Meeting Abstract
Four to six percent of all Americans are affected by seasonal affective disorder (SAD), a form of recurrent depression triggered by reduced exposure to sunlight. In addition to being a seasonal mood disorder, SAD has also been associated with circadian dysfunction, weight gain, and increased carbohydrate consumption. In this study, we are using a diurnal rodent model, the Nile grass rat (Arvicanthis niloticus) to determine how well this species’ symptoms parallel those of humans that are diagnosed with SAD. Grass rats are known to exhibit depressive-like behaviors under short photoperiods; however, their sleep patterns and carbohydrate consumption in response to different photoperiods are unknown. We monitored sleep-wake behaviors using piezoelectric sheets, and measured weight, sucrose consumption, and liver fat content in 45 grass rats in response to short photoperiod (4:20 LD) and neutral photoperiod (12:12 LD) conditions. We found that short photoperiod conditions caused sleep disruption, and that sucrose consumption significantly affected sleep bout duration. For animals under short photoperiod conditions, activity onset occurred 8 hours before lights on (12 hours before lights off), followed by a resting phase, and then by higher intensity activity during the light phase. We found no effect of photoperiod on sucrose consumption, but preliminary results show that liver fat content was higher in animals exposed to the short photoperiod. The grass rats with access to high concentrations of sucrose had higher liver fat across both photoperiod treatments. Our findings suggest that complex interactions between photoperiod, sucrose consumption, and sleep activity should be accounted for when determining grass rats’ suitability as a rodent model for SAD.
