BDNF treatment increases endogenous MT entry into spines. A, Tyrosinated α-tubulin antibody-labeled MTs (yellow arrows) are detected in a small percentage of F-actin-labeled spines under basal conditions (21–28 DIV). B, After a 20 min treatment with 50 ng/ml BDNF, a significantly higher percentage of spines contained an MT at the time of fixation. C, D, Addition of 100 nm nocodazole (C) or 10 nm taxol (D) to the BDNF solution inhibits MT invasions. E, Quantification of the treatments (Kruskal–Wallis test with Dunn's post hoc tests—see Materials and Methods for significance values). Scale bar: (in D) A–D, 5 μm.