Sensory transduction of head velocity and acceleration in the toadfish horizontal semicircular canal

1. Sinusoidal mechanical indentation of the long-and-slender limb of the horizontal semicircular canal and/or utricle was used to produce adequate stimulation of the labyrinth. Indentation of the canal increased, while indentation of the utricle decreased the afferent discharge rate. This follows because indentation of the canal and utricle produce oppositely directed mechanical stimuli as defined by endolymph flow, transcupular pressure, and cupular deflection. Simultaneous in-phase indentations of both the canal and utricle, with amplitudes adjusted to produce equal (but opposite) magnitudes of afferent response modulation, generate destructive interaction that minimizes the afferent modulation, whereas sinusoidal indentation 180 degrees out-of-phase generates constructive interaction that maximizes the afferent modulation. This observation correlates directly with analysis of the labyrinthine elasto-hydrodynamics which predicts that balanced in-phase indentations minimize macromechanical endolymph flow through the ampullary cross section and maximize the dilatational pressure within the ampulla acting equally on both sides of the cupula and across the labyrinthine wall. 2. Two groups of afferents are identified according to their response to balanced sinusoidal indentation of the canal limb and the utricle. In one group there is complete destructive interaction and the afferent response can be effectively nulled by adjusting the relative amplitude and phase of the two stimuli. In the second group a residual afferent response remains that cannot be nulled. The residual is described in the model as unit-specific sensitivity to dilatational pressure acting equally on both sides of the cupula.

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Prevalence and Characteristics of Preoperative Balance Disorders in Cochlear Implant Candidates

Annals of Otology Rhinology & Laryngology ◽

10.1177/000348940811701011 ◽

2008 ◽

Vol 117 (10) ◽

pp. 764-768 ◽

Cited By ~ 14

Author(s):

Eike Krause ◽

Julia P. R. Louza ◽

John-Martin Hempel ◽

Juliane Wechtenbruch ◽

Tobias Rader ◽

...

Keyword(s):

Semicircular Canal ◽

Vestibular Function ◽

Horizontal Semicircular Canal ◽

Group A ◽

Vestibular Function Testing ◽

Group B ◽

Vestibular Function Test ◽

Postoperative Vertigo ◽

Patient’S History ◽

Function Testing

Objectives: The aim of this study was to elucidate the frequency and characteristics of preoperative vertigo symptoms in patients who undergo cochlear implantation (CI), in order to differentiate them from CI-related symptoms. Methods: In a prospective observational study, 47 adult CI candidates were asked about vertigo problems on a questionnaire. A subdivision into 3 groups was done: Group A (probable otogenic vertigo), group B (possible otogenic vertigo), and group C (not otogenic vertigo). Horizontal semicircular canal function was measured. Patients with vertigo complaints were compared to patients without vertigo with regard to the presence of abnormal vestibular function findings. Results: Twenty-five patients (53%) reported preoperative vertigo problems. In 21 (84%), the patient's history suggested a probable (group A) or possible (group B) otogenic origin. Patients with vertigo more often had abnormal findings on vestibular function testing than did patients without vertigo. This difference, however, was not statistically significant. Conclusions: A considerable number of CI candidates have preoperative vertigo symptoms. These cannot be explained by horizontal semicircular canal function alone. In order to understand why CI patients develop postoperative vertigo, analysis of prospective preoperative vestibular function test findings and vertigo symptoms is necessary.

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Cardiac sympathetic afferent sensitivity is enhanced in heart failure

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1999.277.2.h812 ◽

1999 ◽

Vol 277 (2) ◽

pp. H812-H817 ◽

Cited By ~ 27

Author(s):

Wei Wang ◽

Harold D. Schultz ◽

Rong Ma

Keyword(s):

Heart Failure ◽

Sham Group ◽

Discharge Rate ◽

Afferent Fiber ◽

Acute Experiment ◽

Ventricular Pacing ◽

Cardiac Sympathetic Nerve ◽

Afferent Discharge ◽

Rapid Ventricular Pacing ◽

Afferent Response

A previous study from this laboratory has shown that cardiac sympathetic afferent stimulation by epicardial application of bradykinin (BK) and capsaicin was significantly enhanced in the dog with experimental heart failure (HF). The present study determined whether activity from cardiac sympathetic chemosensitive afferent endings is enhanced in HF. Rapid ventricular pacing was induced in six dogs. Five sham dogs served as controls. At the time of the acute experiment, the dogs were anesthetized with pentobarbital sodium (30 mg/kg iv). A thoracotomy was performed in the second intercostal space, and single afferent fiber discharge from the left cardiac sympathetic nerve was recorded. Baseline cardiac sympathetic afferent discharge rate (spikes/s) and its responses to intra-atrial injection of BK were compared between sham and HF groups. Baseline cardiac sympathetic afferent discharge rate in the HF group was significantly elevated compared with the sham group (4.3 ± 0.5 vs. 2.2 ± 0.6 spikes/s, P < 0.05). In addition, cardiac sympathetic afferent responses to left intra-atrial injection of bradykinin (2 and 5 μg/kg) and capsaicin (5 and 10 μg/kg) were also significantly augmented. The sensitized cardiac sympathetic afferent responses to BK (2 and 5 μg/kg, left intra-atrial injection) in the HF group were significantly reduced by the cyclooxygenase inhibitor indomethacin (5 mg/kg iv). The sensitized cardiac sympathetic afferent response to capsaicin (5 and 10 μg/kg, left intra-atrial injection) in the HF group was preserved. It is suggested that the cardiac sympathetic chemosensitive afferent sensitivity is significantly enhanced in dogs with HF even though the baseline cardiac sympathetic afferent discharge is elevated.

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Changes in monkey horizontal semicircular canal afferent responses after spaceflight

Journal of Applied Physiology ◽

10.1152/jappl.1992.73.2.s112 ◽

1992 ◽

Vol 73 (2) ◽

pp. S112-S120 ◽

Cited By ~ 31

Author(s):

M. J. Correia ◽

A. A. Perachio ◽

J. D. Dickman ◽

I. B. Kozlovskaya ◽

M. G. Sirota ◽

...

Keyword(s):

Central Nervous System ◽

Nervous System ◽

Semicircular Canal ◽

Semicircular Canals ◽

Vestibular Stimulation ◽

Horizontal Semicircular Canal ◽

Horizontal Canal ◽

Efferent Connections ◽

The Central Nervous System ◽

Afferent Response

Extracellular responses from single horizontal semicircular canal afferents in two rhesus monkeys were studied after recovery from a 14-day biosatellite (COSMOS 2044) orbital spaceflight. On the 1st postflight day, the mean gain for 9 different horizontal canal afferents, tested using one or several different passive yaw rotation waveforms, was nearly twice that for 20 horizontal canal afferents similarly tested during preflight and postflight control studies. Adaptation of the afferent response to passive yaw rotation on the 1st postflight day was also greater. These results suggest that at least one component of the vestibular end organ (the semicircular canals) is transiently modified after exposure to 14 days of microgravity. It is unclear whether the changes are secondary to other effects of microgravity, such as calcium loss, or an adaptive response. If the response is adaptive, then this report is the first evidence that the response of the vestibular end organ may be modified (presumably by the central nervous system via efferent connections) after prolonged unusual vestibular stimulation. If this is the case, the sites of plasticity of vestibular responses may not be exclusively within central nervous system vestibular structures, as previously believed.

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Afferent Responses During Experimentally Induced Semicircular Canalithiasis

Journal of Neurophysiology ◽

10.1152/jn.01152.2006 ◽

2007 ◽

Vol 97 (3) ◽

pp. 2355-2363 ◽

Cited By ~ 25

Author(s):

Suhrud M. Rajguru ◽

Richard D. Rabbitt

Keyword(s):

Semicircular Canal ◽

Time Course ◽

Discharge Rate ◽

Initial Increase ◽

Vestibular Disorder ◽

Afferent Discharge ◽

Oyster Toadfish ◽

Head Rotations ◽

The Brain

Benign paroxysmal positional vertigo (BPPV) is a common vestibular disorder that results in brief periods of vertigo and nystagmus, when the head is tipped relative to gravity. Symptoms are commonly attributed to the pathological presence of heavy calcium carbonate particles within the lumen of the semicircular canal(s)—a condition termed canalithiasis. In the present work, we induced canalithiasis in an animal model (oyster toadfish, Opsanus tau) by introducing heavy glass microbeads into the lumen of the lateral semicircular canal. Bead movement under the action of gravity and canal afferent nerve discharge were recorded in vivo. When the head was oriented nose-down, beads moved toward the nose and the lateral canal afferent discharge rate increased. Afferents that normally encoded angular velocity during oscillatory head rotations responded with tonic increases in the discharge rate during gravity-dependent bead movement. Other afferents, such as the units that rapidly adapt to a step increase in angular head velocity, responded with an initial increase in discharge rate followed by a period of adaptation. Afferent responses occurred in the complete absence of head movement and quantify the pathological inputs to the brain that arise from canalithiasis. The magnitude and time course of the responses reported here are sufficient to explain the symptoms of BPPV.

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Morphological correlates of response dynamics and efferent stimulation in horizontal semicircular canal afferents of the toadfish, Opsanus tau

Journal of Neurophysiology ◽

10.1152/jn.1991.66.5.1504 ◽

1991 ◽

Vol 66 (5) ◽

pp. 1504-1521 ◽

Cited By ~ 67

Author(s):

R. Boyle ◽

J. P. Carey ◽

S. M. Highstein

Keyword(s):

Hair Cell ◽

Semicircular Canal ◽

Discharge Rate ◽

Dendritic Morphology ◽

Cell Contact ◽

Relative Location ◽

Response Dynamics ◽

Horizontal Semicircular Canal ◽

Dendritic Field ◽

Response Sensitivity

1. We used the intraaxonal labeling technique to study correlations between the terminal dendritic morphology of horizontal semicircular canal primary afferents and their response dynamics to sinusoidal head rotation and combined electrical stimulation of central efferent vestibular neurons. Thirty-eight canal afferents were identified by their sensitivity and phase of response to rotation between 0.1 and 1.0 Hz (+/- 10 degrees/s) and were subsequently labeled with horseradish peroxidase or biocytin. The afferent's dendritic field and synaptic specializations in the neuroepithelium of the crista were examined under light microscopy. 2. Rate and regularity of background discharge of the afferent were not correlated with its axon diameter or relative location of its dendritic field in the crista. 3. Response sensitivity of the afferent to rotation was correlated both with the relative location of its dendritic field in the crista and with the number of terminal endings it possesses. Afferents having low sensitivities, slow dynamics, and few terminal endings supply the peripheral portions of the crista; afferents with higher sensitivities, faster dynamics, and greater number of terminal endings supply the more central portions. It is suggested that the differences in sensitivity among the afferents reflect principally the variations in both the cupular dynamics along the crista and the number of possible hair cell contact sites in the neuroepithelium. 4. Response phase of the afferent was correlated only with the extent of its dendritic processes along the transverse axis of the crista. Afferents having transversely oriented dendritic fields had less phase lags relative to acceleration than did those having a more longitudinally oriented dendritic field. 5. Efferent stimulation produced a change in both the afferent's discharge rate and its response sensitivity to rotation. Afferents discharge rate and its response sensitivity to rotation. Afferents having a centrally located dendritic field and acceleration afferents, defined by their response to rotation, were the most affected by efferent stimulation. These results suggest that efferent innervation is either directed toward, or most efficacious in, the central regions of the crista and that it may select specific hair cell-afferent complexes.

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