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Domestic dog. --- Fecal odor. --- Food choice. --- Food. --- Habituation. --- Predator odor. --- Repellent. --- Sheep. --- Social facilitation. --- Social.

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During early ontogeny, stimuli that pose a threat to an animal change. Unrelated adult male rats may kill young rats, bur infanticide ends around weaning. Predation, on the other hand may increase during early ontogeny when mts begin to extend their activity range. We investigated the developmental course of two defensive responses, immobility and analgesia, in young rats exposed to an adult male rat or to predator cues. Preweaning 14-day-old mts became immobile and analgesic when exposed to the male and showed immobility but not analgesia when exposed to cat odor On Day 26, around weaning, the presence of the male rat no longer induced immobility and analgesia whereas cat odor produced higher levels of immobility and analgesia compared to control and male-exposed animals. This developmental change in responsivity may reflect the differences in the risk of being harmed by a male or a cat during different periods of ontogeny. (C) 2001 John Wiley & Sons, Inc

Activity. --- Adult. --- Analgesia. --- Animal. --- Animals. --- Cat odor. --- Cat. --- Control. --- Cues. --- Defensive behavior. --- Defensive immobility. --- Defensive responses. --- Defensive. --- Dentate gyrus. --- Developmental-changes. --- Emotional motor system. --- Fear. --- Immobility. --- Increase. --- Infanticide. --- Level. --- Male conspecifics. --- Male rat. --- Male-rats. --- Male. --- Neurobiological basis. --- Odor. --- Ontogeny. --- Periods. --- Predation. --- Predator odor. --- Predator. --- Rat. --- Rats. --- Rattus-norvegicus. --- Response. --- Responses. --- Risk. --- Stimuli. --- Stress-induced analgesia. --- Stress. --- Weaning. --- Young-rats. --- Young.

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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

Accumbens. --- Activation. --- Activity. --- Amygdala. --- Anxiety-like behavior. --- Anxiety. --- Area. --- Behavior. --- Behavioral-responses. --- Butyric acid. --- Cortex. --- Defensive behavior. --- Double dissociation. --- Emotional responses. --- Enkephalin. --- Experience. --- Exposure. --- Expression. --- Extended amygdala. --- Fos-related antigen. --- Freezing. --- Gene. --- Genes. --- Individual-differences. --- Infralimbic cortex. --- Infralimbic. --- Level. --- Light. --- Long-term. --- Male-rats. --- Mice. --- Neuronal. --- Neurons. --- Nucleus accumbens. --- Nucleus-accumbens. --- Nucleus. --- Odor. --- Posttraumatic-stress-disorder. --- Predator odor. --- Predator. --- Prelimbic. --- Response. --- Responses. --- Self-stimulation. --- Stressor. --- Test. --- Time. --- Unconditioned fear. --- Ventral tegmental area.