Animals were deeply anesthetized with halothane and decapitated from approximately 10:00 am–11:00 am. Stress animals were sacrificed 24–72 hours following the last stressor. The brain was rapidly removed and hippocampi dissected. Transverse hippocampal slices, 400 μM thick, were cut on a Vibrotome (Leica-Microsystems). Slices were kept in a holding chamber at room temperature at the interface of artificial cerebrospinal fluid (ACSF) and a humidified 95/5% O2/CO2 atmosphere for >1 hr. The slices were then transferred to a submerged recording chamber and perfused with warm (30° C) ACSF: (mM), NaCl, 120; KCl, 3; MgSO4, 2; NaH2PO4, 1; NaHCO3, 25; CaCl2, 2.5; and glucose, 10 and saturated with 95% O2-5% CO2 (pH 7.4). Field potentials (fEPSPs) were recorded from stratum radiatum of CA1 with glass microelectrodes (tip diameter ~4–8 μm) filled with extracellular saline. Stimuli were delivered via a bipolar stimulating electrode 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)
