Excitatory postsynaptic currents (EPSCs) were evoked by electrical pulses delivered at 0.1 Hz frequency (stimulator S-900, Cornerstone by Dagan) through a bipolar stimulus electrode. Picrotoxin (100 µM) was added to the ACSF to block GABAA receptors. The recordings were performed in voltage clamp configuration at +40 mV (Axopatch 200B, Axon Instruments, Union City, CA, USA) [20]. The stable baseline EPSCs were recorded for 5–10 min. Then, 100 µM DL-AP5 was added to perfusion solution to block NMDA receptors, and after 5 min, the remaining current representing AMPA receptor-mediated current was recorded for 5–10 min with continued presence of DL-AP5. The recordings were filtered at 1 kHz and digitized at 20 kHz (Digidata 1322A, Axon Instruments). To calculate the AMPA/NMDA ratio, first the average AMPA receptor-mediated current was subtracted from the average baseline EPSC, revealing the NMDA receptor-mediated current, and then the AMPA/NMDA-ratio was calculated from the peak amplitudes of the currents. One to two cells (only one cell per slice) were studied per mouse. The recordings from different cells from the same animal were averaged and this average was used in the analysis. The drugs used in electrophysiology were purchased from Tocris Bioscience (Bristol, UK).
