Fig. 6. Transgenic BDNF-overexpressing embryos show increased hippocampal synaptogenesis. (A) Immunoblot analysis of the synaptic vesicle proteins synaptophysin and synapsin I, and of the t-SNARE syntaxin1 in forebrain membrane fractions from control (C) and transgenic (BDNF) E18 embryos reveals no major differences between groups. (B,C) Photomicrographs illustrating similar patterns of immunolabeling were observed for synaptophysin in hippocampal sections from wild-type (B) and BDNF-overexpressing (C) E18 embryos. (D,E) Electron micrographs illustrating synaptic contacts (black arrows) in the stratum radiatum of control (D) and transgenic (E) E18 embryos. Note the distinct patterns of distribution of synaptic vesicles in the axon terminal and the increased area of postsynaptic dendrite of transgenic synapses. Open arrow in E points to a putative contact. (F-J) Quantitative analysis illustrating structural alterations in synaptic profiles of E18 transgenic hippocampi. BDNF-overexpressing embryos show a significant increase in the number of synaptic contacts per area (F) and in the number of docked synaptic vesicles per contact (H), whereas the total number of synaptic vesicles per contact is significantly decreased in these embryos compared to wild-type embryos (G). The area of postsynaptic dendrites was significantly increased in transgenic embryos (I) whereas no differences were found for axon terminal area between both groups of animals (J). Values are mean ± s.e.m. White bars, wild type; black bars, transgenic embryos. *P<0.01; **P<0.0001. Scale bars, 400 µm (B,C); 0.5 µm (D,E). AT, axon terminal; D, dendrite; so, sp, sr, slm, CA1, CA3 and DG as in Fig. 1.

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