ID1 levels in the mouse hippocampus (n=7 at each time point) were analyzed using a previously-published method (28 (link)). Hippocampal tissues were homogenized and ID1 levels were determined using a micro bicinchoninic acid (BCA) protein assay kit (Pierce; Thermo Fisher Scientific, Inc., Waltham, MA, USA). Nitrocellulose transfer membranes (Pall Life Sciences, Port Washington, NY, USA) were incubated with rabbit anti-ID1 (1:1,000; sc-488; Santa Cruz Biotechnology, Inc., Dallas, TX, USA), β-actin (1:2,000, sc-47778; Santa Cruz Biotechnology, Inc.) and exposed to peroxidase-conjugated goat anti-rabbit immunoglobulin G (1:2,000; sc-2004; Santa Cruz Biotechnology, Inc.) for 2 h at 4°C and an enhanced luminol-based chemiluminescence kit (Pierce; Thermo Fisher Scientific, Inc.). The results of this analysis were scanned and densitometric analysis, as the relative optical density (ROD), was used for quantification of the bands using Scion Image software, version 2.0 (Scion Corporation, Frederick, MD, USA). A ratio of the ROD was calibrated as a percentage, with control mice designated as 100%.