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At least 19 recordsLinked to original sources
PubMed1992

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

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

Aged↗
PubMed1977

Influence of the saccule, lagena and vertical posterior canal on the ipsilateral horizontal and vertical anterior semicircular canals in Rana esculenta: role of receptor-receptor fibres.

The influence of the efferent vestibular system being eliminated, the spontaneous activity of single afferent fibres of the ampullary nerves of the horizontal and vertical anterior semicircular canals was recorded in the frog. By stimulating electrically the nerves of the vertical posterior canal, lagena or saccule as well as by sectioning these nerves and then using statistical methods, it is shown that the receptor-receptor fibres arising from the above mentioned receptors have generally an inhibitory influence on the afferent activity from the horizontal and vertical anterior canals.

Animals↗
PubMed1992

Selective resection of the semicircular canals of rabbits with preservation of hearing.

The goal of this investigation was to develop a method of surgical removal of the semicircular canals of the rabbit without induction of auditory impairment. Four different surgical techniques were utilized: i) fenestration of the lateral semicircular canal; ii) fibrin glue perfusion of the canal following fenestration; iii) removal of the lateral semicircular canal by drilling after fenestration and fibrin glue perfusion, and iv) removal of all three canals after fenestration and fibrin gluing. Brainstem auditory potentials were recorded repeatedly for up to 3 months after operation and demonstrated preservation of hearing in all rabbits in the first group and in 78% of the second group. In the third group the potentials could be recorded in 67% of the animals and showed a 20 dB deterioration of hearing. After removal of all three semicircular canals residual hearing could be recorded in 50% of the rabbits. These animals regularly showed a 30-40 dB deterioration of hearing. A precise microsurgical technique using fibrin glue and bone chips for interruption of the peri- and endolymph flow proved crucial for hearing preservation.

Animals↗
PubMed1992

Secretion of endolymph by the isolated frog semicircular canal.

Secretion of endolymph is localized in some structures of the inner ear, namely the stria vascularis in the cochlea and the dark cells in the vestibule and in the lower vertebrate inner ear. In isolated semicircular canal it is possible to study separately the endolymphatic composition in the ampulla, which contains the dark cells, and in its non-ampullar part, which is devoid of these cells. Further, in vitro preparation of the semicircular canal provides access to both faces of the epithelium so that different agents can be applied separately to the apical or to the basolateral membranes of the epithelium. In this structure, the following results were obtained: i) in vitro, the semicircular canal secreted a K-rich, positively polarized fluid; ii) this fluid was secreted only in the ampulla of the semicircular canal; iii) the secretion of endolymph was dependent on basolateral Na+, K(+)-ATPase, inhibited by ouabain, and basolateral Na-K-Cl co-transporter, inhibited by bumetanide; iv) approximately 60% of luminal Na absorption occurred across a luminal Na channel inhibited by amiloride; v) the permeability of the paracellular pathway of the semicircular canal epithelium was 7.10(-7) cm/s. These results indicate that endolymph secretion involves basolateral Na+, K(+)-ATPase and Na-K-Cl co-transporter. An Na channel has been shown at the apical membrane.

Animals↗
PubMed1992

Changes in monkey horizontal semicircular canal afferent responses after spaceflight.

Extracellular responses from single horizontal semicircular canal afferents in two rhesus monkeys were studied after recovery from a 14-day biosatellite (COSMOS 2044) orbital spaceflight. On the 1st postflight day, the mean gain for 9 different horizontal canal afferents, tested using one or several different passive yaw rotation waveforms, was nearly twice that for 20 horizontal canal afferents similarly tested during preflight and postflight control studies. Adaptation of the afferent response to passive yaw rotation on the 1st postflight day was also greater. These results suggest that at least one component of the vestibular end organ (the semicircular canals) is transiently modified after exposure to 14 days of microgravity. It is unclear whether the changes are secondary to other effects of microgravity, such as calcium loss, or an adaptive response. If the response is adaptive, then this report is the first evidence that the response of the vestibular end organ may be modified (presumably by the central nervous system via efferent connections) after prolonged unusual vestibular stimulation. If this is the case, the sites of plasticity of vestibular responses may not be exclusively within central nervous system vestibular structures, as previously believed.

Adaptation, Physiological↗
PubMed1979

The development of function of horizontal semicircular canal primary neurons in the rat.

The activity of primary horizontal semicircular canal neurons in newborn rats was compared to similar cells in adults. All animals were anesthetized with ether. Neurons were categorized as regular or irregular on the basis of their spontaneous activity. Horizontal semicircular canal neurons can respond to angular acceleration stimulation at birth. In newborn rats no regularly firing cells could be found, but the percentage of these cells and their average resting rate increased during growth. Neurons in newborn rats differ from those in the adult by having a lower average resting rate, a lower sensitivity to long-duration angular acceleration and taking longer to reach peak increase in firing during the stimulus. Sensitivity reaches adult values by about 4 days although the canal dimensions continue to increase until about 20 days.

Afferent Pathways↗
PubMed1976

Damped pendular rotation nystagmus after unilateral labyrinthectomy or unilateral lateral semicircular canal block in squirrel monkeys.

Using a damped pendular rotation table, which provided an oscillation of 15.5 sec, per-rotatory nystagmus, was evaluated in six squirrel monkeys that underwent unilateral labyrinthectomy and five that underwent unilateral lateral semicircular canal block, both pre- and postoperatively. The bidirectional summation of the nystagmic slow-phase eye speed after unilateral labyrinthectomy and after unilateral lateral semicircular canal block showed similar reduction to about 60 per cent of the values obtained in the pre-operative status. Under the present test situation, both slow-phase eye speed and number of nystagmic beats in the monkeys after unilateral lateral semicircular canal block were larger by the ampullopetal stimulation than those evoked by ampullofugal stimulation. The relation between slow-phase eye speed and number of beats showed similar tendency when we compared pre-operative controls and the group after unilateral lateral semicircular canal block, but the monkeys after unilateral labyrinthectomy depicted different tendencies.

Animals↗
PubMedDate not supplied

[Functional relationships between the horizontal and vertical anterior semicircular canals in the labyrinth of the frog (Rana esculenta L.)].

We have studied the vestibular postrotatory reactions (reactions elicited by the stimulation of the horizontal semicircular canals) in the frog blinded by section of optic nerves, before and after section of the ampullary nerves of the vertical anterior semicircular canals (VAC). 90 frogs have been studied. In 30 frogs the ampullary nerves of the two VAC have been cut; in 60 animals either the ampullary nerve of the right VAC or of the left VAC has been cut. Both after section of the ampullary nerves of the two VAC and after section of the ampullary nerve of one VAC, the postrotatory reactions were decreased in about the half of the animals. The decrease of the postrotatory reactions is not due to a lesion of the ampullary nerves of the horizontal semicircular canals and it may be explained by the existence of functional connections between the VAC and the horizontal canal.

Animals↗
PubMed1992

Hearing results following posterior semicircular canal injury during antesigmoid retrolabyrinthine selective vestibular nerve section.

The disastrous hearing results in six patients whose posterior semicircular canal was entered during antesigmoid mastoid craniotomy for retrolabyrinthine selective vestibular nerve section were reviewed. The injury occurred during skeletonization of the posterior semicircular canal to maximize intracranial exposure of the eighth nerve. All patients had Meniere's disease. Four patients were deafened, and in two, there was either no serviceable hearing or severe hearing impairment in the operated ear. Caution is urged in posterior semicircular canal labyrinthotomy for vertigo and attempted hearing preservation if a patient has symptoms of endolymphatic hydrops.

Craniotomy↗
PubMedDate not supplied

The orientation of the semicircular canals in the guinea pig.

In 10 adult guinea pigs the stereotaxic coordinates of a series of points along each osseous semicircular canal were analysed to yield an equation of that canal plane in stereotaxic space. Angular relationships among the canal planes and between the canal planes and the major stereotaxic planes are presented together with the optimal positions of the head for physiological stimulation of each canal or pair of synergistic canals. The planes of the semicircular canals in each labyrinth are not perpendicular to one another and the planes of contralateral synergistic canals depart from parallelism by about 30 degrees.

Acceleration↗
PubMed1975

A simple technique for thermal stimulation of single semicircular canals.

Two simple thermodes for stimulating single semicircular canals have been designed in order to elicit eye nystagmus. The first, for warm stimulation, is based on the Joule effect: a silver needle is warmed up by means of a coiled nickrome wire. The temperature at the thermode tip is function of current intensity. The thermode for cold stimulation is a device in which a circulating freezing mixture cools a silver needle. The temperature at the thermode tip is proportional to the temperature of the freezing mixture.

Animals↗
PubMed1975

Convergence of afferent impulses from individual semicircular canals of pontine reticular units.

The effect of afferent impulses on single pontine RF units was recorded by means of tungsten microelectrodes in 22 curarized guinea pigs followed thermic stimulation of individual semicircular canals. The labyrinthine stimulation consisted of short-lasting circumscribed heating (45 degrees C) of the canals through a silver thermode. Unitary response to labyrinthine stimulation was characterized by excitation and inhibition of rest discharge rate. Out of 86 units, 66 received bilateral labyrinthine influences responding in greatest number (20 units) to four semicircular canals. Only two units were unaffected. No significant difference in RF responses was noticed between concordant and antagonistic canals. Reticular formation units showed great degree of facilitation of response and convergence of impulses from the single six semicircular canals.

Action Potentials↗
PubMed1978

Fistula of the lateral semicircular canal.

The principles enunciated by Adam Politzer concerning the management of fistula of the lateral semicircular canal are as true today as they were during his time, in spite of the advances made in otologic surgery during the past 25 years or more. If a fistula of the lateral semicircular canal is suspected or proven, the patient's hearing has a greater chance of being preserved if the fistula is left undisturbed. Several illustrative cases are presented.

Adult↗
PubMed1979

Spatial position of the lateral semicircular canal in 14--60-day-old rat heads.

During growth the rat skull straightens considerably due to flexions between skull parts and individual bones. This straightening is defined as orthocephalization. Orthocephalization might also be caused by a change in head posture during growth, i.e. it may be "apparent". In order to study the significance of this phenomenon, radiographs of dried skulls of male rats, 14, 30 and 60 d of age were subjected to angular measurements between the plane of the lateral semicircular canal and the plane of foramen magnum and of the basisphenoid bone, respectively. When the plane of the lateral semicircular canal is placed horizontally, the head is claimed to be in natural position. No changes in the angulation between the lateral semicircular canal and the basisphenoid bone could be revealed, whereas the foramen magnum was shown to rotate upwards and backwards in relation to the plane of the canal. This implies that the orthocephalization which takes place between 14 and 60 d is caused only by angular changes, and that no apparent changes occur due to changes in head posture.

Age Factors↗
PubMed1975

[Responses of the units of the nerve of the frog semicircular canal to caloric stimuli of changing amplitude].

In curarized frogs, responses of isolated neural units of the lateral semicircular canal (LSC) to short local caloric stimuli of different amplitudes (0.5--12.0 degrees C over the canal temperature) inducing excitatory current of endolymph in the LSC, were studied. Estimation of maximal (peak) frequences (PF) in the responses showed the PFs in responses of 52% units (group A) to be either linearly or semilogarithmically related to peak temperature (PT). In 22% units (group B), PFs revealed saturation at PT8--12 degrees C. In 25% units (group C) PFs were related to PT first in direct and then--along with increase of PT--in reverse proportion. Duration of the group A responses is linearly for semilogarithmically related to PT. This was not observed in groups B and C. Two cases of correlation between spontaneous activity and dynamic characteristics of units from groups A and C were found. The results are in agreement with the literature references concerning data obtained in frogs using angular acceleration and stop-stimuli. The controlled caloric stimulus was concluded to be convenient for studying the dynamic characteristics of the semicircular canals afferents.

Acceleration↗
PubMedDate not supplied

The origin of slow potentials in semicircular canals of the frog.

Slow potentials generated in the sensory organ of the ampulla were recorded in isolated semicircular canals of the frog by means of fluid electrodes. These potentials, which may be picked up from the intrampullar fluid and those from the ampullar nerve appear to be generated at different stages of the process taking place in crista ampullaris. Slow intra-ampullar potentials apparently reflect receptor potentials of hair cells. They are preserved after degeneration of the nerve fibre endings and are relatively insensitive to DNP poisoning; their amplitude is maximum at high K+ concentrations. Slow nerve potentials appear to be due to electronic spreading of post-synaptic excitatory potentials generated at cytoneural junctions. They disappear after degeneration of the nerve fibres, in low Ca++ and high Mg++ solutions and are extremely sensitive to DNP poisoning. An analysis of the time-course of the slow ampullar and nerve potentials referred to the discharge of impulses in afferent fibres was performed with a view to interpreting the transduction mechanism of semicircular canals.

Animals↗
PubMedDate not supplied

Neural discharge of medial geniculate body units and single semicircular canal stimulation.

In curarized guinea pigs, 68 neurons of the medical geniculate body (MGB) were tested with vestibular and acoustic stimulations. Single semicircular canals were stimulated thermally. Convergence of acoustic and vestibular afferences on the same MGB unit was observed. Following stimulation of the semicircular canals, activation and inhibition of urinary discharge were recorded, inhibition being predominant, while, when clicks were delivered, bursts of activity occurred. The implications of MGB in vestibular and acoustic integration are postulated.

Acoustic Stimulation↗
PubMed1976

Behavior of horizontal semicircular canal afferents in alert monkey during vestibular and optokinetic stimulation.

The behavior of single vestibular nerve fibers from the lateral semicircular canal was recorded during sinusoidal oscillations of the head, during optokinetic stimulation with the head stationary, and during spontaneous oculomotor behavior in the alert monkey. The response of similar fibers to adequate vestibular stimulation was also studied in some of the animals under deeply anesthetized conditions. In the alert animals all units were spontaneously active and their discharge was modulated only by adequate vestibular stimulation. Ipsilateral horizontal rotations of the head were excitatory for all units. No modification of this basic vestibular response by visual stimulation including full-field striped drum rotation was observed. Furthermore no correlation of unit activity with oculomotor function including voluntary saccadic and pursuit eye movements was found in any of the units. The regularity of spontaneous discharge was the most consistent characteristic that differentiated the unit response into types. Most units were very regular in discharge, but a few were very irregular. The averaging of unit discharge over several cycles of oscillatory head rotation showed that the irregular type units were also consistently modulated by adequate vestibular stimulation. Both regular and irregular type units were found in the anesthetized animals. Unimodal distributions of the quantitative values for unit resting discharge rate, sensitivity, and phase relationship were found. The distributions for these three parameters were similar in the units recorded in the anesthetized animals. Thus at least these characteristics of semicircular canal response seem not to be affected by the vestibular efferent system which should be altered or eliminated in the case of the anesthetized animals.

Action Potentials↗