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PubMed1995

In vitro electrogenic K secretion in the frog semicircular canal: absence of effect of streptomycin.

In vitro, the frog semicircular canal secretes an endolymph-like fluid, i.e. a K-rich, positively polarized fluid. This electrogenic K secretion involved basolateral Na+, K(+)-ATPase and Na-K-Cl co-transporter and a luminal protein possessing sulfhydryl groups blocked by N-ethylmaleimide. Streptomycin, an ototoxic antibiotic, is known to block the non-specific mechano-dependent channels in the sensory cells of the ampulla of the semicircular canal. The aim of the present study was to investigate the possible effect of streptomycin on the K fluxes in the ampulla of the semicircular canal. The posterior frog semicircular canal was isolated and the lumen was filled with perilymph-like solution containing or not containing 0.5 mM streptomycin. The luminal K concentration and the transepithelial potential were measured and the unidirectional K fluxes calculated. The K influxes (into the lumen, pmoles/min/mm2) were 114 +/- 25.9 and 111 +/- 3.2 (mean +/- SE, n = 3) in the absence and presence of streptomycin, respectively. The transepithelial potential was not altered (4.0 +/- 1.08 mV versus 3.4 +/- 1.03 mV, n = 3). When ouabain (10(-3)M) was added to the basolateral solution together with luminal streptomycin, no further alteration occurred as compared with the effect of ouabain alone. These results suggest that in these conditions, the sensory organ does not have a major role in the endolymphatic K secretion in the ampulla of the frog semicircular canal.

Animals↗
PubMed1996

Spatial orientation of semicircular canals and afferent sensitivity vectors in pigeons.

Rotational head motion in vertebrates is detected by the semicircular canal system, whose innervating primary afferent fibers carry information about movement in specific head planes. The semicircular canals have been qualitatively examined over a number of years, and the canal planes have been quantitatively characterized in several animal species. The present study first determined the geometric relationship between individual semicircular canals and between the canals and the stereotactic head planes in pigeons. Stereotactic measurements of multiple points along the circumference of the bony canals were taken, and the measured points fitted with a three-dimensional planar surface. Direction normals to the plane's surface were calculated and used to define angles between semicircular canal pairs. Because of the unusual shape of the anterior semicircular canals in pigeons, two planes, a major and a minor, were fitted to the canal's course. Calculated angle values for all canals indicated that the horizontal and posterior semicircular canals are nearly orthogonal, but the anterior canals have substantial deviations from orthogonality with other canal planes. Next, the responses of the afferent fibers that innervate each of the semicircular canals to 0.5 Hz sinusoidal rotation about an earth-vertical axis were obtained. The head orientation relative to the rotation axis was systematically varied so that directions of maximum sensitivity for each canal afferent could be determined. These sensitivity vectors were then compared with the canal plane direction normals. The afferents that innervated specific semicircular canals formed homogeneous clusters of sensitivity vectors in different head planes. The horizontal and posterior afferents had average sensitivity vectors that were largely co-incident with the innervated canal plane direction normals. Anterior canal afferents, however, appeared to synthesize contributions from the major and minor plane components of the bony canal structure to produce a resultant sensitivity vector that was positioned between the canal planes. Calculated angles between the average canal afferent sensitivity vectors revealed that direction orthogonality is preserved at the afferent signal level, even though deviations from canal plane orthogonality exist.

Afferent Pathways↗
PubMedDate not supplied

Functional model of benign paroxysmal positional vertigo using an isolated frog semicircular canal.

Bull frogs posterior semicircular canals (psc) wee used to simulate the condition of benign paroxysmal positional vertigo (BPPV). The psc was isolated in frog Ringer's solution, and the saccular otoconia were used as a responsible material to stimulate the cupula. When the otoconia were placed on the cupular surface to mimic the condition of cupulolithiasis, the psc ampullary nerve action potentials instantaneously changed according to the direction of the gravity produced by otoconia. When the otoconia were dropped into the canal to mimic the condition of moving otoconia in the canal, the action potentials changed together with the otoconial flow after a latent period. Both cupulolithiasis and moving otoconia are possibly valid mechanisms of BPPV, since they effectively stimulate the cupula. However, moving otoconia with a latent period would better explain clinical features of BPPV.

Action Potentials↗
PubMed2005

Determinants of spatial and temporal coding by semicircular canal afferents.

The vestibular semicircular canals are internal sensors that signal the magnitude, direction, and temporal properties of angular head motion. Fluid mechanics within the 3-canal labyrinth code the direction of movement and integrate angular acceleration stimuli over time. Directional coding is accomplished by decomposition of complex angular accelerations into 3 biomechanical components-one component exciting each of the 3 ampullary organs and associated afferent nerve bundles separately. For low-frequency angular motion stimuli, fluid displacement within each canal is proportional to angular acceleration. At higher frequencies, above the lower corner frequency, real-time integration is accomplished by viscous forces arising from the movement of fluid within the slender lumen of each canal. This results in angular velocity sensitive fluid displacements. Reflecting this, a subset of afferent fibers indeed report angular acceleration to the brain for low frequencies of head movement and report angular velocity for higher frequencies. However, a substantial number of afferent fibers also report angular acceleration, or a signal between acceleration and velocity, even at frequencies where the endolymph displacement is known to follow angular head velocity. These non-velocity-sensitive afferent signals cannot be attributed to canal biomechanics alone. The responses of non-velocity-sensitive cells include a mathematical differentiation (first-order or fractional) imparted by hair-cell and/or afferent complexes. This mathematical differentiation from velocity to acceleration cannot be attributed to hair cell ionic currents, but occurs as a result of the dynamics of synaptic transmission between hair cells and their primary afferent fibers. The evidence for this conclusion is reviewed below.

Afferent Pathways↗
PubMed2000

Sensorineural and conductive hearing loss associated with lateral semicircular canal malformation.

OBJECTIVE: Lateral semicircular canal (LSCC) malformation is one of the most common radiological inner ear malformations. Traditionally, inner ear malformations are thought to be associated with sensorineural hearing loss (SNHL). Recent experience with patients with LSCC malformation suggested that LSCC malformation may be associated with both SNHL and conductive hearing loss (CHL). The auditory phenotype associated with LSCC malformation is not well delineated. The objective of this study is to define the nature of the hearing loss associated with LSCC malformation. STUDY DESIGN: Retrospective review METHODS: Retrospective review of clinical records, audiological evaluation, and imaging studies. RESULTS: Two patients with unilateral and 13 patients with bilateral LSCC malformation were identified. LSCC malformation was associated with CHL in 14% (4 ears), SNHL in 71% (20 ears), normal hearing in 11% (3 ears) and CHL due to atresia in one ear. Hearing loss varied from mild to profound but did not correlate with the severity of LSCC malformation. In bilateral malformation, the hearing loss was asymmetric in half of the cases. Malformation of the posterior limb of the LSCC was always associated with a large vestibular aqueduct. An absent or rudimentary LSCC was invariably associated with a cochlear abnormality. CONCLUSIONS: LSCC malformation, like other inner ear malformations such as large vestibular aqueduct and X-linked mixed deafness with perilymph gusher, can be associated with CHL, SNHL, or normal hearing. Children with unexplained conductive hearing loss often undergo exploratory surgery to improve hearing. Given that inner ear malformations may be associated with a pure CHL, it is critical that children undergo computed tomography scan of the temporal bone prior to undergoing exploratory surgery.

Adolescent↗
PubMed2001

CT and MRI of the semicircular canals in the normal and diseased temporal bone.

Imaging of the semicircular canals specifically is part of the imaging process of the temporal bone in general. The semicircular canals are easily seen on CT images and 3DFT-CISS-weighted MR images, both performed with 1.0-mm-thick slices, or even thinner slices. In selected cases, the T1-weighted images give unique information on the semicircular canals. This article briefly reviews the variety of semicircular canal anomalies that are most frequently present and can be routinely seen on CT and MR examinations of the temporal bone. It also provides a list that can be used by the radiologist in clinical practice to decide which technique, CT or MR, should be used to detect specific anomalies at the level of the semicircular canals.

Humans↗
PubMed2003

Effect of repetition of Semont's manoeuvre on benign paroxysmal positional vertigo of posterior semicircular canal.

If Semont's liberating manoeuvre does not lead to relief of symptoms in benign paroxysmal positional vertigo of posterior semicircular canal after the first session, it can be repeated once again, in refractory cases, whilst symptomatic patients after second manoeuvre require rehabilitation therapy Repeating Semont's manoeuvre several times has proven to progressively increase the percentage of cured patients or it may convert posterior semicircular canal forms to typical incomplete or lateral semicircular canal forms, hence requiring other manoeuvres to achieve vertigo resolution. Aim of study was to assess the effect of liberating manoeuvres repeated up to 4 times and to establish possible passages from one canal to the other during manoeuvres as well as percentage of cases refractory to this therapy, who would then need rehabilitation. Benign paroxysmal positional vertigo was diagnosed in 448 cases of whom 344 (76.8%) of the posterior semicircular canal, 20 (0.45%) the incomplete form of the posterior semicircular canal, 20 (0.45%) subjective positional vertigo and 74 of the lateral semicircular canal (4.2%). Right side was affected in 58.4% of cases, left in 34.5%, and bilateral in 7.1%. All 344 patients underwent Semont's liberating manoeuvre (1st manoeuvre) with first control after 48 hours: if symptoms (typical, atypical nystagmus or paroxysmal vertigo evoked by Dix-Hallpike's manoeuvre) persisted, Semont's liberating manoeuvre was repeated (2nd manoeuvre). In presence of lateral semicircular canal benign paroxysmal positional vertigo conversion, Lempert's manoeuvre was performed instead. Second control was performed after 48 hours and in cases of persistent typical, atypical or lateral semicircular canal nystagmus 3rd manoeuvre was performed. After further 48 hours, third control was carried out: symptomatic patients with typical forms were submitted to 4th manoeuvre, while typical incomplete forms or forms of the lateral semicircular canal underwent Lempert's manoeuvre. In conclusion, symptoms disappeared after 1st manoeuvre in 61.6% of cases; further manoeuvres, carried out in view of possible changes in semeiology of vertigo, increased the percentage of cured patients to 82.5% after the 2nd, 90.7% after 3rd and 94.1% after the 4th. Repeated positioning manoeuvres in benign paroxysmal positional vertigo led to a progressive increase in percentage of cured vertigo, at the same time, allowing detection of those cases converted to multicanal pathology, hence offering the possibility to proceed with appropriate liberating manoeuvres.

Adult↗
PubMed1996

Contributions of single semicircular canals to caloric nystagmus as revealed by canal plugging in rhesus monkeys.

We demonstrated specific responses from the anterior and the posterior semicircular canal to irrigation of the outer ear canal with cold water in the Rhesus monkey. This required i) three-dimensional analysis of the evoked eye movements in the planes of the semicircular canals (canal plane vectors, CPV); ii) assessing these CPV responses in eight different head positions relative to gravity; iii) comparing the responses in 6 normal animals (12 ears) with responses after selective plugging of pairs of semicircular canals (all, both lateral, and right anterior + left posterior). The results showed: i) Irrigation of the outer ear canal with cold water induces thermoconvection also in the posterior and anterior semicircular canals. This can be inferred from the sinusoidal modulation of eye movement components with changes in position of the corresponding semicircular canal plane relative to gravity; ii) Specific vertical canal responses occur exclusively in the direction of the corresponding semicircular canal, though they are superimposed with response components of other origin, one probably related to endolymph shift in the lateral semicircular canal; iii) before possible clinical application, these different response components of vertical canals will need to be determined in humans.

Animals↗
PubMed2001

Plane-specific brainstem commissural inhibition in frog second-order semicircular canal neurons.

Commissural inputs of identified second-order semicircular canal neurons were studied by separate stimulation of each of the three canal nerves on either side in the vitro frog brains. The spatial pattern of these inputs was further investigated in those second-order canal neurons that received a monosynaptic input from only one ipsilateral canal nerve (91%). Since similar results were obtained in the presence as in the absence of the cerebellum, commissural inputs must have been relayed via fibers crossing in the brainstem. Following stimulation of individual semicircular canal nerves, commissural inputs were either inhibitory or excitatory. A commissural inhibition was evoked in the majority of the recorded neurons (79%) by stimulation of the coplanar semicircular canal nerve on the contralateral side. In the remaining neurons, a commissural excitatory input was evoked. A commissural excitation, originating from the two noncoplanar semicircular canals, predominated in most (68%) of the recorded neurons and was independent of the type of second-order canal neuron. The onset latency of the canal plane-specific commissural inhibitory potentials was di- or trisynaptic. Stimulation of the contralateral VIIIth nerve evoked excitatory commissural responses. The canal plane-specific commissural inhibition therefore might have been masked by commissural excitatory responses as in earlier studies. The similar organization of the canal plane-specific commissural inhibition in frog and cat corroborates the notion of a phylogenetically conservative, basic vestibular organization. The presence of a canal plane-unspecific commissural excitation, however, appears to be a feature that is specific to frogs. The functional implications of these similarities and differences are discussed.

Animals↗
PubMedDate not supplied

A comparative study of the isolated anterior and posterior semicircular canals of the bull frog.

The anterior semicircular canals of bull frogs were isolated and the cupula was removed from the crista and the sensory cilia on the crista were depressed toward the canal side by a glass micropipette. Seven points on the crista were selected for stimulation. Decremental time constants of the anterior ampullary nerve action potentials were measured. The longer time constants were measured at the lateral points of stimulation which progressively shortened toward the central point. The overall values of the time constant were significantly shorter than those of the posterior semicircular canal. This indicates that the anterior semicircular canal has a larger number of phasic receptors than the posterior canal.

Action Potentials↗
PubMed2005

[Superior semicircular canal dehiscence syndrome. Embryological and surgical consideration].

OBJECTIVE: Presenting the first case of superior semicircular canal dehiscence syndrome in the Spanish literature and to establish, using embryological studies, the period in wich superior semicircular canal dehiscence originates. MATERIAL AND METHODS: 52 embryos and foetuses, from 6 mm to foetal maturity, were studied. The case of a patient suffering from superior semicircular canal dehiscence syndrome is presented. RESULTS: The superior semicircular canal and the intracranial space are communicated through bony lacunae, in the period between the 24th and 28th week of foetal development, but this communication is discontinued in the 30th week. Permeability of these lacunae, later in life, could result in the development of superior semicircular canal dehiscence syndrome. The clinical results of the surgical repair of this abnormal communication, in this particular case, using a middle fossa approach and a transmastoid approach is presented. CONCLUSIONS: Superior Semicircular Canal Dehiscence Syndrome could be due to an abnormality in foetal development and its genesis, therefore, could be prenatal. Surgical repair via transmastoid approach is a reasonable alternative treatment to the middle fossa approach.

Adult↗
PubMed1997

Particulate matter in the posterior semicircular canal.

The pathoetiology of benign paroxysmal positional vertigo (BPPV) is controversial. Particulate matter within the posterior semicircular canal has been identified intraoperatively in patients with BPPV but has also been reported in non-BPPV patients at the time of translabyrinthine surgery (Parnes LS, McClure JA. Free-floating endolymphatic particles: a new operative finding during posterior semicircular canal occlusion. Laryngoscope 1992;102:988-92; Schuknecht HF, Ruby RRF. Cupulolithiasis. Adv Otorhinolaryngol 1973;20: 434-43; Kveton JF, Kashgarian M. Particulate matter within the membranous labyrinth: pathologic or normal? Am J Otol 1994;15:173-6). The nature of the particulate matter remains unknown. The purpose of this study was to prospectively examine the posterior semicircular canal of patients with and without a clinical history of BPPV for the presence of particulate matter. Seventy-three patients without BPPV symptoms undergoing labyrinthine surgery (vestibular schwannoma excision or labyrinthectomy) and 26 patients with BPPV undergoing the posterior semicircular canal occlusion procedure were compared. Additionally, 70 archived temporal bones without a history of BPPV were examined microscopically for the presence of particulate matter within the lumen of the membranous labyrinth. No particles were observed intraoperatively in any of the 73 patients without a history of BPPV. Particulate matter was observed in 8 of 26 patients at the time of the posterior semicircular canal occlusion procedure for intractable BPPV. Of the 70 temporal bones examined, 31 did not show significant postmortem changes and also did not demonstrate cupulolithiasis or canalithiasis. Particulate matter from within the membranous posterior semicircular canal was removed from one patient at the time of posterior semicircular canal occlusion for intractable BPPV symptoms and was examined by scanning electron microscopy. The particulate matter appeared morphologically consistent with degenerating otoconia. These data show a statistically significant association between the presence of particles within the posterior semicircular canal in this study and the symptom complex of BPPV.

Ear, Inner↗
PubMed2006

Geometry of the semicircular canals of the chinchilla (Chinchilla laniger).

The orientations of the semicircular canals determines the response of the canals to head rotations and, in turn, the brain's ability to interpret those motions. The geometry of chinchillas' semicircular canals has never been reported. Volumetric representations of three chinchilla skulls were generated using a microCT scanner. The centroids of each semicircular canal lumen were identified as they passed through the image slices and were regressed to a plane. Unit vectors normal to the plane representing canal orientations were used to calculate angles between canal pairs. Pitch and roll maneuvers required to bring any canal into the horizontal plane for physiologic investigation were calculated. The semicircular canals of the chinchilla were found to be relatively planar. The horizontal canal was found to be oriented 55.0 degrees anteriorly upward. Pairs of ipsilateral chinchilla canals were not orthogonal and contralateral synergistic pairs were not parallel. Despite this arrangement, the canal plane unit normal vectors were organized to respond with approximately equal overall sensitivity to rotations in any direction. The non-orthogonal chinchilla labyrinth may provide an opportunity to determine whether the frame of reference used by the central vestibular and oculomotor system is based on directions of afferent maximum sensitivity or prime directions.

Afferent Pathways↗
PubMed1992

Free-floating endolymph particles: a new operative finding during posterior semicircular canal occlusion.

Most clinicians accept cupulolithiasis as the pathophysiological mechanism underlying benign paroxysmal positional vertigo (BPPV.) According to this theory, a cupular deposit induces a gravitational effect on the posterior canal crista. Posterior semicircular canal occlusion is a new operative procedure for treating incapacitating BPPV. It is postulated that canal occlusion abolishes endolymph movement within the canal, effectively fixing the cupula and rendering it unresponsive to both angular and linear acceleration (gravity). During two recent canal occlusions, abundant "free-floating particles" were identified within the posterior canal endolymph. When changing the position of the canal in the earth vertical plane, these free-floating particles would move under the influence of gravity. The hydrodynamic drag of the particles would induce endolymph movement with cupular displacement leading to the typical response. This finding supports an alternate explanation to cupulolithiasis as the pathophysiological mechanism underlying BPPV.

Aged↗
PubMed2002

Early histopathologic changes after lateral semicircular canal transection and occlusion in guinea pigs.

Occlusion of the semicircular canals has been used in otoneurologic and skull base surgeries with preservation of hearing. In order to understand the role of occlusion in hearing preservation, we observed early histopathologic changes of the lateral semicircular canal following transection and occlusion in guinea pigs. After surgery, the membranous endolymphatic canal was collapsed, and its torn ends were sealed by intramural bone dust in the bony semicircular canal. On the first postoperative day, the endolymphatic canal was expanded to its normal shape, and the sealing at the torn ends was maintained by the bone dust. These findings suggest that occlusion after semicircular canal injuries, by making blind ducts in the membranous endolymphatic canal, is important for the preservation of postoperative hearing.

Animals↗
PubMed1984

[Physical dimensions influence the functional property of the semicircular canal].

The functional dependence of the semicircular canal upon its physical dimensions was evaluated by measuring the internal radius (r), the radius of curvature (R) and the cupula radius (rC) of the posterior canal in 10 freshly dissected frog labyrinths. These values have been compared to the same parameters of the cat labyrinth. The coefficients I, B, K in the Steinhausen equation were determined for both animals. The A ratio between cupula deflection and endolymph displacement was also calculated by utilizing the Bernard equation. The A ratio is three times larger in the frog than in the cat. It follows that if the same acceleration produces similar endolymph displacements in the posterior canal of both animals, the cupula deflection will be larger in the frog. The solution of the Steinhausen equation in the presence of a constant acceleration, however, reveals that the same stimulus intensity will result in a larger endolymph displacement in the cat posterior canal; similarly, the endolymph displacement directly depends on the duration of the stimulating period in both animals. Contrary to the Bernard assumption, these effects generate a G ratio (psi frog/psi cat) which is less than the Q ratio (A frog/A cat). Moreover, G decreases on increasing the duration of the stimulating period. For stimuli of short duration the semicircular canal of a small animal is expected to exhibit a higher sensitivity than that of a larger one. However, the definitive primary afferent discharge will be largely controlled by the receptor/generator potential properties.

Acoustic Stimulation↗
PubMedDate not supplied

Neurotological evaluation of vertical semicircular canal function in inner ear malformation. A case report.

A 9-year-old boy with inner ear malformation complained of slight deafness and unsteadiness. CT revealed a normal cochlea despite enlargement of the lateral semicircular canals. The vertical semicircular canals developed more or less normally. The caloric test showed complete canal paresis bilaterally; however, a horizontal rotational stimulus elicited a vestibulo-ocular response, which showed only rightward and downward nystagmus, and their maximal slow-phase velocities were low. In addition, the examination of the vertical semicircular canal function using the head-tilted rotation test revealed a more active response, and the maximal slow-phase velocities were higher than those of a standard horizontal rotational test. These results suggest that the function of the vertical semicircular canal was well preserved and that it may have perceived the horizontal acceleration instead of the lateral semicircular canal.

Audiometry, Pure-Tone↗
PubMedDate not supplied

Anatomic variations of the human semicircular canals. A radioanatomic investigation.

The anatomic variations of the semicircular canals were investigated in a series of 95 plastic temporal bone preparations. The results showed a wider range of variability than has been assumed previously. An intraindividual correlation was found between the sizes of the superior and lateral semicircular canals. Observations indicate why a semicircular canal is not invariably delineated on one tomographic plane despite correct positioning for its optimum reproduction.

Humans↗