2.1 Preparation of hippocampal slices
Parasagittal slices of hippocampus (400 µm) were prepared from 2–3-month-old male and female wildtype (WT) C57BL/6 and ArcKR mice (Wall et al. , 2018). Mice were kept on a 12-hour light-dark cycle with slices made 90 minutes after entering the light cycle. In accordance with the U.K. Animals (Scientific Procedures) Act (1986), mice were killed by cervical dislocation and then decapitated. The brain was removed, cut down the mid-line and the two sides of the brain stuck down to a base plate. Slices were cut around the midline with a Microm HM 650V microslicer in cold (2-4°C) high Mg2+, low Ca2+artificial CSF (aCSF), composed of (mM): 127 NaCl, 1.9 KCl, 8 MgCl2, 0.5 CaCl2, 1.2 KH2PO4, 26 NaHCO3, 10 D-glucose (pH 7.4 when bubbled with 95% O2 and 5% CO2, 300 mOSM). Slices were stored at 34°C bubbled with 95% O2 and 5% CO2 for 1-6 hours in aCSF (1 mM MgCl2, 2 mM CaCl2) before use.