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PubMed2003

Familial lateral semicircular canal malformation with external and middle ear abnormalities.

We report a family with inner ear lateral semicircular canal (LSC) malformation and external and middle ear abnormalities. The family had no history of known syndromes or toxic exposures. Distinct phenotypic manifestations were found in three family members. A young girl exhibited bilateral LSC malformation with a right-sided preauricular tag, a mildly deformed auricle, a stenotic external auditory canal, and a constricted middle ear cavity. She had moderate conductive hearing loss in the right ear but normal hearing in the left ear. Her younger brother exhibited right-sided LSC malformation, microtia, external auditory canal atresia, a malformed middle ear cavity, and abnormal auditory ossicles. He had severe mixed hearing loss in his right ear. Their mother exhibited left-sided LSC malformation without external and middle ear abnormalities, and the hearing was normal in her left ear. None of the three cases had vestibular symptoms, and their results of balance tests were appropriate for the corresponding ages. In contrast, significantly decreased LSC function was revealed by caloric tests in an ear with LSC malformation. Previously, LSC malformation may have been underdiagnosed in patients presenting with external and middle ear abnormalities and their relatives, since this malformation is frequently associated with normal hearing and balance or conductive hearing loss only. To our knowledge, this condition has not been described previously. This condition supports a genetic basis for the combination of LSC malformation and external and middle ear abnormalities and may represent an autosomal dominant condition with variable expressivity.

Adult↗
PubMed1996

Determinants of semicircular canal afferent response dynamics in the toadfish, Opsanus tau.

1. Present results determine the relative contributions of the biomechanical and the posttransduction-current (PTC) mechanisms to the sensory process carried out by the horizontal semicircular canal (HC) in the oyster toadfish, Opsanus tau. The role of each element was estimated using in vivo measurements of hair cell receptor potentials and afferent responses elicited by electrical stimuli and mechanical HC indentation. Individual afferent response dynamics are defined here using first-harmonic transfer functions presented in the form of response gain and phase for sinusoidal stimuli from approximately 0.02-30 Hz. Comparison of the response dynamics for the two types of stimuli distinguishes the mechanical and the PTC transfer functions leading to the neural response. The results show that both mechanisms contribute significantly to the overall signal processing performed by the semicircular canals. 2. Endolymphatic polarization and HC indentation. Modulation of the endolymphatic potential by current injection induces a differential voltage across the apical face of the hair cells that drives the transduction current directly via the Nernst-Planck potential. Results show that the electrical impedance of the apical tight junctions is much larger than the basal impedance to ground in O. tau, such that leakage current to the basolateral space is negligible and the voltage-sensitive basolateral currents remain fully functional during polarization of the endolymph (in the frequency range tested). Extracellular afferent responses to endolymphatic polarization were combined with responses to HC indentation to separate the relative contributions of the mechanical and the PTC mechanisms to the overall afferent response dynamics. Data show that more than one-half of the overall signal processing, as defined by the first-harmonic transfer function, persists even when canal mechanics is bypassed. 3. Hair-cell receptor potential modulation during HC indentation. Sharp microelectrodes were used to record the modulation of hair-cell receptor potentials (intracellular voltages) in vivo during physiological levels of sinusoidal HC indentation. Receptor potentials exhibit modulations dominated by the first harmonic and centered about the resting potential. The average gain of the receptor-potential modulation for HC indentation is approximately 0.88 mV/microns indent, corresponding to a value of 0.22 mV/deg/s head velocity, centered near zero phase over the range tested from 0.1-10 Hz. The present receptor potential data fall well short of spanning the full range of gain and phase present in the afferent population. Rather, intracellular hair-cell responses are consistent with the frequency-dependent mechanical activation of the transduction current as determined above. 4. Origins of individual afferent responses. The population of afferent responses forms a continuous distribution that is discussed here in terms of three groups as defined by Boyle and Highstein: velocity-sensitive low gain (LG) afferents, velocity/acceleration-sensitive high gain (HG) afferents, and acceleration-sensitive (A) afferents. The response dynamics of individual afferents were found to be determined by a mix of biomechanical and biophysical factors that vary systematically between these afferent groups. All afferents show low-frequency phase advancement and gain decrease during HC indentation associated with the mechanical lower-corner frequency and high-frequency phase and gain enhancements associated with the PTC processing. In highly phase-advanced afferents (A type), the mechanical response is additive with the PTC processing to achieve broad-band acceleration sensitive neural responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

[Membrane model of the cupula of the vestibular semicircular canals].

A mathematical model of the time-course variations of the cupula of the semicircular canals of the vestibular apparatus is presented. The model is found to be in good agreement with experimental data which suggests that the cupular matter has viscosity-elasticity properties. Their role in the functioning of the vestibular apparatus is discussed in qualitative terms. The applicability of the membrane model to the description of the time-course variations of the cupula is considered.

Animals↗
PubMed1994

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.

Afferent Pathways↗
PubMed2002

Chloride secretion by semicircular canal duct epithelium is stimulated via beta 2-adrenergic receptors.

The ductal epithelium of the semicircular canal forms much of the boundary between the K+-rich luminal fluid and the Na+-rich abluminal fluid. We sought to determine whether the net ion flux producing the apical-to-basal short-circuit current (I(sc)) in primary cultures was due to anion secretion and/or cation absorption and under control of receptor agonists. Net fluxes of 22Na, 86Rb, and 36Cl demonstrated a basal-to-apical Cl- secretion that was stimulated by isoproterenol. Isoproterenol and norepinephrine increased I(sc) with an EC50 of 3 and 15 nM, respectively, and isoproterenol increased tissue cAMP of native canals with an EC50 of 5 nM. Agonists for adenosine, histamine, and vasopressin receptors had no effect on I(sc). Isoproterenol stimulation of I(sc) and cAMP was inhibited by ICI-118551 (IC50 = 6 microM for I(sc)) but not by CGP-20712A (1 microM) in primary cultures, and similar results were found in native epithelium. I(sc) was partially inhibited by basolateral Ba2+ (IC50 = 0.27 mM) and ouabain, whereas responses to genistein, glibenclamide, and DIDS did not fully fit the profile for CFTR. Our findings show that the canal epithelium contributes to endolymph homeostasis by secretion of Cl- under beta 2 adrenergic control with cAMP as second messenger, a process that parallels the adrenergic control of K+ secretion by vestibular dark cells. The current work points to one possible etiology of endolymphatic hydrops in Meniere's disease and may provide a basis for intervention.

Animals↗
PubMed1996

Effects of clofilium, a K channel blocker, on electrogenic K secretion and afferent discharge at the frog semicircular canal. A preliminary report.

Application of clofilium to the endolymphatic side of the isolated frog semicircular canal abolished the transepithelial potential and produced increased K and mannitol outfluxes from the lumen to the dark cells or the basolateral perilymph, with no apparent effect on active K secretion. These results suggest an increased permeability of the paracellular pathway. When applied to the perilymphatic side in the intact labyrinth, clofilium reduced the rates of quantal transmitter release (miniature EPSP frequency), an effect that might arise from a decrease in the transduction current intensity secondary to the reduced transepithelial electrochemical potential for K+. Moreover, afferent spike rates were almost completely abolished at rest as well as during mechanical stimulation. This effect together with a decreased mEPSP amplitude points to a further direct action of clofilium on the afferent postsynaptic terminal. These results suggest a multi-factorial effect of clofilium that would reduce the sensitivity of the vestibular function.

Animals↗
PubMed2005

[The treatment of Semont maneuver for 40 patients with posterior semicircular canal benign paroxysmal positional vertigo].

OBJECTIVE: To evaluate the effectiveness of Semont maneuver for posterior semicircular canal benign paroxysmal positional vertigo (PC-BPPV). METHOD: Forty patients with PC-BPPV were treated with Semont maneuver from January to August in 2004. RESULT: After a single treatment session of Semont maneuver,the symptoms disappeared completely in 32 patients, the first success rate was 80%. Among 19 patients who had only 1 week duration of PC-BPPU, the symptoms disappeared in 16 patients after a single treatment. The symptoms disappeared in 3 patients after twice, 2 patients after 3 times and 1 patient after 4 times of Semont maneuver sessions, the total success rate was 95%. No effectiveness was found 2 patients; PC-BPPU recurred in 5 patients during follow-up and the recurrent rate was 12.5%. it was still effective for another Semont maneuver therapy session. CONCLUSION: The Semont maneuver therapy is safe and effective for PC-BPPV. Repeated Semont maneuver therapy is still effective for them.

Adult↗
PubMed1981

[Relation between the spontaneous activity and dynamic characteristics of primary afferents of the lateral semicircular canal in frogs].

Spontaneous activity (SA) and responses of 68 primary afferents of frog lateral semicircular canal to sinusoidal vibration (frequency band: 0.04-200 Hz, double peak amplitude up to 10 microns) of canal wall were studied in immobilized frogs. The regularity of SA was evaluated by coefficient of variation (CV). 12 units (17.6%) constituted the regular group (CV less than 0.3), 9 units (13.2%)--the irregular group (CV approximately equals 1.0), and 47 units (69.1%)--the intermediate one (CV =0.4-0.9). The correlation between background activity and responses is most clear for the regular group whose dynamic characteristics are: responses only "all round" type; narrow (0.04-0.4 Hz) band of effective vibration frequencies; large (up to 9 sec) time constant to step stimulus. The two other groups are clearly different in their frequency possibilities. The wide range afferents (identified as intermediate) are able to respond to wide band of vibration (0.04-180 Hz) and have the largest gain among the three groups. Their dynamic range is also wide. For high frequency (irregular) units effective band is from 20-60 Hz (from below) up to 120-180 Hz (from above). They may be identified as real vibroreceptors. The other characteristics (CV, time constant to step stimulus, etc.) in the two last groups smoothly pass on from one group to another.

Animals↗
PubMed2000

Convergence patterns of the posterior semicircular canal and utricular inputs in single vestibular neurons in cats.

The convergence of the posterior semicircular canal (PC) and utricular (UT) inputs in single vestibular nuclei neurons was studied intracellularly in decerebrate cats. A total of 160 vestibular neurons were orthodromically activated by selective stimulation of the PC and the UT nerve and classified according to whether or not they were antidromically activated from the spinal cord and oculomotor nuclei into vestibulospinal (VS), vestibulooculospinal (VOS), vestibuloocular (VO), and unidentified vestibular neurons. Fifty-three (33%) of 160 vestibular neurons received convergent inputs from both the PC and UT nerves. Seventy-nine (49%) vestibular neurons responded to PC inputs alone, and 28 (18%) neurons received inputs only from the UT nerve. Of 53 convergent neurons, 8 (15%) were monosynaptically excited from both nerves. Thirty-five (66%) received monosynaptic excitatory inputs from the PC nerve and polysynaptic excitatory or inhibitory inputs from the UT nerve, or vice versa. Approximately one-third of VS and VOS neurons received convergent inputs. A majority of the VS neurons descended to the spinal cord through the lateral vestibulospinal tract, while almost all the VOS neurons descended to the spinal cord through the medial vestibulospinal tract. The convergent neurons were found in all vestibular nuclei but more in the lateral nucleus and descending nucleus. The VS neurons were more numerous than VO neurons or VOS neurons.

Acceleration↗
PubMed1997

Electrophysiology and pharmacology of outward potassium currents in semicircular canal hair cells of toadfish, Opsanus tau.

Outward currents from hair cells from the horizontal semicircular canal (HSCC) of the toadfish were investigated using whole cell patch clamp methods. Two classes of hair cells are found. One class (approx. 10% of cells) showed only a non-inactivating current (IKCa) which was blocked by 2 mM TEA. A second class had both inactivating and non-inactivating currents. The former (IA) was blocked by 4-AP (1 mM) and the latter (IKCa) by TEA (2-20 mM) . While the majority of the cells expressed both these outward currents, due to IA inactivation both currents are functionally present in the same cell only between -60 and -40 mV. At more depolarized membrane potentials, IA was inactivated, suggesting that a single hair cell may have two distinct signalling modes, one dominated by IA at more hyperpolarized membrane potentials and the other by IKCa at depolarized values where ICa is beginning to grow, increasing both amplitude and activation rate of IKCa. The switch between modes will be determined by the amplitude and frequency characteristics of the stimulus and possibly also by actions of efferent transmitters. In current clamp mode, 10% of the HSCC hair cells showed high Q and high frequency resonance, from 44 to 360 Hz at 12 degrees C. These cells expressed only one outward calcium dependent, non-inactivating, TEA sensitive current, characteristic of IKCa. A suggested role for high frequency resonance is as positive feedback to produce a high frequency updating of the stereociliary compliance to most faithfully transduce angular acceleration.

4-Aminopyridine↗
PubMed2006

Superior semicircular canal dehiscence presenting as postpartum vertigo.

OBJECTIVE: To describe the clinical and diagnostic features of superior semicircular canal dehiscence (SSCD) in patients with postpartum vertigo. STUDY DESIGN: Retrospective review, meta-analysis. SETTING: Tertiary neurotologic and audiologic center. PATIENTS: Two women who presented with a history of acute postpartum vertigo and SSCD confirmed on high-resolution computed tomography (CT) were included. Our meta-analysis of the surgical SSCD literature comprised a total of 43 patients. INTERVENTION: Patients with postpartum vertigo and SSCD underwent a complete medical evaluation, audiometric testing, CT imaging, magnetic resonance imaging studies, vestibular evoked myogenic potential testing, and laser Doppler vibrometer testing. Case 2 was managed with a middle fossa craniotomy and SSCD repair. RESULTS: The first patient presented with normal hearing and aural fullness, autophony, and sound sensitivity of the left ear. A 1-mm left-sided SSCD was seen on CT imaging. She is being managed conservatively. The second patient had left-sided conductive hearing loss with sound and pressure sensitivity. The contralateral ear was congenitally deaf. CT imaging revealed a 4-mm left-sided SSCD. Because of her disabling symptoms, the patient underwent a middle fossa craniotomy and superior canal plugging. Her vestibular symptoms resolved with improvement in hearing. Vestibular evoked myogenic potential and laser Doppler vibrometer testing in both cases were consistent with SSCD. CONCLUSION: This is the first description of patients with SSCD presenting after childbirth and should be included in the differential diagnosis of acute postpartum vertigo or disequilibrium. SSCD plugging can provide a stable repair with resolution of symptoms, reversal of diagnostic indicators, and hearing improvement.

Adult↗
PubMed2004

Properties of horizontal semicircular canal nerve-activated vestibulospinal neurons in cats.

Axonal pathways, projection levels, and locations of horizontal semicircular canal (HC) nerve-activated vestibulospinal neurons were studied. The HC nerve was selectively stimulated. Vestibulospinal neurons were activated antidromically with four stimulating electrodes, inserted bilaterally into the lateral vestibulospinal tracts (LVST) and medial vestibulospinal tracts (MVST) at the C1/C2 junction. Stimulating electrodes were also positioned in the C3, T1, and L3 segments and in the oculomotor nuclei. Most HC nerve-activated vestibulospinal neurons were located in the ventral portion of the medial, lateral, and the descending nuclei. Among the 157 HC nerve-activated vestibular neurons, 83 were antidromically activated by stimulation at the C1/C2 junction. Of these 83 neurons, axonal pathways of 56 HC nerve-activated vestibulospinal neurons were determined. Most (48/56) of these had axons that descended through the MVST, with the remainder (8 neurons) having axons that descended through the ipsilateral (i-) LVST. Laterality of the axons' trajectories through the MVST was investigated. The majority of vestibulospinal neurons (24/28) with axons descending through the contralateral MVST were also antidromically activated from the oculomotor nucleus, whereas almost all vestibulospinal neurons (19/20) with axons descending through the i-MVST were not. Most HC nerve-activated vestibulospinal neurons were activated antidromically only from the C1/C2 or C3 segments. Only one neuron that was antidromically activated from the T1 segment had an axon that descended through the i-LVST. None of the HC nerve-activated vestibulospinal neurons were antidromically activated from the L3 segment. It is likely that the majority of HC nerve-activated vestibulospinal neurons terminate in the cervical cord and have strong connections with neck motoneurons.

Animals↗
PubMed1970

Response of semicircular canal dependent units in vestibular nuclei to rotation of a linear acceleration vector without angular acceleration.

1. Recent experiments have shown that rotation of a linear acceleration vector round the head can generate involuntary ocular nystagmus in the absence of angular acceleration. The present experiments examine the suggestion that adequate stimulation of the semicircular canals may contribute to this response.2. Decerebrate cats were located in a stereotaxic device on a platform, slung from four parallel cables, which could be driven smoothly round a circular orbit without inducing significant angular movement of the platform. This Parallel Swing Rotation (PSR) generated a centripetal acceleration of 4.4 m/sec(2) which rotated round the head at 0.52 rev/sec.3. The discharge frequency of specifically lateral canal-dependent neural units in the vestibular nuclei of cats was recorded during PSR to right and left, and in the absence of motion. The dynamic responses to purely angular motion were also examined on a servo-driven turntable.4. Without exception all proven canal-dependent cells examined (twenty-nine cells in nine cats) were more active during PSR in the direction of endolymph circulation assessed to be excitatory to the unit, than during PSR in the opposite direction.5. The observed changes in discharge frequency are assessed to have been of a magnitude appropriate for the generation of the involuntary oculomotor response induced by the same stimulus in the intact animal.6. The findings suggest that a linear acceleration vector which rotates in the plane of the lateral semicircular canals can be an adequate stimulus to ampullary receptors, though an explanation which invokes the modulation of canal cells by a signal dependent upon the sequential activation of macular receptors cannot be positively excluded.

Acceleration↗
PubMed1990

Resting discharge and response dynamics of horizontal semicircular canal afferents of the toadfish, Opsanus tau.

The response dynamics of 66 primary afferents of the horizontal semicircular canal were studied in the toadfish using sinusoidal, rotational stimuli from 0.001-10 Hz at amplitudes of 5-100 degrees/sec. Twelve afferents were also tested to constant velocity trapezoids. Responses to sinusoids were used to classify afferents into 3 broad groups: (1) low-gain afferents that maintain a relatively linear response re: stimulus velocity across most of the frequency and amplitude spectra tested; (2) high-gain afferents that have a velocity sensitivity but also show a high-frequency gain enhancement and phase advance; and (3) so-called acceleration afferents that have a response more in phase with stimulus acceleration than velocity across the tested bandwidth. The afferent's background discharge was examined in relation to its rotational response. Low-gain afferents have regular spacing of interspike intervals. High-gain and acceleration afferents have a widely variable discharge regularity that is apparently unrelated to their rotational responses. Input/output transfer models were fit to the response data to describe the low- and high-pass filtering properties of the 3 afferent groups.

Animals↗
PubMed1978

The response of horizontal semicircular canal afferents to sinusoidal rotation in the cat.

Dynamic characteristics of primary vestibular afferents innervating the horizontal semicircular canal were studied in decerebrate, unanesthetized cats. Activities of individual afferent fibers were recorded intracranially by glass micropipettes. Frequency of sinusoidal rotation was varied from 0.014 Hz to 0.42 Hz, and phase and gain properties were examined. All of the fibers recorded fired spontaneously, and their firing rate ranged from 7 to 128 spikes/sec. Regularity of firing, phase lags, and gains were calculated in individual fibers. There was a tendency that the units with high spontaneous firing rates showed regular firing, larger phase lags, and lower gains that the units with low spontaneous firing rates. The transfer function of the system (firing rate of the primary afferent per angular acceleration of the head) was (formula: see text). A high frequency phase lead component was needed to account for the data obtained, indicating a slight deviation from the relationship predicted by the torsion pendulum model. The present phase properties were compared with those of vestibular nucleus neurons reported previously. It was suggested that a group of vestibular nucleus neurons transmits fairly faithfully the phase properties of primary afferents, and that another group of vestibular nucleus neurons receive additional influences from central structures, exhibiting larger phase lags than primary afferents.

Action Potentials↗