title: The hippocampal CA2 ensemble is sensitive to contextual change.
abstract: Contextual learning involves associating cues with an environment and relating them to past experience. Previous data indicate functional specialization within the hippocampal circuit: the dentate gyrus (DG) is crucial for discriminating similar contexts, whereas CA3 is required for associative encoding and recall. Here, we used Arc/H1a catFISH imaging to address the contribution of the largely overlooked CA2 region to contextual learning by comparing ensemble codes across CA3, CA2, and CA1 in mice exposed to familiar, altered, and novel contexts. Further, to manipulate the quality of information arriving in CA2 we used two hippocampal mutant mouse lines, CA3-NR1 KOs and DG-NR1 KOs, that result in hippocampal CA3 neuronal activity that is uncoupled from the animal's sensory environment. Our data reveal largely coherent responses across the CA axis in control mice in purely novel or familiar contexts; however, in the mutant mice subject to these protocols the CA2 response becomes uncoupled from CA1 and CA3. Moreover, we show in wild-type mice that the CA2 ensemble is more sensitive than CA1 and CA3 to small changes in overall context. Our data suggest that CA2 may be tuned to remap in response to any conflict between stored and current experience.
authors.affiliation: Laboratory for Circuit and Behavioral Physiology, RIKEN Brain Science Institute, Wakoshi, Saitama, Japan 351-0198.
authors.forename: Marie E
authors.initials: ME
authors.lastname: Wintzer
authors.forename: Roman
authors.initials: R
authors.lastname: Boehringer
authors.forename: Denis
authors.initials: D
authors.lastname: Polygalov
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: McHugh
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D056651:CA2 Region, Hippocampal / Q000502:physiology*; D003463:Cues; D003598:Cytoskeletal Proteins / Q000502:physiology; D004777:Environment; D006624:Hippocampus / Q000502:physiology; D007091:Image Processing, Computer-Assisted; D017404:In Situ Hybridization, Fluorescence; D007858:Learning / Q000502:physiology*; D008568:Memory / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009154:Mutation / Q000502:physiology; D009415:Nerve Net / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000502:physiology; D012313:RNA / Q000096:biosynthesis / Q000235:genetics; D012640:Seizures / Q000139:chemically induced / Q000503:physiopathology; D012677:Sensation / Q000502:physiology
chemical_list: D003598:Cytoskeletal Proteins; D009419:Nerve Tissue Proteins; C092069:activity regulated cytoskeletal-associated protein; D012313:RNA
keywords: Arc; CA2; H1a; IEG; context learning; hippocampus