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Query: UMLS:C0012739 (disseminated intravascular coagulation)
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The morphology of growth cones from identified neurons of Aplysia californica was analysed both with video-enhanced contrast differential-interference contrast (VEC-DIC) microscopy, and through serial electron microscopic reconstructions of the same growth cones. The largest structures seen in the living growth cones, the large irregular refractile bodies (LIRBs), were shown in electron micrographs to be unique structures, composed predominantly of dense-core vesicles but including mitochondria and smooth membrane profiles. The LIRBs were stratified in the growth cones, occurring predominantly in sections distant from the substrate and relatively devoid of microtubules. VEC-DIC observations showed that LIRBs formed in the peripheral regions of the organelle-rich central growth cone, and grew in size through fusion with other LIRBs, accumulating into a large central mass in more proximal regions. The distribution of microtubules and LIRBs and the movements of LIRB suggest that there is an overall circulatory pattern in the growth cones, with the delivery of new vesicles occurring at distal areas close to the substrate, and the accumulation and retrograde processing of organelles occurring in more proximal areas away from adhesive contacts.
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PMID:The distribution and movement of organelles in maturing growth cones: correlated video-enhanced and electron microscopic studies. 323 Mar 97

A previous study that used high-resolution video (VEC-DIC) microscopy to examine axonal growth cones of Aplysia giant neurons growing in culture had demonstrated that growth occurs by the extension of veils of membrane between filopodia and the subsequent morphological transformation of these veils, in place, into the swollen, organelle-filled central region of the growth cone and then into the cylindrical axon. The possible involvement of Ca2+ in this sequence of events was now examined using VEC-DIC microscopy. Reduction of [Ca2+]o from the normal level of 11 to 1.3 mM or below or the addition of 20 mM Co2+, which blocks Ca2+ channels, caused a large decrease in the area of immature veil (flat and with few organelles) in the growth cone within minutes. Ba2+, 20 mM, which flows well through Ca2+ channels, and 5 microM A23187, a Ca2+ ionophore, caused new immature veil to form in the presence of reduced [Ca2+]o. Maturation of veil into central region was not inhibited by reduced [Ca2+]o. In fact, the disappearance of immature veil was often the result partly, or entirely, of continued veil maturation in the absence of formation of new veil. The next step in maturation, conversion of the central region to cylindrical axon, was also probably not inhibited by reduced [Ca2+]o. Ca2+ was microapplied to large growth cones that had lost their veils by exposure to reduced [Ca2+]o. There was a strong tendency for the first, or only, incidence of veil formation to occur near the micropipette, the rest of the perimeter of the growth cone remaining quiescent. It is concluded that intracellular Ca2+ plays a role in veil formation and that the site of the Ca2+-dependent step is close to the site of veil formation. If this step is exocytosis, veil forms where there is net addition of membrane. Whether a change in [Ca2+]i, rather than some other factor, normally directly triggers veil formation remains uncertain, but, if it does, then the site of formation, which will strongly influence the direction of axon growth, is probably determined by focal changes in [Ca2+]i within the growth cone.
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PMID:Local role of Ca2+ in formation of veils in growth cones. 324 45