Circadian rhythm - Wikipedia, the free encyclopedia

Circadian rhythm - Wikipedia, the free encyclopedia: "hotosensitive proteins and circadian rhythms are believed to have originated in the earliest cells, with the purpose of protecting the replicating of DNA from high ultraviolet radiation during the daytime. As a result, replication was relegated to the dark. The fungus Neurospora, which exists today, retains this clock-regulated mechanism.
Circadian rhythms allow organisms to anticipate and prepare for precise and regular environmental changes; they have great value in relation to the outside world. The rhythmicity appears to be as important in regulating and coordinating internal metabolic processes, as in coordinating with the environment.[11] This is suggested by the maintenance (heritability) of circadian rhythms in fruit flies after several hundred generations in constant laboratory conditions,[12] as well as in creatures in constant darkness in the wild, and by the experimental elimination of behavioural but not physiological circadian rhythms in quail.[13][14]"

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Circadian rhythm - Wikipedia, the free encyclopedia

Circadian rhythm - Wikipedia, the free encyclopedia: "The rhythms maintain circadian periodicity over a range of physiological temperatures; they exhibit temperature compensation. Some organisms live at a broad range of temperatures, and differences in thermal energy will affect the kinetics of all molecular processes in their cell(s). In order to keep track of time, the organism's circadian clock must maintain a roughly 24-hour periodicity despite the changing kinetics, a property known as temperature compensation."

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Circadian rhythm - Wikipedia, the free encyclopedia

Circadian rhythm - Wikipedia, the free encyclopedia: "Criteria

To be called circadian, a biological rhythm must meet these four general criteria:
The rhythms repeat once a day (they have a 24-hour period). In order to keep track of the time of day, a clock must be at the same point at the same time each day, i.e. repeat every 24 hours.
The rhythms persist in the absence of external cues (endogenous). The rhythm persists in constant conditions with a period of about 24 hours. The rationale for this criterion is to distinguish circadian rhythms from simple responses to daily external cues."

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Circadian rhythm - Wikipedia, the free encyclopedia

Circadian rhythm - Wikipedia, the free encyclopedia: "sleepiness increases and decreases with a period of approximately 24 hours.[5] In 1918, J.S. Szymanski showed that animals are capable of maintaining 24-hour activity patterns in the absence of external cues such as light and changes in temperature.[6] Ron Konopka and Seymour Benzer isolated the first clock mutant in Drosophila in the early 1970s and mapped the "period" gene, the first discovered genetic component of a circadian clock.[7] Joseph Takahashi discovered the first mammalian 'clock gene' (CLOCK) using mice in 1994.[8][9]
The term "circadian" was coined by Franz Halberg in the late 1950s.[10]
[edit]Criteria

To be called circadian, a biological rhythm must meet these four general criteria:"

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Circadian Genes, Rhythms and the Biology of Mood Disorders

Circadian Genes, Rhythms and the Biology of Mood Disorders: "The molecular clock
The primary molecular clock is located in the suprachiasmatic nucleus (SCN) in the hypothalamus, and consists of a transcriptional feedback loop which cycles over the course of approximately twenty-four hours in the absence of environmental input (Reppert and Weaver, 2001; Ko and Takahashi, 2006). The major transcriptional activator consists of a dimer between the Circadian Locomotor Output Cycles Kaput Protein (CLOCK) and Brain and Muscle ARNT-like Protein 1 (BMAL1, also known as ARNTL or MOP3). This complex binds to E-box sequences in the promoters of"
 genes including the Period (Per) and Cryptochrome (Cry) genes. The PER and CRY proteins are translated in the cytoplasm, and are phosphorylated by Casein Kinase I ε and δ (CK1) and Glycogen Synthase Kinase 3β (GSK3β)
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Circadian Genes, Rhythms and the Biology of Mood Disorders

Circadian Genes, Rhythms and the Biology of Mood Disorders: "Indeed some of the major hallmarks of diseases like major depressive disorder (MDD) and bipolar disorder (BPD) are abnormal sleep/wake, appetite, and social rhythms (Boivin, 2000; Bunney and Bunney, 2000; Lenox et al., 2002; Grandin et al., 2006). Depression symptoms are also diurnal with the most severe symptoms occurring typically in the morning (Rusting and Larsen, 1998), and depression is more prevalent in areas of the world that receive little sunlight for extended periods of time (Booker et al., 1991). In addition, one of the most common mood disorders, affecting some 2–5% of the population in temperate climates, is seasonal affective disorder (SAD), a syndrome where depressive symptoms occur only in the winter months when there are shorter days and a later dawn (Lam and Levitan, 2000; Magnusson and Boivin, 2003). Thus, it has long been hypothesized that abnormalities in the molecular clock underlie the development of these disorders. "

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Circadian Genes, Rhythms and the Biology of Mood Disorders

Circadian Genes, Rhythms and the Biology of Mood Disorders: "abnormalities in circadian rhythms may underlie the development of mood disorders such as bipolar disorder, major depression and seasonal affective disorder. Furthermore, some of the treatments that are currently employed to treat mood disorders are thought to act by shifting or “resetting” the circadian clock, including total sleep deprivation and bright light therapy. There is also reason to suspect that many of the mood stabilizers and antidepressants used to treat these disorders may derive at least some of their therapeutic efficacy by affecting the circadian clock. Recent genetic, molecular and behavioral studies implicate individual genes that make up the clock in mood regulation. "

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