not-yet-known not-yet-known not-yet-known unknown Field potential recordings from organotypic slices Organotypic slices were individually transferred to an interface-type chamber with a humidified (5% CO2 / 95% O2) atmosphere at 37 °C. Each slice was visually inspected, ensuring slice integrity and organization. Slices were perfused with aCSF with increased concentration of KCl ([KCl]=8.5 mM, depolarizing/hyperexcitable conditions) or with NBA medium (non-depolarizing conditions), both continuously recirculating at a rate of 2 mL/minute. Recordings were through an extracellular microelectrode (2–4 MΩ resistance, filled with aCSF) placed in the CA3 pyramidal cell layer. The viability of slices was initially tested by recording evoked field population spikes using the S48 Square Pulse Stimulator (Grass). Stimulation (rectangular pulses, 0.1ms, 100-400µA, every 15 seconds) was delivered through a bipolar concentric electrode placed on mossy fibers. After stimulation, spontaneous field potentials were recorded for 90 minutes. Drugs (MRS5474 (250 nM) or CPA (30 nM)) were added to the perfusion medium after an equilibration period of 20 minutes of spontaneous activity recording. No drug was added to the control slices. Recordings were obtained with an Axoclamp 900A amplifier (Axon Instruments, Foster City, CA, USA), digitized with Digidata 1440A (Axon Instruments, Foster City, CA, USA), and stored on a computer with the pCLAMP Software Version 10.7 (Molecular Devices LLC, San Jose, California, USA) to automatically detect spontaneous spikes during a recording. All recordings were band-pass filtered (eight-pole Bessel filter at 60 Hz and Gaussian filter at 600 Hz). The baseline used to detect these spikes was specific to each recording and was settled right above the end of noise oscillations. Interictal epileptiform discharges were defined as individual paroxysmal discharges clearly distinguished from the baseline, with an abrupt change in polarity occurring within several milliseconds. Ictal-like discharges were defined as continuous discharges lasting more than 10 seconds (bursts) or with a minimum frequency of 2 Hz (Berdichevsky et al., 2012). The end of a burst was defined when the inter-spike interval was longer than 2 seconds (Noe et al., 2013). Continuous spike activity with less than 10 seconds duration was not accounted as burst activity. To quantify the epileptiform activity an in-house program written in C++ language was developed to automatically evaluate the number of bursts per slice, the frequency, and the positive peak amplitude (amplitude between the baseline and the peak of the spike) of spikes within a burst and its duration, according to the ictal parameters. The data was given by the mean of a specific intrinsic parameter (frequency or amplitude) within the bursts per slice. To allow comparisons, the values obtained between 10-20 minutes (baseline) after starting the recordings were normalized to 1 within each slice; values obtained at 50–60 minutes and at 80–90 minutes after starting recording were normalised to the baseline condition.