Fig. 6.

p75NTR^−/− sympathetic neurons show enhanced neuritogenesis in response to NGF and do not respond to exogenous BDNF. Phase-contrast micrographs of cultured Coomassie blue-stained (A, B) wild-type and (C, D) p75NTR^−/− murine sympathetic neurons maintained in 50 ng/ml NGF for 2 d and then switched to (A, C) 7.5 ng/ml NGF or (B, D) 7.5 ng/ml NGF plus 100 ng/ml BDNF. As observed in cultured rat sympathetic neurons (Fig.2B), exogenous BDNF inhibited NGF-promoted process outgrowth in wild-type but not p75NTR^−/−murine sympathetic neurons. Note that the degree of process outgrowth is greatly enhanced in p75NTR^−/− neurons, relative to their wild-type counterparts. Scale bar, 65 μm.