Bergen Stress and Sleep Group, BSSG

Andrea Rørvik Marti

Circadian and metabolic consequences of shift work -a rat model

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Shift workers are at risk for metabolic health problems. Previous research suggests circadian rhythm disruption as an underlying mechanism. In my thesis, I investigate the circadian and metabolic consequences of shift work in a rat model, and discuss mechanisms responsible for the observed changes.
To mimic human shift work, rats were kept awake/ working" in rotating wheels for 8h during resting (RW) or active (AW) phase. Body temperature, locomotor activity, food and water intake, and body weight were monitored for one shift work period (4d) and recovery (8d) in constant light conditions (12hL/D), and compared to baseline. A subset of rats was exposed to constant darkness recovery (DD) to assess endogenous rhythmicity.
AW exhibited normal circadian rhythmicity throughout the protocol. RW shifted circadian rhythm during the shift work period, and parameters recovered at different rates: body temperature nadir immediately; locomotor activity nadir after 1day; % activity rhythm remained unrecovered. This indicates internal desynchrony. Data from DD recovery demonstrate desynchronization of endogenous nature. Both groups exhibited negative energy balance during the shift work period, but RW more than AW. Only AW regained body weight during recovery. RW unexpectedly developed resting phase hypothermia in the recovery period.
In conclusion, four days of resting phase activity is sufficient to cause short- and long-lasting circadian and metabolic disruption. Findings are supported by data on circadian and metabolic gene expression, sleep and glucocorticoid levels in the same animals. This model is promising to increase our understanding of the mechanisms contributing to negative effects of shift work.

Andrea Rørvik Marti`s masters thesis was a part of the project "Consequences of night shift simulation on waking performance, sleep, circadian rhythmicity and brain function".

Main supervisor: Janne Grønli
Co-supervisor: Jelena Mrdalj