hCSs were removed from Neurobasal–B-27 medium, quickly fixed to a block of 4% agarose, and covered in ice-cold oxygenated (95% O2 and 5% CO2) ACSF containing 126 mM NaCl, 2.5 mM KCl, 1.25 mM NaH2PO4, 2 mM MgCl2, 2 mM CaCl2, 26 mM NaHCO3 and 10 mM glucose. Slices with a 250 μm thickness were cut using a Leica VT1200 vibrating microtome. After slicing, sections were moved to continuously oxygenated, warm (~32 °C) ACSF. Slices were incubated in warm ACSF for at least one hour before recording.
