Figure 1.

Neurogenesis persists in the adult hippocampus. (A) Schematic representation of hippocampal connectivity. The hippocampus receives its main input via the entorhinal cortex from necortical association areas. The axons of entorhinal cortex neurons (perforant path fibers) synapse onto dentate gyrus granule cells that send their axons (mossy fibers) to area CA3. CA3 pyramidal neurons send axons to area CA1 (Schaffer collaterals). CA1 pyramidal cells then signal back to neocortical association areas. (B) Newborn cells in young adult mice were labeled by the injection of the thymidine analogue BrdU 4 weeks before the animals were killed. Note the BrdU-labeled (blue) newborn cells expressing the pan-neuronal marker NeuN (red) within the inner parts of the dentate gyrus granule cell layer. Only very few astrocytes (S100β in green) are newly generated in the adult hippocampus. (C) Labeling of dividing NSCs and their progeny with a retrovirus reveals the distinct, highly polarized morphology of 4-week-old, newborn granule cells with an apical dendrite extending toward the molecular layer (arrow) and axonal processes growing to area CA3 (arrowheads). gcl, granule cell layer; ml, molecular layer; hl, hilus. Scale bars in B, C: 150 μm.