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Results for “Hair Cells, Vestibular”

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At least 19 recordsLinked to original sources

PubMedDate not supplied

Structure and development of vestibular hair cells in the larval bullfrog.

Structure and development of hair cells in vestibular sensory organs of the larval bullfrog were examined with scanning electron microscopy. The larval vestibular sensory epithelia resembled those of the adult frog. Based on morphology of the ciliary tufts, seven hair cell types were identified. One of them, the type A hair cell, appears to be the morphogenetic precursor of other hair cell types. The size of the stereocilia of type A hair cells is comparable to the surrounding microvilli. The distribution of immature type A hair cells suggests that the periphery of the sensory epithelia is the principal growth zone and the site of formation of new hair cells. However, a far greater number of type A hair cells were found in high frequency sensitive sensory organs (sacculus, amphibian and basilar papillae) than low frequency sensitive vestibular sensory structures (canal cristae, utriculus and lagena). This phenomenon may suggest that the time period required for the maturation of type A hair cells to their ultimate hair cell types in the low frequency sensitive vestibular organs is shorter than in the high frequency sensory structures. It is also possible that the low frequency sensitive vestibular organs may have completed their morphogenetic development in the early larval stages, while morphogenesis of hair cells in the high frequency sensory structures continues throughout the lifetime of a bullfrog.

Animals↗

PubMed1979

Pathological actin in vestibular hair cells of the waltzing guinea pig.

Vestibular type 1 hair cells in the waltzing guinea pig contain needle-shaped inclusion bodies which grow in an uncontrolled fashion associated with the destruction of the cell. The needles are shown to be composed by filaments of actin, a protein identified in the electron microscope by its ability to bind subfragment 1 of myosin. Whereas actin filaments in stereocilia are oriented down towards the cell body, filaments in the needles point up towards the cuticular plate. The hereditary lesion appears to be associated with a defective control of polymerization of actin into filaments.

Actins↗

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↗

PubMed1979

Genesis and maturation of vestibular hair cells.

The embryologic development in vivo and in vitro of mammalian hair cells in the crista ampullaris was continuously followed with regard to structural differentiation and maturation from the terminal mitosis to the morphological condition at partus or equivalent age in vitro. Otocysts were explanted both early and late during embryologic development: 13th and 16 gestation day, respectively. Both in fetal life and during in vitro conditions, the surface structures of the developing hair cell with regular arrangement of kinocilium/stereocilia were first differentiated, followed by a cytologic transformation intracellularly and subsequent development of nerve endings. Hair cells were able to develop without any morphologic contact with the nervous system. The afferent nerve system developed before the efferent nerve system (CBA/CBA mouse).

Animals↗

PubMedDate not supplied

Quantitative analysis of kanamycin ototoxicosis.

The morphological changes after kanamycin intoxication of the inner ear, including both the cochlea and the vestibule, were quantitatively analysed by the surface preparation technique after succinic dehydrogenase staining. 75 guinea pigs were used. The outer hair cells in the basal coil and the inner hair cells in the upper coils of the cochlea were the most severely damaged, but many unusual modes of damage were also revealed. For example, the initial hair cell damage in the cochlea appeared in the upper hair cells. The clearly observed vestibular damage contradicts the general belief that kanamycin is not so toxic to the vestibular hair cells. The utricular macula and the lateral crista were most severely damaged. The delayed ototoxicity of kanamycin was observed for the first time in the vestibular hair cells.

Animals↗

PubMed1979

Extracorporeal preservation. Organ culture of the post-natal mammalian inner ear.

Postnatal (newborn and mature) inner ear organs from CBA/CBA mouse and guinea pig were analysed concerning hair cell survival in an in vitro system. After only a few days in the artificial surroundings a transformation of hair cell characteristics occurred, in the form of either loss of sensory hairs (cochlear hair cells) or hair fusion (vestibular hair cells), although the hair cell itselt survived for a considerably longer time. Intracellular myelin figures became evident after 2--3 days in culture. However, a considerable individual variation among hair cells was observed concerning the ultrastructure of the cell at this stag in vitro. Completely normal hair cells could in rare cases be recognised after 1 week in organ culture (cochlear inner hair cells of the CBA/CBA mouse). Loss of the surface structures of the hair cells is likely to constitute an irreversible transformation not in agreement with the true hair cell characteristics.

Adaptation, Physiological↗

PubMed1979

The inner ear and the in vitro system.

The embryologic labyrinthine development of the CBA/CBA mouse occurs parallell in vivo and in vitro. Regarding post partum inner ears, either as cultured otocysts passing a corresponding time in vitro or inner ear explants of newborn/mature animals, the extracorporal system becomes unable to maintain specialized hair cell structures for more than a few days. The sensory cells themselves, however, survive for considerably longer time. Vestibular hair cells show sensory hair fusion. Cochlear hair cells loose their surface structures but the sensory hair rootlets penetrating into the cuticle are preserved. Post partum inner ears from the guinea pig reacted in a similar way in vitro as did labyrinths from the CBA/CBA mouse.

Animals↗

PubMedDate not supplied

Vestibular neuroanatomy: recent observations.

The modern neuroanatomical technique of using a retrograde axoplasmic tracer (horseradish peroxidase) to label neurons has aided the revelation of several important connections in the vestibular system. The organization of the oculomotor nucleus and the existence of an interneuron in the abducens nucleus have importance in understanding some ocular disorders. A detailed description of the location of vestibulo-ocular neurons to individual extraocular muscles is now available which may provide a basis for understanding how these reflexes function normally and abnormally. Interconnections between the vestibular nuclei are provided by commissural neurons located in the superior, medial and group Y nuclei. These projections are probably of importance in vestibular compensation. A possible hypothesis of vestibular hair cell projection suggests that type I cells project over vestibulo-ocular neurons while type II cells project over commissural pathways.

Hair Cells, Auditory↗

PubMed1979

Synaptic structures in the type II hair cell in the vestibular system of the guinea pig. A freeze-fracture and TEM study.

The synaptic contacts of the type II hair cell in the vestibular system of the guinea pig was described in thin-sectioned and freeze-fractured specimens. Synaptic bodies were present at the apposition with both large and small afferent terminals. About 20% of the synaptic bodies observed consisted of complexes of two or more adjacent synaptic discs. In freeze-fracture replicas, the cytoplasmic leaflet of the hair cell plamalemma beneath the synaptic body had a bar-shaped aggregate of large particles. The size and shape of the particle aggregate was the same as that of the synaptic body. Small plasmalemmal deformations, interpreted as sites of synaptic vesicle exocytosis, were found immediately adjacent to the particle aggregate. On the postsynaptic membrane, an aggregate of intramembrane particles was present at the synaptic junction. The type II hair cell had no gap junctions or close membrane appositions between it an the apposed afferent fiber. Efferent boutons ending on the type II hair cell had no intramembrane particle specialization on the postsynaptic membrane; however those efferent boutons ending on large and small afferent fibers had an aggregate of medium-sized particles on the external leaflet of the postsynaptic bouton beneath the presynaptic active zone.

Animals↗

PubMedDate not supplied

Effect of transverse temporal bone fracture on the fluid compartment of the inner ear.

Five temporal bones exhibiting transverse fractures were studied with a view to determining whether such fractures could lead to symptomatic endolymphatic hydrops. Four out of the five temporal bones showed the fracture line traversing the vestibular aqueduct. Two of these four showed complete obstruction of the endolymphatic duct. One of these had an intact membranous labyrinth and severe endolymphatic hydrops. The other had ruptures of the membranous labyrinth and no hydrops. Three ears exhibited partial preservation of auditory and vestibular hair cells and neurons. These findings are consistent with the concept that a transverse fracture may produce endolymphatic hydrops by obstructing the vestibular aqueduct while preserving enough audiovestibular epithelium and neurons to present as symptomatic Menière's disease.

Adult↗

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↗

PubMedDate not supplied

The effects of mercurial poisoning on the vestibular system.

The sensory epithelium with adjacent nerve endings and the secretory epithelium may both become damaged following mercury chloride intoxication. Peripheral myelinated nerve fibres in the crista ampullaris showed signs of degeneration following chronic poisonins. Ultrastructural alterations of the vestibular hair cells initially occurred in animals free from clinical signs of intoxication. The sensory epithelium and occasionally the secretory cells were affected before signs of ultrastructural damage could be detected in the myelinated nerves.

Animals↗

PubMed1979

Freeze-fracture studies on the synapse between the type I hair cell and the calyceal terminal in the guinea-pig vestibular system.

The apposition between type I hair cells and the calyceal terminals of vestibular ganglion cell peripheral processes was studied in the vestibular epithelium of the guinea-pig, using thin-sectioned and freeze-fractured specimens. Chemical synaptic junctions were exceedingly rare in thin-sectioned specimens, and were not seen in freeze-fracture replicas. Furthermore, no gap junctions were present between the hair cell and the calyx. There were, however, regions along the apposition where the membranes were closely apposed. At these regions, the hair cell was invaginated by cytoplasmic protrusions of the calyx and the plasmalemmata of the two cells were separated by only 6-7 nm. The number and conformation of the close appositions varied between different cells. In freeze-fracture replicas, the closely-apposed plasmalemmata of the hair cell and the calyx had no special distribution of intramembrane particles on either membrane leaflet. However, on the external membrane leaflet of the hair cell, a large patch of widely-spaced, large particles surrounded the regions of close apposition. The corresponding region of the plasmalemma of the calyx had no special distribution of particles on either membrane leaflet. The scarcity of chemical synaptic junctions, the absence of gap junctions between the cells and the unique arrangement of particles in the hair cell plasmalemma surrounding regions of close membrane apposition may indicate an unusual mode of synaptic transmission between the type I hair cell and the calyx.

Animals↗

PubMed1977

[Ototoxic effect of BB-K8 administered to pregnant guinea pigs on development of inner ear of intrauterine litters (author's transl)].

UNLABELLED: Transplacental ototoxic effects of BB-K8 on development of inner ear in intrauterine guinea pigs were evaluated by differential frequency pinna reflex test in range of 20 kHZ to 500 HZ and histopathological examination of spiral and vestibular organs in new born guinea pigs from pregnant ones given BB-K8 i.m. during gestation. MATERIALS AND METHODS: Twenty-five pregnant guinea pigs of the Hartley strain and 63 new-born guinea pigs from the pregnant ones were used in the study. Following antibiotics were given i.m. daily to the 20 pregnant guinea pigs from 7th day of gestation for 56 days. BB-K8 was given at the dose level of 100 mg/kg and 200 mg/kg, respectively. Kanamycin (KM) was administered at the dose level of 100 mg/kg and 200 mg/kg, respectively. Physiological saline solution (1.0 ml/kg) was given i.m. to the pregnant guinea pigs for 56 days. The differential frequency pinna reflex test was performed in the frequency range from 20 kHZ to 500 HZ to determine an extent of frequency of pinna reflex loss. The test was carried out before the start of administration of the antibiotics and once a week during the administration. After the last injection of the antibiotics, intravital perfusion fixation was carried out in the new born animals under anesthesia with nembutal. Histopathological examination was made in celloidin serial sections of the cochlea and vestibulum of the new born animals to observe an extent or degree of hair cell damage. RESULTS: (1) The differential frequency pinna reflex test revealed that new born guinea pigs from the pregnant ones given BB-K8 and KM respectively at the dose level of 100 mg/kg did not show occurrence of pinna reflex loss at any frequency tested. At the dose level of 200 mg/kg, BB-K8 did not result in transplacental hearing impairment in new born guinea pigs, but KM caused transplacental pinna reflex loss in the highest frequencies from 20 k to 15 kHZ in 3 of 10 animals. (2) Histopathological examination detected that unilateral incomplete loss of outer hair cells of the spiral organ confined to the basal end of cochlea was found in 3 of 13 new born guinea pigs from the pregnant ones treated with BB-K8 (100 mg/kg). In the animals, slight damage of hair cells in the vestibular organs occurred in 100%. These hair cell damages were enhanced slightly in the new born guinea pigs from the pregnant ones treated with BB-K8 (200 mg/kg) and much more in the new born ones from the pregnant ones treated with KM (100 mg/kg, 200 mg/kg). (3) These results suggest that BB-K8 has a mild potency to cause transplacental ototoxic damage in the inner ear of intrauterine guinea pigs within the pregnant ones treated for 56 days (normal gestation period approximately 70 days).

Amikacin↗

PubMed1977

The nephrotoxic effect of the ototoxic compound atoxyl.

The arsenical compound atoxyl has been used in labyrinthine research because of its documented effects both on cells engaged in an active transport of ions (secretory epithelia) and sensory epithelia (cochlear hair cells and vestibular sensory cells type I and type II.) In the present experiments both the kidney and the structures of the inner ear were studied. The renal tubules were damaged by exposure to atoxyl. Tubular casts, haemorrhages (both in the tubules and in the renal calices) and tubular epithelial cell necrosis occurred. A common denominator in the ototoxic and the nephrotoxic actions of acute atoxyl poisoning might be a disturbance of the very active ion transport systems of the cells involved.

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↗

PubMed1976

[Ototoxicity of spectinomycin (author's transl)].

Spectinomycin is an aminocyclitol antibiotic, but different in chemical structure from other aminocyclitol antibiotics such as streptomycin, kanamycin and gentamicin. Spectinomycin clinically has been proven to be highly effective in the intramuscular single-dose treatment of gonorrhea. According to NOVAK et al. (1974), all evidence from pharmacological and clinical efficacy studies to date indicates that spectinomycin is free from ototoxic effects at the dose levels recommended for single-dose treatment of gonorrhea (2 or 4 g) or repeated i.m. or i.v. doses, 8g/day. The present experimental study has been made to evaluate the ontoxocic effects of spectinomycin in Hartley strain guinea pigs given i.m. a single-high dose (800 mg/kg or 1,600 mg/kg) and repeated-slightly higher dose (80 mg/kg or 160 mg/kg daily for 4 weeks) respectively. Differential frequency pinna reflex test in frequency range from 20 KHz to 500 Hz revealed that no animals showed disappearance of pinna reflex in the frequencies tested. Histologic examination in serial celloidin sections of the cochlea and vestibulum disclosed that a few animals given a single-high dose of spectinomycin (800 mg/kg or 1,600 mg/kg) and repeated-slightly higher dose or spectinomycin (80 mg/kg daily for 4 weeks) respectively showed limited mild damage of outer hair cells in the spiral organ and of hair cells in the vestibular organ. There were histologically a few focal necrosis in the liver and scattered interstitial cell infiltration around the proximal convoluted tubules which are lined with regenerated epithelial cells in some animals given the single-high dose (800 mg/kg or 1,600 mg/kg) or repeated-slightly higher dose (80 mg/kg or 160 mg/kg daily for 4 weeks) of spectinomycin. Positive correlation between the extent of the hair cell damage and the injury of the liver and kidney was not confirmed. The present study suggests that administration of spectinomycin at the dose levels recommended for single-dose treatment of gonorrhea (2 or 4 g) most probably is free from ototoxic effect.

Animals↗

PubMed1977

Deafness in an old English sheepdog. A case report.

The histopathological features of the inner ears in a case of deafness in an old English sheepdog reveal a cochleo-saccular (Scheibe) type of degeneration. However, also the hair cells in the vestibular part of the labyrinth were reduced in number though there appeared no clinical signs or symptoms of vestibular dysfunction. The present case is the so far only known old English sheepdog with a hearing loss reported in Sweden.

Age Factors↗