Quantitative analysis of BDNF-induced p44/42 MAPK activation by immunofluorescence of phospho-p44/42 levels in Xenopus growth cones. Neurons injected with control, miR-134 mimics and antisense inhibitors were exposed to control saline or BDNF (50 ng/ml) for 30 min. The immunofluorescence intensity of BDNF-exposed growth cones was normalized to that of the corresponding group without BDNF exposure. Numbers indicate the number of growth cones examined. Error bars: the standard error of the mean. Double asterisks: p < 0.001 (Student's t-test).