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Distribution of synaptic ribbons in the developing organ of Corti (1986)

Sobkowicz, H. M. ; Rose, J. E. ; Scott, G. L. ; [et al.]

Springer

Journal of neurocytology 15 (1986), S. 693-714

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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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Biochemical and morphological differentiation of acetylcholinesterase-positive efferent fibers in the mouse cochlea (1990)

Emmerling, M. R. ; Sobkowicz, H. M. ; Levenick, C. V. ; [et al.]

New York, NY : Wiley-Blackwell

Journal of Electron Microscopy Technique 15 (1990), S. 123-143

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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.