Neural stem cell regulation. Neural stem cells in the two adult neurogenic niches, the SVZ and SGZ, can be regulated by (1) diffusible factors (EGF, FGF, TGF-α, VEGF, PEDF, hormones, BMPs, ATP, Wnts and GABA) and their receptors, (2) cell–cell and cell–extracellular environment interactions via membrane-associated ligands and their receptors (Eph/ephrin and Notch/Jagged) or gap junctions and hemi-channels, (3) ligand inhibition (noggin), (4) release of neurotransmitters and other factors from axons (GABA, dopamine (DA), glutamate, acetylcholine (ACh), serotonin (5HT), NO and Shh), (5) basal lamina (sequestration and presentation of diffusible factors, such as growth factors) and ECM proteins (laminin, collagen-1, tenascin-C, LeX, heparan sulphate and chondroitin sulphate proteoglycans), and (6) endothelial cell/blood vessel-mediated cues. The cell types that are able to direct neural stem cell fate choices include cells within the niche (both support cells and stem cells and their progeny) (green), neurons (axonal projection; blue) and endothelial cells/blood vessels (red). Structural elements that likely regulate neural stem cell fate decisions include fractones (in the SVZ) and basal laminae (black lines). In addition, CSF and meningeal projections (not pictured in this figure) are likely important components of the niche. These elements may work in concert or independently to promote neural stem cell self-renewal or differentiation. The key to the right lists some of the factors known to be present in adult neurogenic niches.