1
|
Forbes PA, Kwan A, Mitchell DE, Blouin JS, Cullen KE. The Neural Basis for Biased Behavioral Responses Evoked by Galvanic Vestibular Stimulation in Primates. J Neurosci 2023; 43:1905-1919. [PMID: 36732070 PMCID: PMC10027042 DOI: 10.1523/jneurosci.0987-22.2023] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 01/25/2023] [Accepted: 01/30/2023] [Indexed: 02/04/2023] Open
Abstract
Noninvasive electrical stimulation of the vestibular system in humans has become an increasingly popular tool with a broad range of research and clinical applications. However, common assumptions regarding the neural mechanisms that underlie the activation of central vestibular pathways through such stimulation, known as galvanic vestibular stimulation (GVS), have not been directly tested. Here, we show that GVS is encoded by VIIIth nerve vestibular afferents with nonlinear dynamics that differ markedly from those predicted by current models. GVS produced asymmetric activation of both semicircular canal and otolith afferents to the onset versus offset and cathode versus anode of applied current, that in turn produced asymmetric eye movement responses in three awake-behaving male monkeys. Additionally, using computational methods, we demonstrate that the experimentally observed nonlinear neural response dynamics lead to an unexpected directional bias in the net population response when the information from both vestibular nerves is centrally integrated. Together our findings reveal the neural basis by which GVS activates the vestibular system, establish that neural response dynamics differ markedly from current predictions, and advance our mechanistic understanding of how asymmetric activation of the peripheral vestibular system alters vestibular function. We suggest that such nonlinear encoding is a general feature of neural processing that will be common across different noninvasive electrical stimulation approaches.SIGNIFICANCE STATEMENT Here, we show that the application of noninvasive electrical currents to the vestibular system (GVS) induces more complex responses than commonly assumed. We recorded vestibular afferent activity in macaque monkeys exposed to GVS using a setup analogous to human studies. GVS evoked notable asymmetries in irregular afferent responses to cathodal versus anodal currents. We developed a nonlinear model explaining these GVS-evoked afferent responses. Our model predicts that GVS induces directional biases in centrally integrated head motion signals and establishes electrical stimuli that recreate physiologically plausible sensations of motion. Altogether, our findings provide new insights into how GVS activates the vestibular system, which will be vital to advancing new clinical and biomedical applications.
Collapse
Affiliation(s)
- Patrick A Forbes
- Department of Neuroscience, Erasmus MC, University Medical Center Rotterdam, 3000 CA Rotterdam, The Netherlands
| | | | | | - Jean-Sébastien Blouin
- School of Kinesiology, University of British Columbia, Vancouver, British Colombia V6T 1Z1, Canada
| | - Kathleen E Cullen
- Physiology, McGill University, Montréal, Québec H3G 1Y6, Canada
- Departments of Biomedical Engineering
- Otolaryngology-Head and Neck Surgery
- Neuroscience, Johns Hopkins University, Baltimore, Maryland 21205
- Kavli Neuroscience Discovery Institute, Johns Hopkins University, Baltimore, Maryland 21205
| |
Collapse
|
2
|
Bronson D, Kalluri R. Muscarinic Acetylcholine Receptors Modulate HCN Channel Properties in Vestibular Ganglion Neurons. J Neurosci 2023; 43:902-917. [PMID: 36604171 PMCID: PMC9908319 DOI: 10.1523/jneurosci.2552-21.2022] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Revised: 12/14/2022] [Accepted: 12/22/2022] [Indexed: 01/07/2023] Open
Abstract
Efferent modulation of vestibular afferent excitability is linked to muscarinic signaling cascades that close low-voltage-gated potassium channels (i.e., KCNQ). Here, we show that muscarinic signaling cascades also depolarize the activation range of hyperpolarization-activated cyclic-nucleotide gated (HCN) channels. We compared the voltage activation range and kinetics of HCN channels and induced firing patterns before and after administering the muscarinic acetylcholine receptor (mAChR) agonist oxotremorine-M (Oxo-M) in dissociated vestibular ganglion neurons (VGNs) from rats of either sex using perforated whole-cell patch-clamp methods. Oxo-M depolarized HCN channels' half-activation voltage (V 1/2) and sped up the rate of activation near resting potential twofold. HCN channels in large-diameter and/or transient firing VGN (putative cell bodies of irregular firing neuron from central epithelial zones) had relatively depolarized V 1/2 in control solution and were less sensitive to mAChR activation than those found in small-diameter VGN with sustained firing patterns (putatively belonging to regular firing afferents). The impact of mAChR on HCN channels is not a direct consequence of closing KCNQ channels since pretreating the cells with Linopirdine, a KCNQ channel blocker, did not prevent HCN channel depolarization by Oxo-M. Efferent signaling promoted ion channel configurations that were favorable to highly regular spiking in some VGN, but not others. This is consistent with previous observations that low-voltage gated potassium currents in VGN are conducted by mAChR agonist-sensitive and -insensitive channels. Connecting efferent signaling to HCN channels is significant because of the channel's impact on spike-timing regularity and nonchemical transmission between Type I hair cells and vestibular afferents.SIGNIFICANCE STATEMENT Vestibular afferents express a diverse complement of ion channels. In vitro studies identified low-voltage activated potassium channels and hyperpolarization-activated cyclic-nucleotide gated (HCN) channels as crucial for shaping the timing and sensitivity of afferent responses. Moreover, a network of acetylcholine-releasing efferent neurons controls afferent excitability by closing a subgroup of low-voltage activated potassium channels on the afferent neuron. This work shows that these efferent signaling cascades also enhance the activation of HCN channels by depolarizing their voltage activation range. The size of this effect varies depending on the endogenous properties of the HCN channel and on cell type (as determined by discharge patterns and cell size). Simultaneously controlling two ion-channel groups gives the vestibular efferent system exquisite control over afferent neuron activity.
Collapse
Affiliation(s)
- Daniel Bronson
- Hearing and Communications Neuroscience Training Program, University of Southern California, Los Angeles, California 90057
- Department of Otolaryngology-Head and Neck Surgery, Keck School of Medicine, University of Southern California, Los Angeles, California 90057
- Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90057
| | - Radha Kalluri
- Hearing and Communications Neuroscience Training Program, University of Southern California, Los Angeles, California 90057
- Department of Otolaryngology-Head and Neck Surgery, Keck School of Medicine, University of Southern California, Los Angeles, California 90057
- Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90057
| |
Collapse
|
3
|
Comparing Vestibular Responses to Linear and Angular Whole-Body Accelerations in Real and Immersive Environments. Ann Biomed Eng 2022; 50:575-586. [PMID: 35325362 DOI: 10.1007/s10439-022-02947-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2021] [Accepted: 03/09/2022] [Indexed: 11/01/2022]
Abstract
The vestibular end organs differ in terms of anatomical and physiological characteristics. Sensory modalities' stimuli including visual stimuli and vestibular sensation can influence these organs differently. This paper explores differences between vestibular responses to axial tilts in physical and virtual environments. Four passive whole-body movements (linear: up-down, and angular: yaw, pitch, and roll) were applied to twenty-seven healthy participants once using a hydraulic chair (physical) and once visually using a head-mounted display (virtual). Electrovestibulography (EVestG) was used as the outcome measure to investigate the magnitude of vestibular-response-change in both ears for physical and virtual stimuli. Three features including average action potential (AP) area, AP amplitude, and mean detected firing rate change were used as indices of response. The results show that for both physical and virtual stimuli (1) generally the pitch and roll tilts produce the largest EVestG changes compared to other tilts (2) roll and pitch tilt responses are not significantly different from each other and (3) right side and left side roll tilts' responses are not significantly different. The findings indicate although visually- and physically-induced vestibular responses are different in terms of afferent activity, visual stimuli can still result in distinct responses when exposed to different axial tilts.
Collapse
|
4
|
Context-independent encoding of passive and active self-motion in vestibular afferent fibers during locomotion in primates. Nat Commun 2022; 13:120. [PMID: 35013266 PMCID: PMC8748921 DOI: 10.1038/s41467-021-27753-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Accepted: 12/03/2021] [Indexed: 11/21/2022] Open
Abstract
The vestibular system detects head motion to coordinate vital reflexes and provide our sense of balance and spatial orientation. A long-standing hypothesis has been that projections from the central vestibular system back to the vestibular sensory organs (i.e., the efferent vestibular system) mediate adaptive sensory coding during voluntary locomotion. However, direct proof for this idea has been lacking. Here we recorded from individual semicircular canal and otolith afferents during walking and running in monkeys. Using a combination of mathematical modeling and nonlinear analysis, we show that afferent encoding is actually identical across passive and active conditions, irrespective of context. Thus, taken together our results are instead consistent with the view that the vestibular periphery relays robust information to the brain during primate locomotion, suggesting that context-dependent modulation instead occurs centrally to ensure that coding is consistent with behavioral goals during locomotion. Using experimental and computational approaches the authors show that the vestibular efferent system does not modulate peripheral coding during locomotion. Instead, vestibular afferents unambiguously convey information in a context independent manner.
Collapse
|
5
|
Cullen KE, Wei RH. Differences in the Structure and Function of the Vestibular Efferent System Among Vertebrates. Front Neurosci 2021; 15:684800. [PMID: 34248486 PMCID: PMC8260987 DOI: 10.3389/fnins.2021.684800] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2021] [Accepted: 05/13/2021] [Indexed: 11/13/2022] Open
Abstract
The role of the mammalian vestibular efferent system in everyday life has been a long-standing mystery. In contrast to what has been reported in lower vertebrate classes, the mammalian vestibular efferent system does not appear to relay inputs from other sensory modalities to the vestibular periphery. Furthermore, to date, the available evidence indicates that the mammalian vestibular efferent system does not relay motor-related signals to the vestibular periphery to modulate sensory coding of the voluntary self-motion generated during natural behaviors. Indeed, our recent neurophysiological studies have provided insight into how the peripheral vestibular system transmits head movement-related information to the brain in a context independent manner. The integration of vestibular and extra-vestibular information instead only occurs at next stage of the mammalian vestibular system, at the level of the vestibular nuclei. The question thus arises: what is the physiological role of the vestibular efferent system in mammals? We suggest that the mammalian vestibular efferent system does not play a significant role in short-term modulation of afferent coding, but instead plays a vital role over a longer time course, for example in calibrating and protecting the functional efficacy of vestibular circuits during development and aging in a role analogous the auditory efferent system.
Collapse
Affiliation(s)
- Kathleen E. Cullen
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States
- Department of Otolaryngology, Johns Hopkins University School of Medicine, Baltimore, MD, United States
- Department of Neuroscience, Johns Hopkins University, Baltimore, MD, United States
- Kavli Neuroscience Discovery Institute, Johns Hopkins University, Baltimore, MD, United States
| | - Rui-Han Wei
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States
| |
Collapse
|
6
|
Ashiri M, Lithgow B, Suleiman A, Mansouri B, Moussavi Z. Electrovestibulography (EVestG) application for measuring vestibular response to horizontal pursuit and saccadic eye movements. Biocybern Biomed Eng 2021. [DOI: 10.1016/j.bbe.2021.03.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
|
7
|
Ramakrishna Y, Manca M, Glowatzki E, Sadeghi SG. Cholinergic Modulation of Membrane Properties of Calyx Terminals in the Vestibular Periphery. Neuroscience 2020; 452:98-110. [PMID: 33197502 DOI: 10.1016/j.neuroscience.2020.10.035] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Revised: 10/27/2020] [Accepted: 10/28/2020] [Indexed: 01/10/2023]
Abstract
Vestibular nerve afferents are divided into regular and irregular groups based on the variability of interspike intervals in their resting discharge. Most afferents receive inputs from bouton terminals that contact type II hair cells as well as from calyx terminals that cover the basolateral walls of type I hair cells. Calyces have an abundance of different subtypes of KCNQ (Kv7) potassium channels and muscarinic acetylcholine receptors (mAChRs) and receive cholinergic efferent inputs from neurons in the brainstem. We investigated whether mAChRs affected membrane properties and firing patterns of calyx terminals through modulation of KCNQ channel activity. Patch clamp recordings were performed from calyx terminals in central regions of the cristae of the horizontal and anterior canals in 13-26 day old Sprague-Dawley rats. KCNQ mediated currents were observed as voltage sensitive currents with slow kinetics (activation and deactivation), resulting in spike frequency adaptation so that calyces at best fired a single action potential at the beginning of a depolarizing step. Activation of mAChRs by application of oxotremorine methiodide or inhibition of KCNQ channels by linopirdine dihydrochloride decreased voltage activated currents by ∼30%, decreased first spike latencies by ∼40%, resulted in action potential generation in response to smaller current injections and at lower (i.e., more hyperpolarized) membrane potentials, and increased the number of spikes fired during depolarizing steps. Interestingly, some of the calyces showed spontaneous discharge in the presence of these drugs. Together, these findings suggest that cholinergic efferents can modulate the response properties and encoding of head movements by afferents.
Collapse
Affiliation(s)
- Yugandhar Ramakrishna
- Center for Hearing and Deafness, Department of Communicative Disorders and Sciences, State University of New York at Buffalo, Buffalo, NY, United States; Department of Communication Disorders and Sciences, California State University, Northridge, CA, United States
| | - Marco Manca
- Department of Otolaryngology - Head and Neck Surgery, The Center for Hearing and Balance, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Elisabeth Glowatzki
- Department of Otolaryngology - Head and Neck Surgery, The Center for Hearing and Balance, Johns Hopkins University School of Medicine, Baltimore, MD, United States; Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Soroush G Sadeghi
- Center for Hearing and Deafness, Department of Communicative Disorders and Sciences, State University of New York at Buffalo, Buffalo, NY, United States; Neuroscience Program, State University of New York at Buffalo, Buffalo, NY, United States.
| |
Collapse
|
8
|
Ramakrishna Y, Sadeghi SG. Activation of GABA B receptors results in excitatory modulation of calyx terminals in rat semicircular canal cristae. J Neurophysiol 2020; 124:962-972. [PMID: 32816581 PMCID: PMC7509296 DOI: 10.1152/jn.00243.2020] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Revised: 08/11/2020] [Accepted: 08/12/2020] [Indexed: 12/15/2022] Open
Abstract
Previous studies have found GABA in vestibular end organs. However, existence of GABA receptors or possible GABAergic effects on vestibular nerve afferents has not been investigated. The current study was conducted to determine whether activation of GABAB receptors affects calyx afferent terminals in the central region of the cristae of semicircular canals. We used patch-clamp recording in postnatal day 13-18 (P13-P18) Sprague-Dawley rats of either sex. Application of GABAB receptor agonist baclofen inhibited voltage-sensitive potassium currents. This effect was blocked by selective GABAB receptor antagonist CGP 35348. Application of antagonists of small (SK)- and large-conductance potassium (BK) channels almost completely blocked the effects of baclofen. The remaining baclofen effect was blocked by cadmium chloride, suggesting that it could be due to inhibition of voltage-gated calcium channels. Furthermore, baclofen had no effect in the absence of calcium in the extracellular fluid. Inhibition of potassium currents by GABAB activation resulted in an excitatory effect on calyx terminal action potential firing. While in the control condition calyces could only fire a single action potential during step depolarizations, in the presence of baclofen they fired continuously during steps and a few even showed repetitive discharge. We also found a decrease in threshold for action potential generation and a decrease in first-spike latency during step depolarization. These results provide the first evidence for the presence of GABAB receptors on calyx terminals, showing that their activation results in an excitatory effect and that GABA inputs could be used to modulate calyx response properties.NEW & NOTEWORTHY Using in vitro whole cell patch-clamp recordings from calyx terminals in the vestibular end organs, we show that activation of GABAB receptors result in an excitatory effect, with decreased spike-frequency adaptation and shortened first-spike latencies. Our results suggest that these effects are mediated through inhibition of calcium-sensitive potassium channels.
Collapse
Affiliation(s)
- Yugandhar Ramakrishna
- Center for Hearing and Deafness, Department of Communicative Disorders and Sciences, State University of New York at Buffalo, Buffalo, New York
- Department of Communication Disorders and Sciences, California State University, Northridge, Northridge, California
| | - Soroush G Sadeghi
- Center for Hearing and Deafness, Department of Communicative Disorders and Sciences, State University of New York at Buffalo, Buffalo, New York
- Neuroscience Program, State University of New York at Buffalo, Buffalo, New York
| |
Collapse
|
9
|
Yu Z, McIntosh JM, Sadeghi SG, Glowatzki E. Efferent synaptic transmission at the vestibular type II hair cell synapse. J Neurophysiol 2020; 124:360-374. [PMID: 32609559 DOI: 10.1152/jn.00143.2020] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In the vestibular peripheral organs, type I and type II hair cells (HCs) transmit incoming signals via glutamatergic quantal transmission onto afferent nerve fibers. Additionally, type I HCs transmit via "non-quantal" transmission to calyx afferent fibers, by accumulation of glutamate and potassium in the synaptic cleft. Vestibular efferent inputs originating in the brainstem contact type II HCs and vestibular afferents. Here, synaptic inputs to type II HCs were characterized by using electrical and optogenetic stimulation of efferent fibers combined with in vitro whole cell patch-clamp recording from type II HCs in the rodent vestibular crista. Properties of efferent synaptic currents in type II HCs were similar to those found in cochlear HCs and mediated by activation of α9-containing nicotinic acetylcholine receptors (nAChRs) and small-conductance calcium-activated potassium (SK) channels. While efferents showed a low probability of release at low frequencies of stimulation, repetitive stimulation resulted in facilitation and increased probability of release. Notably, the membrane potential of type II HCs during optogenetic stimulation of efferents showed a strong hyperpolarization in response to single pulses and was further enhanced by repetitive stimulation. Such efferent-mediated inhibition of type II HCs can provide a mechanism to adjust the contribution of signals from type I and type II HCs to vestibular nerve fibers, with a shift of the response to be more like that of calyx-only afferents with faster non-quantal responses.NEW & NOTEWORTHY Type II vestibular hair cells (HCs) receive inputs from efferent neurons in the brain stem. We used in vitro optogenetic and electrical stimulation of vestibular efferent fibers to study their synaptic inputs to type II HCs. Stimulation of efferents inhibited type II HCs, similar to efferent effects on cochlear HCs. We propose that efferent inputs adjust the contribution of signals from type I and II HCs to vestibular nerve fibers.
Collapse
Affiliation(s)
- Zhou Yu
- Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland.,Department of Otolaryngology-Head and Neck Surgery, The Center for Hearing and Balance, and The Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland
| | | | - Soroush G Sadeghi
- Department of Communicative Disorders and Sciences, and Center for Hearing and Deafness, State University of New York at Buffalo, Buffalo, New York.,Neuroscience Program, State University of New York at Buffalo, Buffalo, New York
| | - Elisabeth Glowatzki
- Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland.,Department of Otolaryngology-Head and Neck Surgery, The Center for Hearing and Balance, and The Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland
| |
Collapse
|
10
|
Longridge NS, Lim A, Mallinson AI, Renshaw J. Vestibular suppression of normal bodily sounds. Acta Otolaryngol 2020; 140:401-405. [PMID: 32068478 DOI: 10.1080/00016489.2020.1723807] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Background: Vestibular-evoked myogenic potentials (VEMPs) are present in almost everyone. The proximity of the cochlear and vestibular end organs strongly indicates an overlap of the stimuli to which they respond.Aims/objectives: To determine the loudness of shouting compared to the external auditory canal (EAC) and explore how hyperstimulation of the cochlea and vestibular structures might be prevented.Materials and methods: We compared the loudness and frequency response of sound during shouting, biting and chewing, as well as the measurement of the loudness and frequency of sound in the external auditory canal (EAC) when a calibrated minishaker is applied to the forehead and to the upper incisor teeth.Results: We showed that vibratory sounds produced by vocalizations and oral activities were attenuated when they reached the ear, so that these sounds would not act as vestibular stimulants.Conclusions and significance: Chewing is known to cause a stapedius reflex which suppresses internal sounds to optimize audition of external sounds, while at the same time suppressing vestibular stimulation, which serves to optimize the sensitivity of the vestibular system, in order that it may respond precisely to a threat.
Collapse
Affiliation(s)
- Neil S. Longridge
- Division of Otolaryngology, Department of Surgery, The University of British Columbia, Vancouver, Canada
| | - Anielle Lim
- Department of Audiology, Providence Health Care, Vancouver, Canada
| | - Arthur Ian Mallinson
- Division of Otolaryngology, Department of Surgery, The University of British Columbia, Vancouver, Canada
- Neuro-otology Unit, Vancouver General Hospital, Vancouver, Canada
| | - Jim Renshaw
- Neuro-otology Unit, Vancouver General Hospital, Vancouver, Canada
| |
Collapse
|
11
|
Longridge NS. Vestibular evoked myogenic potentials: what are they for? An opinion; a hypothesis. Acta Otolaryngol 2020; 140:1-3. [PMID: 32149556 DOI: 10.1080/00016489.2019.1704545] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2019] [Accepted: 11/02/2019] [Indexed: 10/24/2022]
Affiliation(s)
- Neil S Longridge
- Division of Otolaryngology, Department of Surgery, Faculty of Medicine, University of British Columbia, Vancouver, Canada
| |
Collapse
|
12
|
Differences Between Physical vs. Virtual Evoked Vestibular Responses. Ann Biomed Eng 2020; 48:1241-1255. [PMID: 31916127 DOI: 10.1007/s10439-019-02446-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Accepted: 12/27/2019] [Indexed: 10/25/2022]
Abstract
Electrovestibulography (EVestG), a technology purported to measure vestibular activity at the vestibular periphery, was used to compare the vestibular responses to two sensory inputs: (1) back-forward physical tilt (with eyes-open and eyes-closed) and (2) virtual reality replica of the back-forward tilt (eyes-open, physically static). Twenty-seven healthy participants (10 females) were tested. From each of the EVestG recordings, two feature curves: (1) average field potential (FP), and (2) distribution of time intervals between the detected FPs were extracted. For the eyes-closed physical tilt, except for the background segment, the FP response curve was generally wider compared to that evoked during the virtual replica tilt (p < 0.05). Moreover, the eyes-closed physical tilt produced longer time intervals between FP's compared to the virtual stimulus. For this measure, for the background segment, the eyes closed and open physical tilt responses were significantly different (p < 0.05) in both ears (repeated measure experimental design). The results support: (1) both vestibular and visual inputs evoking a measurably different EVestG response, (2) the differences between physical and virtual vestibular responses are dependent on the eyes being either open or closed, and (3) for the stimuli used, the modulation of vestibular afferent activity was measurably smaller for virtual than physical stimulation.
Collapse
|
13
|
Efferent Inputs Are Required for Normal Function of Vestibular Nerve Afferents. J Neurosci 2019; 39:6922-6935. [PMID: 31285300 DOI: 10.1523/jneurosci.0237-19.2019] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Revised: 06/28/2019] [Accepted: 07/01/2019] [Indexed: 01/09/2023] Open
Abstract
A group of vestibular afferent nerve fibers with irregular-firing resting discharges are thought to play a prominent role in responses to fast head movements and vestibular plasticity. We show that, in C57BL/6 mice (either sex, 4-5 weeks old), normal activity in the efferent vestibular pathway is required for function of these irregular afferents. Thermal inhibition of efferent fibers results in a profound inhibition of irregular afferents' resting discharges, rendering them inadequate for signaling head movements. In this way, efferent inputs adjust the contribution of the peripheral irregular afferent pathway that plays a critical role in peripheral vestibular signaling and plasticity.SIGNIFICANCE STATEMENT Vestibular end organs in the inner ear receive efferent inputs from the brainstem. Previously, electrical stimulation of efferents was linked to an increase in resting discharges of afferents and a decrease in their sensitivities. Here, we show that localized thermal inhibition of unmyelinated efferents results in a significant decrease in the activity of afferent nerve fibers, particularly those with irregular resting discharges implicated in responses to fast head movements and vestibular compensation. Thus, by upregulating and downregulating of afferent firing, particularly irregular afferents, efferents adjust neural activity sensitive to rapid head movements. These findings support the notion that peripheral vestibular end organs are not passive transducers of head movements and their sensory signal transmission is modulated by efferent inputs.
Collapse
|
14
|
Kwan A, Forbes PA, Mitchell DE, Blouin JS, Cullen KE. Neural substrates, dynamics and thresholds of galvanic vestibular stimulation in the behaving primate. Nat Commun 2019; 10:1904. [PMID: 31015434 PMCID: PMC6478681 DOI: 10.1038/s41467-019-09738-1] [Citation(s) in RCA: 67] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Accepted: 03/21/2019] [Indexed: 11/09/2022] Open
Abstract
Galvanic vestibular stimulation (GVS) uses the external application of electrical current to selectively target the vestibular system in humans. Despite its recent popularity for the assessment/treatment of clinical conditions, exactly how this non-invasive tool activates the vestibular system remains an open question. Here we directly investigate single vestibular afferent responses to GVS applied to the mastoid processes of awake-behaving monkeys. Transmastoid GVS produces robust and parallel activation of both canal and otolith afferents. Notably, afferent activation increases with intrinsic neuronal variability resulting in constant GVS-evoked neuronal detection thresholds across all afferents. Additionally, afferent tuning differs for GVS versus natural self-motion stimulation. Using a stochastic model of repetitive activity in afferents, we largely explain the main features of GVS-evoked vestibular afferent dynamics. Taken together, our results reveal the neural substrate underlying transmastoid GVS-evoked perceptual, ocular and postural responses-information that is essential to advance GVS applicability for biomedical uses in humans.
Collapse
Affiliation(s)
- Annie Kwan
- Department of Biomedical Engineering, McGill University, Montreal, QC, H3G 1Y6, Canada
| | - Patrick A Forbes
- Department of Neuroscience, Erasmus MC, University Medical Center Rotterdam, Rotterdam, 3000 CA, The Netherlands.,Department of BioMechanical Engineering, Delft University of Technology, Delft, 2628 CD, The Netherlands.,School of Kinesiology, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada
| | - Diana E Mitchell
- Department of Physiology, McGill University, Montreal, QC, H3G 1Y6, Canada
| | - Jean-Sébastien Blouin
- School of Kinesiology, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada
| | - Kathleen E Cullen
- Department of Physiology, McGill University, Montreal, QC, H3G 1Y6, Canada. .,Department of Biomedical Engineering, Johns Hopkins University, Baltimore, 21205, MD, USA.
| |
Collapse
|
15
|
Aplin FP, Fridman GY. Implantable Direct Current Neural Modulation: Theory, Feasibility, and Efficacy. Front Neurosci 2019; 13:379. [PMID: 31057361 PMCID: PMC6482222 DOI: 10.3389/fnins.2019.00379] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2018] [Accepted: 04/02/2019] [Indexed: 12/25/2022] Open
Abstract
Implantable neuroprostheses such as cochlear implants, deep brain stimulators, spinal cord stimulators, and retinal implants use charge-balanced alternating current (AC) pulses to recover delivered charge and thus mitigate toxicity from electrochemical reactions occurring at the metal-tissue interface. At low pulse rates, these short duration pulses have the effect of evoking spikes in neural tissue in a phase-locked fashion. When the therapeutic goal is to suppress neural activity, implants typically work indirectly by delivering excitation to populations of neurons that then inhibit the target neurons, or by delivering very high pulse rates that suffer from a number of undesirable side effects. Direct current (DC) neural modulation is an alternative methodology that can directly modulate extracellular membrane potential. This neuromodulation paradigm can excite or inhibit neurons in a graded fashion while maintaining their stochastic firing patterns. DC can also sensitize or desensitize neurons to input. When applied to a population of neurons, DC can modulate synaptic connectivity. Because DC delivered to metal electrodes inherently violates safe charge injection criteria, its use has not been explored for practical applicability of DC-based neural implants. Recently, several new technologies and strategies have been proposed that address this safety criteria and deliver ionic-based direct current (iDC). This, along with the increased understanding of the mechanisms behind the transcutaneous DC-based modulation of neural targets, has caused a resurgence of interest in the interaction between iDC and neural tissue both in the central and the peripheral nervous system. In this review we assess the feasibility of in-vivo iDC delivery as a form of neural modulation. We present the current understanding of DC/neural interaction. We explore the different design methodologies and technologies that attempt to safely deliver iDC to neural tissue and assess the scope of application for direct current modulation as a form of neuroprosthetic treatment in disease. Finally, we examine the safety implications of long duration iDC delivery. We conclude that DC-based neural implants are a promising new modulation technology that could benefit from further chronic safety assessments and a better understanding of the basic biological and biophysical mechanisms that underpin DC-mediated neural modulation.
Collapse
Affiliation(s)
- Felix P Aplin
- Department of Otolaryngology Head and Neck Surgery, Johns Hopkins University, Baltimore, MD, United States
| | - Gene Y Fridman
- Department of Otolaryngology Head and Neck Surgery, Johns Hopkins University, Baltimore, MD, United States.,Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States.,Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD, United States
| |
Collapse
|
16
|
Eatock RA. Specializations for Fast Signaling in the Amniote Vestibular Inner Ear. Integr Comp Biol 2019; 58:341-350. [PMID: 29920589 DOI: 10.1093/icb/icy069] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
During rapid locomotion, the vestibular inner ear provides head-motion signals that stabilize posture, gaze, and heading. Afferent nerve fibers from central and peripheral zones of vestibular sensory epithelia use temporal and rate encoding, respectively, to emphasize different aspects of head motion: central afferents adapt faster to sustained head position and favor higher stimulus frequencies, reflecting specializations at each stage from motion of the accessory structure to spike propagation to the brain. One specialization in amniotes is an unusual nonquantal synaptic mechanism by which type I hair cells transmit to large calyceal terminals of afferent neurons. The reduced synaptic delay of this mechanism may have evolved to serve reliable and fast input to reflex pathways that ensure stable locomotion on land.
Collapse
Affiliation(s)
- Ruth Anne Eatock
- Department of Neurobiology, University of Chicago, Chicago, IL 60637, USA
| |
Collapse
|
17
|
Boyle R, Popova Y, Varelas J. Influence of Magnitude and Duration of Altered Gravity and Readaptation to 1 g on the Structure and Function of the Utricle in Toadfish, Opsanus tau. Front Physiol 2018; 9:1469. [PMID: 30405430 PMCID: PMC6204554 DOI: 10.3389/fphys.2018.01469] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Accepted: 09/28/2018] [Indexed: 11/13/2022] Open
Abstract
Gravity has remained constant during animal evolution and the neural sensory systems detecting acceleration forces have remained remarkably conserved among vertebrates. The utricular organ senses the sum of inertial force due to head translation and head tilt relative to gravitational vertical. Change in gravitational force would be expected to have profound effects on how an organism maintains equilibrium. We characterize the physiology of utricular afferents to applied accelerations in the oyster toadfish, Opsanus tau, in normal 1 g to establish benchmarks, after 1–32-day exposures to 2.24 g (resultant) via centrifugation (hypergravity, HG), after 4- and 16-day exposures to 1.12 g (resultant), and following 1–8 days recovery to HG exposures to study re-adaptation to 1 g. Afferents were also examined during activation of efferent vestibular pathway. Centrifugation at 2.24 g included 228°/s constant angular velocity component, and thus horizontal canal afferent responses to yaw rotation were recorded as an internal control in each fish. Afferents studied after 228°/s rotation for 4 and 16 days without centripetal acceleration, called On-Center-Control, were indistinguishable from their control counterparts. Principal response to HG was an adjustment of afferent sensitivity as a function of magnitude and duration of exposure: an initial robust increase at 3–4 days followed by a significant decrease from 16 to 32 days. Initial increase observed after 4 days of HG took >4 days in 1 g to recover, and the decrease observed after 16 days of HG took >2 days to readapt to 1 g. Hair cells in striola and medial extrastriola macula regions were serially reconstructed in 3D from thin sections using transmission electron microscopy in control fish and fish exposed to 4 and 16 days of HG. Despite the highly significant differences in afferent physiology, synaptic body counts quantified in the same fish were equivalent in their inter-animal variability and averages. No clear role of the efferent pathway as a feedback mechanism regulating afferent behavior to HG was found. Transfer from 1 g to HG imparts profound effects on gravitational sensitivity of utricular afferents and the accompanying transfer from the HG back to the 1 g resembles in part (as an analog) the transfer from 1 g to the micrograms.
Collapse
Affiliation(s)
- Richard Boyle
- National Aeronautics and Space Administration Ames Research Center, Moffett Field, CA, United States
| | - Yekaterina Popova
- National Aeronautics and Space Administration Ames Research Center, Moffett Field, CA, United States
| | - Joseph Varelas
- National Aeronautics and Space Administration Ames Research Center, Moffett Field, CA, United States.,Universities Space Research Association (USRA) Science & Technology Innovation Labs at NASA Ames Research Center, Moffett Field, CA, United States
| |
Collapse
|
18
|
Jones SM, Vijayakumar S, Dow SA, Holt JC, Jordan PM, Luebke AE. Loss of α-Calcitonin Gene-Related Peptide (αCGRP) Reduces Otolith Activation Timing Dynamics and Impairs Balance. Front Mol Neurosci 2018; 11:289. [PMID: 30197585 PMCID: PMC6117397 DOI: 10.3389/fnmol.2018.00289] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Accepted: 07/31/2018] [Indexed: 12/03/2022] Open
Abstract
Calcitonin gene-related peptide (CGRP) is a neuroactive peptide that is thought to play a role at efferent synapses in hair cell organs including the cochlea, lateral line, and semicircular canal. The deletion of CGRP in transgenic mice is associated with a significant reduction in suprathreshold cochlear nerve activity and vestibulo–ocular reflex (VOR) gain efficacy when compared to littermate controls. Here we asked whether the loss of CGRP also influences otolithic end organ function and contributes to balance impairments. Immunostaining for CGRP was absent in the otolithic end organs of αCGRP null (-/-) mice while choline acetyltransferase (ChAT) immunolabeling appeared unchanged suggesting the overall gross development of efferent innervation in otolithic organs was unaltered. Otolithic function was assessed by quantifying the thresholds, suprathreshold amplitudes, and latencies of vestibular sensory-evoked potentials (VsEPs) while general balance function was assessed using a modified rotarod assay. The loss of αCGRP in null (-/-) mice was associated with: (1) shorter VsEP latencies without a concomitant change in amplitude or thresholds, and (2) deficits in the rotarod balance assay. Our findings show that CGRP loss results in faster otolith afferent activation timing, suggesting that the CGRP component of the efferent vestibular system (EVS) also plays a role in otolithic organ dynamics, which when coupled with reduced VOR gain efficacy, impairs balance.
Collapse
Affiliation(s)
- Sherri M Jones
- Department of Special Education and Communication Disorders, University of Nebraska, Lincoln, NE, United States
| | - Sarath Vijayakumar
- Department of Special Education and Communication Disorders, University of Nebraska, Lincoln, NE, United States
| | - Samantha A Dow
- Department of Neuroscience and Del Monte Institute for Neuroscience, University of Rochester Medical Center, Rochester, NY, United States
| | - Joseph C Holt
- Department of Neuroscience and Del Monte Institute for Neuroscience, University of Rochester Medical Center, Rochester, NY, United States.,Department of Otolaryngology, University of Rochester Medical Center, Rochester, NY, United States
| | - Paivi M Jordan
- Department of Otolaryngology, University of Rochester Medical Center, Rochester, NY, United States
| | - Anne E Luebke
- Department of Neuroscience and Del Monte Institute for Neuroscience, University of Rochester Medical Center, Rochester, NY, United States.,Department of Biomedical Engineering, University of Rochester Medical Center, Rochester, NY, United States
| |
Collapse
|
19
|
Aplin FP, Singh D, Santina CCD, Fridman GY. Ionic Direct Current Modulation for Combined Inhibition/Excitation of the Vestibular System. IEEE Trans Biomed Eng 2018; 66:775-783. [PMID: 30010547 DOI: 10.1109/tbme.2018.2856698] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
OBJECTIVE Prosthetic electrical stimulation delivered to the vestibular nerve could provide therapy for people suffering from bilateral vestibular dysfunction. Common encoding methods use pulse-frequency modulation (PFM) to stimulate the semicircular canals of the vestibular system. We previously showed that delivery of ionic direct current (iDC) can also modulate the vestibular system. In this study, we compare the dynamic range of head velocity encoding from iDC modulation to that of PFM controls. METHODS Gentamicin-treated wild-type chinchillas were implanted with microcatheter tubes that delivered ionic current to the left ear vestibular canals and stimulated with steps of anodic/cathodic iDC or PFM. Evoked vestibulo-ocular reflex eye velocity was used to compare PFM and iDC vestibular modulation. RESULTS Cathodic iDC steps effectively elicited eye rotations consistent with an increased firing rate of the implanted semicircular canal afferents. Anodic iDC current steps elicited eye rotations in the opposite direction that, when paired with an adapted cathodic offset, increased the dynamic range of eye rotation velocities in comparison to PFM controls. CONCLUSION Our results suggest that iDC modulation can effectively modulate the vestibular system across a functional range of rotation vectors and velocities, with a potential benefit over a PFM stimulation paradigm. SIGNIFICANCE In conjunction with a safe dc delivery system, iDC modulation could potentially increase the range of simulated head rotation velocities available to neuroelectric vestibular prostheses.
Collapse
|
20
|
Mathews MA, Camp AJ, Murray AJ. Reviewing the Role of the Efferent Vestibular System in Motor and Vestibular Circuits. Front Physiol 2017; 8:552. [PMID: 28824449 PMCID: PMC5539236 DOI: 10.3389/fphys.2017.00552] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Accepted: 07/17/2017] [Indexed: 12/31/2022] Open
Abstract
Efferent circuits within the nervous system carry nerve impulses from the central nervous system to sensory end organs. Vestibular efferents originate in the brainstem and terminate on hair cells and primary afferent fibers in the semicircular canals and otolith organs within the inner ear. The function of this efferent vestibular system (EVS) in vestibular and motor coordination though, has proven difficult to determine, and remains under debate. We consider current literature that implicate corollary discharge from the spinal cord through the efferent vestibular nucleus (EVN), and hint at a potential role in overall vestibular plasticity and compensation. Hypotheses range from differentiating between passive and active movements at the level of vestibular afferents, to EVS activation under specific behavioral and environmental contexts such as arousal, predation, and locomotion. In this review, we summarize current knowledge of EVS circuitry, its effects on vestibular hair cell and primary afferent activity, and discuss its potential functional roles.
Collapse
Affiliation(s)
- Miranda A Mathews
- Sensory Systems and Integration Laboratory, Bosch Institute, Discipline of Biomedical Science, University of SydneySydney, NSW, Australia
| | - Aaron J Camp
- Sensory Systems and Integration Laboratory, Bosch Institute, Discipline of Biomedical Science, University of SydneySydney, NSW, Australia
| | - Andrew J Murray
- Sainsbury Wellcome Centre for Neural Circuits and Behaviour, University College LondonLondon, United Kingdom
| |
Collapse
|
21
|
Mathews MA, Murray A, Wijesinghe R, Cullen K, Tung VWK, Camp AJ. Efferent Vestibular Neurons Show Homogenous Discharge Output But Heterogeneous Synaptic Input Profile In Vitro. PLoS One 2015; 10:e0139548. [PMID: 26422206 PMCID: PMC4589407 DOI: 10.1371/journal.pone.0139548] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2015] [Accepted: 09/15/2015] [Indexed: 11/19/2022] Open
Abstract
Despite the importance of our sense of balance we still know remarkably little about the central control of the peripheral balance system. While previous work has shown that activation of the efferent vestibular system results in modulation of afferent vestibular neuron discharge, the intrinsic and synaptic properties of efferent neurons themselves are largely unknown. Here we substantiate the location of the efferent vestibular nucleus (EVN) in the mouse, before characterizing the input and output properties of EVN neurons in vitro. We made transverse serial sections through the brainstem of 4-week-old mice, and performed immunohistochemistry for calcitonin gene-related peptide (CGRP) and choline acetyltransferase (ChAT), both expressed in the EVN of other species. We also injected fluorogold into the posterior canal and retrogradely labelled neurons in the EVN of ChAT:: tdTomato mice expressing tdTomato in all cholinergic neurons. As expected the EVN lies dorsolateral to the genu of the facial nerve (CNVII). We then made whole-cell current-, and voltage-clamp recordings from visually identified EVN neurons. In current-clamp, EVN neurons display a homogeneous discharge pattern. This is characterized by a high frequency burst of action potentials at the onset of a depolarizing stimulus and the offset of a hyperpolarizing stimulus that is mediated by T-type calcium channels. In voltage-clamp, EVN neurons receive either exclusively excitatory or inhibitory inputs, or a combination of both. Despite this heterogeneous mixture of inputs, we show that synaptic inputs onto EVN neurons are predominantly excitatory. Together these findings suggest that the inputs onto EVN neurons, and more specifically the origin of these inputs may underlie EVN neuron function.
Collapse
Affiliation(s)
- Miranda A. Mathews
- Discipline of Biomedical Science, Bosch Institute, The University of Sydney, Sydney, New South Wales, Australia
| | - Andrew Murray
- Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University, New York, United States of America
| | - Rajiv Wijesinghe
- Discipline of Biomedical Science, Bosch Institute, The University of Sydney, Sydney, New South Wales, Australia
| | - Karen Cullen
- Discipline of Anatomy and Histology, Bosch Institute, The University of Sydney, Sydney, New South Wales, Australia
| | - Victoria W. K. Tung
- Discipline of Biomedical Science, Bosch Institute, The University of Sydney, Sydney, New South Wales, Australia
| | - Aaron J. Camp
- Discipline of Biomedical Science, Bosch Institute, The University of Sydney, Sydney, New South Wales, Australia
- * E-mail:
| |
Collapse
|
22
|
Chagnaud BP, Banchi R, Simmers J, Straka H. Spinal corollary discharge modulates motion sensing during vertebrate locomotion. Nat Commun 2015; 6:7982. [PMID: 26337184 PMCID: PMC4569702 DOI: 10.1038/ncomms8982] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2014] [Accepted: 07/02/2015] [Indexed: 12/29/2022] Open
Abstract
During active movements, neural replicas of the underlying motor commands may assist in adapting motion-detecting sensory systems to an animal's own behaviour. The transmission of such motor efference copies to the mechanosensory periphery offers a potential predictive substrate for diminishing sensory responsiveness to self-motion during vertebrate locomotion. Here, using semi-isolated in vitro preparations of larval Xenopus, we demonstrate that shared efferent neural pathways to hair cells of vestibular endorgans and lateral line neuromasts express cyclic impulse bursts during swimming that are directly driven by spinal locomotor circuitry. Despite common efferent innervation and discharge patterns, afferent signal encoding at the two mechanosensory peripheries is influenced differentially by efference copy signals, reflecting the different organization of body/water motion-detecting processes in the vestibular and lateral line systems. The resultant overall gain reduction in sensory signal encoding in both cases, which likely prevents overstimulation, constitutes an adjustment to increased stimulus magnitudes during locomotion. Corollary discharges inform the central nervous system about impending motor activity. Here, Chagnaud et al. show that, in Xenopus tadpoles, shared efferent neural pathways to the inner ear and lateral line adjust the sensitivity of sensory afferents during locomotor activity.
Collapse
Affiliation(s)
- Boris P Chagnaud
- Department of Biology II, Ludwig-Maximilians-University Munich, Grosshadernerstrasse 2, 82152 Planegg-Martinsried, Germany
| | - Roberto Banchi
- Department of Biology II, Ludwig-Maximilians-University Munich, Grosshadernerstrasse 2, 82152 Planegg-Martinsried, Germany.,Graduate School of Systemic Neurosciences, Ludwig-Maximilians-University Munich, Planegg-Martinsried 82152, Germany
| | - John Simmers
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Université de Bordeaux, CNRS UMR 5287, 33076 Bordeaux, France
| | - Hans Straka
- Department of Biology II, Ludwig-Maximilians-University Munich, Grosshadernerstrasse 2, 82152 Planegg-Martinsried, Germany
| |
Collapse
|
23
|
Lithgow BJ, Shoushtarian M. Parkinson's disease: disturbed vestibular function and levodopa. J Neurol Sci 2015; 353:49-58. [PMID: 25899315 DOI: 10.1016/j.jns.2015.03.050] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2014] [Revised: 03/19/2015] [Accepted: 03/31/2015] [Indexed: 11/15/2022]
Abstract
Evidence indicates Levodopa effects central postural control. As electrophysiological postural control biomarkers, sensory oto-acoustic features were extracted from Electrovestibulography (EVestG) data to identify 20 healthy age and gender matched individuals as Controls from 20 PD subjects before (PDlowmed) and 18 after (PDmed) morning doses of Levodopa. EVestG data was collected using a single tilt stimulus applied in the pitch plane. The extracted features were based on the measured firing pattern, interval histogram and the shape of the average field potential response. An unbiased cross validated classification accuracy of 88%, 88% and 79% was achieved using combinations of 2 features for separating PDlowmed from control, control from PD (combined PDlowmed and PDmed), and PDlowmed from PDmed groups respectively. One feature showed significant correlations (p<0.05) with the Modified Hoehn and Yahr PD staging scale. The results indicate disturbed vestibular function is observed in both the PDmed and PDlowmed conditions, and these are separable. The implication is that Levodopa may also affect peripheral as well as central postural control.
Collapse
Affiliation(s)
- Brian J Lithgow
- Monash Alfred Psychiatry Research Centre, Monash University Central Clinical School and the Alfred Hospital, 4th Floor, 607St Kilda Rd, Melbourne, Victoria, Australia 3004; Diagnostic and Neurosignal Processing Research Laboratory, Monash University, Wellington Rd, Clayton, Victoria, Australia 3180; Diagnostic and Neurosignal Processing Research Laboratory, University of Manitoba, Riverview Health Centre, 1 Morley St, Winnipeg, MB, Canada R3L 2P4.
| | - Mehrnaz Shoushtarian
- Diagnostic and Neurosignal Processing Research Laboratory, Monash University, Wellington Rd, Clayton, Victoria, Australia 3180.
| |
Collapse
|
24
|
Loss of α-calcitonin gene-related peptide (αCGRP) reduces the efficacy of the Vestibulo-ocular Reflex (VOR). J Neurosci 2014; 34:10453-8. [PMID: 25080603 DOI: 10.1523/jneurosci.3336-13.2014] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The neuroactive peptide calcitonin-gene related peptide (CGRP) is known to act at efferent synapses and their targets in hair cell organs, including the cochlea and lateral line. CGRP is also expressed in vestibular efferent neurons as well as a number of central vestibular neurons. Although CGRP-null (-/-) mice demonstrate a significant reduction in cochlear nerve sound-evoked activity compared with wild-type mice, it is unknown whether and how the loss of CGRP influence vestibular system function. Vestibular function was assessed by quantifying the vestibulo-ocular reflex (VOR) in alert mice. The loss of CGRP in (-/-) mice was associated with a reduction of the VOR gain of ≈50% without a concomitant change in phase. Using immunohistochemistry, we confirmed that, although CGRP staining was absent in the vestibular end-organs of null (-/-) mice, cholinergic staining appeared normal, suggesting that the overall gross development of vestibular efferent innervation was unaltered. We further confirmed that the observed deficit in vestibular function of null (-/-) mice was not the result of nontargeted effects at the level of the extraocular motor neurons and/or their innervation of extraocular muscles. Analysis of the relationship between vestibular quick phase amplitude and peak velocity revealed that extraocular motor function was unchanged, and immunohistochemistry revealed no abnormalities in motor endplates. Together, our findings show that the neurotransmitter CGRP plays a key role in ensuring VOR efficacy.
Collapse
|
25
|
Hübner PP, Khan SI, Migliaccio AA. Velocity-selective adaptation of the horizontal and cross-axis vestibulo-ocular reflex in the mouse. Exp Brain Res 2014; 232:3035-46. [PMID: 24862508 DOI: 10.1007/s00221-014-3988-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2013] [Accepted: 05/08/2014] [Indexed: 01/07/2023]
Abstract
One commonly observed phenomenon of vestibulo-ocular reflex (VOR) adaptation is a frequency-selective change in gain (eye velocity/head velocity) and phase (relative timing between the vestibular stimulus and response) based on the frequency content of the adaptation training stimulus. The neural mechanism behind this type of adaptation is not clear. Our aim was to determine whether there were other parameter-selective effects on VOR adaptation, specifically velocity-selective and acceleration-selective changes in the horizontal VOR gain and phase. We also wanted to determine whether parameter selectivity was also in place for cross-axis adaptation training (a visual-vestibular training stimulus that elicits a vestibular-evoked torsional eye movement during horizontal head rotations). We measured VOR gain and phase in 17 C57BL/6 mice during baseline (no adaptation training) and after gain-increase, gain-decrease and cross-axis adaptation training using a sinusoidal visual-vestibular (mismatch) stimulus with whole-body rotations (vestibular stimulus) with peak velocity 20 and 50°/s both with a fixed frequency of 0.5 Hz. Our results show pronounced velocity selectivity of VOR adaptation. The difference in horizontal VOR gain after gain-increase versus gain-decrease adaptation was maximal when the sinusoidal testing stimulus matched the adaptation training stimulus peak velocity. We also observed similar velocity selectivity after cross-axis adaptation training. Our data suggest that frequency selectivity could be a manifestation of both velocity and acceleration selectivity because when one of these is absent, e.g. acceleration selectivity in the mouse, frequency selectivity is also reduced.
Collapse
Affiliation(s)
- Patrick P Hübner
- Balance and Vision Laboratory, Neuroscience Research Australia, Cnr Barker Street and Easy Street, Randwick, Sydney, NSW, 2031, Australia
| | | | | |
Collapse
|
26
|
Leijon S, Magnusson AK. Physiological characterization of vestibular efferent brainstem neurons using a transgenic mouse model. PLoS One 2014; 9:e98277. [PMID: 24867596 PMCID: PMC4035287 DOI: 10.1371/journal.pone.0098277] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Accepted: 04/30/2014] [Indexed: 01/31/2023] Open
Abstract
The functional role of efferent innervation of the vestibular end-organs in the inner ear remains elusive. This study provides the first physiological characterization of the cholinergic vestibular efferent (VE) neurons in the brainstem by utilizing a transgenic mouse model, expressing eGFP under a choline-acetyltransferase (ChAT)-locus spanning promoter in combination with targeted patch clamp recordings. The intrinsic electrical properties of the eGFP-positive VE neurons were compared to the properties of the lateral olivocochlear (LOC) brainstem neurons, which gives rise to efferent innervation of the cochlea. Both VE and the LOC neurons were marked by their negative resting membrane potential <-75 mV and their passive responses in the hyperpolarizing range. In contrast, the response properties of VE and LOC neurons differed significantly in the depolarizing range. When injected with positive currents, VE neurons fired action potentials faithfully to the onset of depolarization followed by sparse firing with long inter-spike intervals. This response gave rise to a low response gain. The LOC neurons, conversely, responded with a characteristic delayed tonic firing upon depolarizing stimuli, giving rise to higher response gain than the VE neurons. Depolarization triggered large TEA insensitive outward currents with fast inactivation kinetics, indicating A-type potassium currents, in both the inner ear-projecting neuronal types. Immunohistochemistry confirmed expression of Kv4.3 and 4.2 ion channel subunits in both the VE and LOC neurons. The difference in spiking responses to depolarization is related to a two-fold impact of these transient outward currents on somatic integration in the LOC neurons compared to in VE neurons. It is speculated that the physiological properties of the VE neurons might be compatible with a wide-spread control over motion and gravity sensation in the inner ear, providing likewise feed-back amplification of abrupt and strong phasic signals from the semi-circular canals and of tonic signals from the gravito-sensitive macular organs.
Collapse
Affiliation(s)
- Sara Leijon
- Center for Hearing and Communication Research, Karolinska Institutet, Stockholm, Sweden
- Department of Clinical Science, Intervention and Technology, Unit of Audiology, Karolinska University Hospital, Stockholm, Sweden
| | - Anna K. Magnusson
- Center for Hearing and Communication Research, Karolinska Institutet, Stockholm, Sweden
- Department of Clinical Science, Intervention and Technology, Unit of Audiology, Karolinska University Hospital, Stockholm, Sweden
- * E-mail:
| |
Collapse
|
27
|
Seseña E, Vega R, Soto E. Activation of μ-opioid receptors inhibits calcium-currents in the vestibular afferent neurons of the rat through a cAMP dependent mechanism. Front Cell Neurosci 2014; 8:90. [PMID: 24734002 PMCID: PMC3973932 DOI: 10.3389/fncel.2014.00090] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2013] [Accepted: 03/11/2014] [Indexed: 11/24/2022] Open
Abstract
Opioid receptors are expressed in the vestibular endorgans (afferent neurons and hair cells) and are activated by the efferent system, which modulates the discharge of action potentials in vestibular afferent neurons (VANs). In mammals, VANs mainly express the μ opioid-receptor, but the function of this receptors activation and the cellular mechanisms by which they exert their actions in these neurons are poorly studied. To determine the actions of μ opioid receptor (MOR) and cell signaling mechanisms in VANs, we made perforated patch-clamp recordings of VANs that were obtained from postnatal days 7 to 10 (P7–10) rats and then maintained in primary culture. The MOR agonist [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO) inhibited the total voltage-gated outward current; this effect was prevented by the perfusion of a Ca2+-free extracellular solution. We then studied the voltage-gated calcium current (Ica) and found that DAMGO Met-enkephalin or endomorphin-1 inhibited the ICa in a dose-response fashion. The effects of DAMGO were prevented by the MOR antagonist (CTAP) or by pertussis toxin (PTX). The use of specific calcium channel blockers showed that MOR activation inhibited T-, L- and N-type ICa. The use of various enzyme activators and inhibitors and of cAMP analogs allowed us to demonstrate that the MOR acts through a cAMP dependent signaling mechanism. In current clamp experiments, MOR activation increased the duration and decreased the amplitude of the action potentials and modulated the discharge produced by current injection. Pre-incubation with PTX occluded MOR activation effect. We conclude that MOR activation inhibits the T-, L- and N-type ICa through activation of a Gαi/o protein that involves a decrease in AC-cAMP-PKA activity. The modulation of ICa may have an impact on the synaptic integration, excitability, and neurotransmitter release from VANs.
Collapse
Affiliation(s)
- Emmanuel Seseña
- Instituto de Fisiología, Universidad Autónoma de Puebla Puebla, México
| | - Rosario Vega
- Instituto de Fisiología, Universidad Autónoma de Puebla Puebla, México
| | - Enrique Soto
- Instituto de Fisiología, Universidad Autónoma de Puebla Puebla, México
| |
Collapse
|
28
|
Abstract
PURPOSE OF REVIEW This review covers the articles published between 2010 and early 2011 that presented new findings on inner-ear efferents and their ability to modulate hair cell function. RECENT FINDINGS Studies published within the review period have increased our understanding of efferent mechanisms on hair cells in the cochlear and vestibular sensory epithelium and provide insights on efferent contributions to the plasticity of bilateral auditory processing. The central nervous system controls the sensitivity of hair cells to physiological stimuli by regulating the gain of hair cell electromechanical amplification and modulating the efficiency of hair cell-eighth nerve transmission. A notable advance in the last year has been animal and human studies that have examined the contribution of the olivocochlear efferents to sound localization, particularly in a noisy environment. SUMMARY Acoustic activation of olivocochlear fibers provides a clinical test for the integrity of the peripheral auditory system and has provided new understanding about the function and limitations of the cochlear amplifier. Although similar tests may be possible in the efferent vestibular system, they have not yet been developed. The structural and functional similarities of the sensory epithelia in the inner ear offer hope that testing procedures may be developed that will allow reliable testing of the vestibular hair cell function.
Collapse
|
29
|
Peusner KD, Shao M, Reddaway R, Hirsch JC. Basic Concepts in Understanding Recovery of Function in Vestibular Reflex Networks during Vestibular Compensation. Front Neurol 2012; 3:17. [PMID: 22363316 PMCID: PMC3282297 DOI: 10.3389/fneur.2012.00017] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Accepted: 01/27/2012] [Indexed: 12/30/2022] Open
Abstract
Unilateral peripheral vestibular lesions produce a syndrome of oculomotor and postural deficits with the symptoms at rest, the static symptoms, partially or completely normalizing shortly after the lesion due to a process known as vestibular compensation. The symptoms are thought to result from changes in the activity of vestibular sensorimotor reflexes. Since the vestibular nuclei must be intact for recovery to occur, many investigations have focused on studying these neurons after lesions. At present, the neuronal plasticity underlying early recovery from the static symptoms is not fully understood. Here we propose that knowledge of the reflex identity and input–output connections of the recorded neurons is essential to link the responses to animal behavior. We further propose that the cellular mechanisms underlying vestibular compensation can be sorted out by characterizing the synaptic responses and time course for change in morphologically defined subsets of vestibular reflex projection neurons. Accordingly, this review focuses on the perspective gained by performing electrophysiological and immunolabeling studies on a specific subset of morphologically defined, glutamatergic vestibular reflex projection neurons, the principal cells of the chick tangential nucleus. Reference is made to pertinent findings from other studies on vestibular nuclei neurons, but no comprehensive review of the literature is intended since broad reviews already exist. From recording excitatory and inhibitory spontaneous synaptic activity in principal cells, we find that the rebalancing of excitatory synaptic drive bilaterally is essential for vestibular compensation to proceed. This work is important for it defines for the first time the excitatory and inhibitory nature of the changing synaptic inputs and the time course for changes in a morphologically defined subset of vestibular reflex projection neurons during early stages of vestibular compensation.
Collapse
Affiliation(s)
- Kenna D Peusner
- Department of Anatomy and Regenerative Biology, George Washington University School of Medicine Washington, DC, USA
| | | | | | | |
Collapse
|
30
|
Eatock RA, Songer JE. Vestibular hair cells and afferents: two channels for head motion signals. Annu Rev Neurosci 2011; 34:501-34. [PMID: 21469959 DOI: 10.1146/annurev-neuro-061010-113710] [Citation(s) in RCA: 158] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Vestibular epithelia of the inner ear detect head motions over a wide range of amplitudes and frequencies. In mammals, afferent nerve fibers from central and peripheral zones of vestibular epithelia form distinct populations with different response dynamics and spike timing. Central-zone afferents are large, fast conduits for phasic signals encoded in irregular spike trains. The finer afferents from peripheral zones conduct more slowly and encode more tonic, linear signals in highly regular spike trains. The hair cells are also of two types, I and II, but the two types do not correspond directly to the two afferent populations. Zonal differences in afferent response dynamics may arise at multiple stages, including mechanoelectrical transduction, voltage-gated channels in hair cells and afferents, afferent transmission at calyceal and bouton synapses, and spike generation in regular and irregular afferents. In contrast, zonal differences in spike timing may depend more simply on the selective expression of low-voltage-activated ion channels by irregular afferents.
Collapse
Affiliation(s)
- Ruth Anne Eatock
- Department of Otology and Laryngology, Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02114, USA.
| | | |
Collapse
|
31
|
St George RJ, Day BL, Fitzpatrick RC. Adaptation of vestibular signals for self-motion perception. J Physiol 2011; 589:843-53. [PMID: 20937715 PMCID: PMC3060364 DOI: 10.1113/jphysiol.2010.197053] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2010] [Accepted: 10/10/2010] [Indexed: 11/08/2022] Open
Abstract
A fundamental concern of the brain is to establish the spatial relationship between self and the world to allow purposeful action. Response adaptation to unvarying sensory stimuli is a common feature of neural processing, both peripherally and centrally. For the semicircular canals, peripheral adaptation of the canal-cupula system to constant angular-velocity stimuli dominates the picture and masks central adaptation. Here we ask whether galvanic vestibular stimulation circumvents peripheral adaptation and, if so, does it reveal central adaptive processes. Transmastoidal bipolar galvanic stimulation and platform rotation (20 deg s−1) were applied separately and held constant for 2 min while perceived rotation was measured by verbal report. During real rotation, the perception of turn decayed from the onset of constant velocity with a mean time constant of 15.8 s. During galvanic-evoked virtual rotation, the perception of rotation initially rose but then declined towards zero over a period of ∼100 s. For both stimuli, oppositely directed perceptions of similar amplitude were reported when stimulation ceased indicating signal adaptation at some level. From these data the time constants of three independent processes were estimated: (i) the peripheral canal-cupula adaptation with time constant 7.3 s, (ii) the central ‘velocity-storage' process that extends the afferent signal with time constant 7.7 s, and (iii) a long-term adaptation with time constant 75.9 s. The first two agree with previous data based on constant-velocity stimuli. The third component decayed with the profile of a real constant angular acceleration stimulus, showing that the galvanic stimulus signal bypasses the peripheral transformation so that the brainstem sees the galvanic signal as angular acceleration. An adaptive process involving both peripheral and central processes is indicated. Signals evoked by most natural movements will decay peripherally before adaptation can exert an appreciable effect, making a specific vestibular behavioural role unlikely. This adaptation appears to be a general property of the internal coding of self-motion that receives information from multiple sensory sources and filters out the unvarying components regardless of their origin. In this instance of a pure vestibular sensation, it defines the afferent signal that represents the stationary or zero-rotation state.
Collapse
Affiliation(s)
- Rebecca J St George
- Neuroscience Research Australia, Barker Street, Randwick, NSW 2031, Australia.
| | | | | |
Collapse
|
32
|
Cullen KE, Brooks JX, Jamali M, Carriot J, Massot C. Internal models of self-motion: computations that suppress vestibular reafference in early vestibular processing. Exp Brain Res 2011; 210:377-88. [PMID: 21286693 DOI: 10.1007/s00221-011-2555-9] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2010] [Accepted: 12/29/2010] [Indexed: 01/11/2023]
Abstract
In everyday life, vestibular sensors are activated by both self-generated and externally applied head movements. The ability to distinguish inputs that are a consequence of our own actions (i.e., active motion) from those that result from changes in the external world (i.e., passive or unexpected motion) is essential for perceptual stability and accurate motor control. Recent work has made progress toward understanding how the brain distinguishes between these two kinds of sensory inputs. We have performed a series of experiments in which single-unit recordings were made from vestibular afferents and central neurons in alert macaque monkeys during rotation and translation. Vestibular afferents showed no differences in firing variability or sensitivity during active movements when compared to passive movements. In contrast, the analyses of neuronal firing rates revealed that neurons at the first central stage of vestibular processing (i.e., in the vestibular nuclei) were effectively less sensitive to active motion. Notably, however, this ability to distinguish between active and passive motion was not a general feature of early central processing, but rather was a characteristic of a distinct group of neurons known to contribute to postural control and spatial orientation. Our most recent studies have addressed how vestibular and proprioceptive inputs are integrated in the vestibular cerebellum, a region likely to be involved in generating an internal model of self-motion. We propose that this multimodal integration within the vestibular cerebellum is required for eliminating self-generated vestibular information from the subsequent computation of orientation and posture control at the first central stage of processing.
Collapse
Affiliation(s)
- Kathleen E Cullen
- Aerospace Medical Research Unit, Department of Physiology, McGill University, Montreal, PQ, H3G 1Y6, Canada.
| | | | | | | | | |
Collapse
|
33
|
|
34
|
Cullen KE, Minor LB, Beraneck M, Sadeghi SG. Neural substrates underlying vestibular compensation: contribution of peripheral versus central processing. J Vestib Res 2010; 19:171-82. [PMID: 20495234 DOI: 10.3233/ves-2009-0357] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The vestibulo-ocular reflex (VOR), which functions to stabilize gaze and ensure clear vision during everyday activities, shows impressive adaptation in response to environmental requirements. In particular, the VOR exhibits remarkable recovery following the loss of unilateral labyrinthine input as a result of injury or disease. The relative simplicity of the pathways that mediate the VOR, make it an excellent model system for understanding the changes (learning) that occur in the brain following peripheral vestibular loss to yield adaptive changes. This mini review considers the findings of behavioral, single unit recording and lesion studies of VOR compensation. Recent experiments have provided evidence that the brain makes use of multiple plasticity mechanisms (i.e., changes in peripheral as well as central processing) during the course of vestibular compensation to accomplish the sensory-motor transformations required to accurately guide behavior.
Collapse
|
35
|
Kandel BM, Hullar TE. The relationship of head movements to semicircular canal size in cetaceans. J Exp Biol 2010; 213:1175-81. [PMID: 20228354 PMCID: PMC2837735 DOI: 10.1242/jeb.040105] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/03/2009] [Indexed: 11/20/2022]
Abstract
The semicircular canals measure head rotations, providing information critical for maintaining equilibrium. The canals of cetaceans (including whales, dolphins and porpoises) are extraordinarily small, making them unique exceptions to the allometric relationship shared by all other vertebrates between canal size and animal mass. Most modern cetaceans have shorter and less flexible necks than those of their ancestors, an adaptation hypothesized to have led to exaggerated head movements during locomotion. These movements are thought to have necessitated a decrease in the size and sensitivity of the canals, increasing their operating range to accommodate increased head motion. We tested whether the size of the semicircular canals in cetaceans is related to their head movements by comparing the rotational head velocities, frequencies and accelerations of the bottlenose dolphin (Tursiops truncatus) and a terrestrial relative, cattle (Bos taurus), using an array of three orthogonal head-fixed miniaturized rotational ratemeters. We collected data during typical locomotion (swimming; trotting) and during behaviors with enhanced head movements (rapid spiraling underwater; bucking). Cattle head movements always exceeded those of dolphins. Maximum head velocities were 528 deg. s(-1) in dolphins and 534 deg. s(-1) in cattle; maximum head frequencies were 2.86 Hz in dolphins and 3.45 Hz in cattle; and maximum head accelerations were 5253 deg. s(-2) in dolphins and 10,880 deg. s(-2) in cattle. These results indicate that accentuated head movements cannot explain the reduced size and sensitivity of cetacean semicircular canals. The evolutionary cause for their reduced canal size remains uncertain.
Collapse
Affiliation(s)
- Benjamin M. Kandel
- Department of Otolaryngology, Washington University School of Medicine, St Louis, MO, USA
| | - Timothy E. Hullar
- Department of Otolaryngology, Washington University School of Medicine, St Louis, MO, USA
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St Louis, MO, USA
- Program in Audiology and Communication Sciences, CID at Washington University School of Medicine, St Louis, MO, USA
| |
Collapse
|
36
|
Abstract
Sensory hair cells are the essential mechanotransducers of the inner ear, responsible not only for the transduction of sound and motion stimuli but also, remarkably, for nanomechanical amplification of sensory stimuli. Here we show that semicircular canal hair cells generate a mechanical nonlinearity in vivo that increases sensitivity to angular motion by amplification at low stimulus strengths. Sensitivity at high stimulus strengths is linear and shows no evidence of amplification. Results suggest that the mechanical work done by hair cells contributes approximately 97 zJ/cell of amplification per stimulus cycle, improving sensitivity to angular velocity stimuli below approximately 5 degrees /s (0.3-Hz sinusoidal motion). We further show that mechanical amplification can be inhibited by the brain via activation of efferent synaptic contacts on hair cells. The experimental model was the oyster toadfish, Opsanus tau. Physiological manifestation of mechanical amplification and efferent control in a teleost vestibular organ suggests the active motor process in sensory hair cells is ancestral. The biophysical basis of the motor(s) remains hypothetical, but a key discriminating question may involve how changes in somatic electrical impedance evoked by efferent synaptic action alter function of the motor(s).
Collapse
|
37
|
Sadeghi SG, Goldberg JM, Minor LB, Cullen KE. Effects of canal plugging on the vestibuloocular reflex and vestibular nerve discharge during passive and active head rotations. J Neurophysiol 2009; 102:2693-703. [PMID: 19726724 PMCID: PMC2777831 DOI: 10.1152/jn.00710.2009] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2009] [Accepted: 08/31/2009] [Indexed: 11/22/2022] Open
Abstract
Mechanical occlusion (plugging) of the slender ducts of semicircular canals has been used in the clinic as well as in basic vestibular research. Here, we investigated the effect of canal plugging in two macaque monkeys on the horizontal vestibuloocular reflex (VOR) and the responses of vestibular-nerve afferents during passive head rotations. Afferent responses to active head movements were also studied. The horizontal VOR gain decreased after plugging to <0.1 for frequencies <2 Hz but rose to about 0.6 as frequency was increased to 15 Hz. Afferents innervating plugged horizontal canals had response sensitivities that increased with the frequency of passive rotations from <0.01 (spikes/s)/( degrees/s) at 0.5 Hz to values of about 0.2 and 0.5 (spikes/s)/( degrees/s) at 8 Hz for regular and irregular afferents, respectively (<50% of responses in controls). An increase in phase lead was also noted following plugging in afferent discharge, but not in the VOR. Because the phase discrepancy between the VOR and afferent discharge is much larger than that seen in control animals, this suggests that central adaptation shapes VOR dynamics following plugging. The effect of canal plugging on afferent responses can be modeled as an increase in stiffness and a reduction in the dominant time constant and gain in the transfer function describing canal dynamics. Responses were also evident during active head rotations, consistent with the frequency content of these movements. We conclude that canal plugging in macaques is effective only at frequencies <2 Hz. At higher frequencies, afferents show significant responses, with a nearly 90 degrees phase lead, such that they encode near-rotational acceleration. Our results demonstrate that afferents innervating plugged canals respond robustly during voluntary movements, a finding that has implications for understanding the effects of canal plugging in clinical practice.
Collapse
Affiliation(s)
- Soroush G Sadeghi
- Department of Physiology, McGill University, 3655 Prom. Sir William Osler, Room 1218, Montreal, Quebec H3G 1Y6, Canada.
| | | | | | | |
Collapse
|