Fig. 5.

The effects of KCl depolarization do not depend on new mRNA synthesis. Nonradioactive in situ hybridization on cultured hippocampal neurons viewed with Nomarski optics. In control conditions, cells were kept in the presence of actinomycin-d for 3.5 hr and then stained with (A) BDNF or (C) TrkB riboprobes. After a pretreatment of 30 min with actinomycin-d, cultures were depolarized for 3 hr in 10 mm KCl in the continuous presence of actinomycin-d and stained with (B) BDNF or (D) TrkB riboprobes. Scale bar (shown inD): 20 μm for A–D. E, Quantitative analysis of the MDDL for BDNF and TrkB mRNAs with actinomycin-d. Bars indicate the fold increase, with respect to controls, of the mean maximal distance at which the in situ labeling was detectable (MDDL). Results are similar for both BDNF and TrkB mRNAs: treatment of control cultures with actinomycin-d for 3.5 hr (C act.D) reduces the MDDL with respect to untreated controls (C), whereas a strong increase of MDDL induced by 3 hr in 10 mm KCl also occurs in the presence of actinomycin-d (3h K act.D). Error bars represent SE. *, Significantly different from controls. The corresponding numerical values, the number of dendrites measured, and the significance values are shown in Table 1.