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At least 847 records · Page 47Linked to original sources
PubMed1982

Cardiovascular responses to lateral semicircular canal stimulation in man.

The cardiovascular effects of aural irrigation with water at 37 degrees C (control subjects, n = 6) or 44 degrees C (experimental subjects n = 11) were assessed from measurements of heart rate, brachial arterial blood pressure and forearm blood flow. The occurrence and intensity of vestibular stimulation was assessed from the electronystagmogram. The procedure had no significant effect on cardiovascular variables in control subjects or in subjects who were exposed to vestibular stimulation but who were not nauseated by it (n = 6). Those subjects who felt nauseous (n = 5) showed a tachycardia and forearm vasodilatation. These results provide no evidence that vestibular stimulation contributes to orthostatic reflexes in man.

Adolescent↗
PubMed1993

Contribution of irregular semicircular canal afferents to the horizontal vestibuloocular response during constant velocity rotation.

1. The effects of constant anodal currents (100 microA) delivered bilaterally to both labyrinths on the horizontal vestibuloocular response (VOR) were studied in squirrel monkeys during steps of angular velocity in the dark. We report that bilateral anodal currents decreased eye velocity approximately 30-50% during the period of galvanic stimulation without a change in the time constant of VOR. The decrease in eye velocity, present during steps of angular velocity, was not observed during sinusoidal head rotation at 0.2, 0.5, and 1 Hz. The results suggest that responses from irregular vestibular afferents influence VOR amplitude during constant velocity rotation.

Acceleration↗
PubMedDate not supplied

Interaction between the saccules and the vertical semicircular canals.

For the experiments 39 cats were used. Selective sectioning of either the anterior or the posterior vertical ampullar nerves was performed bilaterally. Additionally in some cats the utricular nerves were cut, or the saccule extirpated on one or both sides. The otolith organs were stimulated by tilting around the bitemporal axis of the animals. Bilateral sectioning of the anterior ampullar nerve induced vertical nystagmus upwards, which disappeared, if the animals were tilted upside down. When the posterior ampullar nerves were cut bilaterally a vertical nystagmus downwards was obtained, and if the animals were tilted upside down there was a large increase in nystagmus frequency. After unilateral extirpation of the saccule, vertical nystagmus downwards was observed in 50 percent of these experiments. This nystagmus was modulated by tilting. However, if the saccules on both sides were extirpated, no nystagmus could be elicited. The cause of these results is discussed.

Animals↗
PubMed1989

[Mechanisms of development of the dome in the semicircular canals of birds. I. Cellular secretion].

A study of the crista ampullaris of the vestibular apparatus was carried out in chicken embryos. The study group included embryos between stages 24 and 39 of Hamburger-Hamilton. This study elucidates the relationship of the cupula with respect to the epithelium of the crista ampullaris. With electron microscopic examination, the rough endoplasmic reticulum of the crista epithelial sustentacular cells at developmental stage of 31 H-H, demonstrated dilatations containing secretory material. Vesicles, with adhering ribosomes appear to be formed from these dilatations. At later stages of development, the vesicular material took on the characteristics of the fibrillary material composing the cupula. In some cells, secretory vesicles are seen near the apical border of these cells, where they apparently secrete vesicular contents into the endolymphatic space, contributing to the formation of the cupula.

Animals↗
PubMedDate not supplied

Convection, buoyancy or endolymph expansion: what is the actual mechanism responsible for the caloric response of semicircular canals?

The mechanisms underlying caloric nystagmus are still matter of debate. The original theory proposed by Barany and more recently by Pau and Limberg suggested that convective endolymphatic currents were involved. In contrast Gentine et al. suggested that the main mechanism responsible for caloric nystagmus is buoyancy due to calorization of the endolymph, without the need of continuous convective currents. Finally, other authors (Scherer and Clarke, Arai et al.) proposed that thermal expansion or contraction of the endolymph were involved. In the present study experimental conditions have been considered able to discriminate between these different models. The experiments, were carried out on isolated labyrinth preparations of the frog. Only the predictions of the model based on buoyancy were fully consistent with the experimental results whereas those provided by the other models were not.

Animals↗
PubMed1975

The Syndrome of Enlarged Vestibule and Dysplasia of the Lateral Semicircular Canal in Congenital Deafness.

A 5-year-old deaf-mute girl was shown on petrous bone tomography to have bilateral enlarged vestibules with assimilation of the lateral semicircular cannals, bilateral absence of the cochlea, aplasia of the left internal auditory canal with only the facial nerve compartment being present, and hypoplasia of the right internal auditory canal. The embryological basis of these inner ear abnormalities is discussed.

Child, Preschool↗
PubMed1977

Adaptive distortions in the generator potential of semicircular canal sensory afferents.

The generator potential in sensory afferents of frog crista ampullaris was extracellularly recorded from the cut end of the posterior ampullary nerve by means of suction electrodes. A servocontrolled turntable allowed suitable rotatary stimulations. The analysis of the recorded generator potential revealed a different time course from that predicted on the basis of the pendulum model. Adaptation and undershoots in the responses to velocity ramps, steps and sinusoids, were mainly responsible for the deviations, which became very evident only when fairly high acceleration rates were applied. Both adaptation and undershoots were produced presumably by the activation of an electrogenic pump, probably located in nerv terminals contacting the hair cells. In fact, the time course of the generator potential became much more consistent with the predictions from the pendulum model under treatments capable of hindering the ion pump activity.

Acceleration↗
PubMed1976

[Rsponses of the primary afferents of the frog lateral semicircular canal to caloric stimuli following section of the eighth nerve].

In curarized Rana temporaria, after transection of the 8th nerve, responses of 75 primary afferents of the LSC nerve to short local caloric stimule (0.5--12 degrees C over the canal temperature) creating theexcitatory current of LSC endolymph, were studied. In 41 per cent of the units (group A) the maximal (peak) frequencies (PF) of responses were shown to be associated either by linear or semilograithmic relations with the peak temperature (PT). In 23 per cent of the units (group B), PFPS revealed saturation at PT 8-12 degrees C. In 29 per cent of the units (group C), PFs were associated with PTs first by direct and then -- at increasing PTs-- by reverse proportionality. Duration of group A responses was related to PTs either in linear or semilogarithmic way. Comparison with previous data obtained in identical conditions but with intact 8th nerve indicates no noticeable difference in responses where efferent control was excluded.

Animals↗
PubMedDate not supplied

[Disability in patients with benign paroxysmal positional vertigo with posterior semicircular canal involvement].

OBJECTIVE: The aim of this work is to analyze the vestibular function and level of disability in two populations of patients with positional vertigo but with different results in the Dix-Hallpike test. MATERIAL AND METHODS: 114 patients were assessed. In 65 the Dix-Hallpike test was positive (DH+) and in 49 negative (DH). The caloric test was performed as well as the assessment of disability with the pertinent questionnaires for vestibular disability. RESULTS: Patients in the DH+ group showed a higher level of disability in the physical subscale of the DHI and a higher perception of a deteriorated quality of life. Patients in the DH- group showed a more severe disability in the emotional subscale of the DHI. CONCLUSIONS: Once the phenomenon of nystagmus fatigability is ruled out, patients with positional vertigo and DH- must not be considered a minor form of positional vertigo.

Adult↗
PubMed2005

Superior semicircular canal dehiscence: a series of 13 cases.

Increasingly more detailed imaging techniques have recently highlighted the frequent occurrence of bony labyrinthine dehiscence. Among them, superior canal dehiscence (SCD) has been described in a number of cases presenting different features. Here, we report a series of 13 cases, in which the detection of vestibular evoked myogenic potentials (VEMPs) in response to stimuli of abnormally low intensity as compared to normal responses led us to suspect the presence of a 'third window effect'. An accurate HRCT investigation allowed the diagnosis of SCD. Anamnestic and symptomatologic differences seem difficult to explain, although in our opinion a dural rupture could be at the basis of the onset of pathologic manifestations after many years of silence of a probably malformative condition.

Acoustic Stimulation↗
PubMed1994

Functional architecture of vestibular primary afferents from the posterior semicircular canal of a turtle, Pseudemys (Trachemys) scripta elegans.

Physiological studies in many vertebrates indicate that vestibular primary afferents are not a homogeneous population. Such data raise the question of what structural mechanisms underlie these physiological differences and what functional role is played by afferents of each type. We have begun to answer these questions by characterizing the architecture of 110 afferents innervating the posterior canal of Pseudemys scripta. We emphasize their spatial organization because experimental evidence suggests that afferent physiological properties exhibit significant spatial heterogeneity. The sensory surface of the posterior canal comprises paired, triangular hemicristae, which are innervated by two afferent types. Bouton afferents (66% of total afferents) are found over the entire sensory surface. They differ significantly in the shape and size of their collecting areas, number of boutons, soma size, and axon diameter; this morphological variation is systematically related to the afferent's spatial position. In addition, multivariate analyses suggest that bouton afferents may comprise two subtypes: alpha afferents have delicate processes and are found throughout the crista; beta afferents are more robust and are concentrated preferentially toward the canal center. Calyx-bearing afferents comprise two morphological subtypes: dimorphs (13% of total afferents) bear calyceal and bouton endings; calyceal afferents (21%) bear calyceal endings only. Both types occur exclusively in an elliptical region near the center of each hemicrista; their morphology varies with radial distance from the center of this elliptical region. Our data provide evidence that in Pseudemys: (1) the classical vestibular afferent types (bouton, calyx, dimorph) are structurally heterogeneous, and (2) their spatial sampling characteristics are highly structured and distinctive for each type. These spatial patterns may shed light on regional differences in physiological profiles of vestibular afferents, and they raise questions about the role of this spatial heterogeneity in signaling head movement.

Animals↗
PubMed1977

Comprehensive presentation of semicircular canal sensitivity.

It is generally agreed that in order to determine any difference in vestibular sensitivity between the two inner ears, the best clinical procedure involves a quantitative expression of the slow phase nystagmus response to standardized caloric (or rotatory) stimulation. The preferred procedure has involved averaging the slopes of a few of the nystagmus responses during the period of most intense activity and this has been accomplished either arithmetically or by means of an electronic computer. Although, such a sampling is often sufficient to enable a reliable diagnosis, occasions do arise when the results can be misleading unless comprehensive total presentations of the responses from the two labyrinths are available for reliable comparative evaluation. Such a procedure has been developed at the University of Toronto and used for clinical assessment at St. Michael's Hospital. The reliability of the method has been established as the result of testing over 800 patients with various vestibular disorders.

Caloric Tests↗
PubMed2003

Signal processing of semicircular canal and otolith signals in the vestibular nuclei during passive and active head movements.

The vestibular nerve sends signals to the brain that code the movement and position of the head in space. These signals are used by the brain for a variety of functions, including the control of reflex and voluntary movements and the construction of a sense of self-motion. If many of these functions are to be carried out, a distinction must be made between sensory vestibular signals related to active head movements and those related to passive head movements. Current evidence is that the distinction occurs at an early stage of sensory processing in the brain, and the results are evident in the firing behavior of neurons in the vestibular nuclei that receive direct inputs from the vestibular nerve. Several specific examples of how sensory information related to passive and active head movements is transformed in the vestibular nuclei are discussed.

Animals↗
PubMedDate not supplied

Cupula motion in the semicircular canal of the skate, Raja erinacea. An experimental investigation.

An upper bound on the magnitude of semicurcular canal cupula motion was experimentally determined in the isolated labyrinth of the skate, Raja erinacea. To visualize the cupula, a glass pipette was pushed through the ampullary wall, and local regions of the cupula were stained by slow infusion of small amounts of Alcian Blue dye. Caloric stimuli which produced large changes in single unit activity in the ampullary nerve and which often recruited several larger, previously silent units were found to produce on detectable cupula motion as seen through the ampulla wall. However when the cupula was first grossly displaced, motion was thereafter observed in response to identical caloric stimuli. Analysis of afferent responses indicates that the normal range of cupula motion in the skate is below the optical resolution of the method, conservatively estimated as 3--5 micrometers.

Animals↗
PubMed1997

[Bilateral semicircular canal pathology].

The authors report 12 cases of bilateral cupulolithiasis found in 142 subjects diagnosed as having benign paroxysmal positional vertigo. A case history was taken for these patients (4 males, 8 females; average age 28 years) and 10 reported a previous cranial trauma while the remainder did not refer any previous condition of note. All patients had normal cochleovestibular test results and showed no signs of concomitant internal and/or central pathologies. The Hallpike maneuver was able to evoke an intense symmetrical paroxysmal vertigo and this was often accompanied by neurovegetative phenomena while paroxysmal nystagmus always appeared. The patients were treated with a rehabilitative technique: the Brandt-Daroff was preferred as it is better tolerated. Within 15 days all patients had full remission of symptoms and at 6 months after treatment there have been no signs of recurrence. The conclusion is, thus, drawn that while the technical characteristics of the Sémont maneuver make it suitable only for use as rehabilitation in unilateral benign paroxysmal positional vertigo, this experience indicates that the Brandt-Daroff technique is better suited for the bilateral forms of this disorder.

Adolescent↗
PubMed2002

Signal discrimination in the semicircular canals: a role for group I metabotropic glutamate receptors.

Fluorescence immunocytochemistry indicates that enzymatically isolated semi-circular canal (SCC) hair cells express metabotropic glutamate receptors (mGluRs) 1a and 5. Antibody-antigen preadsorption controls proved entirely negative. Applied while mechanically stimulating the posterior SCC with a piezo-electric bimorph, the non-competitive, mGluR5-selective antagonist MPEP-HCl (1 microM-3 mM) dose-dependently reduces mechanically evoked facilitation of afferent discharge rate (IC50 136 microM; n = 4), while having no effect on tonic, unstimulated afferent discharge. It thus appears that group I mGluRs on SCC hair cells are activated during mechanical stimulation, but are not activated under tonic transmitter release conditions. We conclude that group I mGluRs expressed by SCC hair cells may serve as a mechanism for the selective amplification of mechanically evoked transmitter release, thereby enhancing signal discrimination at the VHC-vestibular afferent synapse.(50)

Action Potentials↗
PubMedDate not supplied

The contribution of the lateral semicircular canal to the short latency vestibular evoked potentials in cat.

Short latency vestibular evoked potentials (VsEPs) to angular acceleration impulses (maximal intensity 20,000 degrees/sec2, rise time 1.5-3 msec) were recorded by skin electrodes in cats before and after various surgical procedures. Under general anesthesia, the animals underwent unilateral labyrinthectomy and the VsEPs in response to stimulation of the remaining inner ear in the plane of the lateral semicicular canal (SCC) with the head flexed 20 degrees-25 degrees were recorded as a baseline. The lateral SCC was then selectively obliterated near its ampulla. This induced major changes in the VsEPs recorded in response to stimulation of the remaining inner ear in this plane: the first 2 VsEP waves were absent, and only longer latency, smaller amplitude waves were present in response to both clockwise and counterclockwise stimulation. On the other hand, obliteration of the anterior and posterior SCCs and, in addition, destruction of both maculae were without major effects on the first 2 VsEP waves in response to excitatory stimulation. The results confirm that when the head is flexed 20 degrees-25 degrees and stimulated with angular acceleration impulses in the horizontal plane, the major site of initiation of the VsEPs in cats and probably in man is the crista ampullaris of the lateral SCC.

Acoustic Stimulation↗
PubMed1996

Inactivation of delayed rectifier K+ current in semicircular canal hair cells.

Some properties of the inactivation process of delayed rectifier K+ current (Ik) were investigated in vestibular hair cells of the central region of frog crista ampullaris. These cells were chosen since they exhibited a very large Ik. Experiments were performed on thin slices of sensory epithelium using the whole-cell variant of the patch-clamp technique. Ik showed clear time-dependent inactivation over a period of some seconds, but the current did not completely inactivate even after 30 s depolarizing pulses. Another interesting finding was that inactivation could be well fitted by the sum of two exponentials: at 20 mV depolarization the fast time constant was 291.3 ms and the slow time constant was 2662.3 ms. In addition, an analysis of the steady-state inactivation process of Ik revealed that the inactivation curve was incomplete showing a non-inactivating current at potentials more positive than -50 mV. These results suggested that Ik in hair cells of frog crista ampullaris is composed of more than one component: by at least one inactivating and one non-inactivating component. The possible role of these components in hair cell excitability is discussed.

Animals↗