Fig 1: Validation of two distinct conditional vGluT2 KO lines(A) Left: overview of the hippocampal molecular layers in the ΔNp73-control (ctrl, left) and ΔNp73-KO mouse (KO, right). Expression of ChR2(H134R)-EYFP by CRs in yellow (EYFP). DAPI counterstaining: cyan (DAPI). White dotted lines: borders between layers. SLM, stratum lacunosum moleculare; ml, molecular layer of the dentate gyrus; gcl, granule cell layer; SP, stratum pyramidale.(B) As in (A) but for PDE1c-ctrl and PDE1c-KO animals.(C) Left: regions delimited by the red corners in (A). Insets: individual CRs and p73 nuclear immunoreactivity (magenta). DAPI stain in cyan. Right: summary plot of the linear density of p73-labled CRs in the two genotypes (ctr: blue, KO: red, n = 18 sections and 3 mice per genotype).(D) As in (C) but for PDE1c-ctrl and PDE1c-KO mice (ctrl, n = 10 sections; KO, n = 12 sections, 3 mice per genotype).(E) Left: immunoreactivity of EYFP+ CR terminals (yellow) for vGluT1, vGluT2, and vGluT3 (magenta) in ΔNp73-ctrl (top row) and ΔNp73-KO animals (bottom row). Right: quantification of bouton density according to their specific vGluT labeling (vGluT1, vGluT2, and vGluT3) and genotype (ctrl; KO, n = 6 stacks, 3 mice per genotype).(F) As in (E) but for PDE1c-ctrl and PDE1c-KO mice (n = 6 stacks, 3 mice per genotype). P30 animals.(G) Flash-evoked photocurrents in CRs. Left: averaged traces of photocurrents in ΔNp73-ctrl (ctrl, blue, n = 18 cells, 3 mice) and ΔNp73-KO animals (KO, red, n = 16 cells, 2 mice) are superimposed. Vholding = −60 mV. Circle: current peak; light blue arrow: time of the flash (1 ms duration). Middle: same traces at an expanded timescale. Notice the nearly instantaneous photocurrent during the flash (light blue shaded area). Right: summary plot of all experiments.(H) As in (G) but for PDE1c-ctrl and PDE1c-KO animals (ctrl, n = 22 cells, 5 mice, and KO, n = 20 cells, 8 mice).(I) Postsynaptic responses generated by CRs on interneurons (INs). Left, averaged EPSCs in INs of the molecular layers, following the optogenetic stimulation of CRs (light blue area). Vholding = −60 mV. Middle: same traces at a different timescale. In contrast to the photocurrents in (G), the EPSC follows the flash. Right: summary graph showing impaired transmission in KO (n = 27 cells, 4 mice) versus ctrl animals (n = 38 cells, 7 mice). The schematic shows the direct recording of flash-evoked (blue lightning) photocurrents from a CR and of EPSCs from an IN. The excitatory and glutamatergic nature of the connection is indicated by the (+) symbol and (Glu), respectively.(J) As in (I) but for PDE1c-ctrl (n = 66 cells, 10 mice) and PDE1c-KO mice (n = 48 cells, 9 mice). Boxplots: median (middle dash), lower and upper quartiles (box borders), and minimum and maximum (whiskers).ns, p > 0.05; *p < 0.05; and **p < 0.01.