Affective responses to changes in day length in Siberian hamsters (Phodopus sungorus)

The goal of these experiments was to test the hypothesis that day length influences anxious- and depressive-like behaviors in reproductively photoperiodic rodents. Mate and female Siberian hamsters (Phodopus sungorus) were exposed to tong (16 h light/day; LD) or short (8 h light/day; SD) photoperiods beginning at the time of weaning (day 18). Two weeks later hamsters were subjected to a series of behavioral tests to quantify anxiety-and depressive-like behaviors. In an elevated plus maze, SD mates exhibited longer latencies to enter an open arm, entered fewer open arms, and spent less time exploring open arms relative to LD hamsters. SD mates were likewise slower to enter either of the distal arms of a completely enclosed T-maze, and in a hunger-motivated exploratory paradigm SD mates were slower to enter an open arena for food as compared to LD mates. In a forced-swimming model of behavioral despair, SD mates exhibited immobility sooner, more often, and for a greater total amount of time relative to LD mates. Total activity levels, aversiveness to tight, olfactory function, and limb strength were unaffected by SD, suggesting that the behavioral changes consequent to SD are not attributable to sensory or motor deficits, but rather may arise from changes in general affective state. The anxiogenic and depressive effects of SD were largely absent in female hamsters. Together the results indicate that adaptation to short photoperiods is associated with increased expression of anxiety- and depressive-like behaviors relative to those observed under LD photoperiod conditions. (c) 2004 Elsevier Ltd. All rights reserved.