Meeting Abstract

P1.73  Thursday, Jan. 3  Photoperiod Mediates Effects of Social Stress in Siberian Hamsters CHESTER, E.M.*; DEMAS, G.E.; Indiana University, Bloomington; Indiana University, Bloomington emcheste@indiana.edu

Exposure to stressors during winter, when resources may be limited and energetic demands relatively high, can suppress immunity and increase disease susceptibility and mortality. In many species, however, seasonally recurrent variations in the environment such as changes in day length mediate adaptive physiological and behavioral mechanisms that can buffer the animals from the effects of stress and facilitate survival. In the laboratory, animals housed in short days (SDs) display �winter-like� characteristics (e.g., gonadal regression, reduced body mass, heightened aggression), whereas those housed in long days (LDs) display �summer-like� characteristics. The effects of physical stressors in different photoperiods have been studied, but the effects of social stressors remain unknown. Chronic social stress in LDs increases serum glucocorticoid levels via activation of the hypothalamo-pituitary-adrenal (HPA) axis and has immuno-modulating effects. Here, we test whether a social stressor, defeat by same-sex conspecifics over 5 days, has differential effects on the immune and endocrine systems in male Siberian hamsters housed in LD photoperiod as compared to those housed in SD photoperiod. Animals in each photoperiod were assigned to opponents from either the same photoperiod or different photoperiod. All defeat trials were videotaped for behavioral scoring. Preliminary results indicate a trend where SD animals have lower serum IgG levels than SD control animals. Additional immune, behavioral and hormonal data will be discussed. Collectively, the results of this study contribute to broader understanding of the influence of agonistic social interactions on seasonal patterns of disease susceptibility.