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PubMed2005

Persistence of perilymph fistula mechanism in a completely paretic posterior semicircular canal.

The three dimensional eye movements (search coil technique) of a patient with a completely paretic left posterior semicircular canal as a result of a perilymph fistula (PLF) were studied. The patient still exhibited pressure induced nystagmus that obeyed Ewald's first law. This finding cannot be explained by otolith stimulation, but might indicate that PLF mechanisms either persist in canal plugging or act on the ampulla by directly deflecting the cupula.

Adult↗
PubMed1999

A poroelastic continuum model of the cupula partition and the response dynamics of the vestibular semicircular canal.

Using mixture theory, an axisymmetric continuum model is presented describing the response dynamics of the vestibular semicircular canals to canal-centered head rotation in which the cupula partition is modeled as a poroelastic mixture of interpenetrating solid and fluid constituents. The solid matrix of the cupula is assumed to behave as a linear elastic material, whereas the fluid constituent is assumed to be Newtonian. A regular perturbation analysis of the fluid dynamics in the canal provides a dynamic boundary condition, which acts across the cupula partition. Numerical solution of the coupled system of momentum equations provides the spatio-temporal displacement fields for both the fluid and solid constituents of the cupula. Results indicate that at frequencies above 1 Hz, the fluid constituent is dynamically entrained by the solid matrix such that their motions are bound as if to exist as a single component. The resulting high-frequency response is consistent with the macromechanical response predicted by single-component viscoelastic models of the cupula. Below 1 Hz, the dynamic coupling between the fluid and solid constituents weakens and the transcupular differential pressure is sufficient to force fluid through the mixture with little deformation of the solid matrix. Results are sensitive to the precise value of the cupular permeability. One of the most important distinctions between the present analysis and previous impermeable models of the cupula arises at the micromechanical level in terms of the local fluid flow that is predicted to occur within the cupula and around the ciliary bundles and sensory hair cells. Another important result reveals that the permeation dynamics predicted below 1 Hz gives rise to the same low-frequency macromechanical response as would occur with an impermeable viscoelastic structure having a much greater stiffness. Current estimates of the mechanical stiffness of the cupula, based solely on afferent nerve data, may therefore overestimate the true value intrinsic to the solid matrix by as much as an order of magnitude.

Animals↗
PubMed1994

Potassium currents in mammalian and avian isolated type I semicircular canal hair cells.

1. Type I vestibular hair cells were isolated from the cristae ampullares of the semicircular canals of the Mongolian gerbil (Meriones unguiculatus) and the white king pigeon (Columba livia). Dissociated type I cells were distinguished from type II hair cells by their neck to plate ratio (NPR) and their characteristic amphora shape. 2. The membrane properties of gerbil and pigeon type I hair cells were studied in whole-cell voltage- and current-clamp using the perforated patch technique with amphotericin B as the perforating agent. 3. In whole-cell current-clamp, the average zero-current potential, Vz, measured for pigeon type I hair cells, was -70 +/- 7 (SD) mV (n = 18) and -71 +/- 11 mV (n = 83) for gerbil type I hair cells. 4. At Vz, for both gerbil and pigeon type I hair cells, a potassium current (IKI) was > or = 50% activated. This current deactivated rapidly when the membrane potential was hyperpolarized below -90 mV. 5. IKI was blocked by externally applied 4-aminopyridine (4-AP) (5 mM) and by internally applied 20 mM tetraethylammonium (TEA). It was also reduced when 4 mM barium was present in the external solution. The degree of block by barium increased as the membrane potential became more positive. External cesium (5 mM) blocked the inward component of IKI. When IKI was pharmacologically blocked, Vz depolarized by approximately 40 mV. Therefore IKI appears to be a delayed rectifier and to set the more negative Vz noted for isolated type I hair cells when compared to isolated type II hair cells, which do not have IKI. 6. A second, smaller potassium current was present at membrane potential depolarizations above -40 mV. This current was blocked by 30-50 mM, externally applied TEA, 100 microM quinidine, 100 nM apamin, but not 100 nM charybdotoxin, indicating that this is a calcium-activated potassium current, IK(Ca), different from the maxi-K calcium-activated potassium current found in most other hair cells.

4-Aminopyridine↗
PubMed1989

Morphology of single primary vestibular afferents originating from the horizontal semicircular canal in the cat.

The central projections of physiologically characterized vestibular nerve fibers originating from the horizontal semicircular canal were studied in the vestibular nuclei of adult cats after intracellular staining with horseradish peroxidase (HRP). First, primary nerve fibers were physiologically classified as regular or irregular types on the basis of the regularity of the spontaneous discharge pattern. Then, these two types of fibers were morphologically analyzed and compared following HRP intraaxonal injection. The two types of axons showed a basically similar trajectory in the four major vestibular nuclei. They bifurcated into an ascending and a descending branch in the ventrolateral part of the lateral vestibular nucleus (LVN). The ascending branch extended rostrally and gave off one or two collaterals in the superior vestibular nucleus (SVN), although some of the ascending branches further ran rostrally into the cerebellum. The collaterals, while running medially, gave rise to fine terminal branches with en passant boutons in the SVN, and further coursing caudally, they entered the rostral part of the medial vestibular nucleus (MVN). The descending branch, while running caudally in the lateral part of the LVN and the inferior vestibular nucleus (IVN), gave off several thick collaterals to the MVN and extensive terminals were present in the IVN and MVN. In each primary axon, about one-third of the total terminal boutons were distributed in each of the SVN, the MVN, and the IVN. In contrast to this similarity of the overall axonal trajectory within the vestibular nuclei, both types of axons exhibited several marked differences in diameter and in the mode of terminal arborization. In almost every part of the ramification, the irregular-type fibers were thicker than the regular-type fibers. In the regular-type axons, many small terminal boutons (mean size, 2.4 x 1.4 microns, N = 2,739) were located in close proximity (100-150 microns) to the parent collateral. In the irregular-type axons, slightly larger terminal boutons (mean size, 3.0 x 1.7 microns, N = 1,287), were spread more widely (200-300 microns) around their collaterals. These clear morphological differences between the regular-type and the irregular-type terminal axons were consistently observed in any vestibular nucleus.

Animals↗
PubMed1999

Directional coding of three-dimensional movements by the vestibular semicircular canals.

A morphologically descriptive mathematical model was developed to study the role of labyrinthine geometry in determining sensitivities of each semicircular canal to angular motion stimuli in three-dimensional (3D) space. For this, equations describing viscous flow of the endolymph and poro-elastic response of the cupulae were coupled together and solved within a 3D reconstructed geometry. Results predict the existence of prime rotational directions about which the labyrinth resolves 3D angular movements into separate vectorial components. The components are predicted to be transmitted to the brain separately, one coded by each canal nerve. Prime directions predicted by the model are non-orthogonal, distinct from the anatomical canal planes, and distinct from the directions of rotation which elicit maximal responses of individual canal nerves. They occur for each canal along the intersection of the two null planes defined by its sister canals. Hence, rotation about a prime direction excites only one canal nerve. This contrasts the situation for rotations about anatomical canal planes, or about maximal response directions, where the model predicts activation of multiple canal nerves. The prime directions are sensitive to labyrinthine morphology and, hence, are predicted to vary between species and, to a lesser extent, vary between individual animals. Prime directions were estimated in the present work using a mathematical model, but could be determined experimentally based on the directional sensitivities of individual canal nerves. The model also predicts the existence of dominant eigenmodes and time constants associated with rotation in each of the prime directions. Results may have implications regarding the central representation of angular head movements in space as well as the neuronal mappings between three-canal afferent inputs and motor outputs.

Head Movements↗
PubMed1982

Oculomotor reflexes after semicircular canal plugging in cats.

The horizontal ocular reflexes of cats were studied before and after plugging all 6 semicircular canals (2 cats) or the horizontal canals only (2 cats). After plugging, the vestibulo-ocular reflex (VOR) was virtually absent in the cats with all canals plugged; a small phase-advanced VOR was detectable only at high velocities of rotation. There was no VOR recovery over several months. A compensatory cervico-ocular reflex (COR) appeared within a few days of plugging in all cats, and increased in gain slowly over time. The cats with horizontal canals plugged had little VOR during yaw rotation with the head pitched near 30 degrees down from the stereotaxic plane. When the head was pitched nose up from this null plane, a horizontal VOR appeared and increased as the sine of pitch angle, indicating that the cats relied on normal or increased coupling of vertical canals to horizontal eye movers for generation of compensatory eye movements. Periods of compensatory and anticompensatory eye movements were recorded during downward pitched yaw.

Animals↗
PubMed2004

A mathematical model of the response of semicircular canal and otolith to head rotation under gravity.

The mathematical model of the system composed of two sensors: semicircular canal and sacculus, is presented. The system is described by three series of blocks: biomechanical block, mechanoelectrical transduction mechanism and hair cell ionic currents and membrane potential dynamics. The response of the aforecited system to various stimuli (head rotation under gravity and falling) was investigated. The identification of the model parameters was fulfilled for the experimental data, obtained for the axolotle (Ambystoma tigrinum) in Institute of Physiology, Autonomous University of Puebla, Mexico. The comparative analysis of canal and sacculus membrane potential was realized.

Acceleration↗
PubMed1992

[Resection of the semicircular canal system with preserved hearing--an animal experiment study].

In a previous investigation we selectively resected the lateral semicircular canal of the rabbit, preserving the hearing in 67% of the animals. We now report an attempt to remove all three canals in one step with a microsurgical technique using fibrin glue and bone chips. Brain-stem auditory potentials were recorded at intervals up to 3 months after operation. Residual hearing could be recorded in 50% of rabbits. These animals regularly showed a 30-40 dB deterioration of hearing.

Animals↗
PubMed2005

Clinical manifestations of superior semicircular canal dehiscence.

OBJECTIVES/HYPOTHESES: To determine the symptoms, signs, and findings on diagnostic tests in patients with clinical manifestations of superior canal dehiscence. To investigate hypotheses about the effects of superior canal dehiscence. To analyze the outcomes in patients who underwent surgical repair of the dehiscence. STUDY DESIGN: Review and analysis of clinical data obtained as a part of the diagnosis and treatment of patients with superior canal dehiscence at a tertiary care referral center. METHODS: Clinical manifestations of superior semicircular canal dehiscence were studied in patients identified with this abnormality over the time period of May 1995 to July 2004. Criteria for inclusion in this series were identification of the dehiscence of bone overlying the superior canal confirmed with a high-resolution temporal bone computed tomography and the presence of at least one sign on physiologic testing indicative of superior canal dehiscence. There were 65 patients who qualified for inclusion in this study on the basis of these criteria. Vestibular manifestations were present in 60 and exclusively auditory manifestations without vestibular symptoms or signs were noted in 5 patients. RESULTS: For the 60 patients with vestibular manifestations, symptoms induced by loud sounds were noted in 54 patients and pressure-induced symptoms (coughing, sneezing, straining) were present in 44. An air-bone on audiometry in these patients with vestibular manifestations measured (mean +/- SD) 19 +/- 14 dB at 250 Hz; 15 +/- 11 dB at 500 Hz; 11 +/- 9 dB at 1,000 Hz; and 4 +/- 6 dB at 2,000 Hz. An air-bone gap 10 dB or greater was present in 70% of ears with superior canal dehiscence tested at 250 Hz, 68% at 500 Hz, 64% at 1,000 Hz, and 21% at 2,000 Hz. Similar audiometric findings were noted in the five patients with exclusively auditory manifestations of dehiscence. The threshold for eliciting vestibular-evoked myogenic potentials from affected ears was (mean +/- SD) 81 +/- 9 dB normal hearing level. The threshold for unaffected ears was 99 +/- 7 dB, and the threshold for control ears was 98 +/- 4 dB. The thresholds in the affected ear were significantly different from both the unaffected ear and normal control thresholds (P < .001 for both comparisons). There was no difference between thresholds in the unaffected ear and normal control (P = .2). There were 20 patients who were debilitated by their symptoms and underwent surgical repair of superior canal dehiscence through a middle cranial fossa approach. Canal plugging was performed in 9 and resurfacing of the canal without plugging of the lumen in 11 patients. Complete resolution of vestibular symptoms and signs was achieved in 8 of the 9 patients after canal plugging and in 7 of the 11 patients after resurfacing. CONCLUSIONS: Superior canal dehiscence causes vestibular and auditory symptoms and signs as a consequence of the third mobile window in the inner ear created by the dehiscence. Surgical repair of the dehiscence can achieve control of the symptoms and signs. Canal plugging achieves long-term control more often than does resurfacing.

Adolescent↗
PubMed1997

[Benign postural vertigo and nystagmus of the horizontal semicircular canal].

Benign paroxysmal vertigo and nystagmus are induced not only by the posterior but also by the horizontal semicircular canal. Benign positional nystagmus of the horizontal canal is more often observed than was previously thought. In 10 patients we analyzed the characteristics and the variability of nystagmus which accompanies positional vertigo of the horizontal canal. There are two forms of nystagmus: primary-geotropic, most often paroxysmal nystagmus (7 patients), and primary-apogeotropic, non-paroxysmal nystagmus (3 patients). Interestingly, in 2 patients with the primary-apogeotropic form the nystagmus converted during the examination into the primary-geotropic form. The reverse was not observed. We discuss the possible pathophysiological mechanisms which could be relevant for provoking manoeuvres.

Adult↗
PubMed1987

Prostaglandins in the semicircular canal of the frog.

The synthesis of prostaglandins by ampulla and duct tissue isolated from the frog posterior semicircular canal was investigated in vitro. Ampulla and duct produced PGE2 (9 and 6 pg/structure, respectively) and prostacyclin (26 and 12 pg/structure). In the ampulla, prostaglandins mostly originated from the part containing dark and sensory cells and was not altered by 10(-3) M streptomycin. Prostaglandin levels were time-dependent and temperature-dependent. Arachidonic acid (3 X 10(-5) M) stimulated PGI2 synthesis by ampulla and duct (by 11.4 and 17 times) and PGE2 synthesis by 50 times in both structures. Ionophore A23187 stimulated ampulla and duct PGI2 synthesis (by 4.8 and 5.6 times) and PGE2 synthesis (by 2.4 and 1.8 times). Subcutaneous 100 mg/kg aspirin reduced PGI2 and PGE2 synthesis (ampulla: -87%, -33%; duct: -100%, -33%). Indomethacin (10(-6) M), in vitro, decreased PGI2 and PGE2 synthesis (ampulla: -47%, -47%; duct; -22%, -77%). Within 3 h, aspirin (5 X 10(-6) M) or arachidonic acid (2 X 10(-5) M) did not change Na and K concentrations in endolymph. It is concluded that frog inner ear produces PGI2 and PGE2, mostly from the part containing the dark cells, and that prostaglandins could be involved in the physiology of inner ear.

Animals↗
PubMed1990

Perilymphatic potassium changes and potassium homeostasis in isolated semicircular canals of the frog.

1. Endolymphatic and perilymphatic potassium concentrations were measured with K(+)-sensitive microelectrodes in isolated semicircular canals of the frog. K+ levels were evaluated both at rest and during sinusoidal stimulation (0.05 Hz) of the sensory organ. 2. Mechanical stimulation of hair cells was associated with sinusoidal changes (about 0.2 mM) in the perilymphatic K+ concentration. 3. Perilymphatic K(+)-fluctuations were modified neither by impairment of the synaptic transmission at cyto-neural junctions nor by chronic denervation of the crista ampullaris, thus indicating that K+ ions were actually released by hair cells. 4. Voltage-clamp experiments of the whole sensory organ showed that K+ flows across the crista ampullaris can vary from 3 X 10(11) molecules of K+ s-1 at rest up to about 15 X 10(11) molecules of K+ s-1 during mechanical stimuli. 5. Measurement of intra-ampullar K+ concentration demonstrated that the amount of K+ transported from the perilymph towards the endolymph can be rapidly altered by modifying its perilymphatic levels. This suggests that vestibular organs are endowed with K+ homeostatic mechanisms able to buffer in a very efficient way the concentration of K+ in both the fluids bathing the crista ampullaris. 6. The possible role of K+ homeostatic mechanisms in hair cell adaptation is discussed.

Action Potentials↗
PubMed2000

Calcium currents in hair cells isolated from semicircular canals of the frog.

L-type and R-type Ca(2+) currents were detected in frog semicircular canal hair cells. The former was noninactivating and nifedipine-sensitive (5 microM); the latter, partially inactivated, was resistant to omega-conotoxin GVIA (5 microM), omega-conotoxin MVIIC (5 microM), and omega-agatoxin IVA (0.4 microM), but was sensitive to mibefradil (10 microM). Both currents were sensitive to Ni(2+) and Cd(2+) (>10 microM). In some cells the L-type current amplitude increased almost twofold upon repetitive stimulation, whereas the R-type current remained unaffected. Eventually, run-down occurred for both currents, but was prevented by the protease inhibitor calpastatin. The R-type current peak component ran down first, without changing its plateau, suggesting that two channel types generate the R-type current. This peak component appeared at -40 mV, reached a maximal value at -30 mV, and became undetectable for voltages > or =0 mV, suggestive of a novel transient current: its inactivation was indeed reversibly removed when Ba(2+) was the charge carrier. The L-type current and the R-type current plateau were appreciable at -60 mV and peaked at -20 mV: the former current did not reverse for voltages up to +60 mV, the latter reversed between +30 and +60 mV due to an outward Cs(+) current flowing through the same Ca(2+) channel. The physiological role of these currents on hair cell function is discussed.

Animals↗
PubMed1978

Response characteristics of semicircular canal and otolith systems in cat. I. Dynamic responses of primary vestibular fibers.

1. The activity of cat semicircular canal and otolith afferents was studied during yaw and roll rotations, respectively, to examine their dynamic behavior. 2. A sinusoidal analysis of the canal afferent activities showed that their dynamic characteristics are similar to those of second order vestibular neurons, except for a two to three-fold lower absolute gain. This agrees with earlier studies using angular acceleration steps. 3. Both divisions of the eighth nerve were sampled so as to examine afferents from both the utriculus and sacculus. Within the range of inputs used (+/- 25 degrees lateral tilt), the presumed sacular afferents (inferior division) showed either a gamma- or beta-response. However, the gain of their response was generally much less than for the afferents of the superior division (mostly utricular). This behavior is to be expected on the basis of receptor orientations and the components of gravity acting upon the macular receptors. 4. In response to ramp changes in angular position, some otolith units showed a phasic-tonic response pattern, i.e., an overshoot followed by an adaptation to a new steady state level of activity. The majority of units showed predominantly tonic responses proportional to displacement. 5. During sinusoidal rotations the predominantly tonic units showed small phase leads of 0 to 15 degrees at 0.025 Hz which remained constant or decreased to 0 to -15 degrees at 1.0 Hz. The gains were flat or increased by up to 2 fold. The phasic-tonic units showed greater phase leads, 10 to 50 degrees, and gains which increased from 2 to 8 fold. 6. This behavior of otolith afferents suggests that they can provide information about both the magnitude and the rate of change of linear acceleration stimuli.

Acoustic Maculae↗
PubMed1998

[Canalith repositioning maneuver: proposal of a new therapy for benign paroxysmal positional vertigo of the posterior semicircular canal].

A new therapy is proposed for the treatment of Benign Paroxysmal Positional Vertigo (B.P.P.V.) of the Posterior Semicircular Canal (P.S.C.): the Canalith Repositioning Maneuver (C.R.M.). The need for a new maneuver to treat B.P.P.V. of the P.S.C. arises from the difficulties encountered in daily practice, under particular conditions (i.e. elderly, obese, traumatized patients and in the presence of rachis pain, etc.), to perform the most common rehabilitative techniques such as the Semont Maneuver and Epley's Canalith Repositioning Procedure (C.R.P.). The results achieved using this new technique on a group of 47 consecutive out-patients are presented and compared to those achieved using the Semont Maneuver in an analogous group of 23 patients. C.R.M. and the Semont Maneuver were performed once per treatment session and all patients were checked every 3 days until the symptoms of B.P.P.V. disappeared. Thereafter they were invited to return for check-up if signs of vertigo returned (follow-up 6-25 months). The two techniques proved equally effective: 87.5% of the cases were resolved with C.R.M., 82.6% with the Semont Maneuver. However, the C.R.M. provided other advantages as it resolved the problem immediately (i.e. in a single session) in 81% of the cases vs. 68.4% for the Semont Maneuver. In view of the Canalith theory, the action mechanism envisaged for all three maneuvers--C.R.M., the Semont Maneuver and the Epley C.R.P.--can be explained assuming that the canalith passes from the ampullar to the non ampullar branch of the (P.S.C.) passing finally through the Common Duct and into the Utricle. C.R.M. is a specific treatment for the B.P.P.V. of the P.S.C. and is simple to perform, well tolerated and quite effective. It is indicated in all cases of B.P.P.V. of the P.S.C. both as initial treatment and as alternative to other treatment methods which have proved ineffective or difficult to perform. Indeed, in therapy it is best to be quite skilled in more than one technique, availing oneself of a full range possibilities; in this way the cure can be tailored to the patient in each individual case and not vice versa.

Adolescent↗
PubMed1985

Planar relationships of the semicircular canals in rhesus and squirrel monkeys.

The technique of principal-component analysis was used to define anatomically the semicircular canal planes of the rhesus and squirrel monkeys with respect to the stereotaxic coordinate system. The analyses were performed on a series of points obtained from the dissected osseous labyrinths. A planar equation was defined for each canal plane in the stereotaxic coordinate system and angles were calculated between the 3 ipsilateral canal planes, between synergistic canal pairs and between each canal plane and the stereotaxic planes. The data from both species are similar: the ipsilateral canal planes are nearly orthogonal; synergistic pairs of canal planes are approximately parallel with angles of 2 degrees-12 degrees between pairs in the rhesus monkey and 13 degrees-16 degrees between pairs in the squirrel monkey. The horizontal canal planes form angles of 22 degrees and 18 degrees with the horizontal stereotaxic plane in the rhesus and squirrel monkeys, respectively. A head position of 15 degrees (pitch nose-down) was calculated to produce an optimal head position in both species for maximally stimulating the horizontal canals and minimally stimulating the vertical canals during horizontal angular acceleration. The radii of curvature (R) of the horizontal, anterior and posterior canals were also measured for both species using a calibrated reticle. These measurements indicate that the anterior canal of both species has the largest radius of curvature. This anatomical information is discussed in relation to the available physiological data.

Animals↗