COMPUTER-MODEL - INVESTIGATING ROLE OF FILOPODIA-BASED STEERING IN EXPERIMENTAL NEURITE GALVANOTROPISM

Since early in this century developing axons and dendrites in culture have been reported to grow along electric field lines. It is only in t he last score of years, however, that evidence suggests developing neu rites actually orient in response to the electrical stimulus. We are i nterested in how an imposed electric field appears to speed neurite ou tgrowth in a field-related direction. We ask the question whether enha nced outgrowth in one direction results from streamlining outgrowth in that direction or from differentially catalysing the rate of outgrowt h. Evidence for possible mechanisms of such neurite galvanotropism inc ludes an electric field-dependent redistribution of filopodia, the fin ger-like structures that extend from the growing neurite tip. Using si mple rules based on filopodia-mediated substrate sampling and orientat ion of extending neurites in vitro, we have built a computer model to test the streamlining theory. This in silico model of non-branching ne urite outgrowth in two dimensions possesses the capacity to apportion its sampling efforts relative to a fixed reference representing the or ientation of the field lines of a steady uniform electric field. Our m odel suggests that simple outgrowth patterns observed for experimental neurite galvanotropism-deflected and enhanced neurite growth toward t he negative electrode and reduced neurite growth directed toward the p ositive electrode-may be simulated by tipping the balance of filopodia in the direction of the negative electrode. The existence of an analo gous pattern-generating interaction between an applied electric field and extending neuronal processes would suggest a role for endogenous f ields arising from naturally occurring potential gradients in developi ng organisms. (C) 1997 Academic Press Limited.