Gene expression in rat hippocampal CA1 during the extinction of contextual fear memory

Adult rats (male Lister hooded) were pre-exposed for 3 d for 10 min /d (24 hr interval) to two different novel contexts. On day 4 rats received a single unsignaled scrambled footshock (0.5 mA for 2 s) 2 min into a 3min exposure to one of the two contexts. Rats were either returned to the CS conditioned context (CS+, EXT group) or to the other (CS-, NOR group) context for 10 min, 48h after contextual fear conditioning. Rats were housed in the home cages at all times outside the conditioning and re-exposure components. The novel context chosen to be the conditioned context was counterbalanced across the experimental groups. Rats were killed by CO2 inhalation 2 hours after CS- or CS+ exposure. CA1-enriched dorsal hippocampus was immediately dissected on ice before rapid freezing and storage at -80oC. The CS+ group represents rats that underwent extinction of contextual fear memory.