title: Time course of dorsal and ventral hippocampal involvement in the expression of trace fear conditioning.
abstract: While a number of early studies demonstrated that hippocampal damage attenuates the expression of recent, but not remotely trained tasks, an emerging body of evidence has shown that damage to, or inactivation of, the hippocampus often impairs recall across a wide range of training-testing intervals. Collectively, these data suggest that the time course of hippocampal involvement in the storage or recall of previously-acquired memories may differ according to hippocampal subregion and the particular learning task under consideration. The present study examined the contributions of dorsal (DH) and ventral (VH) hippocampus to the expression of previously-acquired trace fear conditioning, a form of Pavlovian conditioning in which the offset of an initially neutral cue or cues and the onset of an aversive stimulus is separated by a temporal (trace) interval. Specifically, either saline or the GABA-A agonist muscimol was infused into DH or VH prior to testing either 1, 7, 28, or 42 days after trace fear conditioning. The results revealed a marked dissociation: pre-testing inactivation of DH failed to impair performance at any time-point, while pre-testing inactivation of VH impaired performance at all time-points. Importantly, pre-testing inactivation of VH had no effect on the performance of previously-acquired delay conditioning, suggesting that the deficits observed in trace conditioning cannot be attributed to a deficit in performance of the freezing response. Collectively, these data suggest that VH, but not DH, remains a neuroanatomical locus critical to the recall or expression of trace fear conditioning over an extended period of time.
authors.affiliation: Program in Behavioral and Systems Neuroscience, Department of Psychology, Rutgers University, 152 Frelinghuysen Rd., Piscataway, NJ 08854, USA. Electronic address: davidcox@rci.rutgers.edu.
authors.forename: David
authors.initials: D
authors.lastname: Cox
authors.forename: Jennifer
authors.initials: J
authors.lastname: Czerniawski
authors.forename: Fredrick
authors.initials: F
authors.lastname: Ree
authors.forename: Tim
authors.initials: T
authors.lastname: Otto
mesh_terms: D000161:Acoustic Stimulation; D000818:Animals; D003214:Conditioning, Classical / Q000187:drug effects / Q000502:physiology*; D003463:Cues; D005239:Fear / Q000187:drug effects / Q000502:physiology*; D058785:GABA-A Receptor Agonists / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008568:Memory / Q000502:physiology; D009118:Muscimol / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D058785:GABA-A Receptor Agonists; D009118:Muscimol
keywords: Hippocampus; Memory Consolidation; Temporary Inactivation; Trace Fear Conditioning