Adult neurogenesis is tightly regulated through the interaction of neural stem/progenitor cells (NSCs) with their niche. Neurotransmitters, including GABA activation of GABA A receptor ion channels, are important niche signals. We show that adult mouse hippocampal NSCs and their progeny express metabotropic GABA B receptors. Pharmacological inhibition of GABA B receptors stimulated NSC proliferation and genetic deletion of GABA B1 receptor subunits increased NSC proliferation and

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... of neuroblasts in vivo. Cell-specific conditional deletion of GABA B receptors supports a cellautonomous role in newly generated cells. Our data indicate that signaling through GABA B receptors is an inhibitor of adult neurogenesis.