Jagged1 regulates learning-dependent Notch induction and is enriched presynaptically. Fluorescent double-labeling shows the expression of Notch1 (red) following spatial exploration in CTLs and Jagged1cKO (A). Jagged1 labeling (green) is used to validate the absence of Jagged1 in the Jagged1cKO (Jag1cKOs) (A,C). Diagram summarizing the Notch1 fluorescence intensities distribution in randomly picked 69 and 71 CA1 neurons in CTLs and Jagged1cKOs, respectively (p < 0.001) (B). Double immunofluorescence of the Notch1 transcriptional target, Hes5, in CTLs and JaggedcKOs following spatial exploration (C). Diagram summarizing the Hes5 fluorescence intensity distribution in randomly picked 64 and 70 CA1 neurons in CTL and Jagged1cKO, respectively (p < 0.001) (D). Representatives gold Immuno-electron microscopy panels from three WT mice show that Jagged1 particles are localized in presynaptic terminals, bound to presynaptic vesicles (Pre) (E–E‴). Immunogold particles are also apparent at the Postsynaptic density (Post) (E,E″,E‴). Box Plot summarizing the particle counts in presynaptic and postsynaptic terminal areas drawn on Immunoelectromicroscopy micrograph for Jagged1 indicates that the presynapse is enriched with Jag1 particles as compared to the postsynaptic terminal (p < 0.001) (F). Scale bars are: 20 μm in (A), 10 μm in (C), 400 nm in (E–E‴). AU, arbitrary units; Pre, presynaptic; Post, postsynaptic; and Ax, axon.