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At least 163 records · Page 9Linked to original sources

PubMed1980

Discharge properties of afferent fibres of the goldfish semicircular canal with high frequency stimulation.

The horizontal semicircular canals of goldfish were sinusoidally stimulated 0.07 and 63 Hz (about 3 decades). Single afferent fibre recordings showed sinusoidal modulation of discharges. Above 4 Hz the discharges became phase-locked to the stimulus. With increasing frequency the number of spikes per period decreased so that finally only one spike per period remained. At 63 Hz a stimulus of as little as 0.005 degrees was sufficient to drive the units to far above their spontaneous activity. As cupular deflection is less than the angle of body movement, the cupular deflection threshold for modulation of afferent discharges must be much less than 0.005 degrees. Transfer functions of afferent activity were determined. The simple pendulum model does not fit the data. Additional introduction of a third time constant and the low pass properties of the receptor cell membrane, the synaptic delay and the leaky integrator of the post synaptic afferent terminal improve the fit.

Animals↗

PubMed1991

Models of membrane resonance in pigeon semicircular canal type II hair cells.

Pigeon vestibular semicircular canal type II hair cells often exhibit voltage oscillations following current steps that depolarize the cell membrane from its resting potential. Currents active around the resting membrane potential and most likely responsible for the observed resonant behavior are the Ca(++)-insensitive, inactivating potassium conductance IA (A-current) and delayed rectifier potassium conductance IK. Several equivalent circuits are considered as representative of the hair cell membrane behavior, sufficient to explain and quantitatively fit the observed voltage oscillations. In addition to the membrane capacitance and frequency-independent parallel conductance, a third parallel element whose admittance function is of second order is necessary to describe and accurately predict all of the experimentally obtained current and voltage responses. Even though most voltage oscillations could be fitted by an equivalent circuit in which the second order admittance term is overdamped (i.e., represents a type of current with two time constants, one of activation and the other of inactivation), the sharpest quality resonance obtained with small current steps (around 20 pA) from the resting potential could be satisfactorily fit only by an underdamped term.

Animals↗

PubMed1991

[Selective resection of the lateral semicircular canal with hearing preservation--an animal experiment study].

The goal of our investigation was to develop a method for removing parts of the vestibular labyrinth by surgery without inducing a loss of auditory function. Three different surgical lesions were created in the lateral semicircular canal of the rabbit: (1) fenestration; (2) fibrin glue perfusion of the canal following fenestration; and (3) destruction of the semicircular canal by drilling after fenestration and fibrin glue perfusion. Brain-stem auditory potentials were recorded repeatedly up to 3 months after operation. They demonstrated preservation of hearing in all rabbits in the first group, in 78% of the second and 67% of the third group. In the last group a 20 dB deterioration of hearing was regularly noticed. Histological study revealed the utmost importance of the fibrin glue perfusion of the perilymph space of the semicircular canal inducing an interruption of the peri- and endolymph flow. A precise microsurgical technique was crucial for hearing preservation.

Animals↗

PubMed2006

Three-dimensional computed tomographic analysis of the relationship between the arcuate eminence and the superior semicircular canal.

OBJECTIVE: The location of the superior semicircular canal (SSC) is often determined intraoperatively based on its topographic association with the arcuate eminence (AE). This determination is not always possible because of the potential variability in the relationship between these two structures. The goal of this study was to describe the three-dimensional (3-D) relationship between the AE and SSC using 3-D computed tomography (CT) and to evaluate the utility of 3-D CT for preoperative planning for surgical approaches to the middle cranial fossa. METHODS: We studied 11 patients (22 sides) radiographically using 0.8- to 1-mm thick reconstructed CT images. A standard set of structural relationships was measured between the AE, SSC, and other regional landmarks. RESULTS: 3-D CT clearly demonstrated the relationships between traditional landmarks along the petrous ridge and middle cranial fossa. The relationship between the arcuate eminence and SSC was found to be highly variable. The average distance between the tips of the two structures was found to be 5.7 mm (range, 2.7-10.4 mm). CONCLUSIONS: There is significant variability in the relationship between the AE and the SSC. The AE is not a consistent or reliable landmark for identifying the precise position of the SSC. Detailed preoperative information regarding the relationship between the AE, SSC, and other bony landmarks can be easily and quickly assessed using 3-D CT.

Adolescent↗

PubMed2004

Hearing loss with semicircular canal transection and Pseudomonas aeruginosa otitis media.

OBJECTIVE: To determine if Pseudomonas aeruginosa (PA) otitis media (OM) increases the risk of sensorineural hearing loss (SNHL) with semicircular canal transection in the guinea pig model. METHODS: PA was injected transtympanically into both middle ears of pigmented guinea pigs. Saline-injected animals served as controls. Two to 4 days after injection, one horizontal semicircular canal was transected and sealed. Hearing was tested using electrocochleography before and after transection. RESULTS: PA-OM was induced in all PA-injected ears. Five days after semicircular canal transection, click-evoked thresholds were significantly elevated in ears with PA-OM (P = 0.00009) but not in saline-injected ears (P = 0.398). CONCLUSION: Violation of the inner ear in the presence of PA-OM is associated with increased risk of SNHL in the guinea pig. SIGNIFICANCE: Factors unique to PA infection may be responsible for SNHL with labyrinthine injury in humans with chronic otitis media.

Animals↗

PubMedDate not supplied

Treatment of horizontal semicircular canal benign paroxysmal positional vertigo.

We evaluated a new therapeutic maneuver-Prolonged Position on the healthy side, for Benign Paroxysmal Positional Vertigo (BPPV) of the horizontal semicircular canal. We devised this type of physical treatment in accordance with the "canalolithiasis" theory of BPPV, in order to try to free the horizontal semicircular canal of otoconial debris. We compared the results obtained by Prolonged Position with two other physical therapies by dividing our horizontal canal BPPV patients into three therapeutic groups: 1) 35 patients treated with Prolonged Position; 2) 24 patients treated with head shaking in a supine position; 3) 15 patients for whom therapy was omitted. More than 90% of the patients treated with Prolonged Position recovered within 3 days, although 6 patients out of 35 subsequently developed BPPV of the posterior semicircular canal, which then responded well to a particular repositioning maneuver. The results of Prolonged Position were significantly better than those obtained by performing head shaking or by omitting treatment. Prolonged Position can be applied to patients of all ages and general conditions and does not require hospitalization.

Adult↗

PubMed1988

Traumatic perilymphatic fistulae of the lateral semicircular canal.

Fifteen patients with perilymphatic fistulae were evaluated. Of these patients, three had CSF leaks in addition to the perilymphatic fistulae. Eight patients had fistulae of one or both windows; two had fistulae confined to the lateral semicircular canal; and two had combined fistulae of both round window and lateral semicircular canals. All improved dramatically following surgical repair. In the following study, we have shown that perilymphatic fistulae can occur in the lateral semicircular canal, and we suggest exploration of this area when indicated.

Adolescent↗

PubMed1988

[Brain stem neurons of the guinea pig that form projections into the ampullae of the anterior, lateral and posterior semicircular canals].

Brain stem neurons projecting to the ampullae of anterior, lateral and posterior semicircular canals (vestibular efferent neurons) were identified in guinea pigs using, retrograde labelling with horseradish peroxidase. Two groups of such neurons located bilaterally dorsal and ventral to the facial nerve trajectory were classified. A dorsal group contained vestibular efferent neurons to all three canals; these units were located at all the levels of the subependymal granular layer of the floor of the 4th ventricle lateral to the facial nerve genu and abducens nerve nucleus. Vestibular efferent neurons of the ventral group were distributed within different parts of parvocellular and rostral part of the caudal pontine reticular nucleus. Heterogeneity of organization of the vestibular efferent system of semicircular canal ampullae according to cell location and their morphological characteristics are discussed.

Animals↗

PubMed1990

Adenylate cyclase and carbonic anhydrase in the semicircular canal epithelium of the frog Rana esculenta. An ultrastructural cytochemical localization.

Because the secretion of endolymph has been localized in the ampullar part of the frog semicircular canal, we attempted to determine by cytochemical methods the ultrastructural localization of two enzymes that are assumed to play a role in endolymph secretion: carbonic anhydrase and adenylate cyclase. Functionally, the epithelium of the frog semicircular canal can be schematically divided into three areas: sensory (crista ampullaris), secretory (dark cells), and non-sensory and nonsecretory (transitional and undifferentiated cells) areas. Carbonic anhydrase activity was widely distributed in dark cells. Dark cell labeling disappeared in the presence of acetazolamide. The other cells of the canal did not show any carbonic anhydrase labeling except for the supporting cells of the sensory cells. Adenylate cyclase activity was found on the basolateral and apical membranes of dark cells, and on the apical membrane of sensory cells; weak labeling was also observed in the other epithelial cells. In the apical membrane of the dark cells, adenylate cyclase labeling was dependent on the presence of vasotocin, the frog antidiuretic hormone. The dark cells of the frog semicircular canal thus possess the enzyme equipment needed for the secretion of endolymph and its possible hormonal regulation.

Adenylyl Cyclases↗

PubMed1993

Synaptic organization of the vestibulo-collic pathways from six semicircular canals to motoneurons of different neck muscles.

The pattern of inputs from six semicircular canals to neck motoneurons was investigated by stimulating six ampullary nerves electrically and recording intracellular potentials from motoneurons of the rectus capitis dorsalis (RD), the complexus (COMP) and the obliquus capitis caudalis (OCA) muscles at the upper cervical cord of the cat. RD and COMP motoneurons received disynaptic excitation from bilateral anterior and contralateral horizontal ampullary nerves and disynaptic inhibition from bilateral posterior and ipsilateral horizontal ampullary nerves. OCA motoneurons received excitation from ipsilateral vertical and contralateral horizontal ampullary nerves and inhibition from contralateral vertical and ipsilateral horizontal ampullary nerves. Ipsilateral disynaptic inhibitory postsynaptic potentials and contralateral disynaptic excitatory postsynaptic potentials to these motoneurons were mediated by the medial longitudinal fasciculus (MLF) and the other postsynaptic potentials by the extra-MLF pathways. The results indicated that motoneurons of a neck muscle have its own characteristic pattern of inputs from six semicircular canals.

Animals↗

PubMed1985

[Pre- and post-synaptic activity of glutamate on preparations of the frog semicircular canal].

Glutamate (Glu) has at least two sites of action in the frog semicircular canal: the hair cell (presynaptic) and the primary afferent nerve fibres (postsynaptic). Glu's action on the hair cell results in an increased release of the natural transmitter which is responsible for a substantial increase in the frequency of firing in primary afferents. Glu produces a long-lasting depolarization in the afferent nerve fibres which does not by itself elicit any afferent discharge of impulses when the release of the natural transmitter is prevented. The difficulty of reconciling some of the observations made of the effects of Glu in semicircular canals with its presumed role as an afferent transmitter in this organ is discussed.

Animals↗

PubMed2002

The nuclear receptor Nor-1 is essential for proliferation of the semicircular canals of the mouse inner ear.

Nor-1 belongs to the nur subfamily of nuclear receptor transcription factors. The precise role of Nor-1 in mammalian development has not been established. However, recent studies indicate a function for this transcription factor in oncogenesis and apoptosis. To examine the spatiotemporal expression pattern of Nor-1 and the developmental and physiological consequences of Nor-1 ablation, Nor-1-null mice were generated by insertion of the lacZ gene into the Nor-1 genomic locus. Disruption of the Nor-1 gene results in inner ear defects and partial bidirectional circling behavior. During early otic development, Nor-1 is expressed exclusively in the semicircular canal forming fusion plates. After formation of the membranous labyrinth, Nor-1 expression in the vestibule is limited to nonsensory epithelial cells localized at the inner edge of the semicircular canals and to the ampullary and utricular walls. In the absence of Nor-1, the vestibular walls fuse together as normal; however, the endolymphatic fluid space in the semicircular canals is diminished and the roof of the ampulla appears flattened due to defective continual proliferative growth of the semicircular canals.

Animals↗

PubMed1988

The induction and compensation of asymmetric eye movements following unilateral blockage of a horizontal semicircular canal in the rabbit.

The influence of unilateral plugs of the left horizontal semicircular canal (LHC plugs) of rabbits on the development and compensation of asymmetric eye movements evoked by horizontal vestibular stimulation was studied. LHC plugs caused an immediate reduction of 50-65% in the gain of the horizontal vestibuloocular reflex (HVOR). This reduction in gain was achieved without altering the symmetry of the HVOR, and was accompanied by a change in the axial alignment of eye movements evoked by vestibular stimulation about the vertical (HVOR) and longitudinal (VVOR) axes. Postoperative asymmetry of eye movements developed 12-48 hr after the plugging operation. The development of asymmetry was reduced if the rabbit was restrained for 24 hr, thereby minimizing vestibular stimulation following the plugging operation. Over a 3-4 week period, the normal symmetry of eye movements was restored and the axial alignments of the HVOR and VVOR returned to the preoperative values. The gain of the HVOR did not recover. The horizontal cervicoocular reflex (HCOR) was examined before the plugging operation and after compensation of asymmetry was complete. The gain and phase of the HCOR were not altered. A relatively simple set of explanations at a cellular level is proposed to account for the induction and compensation of asymmetric eye movements following a unilateral plug of the horizontal semicircular canal.

Adaptation, Physiological↗

PubMed1996

Adaptation of primate vestibuloocular reflex to altered peripheral vestibular inputs. I. Frequency-specific recovery of horizontal VOR after inactivation of the lateral semicircular canals.

1. The adaptive plasticity of the vestibuloocular reflex (VOR) following a selective lesion of the peripheral vestibular organs was investigated in rhesus monkeys whose lateral semicircular canals were inactivated by plugging of the canal lumen in both ears. Gain and phase of horizontal, vertical, and torsional slow-phase eye velocity were determined from three-dimensional eye movement recordings obtained acutely after the plugging operation, as well as in regular intervals up to 10 mo later. 2. Acutely after plugging, horizontal VOR was minimal during yaw rotation with gains of < 0.1 at all frequencies. Horizontal VOR gain gradually increased over time, reaching gains of 0.4-0.5 for yaw oscillations at 1.1 Hz approximately 5 mo after lateral canal inactivation. This response recovery was strongly frequency dependent: horizontal VOR gains were largest at the highest frequency tested and progressively decreased for lower frequencies. Below approximately 0.1 Hz, no consistent horizontal VOR could be elicited even 10 mo after plugging. 3. The frequency-dependent changes in gain paralleled changes in horizontal VOR phase. Below approximately 0.1-0.05 Hz large phase leads were present, similarly as in semicircular canal primary afferents. Smaller phase leads were also present at higher frequencies, particularly at 1.1 Hz (the highest frequency tested). 4. Consistent with the afferent-like dynamics of the adapted horizontal VOR, per- and postrotatory horizontal responses to constant-velocity yaw rotations were short lasting. Time constants of the slow-phase eye velocity envelope of the horizontal postrotatory nystagmus were approximately 2 s. Nonetheless, a consistent horizontal optokinetic afternystagmus was evoked in plugged animals. 5. A torsional component that was absent in intact animals was consistently present during yaw rotation acutely after lateral canal inactivation and remained approximately constant thereafter. The frequency response characteristics of this torsional component resembled those of the adapted horizontal slow-phase responses: gain decreased and large phase leads were introduced at frequencies below approximately 0.05-0.1 Hz. Torsional responses elicited by roll oscillations in supine position, on the other hand, were indistinguishable in their dynamics from intact animals. No consistent vertical nystagmus was elicited during yaw rotation. 6. Our results show that there is a slow, frequency-specific recovery of horizontal VOR after selective inactivation of the lateral semicircular canals. Both the spatial organization and the dynamic properties of the adapted VOR responses are distinctly different from responses in intact animals, suggesting complex changes in the underlying vestibuloocular circuitry.

Adaptation, Physiological↗

PubMed2004

Function of semicircular canals, utricles and saccules in deaf children.

OBJECTIVE: To study vestibular function in deaf children. MATERIAL AND METHODS: In 36 deaf children the function of the semicircular canals, saccules and utricles was measured by means of caloric testing, recordings of vestibular-evoked myogenic potentials (VEMPs) and measurements of the subjective visual horizontal (SVH) at different body tilts, respectively. RESULTS: In total, 30% of subjects had caloric hypo- or areflexia and 24% had a caloric asymmetry. VEMPs were weak or absent bilaterally in 22% of cases, and asymmetric in 19%. Regarding the utricle, 17% of subjects had a pathologically reduced perception of roll tilt to both sides and 25% had an asymmetry. In total, 30% of subjects were pathologic in all 3 tests and 30% were completely normal. Semicircular canal function correlated best with the function of the saccule. If hearing was better than 90 dB (pure-tone average of 0.5, 1.0 and 2.0 kHz) vestibular function was often normal. For hearing levels of 100-120 dB, otolith function declined significantly. CONCLUSIONS: Vestibular function tends to be preserved up to a point where hearing is nearly extinct. Hearing level correlates more closely with otolith function, especially that of the utricle, than with semicircular canal function.

Adolescent↗

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↗

PubMed2002

Convergence of ipsilateral semicircular canal inputs onto single vestibular nucleus neurons in cats.

Convergent inputs from the ipsilateral semicircular canal nerves onto single vestibular nucleus neurons were investigated in decerebrate cats using intracellular recording after selective stimulation of each ampullar nerve. One hundred and seventy-four neurons were activated by stimulating the anterior semicircular (AC) and/or posterior semicircular canal (PC) nerves. These neurons were also antidromically stimulated and classified according to the pattern of their collateral projections to the oculomotor complex and the spinal cord. Four types were found: vestibulo-ocular (VO), vestibulospinal (VS), vestibulo-oculospinal (VOS), and vestibular (V) neurons, the latter of which were not activated by stimulation of either the oculomotor complex or the spinal cord. Of 174 AC- and/or PC-activated vestibular nucleus neurons, 32 (18%) received convergent inputs from both nerves. These convergent neurons included 11 VS, 6 VOS, and 15 V neurons. We found no VO neurons with convergent input. The vast majority (82%) of AC/PC-activated VS and VOS convergent neurons received excitatory inputs from both nerves, 12% received reciprocal inputs (i.e., excitatory from one and inhibitory from the other), and the remaining neurons received inhibitory inputs from both nerves. By stimulating the horizontal semicircular (HC) and/or PC nerves, 183 neurons were activated. Of these, 44 (24%) received convergent inputs from both nerves. These convergent neurons included 19 VS, 5 VOS, 2 VO, and 18 V neurons. Approximately one-half (46%) of HC/PC-activated VS and VOS convergent neurons received excitatory inputs from both nerves and 42% received reciprocal inputs, and the remaining neurons received inhibitory inputs from both nerves. In both nerve pairs, the percentage of VS neurons was higher (AC/PC, 34%; HC/PC, 43%) than that of VOS or VO neurons. Approximately half of these convergent neurons were located in the lateral nucleus. These results suggest that, during mixed angular head accelerations, the vestibulocollic reflex may be partly accomplished by VS and VOS convergent neurons.

Afferent Pathways↗

PubMed1997

Argon laser irradiation to the semicircular canal.

In order to elucidate the effects of argon laser irradiation on the lateral semicircular canal of the guinea pig, the vestibular labyrinth was histologically studied after irradiation, using the conventional celloidin method. Irrigation of the external meatus with ice water was used to evaluate the function of the semicircular canal by recording caloric nystagmus. When irradiation was performed, a laser probe was approximated to the lateral canal, 0.5 to 1 mm away from the surface of the canal. Each time, power applied was 1.0 W on the dial of the laser machine. The duration of irradiation was 0.5 s. The lateral canal was irradiated one to 15 times. Twenty-five to 87 days after irradiation, the temporal bones were fixed in Heidenhein-Susa solution, removed, and subjected to celloidin processing. The irradiated bony wall of the lateral canal demonstrated charring. Lucent areas were observed around and under the charred area. The semicircular duct showed shrinkage with disappearance of the trabecular mesh. New bone formation was observed along the endosteum of the irradiated area. The lateral canal was completely occluded by ossification with or without fibrosis when sufficient energy was applied. The anterior and posterior canals were normal. Caloric tests using 5 mL of ice water for 5 s failed to elicit nystagmus on the irradiated side.

Animals↗