Fig. 1.

Overview of the hippocampal formation and adult neurogenesis. a Schematic representation of the tri-synaptic pathway. Axons derived from the entorhinal cortex (EC) layer II projects via the perforant pathway (purple) towards the dendrites of the DG granule cells (red). The perforant pathway projects also towards CA3 were they end in boutons, which contact dendrites of pyramidal cells (blue). Mossy fibers (red) originating in the DG granule cells project to the same pyramidal cells in the CA3. Via the Schaffer collateral pathway (blue) the CA3 projects towards pyramidal neurons (green) in the CA1, which also receive input from the EC layer III. CA1 pyramidal neurons project (green) towards layer IV of the same EC. Only in the DG, new-born granule cells (yellow) integrate into this network. b Adult neurogenesis can be divided in three main stages: the precursor cell stage, the early postmitotic maturation phase and the late mitotic maturation phase. Stem cells proliferate in the sub-granular zone (SGZ) where after NPCs migrate into the granular cell layer (GCL). During the late postmitotic phase, the newborn neurons develop dendritic trees protruding into the molecular layer (ML). Different stages are characterized by expression of specific markers. Note that the GR is expressed in radial glia cells, but not early precursor cells. For further details, see main text