Showing papers by "Michael Menaker published in 2005"
TL;DR: Varying the time of the culture procedure relative to the donor animal's light:dark cycle revealed that, unlike some other rat tissues such as liver, the phases of in vitro rhythms of arteries, veins, and heart explants were affected by culture time; this suggests diversity in circadian regulation among components of the cardiovascular system.
Abstract: Acute cardiovascular events exhibit a circadian rhythm in the frequency of occurrence. The mechanisms underlying these phenomena are not yet fully understood, but they may be due to rhythmicity inherent in the cardiovascular system. We have begun to characterize rhythmicity of the clock gene mPer1 in the rat cardiovascular system. Luciferase activity driven by the mPer1 gene promoter is rhythmic in vitro in heart tissue explants and a wide variety of veins and arteries cultured from the transgenic Per1-luc rat. The tissues showed between 3 and 12 circadian cycles of gene expression in vitro before damping. Whereas peak per1-driven bioluminescence consistently occurred during the late night in the heart and all arteries sampled, the phases of the rhythms in veins varied significantly by anatomical location. Varying the time of the culture procedure relative to the donor animal's light:dark cycle revealed that, unlike some other rat tissues such as liver, the phases of in vitro rhythms of arteries, veins, and heart explants were affected by culture time. However, phase relationships among tissues were consistent across culture times; this suggests diversity in circadian regulation among components of the cardiovascular system.
99 citations
TL;DR: Results suggest that in behaviorally arrhythmic rats, oscillators in the pineal, pituitary, and SCN had been arrHythmic or severely damped in vivo, while the cornea oscillator was free running.
Abstract: The phases of central (SCN) and peripheral circadian oscillators are held in specific relationships under LD cycles but, in the absence of external rhythmic input, may damp or drift out of phase with each other. Rats exposed to prolonged constant light become behaviorally arrhythmic, perhaps as a consequence of dissociation of phases among SCN cells. The authors asked whether individual central and peripheral circadian oscillators were rhythmic in LL-treated arrhythmic rats and, if rhythmic, what were the phase relationships between them. The authors prepared SCN, pineal gland, pituitary, and cornea cultures from transgenic Period1-luciferaserats whose body temperature and locomotor activity were arrhythmic and from several groups of rhythmic rats held in LD, DD, and short-term LL. The authors measured mPer1gene expression by recording light output with sensitive photomultipliers. Most of the cultures from all groups displayed circadian rhythms. This could reflect persistent rhythmicity in vivo prior to c...
81 citations
TL;DR: It is argued that reward (or the arousal that accompanies it) may be the final common pathway for such nonphotic circadian inputs in animals via meal-feeding schedules.
Abstract: Mammals organize many of their activities around rhythmic events in their environments. Primary among these events is the daily light–dark cycle. However, for many animals, food availability is rhythmic or quasi-rhythmic and is therefore a potential synchronizing cue. While circadian rhythms in both behavior and physiological activity can be entrained in animals via meal-feeding schedules, the mechanism by which this occurs remains poorly understood. Similarities between the circadian effects of restricted feeding and the effects of chronic methamphetamine treatment may be indicative of a common mechanism. This article argues that reward (or the arousal that accompanies it) may be the final common pathway for such nonphotic circadian inputs.
30 citations