Babu et al. Synaptic activity induces neurogenesis FIGURE 1 | Neural precursor cells in their local microenvironment in vivo and in vitro. (A) Immunohistochemical analysis of a hippocampal section from mouse showing the close association of neural precursor cells with neurons. Confocal image (optical section of 1 µm thickness). Green: Nestin-GFP; Red: Dcx, Blue: NeuN; Scale bar, 25 µm. (B) Confocal projections (56×) of the dentate gyrus (z-stack of 11 optical sections with 2 µm thickness); Green: Nestin-GFP; Red: Dcx; Blue: NeuN; one square in the underlying grid equals 16.4 µm. (C) Calretinin- immunohistochemistry highlights the inner molecular layer. Radial glia-like type-1 cells (Green) reach into this area, which receives the input from the entorhinal cortex. Green: NestinEGFP; Red: Calretinin; Blue: NeuN. (D) Newborn neurons in the adult dentate gyrus are in close neighborhood with neurites in the mouse hippocampus; Green: NestinEGFP, Red: MAP2ab, Blue: Dcx. (E) Representative image of precursor cells differentiated into neurons in co-culture of precursor cells with primary mouse hippocampal neurons. EGFP cells differentiated into neurons and also non-neuronal cells types, presumably glial cell, in co-culture. Green: EGFP (precursor cells); Red: βIII-tubulin (neurons). (F)The neurons generated from precursor cells in co-culture integrate into the underlying neuronal circuit as suggested by the presence of synapses (arrows) onto it indicated by the synaptophysin staining. Green: EGFP; Red: βIII-tubulin, Blue: synaptophysin. Scale bar [in (F) for (C–F)]: C, 250 µm; D, 200 µm; E, 25 µm; F, 50 µm. Frontiers in Neuroscience | Neurogenesis September 2009 | Volume 3 | Article 49 | 4