Muscimol inactivation of the dorsal hippocampus impairs contextual retrieval of fear memory.
Some models of hippocampal function have suggested a role of the hippocampus in contextual memory retrieval. We have examined this hypothesis by assessing the impact of reversible inactivation of the dorsal hippocampus (DH) on the context-specific expression of latent inhibition, a decrement in conditional responding produced by preexposure to a to-be-conditional stimulus. In Experiment 1, rats received tone preexposure either in the context that would later be used for extinction testing (context A) or in a different context (context C); a third group of rats did not receive tone preexposure. All rats then received fear conditioning, which consisted of tone-footshock pairings, in a third distinct context (context B). The following day conditional fear to the tone was assessed in one of the preexposure contexts (context A) by measuring freezing during a tone extinction test. Rats preexposed and tested in the same context exhibited less freezing to the tone than either rats preexposed and tested in different contexts or non-preexposed rats. These results indicate that the expression of latent inhibition is context specific. In Experiment 2, DH inactivation eliminated the context-specific expression of latent inhibition. Compared with saline-infused rats, rats infused with muscimol into the DH exhibited low levels of tone freezing independent of whether they had received tone preexposure in the test context or in a different context. Experiment 3 revealed normal contextual discrimination in rats after DH inactivation. These results suggest the DH is required for contextual memory retrieval in a latent inhibition paradigm.
Holt
W
W
Department of Psychology, University of Michigan, Ann Arbor, Michigan 48109-1109, USA.
Maren
S
S
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D001931:Brain Mapping; D003214:Conditioning, Classical / Q000502:physiology*; D004192:Discrimination, Psychological / Q000502:physiology; D005239:Fear / Q000502:physiology*; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology*; D008297:Male; D011939:Mental Recall / Q000502:physiology*; D009118:Muscimol / Q000494:pharmacology*; D009433:Neural Inhibition / Q000502:physiology; D051381:Rats; D020318:Rats, Long-Evans; D011930:Reaction Time / Q000502:physiology
D009118:Muscimol