Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “LABYRINTH”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,765 records · Page 98Linked to original sources
PubMed1976

[Labyrinth nuclei as observed in dermatofibrosarcoma protuberans and fibroxanthoma (author's transl)].

In the electron microscope the nuclei of benign and malignant tumors as well as the nuclei of normal cells exhibit relatively various structural features. In this study the author reports on two mesenchymal tumors of the skin (one case of dermatofibrosarcoma protuberans and one of fibroxanthoma) with pecular nuclear polymorphism which can be visualized by electron microscopy only.

Adult↗
PubMed1988

A new quantitative model of total endolymph flow in the system of semicircular ducts.

1. A new concept of endolymph flow in the vertebrate vestibular system is presented. This approach describes quantitatively the flow in the entire system of three semicircular ducts interconnected by the utriculus and the crus commune. This approach is quite distinct from the classical theory in which the labyrinth is generally conceived to consist of three separate duct circuits. 2. The present approach shows the following set of distinct differences to the classical view: (a) In a labyrinth composed of three ducts perpendicular to each other the flow is non-zero in the other ducts when the labyrinth is rotated in the plane of a particular duct. (b) In a labyrinth with two equal ducts and with the duct planes under approximately 73 degrees the flow in one duct is zero when the rotation takes place in the plane of the other duct. Previous measurements of duct angles reflect this value surprisingly well. An obtuse or sharp angle between duct planes can lead to better performance of a particular labyrinth because the "external impulses" in the different ducts may amplify or compensate each other. (c) The behaviour of the flow in the entire labyrinth is a non-linear function of direction or rotation (cf. points (d), (e]. (d) Six time constants for the entire labyrinth can be distinguished (three long, three short); the flow in a particular duct is composed of six terms with these time constants. The composition of this flow and thus the relative importance of the terms depends on the positioning of the labyrinth with respect to the rotation vector. (e) The time constants also depend, for different labyrinths, on a shared influence of the dimensions of the ducts and the elastic properties of all three cupulae. (f) The forces in a particular duct depend also on the amount of motion the fluid will acquire in the other ducts. (g) The sensitivity of a particular duct depends also on the dimensions of the other parts in the vestibular system. 3. Equations for a system consisting of two ducts and for the classical single duct system are also given. Both systems are special cases of the three-duct system. The single duct equations are equivalent with equations given by Oman (1980) and Oman et al. (1987) which include the contribution of a wide utriculus. 4. The present theory of endolymph flow is mainly supported by the outcome of previously performed experiments concerning time constants and rotation of human subjects in different planes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

The effect of maternal undernutrition on the growth and development of the guinea pig placenta.

Fetal growth is known to be correlated with the size of the placenta and the exchange surface area. Reduction in the growth of the materno-fetal exchange surface areas may be a mechanism by which the effects of maternal undernutrition on fetal growth are mediated. In the compact placenta of the guinea pig the exchange surface is equivalent to the peripheral labyrinth. The effect of a 40% reduction in maternal feed intake on the growth of the peripheral labyrinth was investigated in pregnant guinea pigs between gestational days 25 and 65. Fetal and placental weights were significantly reduced in the last trimester by 32% and 38% respectively (P < 0.01). Placental efficiency in early gestation was significantly impaired in restricted animals but equivalent to ad lib. fed controls by the last trimester. The volume of the peripheral labyrinth increased as a percentage of the total placental volume with gestational age. Restricted placentae tended to be composed of a smaller volume of peripheral labyrinth tissue in early gestation. It is suggested that maternal undernutrition results in an impaired or delayed expansion of the peripheral labyrinth in early gestation causing a reduction in placental efficiency. By the last trimester the weight of the peripheral labyrinth of restricted animals was reduced by 33% (P < 0.05). The weight of the peripheral labyrinth was also significantly correlated with fetal weight is limited by the size of the peripheral labyrinth in the later stages of gestation.

Animals↗
PubMedDate not supplied

Positional metabolism of benzo(a)pyrene in rat placenta and maternal liver. Comparison of induction effects.

The biotransformation of [14C]benzo(a)pyrene (BP) was studied in vitro in the presence of microsomes prepared from isolated labyrinth and basal zone tissues of the rat placenta, as well as from maternal liver. Pregnant rats, day 14 of gestation, received beta-naphthoflavone (beta NF; 15 mg/kg, ip) or 3-methyl-cholanthrene (3MC; 30 mg/kg, ip). On day 15, placentae were dissected and microsomes were incubated with 17 microM [14C]BP and 2 mM NADPH. Metabolites formed in the incubation flasks were extracted and separated by HPLC utilizing a reverse phase column. Only trace BP metabolism occurred in basal zone microsomes from control, beta NF-, or 3MC-pretreated animals, as well as in labyrinth microsomes from control animals. In contrast, the preadministration of beta NF and 3MC increased labyrinth microsomal BP metabolism by 10- to 15-fold. Labyrinth and maternal liver microsomes from beta NF- and 3MC-treated animals actively converted BP to eight separate metabolites which co-chromatographed primarily with quinones and phenols. The overall formation of BP diol and phenolic metabolites by labyrinth microsomes was appreciably less than was observed for liver preparations. The very low activity of BP-4,5-oxide hydrolase in labyrinth microsomes compared to liver may in part explain the low level of formation of BP diols in placental microsomes. Labyrinth microsomes catalyzed the covalent binding of [3H]BP to calf thymus DNA, and this activity increased 5-fold following beta NF pretreatment. A comparison of induced tissues indicates that the amount of DNA binding in labyrinth microsomes is more extensive than would be expected by the level of total BP metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Effects of deuterium oxide and galvanic vestibular stimulation on visual cortical cell function.

/he spontaneous and evoked unit activities of complex visual cortical cells were recorded from Brodmann's area 18 in immobilized, unanesthetized cats before, during, and after stimulation of the vestibular system. The vestibular system was stimulated by intravenous injection of deuterium oxide (D2O)--a noted nystagmogenic agent (14)--or by direct galvanic stimulation of the labyrinth. Measures of the receptive-field areas, poststimulus time histograms, directional preferences, and the optimal speed of the light bar stimulating the cell were obtained before and after the application of D2O. Directional preferences were determined in a novel manner, using a method derived from a hierarchical clustering technique (19). Data were collected and analyzed from a) visual cortical cells in cats with intact labyrinths, b) visual cortical cells in cats following bilateral labrinthectomies, and c) nonvisual cortical cells in cats with intact labyrinths. In cats with intact labyrinths, D2O changed the optimal length of the light bar that was able to stimulate the cortical cell as well as the path on which it evoked the response of the cell. Both values, which constitute the receptive field of the cell, changed approximately proportionately. This effect usually lasts for less than 4.5 h. The other cellular characteristics were also altered by the D2O. Galvanic stimulation of the labyrinth resembles, in its effects, the injection of D2O. In labyrinth-intact cats, the time course of area 18 spontaneous activity dramatically increased 30 min or more after D2O was administered. It peaked 2-3 h later and still had not returned to preinjection levels even 7 h after the D2O administration. In bilaterally labyrinthectomized cats, the spontaneous activity of the visual cells (and the other cellular characteristics studied) did not change following D2O administration. In nonvisual cells from labyrinth-intact cats, the spontaneous activity demonstrated a slight but significant decrease over time after D2O injection. (The other measures, however, did not change.) In pilot studies (about 2 wk prior to the electrophysiological experiments), the cats were injected with D2O. Within 8-10 min afterward, signs of positional nystagmus commenced; and within 30 min, problems in maintaining balance were noted. This continued for 7-8 h before disappearing. In the labyrinthectomized animals, such effects were not observed. These results, therefore, add support to other evidence that suggests that D2O works directly through the vestibular apparatus to produce the effects it does (and not through interference with certain cellular processes).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Inputs from the ipsilateral and contralateral vestibular apparatus to behaviorally characterized abducens neurons in rhesus monkeys.

1. We made extracellular recordings from neurons in the abducens nuclei of alert rhesus monkeys during electrical stimulation of the vestibular labyrinths with brief current pulses and during smooth pursuit, steady fixation, and the vestibuloocular reflex (VOR) evoked by passive head turns. The responses to electrical stimuli were compared with quantitative measures of the sensitivity of each neuron to eye position and eye velocity. We also compared the strengths of the vestibular inputs from the labyrinths ipsilateral and contralateral to the side of recording. 2. Abducens neurons showed transient excitation after a current pulse was applied to the contralateral labyrinth and transient inhibition after stimulation of the ipsilateral labyrinth. The latency of excitation had a mean value of 1.7 ms and a median value of 1.5 ms. Latency was unimodally distributed with little variation among neurons. Neurons with large responses showed a second phase of excitation that started 2.5 ms after the stimulus. 3. In two of three monkeys, the excitatory responses of abducens neurons to electrical stimulation of the contralateral labyrinth were approximately 3 times as large as their inhibitory responses to stimulation of the ipsilateral labyrinth. The difference in response size was not observed in the third monkey. The asymmetry in the size of the electrically evoked inputs from the two labyrinths was associated with a smaller asymmetry in responses of abducens neurons during the VOR evoked by passive head turns. The increase in firing rate during head rotation away from the side of the recording was almost always larger than the decrease in firing rate during head rotation toward the side of the recording. 4. The size of the neuronal response to electrical stimulation was correlated with the magnitude of the change in discharge rate during eye movements. Single or multiple regression of measures of response amplitude against eye position threshold, sensitivity to eye position, sensitivity to eye velocity, and baseline discharge rate yielded correlation coefficients that ranged from 0.26 to 0.92 in different monkeys. The existence of positive correlations is consistent with a role of the intrinsic properties of abducens neurons in determining recruitment order. However, the existence of large amounts of variability within most of the samples suggests that the recruitment order of abducens neurons also depends on the discharge properties of the afferents to each abducens neuron.

Abducens Nerve↗
PubMed1983

Inhibition of vestibular and neck reflexes in forelimb extensor muscles during the episodes of postural atonia induced by an anticholinesterase in decerebrate cat.

In precollicular decerebrate cats, the multiunit EMG activity of forelimb extensor muscles (e.g. the triceps brachii) was recorded during sinusoidal stimulation of labyrinth and neck receptors at the frequencies of 0.026-0.15 Hz, +/- 10 degrees and the resulting responses were tested during tonic activation of a cholinergic mechanism. In agreement with previous findings, the first harmonic component of the EMG responses to roll tilt of the animal leading to selective stimulation of labyrinth receptors was characterized by an increased activity during side-down tilt and a decreased activity during side-up tilt (labyrinth responses); on the other hand just the opposite changes were elicited for the same directions of neck rotation (neck responses). For the parameters of stimulation reported above, the responses were always related to position and not to velocity of displacement. Intravenous injection of an anticholinesterase (eserine sulphate, 0.10-0.15 mg/kg) which produced a state of postural atonia, associated with bursts of rapid eye movements (REM), similar to that occurring spontaneously in unrestrained cats during desynchronized sleep or REM sleep, also decreased the tonic activity of the triceps brachii and abolished the EMG responses of this muscle to sinusoidal stimulation of labyrinth and neck receptors. This suppression persisted throughout the episode of postural atonia associated with REM bursts. The abolition of the labyrinth and neck reflexes acting on forelimb muscles was not only dependent on the dose of anticholinesterase, but also on the state of the animal. In fact, somatosensory or acoustic stimuli applied during the REM episodes abolished the rhythmic oculomotor activity and determined the prompt recovery of both the decerebrate rigidity and the EMG responses of the triceps brachii to labyrinth and neck stimulation. The postural atonia as well as the tonic depression of the vestibular and neck reflexes acting on forelimb extensor muscles can in part at least be attributed to cholinergic activation of medullary reticulospinal neurons exerting a postsynaptic inhibitory influence on extensor motoneurons. However, since these inhibitory reticulospinal neurons collaborate with excitatory vestibulospinal neurons to the motoneuronal responses during stimulation of labyrinth and neck receptors, we cannot exclude that the suppression of the vestibular and neck reflexes may also depend on occlusion of the unit responses at reticular level.

Animals↗
PubMed1999

[Preoperative evaluation of translabyrinthine cholesteatomas by MRI].

PURPOSE: Hearing preservation is one of the major goals of surgical resection of invasive cholesteatomas. Patients were prospectively evaluated using a 3D-CISS MR acquisition in order to improve the detection of perilymphatic fistulae. MATERIALS AND METHODS: 16 patients (10 M, 6 F) presenting with a primary (1 case) or a secondary (post-otitis) middle ear cholesteatoma extending to the osseous labyrinth (as defined by HR-CT) were evaluated at MR (1.5 T Vision, Siemens). The 3D-CISS sequence (TR: 12.25 ms, TE: 5.90 ms, flip angle: 70 degrees, slice thickness: 1 mm, matrix: 307 x 512, FOV: 200) allowed detection of invasion of the membranous labyrinth using a 3 level grading scale: 1) normal fluids, 2) focal and 3) diffuse obliteration of labyrinthine fluid. RESULTS: While CT showed a definite osseous labyrinthine fistula, the 3D-CISS sequence depicted either a normal membranous labyrinth (9 cases), a focal obliteration of the basal turn (1 case) or lateral semi-circular canal (3 cases) or a diffuse obliteration of the labyrinthine fluid (3 cases). Diffuse obliteration of the labyrinth fluid and 1 out 3 cases of focal obliteration of the semi-circular canal were found to have perilymphatic fistulae at surgery. None of the normal labyrinths were associated with perilymphatic fistula formation. CONCLUSION: The 3D-CISS sequence allows a comprehensive preoperative evaluation of the membranous labyrinth. Loss of signal from the labyrinthine fluid due to invasion or compression of the membranous structures accounts for the lack of specificity of the technique.

Adult↗
PubMed1998

The etiology of idiopathic sudden sensorineural hearing loss. Experimental herpes simplex virus infection of the inner ear.

HYPOTHESIS: Experimentally induced herpes simplex virus type 1 (HSV-1) labyrinthitis provides a suitable model for idiopathic sudden sensorineural hearing loss (ISSHL). BACKGROUND: Viral labyrinthitis has been postulated to play a role in the pathophysiology of ISSHL. Circumstantial evidence is pointing at members of the herpes virus family. Experimental viral labyrinthitis elicited by various virus families leaves a virus-specific pattern of cochlear damage. Herpes viruses provide the best matching pattern in the distribution of cochlear damage when compared with ISSHL postmortem cochlear histopathology. METHODS: Herpetic viral labyrinthitis was induced in guinea pigs using perilymphatic inoculation with HSV-1. A control group was inoculated with the culture medium only. Infection was confirmed by the measurement of HSV antibodies. Hearing was monitored. Cochlear damage was evaluated by light and electron microscopy. RESULTS: In all HSV-1 inoculated animals, rapid loss of hearing occurred. Seroconversion took place, but no systemic manifestations of herpetic infection were observed. The control group showed no cochlear or systemic symptoms. When comparing cochlear histopathology in ISSHL to experimental viral HSV-1 labyrinthitis, strong similarities were found: degeneration of the stria vascularis, destruction of the organ of Corti, loosening of the tectorial membrane, and inflammatory changes in neural structures. CONCLUSIONS: Based on clinical and histopathologic characteristics, experimental HSV-1 labyrinthitis provides a suitable model of ISSHL.

Animals↗
PubMed1999

Size limitations in semicircular duct systems

The present article discusses mechanical requirements and limitations which are applicable to the construction of the system of semicircular ducts, especially to its size. The simplified case of a single, uniform duct system has been considered which can be described by a second order equation of motion. The principal functional quantities for this rotation-sensor are: (1) response speed; (2) sensitivity; and (3) regular flow. The response speed of a single, uniform semicircular duct is characterized by the short time constant (T2) which is dependent on the duct radius (r). Its estimated range is from 0.04 ms in the smallest to 140 ms in the largest known labyrinth. The sensitivity is characterized by the maximal endolymph displacement after a step stimulus (xmax). Its estimated range is from 0.0016 &mgr;m to 5.97 mm (6.56 decades!), assuming an input angular velocity of omega=1 rad s-1. The Reynolds number is a measure for an undisturbed laminar flow. Its estimated range varies from 7.38.10(-4)to 45.1 for omega=1 rad s-1. The above data follow from graphs in which, for a single uniform duct, circuit radius (R) is plotted against duct radius (r) for labyrinths of 233 species belonging to different vertebrate-groups. A relation R =38.9. r1.60was determined. The smallest labyrinth was found in a carp larva (Cyprinus), the largest in a whale shark (Rhincodon). Large whales possess labyrinths of average mammalian size. It is revealed that semicircular duct size is bound by requirements concerning regular flow and by a too low response speed for large labyrinths, and by a too low sensitivity for small labyrinths. Other important quantities are mechanical amplification factors which are a consequence of more complex vestibular constructions than a single uniform duct circuit. Allometric relationships are interpreted as compromises between the quantities mentioned. A hypothesis for the relatively large semicircular duct sizes of fishes, especially Elasmobranchii, compared with mammals and birds is presented. Copyright 1999 Academic Press.

Journal Article↗
PubMed1975

Labyrinthine and vestibulospinal effects on spinal motoneurons in the pigeon.

Experiments were performed on pigeons to investigate the effects of labyrinthine stimulation on motoneurons innervating neck and limb muscles. Intracellular recordings from the ventral horn of the spinal cord in the neck revealed that stimulation of the ipsilateral labyrinth with only a single shock evokes prominent EPSPs and/or IPSPs in the majority of neck motoneurons at thresholds less than 3--4 times the threshold for the labyrinth-evoked N1 potential recorded in the ipsilateral vestibular nuclei. In many neck motoneurons, the latencies of the PSPs were short enough so that no more than two synapses could be involved in their transmission. Recordings were also obtained from identified motoneurons which innervate muscles of the wing or the leg. Stimulation of the labyrinth, even with multiple stimuli, failed to elicit any observable PSPs in limb motoneurons. These data were consistent with other observations that in awake pigeons stimulation of the labyrinth with weak shocks evoked a pronounced turning of the head to the contralateral side, while even strong or multiple stimuli failed to produce any observable movement of wings or legs. Thus in the pigeon the association of the labyrinth with limb muscles is insignificant when compared to the association of the labyrinth with neck muscles. In addition, supraspinal descending fibers in the pigeon may make monosynaptic excitatory and inhibitory contact with spinal motoneurons.

Animals↗
PubMed1998

Localization and migration route of Cephalopina titillator (Diptera: Oestridae) larvae in the head of infested camels (Camelus dromedarius).

The localization and migration routes of Cephalopina titillator larvae were studied in the heads of 45 naturally infested camels. Larvae were located in the pharyngeal cavity (95.6%), the labyrinth of the ethmoid bone (71.1%), the turbinates (28.9%) and the lower nasal meatus (6.7%). Out of 261 first-instar larvae, 73.7% were found in the labyrinth of the ethmoid bone and 26.3% in the turbinates, while 88.9% of second-instar larvae were observed in the pharyngeal cavity and 11.1% in the labyrinth of the ethmoid bone. Most third-instar larvae (91.9%) were found in the pharyngeal cavity, with a few larvae in the labyrinth of the ethmoid bone (6.5%) and lower nasal meatus (1.6%). The first moult occurred in the labyrinth of the ethmoid bone. The second moult was observed in both the labyrinth of ethmoid bone and the pharyngeal cavity. The migration route of these larvae in the infested head was discussed.

Animals↗
PubMed1997

Histopathology of labyrinthine fistulae in chronic otitis media with clinical implications.

The objective of this study was to describe the light microscopic pathology of labyrinthine fistulae in chronic otitis media (COM) in seven temporal bones and to discuss clinical and surgical implications. In COM, labyrinthine fistulae are usually caused by cholesteatoma, with the lateral semicircular canal being the most commonly affected site. Some fistulae are asymptomatic, whereas, others affect the auditory and vestibular systems to varying degrees. Surgical removal of cholesteatoma matrix over a fistula carries a risk of sensorineural hearing loss. Knowledge of the pathology of fistulae may provide a better understanding of their clinical manifestations and may allow a more rational approach to surgical management. The Massachusetts Eye and Ear Infirmary temporal bone collection contains 115 specimens with COM, of which seven specimens show pathologic fistulization of the bony labyrinth. Histologic sections from these seven bones were evaluated with respect to type of COM, location and size of fistula, changes in the inner ear adjacent to the fistula, middle ear and mastoid disease, and pathology in the vestibular and cochlear sense organs. The following conclusions are presented (a) Labyrinthine fistulae can be caused not only by cholesteatoma, but also by granulomatous COM without cholesteatoma and even by localized infection within a canal-down mastoid cavity. (b) Cholesteatoma matrix or inflammatory tissue usually becomes apposed to the endosteum or membranous labyrinth within the fistula. In most cases, reactive inner ear changes do not occur at the fistula site. Occasionally, there is thickening of the endosteum or chronic localized labyrinthitis. (c) Most bones do not show any alterations of the vestibular and cochlear sense organs. Occasionally, there is serous labyrinthitis, which might lead to partial sensorineural hearing loss. (d) A protective "walling-off" phenomenon in the labyrinth is not common. Therefore, if overwhelming infection or surgical trauma breaches the natural barriers of the endosteum/membranous labyrinth, then the fistula may allow rapid dissemination of infection throughout the inner ear.

Adolescent↗