Organotypic hippocampal slices were cut out of the culture insert and positioned in a recording chamber superfused (2–2.5 mL/min) with an external solution containing (in mM): 125 NaCl, 2.5 KCl, 25 NaHCO3, 1.3 MgCl2, 2 CaCl2, 0.4 ascorbic acid and 10 glucose (pH 7.4) and bubbled with 95% O2/5% CO2. Kynurenic acid (2 mM) and picrotoxin (100 μM) were added to the bath solution to block ionotropic glutamate and GABAA receptors, respectively. Bath and chamber temperatures were maintained at 29–30 °C using a TC344C Dual Automatic Temperature Controller (Warner Instruments; Hamden, CT). Whole-cell recordings (Vhold = −60 mV) were made from EGFP-positive CA1 pyramidal neurons using borosilicate pipettes (3–5 MΩ) filled with a K-gluconate pipette solution. All measured and command potentials factored in a junction potential (−15 mV) predicted using JPCalc software (Molecular Devices, LLC). Recordings were amplified with an EPC10 HEKA amplifier, filtered at 2 kHz, digitized at 5–10 kHz using Patchmaster 2x73.2 software (HEKA Elektronik; Bellmore, NY) and stored on hard disk. Stimulation was delivered with a cluster-type stimulating electrode (FHC, Bowdoin, ME) and a DS3 stimulator (Digitimer
