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Short days induce winter-like adaptations in small mammals such as Siberian hamsters (Phodopus sungorus (Pallas, 1773)). Specifically, hamsters adjust food consumption, metabolic processes, and immune function to optimize energetic needs and promote winter survival. One potentially inexpensive behavioral adaptation to increase survival is avoidance of infection. We tested the hypothesis that photoperiod affects avoidance of potentially infected food. In experiment 1, hamsters were weaned into either short or long days with ad libitum food. Three weeks later, hamsters were presented with either skim milk treated with butyric acid (2%), a bacterial product that serves as a potent cue of spoilage, or unadulterated skim milk; consumption was measured. After milk presentation, blood samples were obtained to assess cortisol. In experiment 2, skim-milk consumption was again assessed after 3 weeks in either short or long days. In experiment 3, we tested the hypothesis that food avoidance was due to photoperiod-induced differential neophobia. Short-day hamsters increased milk consumption, which was blocked by butyric acid. Short days increased cortisol concentrations; neither food restriction nor butyric acid affected cortisol concentrations. Photoperiod did not alter neophobic responses. These experiments suggest that short-day hamsters avoid food treated with butyric acid possibly as an adaptive trait to avoid costly winter infections. Les jours courts induisent des adaptations de type hivernal chez les petits mammiferes, tels que les hamsters nains de Dzoungarie (Phodopus sungorus (Pallas, 1773)). En particulier, les hamsters ajustent leur consommation de nourriture, leurs processus metaboliques et leur fonction immunitaire de maniere a optimiser leurs besoins energetiques et de favoriser leur survie durant l'hiver. Une adaptation comportementale potentielle a faible cout pour augmenter la survie est l'evitement des infections. Nous verifions l'hypothese selon laquelle la photoperiode affecte l'evitement de nourriture potentiellement contaminee. Dans l'experience 1, nous avons sevre des hamsters dans des conditions de jours courts ou longs et les avons nourris a volonte. Trois semaines plus tard, nous avons fourni aux hamsters ou bien du lait ecreme traite a l'acide butyrique (2 %), un produit bacterien qui est un puissant indicateur d'avarie, ou alors du lait ecreme sans additif et nous avons mesure leur consommation. Apres la presentation du lait, des prelevements sanguins ont permis de doser le cortisol. Dans l'experience 2, nous avons de nouveau evalue la consommation de lait ecreme apres 3 semaines en conditions de jours courts ou longs. Dans l'experience 3, nous avons teste l'hypothese selon laquelle l'evitement de la nourriture est du a une neophobie differentielle sous l'action de la photoperiode. En conditions de jours courts, les hamsters augmentent leur consommation de lait, qui est cependant enrayee par l'acide butyrique. Les jours courts font augmenter les concentrations de cortisol, mais ni les restrictions alimentaires, ni l'acide butyrique n'affectent les concentrations de cortisol. La photoperiode ne modifie pas les reactions de neophobie. Ces experiences indiquent que les hamsters en conditions de jours courts evitent la nourriture traitee a l'acide butyrique, possiblement comme un trait adaptatif pour ecarter les infections couteuses en hiver. [Traduit par la Redaction], Introduction Small mammals that live in temperate or boreal habitats, including Siberian hamsters (Phodopus sungorus (Pallas, 1773)), have evolved strategies to cope with temporal variations in food availability. Siberian hamsters [...]

ABSTRACT Chronic stress or chronically high glucocorticoids attenuate adult hippocampal neurogenesis by reducing cell proliferation, survival, and differentiation in male rodents. Neurons are still produced in the dentate gyrus during chronically high glucocorticoids, but it is not known whether these new neurons are appropriately activated in response to spatial memory. Thus, the goal of this study was to determine whether immature granule neurons generated during chronically high glucocorticoids (resulting in a depressive-like phenotype) are differentially activated by spatial memory retrieval. Male Sprague Dawley rats received either 40 mg/kg corticosterone (CORT) or vehicle for 18 days prior to behavioral testing. Rats were tested in the forced swim test (FST) and then tested in a spatial (hippocampus-dependent) or cued (hippocampus-independent) Morris Water Maze. Tissue was then processed for doublecortin (DCX) to identify immature neurons and zif268, an immediate early gene product. As expected, CORT increased depressive-like behavior (greater immobility in the FST) however, prior CORT modestly enhanced spatial learning and memory compared with oil. Prior CORT reduced the number of DCX-expressing cells and proportion of DCX-expressing cells colabeled for zif268, but only in the ventral hippocampus. Prior CORT shifted the proportion of cells in the ventral hippocampus away from postmitotic cells and toward immature, proliferative cells, likely due to the fact that postmitotic cells were produced and matured during CORT exposure but proliferative cells were produced after high CORT exposure ceased. Compared with cue training, spatial training slightly increased DCX-expressing cells and shifted cells toward the postmitotic stage in the ventral hippocampus. These data suggest that the effects of CORT and spatial training on immature neurons are more pronounced in the ventral hippocampus. Further, high CORT reduced activation of immature neurons, suggesting that exposure to high CORT may have long-term effects on cell integration or function. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]