NEURITIC GROWTH-RATE DESCRIBED BY MODELING MICROTUBULE DYNAMICS

A model is developed to describe neuronal elongation as a result of th e polymerization of microtubules and elastic stretching of the neurite s by force produced by the growth cone. The model for a single segment with a single growth cone revealed a constant elongation rate, while the concentration of tubulin in the soma rises, and the concentration of tubulin becomes constant in the growth cone. Extending the model to a neurite with a single branch point and two growth cones revealed th e same results. When the assembly or the disassembly rate of microtubu les is unequal in both growth cones, transient retraction of one of th e terminal segments occurs, which results in complete retraction of th e segment when the difference in (dis)assembly rate between the two gr owth cones is large enough. When the model is applied to large trees, a maximal sustainable number of terminal segments as a function of the production rate of tubulin appears. Mechanisms to stop outgrowth are discussed in relation to the establishment of synaptical contacts betw een cells.