| 1. |
- Fridberger, Anders, 1966-, et al.
(författare)
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Imaging hair cell transduction at the speed of sound : dynamic behavior of mammalian stereocilia
- 2006
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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. ; 103:6, s. 1918-1923
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Tidskriftsartikel (refereegranskat)abstract
- The cochlea contains two types of sensory cells, the inner and outer hair cells. Sound-evoked deflection of outer hair cell stereocilia leads to fast force production that will enhance auditory sensitivity up to 1,000-fold. In contrast, inner hair cells are thought to have a purely receptive function. Deflection of their stereocilia produces receptor potentials, transmitter release, and action potentials in the auditory nerve. Here, we describe a method for rapid confocal imaging. The method was used to image stereocilia during simultaneous sound stimulation in an in vitro preparation of the guinea pig cochlea. We show that inner hair cell stereocilia move because they interact with the fluid surrounding the hair bundles, but stereocilia deflection occurs at a different phase of the stimulus than is generally expected. In outer hair cells, stereocilia deflections were approximately 1/3 of the reticular lamina displacement. Smaller deflections were found in inner hair cells. The ratio between stereocilia deflection and reticular lamina displacement is important for auditory function, because it determines the stimulus applied to transduction channels. The low ratio measured here suggests that amplification of hair-bundle movements may be necessary in vivo to preserve transduction fidelity at low stimulus levels. In the case of the inner hair cells, this finding would represent a departure from traditional views on their function.
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| 2. |
- Fridberger, Anders, 1966-, et al.
(författare)
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Internal shearing within the hearing organ evoked by basilar membrane motion
- 2002
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Ingår i: Journal of Neuroscience. - : Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 22:22, s. 9850-9857
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Tidskriftsartikel (refereegranskat)abstract
- The vibration of the hearing organ that occurs during sound stimulation is based on mechanical interactions between different cellular structures inside the organ of Corti. The exact nature of these interactions is unclear and subject to debate. In this study, dynamic structural changes were produced by stepwise alterations of scala tympani pressure in an in vitro preparation of the guinea pig temporal bone. Confocal images were acquired at each level of pressure. In this way, the motion of several structures could be observed simultaneously with high resolution in a nearly intact system. Images were analyzed using a novel wavelet-based optical flow estimation algorithm. Under these conditions, the reticular lamina moved as a stiff plate with a center of rotation in the region of the inner hair cells. Despite being enclosed in several types of supporting cells, the inner hair cells, together with the adjacent inner pillar cells, moved in a manner signifying high compliance. The outer hair cells displayed radial motion indicative of cellular bending. Together, these results show that shearing motion occurs between several parts of the organ, and that structural relationships within the organ change dynamically during displacement of the basilar membrane.
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| 3. |
- Fridberger, Anders, 1966-, et al.
(författare)
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Organ of Corti potentials and the motion of the basilar membrane
- 2004
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Ingår i: Journal of Neuroscience. - : Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 24:45, s. 10057-10063
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Tidskriftsartikel (refereegranskat)abstract
- During sound stimulation, receptor potentials are generated within the sensory hair cells of the cochlea. Prevailing theory states that outer hair cells use the potential-sensitive motor protein prestin to convert receptor potentials into fast alterations of cellular length or stiffness that boost hearing sensitivity almost 1000-fold. However, receptor potentials are attenuated by the filter formed by the capacitance and resistance of the membrane of the cell. This attenuation would limit cellular motility at high stimulus frequencies, rendering the above scheme ineffective. Therefore, Dallos and Evans (1995a) proposed that extracellular potential changes within the organ of Corti could drive cellular motor proteins. These extracellular potentials are not filtered by the membrane. To test this theory, both electric potentials inside the organ of Corti and basilar membrane vibration were measured in response to acoustic stimulation. Vibrations were measured at sites very close to those interrogated by the recording electrode using laser interferometry. Close comparison of the measured electrical and mechanical tuning curves and time waveforms and their phase relationships revealed that those extracellular potentials indeed could drive outer hair cell motors. However, to achieve the sharp frequency tuning that characterizes the basilar membrane, additional mechanical processing must occur inside the organ of Corti.
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| 4. |
- Fridberger, Anders, 1966-, et al.
(författare)
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Sound-induced differential motion within the hearing organ
- 2003
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Ingår i: Nature Neuroscience. - : Nature Publishing Group. - 1097-6256 .- 1546-1726. ; 6:5, s. 446-448
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Tidskriftsartikel (refereegranskat)abstract
- Hearing depends on the transformation of sound-induced basilar membrane vibration into deflection of stereocilia1 on the sensory hair cells, but the nature of these mechanical transformations is unclear. Using new techniques to visualize and measure sound-induced vibration deep inside the moving organ of Corti, we found that two functionally crucial structures, the basilar membrane and the reticular lamina, have different centers of rotation, leading to shearing motion and rapid deformation for the mechanoreceptive outer hair cells. Structural relations within the organ of Corti are much more dynamic than previously thought, which clarifies how outer hair cell molecular motors can have such a powerful effect.
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| 5. |
- Jacob, Stefan, et al.
(författare)
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Rapid confocal imaging for measuring sound-induced motion of the hearing organ in the apical region
- 2007
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Ingår i: Journal of Biomedical Optics. - : SPIE - International Society for Optical Engineering. - 1083-3668 .- 1560-2281. ; 12:2, s. 021005-1-021005-6
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Tidskriftsartikel (refereegranskat)abstract
- We describe a novel confocal image acquisition system capable of measuring the sound-evoked motion of the organ of Corti. The hearing organ is imaged with a standard laser scanning confocal microscope during sound stimulation. The exact temporal relation between each image pixel and the sound stimulus is quantified. The motion of the structures under study is obtained by fitting a Fourier series to the time dimension of a continuous sequence of acquired images. Previous versions of this acquisition system used a simple search to find pixels with similar phase values. The Fourier series approach permits substantially faster image acquisition with reduced noise levels and improved motion estimation. The system is validated by imaging various vibrating samples attached to a feedback-controlled piezoelectric translator. When using a rigid sample attached to the translator, the system is capable of measuring motion with peak-to-peak amplitudes smaller than 50 nm with an error below 20% at frequencies between 50 and 600 Hz. Examples of image sequences from the inner ear are given, along with detailed performance characteristics of the method.
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| 6. |
- Stollberg, Heide, et al.
(författare)
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Wavelet-based image restoration for compact x-ray microscopy
- 2003
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Ingår i: Journal of Microscopy. - : Wiley. - 0022-2720 .- 1365-2818. ; 211:2, s. 154-160
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Tidskriftsartikel (refereegranskat)abstract
- Compact water-window X-ray microscopy with short exposure times will always be limited on photons owing to sources of limited power in combination with low-efficency X-ray optics. Thus, it is important to investigate methods for improving the signal-to-noise ratio in the images. We show that a wavelet-based denoising procedure significantly improves the quality and contrast in compact X-ray microscopy images. A non-decimated, discrete wavelet transform (DWT) is applied to original, noisy images. After applying a thresholding procedure to the finest scales of the DWT, by setting to zero all wavelet coefficients of magnitude below a prescribed value, the inverse DWT to the thresholded DWT produces denoised images. It is concluded that the denoising procedure has potential to reduce the exposure time by a factor of 2 without loss of relevant image information.
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| 7. |
- Tomo, Igor, et al.
(författare)
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Imaging the living inner ear using intravital confocal microscopy
- 2007
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Ingår i: NeuroImage. - : Elsevier. - 1053-8119 .- 1095-9572. ; 35:4, s. 1393-1400
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Tidskriftsartikel (refereegranskat)abstract
- Confocal laser scanning microscopy permits detailed visualization of structures deep within thick fluorescently labeled specimen. This makes it possible to investigate living cells inside intact tissue without prior chemical sample fixation and sectioning. Isolated guinea pig temporal bones have previously been used for confocal experiments in vitro, but tissue deterioration limits their use to a few hours after the death of the animal. In order to preserve the cochlea in an optimal functional and physiological condition, we have developed an in vivo model based on a confocal microscopy approach. Using a ventral surgical approach, the inner ear is exposed in deeply anaesthetized, tracheotomized, living guinea pigs. To label the inner ear structures, scala tympani is perfused via an opening in the basal turn, delivering tissue culture medium with fluorescent vital dyes (RH 795 and calcein AM). An apical opening is made in the bony shell of cochlea to enable visualization using a custom-built objective lens. Intravital confocal microscopy, with preserved blood and nerve supply, may offer an important tool for studying auditory physiology and the pathology of hearing loss. After acoustic overstimulation, shortening and swelling of the sensory hair cells were observed.
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| 8. |
- Tomo, Igor, et al.
(författare)
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Sound-evoked radial strain in the hearing organ
- 2007
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Ingår i: Biophysical Journal. - : Cell Press. - 0006-3495 .- 1542-0086. ; 93:9, s. 3279-3284
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Tidskriftsartikel (refereegranskat)abstract
- The hearing organ contains sensory hair cells, which convert sound-evoked vibration into action potentials in the auditory nerve. This process is greatly enhanced by molecular motors that reside within the outer hair cells, but the performance also depends on passive mechanical properties, such as the stiffness, mass, and friction of the structures within the organ of Corti. We used resampled confocal imaging to study the mechanical properties of the low-frequency regions of the cochlea. The data allowed us to estimate an important mechanical parameter, the radial strain, which was found to be 0.1% near the inner hair cells and 0.3% near the third row of outer hair cells during moderate-level sound stimulation. The strain was caused by differences in the motion trajectories of inner and outer hair cells. Motion perpendicular to the reticular lamina was greater at the outer hair cells, but inner hair cells showed greater radial vibration. These differences led to deformation of the reticular lamina, which connects the apex of the outer and inner hair cells. These results are important for understanding how the molecular motors of the outer hair cells can so profoundly affect auditory sensitivity.
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| 9. |
- von Tiedemann, Miriam, et al.
(författare)
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Brightness-compensated 3-D optical flow algorithm for monitoring cochlear motion patterns
- 2010
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Ingår i: Journal of biomedical optics. - : SPIE-Intl Soc Optical Eng. - 1560-2281 .- 1083-3668. ; 15:5, s. 056012-
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Tidskriftsartikel (refereegranskat)abstract
- A method for three-dimensional motion analysis designed for live cell imaging by fluorescence confocal microscopy is described. The approach is based on optical flow computation and takes into account brightness variations in the image scene that are not due to motion, such as photobleaching or fluorescence variations that may reflect changes in cellular physiology. The 3-D optical flow algorithm allowed almost perfect motion estimation on noise-free artificial sequences, and performed with a relative error of <10% on noisy images typical of real experiments. The method was applied to a series of 3-D confocal image stacks from an in vitro preparation of the guinea pig cochlea. The complex motions caused by slow pressure changes in the cochlear compartments were quantified. At the surface of the hearing organ, the largest motion component was the transverse one (normal to the surface), but significant radial and longitudinal displacements were also present. The outer hair cell displayed larger radial motion at their basolateral membrane than at their apical surface. These movements reflect mechanical interactions between different cellular structures, which may be important for communicating sound-evoked vibrations to the sensory cells. A better understanding of these interactions is important for testing realistic models of cochlear mechanics.
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