BDNF stimulates β1-integrin clustering in the nerve growth cone. (A) Xenopus spinal neuron growth cone immunolabeled for surface β1-integrin after treatment with vehicle alone (Control), or 5 min and 20 min BDNF (50 ng/mL) bath application. Arrowheads denote β1-integrin clusters. Scale bar, 5 μm. (B, C) Quantification of β1-integrin clustering after 5 min and 20 min BDNF treatment expressed as mean number of clusters per growth cone (B) and the percentage of growth cone filopodia that contain at least one β1-integrin cluster (C; see Methods). (D) Quantification of β1-integrin surface levels in the growth cone after 5 min and 20 min BDNF treatment (see Methods). Data are the mean ± standard error of the mean. (n > 200, n/s P > 0.05, *P < 0.01, **P < 0.001, ANOVA with Tukey's post hoc analysis.) BDNF: brain-derived neurotrophic factor.