(A) Confocal images showing RV input neurons in the MS colocalize with PV marker. Arrow heads pointing to PV+ RV+ cells. Scale bar: 50 µm. (B) Percentage of PV+ RV+ out of total RV input cells in the MS (n=3). (C) AAV-DIO-YFP injection scheme to the MS of the PV-Cre mice. (D) Confocal image showing selective targeting of the MS PV neurons through stereotaxic delivery of AAV-DIO-YFP to the PV-Cre mice. Scale bar: 50 µm. (E) Confocal image of sparse AAV-DIO-YFP labeled MS PV projections to the SGZ and hilus. Scale bar: 50 µm. (F) Axonal collaterals from MS PV cells are closely associated with the soma of dentate PV interneurons. Scale bar: 50 µm (top), 20 µm (bottom). (G) YFP viral labeled MS PV neurons in PV-Cre mice (n=6). (H) Connected percentage of MS projections to DG-PV neurons (n=6 for PV-Cre, and n=4 for VGAT-Cre). (I) AAV-DIO-ChR2-YFP injection scheme to the MS in the VGAT-Cre mice. (J) Experimental paradigm for in vivo optogenetic stimulation. (K–M) Density of activated rNSC (nestin+EdU+), proliferating cells (EdU+), and the rNSC pool (nestin+). (n=5 for control, and n=6 for ChR2). ***p<0.001 by Student’s t-test. Values represent mean ± S.E.M. See also Figure S5.