| 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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Local mechanical stimulation of the hearing organ by laser irradiation
- 2006
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Ingår i: NeuroReport. - : Ovid Technologies (Wolters Kluwer Health). - 0959-4965 .- 1473-558X. ; 17:1, s. 33-37
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Tidskriftsartikel (refereegranskat)abstract
- Light produces force when interacting with matter. Such radiation pressure may be used to accelerate small objects along the beam path of a laser. Here, we demonstrate that a moderately powerful laser can deliver enough force to locally stimulate the hearing organ, in the absence of conventional sound. Damped mechanical oscillations are observed following brief laser pulses, implying that the organ of Corti is locally resonant. This new method will be helpful for probing the mechanical properties of the hearing organ, which have crucial importance for the ear's ability to detect sound.
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| 3. |
- Fridberger, Anders, 1966-, et al.
(författare)
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Three-dimensional structure of outer hair cell pillars
- 2009
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Ingår i: Acta Oto-Laryngologica. - : Informa Healthcare. - 0001-6489 .- 1651-2251. ; 129:9, s. 940-945
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Tidskriftsartikel (refereegranskat)abstract
- Conclusions. Electron tomography was used to generate three-dimensional reconstructions of the pillars that connect the cell membrane with the cytoskeleton of the outer hair cell. Results are consistent with the hypothesis that pillars are important for mechanically linking the membrane with the cytoskeleton.Objective: To make a qualitative assessment of the morphology of the sub-membrane pillars of cochlear outer hair cells.Materials and methods. Guinea pig cochleae were fixed and prepared for electron microscopy using protocols described previously. Sections were imaged on an electron microscope equipped with a goniometer. The specimens were tilted through a range of 120°, and an image was acquired at each tilt angle. Filtered back-projection was used to generate three-dimensional reconstructions.Results. Twelve individual pillars were successfully reconstructed. Pillars often connect to the cell membrane through a thin segment, and to the cytoskeleton through a forking structure that may form a central cavity.
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| 4. |
- He, WX, et al.
(författare)
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Reverse wave propagation in the cochlea
- 2008
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 105:7, s. 2729-2733
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Tidskriftsartikel (refereegranskat)abstract
- Otoacoustic emissions, sounds generated by the inner ear, are widely used for diagnosing hearing disorders and studying cochlear mechanics. However, it remains unclear how emissions travel from their generation sites to the cochlear base. The prevailing view is that emissions reach the cochlear base via a backward-traveling wave, a slow-propagating transverse wave, along the cochlear partition. A different view is that emissions propagate to the cochlear base via the cochlear fluids as a compressional wave, a fast longitudinal wave. These theories were experimentally tested in this study by measuring basilar membrane (BM) vibrations at the cubic distortion product (DP) frequency from two longitudinal locations with a laser interferometer. Generation sites of DPs were varied by changing frequencies of primary tones while keeping the frequency ratio constant. Here, we show that BM vibration amplitude and phase at the DP frequency are very similar to responses evoked by external tones. Importantly, the BM vibration phase at a basal location leads that at a more apical location, indicating a traveling wave that propagates in the forward direction. These data are in conflict with the backward- traveling-wave theory but are consistent with the idea that the emission comes out of the cochlea predominantly through compressional waves in the cochlear fluids.
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| 5. |
- Jacob, Stefan, et al.
(författare)
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A digital heterodyne laser interferometer for studying cochlear mechanics
- 2009
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Ingår i: Journal of Neuroscience Methods. - : Elsevier BV. - 0165-0270 .- 1872-678X. ; 179:2, s. 271-277
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Tidskriftsartikel (refereegranskat)abstract
- Laser interferometry is the technique of choice for studying the smallest displacements of the hearing organ. For low intensity sound stimulation, these displacements may be below 1 nm. This cannot be reliably measured with other presently available techniques in an intact organ of Corti. In a heterodyne interferometer, light is projected against an object of study and motion of the target along the optical axis causes phase and frequency modulations of the back-reflected light. To recover object motion, the reflected light is made to interfere with a reference beam of artificially altered frequency, producing a beating signal. In conventional interferometers, this carrier signal is demodulated with analog electronics. In this paper, we describe a digital implementation of the technique, using direct carrier sampling. In order to obtain the necessary reference signal for demodulation we introduce an additional third light path. Together, this results in lower noise and reduces the cost of the system.Within the hearing organ, different structures may move in different directions. It is therefore necessary to precisely measure the angle of incidence of the laser light, and to precisely localize the anatomical structure where the measurement is performed. Therefore, the interferometer is integrated with a laser scanning confocal microscope that permits us to map crucial morphometric parameters in each experiment. We provide key construction parameters and a detailed performance characterization. We also show that the system accurately measures the diminutive vibrations present in the apical turn of the cochlea during low-level sound stimulation.
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| 6. |
- 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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| 7. |
- Simonoska, Rusana, et al.
(författare)
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Inner ear pathology and loss of hearing in estrogen receptor-beta deficient mice
- 2009
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Ingår i: Journal of Endocrinology. - 1479-6805. ; 201:3, s. 397-406
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Tidskriftsartikel (refereegranskat)abstract
- There are well known differences between males and females in hearing. In the present study, the role of estrogen receptor-beta (ER-beta; listed as ESR2 in the MGI Database) in hearing was investigated by comparing hearing and morphology of the inner ear in ER-beta knock-out mice (ER-beta(-/-)) with that of wild-type (WT) littermates. Hearing was analyzed with auditory brainstem response audiometry at 3 and 12 months. The ER-beta(-/-) mice were deaf at 1 year of age, and the morphological analysis showed absence of hair cells and loss of the whole organ of Corti initiated in the basal turn of the cochlea. Furthermore, in ER-beta(-/-), but not in WT mice, the spiral ganglion was lacking many of its neurons. Immunostaining showed the presence of both ER-alpha (listed as ESR1 in the MGI Database) and ER-beta in the nuclei of some neurons in the inner ear in WT mice, but no ER-beta was found in the ER-beta(-/-) mice as expected. ER-alpha staining was predominant in the nuclei of large neurons and ER-beta in nuclei of small neurons and fibroblasts. These results reveal that both ERs are present in the inner ear at specific localizations suggesting subtype-specific functions. It is concluded that ER-beta is important for the prevention of age-related hearing loss. These findings strengthen the hypothesis that estrogen has a direct effect on hearing functions.
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| 8. |
- 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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| 9. |
- 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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| 10. |
- Von Tiedemann, M., et al.
(författare)
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Image adaptive point-spread function estimation and deconvolution for in vivo confocal microscopy
- 2006
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Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 69:1, s. 10-20
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Tidskriftsartikel (refereegranskat)abstract
- Visualizing deep inside the tissue of a thick biological sample often poses severe constraints on image conditions. Standard restoration techniques (denoising and deconvolution) can then be very useful, allowing one to increase the signal-to-noise ratio and the resolution of the images. In this paper, we consider the problem of obtaining a good determination of the point-spread function (PSF) of a confocal microscope, a prerequisite for applying deconvolution to three-dimensional image stacks acquired with this system. Because of scattering and optical distortion induced by the sample, the PSF has to be acquired anew for each experiment. To tackle this problem, we used a screening approach to estimate the PSF adaptively and automatically from the images. Small PSF-like structures were detected in the images, and a theoretical PSF model reshaped to match the geometric characteristics of these structures. We used numerical experiments to quantify the sensitivity of our detection method, and we demonstrated its usefulness by deconvolving images of the hearing organ acquired in vitro and in vivo.
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