For whole-cell patch-clamp recordings, we removed the top PDMS piece of the microfluidic chamber allowing access to the hippocampal neurons attached to the cover glass surface. The neurons were bathed in HEPES-buffered saline (HBS; containing, in mM: 119 NaCl, 5 KCl, 2 CaCl2, 2 MgCl2, 30 Glucose, 10 HEPES, pH 7.4) plus 1 μM TTX. We used an Axopatch 200B amplifier. Whole-cell pipette internal solution contained, in mM: 115 cesium gluconate, 20 cesium chloride, 10 sodium phosphocreatine, 10 HEPES, 0.2 EGTA, 2 MgATP, 0.3 NaGTP (pH 7.3). Neurons with pyramidal-like morphology were voltage-clamped at -70 mV, and series resistance was less than 20 MΩ and left uncompensated. mEPSCs were recording for 20 min in the presence of 1 μM TTX. The recording was continued following addition of a 5 μl bolus of 5 mM APV and 2 mM NBQX to block all fast excitatory synaptic transmission.
