SEARCH · PubMed Health

Results for “Cochlea”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources

PubMed2005

The final stage of cholinergic differentiation occurs below inner hair cells during development of the rodent cochlea.

To gain further insights into the cholinergic differentiation of presynaptic efferent terminals in the inner ear, we investigated the expression of the high-affinity choline transporter (ChT1) in comparison to other presynaptic and cholinergic markers. In the adult mammalian cochlea, cholinergic axons from medial olivocochlear (OC) neurons form axosomatic synapses with outer hair cells (OHCs), whereas axons from lateral OC neurons form axodendritic synapses on afferent fibers below inner hair cells (IHCs). Mouse brain and cochlea homogenates reveal at least two ChT1 isoforms: a nonglycosylated approximately 73 kDa protein and a glycosylated approximately 45 kDa protein. In mouse brain, ChT1 is preferentially expressed by neurons in periolivary regions of the superior olive consistent with the location of medial OC neurons. In the adult mouse cochlea, ChT1-positive terminals are located almost exclusively below OHCs consistent with a medial OC innervation. Between postnatal day 2 (P2) and P4, ChT1-positive terminals are below IHCs and occur after the expression of growth-associated protein 43, synapsin, and the vesicular acetylcholine transporter. By P15, ChT1-positive terminals are mostly on OHCs. Accounting for differences in gestational age, the developmental expression of ChT1 in the rat cochlea is similar to the mouse. However, in older rats ChT1-positive terminals are below IHCs and OHCs. In both rat and mouse, our observations indicate that the onset of ChT1 expression occurs after efferent terminals are below IHCs and express other presynaptic and cholinergic markers. In the mouse, but not in the rat, ChT1 may preferentially identify medial OC neurons.

Animals↗

PubMed2000

Expression of Math1 and HES5 in the cochleae of wildtype and Jag2 mutant mice.

The sensory epithelium within the mammalian cochlea (the organ of Corti) is a strictly ordered cellular array consisting of sensory hair cells and nonsensory supporting cells. Previous research has demonstrated that Notch-mediated lateral inhibition plays a key role in the determination of cell types within this array. Specificallly, genetic deletion of the Notch ligand, Jagged2, results in a significant increase in the number of hair cells that develop within the sensory epithelium, presumably as a result of a decrease in Notch activation. In contrast, the downstream mediators and targets of the Notch pathway in the inner ear have not been determined but they may include genes encoding the proneural gene Math1 as well as the HES family of inhibitory bHLH proteins. To determine the potential roles of these genes in cochlear development, in situ hybridization for Math1 and HES5 was performed on the cochleae of wild-type vs. Jagged2 mutants (Jag2deltaDSL). Results in wild-type cochleae show that expression of Math1 transcripts in the duct begins on E13 and ultimately becomes restricted to hair cells in the sensory epithelium. In contrast, expression of HES5 begins on E15 and becomes restricted to supporting cells in the epithelium. Results in Jag2 mutant cochleae suggest that Math1 transcripts are ultimately maintained in a larger number of cells as compared with wild-type, while transcripts for HES5 are dramatically reduced throughout the epithelium. These results are consistent with the hypothesis that activation of Notch via Jagged2 acts to inhibit expression of Math1 in cochlear progenitor cells, possibly through the activity of HES5.

Aging↗

PubMed2002

Gene expression profiles of the rat cochlea, cochlear nucleus, and inferior colliculus.

High-throughput DNA microarray technology allows for the assessment of large numbers of genes and can reveal gene expression in a specific region, differential gene expression between regions, as well as changes in gene expression under changing experimental conditions or with a particular disease. The present study used a gene array to profile normal gene expression in the rat whole cochlea, two subregions of the cochlea (modiolar and sensorineural epithelium), and the cochlear nucleus and inferior colliculus of the auditory brainstem. The hippocampus was also assessed as a well-characterized reference tissue. Approximately 40% of the 588 genes on the array showed expression over background. When the criterion for a signal threshold was set conservatively at twice background, the number of genes above the signal threshold ranged from approximately 20% in the cochlea to 30% in the inferior colliculus. While much of the gene expression pattern was expected based on the literature, gene profiles also revealed expression of genes that had not been reported previously. Many genes were expressed in all regions while others were differentially expressed (defined as greater than a twofold difference in expression between regions). A greater number of differentially expressed genes were found when comparing peripheral (cochlear) and central nervous system regions than when comparing the central auditory regions and the hippocampus. Several families of insulin-like growth factor binding proteins, matrix metalloproteinases, and tissue inhibitor of metalloproteinases were among the genes expressed at much higher levels in the cochlea compared with the central nervous system regions.

Animals↗

PubMed2001

Semiautomatic segmentation of the cochlea using real-time volume rendering and regional adaptive snake modeling.

The human cochlea in the inner ear is the organ of hearing. Segmentation is a prerequisite step for 3-dimensional modeling and analysis of the cochlea. It may have uses in the clinical practice of otolaryngology and neuroradiology, as well as for cochlear implant research. In this report, an interactive, semiautomatic, coarse-to-fine segmentation approach is developed on a personal computer with a real-time volume rendering board. In the coarse segmentation, parameters, including the intensity range and the volume of interest, are defined to roughly segment the cochlea through user interaction. In the fine segmentation, a regional adaptive snake model designed as a refining operator separates the cochlea from other anatomic structures. The combination of the image information and expert knowledge enables the deformation of the regional adaptive snake effectively to the cochlear boundary, whereas the real-time volume rendering provides users with direct 3-dimensional visual feedback to modify intermediate parameters and finalize the segmentation. The performance is tested using spiral computed tomography (CT) images of the temporal bone and compared with the seed point region growing with manual modification of the commercial Analyze software. Our method represents an optimal balance between the efficiency of automatic algorithm and the accuracy of manual work.

Cochlea↗

PubMed1988

Binaural acoustic stimulation exercises protective effects at the cochlea that mimic the effects of electrical stimulation of an auditory efferent pathway.

Low-level acoustic stimulation of one (contralateral) ear reduced the neural desensitization caused by a simultaneous loud sound exposure in the other (ipsilateral) ear in a loss-related manner. Greatest reductions in the temporary threshold shifts (TTS) in the exposed ear were obtained when the exposure would have caused large amounts of TTS. Low-level exposures (reduced intensity or duration of exposure) which caused low levels of TTS, from which the cochlea could recover relatively quickly, were not affected by the contralateral stimulus. Intermediate levels of TTS showed intermediate levels of reduction for the same contralateral acoustic stimulus. These effects were similar to effects previously demonstrated with electrical stimulation of an efferent pathway to the cochlea, the crossed olivocochlear bundle (COCB); lesioning the COCB prevented the contralateral stimulus from having any effect on TTS due to an ipsilateral exposure. Like COCB stimulation, the contralateral acoustic stimulus had tonic effects, so that reductions in ipsilateral TTS could be obtained even when the contralateral stimulus was presented 5 min before the ipsilateral exposure. With 10 min delay no effect on TTS occurred. The contralateral stimulus did not appear to cause any changes in responses in the ipsilateral cochlea prior to the loud sound exposure. These results are discussed as indicating an interaction between the two inputs at a central locus, leading to activation of the COCB fibres to the cochlea exposed to the loud sound.

Acoustic Stimulation↗

PubMed1988

Cholecalcin (28-kDa CaBP) in the rat cochlea. Development in normal and hypothyroid animals. An immunocytochemical study.

The distribution of cholecalcin (28-kDa calcium-binding protein) in the cochlea of developing rats was followed by immunocytochemistry. In normal animals, the protein first appeared in utero in the cells of Kölliker's organ, a structure involved in the secretion of the tectorial membrane. The inner hair cells, followed by the outer hair cells, then became immunoreactive from the base of the cochlea to the apex. Their cuticular plate, the anchoring structure for stereocilia, was particularly labeled. The cells of Kölliker's organ lost their immunoreactivity after the first postnatal week, the time when they lose their secretory activity. During the same period, when the tunnel of Corti and the space of Nuel open, labeling appeared in the supporting cells. The neurons of the spiral ganglion were stained from the second postnatal week and the fibers of the cochlear nerve after the end of the first month. No difference was induced by thyroid deficiency until the second postnatal week. Thereafter, Kölliker's organ did not transform and its cholecalcin immunoreactivity persisted, together with the secretory activity. As a result, the tectorial membrane was greatly distorted and the mechanical properties of the organ of Corti were dramatically impaired. The supporting cells were labeled although the tunnel of Corti and the space of Nuel did not open. Staining of the spiral ganglion neurons was delayed. All the nervous structures of the cochlea were, however, stained at the end of the first postnatal month, as in normal animals, despite the irreversible complete deafness. Cholecalcin is thus present during development of the cochlea in both non-neuronal and neuronal structures, and is probably involved in very different processes in various types of cells.

Aging↗

PubMed1989

Postnatal development of the efferent innervation of the rat cochlea.

The postnatal development of the efferent innervation of the rat cochlea was studied by intracochlear injection of the fluorescent retrograde neuronal traces Diamidino yellow and Fast blue. Injections were performed on adult rats and on neonatal rats ranging from 0 to 8 postnatal days. It was found that the total number of neurones labelled in the brainstem after intracochlear injection was not significantly different in the newborn rat, compared to the adult. On the basis of cell body location and laterality of projections, there was a clear separation into lateral and medial efferent systems at the earliest postnatal age studied (PO). Evidence was also found in the newborn for a tonotopicity in the lateral system projection similar to that in the adult. Differences between the newborn and adult were a slight but significantly greater number of bilaterally-projecting cells in the newborn, and the presence in the newborn of a small number of cells located in the lateral superior olivary nucleus contralateral to their target cochlea. These were extremely rare in the adult brainstem. Evidence was found for the occurrence of postnatal neuronal death in nuclei of origin of both efferent systems. It is suggested that although the overall extent and general organization of the efferent projection to the cochlea in the rat appears to be established at birth, regressive changes are occurring during the postnatal shaping and maturation of this brainstem-to-cochlea pathway.

Aging↗

PubMed1993

Ontogeny of gamma-aminobutyric acid in efferent fibers to the rat cochlea.

Cochlear efferent innervation originates in two different groups of neurons located in the superior olivary complex. A first group of olivocochlear neurons (lateral efferent neurons) lies in the lateral superior olive. They send axons to the organ of Corti, where they synapse with radial afferent dendrites of primary auditory neurons, postsynaptic to the inner hair cells. The second group of neurons (medial efferent neurons) is found in medial subnuclei of the superior olivary complex and sends axons to synapse with outer hair cells. Subpopulations of both medial and lateral olivocochlear neurons probably use gamma-aminobutyric acid (GABA) as a neurotransmitter. We have used an immunoperoxidase technique to detect GABA-like immunoreactivity (GABA-LI) in postnatal maturing rat cochleas. The GABA-LI appeared in the inner hair cell region by P3 (P1 = birth) and reached a mature appearance by P15-P16. In the outer hair cell region, GABA-like immunoreactive fibers and terminals could not be identified until P9 and they were only found in the apical end of the cochlea. There was a dual gradient of maturation of GABA-LI in the cochlea. The GABA-LI appeared first at the cochlear base and then extended towards the apex. It also appeared earlier (about a week) in the inner hair cell region than in the outer hair cell region. This dual gradient of maturation is in close agreement with previous data concerning the maturation of the cochlea.

Animals↗

PubMed1988

Superior olivary and lateral lemniscal neurons projecting to the cochlea in the guinea pig.

Efferent neurons to the cochlea in the guinea pig were observed in the superior olivary complex and ventral lateral lemniscal nuclei after injection of WGA-HRP into the cochlea via the round window. Of HRP-labeled nerve cells found in the brainstem, about 60% and 10% were located in the ipsilateral lateral superior olivary nucleus (LSO) and the contralateral ventral nucleus of the trapezoid body (VTB), respectively. A few labeled neurons were found in the ipsilateral VTB, contralateral LSO and the bilateral superior paraolivary nucleus (SPO). Seven percent and 5% of the labeled neurons were definitely observed in the ventrocaudal part of the contra- and ipsilateral ventral nucleus of the lateral lemniscus (VLL), respectively. A combination of acetylcholine esterase (AChE) histochemistry with the tracing of retrograde axonal transport of a fluorescent dye (DAPI) revealed that VLL neurons projecting to the cochlea, as well as about 85% of LSO neurons projecting to the ipsilateral cochlea, were AChE-positive.

Acetylcholinesterase↗

PubMed1993

Characterization of muscarinic binding sites in the adult and developing rat cochlea.

The maturation of the cholinergic innervation of the rat cochlea is associated with a transient increase in the muscarinic-receptor activated inositol phosphate synthesis. In order to investigate the mechanisms involved in this transient enhancement of the inositol phosphate response, the binding properties of the cochlear muscarinic receptors were studied during rat cochlear development. Incubating the membranes from 4-day-old, 12-day-old and adult cochleas with [3H]quinuclidinyl benzylate indicates that their respective, mean concentrations of cholinoceptors are 454 +/- 51 (+/- SEM), 39 +/- 2 and 42 +/- 3 fmol/mg of protein. The dissociation constants at equilibrium are 207 +/- 80, 42 +/- 7 and 28 +/- 3 pM for the binding sites of the 4-day-old, 12-day-old and adult cochleas, respectively. Pharmacological characterization of the binding, using selective antagonists, shows that M3 cholinoceptors are expressed in developing and adult cochleas. The data demonstrate that changes in muscarinic receptor affinity and number do not correlate with the previously observed peak of the inositol phosphate metabolism. The transient enhanced inositol phosphate response is therefore not due to changes in cholinoceptors, but probably due to alterations involving the intrinsic activity of the phospholipase C and/or the efficacy of coupling of the transduction system.

Aging↗

PubMed1993

Dopaminergic lateral efferent innervation of the guinea-pig cochlea: immunoelectron microscopy of catecholamine-synthesizing enzymes and effect of 6-hydroxydopamine.

We have used an immunocytochemical approach to gain further data supporting a possible neurotransmitter or neuromodulator function for dopamine at the level of efferent (olivocochlear) innervations of the guinea-pig cochlea. Immunofluorescence screening was first done on cochleas two or seven days after infusion with the neurotoxin 6-hydroxydopamine. Two days after neurotoxin perfusion, the intensity of the tyrosine hydroxylase-like immunoreactivity was decreased in the inner and tunnel spiral bundles of the organ of Corti (and in known noradrenergic sympathetic fibers outside this organ), with respect to the control contralateral cochleas. In cochleas screened seven days after 6-hydroxydopamine infusion, no tyrosine hydroxylase-like immunoreactivity could be found in the organ of Corti. Only occasional faint fluorescence could be detected in sympathetic fibers. In another set of experiments, a pre-embedding immunoperoxidase technique was used to localize tyrosine hydroxylase and aromatic amino acid decarboxylase, another catecholamine-synthesizing enzyme, at the ultrastructural level. With both types of antibody, the same kind of results were observed. Immunoreactivities were only seen in vesiculated fibers within the inner and tunnel spiral bundles, thus are likely in lateral efferent varicosities. These immunostained fibers accounted for approximately half of the efferent profiles in the inner spiral bundle. Within this bundle, the immunoreactive fibers established axodendritic synapses with the radial afferent processes of type I neurons which contacted the inner hair cells. In no case was immunoreactivity to either enzyme observed in the outer hair cell region, at the level of medial efferent terminals. The synaptic localization of tyrosine hydroxylase- and aromatic amino acid decarboxylase-like immunoreactivities in the lateral efferent varicosities of the inner spiral bundle, as well as the effect of 6-hydroxydopamine on the tyrosine hydroxylase-like immunoreactivity in this same bundle, further support the hypothesis that a catecholamine could act as a lateral efferent neurotransmitter or neuromodulator. Based on previous data reporting a lack of dopamine-beta-hydroxylase-like immunoreactivity within the organ of Corti, and the effectiveness of a D2 agonist on the cochlear compound action potential of the auditory nerve, this catecholamine could well be dopamine.

Animals↗

PubMed1983

High-performance liquid chromatographic identification of enkephalin-like peptides in the cochlea.

Met-enkephalin was identified in cochleae from guinea pigs by a combined reversed-phase high-performance liquid chromatographic separation and subsequent radioimmunoassay of the chromatographic fractions. A second Met-enkephalin-immunoreactive fraction was found in the cochlea, with a retention time shorter than that of Met-enkephalin. These findings confirm and extend earlier cytochemical observations, and suggest the differential immunocytochemical staining seen under inner and outer hair cells in the cochlea may be related to different peptides in the two efferent systems innervating the cochlea. Different molecular forms of enkephalin-related peptides may serve different functional or metabolic roles in complex efferent or local regulation of peripheral sensory processing.

Animals↗

PubMed1984

Ultrastructural damage in cochleas used for studies of basilar membrane mechanics.

Cat cochleas used for interferometric studies of basilar membrane mechanics were examined with the electron microscope. The structures most severely damaged in the experimental cochleas are the outer hair cells and the radial afferent fibers to the inner hair cells. Since the basilar membrane and other supporting structures appear to be normal, mechanical changes observed in the experimental cochleas are most probably due to outer hair cell damage. Individual animals with varying degrees of damage showed large differences in the frequency of basilar membrane resonance at the same place in the cochlea. Shifts in tuning of this magnitude could occur as a consequence of hair cell damage only if the stiffness of the stereocilia and associated structures was greater initially than the stiffness of the basilar membrane and gradually decreased with damage. The present series of observations, therefore, suggest that the stiffness of the outer hair cell stereocilia determines basilar membrane tuning.

Animals↗

PubMed1984

Discharge patterns of cat primary auditory fibers with electrical stimulation of the cochlea.

Intact and destroyed cat cochleae were electrically stimulated through round window electrodes. Intact cochleae provided information about fiber properties with acoustic stimuli. With sinusoidal currents thresholds for synchronization were 4-68 microA rms. Thresholds were independent of the fiber's characteristic frequencies and thus of their places of origin in the intact cochleae. This shows large current spread. Phase-locking of the responses to electric stimulation was much stronger than it was to acoustic stimulation. Destroyed cochleae had no spontaneous activity and showed even stronger phase-locking. Thresholds obtained using 0.2 ms per phase biphasic pulse stimuli were 60-350 microApp. Action potentials were found to be released with as little as 0.3 ms latency. The neuronal responses to any electric stimulus differed considerably from the responses to corresponding acoustic stimuli. Vestibular fibers were easily activated by electric stimulation.

Acoustic Stimulation↗

PubMed1987

Velocity of red blood cell flow in capillaries of the guinea pig cochlea.

Velocities of red blood cells (RBCs) in the lateral wall of the cochlea were determined in the anesthetized guinea pig from direct optical microscopic observations. Mean flow velocity of the blood was measured by timing the passage of a fluorescently-labeled subpopulation of RBCs across a measured capillary length. The optical observations were achieved using an intravital microscope equipped for epifluorescence and the measurements were derived from video images acquired with an image intensified television camera. In the third turn of the cochlea the velocity of RBCs differed significantly between two major classes of capillaries. The mean velocity in spiral ligament vessels was 0.12 mm/s while stria vascularis flow was slower (0.08 mm/s). In a typical animal, the range of velocities among different vessels of the ligament was 0.09-0.18 mm/s while it was 0.03-0.10 mm/s for stria vascularis vessels. Corresponding to this velocity difference, the apparent mean vessel diameters for the two types of vessels also differed. Spiral ligament capillaries were 9.3 micron while strial capillaries were 12.2 micron in diameter. Comparison of flow velocity in different turns of the cochlea indicated that the distribution of blood velocity throughout the cochlea lateral wall is constant.

Animals↗

PubMed1987

Immunocytochemical and quantitative studies of Na+,K+-ATPase distribution in the developing chick cochlea.

Immunocytochemical methods were used to examine cryosections of the embryonic and neonatal chicken cochlea in order to study the histological distribution of the Na+,K+-ATPase molecule during maturation. In complementary studies the Na+,K+-ATPase capacity of microdissected freeze-dried substructures of the cochlea was determined fluorometrically. The dark cell of the tegmentum vasculosum exhibited intense immunochemical staining of the convoluted basolateral infoldings. The adjacent light cells demonstrated very little staining. The plasma membrane of the hair cell was also stained as were the first order auditory neurons, including the cell soma. The homogene cells and the supporting cells were unstained. The dark cell was only lightly stained with the antibody at stage 45 but became more intense and selective by the seventh postnatal day. The other cells of the cochlear duct exhibited specific immunofluorescent staining of their plasma membranes from stage 45 onwards and the fluorescent intensity did not change. The tegmentum vasculosum exhibited very high activities of the Na+,K+-ATPase enzyme relative to the other structures of the cochlea. Furthermore, a pronounced gradient of enzymatic activity was detected longitudinally. The proximal tip (or high-frequency end) had a sixteen-fold greater capacity for Na+- and K+-dependent ATP hydrolysis relative to the distal tip (or low-frequency end). The appearance of this enzyme in the tegmentum vasculosum during the development of the cochlea paralleled the known rate of improvement in hearing thresholds.

Animals↗

PubMed1990

Carbachol-induced inositol phosphate formation during rat cochlea development.

The age related-intensity developmental pattern of the phosphoinositide breakdown, which leads to the formation of intracellular second messengers, was investigated in rat cochleas by measuring the accumulation of inositol phosphates induced by carbachol in the presence of LiCl. The accumulation of the phosphoinositide metabolites elicited by this muscarinic agonist is very low at post-natal day 1 and particularly large during the period between post-natal days 8 and 14 with a peak around day 12. In the 25-day-old rat cochlea, carbachol induced a 2-fold increase in inositol phosphates (IPs) accumulation, with respect to the basal control level. The apparent affinities of the carbachol-induced IPs responses are 49.6, 31.6 and 36.7 microM in cochleas of 12-, 16- and 25-day-old rats, respectively, thus suggesting that the specific developmental changes are rather due to a modification in the number of muscarinic cholinergic receptors than to alterations of the apparent affinity of carbachol for its receptors. This developmental pattern of carbachol-elicited IPs accumulation reveals a striking time coincidence with both the efferent synaptogenesis at the outer hair cells (OHCs) level and the period of increased sensitivity of OHCs to aminoglycoside toxicity. Phosphoinositide breakdown may, consequently, play a role in the maturation of OHCs and their efferent supply. In addition, the remaining IPs response measured at 25 post-natal days indicates that muscarinic agonist-mediated IPs metabolism also occurs in mature cochlea, and might be involved in the regulation of OHCs motility.

Aging↗

PubMed1991

Frequency representation in the rat cochlea.

In order to determine the place-frequency map of the rat cochlea, iontophoretic HRP-injections were made into the cochlear nucleus at electrophysiologically characterized positions. Distribution of retrograde HRP transport in cochlear spiral ganglion cells was analysed by means of a three dimensional reconstruction of the cochlea. The map was established for frequencies between 1.2 and 54 kHz, corresponding to positions between 96.5 to 2% of basilar membrane length (base = 0%). At apex of the cochlea the slope of the place-frequency map was below 0.25 mm/octave. The slope increased to a value of 2.1 mm/octave at 34% basilar membrane length, and remained almost constant towards the cochlear base. The close relationship between frequency range of highest sensitivity and maximum receptor- and innervation-density in the rat cochlea is discussed.

Acoustic Stimulation↗