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PubMed1979

Comparative study of the influence of aminoglycoside antibiotics on the activity of the horizontal semicircular canal in the frog.

This work is an electrophysiological study made in the frog. The technique allows one to test and to compare the actions of a number of aminoglycoside antibiotics, directly introduced into the labyrinthic cavity, on the spontaneous activity of a vestibular receptor--the horizontal semicircular canal. The effects of aminoglycoside solutions have been compared with those of physiological solutions (NaCl 7 g/l, Ringer) and of penicillin (not ototoxic). The results obtained show: (1) After the introduction of a physiological solution the activity disappears only very briefly (electrical artefact, probably); after a few minutes the activity returns to its initial value. A similar phenomenon is obtained with penicillin. (2) When used at a dose of 10 microgram, all the aminoglycosides studied generally induced an important and lasting decrease in semicircular canal activity. (3) These aminoglycosides have been classified according to their vestibular local toxicity. Their descending order of influence is as follows: streptomycin, dihydrostreptomycin, amikacin (BBK 8), neomycin, sisomycin, gentamicin and lividomycin, tobramycin, kanendomycin. (4) A parallel can be drawn between local vestibular toxicity and clinical ototoxicity. The role and importance of the hemolabyrinthic barrier are noted and the notion of ototoxicity is discussed.

Amikacin↗
PubMed1986

Epithelial linings of the human semicircular canal. A scanning and transmission electron microscopic study.

We have used scanning and transmission electron microscopy to examine adult human semicircular canals taken at autopsy and an operation. Our findings can be summarized as follows. In the semicircular circular canals obtained at autopsy from a 30-year-old male, non-sensory ciliated cells having 50-60 cilia were seen sporadically in the canal side of the ampulla of the horizontal canal. A labyrinthine specimen taken at operation demonstrated folding of the cell membrane at the base of columnar cells lining the wall of that part of the canal close to the ampulla. Distal to this site, canal wall cells became progressively flattened and their intracytoplasmic organelles were seen to be progressively less abundant. These cells were found to be layered, facing the endolymphatic space. Dense filaments and fibrocytes were present outside these cells, between which were interposed single-layered basement membranes. Since the capillary network present was found to be sparse, we believe that the portion of the canal studied does not produce endolymph but plays a role in the maintenance of the composition of endolymph and perilymph.

Adult↗
PubMed2000

[Morphological studies of the form of the cupula in the semicircular canal ampulla].

BACKGROUND AND OBJECTIVE: The cupula in the ampulla of the semicircular canal, like the tectorial membrane in the cochlea, forms the essential link in transferring endolymph fluid movement stimuli to the hair cells. Clear understanding of physiological cupula movement only started evolving towards the end of the 1970s. Currently, the cupula is assumed to adhere firmly to the ampulla wall, with diaphragm-like displacement in the central section and at the base. PATIENTS/METHODS: In contrast to detailed functional descriptions, there have been very few investigations on cupula morphology. These have proved difficult due to the extremely hydrous structure, which inevitably results in shape distortion during fixation. This difficulty applies particularly to electron microscopy. RESULTS: The present morphological investigations were performed in artificial endolymph on fresh preparations in the salmon (Salmo salar). After staining and isolating the cupula from the ampulla, a precise morphological investigation was performed. A relatively uniform basic structure was observed, with considerable interindividual variability in cupula shape. CONCLUSIONS: Such variability suggests that impairment of cupular form can occur and could be associated with altered peripheral vestibular function.

Animals↗
PubMed1996

Electrical filtering in gerbil isolated type I semicircular canal hair cells.

1. Membrane potential responses of dissociated gerbil type I semicircular canal hair cells to current injections in whole cell current-clamp have been measured. The input resistance of type I cells was 21.4 +/- 14.3 (SD) M omega, (n = 25). Around the zero-current potential (Vz = -66.6 +/- 9.3 mV, n = 25), pulsed current injections (from approximately -200 to 750 pA) produced only small-amplitude, pulse-like changes in membrane potential. 2. Injecting constant current to hyperpolarize the membrane to around -100 mV resulted in a approximately 10-fold increase in membrane resistance. Current pulses superimposed on this constant hyperpolarization produced larger and more complex membrane potential changes. Depolarizing currents > or = 200 pA caused a rapid transient peak voltage before a plateau. 3. Membrane voltage was able to faithfully follow sine-wave current injections around Vz over the range 1-1,000 Hz with < 25% attenuation at 1 kHz. A previously described K conductance, IKI, which is active at Vz, produces the low input resistance and frequency response. This was confirmed by pharmacologically blocking IKI. This conductance, present in type I cells but not type II hair cells, would appear to confer on type I cells a lower gain, but a much broader bandwidth at Vz, than seen in type II cells.

Animals↗
PubMed1991

Non-ampullary plugging of the posterior semicircular canal for benign paroxysmal positional vertigo.

Benign paroxysmal positional vertigo (BPPV) is a common condition which is usually self-limiting. Surgical treatment is rarely required and for many years the mainstay of such treatment has been singular neurectomy (posterior ampullary nerve section). A new operation has recently been described for the treatment of BPPV involving occlusion of the posterior semicircular canal. We have performed this operation on five patients with intractable BPPV and report our results with follow up of between 12 and 36 months from operation. The excellent results of posterior semicircular canal occlusion which have been previously reported in the literature are confirmed by our experience. In our opinion the operation is a safe and effective alternative to singular neurectomy.

Adult↗
PubMed1995

The effect of unilateral posterior semicircular canal inactivation on the human vestibulo-ocular reflex.

The responses to rapid, passive, unpredictable, low amplitude (10-20 degrees), high acceleration (3,000-4,000 degrees/s2) head rotations were used to study the human vestibulo-ocular reflex (VOR) in pitch and yaw plane after unilateral posterior semicircular canal occlusion (uPCO) in 10 subjects. The results from these 10 uPCO subjects were compared with those from 18 normal subjects. The VOR gains at a head velocity of 200 degrees/s in the uPCO subjects were: pitch upward = 0.62 +/- 0.06, pitch downward = 0.87 +/- 0.11, yew ipsilesion = 0.78 +/- 0.06, yaw contralesion = 0.79 +/- 0.10 and in normal subjects were: pitch upward = 0.92 +/- 0.06, pitch downward = 0.96 +/- 0.04, yaw right = 0.88 +/- 0.05, yaw left = 0.91 +/- 0.12 (group means +/- twotailed 95% confidence intervals). The results showed that the pitch-vVOR gain was significantly (p < 0.05) decreased in response to upward head impulses whereas in response to downward, ipsilesion and contralesion head impulses were not significantly different (p > 0.05) from the normals. This study shows that there is 30% permanent residual deficit of the upward pitch-vVOR with an up-down asymmetry in pitch-vVOR gain following inactivation of a single posterior semicircular canal and that compensation of pitch-vVOR function is incomplete.

Adult↗
PubMed1985

Spontaneous and driven responses of semicircular canal primary afferents in the unanesthetized pigeon.

Spontaneous activity from 120 vestibular semicircular canal (SC) primary afferents and driven responses from 20 SC primary afferents to 2.3-decade bandwidth (0.029-6.152 Hz) sum of sinusoidal angular rotations were characterized in 10 unanesthetized pigeons. The results were compared with those previously gathered from barbiturate anesthetized pigeons. The average spontaneous mean firing rate (MFR) of SC primary afferents in unanesthetized pigeons was found to be 168 impulses per second (I/s), n = 120, and is approximately 80% higher than that for SC primary afferents in anesthetized pigeons [93 I/s, n = 149 (Ref. 9) and 92 I/s, n = 124 (Ref. 22)]. The spontaneous discharge of SC primary afferents from unanesthetized pigeons was classified according to the coefficient of variation (CV) of 512-1,024 interspike intervals (ISIs) into regular (CV less than 0.1), intermediate (0.1 less than or equal to CV less 0.4), and irregular (0.4 less than or equal to CV) categories. The percentages of SC primary afferents falling within each CV category were similar for unanesthetized and anesthetized pigeons (22). The relation between the spontaneous mean ISI and its standard deviation (SD) for SC primary afferents in the unanesthetized pigeon is best described by a power function model, which provides a significantly better fit than does a linear model. The parameters of this power function model are similar for SC primary afferents in unanesthetized and anesthetized pigeons (10). The spontaneous ISIs of individual SC primary afferents in the unanesthetized pigeon were found to be distributed either normally, log-normally, or according to the first passage time of the Wiener-Levy (WL) process. The gain of anterior SC primary afferents at 0.25 Hz is similar for anesthetized (2.93 I X s-1 X deg-1 X s-1, n = 14) (11) and for unanesthetized (3.01 I X s-1 X deg-1 X s-1, n = 14) pigeons. Bode plots constructed from the responses to sum sinusoidal angular accelerations reveal that SC primary afferents in unanesthetized pigeons display a phase lead and gain enhancement at frequencies between 0.6 and 6 Hz.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1971

Frequency-response analysis of central vestibular unit activity resulting from rotational stimulation of the semicircular canals.

1. The neural response of semicircular canal-dependent units in the vestibular nuclei of cats has been examined over a frequency range of sinusoidal rotation extending from 0.004 to 0.9 Hz.2. Frequency-response analysis indicates that, over the range examined, the information contained in the neural signal received by the brain stem was similar to that expected from the mechanical end-organ.3. Over the experimental frequency range, the relation between neural response and mechanical stimulus was found to be dominated by a single time constant of about 4 sec, such that two response regions can be defined above and below a stimulus frequency of (1/4) rad/sec ( approximately approximately Hz).4. Above this frequency the information content of the neural signal tends towards that of angular velocity and below that frequency it tends towards that of angular acceleration.5. It is inferred (a) that the so-called ;long' time constant of the cat's horizontal canal is about 4 sec and (b) that during most normal head movements containing frequencies below about 1 Hz the informational mode of neural signals generated in the canal and received in the brain stem probably tends towards that of head angular velocity.6. This seems appropriate for the generation of vestibulo-ocular reflex compensation for head movement and for reflex damping (negative velocity feed-back) of unintended head and body movements.7. The average neural gain of central unit responses is estimated at 1264 action potentials/sec, per degree of cupular deflexion. This high value reflects the very small angles of cupular deflexion assessed on the basis of physical characteristics of the canal.8. The results permit a rough estimate of the elastic restoring coefficient of the cupula in the horizontal canal as 2.05 x 10(-3) dyne. cm.

Acceleration↗
PubMed2001

Mechanism of posterior semicircular canal stimulation in patients with benign paroxysmal positional vertigo.

A quantitative study of the stimuli and vestibulo-ocular response associated with benign paroxysmal positional vertigo (BPPV) was made to test and further develop the canalithiasis theory of BPPV. The angular velocities of the head in the planes of the semicircular canals during the Dix-Hallpike test were measured in four healthy subjects using electromagnetic sensors to record the position of the head in a six degrees of freedom paradigm. Next, the nystagmus reactions in seven patients diagnosed with idiopathic BPPV were recorded with video-oculography. The characteristics of the vestibulo-ocular reflex (VOR) response were analyzed using three-dimensional vector techniques. The angular velocity of the head was primarily, but not exclusively, in the plane of the posterior semicircular canal (PSC) in question. Both the anterior and horizontal canals were also stimulated by a lesser degree. The duration of the motion stimulus in the PSC was < 1.3 s with peak angular velocities of 150 deg/s. The eye response in BPPV patients began 4 s after the test and had a duration of 15-20 s. Peak slow-component eye velocities of about 42 deg/s were reached 3-5 s after onset of nystagmus. The motion of the eye, as predicted by the cupulolithiasis theory, is disconjugated and has torsional, vertical, and horizontal components. In the eye ipsilateral to the tested ear it is primarily torsional (0.80, 0.54, 0.16) and in the contralateral eye it is mainly vertical (0.57, 0.73, 0.08). These results suggest that particles, initially resting on the floor of the cupula dome in the PSC, are perturbed by the Dix-Hallpike test and disperse freely into the endolymph where they are propelled by gravity into the canal lumen. This creates abnormal pressure on the cupula and the specific VOR activation of the ipsilateral superior oblique and the contralateral inferior rectus muscles, whose force vectors are indistinguishable from the measured eye motion vectors. The estimated pressure exerted on the crista is approximately 10(-2) dyn/cm2.

Adult↗
PubMed1999

Long-term results of posterior semicircular canal occlusion for intractable benign paroxysmal positional vertigo.

Benign paroxysmal positional vertigo (BPPV) is a common condition which is usually managed conservatively, surgical intervention being recommended only for those small number of patients in whom it becomes persistent and incapacitating. The results of surgery in 13 patients who underwent posterior semicircular canal occlusion for intractable (> 12 months duration) and incapacitating BPPV are presented with special emphasis on their long-term follow-up. The mean follow-up was 66 months (range, 29-119 months). All patients reported complete and immediate resolution of their positional vertigo, which has been maintained in the long term. Most patients, however, reported some postoperative transient unsteadiness which lasted up to 4 weeks. All patients developed a transient mild conductive hearing loss secondary to a middle ear collection, which usually resolved within 4 weeks. Five patients developed a transient mild high frequency sensorineural hearing loss which resolved in all cases within 6 months. There were no reports of sensorineural hearing loss nor tinnitus in the long term. All patients believed that the operation was beneficial and would undergo it again. Our findings indicate that posterior semicircular canal occlusion is an effective and safe operation in the long term and is the procedure of choice for intractable and incapacitating BPPV rather than singular neurectomy.

Adult↗
PubMed1992

Fenestration and occlusion of the posterior semicircular canal for benign positional vertigo.

Benign positional vertigo is a potentially disabling condition characterized by episodic vertigo following certain provocative head movements. In most patients it is self limiting; however, in a few it may prove intractable, causing considerable social morbidity. In these patients surgery may be considered. Surgery previously involved section of the vestibular or singular nerves, involving a significant risk to hearing and to the facial nerve. Ablation of the labyrinth may even be considered. The new surgical technique of occlusion of the posterior semicircular canal has proved to be curative in most patients with benign positional vertigo with little risk of hearing. This paper describes our experience of fenestration and occlusion of the posterior semicircular canal in four patients.

Adult↗
PubMed2005

Posture control in Pusher syndrome: influence of lateral semicircular canals.

UNLABELLED: Pusher syndrome is an interesting disorder of balance in patients with encephalic lesions characterized by the peculiar behavior of actively pushing away from the non-hemiparetic side and resisting against passive correction, with a tendency to fall toward the paralyzed side. The role of vestibular system on the pushing behavior is not clear. AIM: To evaluate horizontal semicircular canal function in patients with Pusher syndrome, using caloric and rotation tests. STUDY DESIGN: Observational prospective. MATERIAL AND METHOD: We evaluated 9 inpatients with stroke and Pusher syndrome at the neurological unit of HCFMRP-USP. We applied neurological and neuropsychological exams, NIHSS, Scale for contraversive pushing (SCP), caloric and rotation tests. RESULTS: We evaluated 9 patients (5 men) with mean age of 71.8 +/- 5.9 and mean NIHSS of 18.33. Three patients presented contralateral directional preponderance on caloric test and we found four patients with directional preponderance on analysis of the slow phase velocity of rotation test response. CONCLUSION: Our findings indicate that a dysfunction of semicircular canals does not seem to be relevant for the clinical manifestations of the Pusher syndrome.

Aged↗
PubMed1993

Acute and chronic effects of streptomycin applied to the lateral semicircular canal.

In developing the technique of selective chemical vestibulectomy, the destructive effect of streptomycin on the hair cells of the inner ear was well established. However, in both animal and human studies, a rapid onset of the drug's vestibular inhibition was observed in addition to a more slowly developing long-term destructive effect. In previous laboratory studies, streptomycin had been given only by a systemic route, and only the chronic long-term effects had been observed. In this study, an isolated semicircular canal was prepared and streptomycin was placed into the perilymph bathing the canal. The spontaneous and evoked afferent nerve activity were recorded prior to streptomycin application, during application, and after a washout period. During streptomycin application, the activity of the semicircular canal was reversibly inhibited in a dose dependent manner. After a sufficient washout period (5-10 min), the preparation had completely recovered from the drug's effect. Thus, there are two phases in the vestibular inhibition by streptomycin: an early reversible phase that subsequently can transform into a later irreversible phase.

Animals↗
PubMed1992

Magnetic resonance imaging of semicircular canals.

The present paper reports the results of the first investigation of the semicircular canals in a living, small animal by means of high spatial resolution magnetic resonance imaging. This procedure is noninvasive and allows identification of the endolymphatic and perilymphatic spaces yielding a morphology quite consistent with direct anatomical examination.

Animals↗
PubMed1993

Descriptive and experimental analysis of the epithelial remodellings that control semicircular canal formation in the developing mouse inner ear.

The inner ear of the mouse develops from a roughly spherical epithelial vesicle, the otocyst, which undergoes a series of complex shape changes to produce the functionally important parts of an adult inner ear; in particular, a coiled cochlea--which houses the auditory apparatus, a saccule and utricle containing sensors of gravity and linear acceleration, and three precisely shaped and oriented semicircular canals, with which angular acceleration is detected. This paper follows the development of the shape of the mouse inner ear from simple otocyst until a stage when the vesicle has become a rather squat miniature model of its adult self. We have been able to visualize clearly these complex shape changes by injecting an opaque marker into the lumina of a series of fixed ears. We have further concentrated on the mechanism of formation of the semicircular canals using light-, electron-microscopic, and dye-marking techniques. Classic embryological texts describe the canals developing from outpocketings of the epithelial ear rudiment, whose opposite walls meet, fuse, and "disappear" in the central canal plate region to leave a tube of epithelium encircling their margin. To trace the fate of these "disappearing" epithelial cells we have dye-marked all of the otic epithelial cells at a stage prior to canal formation in mouse embryos which we then grow in roller culture until their canals have formed. From these marking experiments we show that the disappearing cells of the canal plate neither die nor become transformed into mesenchymal cells, but rather, most are retracted back into the canal tube epithelium at either side of the site of fusion. We speculate that this mechanism of epithelial resorption may be a common way of "losing" epithelial cells during embryonic morphogenetic remodellings.

Animals↗
PubMed1999

Histologic changes after semicircular canal occlusion in guinea pigs.

HYPOTHESIS: Histologic changes occurring after varying degrees of surgical trauma to the inner ear in guinea pigs can reveal the mechanism of hearing preservation/loss. BACKGROUND: Surgical approaches to the inner ear that allow for hearing preservation have gained increasing acceptance in neurotologic surgery. The mechanisms responsible for hearing preservation and hearing loss after partial labyrinthectomy are as yet poorly understood. METHODS: Ten animals underwent semicircular canal occlusion, suctioning of perilymph, ampullectomy, or wide vestibulotomy. Tone-burst auditory brain stem response (ABR) thresholds were performed at weekly intervals after surgery. After 4 weeks, temporal bone specimens were processed to obtain 10-jim sections from plastic-embedded ears. The histologic findings were correlated with the initial and final ABR thresholds. RESULTS: After surgical occlusion of one or more semicircular canals, ABR thresholds were preserved, as the authors reported previously. Suctioning of inner ear fluid led to transient loss of thresholds with recovery. Ampullectomy produced dichotomous results, with some subjects preserving auditory function and others losing auditory function. Wide vestibulotomy resulted in permanent loss of auditory function in most cases. Histologically, there was intraluminal fibrosis and inflammation near the site of surgical entry. Most specimens showed normal cochlear architecture and hair cell counts, irrespective of the degree of hearing loss. Vestibular hair cells were also well preserved, even when they were close to the site of surgical injury. CONCLUSIONS: These findings suggest that electromechanical changes, rather than cell death, are responsible for changes in auditory and vestibular function after partial labyrinthectomy.

Animals↗