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Results for “Hair Cells, Auditory, Inner”

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At least 19 recordsLinked to original sources
PubMed2026

Acbd7 is essential for preserving hair cell-mediated auditory and vestibular function.

Understanding the molecular basis of hair cell function is essential for elucidating inner ear physiology and developing therapies for auditory-vestibular disorders. Here, we identify acyl-CoA binding domain-containing 7 (Acbd7) as a hair cell-specific gene critical for sensory maintenance. Single-cell transcriptomics of mouse cochlear organoids revealed Acbd7 as a top hair cell-enriched transcript, with its spatiotemporal expression confirmed from embryonic development through adulthood in both auditory and vestibular hair cells. Acbd7‑deficient mice exhibited pronounced hair cell degeneration, characterized by synaptic defects and diminished calcium currents in inner hair cells and loss of outer hair cells. Transcriptomic and proteomic analyses linked Acbd7 to the regulation of Ca2+ signaling and fatty acid metabolism pathways. Our findings establish Acbd7 as a critical regulator of Ca2+ homeostasis and functional integrity in hair cells, thereby elucidating a key mechanism by which a fatty acid metabolism factor sustains hair cell function and providing potential therapeutic targets for inner ear disorders.

Animals↗
PubMed1979

Critical bands following the selective destruction of cochlear inner and outer hair cells.

Critical bandwidths and absolute intensity thresholds were measured in cats before and after kanamycin treatment which induced selective inner and outer hair cell losses. Hair cell losses were measured from cochleograms constructed from surface preparations of the organ of Corti. Results suggested that, for the test frequencies and stimulus intensities employed, critical bandwidths were not affected for frequencies tonotopically located in cochlear regions where only outer hair cells were lost. Critical bands were widened or not measurable only when inner hair cell losses exceeding 40% were also associated with complete loss of outer hair cells. The experiment suggests that cochlear frequency selectivity can be mediated by inner hair cells alone.

Animals↗
PubMedDate not supplied

Organ of Corti in the human fetus: scanning and transmission electronmicroscope studies.

The organ of Corti in the five-month human fetus was studied by transmission and scanning electronmicroscopy. Differentiation of the surface organization of the organ of Corti into a single row of inner and three to four rows of outer hair cells was complete at this stage except at the apical end. The morphological aspects of the hair bundles changed with maturation of the sensory cells; the inner hair cells preceded the outer hair cells in cytodifferentiation at a given location.

Cell Differentiation↗
PubMed1979

Hearing thresholds with outer and inner hair cell loss.

Hearing impairment and related cochlear histopathologic changes were evaluated in experimental animals after treatment with aminoglycoside antibiotics or exposure to intense sound. In the course of treatment with kanamycin, neomycin, or dihydrostreptomycin, permanent hearing loss in monkeys and guinea pigs occurred first at the high frequencies and progressed toward the lows. Exposure to different octave bands of noise at 120 dB SPL in monkeys and chinchillas produced permanent hearing loss at frequencies related to the spectral characteristics of the octave band. In most instances loss of outer hair cells was substantially greater than that of inner hair cells. In fact, the pattern and location of missing outer hair cells on the basilar membrane were most often correlated with threshold shifts of 50 dB or less. Generally inner hair cell loss was observed when the threshold shift was greater than 50 dB. Our data support the place principle and the inference that the outer hair cells are essential for hearing from threshold to about 50 dB SL. The inner hair cells, if functioning normally, apparently take over above that level. Although there is little doubt that such a generalization will, in the long term, be found to have been greatly oversimplified, there is every reason to believe that a combination of behavioral and morphologic procedures, as used in this study, will play an important part in elucidating the differences in functional significance of the two types of hair cells.

Animals↗
PubMed1979

Significance of presynaptic formations in early stages of cochlear synaptogenesis.

Very early stages of cochlear synaptogenesis are described in inner (IHCs) and outer hair cells (OHCs) of cat foetuses. Ten days before birth (DBB) well-formed synaptic contacts were found between afferent dendrites and both IHCs and OHCs. At the IHC level a preliminary stage before functioning has been proposed. But at the OHC level where the adult cell membrane becomes mainly postsynaptic, we could only formulate hypotheses based on phylogenetic considerations (afferents precede efferents), or on embryology (presynaptic specializations play a role in the arrival and growth of fibers around the hair cell).

Animals↗
PubMed1979

Stereocilia mediate transduction in vertebrate hair cells (auditory system/cilium/vestibular system).

The vertebrate hair cell is a sensory receptor that responds to mechanical stimulation of its hair bundle, which usually consists of numerous large microvilli (stereocilia) and a single true cilium (the kinocilium). We have examined the roles of these two components of the hair bundle by recording intracellularly from bullfrog saccular hair cells. Detachment of the kinocilium from the hair bundle and deflection of this cilium produces no receptor potentials. Mechanical stimulation of stereocilia, however, elicits responses of normal amplitude and sensitivity. Scanning electron microscopy confirms the assessments of ciliary position made during physiological recording. Stereocilia mediate the transduction process of the vertebrate hair cell, while the kinocilium may serve primarily as a linkage conveying mechanical displacements to the stereocilia.

Animals↗
PubMed1977

Actin filaments in sensory hairs of inner ear receptor cells.

Receptor cells in the ear are excited through the bending of sensory hairs which project in a bundle from their surface. The individual stereocilia of a bundle contain filaments about 5 nm in diameter. The identity of these filaments has been investigated in the crista ampullaris of the frog and guinea pig by a technique of decoration with subfragment-1 of myosin (S-1). After demembranation with Triton X-100 and incubation with S-1, "arrowhead" formation was observed along the filaments of the stereocilia and their rootlets and also along filaments in the cuticular plate inside the receptor cell. The distance between attached S-1 was 35 nm and arrowheads pointed in towards the cell soma. It is concluded that the filaments of stereocilia are composed of actin.

Actin Cytoskeleton↗
PubMed1978

Scanning electron microscope studies of the papilla basilaris of some turtles and snakes.

The papillae basilares of three species of turtles and four species of snakes were studied by SEM. The papillae of turtle are relatively large among reptiles and are characterized by a long, horizontal middle section resting on wide basilar membrane. Both terminal ends of the papilla extend onto the surrounding limbus in the form of a forked or "T" -shaped end or as a curved, "hook"- like processes. Details vary with the species. In the three species of turtles studied, there were between 1,100 and 1,400 hair cells on a papilla. The tectorial membrane covering the horizontal portion of the papilla is heavy in appearance and tightly attached to the kinocilial bulbs. The terminal ends of the papilla are covered by a thin gelatinous material. In addition, mat-like tectorial network covers the supporting cells and extends from the microvilli of the supporting cells to the overlying tectorial membrane. All hair cells are unidirectionally and abneurally oriented. The supporting cell surfaces form a large part of the papilla and, thus, hair cell density is low. The papillae of the two boid snake species studied are moderately long among snakes and contain a moderate number of hair cells (574 in Epicrates and 710-780 in Constrictor). Papillar form is elongate, avoid, or canoe-shaped. The tectorial membrane may be either highly fenestrated or moderately dense and covers all but a few of the terminal hair cells. A tectorial-like mat covers all but a few of the terminal hair cells. Most hair cells are unidirectionally and abneurally oriented. A few terminal cells in boids may show reverse orientation. Hair cell density is similar to that of turtles.

Animals↗
PubMed1978

Structure of the chicken's inner ear: SEM and TEM study.

The inner ears of 35 adult chickens were studied by TEM, SEM and light microscopy. Two well differentiated hair cell/nerve ending units were present: tall hair cells with small vesiculated nerve endings were located on the attached part of the basilar membrane; short hair cells with large vesiculated nerve endings were located on the free basilar membrane except for the distal tip. In this respect the chicken ear is similar to that of the pigeon. The chickens examined did have some unique features. Sensory cells of lenticular and hemispheric shape were also present at the proximal end. Bundles of long dense tubules were seen frequently within the sensory cell cytoplasm. Kinocilia were absent from the hair bundles of many of the sensory cells. The internal structure of the kinocilia which were present was atypical and consisted of a variable number of doublets. Eight peripheral plus one central doublet were found most frequently.

Animals↗
PubMed1978

The ultrastructure of the basilar papilla of the chick.

The basilar papilla of the chicken was studied by transmission and scanning electron microscopy. It is composed of two distinct types of hair cells, a tall hair cell (THC) and a short hair cell (SHC). Gradual transitions exist between these two forms. The THC occurs mainly in the anterior part of the neuroepithelium and is situated on the superior fibro-cartilagenous plate, while the SHC dominates in the posterior part and is found on the free basilar membrane. The THC is a tall columnar cell with an elongated hexagonal apical surface. One kinocilium and 150 to 220 stereocilia protrude from the center of its surface. The THC makes synaptic contact with several large afferent nerve terminals and with small bouton-shaped efferent terminals. The SHC is short and thick, having a much wider surface area than the THC. From the inferior part of the surface of the SHC 90 to 120 stereocilia protrude, whereas the kinocilium is lacking. The nucleus is located near the base of the cell. Small afferent nerve terminals and extremely large efferent nerve endings synapse with the SHC.

Animals↗
PubMed1979

Hair cell degeneration in guinea pigs intoxicated with kanamycin during intrauterine life; a structural and ultrastructural study.

The structural ototoxic effect of kanamycin during intrauterine life has been shown in guinea pigs. The extent of the loss mostly affected the outer hair cells of the basal part of the cochlea. Ultrastructural studies demonstrated a hair cell degeneration pattern similar to that previously described in adult animals following antibiotic intoxication.

Animals↗
PubMed1979

Morphological changes in afferent vestibular hair cell synapses during the postnatal development of the cat.

In the course of postnatal development in the cat, there is a decrease of about 93% in the total number of synaptic bodies (synaptic balls and synaptic bars) in type I hair cells. In type II hair cells, there is no change in the number of synaptic balls. Simultaneously, the length of specialized neuroepithelial contact increases by approximately 300% during type I hair cell maturation. Only the synaptic bars displaying a polylamellar ultrastructure persist in the type I hair cells of the adult animal. It is suggested that the afferent vestibular synapses of the type I hair cell are transformed during ontogeny.

Animals↗
PubMed1977

Disappearance of afferent and efferent nerve terminals in the inner ear of the chick embryo after chronic treatment with beta-bungarotoxin.

Beta-Bungarotoxin(beta-BT) was applied to chick embryos at 3-day intervals beginning on the 4th day of incubation to see the effect of chronically and massively applied beta-BT, and to investigate the hair cell-nerve relationship in the developing inner ear by electron microscopy. On the 10th day of incubation, nerve terminals had achieved contact with differentiating hair cells, but the acoustico-vestibular ganglion cells of treated animals were decreased in number to one-third of those of the control. By the 14th day, most of the ganglion cells degenerated and disappeared, and only a few nerve terminals were seen in the neuroepithelium. At this time, most of the hair cells lacked synaptic contacts with nerve terminals; but their presynaptic specialization remained intact and they showed evidence of continuing differentiation. On the 17th day, the acoustico-vestibular ganglion cells were completely absent. All the hair cells were devoid of afferent and efferent innervation but were fully differentiated on the 21st day. Beta-BT was found to have a similar destructive effect on cultured spinal ganglion cells. The present study shows that beta-BT kills acoustico-vestibular and spinal nerve cells when applied chronically and massively during development. Furthermore, the differentiation of hair cells proceeds normally, and their presynaptic specializations are maintained when nerve terminals are absent during later developmental stages.

Animals↗
PubMed1979

Tectorial membrane: a possible effect on frequency analysis in the cochlea.

Mathematical analysis and computer and network simulations of the cochlea show that, given appropriate values of specific physical constants, radial shear motion between the tectorial membrane and the reticular lamina may provide the sharpening of frequency analysis observed in cochlear nerve fibers in comparison with the mechanical amplitude distribution on the basilar membrane. According to the analysis, the sharpening occurs through an interaction of the longitudinal mechanical propagation constant of the tectorial membrane with the wavelength on the basilar membrane.

Basilar Membrane↗
PubMedDate not supplied

Macula utriculi in four cases with Meniere's disease.

Four patients suffering from Meniere's disease were labyrinthectomized. Maculae utriculi were removed and studied by electron microscopy. The neuro-epithelia from all four patients appeared fairly normal, considering the age of the patients. However, two types of degenerative change, which could be related to the inner ear disorder, could be distinguished. One was vacuolation of the sensory cell cytoplasm, followed by pycnosis of the nucleus and cell death. The other was cystic degeneration. This started with localized separations between the sensory cell and the nerve chalice. These separations developed into a single cystic cavity. A few large intra-epithelial cysts were found, probably representing the final stage of the cystic degenerative process.

Adult↗