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At least 235 records · Page 13Linked to original sources
PubMed1991

Antidiuretic hormone stimulation of adenylate cyclase in semicircular canal epithelium.

Basal adenosine 3',5'-cyclic monophosphate (cAMP) content and the modulation of its production were studied in the frog's semicircular canal epithelium. This epithelium secretes endolymph, a K(+)-rich, positively polarized fluid. The basal cAMP content measured by microradioimmunoassay was 244 +/- 14.2 fmol/structure per 5 min (n = 30). This content was increased about 8 times by 10(-5) M forskolin. Vasotocin, the frog antidiuretic hormone, increased the cAMP production by factors of 1.3 and 3.3 at concentrations of 10(-8) M and 10(-7) M, respectively. This stimulatory effect of vasotocin was blunted by the addition of alpha 2-adrenergic agonists, such as 10(-8) M-10(-5) M norepinephrine, in the presence of 10(-5) M propranolol, or 10(-5) M clonidine. Prostaglandin E2 at a concentration of 10(-8) M, which did not affect the cAMP production, did not modify the response to vasotocin. Glucagon (10(-6) M), calcitonin (10(-6) M), and parathyroid hormone (10 units/ml) did not affect the cAMP content. Prostaglandin E2 (10(-7) M) and the beta-adrenergic agonist isoproterenol (10(-6) M) stimulated the cAMP production by a factor of 1.6. These results indicate that the frog semicircular canal is a target of both vasotocin and catecholamines and that catecholamines through alpha 2-receptors modulate vasotocin-induced cAMP generation. Further, this interaction might be of physiological relevance in the modulation of ion transport in this structure.

Adenylyl Cyclases↗
PubMed1992

Streptomycin blocks the afferent synapse of the isolated semicircular canals of the frog.

This study aimed to define the acute electrophysiological effects of the perilymphatic perfusion of streptomycin in the sensory apparatus of the semicircular canals of the frog. The ampullary DC potential, the vestibular nerve multiunit discharge, the nerve DC potential and the unitary EPSP activity were recorded in isolated semicircular canals of the frog (Rana esculenta L). The results demonstrated that perilymphatic microperfusion of streptomycin (0.1, 0.3, 1 and 3 mM) reduced both resting and mechanically evoked afferent discharge, while the response of the hair cells remains unchanged. Intracellular recordings from single afferent axons showed that the reduction of the afferent discharge was mainly due to a reduction of the amplitude, but not the frequency, of the EPSPs. These results indicate that streptomycin, when applied in the fluid bathing the synaptic pole of the sensory cells, can act as an antagonist of the vestibular afferent transmitter at the postsynaptic level.

Afferent Pathways↗
PubMed2000

Sudden unilateral hearing loss with simultaneous ipsilateral posterior semicircular canal benign paroxysmal positional vertigo: a variant of vestibulo-cochlear neurolabyrinthitis?

We describe 4 patients who all simultaneously developed a sudden total or partial unilateral sensorineural hearing loss and an unusual acute peripheral vestibulopathy in the same ear characterized by posterior semicircular canal benign paroxysmal positional vertigo with intact lateral semicircular canal function. Two patients also had ipsilateral loss of otolith function. The vertigo resolved in all 4 patients after particle-repositioning maneuvers. The findings of audiometry and vestibular tests indicated that the lesion responsible for this syndrome was probably located within the labyrinth itself rather than within the vestibulocochlear nerve and that it was more likely a viral vestibulocochlear neurolabyrinthitis than a labyrinthine infarction.

Adult↗
PubMed1988

Ultrastructural study of the semicircular canal cells of the frog Rana esculenta.

The ultrastructure of the nonsensory cells (dark cells, transitional cells, and undifferentiated cells) of the frog semicircular canal was studied by using transmission electron microscopy in an attempt to correlate the structure with the functions of these epithelial cells. All the nonsensory cells were linked by tight junctions and desmosomes; this suggested that there is little paracellular ionic transport from perilymph to endolymph. In the dark cell epithelium, the apical intercellular spaces were dilated; in the basal part, numerous basolateral plasma membrane infoldings, containing mitochondria, delimited electron-lucent spaces. The undifferentiated cells and the transitional cells were devoid of any basal membrane infolding. Surrounding the semicircular canal, very flattened and interdigitated mesothelial cells constituted a thin multilayer tissue which limited the perilymphatic space. The morphological aspect of the dark cells suggests that they may play a role in the secretion and/or in the reabsorption of endolymph, which bathes the apical pole of these cells. The undifferentiated and transitional cells can play a role in the maintenance of the endolymphatic ionic composition because of their apical tight junctions and desmosomes.

Animals↗
PubMed1999

Vestibular-evoked myogenic potentials in patients with dehiscence of the superior semicircular canal.

Recently Minor and co-workers described patients with sound- and pressure-induced vertigo due to dehiscence of bone overlying the superior semicircular canal. Identifying patients with this "new" vestibular entity is important, not only because the symptoms can be very incapacitating, but also because they are surgically treatable. We present symptoms and findings for three such patients. On exposure to sounds, especially in the frequency range 0.5-1 kHz, they showed vertical/torsional eye movements analogous to a stimulation of the superior semicircular canal. They also showed abnormally large sound-induced vestibular-evoked myogenic potentials (VEMP), i.e. the short latency sternomastoid muscle response considered to be of saccular origin. The VEMP also had a low threshold, especially in the frequency range 0.5-1 kHz. However, in response to saccular stimulation by skull taps, i.e. when the middle ear route was bypassed, the VEMP were not enlarged. This suggests that the relation between the sound-induced and the skull tap-induced responses can differentiate a large but normal VEMP from an abnormally large response due to dehiscence of bone overlying the labyrinth, because only the latter would produce large sound-induced VEMP compared to those induced by skull taps.

Adult↗
PubMed2002

Inactivation of semicircular canals causes adaptive increases in otolith-driven tilt responses.

Growing experimental and theoretical evidence suggests a functional synergy in the processing of otolith and semicircular canal signals for the generation of the vestibulo-ocular reflexes (VORs). In this study we have further tested this functional interaction by quantifying the adaptive changes in the otolith-ocular system during both rotational and translational movements after surgical inactivation of the semicircular canals. For 0.1-0.5 Hz (stimuli for which there is no recovery of responses from the plugged canals), pitch and roll VOR gains recovered during earth-horizontal (but not earth-vertical) axis rotations. Corresponding changes were also observed in eye movements elicited by translational motion (0.1-5 Hz). Specifically, torsional eye movements increased during lateral motion, whereas vertical eye movements increased during fore-aft motion. The findings indicate that otolith signals can be adapted according to a compromised strategy that leads to improved gaze stabilization during motion. Because canal-plugged animals permanently lose the ability to discriminate gravitoinertial accelerations, adapted animals can use the presence of gravity through otolith-driven tilt responses to assist gaze stabilization during earth-horizontal axis rotations.

Adaptation, Physiological↗
PubMed2001

Regional distribution of calcium currents in frog semicircular canal hair cells.

In the present work we studied the regional expression of voltage-dependent Ca channels in hair cells from the frog semicircular canals, employing whole-cell patch-clamp on isolated and in situ hair cells. Although Ca channels are thought to play a major role in afferent transmission, up to now no data were available regarding their distribution in vestibular organs. The problem appears of interest, especially in the light of recent results showing the presence of multiple Ca current components in semicircular canal hair cells. Our data suggest the presence, in all regions of the crista ampullaris, of two classes of cells, one displaying an inactivating Ca current (R1) and one lacking it. In the former cells, Ca current amplitude decreased from the central to the peripheral zone (the maximal currents being observed in the intermediate zone). Only L-type and R2 current components displayed regional differences in expression, whereas the size and properties of R1, although variable among cells, were not regionalized. However, in cells lacking R1, Ca current amplitudes were similar regardless of cell shape and location. The possible contributions of this Ca current distribution to afferent discharge properties are discussed.

Animals↗
PubMed1993

[Fenestration of semicircular canal for congenital microtia].

The purpose of this paper is to present a surgical method for microtia(small auricle, small external audiotory meatus and small tympanic membrane). 7 cases received fenestration of semicircular canal. During the operation it was found that the patients had congenital absence of oval windows and stapes, significant low position of horizontal facial canal covering the oval windows. It was impossible to perform labyrinthotomy in these patients. The only choice of operation is fenestration of semicircular canal. 7 ears underwent the operation as described. 6 weeks-21 months follow-up showed that all of the 7 ears achieved good hearing results. Range of hearing gain was 35-40 dB and bone-air gap was 25-30 dB.

Adolescent↗
PubMed1991

Human and animal semicircular canal function during circular walking.

It is generally accepted from animal studies that the medial vestibulospinal tract originates in the medial vestibular nucleus, which is supplied from the semicircular canals, and descends only to the upper thoracic levels of the cord. In humans, however, there is some indirect evidence to support the concept that impulses from the semicircular canals reach the lumbosacral cord and influence lower as well as upper extremity activity.

Animals↗
PubMedDate not supplied

Planar relationships of the semicircular canals in man.

Principal-component analyses were determined on a series of points measured from the dissected bony labyrinth of ten human skulls, resulting in planar equations for each of the six semicircular canals. Following this, angles were calculated between the ipsilateral canal planes, between opposite synergistically acting canal planes and between each canal and the Reid stereotaxic planes. Results indicated that pairs of ipsilateral canals were nearly perpendicular, with the excpetion of the angle formed between the anterior and horizontal canal (mean = 111 degrees). Pairs of contralateral synergistic canal planes formed angles of 19 degrees between right and left horizontal canal planes and 23-24 degrees between vertical canal pairs. The horizontal canals formed an angle of 25 degrees with the Reid horizontal plane. Mathematical equations of the semicircular canals were used to predict the optimal head position for rotational and caloric stimulation.

Humans↗
PubMed1991

Adenylate cyclase in the semicircular canal. Hormonal stimulation and ultrastructural localization.

The modulation of the cyclic AMP (cAMP) production and the cytochemical localization of adenylate cyclase were studied in isolated semicircular canal epithelium of the frog. The basal cAMP content, as measured by radioimmunoassay, was 344 +/- 37.8 fmoles/structure/5 min (mean +/- SEM, n = 41). This content was increased 6- to 8-fold by forskolin (10(-7) M to 10(-5) M). Among the tested drugs, only prostaglandin E2, isoproterenol, and vasotocin increased the cAMP production: 1.7-fold by prostaglandin E2 (1.5 X 10(-7) M) and isoproterenol (10(-6) M), and 1.3- and 3.3-fold by vasotocin at 10(-8) M and 10(-7) M, respectively. The addition of alpha 2-adrenergic agonists blunted the stimulatory effect of vasotocin. The adenylate cyclase was evidenced in both the basolateral and apical membranes of the dark cells. Vasotocin stimulated only the apical adenylate cyclase of dark cells. These results indicated that the adenylate cyclase located in the apical dark cells of the semicircular canal was stimulated by the antidiuretic hormone which may be involved in the regulation of the endolymph secretion.

Adenylyl Cyclases↗
PubMed2006

Lateral semicircular canal and vertigo in patients with large vestibular aqueduct syndrome.

OBJECTIVE: To evaluate the hypothesis that there are differences in the morphology of the lateral semicircular canal (LSCC) between patients with large vestibular aqueduct syndrome (LVAS) and control subjects and to investigate the clinical implications of these differences. STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center. PATIENTS: Nine patients (two male patients and seven female patients; age range, 8-54 yr) with LVAS (one patient had unilateral LVAS, and eight patients had bilateral LVAS). Five patients had vertigo, and four patients, including the one with unilateral LVAS, did not have vertigo. MAIN OUTCOME MEASURES: The area of the LSCC was traced on the magnetic resonance imaging console and compared between LVAS patients and 12 control subjects who did not have sensorineural hearing loss. The LSCC fluid-containing area was divided by the sum of the LSCC inner area and the LSCC fluid-containing area for evaluation of the degree of the LSCC dysplasia. RESULTS: The LSCC fluid-containing ratio was significantly larger in LVAS patients than in control subjects. Moreover, the LSCC fluid-containing ratio was significantly larger in the eight ears with vertigo than in the nine ears without vertigo. There was no relationship between hearing level and the LSCC fluid-containing ratio. CONCLUSION: Patients with LVAS may have disturbed morphogenesis of both membranous and bony labyrinths. Our results reveal that the morphology of semicircular canals is clinically associated with vertigo.

Adolescent↗
PubMed1987

Surgical trauma to the lateral semicircular canal with preservation of hearing.

Surgical trauma to the lateral semicircular canal (LSC) is a rare complication which does not always result in cochlear damage. The authors present six such cases, discuss the histopathological findings of one case, and review 12 previous reports. Transient cochlear depression with normalization of function within 6 weeks of trauma occurred in most instances. Vestibular symptoms were pronounced and, although compensation was not delayed, positional dizziness and instability usually persisted for several months and occasionally for a year or more. Histopathological findings (two specimens) were significant for obliterative scarring of the LSC at the site of injury and for the structural integrity of the labyrinth and cochlea. The mechanism of cochlear protection in these cases remains obscure; however, clean injuries away from the ampullary end of the canal occurring in patients without preexisting inner ear disease appear to have a better prognosis. Intraoperative closure of the defect, postoperative bed rest, and antibiotics are the basic elements of management.

Adult↗
PubMedDate not supplied

Experimental study of a frog semicircular canal nerve: influence of the initial cupular position.

The posterior semicircular canal of the frog was stimulated by mechanical endolymphatic flow toward either an ampullofugal (excitatory) or ampullopetal (inhibitory) direction. The magnitudes of the responses as the cupula was moved to various positions were compared. When the same amount of stimulus was given in the same direction, the responses were equal, regardless of the initial position of the cupula.

Action Potentials↗
PubMed1997

Triple semicircular canal occlusion in the guinea pig.

Hearing preservation is possible with translabyrinthine procedures, but the optimal means of sealing the remaining labyrinth has not been determined. The purpose of this study was to compare the effects of mechanical and nonmechanical (CO2 laser-assisted) triple semicircular canal occlusion on hearing in the guinea pig. All three semicircular canals of 19 guinea pigs were treated with one of four techniques: fenestration without packing (control), fenestration with packing, CO2 laser coagulation of the membranous canal without packing, or laser coagulation with packing. Six weeks postoperatively, electrocochleographic thresholds were significantly elevated in one of five ears treated with packing alone, in one of five ears treated with laser and packing, in two of five ears treated with the laser alone, and in all four control ears. Thresholds were significantly elevated in control versus occluded ears (p < 0.05). There were no significant differences between the ears treated with laser or packing. These findings suggest that hearing can be preserved in triple canal occlusion by means of sealing the membranous labyrinth with either CO2 laser coagulation or mechanical packing. Further study on the feasibility of hearing preservation with complete labyrinthectomy is warranted.

Animals↗
PubMed2004

Optimizing the vertebrate vestibular semicircular canal: could we balance any better?

The fluid-filled semicircular canals (SCCs) of the vestibular system are used by all vertebrates to sense angular rotation. Despite masses spanning seven decades, all mammalian SCCs are nearly the same size. We propose that the SCC represents a sensory organ that evolution has "optimally designed." Four geometric parameters characterize the SCC, and "building materials" of given physical properties are assumed. Identifying physical and physiological constraints on SCC operation, we find the most sensitive SCC has dimensions consistent with available data. Since natural selection involves optimization, this approach may find broader use in understanding biological structures.

Animals↗