(1/705) 3D MRI of the membranous labyrinth. An age related comparison of MR findings in patients with labyrinthine fibrosis and in persons without inner ear symptoms.
PURPOSE: We compared MRI of the membranous labyrinth in patients with chronic non-neoplastic inner ear disease and MR signs of labyrinthine fibrosis and controls depending on their age, in order to establish whether there were any MR differences regarding patient age groups, control age groups and between the patients and controls themselves. MATERIALS AND METHODS: Clinical ENT examinations as well as a T2* weighted 3D CISS (Constructive Interference in Steady State) sequence with a slice thickness of 0.7 mm were performed. Our collective was subdivided as follows: 0-19 years (10 controls, 3 patients with chronic non-neoplastic inner ear disease), 20-49 years (55 controls, 8 patients), 50 years and older (40 controls, 22 patients). Detectability of labyrinthine structures (e.g. cochlea, vestibule, semicircular canals) and filling defects were evaluated. RESULTS: In the 3 age-groups of the control collective no significant differences were observed in the membranous labyrinth. However differences concerning labyrinthine detectability emerged between controls and patients in both the 20-49 years and 50 years and older age groups. In the patient collective the 3 age groups showed no significant discrepancy in the mean number of lesions. CONCLUSION: Filling defects of the membranous labyrinth on 3D CISS MR images are pathological even in older persons. We would therefore recommend high resolution T2* weighted MRI in the case of suspected labyrinthine fibrosis. (+info)
(2/705) Responses of sympathetic outflow to skin during caloric stimulation in humans.
We previously showed that caloric vestibular stimulation elicits increases in sympathetic outflow to muscle (MSNA) in humans. The present study was conducted to determine the effect of this stimulation on sympathetic outflow to skin (SSNA). The SSNA in the tibial and peroneal nerves and nystagmus was recorded in nine subjects when the external meatus was irrigated with 50 ml of cold (10 degrees C) or warm (44 degrees C) water. During nystagmus, the SSNA in tibial and peroneal nerves decreased to 50 +/- 4% (with baseline value set as 100%) and 61 +/- 4%, respectively. The degree of SSNA suppression in both nerves was proportional to the maximum slow-phase velocity of nystagmus. After nystagmus, the SSNA increased to 166 +/- 7 and 168 +/- 6%, respectively, and the degree of motion sickness symptoms was correlated with this SSNA increase. These results suggest that the SSNA response differs from the MSNA response during caloric vestibular stimulation and that the SSNA response elicited in the initial period of caloric vestibular stimulation is different from that observed during the period of motion sickness symptoms. (+info)
(3/705) p27(Kip1) links cell proliferation to morphogenesis in the developing organ of Corti.
Strict control of cellular proliferation is required to shape the complex structures of the developing embryo. The organ of Corti, the auditory neuroepithelium of the inner ear in mammals, consists of two types of terminally differentiated mechanosensory hair cells and at least four types of supporting cells arrayed precisely along the length of the spiral cochlea. In mice, the progenitors of greater than 80% of both hair cells and supporting cells undergo their terminal division between embryonic day 13 (E13) and E14. As in humans, these cells persist in a non-proliferative state throughout the adult life of the animal. Here we report that the correct timing of cell cycle withdrawal in the developing organ of Corti requires p27(Kip1), a cyclin-dependent kinase inhibitor that functions as an inhibitor of cell cycle progression. p27(Kip1) expression is induced in the primordial organ of Corti between E12 and E14, correlating with the cessation of cell division of the progenitors of the hair cells and supporting cells. In wild-type animals, p27(Kip1) expression is downregulated during subsequent hair cell differentiation, but it persists at high levels in differentiated supporting cells of the mature organ of Corti. In mice with a targeted deletion of the p27(Kip1) gene, proliferation of the sensory cell progenitors continues after E14, leading to the appearance of supernumerary hair cells and supporting cells. In the absence of p27(Kip1), mitotically active cells are still observed in the organ of Corti of postnatal day 6 animals, suggesting that the persistence of p27(Kip1) expression in mature supporting cells may contribute to the maintenance of quiescence in this tissue and, possibly, to its inability to regenerate. Homozygous mutant mice are severely hearing impaired. Thus, p27(Kip1) provides a link between developmental control of cell proliferation and the morphological development of the inner ear. (+info)
(4/705) Electrical response properties of avian lagena type II hair cells: a model system for vestibular filtering.
Data presented represent the first electrical recordings from avian lagena type II hair cells. The perforated-patch variant of the whole cell recording technique was used to investigate how the macroscopic currents shaped the voltage response of the hair cells. Voltage-clamp data separated cells into two broad classes on the basis of differences in activation rates, rates and degree of inactivation, and pharmacological sensitivity. Current-clamp recordings revealed low-quality membrane voltage oscillations (Qc < 1) during pulse current injections. Oscillation frequency correlated with activation rate of the macroscopic currents. The quality of membrane oscillations (Qc) varied linearly with frequency for cells with little inactivation. For cells with rapid inactivation, no relationship was found between Qc and frequency. Rapid inactivation may serve to extend the bandwidth of vestibular hair cells. The frequency measured from voltage responses to pulsed currents may reflect the corner frequency of the cell. The filtering properties of avian lagena hair cells are like those found in all other vestibular end organs, suggesting that the electrical membrane properties of these cells are not responsible for specializing them to a particular stimulus modality. (+info)
(5/705) Effects of bilateral vestibular lesions on orthostatic tolerance in awake cats.
Previous experiments in anesthetized or decerebrate cats showed that the vestibular system participates in adjusting blood pressure during postural changes. The present experiments tested the hypothesis that removal of vestibular inputs in awake cats would affect orthostatic tolerance. Before the lesion, blood pressure typically remained within 10 mmHg of baseline values during nose-up-pitch body rotations of up to 60 degrees in amplitude. In contrast, bilateral peripheral vestibular lesions altered the pattern of orthostatic responses in all animals, and blood pressure fluctuated >10 mmHg from baseline values during most 60 degrees nose-up tilts in five of six animals. The deficit in correcting blood pressure was particularly large when the animal also was deprived of visual cues indicating position in space. During this testing condition, either a decrease or increase in blood pressure >10 mmHg in magnitude occurred in >80% of tilts. The deficit in adjusting blood pressure after vestibular lesions persisted for only 1 wk, after which time blood pressure remained stable during tilt. These data show that removal of vestibular inputs alters orthostatic responses and are consistent with the hypothesis that vestibular signals are one of several inputs that are integrated to elicit compensatory changes in blood pressure during movement. (+info)
(6/705) Nasal vestibule wall elasticity: interactions with a nasal dilator strip.
We studied the effect of an adhesive external nasal dilator strip (ENDS) on external nasal geometry in 20 healthy Caucasian adults (10 men, 10 women; age 21-45 yr). The recoil force exerted by ENDS was estimated by bending the device (n = 10) with known weights. In the horizontal direction, a small/medium-sized ENDS in situ exerted a unilateral recoil force of 21.4-22.6 g. Application of ENDS resulted in a displacement of the lateral nasal vestibule walls that had both anterosuperior and horizontal components and that was maintained over an 8-h period. The resultant unilateral nasal vestibule wall displacement at the tip of the device was at 47.6 +/- 2.0 degrees to the horizontal (as related to the plane of the device when in situ) and had a magnitude of 3.5 +/- 0.1 mm. ENDS increased external nasal cross-sectional area by 23.0-65.3 mm2. Nasal vestibule wall compliance was estimated at 0.05-0.16 mm/g. Thus ENDS applies a relatively constant abducting force irrespective of nasal width. Variable responsiveness to ENDS may be related to differences in elastic properties of the nasal vestibule wall. (+info)
(7/705) Morphological, morphometric, and functional differences in the vestibular organ of different breeds of the rat (Rattus norvegicus).
In the laboratory rat, differences in shape, dimension and function of the cochlea have been reported for various breeds. In contrast, no comparable investigations to date have been undertaken for the vestibular organ in different breeds of the rat. Vestibular organs of two breeds of rat (Wistar, Sprague-Dawley) were analyzed morphologically and morphometrically by means of microdissection techniques in order to determine the mechanical sensitivity of the cupula according to Oman et al; (Acta Otolaryngol., 1987;103:1-13, 1987). Differences in shape of the lateral semicircular duct exist between the two breeds and the cupular mechanical sensitivity is significantly higher in Wistar than in Sprague-Dawley rats. With respect to the other semicircular ducts, no differences in shape were found between the two strains. The cupular mechanical sensitivity of the anterior semicircular duct, however, is higher in Wistar than in Sprague-Dawley rats. The breeds also differ in the shape of their utriculus; obviously a correlation exists between the latter and the cupular mechanical sensitivity of the semicircular ducts. There are differences in the vestibular organs between the two breeds of the laboratory rat investigated. The cupular mechanical sensitivity of the semicircular duct does not seem to be correlated to body mass. The size and morphology of the utriculus influence the mechanical sensitivity of a single duct, but differences only become significant if other parameters also differ. (+info)
(8/705) Effects of viewing distance on the responses of horizontal canal-related secondary vestibular neurons during angular head rotation.
Effects of viewing distance on the responses of horizontal canal-related secondary vestibular neurons during angular head rotation. The eye movements generated by the horizontal canal-related angular vestibuloocular reflex (AVOR) depend on the distance of the image from the head and the axis of head rotation. The effects of viewing distance on the responses of 105 horizontal canal-related central vestibular neurons were examined in two squirrel monkeys that were trained to fixate small, earth-stationary targets at different distances (10 and 150 cm) from their eyes. The majority of these cells (77/105) were identified as secondary vestibular neurons by synaptic activation following electrical stimulation of the vestibular nerve. All of the viewing distance-sensitive units were also sensitive to eye movements in the absence of head movements. Some classes of eye movement-related vestibular units were more sensitive to viewing distance than others. For example, the average increase in rotational gain (discharge rate/head velocity) of position-vestibular-pause units was 20%, whereas the gain increase of eye-head-velocity units was 44%. The concomitant change in gain of the AVOR was 11%. Near viewing responses of units phase lagged the responses they generated during far target viewing by 6-25 degrees. A similar phase lag was not observed in either the near AVOR eye movements or in the firing behavior of burst-position units in the vestibular nuclei whose firing behavior was only related to eye movements. The viewing distance-related increase in the evoked eye movements and in the rotational gain of all unit classes declined progressively as stimulus frequency increased from 0.7 to 4.0 Hz. When monkeys canceled their VOR by fixating head-stationary targets, the responses recorded during near and far target viewing were comparable. However, the viewing distance-related response changes exhibited by central units were not directly attributable to the eye movement signals they generated. Subtraction of static eye position signals reduced, but did not abolish viewing distance gain changes in most units. Smooth pursuit eye velocity sensitivity and viewing distance sensitivity were not well correlated. We conclude that the central premotor pathways that mediate the AVOR also mediate viewing distance-related changes in the reflex. Because irregular vestibular nerve afferents are necessary for viewing distance-related gain changes in the AVOR, we suggest that a central estimate of viewing distance is used to parametrically modify vestibular afferent inputs to secondary vestibuloocular reflex pathways. (+info)
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