Literatura científica selecionada sobre o tema "Free-running rhythm"

The geographic isolation and the prolonged absence of sunlight during winter make Antarctica an interesting environment for studying circadian rhythms. This study explored the effects of wintering on sleep, hormonal, and electrolyte rhythms in four human subjects living in a small Antarctic base. Up to the last sunset sleep, 6-sulfatoxymelatonin, cortisol, sodium, and potassium rhythms were synchronized within clock time. During the 126 days of winter, when there was no sunlight, the circadian rhythms of all measures free ran in each individual. For example, the free-running periods for the cortisol excretory rhythm were 24 h 29 min, 24 h 45 min, 25 h 7 min, and 25 h 14 min for subjects C, J, K, and G, respectively. The period lengths of C, J, and K were significantly different, whereas there was no significant difference between K and G. The phase relationships between each rhythm remained constant in three out of the four subjects. Total daily output and rhythm amplitude for 6-sulfatoxymelatonin, potassium, and sodium remained constant during the entrained and free-running stages of the study. Significant changes in total daily cortisol excretion were observed during the year with one subject producing less and two subjects more while the rhythms were free running. When the sun reappeared during spring, all rhythms again synchronized and entrained to the daylight. These results show that 1) circadian rhythms can free run, even when the subjects have knowledge of time; and 2) within a small communal group, individuals can maintain unique free-running periods.

The photoperiod-induced clock-shifting in the free running time of the circadian protein and amino acid rhythms was studied in the larval fat body of Bombyx mori. The analysis of peaks and troughs of phase response curves of the rhythm revealed that the fourth and fifth instar larvae grown under normal 12 h light and 12 h dark cycle (LD) showed 7 protein synthetic cycles, while those reared under continuous light (LL) recorded 9.5 cycles in fourth instar and 8 in fifth instar. Under continuous dark (DD), the protein rhythm maintained 8 cycles in fourth instar and 7.5 cycles in fifth instar. Clearly, both LL and DD conditions advance the 24-h free running time of the protein rhythm by durations ranging from 1.6 to 6.5 h. Comparative analysis of protein and amino acid rhythms shows that the photoperiod modulates the free running time of the former by altering the rate of amino acid mobilization.

Without a zeitgeber the circadian rhythms of five physiological functions free-ran with a period length greater than 24 h. Restricted feeding time (RF) masked the free-running rhythms. In addition to masking, entrainment with RF occurred. This process was most evident in locomotor activity and visits to the food box. RF thus had zeitgeber properties in these rabbits. However, in most rabbits the RF zeitgeber was not strong enough to entrain the circadian rhythm completely. A small component free-ran during RF. Following return to continuous food access the whole circadian rhythm resumed to free-run again. In some animals its phase was determined by the RF zeitgeber and in others by the small free-running fraction present during RF. The results suggest that in addition to the light-dark-entrainable circadian oscillator system a feeding-entrainable oscillator exists that takes over phase control of the majority of the rhythm during RF.

Many species show rhythmicity in activity, from the timing of flowering in plants to that of foraging behavior in animals. The free-running periods and amplitude (sometimes called strength or power) of circadian rhythms are often used as indicators of biological clocks. Many reports have shown that these traits are highly geographically variable, and interestingly, they often show latitudinal or longitudinal clines. In many cases, the higher the latitude is, the longer the free-running circadian period (i.e., period of rhythm) in insects and plants. However, reports of positive correlations between latitude or longitude and circadian rhythm traits, including free-running periods, the power of the rhythm and locomotor activity, are limited to certain taxonomic groups. Therefore, we collected a cosmopolitan stored-product pest species, the red flour beetle Tribolium castaneum, in various parts of Japan and examined its rhythm traits, including the power and period of the rhythm, which were calculated from locomotor activity. The analysis revealed that the power was significantly lower for beetles collected in northern areas than southern areas in Japan. However, it is worth noting that the period of circadian rhythm did not show any clines; specifically, it did not vary among the sampling sites, despite the very large sample size (n = 1585). We discuss why these cline trends were observed in T. castaneum.

Abstract Clock is a semidominant X-linked mutation that results in shortening the period of Drosophila melanogaster's free-running locomotor activity rhythm from ca. 24.0 to ca. 22.5 hr. This mutation similarly shortened the phase response curve, determined by resetting activity rhythms with light pulses. Eclosion peaks for Clk cultures were separated by only 22.5 hr instead of the normal 24 hr. Clk was mapped close to, but separable from, another rhythm mutation--period01--by recombination. The estimated distance between these two mutations was short enough to suggest that Clk could be a per allele. If this is the case, the new mutant is unique in that it, unlike other per variants, is associated with essentially normal 1-min courtship song rhythms when Clk is expressed in males. Also, the new rhythm variant could not, in contrast to a short-period per mutation, have its effects on free-running activity rhythms uncovered by deletions. This result, and the lack of coverage of Clk's effects by duplications, suggest that it is not a simple hypomorphic or amorphic mutation.

The causes of age-related disruptions in the timing of human sleep and wakefulness are not known but may include changes in both the homeostatic and circadian regulation of sleep. In Syrian hamsters the free running period of the circadian activity/rest rhythm has been reported to shorten with age. Although this has been observed under a variety of experimental conditions, the changes have been small and their consistency uncertain. In the present study, the wheel running activity/rest rhythm was continuously measured in male Syrian hamsters ( Mesocricetus auratus) in dim constant light (<1 lx) from 8 wk of age until death. Fifteen hamsters survived to at least 90 wk (28%). The average free running period of these hamsters did not change with age. In 18 hamsters that died between 50 and 88 wk, free running period also did not change before death. In contrast to free running period, other measures related to activity level changed significantly with age and before death. Despite changes in the expression of the activity/rest rhythm, the free running period of the hamster circadian pacemaker remained remarkably stable with age.

Shifting the onset of light, acutely or chronically, can profoundly affect responses to infection, tumor progression, development of metabolic disease, and mortality in mammals. To date, the majority of phase-shifting studies have focused on acute exposure to a shift in the timing of the light cycle, whereas the consequences of chronic phase shifts alone on molecular rhythms in peripheral tissues such as skeletal muscle have not been studied. In this study, we tested the effect of chronic phase advance on the molecular clock mechanism in two phenotypically different skeletal muscles. The phase advance protocol (CPA) involved 6-h phase advances (earlier light onset) every 4 days for 8 wk. Analysis of the molecular clock, via bioluminescence recording, in the soleus and flexor digitorum brevis (FDB) muscles and lung demonstrated that CPA advanced the phase of the rhythm when studied immediately after CPA. However, if the mice were placed into free-running conditions (DD) for 2 wk after CPA, the molecular clock was not phase shifted in the two muscles but was still shifted in the lung. Wheel running behavior remained rhythmic in CPA mice; however, the endogenous period length of the free-running rhythm was significantly shorter than that of control mice. Core body temperature, cage activity, and heart rate remained rhythmic throughout the experiment, although the onset of the rhythms was significantly delayed with CPA. These results provide clues that lifestyles associated with chronic environmental desynchrony, such as shift work, can have disruptive effects on the molecular clock mechanism in peripheral tissues, including both types of skeletal muscle. Whether this can contribute, long term, to increased incidence of insulin resistance/metabolic disease requires further study.

Experiments were conducted to determine the anatomic and physiological basis of the dual-oscillator circadian system of female Japanese quail. After blocking of ocular light perception by eye-patching, the circadian body temperature rhythm dissociates into two circadian components in continuous lighting (LL). One component free runs with a period significantly shorter than 24 h [mean period (tau) = 22.7 h] and is driven by an ocular pacemaker, whereas the other component free runs with a period significantly longer than 24 h (tau = 26.3 h). The long free-running rhythm is driven by the same circadian clock that drives the circadian rhythm of ovulation. The expression of the long free-running rhythm in LL depends on the presence of the ovary: body temperature rhythmicity is abolished by ovariectomy. The two free-running oscillators in eye-patched birds showed evidence of mutual interaction. Significantly, the phase relationships that occur as the two oscillators interact can determine whether or not ovulation occurs. The results are discussed in terms of an "internal coincidence" mechanism for photoperiodic time measurement.

An organism’s circadian clock exists as a self-regulating oscillator that can synchronize with its surroundings. This manifests as physiological and behavioral output which can anticipate changes in environment. These rhythms may even persist internally and are known to oscillate at a period (tau) of around 24 hours even in the absence of external cues. In the laboratory, such rhythmic output is known as a free-running period (FRP). Given that circadian rhythms are distributed in a number of taxa as well as their tendency to oscillate along with the solar day, it has been suggested that they result from natural selection. The argument that tone’s clock is adaptive is based on how it is advantageous: the clock instills temporal order among physiological processes as well as enabling one to anticipate external cues. Losing that order in one’s clock has also been associated with a number of metabolic and neurological pathologies. Along with adaptive significance, it has been surmised that an internal clock which synchronizes with one’s surrounding environment is beneficial to an individual. An organism whose free-running period closest matches the rhythmic output of its external environment will exhibit a higher relative fitness as compared to those whose periods deviate from 24 hours. This forms the basis of the ‘circadian resonance hypothesis’. Circadian resonance has been examined in a number of species, from Cyanobacteria to mammals. Collectively, experimental results have supported the rationale that an individual does best when its internal clock resonates with the 24 hour day. The bowl and doily spider, Frontinella communis, not only has its own endogenous rhythm (free-running period), it exhibits an average free-running period of 28.26 hours, deviating from a usual period of ~24 hours. Keeping in mind the circadian resonance hypothesis, an internal clock with such an extreme deviation from the 24 hour day should prove detrimental to one’s overall health. Despite this, Frontinella communis not only has a long clock; among the species, their clocks also appear to be highly variable, FRPs ranging from ~24 to ~33 hours. This study monitored locomotor activity of Frontinella communis to examine whether its free-running period, on average, remained the same throughout its active season (May-September). It was found that average free-running period in F. communis varied significantly over a five-month period. Average FRP appears to peak in June followed by a steady, linear decline as the season continues. A variety of organisms have been shown to exhibit seasonal responses that allow them to cope with environmental change. It is not known whether the change in Frontinella’s FRP is such an advantage or is merely coincidental. Any free running period detected under the alpha level of 0.05 was not ruled significant. Along with the rise and fall of average FRPs, the presence of FRP deemed significant was found to decline as the season ended- 42% of individuals (n= 19) reported as arrhythmic. While age has been found to correlate with circadian desynchrony in other taxa (rats, humans), an association in Frontinella remains to be tested.

A characteristic feature of species of Trichoderma is the production of concentric rings of conidia in response to alternating light-dark conditions. In response to a single burst of light, a single ring of conidia forms at what was the colony perimeter. On the basis of these observations, competency to photoconidiate has been proposed to be due to the age and metabolic rate of the hyphal cell. In this study, conidiation was investigated in five biocontrol isolates (T. hamatum, T. atroviride, T. asperellum, T. virens and T. harzianum) using both a morphological and molecular approach. All five isolates produced concentric conidial rings under alternating light-dark conditions on potato-dextrose agar (PDA), however, in response to a 15 min burst of blue light, only T. asperellum and T. virens produced a clearly, defined conidial ring which correlated with the colony margin at the time of light exposure. Both T. harzianum and T. hamatum photoconidiated in a disk-like fashion and T. atroviride produced a broken ring with a partially filled in appearance. On the basis of these results, it was postulated that competency to photoconidiate is a factor of the metabolic state of the hyphal cell rather than chronological age or metabolic rate. The influence of the source of nitrogen on photoconidiation was assessed on pH-buffered (pH 5.4) minimal medium (MM) amended with glutamine, urea or KNO₃. In the presence of glutamine or urea, T. asperellum and T. harzianum conidiated in a disk, whereas, when KNO₃ was the sole nitrogen source, a ring of conidia was produced. Further, in the presence of increasing amounts of glutamine, the clearly defined photoconidial ring produced on PDA by T. asperellum became disk-like. These results clearly demonstrated that primary nitrogen promotes photoconidiation in these isolates and strongly suggests that competency of a hyphal cell to conidiate in response to light is dependent on the nitrogen catabolite repression state of the cell. The experiments were repeated for all five isolates on unbuffered MM. Differences were apparent between the buffered and unbuffered experiments for T. atroviride. No photoconidiation was observed in T. atroviride on buffered medium whereas on unbuffered medium, rings of conidia were produced on both primary and secondary nitrogen. These results show that photoconidiation in T. atroviride is influenced by the buffering capacity of the medium. Conidiation in response to light by T. hamatum and T. virens was absent in all nitrogen experiments, regardless of the nitrogen source and buffering capacity, whereas both isolates conidiated in response to light on PDA. These results imply that either both sources of nitrogen are required for photoconidiation, or a factor essential for conidiation in these two isolates was absent in the minimal medium. Mycelial injury was also investigated in five biocontrol isolates of Trichoderma. On PDA, all isolates except T. hamatum conidiated in response to injury. On nitrogen amended MM, conidiation in response to injury was again observed in all isolates except for T. hamatum. In T. atroviride, injury-induced conidiation was observed on all medium combinations except the pH-buffered MM amended with glutamine or urea and T. virens conidiated in response to injury on primary nitrogen only, regardless of the buffering capacity. These results have revealed conidiation in response to injury to be differentially regulated between isolates/species of Trichoderma. On unbuffered MM amended with glutamine or urea, conidiation in response to injury occurred at the colony perimeter only in T. atroviride. It was hypothesised that the restriction of conidiation to the perimeter may be due to changes in the pH of the agar. The experiment was repeated and the pH values of the agar under the growing colony measured at the time of light induction (48 h) or injury (72 h). The areas under the hyphal fronts were acidified to below the starting value of the medium (pH 5.4) and the centres of the plates were alkalinised. The region of acidification at the time of stimuli correlated with the production of conidia, which implicates a role for crossregulation of conidiation by the ambient pH. The influence of the ambient pH on injury-induced conidiation was investigated in T. hamatum and T. atroviride on MM amended with glutamine and PDA, pH-buffered from pH 2.8 to 5.6. Thickening of the hyphae around the injury site was observed at the lowest pH values on MM in both T. atroviride and T. hamatum, however no conidia were produced, whereas both Trichoderma species conidiated on pH-buffered PDA in a strictly low pH-dependent fashion. This is the first observation of injury-induced conidiation in T. hamatum. The influence of the ambient pH on photoconidiation was assessed in T. hamatum, T. atroviride and T. harzianum using both buffered and unbuffered PDA from pH 2.8 to 5.2. On buffered PDA, no conidiation in response to light was observed above pH 3.2 in T. hamatum, above 4.0 in T. atroviride and above 4.4 in T. harzianum, whereas on unbuffered PDA it occurred at all pH values tested. It was postulated that conidiation at pH values above 4.4 on unbuffered PDA was due to acidification of the agar. The pH values of the agar under the growing colony were measured at the time of light exposure and in contrast to the MM with glutamine experiments, alkalisation of the agar had occurred in both T. atroviride and T. hamatum. No change in medium pH was recorded under the growing T. harzianum colony. These results indicate that low pH-dependence of photoconidiation is directly related to the buffering capacity of the medium. Recent studies have linked regulation of conidiation in T. harzianum to Pac1, the PacC orthologue. In fungi, PacC regulates gene expression in response to the ambient pH. In these studies pH-dependent photoconidiation occurred only on buffered PDA and on unbuffered PDA conidiation occurred at significantly higher ambient pH levels. It is proposed that the influence of ambient pH on conidiation in the isolates used in this study is not due to direct Pac1 regulation. The T. harzianum isolate used in this study produced profuse amounts of the yellow anthraquinone pachybasin. Production of this secondary metabolite was strictly pH-dependent, irrespective of the buffering capacity of the medium. Studies in T. harzianum have linked Pac1 regulation to production of an antifungal α-pyrone. pH-dependence on both buffered and unbuffered media strongly suggests that pachybasin production may also be under the control of Pac1. Photoconidiation studies on broth-soaked filter paper, revealed rhythmic conidiation in the pachybasin producing T. harzianum isolate. Diffuse rings of conidia were produced in dark-grown cultures and, in cultures exposed to light for 15 min at 48 h, the rings were clearly defined. These results show that conidiation is under the control of an endogenous rhythm in T. harzianum and represent the first report of circadian conidiation in a wild-type Trichoderma. A Free-Running Rhythm (FRR) assay was used to investigate rhythmic gene expression in T. atroviride IMI206040 and a mutant derivative, in which the wc-2 orthologue, blr-2, was disrupted. Over a 3 d period, expression of gpd, which encodes the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase, oscillated with a period of about 48 h. In the Δblr-2 mutant, the gpd rhythm was absent. These results revealed that in T. atroviride, gpd expression is under the control of an endogenous clock and that clock-regulated expression of gpd is associated with a functional BLR complex. Using degenerate primers, a portion of frq, which encodes the N. crassa clock oscillator FREQUENCY, was isolated from T. atroviride and used to probe the FRR assay northern blots. No frq expression was detected at any time point, which suggests that the circadian clock in Trichoderma does not involve FREQUENCY. In a concurrent study, orthologues of rco-1 (rcoT) were isolated and sequenced from T. atroviride and T. hamatum using a combination of degenerate, inverse and specific PCR. RcoT is an orthologue of the yeast global co-repressor Tup1 and in the filamentous fungi, RcoT orthologues have been demonstrated to negatively regulate conidiation. Genomic analysis of all available rcoT orthologues revealed the conservation of erg3, a major ergosterol biosynthesis gene, upstream from rcoT in ascomycetous filamentous fungi, but not in the ascomycetous yeast or in the basidiomycetes. These studies have significantly contributed to our understanding of the regulatory factors controlling conidiation in Trichoderma and have multiple implications for Trichoderma biocontrol; most notable the promotion of conidiation by primary nitrogen and low pH. Incubation conditions can be altered to suit the nitrogen and pH preferences of a biocontrol strain in order to promote cost effective conidial production, however this is not easily achieved in the soil, where the biocontrol strain must perform in a highly buffered environment optimised for plant growth. Successful use of Trichoderma biocontrol strains may involve the screening and targeting of strains to the appropriate pH conditions or the selection of new strains on the basis of capacity to perform under a given range of conditions.

This chapter provides an overview of the incidence, presentation, assessment, diagnosis, and management of the four main circadian rhythm sleep disorders: advanced sleep phase disorder (ASPD), delayed sleep phase disorder (DSPD), free-running (non-24-hour) sleep disorder (FRSD), and irregular sleep–wake rhythm disorder (ISWRD). Following a brief discussion of the daily entrainment of the human circadian clock to the light cycle, and the shifting effects of light and melatonin on the clock, each of the four different disorders are considered in turn. The aim of this chapter is to provide a concise overview of the disorders and the potential treatment strategies for each. The chapter is extensively referenced for further information.

Temporal organization of nervous system function includes daily rhythms driven by a molecular-genetic hypothalamic “clock” with an intrinsic period length of approximately (circa) one day (diem). The resulting circadian rhythm influences all aspects of brain function and internally synchronizes the circadian oscillations inherent in all other body tissues. Idiosyncratic circadian characteristics interact with perceived environmental stimuli to determine each individual’s entrainment pattern of external synchronization with the day-night cycle. Idiosyncratic entrainment patterns that may come to medical attention include delayed, free-running, advanced, or absent sleep rhythms. Prolonged jet travel and shift work are difficult entrainment challenges for most people.

The pineal gland transduces light–dark cycles for the timing of body rhythms by secretion of melatonin, an endogenous indoleamine derived from tryptophan, the concentrations of which in plasma and cerebrospinal fluid are up to 100 times higher at night than in the daytime. This exerts its effects through transmembrane, G-protein coupled receptors (MT1 and MT2), and nuclear receptors primarily in the suprachiasmatic nucleus, pars tuberalis of the pituitary gland and hypothalamus. The natural period of the human circadian system is on average 24.1 to 24.3 h, and the principal resetting agent is light. Exogenous melatonin can shift the timing of the internal clock to earlier and later times, and synchronize a free-running clock that is not properly entrained to the 24-h day, hence it may have a therapeutic role for disorders of sleep rhythm including jet lag, in shift workers, and in blind people.

The second chapter, Exercise, considers the rhythm of our bodies in motion and the complicated relationships between exercise and illness, as both a necessity and a joy. Like eating, the significance of exercise is redefined by illness, and the body is maintained, challenged, and re-known through it. Exercise regimes can provide control, treatment and an alternative form of medication so that through physical activity bodies feel strong, independent, and free in spite of illness. But ill bodies are prone to overexertion, and exercise can reinforce their dependence and vulnerability as well as their strength. For Anna, who has depression, exercise has become a form of self-medication. Running and cycling regularly make her feel less depressed, so she tries to be physically active at least four times a week. Disruption to this routine can cause her mood to plummet quickly, showing the dependence that she has on her body.

The paper introduces a relay feedback oscillator for modeling circadian rhythms in cyanobacteria. The relay feedback oscillator is equipped with low pass filter F(jω), hysteresis-type relay and negative feedback. This negative feedback represents an autoregulatory mechanism of the circadian clock and the notion of this autoregulatory mechanism is based on the well-known Goodwin biochemical oscillator [1]. The relay is responsible for the mediation of both the activation and degradation of oscillator state variables (protein concentrations) and in this way the pacemaker is constituted. Later on, low pass filter poles are identified for the purpose of modeling auto-oscillations with the free running period of 24h and the method of the pole identification consists in an ultimate frequency test providing stability margin of a single-loop composed of the filter and the relay in the feedback. Next, a relay output / input ratio of amplitudes and hysteresis are found out by the graphical test of the single-loop on the stability margin which is carried out in Bode graph. Finally, the output correspondence of relay feedback oscillator model with Miyoshi oscillator [2] is provided because the Miyoshi oscillator is well recognized among biochemical oscillators for species of cyanobacteria.