title: Brief exposure to predator odor and resultant anxiety enhances mesocorticolimbic activity and enkephalin expression in CD-1 mice.
abstract: The present study assessed alterations in mesolimbic enkephalin (ENK) mRNA levels after predator [2,5-dihydro-2,4,5-trimethylethiazoline (TMT)] and non-predator (butyric acid) odor encounter and/or light-dark (LD) testing in CD-1 mice immediately, 24, 48 and 168 h after the initial odor encounter and/or LD testing. The nucleus accumbens, ventral tegmental area, basolateral (BLA), central (CEA) and medial amygdaloid nuclei, prelimbic and infralimbic cortex were assessed for fos-related antigen (FRA) and/or ENK mRNA as well as neuronal activation of ENK neurons (FRA/ENK). Mice exposed to TMT displayed enhanced freezing and spent less time in the light of the immediate LD test relative to saline- or butyric acid-treated mice. Among mice exposed to TMT, LD anxiety-like behavior was associated with increased FRA in the prelimbic cortex and accumbal shell and decreased ENK-positive neurons in the accumbal core. Mice displaying high TMT-induced LD anxiety exhibited increased ENK-positive neurons in the BLA, CEA and medial amygdaloid nuclei relative to mice that displayed low anxiety-like behavior in the LD test after TMT exposure. In the BLA and CEA, 'high-anxiety' mice also displayed increased FRA/ENK after TMT exposure and LD testing. In contrast to neural cell counts, the level of ENK transcript was decreased in the BLA and CEA of 'high-anxiety' mice after TMT exposure and LD testing. These data suggest that increased FRA may regulate stressor-responsive genes and mediate long-term behavioral changes. Indeed, increased ENK availability in mesolimbic sites may promote behavioral responses that detract from the aversiveness of the stressor experience.
authors.affiliation: Institute of Neuroscience, Carleton University, Ottawa, Ontario, Canada.
authors.forename: Andrea L O
authors.initials: AL
authors.lastname: Hebb
authors.forename: Robert M
authors.initials: RM
authors.lastname: Zacharko
authors.forename: Michelle
authors.initials: M
authors.lastname: Gauthier
authors.forename: France
authors.initials: F
authors.lastname: Trudel
authors.forename: Sylvie
authors.initials: S
authors.lastname: Laforest
authors.forename: Guy
authors.initials: G
authors.lastname: Drolet
mesh_terms: D000280:Administration, Inhalation; D000679:Amygdala / Q000033:anatomy & histology / Q000378:metabolism; D000818:Animals; D001007:Anxiety / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology*; D001522:Behavior, Animal / Q000502:physiology; D002540:Cerebral Cortex / Q000033:anatomy & histology / Q000378:metabolism; D004745:Enkephalins / Q000235:genetics*; D005239:Fear / Q000502:physiology*; D008032:Limbic System / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051379:Mice; D009434:Neural Pathways / Q000033:anatomy & histology / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D009714:Nucleus Accumbens / Q000033:anatomy & histology / Q000378:metabolism; D009812:Odorants; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D012903:Smell / Q000502:physiology*; D013315:Stress, Psychological / Q000235:genetics / Q000378:metabolism; D013844:Thiazoles / Q000008:administration & dosage; D015854:Up-Regulation / Q000235:genetics*; D017557:Ventral Tegmental Area / Q000033:anatomy & histology / Q000378:metabolism
chemical_list: C411827:2,5-dihydro-2,4,5-trimethylthiazoline; D004745:Enkephalins; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D013844:Thiazoles