Optimization of spectral-domain optical coherence tomography with a supercontinuum source for in vivo motion detection of low reflective outer hair cells in guinea pig cochleae

The version of record of this article, first published in Optical Review, is available online at Publisher’s website: https://doi.org/10.1007/s10043-021-00654-8.Sound evokes sub-nanoscale vibration within the sensory epithelium. The epithelium contains not only immotile cells but also contractile outer hair cells (OHCs) that actively shrink and elongate synchronously with the sound. However, the in vivo motion of OHCs has remained undetermined. The aim of this work is to perform high-resolution and -accuracy vibrometry in live guinea pigs with an SC-introduced spectral-domain optical coherence tomography system (SD-OCT). In this study, to reveal the effective contribution of SC source in the recording of the low reflective materials with the short total acquisition time, we compare the performances of the SC-introduced SD-OCT (SCSD-OCT) to that of the conventional SD-OCT. As inanimate comparison objects, we record a mirror, a piezo actuator, and glass windows. For the measurements in biological materials, we use in/ex vivo guinea pig cochleae. Our study achieved the optimization of a SD-OCT system for high-resolution in vivo vibrometry in the cochlear sensory epithelium, termed the organ of Corti, in mammalian cochlea. By introducing a supercontinuum (SC) light source and reducing the total acquisition time, we improve the axial resolution and overcome the difficulty in recording the low reflective material in the presence of biological noise. The high power of the SC source enables the system to achieve a spatial resolution of 1.72 ± 0.00 μm on a mirror and reducing the total acquisition time contributes to the high spatial accuracy of sub-nanoscale vibrometry. Our findings reveal the vibrations at the apical/basal region of OHCs and the extracellular matrix, basilar membrane

In vivo tomographic visualization of intracochlear vibration using a supercontinuum multifrequency-swept optical coherence microscope

Choi S., Nin F., Ota T., et al. In vivo tomographic visualization of intracochlear vibration using a supercontinuum multifrequency-swept optical coherence microscope. Biomedical Optics Express 10, 3317 (2019); https://doi.org/10.1364/BOE.10.003317.This study combined a previously developed optical system with two additional key elements: a supercontinuum light source characterized by high output power and an analytical technique that effectively extracts interference signals required for improving the detection limit of vibration amplitude. Our system visualized 3D tomographic images and nanometer scale vibrations in the cochlear sensory epithelium of a live guinea pig. The transverse- and axial-depth resolution was 3.6 and 2.7 µm, respectively. After exposure to acoustic stimuli of 21-25 kHz at a sound pressure level of 70-85 dB, spatial amplitude and phase distributions were quantified on a targeted surface, whose area was 522 × 522 µm2

Rapid optical tomographic vibrometry using a swept multi-gigahertz comb

Choi S., Ota T., Nin F., et al. Rapid optical tomographic vibrometry using a swept multi-gigahertz comb. Optics Express 29, 16749 (2021); https://doi.org/10.1364/OE.425972.We propose a rapid tomographic vibrometer technique using an optical comb to measure internal vibrations, transient phenomena, and tomographic distributions in biological tissue and microelectromechanical system devices at high frequencies. This method allows phase-sensitive tomographic measurement in the depth direction at a multi-MHz scan rate using a frequency-modulated broadband electrooptic multi-GHz supercontinuum comb. The frequency spacing was swept instantaneously in time and axisymmetrically about the center wavelength via a dual-drive Mach-Zehnder modulator driven by a variable radio frequency signal. This unique sweeping method permits direct measurement of fringe-free interferometric amplitude and phase with arbitrarily changeable measurement range and scan rate. Therefore, a compressive measurement can be made in only the depth region where the vibration exists, reducing the number of measurement points. In a proof-of-principle experiment, the interferometric amplitude and phase were investigated for in-phase and quadrature phase-shifted interferograms obtained by a polarization demodulator. Tomographic transient displacement measurements were performed using a 0.12mm thick glass film and piezo-electric transducer oscillating at 10-100 kHz with scan rates in the range 1-20 MHz. The depth resolution and precision of the vibrometer were estimated to be approximately 25 μm and 1.0 nm, respectively

Sparsity-Aware OCT Volumetric Data Restoration Using Optical Synthesis Model

Kobayashi R., Fujii G., Yoshida Y., et al. Sparsity-Aware OCT Volumetric Data Restoration Using Optical Synthesis Model. IEEE Transactions on Computational Imaging 8, 505 (2022); https://doi.org/10.1109/TCI.2022.3183396.In this study, a novel restoration model for the data of optical coherence tomography (OCT) is proposed. An OCT device acquires a tomographic image of a specimen at the scale of a few micrometers using a near-infrared laser and has been frequently adopted to measure the structures of bio-tissues. In certain applications, OCT devices face the problem of extremely weak reflected light and require the help of image processing to estimate the distribution of reflected light hidden in various noises. OCT identifies tomographic structures by searching for peak interference locations and their intensities. Therefore, the challenge of OCT data restoration involves the problem of identifying the interference function and its deconvolution. In this study, a restoration method is given by reducing the problem to a regularized least-squares problem with a hard constraint for the latent refractive index distributions, and an algorithm is derived using a primal-dual splitting (PDS) framework. The PDS has the advantage of requiring no inverse matrix operation and is able to handle high-dimensional data. The significance of the proposed method is verified through simulations using artificial data, followed by an experiment conducted using actual observation of 64 × 64 × 5000 sized voxels

Perinatal Epidermal Growth Factor Signal Perturbation Results in the Series of Abnormal Auditory Oscillations and Responses Relevant to Schizophrenia

Kai R., Namba H., Sotoyama H., et al. Perinatal Epidermal Growth Factor Signal Perturbation Results in the Series of Abnormal Auditory Oscillations and Responses Relevant to Schizophrenia. Schizophrenia Bulletin Open 2, sgaa070 (2021); https://doi.org/10.1093/schizbullopen/sgaa070.Auditory neurophysiological responses, such as steady-state responses, event-related potential P300/P3, and phase-Amplitude coupling, are promising translational biomarkers for schizophrenia, but their molecular underpinning is poorly understood. Focusing on ErbB receptor signals that are implicated in both schizophrenia and auditory processing/cognition, we explored the causal biological links between ErbB signals and these auditory traits with an experimental intervention into rats. We peripherally challenged rat pups with one of the amniotic ErbB ligands, epidermal growth factor (EGF), and characterized its consequence on the series of these auditory electrocorticographic measures. Auditory brainstem responses (ABRs) and cortical ON responses were also assessed under anesthesia to estimate the influence of higher brain regions. An auditory steady-state paradigm revealed attenuation of spectral power and phase synchrony to 40-Hz stimuli in EGF-challenged rats. We observed a reduction in duration mismatch negativity-like potentials and a delay of P3a responses, all of which are relevant to the reported auditory pathophysiological traits of patients with schizophrenia. Moreover, the perinatal EGF challenges resulted in enhanced theta-Alpha/beta and theta-gamma coupling within the auditory cortex and changes in ABRs. However, the EGF challenges retained the normal ranges of cortical ON responses, potentially ruling out their fundamental auditory deficits. Perinatal exposure of an ErbB ligand to rats strikingly reproduced the whole series of aberrant auditory responses and oscillations previously reported in patients with schizophrenia. Accordingly, these findings suggest that developmental deficits in ErbB/EGF signaling might be involved in the auditory pathophysiology associated with schizophrenia

Characterisation of the static offset in the travelling wave in the cochlear basal turn

The version of record of this article, first published in Pflugers Archiv European Journal of Physiology, is available online at Publisher’s website: https://doi.org/10.1007/s00424-020-02373-6.In mammals, audition is triggered by travelling waves that are evoked by acoustic stimuli in the cochlear partition, a structure containing sensory hair cells and a basilar membrane. When the cochlea is stimulated by a pure tone of low frequency, a static offset occurs in the vibration in the apical turn. In the high-frequency region at the cochlear base, multi-tone stimuli induce a quadratic distortion product in the vibrations that suggests the presence of an offset. However, vibrations below 100 Hz, including a static offset, have not been directly measured there. We therefore constructed an interferometer for detecting motion at low frequencies including 0 Hz. We applied the interferometer to record vibrations from the cochlear base of guinea pigs in response to pure tones. When the animals were exposed to sound at an intensity of 70 dB or higher, we recorded a static offset of the sinusoidally vibrating cochlear partition by more than 1 nm towards the scala vestibuli. The offset’s magnitude grew monotonically as the stimuli intensified. When stimulus frequency was varied, the response peaked around the best frequency, the frequency that maximised the vibration amplitude at threshold sound pressure. These characteristics are consistent with those found in the low-frequency region and are therefore likely common across the cochlea. The offset diminished markedly when the somatic motility of mechanosensitive outer hair cells, the force-generating machinery that amplifies the sinusoidal vibrations, was pharmacologically blocked. Therefore, the partition offset appears to be linked to the electromotile contraction of outer hair cells

Integrative and theoretical research on the architecture of a biological system and its disorder

Uchida S., Asai Y., Kariya Y., et al. Integrative and theoretical research on the architecture of a biological system and its disorder. Journal of Physiological Sciences , (2019); https://doi.org/10.1007/s12576-019-00667-8.An organism stems from assemblies of a variety of cells and proteins. This complex system serves as a unit, and it exhibits highly sophisticated functions in response to exogenous stimuli that change over time. The complete sequencing of the entire human genome has allowed researchers to address the enigmas of life and disease at the gene- or molecular-based level. The consequence of such studies is the rapid accumulation of a multitude of data at multiple levels, ranging from molecules to the whole body, that has necessitated the development of entirely new concepts, tools, and methodologies to analyze and integrate these data. This necessity has given birth to systems biology, an advanced theoretical and practical research framework that has totally changed the directions of not only basic life science but also medicine. During the symposium of the 95th Annual Meeting of The Physiological Society of Japan 2018, five researchers reported on their respective studies on systems biology. The topics included reactions of drugs, ion-transport architecture in an epithelial system, multi-omics in renal disease, cardiac electrophysiological systems, and a software platform for computer simulation. In this review article these authors have summarized recent achievements in the field and discuss next-generation studies on health and disease

Characterisation of N-glycans in the epithelial-like tissue of the rat cochlea

Nonomura Y., Sawamura S., Hanzawa K., et al. Characterisation of N-glycans in the epithelial-like tissue of the rat cochlea. Scientific Reports 9, 1551 (2019); https://doi.org/10.1038/s41598-018-38079-0.Membrane proteins (such as ion channels, transporters, and receptors) and secreted proteins are essential for cellular activities. N-linked glycosylation is involved in stability and function of these proteins and occurs at Asn residues. In several organs, profiles of N-glycans have been determined by comprehensive analyses. Nevertheless, the cochlea of the mammalian inner ear, a tiny organ mediating hearing, has yet to be examined. Here, we focused on the stria vascularis, an epithelial-like tissue in the cochlea, and characterised N-glycans by liquid chromatography with mass spectrometry. This hypervascular tissue not only expresses several ion transporters and channels to control the electrochemical balance in the cochlea but also harbours different transporters and receptors that maintain structure and activity of the organ. Seventy-nine N-linked glycans were identified in the rat stria vascularis. Among these, in 55 glycans, the complete structures were determined; in the other 24 species, partial glycosidic linkage patterns and full profiles of the monosaccharide composition were identified. In the process of characterisation, several sialylated glycans were subjected sequentially to two different alkylamidation reactions; this derivatisation helped to distinguish α2,3-linkage and α2,6-linkage sialyl isomers with mass spectrometry. These data should accelerate elucidation of the molecular architecture of the cochlea

Hearing Loss Controlled by Optogenetic Stimulation of Nonexcitable Nonglial Cells in the Cochlea of the Inner Ear

Light-gated ion channels and transporters have been applied to a broad array of excitable cells including neurons, cardiac myocytes, skeletal muscle cells and pancreatic β-cells in an organism to clarify their physiological and pathological roles. Nonetheless, among nonexcitable cells, only glial cells have been studied in vivo by this approach. Here, by optogenetic stimulation of a different nonexcitable cell type in the cochlea of the inner ear, we induce and control hearing loss. To our knowledge, deafness animal models using optogenetics have not yet been established. Analysis of transgenic mice expressing channelrhodopsin-2 (ChR2) induced by an oligodendrocyte-specific promoter identified this channel in nonglial cells—melanocytes—of an epithelial-like tissue in the cochlea. The membrane potential of these cells underlies a highly positive potential in a K+-rich extracellular solution, endolymph; this electrical property is essential for hearing. Illumination of the cochlea to activate ChR2 and depolarize the melanocytes significantly impaired hearing within a few minutes, accompanied by a reduction in the endolymphatic potential. After cessation of the illumination, the hearing thresholds and potential returned to baseline during several minutes. These responses were replicable multiple times. ChR2 was also expressed in cochlear glial cells surrounding the neuronal components, but slight neural activation caused by the optical stimulation was unlikely to be involved in the hearing impairment. The acute-onset, reversible and repeatable phenotype, which is inaccessible to conventional gene-targeting and pharmacological approaches, seems to at least partially resemble the symptom in a population of patients with sensorineural hearing loss. Taken together, this mouse line may not only broaden applications of optogenetics but also contribute to the progress of translational research on deafness