Fig. 3. Histological organization of the hippocampus in transgenic BDNF-overexpressing embryos. (A) Transgenic (BDNF) and control (C) E18 embryos are identified by PCR analysis of the nestin-BDNF construct. As revealed by northern blot analysis, nestin-BDNF transgenic forebrains express about 30-fold higher levels of BDNF mRNA than controls (including endogenous and transgenic mRNAs). Cyclophilin mRNA levels were used as an internal standard. (B,C) Nissl staining of BDNF-overexpressing and control hippocampal sections. The overall hippocampal cytoarchitectonics is preserved in transgenic hippocampi, although transgenic embryos that integrated many construct copies show a double pyramidal layer (arrows in C). (D,E) Calretinin immunostaining shows the correct location of Cajal-Retzius cells in the stratum lacunosum-moleculare (arrows) in both transgenic and wild-type hippocampi. (F) Section from the hippocampus of a BDNF transgenic embryo immunolabeled by the axonal marker L1, showing correct axonal patterns with L1-positive fascicles in the white matter (wm), fimbria (fi) and in the stratum lacunosum-moleculare (slm), mainly corresponding to commissural and entorhino-hippocampal axons. (G) Patterns of entorhino-hippocampal innervation in a BDNF transgenic hippocampus following a DiI injection in the entorhinal cortex. Entorhinal fibers (red) are seen in the fimbria (fi) and in the stratum lacunosum-moleculare (slm). Section counterstained with bisbenzimide (blue). Scale bars, 400 µm. Abbreviations as in Fig. 1.