Fig. 1.

Expression of neurotrophin receptors in embryonic hippocampal neurons after 5 d in culture. a, Neurons were treated for 2 hr with vehicle [control (C)] or the different neurotrophins. Lysates were immunoprecipitated with anti-p75 (192 IgG), run on a Western blot, and probed with anti-p75 (9651). PC12 cell lysates were used as a positive control (+). No signal was detected in PC12 lysates in the absence of the immunoprecipitating antibody (−).b, Hippocampal neurons were treated for 5 min with vehicle (C) or the different neurotrophins and analyzed for tyrosine phosphorylation of the trk proteins (arrowhead). Phosphorylation of trk receptors was induced by BDNF and NT4 and by NT3 treatment, indicating the presence of TrkB and TrkC, respectively, in the neuronal cultures (arrowhead). No TrkA phosphorylation was detected after NGF treatment. c, Hippocampal neurons were immunostained with antibodies against p75, TrkC, or TrkB.Arrows indicate positively stained neurons, andarrowheads indicate negatively stained neurons.