Free-running Period Of Circadian Rhythm Research Articles

Metastasis-associated protein 1 is an integral component of the circadian molecular machinery

The mammalian circadian clock regulates the daily cycles of many important physiological processes, but its mechanism is not well understood. Here we provide genetic and biochemical evidence that metastasis-associated protein 1 (MTA1), a widely upregulated gene product in human cancers, is an integral component of the circadian molecular machinery. Knockout of MTA1 in mice disrupts the free-running period of circadian rhythms under constant light and normal entrainment of behaviour to 12-h-light/12-h-dark cycles. The CLOCK-BMAL1 heterodimer activates MTA1 transcription through a conserved E-box element at its promoter. MTA1, in turn, interacts with and recruits CLOCK-BMAL1 at its own and CRY1 promoters and promotes their transcription. Moreover, MTA1 deacetylates BMAL1 at lysine 538 through regulating deacetylase SIRT1 expression, thus disturbing the CRY1-mediated negative feedback loop. These findings uncover a previously unappreciated role for MTA1 in maintenance of circadian rhythmicity through acting on the positive limb of the clock machinery.

Characterization of Circadian-Associated Pseudo-Response Regulators: II. The Function of PRR5 and Its Molecular Dissection inArabidopsis thaliana

Together with PRR1/TOC1, PRR5 belongs to the small family of Pseudo-Response Regulators (PRRs), which function as clock components of Arabidopsis thaliana. We employed a set of transgenic lines, each of which was designed to misexpress a truncated form of the PRR5 molecule, together with the original transgenic line (named PRR5-ox) that misexpresses the entire PRR5 polypeptide. The results of genetic analysis suggested that PRR5-ox seedlings showed a phenotype of hypersensitivity to red light during early photomorphogenesis in a manner dependent on red light photoreceptors (PhyA and PhyB), but independent of PRR1/TOC1. The set of newly constructed transgenic lines (named PRR5-N-ox and PRR5-C-ox) were also characterized in terms of circadian-associated phenotypes. The results suggest that the N-terminal pseudo-receiver domain of the PRR5 molecule seems to be dispensable for the misexpressed PRR5 molecule to bring about the phenotype of red light sensitivity. However, PRR5-N-ox plants, misexpressing only the pseudo-receiver domain, showed a phenotype of long period of free-running circadian rhythms of certain clock-controlled genes. Considering these and other results, we discuss the structure and function of PRR5 in the context of current views of the circadian clock in higher plants.

Photoperiodic modulation of circadian rhythms in the cricket Gryllus bimaculatus

The waveform and the free-running period of circadian rhythms in constant conditions are often modulated by preceding lighting conditions. We have examined the modulatory effect of variable length of light phase of a 24 h light cycle on the ratio of activity ( α ) and rest phase ( ρ ) as well as on the free-running period of the locomotor rhythm in the cricket Gryllus bimaculatus. When experienced the longer light phases, the α / ρ -ratio was smaller and the free-running period was shorter. The magnitude of changes in α / ρ -ratio was dependent on the number of cycles exposed, while the free-running period was changed by a single exposure, suggesting that there are separate regulatory mechanisms for the waveform and the free-running period. The neuronal activity of the optic lobe showed the α / ρ -ratio changing with the preceding photoperiod. When different photoperiodic conditions were given to each of the two optic lobe pacemakers, the α / ρ -ratio of a single pacemaker was rather intermediate between those of animals treated with either of the two conditions. These results suggest that the storage of the photoperiodic information occurs at least in part in the optic lobe pacemaker, and that the mutual interaction between the bilateral optic lobe pacemakers is involved in the photoperiodic modulation.

Free-running circadian period does not shorten with age in female Syrian hamsters

It has been reported that the free-running period of circadian rhythms shortens with age in mammals, including humans, and this shortening has been suggested to be the underlying cause of early morning awakening and difficulty maintaining sleep in older people. A recent study found that the free-running period of male hamsters does not change with age. The present study extends those findings to female hamsters. We studied the locomotor activity rhythm of 22 female hamsters kept in constant conditions from early adulthood until their death, and compared their data to those from male hamsters. We found no shortening of free-running period with age in the female hamsters, and no difference in free-running period between females and males. In contrast, mean activity level and amount of time per cycle spent running declined with age in females and males. These findings demonstrate that the free-running period in hamsters does not systematically shorten with age, and suggest that alternative explanations for the observed age-related advance of sleep-wake times in humans should be explored.

Free-running period of circadian rhythms is shorter in rats with a genetically upregulated central cholinergic system

The free-running circadian rhythm of drinking activity was monitored in constant darkness in a genetic line of rats, the Flinders Sensitive Line (FSL), which show increased muscarinic receptors in several brain regions. Compared to control rats, the Flinders Resistant Line (FRL), that do not show increased muscarinic receptors, the free-running period of drinking activity was shorter in the FSL rats ( FSL period = 24.02 ± 0.01 vs FRL period = 24.12 ± 0.02; p < .001). In an attempt to determine whether other rhythms were similarly affected, we simultaneously monitored drinking activity, gross motor activity, and core temperature in free-running constant darkness conditions. The results from three FSL and FRL rats showed that the circadian periods of all three rhythms were shorter in FSL rats. These findings indicate that an animal model with an upregulated central cholinergic system demonstrates an accelerated circadian pacemaker.

The effect of old age on the free-running period of circadian rhythms in rat.

The free-running period is regarded to be an exclusive feature of the endogenous circadian clock. Changes during aging in the free-running period may therefore reflect age-related changes in the internal organization of this clock. However, the literature on alterations in the free-running period in aging is not unequivocal. In the present study, with various confounding factors kept to a minimum, it was found that the free-running periods for active wakefulness, body temperature, and drinking behavior were significantly shorter (by 12-17 min) in old than in young rats. In addition, it was found that the day-to-day stability of the different sleep states was reduced in old rats, whereas that of the drinking rhythm was enhanced. Transient cycles were not observed, nor were there any age-related differences in daily totals of the various sleep-wake states. The amplitudes of the circadian rhythms of active wakefulness, quiet sleep, and temperature were reduced, whereas those of paradoxical sleep and quiet wakefulness remained unchanged.

Heavy water lengthens the period of free-running rhythms in lesioned hamsters bearing SCN grafts

Heavy water (D 2O) lengthens the period of free-running circadian rhythms in most organisms. We compared the effect of D 2O on freerunning locomotor activity rhythms in intact and SCN-lesioned (SCN-X) hamsters that had recovered circadian rhythmicity following implantation of SCN grafts. The animals were housed individually in cages equipped with running wheels, and locomotor activity was monitored using a computer-based data acquisition system. At the end of the behavioral tests, animals were anesthetized and perfused. Brain sections were immunostained for vasoactive intestinal peptide (VIP) and vasopressin (VP) to evaluate the extent of the lesion and the presence of a functional graft. The D 2O similarly lengthened the period of free-running activity without affecting amount of activity in both intact and in SCN-X grafted animals. The results indicate that D 2O acts directly on the SCN to lengthen the free-running period, and suggest that coupling between pacemakers within the grafted SCN is as efficient as in the intact SCN.

A neurophysiological study of a lithium-sensitive phosphoinositide system in the hamster suprachiasmatic (SCN) biological clock in vitro

Lithium lengthens the period of free-running circadian rhythms in many species. In mammals the hypothalamic suprachiasmatic nucleus (SCN) has been identified as a biological clock which generates circadian rhythms. The effect of lithium-induced depletion of the intracellular pool of inositol, leading to decreased intracellular second messengers IP 3 and DAG, was examined neurophysiologically. Extracellular recordings were obtained from spontaneously discharging SCN neurones maintained in vitro. Superfusion of slices with lithium-containing (0.1–30 mM) aCSF, but not rubidium-containing aCSF, suppressed neuronal firing in a dose-dependent manner. Lithium-induced suppressed firing was reversed by myo-inositol, but not by epi-inositol. These studies provide evidence for basal phosphoinositide turnover in neurones and implicate a lithium-sensitive phosphoinositide system in the maintenance of the spontaneous discharge activity of SCN neurones.

Maternal entrainment of tau mutant hamsters.

Maternal entrainment of the circadian wheel-running activity rhythm was examined in Syrian hamsters heterozygous for a single gene mutation (tau) that affects the free-running period of circadian rhythms. Heterozygous tau pups were born to and raised by wild-type mothers under constant dim light. The pups' wheel-running activity was recorded after weaning on postnatal day 18 or 24. Pups weaned on day 18 had an average free-running period of 21.70 hr, demonstrating that the tau phenotype was fully expressed at this age. Using the activity onset of the postnatal free-running rhythms as a phase reference, we estimated the phase relationships between the pups and their mothers on days 18 and 24. In contrast to results with wild-type pups, the activity rhythms of tau pups were not in phase with the rhythms of their wild-type mothers; that is, activity onsets of mothers and pups did not coincide. The pups did, however, show synchrony among themselves, indicating that they had been exposed to a synchronizing signal sometime during development. It is likely that this synchronizing signal was provided by the mothers, since pups from different litters showed phase relationships similar to those of their mothers. Thus the mothers provided a signal that was sufficient to cause entrainment, despite the 2-hr difference in free-running period between the mothers and pups. Although the pups' activity rhythms appeared to have been entrained by the mothers, they were clearly free-running by postnatal day 18. The mechanism for entrainment is lost during the course of development, despite continued interaction between the mothers and pups.

Lithium lengthens circadian period in a diurnal primate, Saimiri sciureus

Lithium lengthens the period of free-running circadian rhythms in a variety of species, but this effect has not been demonstrated unequivocally in primates. Because of the possible link between lithium's action on the circadian clock and its therapeutic action in human mood disorders, we tested the ability of lithium to lengthen circadian period in a diurnal primate with circadian properties similar to those of humans. Lithium carbonate was administered in food pellets to 8 adult male squirrel monkeys (Saimiri sciureus) for at least 27 consecutive days. Serum lithium levels on the last day of lithium administration ranged from 0.76 to 2.02 mEq/liter, comparable to the therapeutic range for treatment of bipolar disorder in humans (0.6–1.2 mEq/liter). Circadian periods of perch-hopping activity were longer during lithium treatment than during baseline in 7 of the 8 monkeys (changes of −0.08 to +1.41 hr, mean + 0.55 hr, p = 0.01), and returned toward baseline values when lithium was discontinued. In most cases, the period change was evident within a few days after beginning full lithium dose, and was not accompanied by changes in level or pattern of activity, nor in amplitude of the circadian rhythm. Food consumption and body weight were reduced during lithium treatment, and rebounded on return to lithium-free diet. Period change was related to lithium dose (p < 0.05), but did not correlate with food consumption, body weight, or baseline circadian period. These results, by establishing that lithium lengthens circadian period in primates, suggest that studying the cellular mechanisms of this circadian effect may be relevant to understanding lithium's therapeutic effect on mood in humans.

Creatine accelerates the circadian clock in a unicellular alga.

The circadian clock is considered to be a universal feature of eucaryotic organisms, controlling the occurrence and rates of many different aspects of life, ranging from single enzymatic reactions and metabolism to complex behaviours such as activity and rest. Although the nature of the underlying cellular/biochemical oscillator is still unknown, many substances are known to influence either phase or period of circadian rhythms in different organisms. These include D2O, electrolytes and ion channel inhibitors, small organic molecules such as alcohols and aldehydes, inhibitors of protein synthesis and amino-acid analogues. Certain transmitter and neurochemical drugs also influence the circadian clock in higher animals. We report here that the period of free-running circadian rhythms in the unicellular marine alga Gonyaulax polyedra is shortened by extracts from mammalian cells. The effect is dose-dependent, accelerating the circadian clock by as much as 4 hours per day. The substance responsible for this effect has been isolated from bovine muscle and identified as creatine. Authentic creatine has identical biological effects at micromolar concentrations and is known in animal systems for its involvement in cellular energy metabolism. A period shortening substance with similar chemical properties is also present in extracts of Gonyaulax itself.

Effect of implantation of carbachol pellet near the suprachiasmatic nucleus on the free-running period of rat locomotor activity rhythm.

To clarify the effect of a cholinergic agent on free-running period of circadian rhythm, locomotor activities were continuously recorded in the rat implanted with a paraffin pellet mixed with or without carbachol near the suprachiasmatic nucleus. Implantation of carbachol, but not paraffin alone, resulted in shortening of the free-running period under constant darkness.