Effects of cell-cell contact on neuronal growth cones

Jonathan Knight Ivins, University of Pennsylvania


Growth cones of sympathetic neurons from the superior cervical ganglia of neonatal rats were studied using videomicroscopy. The events that follow contact between growth cones and other cell surfaces, including other growth cones and neurites were characterized. A variety of behaviors occurred upon contact between growth cones. Most commonly, one growth cone collapsed and retracted upon establishing filopodial contact with the growth cone of another sympathetic neuron. Interactions between growth cones and non-neuronal cells never resulted in the growth cone collapsing, suggesting that a specific recognition event was involved. These observations suggest that the superior cervical ganglion may be composed of neurons with different cell surface determinants and that growth cones are able to recognize and respond to these differences. Calcium has been implicated as a prime regulator of growth cone motility. The calcium indicator dye fura-2 and digital imaging fluorescence microscopy was used to determine if changes in intracellular calcium were involved in the phenomenon of contact mediated growth cone collapse. For these experiments, a paradigm in which chick dorsal root ganglion (DRG) growth cones collapse on contact with chick retinal neurites was used. Calcium levels within DRG growth cones were stable during neurite outgrowth. Surprisingly, calcium levels in DRG growth cones also appeared to remain stable during the Period of contact mediated growth cone collapse. Application of a chick brain-derived growth cone collapsing factor to cultures of DRG neurons caused growth cones to collapse but had no effect on calcium levels within the growth cones. Calcium channel antagonists did not interfere with this collapse activity. Agents which raised levels of calcium 2-3 fold above basal levels had no effect on growth cone morphology or motility. These results suggest that the morphological changes associated with the collapse of growth cone structure can be independent of changes in growth cone calcium levels and that other second messengers must be involved in the regulation of these growth cone behaviors.

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Recommended Citation

Ivins, Jonathan Knight, "Effects of cell-cell contact on neuronal growth cones" (1990). Dissertations available from ProQuest. AAI9112577.