Extracellular field potential recordings

For field potential recordings, acute coronal slices containing the IL-PFC were prepared exactly as previously described above (Padula et al., 2015), with the exception that slices were 350 μm in thickness and ACSF contained a CaCl₂ concentration of 2.5 mm. ACSF-filled theta-glass stimulating pipettes were placed in layer II/III, and ACSF-filled recording pipettes (0.3–2 MΩ) were placed in layer V of the IL-PFC. Field EPSPs (fEPSPs) were recorded at 30°C. Input/output curves were generated to determine the maximum stimulation intensity for each recording, and stimulation was adjusted to 50–60% maximum intensity for the duration of each recording. During the baseline period, slices were stimulated at a rate of 0.02 Hz. All drugs were applied for 10 min before high-frequency stimulation (HFS) consisting of five trains (50 Hz stimulation, 2 s duration) with a 30 s intertrain interval (Moussawi et al., 2009). After HFS, fEPSPs were evoked once per minute (0.02 Hz). Synaptic strength/potentiation was measured as the change in the initial onset of the fEPSP (slope) after HFS, relative to the normalized baseline slope, and expressed as a percentage of baseline. Long-term potentiation (LTP) recordings were amplified (gain of 10–50), filtered (0.2–1.2 kHz), and digitized at 10 kHz using an ITC-18 interface.