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Pastras CJ, Curthoys IS, Asadnia M, McAlpine D, Rabbitt RD, Brown DJ. Evidence That Ultrafast Nonquantal Transmission Underlies Synchronized Vestibular Action Potential Generation. J Neurosci 2023; 43:7149-7157. [PMID: 37775302 PMCID: PMC10601366 DOI: 10.1523/jneurosci.1417-23.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Revised: 09/10/2023] [Accepted: 09/13/2023] [Indexed: 10/01/2023] Open
Abstract
Amniotes evolved a unique postsynaptic terminal in the inner ear vestibular organs called the calyx that receives both quantal and nonquantal (NQ) synaptic inputs from Type I sensory hair cells. The nonquantal synaptic current includes an ultrafast component that has been hypothesized to underlie the exceptionally high synchronization index (vector strength) of vestibular afferent neurons in response to sound and vibration. Here, we present three lines of evidence supporting the hypothesis that nonquantal transmission is responsible for synchronized vestibular action potentials of short latency in the guinea pig utricle of either sex. First, synchronized vestibular nerve responses are unchanged after administration of the AMPA receptor antagonist CNQX, while auditory nerve responses are completely abolished. Second, stimulus evoked vestibular nerve compound action potentials (vCAP) are shown to occur without measurable synaptic delay and three times shorter than the latency of auditory nerve compound action potentials (cCAP), relative to the generation of extracellular receptor potentials. Third, paired-pulse stimuli designed to deplete the readily releasable pool (RRP) of synaptic vesicles in hair cells reveal forward masking in guinea pig auditory cCAPs, but a complete lack of forward masking in vestibular vCAPs. Results support the conclusion that the fast component of nonquantal transmission at calyceal synapses is indefatigable and responsible for ultrafast responses of vestibular organs evoked by transient stimuli.SIGNIFICANCE STATEMENT The mammalian vestibular system drives some of the fastest reflex pathways in the nervous system, ensuring stable gaze and postural control for locomotion on land. To achieve this, terrestrial amniotes evolved a large, unique calyx afferent terminal which completely envelopes one or more presynaptic vestibular hair cells, which transmits mechanosensory signals mediated by quantal and nonquantal (NQ) synaptic transmission. We present several lines of evidence in the guinea pig which reveals the most sensitive vestibular afferents are remarkably fast, much faster than their auditory nerve counterparts. Here, we present neurophysiological and pharmacological evidence that demonstrates this vestibular speed advantage arises from ultrafast NQ electrical synaptic transmission from Type I hair cells to their calyx partners.
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Affiliation(s)
- Christopher J Pastras
- Faculty of Science and Engineering, School of Engineering, Macquarie University, Sydney, New South Wales 2109, Australia
| | - Ian S Curthoys
- School of Psychology, Vestibular Research Laboratory, The University of Sydney, Sydney, New South Wales 2050, Australia
- Department of Linguistics, The Australian Hearing Hub, Macquarie University, Sydney, New South Wales 2109, Australia
| | - Mohsen Asadnia
- Faculty of Science and Engineering, School of Engineering, Macquarie University, Sydney, New South Wales 2109, Australia
| | - David McAlpine
- Department of Linguistics, The Australian Hearing Hub, Macquarie University, Sydney, New South Wales 2109, Australia
| | - Richard D Rabbitt
- Departments of Biomedical Engineering, Otolaryngology, and Neuroscience Program, University of Utah, Salt Lake City, Utah 84112
| | - Daniel J Brown
- School of Pharmacy and Biomedical Sciences, Curtin University, Bentley, Western Australia 6102, Australia
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Abolpour Moshizi S, Pastras CJ, Sharma R, Parvez Mahmud MA, Ryan R, Razmjou A, Asadnia M. Recent advancements in bioelectronic devices to interface with the peripheral vestibular system. Biosens Bioelectron 2022; 214:114521. [PMID: 35820254 DOI: 10.1016/j.bios.2022.114521] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Revised: 06/23/2022] [Accepted: 06/27/2022] [Indexed: 11/26/2022]
Abstract
Balance disorders affect approximately 30% of the population throughout their lives and result in debilitating symptoms, such as spontaneous vertigo, nystagmus, and oscillopsia. The main cause of balance disorders is peripheral vestibular dysfunction, which may occur as a result of hair cell loss, neural dysfunction, or mechanical (and morphological) abnormality. The most common cause of vestibular dysfunction is arguably vestibular hair cell damage, which can result from an array of factors, such as ototoxicity, trauma, genetics, and ageing. One promising therapy is the vestibular prosthesis, which leverages the success of the cochlear implant, and endeavours to electrically integrate the primary vestibular afferents with the vestibular scene. Other translational approaches of interest include stem cell regeneration and gene therapies, which aim to restore or modify inner ear receptor function. However, both of these techniques are in their infancy and are currently undergoing further characterization and development in the laboratory, using animal models. Another promising translational avenue to treating vestibular hair cell dysfunction is the potential development of artificial biocompatible hair cell sensors, aiming to replicate functional hair cells and generate synthetic 'receptor potentials' for sensory coding of vestibular stimuli to the brain. Recently, artificial hair cell sensors have demonstrated significant promise, with improvements in their output, such as sensitivity and frequency selectivity. This article reviews the history and current state of bioelectronic devices to interface with the labyrinth, spanning the vestibular implant and artificial hair cell sensors.
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Affiliation(s)
| | - Christopher John Pastras
- School of Engineering, Macquarie University, Sydney, NSW, Australia; School of Medical Sciences, University of Sydney, NSW, Australia
| | - Rajni Sharma
- School of Engineering, Macquarie University, Sydney, NSW, Australia
| | - M A Parvez Mahmud
- School of Engineering, Deakin University, Geelong, VIC, 3216, Australia
| | - Rachel Ryan
- College of Public Health, The Ohio State University, Columbus, OH, 43210, United States
| | - Amir Razmjou
- School of Engineering, Macquarie University, Sydney, NSW, Australia; School of Engineering, Edith Cowan University, Joondalup, Perth, WA, 6027, Australia
| | - Mohsen Asadnia
- School of Engineering, Macquarie University, Sydney, NSW, Australia.
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Stimulus duration and vestibular sensory evoked potentials (VsEPs). Hear Res 2021; 408:108293. [PMID: 34175587 DOI: 10.1016/j.heares.2021.108293] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Revised: 05/10/2021] [Accepted: 06/07/2021] [Indexed: 11/20/2022]
Abstract
Recording the linear vestibular sensory evoked potential (VsEP) relies on moving the head in a prescribed manner to synchronously activate neurons of the gravity receptor organs. One problematic issue in accomplishing this is the potential coactivation of cochlear neurons. Although the major stimulus parameters required to elicit the vestibular response have been characterized, some of the determinants of auditory coactivation have not been clearly addressed. In the present study, we show that the duration of the linear cranial jerk stimulus plays a critical role in avoiding coactivation of auditory responses during VsEP recordings. Acoustic masking procedures are essential when recording the VsEP, particularly when using stimulus durations of less than 1 ms.
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Pastras CJ, Stefani SP, Curthoys IS, Camp AJ, Brown DJ. Utricular Sensitivity during Hydrodynamic Displacements of the Macula. J Assoc Res Otolaryngol 2020; 21:409-423. [PMID: 32783163 DOI: 10.1007/s10162-020-00769-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2020] [Accepted: 07/31/2020] [Indexed: 01/02/2023] Open
Abstract
To explore the effects of cochlear hair cell displacement, researchers have previously monitored functional and mechanical responses during low-frequency (LF) acoustic stimulation of the cochlea. The induced changes are believed to result from modulation of the conductance of mechano-electrical transduction (MET) channels on cochlear hair cells, along with receptor potential modulation. It is less clear how, or if, vestibular hair cell displacement affects vestibular function. Here, we have used LF (<20 Hz) hydrodynamic modulation of the utricular macula position, whilst recording functional and mechanical responses, to investigate the effects of utricular macula displacement. Measured responses included the Utricular Microphonic (UM), the vestibular short-latency evoked potential (VsEP), and laser Doppler vibrometry recordings of macular position. Over 1 cycle of the LF bias, the UM amplitude and waveform were cyclically modulated, with Boltzmann analysis suggesting a cyclic modulation of the vestibular MET gating. The VsEP amplitude was cyclically modulated throughout the LF bias, demonstrating a relative increase (~20-50 %; re baseline) and decrease (~10-20 %; re baseline), which is believed to be related to the MET conductance and vestibular hair cell sensitivity. The relationship between macular displacement and changes in UM and VsEP responses was consistent within and across animals. These results suggest that the sensory structures underlying the VsEP, often thought to be a cranial jerk-sensitive response, are at least partially sensitive to LF (and possibly static) pressures or motion. Furthermore, these results highlight the possibility that some of the vestibular dysfunction related to endolymphatic hydrops may be due to altered vestibular transduction following mechanical (or morphological) changes in the labyrinth.
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Affiliation(s)
- Christopher John Pastras
- The Meniere's Laboratory, School of Medical Sciences, The University of Sydney, Medical Foundation Building, 92-94 Parramatta Road, Camperdown, Sydney, New South Wales, 2050, Australia.
| | - Sebastian Paolo Stefani
- The Meniere's Laboratory, School of Medical Sciences, The University of Sydney, Medical Foundation Building, 92-94 Parramatta Road, Camperdown, Sydney, New South Wales, 2050, Australia
| | - Ian S Curthoys
- Vestibular Research Laboratory, School of Psychology, The University of Sydney, Sydney, New South Wales, 2050, Australia
| | - Aaron James Camp
- The Meniere's Laboratory, School of Medical Sciences, The University of Sydney, Medical Foundation Building, 92-94 Parramatta Road, Camperdown, Sydney, New South Wales, 2050, Australia
| | - Daniel John Brown
- School of Pharmacy and Biomedical Sciences, Curtin University, Bentley, Western Australia, 6102, Australia
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Pastras CJ, Curthoys IS, Brown DJ. Dynamic response to sound and vibration of the guinea pig utricular macula, measured in vivo using Laser Doppler Vibrometry. Hear Res 2018; 370:232-237. [DOI: 10.1016/j.heares.2018.08.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Revised: 08/01/2018] [Accepted: 08/20/2018] [Indexed: 01/12/2023]
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