Light-dark cycle

Pyrocystis lunula (clone T37) can be grown under light-dark cycles as well as under continuous illumination at 20 2°C, in f/2 medium (Guillard and Ryther, 1962) with 0.5% soil extract instead of silicate (Guillard, 1974). The growth is somewhat slower and harvesting may be carried out about 40 days after inoculation, at a cell density of 15,000-20,000 cells/ml. 

An alteration in the endogenous circadian clock, most often elicited by a change in the light/dark cycle, for example when travelling between time zones. 

After dark-condition equilibrium was established, as indicated by the visible spectra, the photo-shift in equilibrium was observed to be completely reversed when the illumination ceased. This photogalvanic effect maintained a mass balance in the system, with no reagent consumed or generated during the dark-light-dark cycle. This observation suggested that the plutonium system in the proper network of a concentration cell... 

Thompson, A. J., A. C. Jackson et al. (2000a). Abscisic acid biosynthesis in tomato Regulation of zeaxanthin epoxidase and 9-cw-epoxycarotenoid dioxygenase mRNAs by light/dark cycles, water stress and abscisic acid. Plant Mol. Biol. 42(6) 833-845. 

Golombek, D. A Cardinali, D. P. (1993). Melatonin accelerates re-entrainment after phase advance of the light-dark cycle in Syrian hamsters. Antagonism by flumazenil. Chronobiol. Int. 10, 435-41. 

Monti, J. M. Jantos, H. (2004a). Effects of L-arginine and SIN-1 on sleep and waking in the rat during both phases of the light-dark cycle. Life Set 75, 2027-34. 

Several studies suggest that cortistatin expression correlates with the sleep homeostat. The concentration of cortistatin mRNA oscillates with the light-dark cycle in rats, with maximal levels at the end of the dark (i.e. active) period. Further, the steady-state concentration of cortistatin mRNA increases four-fold after sleep deprivation, and returns to normal levels after sleep rebound, indicating that the expression of the peptide is associated with sleep demand (Spier de Lecea, 2000). Preliminary studies in cortical slices suggest that cortistatin-14 increases cortical synchronization by enhancing the H-current. Thus, cortistatin and somatostatin may be part of the intrinsic mechanisms of the cerebral cortex that are involved in the maintenance of excitability. 

Changes in the sleep-wake cycle or light-dark cycle can precipitate episodes of mania or depression. Bright light therapy can be used for the treatment of winter depression and can precipitate hypomania, mania, or mixed episodes. 

Proper facilities and care for test animals is not only a matter of regulatory compliance (and a legal requirement), but also essential for a scientifically sound and valid study. Husbandry requires clean cages of sufficient size and continuous availability of clean water and food (unless the protocol requires some restriction on their availability). Environmental conditions (temperature, humidity, and light-dark cycle) must be kept within specified limits. All of these must, in turn, be detailed in the protocols of studies. The limits for these conditions are set forth in relevant NIH and USDA publications. 

Immature female Wistar rats (15 days old) were housed individually in wire mesh cages with solid floors. Artificial light was maintained as a 12/12 h light/dark cycle under standard humidity and temperature conditions. Animals were weaned on conventional standardised laboratory diets. Diet and water were available ad libitum. All animals were acclimatised for 24 h before their injection. The study was conducted in accordance with the OECD Good Laboratory Practice Procedures [21]. 

In calculating exposure times, adjustment needs to be made for light/dark cycles in artificial weathering apparatus. 

Male Sprague-Dawley rats (200-250 g at the start of experimentation) are used. Each rat is individually housed in a polycarbonate cage and maintained on a 12-h light-dark cycle (lights on at 0700 h) with water and food available ad libitum. 

Becker IB, Beer ME, et al (1984) Striatal dopamine release stimulated by amphetamine or potassium influence of ovarian hormones and the light-dark cycle. Brain Res 311(1) 157-160 Becker IB, Molenda H, et al (2001) Gender differences in the behavioral responses to cocaine and amphetamine. Implications for mechanisms mediating gender differences in drug abuse. Ann N Y Acad Sci 937 172-187... 

D. Gonze, M. Roussel, and A. Goldbeter, A model for the enhancement of fitness in cyanobacteria based on resonance of a circadian oscillator with the external light-dark cycle. J. Theor. Biol. 214, 577-597 (2002). 

D. Gonze and A. Goldbeter, Entrainment versus chaos in a model for a circadian oscillator driven by light-dark cycles. J. Stat. Phys. 101, 649-663 (2000). 

Menaker There is old work by Kavanau in the 1960s (Kavanau 1962a,b) which has recently been repeated in hamster (Boulos et al 2002). This clearly shows that natural transitions in light/dark cycles increase the range of entrainment dramatically. The clock will entrain to T cycles much longer or shorter with natural transitions than it will with abrupt transitions. This has to mean something. It isn t clear what it means, but the complexity of the retinal input to the SCN must be functional at some level. Perhaps the function is in getting information about the rate of transition. 

First, the SCN of mCrj1 mCry2r mice appears electrically arrhythmic, independent of whether animals had been kept under a light—dark cycle or in constant darkness. This finding provides direct genetic evidence that mCRY proteins are indispensable for circadian rhythmicity of electrical activity in SCN neurons. Thus, an intact circadian clockwork appears prerequisite for circadian electrical activity in SCN neurons. This finding seems somewhat contradictory to a recent study of Nakamura et al (2002), who demonstrated electrical rhythmicity in SCN slices from arrhythmic homozygous Clock mutant mice. However, this... 

Kosbash There are two things that can be measured he could ask whether the behaviour shifts in any way with respect to the light—dark cycle, and now he also has an electrical peak. The question is, if you throw in to the animal something that shifts the period, would either of these change ... 

Dunlap Over the course of the light/dark cycle light is acting through CO to chronically induce FT. So in long day you are getting more and more, until finally you get enough. 

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