Chronic exposure to artificial light at night dampens rhythms in locomotor activity, metabolism, and sleep in female mice.

Nearly every organism on Earth displays circadian organization of physiology and behavior, which is entrained to 24 h by daily exposure to bright light early during the day. However, the widespread presence of nocturnal electric lighting has blurred the boundary between day and night, leading to temporal desynchrony among individuals. Indeed, <6 weeks exposure to low levels of artificial light at night (ALAN) alters metabolism, energy, and sleep homeostasis in male mice. We hypothesized that ALAN would similarly affect female mice following prolonged exposure. After ≥20 weeks of exposure to dim ALAN, female mice had dampened locomotor rhythms, altered heat generation, respiratory exchange ratio (RER), and sleep. ALAN exposure decreased daily caloric intake, without altering body composition. The period and phase of the rhythm of sleep were significantly increased by ALAN, elevating the time spent sleeping during the active phase, without altering total sleep bout length. Taken together, these data indicate that ALAN impairs the rhythms in core physiological processes in female mice, but the mechanisms mediating these alterations may differ from those in males.