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16 results on '"Suthakar, Kirupa"'

3. Central Projections of Spiral Ganglion Neurons

Author

Muniak, Michael A., Connelly, Catherine J., Suthakar, Kirupa, Milinkeviciute, Giedre, Ayeni, Femi E., Ryugo, David K., Fay, Richard R., Series editor, Popper, Arthur N., Series editor, Dabdoub, Alain, editor, and Fritzsch, Bernd, editor

Published
2016
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14. Changes to the descending auditory system in hearing loss: focus on auditory efferents

Author

Suthakar, Kirupa

Subjects
descending, otorhinolaryngologic diseases, tonotopy, auditory efferent, hearing loss
Abstract

Age related hearing loss (ARHL) affects one in three humans aged over 65 years of age. The most common complaint in ARHL is difficulty understanding speech in noise. Olivocochlear (OC) efferents project from the brain to the cochlea and represent the final stage of the descending auditory pathway. OC efferents are involved in listening in loud environments and protect the cochlea from noise damage. We used anatomical methods to investigate OC efferent cell morphology and top-down patterns of descending input from the inferior colliculus (IC) to determine if deterioration of the descending auditory pathway accompanies peripheral auditory pathology in the mouse. Brightfield, fluorescent, and electron microscopy were used to identify OCs and their synaptic inputs in 1-,3-, and 6-month old mice with normal hearing (CBA/CaH), progressive high frequency hearing loss (DBA/2), and congenital deafness (homozygous Shaker2). Electrophysiologically directed injections in the IC were used to elucidate the tonotopic nature of descending input to the medial OC (MOC) efferent population. In normal hearing mice, the IC provides excitatory synaptic input to MOCs in a tonotopic manner. Higher frequencies project to medially located cells, whereas lower frequencies project to laterally located cells. Synaptic input was retained in hearing loss and congenital deafness, however, the spatial distribution of terminals and MOC somata were significantly altered. Together, these data indicate that the nature and time course of peripheral hearing pathology is correlated with loss of MOC efferent cells and a systematic deviation of descending input from the IC in a frequency dependent manner. Therefore, changes to the descending central auditory pathway may help to explain the difficulty extracting signals from background noise characteristic of ARHL. In the course of investigating OC efferents, we consistently identified a population of cells in the ventral nucleus of the lateral lemniscus that appeared to project to the cochlea. Using immunohistochemical, neuronal tract tracing, and electron microscopic methods, we characterized these ‘dorsal efferents’ with respect to the existing OC populations and provide evidence for their inclusion as a new class of auditory efferents in mouse.

Published
2017
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15. Changes to the descending auditory system in hearing loss: focus on auditory efferents

Author

Ryugo, David, Garvan Institute of Medical Research, Faculty of Medicine, UNSW, McMahon, Catherine, Department of Linguistics, Macquarie University, Suthakar, Kirupa, Garvan Institute of Medical Research, Faculty of Medicine, UNSW, Ryugo, David, Garvan Institute of Medical Research, Faculty of Medicine, UNSW, McMahon, Catherine, Department of Linguistics, Macquarie University, and Suthakar, Kirupa, Garvan Institute of Medical Research, Faculty of Medicine, UNSW

Abstract

Age related hearing loss (ARHL) affects one in three humans aged over 65 years of age. The most common complaint in ARHL is difficulty understanding speech in noise. Olivocochlear (OC) efferents project from the brain to the cochlea and represent the final stage of the descending auditory pathway. OC efferents are involved in listening in loud environments and protect the cochlea from noise damage. We used anatomical methods to investigate OC efferent cell morphology and top-down patterns of descending input from the inferior colliculus (IC) to determine if deterioration of the descending auditory pathway accompanies peripheral auditory pathology in the mouse. Brightfield, fluorescent, and electron microscopy were used to identify OCs and their synaptic inputs in 1-,3-, and 6-month old mice with normal hearing (CBA/CaH), progressive high frequency hearing loss (DBA/2), and congenital deafness (homozygous Shaker2). Electrophysiologically directed injections in the IC were used to elucidate the tonotopic nature of descending input to the medial OC (MOC) efferent population. In normal hearing mice, the IC provides excitatory synaptic input to MOCs in a tonotopic manner. Higher frequencies project to medially located cells, whereas lower frequencies project to laterally located cells. Synaptic input was retained in hearing loss and congenital deafness, however, the spatial distribution of terminals and MOC somata were significantly altered. Together, these data indicate that the nature and time course of peripheral hearing pathology is correlated with loss of MOC efferent cells and a systematic deviation of descending input from the IC in a frequency dependent manner. Therefore, changes to the descending central auditory pathway may help to explain the difficulty extracting signals from background noise characteristic of ARHL. In the course of investigating OC efferents, we consistently identified a population of cells in the ventral nucleus of the lateral lemniscus tha

Published
2017

16. ABRpresto: An algorithm for automatic thresholding of the Auditory Brainstem Response using resampled cross-correlation across subaverages.

Author

Shaheen LA, Buran BN, Suthakar K, Koehler SD, and Chung Y

Abstract

The auditory brainstem response (ABR) is an essential diagnostic indicator of overall cochlear health, used extensively in both basic research and clinical studies. A key quantification of the ABR is threshold, the lowest sound level that elicits a response. Because the morphology of ABR waveforms shift with stimulus level and the overall signal-to-noise ratio is low, threshold estimation is not straightforward. Although several algorithmic approaches have been proposed, the current standard practice remains the visual evaluation of ABR waveforms as a function of stimulus level. We developed an algorithm based on the cross-correlation of two independent averages of responses to the same stimulus. For each stimulus level, the individual responses to each tone-pip are randomly split into two groups. The median waveform for each group is calculated, and then the normalized cross-correlation between these median waveforms is obtained. This process is repeated 500 times to obtain a resampled cross-correlation distribution. For each frequency, the mean values of these distributions are computed for each level and fit with a sigmoid or a power law function to estimate the threshold. Algorithmic thresholds demonstrated robust and accurate performance, achieving 92% accuracy within ±10 dB of human-rated thresholds on a large pool of mouse data. This performance was better than that of several published algorithms on the same dataset. This algorithm has now fully replaced the manual estimation of ABR thresholds for our preclinical studies, thereby saving significant time and enhancing objectivity in the process., Competing Interests: Declaration of interests Luke Shaheen, Seth Koehler, and Yoojin Chung were employees of Decibel Therapeutics or Regeneron Pharmaceuticals at the time of contribution to this publication and may hold company stock and/or stock options. Brad Buran was a paid consultant for Decibel Therapeutics or Regeneron Pharmaceuticals at the time of contribution to this publication.

Published
2024
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