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PubMed1984

Light and electron microscopic studies of the basilar papilla in the duck, Anas platyrhynchos. I. The hatchling.

The intent of this study was to describe in detail the normal structure of the basilar papilla in the duck, Anas platyrhynchos, with light and electron microscopy. The cochlear duct is supported by a ring of dense periotic connective tissue, the limbus. Distribution of hair cells in the basilar papilla follows the general avian pattern. Tall hair cells occupy the neural margin of the papilla. Short hair cells cover the abneural margin from the proximal tip to the middistal area. Intermediate hair cells form a transition zone from genu to distal tip. Patterns of innervation are correlated with hair cell morphology, which supports the classification of hair cells in birds into three groups. Tall hair cells synapse with two to four large afferents and one efferent; intermediate hair cells synapse with one or two afferents and one or two efferents; short hair cells synapse with one small afferent and one or two large efferents. In this relatively primitive species of bird, cuticles in all classes of hair cells reach the plasmalemma on the neural side of the cell, a condition that supports the contention that tall hair cells are more primitive than short hair cells.

Animals↗
PubMed1985

Quantitative studies of auditory hair cells and nerves in lizards.

Because the lizard cochlear duct is anatomically accessible as well as relatively simple in structure it is an excellent model in which to study auditory hair cells, nerve fibers, and innervational patterns. The objectives of this study were to determine the intra- and interspecific variations of auditory hair cell and nerve fiber numbers, nerve fiber/hair cell ratios, and nerve fiber sizes in a varied of lizard species and to relate these to auditory function and phylogeny. Hair cell numbers were determined by SEM and serial frontal sections of the papilla basilaris and nerve fiber numbers and diameters by use of a Zeiss TGZ3 particle counter. The coefficient of variation of hair cell numbers varied from 3.2 to 16.6 (171 specimens, 15 species) and of nerve fiber numbers from 1.2 to 14.4 (381 specimens, 35 species). There was no correlation between hair cell or nerve fiber number and age or sex. The nerve fiber number/hair cell number ratio was 3.5-11.1/1 in small papillae basilares of the iguanid-agamid-anguid type, 2.4-3.2/1 in the teiid type, and 0.6-1.5/1 in the larger specialized papillae of the scincid and gekkonid types. Nerve fibers varied in diameter from 0.8 to 6.0 microns (largest percentage were 2-4 microns) and were unimodally distributed. Larger nerve fibers usually supplied the unidirectionally oriented hair cells of the papilla basilaris. Variations in hair cell and nerve fiber numbers in other vertebrate classes and the functional and phylogenetic aspects of lizard papilla basilaris structure and innervation are discussed.

Animals↗
PubMed1988

Auditory receptor of the red-eared turtle: I. General ultrastructure.

The auditory receptor of the red-eared turtle has been the subject of intensive electrophysiological study within the last decade, yet the details of its ultrastructure have remained uninvestigated. In the present report information is derived from an analysis of specimens prepared for light, scanning electron, and transmission electron microscopy. Attention is focused on the ultrastructure of hair cells, supporting cells, and nerve fibers within the sensory epithelium as well as the basilar membrane upon which it rests. A description of the receptor's relations to surrounding sensory epithelia, the limbus of the cochlear duct, and the basilar membrane is also included. Observations are discussed in the light of similar information from other reptilian auditory receptors and the mammalian organ of Corti.

Animals↗
PubMed1992

Contractile proteins in the hyaline cells of the chicken cochlea.

Hyaline cells are a single layer of epithelial cells found at the inferior edge of the sensory epithelium in the chick cochlea. They rest directly above a specialized region of the basilar membrane at a point where it connects to the fibrocartilaginous skeleton of the cochlear duct. The basal cytoplasm of the hyaline cells contains a bundle of linearly aligned actin filaments that resemble stress fibers in their organization. The actin filaments are anchored in the basal plasma membranes of the cells, which are, in turn, associated with the underlying basal lamina and the extracellular matrix of the basilar membrane. We have used a combination of transmission electron microscopy, differential-interference-contrast and epifluorescence light microscopy, and confocal laser scanning microscopy to study the composition and organization of these actin bundles within the hyaline cells. The bundles are arranged into triangular wedges that are oriented radially across the basilar membrane. Each cell contains one or two actin wedges. Adjacent cells can have them aligned in opposite directions so that in a whole-mount surface preparation they appear as interdigitations. Immunofluorescent staining of the hyaline cells has shown that smooth muscle myosin and alpha-actinin are co-localized to the actin bundles. Smooth muscle myosin is also found throughout the cytoplasm of the cells. The fact that hyaline cells in the chick cochlea are contacted by efferent nerve fibers suggests that these cells may regulate tension on the basilar membrane via the specialized bundle of actin filaments.

Animals↗
PubMed1995

Hair and supporting-cell differentiation during the development of the avian inner ear.

Two monoclonal antibodies and serial section analysis have been used to compare the sites and times at which hair and supporting-cells differentiate in various sensory regions of the chick inner ear during its development. A monoclonal antibody recognising the 275 kD hair-cell antigen, a protein that is specifically associated with the apical surface of hair cells, was used to identify immature hair cells. Another monoclonal antibody, gm-2, which stains the gelatinous membranes of the cochlear duct, sacculus, and utriculus and the epithelial supporting cells of all vestibular structures in the inner ears of early posthatch chicks, was used to detect the onset of supporting-cell differentiation. Although the antigens recognised by the two antibodies are first detected almost simultaneously during the development of each sensory region, their appearance is not always exactly temporally coincident, and their order of appearance, when not coincident, varies between the epithelia but is always the same within any one organ. Also, when the two antigens are first present in any one region, there is not always a very precise overlap in their spatial distribution. These results cannot be explained entirely by a previously proposed model for hair and supporting-cell development in which hair cells differentiate first and prevent undetermined, surrounding cells from becoming hair cells via lateral inhibition. Modified forms of the original model that can accommodate some of these observations are considered and discussed.

Animals↗
PubMed2004

Genomic structure, cochlear expression, and mutation screening of KCNK6, a candidate gene for DFNA4.

KCNK6 encodes a tandem pore domain potassium channel, TWIK-2, that maps to chromosome 19. Both STS and linkage maps established KCNK6 as a positional candidate gene for DFNA4, a form of autosomal dominant nonsyndromic hereditary hearing loss. Identification and characterization of Kcnk6 expression within the mammalian cochlea established the gene as a functional candidate for DFNA4. Identification of Twik-2 expression in the mouse cochlea was initially established via RT-PCR assay of cochlear RNA. Subsequent immunoblot analysis of cochlear homogenate yielded a distinct 35-kDa band corresponding to the calculated molecular weight of the mouse Twik-2. Immunohistochemical studies localized Twik-2 expression in the cochlea predominantly within the stria vascularis. This vascular tissue borders the cochlear duct and is a critical regulator of potassium concentration in the endolymph. Genomic structure of TWIK-2 was subsequently determined and shown to consist of three coding exons with splice acceptor and donor sites in accordance with the consensus GT-AG rule. Two separate DFNA4 families were screened for KCNK6 sequence alterations. No mutations were found, thus excluding TWIK-2 as the DFNA4 candidate disease gene. Nevertheless, expression of Twik-2 within the stria vascularis suggests a potential role for this protein as one of the terminal components of the potassium ion-recycling pathway that contributes toward its reabsorption into the endolymph.

Animals↗
PubMed2004

Cloning and developmental expression of nonmuscle myosin IIA (Myh9) in the mammalian inner ear.

MYH9 encoding a nonmuscle myosin heavy chain has been linked to nonsyndromic and syndromic forms of autosomal dominant hereditary hearing loss, suggesting a critical biological role of this motor protein in the auditory organ. While Myh9 expression has been described in the adult mouse, critical parameters pertaining to its developmental expression remain to be characterized. The current study describes cloning of the mouse Myh9 cDNA and the temporal onset and spatial distribution of Myh9 expression in the inner ear of the developing fetus, the neonate, and the adult. The cloned Myh9 cDNA contained two single-base-pair differences from the published genomic sequence: T990C (G330G) and T5198A (L1733Q). Immunoblotting of embryonic (E15.5) and adult tissues from several organs, including the cochlea, identified a single 250-kDa anti-Myh9-immunoreactive band, supporting an absence of Myh9 splice variants in the fetus and the adult. In situ expression analysis identified Myh9 distributed within the epithelial layer of the otic vesicle at E10.5. Myh9 expression was found to persist within the epithelia surrounding the cochlear duct at E13.5 and E16.5. The sensory cells of the developing cochlea were positive for Myh9 expression at E16.5. Within the neonate and the adult cochlea, Myh9 expression was observed within the sensory hair cells and the supporting hair cells of the organ of Corti, the spiral ligament, and the spiral limbus, but not in the stria vascularis. Identification of Myh9 in the developing and mature inner ear suggests a role for this protein in the development and maintenance of auditory function.

Animals↗
PubMed1991

Temporal pattern of innervation in the developing mouse inner ear: an immunocytochemical study of a 66-kD subunit of mammalian neurofilaments.

We have examined the expression of a 66-kD neurofilament protein (NF-66) in the developing inner ear. Mouse embryos, fetuses, and neonates were fixed in Methacarn, embedded in paraffin, and sectioned. A polyclonal antiserum raised specifically to NF-66 and unreactive to NF-L, -M, -H, and peripherin was used for immunocytochemical staining. NF-66 immunostaining was first detectable in the rhombencephalon at embryonic day (E) 9.5. Immunoreactivity was first detected in the statoacoustic ganglion (SAG) early on E10.5. By late E10.5, the first SAG axons were detectable within the intraepithelial spaces of the otocyst. At E12, NF-66 positivity was detectable in neurites that projected into areas of presumptive vestibular sensory epithelium. Neurites projecting into the presumptive acoustic sensory epithelium were negative. However, at E13, the projections from both the vestibular and the acoustic ganglion (i.e, cochlear duct) were both NF-66 positive. In the cell bodies, NF-66 expression appeared earlier in the vestibular than in the auditory neurons. By E16, neuronal somas in both ganglia were NF-66 positive.

Animals↗
PubMed1977

Noxious effects upon cochlear metabolism.

The influence of various toxic substances and of drugs with ototoxic side effects upon energy generation, energy utilization, and membrane processes of the cochlea were studied. None of the drugs tested interfered with energy generation to as great an extent as did anoxia or cyanide and 2,4-dinitrophenol. Ouabain produced a pronounced interference with energy utilization of the stria vascularis. The "loop" diuretics ethacrynic acid and furosemide produced a reduction of energy utilization of a lesser degree than did ouabain. The "loop" diuretics do not seem to exert their toxic action upon strial Na+K+-ATPase, but may act by interfering with strial adenylate cyclase. Aminoglycoside antibiotics and diuretic and nondiuretic mercurials seem to exert their primary noxious action upon cochlear function by interfering with membrane processes of the structures bounding the cochlear duct.

Action Potentials↗
PubMed1979

Hypothyroidism and the ear: electrophysiological, morphological, and chemical considerations.

There is both clinical and laboratory evidence that hearing loss can result from congenital and acquired hypothyroidism. The reversibility of this process, however, and its incidence and pathophysiology are not universally agreed upon. Laboratory animals rendered hypothyroid with radioactive iodine 131 or propylthiouracil demonstrated normal perilymph sodium and potassium levels but increased auditory thresholds for N1N2 response and brain stem evoked audiometry as well as a crystallized consistency of the bone of the bullae and cochleae, ossicular abnormalities, obliteration of the oval and round window, large dark staining lipid accumulations in Hensen's cells, large intercellular spaces in the stria vascularis with degeneration of the marginal and intermediate cells, inner and outer hair cell degeneration, debris in the cochlear duct, and tectorial membrane irregularity. Otic capsule biochemical alterations were identified which may account for the osseous changes observed morphologically. The morphological, biochemical, and electrophysiological findings in this study support the hypothesis that the cochlea is a site of lesion for sensorineural hearing loss in hypothyroidism. Middle ear changes identified could be responsible for the conductive component.

Animals↗
PubMed2002

Extracellular matrices associated with the apical surfaces of sensory epithelia in the inner ear: molecular and structural diversity.

The ultrastructure and molecular composition of the extracellular matrices that are associated with the apical surfaces of the mechanosensory epithelia in the mouse inner ear are compared. A progressive increase in molecular and structural organization is observed, with the cupula being the simplest, the otoconial membrane exhibiting an intermediate degree of complexity, and the tectorial membrane being the most elaborate of the three matrices. These differences may reflect changes that occurred in the acellular membranes of the inner ear as a mammalian hearing organ arose during evolution from a simple equilibrium receptor. A comparison of the molecular composition of the acellular membranes in the chick inner ear suggests the auditory epithelium and the striolar region of the maculae are homologous, indicating the basilar papilla may have evolved from the striolar region of an otolithic organ. A comparison of the tectorial membranes in the chick cochlear duct and the mouse cochlea reveals differences in the structure of the noncollagenous matrix in the two species that may result from differences in the stochiometry of alpha- and beta-tectorin and/or differences in the post-translational modification of alpha-tectorin. This comparison also indicates that the appearance of collagen in the mammalian tectorial membrane may have been a major step in the evolution of an electromechanically tuned vertebrate hearing organ that operates over an extended frequency range.

Acoustic Maculae↗
PubMed1975

Primary congenital aphakia and the rubella syndrome.

Four embryos from women infected by rubella virus early in pregnancy were investigated histologically. In three of the patients the serological tests were positive; in the fourth the diagnosis of rubella was based solely on the clinical picture. Three of the four embryos showed unilateral severe microphthalmia and primary congenital aphakia. In addition to this defect the right eye of one of the embryos showed a central liquefaction of the lens (cataract). Damage to the internal ear in the form of discontinuities in the epithelium of the cochlear duct were also observed (in two of the three embryos; in the fourth both internal ears were absent in the curettage material). In three of the four hearts there were cells in the myocardium with a markedly eosinophilic cytoplasm.

Abnormalities, Multiple↗
PubMed1993

Unique expression pattern of the FGF receptor 3 gene during mouse organogenesis.

The actions of fibroblast growth factors (FGFs) are mediated via a family of four closely related FGF receptor genes (FGFRs 1-4). FGFR1, FGFR2, and FGFR4 have unique patterns of expression during embryogenesis suggesting that these receptors mediate different functions of FGFs during development. In the present study, we used in situ hybridization analysis to show that FGFR3 also has a unique pattern of expression during organogenesis. Like FGFR1 and FGFR2, FGFR3 was expressed in the germinal epithelium of the neural tube (9.5-16.5 days pc). However, at 1 day postpartum and in the adult brain, FGFR3 was expressed diffusely and localized in cells with morphologic characteristics of glia, a pattern distinctly different from the discrete neuronal expression of FGFR1. FGFR3 was also expressed at high levels in differentiating hair cells of the cochlear duct, but was not detected in other sensory epithelia. Outside the nervous system, the highest level of FGFR3 expression was found in the cartilage rudiments of developing bone. During endochondral ossification, FGFR3 was expressed exclusively in resting cartilage, a pattern distinct from FGFR1 and FGFR2 which are also expressed during this process. Unlike FGFR1 and FGFR2, FGFR3 was not detected in most other epithelial or mesenchymal tissues during these stages of organogenesis. The unique expression pattern of FGFR3 compared with the other FGF receptors strongly suggests that FGFR3 performs specific functions during organogenesis.

Animals↗
PubMed1998

The differential sensitivities of inner ear structures to retinoic acid during development.

In order to examine the mechanisms that underlie development of the inner ear, the normal processes were perturbed using all-trans-retinoic acid (RA). By implanting a resin exchange bead saturated with RA into stage 16 (Hamburger and Hamilton, 1951, J. Morphol. 88, 49-92) embryonic day 2.5 chick ears, it was possible to analyze its in vivo effects on inner ear development. There is a temporal window during which the developing chick inner ear is particularly susceptible to the effects of RA (stages 16-19). This RA period of sensitivity precedes evidence of gross morphologic or histologic differentiation by at least 24 h, suggesting that mechanisms controlling formation of key inner ear structures are already in progress. There is a dose dependence on RA, with increasing doses of RA generating increasingly severe phenotypic abnormalities. Data indicate that these effects are due to differential sensitivities of the various inner ear structures to RA during their formation. In general, the vestibular structures were more susceptible to RA effects than the cochlear duct. Furthermore, nonsensory structures such as semicircular canals seemed to display a greater susceptibility to RA than their associated sensory structures (i.e., cristae). Among the three semicircular canals, the superior canal was the most susceptible to RA treatment, whereas the common crus was particularly resistant, suggesting that the molecular mechanisms for each structure's formation are different. The defect in semicircular canal formation is due to problems in the initial outgrowth of the canal plate which in turn is related to a down-regulation of early otocyst cell proliferation. This perturbation model provides valuable insight into the processes involved in producing the intricate patterning of the inner ear.

Animals↗
PubMed1995

Embryonic expression of the 5-HT3 receptor subunit, 5-HT3R-A, in the rat: an in situ hybridization study.

The role of serotonin as a neurotransmitter in the vertebrate central and peripheral nervous systems has been extensively studied. In addition to its well-defined role in neurotransmission, serotonin has also been implicated in development. We have used in situ hybridization to localize 5-HT3 receptor mRNA in embryonic rat sections from Embryonic Day 10 (E10) to E18. Expression was first detected in the cranial sensory ganglia starting on E10. Expression was later detected in many regions within the developing CNS. In addition to the cranial sensory ganglia, expression was detected in many regions of the peripheral nervous system including dorsal root, sympathetic, and parasympathetic ganglia, and in the myenteric plexus of the enteric nervous system. Expression was also detected in many nonneuronal cell populations including the choroid plexus, cochlear duct, and olfactory epithelium. Expression in regions of active epithelial-mesenchymal interaction such as the tooth bud, lung, and submandibular gland may indicate a role for 5-HT3 receptors in the process of secondary induction.

Animals↗
PubMed1993

The effects of low-frequency ultrasound on the inner ear: an electrophysiological study using the guinea pig cochlea.

By examining 218 albino guinea pigs, electrophysiological methods were used to investigate the effects of low frequency ultrasound at moderate sound pressure levels after long-term exposure to the inner ear. From 10 kHz to 28 kHz, low frequency ultrasound below 100 dB SPL induced significant changes in cochlear microphonics, elevated thresholds and decreased maximum output voltage of action potentials and decreased absolute values of negative potentials of the endocochlear potentials.

Acoustic Stimulation↗
PubMed1996

Effect of cisplatin on the negative charge barrier in strial vessels of the guinea pig. A transmission electron microscopic study using polyethyleneimine molecules.

The anionic sites on the basement membrane in the cochlea are believed to act as a charge barrier. Using polyethyleneimine (PEI) as a cationic tracer, we examined the effects of cisplatin (CDDP) on anionic sites in the basement membrane in the cochlea. Eight Hartley-strain guinea pigs were separated into control (buffer administration) and CDDP groups. Ultrathin sections of the basal and third turns of the cochlear ducts were examined using a transmission electron microscope. A marked decrease of PEI distribution was noted in the strial vessels of the CDDP group compared to the control group. However, the two groups showed no significant differences in PEI particles on the basement membranes in the basilar and Reissner's membranes, or in the basal and third turns. These findings suggest that the charge barrier in the stria vascularis may be easily injured by the administration of CDDP.

Animals↗
PubMed1991

ChAT-like immunoreactivity of olivocochlear fibres on rat outer hair cells during the postnatal development.

Several studies present a great deal of information about putative efferent neurotransmitters and their distribution in the adult and developing cochlea. Anatomical mapping of outer hair cell efferent fibres during ontogeny is still not available. Using quantitative electron microscopy in combination with immunocytochemistry, the distribution of ChAT-like immunoreactivity in the developing rat was investigated. Adult-like immunoreactivity in the whole cochlea is first observed in 30-day-old rats. We localized the adult-like immunoreactivity in all efferent fibres and synapses of the outer hair cells along the entire cochlear duct. An adult-like reaction in the whole cochlea could be observed on the 25th day after birth in two out of three cases. On the 20th postnatal day, no adult-like ChAT immunoreactivity was found, with the exception of one case where labelling was seen in the basal region only. The adult-like ChAT immunoreactivity on the 30th day, 2-3 weeks after the onset of hearing, is the latest maturation of all features of the organ of Corti so far investigated. Synaptogenesis of the outer hair cell efferents reaches an adult-like appearance already on the 16th day after birth.

Animals↗