title: The largest growth cones in the animal kingdom: an illustrated guide to the dynamics of Aplysia neuronal growth in cell culture.
abstract: The marine mollusc, Aplysia californica is a powerful experimental model in cellular and systems neuroscience. Aplysia neurons are large, colored, and located at the ganglionic surface. Because of this, many neurons can be easily identified in terms of their physiological properties, synaptic connections, and behavioral roles. Simple networks can be reconstructed in cell culture and have been widely useful for cellular and molecular biological studies of neuronal growth, synaptogenesis, and learning and memory mechanisms. Here, we show that Aplysia neurons can form truly gigantic growth cones reaching up to 630 μm in diameter making them the largest growth cones ever reported in the animal kingdom. Second, using time-lapse video microscopy we have characterized the dynamics of neuronal outgrowth for 3 identified cell types (mechanosensory neurons, L7 motoneurons, and modulatory MCC neurons) representing 3 major functional classes of neurons. We show both cell-specific and neurite-specific growth characteristics and an irregular oscillatory rate of outgrowth ranging from 20 to 100 μm/h. Third, we characterized the dynamics of axotomy-induced neurite outgrowth as well as extrasomatic localization of β-tubulin mRNA in restricted regions of neuronal processes including growth cones and varicosities. The extrasomatically located mRNAs can be an important pool of neuronal transcripts supporting semiautonomous behavior of growth cones and localized synthesis of proteins in distinct and distant neuronal compartments. The reported data are compared with the existing literature from Lymnaea and Helisoma neurons as well as vertebrate preparations. Finally, our observations can provide an illustrated guide to complex behavior of neurons and glia in cell culture as well as their dependence upon various trophic factors and responses to neuronal injury.
authors.affiliation: The Whitney Laboratory for Marine Bioscience, University of Florida 9505 Ocean Shore Blvd., St Augustine, FL 32080, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Lovell
authors.forename: Leonid L
authors.initials: LL
authors.lastname: Moroz