Growth cone guidance involves changes in growth cone behaviors mediated by environmental signals. Although it is well appreciated that growth cone filopodia are important in detection and response to guidance cues, mechanisms by which guidance cues regulate filopodial dynamics are not understood. Neurotrophins regulate growth cone morphology, but the signaling mechanisms involved are complex and not fully understood. Our evidence suggests that BDNF modulates filopodial dynamics by regulating actin depolymerization through ADF/cofilin. First, BDNF causes a 34% increase in filopodial length on chick retinal ganglion cell (RGC) growth cones. We have shown that BDNF-induced increases in filopodial length are mediated through a RhoA pathway (SFN abstract, 2002). Second, inhibition of Rho kinase (ROCK) with Y-27632 causes a 34% increase in filopodial length, mimicking the effects of BDNF. Further, addition of BDNF to Y-27632-treated cultures has no additional effect on filopodial length. To determine the role of...