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. Samples from individual rats were hybridized to separate microarrays. There was no amplification of cDNA before hybridization. There were 12 separate samples. The CS+ rats (n = 6) represent the extinction group; CS- rats (n = 6) represent a control group that does not undergo extinction. All tissue was taken 2 hours context re-exposure/extinction training.