Sand rats see the light: short photoperiod induces a depression-like response in a diurnal rodent.

The present study examined the effect of simulated change in day length on the behavior of a diurnal rodent, the fat sand rat (a species of gerbil). Animals were housed under a short photoperiod (5/19 light/dark cycle) for 3 weeks and compared with controls living under a 12/12 light/dark cycle. All sand rats then underwent the forced swim test for depression-like behavior, and the open-field test for overall activity. Sand rats exposed to the short photoperiod displayed a significantly earlier sinking in the swim test, but there was no difference between their open-field activity compared with controls. Taking these responses as indicative of depression-like behavior, we suggest that a short photoperiod may induce affective-like changes, and that the sand rat may thus offer an appropriate animal model to explore the effect of photoperiod on normal, and perhaps also abnormal, seasonal mood changes (e.g., SAD), which in humans is a prevalent disorder, with winter depression episodes and spring/summer remissions.