light at night increases depressive-like responses in male C 3 H / HeNHsd mice aura

Daily patterns of light exposure have become increasingly variable since the widespread adoption of electrical lighting during the 20th century. Seasonal fluctuations in light exposure, shift-work, and transmeridian travel are all associated with alterations in mood. These studies implicate fluctuations in environmental lighting in the development of depressive disorders. Here we argue that exposure to light at night (LAN) may be causally linked to depression. Male C3H/HeNHsd mice, which produce nocturnal melatonin, were housed in either a standard light/dark (LD) cycle or exposed to nightly dim (5 lux) LAN (dLAN). After four weeks in lighting conditions mice underwent behavioral testing and hippocampal tissue was collected at the termination of the study for qPCR. Here were report that mice exposed to dLAN increase depressive-like responses in both a sucrose anhedonia and forced swim test. In contrast to findings in diurnal grass rats, dLAN mice perform comparably to mice housed under dark nights in a hippocampus-dependent learning and memory task. TNF and IL1 gene expression do not difearning and memory fer between groups, demonstrating that changes in these pro-inflammatory cytokines do not mediate dLAN induced depressive-like responses in mice. BDNF expression is reduced in the hippocampus of mice exposed to dLAN. These results indicate that low levels of LAN can alter mood in mice. This study along with previous work implicates LAN as a potential factor contributing to depression. Further understanding of the mechanisms through which LAN contributes to changes in mood is important for characterizing isord and treating depressive d Throughout most of evolutionary history, the sun and moon ere the dominant light sources to which mammals were exposed. ecently, exposure to light during the night has increased because f widespread adoption of electric lights. Exposure to light at night LAN) is ubiquitous in modern society and generally considered an nnocuous environmental perturbation. However, the use of elecric lights occurred prior to a strong understanding of circadian iology and too rapidly for adaptations to evolve to counter any eleterious physiological and behavioral changes that may result rom LAN [11]. Abbreviations: LAN, light at night; dLAN, dim LAN. ∗ Corresponding author at: Department of Neuroscience, The Ohio State Uniersity, Wexner Medical Center, 636 Biomedical Research Tower, 460 West 12th venue, Columbus, OH 43210, USA. Tel. : +1 614 688 4674; fax: +1 614 688 4733. E-mail address: fonken.1@osu.edu (L.K. Fonken). 166-4328/$ – see front matter © 2013 Elsevier B.V. All rights reserved. ttp://dx.doi. org/10.1016/j.bbr. 2012.12. 046 ers. © 2013 Elsevier B.V. All rights reserved. Chronic exposure to LAN is implicated as a contributing factor in several human diseases, including breast and prostate cancer [18], heart disease [26], obesity, and type II diabetes [27]. Furthermore, chronic exposure to light at night through activities such as shift work is associated with higher prevalence of mood disorders [6]. Epidemiological studies indicate mood disorders have likely increased in recent decades (reviewed in [16]). Changing diagnostic criteria and increased public awareness are thought to contribute to this trend; however, additional nontraditional environmental factors are likely involved [16]. Elevated exposure to light at night correlates with increasing rates of depressive disorders. Here we test the hypothesis that exposure to light at night causes depression, likely through disruption of the circadian system. The rotation of the earth about its axis produces a highly consistent 24 h pattern of light and dark that varies on a seasonal basis. Many organisms have developed endogenous rhythms, called circadian rhythms that are entrained to this external light/dark cycle.