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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The concentration of free calcium ions in the cytosol has been shown to influence many components of growth cone behaviour, including the extension of filopodia and veils, the addition of new membrane to the plasmalemma, the retraction and disappearance of filopodia, and gross collapse and retraction of the growth cone. A spatially localized modulation of these processes by very local calcium changes has been proposed to underlie the steering of growth cones by gradients of neurotransmitters, voltage and cell adhesion molecules. Such local control can be studied in mouse neuroblastoma cells, where depolarization causes calcium to rise in a limited number of spatially restricted hotspots, triggering a localized advance. We have studied the simple, club-shaped growth cones that are characteristically found on advancing neurites. Depolarization caused calcium to increase most at the distal, leading tip. Agents that disrupt calcium-induced calcium release do not affect growth cone calcium dynamics, ruling out a local release of calcium at the tip as a cause of the gradient. Using cell-attached patch recording, we find that L-type calcium channels are present at a higher density at the distal tip than in the proximal growth cone. Our results show that the calcium gradients seen in depolarized growth cones are a direct consequence of a gradient of calcium channel density.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2013
    Keywords: Key words Calcium oscillations ; Development ; In situ ; Intracellular calcium ([Ca2+]i) measurement ; Neurons ; Zebrafish
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  We have developed a non-invasive technique to measure intracellular calcium ([Ca2+]i) in neurons growing within intact embryos of the zebrafish (Danio rerio). A single blastomere was injected with a calcium-sensitive fluorescent dye (Calcium Green dextran) between the 32- and 128-cell stage and the embryo imaged between 16 h and 20 h postfertilisation using laser scanning confocal microscopy. Labelled nerve cells from embryos preinjected with dye and dissociated at 16 h showed a fluorescence increase (66±22%; n=11) in response to depolarisation with KCl confirming that the dye remained intracellular and was sensitive to calcium. In addition, fluorescence changes in activated muscle cells of intact embryos showed that the dye was capable of responding to [Ca2+]i changes in vivo. Imaging of dye loaded cells over 30-min periods in embryos between 16 and 20 h revealed that the majority of neurons within the brain and spinal cord did not show spontaneous fluorescence changes distinguishable from noise. However, a subset of neurons within the ventral spinal cord exhibited spontaneous, repetitive [Ca2+]i oscillations which may have a functional significance during neuronal development.
    Type of Medium: Electronic Resource
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