title: Arc-Expressing Neuronal Ensembles Supporting Pattern Separation Require Adrenergic Activity in Anterior Piriform Cortex: An Exploration of Neural Constraints on Learning.
abstract: Arc ensembles in adult rat olfactory bulb (OB) and anterior piriform cortex (PC) were assessed after discrimination training on highly similar odor pairs. Nonselective α- and β-adrenergic antagonists or saline were infused in the OB or anterior PC during training. OB adrenergic blockade slowed, but did not prevent, odor discrimination learning. After criterion performance, Arc ensembles in anterior piriform showed enhanced stability for the rewarded odor and pattern separation for the discriminated odors as described previously. Anterior piriform adrenergic blockade prevented acquisition of similar odor discrimination and of OB ensemble changes, even with extended overtraining. Mitral and granule cell Arc ensembles in OB showed enhanced stability for rewarded odor only in the saline group. Pattern separation was not seen in the OB. Similar odor discrimination co-occurs with increased stability in rewarded odor representations and pattern separation to reduce encoding overlap. The difficulty of similar discriminations may relate to the necessity to both strengthen rewarded representations and weaken overlap across similar representations.
  
  
  CONCLUSIONS
  We show for the first time that adrenoceptors in anterior piriform cortex (aPC) must be engaged for adult rats to learn to discriminate highly similar odors. Loss of adrenergic activation in olfactory bulb (OB) slows, but does not prevent, discrimination learning. Both increased stability of the rewarded odor representation and increased pattern separation of the rewarded and unrewarded odors in aPC accompany successful discrimination. In the OB, rewarded odors increase in ensemble stability, but there is no evidence of pattern separation. We suggest that the slow acquisition of similar odor discriminations is related to the differing plasticity requirements for increased stability and pattern separation.
authors.affiliation: Division of Biomedical Sciences, Faculty of Medicine, and.
authors.forename: Amin M D
authors.identifier: http://orcid.org/0000-0002-3776-3699
authors.initials: AM
authors.lastname: Shakhawat
authors.affiliation: Division of Biomedical Sciences, Faculty of Medicine, and.
authors.forename: Ali
authors.identifier: http://orcid.org/0000-0001-9125-0029
authors.initials: A
authors.lastname: Gheidi
authors.affiliation: Division of Biomedical Sciences, Faculty of Medicine, and.
authors.forename: Iain T
authors.identifier: http://orcid.org/0000-0001-7775-0932
authors.initials: IT
authors.lastname: MacIntyre
authors.affiliation: Division of Biomedical Sciences, Faculty of Medicine, and.
authors.forename: Melissa L
authors.initials: ML
authors.lastname: Walsh
authors.affiliation: Department of Psychology, Faculty of Science, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3V6, Canada.
authors.forename: Carolyn W
authors.identifier: http://orcid.org/0000-0001-8641-7998
authors.initials: CW
authors.lastname: Harley
authors.affiliation: Division of Biomedical Sciences, Faculty of Medicine, and qi.yuan@med.mun.ca.
authors.forename: Qi
authors.identifier: http://orcid.org/0000-0002-9837-8495
authors.initials: Q
authors.lastname: Yuan
mesh_terms: D018674:Adrenergic Antagonists / Q000494:pharmacology; D000818:Animals; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004193:Discrimination Learning / Q000187:drug effects / Q000502:physiology*; D004837:Epinephrine / Q000378:metabolism*; D005260:Female; D008297:Male; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009812:Odorants; D066195:Piriform Cortex / Q000166:cytology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012201:Reward; D011984:Sensory Receptor Cells / Q000145:classification / Q000378:metabolism*
chemical_list: D018674:Adrenergic Antagonists; D003598:Cytoskeletal Proteins; D009419:Nerve Tissue Proteins; C092069:activity regulated cytoskeletal-associated protein; D004837:Epinephrine
keywords: Arc; norepinephrine; odor discrimination; olfactory bulb; pattern separation; piriform cortex