| 1. |
- Flock, Å., et al.
(författare)
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Methods for integrating fluorimetry in the study of hearing organ structure and function
- 1997
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Ingår i: Hearing Research. - : Elsevier. - 0378-5955 .- 1878-5891. ; 106:1-2, s. 29-38
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Tidskriftsartikel (refereegranskat)abstract
- The measurement of function in the intact organ of Corti has up to now been achieved by three methods: electrophysiology, mechanical measurement and biochemical analysis. The two former methods have supplied information at the level of single identified cells. We have used a fourth method, optical fluorimetry, to measure hair cell function at the cellular level in the intact organ of Corti. Here we describe the methods involved in fluorescence labelling and video-enhanced microscopy in combination with electrophysiological recording of cochlear microphonic (CM) and summating potentials (SP). The guinea pig temporal bone containing an intact ear drum, ossicular chain and cochlea can be maintained in the isolated state by perfusion of the scala tympani with oxygenated tissue culture medium. Substances added to the perfusate readily diffuse through the basilar membrane into the organ of Corti. In this way cells in the organ can be stained by a number of fluorescent probes which label different structures and functions. Here we have used two dyes which label mitochondria and fluoresce with an intensity proportional to metabolic activity. By simultaneous measurement of CM and SP the functional state of the organ can be monitored.
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| 2. |
- Flock, Å., et al.
(författare)
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Supporting cells contribute to control of hearing sensitivity
- 1999
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Ingår i: Journal of Neuroscience. - : Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 19:11, s. 4498-4507
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Tidskriftsartikel (refereegranskat)abstract
- The mammalian hearing organ, the organ of Corti, was studied in an in vitro preparation of the guinea pig temporal bone. As in vivo, the hearing organ responded with an electrical potential, the cochlear microphonic potential, when stimulated with a test tone. After exposure to intense sound, the response to the test tone was reduced. The electrical response either recovered within 10-20 min or remained permanently reduced, thus corresponding to a temporary or sustained loss of sensitivity. Using laser scanning confocal microscopy, stimulus-induced changes of the cellular structure of the hearing organ were simultaneously studied. The cells in the organ were labeled with two fluorescent probes, a membrane dye and a cytoplasm dye, showing enzymatic activity in living cells. Confocal microscopy images were collected and compared before and after intense sound exposure. The results were as follows. (1) The organ of Corti could be divided into two different structural entities in terms of their susceptibility to damage: an inner, structurally stable region comprised of the inner hair cell with its supporting cells and the inner and outer pillar cells; and an outer region that exhibited dynamic structural changes and consisted of the outer hair cells and the third Deiters' cell with its attached Hensen's cells. (2) Exposure to intense sound caused the Deiters' cells and Hensen's cells to move in toward the center of the cochlear turn. (3) This event coincided with a reduced sensitivity to the test tone (i.e., reduced cochlear microphonic potential). (4) The displacement and sensitivity loss could be reversible. It is concluded that these observations have relevance for understanding the mechanisms behind hearing loss after noise exposure and that the supporting cells take an active part in protection against trauma during high-intensity sound exposure.
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| 3. |
- Fridberger, Anders, 1966-, et al.
(författare)
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Acoustic overstimulation increases outer hair cell Ca2+ concentrations and causes dynamic contractions of the hearing organ
- 1998
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 95:12, s. 7127-7132
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic responses of the hearing organ to acoustic overstimulation were investigated using the guinea pig isolated temporal bone preparation. The organ was loaded with the fluorescent Ca2+ indicator Fluo-3, and the cochlear electric responses to low-level tones were recorded through a microelectrode in the scala media. After overstimulation, the amplitude of the cochlear potentials decreased significantly. In some cases, rapid recovery was seen with the potentials returning to their initial amplitude. In 12 of 14 cases in which overstimulation gave a decrease in the cochlear responses, significant elevations of the cytoplasmic [Ca2+] in the outer hair cells were seen. [Ca2+] increases appeared immediately after terminating the overstimulation, with partial recovery taking place in the ensuing 30 min in some preparations. Such [Ca2+] changes were not seen in preparations that were stimulated at levels that did not cause an amplitude change in the cochlear potentials. The overstimulation also gave rise to a contraction, evident as a decrease of the width of the organ of Corti. The average contraction in 10 preparations was 9 microm (SE 2 microm). Partial or complete recovery was seen within 30-45 min after the overstimulation. The [Ca2+] changes and the contraction are likely to produce major functional alterations and consequently are suggested to be a factor contributing strongly to the loss of function seen after exposure to loud sounds.
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| 4. |
- Ulfendahl, M., et al.
(författare)
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Mechanical response characteristics of the hearing organ in the low-frequency regions of the cochlea
- 1996
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 76:6, s. 3850-3862
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Tidskriftsartikel (refereegranskat)abstract
- 1. With the use of an in vitro preparation of the guinea pig temporal bone, in which the apical turns of the cochlea are exposed, the mechanical and electrical responses of the cochlea in the low-frequency regions were studied during sound stimulation. 2. The mechanical characteristics were investigated in the fourth and third turns of the cochlea with the use of laser heterodyne interferometry, which allows the vibratory responses of both sensory and supporting cells to be recorded. The electrical responses, which can be maintained for several hours, were recorded only in the most apical turn. 3. In the most apical turn, the frequency locations and shapes of the mechanical and electrical responses were very similar. 4. The shapes of the tuning curves and the spatial locations of the frequency maxima in the temporal bone preparation compared very favorably with published results from in vivo recordings of hair cell receptor potentials and sound-induced vibrations of the Reissner's membrane. 5. Compressive nonlinearities were present in both the mechanical and the electrical responses at moderate sound pressure levels. 6. The mechanical tuning changed along the length of the cochlea, the center frequencies in the fourth and third turns being approximately 280 and 570 Hz, respectively. 7. The mechanical responses of sensory and supporting cells were almost identical in shape but differed significantly in amplitude radially across the reticular lamina.
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| 5. |
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