title: Critical role of NMDA but not opioid receptors in the acquisition of fat-conditioned flavor preferences in rats.
abstract: Animals learn to prefer flavors associated with the intake of dietary fats such as corn oil (CO) solutions. We previously reported that fat-conditioned flavor preferences in rats were relatively unaffected by systemic treatment with dopamine D1 and D2 antagonsits. The present study examined whether systemic opioid (naltrexone, NTX) or NMDA (MK-801) receptor antagonists altered the acquisition and/or expression of CO-CFP. The CFP was produced by training rats to drink one novel flavor (CS+, e.g., cherry) mixed in a 3.5% CO solution and another flavor (CS-, e.g., grape) in a 0.9% CO solution. In expression studies, food-restricted rats drank these solutions in one-bottle sessions (2 h) over 10 d. Subsequent two-bottle tests with the CS+ and CS- flavors mixed in 0.9% CO solutions occurred 0.5h after systemic administration of vehicle (VEH), NTX (0.1-5 mg/kg) or MK-801 (50-200 μg/kg). Rats displayed a robust CS+ preference following VEH treatment (85-88%) which was significantly though moderately attenuated by NTX (69-70%). The lower doses of MK-801 slightly reduced the CS+ preference; the high dose blocked the CS+ preference (49%) but also markedly reduced overall CS intake. In separate acquisition studies, rats received VEH or NTX (0.1, 0.5, 1mg/kg) or MK-801 (100 μg/kg) 0.5h prior to 1-bottle training trials with CS+/3.5% CO and CS-/0.9% CO training solutions. Additional Limited VEH groups were trained with intakes limited to that of the NTX and MK-801 groups. Subsequent two-bottle CS+ vs. CS- tests were conducted without injections. Significant and persistent CS+ preferences were observed in VEH (77-84%) and Limited VEH (88%) groups. NTX treatment during training failed to block the acquisition of CO-CFP although the magnitude of the CS+ preference was reduced by 0.5 (70%) and 1.0 (72%) mg/kg doses relative to the Limited VEH treatment (88%). In contrast, MK-801 (100 μg/kg) treatment during training blocked the acquisition of the CO-CFP. These data suggest a critical role for NMDA, but not opioid receptor signaling in the acquisition of a fat conditioned flavor preferences, and at best limited involvement of NMDA and opioid receptors in the expression of a previously learned preference.
authors.affiliation: Neuropsychology Doctoral Sub-Program, The Graduate Center, City University of New York, USA.
authors.forename: J A D
authors.initials: JA
authors.lastname: Dela Cruz
authors.forename: V S
authors.initials: VS
authors.lastname: Bae
authors.forename: D
authors.initials: D
authors.lastname: Icaza-Cukali
authors.forename: C
authors.initials: C
authors.lastname: Sampson
authors.forename: D
authors.initials: D
authors.lastname: Bamshad
authors.forename: A
authors.initials: A
authors.lastname: Samra
authors.forename: S
authors.initials: S
authors.lastname: Singh
authors.forename: N
authors.initials: N
authors.lastname: Khalifa
authors.forename: K
authors.initials: K
authors.lastname: Touzani
authors.forename: A
authors.initials: A
authors.lastname: Sclafani
authors.forename: R J
authors.initials: RJ
authors.lastname: Bodnar
mesh_terms: D000818:Animals; D001069:Appetite Regulation / Q000187:drug effects / Q000502:physiology; D001245:Association Learning / Q000187:drug effects; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D003214:Conditioning, Classical / Q000187:drug effects*; D004041:Dietary Fats; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004435:Eating / Q000187:drug effects*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005518:Food Preferences / Q000187:drug effects*; D008297:Male; D009271:Naltrexone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000502:physiology*; D011957:Receptors, Opioid / Q000502:physiology*
chemical_list: D004041:Dietary Fats; D018691:Excitatory Amino Acid Antagonists; D009292:Narcotic Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D011957:Receptors, Opioid; D009271:Naltrexone; D016291:Dizocilpine Maleate