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At least 1,081 records · Page 60Linked to original sources
PubMed1993

Morphological correlates of functional recovery in the chicken inner ear after gentamycin treatment.

Newly hatched chickens were allowed to survive 6, 10, 15, and 20 weeks after 10 days of gentamycin sulfate treatment. Ultrastructural studies of hair cells and nerve terminals in the auditory receptor organ, the basilar papilla, were carried out with transmission and scanning electron microscopes. Attention was paid to absolute sensory cell (hair cell) numbers, stereocilia maturity and orientation, and reinnervation within a band 100 micron wide centered 1,100 microns from the basal end of the avian cochlea. Sensory cell numbers were equivalent to those of untreated control animals within the study area in the earliest survival group. Both immature and mature appearing hair cells were identified throughout the recovery period. However, the ratio of mature to immature hair cells gradually increased to exceed 95% at 20 weeks. Stereocilia bundle reorientation also occurred throughout the study period. Orientation was often abnormal at 6 weeks, but by 20 weeks more than 95% of the regenerated hair cells were aligned within normal limits established in the control ears. Hair cell differentiation occurring at 10-15 weeks was associated with degeneration of the afferent nerve receptor complexes commonly observed in 6 week survivors. These complexes were replaced by one or two small bouton shaped efferent terminals per cell. At 20 weeks, two or three chalice shaped vesiculated terminals were observed per cell in both the gentamycin treated and control ears. On the basis of these observations normal physiological activity would be predicted at 20 weeks following gentamycin treatment, at which time sensory cell repopulation, maturation, reorientation, and innervation approximates the normal anatomical condition.

Animals↗
PubMed1994

Quantitative analyses of postembryonic hair cell addition in the otolithic endorgans of the inner ear of the European hake, Merluccius merluccius (Gadiformes, Teleostei).

Bony fishes add sensory hair cells to the saccule and lagena of the ear for at least several years after hatching. However, it is not known whether hair cell proliferation occurs for the whole lifetime of an animal, whether proliferation occurs in all endorgans of the ear, or whether the rate of proliferation is the same in all of the endorgans. To obtain answers to these questions, the extent of postembryonic hair-cell proliferation was determined in the saccule, lagena, and utricle of the ear in the European hake, Merluccius merluccius, for fish ranging from 7 to 75 cm in total length (6 months to 9 years of age). Results demonstrated that hair-cell addition continued throughout this period in all three otic endorgans, although endorgan size was proportionally greatest in smaller animals. Of the three endorgans, cell addition was greatest in the saccule. Moreover, far more cells were added to the caudal end of the saccule than to the rostral end. Each saccule of the largest hake had over 900,000 hair cells. It is estimated that each saccule adds approximately 110,000 new hair cells each year (or 302 cells/day) over the life span of the fish studied. A significant number of small ciliary bundles, thought to represent newly proliferated hair cells, was found throughout each endorgan, and the number of such bundles declined as the rate of hair cell proliferation decreased. The results demonstrate that extensive proliferation occurs in all three otolithic endorgans of the ears in a fish and that such proliferation continues for virtually the whole life of the animal. The functional significance of this addition is not known.

Animals↗
PubMed2003

Differential expression of Na,K-ATPase alpha and beta subunit genes in the developing zebrafish inner ear.

We have used whole-mount in situ hybridization to analyze Na,K-ATPase alpha and beta subunit gene expression in the developing zebrafish ear. Four alpha1-like (alpha1a.1, alpha1a.2, alpha1a.4, and alpha1a.5) and two beta (beta1a and beta2b) subunit genes are expressed in ear beginning at mid-somitogenesis. Each gene exhibits a distinct spatial and temporal expression pattern. The alpha1a.1 gene was ubiquitously expressed in the otic epithelium from mid-somitogenesis to 24 hr postfertilization (hpf). Expression of this gene was gradually reduced and by 48 hpf, alpha1a.1 transcripts were no longer detectable in the ear. The alpha1a.2 and alpha1a.5 genes were expressed in regions that correspond to the anterior macula, lateral crista, and semicircular canal projections up to 48 hpf. At later stages, expression of these genes was limited to cells in the dorsolateral septum and semicircular canal projections. alpha1a.4 and beta1a transcripts were ubiquitously expressed during ear development and were present in most otic tissues at 5 days postfertilization (dpf). Expression of the beta2b gene, on the other hand, was restricted to subsets of cells that form sensory epithelia. These results strongly suggest different functional roles for individual Na,K-ATPase genes in zebrafish ear development. Na,K-ATPase genes are likely to represent useful markers for the analysis of zebrafish otogenesis.

Animals↗
PubMed2005

Smaller inner ear sensory epithelia in Neurog 1 null mice are related to earlier hair cell cycle exit.

We investigated whether co-expression of Neurog 1 and Atoh 1 in common neurosensory precursors could explain the loss of hair cells in Neurog 1 null mice. Analysis of terminal mitosis, using BrdU, supports previous findings regarding timing of exit from cell cycle. Specifically, we show that cell cycle exit occurs in spiral sensory neurons in a base-to-apex progression followed by cell cycle exit of hair cells in the organ of Corti in an apex-to-base progression, with some overlap of cell cycle exit in the apex for both hair cells and spiral sensory neurons. Hair cells in Neurog 1 null mice show cell cycle exit in an apex-to-base progression about 1-2 days earlier. Atoh 1 is expressed in an apex-to-base progression rather then a base-to-apex progression as in wildtype littermates. We tested the possible expression of Atoh1 in neurosensory precursors using two Atoh 1-Cre lines. We show Atoh 1-Cre mediated beta-galactosidase expression in delaminating sensory neuron precursors as well as undifferentiated epithelial cells at E11 and E12.5. PCR analysis shows expression of Atoh 1 in the otocyst as early as E10.5, prior to any histology-based detection techniques. Combined, these data suggest that low levels of Atoh 1 exist much earlier in precursors of hair cells and sensory neurons, possibly including neurosensory precursors. Analysis of Atoh 1-Cre expression in E18.5 embryos and P31 mice reveal beta-galactosidase stain in all hair cells but also in vestibular and cochlear sensory neurons and some supporting cells. A similar expression of Atoh 1-LacZ exists in postnatal and adult vestibular and cochlear sensory neurons, and Atoh 1 expression in vestibular sensory neurons is confirmed with RT-PCR. We propose that the absence of NEUROG 1 protein leads to loss of sensory neuron formation through a phenotypic switch of cycling neurosensory precursors from sensory neuron to hair cell fate. Neurog 1 null mice show a truncation of clonal expansion of hair cell precursors through temporally altered terminal mitosis, thereby resulting in smaller sensory epithelia.

Animals↗
PubMed2002

Planar cell polarity in the inner ear: how do hair cells acquire their oriented structure?

Sensory hair cells in the ear and lateral line have an asymmetrical hair-bundle structure, essential for their function as directional mechanotransducers. We examine four questions: (1) how does the planar asymmetry of the individual hair cell originate? (2) How are the orientations of neighboring hair cells coordinated? (3) How is the orientation of a group of hair cells controlled in relation to the ear as a whole? (4) How does the initial cell asymmetry lead to creation of the asymmetrical hair bundle? Studies of the development of hairs and bristles in Drosophila, combined with genetic data from vertebrates, suggest that the answer to questions (1) and (2) lies in asymmetries that develop at the cell cortex and at cell-cell junctions, generated by products of a set of primary planar cell polarity genes, including the transmembrane receptor Frizzled. A separate and largely independent mechanism controls asymmmetric allocation of cell fate determinants such as Numb at mitosis, in Drosophila and possibly in the ear also. Little is known about long-range signals that might orient hair cells globally in the ear, but progress has been made in identifying a set of genes responsible for read-out of the primary polarity specification. These genes, in flies and vertebrates, provide a link to assembly of the polarized cytoskeleton; myosin VIIA appears to belong in this group. The mechanism creating the staircase pattern of stereocilium lengths is unknown, but could involve regulation of stereocilium growth by Ca(2+) ions entering via transduction channels.

Animals↗
PubMed1994

Ba2+ and amiloride uncover or induce a pH-sensitive and a Na+ or non-selective cation conductance in transitional cells of the inner ear.

The membrane potential Vm the cytosolic pH (pHi), the transference numbers (t) for K+, Cl- and Na+/non-selective cation (NSC) and the pH-sensitivity of Vm were investigated in transitional cells from the vestibular labyrinth of the gerbil. Vm, pHi, tK+, tCl-, tNa+/NSC, and the pHi sensitivity of Vm were under control conditions were -92 +/- 1 mV (n = 89 cells), pHi 7.13 +/- 0.07 (n = 11 epithelia), 0.87 +/- 0.02 (n = 22), 0.02 +/- 0.01 (n = 19), 0.01 +/- 0.01 (n = 24) and -5 mV/pH unit (n = 13 cells/n = 11 epithelia), respectively. In the presence of 100 mumol/l Ba2+ the corresponding values were: -70 +/- 1 mV (n = 32), pHi 7.16 +/- 0.08 (n = 6), 0.31 +/- 0.05 (n = 4), 0.06 +/- 0.01 (n = 6), 0.20 +/- 0.03 (n = 10) and -16 mV/pH-unit (n = 15/n = 6). In the presence of 500 mumol/l amiloride the corresponding values were: -72 +/- 2 mV (n = 34), pHi 7.00 +/- 0.07 (n = 5), 0.50 +/- 0.04 (n = 6), 0.04 +/- 0.01 (n = 11), 0.28 +/- 0.04 (n = 9) and -26 mV/pH-unit (n = 20/n = 5). In the presence of 20 mmol/l propionate plus amiloride the corresponding values were: -61 +/- 2 mV (n = 27), pHi 6.72 +/- 0.06 (n = 5), 0.30 +/- 0.02 (n = 6), 0.06 +/- 0.01 (n = 5) and 0.40 +/- 0.02 (n = 8), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride↗
PubMed1979

Development of endolymph during maturation of the mammalian inner ear. A preliminary report.

The development of the elemental composition in the endolymphatic space was investigated during embryologic and early post natal maturation of the CBA/CBA mouse. At birth the elemental distribution was similar in the endo- and perilymphatic spaces. Mature composition of endolymph was reached 6--8 days post partum. The maturation of endolymph corresponded well in time with the morphological maturation of the stria vascularis.

Age Factors↗