The Cost of Activity during the Rest Phase: Animal Models and Theoretical Perspectives

Abstract

For humans, activity during the night is correlated with multiple pathologies that may reflect a lack of harmony among components of the circadian system; however, it remains difficult to identify causal links between nocturnal activity and different pathologies based on the data available from epidemiological studies. Animal models that use forced activity or timed sleep deprivation provide evidence of circadian disruptions that may be at the core of the health risks faced by human night and shift workers. One valuable insight from that work is the importance of changes in the distribution of food intake as a cause of metabolic imbalances associated with activity during the natural rest phase. Limitations of those models stem from the use of only nocturnal laboratory rodents and the fact that they do not replicate situations in which humans engage in work with high cognitive demands or engage voluntarily in nocturnal activity (i.e., human eveningness). Temporal niche switches by rodents have been observed in the wild and interpreted as adaptive responses to energetic challenges, but possible negative outcomes, similar to those associated with human eveningness, have not been systematically studied. Species in which a proportion of animals shows a switch from a day-active to a night-active (e.g., grass rats) when given access to running wheels provide a unique opportunity to model human eveningness in a diurnal rodent. In particular, the mosaic of phases of brain oscillators in night-active grass rats may provide clues about the circadian challenges faced by humans who show voluntary nocturnal wakefulness.

Circadian and photic modulation of daily rhythms in diurnal mammals

“…Although there is considerable inter‐individual variability in activity patterns, such that the so‐called “early larks” or “night owls” whose sleep/wake schedules are significantly advanced or delayed, respectively, compared to the majority of the population, humans in general are most active during the day and sleep at night. Disrupting this natural diurnal pattern, for example, with shift work or other features of a modern lifestyle, can bring with it a high risk for a multitude of pathological conditions (Nunez, Yan, & Smale, ). Thus, diurnal models may make unique contributions to our understanding of the circadian and photic modulation of brain and behavior in humans.…”

Consequences of Artificial Light at Night: The Linkage between Chasing Darkness Away and Epigenetic Modifications

“…Collectively, in diurnal humans, circadian disruption enforced by activity impinging on the inactive period during the nighttime is recurrently associated with a number of health problems. However, a direct link between ALAN-induced circadian disruption and health risks is still difficult to clearly establish as most data are derived from epidemiological and nocturnal animal studies [94]. Therefore, integrating diurnal animal models of chronodisruption with epidemiological and nocturnal model studies would add a significant value in defining potential direct signal transduction pathways mediating the environmental exposure impacts on physiology and health.…”

Melatonin alleviates circadian system disruption induced by chronic shifts of the light‐dark cycle in Octodon degus

“…Thus, the degus show heterogeneity in terms of chronotypes (a continuum from strictly diurnal to nocturnal) . Therefore, this animal species can be a well‐suited animal model in which to assess the detrimental effect of CD on human health, and possible strategies to cope with shift work . In addition, degus exhibit some of human‐like age‐related diseases, such as atherosclerosis, diabetes, cataracts and Alzheimer‐like disease (see for review).…”