title: Dark nights reverse metabolic disruption caused by dim light at night.
abstract: OBJECTIVE
  The increasing prevalence of obesity and related metabolic disorders coincides with increasing exposure to light at night. Previous studies report that mice exposed to dim light at night (dLAN) develop symptoms of metabolic syndrome. This study investigated whether mice returned to dark nights after dLAN exposure recover metabolic function.
  
  
  METHODS
  Male Swiss-Webster mice were assigned to either: standard light-dark (LD) conditions for 8 weeks (LD/LD), dLAN for 8 weeks (dLAN/dLAN), LD for 4 weeks followed by 4 weeks of dLAN (LD/dLAN), and dLAN for 4 weeks followed by 4 weeks of LD (dLAN/LD).
  
  
  RESULTS
  After 4 weeks in their respective lighting conditions both groups initially placed in dLAN increased body mass gain compared to LD mice. Half of the dLAN mice (dLAN/LD) were then transferred to LD and vice versa (LD/dLAN). Following the transfer dLAN/dLAN and LD/dLAN mice gained more weight than LD/LD and dLAN/LD mice. At the conclusion of the study dLAN/LD mice did not differ from LD/LD mice with respect to weight gain and had lower fat pad mass compared to dLAN/dLAN mice. Compared to all other groups dLAN/dLAN mice decreased glucose tolerance as indicated by an intraperitoneal glucose tolerance test at week 7, indicating that dLAN/LD mice recovered glucose metabolism. dLAN/dLAN mice also increased MAC1 mRNA expression in peripheral fat as compared to both LD/LD and dLAN/LD mice, suggesting peripheral inflammation is induced by dLAN, but not sustained after return to LD.
  
  
  CONCLUSIONS
  These results suggest that re-exposure to dark nights ameliorates metabolic disruption caused by dLAN exposure.
authors.affiliation: Department of Neuroscience and Institute for Behavioral Medicine Research, Wexner Medical Center, Ohio State University, Columbus, Ohio 43210, USA. fonken.1@osu.edu
authors.forename: L K
authors.initials: LK
authors.lastname: Fonken
authors.forename: Z M
authors.initials: ZM
authors.lastname: Weil
authors.forename: R J
authors.initials: RJ
authors.lastname: Nelson
mesh_terms: D000818:Animals; D015992:Body Mass Index; D002149:Energy Intake; D015870:Gene Expression; D005951:Glucose Tolerance Test; D008027:Light; D008297:Male; D051379:Mice; D009765:Obesity / Q000453:epidemiology* / Q000209:etiology; D017440:Photoperiod; D015430:Weight Gain