Abstract
There is a long history that protracted periods of circadian disruption, such as through frequent transmeridian travel or rotating shift work, can have a significant impact on brain function and health. In addition, several studies have shown that chronic periods of circadian misalignment can be a significant risk factor for the development of depression and anxiety in some individuals with a history of psychiatric illness. In animal models, circadian disruption can be introduced through either phase advances or delays in the light–dark cycle. However, the impact of chronic phase shifts on affective behavior in rats has not been well-studied. In the present study, male rats were subjected to either weekly 6 h phase advances (e.g., traveling eastbound from New York to Paris) or 6 h phase delays (e.g., traveling westbound from New York to Hawaii) in their light/dark cycle for 8 weeks. The effect of chronic phase shifts was then examined on a range of emotional and cognitive behaviors. We found that rats exposed to frequent phase advances, which mirror conditions of chronic jet lag in humans, exhibited impairments in object recognition memory and showed signature symptoms of depression, including anhedonia, increased anxiety behavior, and higher levels of immobility in the forced swim test. In addition, rats housed on the phase advance schedule also had lower levels of hippocampal neurogenesis and immature neurons showed reduced dendritic complexity compared to controls. These behavioral and neurogenic changes were direction-specific and were not observed after frequent phase delays. Taken together, these findings support the view that circadian disruption through chronic jet lag exposure can suppress hippocampal neurogenesis, which can have a significant impact on memory and mood-related behaviors.
Highlights
Proper circadian rhythms are an important feature of normal health enabling organisms to adapt to daily changes in their environment
Our findings demonstrate that chronic phase advancements of the LD cycle produce clear impairments in object recognition memory along with increases emotional responses, and that disruption in neurogenic processes in the hippocampus may contribute to the changes in affective and cognitive behavior associated with chronic jet lag conditions
Our findings demonstrate that chronic phase advancements of the LD cycle, an experimental model of jet lag, produce impairments in object recognition memory and increases depression and anxiety behavior in male rats
Summary
Proper circadian rhythms are an important feature of normal health enabling organisms to adapt to daily changes in their environment. Short-term misalignment between the endogenous circadian clock and the Neurobehavioral Effects of Chronic Jet Lag desired destination sleep/wake schedule can produce a temporary “jet lag” disorder, which is associated with symptoms of fatigue, gastrointestinal distress, reduced psychomotor coordination, and diminished cognition and mood These symptoms generally dissipate as the circadian clock gradually entrains to the new destinations’ time. Chronic sleep disturbances have been associated with reduced cortical gray matter volume in several brain regions, including the prefrontal cortex (Altena et al, 2010; Sexton et al, 2014) and hippocampus (Joo et al, 2014) These findings underscore that structural and functional brain adaptations can be downstream effects associated with frequent episodes of circadian dysrhythmia and sleep loss
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