Abstract
Humans come in different chronotypes and, particularly, the late chronotype (the so-called owl) has been shown to be associated with several health risks. A number of studies show that laboratory mice also display various chronotypes. In mice as well as in humans, the chronotype shows correlations with the period length and rhythm stability. In addition, some mouse models for human diseases show alterations in their chronotypic behavior, which are comparable to those humans. Thus, analysis of the behavior of mice is a powerful tool to unravel the molecular and genetic background of the chronotype and the prevalence of risks and diseases that are associated with it. In this review, we summarize the correlation of chronotype with free-running period length and rhythm stability in inbred mouse strains, in mice with a compromised molecular clockwork, and in a mouse model for neurodegeneration.
Highlights
Specialty section: This article was submitted to Sleep and Chronobiology, a section of the journal Frontiers in Neurology
There are mice that become active already in the light phase, several hours before “lights off ” [29]. These results suggest that different mouse strains have different chronotypes
In laboratory mice, the chronotype correlates with the τDD; C57Bl/6 mice have a longer τDD and a later chronotype as compared to C3H mice, but the correlation between the τDD and the chronotype is quite moderate [(28); Figure 1]. This correlation between the τDD and the chronotype is absent in some cases: In Cry1 KO as well as in Cry2 KO mice, the chronotypic differences in light/12 h dark (LD) are minimal compared to their background-matched wild-types, despite their large differences in free-running periods [54]
Summary
Martina Pfeffer 1, 2*, Helmut Wicht 1, 2, Charlotte von Gall 3 and Horst-Werner Korf 1, 2. We summarize the correlation of chronotype with free-running period length and rhythm stability in inbred mouse strains, in mice with a compromised molecular clockwork, and in a mouse model for neurodegeneration. In order to describe this phenomenon, the term “chronotype” was coined by Ehret [11], and he provided a very succinct definition of the term: “the temporal phenotype of an organism.”. This definition refers to overt characters and not to a propensity or inclination. Ehret [11] clarifies this ambiguity by visualizing the “chronotype of the rat.” He plots the acrophases of various behavioral, metabolic, and endocrine activities over diurnal (zeitgeber-) time. He implicitly supplies an operational definition of how the chronotype may be measured – by comparing the timing of these acrophases among each other and in relation to the entraining zeitgebers, permitting to distinguish “early” and “late” chronotypes
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