Gene expression in rat hippocampal CA1 after the retrieval of contextual fear memory in the absence of extinction.

Adult rats (male Lister hooded) received a single unsignaled scrambled footshock (0.5 mA for 2 s) 2 min into a 3min exposure to a novel context. 48 hours later, rats were reexopsed to the condition context for 2 min (TEST). One half rats received bilateral microinfusions (1 microlitre/hemisphere) of 2 nmol/microlitre Zif268 antisense ODN (ZIFASO, 5- GGTAGTTGTCCATGGTGG-3in PBS, pH 7.4) or Zif268 missense ODN (ZIFMSO, 5 -GTGTTCGGTAGGGTGTCA-3in PBS, pH 7.4) into the dorsal hippocampus (AP -3.50, relative to bregma), 90 min before TEST. Infusions were made in awake rats via previously surgically implanted indwelling stainless steel cannula. Rats were housed in the home cages at all times outside the conditioning and TEST procedures. Rats were killed by CO2 inhalation 2 hours after TEST. CA1-enriched dorsal hippocampus was immediately dissected on ice before rapid freezing and storage at -80oC. The ZIFSO-infused group potentially represents reconsolidation-impaired rats.

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