Daily rhythms in spontaneous and diazepam-induced anxiolysis in Syrian hamsters

The diurnal variations in spontaneous and diazepam-induced anxiolysis and exploratory behavior were examined in Syrian hamsters in a plus-maze paradigm. The administration of diazepam or flunitrazepam augmented the percentage of time spent in the open arms, the percentage of entries to the open arms, and the number of crosses to both arms, whereas ethyl-beta-carboline injection decreased them. These three behavioral parameters showed significant daily variations, with the maxima being found at night (2400-0400 h). Flumazenil (5 mg/kg) injected at 0400 h decreased significantly the percentage of time spent in open arms and of entries to the open arms, without affecting significantly the total number of entries to both arms. Day-night differences in anxiety-related behavior persisted in hamsters kept under constant darkness for 3 days. Diazepam (0.5 mg/kg) increased the time spent in the open arms at 1600 and 2000 h only, and augmented the percent of entries to the open arms at 2000 h only. The total number of entries to both arms was augmented significantly by diazepam at all time intervals tested, except for 0400 h. The results indicate that Syrian hamsters exhibited significant diurnal changes in anxiolysis-related behavior in the plus-maze paradigm.