCF). A total of 58 dry human adult skulls (116 temporal bones) were studied. The groove for the greater superficial petrosal nerve (GGSPN) and the facial hiatus were used as landmarks in order to expose the superior aspect of the cochlea. Measurements were made of the following distances: a) between the MCF floor and the superficial part of the basal turn (SPBT), b) between the MCF floor and the apex of the cochlea, c) between the SPBT and the GGSPN and d) between the SPBT medially and the first genu of the facial canal laterally. Our results indicate that adequate and reliable surgical access to the bony cochlea could be achieved through the MCF floor.

Cadaver↗

PubMed1986

Actin filaments, stereocilia, and hair cells of the bird cochlea. III. The development and differentiation of hair cells and stereocilia.

The cochleae of chick embryos of 8 days of incubation until hatching (21 days) were examined by scanning electron microscopy. Unlike what one would expect from the literature, the total number of hair cells per cochlea (10,405 +/- 529) is already determined and visible in a 10-day embryo and the growth of the cochlea is a result of the growth in size and surface area of the hair cells. We also find that the hair cells differentiate simultaneously throughout the cochlea and have followed the differentiation of individual hair cells throughout development. During development we find that the total number, hexagonal packing, and orientation of the stereocilia in each hair cell is determined early and accurately (9- to 10-day embryos). The stereocilia then begin to elongate in all the cells of the cochlea at approximately 0.5 micron/day. By Day 12 the tallest stereocilia in each cell are 1.5-1.8 micron long, the mature length for cells at the proximal end of the cochlea. At this point all stereocilia cease elongating, but those along the inferior edge gradually increase in width from 0.11 micron to maximally 0.19 micron in 17-day embryos. When the stereocilia on the inferior edge reach their mature width, widening ceases and the elongation of stereocilia in the distal hair cells begins again. When these stereocilia have attained their mature lengths, they stop growing. Thus elongation and widening of stereocilia are separated in time. During this period, 11 to 13 days, the shape of the tufts at the proximal end of the cochlea changes. This occurs because stereocilia in the front of each tuft are absorbed while others at the sides appear de novo. This rearrangement converts a circular bundle of stereocilia to a rectangular bundle.

Actins↗

PubMed1991

Effects of opening and resealing the cochlea on the mechanical response in the isolated temporal bone preparation.

The isolated temporal bone preparation has been used previously for studying the micromechanical behaviour of the cochlea. Mechanical tuning curves have been obtained from several cells and structures within the hearing organ. In order to obtain access to the apical turns the bony shell of the cochlea has to be opened. To study how the opening affects the mechanical response of the cochlea, experiments were performed in which the cochlea was opened and then sealed with a glass window. Responses were measured from the same identified cells in the opened and in the sealed cochlea. The opening of the cochlea reduced the vibration amplitude mainly at frequencies below 300 Hz. Below the mechanical resonance frequency the slope of the tuning curve became steeper. The shape was not affected appreciably above the resonance frequency. The relative vibration amplitude of different cells remained unchanged by opening and closing the cochlea.

Acoustic Stimulation↗

PubMed1990

Immunocytochemical detection of calcitonin gene-related peptide in the postnatal developing rat cochlea.

Using the immunofluorescence technique, three populations of fibers staining for calcitonin gene-related peptide are identified in postnatal developing cochleas and in adult rat cochleas. During the maturation of the cochlea, the immunostaining first appears in the basal turn and then extends toward the apex of the cochlea. The first population of immunostained fibers belongs to the lateral olivocochlear innervation. It is observed at postnatal day 4 within the inner spiral bundle of the organ of Corti. The second population of calcitonin gene-related peptide-like immunostained fibers belongs to the medial olivocochlear innervation. It is first identified at postnatal day 6 under the outer hair cells, generally in the first row. In the older stages, this population of fibers progressively extends toward the external row of outer hair cells. Finally, the third population of immunostained fibers belongs to the sympathetic supply of the cochlea. They can be identified at postnatal day 6 around the cochlear artery and its branches, and also within the entire modiolus. Our results confirm the presence of calcitonin gene-related peptide in fibers of the lateral and medial efferent innervations of the cochlea. They indicate an early appearance of calcitonin gene-related peptide in the developing cochlea, before the onset of the cochlear function, suggesting for this peptide either a neurotrophic function or a regulation of the early cochlear potentials at the level of the lateral efferent synapses.

Aging↗

PubMed2005

Role of cochlear integrity in cochlear nucleus glucose metabolism and neuron number after cochlea removal in aging broiler chickens.

In the chicken auditory system, cochlear nucleus (nucleus magnocellularis, NM) neurons receive their only excitatory input from the ipsilateral cochlea. Cochlea removal (CR) results in an immediate decrease in NM neuron electrical activity, followed by death of approximately 30% of NM neurons. Previous work showed a decrease in NM activity and subsequent loss of NM neurons in all chicks. Egg layer adults showed NM neuron loss after CR, while neuron number remained stable in broiler adults. This suggested that effects of CR on NM were age- and breed-dependent. We now know that most aging egg layer chickens maintain largely normal cochleae throughout adulthood. Some exhibit cochlear damage with age. The converse is true of broiler chickens. Most aging broiler chickens display cochlear degeneration, with some maintaining normal cochlear anatomy throughout adulthood. The presence of extensive cochlear damage may alter the effect of CR on NM, leading to the described differences. Here, we examine the effect of unilateral CR on NM glucose metabolism and neuron number in 2, 30, 39, and 52 week-old broiler chickens found to have normal cochleae. Chickens with damaged cochleae were excluded. Using 2-deoxyglucose uptake to evaluate bilateral NM glucose metabolism, we found significantly decreased uptake ipsilateral to CR at each age examined. Bilateral cell counts revealed significant neuron loss ipsilateral to CR at each age examined. This suggests that NM glucose metabolism decreases and subsequent neuron death occurs in aging broiler chickens when a normal cochlea is removed. The status of the cochlea must play a role in the effect of deafferentation on NM glucose metabolism and neuron survival. The effect of CR appears to be dependent upon neither age nor breed, but upon cochlear integrity instead.

Aging↗

PubMed2001

Immunolocalization of the calcium binding S100A1, S100A5 and S100A6 proteins in the dog cochlea during postnatal development.

The immunolocalization of three members of the S100 calcium-binding protein family was investigated in the dog cochlea during normal postnatal development. Sections of decalcified and paraffin-embedded cochleae from 16 beagle puppies aged from birth to 3 months were treated with polyclonal antisera raised against the human recombinant S100A1, S100A5, and S100A6 proteins. At birth, in the dog cochlea, S100A1 was expressed in the immature Deiter's cells, and slightly in the pillar cells. From the second week, S100A1 was detected in the supporting structures of the organ of Corti, i.e. the Deiter's, the pillar, the border, and the Hensen's cells, and in the reticular membrane. From birth onwards, S100A5 remained a neuronal-specific protein, only located in a subpopulation of neurons in the spiral ganglion. S100A6 was not expressed at birth. From the second week of life, the Schwann cells and nerve sheaths in the modiolus, in the spiral ganglion, and running in the direction of the organ of Corti exhibited S100A6-labeling. From the 12th postnatal day, some scattered intermediate cells started to express S100A6 protein in the stria vascularis. The number of labeled intermediate cells increased during the third week. At adult stage, the intermediate cells were S100A6-stained with cytoplasmic labeling throughout the stria vascularis from the base to the apex of the cochlea. None of the other cochlear structures expressed the S100 proteins under study during the postnatal development of the dog cochlea. The S100A1, S100A5, S100A6 immunostaining was limited to specific cell types in dog cochlea. These S100 proteins were useful markers in the study of supporting cells, neurons, nerve fibers sheaths and stria vascularis (S100A6) during the normal postnatal development of the dog cochlea.

Animals↗

PubMed1998

Expression of mRNA encoding vasopressin V1a, vasopressin V2, and ANP-B receptors in the rat cochlea.

The expression of mRNAs encoding vasopressin V1a, V2, and ANP-B receptors in the rat cochlea was examined by PCR and in situ hybridization. After reverse-transcription of rat cochlear RNA, cDNA was amplified by PCR using pairs of primers specific to these receptors. After subcloning of the PCR products, clones with sequences identical to those cloned previously from the rat liver (V1a receptor), kidney (V2 receptor) and brain (ANP-B receptor) were obtained. The localization of expression of those receptors in the developing and adult rat cochlea was examined by in situ hybridization using 35S-labeled cRNA probes. The V1a and V2 receptors were expressed throughout the whole of the neonatal rat cochlea, while no expression was detected in the adult cochlea. The ANP-B receptor was expressed throughout the whole of the neonatal cochlea. In the adult cochlea, expression was observed in the spiral ganglion and the spiral ligament. These results suggest that vasopressin may play a role in the development of the cochlea, and that natriuretic peptide may play a role in the function of the spiral ganglion and the spiral ligament.

Aging↗

PubMed2001

Three-dimensional spiraling finite element model of the electrically stimulated cochlea.

OBJECTIVE: The objective of the article is to provide an accurate model of the human cochlea with which potential distributions and thus neural excitation patterns around cochlear implant electrodes can be determined. Improvements on previous models of the implanted cochlea are that this model 1) includes the spiral nature of the cochlea as well as many other anatomical details (and it is a model of the human cochlear rather than the guinea pig cochlea), and 2) facilitates modeling of different electrode geometries, array locations and electrode separations without changing the structure of the model. DESIGN: A three-dimensional spiraling finite element model of the human cochlea was created. The model incorporates the effect of neighboring canals and conduction along the fluid-filled canals of the cochlea. Potential distributions are used as inputs to a nerve fiber model to investigate auditory nerve excitation patterns around intracochlear electrode arrays. RESULTS: Potential distributions around intracochlear electrodes generated with the finite element model are presented. The effects of electrode separation, electrode geometry and array location on excitation threshold, excitation spread and ectopic excitation (i.e., excitation of nerve fibers at an undesirable location) are demonstrated. CONCLUSIONS: The following conclusions should be considered preliminary, as their accuracy depends on the exactness of the underlying model. The spiraling geometry of the cochlea causes asymmetry in potential distributions. The location of electrodes along the length of the basilar membrane has a stronger influence on the site of excitation than the polarity of the leading phase of the stimulus. Array location is the primary parameter that controls excitation spread. Threshold currents and the effect of ongoing loss of peripheral dendrites on threshold currents can be limited by placing arrays close to the modiolus. Point electrode geometries are recommended above banded electrode geometries only when the array can be placed close to the modiolus. There is a tradeoff between array location and the degree of ectopic stimulation caused by a specific array location. Bimodal excitation patterns exist at comfortable stimulus intensities for longitudinal bipolar electrode configurations. It is shown that an electrode configuration with an electrode separation of approximately half that of the bipolar electrode separation of the Nucleus electrode can be used instead of radial and offset radial electrode configurations to create unimodal excitation patterns. The stimulation resolution of cochlear implant electrode arrays can potentially be improved by increasing the number of electrode contacts in an array.

Cochlea↗

PubMed2001

The expression of apoptosis-related proteins in the aged cochlea of Mongolian gerbils.

OBJECTIVE: Apoptotic changes have been reported in the aged gerbil cochlea and are speculated to be one of the principal causes of presbyacusis. The objective of the study was to determine the underlying mechanism of apoptotic change in the aged gerbil cochlea. STUDY DESIGN: Prospective controlled animal study. METHODS: We examined the tissue distribution of bcl-2, bax, caspase-3p20, and caspase-3p32 using immunohistochemical techniques in the young and aged gerbil cochlea, together with the measurement of the distortion product of otoacoustic emission (DPOAE). RESULTS: Aged gerbils showed a significant reduction of the DPOAE amplitude as compared with that of the young gerbils, suggesting a disturbance of the auditory function in the aged cochlea. There was a significant decrease in the number of bcl-2-positive cells in the aged gerbils. The expression of bax in the aged group was slightly increased but did not significantly differ from that in the young gerbils. A significantly increased number of caspase-3p20-positive cells was observed in the organ of Corti, spiral ganglion, and lateral wall of cochlea in the aged gerbils as compared with those of the young gerbils. There was no significant difference in the expression levels of caspase-3p32 between the young and aged groups. In the aged cochlea, the degree of deterioration of DPOAE responses was compatible with those of both the reduction of bcl-2 and the activation of caspase-3p20. CONCLUSION: These data suggest that the suppression of bcl-2 protein expression may lead to apoptosis-induced presbyacusis through activation of caspase-3 in the aged gerbil cochlea.

Age Factors↗

PubMed2004

Immunohistochemical localization of histamine receptors in rat cochlea.

OBJECTIVE: Histamine may have physiologic functions in the inner ear. The locations of histamine receptors, however, have not yet been identified in the mammalian cochlea. The aim of this study was to investigate the localization of histamine receptor subtypes (H1, H2, and H3 receptors) in rat cochlea. METHODS: Immunohistochemistry was performed with antibodies specific for each of the histamine receptors (H1, H2, and H3). To identify the type I and II spiral ganglion cells in the cochlea, some cryostat sections were double stained with antibodies to both a histamine receptor and neurofilament 200 kD, which predominantly stains type II spiral ganglion cells in the cochlea. RESULTS: All H1, H2, and H3 receptor immunoreactive staining was limited to the spiral ganglion cells of the cochlea. Spiral ganglion cells with positive immunoreactivity to the neurofilament 200 kD antibody were stained only slightly by histamine H1, H2, and H3 receptor antibodies, indicating that histamine receptor immunoreactivity is specific to type I ganglion cells. CONCLUSIONS: These findings indicate that histamine receptors are present in the cochlea and support the hypothesis that histamine plays a physiologic role in the cochlea.

Animals↗

PubMed1989

CT-scanning of the cochlea in Pendred's syndrome.

The inner ears of 5 adult patients with Pendred's syndrome were investigated using a Siemens SOMATOM DRG. Five normal hearing adults participated in the investigation as a control group. The CT-scanning comprised 10-15 consecutive scans of the cochlea. The CT evaluation was performed using both a special bone setting and a soft tissue setting. The cochlear content was quantitatively evaluated by drawing an irregular region of interest on the bone pictures. The region of interest was then transferred to the soft tissue pictures by means of the standard program of the CT-scanner. The resulting mean values of attenuation expressed in Hounsfield Units were significantly lower in the Pendred cochleas than in the normal cochleas. At the same time a typical Mondini malformed cochlea was demonstrated in all patients with Pendred's syndrome. The lower values of attenuation of the cochlea in Pendred's syndrome reflect the rudimentarily developed infra-cochlear osseous structures in this disease. We conclude that CT-scanning of the cochlea using this procedure is reliable enough to replace the conventional axial-pyramidal tomography when a Mondini cochlea is suspected.

Adult↗

PubMed2003

Lack of Bdnf and TrkB signalling in the postnatal cochlea leads to a spatial reshaping of innervation along the tonotopic axis and hearing loss.

Members of the neurotrophin gene family and their high-affinity Trk receptors control innervation of the cochlea during embryonic development. Lack of neurotrophin signalling in the cochlea has been well documented for early postnatal animals, resulting in a loss of cochlear sensory neurones and a region-specific reduction of target innervation along the tonotopic axis. However, how reduced neurotrophin signalling affects the innervation of the mature cochlea is currently unknown. Here, we have analysed the consequences of a lack of the TrkB receptor and its ligand, the neurotrophin brain-derived neurotrophic factor (Bdnf), in the late postnatal or adult cochlea using mouse mutants. During early postnatal development, mutant animals show a lack of afferent innervation of outer hair cells in the apical part of the cochlea, whereas nerve fibres in the basal part are maintained. Strikingly, this phenotype is reversed during subsequent maturation of the cochlea, which results in a normal pattern of outer hair cell innervation in the apex and loss of nerve fibres at the base in adult mutants. Measurements of auditory brain stem responses of these mice revealed a significant hearing loss. The observed innervation patterns correlate with opposing gradients of Bdnf and Nt3 expression in cochlear neurones along the tonotopic axis. Thus, the reshaping of innervation may be controlled by autocrine signalling between neurotrophins and their receptors in cochlear neurones. Our results indicate a substantial potential for re-innervation processes in the mature cochlea, which may also be of relevance for treatment of hearing loss in humans.

Animals↗

PubMed2002

Comparative immunohistochemical localizations of aquaporin-1 and aquaporin-4 in the cochleae of three different species of rodents.

The species-specific difference of the immunohistochemical localization of aquaporin-1 (AQP1) and aquaporin-4 (AQP4) was investigated in the cochleae of the 3 different species of rodents, including guinea pig, mouse and Mongolian gerbil. In the guinea pig cochlea, intense AQP1-like immunoreactivity was present in the type III fibrocytes in the spiral ligament and the mesenchymal cells just below the basilar membrane. Immunostaining was also found in some type IV fibrocytes in the spiral ligament, fibrocytes in the spiral limbus and mesenchymal cells lining the perilymphatic space against the bony otic capsule. In contrast, no remarkable immunostaining was found in the basilar membrane of the mouse cochlea. The medial part of the Reissner's membrane was positively immunostained with anti-AQP1 antibody only in the mouse cochlea. In the gerbil cochlea, AQP1-like immunoreactivity was weak compared with the other 2 species. AQP4 was found in the cochlear supporting cells, including Claudius cells, Hensen's cells and inner sulcus cells of the 3 rodent species. AQP4 was also expressed in some interdental cells of the spiral limbus. Weak immunoreactivity was also found in the root cells only in the upper turns of the guinea pig cochlea. In contrast, no detectable immunoreactivity was found in the root cells of the other 2 species. The results obtained in the present study provide the first evidence for the existence of the species differences in the expression of the AQP1 and AQP4 proteins in the rodent cochlea.

Animals↗

PubMed1999

Speech recognition after implantation of the ossified cochlea.

OBJECTIVE: Insertion of complex, multichannel cochlear implant (CI) electrode arrays into ossified cochleas is now performed routinely. This study describes the hearing results obtained in a consecutive series of 21 patients with obstructed cochleas and compares these results to those in patients with open cochleas. The purpose of this study was to determine whether patients with ossification have speech perception results that are inferior to those of patients with no evidence of cochlear bone formation. STUDY DESIGN: Retrospective analysis of consecutive clinical series. METHODS: CI database review of 191 CI procedures at the University of Miami Ear Institute between 1990 and 1997 showed that 24 (13%) procedures were performed on patients with ossified cochleas. Open-set speech recognition scores obtained on the 11 pediatric and 7 adult English-speaking patients are compared to scores of 51 adult and 61 pediatric English-speaking CI patients with open scala. RESULTS: Results of open-set speech recognition measures in adults and children with ossified cochleas were not significantly different from those of the reference groups. CONCLUSION: Speech recognition results of patients with ossified cochleas are essentially equal to those of patients with open cochleas. Degree of obstruction appears to have less effect on outcome than other factors such as duration of profound deafness or communication methodology in children among this group.

Adolescent↗

PubMed2002

[Lipopolysaccharide enhances DNA binding activity of nuclear factor-kappa B in the mouse cochlea].

OBJECTIVE: To ascertain whether inoculation of lipopolysaccharide (LPS) into the mouse cochlea might induce enhancement of DNA binding activity of NK-kappa B and to establish a positive model of NF-kappa B activation in the cochlea. METHODS: Two groups of CBA mice were transtympanically injected either with 10 micrograms of LPS or an equal volume of saline. The nuclear proteins of the cochlea were extracted, quantitated and bound with 32P-radiolabeled oligonucleotide probe for NF-kappa B. The bound and free probes were separated by electrophoresis on a 4.5% native polyacrylamide gel. Supershift assays were carried out using the antibodies against NF-kappa B subunit P65 and P50. RESULTS: The radiolabeled probe bound differently to nuclear extracts from the LPS-treated and the saline-treated mouse cochleae, showing that LPS inoculation significantly increased NF-kappa B binding activity. Supershift analysis demonstrated that the enhancement of DNA binding activity was related to both P65 and P50 subunits. CONCLUSION: LPS could induce NF-kappa B activation in the cochlea. Moreover, this study implies that tissues from LPS-inoculated cochlea might serve as a useful positive control in the study on activation of NF-kappa B in cochlea.

Animals↗

PubMed1994

Cell division in the gerbil cochlea after acoustic trauma.

The recent discovery of hair cell regeneration in the avian inner ear raises the possibility that hair cell regeneration might occur in the mammalian cochlea as well. The authors used 3H-thymidine labeling to detect mitotic activity in the cochleas of normal 3-week old gerbils exposed to acoustic trauma. Following an acoustic insult that caused progressively more severe damage in an apical to basal progression, 3H-thymidine was injected for 5 days. Control animals were not exposed to the acoustic insult. The gerbils' cochleas were sectioned and processed for autoradiography. In the control cochleas, there were extremely rare labeled cells in the stria, the spiral ligament, and the glial cells around the acoustic nerve fibers. In the damaged cochleas, no evidence of hair cell regeneration or of any cell division within the normal sensory epithelial structures was seen. Three labeled cells were seen in intercellular spaces within the sensory epithelium; they appeared to be macrophages. Frequent cell division was seen in numerous other regions of the damaged cochleas and among glial cells adjacent to the acoustic nerve fibers. It is concluded that there is no evidence for hair cell regeneration following acoustic trauma in the gerbil, but acoustic trauma does induce cell division in numerous other areas of the cochlea.

Animals↗