Slices were placed in the recording chamber and were continuously superfused in aCSF (2 ml/min) warmed to approximately 30°C (Lack et al., 2008). Electrodes were filled with an extracellular pipette solution containing 150mM NaCl. Ensemble postsynaptic potentials were evoked every 30 sec by brief (0.2 msec) square-wave electrical stimulation within the external capsule (EC) along the lateral border of the BLA. These synaptic responses are referred to as field excitatory postsynaptic potentials (fEPSPs) throughout the manuscript and were completely sensitive to both the AMPA/kainate receptor antagonist DNQX (20 μM) and to tetrodotoxin (1 μM; not shown). For the ATPA-induced plasticity experiments, maximal fEPSP responses were determined in every slice; the stimulus intensity that evoked 50% maximal amplitude was used for the baseline period. All field experiments were recorded in the presence of 10 μM bicuculline methiodide. Baseline fEPSPs were recorded for 10 minutes prior to application of the kainate receptor agonist ATPA ((RS)-2-Amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) propanoic acid; 5 μM) for 15 minutes; the slice was then washed for 40 minutes in drug-free aCSF. fEPSP recordings were acquired with an Axoclamp 2B amplifier
