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PubMedDate not supplied

Obliteration of the ductus reuniens.

The ductus reuniens was successfully obliterated in 52 guinea pig ears. Histopathological study showed that a majority of these specimens demonstrated cochlear hydrops, saccular collapse and normal utricle. These results support the theory of longitudinal flow of endolymph from the cochlea toward the endolymphatic sac via the ductus reuniens and saccule. A major source of endolymph in the saccule appears to be the scala media. In another set of 11 animals in which the ductus reuniens was first obstructed and two months later the endolymphatic duct was blocked, endolymphatic hydrops was shown in the cochleae, saccules, and utricles of all but one. The evidence suggests that cochlear hydrops was caused by obliteration of the ductus reuniens, and the saccular and utricular hydrops occurred subsequently as the result of blockage of the endolymphatic duct. Remnants of otolithic membrane which were attached to the distended saccular wall indicate that the membrane which had collapsed onto the macula after obliteration of the ductus reuniens is capable of subsequent distension. This experiment supports the concept of endolymph flow from the utricle and canals toward the endolymphatic sac. A blocked cutus reuniens might also explain the pathophysiological basis for the auditory form of Meniere's disease.

Animals↗
PubMed1985

Transneuronal transport in the vestibular and auditory systems of the squirrel monkey and the arctic ground squirrel. II. Auditory system.

Transneuronal transport in the auditory system of the squirrel monkey and the arctic ground squirrel was studied after implantation of tritiated protein or glycoprotein precursors into the ampulla of a single semicircular duct. In both species, essentially the same pattern of transneuronal transport extended beyond the cochlear nuclei to the central nucleus of the inferior colliculus (CNIC), after survival periods ranging from 9 to 33 days. Animals displayed dense labeling over nearly all auditory receptors, nearly all portions of the spiral ganglion and throughout the cochlear nuclei (CN). Labeled fibers, mainly in the ventral acoustic stria, terminated over the ipsilateral lateral superior olive (LSO) and the lateral aspect of medial superior olive (MSO). Fibers continuing medially, decussated in an orderly manner, and terminated over the opposite medial nucleus of the trapezoid body (MNTB) and medial aspect of MSO. Labeled fibers projecting into the opposite lateral lemniscus (LL) terminated in the ventral nucleus of the lateral lemniscus (VNLL) and the CNIC. Fibers, but few terminals, were noted over the dorsal nucleus of the LL. The ipsilateral LL contained comparatively few labeled fibers, but sparse terminations occurred over portions of VNLL and CNIC. No transport of [3H]precursors was noted in the peripheral nuclei of the inferior colliculus or in the medial geneculate body on either side. Massive transport via the contralateral LL and the profuse terminals in the opposite CNIC suggested transneuronal transport via secondary and higher order auditory fibers. Although the largest number of fibers in the contralateral LL probably arose from the cochlear nuclei, higher order fibers also may have arisen from the ipsilateral LSO and the contralateral MSO and VNLL. Small numbers of fibers in both species descended from the region of the superior olivary complex (SOC) ventral to the facial motor nucleus. In the ground squirrel, scant auditory projections were traced into the opposite cochlear nuclei. Tritiated precursors in the endolymph passed most readily from labyrinth to cochlea, and transneuronal transport was more extensive in the auditory pathways than in the vestibular system at comparable times. Centrally transported [3H]fucose was cleared more promptly than [3H]proline in monkeys.

Animals↗
PubMed1998

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.

Adolescent↗
PubMed1984

Pathogenesis of experimental endolymphatic hydrops.

The protein content and the d.c. potential of the endolymph differs in the various parts of the endolymphatic space (cochlea, utricle, semicircular canals and endolymphatic sac) as also does the ion composition (chloride, potassium, sodium). 12 months after obliteration of the endolymphatic sac and duct in guinea pigs the d.c. potential falls, whereas, the sodium activity increases. The endolymphatic hydrops is not caused by an increased colloid osmotic pressure. The increased water-binding capacity of the cochlear endolymph is correlated with the increased Na+ activity.

Animals↗
PubMed1989

[Experimental study on early development of rat ear in vitro using whole embryo culture].

Rat embryos were explanted on late 11 day of gestation and cultured for 24 hours in rotating bottles with the yolk sac opened. Rat serum was used as culture medium and culture bottles were filled with 5% CO2 + 95% O2 gas mixture as gas phase. At the time of explantation and the end of the culture period, differentiation and growth of the embryos were monitored by counting somites and measuring crown rump length. About part of the embryos, protein determinations were made to measure growth. These data were compared with values found for 12 and 13 day embryos. The results for cultured embryos showed slight retardation in their differentiation and slight depression in the growth. At the same time to study early inner ear development in vitro, 9 of the other cultured embryos were serially sectioned and observed by light microscopy. In the cultured embryos endolymphatic duct elongated and acoustico-facial ganglion enlarged remarkably. Otocysts became flattened and elongated ventrally. Vestibular and cochlear portion were identifiable in the otocysts. Nerves arose from the ganglion reached to brain centrally and wall of pharynx peripherally. There was no significant difference in inner ear development between 13 day and the cultured embryos. This culture system should prove useful for studies on early inner ear development of mammalian embryos.

Animals↗
PubMedDate not supplied

Endolymphatic hydrops with absence of vein in paravestibular canaliculus.

Unilateral endolymphatic hydrops is described associated with absence of the vein in the paravestibular canaliculus (PVC), and with decreased vascularity of the vestibular aqueduct and endolymphatic sac. The venous return from the vestibule was normal as far as the junction of the branches forming the PVC vein. At this junction, a blind venous loop was formed with no continuation of venous drainage through the PVC. This probably represents a developmental anomaly. The decreased vascularity of the endolymphatic sac may be related to the absence of the PVC vein. However, anatomical and functional relationships of these vessels are not clear and need further study. Perisac fibrosis and endosteal bone formation are possibly secondary to the decrease in vascularity. A large chronic rupture of the inferior saccule wall probably accounts for the absence of vertigo and the relatively mild degree of cochlear endolymphatic hydrops.

Aged↗
PubMed1989

Calcitonin-gene-related-peptide-immunoreactive innervation of the rat head with emphasis on specialized sensory structures.

The distribution of calcitonin-gene-related peptide-like immunoreactivity (CGRP-IR) was studied in sections of decalcified rat head and selected whole-mount preparations in order to address the complex peptidergic innervation patterns in peripheral cephalic specialized zones and to examine neuronal ganglia in situ. Labeled neuron somata in trigeminal, glossopharyngeal, and vagal ganglia comprised a large proportion of small to medium size type B ganglion cells. Parasympathetic ganglia (ciliary, otic, sphenopalatine, submandibular) revealed a small population of labeled somata and numerous perisomatic IR axons, whereas sympathetic ganglion cells (superior cervical) were devoid of label though richly innervated by perisomatic IR axons. The gustatory geniculate ganglion contained only a few labeled neurons and axons. Coarse peripheral CGRP-IR axons were traced to skeletal muscle motor end plates (e.g., lingual, tensor tympani, etc.), and thin sensory axons most densely innervated the cornea, iris, general integument, all mucosal epithelia lining the tympanic, nasal, sinus and oropharyngeal cavities, and the cerebral meninges. Blood vessels, glands, ducts, and their orifices were often heavily innervated, and specific specializations and exceptions are discussed. Distinctive patterns of IR innervation characterized the various specialized sensory systems, including 1) cochlear and vestibular hair cells; 2) lingual, palatal, oropharyngeal, and laryngoepiglottal taste buds; 3) main olfactory epithelium and axons projecting to glomeruli in specific sectors of main olfactory bulb; 4) septal-olfactory organ; 5) vomeronasal organ; and 6) the nervus terminalis system. Secretory epithelia (ciliary body, choroid plexus, and stria vascularis) were notably lacking in CGRP-IR. Despite the multiplicity of functionally distinct CGRP neuronal and axonal populations, certain generalizations merit consideration. The extensive innervation of chemosensory nasal and oral epithelia may contribute to specific chemical sensitivities (e.g., relating to olfactory and gustatory senses) as well as evoking "nociceptive" responses to chemical irritants as part of a "common chemical sense." An efferent role for some of these peptidergic afferent axons may also be inferred from their specific distributions. Sites involved in regulating access to and sensitivity of sense organs to external stimuli (e.g., cochlear and vestibular hair cells, taste bud orifices, and main olfactory epithelium) are heavily innervated. Other IR axons are in position to exert control over airflow through nasal turbinates, glandular secretion, blood circulation, and duct transport systems.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1996

High-resolution T2-weighted MR imaging of the inner ear using a long echo-train-length 3D fast spin-echo sequence.

The purpose of this study was to assess the value of a long echo-train-length 3D fast spin-echo (3D-FSE) sequence in visualizing the inner ear structures. Ten normal ears and 50 patient ears were imaged on a 1.5T MR unit using a head coil. Axial high-resolution T2-weighted images of the inner ear and the internal auditory canal (IAC) were obtained in 15 min. In normal ears the reliability of the visualization for the inner ear structures was evaluated on original images and the targeted maximum intensity projection (MIP) images of the labyrinth. In ten normal ears, 3D surface display (3D) images were also created and compared with MIP images. On the original images the cochlear aqueduct, the vessels in the vicinity of the IAC, and more than three branches of the cranial nerves were visualized in the IAC in all the ears. The visibility of the endolympathic duct was 80%. On the MIP images the visibility of the three semicircular canals, anterior and posterior ampulla, and of more than two turns of the cochlea was 100%. The MIP images and 3D images were almost comparable. The visibility of the endolymphatic duct was 80% in normal ears and 0% in the affected ears of the patients with Meniere's disease (p < 0.01). In one patient ear a small intracanalicular tumor was depicted clearly. In conclusion, the long echo train length T2-weighted 3D-FSE sequence enables the detailed visualization of the tiny structures of the inner ear and the IAC within a clinically acceptable scan time. Furthermore, obtaining a high contrast between the soft/bony tissue and the cerebrospinal/endolymph/ perilymph fluid would be of significant value in the diagnosis of the pathologic conditions around the labyrinth and the IAC.

Adult↗
PubMed1984

Single cochlear fibre responses in guinea pigs with long-term endolymphatic hydrops.

Some cochlear fibre response properties have been measured in two GPs approximately one year after induction of endolymphatic hydrops (by surgical obliteration of the endolymphatic sac and duct). These animals are considered as models of the effects of hydrops in Menière's disease, and the purpose of the study was to examine any modifications of fibre response properties which may underly auditory symptoms of the disease in man. Neurones towards more apical cochlear regions (with low characteristic frequencies) showed the greatest deterioration in tuning properties; on average, in the 1-6 kHz range, Q10dB values were reduced by a factor of two compared with normal animals. Discharge rate versus intensity functions of such units were abnormally steep, with dynamic ranges reduced by 10-20 dB. Towards higher frequency regions neurone response properties showed less deterioration (contrasting with many other types of cochlear pathology where, in general, the high frequency basal region exhibits greatest vulnerability). We have also observed in a few units an abnormal bursting in both spontaneous and driven discharge. Interspike intervals during burst are less than 1 ms (within relative refractory period). These findings are related to the auditory symptoms of Menière's disease, in particular, poor frequency selectivity, loudness recruitment and tinnitus.

Action Potentials↗
PubMed1994

Endolymph calcium increases with time after surgical induction of hydrops in guinea-pigs.

The ionized Ca2+ concentration in cochlear endolymph is normally extremely low. Previous studies have shown that endolymph Ca2+ levels become elevated when measured at long intervals after endolymphatic hydrops is surgically induced. The present study was designed to investigate how rapidly endolymph Ca2+ increases following endolymphatic duct ablation. Hydropic animals were tested at either 4 days, 4 weeks, 8 weeks or 16 weeks after surgery. In each animal endolymph Ca2+ and endocochlear potentials were measured in all four cochlear turns using double-barreled Ca(2+)-sensitive electrodes. Cochlear sensitivity was assessed using compound action potential thresholds. Our results confirm that hydropic animals show an elevation of endolymph Ca2+ and a reduction of EP which is initially small, but becomes more pronounced at longer times after surgery. At 16 weeks endolymph Ca2+ was increased by an average factor of 20 in the basal turn and 7.5 in the fourth turn. These findings suggest that endolymph Ca2+ changes may not be the primary factor responsible for hydrops generation, but probably contribute to cochlear dysfunction in later phases of hydrops. For some experimental groups, the elevation of AP threshold was more closely correlated with endolymph Ca2+ level than it was with endolymph volume. Endolymph Ca2+ changes must therefore be considered in order to account for dysfunction in the hydropic cochlea.

Action Potentials↗
PubMed1992

Cochlear blood flow and microvascular resistance changes in response to hypertonic glycerol, urea, and mannitol infusions.

The effect of hyperosmotic agents on cochlear blood flow (CBF) was tested in normal guinea pigs and in guinea pigs having prior unilateral operations to ablate the endolymphatic duct. Laser-Doppler-measured CBF was normalized to remove apparent changes related directly to systemic blood pressure. Hyperosmotic fluids were given via venous infusion: glycerol (20% and 40% solutions), urea (10%, 30%, and 40% solutions), and mannitol (40% solution). All agents were dissolved in 0.9% saline and the mixtures were given at a rate of 0.3 to 0.6 mL/min for 5 minutes. Control infusions were of 0.9% saline and isotonic dextran 70 (Pharmacia). All hyperosmotic infusions resulted in similar increases in normalized cochlear blood flow (nCBF) that extended to a maximum of 300% of the baseline value in a dose-dependent way during the infusion time period. Within approximately 30 minutes following infusions, nCBF had returned to baseline levels. Saline infusion alone had little effect on nCBF, but isotonic dextran 70 gave a sustained increase to 122% of the baseline levels. There was no difference between the responses of nCBF in hydropic and normal cochleas for either control or hyperosmotic solutions. Measurements of systemic hematocrit at time intervals during and following the infusions showed that transient reductions of up to approximately 8% (for the maximum osmotic challenge) occurred during the infusion. It is concluded that the hyperosmotic treatments tested here are equally effective for short-term enhancements of nCBF in both normal and hydropic cochleas. The basis of the flow increase is partially rheologic and partially due to a local vasodilation.

Animals↗
PubMed1994

Fine structure of the human cochlear aqueduct: a light and transmission electron microscopic study of decalcified temporal bones.

The morphologic features of the human cochlear aqueduct were examined using both light and electron microscopy. The lumen of the cochlear aqueduct was observed to be filled with dense, irregular connective tissue corresponding to dura mater. At the entrance to the cerebrospinal fluid space, the dense connective tissue in the ductal lumen was covered with a thin layer of a few flattened cells, which was contiguous with the arachnoid membrane of the brain. A simple low cuboidal epithelium also separated the perilymphatic space from the lumen of the duct. Our observations confirm the presence of a barrier membrane at the opening to the perilymphatic space, and suggest that no transport occurs in the human cochlear aqueduct.

Cochlear Aqueduct↗
PubMed1999

Apoptosis during inner ear development in human and mouse embryos: an analysis by computer-assisted three-dimensional reconstruction.

Apoptosis in the developing inner ear tissue of human (Carnegie stage 14 to 21, approximately 5 to 8 weeks of gestation) and mouse (10.5 to 14 days of gestation) embryos was systematically analyzed by a computer-assisted three-dimensional reconstruction of the serial histological sections and by the TUNEL method. Morphogenetic events such as folding between the utricular portion and endolymphatic duct, constriction of the junction of the saccule with the cochlea and folding of the vestibular portion to form the semicircular ducts were accompanied by a localized distribution of apoptosis. The apoptosis was also related to the innervation of the cochlear and vestibular epithelia from the sensory ganglion of the eighth cranial nerve and the differentiation of the otic epithelia into the sensory epithelia. These results suggest that apoptosis plays an important role in the development of the inner ear.

Animals↗
PubMed2002

The retinoic acid receptors RARalpha and RARgamma are required for inner ear development.

To define the signal transduction pathway of retinoic acid during inner ear development, we analyzed the expression patterns of transcripts encoding the three retinoic acid receptors (RARalpha, beta, and gamma) and related them to phenotypes resulting from single or compound inactivation of these nuclear receptors. The expression of all three RARs was observed in the developing mouse otocyst as early as embryonic day 10.5 (E10.5)-E12.5 and continued into adulthood. Expression domains of the three RAR receptors, however, were largely non-overlapping: RARalpha was predominantly expressed in the developing sensory epithelium, RARbeta in inner ear mesenchymal tissues and RARgamma in the differentiating otic capsule. In the adult, RARalpha and RARgamma transcripts were found in the organ of Corti and the spiral ganglion, whereas RARbeta transcripts were localized in mesenchyme-derived tissues. RARalpha, beta, and gamma null mutant mice, as well as RARalpha/RARbeta and RARbeta/RARgamma combined null fetuses, did not present any noticeable morphological abnormalities in the inner ear. In contrast, RARalpha/RARgamma null mutants displayed a severe hypoplasia of the otocyst that was already visible at E10.5 without any visible endolymphatic duct. The hypoplastic otocyst in RARalpha/RARgamma null mutants was characterized by impaired chondrocyte differentiation and neural development. After the second week of gestation, these mutant fetuses lacked all of the semi-circular canals and the endolymphatic duct and displayed strong anomalies in the inner ear structures. The morphological deficits were generally more severe in the cochlear portion than in the vestibular portion of the inner ear. Altogether, these results demonstrate that RARalpha and RARgamma play an essential role in the initial differentiation of otic placode derivatives, whereas RARbeta plays a minimal role in this process.

Animals↗
PubMed2002

Temporal bone anomalies in the branchio-oto-renal syndrome: detailed computed tomographic and magnetic resonance imaging findings.

OBJECTIVE: To inventory computed tomographic and magnetic resonance imaging findings in the branchio-oto-renal (BOR) syndrome. STUDY DESIGN: A prospective computed tomographic and magnetic resonance imaging study on a family with the BOR syndrome. SETTING: Department of medical imaging and magnetic resonance imaging at St. Jan Brugge, Brugge, Belgium. PATIENTS: Eight affected members of a Belgian family. Younger affected family members were excluded because of their age. RESULTS: Computed tomography showed inner ear malformations in all eight affected patients. Magnetic resonance imaging was performed on five patients and showed inner ear malformations. To define hypoplasia or congenital enlargement of the inner ear structures, measurements obtained from a control group of normal subjects were used for comparison. Almost symmetrical cochlear abnormalities were observed on the three-dimensional Fourier transformation-constructive interference in steady state images of the five patients who underwent magnetic resonance imaging; four had dysplasia of the cochlea, and one had hypoplasia. The vestibule was slightly enlarged in one patient; computed tomography and magnetic resonance imaging showed semicircular canal malformations. Magnetic resonance imaging clearly showed bilateral enlarged endolymphatic sacs and ducts, whereas computed tomography showed only unilateral widening of the vestibular aqueduct and borderline widening of the vestibular aqueduct. Magnetic resonance imaging showed bilateral hypoplasia of the cochlear branch of the eighth nerve in one patient. CONCLUSION: Hypoplasia and dysplasia of the cochlea were consistent findings, and only magnetic resonance imaging was able to evaluate the intracochlear changes in detail and corrected computed tomography in most patients. Moreover, magnetic resonance imaging also detected bilateral hypoplasia of the cochlear branch of the eighth nerve in one patient. A widened vestibular aqueduct and a widened vestibular sac were frequent but not obligatory features of the BOR syndrome. Other malformations of the middle ear included a reduced middle ear cavity and malformations of the ossicular chain.

Adolescent↗
PubMed2005

The relationship of the round window membrane to the cochlear aqueduct shown in three-dimensional imaging.

The round window membrane and cochlear aqueduct complex in the guinea pig are reconstructed with 3D-imaging, using orthogonal plane fluorescence optical sectioning (OPFOS). The 3D-images show that the periotic duct and the aqueduct are connected to a pouch-like extension of the round window. The function of this may be regulation of aqueduct flow resistance under the influence of a pressure difference between inner ear fluid and middle ear.

Animals↗