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At least 433 records · Page 24Linked to original sources
PubMed2006

Axonal pathways and projection levels of anterior semicircular canal nerve-activated vestibulospinal neurons in cats.

Using collision tests of orthodromically and antidromically generated spikes, we studied the axonal pathways, axonal projection levels, and soma location of anterior semicircular canal (AC) nerve-activated vestibulospinal neurons in decerebrate cats. AC nerve-activated vestibulospinal neurons (n=74) were mainly located in the ventral portion of the lateral vestibular nuclei and the rostral portion of the descending vestibular nucleus, which is consistent with previous studies. Of these neurons, 15% projected through the ipsilateral (i-) lateral vestibulospinal tract (LVST), 74% projected through the medial vestibulospinal tract (MVST), and 11% projected through the contralateral (c-) LVST. The vast majority (78%) of AC nerve-activated vestibulospinal neurons were activated antidromically only from the cervical segment of the spinal cord; 15% of neurons were activated from the T1 segment and only one neuron was activated from the L3 segment. AC nerve-activated vestibulospinal neurons may primarily target the neck muscles and thus contribute to the vestibulocollic reflex. Most of the c-LVST neurons were also activated antidromically from the oculomotor nucleus, suggesting that they are closely related to the control of combined eye-head movements.

Action Potentials↗
PubMed1976

Analysis of afferent responses from isolated semicircular canal of the guitarfish using rotational acceleration white-noise inputs. I. Correlation of response dynamics with receptor innervation.

The small-signal linear characteristics of afferent responses from the isolated semicircular canal were described by the use of white-noise rotational acceleration inputs. The results, based on cross-correlation analysis, showed a striking and systematic variation in linear system impulse response characteristics from afferents which innervated different regions of the receptor. Afferents from centrally located nerve bundles innervating the crest region of the crista exhibited an initial maximum response amplitude followed by a rapid decay. In contrast, afferents from extreme rostral and caudal nerve bundles innervating the crista slopes exhibited an initial rise up to a low-amplitude maximum followed by a slower decay. These results imply that the afferents innervating a single canal do not merely carry redundant information concerning current head acceleration, but could be considered an ensemble of specific classes of filters that are tuned individually to specific classes of head movements. On the basis of these considerations, a new hypothesis of matched filter detection was proposed as relevant to information processing and dynamic control in central vestibular pathways.

Animals↗
PubMed1983

Response of cat semicircular canal afferents to sinusoidal polarizing currents: implications for input-output properties of second-order neurons.

1. We studied the response of cat vestibular afferents, most likely innervating the semicircular canals, to sinusoidal polarizing currents applied to an electrode implanted near the horizontal ampulla. 2. Electrode implantation abolished responses to natural stimulation and reduced the level of resting activity compared to a population of afferents from unimplanted animals. The distribution of coefficients of variation of resting activity was, however, similar to that seen when the labyrinth is intact. 3. Many fibers were modulated sinusoidally by polarizing currents in the frequency range 0.175-4 Hz. Phase was mainly constant and typically led stimulus negativity by approximately 14 degrees, although about half the regular fibers had a phase lead that increased with frequency. Mean sensitivity (spikes X s-1 X microA-1) of regular and irregular fibers increased by a factor of about 1.5 over the frequency studied. Absolute sensitivity was about 7 times higher for irregular than for regular fibers. The overall behavior of the afferents could be well described by a transfer function in the form, sk, with 0 less than k less than 1. 4. We compared the response of afferent fibers to sinusoidal current with the response of second-order neurons studied under similar conditions in earlier experiments (15, 23). While the slopes of the sensitivities were similar, second-order neurons developed a phase advance over afferents at frequencies around 1 Hz. This difference in dynamics can be described by a transfer function in the form tau S + 1, with tau = 12 ms. This predicts that second-order neurons can develop a phase lead of about 25 degrees with respect to afferents at 6 Hz, a frequency still in the physiological range. It remains to be determined whether this applies to a particular subset of second-order neurons contributing to vestibulocollic reflexes.

Afferent Pathways↗
PubMed1990

Bilateral semicircular canal aplasia with near-normal cochlear development. Two case reports.

Congenital malformations of the vestibular labyrinth (pars superior) are rare. We present two patients with computed tomographic findings of bilateral semicircular canal aplasia with normal or near-normal cochleas. Initial bone conduction thresholds were within normal limits, although both patients had significant conductive hearing losses due to congenital middle ear malformations. Bithermal caloric responses were absent in both. To our knowledge these are the first reports of vestibular aplasia concomitant with normal or near-normal cochlear development. These findings conflict with conventional hypotheses that state that inner ear malformations result from arrested development during the normal stages of inner ear embryogenesis.

Adult↗
PubMed1988

Planar relations of semicircular canals in awake, resting turtles, Pseudemys scripta.

As part of a project aimed at elucidating mechanisms of vestibulocollic control in the red-eared turtle Pseudemys scripta, we have calculated the planar relations of its semicircular canals using principal-components analysis. This information is prerequisite to understanding the pattern of canal activation that is set up by head movement of any spatial form. In addition, we have developed a method for monitoring canal orientation in an awake, behaving animal, and we have used this technique to assess canal position in resting turtles. Our results indicate that ipsilateral canals in Pseudemys are not mutually orthogonal, nor are complementary canals precisely coplanar, although they approach this idealized condition more closely than do the canals of several other vertebrates for which quantitative data exist. One significant departure from the perfectly orthogonal configuration is that both verical canals are rotated slightly toward the frontal plane; thus, Pseudemys should be somewhat more sensitive to head roll than to head rotation in other planes. Radiographic analyses of awake, resting turtles indicate that the anterior interparietal suture is held aligned with the earth horizontal and midsagittal plane. The horizontal canal is pitched up (open anterior) 3-4 degrees relative to the earth horizontal.

Animals↗
PubMed1978

Cupular movement and nerve impulse response in the isolated semicircular canal.

The aim of the study was to record nerve impulse responses to controlled displacements of the cupula and relate these to observations of cupular motion. The preparation was the skate semicircular canal, isolated and maintained in a chamber. The canal was cut and tied tightly to an oil-filled tube driven by a 1 microliter syringe. In some experiments dye was used to make the face of the cupula visible. Small volume displacements (0.02 microliter) caused a billowing of the central portion of the cupula, whereas for repeated large displacements (0.1 microliter) the top of the cupula moved along the roof of the ampulla. Displacements of the latter amount were close to saturation in the characteristic functions (spike rate versus volume displacement) of nerve firing. It seems that the discharge rate of tonically responding units in the skate crista ampullaris rather faithfully record the force acting on the cupula. The motion of the base of the cupula rather than its tip appears to be the relevant parameter in setting the level of excitation in the sensory cells within the physiological range of stimulation. Such a mode of operation would ensure the highest sensitivity of the sense organ.

Animals↗
PubMed2006

Three-dimensional analysis of benign paroxysmal positional nystagmus in a patient with anterior semicircular canal variant.

OBJECTIVE: To show the positional nystagmus in a patient who had suffered from benign paroxysmal positional vertigo (BPPV) that was thought to be caused by involvement of the anterior semicircular canal (ASCC) (A-BPPV). STUDY DESIGN: Retrospective case report. SETTING: City hospital. PATIENT: The present study reports a rare case of A-BPPV in a 41-year-old woman. CASE REPORT: The patient is 41-year-old woman who developed a positional vertigo after playing volleyball on March 22, 2005 and consulted our hospital the next day. When left Dix-Hallpike maneuver was performed, she showed a positional nystagmus of which fast phase direction of the torsional component was clockwise while that of the vertical component was downward. We plotted the slow phase eye velocity of the positional nystagmus during the left Dix-Hallpike maneuver on three-dimensional coordinates that showed the axis of the positional nystagmus to be perpendicular to the plane of the right ASCC. CONCLUSION: These results suggested that the patient was suffering from A-BPPV.

Adult↗
PubMed1983

Central projections of vestibular afferents from the horizontal semicircular canal in the carpet shark Cephaloscyllium isabella.

This study utilizes anterograde axonal transport of cobaltous-lysine and conventional silver-staining techniques to study the central projections of the horizontal semicircular canal branch of the VIII nerve within the vestibular nuclei of the carpet shark Cephaloscyllium isabella. Two major terminating axon fields were observed, one caudal and one rostral to the entrance of the VIII nerve, corresponding to the ventral vestibular nucleus and superior vestibular nucleus, respectively. Both fields appear to be located within the ventral portion of the nuclei indicating an apparent subdivision of the VIII nerve projections within the brainstem. The resolution of the sensitive cobalt tracer indicates the presence of both dendritic and pericellular termination of these primary afferent fibres. In the area immediately caudal to the entrance of the VIII nerve a number of labelled primary afferent fibres project to the ventral region of the intermediate nucleus. Other fibres follow the visceral sensory root VII and terminate proximal to the sulcus limitans of His within the dendritic field of the neurons of the nucleus magnocellularis. Some fibres turn ventromedially from the main group of the ascending fibres and terminate in the area of the inferior reticular formation.

Afferent Pathways↗
PubMed2005

Preoperative antibiotic and steroid therapy and hearing loss caused by semicircular canal transection in pseudomonas otitis media.

OBJECTIVE: The purpose of this experiment was to determine whether preoperative administration of antibiotics and corticosteroids can attenuate the severity of hearing loss (HL) with semicircular canal (SC) transection in a guinea pig model of Pseudomonas aeruginosa (PA) otitis media (OM). Study design and setting Prospective and controlled. METHODS: OM was induced in 64 pigmented guinea pigs by bilateral, transtympanic injection of PA. Two to 4 days later, 1 horizontal SC was randomly transected. In the 1st series, antibiotic therapy was initiated either immediately before or after surgery. In the 2nd series, all animals received preoperative antibiotics, and half received dexamethasone before surgery. Hearing was tested before and after surgery. RESULTS: PA was recovered in all ears. SC transection was associated with significant HL. HL was better in animals given antibiotics preoperatively (clicks, 16 versus 32 dB, P = 0.0220). Addition of preoperative steroids did not significantly further reduce HL (7 versus 14 dB for clicks, P = 0.6919). CONCLUSIONS: HL caused by SC transection in PA OM may be attenuated with preoperative antibiotic therapy in the guinea pig.

Animals↗
PubMed2004

Semicircular canal fenestration - improvement of bone- but not air-conducted auditory thresholds.

Auditory stimulation can, under certain circumstances, activate the vestibular end organs and this is facilitated by fenestration of a semicircular canal (SCC). Several fenestrated profoundly deaf patients reported improvements in their bone- (BC) but not air-conducted (AC) thresholds. Bone conduction auditory thresholds have been reported to be better than normal in several patients with thinning or absence of bone over a SCC (dehiscence). This phenomenon was carefully studied in the fat sand rat (Psammomys obesus) by recording auditory brainstem evoked responses to BC and AC auditory stimulation, before and after SCC fenestration. Fenestration would be expected to decrease the pressure difference across the cochlear partition, causing a reduction in the amplitude of the classical base to apex input traveling wave, and should therefore lead to an elevation in AC and BC thresholds. Instead, BC thresholds decreased (i.e. improved) following fenestration (by 7.0+/-4.2 dB; P<0.005), while AC thresholds did not change. Thus the cochlea becomes more sensitive to BC, but not AC, stimulation in the presence of a SCC fenestration. This may be due to the removal by the fenestration of a factor impeding BC cochlear responses, or by the addition of a facilitating factor. The result that the SCC fenestration did not affect AC threshold provides support for the concept that at low intensities the outer hair cells are directly activated by components of the fluid pressures surrounding them, which alternate at audio-frequencies. These cochlear fluid audio-frequency pressures are induced by stapes footplate movement and not by a base to apex input traveling wave. The audio-frequency pressures would not be affected by SCC fenestration. The outer hair cell motility thus induced somehow excites the inner hair cells and the auditory nerve fibers. At low intensities the outer hair cell motility causes localized displacement at the appropriate position on the basilar membrane.

Acoustic Stimulation↗
PubMed1996

Enhanced retrosigmoid exposure with posterior semicircular canal resection.

A subset of patients with acoustic neuromas and useful hearing have tumors that are inadequately approached by both middle fossa and retrosigmoid techniques. The enhanced retrosigmoid technique combines the hearing preservation of posterior semicircular canal ablation to achieve lateral internal auditory canal exposure with the ample cerebel-lopontine angle exposure of the standard retrosigmoid technique.

Cerebellopontine Angle↗
PubMed1990

Axonal trajectories of inhibitory vestibulocollic neurons activated by the anterior semicircular canal nerve and their synaptic effects on neck motoneurons in the cat.

Somatic location, axonal trajectories and synaptic effects of inhibitory vestibulocollic neurons which were activated by selective stimulation of the anterior semicircular canal nerve (ACN) were studied in the anesthetized cat. ACN stimulation evoked disynaptic inhibitory postsynaptic potentials (IPSPs) in neck flexor motoneurons. This was seen in all the (64/64) tested motoneurons innervating the ipsilateral (i-) longus capitis (LC) and the i-sternocleidomastoideus (SCM) muscles and in 86% (38/44) of the motoneurons innervating the contralateral (c-) LC muscle. The inhibitory relay neurons, identified by orthodromic and antidromic responses to stimulation of the ACN and the i- and c-LC motoneuron pools, were classified as VCi (vestibulocollic neurons sending an axon to the i-LC motoneuron pool) and VCc (vestibulocollic neurons sending an axon to the c-LC motoneuron pool) neurons. Neither VCi nor VCc neurons were activated antidromically by localized stimulation of the ascending medial longitudinal fasciculus (asc. MLF) or the 3rd nuclei. They were located in the medial, descending and ventral lateral vestibular nuclei. It was also observed that VCi neurons produced unitary IPSPs in i-LC and i-SCM motoneurons in the C1 segment. Inhibitory synapses were estimated to be on the cell somata and/or the proximal dendrites of the motoneurons.

Animals↗
PubMed1991

Synaptic bodies and vesicles in the calix type synapse of chicken semicircular canal ampullae.

Calix afferent fibers generate depolarizing DC (direct current) and superimposed AC (alternating current) potentials in response to a vibrating stimulation of the hair bundle in an isolated preparation of a chicken semicircular canal ampulla. The wave form of the postsynaptic potential appears similar to the transduction potential of hair cells, which suggests electrical transmission in the calix type synapse. However, synaptic bodies and vesicles were found by EM observation instead of gap junctions in the hair cell presynaptic to the calix afferent. The number of synaptic body was 11-12/hair cell. These structures support chemical transmission in the calix type synapse.

Animals↗
PubMed1976

[Action of vestibular receptors pn the spontaneous afferent activity of an ipsilateral semicircular canal in the frog].

In the frog, the influence of both the part of the efferent system which depends on ipsilateral vestibular inputs and the receptor-receptor fibre system on the afferent activity of semicircular canals is either null or facilitatory. The receptor-receptor fibre system being inhibitory, it seems that the part of the efferent vestibular activity which depends on ipsilateral vestibular inputs is facilitatory, which agrees with previous results.

Animals↗
PubMed2004

Far advanced otosclerosis and intractable benign paroxysmal positional vertigo treated with combined cochlear implantation and posterior semicircular canal occlusion.

This paper presents a combined procedure for the management of intractable benign paroxysmal positional vertigo (BPPV) and profound hearing loss in a patient with far advanced otosclerosis. The procedure comprised of a posterior semicircular canal occlusion and cochlear implantation as one combined procedure in the same ear. The combined approach added little to the operative morbidity and proved effective in this patient's management. A search of the literature reveals this to be a unique case.

Cochlear Implantation↗
PubMed1989

Studies of solitary semicircular canal hair cells in the adult pigeon. I. Frequency- and time-domain analysis of active and passive membrane properties.

1. Hair cells were enzymatically dissociated from the neuroepithelium (cristae ampullares) of the semicircular canals of white king pigeons (Columba livia). Those hair cells determined to be type II by an anatomic criterion, the ratio of the minimum width of the neck to the width of the cuticular plate, were studied with the use of the whole cell patch-clamp technique. 2. The mean +/- SD zero-current membrane potential, Vz, was found to be -54 +/- 12 mV for anterior crista hair cells (n = 71), -62 +/- 14 mV for posterior crista hair cells (n = 14), and -55 +/- 12 mV for lateral (horizontal) crista hair cells (n = 18). The mean +/- SD value of Vz for hair cells from all cristae (n = 103) was -56 +/- 13 mV. 3. Active and passive membrane properties were calculated in the time domain, in voltage- or current-clamp mode, from responses to voltage or current pulses and, in the frequency domain, by fitting a membrane model to admittance magnitude and phase data resulting from current responses to sum-of-sines voltages at different d.c. levels of voltage-clamp membrane potential. 4. The average value +/- SE of input resistance (Rin), over the range from -100 to -60 mV, was found to 1.5 +/- 0.3 G omega from a mean-voltage-as-a-function-of-current plot, V-I, (n = 7) and a mean of 1.4 +/- 0.3 G omega from individual (n = 15) current-as-a-function-of-voltage plots, I-V. A lower mean value 0.8 +/- 0.4 G omega was obtained for the input resistance from frequency-domain calculations for a different set of cells (n = 21). Also, in two different sets of cells, average input capacitance (Cin) was determined to be 12 +/- 3 pF (n = 7) from time-domain estimates and 14 +/- 3 pF (n = 21) from frequency-domain estimates. The (Rin)(Cin) product was 11 ms based on frequency-domain estimates and 17 ms from time-domain estimates. 5. I-V curves for hair cells voltage clamped at -60 mV showed some anomalous rectification for hyperpolarizations between -60 and -120 mV but no detectable N-shape for depolarizations between -50 and 90 mV. The I-V relation showed increasing slope with depolarization through the resting potential (Vz) and increased linearly between -40 and 80 mV; the best-fit straight-line maximum slope conductance for six cells over this range was 17.4 +/- 0.3 nS.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

The contribution of the horizontal semicircular canals to the response to off-vertical-axis rotation in the cat.

The response to off-vertical-axis rotation (OVAR) was measured in cats under circumstances in which the signals from the horizontal semicircular canals and otoliths were opposed. Opposition was achieved by sudden acceleration or deceleration during constant velocity OVAR. The degree of opposition was expressed as a canal/otolith ratio where a ratio of unity indicated agreement. For a canal/otolith ratio of 1, the OVAR gain (eye velocity/stimulus velocity) was 0.73 (+/- 0.13). The steady-state OVAR response was, however, reduced if the canals and otoliths were opposed. The reduction depended on the degree of opposition with a fall-off of 0.15 gain/(unit of canal/otolith ratio). These findings are discussed with respect to the central velocity store and the mechanism underlying the generation of the OVAR response.

Acceleration↗