Neuronal circuitry mechanism regulating adult quiescent neural stem-cell fate decision

Adult neurogenesis arises from neural stem cells within specialized niches^1–3. Neuronal activity and experience, presumably acting upon this local niche, regulate multiple stages of adult neurogenesis, from neural progenitor proliferation to new neuron maturation, synaptic integration and survival^{1, 3}. Whether local neuronal circuitry has a direct impact on adult neural stem cells is unknown. Here we show that in the adult hippocampus nestin-expressing radial glia-like quiescent neural stem cells^4–9 (RGLs) respond tonically to the neurotransmitter GABA via γ₂ subunit-containing GABA_A Rs. Clonal analysis⁹ of individual RGLs revealed a rapid exit from quiescence and enhanced symmetric self-renewal after conditional γ₂ deletion. RGLs are in close proximity to GAD67⁺ terminals of parvalbumin-expressing (PV⁺) interneurons and respond tonically to GABA released from these neurons. Functionally, optogenetic control of dentate PV⁺, but not somatostatin- or vasoactive intestinal polypeptide (VIP)-expressing, interneuron activity can dictate the RGL choice between quiescence and activation. Furthermore, PV⁺ interneuron activation restores RGL quiescence following social isolation, an experience that induces RGL activation and symmetric division⁸. Our study identifies a niche cell-signal-receptor trio and a local circuitry mechanism that control the activation and self-renewal mode of quiescent adult neural stem cells in response to neuronal activity and experience.