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At least 271 records · Page 15Linked to original sources

PubMed1989

Studies of solitary semicircular canal hair cells in the adult pigeon. II. Voltage-dependent ionic conductances.

1. The ionic conductances present in putative type II hair cells enzymatically dissociated from the anterior, posterior, and lateral semicircular canal cristae of the white king pigeon (Columba livia) vestibule were studied under whole cell voltage clamp. 2. Two classes of voltage-dependent potassium conductances were distinguishable on the basis of the time course of activation and inactivation and pharmacologic sensitivity. The rapid potassium conductance, IA, as inhibited by 6 mM 4-aminopyridine (4-AP), whereas the slow potassium conductance, IK, was inhibited by 50 mM tetraethylammonium (TEA). These conductances were not affected by extracellular calcium removal. IA was quite similar to the rapidly-inactivating A-current of molluscan soma, whereas IK was more like the delayed rectifier of molluscan soma. 3. The steady-state inactivation of IA occurred over a potential range from -100 to -40 mV. The threshold for activation of IA occurred between -60 and -50 mV. The slope conductance of the I-V curve over a range of -50 to -20 mV was 13.7 nS when the conditioning pulse was -100 mV, and we estimate it to be approximately 1-2 nS from the resting membrane potential of -56 mV. 4. The steady-state inactivation of IK was approximately 60% at -40 mV and was completely removed at -80 mV. The threshold for activation of IK was between -50 and -40 mV. The slope conductance of the I-V curve over a range of -50 to -20 mV was 10.5 nS when the conditioning pulse was -80 mV, and we estimate it to be approximately 6-7 nS from the resting potential of -56 mV. 5. At -56 mV (the average resting membrane potential of putative type II semicircular canal hair cells), approximately 10-14% of IA channels and approximately 57-70% of IK channels were not inactivated: thus IA and IK can contribute to the outward current during small depolarizations from rest. 6. A small calcium-dependent outward current, IK(Ca), could be elicited during step depolarizations from a holding potential of -40 mV. This calcium-dependent current was active over the range of -20 to +40 mV. 7. Inward currents could not be detected when the cells were exposed to normal physiological solutions. However, when the outward currents were blocked with internal cesium and the external solution contained 20 mM barium, sustained inward currents with rapid activation kinetics could be detected. The threshold for activation of the inward current occurred at -40 mV, and the I-V relationship peaked at -10 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

4-Aminopyridine↗

PubMedDate not supplied

The importance of potassium in the function of frog semicircular canals.

The slow potentials and afferent discharge of impulses in frog semicircular canals have been studied at different endolymphatic and perilymphatic K+ concentrations. Results indicate that the presence of K ions in the bathing fluids is essential for maintaining the receptor function in crista ampullaris, although very low concentrations of this ion in the perilymph are sufficient to preserve the receptor responsiveness to mechanical stimuli. The hypothesis is put forward that K+ may be pumped from the exterior of the canal towards the intracupular structures, where it accumulates. A K-rich endolymphatic environment does, however, appear to be necessary to ensure the resting activity of ampullar receptors and their ability to be "disfacilitated" during inhibitory cupula deflections.

Action Potentials↗

PubMed1985

An experimental study on the frog semicircular canal--functions of cupula and vestibular ganglion.

An isolated frog posterior semicircular canal was stimulated either by mechanical or thermal endolymphatic flow. Ampullofugal stimulation induced action potentials from the posterior ampullary nerve. These potentials adapted in six to eight seconds. While mechanical endolymphatic flow was induced, the cupula maintained its shift position without swinging back to the neutral point. This indicates that adaptation is mainly of sensorineural origin. When the canal was stimulated by a piece of frozen Ringer's solution, an increase in spike discharge was observed. The responses from the vestibular nerve trunk were compared to those from the posterior ampullary nerve. The time course of the response was shorter and the maximum spike count was smaller in the recordings from the vestibular nerve trunk.

Action Potentials↗

PubMed1983

[Postsynaptic potentials of motor neurons of neck muscles in the cat evoked by stimulation of the horizontal semicircular canals].

PSPs, evoked by stimulation of the ipsi- and contralateral horizontal semicircular canals (HSC) in motoneurons of neck muscles, were studied in acute experiments on cats under chloralose-nembutal anesthesia. Ipsilateral stimulation evoked EPSP with latencies ranging from 1.8 to 10.0 ms in 25 motoneurons and IPSP with latencies 1.9-3.9 ms in 10 motoneurons. Calculation of conduction time from ipsilateral canal via Deiters nucleus to neck motoneurons gives reason to consider EPSP with latencies less than 3.8 ms as disynaptic, and those with greater latencies as polysynaptic. Contralateral stimulation evoked EPSP with latencies 1.8-6.0 ms in 19 motoneurons and IPSP with latencies 3.2 and 3.9 ms in 2 motoneurons. Possible pathways conducting these influences and their functional role are discussed.

Animals↗

PubMed2006

Endolymphatic sac tumor located around semicircular canals.

We report a case of endolymphatic sac tumor (ELST). A 48-year-old female had recurrent and slowly progressive hearing loss, accompanied with dizziness like Meniere's disease. A tumor was located around the semicircular canals, and was detected on CT and MRI. The patient underwent total removal of the tumor using a transmastoid approach. Histopathological examinations agreed with features of an ELST. The tumor was highly suspected to have originated from the rugose portion of the endolymphatic sac or the endolymphatic duct, based on surgical and imaging studies. Structure of the membranous labyrinth was preserved regardless of the existence of the tumor around semicircular canals with bone destruction. ELSTs seem to have an osteolytic or osteophilic nature, by examining patterns of tumor infiltration.

Ear Neoplasms↗

PubMed1994

Changes of ampulla pressure in the semicircular canal of pigeons by caloric stimulation.

Still now several hypotheses about the mechanisms of the caloric nystagmus have been in conclusive. In this study we confirmed the convection effect and the volume change effect of the endolymph in horizontal semicircular canal following the caloric stimulation using pigeons (Columba livia). Although the direction of the caloric nystagmus depended on the head position and the stimulus site of calorization, the caloric nystagmus disappeared after plugging of horizontal semicircular canal. On the other hand, the ampulla pressure increased by cold calorization and decreased by hot calorization and these pressure changes had no relation to the head position. These results show that the main role of the mechanisms of the caloric nystagmus under 1G is the convection effect but the volume change effect may act on the caloric nystagmus not only under 1G but also under microgravity.

Animals↗

PubMed2002

Dehiscence of the bony roof of the superior semicircular canal in the middle cranial fossa.

Spontaneous dehiscence of the superior semicircular canal (SSC) in the middle cranial fossa is rare and may cause clinical problems. This dehiscence was investigated in cadaveric and dried temporal bone specimens. One cadaveric specimen showed a spontaneous defect: the dehiscence was a symmetrical, elongated ellipse with smooth margins. Four of 244 dry bone specimens showed bony defects in the roof of the SSC, however, only one specimen was thought to have a spontaneous defect. Based on computer-simulation models, we hypothesized that spontaneous defects of the SSC may arise during the fetal period. Although rare, this defect may cause problems in middle cranial fossa surgery and may relate to certain vertiginous disorders.

Aged↗

PubMed1980

Electrical activity of isolated semicircular canal in the frog. Action of streptomycin.

1. An isolated frog semicircular canal was placed in a two-compartment perspex chamber which allowed the fluids bathing the inside (endolymph) and the outside (perilymph) of the canal to be replaced separately. Mechanical stimulation (MS) of the ampullar receptors was performed by sinusoidal cupular movement. 2. Streptomycin sulfate in the perilymph reduced promptly, strongly and reversibly nerve spontaneous activity (SA) recorded on the ampullar nerve. Streptomycin sulfate also reduced reversible and weakly the slow potentials recorded either near the crista ampullaris (Adc) or on the ampullar nerve (Ndc) and the modulation of firing rate (delta Fms) all these activities being evoked by a mechanical stimulation. 3. Streptomycin sulfate injected into ampullar endolymph reduced promptly and strongly the Adc, Ndc, and delta Fms. When its concentration was higher 0.2 mg/ml, the SA was also reduced about 40 min later. 4. It is concluded that streptomycin sulfate alters weakly and reversibly spike generation process and synaptic transmission; it inhibits strongly and reversibly the resting discharge and it inhibits strongly and may be partly reversibly the transduction mechanisms.

Animals↗

PubMed1997

Postmeningitic labyrinthine ossification primarily affecting the semicircular canals.

In a series of six cochlear-implant candidates, including three small children, labyrinthine ossification in various stages of development was observed at CT. In four of the candidates the ossifying process was more advanced in the semicircular canals than in the cochleae, and in two equally distributed. The ossifying process developed during a period of 4-5 months in two of the children. Asymmetry of its extension was found in four patients. The causative organisms were Hemophilus influenzae and Streptococcus pneumoniae. The radiologic assessment of cochlear-implant candidates should include the semicircular canals where the ossification may start, and herald the development of cochlear ossification.

Adult↗

PubMed1990

[Analysis of field potentials in the postcruciate dimple evoked by stimulation of the ampullary nerve of the posterior semicircular canal in cats].

Field potentials evoked by stimulation of the posterior semicircular canal nerve (PCN) were studied in the postcruciate dimple (PCD) in anesthetized cats. When weak stimulation was provided, field potentials composed of 3 components of small positive, large positive and large negative waves were observed on the surface of the PCD. The field potentials could be observed at the stimulus intensity weaker than 1.5 x N1T. The latencies of initiation of the 3 components were 2.32 +/- 0.75 (mean +/- S.D.; n = 37), 3.75 +/- 0.92 (mean +/- S.D.; n = 99) and 9.34 +/- 2.81 (mean +/- S.D.; n = 101), respectively. The large positive wave of the maximum amplitude was recorded in the lateral part of the PCD. In this point, the large and small positive waves reversed their polarity at the layer III and V, respectively, which located about 500 microns and 1000 microns deep from the surface. Stimulations of the whole vestibular nerve (WVN) and the deep radial nerve (DR) shared response areas of field potentials. These findings agreed with the previous results as to a neuronal convergence of the somatic and vestibular inputs in the cat.

Animals↗

PubMed2000

Neural processing of gravito-inertial cues in humans. I. Influence of the semicircular canals following post-rotatory tilt.

Sensory systems often provide ambiguous information. Integration of various sensory cues is required for the CNS to resolve sensory ambiguity and elicit appropriate responses. The vestibular system includes two types of sensors: the semicircular canals, which measure head rotation, and the otolith organs, which measure gravito-inertial force (GIF), the sum of gravitational force and inertial force due to linear acceleration. According to Einstein's equivalence principle, gravitational force is indistinguishable from inertial force due to linear acceleration. As a consequence, otolith measurements must be supplemented with other sensory information for the CNS to distinguish tilt from translation. The GIF resolution hypothesis states that the CNS estimates gravity and linear acceleration, so that the difference between estimates of gravity and linear acceleration matches the measured GIF. Both otolith and semicircular canal cues influence this estimation of gravity and linear acceleration. The GIF resolution hypothesis predicts that inaccurate estimates of both gravity and linear acceleration can occur due to central interactions of sensory cues. The existence of specific patterns of vestibuloocular reflexes (VOR) related to these inaccurate estimates can be used to test the GIF resolution hypothesis. To investigate this hypothesis, we measured eye movements during two different protocols. In one experiment, eight subjects were rotated at a constant velocity about an earth-vertical axis and then tilted 90 degrees in darkness to one of eight different evenly spaced final orientations, a so-called "dumping" protocol. Three speeds (200, 100, and 50 degrees /s) and two directions, clockwise (CW) and counterclockwise (CCW), of rotation were tested. In another experiment, four subjects were rotated at a constant velocity (200 degrees /s, CW and CCW) about an earth-horizontal axis and stopped in two different final orientations (nose-up and nose-down), a so-called "barbecue" protocol. The GIF resolution hypothesis predicts that post-rotatory horizontal VOR eye movements for both protocols should include an "induced" VOR component, compensatory to an interaural estimate of linear acceleration, even though no true interaural linear acceleration is present. The GIF resolution hypothesis accurately predicted VOR and induced VOR dependence on rotation direction, rotation speed, and head orientation. Alternative hypotheses stating that frequency segregation may discriminate tilt from translation or that the post-rotatory VOR time constant is dependent on head orientation with respect to the GIF direction did not predict the observed VOR for either experimental protocol.

Adult↗

PubMed1987

Inhibitory connections of ipsilateral semicircular canal afferents onto Renshaw cells in the lumbar spinal cord of the cat.

1. In intercollicularly decerebrate cats, the excitability of lumbar spinal Renshaw cells (tested by single shocks to ventral roots and deafferented muscle nerves) decreased for 600-1000 ms after conditioning electrical stimulation of ipsilateral semicircular canal nerves. 2. Conditioning stimulation of posterior canal afferents and combined stimulation of anterior and lateral canal afferents were equally effective in causing inhibition of Renshaw cells. No significant differences were observed for Renshaw cells excitable from hind-limb flexor or extensor nerves. 3. Inhibition appeared when one to five stimuli were applied to the canal afferents and arrived at the spinal segmental level 11-15 ms after the onset of conditioning stimulation. 4. Evidence is adduced to suggest that the inhibitory effects on Renshaw cells following stimulation of semicircular canal afferents were mediated directly, i.e. they were not caused by alterations of motoneurone activity. 5. Excitation of Renshaw cells due to stimulation of the canal afferents was rarely observed; it could not be excluded that it was secondary to motoneurone discharges. 6. It is suggested that vestibular inhibition of Renshaw cells ensure a high gain of hind-limb alpha-motoneurones during postural adjustments following a massive disturbance of body equilibrium.

Action Potentials↗

PubMed1989

Effect of phenazine methosulfate on electrophysiological activity of the semicircular canal: antioxidant properties of trimetazidine.

Ischemia strokes appear to be the main source of cochleo-vestibular dysfunctions of peripheral origin. The present study aimed to investigate the action of oxygen free radicals on the bioelectric activity of the labyrinthine epithelium, using the frog semicircular canal as an in vitro preparation. We also examined the possible effect of the antianginal drug, trimetazidine (TMZ), under physiological conditions and during the administration of phenazine methosulfate (PMS). The model allows the ionic composition of endolymphatic and perilymphatic fluids bathing the semicircular canal to be dealt with separately. Spontaneous afferent vestibular nerve activity and the endolymphatic potential were recorded under resting conditions. Three additional parameters were investigated during mechanical displacement of the endolymphatic fluid: the ampullar direct current, the nerve direct current and the frequency of the evoked afferent spikes. Addition of TMZ (10(-6) and 10(-5) M, 50 min) into the perilymphatic compartment did not induce significant modifications of the different bioelectrical signals. Generation of oxygen free radicals, through administration of PMS (10(-5) M, 15 min) into the perilymphatic compartment, caused an impairment of all bioelectrical signals, except the ampullar direct current. The spontaneous activity, nerve direct current and frequency of afferent evoked spikes signals were significantly reduced 75 min after the start of PMS administration (-64, -17 and -32%, respectively). In contrast, there was a marked increase of the endolymphatic potential signal (+51%). Addition of TMZ (10(-6) or 10(-5) M) into the perilymph solution reversed the effect of PMS on all bioelectrical signals. These results indicate that TMZ acts as an antioxidant molecule which is capable of protecting the labyrinthine epithelium from the deleterious effect of oxygen radicals. Our data suggest that the protective effect of TMZ on ischemia-induced cochleo-vestibular dysfunctions may be accounted for by the antioxidant properties of this antianginal drug.

Animals↗

PubMed1995

Posterior semicircular canal occlusion for benign paroxysmal positional vertigo--CO2 laser-assisted technique: preliminary results.

Benign paroxysmal positional vertigo (BPPV) is a common vestibular end-organ disorder that in the majority of patients resolves with conservative management. In the occasional patient who has unremitting BPPV despite conservative treatment, posterior semicircular canal occlusion (PCO) may be effective in eliminating symptoms. In an attempt to minimize the risk of hearing loss, a modified procedure was developed that uses the CO2 laser to shrink the membranous vestibular posterior semicircular canal prior to mechanically plugging the canal. Preliminary results of this CO2 laser-assisted occlusion technique used in four patients are presented.

Aged↗

PubMed1982

Semicircular canals: measurement of endolymphatic and cupular displacements at threshold.

The left horizontal semicircular canal of the leopard frog (Rana pipiens) was exposed and the entire intact nerve was draped over a platinum-iridium hook for recording action potentials (a.p.'s). The preparation was then rotated sinusoidally in the horizontal plane at 0.3 Hz with varying angular displacements. The arm of the canal was then transected, and a fine micropipette ligated in place in one end of the arm. Artificial endolymph was pumped into and out of the canal at the same frequency, while the amplitude of the displacement was varied from sub-threshold to supra-threshold values as determined from the resulting a.p. train. By comparing the two a.p. trains, it was determined that the movement of endolymph in the canals was 5.3 x 10(-8) cm3/deg/s, and that the threshold displacement of the midpoint of the cupula was 7.6 x 10(-5) cm (0.76 micrometers).

Action Potentials↗

PubMedDate not supplied

Post-natal bone growth in the semicircular canals of the dog.

Dogs from the same litter, divided into three groups aged 10, 25, and 50 days, received an intraperitoneal injection of tetracycline for two successive days. The temporal bones were fixed, embedded in methylmethacrylate, sectioned in to a single 100 microns thick section along the main axis of the anterior and lateral semicircular canals, grounded by hand to 30 microns and observed at UV light. The new bone tissue is laid down both at the endosteal and endochondral bone of the anterior and lateral semicircular canals. The bone deposition decreases with the age of the animal and earlier at the endosteum than at the endochondral bone.

Aging↗

PubMed1998

Evaluation of vertical semicircular canal function by the caloric test--a study on patients with benign paroxysmal positional vertigo.

The morbidity of benign paroxysmal positional vertigo (BPPV) was investigated from the functional standpoint by analyzing nystagmus elicited by the caloric test. As a result of an investigation of the three (horizontal, vertical and torsional) components of the nystagmus elicited by the caloric stimulus (cold water), the vertical nystagmus differed in direction between the left and the right ear in 3 out of the 4 BPPV cases. The vertical nystagmus elicited by the caloric stimulus reflected the functions of the anterior and posterior semicircular canals, and investigation of the difference in function between the anterior and posterior semicircular canal from the direction of the vertical nystagmus appeared to be feasible.

Adult↗

PubMedDate not supplied

Posterior semicircular canal type benign paroxysmal positioning vertigo with ageotropic paroxysmal positioning nystagmus.

We report on 3 patients with typical benign paroxysmal positioning vertigo (BPPV) and atypical, paroxysmal positioning nystagmus. When the Dix-Hallpike test was performed, the patients exhibited an ageotropic nystagmus, different from that classically described in posterior semicircular canal BPPV. It was torsional-vertical with the vertical component beating downwards, and the torsional component was beating away from the lowermost ear. In both left and right Dix-Hallpike positions, the upper poles of the eyes were turning away from the lowermost ear. The atypical ageotropic paroxysmal positional nystagmus of the posterior semicircular canal was observed in the evolution of the BPPV in 2 patients and on the first examination in the third. Two patients had changing patterns of paroxysmal positioning nystagmus.

Adult↗