Fig. 3. TrkB.T1 expression in hippocampal neurons increases the number of dendritic filopodia. (A) Typical examples of the morphology of TrkB.T1-GFP-, TrkB.FL-GFP- and GFP-expressing hippocampal neurons (at 11 DIV, 3 days after transfection). The increased number of filopodia in TrkB.T1-GFP expressing neurons lead to a ruffled appearance (left) compared to the much smoother TrkB.FL-GFP and GFP controls. (B) The increase in density of filopodia was highly significant (n=26-91 cells, 5-13 independent experiments, P<10^–5). (C) Sholl analysis of all neurons from B. The expression of TrkB.T1-GFP, had no significant effect on the complexity of the dendritic tree. (D) Typical dendrite of a TrkB.T1-GFP expressing hippocampal neuron (green, at 10 DIV). Phalloidin-TRITC staining (red) of TrkB.T1-GFP-induced filopodia revealed their filamentous actin content, which is characteristic for filopodia. Scale bars: 10 µm (A); 5 µm (D).