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  • 1
    Electronic Resource
    Electronic Resource
    Tunnel crossing fibers and their synaptic connections within the inner hair cell region in the organ of corti in the maturing mouse (1998)
    Springer
    Anatomy and embryology 198 (1998), S. 353-370 
    Details
    ISSN: 1432-0568
    Keywords: Key words Auditory ; GABAergic system ; Sensory cells ; Afferent innervation ; Olivocochlear innervation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Combined ultrastructural and immunocytochemical studies reveal that in the adolescent 12- to 17-day-old mouse the afferent tunnel crossing fibers that innervate outer hair cells receive synaptic contacts from three distinct sources: the GABAergic fibers (GABA= gamma-aminobutyric acid) of the lateral olivocochlear bundle, the non-GABAergic efferent tunnel crossing fibers, and the inner hair cells themselves. The GABAergic fibers give off collaterals that synapse with the afferent tunnel fibers as they cross the inner hair cell region. These collaterals also form synapses with afferent radial dendrites that are synaptically engaged with the inner hair cells. Vesiculated varicosities of nonGABAergic efferent tunnel fibers also synapse upon the outer spiral afferents. Most of this synaptic activity occurs within the inner pillar bundle. Distinctive for this region are synaptic aggregations in which several neuronal elements and inner hair cells are sequentially interconnected. Finally, most unexpected were the afferent ribbon synapses that inner hair cells formed en passant on the shafts of the apparent afferent tunnel fibers. The findings indicate that: (1) the afferent tunnel (i.e., outer spiral) fibers may be postsynaptic to both the inner and the outer hair cells; (2) the non-GABAergic efferent and the afferent tunnel fibers form extensive synaptic connections before exiting the inner pillar bundle; (3) the GABAergic component of the lateral olivocochlear system modulates synaptically both radial and outer spiral afferents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004290050190
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  • 2
    Electronic Resource
    Electronic Resource
    Distribution of synaptic ribbons in the developing organ of Corti (1986)
    Springer
    Journal of neurocytology 15 (1986), S. 693-714 
    Details
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Studies of synaptogenesis in the developing organ of Corti in the intact mouse and in culture indicate that the inner and outer hair cells contain three populations of synaptic ribbons, i.e. ribbons adjacent to nerve fibres, free intracellular ribbons and misplaced ribbons apposed to non-neuronal elements. Ribbons adjacent to nerve fibres can be further classified into: ribbons synaptically engaged, ribbons participating in formation of presynaptic complexes only and ribbons that are not engaged to the hair cell membrane. In the developing innervated cultures the ribbon distributions are similar to those in the normal animal. Inner and outer hair cells differ in distribution of the ribbons. In the inner hair cells the ribbons adjacent to the nerve fibres are dominant (over 90%) and most of them (88%) are synaptically engaged. In the outer hair cells the presynaptic ribbons dominate the population (up to 60%) during the first postnatal week when the cells acquire afferent synaptic connections. This stage is followed by a marked reduction in the number of all ribbons. In the intact animal the rapid decrease results in a relative increase of misplaced and free ribbons. These changes are presumably due to the loss of some of the afferents. In the denervated hair cells the distribution of ribbons indicated the presence of conspicuous scatter. In the areas of incomplete denervation, however, the ribbons are apposed to the preserved fibres. Despite denervation, most of the ribbons develop the entire presynaptic complex in apposition to non-neuronal structures. The different populations of synaptic ribbons appear to reflect different stages in synapse formation. Possibly, the synaptic body originates in the interior of the hair cell and subsequently migrates to the cell membrane. In any case, a nerve fibre appears critical in influencing the location of the synaptic ribbon. At the apposition of the ribbon to the hair cell membrane, presynaptic densities are formed and the ribbon appears to become anchored. Typically, the nerve fibre membrane apposed to the presynaptic complex responds with the formation of postsynaptic densities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01625188
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  • 3
    Electronic Resource
    Electronic Resource
    Development of acetylcholinesterase-positive neuronal pathways in the cochlea of the mouse (1989)
    Springer
    Journal of neurocytology 18 (1989), S. 209-224 
    Details
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Development of the cholinergic enzymes, choline acetyltransferase (ChAT) and AChE, and of the AChE-positive innervation in the cochlea was studied biochemically and morphologically in the postnatal mouse up to 26 days. Both ChAT and AChE are already present at birth in levels comparable to 50 and 20% of near-adult values, respectively. Increases in the enzymatic activities occur mainly during the second postnatal week. ChAT increases primarily in the basal turn; the specific activities in the basal and mid turns become about equal and at least twice of the values found in the apex. AChE increase continues throughout the entire cochlea; at all times its activity is highest in the base and lowest in the apex. In the light microscope, AChE-positive fibres are seen to enter the organ in the intraganglionic bundle during late foetal development and travel upwards via radial bundles. The fibres destined for outer hair cells usually differentiate first and take a separate route. They either cross the prospective tunnel of Corti directly or take a spiral course in front of inner pillar cells to form the inner pillar bundle. The tunnel fibres are radially oriented and provide the innervation to outer hair cells in narrow vertical sectors. In most cases, the outer hair cells are being innervated by the 4th day. Between the 4th and the 6th day, the tunnel fibres reach the outer hair cells in the third row; the first and second outer spiral bundles are formed. The AChE-positive innervation of the inner spiral bundle and plexus forms in short segments, and the bundle may be still discontinuous even by the 6th day. By the 12th day the innervation is complete. In the electron microscope, the stain for AChE may allow identification of growing efferent fibres before their ultrastructural differentiation. Both ChAT and AChE activities are early markers of the differentiating efferent system. An ingrowth of the cholinergic fibres to the entire cochlea occurs before birth. The greatest increase of AChE occurs between the 4th and 10th day, relating in time to efferent synaptogenesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01206663
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  • 4
    Electronic Resource
    Electronic Resource
    Presynaptic fibres of spiral neurons and reciprocal synapses in the organ of Corti in culture (1993)
    Springer
    Journal of neurocytology 22 (1993), S. 979-993 
    Details
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Isolated segments of the newborn mouse organ of Corti were explanted together with the spiral ganglion components. Within the innervation provided by the spiral neurons, we observed presynaptic vesiculated nerve endings that form reciprocal ribbon-afferent/efferent synapses with inner hair cells. These intracochlear presynaptic fibres are characteristically located between adjoining inner hair cells, on the modiolar side, low and close to the supporting cells. The presynaptic fibres display different modes of synaptic connectivity, forming repetitive reciprocal synapses on single inner hair cells or on adjoining hair cells, or connecting adjoining inner hair cells through simultaneous efferent synapses. Many presynaptic fibres exhibit a distinctive ultrastructure: defined clusters of synaptic vesicles, dense core vesicles, coated vesicles, and mitochondria. These organelles occur focally at the synaptic sites; beyond the efferent synaptic specializations, the endings appear quite nondescript and afferent-like. We believe that the reciprocal synapses, although observed in cultures of the organ of Corti, represent real intracochlear synaptic arrangements providing a feedback mechanism between the primary sensory receptors and a special class of spiral ganglion cells that have yet to be recognized in the organin situ.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01218355
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  • 5
    Electronic Resource
    Electronic Resource
    GABA-like immunoreactivity in the cochlea of the developing mouse (1989)
    Springer
    Journal of neurocytology 18 (1989), S. 505-518 
    Details
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary GABA-like immunoreactivity was studied in surface preparations of cochleas from postnatal developing mice, and GAD-like immunoreactivity was studied in the adult. GABA-positive fibres are already present at birth; they innervate both the inner and outer hair cells and some spiral ganglion cells. The GABA-positive fibres that enter via the intraganglionic bundle send collaterals to the spiral ganglion and to the hair cell region. Fibres that enter along the central processes of spiral neurons end predominantly among the spiral ganglion cells. A few spiral neurons display pericellular rings of GABA-positive boutons at birth. In older animals, the endings occur on a small number of spiral ganglion cells either as rings or as brush formations. The early GABA-positive fibres reach the inner hair cells around the second day and the outer hair cells (of the upper turns only) around the seventh day. In 12-day animals, tunnel fibres arborize in the outer hair cell region; their collaterals make contacts with the outer hair cells within four to eight cell-wide segments, distributing the endings high, up to the reticular plate. In older animals, fibres (both GABA- and GAD-positive) may innervate single vertical rows of outer hair cells. In the maturing and the adult cochlea, the GABA-positive component of the inner spiral bundle is conspicuous and extends along the entire cochlear length, but the innervation of the outer hair cells comprises only the mid and apical turns. GABA-positive nerve cells occur among the small vestibular neurons, occasionally among the cells of eighth nerve nucleus and only exceptionally in the spiral ganglion. In the adult animal, GAD-positive cells, although uncommon, were observed among the spiral neurons. In the developing animal, GABA-positive fibres give rise to transitory formations: (1) a convoluted plexus running beneath and among the radial bundles and (2) a sparse plexus, continuous with the inner spiral bundle and running in the upper plane of the inner spiral sulcus. GABA-like immunoreactivity was also observed in neuronal growth cones and in some fibres running along blood vessels. In conclusion, GABA immunoreactive fibres appear to reach the cochlea by two routes: via the intraganglionic bundle and to a much lesser extent via the central bundles of the spiral ganglion. The fibres innervate sensory cells and also some spiral neurons. The occasional presence of GABA-positive neurons in the vestibular ganglion, in the VIIIth nerve nucleus, and exceptionally among the spiral neurons raises the possibility of a local GABAergic circuitry within the inner ear.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01474546
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  • 6
    Electronic Resource
    Electronic Resource
    Patterns of hair cell survival and innervation in the cochlea of the Bronx waltzer mouse (1991)
    Springer
    Journal of neurocytology 20 (1991), S. 886-901 
    Details
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A massive loss of inner hair cells typifies the cochleae of Bronx waltzer mutant mice. We have characterized the surviving inner hair cells and their modified innervation by immunocytochemistry using antibodies against neuron-specific enolase, with additional stains for neural cell adhesion molecule and neurofilaments, and by electron microscopy. The surviving inner hair cells vary in size, neuron-specific enolase content and innervation. All neuron-specific enolase-positive cells are innervated by neuron-specific enolase-positive endings. There is apparent correspondence between the neuron-specific enolase immunoreactivity of sensory cells and their innervation. Well-stained cells are richly innervated (and large) while lightly stained cells receive fewer nerve endings. Neuron-specific enolase-negative inner hair cells innervated either by neuron-specific enolase-positive or -negative nerve endings are very rare. Ultrastructurally, the surviving inner hair cells vary from those of a normal morphological appearance to underdeveloped or vacuolated. Most of the apparently normal inner hair cells are associated with few nerve endings; instead nerve growth cones are abundant in the adjacent inner spiral sulcus epithelium. Cells forming ribbon synapses with afferent endings are rare. The contingent of efferent endings in the inner spiral bundle depends on the presence of afferent endings. The absence of inner hair cells and the uneven distribution of nerve endings on the surviving cells results in the disruption of normal innervation patterns, especially in the thinning out or discontinuation of the inner spiral bundle and an uneven distribution of tunnel fibres. We infer that the sprouting of nerve endings and their convergence on a selected population of the surviving inner hair cells represents a compensatory regenerative phenomenon in response to the loss and the genetic defect of the remaining inner hair cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01190467
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  • 7
    Electronic Resource
    Electronic Resource
    The kinocilium of auditory hair cells and evidence for its morphogenetic role during the regeneration of stereocilia and cuticular plates (1995)
    Springer
    Journal of neurocytology 24 (1995), S. 633-653 
    Details
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Auditory hair cells that survive mechanical injury in culture begin their recovery by reforming the kinocilium. This study is based on cultures of the organ of Corti of newborn mice and two control animals. The axonemal patterns were examined in 165 kinocilia in cross-section. In the immature and regenerating kinocilium, one of the normally peripheral doublets is frequently located inward, forming the modified 8 + 1 (double) form; the distribution of the remainingmicrotubules is irregular. As the cell matures, the 9 + 0 form predominates. Overall, 34–61% of auditory kinocilia consist of 9 + 0 microtubules. The 9+2 (single) form, previously thought to characterize the organelle, occurs only in about 3–14%, whereas the remaining population comprises the modified 8 + 1 (double) form. Normally, the kinocilium lasts only about 10 postnatal days; however, post-traumatic hair cells reform their kinocilia regardless of age. Concomitant with the regrowth of the kinocilium, the basal body and its cilium take a central location in the cuticular plate, stereocilia regrow, and the cytoplasmic area adjacent to the basal body displays pericentriolar fibrous densities, growth vesicles, and microtubules, all surrounded by actin filaments. Pericentriolar bodies nucleate microtubules. Involvement of microtubules is seen in the alignment of actin filaments and in the formation of the filamentous matrix of the cuticular plate. We propose that reformation of the kinocilium in recovering post-traumatic hair cells indicates the possible role of its basal body in the morphogenesis and differentiation of cuticular plates and stereocilia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01179815
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  • 8
    Electronic Resource
    Electronic Resource
    Biochemical and morphological differentiation of acetylcholinesterase-positive efferent fibers in the mouse cochlea (1990)
    New York, NY : Wiley-Blackwell
    Journal of Electron Microscopy Technique 15 (1990), S. 123-143 
    Details
    ISSN: 0741-0581
    Keywords: AChE ; ChAT ; Immunoreactivity ; Electron microscopy ; Acetyltransferase ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: We have compared the biochemical expression of cholinergic enzymes with the morphological differentiation of efferent nerve fibers and endings in the cochlea of the postnatally developing mouse. Choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) are present in the newborn cochlea at specific activities 63% and 25%, respectively, of their mature levels. The relative increases in ChAT, in AChE, and in its molecular forms over the newborn values start about day 4 and reach maturity by about day 10. The biochemical results correlate well with the massive presence of nerve fibers stained immunocytochemically for ChAT and AChE or enzymatically for AChE in the inner and outer hair cell regions. Ultrastructural studies, however, indicate the presence of only few vesiculated fibers and endings in the inner and outer hair cell regions. The appearance of large, cytologically mature endings occurs only toward the end of the third postnatal week. The discrepancy may be resolved in the electron microscope using the enzymatic staining for AChE. Labeling is seen on many nonvesiculated fibers and endings in the hair cell regions, suggesting that the majority of the efferent fibers in the perinatal organ may be biochemically differentiated but morphologically immature. The results may imply that the efferents to inner and outer hair cells develop earlier than indicated by previous ultrastructural studies. Moreover, the pattern of development suggests that in the cochlea, as in other tissues, the biochemical differentiation of the efferent innervation may precede the morphological maturation.
    Additional Material: 25 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jemt.1060150205
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