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PubMedDate not supplied

Otologic manifestations of the hydantoin syndrome.

The temporal bones of a newborn infant with hydantoin syndrome showed multiple middle ear and inner ear anomalies. There was a constellation of bony and membranous defects involving the oval and round windows, cochlear ducts, cochlear aqueducts, endolymphatic ducts and sacs, and vestibular labyrinths. To the authors' knowledge, supernumerary vestibular sensory epithelial structures and an inner ear epidermoid cyst have not been previously reported. Wide communications between the subarachnoid space and inner ear were of surgical relevance.

Abnormalities, Drug-Induced↗
PubMedDate not supplied

Expression of Pax2 and patterning of the chick inner ear.

Early regionalized gene expression patterns within the otocyst appear to correlate with and contribute to development of mature otic structures. In the chick, the transcription factor Pax2 becomes restricted to the dorsal and entire medial side of the otocyst by stage 16/17. The dorsal region of the otocyst forms the endolymphatic duct and sac (ED/ES), and the cochlear duct is derived from the ventromedial region. In the mouse, however, Pax2 expression is reported only in the ventromedial and not the dorsal otocyst. In Pax2 null mice, the cochlea is missing or truncated, but vestibular structures differentiate normally. Here we demonstrate that in the chick, the emerging ED/ES express high levels of Pax2 even when the position of the emerging ED is altered with respect to its environment, either by 180 degrees otocyst rotations about the anterior/posterior axis or transplantation of the otocyst into the hindbrain cavity. However, the Pax2 expression pattern is plastic in the rest of the otic epithelium after 180 degrees rotation of the otocyst. Pax2 is upregulated on the medial side (formerly lateral), and downregulated on the lateral side (formerly medial and expressing Pax2) indicating that Pax2 expression is influenced by the environment. Although Pax2 is upregulated in the epithelium after 180 degrees rotations in the region that should form the cochlear duct, cochlear ducts are truncated or absent, and the ED/ES emerge in a new ventrolateral position. Ablation of the hindbrain at the placode or early otic pit stage alters the timing of regionalized Pax2 expression in the otocyst. The resulting otocysts and ears are generally smaller, vestibular structures are abnormal, ED/ES are missing but cochlear ducts are of normal length. The hindbrain and dorsal periotic mesenchyme provide unique trophic and patterning information to the dorsal otocyst. Our results demonstrate that the ED is the earliest structure patterned in the inner ear and that the hindbrain is important for its specification. We also show that, although normal Pax2 expression is required for cochlear duct development, it is downstream of ventral otocyst patterning events.

Animals↗
PubMed2002

Complementary and layered expression of Ephs and ephrins in developing mouse inner ear.

The distributions of the Eph-class receptors EphA4 and EphB1, and their ligands ephrin-A2, ephrin-B1, and ephrin-B2, were analysed by immunostaining in the mouse inner ear. Complementary patterns of EphA4 and its potential ligand ephrin-A2 were found, with ephrin-A2 in many of the structures lining the cochlear duct and within the cochlear nerve cells, and EphA4 in the deeper structures underlying the cochlear duct and in the cells lining the nerve pathway. EphB1 and its potential ligands ephrin-B1 and ephrin-B2 showed a segregated layered expression in the lateral wall of the cochlear duct (the external sulcus), which together with EphA4 expressed in the area, form a four-layered structure with an alternating pattern of receptors and ligands in the different layers. This arrangement gives the potential for different bidirectional Eph-mediated interactions between each of the layers. The results suggest that the Eph system in the cochlea may have a role in maintaining cell segregation during phases of cochlear development.

Animals↗
PubMed2002

Na+,K+-ATPase activity and ultrastructural localization in the tegmentum vasculosum in the cochlea of the duckling.

The tegmentum vasculosum of the avian cochlear duct mimics the stria vascularis of the mammalian cochlear duct in both location and structure, and previous studies indicate that it may be its functional counterpart with regard to endolymph synthesis. In the present study, we report on the enzymatic activity and ultrastructural localization of the Na+,K+-ATPase in the tegmentum vasculosum of the duckling. Na+,K+-ATPase activity was determined by measuring K+-dependent, ouabain-sensitive p-nitrophenyl phosphatase (p-NPPase) activity in homogenates of dissected regions of the cochlear duct. The ultrastructural localization of the Na+,K+-ATPase was identified using K+-dependent, ouabain-sensitive, p-NPPase cytochemistry. Specific enzyme activity was localized primarily in homogenates of the tegmentum vasculosum (2.27 micromol p-nitrophenyl phosphate/mg protein/min) when compared to homogenates of the entire cochlear duct (0.69 micromol p-nitrophenyl phosphate/mg protein/min). Reaction product for p-NPPase was localized primarily along the basolateral plasma membrane folds of the dark cells. The cytochemical deposits appeared to be located exclusively on the cytoplasmic side of the plasma membrane. The light cells were devoid of reaction product. Biochemical and cytochemical localization of p-NPPase activity on the basolateral plasma membrane folds of the dark cells of the tegmentum vasculosum in conjunction with the ultrastructural morphology of these cells is compatible with a Na+,K+-ATPase-dependent ion transport function related to endolymph synthesis.

4-Nitrophenylphosphatase↗
PubMed1991

Frequency representation and spiral ganglion cell density in the cochlea of the gerbil Pachyuromys duprasi.

The tonotopic map of the cochlea in the gerbil Pachyuromys duprasi was analysed by local iontophoretic HRP-application into physiologically defined regions of the cochlear nucleus and mapping of subsequent HRP transport patterns in cochlear spiral ganglion cells. Furthermore the spiral ganglion cell density along the cochlear duct was determined. The cochlear tonotopic map was established in the frequency range between 0.6 and 17.5 kHz. These frequencies corresponded to locations between 86 and 3% basilar membrane length (0% = cochlear base). It was found that the slope of the place-frequency map varied with frequency, the maximum slope being found between 1 and 4 kHz. This frequency range corresponds to the frequency range of highest auditory sensitivity as determined from cochlear microphonic recordings (Plassmann et al., 1987). The density of spiral ganglion cells also varied along the cochlear duct. A pronounced maximum (1927 cells/mm) was located at around 70% basilar membrane length, compared to values of 800 cell per mm near the cochlear apex and base. This region of high ganglion cell density also corresponds to the frequency range of highest auditory sensitivity.

Acoustic Stimulation↗
PubMed1975

Proliferation gradients in the inner ear of the monkey (Macaca mulatta) embryo.

Radioautographic studies were conducted on early developmental stages of the inner ear in monkey (Macaca mulatta) embryos ranging in age from stage 11 to stage 20 (25 to 39 days' gestation) and labeled for one hour with [3H] thymidine. The most active period of proliferation occurred at stage 13, at which time all regions of the otocyst, including the endolymphatic duct, were heavily labeled. In subsequent stages the dorsal portion of the endolymphatic duct failed to incorporate label, whereas proliferation continued in the ventral portion of the duct near its communication with the medial wall of the otocyst. The duct thus appeared to grow upward as a result of cell division from below. Mitotic activity continued in the remainder of the otocyst although there was a progressive temporal decrease in the labeling index. Spatial gradients also occurred, with dorsal and lateral regions less active than ventral and medial ones. As the otocyst differentiated, the cells in various areas became attenuated. These flattened cells were still capable of undergoing cell division, as indicated by the presence of labeled nuclei in all regions of the utricle, saccule, semicircular ducts, and cochlear duct.

Animals↗
PubMed1990

Micro-architectures of the osseous spiral laminae and spiral limbus in the mouse cochlea: a scanning electron microscopic study on the morphological basis of the auditory mechanics.

The auditory mechanics in the cochlea are closely related to the structural variations along the cochlear duct. In this study, the auditory teeth of the spiral limbus and the primary and secondary osseous spiral laminae in the mouse were examined along the entire course of the cochlear spiral by scanning electron microscopy (SEM) after removing the cochlear duct epithelium or the organic material with chemical maceration methods. The cochlear canal consisted of a hook and a spiral of one and half turns and the three-dimensional images and surface structures of the connective tissue forming the spiral limbus including the auditory teeth and the osseous spiral laminae are well demonstrated; the widths of the primary and secondary laminae, the spiral fissure between the two laminae, the tympanic lip, and the vestibular lip with the auditory teeth were measured, and the population density of the auditory teeth were determined in the hook and every half turn. The findings suggest that, in the cochlea the width of the basilar membrane increases in the hook and is almost constant in the spiral portion, the amount of fibers in the basilar membrane linearly decreases from the base to the apex, the displacement mode of the pillar cells during basilar membrane vibrations differs between the apical region lacking the bony edge of the tympanic lip and the other regions with bony edge, the connective tissue fibers from the auditory teeth are inserted to the bone surface of the primary lamina to support the teeth, the teeth on the marginal side of the vestibular lip maintain the stability of the tectorial membrane which is vibrating together with the basilar membrane in response to high frequency sounds on the basal side of the cochlear duct and low frequencies on the apical side, and the interdental cells on the Reissner membrane side maintain the size of the tectorial membrane which shows a linear increase in size from the base to the apex of the cochlear duct.

Animals↗
PubMed1997

Localization of secretory phospholipase A2 in mouse cochlear tissues and cultured cells.

OBJECTIVE: To localize the expression of secretory phospholipase A2 (sPLA2) in the cochlear duct. DESIGN: By means of an immunocytochemistry technique that used rabbit anti-porcine pancreatic phospholipase A2 antiserum, sPLA2 sites were identified in vivo and in vitro in the adult mouse cochlear duct. SUBJECTS: Eight C57BL/6N normal adult male mice (11-12 weeks old) (6 mice for the in vivo study, 2 mice for the in vitro study). RESULTS: Different patterns of immunostaining for sPLA2 were observed in tissues of the cochlear duct. High levels of sPLA2 were detected in the following areas: the basal cells of the stria vascularis, the organ of Corti, the spiral ganglion, and the cochlear nerve; moderate levels of sPLA2 were found in the suprastrial and poststrial portions of the spiral ligament; low levels of sPLA2 were observed in the marginal and intermediate cells of the stria vascularis and the infrastrial portion of the spiral ligament. Immunoreactivity for sPLA2 also was detected in cultured marginal cells of the stria vascularis and in fibrocytes of the spiral ligament. CONCLUSIONS: Secretory phospholipase A2 is present in mouse cochlear tissues and individual cultured cells. These results suggest that the levels of sPLA2 expression in the cochlear duct are cell specific.

Animals↗
PubMed1984

Morphologic study of effects of kanamycin on the developing cochlea of the rat.

The development of the rat inner ear starts about day 9 of a 22-day gestational period. The sensory and supporting cells are morphologically identifiable by day 18 of gestation; however, auditory function is not evident until day 9 postnatally. The organ of Corti attains adult maturity about day 16 postnatally. Morphologic and physiologic studies have shown that administration of sublethal doses of aminoglycosidic antibiotics, including kanamycin, damages the sensory and supporting cells of the inner ear in mammals. This results in the impairment of auditory function. This study was designed to determine the earliest stage in cochlear duct development at which kanamycin toxicity can be morphologically detected. A sublethal dose of kanamycin was administered to pregnant rats on days 10 through 20 of gestation and to neonates from days 1 to 8 or from days 8 to 16 postnatally. The inner ears were dissected and processed for light microscopic and ultrastructural observations. The cochlear ducts of fetuses exposed in utero to kanamycin and those of neonates exposed from days to 1 to 8 postnatally were unaffected. Kanamycin toxicity was evident in the cochlear ducts of neonates exposed from days 8 to 16 postnatally. The most severe damage occurred in the basal coil of the cochlea where in many instances sensory cells were totally absent. The sensory cells in the middle and apical coils exhibited abnormal morphology. These results suggest: (1) kanamycin does not have any permanent toxic effects on the rat cochlear duct during gestation and the first week of postnatal life. This provides a basis for further studies into the possible pharmacologic application of this finding in humans. (2) A correlation exists between the initiation of auditory function and the vulnerability of the organ of Corti to kanamycin toxicity.

Age Factors↗
PubMed2003

Forced activation of Wnt signaling alters morphogenesis and sensory organ identity in the chicken inner ear.

Components of the Wnt signaling pathway are expressed in the developing inner ear. To explore their role in ear patterning, we used retroviral gene transfer to force the expression of an activated form of beta-catenin that should constitutively activate targets of the canonical Wnt signaling pathway. At embryonic day 9 (E9) and beyond, morphological defects were apparent in the otic capsule and the membranous labyrinth, including ectopic and fused sensory patches. Most notably, the basilar papilla, an auditory organ, contained infected sensory patches with a vestibular phenotype. Vestibular identity was based on: (1) stereociliary bundle morphology; (2) spacing of hair cells and supporting cells; (3) the presence of otoliths; (4) immunolabeling indicative of vestibular supporting cells; and (5) expression of Msx1, a marker of certain vestibular sensory organs. Retrovirus-mediated misexpression of Wnt3a also gave rise to ectopic vestibular patches in the cochlear duct. In situ hybridization revealed that genes for three Frizzled receptors, c-Fz1, c-Fz7, and c-Fz10, are expressed in and adjacent to sensory primordia, while Wnt4 is expressed in adjacent, nonsensory regions of the cochlear duct. We hypothesize that Wnt/beta-catenin signaling specifies otic epithelium as macular and helps to define and maintain sensory/nonsensory boundaries in the cochlear duct.

Animals↗
PubMed1983

Inner ear pathology associated with Reye's syndrome.

Severe pathological changes were observed in the inner ear tissues of a 2-month-old patient who died of Reye's syndrome after 5 days of hospitalization. In the organ of Corti, the inner hair cells appeared to be more severely damaged than the outer hair cells. Various degrees of degeneration were observed in all non-sensory epithelial cells lining the cochlear duct. In most turns of the cochlear duct, Reissner's membrane was ruptured and/or collapsed onto the organ of Corti. Likewise, both sensory and non-sensory cells of the vestibular end organs were markedly degenerated. These observations suggest that the inner ear tissues are acutely affected in patients with Reye's syndrome, and that the changes may cause impairment of hearing and/or equilibrium in patients who recover.

Acoustic Maculae↗