Circadian rhythms.

Section on Biochemical Pharmacology, National Institute of Mental Health, Bethesda, MD 20892.
Brain Research Reviews (Impact Factor: 5.93). 18(3):315-33.
Source: PubMed


Circadian rhythms are a ubiquitous adaptation of eukaryotic organisms to the most reliable and predictable of environmental changes, the daily cycles of light and temperature. Prominent daily rhythms in behavior, physiology, hormone levels and biochemistry (including gene expression) are not merely responses to these environmental cycles, however, but embody the organism's ability to keep and tell time. At the core of circadian systems is a mysterious mechanism, located in the brain (actually the suprachiasmatic nucleus of the hypothalamus) of mammals, but present even in unicellular organisms, that functions as a clock. This clock drives circadian rhythms. It is independent of, but remains responsive to, environmental cycles (especially light). The interest in temporal regulation--its organization, mechanism and consequences--unites investigators in diverse disciplines studying otherwise disparate systems. This diversity is reflected in the brief reviews that summarize the presentations at a meeting on circadian rhythms held in New York City on October 31, 1992. The meeting was sponsored by the Fondation pour l'Etude du Système Nerveux (FESN) and followed a larger meeting held 18 months earlier in Geneva, whose proceedings have been published (M. Zatz (Ed.), Report of the Ninth FESN Study Group on 'Circadian Rhythms', Discussions in Neuroscience, Vol. VIII, Nos. 2 + 3, Elsevier, Amsterdam, 1992). Some speakers described progress made in the interim, while others addressed aspects of the field not previously covered.

Download full-text


Available from: Sat Bir Singh Khalsa, May 20, 2014
  • Source
    • "In addition to changes in sleep architecture, there are changes in the circadian rhythm of body temperature in older adults compared to young adults. A circadian rhythm is the variation in body functions and behaviors that occur in a regular pattern around a 24 hour time interval (Aronson et al., 1993; Aschoff, 1984). Body temperature variation and the sleep wake cycle each follow a circadian rhythm. "
    [Show abstract] [Hide abstract]
    ABSTRACT: A single-group crossover design was used to examine the effects of a warm footbath on body temperatures, distal-proximal skin temperature gradient (DPG), and sleep outcomes in 15 Taiwanese elders with self-reported sleep disturbance. Body temperatures and polysomnography were recorded for three consecutive nights. Participants were assigned randomly to receive a 41 degrees C footbath for 40 minutes before sleep onset on night 2 or night 3. Mean DPG before lights off was significantly elevated on the bathing night. There were no significant differences in sleep outcomes between the two nights. However, when the first two non-rapid eye movement (NREM) sleep periods were examined, the amount of wakefulness was decreased in the second NREM period on the bathing night.
    Full-text · Article · Oct 2008 · Research in Nursing & Health
  • [Show abstract] [Hide abstract]
    ABSTRACT: A pulse of light is capable of inducing the circadian phase-dependent gene expression in neurons. The phase or amplitude of the circadian rhythms can be modulated by critically timed exposures to light. A significant heritability for the light-induced responses has been observed in hamsters. In humans, light has been used for treatment of the light-dependent winter depressive disorder. A genetic predisposition for high responsiveness to light may occur in patients with winter depression. The altered gene expression induced by light may account for a unique sensitivity to light and mediate the anti-depressant effect of light treatment.
    No preview · Article · Sep 1994 · Annals of Medicine
  • [Show abstract] [Hide abstract]
    ABSTRACT: Zawilska JB. Clonidine in vivo mimics the acute suppressive but not the phase-shifting effects of light on circadian rhythm of serotonin N-acetyltransferase activity in chick pineal gland. J. Pineal Res. 1994; 17: 63–68. ©Munksgaard, 1994 Comparative in vivo studies on effects of pulses of light and clonidine, a selective agonist of α2-adrenergic receptors, on the circadian rhythm of serotonin N-acetyltransferase (NAT) activity in chick pineal gland were performed. Six-hour pulses of white light caused an acute suppression of the nocturnal NAT activity and phase-dependent phase shifts of the circadian rhythm of the enzyme activity relative to controls. Systemic administration of clonidine acutely suppressed NAT activity of chick pineal gland, but did not affect the phase of subsequent cycles in constant darkness. These results give further support to the concept based on in vitro studies that α2-adrenergic receptors are involved in regulation of melatonin biosynthesis in chick pineal gland by a mechanism distal to the pacemaker that generates the circadian melatonin rhythm.
    No preview · Article · Oct 1994 · Journal of Pineal Research
Show more