Chronic citalopram treatment ameliorates depressive behavior associated with light at night

Chronic exposure to light at night (LAN) is a circadian disruptor and may be linked to various health risks, including mood disorders. We recently demonstrated that chronic exposure to dim (5 lux) LAN provokes depressive-like behaviors and reduced hippocampal CA1 dendritic spine density in female hamsters. Whether this model is responsive to selective serotonin reuptake inhibitors remains unspecified. In this study, we exposed hamsters to 5 lux LAN and treated with citalopram to determine effects on depressive-like behavior and CA1 dendritic spine density. Female hamsters were ovariectomized at adulthood and housed in either a standard light-dark cycle (LD) or dim LAN (dLAN). After 4 weeks exposure, treatment with either citalopram or vehicle was administered for 2 weeks while hamsters remained in experimental lighting conditions. Depressive-like behavior was assayed using the forced swim test and brains were processed for Golgi-Cox staining and analyzed for dendritic spine density. Treatment with citalopram rescued behavior in the forced swim test in hamsters housed in dLAN, but had no effect on hamsters housed in LD. Dendritic spine density in CA1 was moderately improved by citalopram treatment, but not fully restored. These results validate our LAN paradigm as a depression model by showing citalopram selectively improves depressive-like behavior in dLAN conditions, but not in LD conditions. These data also suggest standard SSRI therapy may be effective for individuals experiencing depression related to circadian disruption and LAN exposure, such as shift workers.