title: Endogenous opioids and their role in odor preference acquisition and consolidation following odor-shock conditioning in infant rats.
abstract: We assessed the neurochemical basis of olfactory learning induced by presentations of odor and moderate shock in infant rats. Paradoxically, shock conditioning produces an odor preference in 8-day-olds, but an odor aversion in 12-day-olds. Studies have demonstrated the importance of opioids in early olfactory learning; their specific role remains undefined. In this study, postnatal Days 8 and 12 pups were systemically injected with naltrexone, a nonspecific opioid antagonist, or saline and received either paired or backward presentations of odor-moderate shock or odor-only presentations. Blocking the opioid system during conditioning disrupted acquisition of the Day 8 odor preference, but not the Day 12 odor aversion. Additional Day 8 pups were given naltrexone posttraining. Naltrexone not only blocked consolidation of an odor preference but also yielded an odor aversion. These results suggest that the opioid system has a critical role in both olfactory learning and consolidation of odor preferences during the sensitive period.
authors.affiliation: Department of Zoology, University of Oklahoma, Norman, OK 73019, USA.
authors.forename: T L
authors.initials: TL
authors.lastname: Roth
authors.forename: R M
authors.initials: RM
authors.lastname: Sullivan
mesh_terms: D000367:Age Factors; D000375:Aging / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D001245:Association Learning / Q000502:physiology*; D001362:Avoidance Learning / Q000502:physiology; D002755:Choice Behavior / Q000502:physiology; D003214:Conditioning, Classical / Q000502:physiology*; D004597:Electroshock; D005239:Fear / Q000502:physiology*; D005260:Female; D008297:Male; D011939:Mental Recall / Q000502:physiology*; D009812:Odorants; D018847:Opioid Peptides / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans; D011957:Receptors, Opioid / Q000502:physiology; D012903:Smell / Q000502:physiology*
chemical_list: D018847:Opioid Peptides; D011957:Receptors, Opioid