located in stratum radiatum, between CA3 and CA1. Signals were recorded with an amplifier (Model 773, WPI Inc. or Model IE-251A, Warner Instruments Inc.), digitized at 10 kHz with an AD interface (Digidata 1440A, Axon Instruments or PCI-6259, National Instruments) and analyzed with either pClamp 10.0 (Axon Instruments) or WinLTP software. Only fEPSPs that could achieve or exceed an initial amplitude of 1.0 mV were recorded. Stable baseline responses (10–15 min) were recorded prior to experimental manipulation. During pharmacological experiments, fEPSPs were adjusted to ~0.8 mV prior to beginning a baseline. Following the baseline period, drugs were bath-applied for 30–45 min or delivered continuously throughout the entire experiment. Synaptic plasticity experiments began with fEPSPs adjusted to ~0.5 mV and involved delivering a weak theta-burst stimulation (TBS; 10 bursts of 5 stimuli, 100 Hz within burst, 200 ms interburst interval) following the baseline period.
