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At least 73 records · Page 4Linked to original sources
PubMed1995

Carbon dioxide laser occlusion of the guinea pig posterior semicircular canal.

Preservation of hearing is possible with selective ablation of the vestibular system and mechanical occlusion of the semicircular canals. Complete ablation of all three canals would improve exposure of the internal auditory canal fundus (e.g., for acoustic tumor exposure), but mechanical packing of the vestibule would disrupt normal sound transduction. This study was designed to assess the feasibility of preserving hearing with CO2 laser occlusion, without mechanical packing of the posterior semicircular canal membranous labyrinth. Twenty adult Hartley guinea pigs underwent occlusion of the right posterior semicircular canal with one of three techniques: mechanical packing, laser coagulation, or laser coagulation with mechanical packing. Electrocochleographic thresholds to clicks and 1-kHz and 8-kHz tone bursts did not change significantly 6 weeks after posterior semicircular canal occlusion with any of these techniques. Histopathologic examination revealed complete canal occlusion with all methods. These findings suggest that mechanical occlusion and CO2 laser occlusion of the posterior semicircular canal do not significantly affect cochlear function in the guinea pig. CO2 laser occlusion of the membranous labyrinth may prove useful for more extensive selective vestibular ablation by obviating the need for mechanical packing of the labyrinth.

Acoustic Stimulation↗
PubMed2002

System design and performance of a unilateral horizontal semicircular canal prosthesis.

We have reported preliminary results regarding a prototype semicircular canal prosthesis and concluded that it can provide rotational cues to the nervous system. This paper presents the system design of the prosthesis, and also reports the prosthesis system performance and effectiveness. The prosthesis delivers electrical pulses to the nerve branch innervating the horizontal semicircular canal on one side via implanted electrodes. To allow us to encode both directions of angular velocity, the baseline stimulation pulse frequency was set at 150 Hz, which is somewhat higher than the average firing rate of afferents innervating the semicircular canals in normal guinea pigs (approximately 60Hz). A sensor measures angular velocity to modulate (increase or decrease) the pulse rate. The prosthetic system was provided to a guinea pig whose horizontal canals were surgically plugged. The animal responded to the baseline stimulation initially and adapted to the baseline stimulation in roughly one day. After this baseline adaptation the animal responded to yaw rotation, showing that the function of the canals was partially restored. The experiments also show that the nervous system adapts to the artificial rotational cue provided via electrical stimulation.

Animals↗
PubMed2005

Experimental selective posterior semicircular canal laser deafferentation.

In this experimental study, we attempted to perform selective deafferentation of the posterior semicircular canal ampulla of guinea pigs using carbon dioxide laser beam. The results of this study document the efficacy of this procedure in achieving deafferentation of the posterior semicircular canal safely with regards to the other semicircular canals, the otolithic organ and the organ of hearing. Moreover, the procedure is performed with relative ease compared with other procedures previously described for selective deafferentation of the posterior semicircular canal. The clinical application of such a procedure for the treatment of intractable benign paroxysmal positional vertigo in humans is suggested.

Animals↗
PubMed1988

Secretion of endolymph by semicircular canals of the shark.

The semicircular canals of the vestibular labyrinth of the dogfish shark, Squalus acanthias, may serve as a simple in vitro system for the study of the ionic transport mechanisms involved in endolymph formation. Electron microscopy showed that the epithelium was made up of at least three distinct cell types divided into separate regions running the length of the canals. Secretion of endolymph was studied in isolated canals by the split droplet method; when the lumens of the canals were filled with shark Ringer a potassium-rich fluid was secreted into the lumen at a rate of 0.34 microliter.cm-2.min-1. The K concentration of the secreted fluid averaged 112 mM; the calculated rate of K secretion was 2.3 mumol.cm-2.h-1, comparable to recent measurements in mammalian utricle. Fluid secretion was dependent on active transport and was inhibited by ouabain, bumetanide, or methazolamide in the external bathing solution. Fluid secretion was unaffected by the K channel blocker, Ba, in the luminal droplet or by the adenylate cyclase stimulator, forskolin, in the external bathing solution. For electrophysiological analysis, isolated canals were perfused in a chamber designed for voltage/current clamping; an axial wire was inserted into the canal lumen and constant-current pulses were passed to determine tissue resistance. When the luminal fluid was high-K Ringer, transepithelial potential difference was -1.1 mV (lumen negative) and resistance 37 omega.cm2. Dilution and bi-ionic potential measurements showed that the epithelium of the canals exhibited only slight cation selectivity. These results are consistent with a model for endolymph secretion involving cotransport secondary to the ion gradients created by the Na+-K+-ATPase.

Animals↗
PubMed2006

Partial absence of the posterior semicircular canal in Alagille syndrome: CT findings.

We report a case of bilateral partial absence of the posterior semicircular canals (with normal lateral semicircular canals) imaged with CT in a patient with Alagille syndrome. Similar histologic findings have been reported in the pathology literature. This association has been previously reported only for Waardenburg syndrome in the imaging literature. We review the imaging findings and embryology of the semicircular canals, and suggest that this abnormality is specific to patients with Alagille or Waardenburg syndrome.

Alagille Syndrome↗
PubMed2001

Functional physiology of the semicircular canal ampulla.

Physiology of the semicircular canal (sc) was studied by applying different manipulations to the isolated frog sc. Function of the cupula was investigated by mapping out the mechanical sensitivity on the cupular surface and by removing and replacing the cupula. The cupula was found to be most essential for effective activation of sc receptors. Responses of sc receptors to direct temperature change were studied. The sc nerve discharge increased and decreased due to cool and warm temperature change respectively. This suggests a possibility of direct temperature effect as one of the mechanisms of caloric response.

Action Potentials↗
PubMedDate not supplied

Action of streptomycin and calcium on the apical membrane of hair cells of the frog isolated semicircular canal.

An isolated frog posterior semicircular canal was placed in a two-compartment perspex chamber allowing separate perfusions of the peri- and endolymphatic space with adequate saline solutions. The ampullar receptors were mechanically stimulated with a hydraulic device which imposed sinusoidal movements to the cupulo-endolymphatic system at low frequency (0.10 Hz). Slow potentials recorded with non-polarizable Ag/AgCl electrodes near the crista ampullaris (Adc) and on the ampullar nerve (Ndc) were displayed together with an analog signal of the mechanical stimulation and with the nerve spike frequency, on a strip chart. The streptomycin action or the high calcium concentration action (these two substances being administered together or separately into the ampullar space) indicated that the streptomycin seemed to block mechano-dependent channels (non-specific) assumed to be included into the hair cell apical membrane. The synaptic transmission process was altered by streptomycin but was improved by the high calcium concentration. Also, the mechanisms which would control the spontaneous release of a neurotransmitter, seemed, at least partly, different from those controlling the neurotransmitter release in response to a mechanical stimulation; these last ones were less sensitive to the calcium action.

Action Potentials↗
PubMed2003

A new rotational test for vertical semicircular canal function.

OBJECTIVE: We developed a new rotating chair in order to assess the function of the vertical semicircular canal (VSCC) by analyzing VSCC-induced post-rotatory nystagmus (PRN). METHODS: We examined 14 healthy subjects, wearing goggles equipped with an infrared CCD camera, and sitting on a chair which was designed to stimulate a pair of the VSCCs by tilting the head 60 degrees backward with a 45 degrees rotation to the left or right side from the sagital plane. The time constant (TC) or maximal slow phase eye velocity (MSPEV) of the vertical component of four kinds of PRN were analyzed in four corresponding rotatory conditions, and used as functional index of the corresponding VSCC. RESULTS: The mean values of MSPEV in both anterior semicircular canal (ASCC) and posterior semicircular canal (PSCC)-induced PRN tended to be lower (P<0.10) than those induced by the lateral semicircular canal (LSCC). The result suggests that the threshold to the angular velocity in the VSCC is lower than that in the LSCC. The mean values of TC in both ASCC and PSCC-induced PRN were significantly lower (P<0.05) than those induced by the LSCC. CONCLUSION: The significant reduction of TC in VSCC-induced PRN compared with LSCC-induced PRN indicates that VSCC function is less affected by velocity storage mechanisms than LSCC function. The rotational test with respect to the VSCC can be used as a tool for assessing vertical canal function.

Adult↗
PubMed2000

Posterior semicircular canal nystagmus is conjugate and its axis is parallel to that of the canal.

A patient with a postoperative fistula of the left posterior semicircular canal is presented. Negative pressure in the external ear canal produced upbeat-torsional nystagmus, which was recorded in three dimensions using binocular scleral search coils. The nystagmus was conjugate, without skew deviation, and its trajectory corresponded to the anatomic axis of the left posterior canal. The current study helps validate Ewald's first law in humans: the axis of nystagmus should match the anatomic axis of the semicircular canal that generated it. This law is clinically useful in diagnosing pathology of the vestibular end-organ, such as benign paroxysmal positional vertigo or the superior semicircular canal dehiscence syndrome.

Aged↗
PubMed1995

Compensation of the human vertical vestibulo-ocular reflex following occlusion of one vertical semicircular canal is incomplete.

The vestibulo-ocular reflex (VOR) was studied in nine human subjects 2-15 months after permanent surgical occlusion of one posterior semicircular canal. The stimuli used were rapid, passive, unpredictable, low-amplitude (10-20 degrees), high-acceleration (3000-4000 degrees/s2) head rotations in pitch and yaw planes. The responses measured were vertical and horizontal eye rotations, and the results were compared with those from 19 normal subjects. After unilateral occlusion of the posterior semicircular canal, the gain of the head-up pitch vertical VOR--the vertical VOR generated by excitation from only one and disfacilitation from two vertical semicircular canals--was reduced to 0.61 +/- 0.06 (normal 0.92 +/- 0.06) at a head velocity of 200 degrees/s. In contrast the gain of the head-down pitch vertical VOR--the VOR still generated by excitation from two, but disfacilitation from only one vertical semicircular canal--was within normal limits: 0.86 +/- 0.11 (normal 0.96 +/- 0.04). The gain of the horizontal VOR in response to yaw head rotations--ipsilesion 0.81 +/- 0.06 (normal 0.88 +/- 0.05) and contralesion 0.80 +/- 0.11 (normal 0.92 +/- 0.11)--was within normal limits in both directions (group means +/- two-tailed 95% confidence intervals given in each case). These results show that occlusion of just one vertical semicircular canal produces a permanent deficit of about 30% in the vertical VOR gain in response to rapid pitch head rotations in the excitatory direction of the occluded canal. This observation indicates that, in response to a stimulus in the higher dynamic range, compensation of the human VOR for the loss of excitatory input from even one vertical semicircular canal is incomplete.

Adaptation, Physiological↗
PubMed1994

Input patterns and pathways from the six semicircular canals to motoneurons of neck muscles. I. The multifidus muscle group.

1. The pattern of connections between the six semicircular canals and neck motoneurons of the multifidus muscle group was investigated by recording intracellular potentials from motoneurons in the upper cervical cord of anesthetized cats. 2. Synaptic potentials were recorded in motoneurons of the rectus capitis posterior (RCP) muscle at C1, the obliquus capitis inferior (OCI) muscle at C1 and C2, and the cervical multifidus muscle (Multi) at C4 in response to electrical stimulation of individual ampullary nerves of the six semicircular canals. Excitatory or inhibitory postsynaptic potentials (EPSPs or IPSPs, respectively) were evoked by separate stimulation of individual ampullary nerves in all of the neck motoneurons. Virtually all of the neck motoneurons received convergent inputs from the six ampullary nerves. 3. Motoneurons that supplied a single muscle had a homogeneous pattern of input from the six semicircular canals. There were two patterns of input from the six semicircular canals to motoneurons of the multifidus muscle group. RCP and Multi motoneurons were excited by stimulation of the bilateral anterior canal nerves (ACNs) and the contralateral lateral canal nerve (LCN) and inhibited by stimulation of the bilateral posterior canal nerves (PCNs) and the ipsilateral LCN. This input pattern is similar to that previously observed in other dorsal extensor muscles, whereas the other input pattern observed in OCI motoneurons is entirely new. OCI motoneurons at C1 and C2 were excited by stimulation of the ipsilateral ACN, PCN, and the contralateral LCN and inhibited by stimulation of the contralateral ACN, PCN, and the ipsilateral LCN. 4. Most postsynaptic potentials (PSPs) were disynaptic, but there were trisynaptic inhibitory connections between the contralateral ACN and PCN and OCI motoneurons, and between the contralateral PCN and RCP motoneurons. 5. The pathways for mediating these inputs from different semicircular canals to neck motoneurons were determined by making lesions in the lower medulla. Transection of the ipsilateral medial longitudinal fascicle (MLF) abolished the following potentials: all disynaptic PSPs in RCP motoneurons except the disynaptic EPSPs from the ipsilateral ACN, and in OCI motoneurons, disynaptic PSPs from the bilateral LCNs, and disynaptic IPSPs from the contralateral PCN. Complete bilateral section of the MLF did not affect the disynaptic EPSPs from the ipsilateral ACN in RCP motoneurons, the disynaptic EPSPs from the ipsilateral ACN and PCN in OCI motoneurons, nor the trisynaptic IPSPs from the contralateral ACN and PCN in COI motoneurons and from the contralateral PCN in RCP motoneurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1980

Regional difference in susceptibility to damage of vestibulo-semicircular canals in experimental labyrinthine lesion.

In the study on regional difference in susceptibility to damage of vestibulo-semicircular canals upon causing labyrinthine lesion by four different procedures, namely, by intracranial approach, through the middle ear, through the facial nerve and by means of experimental endolymphatic hydrops, the following results were obtained. 1. The crista of posterior semicircular canal among the semicircular canals and the macula of the saccule within the vestibule were most susceptible to impairment. In other words, the most susceptible region was the so-called pars inferior. In regard to the impairment of the cupulas, the posterior semicircular canal was the most susceptible region. 2. Recovery from markedly reduced caloric nystagmus within a short period so as to see provocation of caloric nystagmus may result from the reconstruction of the cupulas and the normalization of vacuole-like findings of the sensory epithelium.

Animals↗
PubMed2005

Diagnostic and treatment strategy of lateral semicircular canal canalolithiasis.

A new strategy for the diagnosis and treatment both of geotropic and apogeotropic Lateral Semicircular Canal Benign Paroxysmal Positional Vertigo is proposed. To this end, a new strategy of approach to Lateral Semicircular Canal Benign Paroxysmal Positional Vertigo is described in order to rapidly highlight both the side and the affected canal. Thus, in the first treatment session, using the so-called "strategy of the minimum stimulus", a large percentage of cases are successfully treated, with the lowest number of vertigos for the patient. Following a review of the literature, 269 case studies, personally observed over a 4-year period, are described. The diagnostic strategy is performed by a single manoeuvre to determine whether the posterior semicircular canal or the lateral canal is affected. In the latter case, it is possible to highlight the affected sides both of the geotropic and apogeotropic forms. The therapeutic strategy comprises several liberatory manoeuvres, barbecue rotation techniques (Vannucchi-Asprella, Lempert), and Gufoni manoeuvre by continuously monitoring the ampullofugal movement of the otoliths. Almost 98% of cases are successfully treated at the first treatment diagnostic-therapeutic session. This approach to Lateral Semicircular Canal Benign Paroxysmal Positional Vertigo allows a two-fold goal to be achieved, i.e., to effect both diagnosis and treatment at the first examination. Furthermore, thanks to the philosophy of the approach to Benign Paroxysmal Positional Vertigo, called the "Strategy of the minimum stimulus", patient compliance is very good since a very small number of vertigos are produced, and few neuro-vegetative disorders.

Follow-Up Studies↗
PubMed2000

Prototype neural semicircular canal prosthesis using patterned electrical stimulation.

The design of a prototype semicircular canal prosthesis is presented along with preliminary results. This device measures angular velocity of the head (+/-500 degrees/s) using a piezoelectric vibrating gyroscope. With a digital filter this velocity is filtered to match the dynamic characteristics of the semicircular canals, which are the physiological rotation sensors of the vestibular system. This digitally filtered signal is used to modulate the pulse rate of electrical stimulation. The pulse rate is varied between 50 and 250 Hz via a sigmoidal lookup table relating pulse rate to angular velocity; the steady-state rate is 150 Hz. A current source utilizes these timing pulses to deliver charge balanced, cathodic-first, biphasic, current pulses to the nerves innervating the semicircular canal via platinum electrodes. Power is supplied via lithium batteries. dc/dc converters are used to generate regulated +/-5 V supplies from the batteries. All of the components are contained in a small, lightweight, Nylon box measuring roughly 43 mm x 31 mm x 25 mm, which can be mounted on the top of an animal's head. This device has been tested in guinea pigs having surgically implanted platinum electrodes, and the results show that the prosthesis can provide a rotational cue to the nervous system.

Animals↗
PubMedDate not supplied

Otx1 gene-controlled morphogenesis of the horizontal semicircular canal and the origin of the gnathostome characteristics.

The horizontal semicircular canal of the inner ear is a unique feature of gnathostomes and is predated by the two vertical semicircular canals, which are already present in lampreys and some fossil, armored jawless vertebrates regarded as close relatives of gnathostomes. Inactivation in mice of the orthodenticle-related gene Otx1 results in the absence of this structure. In bony fishes and tetrapods (osteichthyans), this gene belongs to a small multigene family comprising at least two orthology classes, Otx1 and Otx2. We report that, as in the mouse, xenopus and zebrafish, Otx1- and Otx2-related genes are present in a chondrichthyan, the dogfish Scyliorhinus canicula, with an Otx1 expression domain in the otocyst very similar to those observed in osteichthyans. A strong correlation is thus observed in extant vertebrates between the distribution of the horizontal semicircular canal and the presence of an Otx1 ortholog expressed in the inner ear, which supports the hypothesis that the absence of this characteristic in Otx1-/- mice may correspond to an atavism. The same conclusion applies to two other gnathostome-specific characteristics also deleted in Otx1-/- mice, the utriculosaccular duct and the ciliary process. Together with functional analyses of Otx1 and Otx2 genes in mice and comparative analyses of the Otx gene families characterized in chordates, these discoveries lead to the hypothesis that some of the anatomic characteristics of gnathostomes have appeared quite suddenly and almost simultaneously in vertebrate evolution, possibly as a consequence of gene functional diversifications following duplications of an ancestral chordate gene.

Animals↗
PubMed2001

Vertical semicircular canal function: a study in patients with benign paroxysmal positional vertigo.

A pendular rotation test in a head-tilted position (60 degrees backwards and rotated 45 degrees to either the right or left) was performed in 7 patients with benign paroxysmal positional vertigo (BPPV). Patients were rotated 360 degrees at a frequency of 0.1 Hz (maximum speed 114 degrees/s). The excitability of vertical semicircular canals was evaluated using this test procedure. Using an infrared CCD camera and a PC, evoked nystagmus was analyzed in order to determine the morbidity of BPPV. A statistically significant difference (p < 0.05) was found in the maximal slow-phase eye velocity between nystagmus from the anterior semicircular canal and nystagmus from the posterior semicircular canal. The excitability of the posterior semicircular canal in the affected ear was lower than that of the anterior semicircular canal. However, when vertigo and nystagmus disappeared, the difference in excitability was improved. The present results indicate some functional deterioration of the posterior semicircular canal in BPPV cases, suggesting the participation of both mechanical (dumping by mass) and organic (peripheral end organ) factors in causing morbidity.

Adult↗
PubMedDate not supplied

Semicircular canal orientation in the adult resting rabbit.

Photographs of rabbits in the alert resting position were used to record head position. Semicircular canals were surgically exposed and points measured along each canal were used to compute the best-fit plane using a least-squares method. Computations of mean best-fit planes showed that the horizontal canals were not carried horizontally in the rabbit. The anteromedial edges were superior by 16 degrees. The anterior canals were vertically oriented and made an angle of 43 degrees to the sagittal plane. The posterior canal was tipped in the anterior direction slightly and also made an acute angle (26 degrees) with the frontal plane. Rabbit semicircular canals deviated significantly from orthogonality. The range was 86 degrees (anterior canals) to 133 degrees (posterior canals). Thus, there were no co-planar canals. Such semicircular canal geometry has implications for the neural circuitry controlling posture in the rabbit.

Animals↗
PubMed1998

Contribution of the vertical semicircular canals to the caloric nystagmus.

Modulation of the caloric nystagmus in response to repositioning the plane of one vertical semicircular canal from gravitational horizontal to vertical during continuous caloric stimulation was used to measure the vertical canal's contribution to the nystagmus. The rationale was to examine the thermovective response from one vertical canal at a time, after a temperature gradient had been established across its two limbs. The nystagmus was measured and analysed in three dimensions using orthogonal head-referenced coordinates. The magnitude of each semicircular canal's contribution to the overall caloric response, the canal vector, was determined in non-orthogonal, contravariant semicircular canal plane coordinates. By using the canal plane reorientation technique and contravariant canal plane coordinates, we were able to measure the proportional thermovective response magnitude generated by each vertical canal during caloric stimulation. We found that the anterior canal contributed about one-third and the posterior canal about one-tenth as much as the lateral canal did to the overall caloric response magnitude when it was reoriented from horizontal to vertical. Comparison of the eye rotation axis before and after each vertical canal plane reorientation, with the geometry of the stimulated semicircular canals, also showed directional modulation of the caloric nystagmus by the vertical canal response. When one vertical canal plane was horizontal during caloric stimulation, the eye rotation axis aligned with the resultant of the other vertical canal and the lateral canal response axes. After vertical canal plane reorientation, the eye rotation axis realigned towards the resultant of the maximally stimulated vertical canal and the lateral canal, by 55.2+/-33.9 degrees (mean+/-SD) after anterior canal plane reorientation and by 32.3+/-21.2 degrees after posterior canal reorientation.

Adult↗