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The increase in prevalence of depression in the later decades of the 20th century suggests a role for recent environmental changes. Chronic exposure to artificial light at night is one possible factor. In this study, hamsters were exposed to nighttime darkness or dim artificial light.
Nighttime artificial light was associated with depression-like behaviors, lower hippocampal expression of the brain-derived neurotrophic factor gene, lower dendritic spine density, and enhanced gene expression of tumor necrosis factor α (TNF-α). These changes were reversed within 2 weeks of removing light exposure. Changes in behavior (but not in dendritic spine density) were also reversed by intracerebral injection of a TNF antagonist (supplied by the manufact…