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PubMed1999

Position-dependent expression of inwardly rectifying K+ currents by hair cells of frog semicircular canals.

The identity and the expression of inwardly rectifying ionic currents were studied using the whole-cell variant of the patch-clamp technique in frog semicircular canal hair cells in situ. The currents were examined in club-, cylindrical- and pear-shaped sensory cells located in three discrete regions of the crista. A unique current of I(K1) type was distinguished based on its K+ selectivity, rapid monoexponential activation, dependence of activation on external K+ and blockade by Ba2+ and Cs+. I(K1) was found in virtually all cylindrical hair cells of the central region and in club-shaped cells located in the halves of the peripheral regions closest to the centre of the crista. Pear-shaped cells of the intermediate regions showed no inward rectification. The I(K1) density (pA/pF) varied along the crista depending on cell position, being maximal in cells located in the middle of the central region and decreased towards its ends. In the peripheral regions, the gradient of I(K1) increased towards the centre of the crista. Current clamp experiments showed that sensory cells having larger I(K1) constantly exhibited more negative resting potentials and required more depolarizing current to elicit an active response than cells having small or no I(K1).

Animals↗
PubMed1993

Torsion of the human semicircular canals and its influence on their angular relationships.

We used a computer-aided three-dimensional reconstruction and measurement method to measure torsion of the the semicircular canals (SCCs) in 10 normal human temporal bones from 10 individuals (3 months to 76 years old). Torsion of each SCC was measured as the angle between the "standard line" (the line connecting the ampullated and nonampullated ends of the SCC) and the plane of greatest SCC torsion. Torsion was greatest for the anterior SCC (16.4 +/- 3.6 degrees), followed by the lateral SCC (9.5 +/- 6.7 degrees) and the posterior SCC (8.5 +/- 4.2 degrees). The angles between the overall plane described by each SCC and the other SCCs between the anterior and lateral, the anterior and posterior, and the posterior and lateral SCCs were also measured and were found to be 78.7 +/- 10.0, 107.9 +/- 5.5, and 87.3 +/- 6.9 degrees, respectively. Finally the angles between the torsion plane of each SCC and the others were measured and found to be 92.6 +/- 15.4, 95.8 +/- 11.2, and 90.9 +/- 8.3 degrees, respectively. These results indicate that on average torsion in the SCCs tend to bring the angle between pairs of SCCs close to a right angle. This tendency to have a right angle between SCCs is thought to promote optimal vestibular function. Speculation is offered regarding the etiology of the greater torsion of the anterior SCC.

Adolescent↗
PubMed2006

IP3 receptor in the hair cells of frog semicircular canal and its possible functional role.

The presence and functional role of inositol trisphosphate receptors (IP3R) was investigated by electrophysiology and immunohistochemistry in hair cells from the frog semicircular canal. Intracellular recordings were performed from single fibres of the posterior canal in the isolated, intact frog labyrinth, at rest and during rotation, in the presence of IP3 receptor inhibitors and drugs known to produce Ca2+ release from the internal stores or to increase IP3 production. Hair cell immunolabelling for IP3 receptor was performed by standard procedures. The drug 2-aminoethoxydiphenyl borate (2APB), an IP3 receptor inhibitor, produced a marked decrease of mEPSP and spike frequency at low concentration (0.1 mm), without affecting mEPSP size or time course. At high concentration (1 mm), 2APB is reported to block the sarcoplasmic-endoplasmic reticulum Ca2+-ATPase (SERCA pump) and increase [Ca2+]i; at the labyrinthine cytoneural junction, it greatly enhanced the resting and mechanically evoked sensory discharge frequency. The selective agonist of group I metabotropic glutamate receptors (RS)-3,5-dihydroxyphenylglycine (DHPG, 0.6 mm), produced a transient increase in resting mEPSP and spike frequency at the cytoneural junction, with no effects on mEPSP shape or amplitude. Pretreatment with cyclopiazonic acid (CPA, 0.1 mm), a SERCA pump inhibitor, prevented the facilitatory effect of both 2APB and DHPG, suggesting a link between Ca2+ release from intracellular stores and quantal emission. Consistently, diffuse immunoreactivity for IP3 receptors was observed in posterior canal hair cells. Our results indicate the presence and a possibly relevant functional role of IP3-sensitive stores in controlling [Ca2+]i and modulating the vestibular discharge.

Action Potentials↗
PubMed1984

Pharmacology of the isolated semicircular canal: effect of GABA and picrotoxin.

We have investigated the proposal that gamma aminobutyric acid (GABA) is the afferent transmitter in the vestibular system using the isolated posterior semicircular canal of the bullfrog (Rana catesbeiana). This was done by examining the effects of GABA and picrotoxin on the evoked response of neural units in the posterior ampullar nerve. GABA had no effect on evoked response up to 1 mM, and inhibited the evoked response at 10 mM. Picrotoxin, a GABA antagonist, had no effect on evoked response between 5 microM and 100 microM. These results indicate that GABA is not the afferent transmitter in the vestibular system.

Animals↗
PubMed1976

Tonic influence of the efferent vestibular system on the spontaneous afferent activity from semicircular canals in the frog (Rana esculenta L.).

In the frog we have recorded the spontaneous activity of single afferent fibres of the ampullary nerves of the left horizontal semicircular canal (HC) and vertical anterior canal (VAC) in isolated head preparations. The recordings have been made in 4 experimental situations: intact preparations; preparations whose brain was destroyed; preparations whose contralateral vestibular nerve had been cut between Scarpa's ganglion and the brain; preparations where either an ampullary nerve (that of the HC or of the VAC) or the utricular nerve had been cut contralaterally. From our results, it appears that the efferent vestibular system has a tonic influence on the afferent activity from HC and VAC; the influence of the part of the efferent vestibular system (EVS) activity depending on contralateral vestibular inputs is inhibitory, while the influence of the part of the EVS activity depending on ipsilateral vestibular inputs might be facilitatory.

Animals↗
PubMed2004

Dynamics of the vestibulo-ocular reflex in patients with the horizontal semicircular canal variant of benign paroxysmal positional vertigo.

OBJECTIVE: Two types of direction-changing positional nystagmus, the geotropic and apogeotropic variants, are observed in patients with the horizontal semicircular canal (HSCC) type of benign paroxysmal positional vertigo (H-BPPV). In this study, we assessed the dynamics of the vestibulo-ocular reflex (VOR) of the HSCC in patients with H-BPPV. MATERIAL AND METHODS: Patients were rotated about the earth-vertical axis at frequencies of 0.1, 0.3, 0.5, 0.7 and 1.0 Hz with a maximum angular velocity of 50 degrees/s. Eye movements were recorded on a video imaging system using an infrared charge-coupled device (CCD) camera, and our new technique for analyzing the rotation vector of eye movements in three dimensions was used. RESULTS: In the patients with geotropic positional nystagmus, there were no differences in VOR gain between rotation to the affected and unaffected sides at frequencies of 0.1-1.0 Hz. Although no differences in VOR gain at frequencies of 0.3-1.0 Hz were noticed in patients with apogeotropic positional nystagmus, the VOR gain at 0.1 Hz was significantly smaller on rotation to the affected compared to the unaffected side. CONCLUSION: The results indicate that cupulolithiasis in the HSCC affected the dynamics of the HSCC-ocular reflex at 0.1 Hz, but not at higher frequencies, and that canalolithiasis in the HSCC does not change the VOR gain of the HSCC at any frequency. It is suggested that cupulolithiasis causes transient impairment of HSCC function by means of its mechanical restriction of movements of the cupula.

Adult↗
PubMed2005

Orientation of human semicircular canals measured by three-dimensional multiplanar CT reconstruction.

Analysis of vestibulo-ocular reflex experiments requires knowledge of the absolute orientations (with respect to skull landmarks) of semicircular canals (SCC). Data relating SCC orientations to accessible skull landmarks in humans are sparse, apart from a classic study of 10 skulls, which concluded that the horizontal and anterior SCC are not mutually orthogonal (111 +/- 7.6 degrees). Multiple studies of isolated labyrinths have shown the inter-SCC angles are close to 90 degrees. We hypothesized that a larger sample would yield mean absolute SCC orientations closer to the mutual orthogonality demonstrated for isolated labyrinths. We measured canal orientations with respect to accessible skull landmarks using 3-D multiplanar reconstructions of computerized tomography scans of the temporal bones of 22 human subjects. Images were acquired with 0.5-mm thickness and reconstructed with in-plane resolution of 234 microm. There was no significant difference between the left and a mirror image of the right (p > 0.57 on multiway ANOVA of orientation vector coefficients), so data were pooled for the 44 labyrinths. The angle between the anterior and posterior SCC was 94.0 +/- 4.0 degrees (mean +/- SD). The angle between the anterior and horizontal SCC was 90.6 +/- 6.2 degrees. The angle between the horizontal and posterior SCC was 90.4 +/- 4.9 degrees. The direction angles between a vector normal to the left horizontal SCC and the positive Reid's stereotaxic X (+nasal), Y (+left), and Z (+superior) axes were 108.7 +/- 7.5 degrees, 92.2 +/- 5.7 degrees, and 19.9 +/- 7.0 degrees, respectively. The angles between a vector normal to the left anterior SCC and the positive Reid's stereotaxic X, Y, and Z axes were 125.9 +/- 5.2 degrees, 38.4 +/- 5.1 degrees, and 100.1 +/- 6.2 degrees, respectively. The angles between a vector normal to the left posterior SCC and the positive Reid's stereotaxic X, Y, and Z axes were 133.6 +/- 5.3 degrees, 131.5 +/- 5.1 degrees, and 105.6 +/- 6.6 degrees, respectively. The mean anterior SCC-contralateral posterior SCC angle was 15.3 +/- 7.2 degrees. The absolute orientations of human SCC are more nearly orthogonal than previously reported.

Adult↗
PubMed1997

Three hundred sixty-degree rotation of the posterior semicircular canal for treatment of benign positional vertigo: a placebo-controlled trial.

The canalithiasis hypothesis proposes that benign positional vertigo (BPV) is caused by dislodged otoconia that settle in the posterior semicircular canal (PSC). When head position is changed these particles move within the canal and induce abnormal endolymph flow. To clear the PSC from debris we developed a procedure that consists of a full circle of backward head rotation in the exact plane of the canal. Patients were seated in a three-dimensional motion device that rotated in steps of 110 degrees every 30 seconds. The first part of the study was conducted as an open trial; the second part followed a single-blinded, placebo-controlled design: Forward rotation (placebo) was applied first and backward rotation was applied 1 week later if BPV persisted. All patients were assessed with a symptom diary and, in the controlled trial, also with the Dix-Hallpike maneuver. In the open study 10 of 15 patients became asymptomatic after one treatment session. In the controlled trial all 15 patients remained symptomatic after forward rotation while 10 of 14 undergoing backward rotation were relieved from positional vertigo immediately (p = 0.004). The presence of secondary nystagmus during the procedure indicated a favorable outcome. Our findings provide evidence for the efficacy of canal-clearing procedures that validate the canalithiasis hypothesis of BPV.

Calculi↗
PubMedDate not supplied

The acetylcholine receptors of the semicircular canal in the frog (Rana pipiens).

We present preliminary evidence that acetylcholine has three distinct modes of action on the discharge rate of afferent fibers from the frog isolated semicircular canal. These are: (I) a facilitatory effect which is of mixed muscarinic-nicotinic type and is mediated by a receptor which we call "atropine-preferring'; (II) a suppressive effect unmasked by atropine and antagonized by strychnine whose action is mediated by a "strychnine-preferring" receptor; (III) a suppressive effect produced by the cholinesterase inhibitors eserine and echothiophate, which being antagonized by curare, is mediated by a "curare-preferring" receptor.

Acetylcholine↗
PubMed1999

[Particle repositioning maneuver for benign paroxysmal positional vertigo of posterior semicircular canal].

OBJECTIVE: To determine the effectiveness of particle repositioning maneuver (PRM) for the treatment of benign paroxysmal positional vertigo (BPPV). METHODS: Thirty one patients with BPPV of the posterior semicircular canal treated between July 1996 and June 1998 were retrospectively analyzed. Patients received a single treatment of PRM based on the hypothesis that the vertigo and nystagmus of BPPV were due to debris floating in the long arm of the posterior canal (canalithiasis). Treatment outcome was classified as cure (asymptomatic), improvement reduction of symptoms > 50%, or no change. RESULTS: After a single treatment of PRM, complete remission of vertigo and nystagmus were found in 67.7% of the patients and improvement of the symptoms was found in 19.4% of the patients. The total improvement rate was 87.1%. CONCLUSION: The particle repositioning maneuver was effective for most of the patients with benign paroxysmal positional vertigo and can be recommended as the first-line treatment modality.

Adult↗
PubMedDate not supplied

Anterior semicircular canal benign paroxysmal positional vertigo and positional downbeating nystagmus.

PURPOSE: The aim of this study was to describe the clinical features and video-oculographic findings in patients with anterior semicircular canal benign paroxysmal positional vertigo (BPPV). MATERIALS AND METHODS STUDY DESIGN: This is a prospective case series. SETTING: The study was set at an outpatient clinic in a general hospital. PATIENTS: Fourteen individuals with symptoms of BPPV and positional downbeating nystagmus (pDBN) were included in the study. The diagnosis was based on a history of brief episodes of vertigo and the presence of pDBN confirmed in the video-oculographic examination during Dix-Hallpike test (DH) or head-hanging maneuver. INTERVENTION: Patients were treated by particle repositioning maneuver and the effectiveness was evaluated at 7, 30, and 180 days posttreatment. The treatment was repeated up to 4 times if pDBN was persistent. MAIN OUTCOME MEASURES: The main outcome measure is the number of patients without pDBN at 30 and 180 days. RESULTS: Video-oculography showed a predominant pDBN in response to DH. Of the 14 patients, 7 had arterial hypertension, and 5 of 14 cases presented abnormalities on the caloric test. Horizontal spontaneous nystagmus was found in 3 of 14 individuals. Positional nystagmus at different positional test was observed in 5 of 14 individuals, suggesting the involvement of several canals. Of the 14 patients, 10 (71%) did not present vertigo, and the positional tests were negative at 30 days. However, 3 cases presented a positive DH with persistence of BPPV episodes and pDBN at 30 days, and another developed a contralateral posterior canal affectation. One of the patients maintained a persistent pDBN at 180 days despite the repeated maneuvers. CONCLUSIONS: Video-oculography demonstrates that anterior canal BPPV is characterized by a predominant downbeating nystagmus in response to DH. These individuals may show alterations in the vestibular caloric, and they can have multicanal affectation.

Adult↗
PubMed2000

Influence of gravity on the spatial orientation of eye nystagmus induced by unilateral lesion of horizontal semicircular canal.

The influence of gravity in the orientation and slow phase eye velocity of the ocular nystagmus following unilateral damage of the cupula in the ampulla of the horizontal semicircular canal (UHCD) was investigated. The nystagmus was analysed at different sagittal head positions using the x-y infrared eye monitor technique. The nystagmus was almost horizontal at 0 degrees head pitch angle and remained partially fixed in space when the head was pitched upward or downward. The reorientation gain of the slow and quick phases was high (about 0.75) within +/- 45 degrees of head pitch angle, but beyond this range, it decreased greatly. The gain value depended on the lesion extension to otolithic receptors. The absolute value of the slow phase eye velocity of UHCD nystagmus was also modified systematically by the head pitch, showing a reduction in the upward and an increase in the downward.

Animals↗
PubMed1994

Fenestration and occlusion of posterior semicircular canal for patients with intractable benign paroxysmal positional vertigo.

A series of 15 patients with intractable benign paroxysmal positional vertigo (BPPV) who had fenestration and occlusion of the posterior semicircular canal (FOP) surgery commencing in December 1990 are reported. Follow-up was from 14 to 40 months. All patients reported a cure of their positional vertigo. No patient regretted having the surgery. All patients had a negative Dix-Hallpike test post-operatively and the test remained negative for the duration of follow-up. Eight patients had a mild high frequency sensorineural hearing (SNHL) loss post-operatively which had almost recovered six months later. No patient reported any change in their hearing following surgery. Of the 10 patients who did not have pre-operative tinnitus, six developed tinnitus but it was not considered significant by them. All patients developed mild unsteadiness following surgery which gradually improved with mobilization and physiotherapy if necessary. The operation preserves hearing, is technically straightforward, well-tolerated and effective.

Adult↗
PubMed1985

A light and transmission electron microscope study of the neural processes within the pigeon anterior semicircular canal neuroepithelium.

This report addresses two questions. First, what is the incidence and distribution of multiple type I hair cells within a single NC in the pigeon's anterior semicircular canal crista? Second, are the synaptic structures found in the avian anterior crista similar to those found in the mammalian crista and if so are they different for single and multiple hair cell calyxes? Three pigeon anterior cristae were studied using interference LM and one pigeon anterior crista was studied using TEM. The light microscope studies showed that about 28% of the NCs studied contained a single type I hair cell; 64% contained 2-5 type I hair cells; and about 8% contained 6-12 type I hair cells. It was noted that the largest number of type I hair cells/unit area was located on the lower slopes of the crista while the smallest number of type I hair cells/unit area was located on the upper slopes and apex of the crista. The TEM studies showed that of 51 hair cells studied, 35% were type II hair cells and 65% were type I hair cells. These studies also showed that synaptic structures described in mammals are also seen in the pigeon. So far, in our preliminary studies we have been unable to demonstrate any difference in synaptic structures associated with single calyxes and those associated with multiple calyxes.

Animals↗
PubMed2001

Individual semicircular canal function in superior and inferior vestibular neuritis.

OBJECTIVE: To examine the concept of selective superior and inferior vestibular nerve involvement in vestibular neuritis by studying the distribution of semicircular canal (SCC) involvement in such patients. BACKGROUND: Vestibular neuritis was traditionally thought to involve the superior and inferior vestibular nerves. Recent work suggests that in some patients, only the superior nerve is involved. So far there are no reported cases of selective involvement of the inferior vestibular nerve. METHODS: The authors measured the vestibuloocular reflex from individual SCC at natural head accelerations using the head impulse test. The authors studied 33 patients with acute unilateral peripheral vestibulopathy, including 29 with classic vestibular neuritis and 4 with simultaneous ipsilateral hearing loss, 18 healthy subjects and 15 surgical unilateral vestibular deafferented patients. RESULTS: In patients with preserved hearing, eight had deficits in all three SCC, suggesting involvement of the superior and inferior vestibular nerves. Twenty-one had a lateral SCC deficit or a combined lateral and anterior SCC deficit consistent with selective involvement of the superior vestibular nerve. Two patients with ipsilateral hearing loss had normal caloric responses and an isolated posterior SCC deficit on impulsive testing. The authors propose that these two patients had a selective loss of inferior vestibular nerve function. CONCLUSION: Vestibular neuritis can affect the superior and inferior vestibular nerves together or can selectively affect the superior vestibular nerve.

Adult↗
PubMed2003

Effect of semicircular canal stimulation on the perception of the visual vertical.

UNLABELLED: The subjective visual vertical (SVV) is usually considered a measure of otolith function. Herewith we investigate the influence of semicircular canal (SCC) stimulation on the SVV by rotating normal subjects in yaw about an earth-vertical axis, with velocity steps of +/- 90 degrees /s, for 60 s. SVV was assessed by setting an illuminated line to perceived earth vertical in darkness, during a per- and postrotary period. Four head positions were tested: upright, 30 degrees backward (chin up) or forward, and approximately 40 degrees forward from upright. During head upright/backward conditions, a significant SVV tilt (P < 0.01) in the direction opposite to rotation was found that reversed during postrotary responses. The rotationally induced SVV tilt had a time constant of decay of approximately 30 s. Rotation with the head 30 degrees forward did not affect SVV, whereas the 40 degrees forward tilt caused a direction reversal of SVV responses compared with head upright/backward. Spearman correlation values (Rho) between individual SCC efficiencies in different head positions and mean SVV tilts were 0.79 for posterior, 0.34 for anterior, and - 0.80 for horizontal SCCs. Three-dimensional video-oculography showed that SVV and torsional eye position measurements were highly correlated (0.83) and in the direction opposite to the slow phase torsional vestibuloocular reflex. IN CONCLUSION: 1) during yaw axis rotation without reorientation of the head with respect to gravity, the SVV is influenced by SCC stimulation; 2) this effect is mediated by the vertical SCCs, particularly the posterior SCCs; 3) rotationally induced SVV changes are due to torsional ocular tilt; 4) SVV and ocular tilts occur in the "anticompensatory," fast phase direction of the torsional nystagmus; and 5) clinically, abnormal SVV tilts cannot be considered a specific indication of otolith system dysfunction.

Acceleration↗