Surgery

Excitotoxic lesions of BLA (n = 8) and ventral OFC (n = 8) were performed using aseptic stereotaxic techniques under isoflurane gas (1–5% in O2) anesthesia prior to behavioral testing and training. Before surgeries, all animals were administered 5 mg/kg s.c. carprofen (NADA #141–199, Pfizer, Inc., Drug Labeler Code: 000069) and 1cc saline. After being placed into a stereotaxic apparatus (David Kopf; model 306041), the scalp was incised and retracted. The skull was then leveled to ensure that bregma and lambda are in the same horizontal plane. Small burr holes were drilled in the skull to allow cannulae with an injection needle to be lowered into the BLA (AP: −2.5; ML: ± 5.0; DV: −7.8 (0.1 μl) and −8.1 (0.2 μl) from skull surface) or OFC (0.2 μl, AP =+3.7; ML = ±2.0; DV = −4.6). The injection needle was attached to polyethylene tubing connected to a Hamilton syringe mounted on a syringe pump. N-Methyl-D-aspartic acid (NMDA, Sigma-Aldrich; 20 mg/ml in 0.1 m PBS, pH 7.4; Product # M3262) was bilaterally infused at a rate of 0.1 μl/min to destroy intrinsic neurons. After each injection, the needle was left in place for 3–5 min to allow for diffusion of the drug. Sham-lesioned group (n = 8) underwent identical surgical procedures, except no NMDA was infused. All animals were given one-week recovery period prior to food restriction and subsequent behavioral testing. During this week, the rats were administered 5 mg/kg s.c. carprofen (NADA #141–199, Pfizer, Inc., Drug Labeler Code: 000069) and their health condition was monitored daily.