Rodent of the Week: Light at night linked to depression

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Lots of research suggests that our bodies are adapted to sleep during darkness and become active during daylight. Disruptions in circadian rhythms may increase the risk of metabolic diseases and some types of cancer. Now, a study in mice has found, being exposed to light at night for prolonged periods of time may contribute to depression.

Researchers at Ohio State University found that mice housed in a lighted room 24 hours a day exhibited more symptoms of depression than did mice that had a normal light-dark cycle. When mice that lived in constant light had the option to escape into an opaque tube, they showed fewer symptoms of depression than mice who did not have an escape from 24-hour light. The depression tests in mice involved things like measuring how much sugar water they drank.

One interesting twist in the study, however, revealed that mice housed in constant light seemed to have lower levels of anxiety; they had lower levels of corticosterone, a stress hormone linked to anxiety. But these mice may simply have adapted to the constant light, which resulted in fewer signs of anxiety, the researchers said.

The study contributes to the growing body of research that circadian rhythms are highly influential in health.

‘The increasing rate of depressive disorders in humans corresponds with the increasing use of light at night in modern society,’ Randy Nelson, a co-author of the paper and professor of neuroscience, said in a news release. ‘Many people are now exposed to unnatural light cycles, and that may have real consequences for our health.’

The study was presented this week at the annual meeting of the Society for Neuroscience in Chicago. It will be published in December in the journal Behavioural Brain Research.

-- Shari Roan