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)
Differential transcriptional control as the major molecular event in generating Otx1-/- and Otx2-/- divergent phenotypes.
Otx1 and Otx2, two murine homologs of the Drosophila orthodenticle (otd) gene, show a limited amino acid sequence divergence. Their embryonic expression patterns overlap in spatial and temporal profiles with two major exceptions: until 8 days post coitum (d.p.c. ) only Otx2 is expressed in gastrulating embryos, and from 11 d.p.c. onwards only Otx1 is transcribed within the dorsal telencephalon. Otx1 null mice exhibit spontaneous epileptic seizures and multiple abnormalities affecting primarily the dorsal telencephalic cortex and components of the acoustic and visual sense organs. Otx2 null mice show heavy gastrulation abnormalities and lack the rostral neuroectoderm corresponding to the forebrain, midbrain and rostral hindbrain. In order to define whether these contrasting phenotypes reflect differences in expression pattern or coding sequence of Otx1 and Otx2 genes, we replaced Otx1 with a human Otx2 (hOtx2) full-coding cDNA. Interestingly, homozygous mutant mice (hOtx2(1)/hOtx2(1)) fully rescued epilepsy and corticogenesis abnormalities and showed a significant improvement of mesencephalon, cerebellum, eye and lachrymal gland defects. In contrast, the lateral semicircular canal of the inner ear was never recovered, strongly supporting an Otx1-specific requirement for the specification of this structure. These data indicate an extended functional homology between OTX1 and OTX2 proteins and provide evidence that, with the exception of the inner ear, in Otx1 and Otx2 null mice contrasting phenotypes stem from differences in expression patterns rather than in amino acid sequences. (+info)
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)
Short- and long-term consequences of canal plugging on gaze shifts in the rhesus monkey. I. Effects on gaze stabilization.
Short- and long-term consequences of canal plugging on gaze shifts in the rhesus monkey. I. Effects on gaze stabilization. To study the contribution of the vestibular system to the coordinated eye and head movements of a gaze shift, we plugged the lumens of just the horizontal (n = 2) or all six semicircular canals (n = 1) in monkeys trained to make horizontal head-unrestrained gaze shifts to visual targets. After the initial eye saccade of a gaze shift, normal monkeys exhibit a compensatory eye counterrotation that stabilizes gaze as the head movement continues. This counterrotation, which has a gain (eye velocity/head velocity) near one has been attributed to the vestibuloocular reflex (VOR). One day after horizontal canal plugging, the gain of the passive horizontal VOR at frequencies between 0.1 and 1.0 Hz was <0.10 in the horizontal-canal-plugged animals and zero in the all-canal-plugged animal. One day after surgery, counterrotation gain was approximately 0.3 in the animals with horizontal canals plugged and absent in the animal with all canals plugged. As the time after plugging increased, so too did counterrotation gain. In all three animals, counterrotation gain recovered to between 0.56 and 0.75 within 80-100 days. The initial loss of compensatory counterrotation after plugging resulted in a gaze shift that ended long after the eye saccade and just before the end of the head movement. With recovery, the length of time between the end of the eye saccade and the end of the gaze movement decreased. This shortening of the duration of reduced gain counterrotation occurred both because head movements ended sooner and counterrotation gain returned to 1.0 more rapidly relative to the end of the eye saccade. Eye counterrotation was not due to activation of pursuit eye movements as it persisted when gaze shifts were executed to extinguished targets. Also counterrotation was not due simply to activation of neck receptors because counterrotation persisted after head movements were arrested in midflight. We suggest that the neural signal that is used to cause counterrotation in the absence of vestibular input is an internal copy of the intended head movement. (+info)
Firing behavior of vestibular neurons during active and passive head movements: vestibulo-spinal and other non-eye-movement related neurons.
The firing behavior of 51 non-eye movement related central vestibular neurons that were sensitive to passive head rotation in the plane of the horizontal semicircular canal was studied in three squirrel monkeys whose heads were free to move in the horizontal plane. Unit sensitivity to active head movements during spontaneous gaze saccades was compared with sensitivity to passive head rotation. Most units (29/35 tested) were activated at monosynaptic latencies following electrical stimulation of the ipsilateral vestibular nerve. Nine were vestibulo-spinal units that were antidromically activated following electrical stimulation of the ventromedial funiculi of the spinal cord at C1. All of the units were less sensitive to active head movements than to passive whole body rotation. In the majority of cells (37/51, 73%), including all nine identified vestibulo-spinal units, the vestibular signals related to active head movements were canceled. The remaining units (n = 14, 27%) were sensitive to active head movements, but their responses were attenuated by 20-75%. Most units were nearly as sensitive to passive head-on-trunk rotation as they were to whole body rotation; this suggests that vestibular signals related to active head movements were cancelled primarily by subtraction of a head movement efference copy signal. The sensitivity of most units to passive whole body rotation was unchanged during gaze saccades. A fundamental feature of sensory processing is the ability to distinguish between self-generated and externally induced sensory events. Our observations suggest that the distinction is made at an early stage of processing in the vestibular system. (+info)
Integration of vestibular and head movement signals in the vestibular nuclei during whole-body rotation.
Single-unit recordings were obtained from 107 horizontal semicircular canal-related central vestibular neurons in three alert squirrel monkeys during passive sinusoidal whole-body rotation (WBR) while the head was free to move in the yaw plane (2.3 Hz, 20 degrees /s). Most of the units were identified as secondary vestibular neurons by electrical stimulation of the ipsilateral vestibular nerve (61/80 tested). Both non-eye-movement (n = 52) and eye-movement-related (n = 55) units were studied. Unit responses recorded when the head was free to move were compared with responses recorded when the head was restrained from moving. WBR in the absence of a visual target evoked a compensatory vestibulocollic reflex (VCR) that effectively reduced the head velocity in space by an average of 33 +/- 14%. In 73 units, the compensatory head movements were sufficiently large to permit the effect of the VCR on vestibular signal processing to be assessed quantitatively. The VCR affected the rotational responses of different vestibular neurons in different ways. Approximately one-half of the units (34/73, 47%) had responses that decreased as head velocity decreased. However, the responses of many other units (24/73) showed little change. These cells had signals that were better correlated with trunk velocity than with head velocity. The remaining units had responses that were significantly larger (15/73, 21%) when the VCR produced a decrease in head velocity. Eye-movement-related units tended to have rotational responses that were correlated with head velocity. On the other hand, non-eye-movement units tended to have rotational responses that were better correlated with trunk velocity. We conclude that sensory vestibular signals are transformed from head-in-space coordinates to trunk-in-space coordinates on many secondary vestibular neurons in the vestibular nuclei by the addition of inputs related to head rotation on the trunk. This coordinate transformation is presumably important for controlling postural reflexes and constructing a central percept of body orientation and movement in space. (+info)
Targeted mutagenesis of the POU-domain gene Brn4/Pou3f4 causes developmental defects in the inner ear.
Targeted mutagenesis in mice demonstrates that the POU-domain gene Brn4/Pou3f4 plays a crucial role in the patterning of the mesenchymal compartment of the inner ear. Brn4 is expressed extensively throughout the condensing mesenchyme of the developing inner ear. Mutant animals displayed behavioral anomalies that resulted from functional deficits in both the auditory and vestibular systems, including vertical head bobbing, changes in gait, and hearing loss. Anatomical analyses of the temporal bone, which is derived in part from the otic mesenchyme, demonstrated several dysplastic features in the mutant animals, including enlargement of the internal auditory meatus. Many phenotypic features of the mutant animals resulted from the reduction or thinning of the bony compartment of the inner ear. Histological analyses demonstrated a hypoplasia of those regions of the cochlea derived from otic mesenchyme, including the spiral limbus, the scala tympani, and strial fibrocytes. Interestingly, we observed a reduction in the coiling of the cochlea, which suggests that Brn-4 plays a role in the epithelial-mesenchymal communication necessary for the cochlear anlage to develop correctly. Finally, the stapes demonstrated several malformations, including changes in the size and morphology of its footplate. Because the stapes anlage does not express the Brn4 gene, stapes malformations suggest that the Brn4 gene also plays a role in mesenchymal-mesenchymal signaling. On the basis of these data, we suggest that Brn-4 enhances the survival of mesodermal cells during the mesenchymal remodeling that forms the mature bony labyrinth and regulates inductive signaling mechanisms in the otic mesenchyme. (+info)
Influence of surgical plugging on horizontal semicircular canal mechanics and afferent response dynamics.
Mechanical occlusion of one or more of the semicircular canals is a surgical procedure performed clinically to treat certain vestibular disorders and used experimentally to assess individual contributions of separate canals and/or otoliths to vestibular neural pathways. The present experiments were designed to determine if semicircular canal afferent nerve modulation to angular head acceleration is blocked by occlusion of the endolymphatic duct, and if not, what mechanism(s) might account for a persistent afferent response. The perilymphatic space was opened to gain acute access to the horizontal canal (HC) in the oyster toadfish, Opsanus tau. Firing rate responses of HC afferents to sinusoidal whole-body rotation were recorded in the unoccluded control condition, during the process of duct occlusion, and in the plugged condition. The results show that complete occlusion of the duct did not block horizontal canal sensitivity; individual afferents often exhibited a robust firing rate modulation in response to whole-body rotation in the plugged condition. At high stimulus frequencies (about >8 Hz) the average sensitivity (afferent gain; spikes/s per degrees /s of head velocity) in the plugged condition was nearly equal to that observed for unoccluded controls in the same animals. At low stimulus frequencies (about <0.1 Hz), the average sensitivity in the plugged condition was attenuated by more than two orders of magnitude relative to unoccluded controls. The peak afferent firing rate for sinusoidal stimuli was phase advanced approximately 90 degrees in plugged canals relative to their control counterparts for stimulus frequencies approximately 0.1-2 Hz. Data indicate that afferents normally sensitive to angular velocity in the control condition became sensitive to angular acceleration in the plugged condition, whereas afferents sensitive to angular acceleration in the control condition became sensitive to the derivative of acceleration or angular jerk in the plugged condition. At higher frequencies (>8 Hz), the phase of afferents in the plugged condition became nearly equal, on average, to that observed in controls. A three-dimensional biomechanical model of the HC was developed to interpret the residual response in the plugged condition. Labyrinthine fluids were modeled as incompressible and Newtonian; the membranous duct, osseous canal and temporal bone were modeled as visco-elastic materials. The predicted attenuation and phase shift in cupular responses were in close agreement with the observed changes in afferent response dynamics after canal plugging. The model attributes the response of plugged canals to labyrinthine fluid pressure gradients that lead to membranous duct deformation, a spatial redistribution of labyrinthine fluids and cupular displacement. Validity of the model was established through its ability to predict: the relationship between plugged canal responses and unoccluded controls (present study), the relationship between afferent responses recorded during mechanical indentation of the membranous duct and physiological head rotation, the magnitude and phase of endolymphatic pressure generated during HC duct indentation, and previous model results for cupular gain and phase in the rigid-duct case. The same model was adjusted to conform to the morphology of the squirrel monkey and of the human to investigate the possible influence of canal plugging in primates. Membranous duct stiffness and perilymphatic cavity stiffness were identified as the most salient model parameters. Simulations indicate that canal plugging may be the most effective in relatively small species having small labyrinths, stiff round windows, and stiff bony perilymphatic enclosures. (+info)