CXCR4 and brain ischemia: It is noteworthy that CXCR4 is expressed in the NPCs and the actions of the SDF-1/CXCR4 complex are critical for the migration of NPCs to SDF-1-riched injury sites after cerebral ischemia (Imitola et al., 2004; Thored et al., 2006; Shyu et al., 2008).