2018 年 39 巻 1 号 p. 47-55
Circadian disruption affects the pathogenesis and development of various diseases. Depression is one of the most common diseases that relate to circadian rhythm. In this study, we analyzed the effects of daily light/dark (LD) conditions on depression and other symptoms, and also analyzed the mixed effects of LD conditions and corticosterone treatment. Male adult C57BL/6 mice were treated with corticosterone in a normal LD cycle of 12 hours light and 12 hours dark (LD12 : 12), short day conditions of 6 hours light and 18 hours dark (LD6 : 18), or long day conditions of 21 hours light and 3 hours dark (LD21 : 3). The activity rhythms of mice in aberrant LD conditions were entrained within 2 weeks. After 6 weeks of exposure, several behavioral tests were conducted. Corticosterone induced body weight gain and depression-like symptoms. The short or long LD conditions had little effect on vehicle-treated mice behavior. However, the aberrant LD conditions exacerbated the corticosterone-induced symptoms. Mice treated with corticosterone in LD6 : 18 showed exacerbated depression-like symptoms in a novelty suppressed feeding test. On the other hand, LD21 : 3 did not show any effects on mood, but enhanced corticosterone-induced body weight gain. These results indicated that aberrant LD conditions could act as an exacerbating factor for corticosterone-induced symptoms, and that short and long photoperiods induce different psychological and physiological changes. This corticosterone + aberrant LD model could be a useful animal model for investigating the effect of LD conditions on depression, obesity, and other symptoms in stressful circumstances.