Fig. 2. NTF-dependent and NTF-independent types of axonal growth differ in their sensitivity to signal transduction inhibitors. The SFK inhibitor SU6656 (SU) inhibits NTF-dependent axonal growth after 12 hours in culture (A,G,H). SU6656 (2 µM) does not affect axonal growth in the absence of exogenous NTFs after 40 hours in culture (B,J,K). (C) Axonal growth induced by NGF and NRTN is blocked by Src dominant negative protein transduced in an adenoviral vector (SrcDN AV). GFP-expressing adenoviral vector (GFP AV) was used as a control. (D) SrcDN AV does not inhibit the NTF-independent type of axonal growth. In C and D low laminin concentrations (20 and 50 ng/cm², respectively) were used for precoating. Cultures were maintained for 90 hours. The Cdk5 inhibitor roscovitine (Rosc) does not affect NRTN-, GDNF- or NGF-dependent outgrowth at 12 hours in culture (E,I). Roscovitine inhibits axonal growth after 40 hours in culture (F,L) (no NTFs added). In A,C,E,G,H,I, NTFs were applied where indicated at 100 ng/ml. In A,B,E,F,H,I,K,L, all NTFs and inhibitors were applied when plating neurons. In A, a significant difference between the samples treated with NTFs versus NTFs+SU is indicated with asterisks. In E,F,I,L, roscovitine was applied at 50 µM. Cultures were maintained for the indicated time periods, then fixed and stained for PGP 9.5. All values are means ± s.e.m. of three experiments. Bars, 20 µm.