Fig. 4.
Neurotrophins induce apoptosis of neurons expressing p75 in the absence of trk receptors. Hippocampal neurons were treated with NGF (a–c), BDNF (d–f), or NT3 (g–i) for 6 hr. All cultures were immunostained with anti-p75 (192 IgG;a, d, g) and labeled with Hoechst 33342 (c, f, i) to identify the nuclei of apoptotic cells. NGF-treated cultures were immunostained with anti-pan-Trk (b), BDNF-treated cultures were labeled with anti-TrkBin(e), and NT3-treated cultures were labeled with anti-TrkCin2 (h). Chromatin condensation, indicative of apoptosis, was detected in neurons that expressed p75 in the absence of the relevant trk receptor (arrowheads). Healthy nuclei in neurons expressing both p75 and the relevant trk are indicated with arrows. Scale bar, 20 μm.