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fitness is reduced if organisms are housed under LD cycles that differ from
the inherent period of the organism. While the relatively long gestation and
lifespan of mammals limits the number of comparable studies conducted,
some evidence indicates that circadian misalignment imposes a biological
cost that can decrease lifespan and accelerate the aging processes.
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4.1.1 Environmental models
Halberg and Cadotte first demonstrated that mortality was increased in mice
line of Syrian hamsters predisposed to develop cardiomyopathy: weekly
was postulated that this result reflected the effect of circadian disruption
rather than increased light exposure as constant light can produce therapeu-
can also have profound effects on lifespan, with aged mice displaying a
changes in season can also affect lifespan, with mouse lemurs held under
accelerated seasonal cycles displaying a 30% reduction in average lifespan.
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Similarly, rapid and repeated changes in day length decreased the lifespan
of flies.
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4.1.2 Genetic models
Recent studies have provided evidence that molecular deficits in circadian
clock function decrease survival and accelerate aging, despite earlier sugges-
lifespan with pervasive organ dysfunction occurs when heterozygote tau
mutant hamsters are housed under static 24 h LD cycles to which they
mutant hamsters, which fail to entrain entirely, did not display a significantly
increased mortality (9% decrease in median lifespan), prompting the sugges-
tion that misalignment (like that which occurs in jetlag and shift work) may
incur worse physiological costs than lack of entrainment (as in non-24 h
sleep/wake disorder). In addition, it is now appreciated that
bmal1
mice
display an increased mortality and accelerated development of age-related
rate of aging and a 13% decrease in average lifespan has been reported for
/
It is unclear whether pathology would emerge if
bmal1
and
clock
mutant mice were permitted to live arrhythmic under
constant conditions, but this question is of interest given previous work on
/
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