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1.
Through thin-section and freeze-fracture electron microscopy, we identify structural correlates of an intense vesicular traffic in a narrow band of cytoplasm around the cuticular plate of the bullfrog vestibular hair cells. Myriads of coated and uncoated vesicles associated with longitudinally oriented microtubules populate the narrow cytoplasmic region between the cuticular plate and the actin network of the apical junctional belt. If microtubules in the sensory hair cells, like those in axons, are pathways for organelle transport, then the characteristic distribution of microtubules around the cuticular plate represents transport pathways across the apical region of the hair cells. This compartmentalized membrane traffic system appears to support an intense vesicular release and uptake along a band of apical plasma membrane near the cell border. Functions of this transport system may include membrane recycling as well as exocytotic and endocytotic exchange between the hair cell cytoplasm and the endolymphatic compartment.  相似文献   

2.
Laser scanning confocal microscope (LSCM) enables one to observe both the surface structure and the inner configuration in the same specimen, by its possibility of direct, non-invasive serial optical sectioning of whole mounted specimens. The potential value of LSCM in the field of inner ear morphological study was evaluated. The configuration of upper parts of organ of Corti was observed with the LSCM combined with double-stained fluorescence immunohistochemistry technique. The actin filament of hair cells by phalloidin, and the cytokeratin of supporting cells by monoclonal pan-anticytokeratin antibody. The stereocilia, cuticular plate, and the cuticle-free area of hair cells were well demonstrated. In the same specimen, the head plate of outer pillar cell, the phalangeal apical plate and the phalangeal process of Deiter cells were clearly showed as well. LSCM provide a new tool to the morphological study of organ of Corti.  相似文献   

3.
Recent studies suggest that macrophages may influence early stages of the process of hair cell regeneration in lateral line neuromasts; numbers of macrophages were observed to increase prior to increases in hair cell progenitor proliferation, and macrophages have the potential to secrete mitogenic growth factors. We examined whether increases in the number of leukocytes present in the in vivo avian inner ear precede the proliferation of hair cell precursors following aminoglycoside insult. Bromodeoxyuridine (BrdU) immunohistochemistry was used to identify proliferating cells in chicken auditory and vestibular sensory receptor epithelia. LT40, an antibody to the avian homologue of common leukocyte antigen CD45, was used to label leukocytes within the receptor epithelia. Macrophages and, surprisingly, microglia-like cells are present in normal auditory and vestibular sensory epithelia. After hair cell loss caused by treatment with aminoglycosides, numbers of macrophage and microglia-like cells increase in the sensory epithelium. The increase in macrophage and microglia-like cell numbers precedes a significant increase in sensory epithelial cell proliferation. The results suggest that macrophage and microglia-like cells may play a role in releasing early signals for cell cycle progression in damaged inner ear sensory epithelium.  相似文献   

4.
Spectrin is a cytoskeletal protein found in the cortex of many cell types. It is known to occur in cochlear outer hair cells (OHCs) with previous immunoelectron microscopical studies showing that it is located in the cuticular plate and the cortical lattice. The latter is a network of filaments associated with the lateral plasma membrane that is thought to play a role in OHC motility. Spectrin has also been found in inner hair cells (IHCs) and supporting cells using immunofluorescent techniques, but its ultrastructural distribution in these cells has not yet been described. This has, therefore, been investigated using a monoclonal antibody to alpha-spectrin in conjunction with pre- and post-embedding immunogold labelling for transmission electron microscopy. Labelling was found in a meshwork of filaments beneath the plasma membranes of both IHCs and supporting cells and, in pillar cells, close to microtubule/microfilament arrays. It was also found in association with the stereocilia of OHCs and IHCs and, as expected, in the cortical lattice and cuticular plate of OHCs. Thus, spectrin is a general component of cytoskeletal structures involved in maintaining the specialised cell shapes in the organ of Corti and may contribute to the mechanical properties of all the cell types examined.  相似文献   

5.
The motile response of the isolated vestibular hair cell induced by a neurotransmitter was studied. After application of both physostigmine and acetylcholine (Ach) as well as glutamic acid, shortening or tilting of the neck of the guinea pig hair cell was observed. These findings suggest that the effect of a neurotransmitter in the neck region as well as the efferent neuron is involved in the motile response. The location of F-action in isolated vestibular hair cells was investigated by using FITC-labeled phalloidin. In freeze-fixed vestibular hair cells, marked labeling was noted in the hair bundle, cuticular plate and throughout the cytoplasm. After application of both physostigmine and Ach, the labeling in the cuticular plate and the cytoplasm became more intense than that in the hair bundle. Alteration of this phalloidin-labeling pattern suggests that actin could play an important role in the self movement of vestibular sensory cells. The shape of the bull frog hair cell also changed after application of Ach. At the same time, spontaneous discharge and the time constant of the posterior semicircular canal nerve activity decreased. These results suggest that an adaptation mechanism induced by change in the cell shape and membrane potential inhibits the activity of the afferent neuron. Furthermore, these active events could be closely related to the active regulation of vestibular hair cell transmission.  相似文献   

6.
In the adult mammalian cochlea, post-injury hair cell losses are considered to be irreversible. Recent studies in cochlear explants of embryonic rodents show that the organ of Corti can replace lost hair cells after injury. We have investigated this topic in vivo during the period of cochlear development. Rat pups were treated with a daily subcutaneous injection of 500 mg/kg amikacin for eight consecutive days between postnatal day 9 (PND 9) and PND 16. During this period the organ of Corti is not fully mature, but hair cells are hyper-sensitive to aminoglycoside antibiotics. Scanning and transmission electron microscopy was used to evaluate morphological changes in the organs of Corti during the treatment and at different post-treatment periods, up until PND 90. A massive loss in outer and inner hair cells was observed at least as early as PND 14. A prominent feature in the apical part of cochleas at PND 21 and 35 was the transient presence of small atypical cells in the region of pre-existing outer hair cells. These atypical cells had tufts of microvilli reminiscent of nascent stereociliary bundles. A second striking observation was the replacement of degenerating inner hair cells by pear-shaped supporting cells throughout the cochlea. These cells were covered with long microvilli, and their basal pole was contacted by both afferent and efferent fibers, as in the early stages of inner hair cell maturation. At PND 55 and 90, these features were not clearly observed due to further cytological changes in the organ of Corti. It is possible that an attempt at hair cell neodifferentiation could occur in vivo after an amikacin treatment in the rat during the period of cochlear hyper-sensitivity to antibiotic.  相似文献   

7.
Many studies of the outer hair cells in cochlea have demonstrated active motility. However, very few studies have been done on vestibular hair cells. This study was designed to demonstrate the motile responses of isolated vestibular hair cells of the chick, induced by potassium promoting contraction. Reversible cell shape changes were observed in 4 of 6 type I hair cells and 3 of 5 type II hair cells by applying the contraction solution. The cell shape changes were revealed mainly in the cuticular plate and infracuticular region. It was suggested that contraction in the cuticular plate of the isolated hair cells might be converted into tension which increases the stiffness of the sensory hairs and restricts their motions, based on the results of the present study, and the structure of contractile proteins and hair behaviors reported by previous investigators.  相似文献   

8.
The expression of mRNA encoding plasma membrane calcium ATPase (PMCA) subunit isoforms (1-4) and splice variants was examined in the adult and developing rat cochlea by PCR and in situ hybridization. High levels of PMCA mRNA expression were observed in the neurons of the spiral ganglion, and in hair cells. Spiral ganglion neurons expressed PMCA 1-3 beginning in embryonic development, reaching high levels shortly after birth, and continuing into adulthood. Inner hair cells expressed PMCA 1 at moderate levels from birth to the time of onset of cochlear function on postnatal day 12, and strongly from then until adulthood. Outer hair cells expressed PMCA 2 at high levels from shortly after birth through adulthood. The data suggest that the calcium clearance requirements of inner and outer hair cells are distinct. PMCA 2 is the isoform with the highest affinity for calmodulin, and has also been associated with high levels of inositol triphosphate. Its presence in outer hair cells suggests that regulation of the enzyme by calmodulin may be particularly important for this hair cell type. It further suggests that inositol phosphate may play a unique role in the outer hair cell.  相似文献   

9.
Excitable cells use ion channels to tailor their biophysical properties to the functional demands made upon them. During development, these demands may alter considerably, often associated with a change in the cells' complement of ion channels. Here we present evidence for such a change in inner hair cells, the primary sensory receptors in the mammalian cochlea. In mice, responses to sound can first be recorded from the auditory nerve and observed behaviourally from 10-12 days after birth; these responses mature rapidly over the next 4 days. Before this time, mouse inner hair cells have slow voltage responses and fire spontaneous and evoked action potentials. During development of auditory responsiveness a large, fast potassium conductance is expressed, greatly speeding up the membrane time constant and preventing action potentials. This change in potassium channel expression turns the inner hair cell from a regenerative, spiking pacemaker into a high-frequency signal transducer.  相似文献   

10.
11.
Combined ultrastructural and immunocytochemical studies reveal that in the adolescent 12- to 17-day-old mouse the afferent tunnel crossing fibers that innervate outer hair cells receive synaptic contacts from three distinct sources: the GABAergic fibers (GABA = gamma-aminobutyric acid) of the lateral olivocochlear bundle, the non-GABAergic efferent tunnel crossing fibers, and the inner hair cells themselves. The GABAergic fibers give off collaterals that synapse with the afferent tunnel fibers as they cross the inner hair cell region. These collaterals also form synapses with afferent radial dendrites that are synaptically engaged with the inner hair cells. Vesiculated varicosities of non-GABAergic efferent tunnel fibers also synapse upon the outer spiral afferents. Most of this synaptic activity occurs within the inner pillar bundle. Distinctive for this region are synaptic aggregations in which several neuronal elements and inner hair cells are sequentially interconnected. Finally, most unexpected were the afferent ribbon synapses that inner hair cells-formed en passant on the shafts of the apparent afferent tunnel fibers. The findings indicate that: (1) the afferent tunnel (i.e., outer spiral) fibers may be postsynaptic to both the inner and the outer hair cells; (2) the non-GABAergic efferent and the afferent tunnel fibers form extensive synaptic connections before exiting the inner pillar bundle; (3) the GABAergic component of the lateral olivocochlear system modulates synaptically both radial and outer spiral afferents.  相似文献   

12.
The progression of recovery of the vestibular sensory epithelia of guinea pigs after gentamicin-induced hair cell injury was assessed quantitatively and qualitatively. Evaluations were made of the number of cells bearing hair bundles by using scanning electron microscopy (SEM) and of identifiable hair cells in thin sections. Both assessment procedures showed that an initial loss of hair cells in utricular maculae is followed by significant recovery in the number of hair cells present. SEM also showed recovery in saccules comparable to that in utricles. During the recovery, progressive maturation of hair bundles, which exhibited features similar to those seen during normal ontogenetic development of hair cells, could be identified. The pattern and extent of hair cell loss and subsequent reappearance revealed by SEM corresponded with that derived from analysis of thin sections. This suggests that repair of nonlethally damaged hair cells is unlikely but, rather, that new hair cells are produced. An apparent decrease in supporting cell numbers was observed coincident with the increase in hair cell numbers. This complements previous morphological observations, which have suggested new hair cells arise from direct, nonmitotic transdifferentiation of supporting cells. The quantitative analyses indicate that more than half of the hair cells that are lost are replaced, but the recovery process does not result in complete restoration of the epithelium. Eight months after the end of drug treatment, the number of hair cells present was still significantly less than normal, and several other abnormalities persisted. There was also no evidence of any hair cell recovery in the organ of Corti. Thus, there appear to be limitations on the capacity for spontaneous replacement of lost hair cells in the mammalian inner ear.  相似文献   

13.
The arrangement and structure of sinus hair muscles in the snout of the shrew, Sorex unguiculatus, were studied by electron microscopy and serial section light microscopy. Both striated and smooth muscles are directly associated with sinus hair follicles. The striated muscle fibers originate from the base of a follicle and insert onto the superficial portion of adjoining caudally positioned follicles. Some fibers insert into the corium instead of inserting into a follicle. The fibers show a fine structure typical of red fibers. Smooth muscle cells form a network with elastic fibers beneath the corium. Some cells are directly attached to the capsule of the sinus, thus forming a type of M. arrector pili. Striated muscle febers that appear to end in the corium are connected with the smooth muscle network through the elastic fibers which appear to function as the tendon of these two types of muscle cell.  相似文献   

14.
The outer hair cell (OHC) is known to have the ability to change its length in response to voltage changes across its membrane. The apparent function of this OHC motility is to enhance the tuning of the basilar membrane. The model presented in this paper represents the displacement-to-voltage and voltage-to-displacement transducers of the OHC explicitly, each as low-pass filter functions. The model results show that this OHC representation is sufficient to provide a model of cochlear mechanics with mechanical tuning at the inner hair cell which is comparable to the threshold tuning curves observed in single auditory nerve fibers. The enhancement of tuning provided by OHC motility can be interpreted as the combined action of a cochlear amplifier and a second filter. This model demonstrates that realistic cochlear tuning does not require intrinsic resonance in any cochlear structure other than the basilar membrane.  相似文献   

15.
HYPOTHESIS: Bullfrog vestibular hair cells are capable of regenerating in vitro. BACKGROUND: Recent studies have established that sensory organs in the inner ear of vertebrates continue to produce hair cells after birth. However, the mechanisms responsible for the regulation of this process are not well understood. The current study reports the development of a novel method for the culture of dispersed cells from the bullfrog inner ear. METHODS: New hair cell formation in this in vitro preparation was shown by sequential photomicroscopy. Studies with the selective marker for mitotic activity 5-bromo-2-deoxyuridine (BrdU) were done to estimate the level of cell proliferation and to quantify postmitotic hair cell formation. Finally, confirmation of cell type was obtained by scanning electron microscopy and by the use of specific markers for hair cells. RESULTS: Once the optimal culture conditions were established in the initial experiments, the formation of new hair cells was directly visualized in all unstained live cultures and fixed preparations without exception. Asymmetric division of progenitor cells, with subsequent differentiation of one of the daughter cells into new hair cells, also was documented by photomicroscopy. Approximately 12% of the cells were labeled with BrdU, of which 6% were hair cells, showing that new hair cell formation was subsequent to mitotic division in vitro. The identity of newly formed hair cells was verified as follows: 1) morphologically by scanning electron microscopy; 2) by positive labeling with phalloidin-rhodamine, a marker for actin; and 3) by positive calmodulin immunocytochemistry. CONCLUSIONS: This study reports the development of an in vitro culture preparation in which undifferentiated epithelial cells proliferate to become new hair cells. Evidence is provided of division of hair cell progenitors and subsequent differentiation of the daughter cells as one of the mechanisms involved in new hair cell formation in the culture preparation. This newly developed cell culture technique provides a powerful tool for further study of the process of hair cell formation in the vestibular end organ.  相似文献   

16.
Forward masking of the auditory brainstem response (ABR) was achieved by increasing the time interval from 0 to 12 ms between the masker offset and the probe onset. The forward masking response demonstrated a near linear function with an approximate 3.0-dB increase in masking threshold for every millisecond interval increase in the control guinea pig. The slope of the masking curve at selected frequencies together with the quantification of hair cell loss through the analysis of cochlear surface morphology was studied before and after chemical insult. The intracochlear infusion of sodium salicylate caused an approximately 45-dB threshold shift of the ABR whereas the slope of the forward masking curve was not significantly different from the control values at the tested frequencies (1, 4, and 8 kHz). Systemic kanamycin administration (400 mg/kg body weight for 9 consecutive days) caused a permanent ABR threshold shift of 43-63 dB at 1, 4, and 8 kHz. The slope of the forward masking curve was not significantly different at 1 kHz despite significant outer hair cell loss. The slope of the forward masking curve at 4 and 8 kHz showed significant reductions at the time intervals between 0 and 4 ms. Analysis of the kanamycin-treated cochleae revealed not only significant outer hair cell loss throughout the cochlea but significant inner hair cell and inner pillar cell loss in the basal end of the cochlea. The results suggest that the outer hair cells are not needed for maintaining a normal forward masking curve, whereas the slope of the forward masking curve is sensitive to alterations induced to either the inner hair cells or the inner pillar cells.  相似文献   

17.
Localization of fodrin, a membrane skeletal protein, in the outer hair cell of the guinea pig cochlea was examined by immunocytochemical techniques. By immunofluorescence microscopy, fodrin was observed in the cuticular plate, in the infracuticular network and along the lateral wall. By immunoelectron microscopy of ultrathin cryosections, labeling for fodrin along the lateral wall was localized between the cell membrane and the outermost layer of the subsurface cisternae. Furthermore, pre-embedding immunoelectron microscopy of permeabilized specimens showed that most immunogolds for fodrin were on the thin cross-linking component of the cortical lattice. The results indicate that fodrin is a constituent of the cortical lattice which is thought to play an important role in outer hair cell motility.  相似文献   

18.
The work describes the system of efferent terminals that interconnect inner hair cells through a chain of direct somatic synapses organized in repetitive patterns. The efferent boutons were discovered in the apical turns of 12-day-old (hearing) mice. Clusters or short rows of vesiculated boutons are located between adjoining hair cells at the lower half of the receptors, close to their modiolar side. The individual endings, about 1.2 microns in diameter, adjoin inner hair cells and form one synapse per hair cell. On the hair cell side, the synaptic contact is apposed by a classical postsynaptic cisterna. Within a cluster of endings, some synapse simultaneously with either or both neighbouring inner hair cells. The efferent boutons also connect synaptically with each other and with other--different in type--vesiculated and nonvesiculated endings. These endings seem to derive from the climbing collaterals of the inner spiral bundle, and we believe them to be GABAergic.  相似文献   

19.
Hair cells, the sensory receptors of the mammalian inner ear, have long been thought to be produced only during embryogenesis, and postnatal hair cell loss is considered to be irreversible and is associated with permanent hearing and balance deficits. Little is known about the factors that regulate hair cell genesis and differentiation. The mitogenic effects of insulin and transforming growth factor alpha (TGFalpha) were assayed in vivo in normal and drug-damaged rat inner ear. Tritiated thymidine and autoradiographic techniques were used to identify cells synthesizing DNA. Simultaneous infusion of TGFalpha and insulin directly into the inner ear of adult rats stimulated DNA synthesis in the vestibular sensory receptor epithelium. New supporting cells and putative new hair cells were produced. Infusion of insulin alone or TGFalpha alone failed to stimulate significant DNA synthesis. These results suggest that exogenous growth factors may have utility for therapeutic treatment of hearing and balance disorders in vivo.  相似文献   

20.
Nitric oxide synthase III (NOS III) was identified in the guinea pig cochlea on an ultrastructural level using a post-embedding immunolabeling procedure. Ultrathin sections of London Resin (LR) White-embedded specimens were incubated with various concentrations of a commercially available antibody to NOS III and the immunoreactivity visualized by a gold-labeled secondary antibody. Analysis of ultrathin sections of the organ of Corti in the second turn of the cochlea showed that NOS III could be localized in the endothelial cells of the blood vessels under the basilar membrane, which was comparable to its location in similar cells types in various biological systems. Besides this, NOS III was also found in the cytoplasm and in the nuclei of inner and outer hair cells. Immunoreactivity was not distributed homogeneously within receptor cells. Numerous gold particles could be identified at the border of the cuticular plates, in the middle parts of the stereocilia and in the cytoplasm. Gold-labeled anti-NOS III antibodies in these sites were seen mostly on the cytoplasmic side of the submembranous cisterns in the vicinity of mitochondria and in the central parts of the hair cells, whereas the cisterns were nearly free from any immunoreactivity. NOS III was also detected in the efferent and afferent nerve endings that were located at the basal and basolateral side of the outer hair cells. Some immunoreactivity was visible in different nerve fibers of the inner and outer spiral tunnels. Besides this, gold-labeled antibodies were also present in the cuticular plate of inner and outer pillar cells, in the cytoskeletal elements located in the apical parts of Deiters cells, forming the lamina reticularis, and in the cytoskeletal-containing region of the cytoplasm of those Deiters cells located at the basal side of the outer hair cells. The role of the NOS III immunoreactivity identified in the organ of Corti was consistent with respect to hair cell and tissue modulation.  相似文献   

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