title: Chemogenetic silencing of neurons in retrosplenial cortex disrupts sensory preconditioning.
abstract: An essential aspect of episodic memory is the formation of associations between neutral sensory cues in the environment. In light of recent evidence that this critical aspect of learning does not require the hippocampus, we tested the involvement of the retrosplenial cortex (RSC) in this process using a chemogenetic approach that allowed us to temporarily silence neurons along the entire rostrocaudal extent of the RSC. A viral vector containing the gene for a synthetic inhibitory G-protein-coupled receptor (hM4Di) was infused into RSC. When the receptor was later activated by systemic injection of clozapine-N-oxide, neural activity in RSC was transiently silenced (confirmed using a patch-clamp procedure). Rats expressing hM4Di and control rats were trained in a sensory preconditioning procedure in which a tone and light were paired on some trials and a white noise stimulus was presented alone on the other trials during the Preconditioning phase. Thus, rats were given the opportunity to form an association between a tone and a light in the absence of reinforcement. Later, the light was paired with food. During the test phase when the auditory cues were presented alone, controls exhibited more conditioned responding during presentation of the tone compared with the white noise reflecting the prior formation of a tone-light association. Silencing RSC neurons during the Preconditioning phase prevented the formation of an association between the tone and light and eliminated the sensory preconditioning effect. These findings indicate that RSC may contribute to episodic memory formation by linking essential sensory stimuli during learning.
authors.affiliation: Department of Psychological and Brain Sciences, Dartmouth College, Hanover, New Hampshire 03755.
authors.forename: Siobhan
authors.initials: S
authors.lastname: Robinson
authors.affiliation: Department of Psychological and Brain Sciences, Dartmouth College, Hanover, New Hampshire 03755.
authors.forename: Travis P
authors.initials: TP
authors.lastname: Todd
authors.affiliation: Department of Psychological and Brain Sciences, Dartmouth College, Hanover, New Hampshire 03755.
authors.forename: Anna R
authors.initials: AR
authors.lastname: Pasternak
authors.affiliation: Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire 03756, and.
authors.forename: Bryan W
authors.identifier: http://orcid.org/0000-0002-3181-6075
authors.initials: BW
authors.lastname: Luikart
authors.affiliation: Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire 03756, and.
authors.forename: Patrick D
authors.initials: PD
authors.lastname: Skelton
authors.affiliation: Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Urban
authors.affiliation: Department of Psychological and Brain Sciences, Dartmouth College, Hanover, New Hampshire 03755, david.j.bucci@dartmouth.edu.
authors.forename: David J
authors.initials: DJ
authors.lastname: Bucci
mesh_terms: D000818:Animals; D001245:Association Learning / Q000187:drug effects / Q000502:physiology*; D002540:Cerebral Cortex / Q000187:drug effects / Q000502:physiology*; D003024:Clozapine / Q000031:analogs & derivatives / Q000494:pharmacology; D003213:Conditioning, Psychological / Q000187:drug effects / Q000502:physiology*; D003463:Cues; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans
chemical_list: D003024:Clozapine; C079149:clozapine N-oxide
keywords: DREADD; episodic; hippocampus; learning; parahippocampal; retrosplenial