| 1. |
- Felder, E, et al.
(författare)
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Quantitative evaluation of cochlear neurons and computer-aided three-dimensional reconstruction of spiral ganglion cells in humans with a peripheral loss of nerve fibres
- 1997
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Ingår i: Hearing Research. - 0378-5955 .- 1878-5891. ; 105:1-2, s. 183-190
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Tidskriftsartikel (refereegranskat)abstract
- Quantitative data on human cochlear neuronal elements were collected from various regions in five patients with high-tone hearing loss due to presbycusis and in two patients with normal hearing. The number of nerve fibers was assessed in the spiral lamina and in the inner acoustic meatus together with counts of spiral ganglion cells. The results show that the number of neurons decreased peripherally, i.e., with increasing distance from the central nervous system in patients with high-tone hearing loss due to presbycusis. In two patients with normal hearing no significant difference in the number of neurons was found in the lamina spiralis as compared to the inner acoustic canal. Computer-aided 3-dimensional reconstruction of the human spiral ganglion displayed large bipolar neurons (type I cells), but also large ganglion cells with one missing axon. The results may indicate that a slow retrograde degeneration occurs from the periphery towards the spiral ganglion in presbycusis. Transmission electron microscopy analysis of freshly fixed human spiral ganglions displayed interneural connections. It is speculated whether a trophic supply from other neurons at the level of the spiral ganglion can prevent or delay further degeneration of the central axon.
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| 2. |
- 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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| 3. |
- Fridberger, Anders, 1966-, et al.
(författare)
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Alterations of basilar membrane response phase and velocity after acoustic overstimulation
- 2002
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Ingår i: Hearing Research. - : Elsevier. - 0378-5955 .- 1878-5891. ; 167:1-2, s. 214-222
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the physiology of noise-induced hearing loss, the sound-induced vibrations of the basilar membrane (BM) of the inner ear were measured in living anesthetized guinea pigs before and after intense sound exposure. The vibrations were measured using a laser Doppler velocimeter after placing reflective glass beads on the BM. Pseudo-random noise waveforms containing frequencies between 4 and 24 kHz were used to generate velocity tuning curves. Before overstimulation, sharp response peaks were seen at stimulus frequencies between 15 and 17 kHz, consistent with the expected best frequency of the recording location. The response to low level stimuli lagged the high level ones by up to 90 degrees at the characteristic frequency. Following exposure to loud sound, the BM vibrations showed a pronounced reduction in amplitude, primarily at low stimulus levels, and the best frequency moved to approximately 12 kHz. At higher levels, the reduction was either absent or much smaller. In addition to the amplitude changes, increased phase lags were seen at frequencies near the characteristic frequency. In animals with more severe exposures, response phases were altered also at frequencies showing no change of the amplitude. The phase was independent of stimulus level after severe exposures.
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| 4. |
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| 5. |
- Takumida, Masaya, et al.
(författare)
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Lipopolysaccharide-induced expression of inducible nitric oxide synthase in the guinea pig organ of Corti
- 2000
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Ingår i: Hearing Research. - 0378-5955 .- 1878-5891. ; 140:1-2, s. 91-8
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the investigation was to ascertain whether inoculation of bacterial lipopolysaccharide (LPS) into the cochlea of the guinea pig could elicit formation of inducible nitric oxide synthase (iNOS). Immunohistochemical study revealed that immunoreactivity to iNOS was seen below outer hair cells representing nerve fibers and synaptic nerve endings. iNOS-staining could also be observed in phalangeal dendrites of Deiter's cells pointing to the cuticular membrane, Hensen's cells and on stria vascularis 48 h after inoculation with LPS. Immunohistochemical investigation with a specific anti-nitrotyrosine antibody also revealed intense immunoreactivity identical to that of iNOS, suggesting formation of peroxynitrite in the organ of Corti by the reaction of NO with O(2)(-). On the basis of these findings, it can be concluded that NO together with O(2)(-), which form the more reactive peroxynitrite, are the most important pathogenic agents in LPS-induced damage of cochlea in the guinea pig.
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| 6. |
- Anderson, Malin, et al.
(författare)
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Structure and locomotion of adult in vitro regenerated spiral ganglion growth cones : a study using video microscopy and SEM
- 2006
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Ingår i: Hearing Research. - : Elsevier BV. - 0378-5955 .- 1878-5891. ; 215:1-2, s. 97-107
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Tidskriftsartikel (refereegranskat)abstract
- Neuronal development and neurite regeneration depends on the locomotion and navigation of nerve growth cones (GCs). There are few detailed descriptions of the GC function and structure in the adult auditory system. In this study, GCs of adult dissociated and cultured spiral ganglion (SG) neurons were analyzed in vitro utilizing combined high resolution scanning electron microscopy (SEM) and time lapse video microscopy (TLVM). Axon kinesis was assessed on planar substratum with growth factors BDNF, NT-3 and GDNF. At the nano-scale level, lamellipodial abdomen of the expanding GC was found to be decorated with short surface specializations, which at TLVM were considered to be related to their crawling capacity. Filopodia were devoid of these surface structures, supporting its generally described sensory role. Microspikes appearing on lamellipodia and axons, showed circular adhesions, which at TLVM were found to provide anchorage of the navigating and turning axon. Neurons and GCs expressed the DCC-receptor for the guidance molecule netrin-1. Asymmetric ligand-based stimulation initiated turning responses suggest that this attractant cue influences steering of GC in adult regenerating auditory neurites. Hopefully, these findings may be used for ensuing tentative navigation of spiral ganglion neurons to induce regenerative processes in the human ear.
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| 7. |
- Ashmore, J, et al.
(författare)
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The remarkable cochlear amplifier
- 2010
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Ingår i: Hearing research. - : Elsevier BV. - 1878-5891 .- 0378-5955. ; 266:1-2, s. 1-17
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Tidskriftsartikel (refereegranskat)
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| 8. |
- Asp, Filip, et al.
(författare)
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The effect of simulated unilateral hearing loss on horizontal sound localization accuracy and recognition of speech in spatially separate competing speech
- 2018
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Ingår i: Hearing Research. - : Elsevier BV. - 1878-5891 .- 0378-5955. ; 357, s. 54-63
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Tidskriftsartikel (refereegranskat)abstract
- Unilateral hearing loss (UHL) occurs in 25% of cases of congenital sensorineural hearing loss. Due to the unilaterally reduced audibility associated with UHL, everyday demanding listening situations may be disrupted despite normal hearing in one ear. The aim of this study was to quantify acute changes in recognition of speech in spatially separate competing speech and sound localization accuracy, and relate those changes to two levels of temporary induced UHL (UHL 30 and UHL 43 ; suffixes denote the average hearing threshold across 0.5, 1, 2, and 4 kHz) for 8 normal-hearing adults. A within-subject repeated-measures design was used (normal binaural conditions, UHL 30 and UHL 43 ). The main outcome measures were the threshold for 40% correct speech recognition and the overall variance in sound localization accuracy quantified by an Error Index (0 = perfect performance, 1.0 = random performance). Distinct and statistically significant deterioration in speech recognition (2.0 dB increase in threshold, p < 0.01) and sound localization (Error Index increase of 0.16, p < 0.001) occurred in the UHL 30 condition. Speech recognition did not significantly deteriorate further in the UHL 43 condition (1.0 dB increase in speech recognition threshold, p > 0.05), while sound localization was additionally impaired (Error Index increase of 0.33, p < 0.01) with an associated large increase in individual variability. Qualitative analyses on a subject-by-subject basis showed that high-frequency audibility was important for speech recognition, while low-frequency audibility was important for horizontal sound localization accuracy. While the data might not be entirely applicable to individuals with long-standing UHL, the results suggest a need for intervention for mild-to-moderate UHL.
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| 9. |
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| 10. |
- Berggren, Diana, et al.
(författare)
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Spontaneous hair-cell renewal following gentamicin exposure in postnatal rat utricular explants
- 2003
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Ingår i: Hearing Research. - 0378-5955 .- 1878-5891. ; 180:1-2, s. 114-125
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Tidskriftsartikel (refereegranskat)abstract
- We have established an in vitro model of long-time culture of 4-day-old rat utricular maculae to study aminoglycoside-induced vestibular hair-cell renewal in the mammalian inner ear. The explanted maculae were cultured for up to 28 days on the surface of a membrane insert system. In an initial series of experiments utricles were exposed to 1 mM of gentamicin for 48 h and then allowed to recover in unsupplemented medium or in medium supplemented with the anti-mitotic drug aphidicolin. In a parallel control series, explants were not exposed to gentamicin. Utricles were harvested at specified time points from the second through the 28th day in vitro. Whole-mount utricles were stained with phalloidin-fluorescein isothiocyanate and their stereociliary bundles visualized and counted. In a second experimental series 2'-bromo-5'deoxyuridine labeling was used to confirm the antimitotic efficacy of aphidicolin. Loss of hair-cell stereociliary bundles was nearly complete 3 days after exposure to gentamicin, with the density of stereociliary bundles only 3-4% of their original density. Renewal of hair-cell bundles was abundant (i.e. 15x increase) in cultures in unsupplemented medium, with a peak of stereociliary bundle renewal reached after 21 days in vitro. A limited amount of hair-cell renewal also occurred in the presence of the anti-mitotic drug, aphidicolin. These results suggest that spontaneous renewal of hair-cell stereociliary bundles following gentamicin damage in utricular explants predominantly follows a pathway that includes mitotic events, but that a small portion of the hair-cell stereociliary bundle renewal does not require mitotic activity.
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