Mice exposed to dim light at night exaggerate inflammatory responses to lipopolysaccharide

Sep 10, 2013Brain, behavior, and immunity

Dim light at night increases mice’s inflammatory responses to bacterial toxin

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Abstract

Exposure to 4 weeks of dim light at night (LAN) elevated inflammatory responses in mice.

Chronic LAN exposure is associated with increased microglia pro-inflammatory cytokine expression following LPS administration.
Mice subjected to dimly lit nights experienced exaggerated changes in body temperature after LPS injection.
Diminished light exposure resulted in a prolonged sickness response in mice after the LPS challenge.
While sickness behavior was similar immediately after LPS injection, dLAN mice exhibited greater reductions in activity and increased weight loss 24 hours later.
These findings suggest that even low levels of light pollution may disrupt inflammatory responses.

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The mammalian circadian system regulates many physiological functions including inflammatory responses. Appropriately timed light information is essential for maintaining circadian organization. Over the past ∼120 years, urbanization and the widespread adoption of electric lights have dramatically altered lighting environments. Exposure to light at night (LAN) is pervasive in modern society and disrupts core circadian clock mechanisms. Because microglia are the resident macrophages in the brain and macrophages contain intrinsic circadian clocks, we hypothesized that chronic exposure to LAN would alter microglia cytokine expression and sickness behavior following LPS administration. Exposure to 4 weeks of dim LAN elevated inflammatory responses in mice. Mice exposed to dimly lit, as compared to dark, nights exaggerated changes in body temperature and elevated microglia pro-inflammatory cytokine expression following LPS administration. Furthermore, dLAN mice had a prolonged sickness response following the LPS challenge. Mice exposed to dark or dimly lit nights had comparable sickness behavior directly following the LPS injection; however, dLAN mice showed greater reductions in locomotor activity, increased anorectic behavior, and increased weight loss than mice maintained in dark nights 24h post-LPS injection. Overall, these data suggest that chronic exposure to even very low levels of light pollution may alter inflammatory responses. These results may have important implications for humans and other urban dwelling species that commonly experience nighttime light exposure.

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Mice exposed to dim light at night exaggerate inflammatory responses to lipopolysaccharide

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