The chemokine stromal cell-derived factor-1 regulates GABAergic inputs to neural progenitors in the postnatal dentate gyrus.

Stromal cell-derived factor-1 (SDF-1) and its receptor CXC chemokine receptor 4 (CXCR4) are important regulators of the development of the dentate gyrus (DG). Both SDF-1 and CXCR4 are also highly expressed in the adult DG. We observed that CXCR4 receptors were expressed by dividing neural progenitor cells located in the subgranular zone (SGZ) as well as their derivatives including doublecortin-expressing neuroblasts and immature granule cells. SDF-1 was located in DG neurons and in endothelial cells associated with DG blood vessels. SDF-1-expressing neurons included parvalbumin-containing GABAergic interneurons known as basket cells. Using transgenic mice expressing an SDF-1-mRFP1 (monomeric red fluorescence protein 1) fusion protein we observed that SDF-1 was localized in synaptic vesicles in the terminals of basket cells together with GABA-containing vesicles. These terminals were often observed to be in close proximity to dividing nestin-expressing neural progenitors in the SGZ. Electrophysiological recordings from slices of the DG demonstrated that neural progenitors received both tonic and phasic GABAergic inputs and that SDF-1 enhanced GABAergic transmission, probably by a postsynaptic mechanism. We also demonstrated that, like GABA, SDF-1 was tonically released in the DG and that GABAergic transmission was partially dependent on coreleased SDF-1. These data demonstrate that SDF-1 plays a novel role as a neurotransmitter in the DG and regulates the strength of GABAergic inputs to the pool of dividing neural progenitors. Hence, SDF-1/CXCR4 signaling is likely to be an important regulator of adult neurogenesis in the DG.